UV-curable inkjet ink, also known as UV ink, is an inkjet ink that has appeared and developed rapidly in recent years. It is especially used in digital flatbed printers. It can be applied to hard plates, soft materials, Foam material, PVC, Plexiglas, wood, metal sheet and other substrates. Because of its wide substrate adaptability and environmental friendliness (no chemical volatile components are discharged), it is favored by users. The domestic and foreign markets mainly promote photocurable ink flatbed printers, including international manufacturers specializing in outdoor printing equipment such as Wittur, Sai Angel, and Japan's MIMAKI, which focuses on indoor photo equipment (launches drum-type photo based on UV-curable ink) Machine), domestic equipment manufacturers have set foot in them including Runtianzhi, Taiwei, flying boat and so on. The following is a brief introduction to the development and composition of UV-curable inks.
1. Introduction of UV-curable ink
UV-curable inks use the radiation energy of UV to cause the photoinitiator in the liquid UV material to be stimulated into free radicals or cations, thereby initiating a chemical reaction of the unsaturated double bonds in the UV material, forming a cured body structure . It fully complies with the "3E principle". The so-called 3E, which is Energy, saves energy, there is no need to heat the substrate in ultraviolet light, generally ultraviolet light curing is 1/5 of thermal curing; Ecology, ecological environment protection, ultraviolet light curing material contains no or only a small amount of solvent At the same time, the energy used for UV curing is electrical energy, no fuel or gas, and no CO2 generation, so UV curing is known as "green technology"; Economy, economy, UV curing device is compact, assembly line production, processing speed is fast, thus saving space on the site , High labor productivity, UV curing process to ensure that the film is thinner, and has excellent performance, thereby reducing raw material consumption, which is conducive to reducing economic costs.
UV-curable ink is developed on the basis of photo-curable coating. As a new type of environmentally friendly ink, it has energy saving, no solvent discharge, no pollution to the environment, high production efficiency, suitable for heat sensitive substrates, The advantages of excellent printed products and low equipment investment have been valued by countries all over the world. They have been successfully applied in many fields such as coatings, inks, adhesives, printing plates, electronics industry, micro-processing and rapid prototyping.
2. Composition of UV curing ink
UV-curable ink is mainly composed of photo-curable resin (photoactive oligomer), reactive diluent (diluted monomer), photoinitiator, colorant, additives, etc. The components are now described as follows:
1). Photocurable resin, also known as oligomer, is a low-molecular polymer containing unsaturated functional groups, most of which is acrylate-terminated oligomer. It is the main film-forming substance of ink, and its content is about 30% -50%. Its performance largely determines the physical properties, chemical properties, printability and printability of the ink.
2.) The reactive diluent is also called monomer. The monomer plays a key role in the system. It not only adjusts the viscosity, but also forms a film-forming substance. The final properties of the film, the curing kinetics of the reaction, the degree of polymerization, and the formation The properties of the polymer have a direct impact. Low viscosity and solubility are the properties of ideal monomers.
3). A small amount of photopolymerization initiator is added to the photoinitiator ink. Under the action of ultraviolet light, the photoinitiator absorbs light quanta, decomposes to generate free radicals, and initiates polymerization of unsaturated double bonds, and polymer molecules interact to form a network Like the structure, when the free radical loses its activity, the chain growth ends. At this time, the ink is completely cured.
4). Colorant, the colorant in UV-curable ink is pigment. Generally, if a system contains pigments, its application performance is largely affected by the pigment performance. These effects include the stability to light, heat, climate, organic solvents, etc., involving the dispersion of processing, flowering, and color matching of the final product. Pigment is the key to determine the color and optical properties of the final product, and color and optical characteristics are closely related to the nature of the pigment and its dispersion, ie particle size. Under the same composition, the hue, tinting power and hiding power are all related to the dispersion degree of the pigment particles.
5). Additives, in order to improve certain properties of products, when formulating UV-curable resins, it is often necessary to add an appropriate amount of leveling agents, plasticizers, polymerization inhibitors, wetting agents, defoamers, heat stabilizers Wait. It should be emphasized here that the addition of these additives will cause the problem of aging and deterioration of the film layer, and may also have a certain impact on the curing system.
3. Inkjet ink and UV-curable inkjet ink
Inkjet inks are divided into three categories according to their main components: water-based inks, solvent-based inks, and UV-curable inkjet inks. Water-based ink has low cost, no pollution, and bright colors, but because of the slow evaporation rate of water, the pictures ejected by water-based ink are not easy to dry and be absorbed by the medium (it requires a special coating on the printing medium), which is mainly used in paper And all kinds of fibers (cloth) as the substrate, coated printing media. For solvent-based inks, the solvent will be directly fused with the medium, the medium is not required to be coated, and its evaporation rate is fast, which meets the requirements of high-speed printing. But the biggest problem with solvent-based inks is environmental protection, because of the high content of volatile organic compounds in the ink, it will definitely be subject to many restrictions in the long run. UV-curable ink (UV-CURABLEINKJETINK) as a special solvent ink, cured immediately after exposure to ultraviolet light, firmly adhered to the surface of the medium, and will not be dissolved in water or other organic solvents. On the one hand, it solves the problem that the water-based ink is not easy to dry, and because there is no organic matter discharged (VOC is almost 0) during the curing process, there is no longer the environmental protection problem of the solvent-based ink, thus greatly expanding the application field of inkjet technology , So that the inkjet printer can almost directly print on any material.
The main advantages of UV-curable inkjet technology can be summarized as follows:
· Volatile matter (VOC) is almost 0, making the workshop more environmentally friendly
· Infinite high-speed printing to meet higher throughput
· Can print high-quality, high-gloss pictures
· Both hard substrates and soft substrates can achieve satisfactory results
· No need for high energy consumption equipment such as heaters due to instant curing
· UV curing has broad prospects for sustainable development
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