Why does the outer packaging ink fade?

　　The fading and discoloration of printing products are mainly caused by the ink performance, but some are caused by the art of the printer, and the ink is also easy to cause fading and discoloration when encountering acids, bases, sulfides, alcohols, such as methanol, ethanol (alcohol), glycerol, surfactants and other chemicals:

　　1. Ink penetration and conjunctival discoloration: during the printing process, the ink color of the printed matter is dark when it is first printed. However, after a period of time, the ink color will become pale, which is not the reason why the ink is not light resistant, but mainly the reason why the ink penetrates and the conjunctiva during the drying process. The light shines on the pigment particles through the connecting material, and the colored light reflected after the selective absorption of sunlight by the pigment presents color. The deeper the light passes through the ink film, the more saturated the colored light will be reflected. Therefore, the thicker the ink layer is, the thicker the color is, and the more transparent the color is. The newly printed product has a thick ink layer. However, after drying, a large part of the binder in the ink will penetrate into the interior of the paper fiber, so the ink layer after drying should be thinner, so that the color will become lighter. When printing, the color should be slightly thicker than the original color sample, so the ink will meet the requirements of the original color after drying.

　　2. Discoloration of printing ink due to lightfastness: We should try to use printing ink with good lightfastness when adjusting printing ink. Any printing ink will fade to varying degrees under sunlight or other light sources. When preparing light color printing ink, we should estimate the lightfastness of printing ink after being diluted. For example, light lake blue is better to use phthalocyanine blue than malachite blue, because phthalocyanine blue is more light resistant and not easy to change color. Gray ink can add black ink and phthalocyanine ink slightly in white ink; The emerald green color can be monochrome phthalocyanine green. If it is not yellow enough, you can add bright resin yellow ink. If it is bright enough, you can add white ink. If you add chrome yellow ink to malachite blue, it will become yellow for a long time.

　　If the products we print are advertising pictures, publicity pictures, New Year pictures, etc. pasted outdoors, because these products are directly exposed to the sun, under the action of ultraviolet rays in the sun, wind and rain, the bright colors that have been printed for a long time are easy to fade. It is found that only the black and blue ink still exists. Light color, yellow ink and red ink all fade. Therefore, in order to reduce the fading after solar ultraviolet radiation, it is better to print the y and m colors first in the color sequence of four color overprint, and then print the C and BK colors at the back. In this way, the overprint of the last C and BK colors has the effect of light resistance and heat resistance, so as to reduce the fading of printed products.

　　3. Loose and rough discoloration of paper: If the smoothness of the printed paper is poor, and the surface of the paper is rough and loose, such as offset paper, relief paper, newsprint, kraft paper, etc., the paper is highly absorbent, and the particles of ink pigment are small. In the slow drying process, the ink is gradually absorbed by the paper along with the connecting material, so the ink color becomes light. The paper's absorption of ink and the increase of the ink's penetration into the paper will lead to the separation of the binder and the pigment, which will cause the ink film to become thinner, discolored, and poor gloss. To reduce the paper's absorption and penetration time, it is necessary to increase the drying speed accordingly, and increase the amount of red and white dry oil in the ink.

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