3. Mixed ink
With ordinary ink printing, only after the ink film is completely dried and UV glazing can get a good glazing effect. Therefore, if on-line coating is used, the coating effect is not ideal. If you perform off-line glazing, in order to prevent back-smearing of the printed matter during the drying stage, it is necessary to spray the powder, and dusting will cause the sand surface of the original bright and smooth surface of the printed sheet to affect the appearance of the printed stencil.
Mixed ink is a new type of ink prepared by mixing ordinary ink components with UV curing materials. The ink is printed on a conventional sheet-fed press and irradiated with UV light, and then UV glazing can be performed on-line, and the UV varnish can be rapidly cured on the paper to obtain a uniform high gloss glazing effect.
Mixed ink printing has the following features:
(1) Mixed ink printing combines the characteristics of UV-cured ink and traditional offset ink, so that the ink can be UV-cured to maximize the characteristics of UV ink. The ink can be instantly cured, greatly reducing energy consumption, reducing production, storage, and disposal costs and increasing production efficiency.
(2) Mixed ink printing does not require special ink rollers, blankets, and fountain solutions. In this way, mixed inks can be used when on-line glazing is required, and ordinary inks are used when not glazing. As is the case with normal ink printing, different ink rollers, blankets, and mixed inks may have some effects when used together.
(3) Printing with mixed inks, the gloss will not fade after UV polishing, and it is especially suitable for printing products with high demand for ink coverage.
(4) The ink balance of the mixed ink is relatively easy to control. Because the UV component in the mixed ink does not cure without being irradiated by the UV lamp, the mixed ink is always flowing on the printing machine and does not cause crusting on the ink roller like a normal ink and causes a printing failure.
(5) Printing with Mixed Ink Due to instant drying, UV coating can be applied on-line on the press without the need for water-based varnishes. The print quality is no worse than ordinary offset inks.
(6) The mixed ink can print clear dots and improve the printing quality.
(7) At present, most CTP plates should not be printed using UV inks, but they can be printed using mixed inks.
(8) Less investment with mixed inks. For printers that already have UV technology, they only need to purchase a mixed ink. For printers that do not use UV technology, after investing in mixed inks, they only need to invest in UV curing equipment and UV lamps.
(9) The mixed ink has a wide range of applications, and is suitable for printing on plastics, aluminum foils, metallic papers and other very absorbent substrates, in addition to printing on paper. Solved the problem of ink drying on non-absorbent substrates.
(10) In addition to the use of sheetfed printers, mixed inks can also be used in narrow web presses.
Mixed inks are now being used more and more to print products with high gloss requirements, such as photo albums, pharmaceuticals, and cosmetic packaging boxes.
4. New 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, monomer adsorption will no longer occur. To the surface phenomenon. 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 diluent
Many acrylic acid functional monomers used as reactive diluents, due to their high toxicity, have a large effect on 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. New Photoinitiator
Acylphosphine oxide photoinitiators are currently being developed for the purpose of curing the depth of the ink film and the colored film layer well. 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 photoinitiators are small molecule photoinitiators,
It is easy to volatilize and migrate during storage, resulting in low photopolymerization efficiency, unpleasant odor, and even toxicity, which affects 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 high efficiency. 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 lamps. 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.