With the progress of China's printing industry, the development momentum of China's ink manufacturing industry is very rapid. The technical indicators of the main products of domestic large-scale ink manufacturing enterprises have reached or approached the advanced level of similar foreign products. In addition to basically meeting the needs of the domestic printing industry and packaging and decoration industry, they are also exported to many countries and regions in the world and achieved export earnings. However, we must realize that compared with the international advanced level, there is still a certain gap in China's ink manufacturing industry, mainly manifested in the lag of production technology and packaging level, the poor consistency of domestic raw material quality, scientific research and development capabilities and analytical methods need to be further improved , Poor environmental awareness, etc. The key targets for the future development of the ink industry are commercial rotary offset printing inks, high-grade offset printing inks, environmentally friendly inks and special varieties of inks. Offset UV ink is one of the special types of ink. 1. The characteristics of offset ultraviolet (UV) ink Compared with ordinary inks, UV inks have good printability, color stability, overprinting effect and brightness. ①Its curing speed is fast, and it can be cured within a few seconds under ultraviolet light irradiation, especially in packaging printing, it is often necessary to print a large area on the ground, which requires a higher density, so it has to increase the amount of ink, which The problem of drying becomes very important when the ink is not easy to dry, which often affects the efficiency of printing production. With ultraviolet light-curable ink, this problem is solved. ②Ultraviolet ink can also prevent the ink from peeling, which solves the worries when the offset press is stopped. ③It has good conjunctiva and has good adhesion to various substrate materials. Since the UV ink does not contain solvents, the thickness of the cured ink layer is basically the same as the thickness of the printed ink layer. The UV ink per unit weight is compared with ordinary ink The printing area is 30% -50% larger. There is no penetration during curing, and it can be printed on non-absorbent printing materials, such as card printing, etc. This is an area that ordinary offset inks cannot enter. ④Because the ultraviolet ink does not need to be sprayed during printing, the printing environment is well improved, and the troubles caused by powder spraying to post-press processing are avoided, such as the impact on the glazing and laminating effect, and Can be connected processing. ⑤UV ink is bright in color, and its scratch resistance, wear resistance, acid and alkali resistance are better than ordinary inks. Therefore, although its price is much more expensive than ordinary inks, it is still widely used. 2. Composition of offset ultraviolet ink (UV) Ultraviolet ink is composed of connecting materials, pigments, photosensitizers and auxiliary agents. ①The connecting material is a kind of adhesive fluid, which plays a connecting role. It is composed of photo-curable resin, prepolymer, crosslinking agent (monomer crosslinking agent and prepolymer crosslinking agent), etc. The connection material increases the fluidity of the ink, so that the ink can be transferred from the ink fountain to the printing plate to the substrate, complete the good ink transfer, and produce chain polymerization under the action of a certain wavelength of light. On the printed side. The connecting material is the main flowing part of the ink and the heart of the ink. ②As a diluent, the cross-linking agent can reduce the viscosity of the ink, improve the printability, and play a role of cross-linking and curing in the photopolymerization reaction. ③Because some materials in the linking material cannot directly absorb the energy of the photon, it is necessary to add a photosensitizer, also called a photoinitiator, to the ink. Under the action of a certain wavelength of light, the photosensitizer molecule decomposes into two free radicals. The electrons in the molecule jump from a low energy level to a high energy level and generate vibrations, which splits the unsaturated double bonds in the photocurable resin and photosensitive diluent, produces chain polymerization, and further crosslinks and solidifies. ④The auxiliary agent is an additional part in the ink except the main part, mainly some waxy substances, such as microcrystalline wax polyethylene wax and so on. The auxiliary agent can reduce the viscosity of the ink and enhance the wear resistance of the ink film. 3. Precautions when using ultraviolet (UV) ink for offset printing ①When blending UV inks, photo-curable inks can be blended with each other, but cannot be mixed with ordinary inks. When printing, when the ordinary ink is changed to ultraviolet ink, the printing part of the machine must be thoroughly cleaned with a special cleaning agent, otherwise there will be poor ink drying and poor ink sticking. ②The auxiliary materials of ultraviolet ink mainly include adhesive remover, drier, hardener, thinner and so on. The main function of the debonding agent is to reduce the viscosity of the ink. The amount of the debonding agent is generally 5% of the ink. Too much will cause the ink adhesion to decrease; the role of the drier is to accelerate the curing speed of the ink. The amount is generally the ink 2%, the role of the hardener is to enhance the wear resistance of the ink, the dosage is generally 5% to 10% of the ink; the role of the thinner is to increase the fluidity of the ink, the dosage is generally 3% to 5% of the ink, the dosage Too much will cause poor drying of the ink film. ③Inspection method for sufficient ink curing: the back of the printed matter should be clean, non-sticky and dirty, and the ink film should be non-sticky when touched by hand; twist and press under the pressure of 50N with the thumb, and the ink film will not be indented or broken; Ink film, no scratches. 4. Offset ultraviolet (UV) ink printing process requirements ①Color sequence arrangement: The problem of color sequence arrangement of UV offset printing is more complicated. Because different colors absorb UV photons differently, the drying rate of different inks is also different. Magenta ink has the best permeability to ultraviolet rays, followed by yellow ink, cyan ink, and black ink. Since black ink is a total absorption spectrum in physics, white ink is a total reflection spectrum, which affects the absorption of ultraviolet light by the photosensitizer, thereby affecting the drying speed, so the color sequence arrangement should be white, black, blue, yellow Red ink makes the poorly transparent ink absorb as many photons as possible, enhancing its curing effect. Such a color sequence arrangement is particularly effective in monochrome or two-color printing. Because this is equivalent to adding a light curing opportunity to white ink and black ink, the drying effect is naturally good; in a multi-color printing machine with multiple sets of ultraviolet lamp drying devices, this color sequence arrangement is also reasonable; When printing in color, the line or text version should be printed first, and the field version with a deep ink color and a small area should be printed first, and the large-area field version should be printed afterwards. The area of ​​the ink film is smudged and scratched. ②Fountain solution: For multi-color offset presses with an alcohol dampening device, the original solution of the water bucket should be replaced with a special UV original solution of the water bucket, and the alcohol remains unchanged. In monochrome offset printing, alcohol can be added to the water to reduce the amount of water, reduce the emulsification of the ink, reduce the surface tension of the ink, and increase the drying speed of the ink. To clean, use special UV car wash water. If there is no special UV car wash water, use absolute ethanol or xylene. ③ Printing plate: Due to the strong corrosiveness of UV ink and UV car washing water, the printing resistance of ordinary PS plate is very low, generally around 1000-2000 printing, so special UVPS plate or baked ordinary PS plate should be used. In the case of a temperature of 250 ° C., the ordinary PS plate cooked according to the conventional method requires a baking plate for 10 to 15 minutes, and the CTP plate also requires a baking plate for 10 to 15 minutes. ④The choice of UV lamp: the experiment proves that when the printing rate is 300 rpm, three 8KW UV lamps are used; when the printing rate is 6000 ～ 8000 rpm, six 8KW UV lamps can only be used to achieve complete printing. dry. When the drying effect is indeed unsatisfactory, the photosensitizer can be added appropriately, and the amount added depends on the degree of drying. The effective wavelength range of UV curing is 200-400nm, and the wavelength of some light sources in the printing workshop is also in this range, which will cause the surface layer of the ink to slightly cure, so attention should be paid to the influence of ambient light on the drying of ultraviolet ink. Due to the special drying method of ultraviolet ink, it is suitable for printing absorbent and non-absorbent materials and other special materials, and the printing effect is excellent and the printing performance is stable. With the solution of the UV printing technology problems, the future UV offset printing will be Have greater room for development.
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