The main components of UV inks include pigments, oligomers, monomers (active diluents), photoinitiators and various additives. Among them, the resin and the reactive diluent play a role of fixing the pigment and providing the film forming property; the pigment gives the ink a moderate color and hiding power to the substrate; and the photoinitiator requires that the photon-induced polymerization can still be absorbed under the interference of the pigment. UV printing application market from the printing process, UV ink fixation speed, good film performance, good adhesion to various types of substrates, and scratch resistance, abrasion resistance, acid, alkali and other properties are more common The ink is good, so although it is much more expensive than ordinary ink, it is still widely used. The following categories are currently used in the field of UV ink printing.

1. Non-absorbent materials such as polyethylene (PE) film, polyvinyl chloride (PVC) film, polypropylene (PP) film, metal foil, and non-absorbent special materials. If these substrates are printed with common solvent inks, they will require a certain amount of drying time. Usually, dusting, drying racks, or other additives are added to the inks. UV inks do not have such problems at all.

2. Metal material printing When UV ink printing is used on the surface of metal materials, the curing process can be shortened and the original curing device can be simplified. At the same time, the good curability and conjunctival properties of the UV ink surface can not only improve post-printing processing characteristics, but also improve the appearance quality of the product.

3. Printing of Commercial Paper Printing Commercial paper printing materials and inks used for printing are special, such as carbonless paper, thermal paper, magnetic ink, anti-counterfeiting ink, etc., and require inks with certain resistance to discoloration, heat resistance and stability. Therefore it is best to use UV inks or UV Varnish. At the same time, due to the speed of ticket printing equipment and the small amount of ink, it also has the advantage of using UV ink printing.

UV printing process adaptability

1.UV offset printing

Offset printing can be divided into sheetfed offset printing and web offset printing according to the status of the substrate. Sheetfed offset printing is suitable for printing on paper, cardboard, plastic sheet and metal foil; web offset printing is faster, suitable for large-volume books and newspapers. , business forms and sticker printing. The use of UV inks in offset printing mainly considers the following issues: ink curing of non-absorbing substrates; ink emulsification may hinder the adhesion of inks to substrates; web presses are fast and require ink curing speed and printing speed. Matching, especially for adhesive printing and security printing using special inks, UV inks print better than resin offset inks.

Offset printing is used for printing of fine products. UV curing can reduce the loss of fine dots and increase the ink transfer rate of overprinting. When selecting the ink raw materials, the effects of each component on the UV ink must be comprehensively considered to ensure the best printing effect. Because offset ink film is generally 2 ~ 3μm, although beneficial to light curing, but the ink film is thin, the hiding power of the pigment on the printing surface will be affected, so generally to increase the pigment content in the formula; and increase the pigment content, ink film The light transmission performance will be reduced, not conducive to UV curing; and the ink film itself is thin, if the pigment wettability is not good, pigments, fillers are easily exposed to the ink film surface, affecting the ink film gloss, so choose to disperse more Good paint. The following points should also be noted when using UV offset printing.

(1) Different types of substrates should be selected for different inks. The light transmittance, the curing rate, the hiding of the ink, and the glossiness of the surface of the ink should be taken into consideration.

(2) In color printing, the ability of various pigments to absorb UV photons is different, and their transmittance is from high to low as M, Y, C, BK, so the curing degree of each color ink is also different. The transmittance directly affects the photon's excitation energy of the photoinitiator. Therefore, the printing color sequence should be ranked as BK, C, Y, and M, so that the ink with poor light transmission can absorb as many photons as possible to enhance the curing effect.

(3) The use of the alcohol dampening system can reduce the surface tension of the ink and promote the curing effect. In the printing process, the dampening area (blank portion) of the printing plate can be intensified with a fountain solution to ensure that the lipophilic area is adequate. Intimate ink, the hydrophilic area does not ink.

Improve the ink formulation and add the appropriate additives can increase the hydrophobicity of the ink, but the hydrophobicity will lead to ink shrinkage of the edge of the image, the loss of fine levels, dot boundaries are not clear, affect the quality of printed products.

(4) UV printing has high requirements on the surface strength of the paper, and the surface strength is not enough to cause pulling faults. When printing with gold or silver cardboard, the surface of such paper is smooth, and the affinity for ink is small, and the second color is easy to overprint. Pull out the first color ink. Therefore, in UV printing, papers with large surface tension should be selected, and the color sequence should be properly arranged to adjust the relevant process parameters in the printing process so as to avoid and reduce the above phenomenon.

2.UV flexo printing

Flexographic printing is a kind of printing technology that has developed rapidly in recent years. The graphic and textual parts of the printing plate are higher than the non-graphical parts, and they are flexible. They can express the subtle levels and outlines of the graphic parts. In addition, its applicable printing materials are very extensive, in addition to the traditional paper, some non-absorbable printing materials, such as plastic film, aluminum foil composite paper, glass paper, etc. can also use flexographic printing. The use of UV ink for flexographic printing, in addition to attention should be paid to coloring, curing and adhesion problems, but also must pay attention to ink components on the ink viscosity, rheological effects in order to obtain better printability and stability.

The flexographic printing process determines that the UV ink used should not have a high viscosity. Conventional flexo printing inks are solvent-based and water-based. They require a large amount of solvent or water to adjust the viscosity. Due to the large amount of solvents used, most flexographic printing inks are similar to Newtonian fluids in terms of rheology, causing ink settling and instability. Therefore, imparting appropriate thixotropy to the flexographic printing ink can prevent the pigment flocculating from settling.

UV flexographic printing inks use reactive diluents to reduce the viscosity of the system, and therefore their viscosity may generally be higher than solvent-based flexographic printing inks. Although the viscosity of UV flexo printing inks is lower than that of screen printing and offset printing inks, the addition of pigments will increase the viscosity, especially when the wetting, dispersion, and stability of the pigments are not handled properly. In addition, the influence of pigments on the rheological properties of inks is more important, and the appropriate thixotropy is beneficial because when there is a degree of pseudo-plasticity in the cross-linking of the molecules inside the ink, there is no ink dispersion system for pigment dispersion stabilizers. The viscosity of the ink roller on high-speed operation will drastically drop, but when the ink roller enters the printing position where the ink roller enters a relatively low speed, the viscosity will quickly rise and the wetting effect on the surface of the substrate will be too poor to be suitable for printing. The ink containing a suitable dispersion stabilizer has a certain stability, and its own viscosity is not high, after a high shear, the viscosity rises slowly and the printing adaptability is better.