UVLED double coating system means that two coating units are usually located at the end of the printing press. In order to eliminate or reduce the loss of gloss, the possibility of UV varnish penetrating into the ink or the substrate, a layer of aqueous varnish must be applied between the wet UV offset ink and the final UV varnish to isolate the UV offset ink, and When drying with infrared or thermal radiation, it can be used as the basis for UV varnish adhesion. At the same time, each glazing unit must have an integrated drying device, which increases the size and equipment cost of the printing press, but the gloss range that the UVLED double glazing machine can achieve is larger than that of the pure UV printing machine.
In addition to the use of water-based glazing oil plus UV glazing oil, the UVLED dual glazing system can also be used to apply the same water-based glazing oil twice. For example, in order to improve the final gloss, two layers of glazing are applied on the substrate Oil, etc .; or applying two different varnishes, such as applying standard varnish through the first varnishing unit and applying special effect pigments through the second varnishing unit. There is another type of UVLED double glaze printing machine, that is, a flexographic printing unit and a drying device are installed before the first offset printing unit, so as to apply an opaque white or special effect primer.
Prints that use the UVLED dual glazing system sometimes exhibit yellowing. There are two main reasons: one is that the UV glazing oil itself turns yellow; the other is that during the glazing process, the glazing oil only solidifies on the surface of the printed product. The interior is not completely cured. The yellowing of varnish is related to the oligomer and reactive diluent used in it have a certain yellow color. Therefore, colorless oligomer and reactive diluent should be used to prepare varnish. In addition, the photoinitiator of the UVLED dual glazing system also has a great influence. Some photoinitiators will make the system yellow after curing, such as benzoin dimethyl ether, so you should avoid using such photoinitiators to formulate varnishes.
During the UV glazing process of the UVLED dual glazing system, when the glazing oil is not completely cured, the glazing oil thinner inside it will be gradually absorbed by the ink and paper, and at the same time it will act on the binder in the ink and cause the oil to lose . The pigment is not sufficiently protected, and the pigment particles are free. At this time, the smoothness of the surface of the paper coating and the ink layer will decrease. The rough surface will diffuse light reflection, so adding some white components of the plant to the color will increase the brightness and decrease the saturation, giving the overall feeling of yellowing and lightening of the color. Therefore, the UVLED dual glazing system should increase the curing speed of the UV varnish or select an efficient ultraviolet curing light source; in addition, the use of aqueous UV varnish can avoid the chemical effects of the thinner Liu ink layer and paper coating, which can be avoided Yellowing of printed matter.
Advantages of UVLED double coating system:
(1) No environmental pollution, no solvent volatilization, both safe and environmentally friendly
(2) Fast drying speed and high production efficiency. Since the photo-curing reaction can be completed in an instant, the UV varnish can be directly stacked or enter the next process after printing and curing, which speeds up the production process and improves the production efficiency
(3) Not limited by the type of substrate, not only can be used for glazing on the surface of paper, aluminum plate, plastic materials, etc., but also used for glazing on the surface of polymer boards, furniture, metal materials, wireless materials, etc.
(4) The volume of the UV curing machine is small, and the effective utilization rate is high. Therefore, the site and energy are greatly saved, and the investment in equipment in the early stage is reduced.
(5) The surface of the printed matter after UV glazing has high hardness, is resistant to friction, is not prone to scratches, and has strong chemical resistance.
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