After screen printing, the size of the printed matter sometimes expands. master of print size expansion
The main reason is that the viscosity of the ink is relatively low and the fluidity is too large; the size of the screen printing plate is enlarged during production, which is also one of the reasons for the expansion of the printing size. In order to avoid excessive ink fluidity, resulting in larger printing size, a certain amount of thickener can be added to the ink to reduce the fluidity of the ink; fast-drying ink can also be used to speed up the drying speed of the ink after printing. When making screen printing plates, it is necessary to ensure the quality of the screen printing plates.
Using the same screen, photosensitive glue and stripper, why the stripping effect is different?
In the first case, it is affected by various conditions in the plate making process, such as drying temperature, drying time and printing time, and the second is affected by the performance of the ink. The hydrophilic group – -OH in the film gradually decreases, which makes it difficult to remove the film; the third is that the screen plate is stored for a long time, and the film is aging and dehydrated. Why does the exposed film fall off during washing? The exposed film falls off during washing, mainly due to the following reasons: insufficient exposure,
The photosensitive adhesive is sensitized, and the photosensitizer fails. Therefore, to ensure that the exposure effect reaches the entire screen coating, the dyed screen and copper screen must increase the exposure time, and ensure that a sufficient amount of sensitizer is thoroughly mixed with the latex. The post-processing of screen printing mainly includes the following steps:
1. Check the quality of the screen printing plate, including whether the graphics and texts are fully developed, whether the graphic and text dots and lines have burrs, incomplete, broken pens, and whether the mesh holes are sealed, etc. If the above conditions are found, it should be remedied in time. If this cannot be remedied, re-plate may be considered to ensure printing
quality.
2. Check whether there are air bubbles and blisters in the omentum, and whether the four sides near the screen frame are closed. The air bubbles and blisters should be remedied in time, and the meshes that are not sealed on the four sides should be sealed to avoid ink leakage during printing.
3. Check whether the printing positioning mark meets the requirements of the printing order. Paste the bonding part of the screen and the screen frame with tape to improve the bonding firmness of the screen and the screen frame. Paste the plate label and paste the plate label on the unified frame position. The plate label should generally indicate the following contents: print name, color, number of colors, number of screen meshes, number of plate lines, type of photosensitive material, plate-making date , plate maker, etc.
What problems should be paid attention to in screen drying? First of all, since screen production requires a dust-free environment, the cleaning of the oven is very important, but some units do not pay much attention to this. For example, some drying equipment is powered by electricity After the hair dryer was changed to an oven, there was a lack of effective management, and some sundries would be put into the oven for drying together with the screen plate, and the sanitation of the oven was neglected, unknowingly buried quality hidden dangers. Secondly, when the screen plate coated with photosensitive adhesive is placed in the oven to dry, the temperature should not be too high, and the drying time should not be too long. Because the temperature is too high, the photoresist will undergo thermal cross-linking reaction. If the drying time is too long, the normal operation of exposure will be affected, resulting in the screen plate being scrapped due to the impermeability of screen development after printing. Therefore, in general, the temperature of the oven The temperature should be controlled between 30 ~ 45C. In order to shorten the drying time, you can also put some dehumidifier in the oven. In addition, the drying temperature of the screen also affects the water content of the screen, which has a great impact on the printing durability of the screen, especially when it is dried in the air, it is easy to generate static electricity; however, for special printing requirements, the photosensitive adhesive is applied thicker. The drying time of the screen should be appropriately extended.
In addition, some screens will degumming after drying in an oven or during printing operations, which is caused by the uneven and incomplete drying of the screen due to the residual moisture between the tape used for stretching the screen and the screen frame. The newly stretched screen printing plates are all tape-pasted during the revision operation.
The main reasons that affect the deviation of printing accuracy are: when making multi-color overprint (halftone) screens, the screen drying temperature is different; the screen tension is low or the overprint (halftone) screen tension is different; Uneven drying of the plate; using an old, weak screen frame to make a plate, or the screen frame has been deformed, resulting in a deviation of the printed image due to the poor stability of the screen frame (these problems can be detected with a negative film); when multi-color overprinting, the screen The distance is inconsistent; the squeegee used has been deformed; the size of the substrate has changed due to certain factors.