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Screen printing common problems and solutions

Addtime：2015/7/4 16:34:00 Hits：1864

Screen printing common problems and solutions
Cause screen printing fault produced a number of factors involved in printing, squeegee, ink, equipment, printing material and operating technology. Screen Printing fault generation, mostly complex cross-impact results for several reasons. This is when the operation of the workers is determined to find the cause, take appropriate measures to address pay special attention.
1, plug network refers to graphic screen printing mesh portion is blocked, the printing ink can not be transferred to the substrate on the phenomenon. This phenomenon can seriously affect the quality of printing, and even cause can not be normal printing. CAUSE plug network phenomenon are complex, generally have the following reasons. ① substrate material screen printing substrate material is varied, its surface texture properties is a cause plug network phenomenon. For example: Paper type, wood type, etc. fabric substrate surface smoothness is low, poor surface strength, the printing process is relatively easy to produce out of powder, hair loss phenomenon, will result in a screen printing plug network. ② ambient temperature, humidity screen printing workshop temperature and relative humidity constant. If the temperature is too high, the relative humidity is too low, the ink solvents will evaporate quickly, causing the viscosity of the ink increases, the ink clogging. If the printing process down time, will produce plug network phenomenon, longer plug network more serious. If the ambient temperature is too low, the ink fluidity, but also prone to plug network phenomenon. ③ halftone screen if you make a good place for too long, more or less in the preservation process will adhere to dust, if not clean, it will cause a plug network printing. ④ printing pressure during printing embossing force is too large, squeegee squeegee portion bent squeegee blade with the screen and not the line then angle substrates, and was face contact, so that each squeegee can not The ink is scraped, leaving residual ink, after a period of time will cause conjunctival plug network. ⑤ Screen and substrate gap improper gap between the screen and the substrate is not too small, if the gap is too small, can not scratch the plate from India substrates, when the screen lifted, certain ink adhered to the bottom of the plate , it is likely to cause plug network. ⑥ large screen printing ink, when the ink pigments and other solids particles easily clogged mesh phenomenon. In addition, the selected screen mesh particle size and area of the through hole a bit smaller compared to the ink, the ink is not easy to block network coarser particles is one of the reasons the phenomenon occurs through the mesh. Jackpot network because larger ink particles and cause, must consider choosing suitable ink fineness. Ink drying too quickly in the printing process, making it easy to plug network failure, especially when using evaporation drying type ink such phenomena more break out, so when the printing must choose the appropriate solvent control the drying speed. When using the ink to consider the impact of the season, you can use the quick-drying ink winter, summer should be replaced with other types of ink. The use of oxidative drying inks, plug network phenomenon was not a lot, but if excessive use of desiccant, especially plug network phenomenon also occurs in the summer. The printing process, since the ink viscosity increases caused by plug network, the reason is: the plate ink solvent evaporation, ink viscosity, thereby clogging the mesh phenomenon. If the printed version of the graphic area is small, less ink consumption, it is easy to create plug network, improve the fluidity of the ink can be solved by reducing the ink viscosity.

2, the ink on a substrate fixing ① ink itself is not strong enough to cause adhesion of the ink film fixation is not strong, then it is best to replace the ink for printing; when using a solvent diluted ink solvent improper use can also occur if the ink film is not fixed prison, appeared ink and substrate bond is not strong phenomenon. ② before printing on substrates strict degreasing is very important, when attached to the substrate surface oils, adhesives, dust and other material things, it will cause bad ink and substrate bonding. ③ plastic surface treatment prior to printing ink can also cause insufficient fixation failure is not strong, as a polyethylene film printing material in the printing in order to improve the adhesion properties of the ink, must be subjected to surface treatment. ④ metal material must be degreased after dust removal treatment before printing, drying should be carried out after the printing ink according to the required temperature, if the drying process will produce improper ink film exfoliation phenomenon. ⑤ glass and ceramic items like, should be carried out after printing a high temperature sintering process so long as the temperature suitable adhesion will be good.

3, edge defects halftone ink film making process itself or a problem with the printing ink film will appear jagged edge burrs (including incomplete or broken) causes glitches are the following. ① Photoresist resolution is not high, so fine lines appear broken or incomplete. ② making process underexposed time or the exposure time is too long, not fully developed, the plate graphic jagged appear jagged out. ③ screen surface is not smooth, when printing, there are gaps between the screen and the substrate, ink vacant penetration, resulting in the printing ink edge burr. ④ printing process, because the version of the film after contact with solvents can swell and warp and weft to swell to varying degrees, so that version of the mask surface uneven phenomenon occurs, screen and substrate contact surface partial gap occurs when printing. Solution is as follows: · selection of high mesh screen plate. · Selection of high resolution photographic material plate. · Making certain screen plate thickness, in order to reduce the swelling deformation. · Skew Stretching method Stretching as far as possible, the best angle of 22.5 °. · Fine line printing, maximize the use of indirect legal version of the plate, because the indirect legal version may appear less burr. · In the plate making and printing process, try to control the temperature expansion factor, using expansion coefficient of the photosensitive material. · Improve plate quality assurance entire screen plate surface is smooth, the edges of the halftone line hair neat. · High pressure spray gun wash screen to improve development results. · Distance between the screen and the substrate, squeegee angle, printing press should be appropriate.

4, inking uneven thickness of the ink film is uneven. The reasons are: ink formulation bad; normal deployment of ink mixed with ink Paper, printing, due to the effect of the solvent swell, soften, will be thoroughly clogging the ink, the ink can not pass. Workaround: ink (especially the used ink) after deployment, once again before use to filter use; when re-using already used plates must be completely removed in the version attached to the frame of the old ink; printing station The irregularities also affect the ink evenly thin projecting portion of the ink, the ink layer thickness recess

5, dust and foreign objects attached version of the pinhole ① caused phenomenon. If dust and foreign matter attached to the screen, blocking screen openings can also cause pinholes. Can before the formal printing, with strong ink paper, the number of printed sheets, you can remove the dust from the edition. Due to the plate, washed developing sol attached mesh if some of it is not easy to deal with. ② cleaning the surface of the substrate before printing: aluminum, glass, acrylic panels prior to printing so that the surface should be clean after the pre-treatment. Substrates, should be immediately printed. When moving substrates, the hand will be attached to the fingerprint surface printing, resulting in the formation of pinholes during printing, it should be noted that after the pre-treatment, should be immediately printed. When moving substrates, the hand will be attached to the fingerprint surface printing, resulting in the formation of pinholes during printing, it is also noted.

6, the ink film sometimes printed bubble after bubble, bubble occurs because the following aspects. ① substrates prepress poor substrate surface adhesion of dust and traces of oil and other substances. ② air bubbles in the ink. To adjust ink viscosity, often adding in the ink solvent, additive during mixing, will produce some bubbles, low viscosity inks will naturally degassing, high-viscosity ink is not naturally degassing. These bubbles printing, some due to the transfer of ink and natural elimination, some are getting bigger. To remove these bubbles, often use an antifoaming agent, a defoaming agent added is generally an amount of about 0.1% to 1%, but if more than a predetermined amount to cause foaming action. ③ printing speed is too fast or uneven printing speed will produce bubbles. At this point it should be appropriate to reduce the printing speed, maintaining the uniformity of the printing speed.

7, the network marks of illiquid since the ink, the ink film surface printed signs sometimes mesh. Screen printing process, when the plate lifted and transferred to the ink on the substrate flow on its own track filled network, the ink film surface smooth. If the ink illiquid screen lifted, the ink flow is relatively small, the screen marks can not be filled, will not get the smooth surface of the ink film. To prevent the screen marks appear on printed matter, consider using the following methods: using mobility of the ink for printing; consider using slow drying of ink, the ink flow time increases gradually flattened ink and cured; at the plate when you try to use thinner wire monofilament mesh.

8, trapping poor overlapping ink film is called overprinting. When the multi-color printing, the printed ink film, and then after the printing ink can not be printed clearly on this issue will appear on. For example: oxidative polymerization type ink, in order to promote the desiccant excessive dosage, oxidation and hardening of the ink film is over, make the two-color inks are mutually exclusive; if excessive volatile inks add defoamer in the ink film film formed on the surface, hinder overprint. Its solution be: Use good ink trapping performance, lower the ink viscosity, adding additives in the ink, reducing the ink drying speed.

9, because drawing phenomenon is caused by the drawing: Ink uneven ground; scrape off the printing ink plates slow version; a small layout area surrounding the printed image; there is static electricity, resulting in an ink drawing; or squeegee angle is too small.

10, graphic printing products upsizing the ink viscosity is low and liquidity is too large, and sometimes there will be printed after the network brush upsizing phenomenon. Screen size to expand in the production, is caused by an enlarged print size reasons. To avoid ink fluidity caused by excessive printing ink film becomes large in size, consider adding a certain amount of excess liquidity in the ink thickener to reduce the fluidity of the ink; You can also use fast-drying ink, accelerate the ink drying rate after printing, to reduce the flow of ink. In the production of network printing, to ensure that screen quality.

11, the ink film crack crack ink film is due to the solvent and temperature variations caused by large China itself substrate material factors will lead to the ink film cracking phenomenon. In order to prevent the occurrence of cracking, to be considered in the selection of the solvent properties of the ink and substrate solvent resistance. Selection solvent resistance, oil resistance and strong material as the substrate material, and to keep the workshop constant temperature, in multi-color overlay To fully dry after each color printing, and strictly control the drying temperature, can effectively prevent the ink film tortoise the occurrence of cracking phenomenon.

12, Zi Zi ink means ink blots substrates graphic part and a dark tone appear blotchy part, this phenomenon undermines the printing results. There are several reasons: the ink drying too slow; too thin ink; ink thixotropy too; static electricity; ink pigment dispersion bad, because the polar effect pigment particles, causing the particles to each other aggregation occurs color dot blot. The solution is: to improve the flow of ink, the use of quick-drying solvent, as far as possible with high viscosity ink, maximize the use of a small amount of oil-absorbing pigment ink is made to minimize the effects of static electricity.

13, on the back of the back offset offset refers to the accumulation in the printing ink adhered to the following printed on the back of a print above phenomenon. Mainly on the back of offset ink drying is poor. The way to solve the back of the offset is to adjust the ink viscosity, the use of quick-drying ink, ink add driers, semi-finished surface of the powder, or add liner.

14, adhesions in the accumulation process, the adhesion phenomenon occurs between the printed product. Blocking phenomenon makes print quality problems, or even scrapped, adhesions because of the following aspects. ① After printing, the ink is not dry, it will print stacked pile up, causing smearing and blocking phenomenon. ② When the softening point of the network brush ink synthetic resin film material is relatively low or ink used is a thermoplastic resin, this resin is poor patience. If the residual film after the printing ink solvent, the ink film will soften, resulting in a print adhesion. Especially in the summer, due to the relatively high temperatures can easily lead stick with print between the phenomenon. ③ printing ink to the substrate has a certain dissolution, it can also cause adhesions between prints. Some ink solvent solubility of the substrate is large, after the printing ink to the substrate surface to produce a certain amount of dissolved, then although the surface of the ink has dried, but the contact with the substrate portion of the ink is still wet, in laminated gravity under the effect of blocking phenomenon occurs. If the substrate material is a soft polyethylene material, polyethylene material after printing part of a plasticizer film transfer to Mexico, resulting in softening of the ink film, it can lead to the occurrence of adhesion phenomenon. To prevent the blocking phenomenon, we must first choose suitable solvent inks and printing materials; Second, we must choose the faster drying ink, and pay attention to fully dry; in strict accordance with technical requirements of the operation.

15, threw ink, ink bleeds lost part of printing graphics, called throw ink failure. The reasons are: part of the injury of the squeegee edge; scraping too much pressure; the gap between the substrate and the screen is too large; Edition box deformation, local indentation is not enough; the high viscosity of the ink; ink does not even; screen too small; printing was speeding. If not addressed, and the ink mixed with dirt after the substrates to be printed, because the pressure of the blade so that the stencil damage, underexposure plate pinholes, etc., but also make the leakage phenomenon of ink film version, available tape Paste made from the back of the edition emergency department again. In the manual feed printing process, the metal plate and rigid plastic plate classes into the printing station, prone to sharp pierce the film version of the case, we should be careful to avoid; in order to prevent ink leakage, to be printed before the start of the plates for inspection or repair, pinhole stencil to make a good, all around the plate to fully strengthen, and then start printing.

16, mainly due to image distortion squeegee pressure on the screen when run too much or unevenly, so that the screen extends cause image distortion. Scraping plate platen printing ink on the plate can make line contact between the plate and the printed material can be printed not too much pressure. Screen printing is a variety of printing methods platen smallest of print, forget this is not a good print to print.

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