First, the ink is not resistant to light discoloration and fading
Under the direct irradiation of sunlight, its hue and brightness will change to different degrees. An ink that is absolutely resistant to light without changing its tone cannot be found. Under the action of strong sunlight, the tone of all inks may change to a different extent. This change can be divided into two types.
1. Fading: under the action of sunlight and ultraviolet rays, the light resistance of the ink is relatively poor, the original bright luster is lost, and the color becomes pale and gray white. Especially for light tone ink and four-color printing plate, yellow and red fade faster, while cyan and black fade slower.
2. Discoloration: on the contrary to the fading of ink color of self-adhesive printing, the tone changes to dark and the color changes under the action of sunlight. People call this kind of transformation discoloration.
Secondly, the characteristics of paper
Surface smoothness of paper. The smoothness of paper surface is closely related to the reproduction of impression. The paper is not smooth. Generally, it needs a lot of pressure to make it better contact with ink. For example, the ink viscosity, fluidity and ink layer thickness maintain a corresponding amount, and increasing the pressure often increases the printing spreading area. At the same time, the low concave parts of the paper are still in poor contact.
Absorption of paper. The absorbability of paper is also directly related to the reproduction effect. Usually, when self-adhesive printing loose paper, if the ink fluidity is large and the viscosity is small, the paper will absorb more ink layer connecting materials. If the diameter of pores is larger than the diameter of pigment particles, even pigments will be sucked in, which will reduce the saturation of imprinting. The thickness of the ink layer needs to be properly increased.
Finally, the influence of paper permeability on color
The relatively large permeability of the paper will reduce the thickness of the ink layer, and the large pores on the surface of the paper will still make some pigment particles penetrate into the paper, so the color will feel lighter. Therefore, when using paper with rough surface and loose texture, and paper with large ink fluidity, special attention should be paid to discoloration.