The characteristic of the decorative texture of screen printing is natural and disordered. The decorative texture of gravure printing is different. It is formed by plate making. First of all, according to the design requirements, the matte, wrinkle, ice flower, refracting, coral and other textures should be made on the gravure printing plate cylinder in the form of mesh or line. When printing, use a scraper to scrape off the excess ink on the plate, and transfer the ink in the mesh Onto the substrate. Therefore, the decorative texture of gravure printing depends on the plate-making and matching with the ink. The plate-making process is very important. It directly affects the printing effect. For example, when making a frosted plate, the mesh can be made into a circle, regular hexagon, diamond, square, triangle and other shapes. The effects of the printing are different. Factors such as the number of network lines, the depth of the network hole, and the width of the network wall also have an influence on the final printing effect. If it is made with thick lines and large mesh holes, no matter how the printing process is adjusted and the ink is changed, high-quality fine matte, wrinkles, ice flowers and other textures cannot be printed. In other words, the decorative texture of gravure printing is artificial and orderly, which also determines the good reproducibility and anti-counterfeiting function of the gravure printing method. When making a plate, you can make coarse frosted, fine frosted, wrinkled, iced, refracted and other textures on the same plate cylinder as needed, and you can get all the effects in one printing, without having to go through multiple printings like screen printing, and each The textures can be combined seamlessly, which solves the problem of overprinting in screen printing. However, the development of UV gravure decorative inks is very difficult, mainly due to the following aspects.
(1) The speed of gravure printing is very fast, generally above 100m / min, and the printing ink layer is also thick, so it is very difficult to completely cure the ink. Relatively speaking, the screen printing speed is only 10 ~ 30m / min, curing is relatively thorough.
(2) UV gravure has the problem of unclean ink. During the gravure printing process, when the ink is transferred to the plate cylinder, the excess ink on the plate must be scraped off with a squeegee to ensure that there is enough ink in the mesh and there is no ink in the blank space, otherwise "dirty" Version". Generally speaking, the viscosity of solvent-based gravure ink is very low and it is very easy to scrape off, while the viscosity of UV gravure ink is much higher and difficult to scrape off. This is because the viscosity of the reactive diluent in UV ink is very high, and A sufficient amount of high viscosity semi-polymer must be added to ensure good adhesion fastness and fast curing speed. This is one of the reasons why UV gravure inks are rarely used in production until now.
(3) After the UV gravure decorative ink is transferred to the substrate, it must be kept in its original state before curing, and it cannot be leveled, otherwise good prints will not be obtained, but this increases the difficulty of scraping ink.
Now the UV gravure decorative ink has achieved a good printing effect. Although there are many varieties, unlike the screen printing ink, the UV gravure decorative ink does not have frosting, wrinkles, ice flowers, and refraction. It can simultaneously There are only differences in texture between the various decorative textures on the printing plate cylinder. If the printed matter is mainly matte, ink with high coverage is needed; if the printed matter is mainly refractive, then high transparency and high refractive index ink should be used; if the printed matter is mainly wrinkled or iced, you must use both. Ink varieties. In other words, the choice of ink type depends on the theme of the printed matter.
Gravure printing machines for printing decorative textures include sheet-fed gravure printing machines and rotary gravure printing machines. Due to the reasons mentioned earlier, high-quality UV gravure inks are difficult to come out, so most imported and domestic rotary gravure printing machines do not have UV curing devices. If you want to print UV gravure decorative inks, you must install a UV curing device. The UV curing device consists of a medium-pressure mercury lamp, a reflector and a protective cover. The working pressure of the medium-pressure mercury lamp is 1.33 × 104Pa, and the ratio of the 365nm and 366.5nm spectral lines in the emission spectrum is relatively high. Most photo-initiated systems have strong absorption in this spectral line region, which is extremely important for the curing of UV inks. important. In addition, the power density of the medium-pressure mercury lamp used is 80-240 W / cm, and the actual light-emitting area of ​​the lamp tube is slightly larger than the maximum width of the cured area. If 80W / cm lamp tube is selected, at least 3 lamps must be installed; if lamp tube with power density greater than 120W / cm is selected, at least 2 lamps must be installed. In actual use, the greater the power density of the lamp, the stronger the penetration of UV light, and the better the curing effect. Two 120W / cm lamps and three 80W / cm lamps, the total power density of the two is the same, but the curing effect of the former is better than the latter.
Pay attention to the following points when installing the UV curing device:
(1) To install aluminum reflector.
(2) Pay attention to the protection of UV light and discharge ozone out.
(3) The UV lamp tube must be cooled.
(4) Pay attention to explosion protection.
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