Decorative texture screen printing method
The inks used in decorative printing are all UV inks, first of all due to the fast curing speed of UV inks and good printing quality. Even if the commonly used solvent-based inks use infrared drying, the curing is relatively slow. The curing of water-based inks is of course slower, while UV inks can be cured in only 3 to 5 seconds, or even less than 1 second. Second, frosted and refracted. Decorative textures such as coral must be cured instantaneously after printing. Decorative textures such as screen printing wrinkles and ice flowers must be cured by ultraviolet light to cause uneven surface shrinkage, so they can only be printed with UV inks.
The decorative texture of screen printing has the advantages of simple equipment, less investment and quick launch. When making a plate, most of the parts on the screen that need to be printed with decorative texture are blank (except for the refractive effect), when printing. Decorative ink can be missed on the substrate. Create the desired texture through the inherent characteristics of various screen printing inks.
Matte printing is one of the most common applications in decorative printing and is widely used in cigarettes. Printing of packaging for wine, cosmetics and health products. The formulation of the matte screen printing ink contains not only the semi-polymer, reactive diluent and photoinitiator necessary for general UV inks, but also some granular materials with a size of 5-50 μm and a content of 5% to 40%. When printing, use a scraper to press the ink, so that the ink is transferred to the substrate (usually gold or silver cardboard) through the mesh of the screen. When the ink is printed on gold and silver cardboard, the particles are also transferred to the gold and silver cardboard at the same time. Due to the effect of surface tension, the slurry in the ink will agglomerate to the surface of these particles and form There are many large particles with these particles as the core and the outer surface of the cured resin, which is what we call frosted particles.
It can be seen that the generation and distribution of frosted particles are random. There are many factors that affect the size, color tone and distribution of the frosted particles. In addition to the ink formula, the mesh size, the shape of the blade, the angle of the blade, the old and new blades, the distance between the screen and the substrate. Squeegee speed, force, and substrate performance all have an impact on the formation of frosted particles. In addition, the scraping of ink is like filtering the ink. The resin and fine particles in the ink are more likely to pass through the screen, while the coarse particles are more accumulated in the residual ink, so the composition of the ink will occur after each scraper scrapes Changes, the printed matte texture will also change. Due to the influence of the above factors, even in the same batch of prints, almost all of them are different. This determines that the matte effect of screen printing is only decorative function, no anti-counterfeiting function.
Wrinkles are another important variety of decorative printing. They are formed by uneven shrinkage when the ink is cured, and are composed of many criss-cross lines that cross. When printing wrinkle ink by screen printing method, 100-250 mesh screen should be used, the thickness of the printing ink layer is 10-40 m, firstly pre-irradiate with a low-pressure mercury lamp to make the surface layer of the ink solidify and shrink in advance, and then use Irradiation with medium pressure mercury lamp completely cures the ink. Due to the different curing speed of the ink surface layer and the inner layer, the resulting tension causes uneven shrinkage and even wrinkling. There are many factors affecting the thickness and shape of wrinkles, such as the thickness of the printing ink layer, the size of the screen mesh, especially the power and distance of the pre-irradiated low-pressure mercury lamp, and the speed of the conveyor belt. Therefore, when the wrinkle texture is printed by the screen printing method, even in the same batch of printed matter, each wrinkle has a significant difference.
The ice flower texture is crystal clear and very beautiful. An ice pattern is composed of many small "wafers", and each "wafer" contains many lines with different lengths and shapes. The ice effect is printed with a special UV ice ink. When this ink is irradiated with UV light at a higher temperature, it will produce uneven curing shrinkage, thereby forming crystal grains. If the curing speed is too fast, beautiful crystal grains cannot be obtained. Therefore, the curing speed of UV screen printing ice flower ink is very slow, the curing temperature is high, and the energy consumption is very high. In order to print the effect of ice flowers, a domestic printing plant invested in a UV curing machine, using 9 sets of 6.3kW UV lamps, and can only print more than 600 folios per hour.
At present, some equipment manufacturers have developed a new type of UV curing equipment. Although the curing speed has been improved, the quality of the crystal grain is very poor. Ice printing is affected by many factors such as the thickness of the ink layer, the intensity of the UV lamp, the temperature, the curing speed and other factors. It has great randomness and arbitrariness. Not only the ice effect of each printed product is different, but also different parts of the same printed product The difference is that the process is unstable and the product consistency is extremely poor. Therefore, the screen-printed ice flower is still in the stage of proofing or small batch production.
Two other important effects in decorative printing are coral and refraction. The so-called coral is actually foam, but the foam gathers together and looks like coral. The effect of printing coral is UV screen printing coral ink. The surface tension of the ink is very small. During printing, the ink is transferred to the gold and silver cardboard through the screen under the pressure of the scraper. When the screen rebounds, bubbles are generated. The characteristic of this ink is that it can keep the air bubble as it is in the ink layer, and after curing by UV light irradiation, the so-called coral effect is formed.
In decorative screen printing, refraction is special. The formation of other decorative textures is naturally formed by the inherent characteristics of the ink and is disordered. Refraction is made of many parallel dense lines in the screen. When printing, the refractive ink is scraped onto the gold and silver cardboard to produce a dense parallel grating to refract the incident light, thereby forming a refractive effect. Generally speaking, a screen with a line density of more than 4 lines / mm can achieve a better refractive effect.
There are many types of screen printing decorative inks, but each ink can only print one effect. For example, the matte ink can only print the matte effect, and cannot be used for the printing of wrinkles and ice flowers. Moreover, even the matte ink is coarse. There are several types of medium and fine, each with its own use. If there are several decorative textures such as coarse sand, fine sand, wrinkles, and refractions in the same print, they must be separately plated and printed with corresponding inks according to the process requirements of each ink, which is not only very troublesome, but also difficult Register, the scrap rate is extremely high.
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