Plastic Printing Technology Introduction

The common sense of UV printing on the surface of plastic film The uv ink printing or uv coating on the surface of plastic substrates has become increasingly popular, and this is a challenging task. Plastic printing materials have been used in the printing industry for decades. With the prevalence of uv ink varnish, uv ink printing on plastic substrates has brought new topics to printing companies and ink factories. What is the biggest problem? The uv ink varnish firmly adheres to the surface of the plastic substrate, that is, adhesion problems.

1. Surface tension of plastic substrates
When printing plastics, the surface tension of the plastic substrate is the first factor to be considered first. Many plastic films have low surface tension before they are processed. Generally, they need to be surface-treated to increase the surface tension of the plastic substrate. After processing, they usually reach 40dyncm2 or even higher. In general, plastic sheet suppliers have surface-treated plastics, but the effect is quickly lost.

For printers, the connection process is the best solution to ensure that the surface tension of the plastic substrate during printing is maintained within an acceptable range. Corona discharge (oxidation) treatment is the most common treatment method. It is applied to the surface treatment of various plastic films without damaging temperature-sensitive plastic substrates. Corona discharge uses high-frequency high-pressure or medium-frequency high-voltage discharge, the plastic surface is treated to make its surface active, porous, in order to improve the adhesion of the plastic film surface to the ink and improve the printability of the film. For example, after a common pe film is subjected to corona discharge treatment, unsaturated bonds such as carboxyl groups and carbonyl groups are formed on the pe molecular chain. After the surface is oxidized, pe molecules are converted into polar molecules, increasing the surface energy. Generally, the surface tension of pe increases from 31dyncm2 to 39-40dyncm2, which increases the wettability and adhesion of the pe film to the uv ink varnish, thereby increasing the imprinting firmness.

The flame method is more used in the surface treatment of high temperature-resistant plastic products, so that the plastic under the effect of instantaneous high temperature, remove the surface oil and melt the surface layer to improve the ink ability; also use chemical treatment, but this method is usually Used in conjunction with corona discharge treatment, the chemical treatment uses an oxidizing agent to treat the surface of the polyolefin plastic to form polar groups on the surface, thereby allowing the surface of the plastic substrate to adhere well to the uv ink varnish. In order to detect the effects of the plastic substrate surface treatment, plastic film printing manufacturers are better equipped with dyne test pens.

In the treated plastic film, the surface tension of the ink is lower than the surface tension of the plastic film. In the same way, in order that the optical oil wets well on the ink surface and firmly adheres to the surface of the ink, the surface tension of the optical oil is lower than the surface tension of the ink. Therefore, the selection of raw materials for uv ink formulations is very sophisticated, in order to obtain acceptable surface tension. Studies on a variety of ink formulations have found that solvent-based inks generally have lower surface tensions than other types of inks and can therefore be wetted on a variety of plastic film surfaces. Therefore, the surface treatment of plastic substrates, especially uv ink printing is particularly critical.

2. Plastic substrate expansion and permeability
Unlike many commonly used printed papers and cardboards, the surface of the plastic substrate does not have micropores that let the varnish penetrate into its interior. However, some plastic substrates may swell when exposed to some uv inks. Therefore, the use of this feature allows the use of plastic substrates with certain uv inks to allow the ink varnish to penetrate the interior of the plastic substrate. At the time of curing, due to the internal penetration of the ink varnish, a strong and strong adhesive effect can be formed between the varnish of the ink and the surface of the plastic substrate. In addition, the temperature of the workshop can also be increased to enhance the penetration effect between the plastic substrate and the ink varnish, which is also one of the ways to improve the adhesion between the uv ink varnish and the plastic film.