The characteristics of screen printing decorative texture are natural and disorder. The decorative texture of gravure is different. It is formed by plate making. First, we should make the grind, wrinkle, ice flower, refraction, coral and other textures in the form of net hole or line on the gravure plate roller, and scrape the excess ink with the scraper, and transfer the ink in the net point to the print. Therefore, the decorative texture of gravure depends on plate making and matching with ink. The plate making process is very important, which directly affects the printing effect. For example, when making a sanding plate, the net points can be made into circular, hexagon, diamond, square, triangle and other shapes. The effect of printing is different, and the number of net lines, the depth of the net hole, the width of the net wall and so on have a shadow on the final printing effect. Ringing. If you make the thick line number and big net point, no matter how to adjust printing process and change the ink, you can not print high-quality fine grit and wrinkles, ice and other textures. That is to say, the decorative texture of intaglio printing is artificial and orderly, which determines that the intaglio printing method has good reproducibility and anti-counterfeiting function. When making the plate, we can make the coarse grind, fine grind, wrinkle, ice flower, and refraction on the same plate roller, which can get all the effect at the same time. Printing problems. But the development of UV gravure decorative ink is very difficult, mainly due to the following aspects.
(1) gravure printing speed is very fast, generally more than 100m/min, printing ink layer is also thick, so it is very difficult to make the ink curing thoroughly. Comparatively speaking, the speed of screen printing is only 10 ~ 30m/min, and the curing is more thorough.
(2) there is a difficult problem in UV gravure printing. In the process of intaglio printing, when the ink is transferred to the plate roller, we must first use the scraper to scrape the excess ink in the layout to ensure that there is enough ink in the net hole, and there is no ink in the blank, otherwise the "dirty edition" will appear. Generally speaking, the viscosity of the solvent intaglio ink is very low, and it is very easy to scrape the net, and the viscosity of the UV intaglio ink is much higher and difficult to clean. This is due to the high viscosity of the active diluent in the UV ink, and a sufficient amount of high viscosity semi polymer must be added to ensure good fastness and faster curing speed. . This is also one of the reasons why UV gravure ink has rarely been used for production.
(3) after the transfer of UV intaglio printing ink to the substrate, it must be kept in shape before curing, and can not be leveled, otherwise it will not get good print, but this also increases the difficulty of ink scraping.
Now UV gravure printing ink has achieved good printing effect, although there are many varieties, but different from the screen printing ink, UV intaglio printing ink does not exist in grinding, wrinkle, ice flower and refraction. It can be used to print various decorative patterns on the plate roller at the same time. There is only a difference in texture between them. . If the printing is mainly made of sand, it is necessary to use the ink with high cover rate; if the printed matter is mainly refracted, it should choose the ink with high transparency and high refractive index; if the print is dominated by wrinkles or ice flowers, it is necessary to use both the two kinds of ink. That is to say, the type of ink to choose depends on the theme of the printed matter.
Gravure press for printing decorative texture has sheet fed gravure press and rotary gravure press. Because of the previous reasons, high quality UV intaglio ink is difficult to come out. Therefore, most of the imported and domestic rotation gravure machines have no UV curing device. If you want to print the UV gravure printing ink, you must install the UV curing device. The UV curing device is composed of a medium pressure mercury lamp, a reflector and a protective cover. The working pressure of medium pressure mercury lamp is 1.33 x 104Pa, and the ratio of 365nm and 366.5nm spectrum is higher in emission spectrum. Most photoinitiating systems have strong absorption in the spectrum area, which is very important for the curing of UV ink. In addition, the power density of the medium pressure mercury lamp is 80 ~ 240W/cm, and the actual luminous area of the lamp tube is slightly larger than the maximum width of the solidified area. If the 80W/cm lamp is selected, there should be at least 3 installation. If the lamp with a power density greater than 120W/cm is installed, there should be at least 2 installation. When used in practice, the greater the power density of the tube, the stronger the penetration of UV light, the better the curing effect. The total power density of 2 120W/cm lamps and 3 80W/cm tubes is the same, but the former has better curing effect than the latter.
The following points should be paid attention to when installing the UV curing device.
(1) to install an aluminum reflector.
(2) pay attention to the protection of UV light and discharge ozone from the outside.
(3) the UV lamp must be cooled.
(4) pay attention to explosion protection.