Screen printing decorative features are natural, unordered, gravure decorative texture is different, it is formed by plate making. First, according to the design requirements, sanding, wrinkles, ice, refraction, coral and other textures should be made on the gravure plate cylinder in the form of net holes or lines. During printing, scrape the excess ink on the plate surface and transfer the ink in the net cavity. On the substrate. Therefore, the gravure decorative texture depends on the plate making and the ink mix. Platemaking process is very important, it directly affects the printing effect, such as the production of frosted printing plate, the cell site can be made into a round, regular hexagonal, diamond, square, triangle and other shapes, the printed effect is different, and plus Factors such as the number of screen lines, the depth of the cell site, and the width of the network wall also affect the final printing effect. If the number of thick lines or large cells is made, no matter how the printing process is adjusted and the ink is changed, fine textured sand, wrinkles, ice and other textures cannot be printed. In other words, the gravure decorative texture is artificial and orderly, which also determines the gravure printing method has a good reproducibility and anti-counterfeiting capabilities. At the time of plate making, coarse sanding, fine sanding, wrinkle, ice flower, refraction and other textures can be made on the same plate cylinder as required, and all effects can be obtained in one printing, without having to undergo multiple printings like screenprinting, and each The textures can be seamlessly combined to solve the overprinting problems in screen printing. However, it is very difficult to develop UV gravure decorative ink. The main reasons are as follows.
(1) The gravure printing speed 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, screen printing speed is only 10 ~ 30m/min, curing more thoroughly.
(2) UV gravure has the problem that the ink is not clean. In the gravure process, when the ink is transferred to the plate cylinder, the excess ink on the plate must be scraped with a squeegee to ensure that there is enough ink in the cell, and there is no ink in the space, otherwise it will appear dirty. Version". In general, the solvent-based gravure ink has a very low viscosity and is very easy to clean. The UV gravure ink has a much higher viscosity and is difficult to clean. This is because the viscosity of the reactive diluent in the UV ink is very high, and A sufficient amount of high-viscosity hemimer must be added to ensure good adhesion fastness and faster cure speed. This is one of the reasons why UV gravure printing inks are rarely used for production.
(3) After the UV gravure printing ink is transferred to the substrate, it must remain in the original state before curing, and it cannot be leveled. Otherwise, good prints will not be obtained, but this will increase the difficulty of scraping ink.
Now, UV gravure decorative inks have achieved very good printing results. Although there are many varieties, unlike UV screen printing inks, UV gravure decorative inks do not have any differences such as matte, wrinkles, icy flowers, and refractive index. It can simultaneously There are various decorative textures on the printing plate cylinder, and there is only a difference in texture between them. If the print is mainly frosted, ink with high coverage is required; if the print is mainly based on refractive index, high transparency and high refractive index inks should be used; if the prints are dominated by wrinkles or ice, they must be balanced. Ink varieties. In other words, the type of ink used depends on the subject of the print.
Gravure machines for printing decorative textures include sheet-fed gravure printers and rotogravure machines. Due to the aforementioned reasons, high-quality UV gravure inks are difficult to produce, so most of the imported and domestic rotary gravure machines do not have UV curing devices. If UV gravure decorative inks are to be printed, UV curing devices must be installed. 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 1.33×10 4 Pa, and the proportion of the 365 nm and 366.5 nm lines in the emission spectrum is relatively high. Most of the photoinitiation systems have strong absorption in this line region, which is extremely effective for UV ink curing. 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 is slightly larger than the maximum width of the cured area. If 80W/cm lamp is used, at least 3 must be installed; if the lamp with power density greater than 120W/cm is used, at least 2 must be installed. In actual use, the greater the power density of the lamp, the stronger the penetrating power of UV light and the better the curing effect. Two 120W/cm lamps and three 80W/cm lamps have the same total power density, but the former has a better curing effect than the latter.
When installing a UV curing device, pay attention to the following points:
(1) Install the aluminum reflector.
(2) Pay attention to protection against UV light and discharge ozone outside.
(3) UV lamps must be cooled.
(4) Note explosion protection.
Source: Greater China Graphic Arts Network