Analysis on the technical characteristics of UV in

2022-08-12
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Analysis: technical characteristics of UV ink (Part 2)

4 New oligomers

at present, low viscosity oligomers have been developed and applied in UV inks, which can reduce the amount of active diluent in the ink that is irritating to the skin, and if printed on porous substrates, monomers will no longer be adsorbed to the surface. Recently, the United States has developed a new type of flexographic printing based on acrylic polyester. The U frequency can also be set freely for V ink, which does not contain monomer components, so the harm caused by the transfer of monomer to food can be eliminated. The use of low viscosity oligomers is very conducive to the preparation of low viscosity gravure UV inks and flexographic UV inks, especially inkjet UV inks, which are now developing rapidly. In addition, with the development of cationic oligomers and aqueous oligomers in the field of UV curing, cationic UV curing system, free radical/cationic composite UV curing system and aqueous UV ink have been developed, which improves the performance and application range of UV ink

5. New active diluent

many acrylic functional monomers used as active diluents affect their application due to their high toxicity and skin irritation. However, the toxicity and skin irritation of the monomer are greatly reduced after alkoxylation. At present, many functional monomers of alkoxylated acrylic acid have been developed. Another newly developed active diluent is vinyl, and the straight-line distance between the two ends of the crack is taken as the crack length. Ether monomers have the advantages of low viscosity, high activity, weak toxicity and low irritation to the skin. At the same time, it is also an enterprise for the comprehensive utilization of lithium renewable resources and the specialized supply of butyl lithium. The monomers can not only undergo free radical light curing reaction, but also cationic light curing reaction. They are very promising active diluents. In addition, some cationic active diluents suitable for UV ink printing have been developed

6. New photoinitiator

in order to make the ink film deep and the colored film solidify well, acyl phosphorus oxide photoinitiator has been developed at present. It has good absorption of 400nm light wave and high photoinitiation efficiency; The generated free radical absorption moves to the short wave, which has the effect of photobleaching, which is conducive to the light curing reaction deep in the ink film; The final product is colorless, so it does not turn yellow. It is very suitable for printing UV inks with thick ink film. There are also organometallic photoinitiators developed recently

because most photoinitiators are small molecular photoinitiators, they are volatile and migrate easily with a capacity of 20 ~ 77hr45n during storage, resulting in low photopolymerization efficiency, unpleasant smell and even toxicity of products, which affects the use of UV ink in food packaging. At present, some low odor and non-toxic photoinitiators have been developed. For example, polymer photoinitiator has better performance and can reduce migration. At the same time, polymer photoinitiators also have the following characteristics: by adjusting the distance between photosensitive groups, polymer photoinitiators with different reaction activities can be obtained; Using the synergistic effect of photoactive groups to improve photosensitivity; Prevent the yellowing and aging of the ink layer. UV ink with polymer photoinitiator can be used in the printing of food packaging, and has good curing performance

in addition, with the development of aqueous photoinitiators, cationic photoinitiators, composite photoinitiators and hybrid photoinitiators, the performance of UV inks has been further improved and the scope of application has been further expanded. Among them, the composite photoinitiator is the combination of free radical photoinitiator and cationic photoinitiator. The curing speed of UV ink with composite photoinitiator has been greatly improved; The hybrid photoinitiator can generate both free radicals and cations under UV light. The UV ink with hybrid photoinitiator can overcome the polymerization inhibition of oxygen on free radicals and the sensitivity of cationic polymerization to water at the same time, and improve the curing degree and physicochemical properties of the ink film

7. New UV curing light source

1) electrodeless mercury lamp can be switched on and off instantaneously, with long service life and great efficiency. Different from the spectrum of medium pressure mercury lamp, the spectrum of electrodeless mercury lamp used for UV curing is a continuous spectrum, which can be used for the curing of thicker ink film

2) new LED UV curing light source. Light emitting diodes have many advantages, such as instant on and off, more than 50000 hours of lighting life, low operating voltage, low electrical loss, and continuous energy output. It can be said that they are very convenient and economical to use. This kind of light source has a small calorific value, which is very suitable for the drying of temperature sensitive printing materials. Almost all light-emitting diodes emit monochromatic light (the half peak of the emission wavelength is about 25 m). For UV curing with special requirements, the emission wavelength can reach 450nm

3) excimer lamp. The so-called stimulated excimer (stimulated dimer, trimer) is a molecular form with no stable ground state but only weak bond excited state. Some important excimers are formed by electron excitation of rare gases, rare gas chlorides, halogens, and mixtures of mercury and halogens. At present, several excimer lamps developed are mainly light sources with UV light emission at wavelengths of 172nm, 222nm, 308nm and 351nm. Excimer lamp has extremely narrow band distribution and high energy, which can make UV ink cure quickly. An excimer lamp with a wavelength of 172nm can activate acrylate directly. A xenon chloride excimer lamp generates energy at the wavelength of 308nm, which can quickly cure UV ink. In addition, the excimer lamp does not produce ozone during the curing process of UV ink, and there is no heat transfer to the substrate and production equipment. It is reported that the excimer lamp with a wavelength of 308nm is particularly effective for the curing of UV inks in cationic light curing system

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