Detailed explanation of glass screen printing technology

Tempered glass screen printing process introduction, professional tempered glass panel processing factory, customized processing

From the traditional glass screen printing to the emerging LED, touch panel printing, screen printing technology throughout the entire glass industry, and in which play a pivotal role.

So as one of the important areas in the screen printing industry, how important role does glass screen printing play in the screen printing industry?

Brief Introduction of Glass Screen Printing Technology

Glass screen printing, is the use of screen printing plate, the use of glass glaze, decorative printing on glass products. Glass glaze, also known as glass ink, glass printing material, it is a paste printing material made of a mixture of coloring material and binder. The coloring material is composed of inorganic pigments and low melting point flux (lead glass powder); the binding material is commonly known as lentil oil in the glass screen printing industry. After the printing of glass products, to fire in the furnace, to 520~600 ℃ temperature for firing, printed on the glass surface of the glaze can be consolidated on the glass, forming a colorful decorative pattern. If the screen printing and other processing methods and use, will get a more ideal effect. For example, the use of polishing, engraving, etching and other methods before printing or after printing on the glass surface processing, can double improve the printing effect.

Application fields of glass screen printing technology

The application of screen-printed flat glass and its market prospects Screen-printed flat glass is widely used in every corner of people's lives: you can easily find them in display windows, building space partitions, building appearance beautification, car windshields and inlaid glass. At the same time. They are also widely used in furniture decoration and game tools, as well as countless decorative and artistic creations. The screen printing also became part of the creative design work of glass manufacturing. One can print color images directly onto the glass surface by screen printing. In addition, it can also be used to temporarily cover the non-graphic part of the glass surface, or to print additives such as preservatives on part of the glass surface, so that it is not affected by the etching or frosting process. In contrast, you can also screen print special ink directly to create an etching or frosting effect. Sometimes. People will also use the strong covering ability of screen printing, such as printing a thin layer of conductive material on the glass, which is used to make anti-icing (frost) devices for windows.

Screen printing continues to expand in the field of flat glass decoration. In addition to being suitable for printing materials of various materials, another important factor is that it can meet flat glass substrates of different sizes and weights in a wide range. Moreover, due to the absolute advantage of screen printing in large format image printing, it has strengthened its leading position in the development of the entire flat glass printing industry. Especially in recent years, the demand for large-format flat glass printing has risen sharply. In fact, due to the rapid development of screen printing in the field of large format flat glass decoration, printing equipment manufacturers are constantly improving to meet the increasingly demanding printing requirements, especially in areas such as flat glass, resulting in many of the world's most flexible The equipment is widely used in the printing of building boards. The application of screen printing in flat glass decoration will continue to develop and expand its application field in glass decoration. Screen printing machine has a faster printing material transfer system, as well as a more advanced power supply system, combined with a powerful PLC (logic controllable device)

In addition, the demand for glass screen printing technology in the automotive industry is also very strong. In addition to the pure optical color application using screen printing, various functional layers (such as the heat conductor on the rear window) have also been modified. Conductive body path and the best structure (such as the rear window heating device) must be imprinted in a stable way in time and ensure excellent quality.

Glass detection technology has attracted much attention

At this year's Shanghai Glass Exhibition, we noticed that another outstanding feature is that glass inspection technology and equipment have received widespread attention, especially for some high-tech value-added glass screen printing products, such as LED, touch screen and The above-mentioned automotive glass, solar substrate, etc. These products have strict requirements on quality and yield, so with the development of science and technology, more and more glass screen printing enterprises begin to pay close attention to and control the quality of finished glass products, which makes glass testing technology become another hot field in the glass industry.

So on the glass screen printing technology, its processing process often appear what quality problems?

Glass screen printing process prone to problems

paste version

1. Paste version, also known as blocking version, refers to the screen printing plate graphic through-hole part in the printing ink can not be transferred to the substrate on the phenomenon. The appearance of this phenomenon will affect the quality of printing, and even normal printing will not be possible in severe cases. The causes of the paste phenomenon produced in the screen printing process are intricate. The reasons for the paste can be analyzed from the following aspects: ① The reason for the glass: the glass surface is not cleaned, and there are still watermarks, paper prints, mimeographs, handprints, dust particles and other dirt. Thus causing the paste version; ② workshop temperature, humidity and ink properties. The screen printing workshop requires a certain temperature of about 20 ℃ and relative humidity of about 50%. If the temperature is high and the relative humidity is low, the volatile solvent in the ink will quickly volatilize, and the viscosity of the ink on the screen will become higher, thus blocking the mesh. Another point should be noted that if the downtime is too long, it will also produce the phenomenon of paste, and the longer the time, the more serious the paste. Secondly, if the ambient temperature is low, the poor fluidity of the ink is also prone to paste version; ③ the reason for the screen printing plate. The screen printing plate can be used after being rinsed with water and dried before use. If the plate is not printed in time after being placed for too long. In the preservation process more or less will adhere to the dust, printing if not cleaned, it will cause the paste. Causes of printing pressure. If the imprinting force is too large in the printing process, the scraper will bend. The scraper is not in line contact with the screen printing plate and the glass, but in surface contact, so that the ink can be scraped clean every time the ink is scraped, leaving residual ink, which will cause conjunctiva paste after a certain period of time. The screen printing plate and glass gap improper reasons. The gap between the screen printing plate and the glass cannot be too small. If the gap is too small, the screen plate cannot be separated from the glass in time after the screen printing plate is scratched. When the screen printing plate is lifted, the bottom of the printing plate is stuck with certain ink, which is also easy to cause paste plate. The reason for the ink, in the screen printing ink pigments and other solid particles are large, it is easy to block the mesh phenomenon. In addition, the selected screen mesh and through-hole area and the ink particle size is smaller than some, so that the coarse particles of ink is not easy to pass through the mesh and the phenomenon of sealing is also one of the reasons. Due to the large ink particles caused by the paste version, can be solved from the manufacture of ink, the main method is to strictly control the fineness of the ink.

In the printing process, the ink viscosity increases caused by paste version, the main reason is that the screen printing plate on the ink solvent evaporation, resulting in increased ink viscosity, and the occurrence of sealing network phenomenon. If the printing area is relatively large, the ink on the screen printing plate consumes more, and the paste plate phenomenon is less. If the graphic area is small and the ink consumption on the screen printing plate is small, it is easy to cause the paste plate. The countermeasure is to adopt the principle of adding ink a small amount of many times. The poor fluidity of the ink will cause the ink to produce paste when it does not pass through the screen. This situation can be solved by reducing the viscosity of the ink and increasing the fluidity of the ink without affecting the printing quality. After the occurrence of paste plate failure, can be aimed at the nature of the ink on the plate, the use of appropriate solvent scrub. The main point of scrubbing is to start from the printing surface and wipe gently from the middle to the periphery. Check the printing plate after wiping. If there is any defect, it should be repaired in time. Printing can be restarted after repair. It should be noted that every time the film is scrubbed, it becomes thinner. If the film is significantly damaged during wiping, it will have to be printed in a new version. 2. The ink is not fixed on the glass. When printing on the glass, it is very important to check the glass for strict degreasing and pretreatment before printing. When the glass surface is attached to grease, adhesive, dust and other substances, it will cause poor adhesion between ink and glass. The ink itself is not enough to cause the ink film is not fixed, it is best to replace other types of ink for printing. Improper selection of dilution solvent will also appear the phenomenon of ink film adhesion is not strong, in the selection of dilution solvent to consider the nature of the ink, in order to avoid the phenomenon of ink and substrate adhesion is not strong. 3. Inking Unevenness The film thickness of ink is uneven due to various reasons. As far as ink is concerned, the ink is poorly formulated, or the normally formulated ink is mixed into the ink skin. During printing, due to the expansion and softening of the solvent, the mesh that should penetrate the ink is blocked, which acts as a plate film, making the ink unable to pass through. In order to prevent this failure, the deployment of the ink (especially the old ink), before use to use the screen filter once again. When reusing the used printing plate, the old ink attached to the plate frame must be completely removed. When the printing plate is stored after printing, it should be fully washed (including the squeegee). If the tip of the front end of the ink return plate is damaged, there will be a trace along the movement direction of the scraper. When printing glass, there will be obvious ink unevenness. Therefore, the front end of the scraper must be well protected so that it will not be damaged. If it is damaged, it is necessary to grind carefully with a grinding machine. Furthermore, the unevenness of the printing table also affects the uniformity of inking. The ink layer of the convex part is thin, and the ink layer of the concave part is thick, and this phenomenon is also called ink unevenness. In addition, if there is dust on the back of the substrate or on the printing table, the above failure will also occur.

pinhole phenomenon

The pinhole phenomenon is the most headache problem for the staff engaged in glass screen printing. The causes of pinholes are also varied, many of which are currently unexplained, and some are still quality management problems. Pinhole is one of the most important inspection items in printing product inspection. ① dust and foreign matter attached to the plate. When making a plate, some sol will be mixed in with water washing and developing. In addition, in the emulsion coating, there are dust mixed, attached to the screen will produce pinholes. These can be found and repaired in time if attention is paid to inspection during the test. If dust and foreign matter adhere to the screen, blocking the screen opening will also cause pinhole phenomenon. Before the formal printing, carefully check the screen to eliminate the dirt on the plate; ② cleaning of the glass surface. The glass plate should be pre-treated before printing to make its surface clean, immediately after printing. If the glass is not printed immediately after processing, it will be contaminated again. After pretreatment, dirt such as grease can be removed, and dust attached to the surface can also be removed. Special attention should be paid to the fact that when the glass is moved by hand, the fingerprint of the hand will also be attached to the printing surface, and pinholes will be formed during printing.

Bubbles appear

Bubble glass in the ink after printing bubbles sometimes appear, the main reasons for the bubbles are the following aspects: ① substrate prepress processing. Substrates such as dust and oil stains attached to the surface of the substrate; ② bubbles in the ink. In order to adjust the ink, when adding solvents and additives for stirring, some bubbles will be mixed into the ink. If it is placed regardless, the ink with low viscosity will defoam naturally, while the ink with high viscosity cannot defoam naturally. Some of these bubbles in the printing, due to the transfer of ink and natural elimination, and some have become larger and larger. In order to remove these bubbles, a defoamer is used, and the amount of defoamer in the ink is generally 0. 1 ~ 1%, if more than the specified amount will play a foaming effect. Even if the ink is foamed after transfer, as long as the wettability of the substrate and the fluidity of the ink are good, the bubbles on the surface of the printing ink film will gradually be eliminated, and the ink will form a flat printing ink film. If the ink bubbles are not eliminated, the ink film will form a ring-shaped uneven film surface. Generally, when the bubbles in the ink pass through the screen, they can also be defoamed due to the effect of the screen; ③ The printing speed is too fast or the printing speed is uneven. The printing speed should be appropriately reduced to maintain the uniformity of the printing speed. 6. Electrostatic fault electrostatic current is generally very small, but the potential difference is very large, and can appear to attract, repel, conductive, discharge and other phenomena. The adverse effects of screen printing. When the screen is printed, the rubber part and the screen are charged due to the pressure scraping of the squeegee rubber. The screen itself is charged, which will affect the normal inking and cause the blocking failure; the screen will be sucked at the moment of the substrate output; the method to prevent static electricity. Methods to prevent static electricity generation are: adjust the ambient temperature, increase the air humidity, the appropriate temperature is generally about 20 ℃, relative humidity of about 60%; can make static electricity in the wet air transfer; reduce the screen distance, reduce the printing speed.

Printing size expansion

The main reason for the expansion of the printing size is that the ink viscosity is relatively low and the fluidity is too large; the screen printing plate is enlarged in size when it is made, which is also the reason for the expansion of the printing size. In order to avoid the ink fluidity is too large and cause the ink to overflow around after printing, resulting in larger printing size, can consider increasing the ink viscosity, in order to reduce the fluidity of the ink. In the production of screen printing plate, to strictly ensure the quality of the screen plate, to ensure the tension of the screen. 8. A part of the ink leakage film of the printing plate is called ink leakage fault. The reason is: part of the scraper is injured; The pressure of scraping ink is large; The gap between the plate and the glass is too large; The plate frame is deformed greatly and the local printing pressure is not enough: the ink is uneven; The screen is too thin; The printing speed is too fast, etc. If dust is mixed into the glass and ink and printing is carried out without treatment, the plate film will be damaged due to the pressure of the squeegee. Insufficient exposure during plate making will cause ink leakage from the plate film. At this time, adhesive tape can be used to paste it from the back of the plate for emergency treatment. If this operation is not very fast, it will make the layout of the ink dry, have to use solvent to wipe the whole plate. Wiping the plate is also the cause of the plate film peeling, so it is best to avoid it. The ink leakage of the plate often occurs in the part where the ink stays, so it is best to strengthen this part when making the plate.

The graphic part and the dark part appear blotchy.

Zi ink refers to the spot-like marks on the graphic part and the dark part on the glass surface, which damages the printing effect. Glass screen printing is easy to produce this phenomenon. The reasons are as follows: the printing speed and the drying of the ink are too slow; The ink layer is too thin; The ink thixotropy is large; The influence of static electricity; The pigment dispersion in the ink is poor. Due to the polarity of the pigment particles, the particles aggregate each other and the color spots appear. The improvement method is: improve the fluidity of the ink; the use of fast drying flux; as far as possible with high viscosity ink printing: increase the wet film thickness of the ink, try to use the ink made of small oil absorption pigment: minimize the impact of static electricity. 10. When the image is deformed and printed, the pressure applied to the printing plate by the squeegee can make a line contact between the printing plate and the printed object, not more than that. If the printing pressure is too large, the contact between the printing plate and the substrate will cause the screen to expand and contract, resulting in deformation of the printed image. Screen printing is a kind of printing with the smallest pressure in various printing methods. If we forget this, we can't print a good print. If you do not increase the pressure can not print, should reduce the gap between the layout and the glass surface, so that the pressure of the squeegee can be reduced.

Conclusion

At present, glass screen printing technology is changing towards the processing field of high-tech content and high-tech added value. Products such as touch screens, liquid crystal substrates, and solar photovoltaic substrates mentioned earlier have gradually become an inseparable part of the current field of electronic information products. I believe that with the passage of time, glass screen printing technology will provide more support for the glass industry and even electronics, construction, energy and other fields.

Four Quality Problems and Treatment in Screen Printing Operation

1 Line distortion

The number of screen printing is too large, which is caused by the relaxation of the screen template. The distance between the positioning loose screen and the substrate changes; The included angle between the scraper and the substrate is incorrect, or the force is uneven; The consistency of the printing material is too thin or too dry; After cleaning the printing surface of the reworked workpiece, the solvent will not dry up to screen printing, etc.

2 pattern or line hair flower

The printing material is too thin and the force is too large when scraping. The printing material is unevenly adjusted (the solvent in the printing material is unevenly dispersed); After wiping the net, the solvent or cleaning agent on the net mold is not dry, or the surface cleaning agent is not dry or clean when the workpiece is reworked. After the first scratch, the sealing force of the printing material is too large, causing a small amount of printing material to squeeze out the mesh; in the printing, the speed of the scraper movement (movement) is too large in the effective area of the substrate, and the printing is stopped or repeated. The fineness of the printing material does not match the selected mesh.

3 pattern line edge burr, notch, cam, etc.

The surface of the printing substrate is not clean and oily. Printing material is too sticky, dirt on the net mold has not been removed, printing material particles are large, high mesh wire mesh cannot pass; Silk screen drying speed is too fast, silk screen workplace ventilation; Quick-drying printing material failed to seal the net in time, resulting in netting; Uneven force during scraping, large or small; The surface of the substrate is uneven, etc.

4 pitting printing material is too sticky, and has impurities and blocked holes; Or the printing material is too sticky and the scraping force is insufficient;

When the printing material is mixed, the maturity period is not enough, the residual bubbles in the printing material are not clean, and the bubbles are caused by sticking to the printing material after screen printing. The surface of the substrate is not clean, dust and other influences, improper force during printing, light and uneven or scraping, insufficient force; The printing material on the substrate is not dry, caused by dust in the storage place; Under suitable conditions of printing materials, the distance between the screen plate and the substrate is too large; pre-press screen cleaning is not thorough. 5 In silk screen printing, there is a problem with the included angle between the screen scraping plate and the substrate. They are not in line contact, but in small plane contact. The distance between the screen plate and the substrate is small, or the tension of the screen plate is small; During silk screen printing, the embossing force is too large and the ink layer is thick and sticks to the net. The printing material is too thick, etc. 6 Solutions Carefully analyze the reasons that affect the quality and solve them according to the causes. As for the quality problems arising from non-scratch printing operations, such as net stretching, optimal distance, screen printing template making, workpiece surface treatment and printing material matching, etc. will all affect the quality of screen printing.

Causes and Elimination of Paste Phenomenon in Different Printing Processes

The term paste version is often interpreted as dirty, blocked or dyed, and different pastes will appear in different forms of printing. In recent years, the paste plate has repeatedly appeared in transparent ink printing and composite ink printing. Such as offset printing paste version, often due to ink imbalance (potion and ink pH difference) caused. The gravure paste version is mostly caused by the scraping of the scraper, and it mostly appears in summer with high temperatures. When we discuss this failure, it is not difficult to find that the ink of printing ink determines the production of this phenomenon. It is impractical to generally determine what is the reason and what is the situation, which hinders us in the actual operation of printing in a very short time to remedy and eliminate.

Paste plate of 1. relief

The most obvious printing phenomenon, such as "product", "day", "mouth" and so on, is filled with ink into a solid state, and even dots into a piece, so it is often called blocking plate. The main reasons are:

(1) the dry ink is too large, so that the ink early dry or sticky too much, resulting in paper or plastic ink layer dots or paper, plastic debris concentrated on the plate or dot part;

(2) The ink dries too fast, the ink in the ink fountain crust or dry hard particles;

(3) The ink is too thin, and the ink is squeezed out under printing pressure;

(4) too much paper or plastic absorption binder, resulting in excessive pigment content in the ink;

(5) the roller has defects or not through the heart;

(6) The printed relief is not flat or too high;

(7) Too thick ink is used on plywood paper or smooth plastic (especially plastic woven bags);

(8) to the amount of ink is too much or dry too slow.

The method of exclusion is:

(1) the use of dry and reasonable and thick ink;

(2) high-tone parts or dot parts to reduce the pressure;

(3) re-filter ink 15 ~ 25μm);

(4) in the printing on the side of the base paper, plastic separated or change the substrate;

(5) in the thick ink to add diluted ink additives, in order to improve the flow rate of ink;

(6) to speed up the dry ink or solvent;

(7) dye type ink should reduce the content of resin;

(8) reduce the amount of ink or add slow ink inhibitor;

(9) Do not let the wind on the drying device blow to the plate;

(10) Add TM3 or silicone oil in the ink.

A paste plate for 2. lithography (printing).

1. The lithographic (printing) oil (greasy) is expressed in the form of: the graphic lines are spread out and expanded without being clear and complete, and there are dirty marks of varying degrees of ink in the blank area, especially the rubber blanket is also glued with pieces of ink. The reasons for this are:

(1) The water absorption part on the printing plate forms an ink absorption center, causing the surfactant in the paper or plastic ink layer to migrate to the water absorption area.

(2) The pH value difference between ink and water is too large (that is, the ink is often said to be unbalanced), which causes the metal of the printing plate to be dissolved by the acid in the liquid medicine and the printing plate is not clean.

(3) In the use of lead-containing slurry dry oil, especially when the amount is too much, the dry oil is destroyed by highly acidic liquid medicine, which is covered by a thin layer of ink (often resulting in yellowing of the entire layout). Since the ink layer interferes with the control of the wetting, the oil stains.

(4) The ink is too oily and too thick, resulting in insufficient water on the layout.

(5) The non-printing area is due to lack of inductive treatment and high pressure of the ink roller, improper addition of desiccant, and poor quality or poor installation of the water roller.

The usual treatment is:

(1) The pH value of the ink should be lowered, close to the pH value of the liquid medicine;

(2) add wax or sodium silicate in the ink;

(3) Check the quality of the printing plate and the water roller;

(4) control the printing speed;

(5) ink as thin as possible;

(6) choose oily small and thick ink.

2. Lithographic (printing) dirty form is the form of printing plate is full of slight ink, and easily transferred to the blanket, and then transferred to the paper or plastic printing. Sometimes it is easy to wipe off, but it quickly reappears, and there is staining in the potion. According to the phenomenon of floating dirty, it is often believed that the ink floating on the water or dissolved in water caused. Therefore, it is also called disaster water or ink bleeding. The reason is:

(1) The surface active substance in the paper is leached to form an emulsion of ink in water, and then covered with the moisture absorption part of the printing layout.

(2) The pigment in the ink is poor in lipophilicity and is not fully wetted by the binder (for example, the ink made of the yellow pigment is easy to run into the water).

(3) When the synthetic resin is used to dissolve the binder at a low temperature and the content of the ink oil is relatively high, it is very easy to cause the ink to emulsify.

The usual approach is:

(1) The ink should be stored for a period of time after it is produced;

(2) the resin in the ink should have better wettability of the pigment;

(3) as far as possible to reduce the acid value of the liquid medicine, and reduce the amount of ink;

(4) adding viscous resin liquid;

(5) the use of oil absorption or surface with hydrophobic additives treated pigments and so on.

3. Lithographic (printing) dirty form is the appearance of large ink spots in the non-printing area. The reasons for this are:

(1) The printing pressure and the operation of the printing machine destroy the isolation film on the printing plate and expose the metal, which will be immediately affected by trace surface activity, polarity, free fatty acid and other substances, resulting in pollution after these places absorb ink.

(2) A dirty plate produced by an excessive residual ink layer left on the plate at the time of development of the printing plate.

(3) The ink is too thin and oily, soft, and sticky, which is easy to cause the ink roller to slip and then make the water roller dirty.

(4) In addition to the induction treatment is not appropriate or the glue is not good.

(5) the lack of water on the printing plate and the low acidity of the liquid medicine lead to the absorption of ink by the water roller.

There are also dirty marks inherent in the PS version, and so on.
The usual treatment is:

(1) ink to add ink (resin liquid);

(2) the content of grease and oil in the ink to minimize some;

(3) increase the amount of water supply, especially increase the acid value of the liquid medicine;

(4) the use of large concentration of ink as far as possible to make some of the print thin;

(5) the selection of higher surface tension of the liquid medicine;

(6) Adjust the imprinting force between the printing plate and the rubber roller;

(7) reduce the desiccant;

(8) exchange faster drying type of resin ink.

Paste plate of 3. gravure (gravure)

In plastic printing, especially in the manufacture of composite inks, small print or hierarchical layout patterns can not be printed, and even the surface of the substrate has formed different shades of ink. Some people think that it is due to poor adhesion (with) caused, do not speak scientifically to add to promote adhesion of the tackifier (resin) agent, although it can overcome the disadvantages of pulling off, but excessive addition will often lead to ink film softening, which can not control the paste version (dyeing). The reason is:

(1) due to floating color caused by its surface and metal gravure, scraper affinity;

(2) the acid value of the composite resin is too low;

(3) The ink has a strong wettability to the chrome-plated surface on the intaglio, resulting in a scraper that cannot clean the ink;

(4) Slow scraper or wrong angle;

(5) The surface of the cylinder is rough;

(6) The initial drying (period) of the ink is too slow (for example, ethyl acetate (fast-drying solvent) is introduced into the printing ink system, and it is appropriate to print the film within 1~3S.

(7) In a high humidity environment, the charged ink has an affinity for chromium (increase the proportion of antistatic agent).

(8) the printing speed is too slow or the printing plate caused by poor paste.

How to troubleshoot this fault:

(1) If the chrome-plated surface of the new cylinder is rough, add a quick-drying solvent to the ink to form a thin layer of ink between the scraper and the impression cylinder. After two hours or even several hours, polish the chrome surface and replace it with a normal mixed solvent (for example, 7 parts of ethyl acetate, 2 parts of toluene, 1 part of butyl acetate or 8 parts of ethyl acetate and 2 parts of toluene.

(2) if the ink has impurities such as pigment particles and paper, plastic, should increase the solvent, the best treatment method is to use 250 mesh screen filter ink.

(3) Change to a new scraper blade and adjust its angle.

(4) If it is caused by slow drying ink, add fast drying solvent to dilute the ink. On the contrary, if it is caused by fast drying ink, slow drying solvent or silicone oil can be added to slow down the drying.

(5) If the ink is dried in the plate cavity due to blowing, the blowing angle should be adjusted to generally increase the speed of the printing machine or re-plate making.

(6) add solvent to reduce the viscosity of the ink or add anti-dirt removal agent (such as wax, etc.) and so on.

(7) Add gold oil or resin liquid, or change the ink without particles.

Analysis of the causes of ink blooms in embossing

Print layout ink color uniformity, bright colors, is the basic requirements of product quality. In particular, some color printing packaging and decoration products, due to the large printing layout, the amount of ink is also increased accordingly, so that the thickness and uniformity of the ink layer of the layout directly affect the appearance quality of the product. The ink color of the layout is one of the quality problems that are easy to appear in the color printing products of the letterpress process. The reason is caused by the error factors in the process and the abnormal operation technology. There are defects in the equipment and defects in the raw materials. Therefore, only a correct understanding of the causes of product printing ink color hair, in order to fundamentally solve the problem, to achieve a better elimination of printing products ink color hair quality failure purposes.

1. ink blooms caused by unsuitable material properties of printing plate backing

In fact, maintaining a constant printing pressure is an important condition to ensure the stable quality of printing ink, and the factors that affect the printing pressure, in addition to the accuracy of the equipment, are also related to the characteristics of the base (base) material of the printing plate. For example, printing machines with letterpress flattening and circular flattening structures, copper, zinc or resin plates used for printing need to be pasted with the base plate to print. It can be seen that the bottom support plays an important role in bearing pressure in printing, which requires that it should have the good advantages of solid, firm, pressure resistance and no deformation, so as to ensure the stability of printing ink color quality. The process practice shows that the traditional plywood materials used as printing plates not only have many disadvantages, such as low printing resistance rate of printing plates, inaccurate overprinting of products, etc., but also easy to produce poor ink color transfer, causing uneven or insufficient ink layer of the layout, which is mainly due to the defects of poor firmness and easy deformation of the wooden base itself, it is difficult to transfer the ink layer on the layout evenly to the printed sheet, and it is easy to produce ink color flower phenomenon. In order to avoid this situation, it is necessary to close the pad plate technology. When the printing plate is under the pad, it must be evenly and firmly padded. For the layout with large printing area, it is better to use metallic plate holder die cutting and hot stamping indentation, such as magnetic plate holder, aluminum plate holder, etc. Metal plate holder has the advantages of flatness, good firmness and high compressive strength, which can better ensure the stability of printing pressure and effectively prevent the occurrence of printing ink color flower quality problems.

Printing ink blooms caused by poor 2. machine or adjustment

When the aging of the machine causes obvious wear and looseness of the roller shaft head, bearing, gear, rack, ink roller system and linkage stamping parts, it will affect the printing pressure and the stability and uniformity of the printing ink. In this case, if the printing area is large plate products, it is easy to appear ink color flower phenomenon. In order to prevent the occurrence of this undesirable phenomenon, attention should be paid to the maintenance of the equipment, especially the stamping of the machine and the associated parts such as the ink roller bearings, to maintain a good lubrication state, to prevent the key parts of the machine from wearing and loosening. In addition, the position of the ink roller is not suitable for printing ink color. Therefore, the contact between the ink roller and the ink-string iron roller and the printing plate should be uniform, and the pressure should be moderate, so as to prevent the phenomenon of printing ink color flower caused by poor contact of the ink roller.

Ink-color blooms caused by 3. lining discomfort

The lining is the medium of printing pressure and layout ink layer transfer. The material characteristics of the lining and the quality of the lining directly affect the ink quality of the printed matter. If the deformation coefficient of the lining is large, the flatness is poor, and the ink color of the printed layout is prone to blooms. Therefore, only according to the characteristics of printing, scientific and reasonable selection of lining materials, so that the lining in the printing to maintain good stability, in order to ensure the stability of the ink color quality. According to the practical experience of the production process, when printing plates or screen plates with soft resin plates, hard lining materials with hard texture, strong toughness and small deformation coefficient, such as cardboard, kraft paper, insulating paper and film base, should be selected, and the quality of printing ink is relatively stable. If the use of hard copper, zinc plate printing plate products, due to the flatness of this kind of plate, gloss and ink affinity is relatively poor, should choose a certain degree of elasticity of neutral, such as cloth, blanket, nylon cloth, fine grain cloth, offset paper and newspapers, etc., so as to better prevent the occurrence of ink color hair quality defects.

The phenomenon of printing ink blooming caused by the discomfort of 4. plate selection

Plate products if the use of zinc plate material printing large area of the product, but also prone to ink flower phenomenon. The main reasons are: oxidation on the surface of the plate to form a "sand hole" shape, as well as high baking temperature, high level of corrosive liquid and poor ink affinity of the plate, which make the ink layer of the plate and the surface of the plate have poor contact during printing, thus causing the appearance of ink color blotting. In this regard, the solution is: grinding the surface of the printing plate with charcoal, so that the slight roughness of the layout can be eliminated or reduced, and the printing pressure and ink supply should be appropriately increased when printing. For printing fine plate products, it is best to use solid resin plate for printing. The plate is soft in texture, and has good gloss and ink affinity, which can better avoid the phenomenon of printing ink and ensure the ink quality of the product layout.

Printing ink blooms caused by poor 5. paper material

Production practice shows that the rough surface of the paper has a large ink absorption capacity, which is due to the interweaving of paper fibers to produce a certain gap, the concave paper surface is easy to produce poor contact with the printing plate, and a large amount of ink is needed to meet the ink absorption demand of the paper surface. In this regard, if the printing pressure is insufficient and the ink layer is coated thin, it is easy to cause the ink layer of the printed layout to appear flowered. Therefore, when printing paper with poor smoothness, the printing pressure should be appropriately increased, and the coating amount of ink should also meet the requirements of uniform inking and receiving of ink on the layout, so as to prevent the occurrence of quality problems of printing ink color.

6. ink blooming phenomenon caused by improper use of ink additives

Tackifier, anti-sticking agent, etc. are auxiliary materials for the deployment of ink, adding appropriate amount and proper usage can play a certain anti-sticking effect. However, if the amount is too much or uneven stirring, etc., it is very easy to cause the ink color of the printed product to appear flower phenomenon. In particular, the incorrect use of the anti-adhesive agent is more likely to cause the problem of printing ink quality failure. If the anti-adhesive is directly added to the ink without stirring evenly, then the ink affinity of the printing plate will be greatly weakened after the anti-adhesive with coarse particles is transferred to the printing plate, and the printed ink color will appear flower defects. Therefore, the correct use of anti-adhesive is a crucial part, the amount of anti-adhesive added to the ink is generally not more than 4%. When mixing, the anti-sticking agent should be diluted with bright gloss oil or ink mixing oil and stirred evenly to make it a liquid with certain fluidity. In this way, it can be evenly distributed into the ink after repeated stirring. In this way, printing can not only play a better anti-sticking effect, but also prevent the ink from blooming.

To sum up, as long as we pay attention to conscientiously sum up the production experience in the production process practice, accurately understand and master the various reasons that cause the ink color of printed products, so as to take corresponding process technical measures and close the process and operation technology, blindness in process operation can be avoided, so that other packaging can not only improve the production efficiency, but also effectively ensure the ink color quality of products.

Tension Control in Gravure Printing

Gravure tension control system analysis generally includes the following.

1. Tension zoning and control requirements of each area

The tension control of the gravure printing machine is generally divided into four areas, namely, the unwinding tension zone, the feeding traction tension zone, the discharging traction tension zone and the winding tension zone, which are separated by the rubber pressure roller driven by the belt. The printing area is from the feed drive roller to the discharge drive roller, and the requirement for the tension of the printing area is that the tension is constant, because only under the condition of constant tension can the registration be guaranteed. The unwinding tension serves the constant tension of the printing area. The requirement for the unwinding area is to release the material roll into the printing area to ensure that the transmitted tension can be kept constant regardless of the size of the roll diameter. Otherwise, the fluctuation of tension will directly affect the constant tension of the printing area, thus affecting the registration. The winding tension is different. In this area, multi-color printing has been completed, just smooth winding. According to the different winding quality requirements, there are constant tension winding and variable tension winding. The common decreasing tension winding (also known as taper winding) refers to the latter. Since variable tension winding may affect the registration accuracy of the last printing color group, the printing area is effectively separated from the winding area, and the material roll is driven to advance from the printing area to the winding area, so that the printing area still maintains constant tension, while the winding area decreases tension, which is realized by the rubber pressing roller mechanism driven by the belt. Both segmented control and overall coordination, so that the tension of each area is multi-color registration service, which is the key point of rotary printing in tension control, and so is rotary gravure printing.

2. Tension detection and feedback of each area

Each area generally has an independent detection device, such as a tension roller detection device composed of a resistance strain gauge sensor, a capacitance sensor, etc., and a position detection control device composed of a floating roller and a potentiometer. The functions of these detection circuits with different structures in the whole system are obviously different. The tension roller detection device responds quickly, but lacks the control ability for the system stability caused by the quality problem of the roll itself. Although the position control device does not directly detect the tension, it controls the relative position of the printing material in the floating roller paper path to remain stable under normal tension, thus achieving the purpose of controlling the constant tension. The position control device can slow down the tension fluctuation caused by the quality problems of raw materials such as the roll diameter is not round through the floating roller paper path, which is not achieved by the tension roller detection device.

3. Tension actuator

Commonly used tension actuators include electromagnetic or magnetic powder clutch/brake, pneumatic clutch/brake and servo motor

A miniature actuator motor on a 360 ° gearbox is also included in the conventional gear transmission system. It is worth noting that according to the automatic control theory, the clutch brake mechanism belongs to the first-order linear link, but because the linear segment only occupies the middle segment in the whole curve area, and the high end and low end of the curve area are mainly imitated linear, and there is still a distance from the requirements of linear control, so this execution function is still defective. Servo motor belongs to the second-order link, under the existing control theory, stability and follow-up can be taken into account, so the advanced tension control system generally adopts servo motor direct drive control.

4. Compensation for mechanical synchronous speed loss during roll transfer

There are three reasons for the loss of mechanical synchronization speed: the printing pressure applied to the entire web width, the surface friction of the printing material in contact with the guide roller, and the resistance caused by the inflexible bearing of the guide roller.

Which plays a major role in each color group of rubber pressure roller on the printing material applied pressure, this transfer process must be applied pressure, gravure printing in all printing process is the largest. According to experience, for different printing materials, the hardness of the rubber pressure roller is different, and the pressure applied is also different. For example, for film printing materials, rubber pressure rollers with Shore hardness of 65~70 degrees are generally used, with a unit pressure of 900 kg/m; For paper printing materials, rubber pressure rollers with Shore hardness of 70~80 degrees are used, with a unit pressure of 1800 kg/m; For cardboard printing materials, rubber pressure rollers with Shore hardness of 80~90 degrees are used, and the unit pressure is 4500 kg/m. The use of different hardness of the rubber pressure roller and apply different pressure, the synchronous speed of the transfer of the printing material is obviously different, the softer the rubber pressure roller, the greater the pressure applied, the greater the loss of mechanical synchronization speed.

The traditional approach to compensating for mechanical synchronization speed loss is to increment the diameter of each color group drive roller (I. e., plate roller). As we all know, the linear velocity V = 2πrn. If the linear velocity of the plate roller is to be adjusted during printing, the rotation speed n of the plate roller can be adjusted (I .e. the method of increasing the rotation speed of the motor of each color group plate roller used in the current servo gravure press) or the diameter of the plate roller can be adjusted (I .e. the traditional method of increasing the diameter of the plate roller for more than 20 years). However, this compensation is based on experience rather than precise calculations. Obviously, the characteristics of the substrate material is different, the width of the applied pressure is different, the loss of mechanical synchronous speed is different, so the exact compensation value should also be different. However, the method of increasing the diameter of the plate roller by 0.02~0.03mm (or even 0.04mm) is used to compensate, which can only be based on the "fuzzy" algorithm.

When the domestic printing machine industry developed the servo-type gravure printing machine, it was initially believed that the law of increasing the diameter of the plate roller could be eliminated, because when setting the rotation speed of the servo motor of each color group plate roller, the amplification amount brought by the increasing diameter of the plate roller could be calculated in advance, so the servo-type gravure printing machine did not have to interchange the printing color sequence like the traditional gravure printing machine. However, printing practice has proved that even if the servo-type gravure printing machine has increased the rotation speed of each color group plate roller motor, if the plate roller continues to increase in diameter, the printing registration effect is much better than when the plate roller diameter does not increase. This shows that the current gravure servo system can only be limited to the scope of experience in compensating the loss of synchronous speed, and there is still a lot of distance from the real sense of compensation control.

5. Set control

The register control of gravure printing must be based on stable tension control. Only after the above four problems are basically solved, the accurate register of gravure printing is possible. The industry has some misunderstandings about the registration problem, especially for servo-type gravure machines, which believe that the encoder accuracy can reach millions of times per second, and the registration is definitely no problem. In fact, in the actual process of registration, the computer is not tracking the cursor itself, but the trend of cursor movement. This is like shooting a bird with a gun. It is not to pull the trigger only after seeing the bird, but to calculate the advance amount according to the bird's movement trajectory. It is reliable to shoot the bird in this way. The same is true of the registration system of the gravure printing machine. The cursor movement trend is the premise of registration. If the cursor movement trend of printing [Encyclopedia Weibo] on the printing material cannot be controlled, even if the servo motor is equipped with an encoder of 4 million times per second, the registration error is likely to exceed the standard, and the registration loss may be unexpectedly large.

6. Compensation of deformation of printing material

The synchronous speed compensation of the printing material in operation can be guaranteed by servo machine, but there is no reliable compensation method for the deformation of the printing material itself. In film printing, for example, different types of film, in the same thickness and width conditions, the stretching deformation is not the same; for different thicknesses of the same film, such as 20μm and 40μm thick BOPP film. Under the same drying conditions, the stretching deformation of the two is also different. Taking paper as an example, the same material and thickness of paper with a moisture content of 5% and 8% has different deformation data under the same drying conditions. For these differences, it is necessary to establish a mathematical model and load it in the mathematical model of registration control in order to effectively control the printing registration accuracy. If this is not the case, the registration accuracy of gravure printing can only rely on the use of thick and not easy to deform the printing material, such as PET film to ensure. At the gravure printing production site, we often hear front-line operators complain that the printing plate is not good or the printing material is not good, resulting in inaccurate color registration or registration error exceeding the standard in the printing process, resulting in cost loss. However, when checking the printing plate and the printing material, we really can't give any reason to get the desktop. According to the author, this is the main reason.

How to choose the right printing ink?

 

Any color is represented by the three characteristics of hue, lightness and saturation, so the above three factors must be considered in the color matching process. Although black is theoretically a complete absorption of light, black ink is still shiny. Ink is a pigment (toner) and resin binder grinding, pigment particles wrapped around a layer of nearly transparent resin oil, this layer of resin oil has refraction and reflection of light, so we can feel the black ink printing on the substrate still has a certain luster. In the process of ink color matching, the ink used should be determined according to the actual printing process, the thickness of the ink layer, the printing substrate and other conditions. In the choice of ink, to consider the ink itself gloss, hue, tinting strength, hiding power.

1. The gloss can be measured by the instrument, can also be judged by the naked eye, usually in the color matching process only by the naked eye. Gloss actually refers to the degree of the ability of the ink printing sample to reflect light in the same direction after being irradiated by light. It directly affects the appearance of printed matter and is a very important indicator. At the same time, in the choice of ink, to distinguish the ink itself is bright, semi-gloss or matte type ink, to avoid mixing errors.

Hue is the basic characteristic of color and is used for qualitative difference. When matching colors, we must first consider whether the hue is consistent. The detection method is usually to scrape the color of the sample paper or to simulate printing, and to observe and compare the standard sample and the sample by human eyes.

3. hiding power is the degree to which the ink covers its ground color. The better the hiding power, the worse the transparency, and the transparency affects the efficiency of the ink set and the degree of influence by the printing substrate.

4. Tinting strength is a method of indicating the concentration of ink. The determination is based on a certain amount of ink and then add a certain amount of standard white ink dilution mixing, and then compared with the standard method. The strong and weak color difference reflects the degree of color mixing of the ink and affects the film thickness of the printing ink.

Through the color identification of scratch paper to do scratch color test (Drowdown), you can compare the ink sample and standard sample in gloss, hue, hiding power differences in three aspects. Specific method: Put standard ink in the upper left corner of the identification paper and color matching ink in the upper right corner. The distance between the two is about one centimeter. Use a scraper to flatten the thin part and quickly spread the thick part with light force at an angle nearly perpendicular to the scraping paper.

After the surface of the ink is dried, the hue of the ink can be observed in the thin part, the covering power and transparency of the ink can be identified in the black belt part, the difference in gloss between the two can be judged in the thick part and the appearance of the whole color can be observed. Usually black and color inks use white scratch paper, while white ink uses black scratch paper.

 

 

Technology of screen printing plastic shell

1. Ink preparation

Judgment method for the degree of concentration and thinning: the degree of concentration should be based on the fact that after the ink passes through the screen, the screen mesh or drawing does not appear on the printing surface. The degree of dilution is best when placed on the screen, and the ink can pass through the mesh by its own weight but not drop. When the printed lines are thin, the points should be diluted, and vice versa, the points should be concentrated.

2. Screen selection

The quality of the silk cloth is uniform with the wire diameter and the mesh number is accurate and consistent, which is stable in quality.

General selection of mesh is 450~500 mesh. Fine line, high ink fineness, poor absorption of the substrate, should choose the number of high mesh screen, on the contrary, should choose the number of low mesh screen.

The position and size of the graphic on the screen during plate making should be determined according to the structure and size of the substrate and the position of the graphic on the substrate. If the design is not good, it will affect the quality of screen printing, or even screen printing. In addition, it is best to use a screen printing for pictures and texts on the same printed object. If it is divided into more than two screen printing, the process will reduce the pass rate of screen printing.

3. Scraper selection

The material of the scraper is mostly polyurethane. The polyurethane rubber scraper has good abrasion resistance, solvent resistance and resilience. Its hardness is 60~80 Shore. Screen tension, surface flatness good substrate, should choose high hardness scraper. On the contrary, should choose low hardness.

When printing on curved surfaces, low-degree spherical surfaces or substrates with poor flatness (local protrusion), the width of the scraper should be narrow and not wide.

4. Web positioning

The fixture materials used in the factory are metal, wood, plywood, PVC transparent sheet. Such as positioning difficult, substrate size and small, should choose metal fixture.

If the article is closer to the edge of the substrate, a piece of plane wood as high as the edge of the substrate should be fixed beside the substrate to avoid easy pasting of pictures and texts.

Net distance is generally 1.0~2.5mm. If the printing pattern is easy to paste or reticulated, the screen distance should be adjusted.

5. Screen printing process

Scraping pressure is high, the amount of ink is more, but the screen is easy to deform, so the scraping pressure should not be high. Scraping speed is usually 60~200 mm/s. Scraping speed, less ink, but not easy to block the net. Therefore easy to block the net of ink, scratch speed should be faster.

Scraping routes are straight line, oblique line and curve. It should be selected according to the flatness of the substrate and the distribution of the picture and text on the substrate. When the length of the scraping route is long and the ink consumption is large, the amount of scraping should be more or even a layer of ink should be scraped first, and then scraped.

The screen printing experience introduced in this paper is suitable for screen printing on rigid plastic shells.

The most common screen printing quality problems are missing words and paste words. Therefore, once this kind of problem occurs, it can also be solved from the above five aspects.

 

Three Objective Factors Affecting the Quality of Printing Products

1. Printing Consumables

Including paper, ink, plate and fountain solution have different properties, and these properties will have a direct impact on printing. Before printing, we must first master the performance and printing suitability of various consumables, avoid the factors that may affect printing, and carry forward the characteristics that have a positive effect on printing. Many printing products have different requirements for printing effect. Some packaging and printing products require beautiful colors, while some book printing products require soft colors and not dazzling. When selecting printing materials, users should pay attention to the needs of printing products and find out all kinds of consumables suitable for printing.

For example, when printing all kinds of labels, high-grade coated paper with high whiteness, good surface smoothness and good opacity should be selected for printing. In addition, some products need to be exposed to the outside for a long time. When choosing ink and paper, the sun resistance will be a performance index that needs special attention. Sometimes, when printing different kinds of products by offset printing, the requirements for blanket hardness are also different, the choice should be targeted.

As long as we fully consider the existence of some external factors that affect the quality of products, give full play to the advantages and overcome the defects in production, the quality of printed products can be improved to a certain extent.

2. printing equipment

Including the normal operation rate of related equipment in the production process, the input of various auxiliary equipment and whether the mutual matching relationship meets the requirements will have a certain impact on the quality of printed products. Any book or packaging and printing products are mostly processed by several or more than a dozen processes, including printing, binding, polishing, bronzing, etc., and the operation of these processes is generally inseparable from the equipment. The quality of the equipment, whether the operation is convenient, and whether the equipment used in the next process can better process and produce the products produced by the equipment in the previous process, etc, will have a certain impact on the quality of printing products.

If the equipment often fails, it will not be able to fully play the functions of the equipment. The semi-finished products processed by printing or other processes will have various quality defects, thus unable to guarantee the final quality of the product, which is the key to ensure the normal operation rate of the equipment. In addition, some equipment in the use of the process for the environment and other objective factors also have certain requirements, when not up to these requirements will directly affect the quality of products, visible, to ensure the normal operation of the equipment to ensure the quality of printed products.

3. printing environment

Including printing and other processes in the production process of the ambient temperature, humidity, dust and light and many other environmental factors, these factors will affect the quality of printed products in each process. Changes in the environment will have a certain impact on printing. In offset printing, especially flat sheet offset printing, changes in environmental humidity will directly cause paper to absorb water or lose water, causing paper deformation, affecting paper walking and overprinting in the printing process, and reducing the quality of printed products. The change of temperature and the size of dust in the printing environment also have certain effects on the properties of ink and paper in offset printing, it will affect the quality requirements of the surface ink layer drying and color uniformity of the printed product to varying degrees, resulting in varying degrees of reduction in the quality of the printed product.

Flexo, gravure-based packaging and printing methods are more sensitive to changes in ambient temperature and humidity. Excessive temperature and low humidity are not conducive to the drying of ink (especially water-based ink), resulting in quality defects such as paste and napping, while excessive dust will cause quality defects such as false printing on the field layout of printed products.

In the printing process and the various processes of processing printed products, it is necessary to ensure the constant ambient temperature and humidity as much as possible, and reduce the dust in the air, so as to ensure the stability of the final printed product quality. In short, to ensure the stability of the quality of printing products, it is necessary to avoid the side effects of adverse factors on the printing quality in actual production, and fully explore the promotion of favorable factors. Only in this way can the quality of printing products be stable.

 

Analysis of why the print is dirty

Quality is the lifeblood of the survival and development of enterprises, in the actual operation process, a little careless will cause the printing with dirty, directly affect the quality of printing. The following I will summarize the long-term practice in the face of these failures can be timely and accurately ruled out.

1. Water spots. According to the principle of oil-water incompatibility, if the paper with water droplets, the print will leave a water spot. Cause analysis:

(1) If the air pump is in a high temperature and humidity environment, the offset press is placed in the air-conditioning workshop, and the moisture in the humid air is blown into the cool environment through the air pump, which will condense salty water droplets and blow them onto the paper through the presser foot and the paper separating nozzle.

(2) Many offset press buckets are made of iron sheet or copper-plated iron sheet. Due to the corrosive nature of acidic wetting liquid, the buckets will gradually corrode to form sand holes over time. Some sand holes are very small and can only drop two or three drops of water per minute. In this way, water spots that are sometimes absent will occur on the printed products. Therefore, the operator is required to carefully check the water bucket against the light and solder the sand holes when they are found.

(3) Some offset presses are not well maintained. Operators never clean the water bucket. In addition, when cleaning the ink roller, the ink on the ink roller splashes around with the cleaning agent, and those thrown into the water bucket form scale together with the fluff of the water roller. With the rotation of the water bucket roller, they accumulate between the water bucket roller and the wall of the water bucket, forming hard slag over time. When the bucket roller rotates, the hard residue will drop down the bucket wall from time to time with the water on the bucket roller, forming water spots on the prints.

(4) When the printing plate needs emergency water supply due to small water paste, the water bucket roller will pass a large amount of water to the water transfer roller, and the water transfer roller will drip the excess water during the transfer and extrusion process of the water transfer roller. A water baffle is installed under the water bucket of J2108 machine, which works well, but it is necessary to avoid too much water and dripping down. However, J4104 and other models do not have water baffles, so it is enough to stop in case of emergency water supply.

2. Oil spots. Since the viscosity of the oil is much lower than that of the ink, the oil droplets will expand on the surface of the blanket after being pressed, and make the ink produce a reverse impression, which is a circular oil spot on the printed crystal. Cause analysis:

(1) The lubrication of the paper feeding head is important and necessary. When refueling, wipe less frequently. After refueling, start the machine and the paper feeder to let the oil drip down during movement and wipe it again to ensure that there will be no excess oil dripping on the paper during normal printing.

(2) Focus on checking the air pump. If the air pump sprays oil, the presser foot and the paper separation nozzle will blow out many oil droplets in the form of oil mist splashing on the tip of the paper. Touch the oil filler cap (with small holes on it) on the oil chamber of the air pump with your hand to check whether there is any gas ejection. If not, the oil return effect of the air pump is not good.

(3) The transmission rod and bevel gear at the lower part of the pull gauge also need to be lubricated. Of course, only a little less or a little butter can be applied to it. If you add too much oil, the paper will stick to the paper during the pulling process.

(4) The gripper shaft and the supporting spring rod on the paper delivery teeth move frequently. If the lubrication effect is not good, it is easy to cause wear and tear, resulting in poor gripper and inaccurate overprinting. Therefore, be very careful when adding lubricating oil, wipe it while adding oil, transport it, and then wipe it with a rag after a period of time. However, many operators often do not add it because they are afraid that the oil will pollute the paper, resulting in wear of the spring lever and pin.

(5) During the refueling process, the paper transfer roller and the paper take-up guide rod are easy to get oil stains, so pay special attention when refueling, and check and clean frequently if necessary.

3. Eyes-like spots, pigmentation or white spots. If there is a spot on the printing plate, it will leave eye-like spots on the printing crystal. If there is a spot on the rubber blanket, it will leave a spot-like color spot or white spot on the printing crystal. Cause analysis:

(1) the surface strength of the paper in contact with water and ink, easy to produce powder. The phenomenon of napping, adhering to the blanket or plate.

(2) When taking ink from the ink tank, the dry ink skin and ink residue should be removed because of the ink skin. Once the ink residue falls into the ink bucket, it will be transferred to the printing plate.

(3) There are many fluff on the water roller pile. When printing the field version, it is easy to leave burr-like and filamentary traces on the printed product. Now there is a kind of nylon water glue velvet that is not easy to shed. If it is wrapped on the water roller, the effect will be very good. Sometimes, a water roller pile is used in several colors, and it is covered with ink residue, which will be transferred to the printing plate during the water transfer process.

(4) The cleaning and maintenance of rubber rollers is very important, but some operators do not attach importance to this work and do not take off one by one for cleaning. The rubber roller is subjected to high temperature friction and ink. Corrosion of the solvent forms cracks, especially at both ends of the rubber roller. During printing, the ink residue from the cracked rubber roller sticks to the printing plate and is difficult to clean.

(5) In order to prevent dirt and dust on the printed matter, taking into account some paper powder more, in the printing of the paper above the powder. The paper powder will adhere to the blanket as the paper is imprinted, and then transferred to the printing plate. Therefore, the dusting should be arranged in the last color as far as possible. If dusting is necessary, attention should also be paid to the size of dusting amount. The smaller the better on the premise of non-sticky dirt, and the air can be printed again if necessary.

4, powder. Spray powder splashes on the print, because the ink is not completely dry and the print appears a mass of powder. Cause analysis:

(1) If the machine that needs powder spraying cannot be cleaned and maintained for a long time, the paper suction bracket and chain will be used. The paper press fan will be covered with powder. When printing, the powder will fall on the newly printed product due to machine jitter or rotation of the platen fan.

(2) When spraying powder, if the heating switch is not turned on, the dry powder will condense into blocks in a humid environment. Some of the machine's powder injection valve is installed in the hood (such as J4104 machine), the oil will drip on the powder injection valve when the oil is automatically refueled in the hood, forming sludge with the powder in the valve. These powder blocks and sludge are blown down by the blowing pipe, leaving powder masses on the printed products, so the powder spraying channel must be kept in a clean and dry environment.

5. Due to improper operation and other human reasons caused by the printing with dirty. Cause analysis:

(1) In order to improve the quality of printed products, the paper must be flat, crisp and easy to separate. So the operator needs to knock on the paper. After printing some large areas full of dark colors (such as red and purple), the paper is easy to curl down, and these curled paper cannot be transported normally, so special care should be taken when handling these papers. If you hit too hard, it will inevitably cause creases on the paper, and white streaks will appear where there are creases. The correct method is only to gently press up a pressure, so that the paper gripper and drag tip can be flat.

(2) Operators often need to take a stack of newly printed prints to the viewing table to check the color registration. For some full plates, large areas of printing to take less light, otherwise it is easy to cause printing sticky dirty. Because these prints have a large amount of ink, they will curl down on the paper receiving table, so it is not easy to take samples from the machine table, and the machine speed is fast, so be careful not to scratch the prints.

(3) After the product is printed, wait a moment before waking up or blanking to prevent the printed product from sticking dirty when moving the paper by hand.

6. Rub dirty. Scratches and scratches may occur during paper feeding, embossing and receiving. Shaking injury. Cause analysis:

(1) The paper receiving wheel on the paper receiving roller presses the paper under pressure after the paper delivery nozzle blows air. If the ink is not dry, two color spots will be left on the paper. For example, the paper receiving wheel of J2108 machine has a large stroke and the control cam is steep. Because the paper receiving wheel is pressed down quickly and heavily, there will be two spots on the paper.

(2) When the paper passes through the paper feeding table, the paper receiving wheel and the paper pressing wheel. The brush wheel and paperweight ball will drag out two or three ink marks, especially when the paper is delivered by the paper teeth and the paper is delivered quickly, the brush wheel and paperweight ball are easy to drag out marks.

(3) One of the rollers of J2108 and J4104 machines is a twist roller. When the front and back sides are printed, especially the back side is printed with dark ink, several "tooth marks" will be "picked out". Therefore, when opening materials, try to leave a little white edge for the drawing gauge to pull paper, and also pay attention to the direction of the grip when printing plates, and put light-colored (such as light yellow, light cyan, etc.) ink at the drawing gauge. Therefore, it is necessary to fully consider the defects of the domestic drawing rules.

(4) When delivering paper, due to the relatively stiff paper with a printing quantitative of more than 350g/m2, the paper is easy to scratch when the upper swing front gauge returns, such as J2108 and J4104 machines. When the paper roller is transferring paper, due to the small swing angle in front of the hem, scratches are easy to be scratched on the back of the printed product, causing the reverse side to be dirty, such as PZ2660 machine, etc.

(5) The printing surface of the paper transfer roller of the multi-color machine is wrapped on the roller during the paper transfer process. Due to insufficient cleaning and maintenance of the machine, the residual ink on the roller will leave filiform marks on the printed products, so it is better to print the large-area printed layout in the last color to avoid dirt on the paper transfer roller.

(6) After being embossed by the embossing cylinder, the printed matter is held by the paper receiving teeth and transported by the paper turning wheel to the paper receiving table. Since there is no anti-rubbing cloth on the domestic paper turning wheel, traces will be dragged out on the printed products, which are mainly at the tip of the paper, so the paper turning wheel should be reasonably adjusted according to the specific situation. If the trademark is printed, two spaces should be consciously left at the joint of the trademark. If the instruction manual is printed, the paper turning wheel should be adjusted at the spine of the book. If printing a picture, do not put the paper turning wheel at the same color block, but place it at a brightly colored place, even if there is a scratch, it is not obvious.

(7) The drum diameter of J2104 and PZ2660 machines is small. When printing paper with a quantitative weight of more than 200g/m2 (WH47-NP paper with a quantitative weight of more than 105g/m2), because the paper has a certain stiffness, it will not be wrapped on the surface of the drum flatly. In the process of movement, it is affected by the centrifugal force in the N direction and wrapped on the bar and pressing shaft. According to the specific conditions, reasonably distribute and install the paper guide bar, or pad sponge and other wraps on the bar or embossing shaft to hold the paper from being thrown out and scratched.

(8) printing large area dark. Special color ink, if the slow paper suction is too large. If the tooth is opened too early, the paper will fall too early, and a piece of print will rub and cause the print to be scratched. In addition, due to the quality of the PS version caused by a variety of dirty, there have been many articles introduced, in this no longer analysis.

 

Comparison of the use of plastic melting ink and water-based ink in printing

In the field of printing, from the perspective of environmental protection, all products containing PVC components, including plastic melt inks, will gradually be left out, and the use of water-based inks will become more and more common. But the problem is that printers have become accustomed to the use of plastic melt ink, they use the same method to use water-based ink, and in the same way to evaluate the printing effect of water-based ink, this is absolutely wrong concept, this paper will be plastic melt ink and water-based ink to compare, and details the use of water-based ink.

Manufacture of environmentally friendly plastic melt ink

Although plastic melting ink is not as good as water-based ink in hand feeling, hygroscopicity and air permeability, people still hope to have a PVC-free plastic melting ink substitute product. The printed image is similar to plastic melting ink in hand feeling, visual sensation and tensile deformation. This idea has been deeply rooted in the clothing printing industry, because the clothing printed by plastic melting ink has too much influence on the vast number of consumers, and consumers not only accept this kind of clothing, and also expect it to last. In the future, clothing consumers may require that the printed pattern is still as soft as water-based ink, or the printed pattern looks worn badly, as if the plastic melt ink is not solidified and completely washed away.

Customers are always right. In order to meet the needs of customers, ink manufacturers have produced imitation plastic melt ink. Its printing effect is similar to that of plastic melt ink, but its stretchability is very good. Now many garments in Australia are printed with imitation plastic melt ink. What is not ideal is that this kind of imitation plastic melt ink is inconvenient to use, so ink manufacturers still spend their energy on the research and production of water-based ink.

In order to encourage printers to use water-based inks instead of melting inks, manufacturers of water-based inks have indeed made some efforts. They have invested in many aspects, such as advertising, participating in exhibitions, and conducting product promotion seminars.

Molten ink is accepted by most printers because it is easy to operate and is welcomed by customers. When it comes to the convenience of plastic melting ink, it mainly means that it will not dry on the screen and is not limited by time. Sometimes the ink can be placed on the screen for a weekend or even up to two weeks without drying. The printer can then print, while the water-based ink will evaporate and dry when placed on the screen for a long time. Therefore, the printer is not willing to discard the plastic melting ink and use water-based ink, this makes their work more difficult. Some small garment printers believe that if the government does not allow the use of plastic melting ink one day, they will have to leave the business behind closed doors.

If only allow the use of water-based ink, some of the larger garment printing factory can only lose the hands of the business and find other ways to make money. For these reasons, ink manufacturers strive to develop water-based inks with the printing characteristics of melt inks, rather than producing a water-based ink to replace melt inks. With the government's policy to reduce the use of plastic ink, ink manufacturers mainly to the majority of plastic ink manufacturers as the object, the production of easy-to-use water-based ink, as long as the printer actively cooperate with the use of water-based ink is also easy to operate.

General transparent water-based ink is very easy to flow and can be printed continuously without drying on the screen. However, the problem is that if water-based ink is treated as plastic melting ink, water-based ink will eventually block the mesh. In order to make users of plastic melting ink use water-based ink smoothly, ink manufacturers will conduct research again. For ink manufacturers, the most difficult problem to solve is that the general printing steps of plastic melting ink are completely unsuitable for the printing procedure of water-based ink. The printing steps of this common plastic melting ink are called the worst printing scheme (WCS).

We chose 230T screen to do the experiment. The lines in the printed image range from half a millimeter to several millimeters. Of course, there are also on the spot. The experiment is carried out at room temperature with a relative humidity of 30%. The printing ink is general black transparent water-based ink. When the ink color starts to darken during the printing process, we add a little water to prevent the ink from blocking the screen plate. If one color ink is printed, if the ink is not covered on the screen again, just like printing plastic melting ink, the water-based ink will block the screen when printing for about 4 minutes, and the two ends of some fine lines cannot be printed. After another 2 minutes, 50% of the fine lines or more lines cannot be printed. The printing time of water-based ink is long, and the washing fastness of printed fabrics will decrease.

water-based ink printing

In order to maximize the printing time of the water-based ink, the printed image is preferably free from fine lines or dot images. In particular, in the case of printing with the covering water-based ink and the discharge ink, the image line width is not less than 1.5mm. When printing water-based ink on black fabric, it is recommended that the printer consider it in turn, that is, printing black ink on white fabric, because the water-based ink has good air permeability and feel, and customers will not feel heavy when wearing this type of clothing.

Some covering water-based inks can be wet-press wet printing on white substrates, but according to the characteristics of existing water-based inks and printing equipment, water-based inks will fail after a period of time, because WCS printing schemes are very unsuitable for covering inks. We use 156T screen to print white base material at room temperature with a relative humidity of 35% and print patterns on the white base material. When each color is printed, we ensure that the ink is re-coated on the screen plate and water is added to the ink from time to time. This can print for 4 hours, while the 0.5mm wide line cannot be printed only at both ends, and the 1mm wide line is printed well.

If the color is printed and the ink is not re-coated on the screen, the 0.5mm wide line cannot be printed after 8 minutes, while the line thinner than 2mm cannot be printed after 12 minutes, which is a big problem for the printing workers who often use plastic melt ink printing. Of course, the experiment here is only a comparison and does not reflect the printing characteristics of other covering inks or water-based inks.

Using the existing screen printing conditions, printing workers who mainly use plastic melt ink can use discharge ink to print on dark clothing. The discharge ink should be printed on the garment that can be discharged and the drying time of the ink should be long enough to obtain good washing fastness, good printing color and good hand feeling of the printed image. Even if the drying time is long enough, the washing fastness of the garment printed with discharge ink is still not as good as that printed with normally solidified plastic melt ink. However, if we want to replace the plastic melt ink with discharge ink and do not require high hand feeling of the printed image, we can print a layer of transparent protective oil on the image printed with discharge ink to solve the problem of poor washing fastness. So far, there is no effective chemical agent that can reduce the curing time of the discharge ink.

Prevent template breakage and adjust screen production process

Stencil fracture is a common failure of printing water-based ink. Therefore, water-resistant photosensitive emulsion should be used, exposed completely and dried completely, so as to enhance the water resistance of the stencil. It is recommended to use a hard film agent, especially when printing dye discharge ink.

However, through experiments, the above-mentioned truth seems to be outdated, because when the WCS scheme was implemented to clean the screen blocked by water-based ink, it was not as expected, that is, the water-resistant photosensitive emulsion and hard film agent of American Yi Linglong (Ulano) were used, and the exposure was correct, but when the screen blocked by water-based ink was cleaned, the template where the fine lines were still broken. In this case, experts used water seal oil, which is usually used on wooden decks. Experts coated the water seal oil on the screen plate with cloth, blow-dried the image part, and dried the screen plate with a drying box. Before finishing work every day, they treated the screen plate again in the same way, so that the template not only did not break, but also the place blocked by ink was easy to clean. Experts through the test of some variables, so the water seal oil included in the screen auxiliary materials, before printing must use water seal oil. When printing with water-based inks, the following auxiliary materials are required:

Water seal oil: This material is available in building stores, coated on the screen before printing and processed at the end of each day.

Water resistant tape: It is important to use the right tape. When the tape is sealed, the air should be fully driven away to ensure sufficient adhesion.

Multi-functional cleaning agent: this multi-functional cleaning agent for spray packaging, available in the market. It can not only clean the dry and solid ink, but also gently spray on the back of the screen to open the blocked mesh.

Mesh cleaner: If the multifunctional cleaner cannot remove dirt, you can use the screen cleaner to clean the screen.

Nail polish: You can buy it in the supermarket. The nail polish can quickly seal the needle eye on the stencil, and the nail polish is resistant to water. Colored nail polish is better than colorless nail polish.

Bucket and sponge: printing with water-based ink, should be prepared more than one bucket of water (each color ink a bucket of water) and some sponge, so that cleaning dirt is very convenient, especially when printing discharge ink, need to clean hands contaminated ink.

Paper towel or rag: After cleaning the screen, you need to wipe the screen with paper towel or rag. When printing ink, you must use paper towel to dry the back of the screen.

Plastic film: In the printing gap, in order to prevent the water-based ink from drying on the screen, the plastic film can be covered on the screen.

Avoid ink drying on the screen

Before printing, it is necessary to consider which method is used to avoid the ink drying on the screen, especially to prevent the ink from drying on the image part. The key to the success and failure of printing water-based inks lies in the reasonable operation of the ink. When printing plastic melting ink, the printer can not consider the drying problem of plastic melting ink, and the plastic melting ink can be placed on the screen without worrying about it until it is time to add ink or remove ink and no longer print. However, printing water-based ink needs to form the habit of paying close attention to ink frequently. If you are not ready for printing, don't put ink on the screen. Try to eliminate the factors that make the ink dry. For example, it is better to turn off the fan in the printing workshop.

Tips for cleaning the screen

If the printing is finished or it takes a long time to continue printing, you need to scrape the ink from the image part of the screen to the bottom of the screen, and wipe the image part of the screen with a wet sea surface. If necessary, you can also use the screen cleaning agent to clean the image part to prevent the ink from drying on the screen, and finally put the ink back into the packaging tank. If there is still ink or dirt on the non-image part of the screen, it will not affect the re-printing, and all the dirt on the screen will be removed during the screen recycling process.

A New Drying Method for Water-based Ink

The equipment used to cure the melt ink is not suitable for the curing of water-based inks. In addition to discharge printing ink, other water-based inks contain chemical cross-linking agent, water-based ink can only be fully dried to ensure the washing fastness of printed images. Some printing plants choose air drying method for curing water-based ink, and some printing plants make the printed matter directly in contact with the hot platform before the ink is dried, so that the water evaporates, and then the printed matter is put into the oven.

Before the paper is coated, it is necessary to use a drying device to remove the moisture in the paper. This drying device is also suitable for eliminating the moisture in the water-based ink. Perhaps the most reasonable way to remove moisture is to avoid adding water to the print. So if it is possible to print a transparent ink on a light or white fabric, this means that a fine screen printing of the transparent ink is used, so that there will be little moisture.

Adjust the printing process or means

Printing water-based ink do not like printing plastic melt ink as the operation. In general, the screen distance for printing water-based ink is not big, and the use of moderate hardness of the rubber, printing pressure minimum is the key to water-based ink printing. When printing discharge ink, the printing pressure of the squeegee is required, and the faster the printing speed, the better the effect. This can be done by trying to print several times and then recording the best results.

Some imitation plastic melt ink products printing feel is not as soft as plastic melt ink, you can use the printing cover printing oil, adding chemical crosslinking agent and other methods to improve the printing feel, and improve the printing image washing fastness. A German company began printing water-based inks on fabrics a few years ago. They did not use flash curing methods, but used ultra-low temperature methods to cure water-based inks.

Production of equipment suitable for water-based ink printing

At present, most of the textile printing equipment is based on plastic melt ink printing, water-based ink drying oven should have air flow, in order to speed up the drying speed of the ink, and most infrared oven without air flow, if you increase the air flow, the drying temperature will drop.

Flash curing is very effective for the drying of plastic melting ink printed on dark clothing, but it is not suitable for the drying of water-based ink, because it takes only 10 seconds to 15 seconds to flash curing for plastic melting ink, and water-based ink will never have this feature. In Europe, ultra-low temperature printing platforms were used to freeze water-based inks. A few years ago, some people used hot printing platforms to print water-based inks, but this did not change the idea that printers insisted on using melt inks.

If the printer's concept changes and wants to use water-based inks, equipment manufacturers will consider the drying of water-based inks on the screen when producing printers. If one day printers use water-based ink to print textiles, equipment manufacturers will consider the possibility of designing an automatic closing device for the screen. When printing is stopped, the screen will be automatically closed and the ink will not dry on the screen.

If the external conditions that accelerate the drying of aqueous inks are eliminated, the printer needs to consider how to slow down the drying of the ink rather than adding more retarders. Because too much retarder will reduce the washing fastness of clothing, and ink manufacturers have added a certain amount of retarder in the production of ink. In order to prevent the ink from drying, some printers cover the screen with plastic film or cover the whole screen with plastic bags when printing water-based inks that do not contain cross-linking agents. Then they go home from work or spend weekends, and then take off the plastic film or plastic bags when they go to work to continue printing.

When printing with water-based ink, the plastic film is used to cover the screen and add some water to the ink from time to time to make the ink shiny. This is a very effective method to prevent the ink from drying. Even if the discharge ink and the covering water-based ink are not dried, they will gel with the increase of time. Therefore, when the printing is restarted, wipe the image part of the screen with a damp sponge to make the ink flow again. This method is not suitable for inks containing catalysts or low-temperature chemical cross-linking agents, because the catalyst or cross-linking agent will solidify and deteriorate.

Conclusion

Since the water-based ink can not penetrate into each thread of the fabric, it is normal to see that the printed image is broken when the fabric is stretched. If the customer requires that the fabric be printed with water-based ink, this fact should be recognized, and cannot be compared with the printing effect and printing feel of the plastic melting ink.

Once the printer has mastered the printing skills of water-based ink, water-based ink is not only a substitute for plastic melting ink. Monochrome pedal sports caps printed with reflective water-based ink cost US $50 each, while the market price of six-color T-shirts printed with plastic melting ink is only US $5. Which printing order would you like to take? People who often run and exercise will definitely stand in line to buy T-shirts printed with reflective ink, because wearing reflective T-shirts is obvious in the dark and easy to be noticed, making runners feel more secure.

Printing plastic melting ink on cotton cloth, the printing image can not be ironed, and water-based ink printing clothing can not only be ironed, but also dry-cleaned. In short, there are many advantages of printing with water-based inks, so printers may wish to try it yourself.

 

 

Analysis of the causes of poor ink transfer in the offset printing process

In the offset printing process, water and ink are two very important substances in the ink transfer process. Water is fountain solution, ink is offset printing ink. Only when water and ink can be transferred well, the printed matter can be fine. However, due to the ink transfer is affected by many uncertain factors, ink control has become the most difficult key problem in offset printing. In the offset printing production process, there will be a variety of ink transfer failures, one of which is the ink roller sometimes on the powder situation, and lead to poor ink transfer.

The so-called "ink roller on the powder", that is, in the offset printing process, after the printing machine runs for a period of time, the powder particles appear on the ink roller, and the ink is deposited in the unwanted area (such as on the ink roller) or the ink roller deinking ink transfer poor phenomenon. This printing failure occurs mainly because the powdery particles on the ink roller have lipophilic or hydrophilic properties. So what are these powdery particles and where did they come from?

In the offset printing process, the materials that continuously enter the printing press from the outside are mainly substrates, inks and fountain solutions. Therefore, these powder particles must be brought in directly or indirectly by these three substances.

In general, if the quality of the substrate surface is not good, it is possible to bring the powdery particulate matter directly into the printing ink system. For example, when the surface of the paper itself with a large amount of paper powder or other powder, these dirt will be transferred to the ink transfer system through the printing plate with the embossing process, resulting in the occurrence of "powder on the ink roller" failure. The solution is to print production by replacing the substrate with a clean surface. In addition, the paper surface itself is clean, however, due to the insufficient tightness of the coating on the surface of the paper, powder and lint fall off during the imprinting process, and the transfer of the printing plate to the ink transfer system will also lead to the failure of "powder on the ink roller". This situation can be solved by reducing the speed of the vehicle, reducing the ink viscosity or replacing the paper with better quality.

In addition to the substrate directly to the powder particles into the printing system, the chemical reaction between the fountain solution and the ink may appear calcium precipitation, thus indirectly bringing the powder particles into the printing system.

The main component of fountain solution is water, and the hardness of water quality is different from place to place. Generally, the total hardness of soft water is 0 ~ 30ppm, and the total hardness of hard water is above 60ppm. When the water quality is hard (that is, when the Ca content is high), it usually leads to the contact of Ca with the resin in the ink to form saponified calcium, and in contact with the acid in the acid fountain solution, it will produce calcium salts such as lemon calcium or calcium phosphate. Saponified calcium is lipophilic, which will cause the ink to be deposited in unwanted areas, making the surface of the rubber roller crystallized, resulting in poor water and ink transfer. However, calcium salt is hydrophilic, which will hinder the ink transfer and lead to the deinking of the ink roller. Therefore, the solution to the problem is to use soft water with small Ca content as much as possible to deploy or dilute the fountain solution. At the same time, the fountain solution that can effectively reduce calcium deposition should be selected to eliminate the influence caused by excessive calcium ions.

 

Technical standard points of plexiglass signage screen printing

In the sign production process, the decisive role is the screen printing plate and substrate pretreatment process technology and printing points and screen printing ink selection.

1. screen printing plate:

1. Engraving method of paint film:

It is a kind of manual plate making method, which is relatively simple. Can be printed generally less delicate monochrome patterns and text.

(1) Spray engraving paint film paper: Stick the tracing paper on the flat wood plate with paste, mix 1 part of rubber water (volume ratio) and 1 part of gasoline with a pen, evenly coat it on the paper surface, spray soft varnish 3-5 times after drying, dry it in an oven at 40-50 degrees after each spraying, and spray the paint film thickness to 5-6mm, the paint film shall be bright, uniform, free of bubbles and stains.

(2) Carving graphics: stick the paint film paper on the graphics, carve according to the graphics with a carving knife, a round knife and a ruler, and gently remove the paint film.

(3) Posting: After carving the figure, it can be pasted on the screen frame made in the past. The method is to put the engraved paint film under the net frame and press it tightly, and wipe it gently with cotton dipped with a little thinner until the paint film and the screen are firmly bonded. After drying for a few minutes, remove the tracing paper. If the paper does not fall off completely, wipe it off with cotton. The blank part is coated with a layer of nitrocellulose paint to block the mesh of the screen. It can be printed after drying.

2. Carbon paper printing method:

It is also a relatively simple manual plate making method.

(1) cutting photosensitive paper: photosensitive paper is a kind of carbon paper made of a mixture thickly coated with oxygen barium base paper, which is cut according to the size of the figure for later use.

(2) Sensitization: Soak in a solution prepared by 500 milligrams and 20 grams of ammonium dichromate for 3-5 minutes, take out the carbon paper, and drain the water.

(3) Exposure: Stick carbon paper flat on clean glass, with the adhesive film upward, cover the bottom plate of positive polyester film on the top, and expose it with a plate printer for 8-12 minutes.

(4) Development: After exposure, soak in warm water of 40~50 degrees for several minutes to make the adhesive film and the positive plate naturally separate from the zinc oxide base paper, and carefully develop with warm water until the force shape is clear.

(5) Pasting: Place the prepared plate under the mesh frame of the pre-stretched mesh, cover several layers of newspapers on the mesh, press on the glass plate, and press with a weight of 1-2kg/cm2. At this time, the adhesive film and the mesh are firmly pasted, the heavy objects and newspapers are removed, the adhesive film is dried with an electric furnace, and then the base paper is removed, and the adhesive film pattern is transferred to the mesh. Carefully check the graphics for defects, after passing the graphics around the screen coated with a layer of nitro enamel protection, the screen printing plate installed in the printing plate, ready for printing. The scope of application of this plate making method is the same as the film engraving method.

3. Photosensitive plate making method: the printing plate used in silk screen printing requires high precision, and generally adopts advanced direct, indirect and straight photosensitive plate making methods.

A, direct plate making method:

(1) The post frame is made of aluminum frame, and there is no need to stretch the net for mobility. The air pressure is 5-6kg/cm2, and acetal adhesive net is used. The degree of tightness is measured by tension. The tension is 5-7kg, and the sinking size should be less than 2mm.

(2) Cleaning the screen: use washing powder, detergent, ethanol, etc. as a cleaning lotion, clean both sides of the screen, rinse with clean water, and dry with hot air for later use. The purpose is to make the network can better adhesion with photosensitive glue.

(3) scraping bucket (coating bucket, coating device): coating photosensitive glue scraping bucket can be made of stainless steel, can also be made of plexiglass plate scraper. Its length is generally slightly smaller than the inner diameter of the wire mesh frame (several scraping buckets with different lengths are matched into a set of spare) B. The edge of the scraping bucket must be thin and not sharp, smooth and straight, and no defects such as bumps, burrs, scars, etc. are allowed to affect the quality of plate making. When coating screen photosensitive glue, drying it once every three times, 3-4 times continuously until the film reaches the required thickness, and then exposure.

(4) the temperature of the drying oven, it is ideal to use a drying oven with adjustable temperature. The drying temperature of the photosensitive glue is generally controlled at about 40 degrees. If the baking time is too long or the temperature is too high, the quality of the photosensitive layer will be affected.

(5) Safety light: The lighting source of the studio generally uses orange, yellow or red light as the safety light, but from a visual point of view, the orange light source is more comfortable. Its brightness should be so that all objects can be clearly seen.

(6) Inspection of the bottom plate: Before printing, the bottom plate must be carefully checked, including dust on the surface, blackness of the bottom plate, broken lines, sand hole defects and other items, as well as whether the front and back of the image text meet the requirements.

B. Indirect method:

(1) Prepare the net frame and photosensitive film: clean the stretched net frame (nylon wire with 220-260 mesh) with 10% sodium phosphate aqueous solution to remove oil stains.

Wire mesh photosensitive film is a photosensitive adhesive with polyvinyl alcohol as the main body. The film is coated with gelatin as the main body photosensitive agent on a 0.12-0.06mm transparent plastic film base. Before use, the size of the pattern is connected, with each side 20mm wide. The powder dirt on the film is wiped clean with cloth.

(2) Exposure: Press the film and the bottom plate tightly in the printer, and expose it with a carbon lamp or xenon lamp. The distance between the screen frame and the light source is 50-60cm, and the exposure time is 2-6 minutes.

(3) Development: After exposure, place the phenanthrene film on a flat plate, soak the omentum with warm water for 1-2 minutes, spray with a water nozzle, and remove the non-photosensitive part (graphic part) from the printing plate and the developed phenanthrene film with water until the graphic is clear.

(4) Sticking film: Stick the exposed film surface on the silk screen, and use rubber plates or other straight plates on the back of the human film to gently scrape and paste the film to make the film contact with the net firmly, immediately place it in an oven, bake at a temperature of 55±2 degrees for 8-12 minutes, after drying, fix the net frame on the printing plate table for trial printing.

(6) film removal method: in the process of exposure and development, when the plate is found to be unqualified, the film can be brushed off with warm water immediately and remade. If the version has been dried or produced for a period of time before going to the film, one portion of industrial sodium hypochlorite and one portion of water can be used and soaked for 10-20 minutes. Or 5% sodium hydroxide aqueous solution heating treatment screen, can remove the film.

C, straight plate making method:

Straight between the method is the direct method and indirect method of mixed plate-making method, it is different from the indirect method, the indirect method first in the film film on the image and then to the screen transfer paste, and the straight between the method is the first film film transfer paste on the screen after exposure to make images.

Pre-processing of 2. substrates:

Signs of the printing materials are mainly aluminum, copper, stainless steel, aluminum, the amount of plexiglass. There are also plastic, polyester, paper and so on.

Aluminum signs are widely used in the variety of signs, with beautiful, bright, high hardness, good wear resistance, wide application, large amount of characteristics. Used in machinery, electronics, instruments, meters, household appliances, daily hardware, clocks, daily cosmetics packaging, etc.

There are many methods for the pretreatment of aluminum substrates. According to the application, there are mainly degreasing, sandblasting, wire drawing, polishing, and oxygen grease.

1. Degreasing: In order to make the surface of the aluminum substrate have a certain ink affinity, the oil layer and oil stains on the surface need to be removed, and cotton yarn can be dipped in gasoline to wipe. Alkaline solution can also be used for chemical degreasing, such as sodium sulfate 30-50g/L, sodium phosphate 40-60g/L, sodium silicate 10-15g/L, at a temperature of 60-70 degrees in 2-5 minutes to remove oil.

2, sandblasting: sandblasting is to improve the adhesion of ink and metal materials, usually use a special sandblasting machine for spray treatment, if 0.5-1mm thick aluminum plate, sand blasting with a diameter of 0.05-0.15mm, can also be used river sand, after screening.

3. Wire drawing: also known as stranding, it is to process fine linear lines on the surface of aluminum plate by mechanical friction. It is a relatively new surface decorative treatment process that can overcome defects such as scratches on the surface of aluminum. Increase the use of materials. There are two kinds of wire drawing: thick wire and fine wire. Generally, stainless steel wire brush or scouring pad with a diameter of 0.1mm can be used, or nylon abrasive belt can be used for processing.

4. Polishing: It is to overcome the surface defects of aluminum-based materials and improve the smoothness of the surface. Polishing is divided into mechanical polishing and chemical polishing. Mechanical polishing is the use of cloth wheel polishing machine, chemical polishing in acidic solution, such as sulfuric acid 15%, nitric acid 10%, temperature 90-100 degrees, the time is 2-3 minutes.

5, oxidation: the surface of the aluminum plate after polishing has residual polishing soap, the application of plate yarn dipped in gasoline to wipe, and then chemical to oil, and then immersed in nitric acid solution (nitric acid and water 1:1 ratio),10 minutes after the removal, and then put into the oxidation tank for electrochemical oxidation. Formula of oxidation solution: nitric acid 160-200 g/ml, temperature 10-20 degrees, time 30 minutes.

The oxidized aluminum plate is fully washed and dried, and a layer of uniform pore oxide layer is formed on the surface, that is, the oxide film, which should avoid dirt pollution. The oxidized aluminum plate is best printed immediately. If it cannot be printed immediately, it should be wrapped with soft paper spacers or placed directly on the air-drying rack for no more than one week.

The oxide layer on the surface of the aluminum plate can absorb dyes, water and other salts, so there is no need to touch the surface with hands or greasy things during silk screen printing. When the ink is printed on the oxide layer, the ink penetrates into the pores. The heating of the next process is to accelerate the ink to penetrate into the pores until all the surface pores covered by the ink are filled.

The ink printed on the surface rarely spreads or does not spread, and the text and pattern are well guaranteed to be precise and clear.

6. Closed: Its function is to seal the ink firmly in the pores and never overflow or spread. For the parts not covered by the ink, the sealing effect is to fill the gap of the oxide film, make it impermeable, and strengthen the corrosion resistance of the surface. Nickel sulfate solution is generally used for sealing. Formula: nickel Hanate 10-12 ml, temperature 80-90 degrees, 10-15 minutes. After sealing the hole and then hand or other things with oil contact surface, with the general cleaning agent can be washed off.

3. screen printing ink (coating):

In today's metal signs or non-metallic plate screen printing, printing ink can be used more, but the choice of suitable ink (paint) is not easy. Signs screen printing ink commonly used have the following:

1. Baking enamel paint:

It is a single-liquid formula, cross-linked when heated, and has good storage performance. It can be stored for 6 months to a year. Has a good finish, wear resistance, chemical resistance and weather resistance, so the most common use. Alkyd, acrylic and polyester have these properties. Epoxy resin has a tendency to fracture and pulverization, and is generally not used outdoors, but it dries quickly and has good chemical resistance. Alkyd enamels are most widely used for their balanced physical properties, such as chemical and weather resistance, formability, hardness and gloss.

2. Air drying enamel:

Commonly used drunk acid made, with oxygen in the air, through the reaction to achieve curing. The performance of the enamel is determined by the type and amount of oil used. The longer the oil drying time, the longer the drying time of the enamel. When the drying speed is used as the condition, the paint with long drying time generally has good surface durability. These paints are mostly used for outdoor metal signs.

3, dissolved volatile ink:

Rely only on solvent evaporation to achieve drying. The final properties of the coating depend on the properties of the materials inherent in the polymer prior to formulation into a liquid. Such polymers contain thermoplastic acrylic. The screen printing ink, which is mainly composed of volatilization, is usually damaged by dissolution. There are some insoluble in gasoline and alcohol acrylic acid, which can be in contact with the film surface, and therefore, thermoplastic acrylic, ethylene and other soluble polymer-based inks are mostly used on plastic substrates.

4. Double liquid type ink:

Epoxy fingers or polyurethanes are common, although there are many others. The two-liquid system, which is often used in materials, is the wisest choice to save energy. Its coating quality is high, but mixing is not convenient. In addition, according to the use of the product to choose, if the product may be used outdoors, but also with some flexibility, then the choice of aliphatic hydrocarbon as the main body of urethane ink. The two-liquid epoxy ink on the market now has almost the same performance as the baking enamel, but the formability is not good enough.

5. Ink additives:

Like other inks, metal screen printing inks also contain additives, which are a small amount of chemical agents in the production to improve the performance of the ink film. Some can accelerate curing or initiate curing, while others can make bubbles burst and ink Uniformity reduces the possibility of conjunctiva. According to the specific formula, the manufacturer mixes the additives with the ink, and what the printer needs is to dilute the ink to a consistency suitable for printing.

4. printing:

The quality of screen printing, the thickness of the ink layer and screen thickness, ink viscosity, scraper hard filling, angle, plate making methods are closely related.

1. Silk plate and positioning: aluminum plate material is positioned by three points. When printing, first print light color, and then print dark.

2. The distance between the printing plate and the substrate is 1-2mm, and the distance is related to the choice of the screen. The nylon screen has good elasticity and large flexibility, generally 2-3mm.

3. The polyurethane rubber plate for scraper has a hardness of 70-75 degrees and a thickness of 8-9mm. The angle of the scraper during printing is 70 degrees, and the speed of the scraper should move in a straight line at a uniform speed.

4. Fit protective film: For printed signs, in order to avoid trauma during cutting and transportation, transparent pressure-sensitive adhesive protective film should be pasted on the surface and double-sided adhesive paper should be pasted on the back.

5, cutting: with a small shear bed, forming available hole positioning or edge positioning stamping