4. Novel oligomers Currently, low-viscosity oligomers have been developed and used in UV inks to reduce the amount of reactive diluents in the ink that are irritating to the skin, and if printed on porous substrates, not Monomer adsorption onto the surface will occur again. Recently, the United States has developed a new type of flexographic printing UV ink based on acrylic polyester, which does not include monomer components and thus eliminates the hazards of monomer transfer to food. The use of low-viscosity oligomers is very beneficial for the formulation of low-viscosity gravure UV inks and flexo-printing UV inks, and in particular inkjet ink UV inks, which are now gaining momentum. In addition, with the development of cationic oligomers and aqueous oligomers in the UV curing field, cationic photocuring systems, free radical/cationic photocuring systems, and waterborne UV inks have been developed to improve the performance and application of UV inks. range.
5. New reactive diluents Many acrylic functional monomers used as reactive diluents, due to the greater toxicity, the impact of the application of large skin irritation. However, the toxicity and skin irritation of the monomers after alkoxylation are greatly reduced. Many alkoxylated acrylic functional monomers are currently developed. Another class of newly developed reactive diluents are vinyl ether monomers, which have the advantages of low viscosity, high activity, weak toxicity, and low irritation to the skin. At the same time, these monomers can both undergo radical photo-curing reactions and cationic photo-curing reactions, making them very promising reactive diluents. In addition, there are some cationic cationic reactive diluents that are suitable for UV ink printing.
6. Novel Photoinitiators Acylphosphine oxide photoinitiators are currently being developed for the deep curing of the ink film and the colored film layer. It has good absorption of 400nm light wave, high photoinitiating efficiency; the generated radical absorption shifts to shortwave, has a "photobleaching" effect, is beneficial to the photocuring reaction in the depth of the ink film; the final product is colorless, so No yellowing, it is very suitable for screen printing UV ink with thick ink film. There are also newly developed organic metal photoinitiators for such photoinitiation.
Since most of the photoinitiators are small molecule photoinitiators, they tend to volatilize and migrate during storage, resulting in low photopolymerization efficiency, unpleasant odors, and even toxicity, affecting the use of UV inks in food packaging. At present, some low-odor, non-toxic photoinitiators have been developed. For example, polymer photoinitiators, which have better performance, can reduce the migration. At the same time, the polymer photoinitiator also has the following characteristics: by adjusting the distance between the photosensitive groups, a polymer photoinitiator with different reactivity can be obtained; the synergistic effect of the photoactive group can be utilized to improve the photosensitivity; and the ink layer can be prevented from yellowing. Change and aging. UV inks using polymer photoinitiators can be used for food packaging printing and have good curing properties.
In addition, with the development of aqueous photoinitiators, cationic photoinitiators, complex photoinitiators, and hybrid photoinitiators, the performance of UV inks has been further enhanced and the range of applications has been further expanded. Among them, the composite photoinitiator is a combination of a radical photoinitiator and a cationic photoinitiator, and the UV photocuring speed using the complex photoinitiator has been greatly improved; and the hybrid photoinitiator is under UV light, both It can generate free radicals and generate cations. UV inks that use hybrid photoinitiators can overcome the inhibition of free radicals by oxygen and the sensitivity of cationic polymerization to water, and increase the curing degree and physical and chemical properties of the ink film.
7. New UV curing light source 1) The electrodeless mercury lamp can be switched instantaneously, with long life and great efficacy. Unlike the spectrum of medium-pressure mercury lamps, the spectrum of UV-cured electrodeless mercury lamps is a continuous spectrum that can be used for curing thicker ink films.
2) New LED UV curing light source. Light-emitting diodes have many advantages, such as: instant on and off, more than 50,000 hours of lighting life, low operating voltage, low electrical loss, and continuous energy output, etc. It can be said to be very convenient and economical to use. This kind of light source itself generates little heat and is ideal for drying temperature-sensitive prints. The light emitting diode emits almost monochromatic light (half peak of the emission wavelength is about 25μm), and for special UV curing, the emission wavelength can reach 450nm.
3) Excimer light. The so-called excimer (stimulated dimer, trimer) is a molecular form that has no stable ground state but exhibits only a weak bond excited state. Some of the important excimer molecules are formed by the electron excitation of noble gases, rare gas chlorides, halogens, and mercury and halogen mixtures. Currently, several excimer lamp products have been developed, mainly including light sources emitting UV light at wavelengths of 172 nm, 222 nm, 308 nm, and 351 nm. Excimer lamps have a very narrow band and are highly energetic, allowing UV inks to cure quickly. An excimer lamp with a wavelength of 172 nm can directly activate the acrylate. The energy generated by a cesium chloride excimer lamp at a wavelength of 308 nm enables the UV ink to cure quickly. In addition, excimer lamps do not generate ozone during the curing of UV inks and do not transfer heat to substrates and production equipment. It is reported that an excimer lamp with a wavelength of 308 nm is particularly effective for the curing of cationic UV curable UV inks.
5. New reactive diluents Many acrylic functional monomers used as reactive diluents, due to the greater toxicity, the impact of the application of large skin irritation. However, the toxicity and skin irritation of the monomers after alkoxylation are greatly reduced. Many alkoxylated acrylic functional monomers are currently developed. Another class of newly developed reactive diluents are vinyl ether monomers, which have the advantages of low viscosity, high activity, weak toxicity, and low irritation to the skin. At the same time, these monomers can both undergo radical photo-curing reactions and cationic photo-curing reactions, making them very promising reactive diluents. In addition, there are some cationic cationic reactive diluents that are suitable for UV ink printing.
6. Novel Photoinitiators Acylphosphine oxide photoinitiators are currently being developed for the deep curing of the ink film and the colored film layer. It has good absorption of 400nm light wave, high photoinitiating efficiency; the generated radical absorption shifts to shortwave, has a "photobleaching" effect, is beneficial to the photocuring reaction in the depth of the ink film; the final product is colorless, so No yellowing, it is very suitable for screen printing UV ink with thick ink film. There are also newly developed organic metal photoinitiators for such photoinitiation.
Since most of the photoinitiators are small molecule photoinitiators, they tend to volatilize and migrate during storage, resulting in low photopolymerization efficiency, unpleasant odors, and even toxicity, affecting the use of UV inks in food packaging. At present, some low-odor, non-toxic photoinitiators have been developed. For example, polymer photoinitiators, which have better performance, can reduce the migration. At the same time, the polymer photoinitiator also has the following characteristics: by adjusting the distance between the photosensitive groups, a polymer photoinitiator with different reactivity can be obtained; the synergistic effect of the photoactive group can be utilized to improve the photosensitivity; and the ink layer can be prevented from yellowing. Change and aging. UV inks using polymer photoinitiators can be used for food packaging printing and have good curing properties.
In addition, with the development of aqueous photoinitiators, cationic photoinitiators, complex photoinitiators, and hybrid photoinitiators, the performance of UV inks has been further enhanced and the range of applications has been further expanded. Among them, the composite photoinitiator is a combination of a radical photoinitiator and a cationic photoinitiator, and the UV photocuring speed using the complex photoinitiator has been greatly improved; and the hybrid photoinitiator is under UV light, both It can generate free radicals and generate cations. UV inks that use hybrid photoinitiators can overcome the inhibition of free radicals by oxygen and the sensitivity of cationic polymerization to water, and increase the curing degree and physical and chemical properties of the ink film.
7. New UV curing light source 1) The electrodeless mercury lamp can be switched instantaneously, with long life and great efficacy. Unlike the spectrum of medium-pressure mercury lamps, the spectrum of UV-cured electrodeless mercury lamps is a continuous spectrum that can be used for curing thicker ink films.
2) New LED UV curing light source. Light-emitting diodes have many advantages, such as: instant on and off, more than 50,000 hours of lighting life, low operating voltage, low electrical loss, and continuous energy output, etc. It can be said to be very convenient and economical to use. This kind of light source itself generates little heat and is ideal for drying temperature-sensitive prints. The light emitting diode emits almost monochromatic light (half peak of the emission wavelength is about 25μm), and for special UV curing, the emission wavelength can reach 450nm.
3) Excimer light. The so-called excimer (stimulated dimer, trimer) is a molecular form that has no stable ground state but exhibits only a weak bond excited state. Some of the important excimer molecules are formed by the electron excitation of noble gases, rare gas chlorides, halogens, and mercury and halogen mixtures. Currently, several excimer lamp products have been developed, mainly including light sources emitting UV light at wavelengths of 172 nm, 222 nm, 308 nm, and 351 nm. Excimer lamps have a very narrow band and are highly energetic, allowing UV inks to cure quickly. An excimer lamp with a wavelength of 172 nm can directly activate the acrylate. The energy generated by a cesium chloride excimer lamp at a wavelength of 308 nm enables the UV ink to cure quickly. In addition, excimer lamps do not generate ozone during the curing of UV inks and do not transfer heat to substrates and production equipment. It is reported that an excimer lamp with a wavelength of 308 nm is particularly effective for the curing of cationic UV curable UV inks.
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