The factors of discoloration and discoloration of prints are decomposed in detail

1. Discoloration of the ink drying process In the printing process, the freshly printed ink ink and the dried ink ink are compared. The freshly printed ink is darker. After a certain period of time, the ink will become lighter after the print is dried. This is not the problem that the ink does not resist light fade and discoloration. It is mainly the discoloration caused by the ink penetrating and oxidizing the conjunctiva during the drying process. The letterpress ink is mainly based on osmotic drying. The product that has just been printed on the printing press table has a thicker ink layer, and it takes a while for the penetrating and oxidizing conjunctiva to dry. Then, a large part of the binder in the ink will penetrate into the inside of the paper fibers, and the ink layer after drying through the oxidized conjunctiva will become thinner and the color will become lighter. This is an unavoidable phenomenon that is often seen. In the printing, the ink color should be controlled to be slightly darker than the color of the original printing sample. When the ink is dry, the color of the proof ink will be met.

The color rendering mechanism of prints is carried out by subtractive coloration. Sunlight, fluorescent lamps, incandescent lamps, and other light particles that illuminate fine particles of ink pigments. The color light reflected by the selective absorption of light by the pigment can show beautiful colors. The deeper the light passes through the ink film, The reflected color light becomes more saturated, so the ink layer is thicker and the color is deeper; the transparency of the ink is good and the color is brighter.

2, the ink itself is not resistant to light faded ink fade after light, discoloration is inevitable, all inks will have different levels of fade after light, discoloration. Light color ink fades after a long period of light exposure, discoloration is serious. Yellow, magenta, and green fade quickly, while blue, blue, and black fade slowly. The actual work in the transfer of ink, should try to use good lightfastness performance, adjust the color should pay attention to the lightfastness after the ink dilute, in the deployment of ink should also consider several colors of ink between the performance of lightfastness Sex. Outdoor advertising posters due to exposure to sunlight easily fade, we must consider the lightfastness of ink. The same blue ink, indigo blue than light blue, peacock blue light, not easy to change color. Gray can be a little black ink and white turnip ink in white ink; Emerald green available in a single color phthalocyanine green, not enough yellow, then you can add lighting resin yellow ink, if you add a little more white ink color more vivid. If you use peacock blue and chrome yellow ink, it will fade, change color, and yellow over time.

3, the acidity of the paper on the ink fade, discoloration of the general situation, the paper is weak alkaline. The ideal paper has a pH value of 7 and is neutral. Due to the need to add caustic soda (NaOH), sulfides, chlorine, and other chemicals in the papermaking process, improper handling in the pulp and papermaking process may cause paper. Acidic or alkaline. There is a certain amount of residual chlorine and organic acid in the slurry. If not properly processed, the paper produced is acidic; if alkaline fillers and colorants are used in the papermaking process, there is residue in the slurry. Alkaline solution, but without the necessary treatment, so that the resulting paper is alkaline. 1 The acidity and alkalinity of paper has a great influence on the printing process and the color durability of prints. Paper acidity and alkalinity have a direct effect on the drying of the oxidized conjunctiva of the blot, and the acid blotting of the large paper blots is particularly slow, because the acidic substances can inhibit the drying of the imprinted conjunctiva. 2 The acidity and alkalinity of the paper can also cause the ink to fade or discolor. Raw paper pH value is less than 7 is acidic, is more than 7 is alkaline, acid strong paper and due to the water bucket solution is also weak acid and other factors, it will affect the ink, make it discoloration, such as peacock blue acid after the green . 3 ink alkali resistance worse. Basically all inks will fade or change color when they encounter alkali. The chrome yellow ink base turns red, and the paper in the basket is alkaline and fades. In particular, gold ink, silver ink, and electro-aluminum foil gold foil will lose their original luster when they encounter alkaline substances. The golden light color turns into pale yellow, silver ink turns black and does not shine, and the adhesion is reduced, often resulting in scrapping of printed materials. .