From traditional glass screen printing to emerging LED and touch panel printing, screen printing technology runs through the entire glass industry and plays a pivotal role in it.
So as one of the important fields in the screen printing industry, how important is the role of glass screen printing in the screen printing industry?
1. Brief introduction of glass screen printing technology
Glass screen printing is the use of screen printing plates and glass glazes for decorative printing on glass products. Glass glaze is also called glass ink and glass printing material. It is a paste-like printing material formed by mixing and stirring coloring materials and connecting materials. The coloring material is composed of inorganic pigments and low-melting flux (lead glass powder); the linking material is commonly known as lee board oil in the glass screen printing industry. After printing, the glass products should be fired in the furnace at a temperature of 520 ~ 600 ℃, and the glaze printed on the glass surface can be consolidated on the glass to form a colorful decorative pattern. If screen printing is used in combination with other processing methods, more ideal results will be obtained. For example, by polishing, engraving, etching and other methods to process the glass surface before or after printing, the printing effect can be doubled.
2. 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 all corners of people's lives: you can easily find it in places such as display windows, architectural space division, building beautification, car windshield and mosaic glass Their figure. Simultaneously. They are also widely used in furniture decoration and game tools, as well as countless decoration and artistic creation. Screen printing has subsequently become 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 parts of the glass surface, or print auxiliary agents such as preservatives on some areas of the glass surface, so that it will not be affected by the etching or sanding process. Relatively, special inks can also be screen printed directly to create an etching or matte effect. sometimes. People will also take advantage of 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 different weights in a wide range. Moreover, due to the absolute advantages of screen printing in ultra-large format image printing, it has further strengthened its leading position in leading 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 more demanding printing requirements, especially in areas such as 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 flat glass decoration will continue to develop and continue to expand its application in glass decoration. The screen printing machine has a faster printing material conveying system, and a more advanced power supply system, combined with a 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 applications using screen printing, various functional layers (such as the thermal conductor on the rear window) have also been modified. A good structure (such as a rear window heating device) must be embossed in a stable manner in a timely manner and ensure excellent quality.
Third, the glass screen printing process is prone to problems
So as far as the glass screen printing technology is concerned, what quality problems often occur during its processing?
1. Paste
The paste version is also called blocking version, which refers to the phenomenon that the screen through-hole portion of the screen printing plate cannot transfer ink to the substrate during printing. The appearance of this phenomenon will affect the printing quality, even in serious cases, it will not be able to print normally. The cause of the scumming phenomenon that occurs during the screen printing process is complex. The reasons for lay-up can be analyzed from the following aspects:
â‘ The reason of the glass: the surface of the glass is not cleaned, and there are watermarks, paper marks, oil marks, handprints, dust particles and other dirt. Thus causing lay-up;
② Reasons for workshop temperature, humidity and ink properties. 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 will become high, thereby blocking Live mesh. Another point that should be noted is that if the downtime is too long, it will also cause the phenomenon of pasting, the longer the time, the more serious the pasting. Secondly, if the ambient temperature is low, the poor fluidity of the ink is also easy to produce paste;
â‘¢ The reason for the screen printing plate. The prepared screen printing plate should be washed with water and dried before use. If it is placed for a long time after making a plate, it will not be printed in time. In the storage process, more or less dust will adhere. If it is not cleaned during printing, it will cause paste.
â‘£The reason of printing pressure. Excessive embossing force during the printing process will cause the squeegee to bend. The squeegee is not in line contact with the screen plate and glass, but is in surface contact, so that each time the squeegee can wipe the ink clean, leaving residual ink After a certain period of time, the conjunctiva will cause paste.
⑤ Reason for improper gap between screen printing plate and glass. The gap between the screen printing plate and the glass should not be too small. If the gap is too small, the screen cannot be separated from the glass in time after scraping. When the screen printing plate is lifted, a certain amount of ink is stuck on the bottom of the plate, which is also easy to cause paste board. ⑥ The reason for the ink is that when the pigments and other solid particles in the screen printing ink are large, the phenomenon of blocking the mesh is likely to occur. In addition, the number of screen meshes and the area of ​​the through holes selected are smaller than the particle size of the ink, making it easier for coarser particles of ink to pass through the mesh and cause the screen sealing phenomenon. For paste plates caused by large particles of ink, it can be resolved from the time of manufacturing the ink. The main method is to strictly control the fineness of the ink.
During the printing process, the increased viscosity of the ink causes paste printing. 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 screen sealing phenomenon. If the area of ​​the printed image and text is relatively large, the ink consumption on the screen printing plate is large, and the phenomenon of paste-up is less. If the graphic area is small and the ink consumption on the screen printing plate is low, it is easy to cause scumming. The countermeasure is to use a small number of times to add ink. Poor fluidity of the ink will cause the ink to paste when it does not pass through the screen. This situation can be solved by reducing the viscosity of the ink and improving the fluidity of the ink without affecting the printing quality. After the pasting failure occurs, you can use an appropriate solvent to scrub 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 periphery. Check the printing plate after wiping, if any defects should be repaired in time, and printing can be restarted after repairing. It should be noted that every time the plate film is scrubbed, it becomes thinner. If the plate film is damaged during the wiping, it has to be replaced with a new version.
2. The ink is not firmly fixed on the glass
â‘ When printing on glass, it is important to strictly degrease and inspect the glass before printing. When oils, adhesives, dust, etc. are attached to the glass surface, it will cause poor adhesion between the ink and the glass. â‘¡ Insufficient adhesion of the ink itself causes the ink film to be not firmly fixed. It is better to replace other types of ink for printing. Improper selection of the dilution solvent will also result in the phenomenon of poor adhesion of the ink film. When selecting the dilution solvent, the nature of the ink should be considered to avoid the phenomenon that the adhesion of the ink and the substrate is not strong.
3. Uneven ink
The thickness of the ink film is uneven due to various reasons. In terms of ink, 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 ink should pass through. The mesh is blocked, which acts as a plate film, making the ink unable to pass through. In order to prevent this kind of malfunction, the prepared ink (especially the old ink) should be filtered with a net before use. When reusing an already used printing plate, the old ink attached to the frame must be completely removed. When storing the printing plate after printing, it should be washed thoroughly (including the squeegee). If the tip of the ink return plate is damaged, a trace will appear in the direction of the blade movement. When printing glass, there will be obvious ink unevenness. Therefore, the front end of the squeegee must be well protected from damage. If it is damaged, it must be carefully ground with a grinder. In addition, the unevenness of the printing table will also affect the ink uniformity. The ink layer on the convex part is thin, and the ink layer on the concave part is thick. This phenomenon is also called unevenness in ink. In addition, if dust adheres to the back of the substrate or the printing table, the above failures will also occur.
4. Pinhole phenomenon
The pinhole phenomenon is the most headache problem for the staff engaged in glass screen printing. The reasons for the occurrence of pinholes are also varied, many of which are currently unexplained, and some are quality management problems. Pinhole is one of the most important inspection items in the inspection of printed products. â‘ Dust and foreign matter attached to the plate. When making a plate, some sol will be mixed into it by washing with water. In addition, when the emulsion is applied, dust is also mixed in, and pinholes are generated when it adheres to the screen. During the test, if you pay attention to inspection, you can find and make timely repairs. If dust and foreign objects adhere to the screen, blocking the screen opening will also cause pinholes. Before the formal printing, you should carefully check the screen to eliminate the dirt on the plate; â‘¡ the cleaning of the glass surface. The glass plate should be pre-treated before printing to make its surface clean and then printed immediately. If the glass is not printed immediately after being processed, it will be contaminated again. After pretreatment, it can remove grease and other dirt, and at the same time, it can also remove dust attached to the surface. Pay special attention to the fact that when you move the glass by hand, the fingerprints of your hands will also adhere to the printed surface, forming pinholes during printing.
5. Bubbles appear
Bubble glass sometimes appears bubbles on the ink after printing. The main reasons for the bubbles are as follows: â‘ The substrate is not well processed before printing. Dust and oil stains are attached to the surface of the substrate; â‘¡ bubbles in the ink. In order to adjust the ink, when adding solvents and additives to stir, some bubbles will be mixed into the ink. If left untouched, the ink with low viscosity will naturally defoam, while the ink with high viscosity may not defoam naturally. Some of these bubbles are naturally eliminated in the printing process due to the transfer of ink, while others have become larger and larger. In order to remove these bubbles, an anti-foaming agent is used. The amount of anti-foaming agent added to the ink is generally about 0.1 to 1%. If it exceeds the specified amount, it will have a foaming effect. Even if foaming occurs after the transfer of ink, 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 be gradually eliminated, and the ink forms a flat printing ink film. If the ink bubbles are not eliminated, the ink film will form a ring-shaped uneven film surface. In general, the bubbles in the ink can be deaerated when passing through the screen; â‘¢ bubbles can also be generated if the printing speed is too fast or the printing speed is uneven. The printing speed should be properly reduced to maintain the uniformity of the printing speed.
6. Static breakdown
Electrostatic current is generally very small, but the potential difference is very large. At first, phenomena such as attraction, repulsion, conduction, and discharge can occur. ①Adverse effects on screen printing. During printing, the rubber part and the screen are electrified due to the pressure of the scraper rubber. If the screen is electrified, it will affect the normal inking and cause blockage faults; it will be attracted by the screen at the moment the substrate is output; ②A method to prevent static electricity. The methods to prevent static electricity are: adjust the ambient temperature and increase the air humidity. The appropriate temperature is generally about 20 ℃, the relative humidity is about 60%; the static electricity can be transmitted in the humid air; reduce the mesh distance and reduce the printing speed.
7. Expanded printing size
The main reason for the enlargement of the printing size is that the ink viscosity is relatively low and the fluidity is too large; the enlargement of the size of the screen printing plate at the time of production is also the cause of the enlargement of the printing size. In order to avoid the excessive fluidity of the ink and cause the ink to overflow to the surroundings after printing, resulting in a larger printing size, it may be considered to increase the viscosity of the ink to reduce the fluidity of the ink. When making screen printing plates, we must strictly guarantee the quality of screen printing plates and the tension of screen printing plates.
8. Ink leakage of printing plate
A part of the plate film is leaking ink, which is called a leaking ink failure. The reasons are: a part of the scraper is damaged; the pressure of the scraping ink is large; the gap between the plate and the glass is too large; the plate frame is deformed and the local printing pressure is not enough: Ink is uneven; screen is too fine; printing speed is too fast. If dust is mixed on the glass and the ink, and printing is performed without treatment, the plate film will be damaged due to the pressure of the squeegee; if the exposure is insufficient during plate making, pinholes, etc., will cause the plate film to leak ink. At this time, you can use adhesive tape to paste from the back of the plate for emergency treatment. If this operation is not very rapid, the ink on the plate surface will be dried, and the entire plate will have to be wiped with a solvent. Wiping the plate is also the cause of the peeling of the plate film, 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 better to strengthen this part when making a plate.
9. Spots appear in the graphics and dark parts
Moisture 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 easy, causing 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 is thixotropic; the effect of static electricity; the pigment dispersion in the ink is poor, due to the polar effect of the pigment particles, the particles agglomerate with each other and appear color 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 thickness of the wet film of the ink, try to use ink made of pigments with small oil absorption: minimize the effect of static electricity .
10. Image distortion
The printing pressure added to the printing plate by the squeegee during printing can make the printing plate and the printed object be in line contact, it should not exceed. If the printing pressure is too large, the contact between the printing plate and the substrate will cause the screen to expand and contract, causing the printed image to deform. Screen printing is the printing with the least pressure among various printing methods. If we forget this, we can not print good prints. If you cannot print without increasing the pressure, you should reduce the gap between the plate and the glass surface, so that the pressure of the scraper can be reduced.
At present, the glass screen printing technology is changing to the processing field with high technological content and high-tech added value. Products including the aforementioned touch screen, liquid crystal substrate, solar photovoltaic substrate, etc. have gradually become an integral part of the 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 various fields such as electronics, construction, energy and so on. 
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