Factors Affecting Offset Color Identification

In the offset printing process, for the offset printing operators mainly based on color image printing and copying, they often contact colors and identify colors. They must not only have normal visual judgment, but also have keen visual observation capabilities. Color blindness and color weakness are not suitable for color printing. Even for people with normal vision, different light sources, such as the whiteness of the paper, the ambient color, and the relationship between the paper absorbability and the imprinted ink layer, many factors will affect the color identification.

First, the impact of lighting sources on color discrimination

The color of the color body is represented by the light of a specific wavelength, so to accurately compare the color of the color body, the light source is a very important condition. In the offset printing process, there are two kinds of lighting sources, natural light and artificial light source. In order to accurately determine the color needs, whether it is natural light or artificial light source, pure white light standard light source is the most suitable for viewing the color. Direct sunlight is yellow, indirect sunlight is better, no color cast, blue under blue sky, incandescent under orange red, under fluorescent light blue violet, only the proportion of indirect sunlight is equal to the three primary colors, which belongs to white light. Irradiating the color body with white light makes the reflection or absorption of the light body more standard. It can be seen that the use of natural light as the lighting source, the best use of relatively stable indirect sunlight, so that in the offset printing shop, when installing the machine, you should consider to see the sample table placed in indirect sunlight lighting position, fluorescent lamp reflectors should always be maintained Clean, remove dust and dirt, avoid the use of blue, yellow and so on. The light source illuminates the printed sample in the vertical direction at an angle of 45°, so the sample stage should have a corresponding slope.

Second, the whiteness of paper

The ideal whiteness of printing is 100% total reflection, especially the identification of color. It is necessary to realize the importance of whiteness of paper, especially the paper which is one of the main factors for distinguishing color, and the blank paper bearing the color of the color. Whiteness plays a decisive role in the appearance of hue, brightness and saturation. Usually, the coated paper coated with fine products requires a reflectance of more than 85%. The paper used for proofing during offset printing should be the same as the whiteness of the officially printed paper, otherwise it is difficult to accurately evaluate the ink color effect. It must first be stipulated that paper with sufficient whiteness be used. In the printing process of the same batch of products, the used paper should have the same color, otherwise, it is impossible to keep the ink of the product consistent.

Third, the impact of environmental color

Ambient colors also have a significant effect on correct color discrimination. Similarly, when observing and analyzing colors, the process of seeing must avoid the illusion of color. A color in a specific environment, the human eye vision due to psychological effects easily lead to illusion, need to know it, so as to avoid the color of the environment caused by the color error. The same is a kind of green, placed in a yellow environment, with a greenish-white contrast to a bluish; while green is placed in a colored environment, it is yellowish. The same is the gray background, reddish in the green environment. The black 50% dot gray block is placed in a black solid and 10% dot environment, and the brightness of the two is noticeably different. These are the results of discoloration caused by the illusion of color. From this reasoning, when distinguishing the color of a certain color body, it is necessary to avoid the influence of the environmental color. When comparing the colors of a plurality of sets of color printing products, it is necessary to pay attention to covering other colors. At the same time, in the case of proofs and printing-like solid patches, it can be grouped together, and the interference of ambient colors must be eliminated, so as to avoid the color deviation due to the visual effect.

Fourth, the relationship between the absorption of the paper and the ink layer

Due to the great difference in the absorption of inks on various papers, the absorptivity of coated paper is small, and the absorptivity of letterpress paper and offset paper is large. The paper with high absorbency often causes the imprinted ink layer to solidify and has a large loss in the drying process. . Since the binder of the ink is absorbed into the fibers of the paper, the gloss of the print will be affected, and the surface will become rough and the color will change. When printing fine products, be careful to use paper that cannot absorb too much. In addition, when printing offset printing, the dry, wet ink color of the blotted ink color is different. Offset ink color is just printed out of the wet state of the ink, the color is darker. After the offset ink blot is dry, it will be lighter. Therefore, when distinguishing colors, it is necessary to fully estimate its influence and increase the thickness of the ink layer within the allowable range in order to compensate for possible loss of color density. When using poor quality, loose structure, rough surface paper, in order to avoid ink color error may occur when the sample can be printed for a certain period of time, to be dry, then determine the degree of color. The thickness of the ink layer is controlled by the amount of ink, the general ink law:

1. The number of outlets is 133L/in, 150L/in, 175L/in, etc. The higher the number of outlets, the more they are to be avoided. The use of too much ink causes the spread of outlets to expand, and the amount of ink used should be reduced.

2. Field products can increase the amount of ink and make the ink layer thicker.

3, the paper is relatively rough, strong absorption, to increase the use of ink, the paper is smoother and smoother, poor absorption, can be used to reduce the amount of ink.

Fifth, when comparing color samples, what factors will affect the color

When offset printing is compared with the printing ink color sample and printing ink color size and hue is exactly the same, the environmental color has a greater impact, as well as light (sunlight) brightness and darkness and color cast, and each person's color blindness physiological phenomena have a certain impact. When looking and signing, the sample should be framed and framed to reduce the influence of ambient color. In addition, the Y color is judged by its opposite color, blue-violet (B) glass, Y size ink size and dot gain, RC, CT (green)  m, and the glass plate is judged by its opposite color and color filter method. Use a color densitometer to measure dot changes. Under the unified standard light source, look at the color of ink and determine the color when comparing colors: red and green, white, and black; when you are tired, look for color errors. You should first look at the green trees and adjust the visual fatigue.