Talking about screen printing of glass
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Glass screen printing refers to a screen printing method in which a glass plate or a glass container is used as a main product. The use of glass has a long history in China, and even in today's modern era, glass still plays an important role in our lives. At present, the financial crisis originating on Wall Street in the United States, such as the "tsunami", generally impacts the nerves of the world and has a certain impact on the economies of all countries in the world.
Since 2008, the soaring international oil prices, the appreciation of the renminbi, and the reduction of export tax rebates have already had a negative impact on the export-oriented enterprises of China's screen printing industry. The global financial crisis broke out, printing on the original low profit and difficult operation. For enterprises, it is even worse, especially for small and medium-sized packaging and printing companies. In addition, after the implementation of the new labor law, the increase in labor costs has increased the operating costs of screen printing companies, coupled with the serious collateral of their downstream customers, resulting in a tight or even broken capital chain, increasing the difficulty of screen printing enterprises. Therefore, screen printing companies should rationally combine the actual situation of the enterprise with the characteristics of the products, and serve customers with the lowest production cost and the highest production efficiency. Under the conditions of coexistence of these opportunities and challenges, the application of screen printing on glass products is undoubtedly a very effective response measure, which can increase the market development efforts and open a variety of marketing channels.
As a building decoration material, glass has the advantages of being flat and transparent, covering wind and rain, and easy to scrub. After the screen printing, the glass used for indoor and outdoor decoration is more popular, which greatly satisfies people's life and aesthetic needs. All kinds of beautiful and beautiful patterns compete with each other and make the best of it. Now glass containers have begun to develop into medical supplies and industrial products. The high quality of glass products decorated with screen printing technology will become a new growth point for glass printing.
First, the screen printing process of glass
According to the principle of screen printing, the ink is printed on the surface of the glass, and then the curing method of the ink is used, and the printed pattern is firm and durable. The process flow is as follows:
Stretching net→sizing→drying→printing→developing→drying
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Flat glass → cutting → edging → cleaning and drying → printing
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Sintering
1. Suitable for printing glass
Cut the glass according to the user's requirements, it can be regular shape, or it can be irregular shape, then it can be edged and ground, then cleaned and dried for use. Special care should be taken here that there should be no water marks on the glass surface.
2. Screen selection
The screen printing plate for glass printing is the same as the general screen printing plate, and the glass screen printing plate is made of synthetic fiber mesh, stainless steel wire mesh and natural fiber mesh. When printing general color materials, the above-mentioned screens can be used, generally using inexpensive synthetic fiber mesh; when used as gold and silver decoration, stainless steel wire mesh cannot be selected. The specifications of the wire mesh are generally 270 to 300 mesh.
3. Frame selection
At present, the frame that is relatively regular and has little deformation is an aluminum alloy frame, and its size should be larger than the pattern. The specific size should be that the outer edge of the pattern should be between 70 and 100 mm from the frame. In addition to selecting the frame, its strength is very important, the key is that the rigidity in the horizontal direction is sufficient. 4. Stretching the net and the mesh frame, combining the two, this is the stretch net. There are many ways to stretch the net. It can be manually, maneuvered or pneumatic. At present, the more advanced, high-quality screen is a pneumatic stretcher. The requirement of the stretch net is that the tension is uniform, the web warp and weft are kept vertical, and the adhesive mesh is firm and cannot be slack.
5. Select photosensitive adhesive
Currently, commercially available photosensitive adhesives are dichromate, diazonium, and iron salts. Silk screen printing requires the photosensitive adhesive: good plate making performance and easy coating. The sensitizing spectrum ranges from 340 to 440 nm, with good developing performance, high resolution, good stability, easy storage, economical, non-toxic and pollution-free. The requirements for printing on photosensitive materials are: the printing film formed by the photosensitive material is adapted to the performance requirements of different kinds of inks, has a considerable printing durability, can withstand the scraping pressure of the squeegee plate a certain number of times; the bonding force with the screen is good, when printing Does not produce a film release failure; easy to peel, which is conducive to the recycling of the screen plate.
6. Printing version
After selecting the above materials, the photosensitive adhesive is applied in the dark room; the requirements are uniform and then dried, and it is generally required to apply twice. The printing plate is required to be exposed on a cold light source printing machine, and the exposure time is determined according to the pattern, generally between 12 and 30 minutes. Screen printing screens are produced after exposure and development.
7. Printing
There are several types of flat glass printers: manual, semi-automatic and fully automatic. The manual press is suitable for small-volume, small-size flat glass. The semi-automatic and fully automatic printing machine is suitable for printing in large quantities and large specifications, and has the advantages of accuracy and speed. The largest semi-automatic press can print 2000 x 1500 mm glass. Fully automatic printing machines are generally used for the printing of automobile windshields, and several companies abroad can provide such equipment.
8. Ink
Inorganic glass screen printing uses two kinds of inks, one of which is that the inorganic pigments are ground to a certain degree of fineness. Adding acrylic resin, the screen is printed on the surface of the glass, and it needs to be fired at high temperature (above 600 °C) for 1-2 minutes. The ink layer and the glass surface are melted together, and the fastness is excellent. The heat resistance temperature of this ink is above 600 °C. However, because this screen printing process is costly and complicated, it is rarely used in the screen printing industry. The other is an inorganic glass ink which uses a polymer compound as a binder, and both the amino type and the epoxy type need to be baked, and the domestic market is extensive. The applied ink is baked at l300 ~ l 400 ° C for 30 min after screen printing, and the heat resistance temperature of this ink is relatively low. However, the baking time is longer, the ink has good fastness and hardness, and the brightness is also very good, and can resist the corrosion of low concentration electrolyte and solvents such as ethanol, acetone, benzene and cyclohexanone.
9. Sintering
Glass is an amorphous inorganic material that softens as the temperature increases, and when heated to the softening temperature of the glass, the glass deforms. The glass glaze is decorated on the surface of the glass by silk screen printing, and needs to be fixed to the glass surface by high temperature sintering, but the sintering temperature must be lower than the softening temperature of the decorative glass to ensure that the decorative glass is not deformed. Generally, the glass glaze has a sintering temperature of not higher than 520 ° C, and is usually controlled at 480 to 520 ° C. Low-temperature glass glazes are produced by several manufacturers in China, and the prices are relatively low. Several foreign companies can also provide similar products, but the price is one to twenty times different from that of domestic ones. Domestic consumption levels have not yet reached the level of using such glazes, but the glazes provided abroad are indeed much better than the domestic colors and levels.
To improve the quality of decorative glass, it is inevitable to improve the grade of glaze. The sintering equipment has a flame furnace and a resistance furnace, and the resistance furnace is divided into a vertical hanging type and a horizontal roller type according to the hanging manner of the glass. The vertical hanging sintering furnace has the advantages of small sintering deformation and a yield of more than 95%, but the equipment is complicated. The horizontal roller type adjustment is not easy to deform and the yield is low. In addition, it is also feasible to use a horizontal tempering furnace to produce decorative glass. The grade of the product is improved and the safety is guaranteed. It is an ideal sintering method. [next]
Second, the glass screen printing process is prone to failure
The occurrence of silk screen failures is partly due to a single aspect, but more is the result of cross-effects of various causes. This is the operator's judgment of the cause of the failure of the glass screen printing, and pay special attention when taking corresponding countermeasures:
1. Paste
Paste plate, also known as blockage, refers to the phenomenon that the through-hole portion of the screen printing plate cannot transfer ink to the substrate during printing. The appearance of this phenomenon will affect the quality of printing, and even in normal cases, normal printing will not be possible.
The cause of the paste phenomenon generated during the screen printing process is complicated. The reasons for paste can be analyzed from the following aspects:
① glass reasons: the glass surface is not cleaned, there are watermarks, paper printing, mime printing, fingerprints, dust particles and other dirt. Thus causing a paste;
② reasons for the temperature, humidity and ink properties of the workshop. The screen printing workshop requires a certain temperature of about 20 ° C and a relative humidity of about 50%. If the temperature is high and the relative humidity is low, the volatile solvent in the ink will quickly evaporate, and the viscosity of the ink on the screen becomes high, thereby blocking Live the mesh. Another point to note is that if the downtime is too long, it will also produce a paste phenomenon. The longer the time, the more serious the paste. Secondly, if the ambient temperature is low, the ink flowability is poor and the paste is easily generated;
③ reasons for screen printing. The prepared screen printing plate can be used after being rinsed with water and dried before use. If you put it in a good version, it will not be printed in time. Dust is more or less adhered during the preservation process, and if it is not cleaned during printing, it will cause a paste.
④ reasons for printing pressure. Excessive embossing force during printing will cause the squeegee to bend. The squeegee is not in line contact with the screen printing plate and the glass, but is in surface contact, so that the ink can be scraped clean each time the squeegee is left, leaving residual ink. After a certain period of time, the conjunctiva will cause a paste.
⑤ screen printing plate and glass gap is not the reason. The gap between the screen printing plate and the glass should not be too small, the gap is too small. After the squeegee printing, the screen plate cannot be separated from the glass in time. When the screen printing plate is lifted, a certain ink is stuck on the bottom of the printing plate, which is easy to cause paste. board.
⑥ The reason for the ink is that when the pigment of the screen printing ink and other solid particles are large, the phenomenon of blocking the mesh is likely to occur.
In addition, the mesh size and the through-hole area of the selected mesh are smaller than the particle size of the ink, and it is also one of the reasons why the ink of the coarser particles is not easily passed through the mesh. The paste caused by the large particles of the ink can be solved from the time of manufacturing the ink, and the main method is to strictly control the fineness of the ink.
In the printing process, the viscosity of the ink is increased to cause the paste, the main reason is that the ink solvent on the screen printing plate evaporates, resulting in an increase in the viscosity of the ink, and a phenomenon of sealing the net occurs. If the printed graphic area is relatively large, the ink on the screen printing plate consumes a lot, and the paste phenomenon is less. If the image area is small and the ink consumption on the screen printing plate is small, it is easy to cause a paste. The countermeasure is to use a small number of ink replenishment principles. The poor fluidity of the ink causes the ink to form a paste when it is not passed through the screen. This can be solved by reducing the viscosity of the ink and improving the fluidity of the ink without affecting the print quality. After a paste failure occurs, it can be scrubbed with a suitable solvent for the nature of the ink on the plate. The main point of scrubbing is to start from the printing surface and gently wipe from the middle to the outside. Check the plate after wiping. If there is any defect, it should be repaired in time. After the repair, the printing can be restarted. It should be noted that the plate is thinned every time it is scrubbed. If the film causes a major defect in the film, it has to be replaced with a new one.
2. The ink is not firmly fixed on the glass
① When printing on glass, it is important to perform strict degreasing and pre-treatment inspection of the glass before printing. When a substance such as grease, a binder, or a dust adheres to the surface of the glass, the ink and the glass are poorly bonded.
② Insufficient adhesion of the ink itself causes the ink film to be fixed firmly. It is best to replace other types of ink for printing. If the dilution solvent is improperly selected, the ink film may not adhere well. When selecting a dilution solvent, the properties of the ink should be considered to avoid the phenomenon that the ink and the substrate are not firmly bonded.
3. Inaccurate ink
The thickness of the ink film is not uniform. The reason is various. In terms of ink, the ink is poorly formulated, or the ink that is normally blended is mixed with the ink. When printing, it expands and softens due to the action of the solvent, and should be ink-permeable. The mesh is blocked and acts as a plate to prevent the ink from passing. In order to prevent this kind of malfunction, the formulated ink (especially the old ink) should be filtered once and used before use. When reusing a used plate, the old ink attached to the frame must be completely removed. When the plate is kept after printing, it should be fully washed (including the scraper). If the tip of the front end of the ink return plate is damaged, a trace will appear along the moving direction of the squeegee. When printing glass, there is a noticeable unevenness in the ink. Therefore, the front end of the squeegee must be well protected from damage, and if it is damaged, it must be carefully ground with a grinder. Furthermore, the unevenness of the printing table also affects the uniformity of the ink. The ink layer of the convex portion is thin, and the ink layer of the concave portion is thick. This phenomenon is also called unevenness of ink. In addition, if the back of the substrate or the printing table is dusty, the above failure may occur.
4. Pinhole
Pinhole phenomenon is the biggest headache for workers engaged in glass screen printing. There are many reasons for pinholes to occur, many of which are currently unexplained, and some are quality management issues. Pinholes are one of the most important inspection items in the inspection of printed products.
① Dust and foreign matter attached to the plate. At the time of plate making, there will be some sol in the washing and developing. In addition, when the emulsion is applied, dust is also mixed in, and pinholes are formed by adhering to the screen. These can be found and repaired in time when the test is carried out. If dust and foreign matter adhere to the screen, blocking the screen opening can also cause pinholes. Before the official printing, you should 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 the surface clean and print immediately. If the glass is processed, it will not be printed immediately and will be contaminated again. Pre-treatment removes dirt such as grease and, at the same time, removes dust adhering to the surface. Pay special attention to the fact that when the glass is moved by hand, the fingerprint of the hand will also adhere to the printing surface, and pinholes will be formed during printing.
5. Bubbles
The glass sometimes has bubbles on the ink after printing. The main reasons for the bubble are as follows: 1. The substrate is poorly printed before printing. The surface of the substrate is attached with dust and oil stains; 2 bubbles in the ink. In order to adjust the ink, when adding solvent and additives for stirring, some bubbles will be mixed in the ink. If left unattended, the ink with low viscosity will naturally defoam, and some inks with high viscosity will not be naturally defoamed. Some of these bubbles are naturally removed during printing due to the transfer of ink, and some are becoming larger and larger. In order to remove these bubbles, an antifoaming agent is used, and the amount of the antifoaming agent in the ink is generally about 0.1 to 1%, and if it exceeds a predetermined amount, it will act as a foaming action. Even if the ink is transferred after the transfer, as long as the wettability of the substrate and the fluidity of the ink are good, the bubbles on the surface of the printed ink film are gradually eliminated, and the ink forms a flat printed ink film. If the ink bubbles are not eliminated, the ink film forms an annular uneven film surface. Generally, the bubbles in the ink can be defoamed by the action of the screen when passing through the screen; 3 the printing speed is too fast or the printing speed is uneven, and bubbles are generated. The printing speed should be appropriately reduced to maintain the uniformity of the printing speed.
6. Electrostatic failure
The electrostatic current is generally small, but the potential difference is very large, and there may be phenomena such as attraction, repulsion, conduction, and discharge. 1 adverse effects on screen printing. The screen at the time of printing heats the rubber portion and the screen due to the pressure scraping of the blade rubber. When the screen itself is charged, it will affect the normal inking and cause the jamming failure; it will be sucked by the screen at the moment of the output of the substrate; 2 The method of preventing static electricity. The methods for preventing static electricity generation include: adjusting the ambient temperature and increasing the humidity of the air. The appropriate temperature is generally about 20 ° C, and the relative humidity is about 60%; the static electricity can be transmitted in the wet air; the mesh distance is reduced, and the printing speed is reduced.
7. The finished ink film size is enlarged
After screen printing, there is sometimes an increase in print size. The main reason for the increase in printing size is that the viscosity of the ink is relatively low and the fluidity is too large; the size of the screen printing plate is enlarged during the production, which is also the cause of the enlargement of the printing size. In order to avoid excessive ink flow and cause the ink to flow around after printing, resulting in a large printing size, it is conceivable to increase the viscosity of the ink to reduce the fluidity of the ink. When making screen printing plates, the quality of the screen plate should be strictly guaranteed to ensure the tension of the screen plate. [next]
8. The printing plate leaks ink
Part of the film leaks ink, which is called ink leakage failure. The reason is: a part of the scraper is injured; the pressure of the ink is large; the gap between the plate and the glass is too large; the frame is deformed greatly, and the partial printing pressure is not enough: The ink is not uniform; the screen is too fine; the printing speed is too fast. If dust is mixed on the glass and in the ink, and the printing is performed without treatment, the film may be damaged by the pressure of the squeegee; the pinhole may be formed by insufficient exposure during plate making, and the film may be leaky. At this time, an adhesive tape or the like can be attached from the back side of the plate for emergency treatment. If this operation is not very rapid, the ink of the layout will be dried, and the entire plate has to be wiped with a solvent. The wiping plate is also responsible for the peeling of the film, so it is best to avoid it. The ink leakage of the plate often occurs in the portion where the ink stays, so it is preferable to strengthen this portion during plate making.
9. Ink
The ink is a speckle-like imprint of the graphic part and the dark part of the glass surface, which impairs the printing effect. Glass screen printing is easy and produces 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, and the particles agglomerate and appear color due to the polarity action of the pigment particles. Dot blot. The improved method is: improve the fluidity of the ink; use fast-drying flux; print with high viscosity ink as much as possible: increase the wet film thickness of the ink, try to use ink made of pigment with small oil absorption: minimize the influence of static electricity .
10. Image distortion
The printing press applied to the printing plate by the squeegee can make the line contact between the printing plate and the printed matter, and it should not be exceeded. If the printing pressure is too large, the printing plate will contact the inside of the substrate, which will cause the screen to expand and contract, causing the printed image to be deformed. Screen printing is one of the smallest printing methods in various printing methods. If we forget this, we can't print good prints. If the pressure cannot be printed without increasing the pressure, the gap between the layout and the glass surface should be reduced, so that the pressure of the squeegee can be reduced.
Third, the application of screen printing flat glass and its market prospects
Screen printing flat glass is widely used in every corner of people's lives: you can easily find them in display windows, building space partitions, building exteriors, car windshields and mosaic glass. Simultaneously. They are also widely used in furniture upholstery and game tools, as well as in countless decorative and artistic creations. Screen printing has also become part of the creative design work for glass manufacturing. People can print color images directly onto the glass surface by screen printing. In addition, it can also be used to temporarily cover the untextured portion of the glass surface, or to print additives such as preservatives in portions of the glass surface that are not affected by etching or sanding. In contrast, special ink can be directly screen printed to create an etching or sanding effect. sometimes. People also rely on the strong hiding power of screen printing, such as printing a thin layer of conductive material on the glass, used to make anti-ice (frost) devices for windows.
Screen printing continues to expand in the field of flat glass decoration. In addition to its suitable printing materials for various materials, another important factor is that it can meet a wide range of flat glass substrates of different sizes and weights. Moreover, due to the absolute superiority of screen printing in ultra-large format image printing, it has strengthened its leading position in the development of the entire flat glass printing industry. In particular, 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 adapt to increasingly demanding printing requirements, especially in the field of 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 the decoration of flat glass will continue to develop and continue to expand its application in glass decoration. The screen printing machine has a faster substrate conveying system, as well as a more advanced power supply system, combined with a powerful PLC (Logic Controllable Device), which improves productivity and image quality, ensuring its market in the decorative flat glass market. Constantly expanding.