UV printing process and ink working principle

UV printing is a printing process that uses ultraviolet light to dry and cure inks. It requires inks containing photosensitizers to be compatible with UV curing lamps. UV inks already cover areas such as offset printing, screen printing, inkjet printing, and pad printing.

UV curing ink

Ultraviolet curing inks are ultraviolet (UltraViolet) light waves under the irradiation of crosslinking reaction, can instantly change from liquid to solid ink, it is also known as "UV" ink. Its main components include photopolymerizable prepolymers, photosensitive photosensitive monomers, organic pigments, photopolymerization initiators, and additives. Among them, the photopolymerization initiator is the most important component in the UV ink and is the beginning of the photopolymerization reaction. Commonly used photopolymerization initiators include aromatic ketones and the like. Curing/drying principle of UV-curing inks The main reason for UV-curable inks is due to the effect of ultraviolet rays. Under the irradiation of ultraviolet rays, the photopolymerization initiator in the UV ink absorbs photons of a certain wavelength and then turns into free molecules and becomes free radicals. Then, the intermolecular energy transfer causes the polymerizable prepolymer and the photosensitive monomer to become excited, resulting in charge transfer complexes, continuous cross-linking polymerization between the complexes, and curing to form a film.

The curing process of UV ink is a photochemical reaction process. Under the action of ultraviolet energy, the prepolymer is cured in a very short time. In addition to the surface curing of the ink, the ultraviolet ray can penetrate the liquid ultraviolet curing. In the ink, it stimulates further curing of the deep ink film. In traditional inks, oil-based inks are solidified by oxidation, while solvent-based or water-based inks are primarily cured by the evaporation of water or solvents, and some inks can penetrate the paper. Therefore, compared with the traditional inks, the polymerization drying of the UV-curable inks is more thorough, without any evaporation or solvent contaminants, and the ink film is cured 100%.

The main features of UV curing oil

1. Excellent drying performance. Since UV inks only dry when irradiated with ultraviolet light, even if the ink is stored in the ink fountain for a long period of time, the performance of the ink can be kept stable, and no crusting on the ink roller will occur. Once exposed to UV light, the ink can be instantaneously dry and thorough. Its curing time is very short. Generally, only 1/10S can be completely dried and fixed on the surface of the substrate. For traditional thermosetting inks and sheetfed papers. Offset printing inks, the drying time may take several minutes or even several days to completely dry, so the use of UV curing ink printing jobs, delivery time is short, can be comparable with flexo, gravure, and greatly enhance the printing production efficiency .

2. Conducive to the post-processing process. UV ink printing followed by UV glazing machine processing, obtained print gloss, and the surface smooth and uniform. After coating with the machine, the packaging and processing processes such as die cutting, creasing, gluing, and bronzing can be completed immediately, which is very beneficial to the needs of high-speed printing development.

3. Durability is good. In addition to providing bright, bright colors, UV-curable inks also have strong anti-friction properties. The chemical substance in the UV ink forms a polymer three-dimensional network polymer through a cross-linking reaction. Therefore, the use of the UV ink can make the ink layer of the ink product strong, fast-drying and cross-linked. Such ink layer has a high abrasion resistance. And chemical resistance. Many of the prints printed on the coated paper by the uv ink for direct mailing can withstand multiple folds and can withstand strong radiation upon re-laser printing, so the UV ink can be used for overwrap printing requiring wear.

4. Good environmental performance. Another important characteristic of UV-curable inks is its environmental performance. Since UV inks cure to a solid content of nearly 100%, they are virtually free of VOCs (organic volatiles), meaning that they will not or rarely evaporate during curing. Organic compounds will not cause more harmful environmental pollution, but also less waste, and save energy, do not have to worry about dealing with harmful flammable and explosive materials, it is an environmentally friendly ink.

5. Strong printability, can meet the needs of a variety of substrates. Of course, UV-curable inks also have some drawbacks: some require NBR or EPDM rollers, and sometimes special blankets may be needed. The blanket may also require special cleaning agents to prevent the blanket from shrinking, expanding, or reducing the quality of the blanket. . Second, it costs more than traditional inks. However, the high cost is worth compared to the final print performance.

UV printing and glossing can carry out various value-added printing techniques on various materials including metal foils and plastics. Growing demand for UV The continuous development of the UV market has continued for many years. The annual growth rate in the world is nearly three times higher than the industry average for printed products, and the growth in sheetfed and many flexo applications is even greater. Is strong.