The treatment of the most popular UV varnish on th

2022-07-31
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The treatment of UV varnish on the post press surface of paper products

I. the development and application of post press surface treatment of printed matter

the purpose of surface treatment of printed matter is to improve the gloss of printed matter and prevent damage and dirt on the surface of printed matter. At present, it is widely used in high-grade printed matter such as cartons, publications and trademarks

the application of varnish on the surface of printed matter began at the end of the 19th century. At that time, the processing method was to dissolve the turpentine into the volatile oil, then apply the solution to the printed matter with a brush, and finally dry it at room temperature

mechanical roller coating began to appear in the mid-1940s. In the mid-1950s, with the introduction of chlorine grease coating, varnish used to improve the gloss of printing products developed rapidly

In the early 1960s, there was a processing method of combining paper and vinyl chloride and other plastic films with adhesive through a laminating machine. Subsequently, in order to reduce the processing cost, the calendering method of applying the coated varnish to the printed products by hot embossing with aluminum plates to improve the gloss began to be popularized

in the mid-1960s, the border polishing machine was introduced in the calendering process, and the printing compound machine was introduced in the lamination process, which made the processing methods diversified and high-speed

a variety of resins used for coating varnish have been applied from natural resin at the beginning to nitrocellulose, styrene, vinyl chloride, polyamide, acid, polyurethane, acrylic resin, etc. In addition, a variety of additives have been developed to greatly improve the film performance

the drying method has developed from gas baking or evaporation drying heated by ultraviolet oven to hot air drying, potential curing, room temperature curing, ultraviolet curing, etc., which can quickly make the coating become a high-strength conjunctiva. There are solvent-based, water-based, lotion type, solvent-free and other varieties of coating varnish. In addition to the coating method of coating adhesive when coating wax, the coating process is more the precoating method of Hefei uncoated adhesive

according to statistics, at present, more than 80% of the packaging cartons and more than 60% of the printed publications are surface treated in various ways

II. Comparison between UV varnish surface processing and other types of surface processing

in order to prevent scratches and dirt on the box making machine assembly line or during handling, which will affect the value of the goods, the paper printed matter used for packaging should have good friction resistance, water resistance, dirt resistance and other properties. At the same time, in order to improve the product grade and enhance the product appeal, it is often necessary to carry out post press surface treatment on the printed matter. There are many ways to process the surface of paper mouth after printing, such as coating varnish, calendering or coating. In terms of varnish coating, according to the different types of varnish used, it can be divided into oily varnish coating, non oily varnish coating, UV varnish coating, etc. Recently, in order to meet the requirements of environmental protection, the varnish used for surface processing is gradually changing from solvent based varnish to water-based varnish. The use of UV curing varnish (hereinafter referred to as UV) not only meets the requirements of environmental protection, but also has the advantages of drying, good on-board stability, easy cleaning, and can shorten the waiting time for post-processing. Moreover, after being coated with UV varnish, the printed matter has good friction resistance, scratch resistance and high gloss. In a word, surface processing with UV varnish can not only simplify operation, save energy and reduce consumption, but also improve product quality, so it has attracted more and more attention. UV varnish has better surface performance than film covering and calendering, which can meet the high requirements of packaging carton on friction resistance, gloss, resistance, etc., and can achieve the same effect as that of pasting OPP film on high-grade printing paper with the demand of maximizing profits. Therefore, UV varnish coating is a good choice for paper products

III. UV coater type

the gloss processing of the printing surface is mainly used for sheet fed printing. For UV, its accessories are worth 130 euros (143 US dollars). Generally, the following kinds of coating machines can be selected for varnish coating

the first is a high-efficiency roller coater for thick paper. It is composed of rollers rotating in the same direction. It can be divided into many models according to different combinations of rollers and different angles of center lines between rollers

the second type is a gripper type fabric making machine suitable for 80-200g/m square paper. In order to transport paper, it has gripper teeth to hold the paper in the imprint drum, middle drum and discharge section

the other two are gravure type gravure coater and protruding type flexible sheet coater, mainly for local coating. More than 70% of the high-end products of gravure fabric technology are coated by imported machines, which can make the local image bright and the coating uniform. However, the coating amount 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. And flexo coating protection? This edge is easy and this edge is not clear-cut. However, it is relatively easy to adjust and modify the coating amount. After coating with any of the above coaters, the solvent is generally volatilized in a hot-air oven or an infrared oven, and then cured by UV or directly through UV

when the paper is coated with UV varnish, the off-line method of printing first and then coating varnish in the add-on mode can be adopted. The processing speed is generally 30-60m/min. Now, in order to improve the processing speed, the online mode of varnish coating while printing is gradually increasing, mainly including the following three modes

1) offset printing machine blanket coating

processing speed 7000-9000 sheets/hour

curve has a small platform of fluctuation 2) gravure rotary printing machine final unit coating

processing speed 100-200 M/min

3) flexographic printing machine final unit and special coating machine

processing speed 100-200 M/min

(to be continued)

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