Apply (or spray, print) a colorless and transparent coating on the surface of the printed matter. After leveling, drying, calendering and curing, a thin and uniform transparent bright layer is formed on the surface of the printed matter to enhance the smoothness of the carrier surface. The glazing process, which protects the finishing processing functions of printed graphics, has become an important means of post-press finishing, and has achieved great results in the packaging and processing of foreign trade export products. In the technical innovation of pre-press digital networking and printing multi-color high efficiency, only after the use of high-tech to achieve exquisite automation can complete the overall revolution of printing technology. At present, due to the unique advantages of UV glazing technology, it has obvious advantages in the development of post-press processing. It is widely used in packaging and decoration, book covers, albums, trademarks, advertisements, calendars, large-scale decoration, posters and other printed products Surface finishing process.
The glazing process can be divided into solvent volatile glazing, UV glazing (ultraviolet glazing) and thermal curing glazing according to the drying method of glazing oil.
Advantages of UV coating
UV varnishing is ultraviolet curing varnishing. It uses UV varnish. After being coated on the surface of the printed matter, the ultraviolet light irradiates the varnish and can be cured in a short time. The basic principle is: under the irradiation of ultraviolet light, the photoinitiator in the UV varnish absorbs the radiation energy to form free radicals or cations, which initiates the polymerization and crosslinking reaction of the monomer and the prepolymer in a short time The polymer cured into a three-dimensional network structure.
Now that people gradually understand and master the UV glazing technology, and the price of UV coatings is greatly reduced, UV glazing technology has been rapidly promoted and applied in the field of packaging and printing due to its unique advantages. Data show that the application of UV glazing technology is growing at a rate of 12-14% per year. It is believed that ultraviolet glazing technology will become the main process of post-press processing to increase the added value of products. Compared with other coating methods, UV coating has the following advantages:
1. Safety and environmental protection.
The UV coating process uses UV coatings. UV coatings are composed of oligomers, reactive diluents, photoinitiators, photosensitizers, and additives. They are 100% solids. There is no solvent volatilization, which is safe and non-polluting. Green products for the environment. Especially in the era of promoting "green packaging", the environmental protection advantages of the ultraviolet glazing process in post-press processing have been well recognized.
2. Not limited by the type of substrate.
3. Working at low temperature, it can be used for the printing of heat-sensitive substrates (such as plastic).
4. High product quality.
UV coating has fast light curing speed, high hardness, good wettability, strong adhesion, and has high disturbability, wear resistance and gloss value. The surface of the printed product glazed by UV is smooth and bright, high in hardness, resistant to friction, not easy to appear scratches, and has the advantages of waterproof and no odor.
5. The printed substrate after glazing can be processed immediately, and has high adaptability in cutting, forming, folding and other aspects.
6. High efficiency and low cost.
The ultraviolet wavelength is 200-400nm, which is invisible light. The UV light curing uses a long wave ultraviolet (UVA) with a wavelength of 316nm. The UVA light curing speed is fast, and the UV oil can be cured into a uniform coating in 1-2 seconds. The production efficiency is high, and the general drying speed can reach 100-300 meters / minute; compared with the glazing and calendering process, its equipment covers a small area, and the overall cost of material consumption and energy consumption costs is reduced.
UV coating method
There are many types of UV coating, and there are many classification methods, mainly the following classification methods:
A. Press the relationship between glazing machine and printing machine
According to the relationship between glazing machine and printing machine, glazing can be divided into offline glazing and online glazing. Offline glazing uses a special glazing machine to glaze the printed products, that is, printing and glazing are carried out on their own dedicated equipment. This glazing method is more flexible and convenient, and the equipment investment is small, which is more suitable for professional post-press processing and production Used by manufacturers, but this glazing method increases the transportation transfer between printing and glazing processes, and the production efficiency is low; online glazing directly connects the glazing unit to the printing machine, that is, printing and glazing are in the same machine On the go, fast speed, high production efficiency, low processing cost, reducing the handling of printed products, overcoming various quality failures caused by powder spraying, but online glazing to glazing technology, glazing oil, drying device and The requirements for glazing equipment are high.
B. Press the glazing method
According to the glazing method, glazing can be divided into roller coating glazing and printing glazing. Roller coating is the most common method of coating. The coating roller applies the varnish uniformly on the surface of the printed product. The varnish is applied to the printed product through the varnishing plate, so it can be performed. Partial glazing, currently commonly used are gravure glazing, flexographic glazing, offset printing glazing and silk screen glazing.
C. According to glazing product type
According to the types of glazing products, glazing can be divided into full-frame surface glazing, partial glazing, extinction glazing and artistic glazing. The main function of full-width surface gloss is to protect the printed matter and improve the surface gloss of the printed matter. The full-width surface gloss is generally carried out by roller coating; local glazing is generally to glaze the printed graphics on the printed matter. The high-gloss screen of the glazing part is compared with the low-gloss screen without the glazing part to produce a wonderful artistic effect. The partial glazing is carried out by printing glazing; the matting glazing is made of UV matte oil, and The effect of ordinary glazing is the opposite. It is to reduce the gloss of the surface of the printed matter, which produces a special effect. Since the high gloss has a certain degree of stimulation to the human eye, extinction glazing is currently a popular kind of glazing. Light method; the function of artistic glazing is to obtain special artistic effects on the surface of glazed products. For example, using UV pearl glazing oil to glaze the surface of the printed product will cause the pearlescent effect on the surface of the printed product, making the printed product noble and elegant .
Laminated UV glazing opens up new world
UV varnishing of coated products is a method of printing one or two varnishes on the whole or part of the surface of the printed product to obtain a bright UV varnish layer on the surface of the printed product. After the film is coated with UV varnish, it can enhance the light resistance of the ink and improve the gloss and three-dimensional sense of the printed matter. Form a strong contrast. Both full-page glazing and partial glazing can be used.
However, the following problems often occur in UV coating of coated products: the first brightness is not good, mainly because of uneven coating of varnish or excessive dilution of varnish, the viscosity is too low, then you need to adjust the glazing machine and improve the light The viscosity of the oil; the second is the adhesion of the printed product because the UV varnish coating is too thick; third, the viscosity of the UV varnish is too small, the coating is too thin will cause the surface of the UV varnish layer to bloom, and the viscosity of the varnish needs to be increased. Increase the thickness of the coating; the fourth is the white spots and pinholes on the surface of the UV varnish layer, which needs to be searched for from various reasons, such as: whether the UV varnish coating is too thin, whether the amount of ethanol diluent added is too high, Whether there is a lot of dust on the surface of the film; the fifth problem is that the varnish layer and the graphics are staggered, which is caused by inaccurate overprinting.
Although the UV glazing technology of film products has appeared in China soon, it has developed rapidly. Both in the field of commercial printing and packaging printing, it has achieved good response and application. It can be said that the application prospect of the UV glazing technology of the film products is very broad.
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