First of all, the ink is poorly mixed, or the normally mixed ink is mixed into the ink skin. When mesh for screen printing, the solvent swells and softens the mesh. The holes are blocked, which acts as a plate film and prevents the ink from passing through.
In order to prevent this kind of trouble, the mixed ink (especially the old ink, it should be filtered with mesh before using it). When the used printing plate is reused, the old ink attached to the plate frame must be completely removed. Before mesh for screen printing plate storage, wash it thoroughly (including the scraper). If the above requirements are done, uneven ink will not occur.
If the tip of the front end of the printing board is damaged, a streak will appear along the movement direction of the scraper. Especially when mesh for screen printing transparent materials, there will be obvious uneven inking. Therefore, the front end of the printing plate must be well protected from damage. If it is damaged, grind it carefully with a grinder.
The unevenness of the mesh for screen printing table will also affect the inking uniformity. The ink layer in the convex part is thin, and the ink layer in the concave part is thick. This phenomenon is also called uneven inking. In addition, if dust is stuck to the back of the substrate or the printing table, the above-mentioned problems will also occur.
Secondly, the substrate sometimes has bubbles on the ink after printing.The main reasons are as follows:
① The substrate is not clean before printing. Dust and oil stains on the surface of the substrate.
② Air bubbles in the ink. In order to adjust the ink, when adding solvents and additives to stir, some bubbles will be mixed in the ink. If left alone, inks with low viscosity will naturally defoam, and some inks with high viscosity cannot naturally defoam. Some of these bubbles are naturally eliminated due to the transfer of ink during printing, while others are getting larger and larger. To remove these bubbles, a defoamer is used. The amount of defoamer added to the ink is generally about 0.1% to 1%. If it exceeds the prescribed amount, it will air bubbles.
Even if the ink is foamed after the ink is transferred, as long as the substrate is wet and the ink has good fluidity, the air bubbles on the surface of the printing ink film will gradually disappear, and the ink will form a flat printing ink film. If the ink bubbles are not eliminated, the ink film will form a ring-shaped uneven film surface. When the air bubbles in the ink pass through the screen, they can be defoamed due to the effect of the mesh for screen printing. In addition, when the ink is mixed and stirred with hot water or boiling water, it will have a good defoaming effect.
③ The printing speed is too fast or uneven is also a reason. Reduce the printing speed appropriately to maintain the uniformity of the printing speed.
If it still doesn't work, consider using other types of inks.
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