Method 3 for ultraviolet (UV) coating after common ink printing

8 Drying is the key

In a few seconds, the color and glossy materials are applied to the substrate. Although suppliers try their best to make these layers quickly from liquid to solid, high speed printing has limitations. Therefore, the coating process must be supported by the drying method chosen.

1 Drying is determined by the production speed

High-speed production is of course what we want, but it must be remembered that the drying method described only contributes to the drying device. With the increase of production speed, it is difficult to completely dry and harden. After printing, this situation directly results in the reaction of the upper and lower sides of the delivery stack sheet, and if it can be seen, it is called a back-grinding. The quality characteristics of UV varnish prints can be stabilized after days. Depending on the ink and coating used, gloss and bond quality can still change after 24 hours. However, changes are not always a disadvantage.

To keep the surface of the high-speed hardening coating stable, after drying, it must not be allowed to change underneath. Sheets pile up one by one on the take-up pile and are under considerable pressure. Therefore, the surface of the sheet is required to be sufficiently hardened to ensure that it is not damaged by contact with the back of the previous sheet. This hardened surface is due to the proper beam energy generated by the UV drying device.

Drying raises the temperature of the delivery pile, causing smearing on the back and even paper sticking. Therefore, the most important thing is to apply proper dry energy at the right time. Therefore, after printing and glazing units, IR lamps are really needed, plus cold and hot air and pumping gas. It is recommended to use two transfer forms of extended drying unit between the two coating units. If you think that only the drying time determines the gloss effect, then add a transfer part between the two coating units to ensure that the production speed can be increased by 40% without affecting the gloss effect. The output energy of the drying device must match the production speed. The output energy of UV must follow the speed of the printing press, but the nonlinear relationship. The output energy of IR is linear mode.

As the speed of the press increases, the gloss decreases as ink coverage changes. As described above, the time interval for applying each coating determines the formation of a stable "base layer." The paper moved between the printing units at a rate of 10,000 sheets per hour and the ink penetrated into the paper in less than a second. These tests show that, at normal production speeds, the gloss of the printing ink on the first and last printing units is compared, resulting in poor gloss of the final printing ink. These conditions can be used as a reference, which is helpful for us to compose the layout and determine the printing sequence. However, when printing with ordinary inks, the gloss decreases as the printing speed increases. The inherent problem with this ink is an irreversible fact. It has been said that the selective combination of inks, coatings and drying devices can minimize the loss of quality.

to sum up

The effect achieved by ultraviolet (UV) coating depends mainly on the substrate. The effect of coating a high-gloss dispersion-type coating on a substrate is to provide a reference to the high coverage of the ink, resulting in the desired effect of UV coating on the substrate. Lower, but can improve the adhesion of the coating by improving the composition of the ink and its affinity with the primer by using high-concentration pigments and ink with good absorption, and the bonding condition is really stable after printing for several days. The correct selection of the type and amount of primer used is a decisive factor in the achievable gloss. Ultraviolet (UV) coatings are used as the surface layer to help prevent scratching; at the same time, if the coating is uniform, it can be bright. The surface through the purchase of appropriate machine components, especially dry parts, and pay attention to a reasonable match with the material, is a prerequisite for the printer to achieve the best results.