Selection of varnish after flexo printing
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For flexo printing, post-press glazing is an unusual thing, because glazing can improve the water resistance and wear resistance of printed matter to a certain extent, and at the same time it can also beautify products and enhance product quality. At the same price level, many post-press processing methods are not comparable to the glazing effect. Therefore, in the past 10 years, the development of varnish technology has been quite rapid, chemical raw materials have become cheaper, applications have become wider and wider, and performance has become more stable.
At present, UV glazing plays an important role in flexographic glazing, and generally adopts online mode. The UV curing device consists of one or two UV lamps and a reflecting device. Water-based inks can be printed with UV varnish after printing, which can protect water-based inks. Of course, there are also some special occasions requiring water-based varnish. For example, when the final product needs to be printed, it must be printed with special water-based varnish. Other manufacturers will choose water-based varnish for matt glazing. Because UV matt oil tends to thicken when printing long plates.
There are often some inexplicable faults in the UV glazing process. This article lists the nine major problems common in flexo UV glazing and their solutions. I would like to share with you.
1. Yellow coating
The main reason for the yellowing of UV varnish after curing is generally twofold: First, the UV varnish has been left for too long, and it has turned yellow, especially the yellowing phenomenon of inferior varnish is more serious; UV varnish is over-cured.
Solution: If it is the quality problem of UV varnish itself, you must replace the UV varnish; if it is caused by overexposure, it is necessary to reduce the power of the UV source or increase the glazing speed.