What are the common problems in glass screen printing technology?

What are the common problems in glass screen printing technology?

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

So, as one of the important fields in the silk screen industry, how important is the role of glass silk screen printing in the silk screen industry?

First, the introduction of glass screen printing technology

Glass screen printing is the use of screen printing plates, using glass glazes, decorative printing on glass products. Glass glaze is also called glass ink and glass printing material. It is a paste printing material which is obtained by mixing and mixing coloring materials and binders. The coloring material is composed of an inorganic pigment and a low melting point flux (lead glass powder); the binder is commonly known as a slab oil in the glass silk screen industry. After printing, the glass products should be placed in a fire furnace and fired at a temperature of 520~600 °C. The glaze printed on the glass surface can be fixed on the glass to form a colorful decorative pattern. If you use silk screen together with other processing methods, you will get better results. For example, polishing, engraving, etching, etc., the glass surface is processed before or after printing, and the printing effect can be doubled.

Second, the application field of glass screen printing technology

The application of screen printing glass and its market prospects Screen printing glass is widely used in every corner of people's life: you can easily find in the display window, building space partition, building appearance, car windshield and mosaic glass Their figure. 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 on 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 matte 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 most flexible in the world. 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. Screen printing machine has a faster substrate conveying system, as well as a more advanced power supply system, combined with powerful PLC (Logic Controllable Device)

In addition, the automotive industry's demand for glass screen printing technology is also very strong. In addition to the pure optical color application using screen printing, various functional layers (such as thermal conductors on the rear window) have also been modified with conductive pathways and most Good structures (such as rear window heaters) must be stamped in a stable manner in a timely manner and ensure excellent quality.

Third, the glass silk screen process is prone to problems

So what are the quality problems that often arise in the process of glass screen printing?

1, paste version

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 hole. Another point to note is that if the downtime is too long, it will also produce a paste phenomenon, the longer the paste, 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 washed 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 adhered to 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 develop 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 method of scrubbing starts from the printing surface and gently wipes from the middle to the periphery. Check the printing 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 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, uneven 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 phenomenon

The pinhole phenomenon is the most 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 a printed product inspection. 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 can be repaired in time when the test is carried out. If dust and foreign matter adhere to the screen, blocking the screen opening will also cause pinholes. Before the official printing, the screen should be carefully checked to eliminate the dirt on the plate; 2 the 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 appear

Bubble 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 added to the ink is generally about 0.1 to 1%, and if it exceeds a predetermined amount, it will foam. 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, if the printing speed is too fast or the printing speed is uneven, bubbles will also be 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. The screen itself is charged, which will affect the normal inking and cause blockage 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, printing size expansion

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 overflow 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.

8, the printing plate leaks ink

Part of the membrane leaks ink, which is called ink leakage failure. The reason is that a part of the scraper is injured; the pressure of the scraping ink is large; the gap between the plate and the glass is too large; the deformation of the frame is large, and the partial printing pressure is insufficient: 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 printing is performed without treatment, the film may be damaged by the pressure of the squeegee; if the exposure is insufficient at the time of plate making, pinholes may occur, which may cause the film to leak ink. 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, the graphic part and the dark part of the spot appear

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, resulting in deformation of the printed image. 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.

At present, glass screen printing technology is transforming into a high-tech, high-tech value-added processing field. Products including touch screens, liquid crystal substrates, and solar photovoltaic substrates mentioned above have gradually become an integral part of the current electronic information products field. It is believed that over time, glass silk screen technology will provide more support for the glass industry and even electronics, construction, energy and other fields.