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Advanced Screen Printing

The glass screen printing process problems shooting

[ Size:L M L ]Data:2021-7-30 Edit: Hits:1727

JUIST glass screen printing technology includes traditional glass screen printing to emerging LED, touch panel, LIQUID crystal substrate, solar photovoltaic substrate printing, is the use of screen plate, using glass glaze, decorative printing on glass products. Glass glaze is also called glass ink, glass printing material, it is a paste printing material mixed by coloring material and binder. The colouring material is composed of inorganic pigment and low melting point flux (lead glass powder). Connecting material in the glass screen printing industry commonly known as late. The printed glass products should be fired in a furnace at 520~600℃, so that the glaze printed on the surface of the glass can be consolidated on the glass and form gorgeous and colorful decorative patterns. If screen printing is used with other processing methods, a better result will be obtained. For example, the use of polishing, engraving, corrosion and other methods in the printing before or after the printing of the glass surface processing, can double improve the printing effect. The JUIST screen printer has a faster transfer system for printing materials and a more advanced power supply system, combined with powerful PLC (logic Controlled device). In addition to the pure optical color applications that use screen printing in the automotive industry, Various functional layers (e.g., heat conductors on the rear window) are also modified to conduct conductive pathways and the best structures (e.g., heating units on the rear window) must be imprinted in a timely and stable manner to ensure excellent quality.



The glass screen printing process is prone to problems

1, paste version
Paste, also known as blocking plate, refers to the screen printing plate graphic through hole part in the printing can not transfer ink to the substrate phenomenon. The appearance of this phenomenon will affect the printing quality, serious even can not be normal printing. The reasons for the pasting phenomenon in screen printing are complicated. The reasons for pasting can be analyzed from the following aspects:
(1) the reason for the glass: the glass surface is not clean, there are watermark, paper printing, mimeograph, fingerprint, dust particles and other dirt. Resulting in paste version;
(2) workshop temperature, humidity and ink properties. 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 evaporate, and the viscosity of the ink on the screen becomes high, thus blocking the mesh. Another point should be noted that if the downtime is too long, it will also produce paste phenomenon, the longer the paste is more serious. Secondly, if the ambient temperature is low, ink fluidity is also easy to produce pastes;
③ screen printing plate reasons. The finished screen printing plate can be used after rinsing with water and drying before use. If a good version after placing too long not timely printing. In the preservation process more or less will adhere to the dust, if not cleaned when printing, it will cause paste.
④ The reason of printing pressure. In the printing process, the imprint force is too large, will make the scraper bending, the scraper and screen printing plate and glass is not line contact, but surface contact, so that each time the scraping can be scratched clean ink, and leaving the residual ink, after a certain time will conjunctival paste.
⑤ Screen printing plate and glass gap improper reasons. The gap between the screen plate and the glass can not be too small, the gap is too small after scraping the screen plate can not be timely out of the glass, screen plate raised, the bottom of the plate with a certain ink, it is also easy to cause paste board. The reason for the ink, in the screen printing ink pigment and other solid particles are large, it is easy to block the phenomenon of mesh. In addition, the number of mesh and through the hole area and ink particle size is smaller, so that the coarse particles of ink is not easy to pass through the mesh and sealing phenomenon is one of the reasons. For ink particles caused by larger paste, can be solved from the manufacturing of ink, the main method is to strictly control the fineness of ink.

In the printing process, the increase of ink viscosity resulting in paste, the main reason is that the evaporation of ink solvent on the screen printing plate, resulting in the increase of ink viscosity, and the phenomenon of sealing. If the printing area is large, screen printing ink consumption on the plate, paste version of the phenomenon is less. If the area of text and text is small, screen printing ink consumption is less, it is easy to cause paste, the strategy is to use a small number of ink principle. The fluidity of the ink is poor, so that the ink is not through the screen when the paste, this situation can be solved by reducing the viscosity of the ink to improve the fluidity of the ink without affecting the printing quality. After the failure of the paste version, the nature of the ink on the version can be used to scrub with the appropriate solvent. The key to scrub is to start from the printing surface, from the middle to the periphery of the gently wipe. Check the printing plate after wiping, if there is a defect should be repaired in time, after repair can start printing again. It should be noted that every time the film is scrubbed, it will become thinner. If the major defect of the film is caused by wiping, it will have to change the new version of printing.
2, the ink is not fixed on the glass
(1) When printing glass, it is important to check the strict degreasing and pretreatment of glass before printing. When the glass surface attached to grease, binder, dust and other substances, will cause ink and glass bonding poor. 

(2) the ink itself is not strong enough to cause the ink film fixation, 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 bonding is not strong.



3. Uneven inking
Ink film thickness is not uniform, the reason is a variety of ink, ink is bad deployment, or normal deployment of ink mixed with the ink, printing, due to the effect of solvent expansion, softening, will be through the ink mesh, played the role of the film, the ink can not pass. In order to prevent this fault, after the deployment of ink (especially old ink), before use to use a net filter again. When reusing a used plate, the old ink attached to the frame must be completely removed. When storing the printing plate after printing, wash it thoroughly (including the scraper). If the tip of the front end of the ink board is injured, there will be a trace along the direction of the movement of the scraper. When printing glass, there will be a significant inky. Therefore, the front end of the scraper must be well protected, so that it does not occur damage, if the damage, it is necessary to grind carefully with a grinder. In addition, the convex printing table will also affect the ink uniformity. Convex ink layer is thin, concave ink layer is thick, this phenomenon is also known as uneven ink. In addition, the back of the substrate or the printing table with dust, will also produce the fault.

4. Pinhole phenomenon
Pinhole phenomenon is the most headache for the staff engaged in glass screen printing. The causes of pinhole occurrence are various, many of which are currently unexplained causes, and some are 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. Platemaking, washing development will have some sol mixed in. In addition, in the emulsion coating, there are dust mixed, attached to the screen will produce pinholes. These in the test, if attention to check, can be found and can be timely repair. If dust and foreign matter attached to the screen, the screen opening will also cause pinhole blockage. Before formal printing, to carefully check the screen, eliminate the dirt on the plate; (2) Cleaning the glass surface. The glass plate should be processed before printing to make its surface clean and then printed immediately. If the glass is processed, it will be contaminated again if it is not printed immediately. 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 when moving glass by hand, the fingerprint of the hand will also adhere to the printing surface, forming pinholes during printing.

5. Bubbles appear
Bubble glass in ink after printing sometimes appear bubbles, the main reasons for bubbles are as follows: (1) the substrate prepress treatment is bad. Substrate surface attached to dust and oil marks and other substances; ② The air bubbles in the ink. In order to adjust the ink, adding solvents, additives to stir, ink will be mixed with some bubbles, if placed regardless, low viscosity of the ink will natural defoaming, high viscosity of the ink some can not natural defoaming. Some of these bubbles in printing, due to the transfer of ink and natural elimination, some are getting bigger and bigger. In order to remove these bubbles, to use defoaming agent, ink defoaming agent added amount is generally about 0.1 ~ 1%, if more than the specified amount but will play a foaming role. Even if the ink is foamed after transfer, as long as the substrate moisture and ink mobility is good, the bubbles on the surface of the printing ink film will gradually eliminate, and the ink will form a flat printing ink film. If the ink bubbles are not eliminated, the ink film will form a ring of uneven film surface. General ink bubbles through the screen, also due to the role of the screen can debubble; ③ Too fast printing speed or uneven printing speed will also produce bubbles. Printing speed should be properly reduced to maintain uniformity of printing speed.



6. The static electricity is faulty



Electrostatic current is generally very small, but the potential difference is very large, along with the phenomenon of attraction, repulsion, conduction, discharge. (1) The adverse effects on screen printing. During the printing screen, the rubber part and the screen are electrified due to the pressure scraping of the scraper rubber. Wire mesh itself, will affect the normal ink, block plate failure; In the substrate output moment will be attracted by the screen; ② Methods to prevent static electricity. The methods to prevent electrostatic generation are: adjust the ambient temperature, increase the air humidity, the appropriate temperature is generally about 20℃, relative humidity about 60%; Can make static electricity in the wet air transmission; Reduce the screen spacing, reduce the printing speed.



7, printing size expansion



The main reason for the enlargement of printing size is that the ink viscosity is relatively low and the fluidity is too large; Screen printing plate in the production of the size of the expansion, is also caused by the expansion of printing size. In order to avoid excessive ink fluidity resulting in the printing ink flowing around, resulting in larger printing size, we can consider increasing the ink viscosity to reduce the fluidity of the ink. In the production of screen printing plate, to strictly ensure the quality of the screen, to ensure the tension of the screen.



8, printing plate leakage



Part of the plate film leakage, known as leakage fault, the reason is: part of the scraper is injured; Scraping ink pressure is large; The gap between the plate and the glass is too large; Large deformation of the plate frame, local printing pressure is not enough: ink is not uniform; Screen is too fine; Printing speed is too fast. If the glass and ink mixed with dust, without treatment for printing, because of the scraper pressure will make the film damaged; When plate exposure is insufficient to produce pinholes, will make the film ink leakage phenomenon. At this time, available tape tape from the back of the plate affixed to do emergency treatment. If this operation is not very fast, it will dry the printing ink of the layout and have to wipe the whole version with a solvent. Wipe version is also the cause of the version of the film peel, so it is best to avoid. Version of the ink leakage in the ink stay part often occurs, so it is best to strengthen this part in the plate.



9, the picture and text part and the dark part appear spots



Ink refers to the glass surface graphic part and dark part of the blotchy imprint, this phenomenon has damaged the printing effect. Glass screen printing is easy to produce this phenomenon. The reasons are as follows: printing speed and ink drying is too slow; Ink layer is too thin; Ink thixotropy; Electrostatic influence; Ink pigment dispersion, due to the polarity of pigment particles, particles agglutination, color blots. The improvement method is: improve the fluidity of ink; Use a quick-drying flux; Printing with high viscosity ink as far as possible: increase the wet film thickness of the ink, try to use ink made of small oil absorption pigment: minimize the impact of static electricity.





10, image deformation

Printing by the scraper added to the printing plate, can make the printing plate and printed between the line contact can be, do not exceed. Printing press is too large, printing plate and substrate inside contact, will make the screen expansion, resulting in the deformation of the printing image. Screen printing is a kind of printing with the smallest pressure in various printing methods. If we forget this, we can't print good prints. If you cannot print without increasing the pressure, the gap between the plate and the glass surface should be narrowed, so that the pressure of the scraper can be reduced.

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