The screen printing process of glass 2021-04-27

　　Glass screen printing refers to the screen printing method used for glass panels or glass containers as the main products. The use of glass has a long history in China, and even in modern times, glass still plays an important role in our lives. Currently, the financial crisis originating from Wall Street in the United States is like a tsunami that is impacting the nerves of the world and has had a certain impact on the economies of countries around the world.
　　Since 2008, the soaring international oil prices, the appreciation of the Chinese yuan, and the reduction of export tax rebates have had a negative impact on export-oriented enterprises in China's screen printing industry. The outbreak of the global financial crisis has made it even worse for printing enterprises that were originally low profit and difficult to operate, especially small and medium-sized packaging printing enterprises. In addition, after the implementation of the new labor law, the increase in labor costs has increased the operating costs of screen printing enterprises. In addition, serious deposits from downstream customers have caused a tight or even broken financial chain, increasing the difficulty of screen printing enterprises. Therefore, screen printing enterprises should rationally combine their actual situation and product characteristics, and serve customers with the lowest production cost and highest production efficiency. Under the conditions of both opportunities and challenges, applying screen printing to glass products is undoubtedly an effective response measure, which can increase market expansion and open up various marketing channels.
　　Glass, as a decorative material for buildings, has the advantages of being flat and transparent, able to block wind and rain, and easy to clean. After being printed on the internet, glass is even more popular for indoor and outdoor decoration, greatly meeting people's life and aesthetic needs. Various beautiful patterns compete with each other, creating exquisite and exquisite works. Nowadays, glass containers have begun to develop towards pharmaceutical and industrial products. The high-quality and quantified use of screen printing technology to decorate glass products will become a new growth point for glass printing.
　
The screen printing process of glass
　　According to the principle of screen printing, ink is printed on the surface of glass, and then ink curing measures are used to print patterns that are firm and durable. The process flow is as follows:
　　Stretching → Sizing → Drying → Plate drying → Developing → Drying
　　↓
　 Flat glass → Cutting → Grinding → Cleaning and drying → Printing
　　↓
　　sinter
　　1. Glass suitable for printing
　　According to user requirements, glass can be cut into regular or irregular shapes, then chamfered, ground, cleaned, and dried for later use. Special attention should be paid here that there should be no water stains on the surface of the glass.
　　2. Selection of Screen
　　The screen printing plate used for glass printing is the same as the general screen printing plate. The glass screen printing plate uses synthetic fiber screen, stainless steel screen, and natural fiber screen. When printing general color materials, the above-mentioned silk screens can be used, and generally inexpensive synthetic fiber silk screens are selected; When used as gold and silver decoration, stainless steel wire mesh cannot be chosen. The specifications of the screen are generally 270-300 mesh.
　　3. Selection of Netframe
　　At present, the more formal and less deformed mesh frame is aluminum alloy mesh frame, which should be larger than the pattern. The specific size should be between the outer edge of the pattern and the mesh frame, which should be between 70-100mm. In addition, the strength of the mesh frame is important, and the key is sufficient rigidity in the horizontal direction.
　　4. The selection of a mesh and a mesh frame, combined with the two, is called a mesh. There are many ways to stretch the mesh, including manual, motorized, and pneumatic methods. Currently, the most advanced one that can stretch high-quality mesh is the pneumatic stretch machine. The requirements for stretching the net are uniform tension, the warp and weft lines of the net should be kept vertical, and the adhesive should be firm and not loose.
　　5. Select photosensitive adhesive
　　Currently, the photosensitive adhesives available on the market include dichromate, diazonium, and iron salt systems. The requirements for screen printing plate making for photosensitive adhesive are: good plate making performance and easy coating. The photosensitive spectrum ranges from 340 to 440nm, with good development performance, high resolution, good stability, easy storage, economic and hygienic, non-toxic and pollution-free. The requirements for printing on photosensitive materials are: the film formed by the photosensitive material can adapt to the performance requirements of different types of inks, have considerable printing resistance, and can withstand a considerable number of scratches and pressures from the ink scraper; Good adhesion with the screen, no delamination failure occurs during printing; Easy to peel off, conducive to the regeneration and utilization of screen materials.
　　6. Sun printing
　　After selecting the material above, apply photosensitive adhesive in the darkroom; It is required to be uniform and then dry, and generally requires two coats of coating. Printing requires exposure on a cold light source printing machine, and the exposure time should be determined based on the pattern, generally between 12-30 minutes. After exposure and development, a silk screen is produced.
　　7. printing
　　There are several types of printing machines for flat glass, including manual, semi-automatic, and fully automatic. Manual printing machines are suitable for small batches and small specifications of flat glass. Semi automatic and fully automatic printing machines are suitable for printing in large quantities and specifications with multiple colors, and have the advantages of accuracy and speed. The largest semi-automatic printing machine can print 2000 × 1500mm size glass. Fully automatic printing machines are generally used for printing car windshields, and several foreign companies can provide such equipment.
　　8. printing ink
　　Inorganic glass screen printing uses two types of inks, one is the inorganic pigment that is ground to a certain fineness. In addition, acrylic resin is added and screen printed on the surface of the glass. It needs to be baked at high temperature (above 600 ℃) for 1-2 minutes, and the ink layer and the surface of the glass melt together, resulting in excellent fastness. The heat resistance temperature of this ink is above 600 ℃. However, due to the high cost and complexity of this screen printing process, it is rarely used in the screen printing industry. Another type is inorganic glass ink that uses polymer compounds as binders. Both amino and epoxy types require baking and have a wide domestic market. The ink used is baked at l300-400 ℃ for 30 minutes after screen printing, and the heat resistance temperature of this type of ink is relatively low. However, the baking time is longer, the ink has good fastness and hardness, and the brightness is also very good. It can withstand the corrosion of low concentration electrolytes and solvents such as ethanol, acetone, benzene, and cyclohexanone.
　　9. Sintering
　　Glass is an amorphous inorganic material that softens with increasing temperature. When heated to the softening temperature of glass, it will deform. Glass colored glaze is decorated on the surface of glass through silk screen printing, and needs to be solidified on the glass surface through high-temperature sintering. However, the sintering temperature must be lower than the softening temperature of the decorated glass to ensure that the decorative glass does not deform. The sintering temperature of general glass glaze is not higher than 520 ℃ and is usually controlled between 480-520 ℃. There are several domestic manufacturers producing low-temperature glass glaze, and the price is also relatively low. There are several foreign companies that can also provide similar products, but the prices differ by ten to twenty times compared to domestic ones. The domestic consumption level has not yet reached the level of using this type of glaze, but the glaze provided by foreign countries is indeed much better in color and texture than in China.
　　It is inevitable to improve the quality of decorative glass and elevate the grade of glaze. Sintering equipment includes flame furnace and resistance furnace. Resistance furnace is divided into vertical hanging type and horizontal roller conveyor type according to the hanging method of glass. Vertical hanging sintering furnace has the advantages of small sintering deformation and a yield of over 95%, but the equipment is complex. Poor adjustment of the horizontal roller conveyor is prone to significant deformation and low yield. In addition, it is also feasible to use a horizontal tempering furnace to produce decorative glass, which improves the grade of the product and ensures safety, making it an ideal sintering method.
　　
The faults that are prone to occur in the screen printing process of glass
　　The occurrence of screen printing faults is partly due to a single factor, but more often it is the result of the cross influence of various reasons. This is something that operators should pay special attention to when determining the cause of the malfunction in glass screen printing and taking corresponding measures:
　　1. Paste version
　　Paste plate, also known as blocking plate, refers to the phenomenon where the through-hole part of the screen printing plate cannot transfer ink to the substrate during printing. The occurrence of this phenomenon can affect the printing quality, and in severe cases, it may even prevent normal printing.
　　The reasons for the phenomenon of plate sticking during screen printing are complex and intricate. The reasons for pasting can be analyzed from the following aspects:
　　① Reason for glass: The surface of the glass has not been cleaned, and there are still stains such as watermarks, paper marks, oil marks, fingerprints, dust particles, etc. As a result, it causes a paste version;
　　② The reasons for workshop temperature, humidity, and ink properties. The screen printing workshop requires a certain temperature of around 20 ℃ and relative humidity of around 50%. If the temperature is high and the relative humidity is low, the volatile solvents in the ink will quickly evaporate, causing the viscosity of the ink on the screen to increase and blocking the mesh holes. Another point to note is that if the downtime is too long, it can also cause plate sticking, and the longer the time, the more severe the plate sticking. Secondly, if the ambient temperature is low and the ink flowability is poor, it is also easy to produce a sticky plate;
　　③ The reason for screen printing. The prepared screen printing plate can only be used after being rinsed with water and dried before use. If the finished version is left for too long and not printed in a timely manner. During the storage process, dust may adhere to the plate to a greater or lesser extent, and if not cleaned during printing, it can cause plate sticking.
　　④ The reason for printing pressure. During the printing process, excessive imprinting force can cause the scraper to bend. The scraper is not in direct contact with the screen printing plate and glass, but rather in face-to-face contact. This way, each scraping can clean the ink, leaving residual ink. After a certain period of time, it will form a film and cause the plate to become sticky.
　　⑤ The reason for the improper gap between the screen printing plate and the glass. The gap between the screen printing plate and the glass should not be too small. If the gap is too small, the screen printing plate cannot detach from the glass in time after scraping. When the screen printing plate is lifted, a certain amount of ink is stuck to the bottom of the plate, which can also easily cause the plate to stick.
　　⑥ The reason for the ink is that when the pigments and other solid particles in screen printing ink are large, it is easy to block the mesh holes.
　　In addition, the selected mesh size and through-hole area of the screen are smaller than the particle size of the ink, making it difficult for coarser ink particles to pass through the mesh and cause screen sealing. This is also one of the reasons. The problem of plate sticking caused by large ink particles can be solved by strictly controlling the fineness of the ink during the manufacturing process.
　　During the printing process, the increase in ink viscosity causes plate sticking. The main reason is that the ink solvent on the screen printing plate evaporates, causing an increase in ink viscosity and resulting in screen sealing. If the printing area is relatively large, the ink consumption on the screen printing plate is more, and the phenomenon of plate sticking is less. If the image and text area is small and the ink consumption on the screen printing plate is low, it is easy to cause plate sticking. The solution is to use the principle of adding ink in small quantities multiple times. The poor fluidity of ink can cause the ink to form a paste without passing through the screen. This situation can be solved by reducing ink viscosity and improving ink fluidity without affecting printing quality. After a paste failure occurs, appropriate solvents can be used to scrub the ink on the plate according to its properties. The key to wiping is to start from the printed surface and gently wipe from the middle to the periphery. After wiping, check the printing plate. If there are any defects, they should be repaired in a timely manner. After repairing, printing can be restarted. It should be noted that every time the film is wiped, it becomes thinner. If significant damage is caused to the film during wiping, a new version of printing must be replaced.
　　2. Ink not firmly fixed on glass
　　① When printing glass, it is important to conduct strict degreasing and pre-treatment checks on the glass before printing. When substances such as grease, adhesives, and dust adhere to the surface of glass, it can cause poor adhesion between ink and glass.
　　② The insufficient adhesive strength of the ink itself causes the ink film to not adhere firmly. It is best to replace it with other types of ink for printing. Improper selection of diluent solvents can also lead to weak adhesion of ink film. When selecting diluent solvents, the properties of the ink should be considered to avoid weak adhesion between the ink and the substrate.
　　3. Uneven ink application
　　The uneven thickness of the ink film is caused by various reasons. In terms of ink, it is due to poor ink mixing, or the ink mixed with the ink skin during normal mixing. During printing, due to the effect of the solvent, it expands and softens, blocking the mesh holes that should pass through the ink and acting as the plate film, making it impossible for the ink to pass through. To prevent such malfunctions, the blended ink (especially old ink) should be filtered with a mesh before use. When reusing a used printing plate, it is necessary to completely remove the old ink attached to the plate frame. When storing the printing plate after printing, it is necessary to wash it thoroughly (including the scraper). If there is damage to the tip of the ink return plate, there will be marks along the direction of the scraper's movement. When printing glass, there will be obvious ink unevenness. So, it is necessary to protect the front end of the scraper well to prevent damage. If it is damaged, it should be carefully ground with a grinder. Furthermore, the unevenness of the printing table can also affect the uniformity of ink application. The ink layer on the convex part is thin, while the ink layer on the concave part is thick, which is also known as uneven ink application. In addition, if there is dust adhering to the back of the substrate or the printing table, the above faults can also occur.
　　4. pinhole
　　The phenomenon of pinholes is the most headache inducing problem for workers engaged in glass screen printing. The causes of pinholes are also diverse, many of which are currently inexplicable, and some are still quality management issues. Pinholes are one of the most important inspection items in printing product inspection.
　　① Dust and foreign objects attached to the board. During plate making, there may be some sol mixed in during water washing and development. In addition, during emulsion coating, dust can also mix in and adhere to the screen, resulting in pinholes. If these are checked carefully during the experiment, they can be discovered and promptly repaired. If dust and foreign objects adhere to the screen, blocking the opening of the screen can also cause pinholes. Before formal printing, it is necessary to carefully inspect the screen and eliminate any dirt on the plate;
　　② Cleaning of glass surface. Glass panels should undergo pre-treatment to ensure their surface is clean before printing. If the glass is not printed immediately after treatment, it will be contaminated again. After pre-treatment, it can remove grease and other dirt, as well as dust adhering to the surface. Special attention should be paid when moving glass by hand, as fingerprints may also adhere to the printing surface, forming pinholes during printing.
　　5. bubble
　　Glass sometimes produces bubbles on ink after printing, and the main reasons for the bubbles are as follows: ① Poor prepress treatment of the substrate. Dust and oil stains adhering to the surface of the substrate; ② Bubbles in ink. To adjust the ink, when adding solvents and additives for stirring, some bubbles will be mixed in the ink. If left unattended, low viscosity ink will naturally defoaming, while high viscosity ink may not naturally defoaming. Some of these bubbles are naturally eliminated during printing due to the transfer of ink, while others become larger and larger. To remove these bubbles, defoamers should be used, and the amount of defoamer added to the ink is generally 0. About 1%, if the specified amount is exceeded, it will actually have a foaming effect. After ink transfer, even if it foams, as long as the substrate's wetness and ink fluidity are good, the bubbles on the surface of the printing ink film will gradually disappear, forming a flat printing ink film. If the ink bubbles are not eliminated, the ink film will form a circular and uneven film surface. Generally, bubbles in ink can also be defoaming due to the action of the screen when passing through it; ③ Excessive printing speed or uneven printing speed can also produce bubbles. Printing speed should be appropriately reduced to maintain uniformity of printing speed.
　　6. Static electricity malfunction
　　The electrostatic current is generally very small, but the potential difference is very large, which can lead to phenomena such as attraction, repulsion, conductivity, and discharge The adverse effects on screen printing. The screen during printing is charged to the rubber part and screen due to the pressure and scraping of the scraper rubber. The wire mesh itself is charged, which can affect normal ink application and cause plate blockage faults; At the moment of output of the substrate, it will be sucked up by the screen; ② Methods to prevent static electricity. The methods to prevent static electricity include adjusting the ambient temperature and increasing air humidity. The appropriate temperature is generally around 20 ℃ and the relative humidity is around 60%; Can transfer static electricity in humid air; Reduce screen spacing and printing speed.
　　7. Expanded size of finished ink film
　　After screen printing, sometimes the printing size may expand. The main reason for the expansion of printing size is that the ink viscosity is relatively low and the fluidity is too high; The enlargement of screen printing plate size during production is also the reason for the enlargement of printing size. To avoid excessive ink fluidity causing ink to overflow in all directions after printing, resulting in larger printing dimensions, it is possible to consider increasing ink viscosity to reduce ink fluidity. When making screen printing plates, it is necessary to strictly ensure the quality of the screen and ensure the tension of the screen.
　　8. Printing plate ink leakage
　　A part of the film is leaking ink, which is called an ink leakage fault. The reason is that a part of the scraper is damaged; The pressure of scraping ink is high; The gap between the plate and the glass is too large; Large deformation of the frame, insufficient local printing pressure: uneven ink; The screen is too fine; Printing speed is too fast, etc. If dust is mixed into the glass and ink before printing without treatment, the film will be damaged due to the pressure of the scraper; Insufficient exposure during plate making, such as pinholes, can cause ink leakage in the plate film. At this point, emergency measures can be taken by attaching adhesive tape or other materials from the back of the plate. If this operation is not done very quickly, it will cause the ink on the plate to dry, and the entire plate will have to be wiped with a solvent. Wiping the plate is also a cause of film peeling, so it is best to avoid it. Ink leakage often occurs in the area where the ink stays, so it is best to strengthen this part during plate making.
　　9. mottling
　　Zimo refers to the appearance of speckled marks on the graphic and dark parts of the glass surface, which damages the printing effect. Glass screen printing is prone to this phenomenon. The reasons are as follows: printing speed and slow drying of ink; The ink layer is too thin; Ink has high thixotropy; The influence of static electricity; Poor dispersion of pigments in ink, due to the polarity of pigment particles, particles aggregate with each other, resulting in color spots and imprints. The improvement method is to improve the fluidity of the ink; Use quick drying flux; Try to print with high viscosity ink as much as possible: increase the wet film thickness of the ink, and use ink made with pigments with low oil absorption as much as possible: minimize the impact of static electricity.
　　10. Image deformation
　　When printing, the pressure applied by the scraper to the printing plate can make linear contact between the plate and the printed object, and should not exceed. Excessive printing pressure can cause the printing plate to come into contact with the substrate, causing the screen to stretch and deform, resulting in distorted printing images. Screen printing is the type of printing with the smallest printing pressure among various printing methods. If we forget this, we cannot produce good printed materials. If printing cannot be done without increasing pressure, the gap between the layout and the glass surface should be reduced, so that the pressure of the scraper can be reduced.
　
The application and market prospects of screen printed flat glass
　　Screen printed flat glass is widely used in every corner of people's lives: you can easily find their presence in display windows, building space zoning, building exterior beautification, car windshields, and inlaid glass. At the same time. They are also widely used in furniture decoration and gaming tools, as well as countless decorations and artistic creations. Screen printing has also become a part of creative design work in glass manufacturing. People can directly print color images onto the surface of glass through screen printing. In addition, it can also be used to temporarily cover the non graphic parts of the glass surface, or to print preservatives and other additives in certain areas of the glass surface, so that they are not affected by etching or sanding processes. On the other hand, specialized ink for screen printing can also be directly used to create etching or frosting effects. Sometimes. People also use the strong covering ability of screen printing, such as printing a thin layer of conductive material on glass, to make anti icing (frost) devices for windows.
　　Screen printing is constantly expanding 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 a wide range of flat glass substrates of different sizes and weights. Moreover, due to the absolute advantage of screen printing in ultra large format image printing, it has further 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 sharply increased. 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 increasingly stringent printing requirements, especially in areas such as flat glass, which has led to many of the world's most flexible equipment being widely used for printing building panels.
　　The application of screen printing in flat glass decoration will continue to develop and expand its application areas in glass decoration. The screen printing machine has a faster material transfer system and a more advanced power supply system, combined with a powerful PLC (logic controllable device), to improve productivity and image quality, ensuring its continuous expansion in the decorative flat glass market.