When the ink is irradiated by sunlight, its color and brightness will change to different degrees. There is no ink that is absolutely light-resistant and does not change the hue. Under the strong sunlight, the color of all inks will change to different degrees. This change can be divided into two types.

Offset printing plates are inseparable from the use of wetting fluid to wet the blank parts of the printing plates. Offset printing is watered first and then inked. Emulsification is inevitable when water is used.

The color of the ink will lighten after emulsification, but it can restore the original color after the water evaporates. Therefore, the greater the water, the greater the amount of emulsification, which will cause discoloration. In particular, color and ink with completely different emulsification degrees are mixed together, and the phenomenon of discoloration is particularly prominent.

The smoothness of the paper surface is closely related to the imprint copying. The uneven paper surface often requires a lot of pressure to make the ink have good contact with it. For example, the ink viscosity, fluidity, and ink layer thickness are maintained at a certain amount. Increasing the pressure often increases the spreading area of the print. At the same time, the concave parts of the paper are still in poor contact, such as: coated paper and newsprint printed on the same printing plate If the imprinting effect is quite different, the different copying effects can be clearly compared.

The absorbency of the paper is also directly related to the copying effect. Usually when printing loose-textured paper, if the ink fluidity is large and the viscosity is small, the paper will absorb more ink layer binder, if the diameter of the pores Larger than the diameter of the pigment particles, then even the pigment will be inhaled, which reduces the saturation of the print. Need to appropriately increase the thickness of the ink layer.

However, increasing the thickness of the ink layer will cause "spreading" at the moment of imprinting, which will affect the effect of print copying. Paper with low absorption can make most of the ink film appear on the surface of the paper, so that the imprinted ink layer has better saturation.

The high permeability of the paper will reduce the thickness of the ink layer and the large pores on the surface of the paper. It will also cause part of the pigment particles to be penetrated into the paper at the same time, so the color and luster will have a lightening feeling. For this reason, use paper with rough surface and loose texture, and paper with high ink fluidity, pay attention to discoloration.

In the drying process of the ink, the bright and fast-drying glue printing ink is mainly dried by the oxidized conjunctiva type. Before the offset printing ink is dried, there is a fixation stage. The oxidative polymerization of the ink is an exothermic reaction. If it dries too fast, it will release a lot of heat. If the heat is dissipated slowly, it will change the color of the heat-labile pigment.

For example: the golden color ink becomes darker and loses its original luster.

During printing, the printed sheets are stacked in piles on the delivery table. Due to the excessive stacking, the printing ink in the middle part of the printed sheet is oxidized and polymerized to exothermic reaction, and the heat is not easy to dissipate. If the temperature is too high, the middle part discolors more.

Light color inks are cool colors, light yellow, emerald green, turquoise and other intermediate color inks, do not use red dry oil, because red dry oil itself has a darker purple-red color, which will affect the color of light color ink.

The white dry oil looks white, but after oxidizing the conjunctiva, it is light brown. If the amount of white dry oil is large, the blot may become yellowish-brown if it dries up, and the dark color inks such as blue, black and purple will be dried with red The oil color will not be greatly affected.

The pH value of the printed paper is 7, and the neutral paper is the most ideal. Generally, the ink made of inorganic pigments is less resistant to acid and alkali, and the organic pigments are more resistant to acid and alkali, especially the medium blue and dark blue inks meet alkali. It will fade.

The color of the medium yellow becomes reddish when encountering alkali, while the hot-stamped electrochemical aluminum foil and printed gold will turn into pale yellow when encountering alkaline substances. For alkaline adhesives, if the packaging and decoration printing products are packaging alkaline substances such as soap, soap, washing powder, etc., the alkali resistance and saponification resistance of the ink must be considered.

Most printed products will inevitably appear yellowish in long-term storage. The reasons are as follows.

The fiber in the paper contains a lot of lignin and changes color. For example, newspapers printed on newsprint are the easiest to turn yellow and become brittle.

Most of the color printing products of offset printing four-color dot overprinting are under the sunlight, weather, wind and rain, outdoor high temperature erosion, etc., because the pigments are not light and heat resistant, they change color or fade.