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There are many factors that affect the quality of flexographic printing, especially the drying problem of water-based inks. In the production process, we often encounter the phenomenon of fast drying and slow drying of ink, we need to adjust. The drying speed of flexographic water-based ink in the printing process should be moderate. If it is slow drying, the drying process should be fast, which causes a very contradictory printing process. Therefore, the performance of the ink and the ability of the drying equipment on the printing press determine the production speed of the printing press. In turn, the higher printing speed can shorten the exposure time of the ink in the air, and dry slowly after printing.
If the water-based ink dries too slowly, it will cause poor drying of the printed matter, the ink will stick to the paper guide roller, the printed matter will lose its gloss, and it will affect the overprinting effect and cause print quality problems. If the water-based ink dries too quickly, it will transfer poorly, which will easily cause blockage, jagged edges will appear on the imprint, and the ink will dry to the surface of the printing plate. If the water-based ink dries too fast, it will also cause scratches on the surface of the printed matter when printing the screen version. The reason is that the ink has dried before printing on the surface of the printing material during the printing process. Off.
For the use of flexo water-based inks, there are the following suggestions:
1. Properly increase the pH value of the ink to reduce the drying speed of the printing process without affecting the drying speed. The pH value is generally controlled at 8.5 to 9.5. If the drying is too fast, the pH value should be controlled above 9 by adding stabilizers, but it should not exceed 9.5, otherwise the ink properties will change. The surface tension of the ink is lower, the screen version is more likely to block the plate, and the drying will become slower.
2. Without affecting the printing speed, try to make the ink drying speed slower during the printing process. This can be adjusted by slowing down the desiccant. The amount of slow drying agent required for inks of different manufacturers is different, generally not more than 5%. After adding the slow drying agent, the ink will thicken and the pH will decrease. Therefore, when adding the slow drying agent, water and stabilizer should be added to control the ink viscosity and pH.
3. When printing thin paper products, reducing the drying speed of ink can reduce the warpage of the paper. This usually requires the addition of slow-drying agents or retarders to adjust. The reason is that the water and alcohol in the ink after the printing of the water-based ink volatilize, loosen the tight sides of the paper and cause warpage. The effect of slowing down the drying agent is to prevent the ink from drying out instantly and reduce warpage.
4. Enhance the convection speed of the air in the oven, which can obviously speed up the drying speed of the printed matter. Because the water-based ink contains a large amount of water and alcohol, enhanced convection can reduce the relative humidity in the oven and accelerate the evaporation of the solvent.
5. Adding slow-drying agent can solve the scratches of the printed matter and the surface of the varnish. Ink drying too fast will cause the ink to dry on the surface of the printing material before entering the penetration stage, resulting in insufficient adhesion, and the ink layer is easy to fall off. When overprinting or glazing, the latter color printing plate will stick the ink of the previous color. This can also be adjusted by changing the color sequence or reducing the ink viscosity.
6. Adding slow-drying agent and speeding up can alleviate the blocking phenomenon. If the printing speed is too slow, the ink will spread on the printing plate, causing dot adhesion. However, if the ink dries too fast, the ink will not be fully transferred, causing ink to accumulate around the dots, causing blockage.
7. The paper guide roller generates heat, which can also accelerate the drying speed of the printed matter. When we use a large amount of ink when printing products, if the drying capacity of the printing machine is limited, the speed will not be fast every time the machine is turned on. After a period of time, the speed will have a certain room for improvement. This is why the paper guide roller heats up. . The ink is not easy to stick to the surface of the paper guide roller after it heats up. Before starting, the independent drying device is opened in advance. The machine can be turned off immediately after the machine is turned on, so that the equipment can accumulate the maximum heat in the shortest time. The vehicle speed can be increased quickly.
8. When the amount of ink used in printed products is large, try to use high-density inks and anilox rollers with a higher line number, which is conducive to the drying of printed products and can also reduce the phenomenon of water marks.
9. The ink viscosity required for higher printing speed is lower, which is conducive to the transfer of ink.
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