Several difficulties in gravure printing

Several difficulties in gravure printing process under normal conditions, the traditional gravure printing process to achieve the above requirements should not be difficult. However, due to many factors influencing the production process, it is difficult to control the residual solvent.

1. The intaglio electronic engraving gravure has generally a chamfered pyramidal cell, the depth of the cell site is 50-60 Um, and is affected by the shape of the orifice. The ink at the bottom of the pyramidal cell hole is difficult to be transferred out during the printing process. The actual depth of the cell site is generally 30-40um. Over time, it is prone to blocking phenomenon, especially in the small area of ​​the high-light site is more likely to clog, resulting in the loss of small dots on the print. Although it is possible to mitigate or reduce such problems by adjusting the position of the doctor blade or hot air in the oven, it does not always work.

As a result, many operators have had to add slow-drying solvents (such as xylene, butanone, butyl ester, etc.) to the ink. These slow-drying solvents have a high boiling point and must be well-stuffed, otherwise they may bury the solvent residue.

2. Ink gravure printing ink is mainly based on solvent type ink. Although gravure ink has appeared in the domestic market in recent years, it has not become mainstream ink. Solvent-based inks are classified as benzene and non-benzene, and benzene inks are being phased out. Solvent-based gravure inks use various solvents to form toxic and harmful exhaust gases.

Gravure ink commonly used resin generally have polyamide, polyvinyl butyral, chlorinated polypropylene, polyester and so on. Different resins have different releasability to solvents. Some resins have poor solvent release properties, but printability is good and prices are relatively cheap, often becoming mainstream products. However, the flexible packaging printing plant is also prone to solvent residue problems when using this type of ink to print flexible packaging products. In the printing process, in order to avoid the loss of small dots or the phenomenon of “false drying” of the ink, the temperature of the drying oven cannot be set too high.

In addition, the last group of printing units of the gravure printing press is too close to the winding unit, so that the printed film winds up when the ink is not dry, which is also a great hidden danger of solvent residue. For this reason, the position of the winding position should be adjusted. The gravure printing machine previously used by the author did not immediately wind up after the last color was printed; it was passed through the guide roller and returned to the position before the first color group, thus increasing the drying distance for a long period of time, enabling the solvent to Fully volatile, minimize solvent residue.

4. When dry compound dry compounding, the amount of glue, drying temperature, compounding speed, exhausting capacity of the compounding machine, and waste disposal system will affect the solvent residue of the compound product. However, it is not easy to completely solve this problem, and the residual solvents in the printing stage cannot be solved. The dry compound control is no better, and it does not help.