Causes of screen printing failures are due to many factors such as printing plates, squeegees, inks, equipment, substrate materials, and handling techniques. The occurrence of screen printing faults is mostly the result of intricate and cross-cutting causes. This is especially important for operators when judging the cause of failure and taking appropriate countermeasures.
Attention.
1, plug network
Plug mesh refers to the phenomenon that the screen printing plate hole is partially blocked, and the printing ink cannot be transferred to the substrate. this phenomenon
The appearance of this product will seriously affect the printing quality and even prevent normal printing. The phenomenon of plugging is complicated
In general, there are the following reasons.
1 Substrate materials Screen printing substrate materials are various, and its surface texture property is one of the reasons for the plug network phenomenon. For example, substrates such as paper, wood board, and fabrics have low surface smoothness and poor surface strength. They are liable to cause powder fallout and hair loss during the printing process, which can cause screen printing plates to clog.
2 Ambient temperature, humidity The screen printing shop's temperature and relative humidity requirements remain constant. If the temperature is too high and the relative humidity is too low, the solvent in the ink will rapidly evaporate, causing the viscosity of the ink to become large and the ink to clog the mesh. If the downtime in the printing process is too long, plugging will also occur. The longer the time is, the more serious the plugging will be. If the ambient temperature is too low, the fluidity of the ink is deteriorated, and the plugging phenomenon is also likely to occur.
3 Screen If the prepared screen is placed too long, dust will adhere to more or less during the preservation process. If the screen is not cleaned during printing, it will cause plugging.
4 Printing pressure During the printing process, when the imprinting force is too large, the squeegee squeegees will be bent partially. The edge of the squeegee is not in line with the screen and the substrate, but is in surface contact, so that each squeegee cannot be printed. The ink is scraped clean, leaving behind residual ink, which can constrict the film for a period of time.
5 The gap between the screen and the substrate is improper. The gap between the screen and the substrate should not be too small. If the gap is too small, the plate cannot be separated from the substrate after the squeegee is printed. When the screen is raised, some ink adheres to the bottom of the plate. , it is also easy to cause plug network.
6 Ink When the particles of pigments and other solid materials in the screen printing ink are large, the phenomenon of blocking the mesh holes is likely to occur. In addition, the mesh size and through-hole area of ​​the selected mesh are smaller than the particle size of the ink, so that the phenomenon that the coarse-grained ink does not easily pass through the mesh and block the mesh is also one of the reasons. For the plug mesh caused by the large ink particles, it must be considered to select the appropriate ink for fineness.
Ink drying in the printing process is too fast, easily causing plug network failure, especially when using volatile drying ink this phenomenon is more breakthrough, so when printing must choose the right solvent to control the drying speed. In the use of ink to consider the impact of the season, you can use fast-drying ink in winter, in the summer, you must change to other types of ink. With the use of oxidative drying inks, there are not many plug-in net phenomena, but if an excessive amount of desiccant is used, a plug-in phenomenon occurs particularly in the summer. During the printing process, due to the increased viscosity of the ink, the plug mesh is caused by the following reasons: the solvent of the ink on the printing plate evaporates, the viscosity of the ink increases, and the meshing phenomenon occurs. If the plate has a small graphic area and less ink consumption, it can easily cause plugging, which can be solved by lowering the viscosity of the ink and improving the fluidity of the ink.
2, the ink is not firmly fixed on the substrate
1 Insufficient adhesion of the ink itself causes the ink film to be stuck firmly. In this case, it is better to replace the ink for printing; dilute the ink with a solvent.
If the solvent is used improperly, the ink film will not be firmly fixed, and the ink and the substrate will not stick together.
2 Strict degreasing of printing materials before printing is very important, when the surface of the printing material adheres to grease, adhesives, dust
In the case of worms and other substances, poor adhesion between the ink and the substrate can result.
3Insufficient surface treatment of plastic products before printing can also result in failure of ink fixation, polyethylene film as a printing material,
To improve the adhesion with the ink during printing, surface treatment must be performed.
4 Metal materials must be degreased and dust-removed before they can be printed. After printing, they should be dried according to the required temperature of the ink.
Reason, if the improper drying treatment will also produce ink film peeling phenomenon.
5 Items such as glass and ceramics must be sintered at high temperatures after printing, so as long as the temperature is properly treated, adhesion will be good.
3, ink film edge defects
There is a problem with the web version or the plate making process. There are jagged burrs (including incomplete or broken lines) on the edge of the printed ink film.
The reasons for the thorns are as follows.
1 The sensitivity of the photosensitive adhesive is not high, making fine lines appear broken or incomplete.
2 In the process of plate-making, the exposure time is insufficient or the exposure time is too long, the development is not enough, the edge of the printing plate graphic is not neat, and there is a jagged appearance.
3 The surface of the screen is not smooth. When printing, there is a gap between the screen and the substrate. The ink is suspended and infiltrated, causing the edge of the printing ink.
There are glitches.
4 During the printing process, due to the swelling of the printing film after contact with the solvent, and the degree of expansion in the warp and weft directions, the mask sheet
Surface uneven phenomenon, printing screen and the substrate contact surface local gap.
The solution is as follows:
· Use high mesh screen plate.
· Select high-sensitivity photosensitive material plate making.
· Produce a certain thickness of screen printing plate to reduce the expansion deformation.
· Stretch the net by stretching the net as much as possible. The best angle is 22.5°.
· Fine line printing, using indirect plate making as much as possible, because
There may be fewer glitches on the plates.
• In the process of plate making and printing, try to control the temperature expansion factor and use a photosensitive material with a small expansion coefficient.
Improve the quality of plate making to ensure that the surface of the screen plate is completely smooth.
The edges of the screen lines are neat.
• Use a high pressure water jet to wash the screen to improve the development.
· The distance between the screen and the substrate, the angle of the squeegee, and the printing pressure should be appropriate.
4, ink uneven
Ink film thickness is uneven. The reasons are: poor ink formulation; normally formulated ink mixed with ink, when printed, due to dissolution
The role of the agent swells and softens, clogging the mesh that should penetrate the ink, and making the ink unacceptable. Solution: The formulated ink (especially the used ink) should be filtered and reused before use; when the used printing plate is reused, the old ink attached to the plate must be completely removed; The unevenness will also affect the evenness of the ink, the convex ink layer is thin, and the ink thickness of the concave layer
5, pinhole
1 Dust and foreign objects attached to the plate cause the phenomenon. If dust and foreign matter adhere to the screen, blocking the screen openings can also cause pinholes. It is possible to remove these dusts from the plate after printing a few sheets of paper with strong ink absorbency before the official printing. Due to the rinsing development, some sols are difficult to handle due to the sol being attached to the mesh.
2 Cleaning of the surface of the substrate before printing: The aluminum plate, glass plate, acrylic plate, etc. should be pre-treated to make the surface clean before printing.
Substrate should be printed immediately. When the substrate is moved, the fingerprint of the hand is also attached to the printing surface, resulting in the formation of pinholes during printing. This should be noted that after the pretreatment, it should be printed immediately. When handling substrates, the fingerprint of the hand will also adhere to the printed surface, causing pinholes during printing. This should also be noted.