Third, the ink film edge defects
In screen printing products, a common problem is the occurrence of jagged gross margins (including defects or breaks) at the edges of the printed ink film. There are many reasons for glitches, but the main reason is the quality of screen printing.
1 The sensitivity of the photosensitive adhesive is not high, resulting in broken lines or incomplete lines.
2 The exposure time is insufficient or the exposure time is too long, the development is not sufficient, and the edge of the screen printing graphic is not neat, and appears jagged. For a good screen printing plate, the edges of the graphic should be smooth and neat.
3 When the surface of the screen printing plate is uneven, when printing is performed, there is still a gap between the screen printing plate and the substrate. Due to the penetrating infiltration of the ink, burrs occur on the edges of the printing ink.
4 During the printing process, due to the swelling of the printing film after exposure to the solvent, and the degree of swelling in the latitude and longitude are different, the surface of the printing film is uneven. During the printing, the screen printing plate and the substrate contact surface appear locally; Infiltration, the ink film will appear burrs.
In order to prevent the appearance of jagged haircuts, the solution can be considered from the following aspects:
1 Use high mesh screen plate making;
2 Select high-sensitivity photosensitive material plate making;
3 Make a certain thickness of screen printing plate to reduce the expansion deformation;
4 Stretching the net by stretching the net as much as possible, the best angle is 22.5°;
5 Fine line printing, as far as possible the use of indirect plate making law, because the indirect law plate burr may be smaller;
6 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;
7 Improve the quality of plate making, ensure that the surface of the screen plate is smooth, and the edges of the screen lines must be neat;
8 Spray the screen printing plate with a water jet gun to improve the development effect;
9 The distance between the screen plate and the substrate, the angle of the squeegee, and the printing pressure should be appropriate.
Fourth, ink uneven
Ink film thickness is uneven due to a variety of reasons. In terms of ink, the ink is poorly formulated, or the normally formulated ink is mixed with ink. When printing, the ink expands and softens due to the effect of the solvent. Mesh hole is blocked, play the role of the plate, so that the ink can not pass.
In order to prevent such failures, the formulated ink (especially the old ink) should be screen-filtered before use. When you reuse a used plate, you must completely remove the old ink that has adhered to the plate. When the plates are stored after printing, they must be fully washed (including scrapers). If done according to the above requirements, the incident of inking wood will not happen.
If the tip of the razor plate is damaged, a trace will appear along the direction of movement of the squeegee. In particular, when printing transparent materials, there will be obvious ink inconsistencies. Therefore, the front end of the plate must be well protected from damage, and if it is damaged, it must be ground carefully with a grinder.
The unevenness of the printing table also affects the uniform ink. The convex ink layer is thin and the recessed ink layer is thick. This phenomenon is also called ink inhomogeneity. In addition, if the back surface of the substrate or the printing table adheres with dust, the above failure may occur.
V. Pinhole
The phenomenon of pinholes is the biggest headache for screen printing workers. If it is the printing of opaque objects such as billboards and thick paper, such holes that are not easily observed are generally not a problem. However, when precise printing is performed on aluminum plates, glass, and acrylic plates, post-processing and etching processes are not allowed to generate pinholes. In addition, the reasons for the occurrence of pinholes are also varied. Many of them are reasons that cannot be explained at present, and some are still problems with quality management. Pinholes are one of the most important inspection items in the inspection of printed products.
1 Dust and foreign objects attached to the plate. At the time of plate making, there are some sols mixed into the water wash image. In addition, when the emulsion is applied, dust may be mixed in, and pinholes may be formed on the screen. These tests can be found and repaired promptly if they are checked. If dust and foreign matter adhere to the screen, blocking the screen openings can also cause pinholes. Before the official printing, if the use of strong ink absorption paper, after several printing, you can remove the dust from the plate.
2 substrate surface cleaning. Aluminum plates, glass plates, acrylic plates, etc. should be pre-treated to make their surfaces clean before printing. After the substrate has been pretreated, it should be printed immediately. In multicolor printing, a method of rubbing with alcohol prior to printing is generally used. In addition, semi-automatic and fully automatic ultrasonic cleaners can also be used. After pre-treatment, dirt such as grease can be removed, and dust attached to the surface can also be removed.
Washing machine detergent is often mixed with broken fibers, this detergent is soluble in alcohol, when cleaning the surface of the substrate, it tends to form a thin surfactant film, when the ink is printed on the film pinholes occur. Therefore pay special attention when using cleaning agents and alcohol. When carrying the substrate by hand, the fingerprint of the hand will also adhere to the printed surface, forming pinholes during printing.