UV glazing

A layer of colorless and transparent paint is applied (or sprayed or printed) on the surface of the printed matter to form a thin and uniform transparent bright layer on the surface of the print after being leveled, dried, calendered, and cured to enhance the smoothness of the surface of the support. The glazing process for the protection of printed graphics and texts has become an important means of finishing after printing and has achieved great results in the processing of foreign trade export products. In the technological innovation of prepress digital network and high-efficiency multi-color printing, post-press processing can only accomplish the complete revolution of printing technology by using high technology to achieve exquisite automation. At present, due to its unique advantages, UV glazing technology has obvious advantages in the development of post-press processing and is widely used in packaging, decoration, books and magazine covers, albums, trademarks, advertisements, calendars, large-scale decoration, posters, and other printed matter. The surface finishing process.

The glazing process is based on the drying method of varnish, which can be divided into solvent evaporation varnish, UV varnish (ultraviolet varnish) and thermal curing varnish.

The advantages of UV coating

UV varnish is ultraviolet curing and varnish. It uses UV varnish, and after coating on the surface of printed matter, ultraviolet light can irradiate varnish and can be cured in a very short time. The basic principle is: under the irradiation of ultraviolet light, the photoinitiator in the UV coating oil absorbs radiation energy to form free radicals or cations, initiates the polymerization and cross-linking reaction between the monomer and the prepolymer, and in a short time Cured into a three-dimensional network of high-molecular polymers.

With the gradual understanding and mastery of UV glazing technology and the drastic reduction in the price of UV coatings, UV glazing technology has gained rapid application in the field of packaging and printing with its unique advantages. According to statistics, the application of UV coating technology is increasing at a rate of 12-14% per year. It is believed that ultraviolet glazing technology will become the main process of post-press processing that adds value to products. Compared with other coating methods, UV coating has the following advantages:

1, safety and environmental protection.

The UV coating process uses UV coating. The UV coating consists of oligomers, reactive diluents, photoinitiators, photosensitizers, and additives. It has a solid content of 100%. There is no solvent evaporation factor and it is safe and non-polluting. Environmental green products. Especially in the era of advocating “green packaging”, the environmental protection advantages of ultraviolet glazing technology in post-press processing have been well recognized.

2, not subject to restrictions on the types of substrates.

3, work at low temperatures, can be used for printing thermal-type substrates (such as plastic).

4, high product quality.

UV coating has fast photocuring speed, high hardness, good wettability, strong adhesion, and high interference, abrasion resistance and gloss value. The surface of UV-printed prints is smooth, high in hardness, and resistant to abrasion. It is not prone to scratches and has the advantages of waterproofness and odorlessness.

5, after the polishing of substrates, can be processed immediately, in the cutting, forming, folding, etc. have a higher adaptability.

6, high efficiency and low cost.

Ultraviolet wavelength is 200-400nm, which is invisible light. UV-curing uses long-wave ultraviolet (UVA) wavelength of 316nm. UVA curing speed is fast, and UV oil can be cured into a uniform coating within 1-2 seconds. The production efficiency is high, and the general drying speed can reach 100-300 meters per minute. Compared with the glazing and calendering process, the equipment covers an area that is small, and the overall cost of material consumption, energy consumption, and other expenses is reduced.

UV coating method

There are many UV glazing methods, and there are many classification methods. There are mainly the following classification methods:

A. Press the relationship between the machine and the printing press

According to the relationship between polishing machine and printing machine, coating can be divided into offline coating and online coating. Off-line glazing adopts special glazing machine to polish the printed matter, namely, printing and glazing are performed on their own special equipment. This glazing method is more flexible and convenient, the equipment investment is small, and it is more suitable for professional postpress production. Manufacturers use, but this way of glazing increases the transfer between the printing and glazing processes, the production efficiency is low; online coating is directly after the glazing unit is connected to the printing machine, that is, printing, glazing in the same machine On the move, speed, high production efficiency, low processing costs, reducing the handling of printed products, to overcome the various types of quality problems caused by dusting, but the on-line coating of glazing technology, polishing oil, drying equipment and The requirements for coating equipment are high.

B. Press method

According to the glazing method, glazing can be divided into roller coating and printing glazing. Roller coating is the most common coating method. The coating roll applies the entire coating on the surface of the printing material. The printing coating coats the coating with the coating on the printing surface. Local glazing, currently used in gravure coating, flexo coating, offset printing and screen polishing.

C. Pressing the product type

According to the product type of glazing, glazing can be divided into full-width light, partial glazing, extinction glazing and artistic glazing. The main function of the full-width light is to protect the printed matter and improve the surface gloss of the printed matter. The light of the full width is generally applied by the roller coating method; the partial light is generally applied to the graphic part to be emphasized on the printed material. The use of the high gloss part of the gloss part is compared with the low gloss part without the gloss part to produce wonderful artistic effects. The partial gloss is applied by the method of printing gloss; the matte gloss is UV matte oil, and The effect of ordinary glazing is just the opposite. It is to reduce the glossiness of the surface of the printed matter, resulting in a special effect. Excessive glazing is a more popular method because the glossiness is too high to stimulate the human eye to a certain degree. The mode of light; the role of artistic glazing is to make the surface of glazing products obtain special artistic effects. For example, the use of UV pearlescent varnish to polish the surface of printed products will make the surface of printing products produce pearlescent effects, making the printed products look noble and elegant. .

Film UV coating to create a new world

UV coating of coated products is the method of coating the surface of printed products with one or two varnish in whole or in part to obtain a bright UV light film layer on the surface of printed products. After the film is coated with UV varnish, the light resistance of the ink can be enhanced, and the gloss and three-dimensionality of the printed matter can be improved. Create a strong contrast. Both full version and partial glazing can be used.

However, the UV glazing of coated products often causes the following problems: The first brightness is poor, mainly due to the uneven coating of the varnish or the excessive dilution of the varnish, and the viscosity is too low. In this case, the glazing machine needs to be adjusted and the light is improved. Oil viscosity; the second is due to the adhesion of UV light oil coating too thick printed products; Third, UV light oil viscosity is too small, the coating is too thin will cause the UV light oil layer surface bloom, need to increase the viscosity of the light oil, Increase the thickness of the coating; the fourth is the phenomenon of white spots and pinholes on the surface of the UV lacquer layer, which requires a variety of possible reasons, such as whether the UV varnishes are too thin and the amount of ethanol diluent added is too high. Whether there is more dust on the surface of the film layer; the fifth problem is that the light oil layer and the picture and text are staggered, which is caused by overprinting.

Although the UV coating technology of film-covered products appeared soon in China, its development speed is very fast. Both in the field of commercial printing and in the field of packaging and printing, it has achieved very good responses and applications. It can be said that the application prospects of UV coating technology for coated products are very broad.




Source: International Printing