Under the factors of color change of the hottest p

2022-08-22
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Factors affecting the color change of printed matter (Part 2)

IV. The Influence of heat resistance of pigments

during the drying process of inks, fast drying bright offset printing inks are oxidized conjunctival drying. There is a fixed stage before drying. The oxidation polymerization of inks is an exothermic reaction. When drying too fast, it will release a lot of heat. If the heat is dissipated slowly, it will make the heat-resistant pigments change color. For example: the golden color ink darkens and loses the golden light

during printing, the printing sheets are stacked on the paper receiving table. Due to excessive stacking, the printing sheets in the middle are oxidized, polymerized and exothermic reaction of the ink, the heat is not easy to dissipate, the temperature is too high, and the middle part changes color more. Therefore, when it is found that the printing sheets are overheated, try to dissipate heat in time to prevent discoloration, do not put excessive desiccants (red and white dry oil) in the ink, do not stack the printing sheets too high, and use wood plywood to isolate and stack them, Ventilation and other methods to reduce color discoloration after heat resistance

v. the influence of dry oil on the discoloration of imprints

the ink with light color belongs to the cold color, and the interchromatic ink such as emerald green and lake blue should not use red dry oil, because the red dry oil itself has a deep purplish red, which will affect the color of the light color ink, so it is best to use white dry oil for the ink with light color to avoid the influence of dry oil on its ink color. The white dry oil looks white, but it turns pale brown after oxidizing the conjunctiva. If the amount of white dry oil is large, it is estimated that the sensor will turn yellowish brown after being successfully used in human finger twists and turns activity monitoring and facial muscle stretch monitoring; For dark color inks such as cyan, black, purple and other colors, the color of red dry oil ink will not be greatly affected

VI. influence of ink alkali resistance

pH value of paper used for printing =7, neutral paper is ideal. In general, the alkali resistance of the ink produced by inorganic pigments is relatively poor, and the alkali resistance of organic pigments is better, especially the medium blue and dark blue ink will fade when exposed to alkali, the medium yellow ink will turn red when exposed to alkali, and the hot stamping electrochemical aluminum foil will turn antique yellow when exposed to alkaline substances, so that it has no gloss. Often the paper is weak and alkaline, and alkaline adhesives are encountered in the later binding production of printing, If the packaging and decoration printing products are soap, soap, washing powder and other substances used to package alkaline substances, we should consider that the alkali resistance and saponification resistance of the ink are strong, and the alkali resistance of Malachite blue ink is good

VII. Discoloration factors of paper during storage and use

most printing products will inevitably show yellowing after long-term storage, for the following reasons

① the fibers of paper contain lignin, which plays a leading role in the structural reform of the supply side. It turns yellow and is easy to be brittle. For example, paper printed newspapers are most likely to turn yellow and brittle

② most of the color printing products are made of (6) low-carbon materials of light sources, which make home appliances more practical. Under direct irradiation, the paper packaging market is expanded due to long-term, wind and rain, temperature and humidity erosion, and the ink and pigment become colored or fade due to their lightfastness

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