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Decorative texture screen printing method
The inks used for decorative printing are all UV inks. The first is that UV inks cure fast and print quality is good. Even if the commonly used solvent-based inks use infrared drying, the curing is slower. The curing of aqueous inks is, of course, slower, and UV inks require only 3 to 5 seconds or even less than 1 second to cure. Second, scrub, refraction. Decorative textures, such as corals, must be instantaneously cured after printing. Screen printing wrinkles, ice and other decorative textures must be cured by UV irradiation to cause uneven surface shrinkage, and therefore can only be printed with UV inks.
Matte printing is the most common type of application in decorative printing and is widely used in the printing of tobacco, wine, cosmetics and health products. In addition to the semi-polymers, reactive diluents and photo-initiators necessary for general UV inks, the matte screen printing ink formulation also contains some granular materials with a size of 5 to 50 μm and a content of 5% to 40%. During printing, the ink is pressed with a squeegee to transfer the ink to the substrate (usually gold or silver cardboard) through the mesh of the screen. When the ink is printed on gold or silver paper, the particles are also transferred to the gold and silver paper. Due to the surface tension, the ink in the ink will agglutinate to the surface of these particles. After being cured by UV light, the ink will form. There are many large particles that have these particles as the core and are surrounded by a solidified resin, which we call sanding particles.
It can be seen that the generation and distribution of the matte particles are random. There are many factors that affect the size, color and distribution of the matte particles. In addition to the ink formulation, the size of the mesh, the shape of the doctor blade, the angle of the doctor blade, the oldness of the doctor blade, the distance between the screen and the substrate, the speed of the doctor, the size of the force, the properties of the substrate, etc. There are nine directions for the formation of matte particles. In addition, ink scraping is like filtering the ink. The resin and fine particles in the ink are easier to pass through the screen, while the coarse particles are more accumulated in the residual ink. Therefore, the composition of the ink will occur after each scraping. Changes, the printed matte texture will also change. As a result of the above factors, the influence of many factors has caused almost all of them to be different even in the same printed matter. This determines that the matte effect of screen printing is only decorative function and no anti-counterfeiting function.
Wrinkles, another important type of decorative printing, are formed by the uneven shrinkage of the ink during curing and consist of many criss-cross lines. When using screen printing method to print wrinkle ink, 100 mesh to 250 mesh screen should be used. The thickness of the printing ink layer is 10 nm to 40 nm. Pre-irradiation with a low-pressure mercury lamp is first performed to partially cure and shrink the ink surface in advance, and then Exposure to mercury vaporized lamps causes the ink to cure completely. Due to the difference in the curing speed of the ink surface layer and the inner layer, the generated tension causes uneven shrinkage and wrinkling. There are many factors that affect the thickness, shape, etc. of the wrinkles, such as the thickness of the printing ink layer, the size of the screen mesh, and particularly the power and distance of the pre-irradiated low-pressure mercury lamp, the conveyor speed, and the like. Therefore, when the wrinkle texture is printed by the screen printing method, there is a clear difference in the wrinkles of each sheet even in the same printed matter.
Ice flower crystal clear, very beautiful. An ice pattern consists of many small "wafers," each of which contains many lines of different lengths and shapes. The ice flower effect is printed with a special UV ice-printing ink. When the ink is exposed to UV light at a relatively high temperature, uneven curing shrinkage is generated and the crystal grain is formed. If the curing speed is too fast, beautiful grain patterns cannot be obtained. Therefore, the UV screen printing ice printing ink has a very slow curing speed, a high curing temperature, and a very high energy consumption. A printing factory in China has invested in a UV curing machine for the purpose of printing ice flowers. It uses 9 sets of 6.3 kW UV lamps and can print more than 600 folios per hour.
At present, some equipment manufacturers have developed new types of UV curing equipment. Although the curing speed has been improved, the quality of the grain lines is very poor. Ice print is influenced by many factors such as ink layer thickness, UV lamp intensity, temperature, curing speed, and so on. It has great randomness and arbitrariness. Not only does each print have different ice print effects, but also different parts of the same print are different. , Process instability, poor product consistency. Therefore, the screen printing ice flower still remains in the proofing or small batch production stage.
The other two important effects in decorative printing are corals and refractions. The so-called coral is actually a bubble, but it is just a bubble that looks like a coral. The effect of printing corals is UV screen printing coral ink. The surface tension of the ink is very small. When printing, the ink is transferred to the gold and silver card paper through the screen under the action of the blade pressure. When the screen is rebounded, bubbles are generated. The ink is characterized by being capable of stabilizing the air bubbles in the ink layer as it is. After being cured by UV light, a so-called coral effect is formed.
In decorative screen printing, the refraction is rather special. The formation of other decorative textures is naturally formed by the inherent characteristics of the ink. It is disorderly, and the refraction is made in the screen to make many parallel and dense lines. When printing, the refraction ink is scraped onto the gold and silver card paper to generate a dense parallel grating, and the incident light is refracted to form a refraction effect. In general, the screen density of 4 screens/mm or more can achieve better refraction effect.
There are many types of screen printing decorative inks, but each kind of ink can only print one effect. For example, matte inks can only print frosted effects and cannot be used for printing such as wrinkles and icy flowers. Moreover, even if the matte ink is also thick, medium, fine, etc., each have their own use. If there are several kinds of decorative textures such as coarse sand, fine sand, wrinkles, and refraction in the same printed matter, they must be plated separately and printed in multiple times according to the process requirements of each type of ink, which is not only very troublesome, but also difficult. Registered, scrap rate is extremely high.
Printing texture screen printing method
The screen printing decorative texture has the advantages of simple equipment, low investment, and quick implementation. At the time of plate making, the part of the screen where the decorative texture is to be printed is mostly blank (except for the refraction effect), and the decorative ink can be printed on the substrate at the time of printing. The desired texture is produced by the inherent properties of various screen printing inks. .