Treatment of UV Varnish on the Finished Surface of Paper Products

First, the development and application of printed surface treatment after printing

The surface treatment of printed matter is used for the purpose of improving the gloss of printed matters and preventing the surface of the printed matter from being damaged or contaminated. Currently, it is widely used in advanced prints such as paper boxes, publications, and trademarks.

The application of lacquer on the surface of printed matter started at the end of the 19th century when the processing method was to dissolve the turpentine into the volatile oil, then apply the solution to the print with a brush, and finally dry it at room temperature.

In the middle of the 1940s, mechanical coating by rollers began. In the mid-fifties, with the introduction of chlorine to grease coatings, gloss oils used to increase the gloss of prints have developed rapidly.

In the early 1960s, there was a way of processing yesterday through laminating machines to bond paper and vinyl chloride plastic films with adhesives. Later, in order to reduce such processing costs, a calendering method in which the gloss of the coated optical oil is hot-imprinted on the printed product to enhance the gloss has been popularized.

In the mid-1960s, the frontier polishing machinery was introduced in the calendering process, and a laminating process introduced a printing laminating machine to diversify and speed up the processing methods.

The resins used for the coating of varnish have been applied from the very beginning of natural resins to nitrocellulose, styrene, vinyl chloride, polyamides, acids, polyurethanes, acrylics, and others. In addition, a variety of additives have also been developed, greatly improving the coating performance.

The drying method is developed from gas baking or evaporation drying of the ultraviolet oven heating to hot air drying, solid-solidification, room-temperature curing, ultraviolet curing, etc., and the coating can quickly become a high-strength conjunctiva. Varnish for coating is solvent-based, water-based, emulsion-based, and solvent-free. In addition to the film coating method in which the adhesive coating agent is coated during the coating process, a precoating method of Hefei non-coating adhesive agent is more common.

According to statistics, more than 80% of packaging cartons and over 60% of printed publications are surface-treated in various ways.

Second, UV Varnish surface processing and other types of surface processing

In order to prevent scratching and dirt in the process of the cartoning machine line or during transportation, affecting the value of the goods, the printed paper used for packaging should have good properties such as abrasion resistance, water resistance, and dirt resistance, and also in order to improve product quality. To enhance product appeal, it is often necessary to carry out post-print surface treatment of printed products. There are various methods for the post-printing surface treatment of the paper port, which can be applied by the method of coating varnish, or by calendering or laminating. For the coating of varnish, depending on the type of varnish used, it can be divided into oil varnish, varnish coating, UV varnish coating, and the like. Recently, in order to meet environmental protection requirements, the varnish used for surface processing is gradually being converted from a solvent-based varnish to an aqueous varnish. The use of UV-curable (hereinafter referred to as UV) Varnish not only meets the requirements of environmental protection, but also has the advantages of being dry, good on-board stability, easy to clean, can be shortened to wait for post-processing, etc., and coated with UV Varnish, Prints have good rub resistance, finger resistance, and high gloss. In short, the use of UV Varnish for surface processing not only simplifies operations, saves energy and reduces consumption, but also improves product quality, and is therefore attracting more and more attention. The UV varnish is superior to the film and calender with better surface properties. It can meet the high requirements of the carton for friction resistance, gloss, and resistance. It can achieve the same effect as the OPP film on the advanced printing paper. . Therefore, it is a good choice for paper products to be coated with UV varnish.

Third, UV coating machine type

Gloss finishes on printed surfaces are mainly used for sheetfed printing. The following $ coating machines are generally available for UV varnish coating.

The first is a high-efficiency roller coating machine for thick paper. It is composed of rollers rotating in the same direction. According to different combinations of rollers and different centerline angles between rollers, it can be divided into many types.

The second type is a paper gripper suitable for 80-200 g/m2 square paper. To convey paper, it has a gripper to hold the paper in the impression cylinder, intermediate drum, and paper delivery section.

The other two are the Gravure Gravure Coater and the Fabricated Flexible Sheet Facing Machine. The gravure printing machine can make the local image vivid and the coating uniform. However, the amount of coating can only be adjusted by one. As long as the number, depth, and shape of gravure lines are not changed, the coating amount cannot be increased or decreased. However, the flexibility of the coating ensures that this edge is easily contoured and lacks clarity. However, the adjustment of the coating amount and the revision are relatively easy to apply using any of the above coating machines. Generally, a hot-air oven or an infrared oven is used to evaporate the solvent, and then ultraviolet curing or direct UV curing is used.

When the paper is coated with UV varnish, it can be printed first, and the varnish can be coated off-line when it is added later. This processing speed is generally 30-60 m/min. In order to increase the processing speed, online methods that use photo-oil coating at the time of printing are gradually increasing. The following three methods are mainly used.

1) offset printing blanket coating

Processing speed 7000-9000 sheets/hour

2) Gravure printing rotary press final unit coating

Processing speed 100-200 m/min

3) Flexo printing press final unit and special coating machine

Processing speed 100-200 m/min

(to be continued)