Third, the ink film edge defects
In screen-printing products, the problem that often arises is the appearance of jagged burrs (including incomplete or broken lines) at the edges of the printed ink film. There are many reasons for glitches, but the main reason is the quality of screen printing.
Sensitive adhesive resolution is not high, resulting in fine lines appear broken or incomplete.
If the exposure time is not enough or the exposure time is too long, the development will be insufficient, and the edge of the screen printing graphic will not be neat and appear serrated. For a good screen printing plate, the edges of the graphic should be smooth and neat.
The surface of the screen printing plate is not smooth. When printing is performed, there is still a gap between the screen printing plate and the substrate. Due to the ink penetrating into the space, the burrs on the edges of the printing ink are reproduced.
During the printing process, due to swelling of the printing film after contact with the solvent, and the degree of swelling in the latitude and longitude is different, the surface of the printing film is uneven. During the printing, a gap appears between the screen printing plate and the surface of the printing material, and the ink floats through the ink. There will be glitches on the film.
To prevent the occurrence of saw-tooth burrs, consider the following solutions:
Select high screen mesh plate making;
Choose high-sensitivity photosensitive materials for plate making;
Make a certain thickness of screen printing plate to reduce the expansion deformation;
Stretch the stretch net as much as possible, the best angle is 22.5. ;
Fine line printing, plate making as much as possible using indirect plate making, because indirect plate making may be less glitch;
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, ensure that the surface of the screen plate is smooth, and the edges of the screen lines must be neat;
Spray the screen plate with a water jet gun to improve the development effect;
The distance between the screen plate and the substrate, the scraper angle, 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 this is done as described above, accidents with ink unevenness will not happen.
If the tip of the squeegee is damaged, there will be a trace along the direction of movement of the squeegee. In particular, when printing transparent materials, there will be significant ink inconsistencies. Therefore, the front end of the squeegee must be well protected so that no damage occurs, and if it is damaged, it is necessary to grind it 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.
Dust and foreign objects attached to the plate. At the time of plate making, there will be some sol mixed in the water development. 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.
Or boiled water will have a better defoaming effect.
For transparent inks such as red, blue, and green, the linking material of these inks has the feature of easy foaming due to the small proportion of organic pigments in fine particles. If the corresponding thinner, tackifier or release agent is added, the ink can also be converted into a stable ink with good printability.
The printing speed is too fast or the printing speed is uneven. Appropriately reduce the printing speed and maintain the uniformity of printing speed.
If none of the above measures can eliminate air bubbles in prints, consider using other types of ink.
Source: Wujiang Golden Eagle Copper Sign Factory