As the main raw material for printing, paper's performance determines the quality of printing ink color. Only the paper with good performance can get better color rendering of printed products. Therefore, to correctly understand the relationship between the performance of paper and the color of printed products, according to the characteristics of printed products and process conditions, the rational selection of paper for printing is of great practical significance for improving product quality.
1. The relationship between paper smoothness and color rendering effect
Smoothness is a technical indicator to evaluate the degree of unevenness of the surface of the paper. It is a physical quantity that indicates the smoothness, smoothness and uniformity of the surface of the paper. That is, under certain vacuum conditions, a certain volume of air can be used to test the surface and smoothness of the paper under a certain pressure The time required to flow between glass surfaces is measured in seconds. The higher the number of seconds, the better the smoothness of the paper. The better the smoothness of the paper, the more uniform and complete the contact between the paper surface and the printing plate during printing, the more sufficient the transfer of the ink layer on the layout (relief) or blanket, and the better the color rendering of the printed product. Conversely, for papers with poor smoothness, the ink transfer is uneven and inadequate, and the paper has strong penetrability for the amount of ink, and the color rendering effect is also poor. Therefore, when printing fine products, the finer the screen line and the smaller the dot diameter, the more smooth the paper should be used for printing, so as to make the original reproducible.
Second, the relationship between paper gloss and color rendering effect
Paper gloss refers to the degree of specular reflection on the paper surface, expressed as a percentage. The higher the gloss of the paper, the more the surface can reflect light like a mirror, and the brighter the appearance of the paper. In fact, in addition to specular reflection, there is diffuse reflection on the paper surface, which reduces the gloss of the paper. The paper with high gloss has brighter ink color and better visual effect. It can be said that the smoother the paper, the higher the gloss, and the higher the gloss of the color of the printed product. The glossiness and smoothness of the paper are closely related, but the glossiness is not smoothness. The shiny surface of the paper is not necessarily the smooth surface. From the point of view of the gloss characteristics of paper, it is very practical to choose the appropriate paper for printing according to the characteristics of the printed matter. For books and periodicals with mainly text, it is better to use paper with normal glossiness to avoid reflection, so that the eyes will not be tired for a long time. The printing is mainly based on the plate, the paper with high gloss should be selected to make the printed ink uniform, thick and bright.
3. The relationship between paper whiteness and color rendering effect
Paper whiteness refers to the ability of the paper to fully reflect after being irradiated by light. It is also known as the brightness of the paper and is expressed as a percentage. The higher the whiteness of the paper, the more accurately the color characteristics of the ink can be expressed on its surface. This is because white paper needs to reflect back the color light synthesized by subtractive color through the transparent ink layer. Therefore, the paper with high whiteness can reflect almost all the color light, making the printed ink color bright and pleasing, and the visual effect is good. The paper with low whiteness, because it only absorbs part of the color light, can not faithfully show the contrast of the light and dark parts, and it is easy to cause color cast. Some of them appear yellowish, some appear reddish, some appear greenish, others appear blued and so on. When the paper itself is discolored, the color printed on the paper is the effect of the combined color of the ink and the paper. This will inevitably cause some color cast. Based on this situation, it is necessary to whiten the paper during printing. The degree and color cast are analyzed against the original manuscript, and the purpose of correcting color cast is achieved by taking appropriate measures. For example, when the color of the paper is yellowish, it is not suitable to use dark yellow, peacock blue and scarlet inks. That is to say, according to the characteristics of the paper color, the ink should be properly selected to eliminate the color cast. On the other hand, the color shift can be corrected by the ink adjustment process.
4. The relationship between paper absorption and color rendering
The absorbency of paper refers to the absorption capacity of the paper to the binder and its solvent in the ink, usually expressed as a percentage. The absorption of paper is also called ink absorption, and its strength is very sensitive to the performance of the printing hue and the gloss of the ink layer. Paper with strong ink absorption, the color of the printed ink is easy to fade, and the ink layer also lacks gloss. In addition, because most of the binder in the ink is absorbed by the fiber structure of the paper, the pigment particles are not sufficiently protected, and the ink film on the printed product is not strong, which is easy to cause the powder to "pulverize". Conversely, if the paper's ink absorption is too weak, the ink layer of the printed product will not adhere well, and the print will not dry easily, which will easily cause the back of the printed product to smudge. Therefore, according to the use characteristics of the printed matter, choose the appropriate absorption paper for printing, in order to better ensure the printing quality. For printing newspapers, it is advisable to use highly absorbent newsprint to meet the high-speed, urgent, and economical use characteristics. For finely printed products, bright colors require weak absorption of paper, such as glass cards and coated paper. Among the above paper properties that affect the color rendering of printed matter, the most prominent is the gloss and absorbency of the paper. The comprehensive effect of paper absorbency and gloss on the ink color effect of the printed product, called the surface efficiency of the paper, can be calculated according to the following formula:
PSE (%) = (100-A (%) + G (%)) / 2
In the formula: PSE stands for paper surface efficiency; A is the ink absorption capacity of the paper; G is the glossiness of the paper. The process test can show that when the surface efficiency of the paper is high, under the same process conditions, the color intensity of the ink is the largest, while the color deviation and the grayscale are the smallest. The research and testing of paper surface efficiency is an important part of realizing process data and standardization. It is very important for correcting color deviation and ensuring product printing quality. Therefore, to correctly understand and recognize certain properties of paper on printed products The effect of color rendering is undoubtedly beneficial.
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