Prints that use UV glazing sometimes appear yellowing. There are two main reasons: one is that the UV glazing oil itself yellows; the second 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 influence of photoinitiators is also great. Some photoinitiators will make the system yellow after curing, such as benzoin dimethyl ether, so you should avoid using such photoinitiators to prepare varnishes.
During the glazing process, if the interior of the glazing oil is not completely cured, the glazing oil thinner inside it will gradually be absorbed by the ink and paper, and at the same time it will act on the binder in the ink, causing the loss of grease. 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 curing speed of UV varnish should be increased or an efficient ultraviolet curing light source should be selected. In addition, the use of water-based UV varnish can avoid the chemical effect of the thinner Liu ink layer and paper coating, and can avoid the yellowing of printed products.
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