Paper performance and print color
Paper is the main raw material for printing, and its performance determines the quality of printing ink. Only good performance paper can get better print coloring effect. Therefore, correctly understanding the relationship between paper performance and color rendering of printed products, according to the characteristics of printed products and process conditions, rational selection of paper for printing has important practical significance for improving product quality.
First, the relationship between paper smoothness and coloring effect
Smoothness is a technical index for evaluating the degree of unevenness on the surface of paper. It is a physical quantity indicating the smoothness, smoothness and uniformity of the surface of the paper. That is, under a certain vacuum condition, a certain volume of air is made and the surface of the paper test sample under a certain pressure is smooth. The time required to flow between the 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 and the printing plate during printing, the more the ink layer on the layout (emboss) or blanket is transferred, and the better the color rendering effect of the printed product. On the contrary, paper with poor smoothness, ink transfer is not uniform, insufficient, and the paper has strong permeability to the amount of ink, and the color rendering effect is also poor, and it is easy to make the ink color of the printed product light and fade. Therefore, if the printed product is fine, the finer the network cable and the smaller the diameter of the dot, the more smooth the paper should be printed, so that the original can be reproducible.
Second, the relationship between paper gloss and coloring effect
Paper gloss is the degree of specular reflection on the surface of the paper, expressed as a percentage. The higher the gloss of the paper, the more the surface can reflect light like a mirror, and the more it shows the bright appearance. In fact, in addition to specular reflection, there is diffuse reflection on the surface of the paper, which reduces the gloss of the paper. For papers with high gloss, the more vivid the printed ink, the better the visual effect of the ink. It can be said that the smoother the paper, the higher the gloss, and the higher the gloss of the printed product. There is a close relationship between the gloss and smoothness of the paper, but the gloss is not smooth, and the shiny surface of the paper is not necessarily a smooth surface. From the point of view of the glossiness of the paper, it is very practical to select the appropriate paper for printing according to the characteristics of the print. For example, if the layout is text-based, the paper should be made of glossy paper to avoid reflection, so that the eyes will not be tired for a long time. For the printing of the plate based on the plate, it is advisable to use paper with high gloss to make the printed ink uniform, thick and bright.
Third, the relationship between paper whiteness and coloring effect
Paper whiteness refers to the ability of paper to be totally reflected after being exposed to light, and is also known as the brightness of paper, expressed as a percentage. The higher the whiteness of the paper, the more the surface of the paper can accurately represent the color of the ink. This is because the white paper reflects the color light synthesized by the color reduction of 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. Paper with low whiteness, because it only absorbs part of the color light, can not faithfully express the contrast between the light and dark parts, and easily cause color cast. If some appear yellowish, some appear reddish, some appear greenish, some appear blue and so on. When the paper itself is color cast, the color printed on the paper is the effect of the combination of ink and paper. This will inevitably lead to some color cast. Based on this situation, it is necessary to white the paper when printing. The degree of color and color cast are analyzed against the original, and appropriate measures are taken to achieve the purpose of correcting the color cast. For example, when the color of the paper is yellowish, it is not suitable to use inks of dark yellow, peacock blue and red, etc., that is, according to the characteristics of the paper color, the ink should be correctly selected to eliminate the color cast. On the other hand, the color shift can be corrected by the ink adjustment process.
Fourth, the relationship between paper absorption and coloring effect
The absorbency of paper refers to the ability of paper to absorb the binder and its solvent in the ink, usually expressed as a percentage. The absorbency 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 ink color of the printed product is easy to fade, and the ink layer lacks gloss. In addition, since the binder in the ink is mostly absorbed by the fiber structure of the paper, the pigment particles are not sufficiently protected, and the ink film on the print is not strong, which tends to cause "pulverization" of the print. On the other hand, if the ink absorbency of the paper is too weak, the printed ink layer will not adhere well, and the print will not be easily dried, which may easily cause the back of the print to be dirty. Therefore, according to the use characteristics of the printed products, it is better to ensure the printing quality by selecting the paper with suitable absorption for printing. For example, newspapers should use absorbent newsprint to meet the characteristics of high speed, emergency use and economy. For fine-printed products, if the color is bright, the paper should be weakly absorbed, such as glass cards and coated paper. Among the above-mentioned paper properties that affect the color rendering effect of the print, the most prominent is the gloss and absorbency of the paper. The combined effect of the absorbency and gloss of the paper on the ink color effect of the print, called the surface efficiency of the paper, can be calculated by the following formula:
PSE (%) = (100-A (%) + G (%)) / 2
Where: PSE stands for paper surface efficiency; A is the paper's ink absorption capacity; G is the paper's gloss. The process test shows that when the surface efficiency of the paper is high, the ink has the highest color intensity and the minimum color shift and gray scale under the same process conditions. Research and testing of paper surface efficiency is an important part of achieving process data and standardization. It is of great significance to better correct color deviation and ensure product printing quality. Therefore, it is necessary to correctly understand and understand certain properties of paper. The effect of the color effect is undoubtedly beneficial.