Thin paper printing shrinkage problem
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In order to improve production efficiency, today's flexographic printing presses pay great attention to improving drying capacity. Generally, various drying methods such as natural wind, hot air and infrared rays are used. Some combined mechanical devices have two sets of UV curing systems. In this way, in the proofing or production, a phenomenon will be found, that is, a set of the same set of film, the lateral size will be biased, the error is less than 1 mm; the error is 2 mm - 3 mm. In actual production, if there is no problem with the film or the printing plate, the deviation of the lateral dimension is caused by the two opposite processes of printing wetness and drying.
About 50% of the water-based ink is water. Then, for thin paper, if the water-based ink is printed on a large area, the surface of the paper will be swollen and widened. The larger the printing area, the lower the number of anilox lines. The phenomenon of widening is more obvious. When drying is performed after printing, the paper is narrowed by shrinkage, and the larger the amount of heating, the more the water volatilizes, and the narrower the paper width becomes. Most flexo press heating and drying systems (including UV curing systems) have a minimum speed starting point, such as 20 m/min. For safety reasons, the infrared and UV drying units are not turned below this speed; they are turned on at or above this value. If the boot speed is slightly higher than this speed value, the paper is heated much and the shrinkage is noticeable.
The farther apart the unit, the greater the lateral overprint error. Therefore, in the printing production process, the speed of the printing machine should be increased as much as possible and unnecessary hot air and infrared drying should be minimized to avoid lateral overprinting errors. In addition, in a single printing process, the machine speed is suitably increased, and the overprinting error also occurs. Tension, mechanical speed and temperature have a constant value, often 1:1.2 (1.3):1.