UV ink is an ink that does not use solvents, has fast drying speed, good gloss, bright colors, good water resistance, solvent resistance and wear resistance. At present, UV ink has become a more mature ink technology, and its pollutant emissions are almost zero. UV (ultraviolet light curing) ink refers to the use of ultraviolet light of different wavelengths and energies to polymerize the monomers in the ink binder into polymers under ultraviolet irradiation, so that the ink is filmed and dried. UV inks are also inks. As inks, they must have brilliant colors (except in special cases), good printability, and suitable curing and drying rate.
In addition, UV inks also have the following characteristics: ink curing of non-absorbent printing materials; ink emulsification may hinder the adhesion of ink to substrates; rotary presses are fast, requiring the ink curing speed to match the printing speed, especially not Dry offset printing and security printing using special inks, UV ink printing effect is better than resin offset printing ink. Taking into account the above performance, printing companies generally use UV inks in offset printing.
However, the printing industry should also pay attention to the following points when using UV offset printing.
(1) Different types of substrates should choose different inks, and comprehensive consideration should be given to the transparency of the ink, the curing rate, the coverage of the ink, and the gloss of the surface of the printed product.
(2) In color printing, the ability of various pigments to absorb UV photons is different, and the transmittance is M, Y, C, BK from high to low, so the curing degree of each color ink is also different. Transmittance directly affects the excitation energy of photons to photoinitiators, so it is advisable to arrange the printing color sequence as BK, C, Y, and M, so that the ink with poor transparency can absorb as many photons as possible and enhance its curing effect.
(3) The use of alcohol dampening system can reduce the surface tension of the ink and promote curing, and in the printing process, the dampening liquid can be used to strengthen the oleophobic area (blank part) of the printing plate to ensure that the lipophilic area is sufficient Ink-friendly, hydrophilic areas are not inked.
Improving the ink formulation and adding corresponding additives can increase the hydrophobicity of the ink, but too strong hydrophobicity will cause ink shrinkage at the edge of the image, loss of fine layers, unclear dot boundaries, etc., affecting the quality of printing.
(4) UV printing has high requirements on the surface strength of the paper. If the surface strength is not enough, it is prone to hair failure. When printing with gold or silver cardboard, the surface of this type of paper is smooth, and the affinity for the ink is small. Pull off the first color ink. Therefore, in UV printing, paper with a large surface tension should be selected, the color sequence should be reasonably arranged, and the relevant process parameters in the printing process should be adjusted to avoid and reduce the occurrence of the above phenomenon.
According to the survey, UV curing technology was applied to industrial production in the early 1960s, but it was not used by the printing industry to a limited extent until the 1970s. With the development of modern technology, UV ink and its curing and drying technology are becoming more and more perfect. In the late 1990s, UV technology was widely used in the field of offset printing. In recent years, UV offset printing has developed very rapidly, with an annual growth rate of more than 10%. In the packaging and printing field in Europe and America, UV inks account for about 65% of the total sales volume of offset printing inks.
UV inks are usually composed of pigments, pre- (oligomers), reactive diluents, photoinitiators and additives. It does not contain solvents. The solid content of the ink after curing is close to 100%, and it contains almost no VOC (organic volatiles). The process will not cause more harmful environmental pollution, without the need to invest in environmental management facilities and security protection equipment, making UV ink listed as "the most suitable environmentally friendly material." Because UV inks or varnishes do not require the use of organic solvents, they can effectively save petroleum resources, while reducing the damage to the living environment, saving costs caused by air purification, and improving working environment and health problems. Therefore, compared with traditional offset printing technology, UV offset printing technology has many obvious low-carbon printing features.
The green characteristics of UV offset printing, such as no VOC emissions, low energy consumption, and low production cost, will make it occupy a very important position in the low carbon and green road of offset printing. Because, with the development of social economy and the improvement of people's awareness of environmental protection, the low carbonization and greening of printing is the only way for the printing industry, which shows that the offset printing market is vast, and the offset printing market will definitely drive the development of the UV ink market.
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