During the printing and storage of printed materials, the hue, lightness, and saturation often change. Whether it is a single-color ink, or an ink of more than two colors, the color may become darker under the internal and external effects. May fade. The standard of high-quality printed matter is: the ink color of a batch of products should be consistent before and after, and the color should be bright, and at the same time, it should meet the ink hue and ink color of the proof. There are many factors that affect the color change of printed matter, and there are roughly the following aspects.
First, the ink is not resistant to light discoloration and fading
Under the sunlight, the color and brightness of the ink will change to different degrees. There is no ink that is absolutely light-fast without changing the hue. Under the strong sunlight, all ink colors will change to varying degrees. This change can be divided into two types.
1. Fading: Under the action of sunlight and ultraviolet light, the ink has poor light resistance, loses its original bright color, and becomes paler in color. Especially for light-colored inks and four-color process printing, the yellow and red colors fade faster, while the cyan and ink colors fade more slowly.
2. Discoloration: Contrary to the black fading of printed matter ink, the color changes deeper and darker under the influence of sunlight, and the color also changes. People call this change discoloration.
Second, the effect of emulsification on the color of the imprint
Offset printing plates are inseparable from moistening the blank part of the printing plate with wetting fluid. Offset printing is to apply water first and then inking. It is inevitable that emulsification will occur when using water. After emulsification, the color of the ink will lighten, 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 inks with completely different emulsification levels are adjusted together, and the phenomenon of discoloration is particularly prominent.
3. The relationship between the nature of the paper and the imprinted copy
1. The surface smoothness of the paper. The smoothness of the surface of the paper is closely related to the copying of the imprint. Unsmooth paper often requires a lot of pressure to make the ink have good contact with it. If the ink viscosity, fluidity, and ink layer thickness are kept at a certain amount, increasing the pressure often increases the footprint spreading area. At the same time, the low concave parts of the paper still have poor contact, such as: coated paper and newsprint printed on the same printing plate If there is a big difference in the imprinting effect, you can clearly compare the different copying effects.
2. Absorbency of paper. The absorbency of the paper is also directly related to the copying effect. Generally, when printing paper with a loose texture, if the ink has high fluidity and low viscosity, the paper will absorb more ink layer connection material, if the capillary smuggling If it is larger than the diameter of the pigment particles, even the pigment will be sucked in, which reduces the saturation of the print. The thickness of the ink layer needs to be increased appropriately. However, increasing the thickness of the ink layer will cause "spreading" at the moment of imprinting, which will affect the reproduction effect of the imprint. The paper with low absorption can make most of the ink film appear on the surface of the paper, so that the printed ink layer has better saturation.
Fourth, the effect of paper permeability on color
The large permeability of the paper will reduce the thickness of the ink layer, the pores on the surface of the paper will be large, and some of the pigment particles will also be penetrated into the paper at the same time, so the color will feel lighter. For this reason, use paper with a rough surface and a loose texture, and paper with large ink flow, pay attention to discoloration.
Fifth, the effect of pigment heat resistance
In the drying process of the ink, the bright quick-drying offset printing ink is mainly based on the drying of oxidized conjunctiva. There is a fixation stage before the offset ink is dried. The oxidative polymerization of the ink is an exothermic reaction. When it is dried too quickly, it will release a lot of heat. If the heat is radiated slowly, it will discolor the heat-resistant pigment. For example, the golden color ink becomes darker and loses its original luster.
During the printing, the printed sheets are stacked on the receiving table. Due to the excessive stacking, the printed ink in the middle part oxidizes and polymerizes exothermic reaction, the heat is not easy to dissipate, and the temperature in the middle part is too high.
6. Effect of dry oil on discoloration of blots
Light color inks are cool colors, light yellow, emerald green, lake blue and other intermediate color inks, do not use red dry oil, because red dry oil itself has a deeper fuchsia, which will affect the color of the light color ink.
White dry oil looks white, but it is light brown after oxidizing the conjunctiva. If the amount of white dry oil is large, the blot may dry up to yellowish brown, and dark color inks such as blue, black, and purple use red dry The oil color will not be greatly affected.
Seven, the impact of ink intolerance on the imprint color
The PH value of the printed paper is 7, and the neutral paper is the most ideal. The inks made of general inorganic pigments have poor acid and alkali resistance, and the organic pigments have good acid and alkali resistance, especially the medium blue and dark blue inks meet alkali It will fade. When the medium yellow meets alkali, the color becomes reddish, and the hot-printed anodized aluminum foil and gold print will become pale yellow when they encounter alkaline substances, and there is no glossiness. The paper is often weaker and more alkaline. Containing alkaline adhesives, if the packaging and decoration printing products are packaging alkaline substances such as soap, toilet soap, washing powder, etc., the alkali resistance and saponification resistance of the ink must be considered. Peacock blue ink has better alkali resistance.
8. Discoloration factors during storage and use of printed matter
Most printed products are stored for a long time, it will inevitably appear yellowish phenomenon, the reasons are as follows:
1. The fiber in the paper contains much lignin and changes color. For example, newspapers printed on newsprint are most likely to turn yellow and brittle.
2. Most of the color printing products with offset four-color dot overprinting are exposed to sunlight, long days, wind and rain, and high temperature erosion outdoors. Because the pigments are not light-resistant and heat-resistant, they change color or fade.
Mulberry Silk Scarf,Custom Design Logo Scarf,Cotton Satin Silk Scarves,Silk Scarf Pattern Geometric
Shenzhen Xinmingcai Clothing Co,.Ltd , https://www.xmcsz.com