The Effect of Newsprint Performance on Color Newspaper Printing

In color newspaper printing, newsprint is a substrate, and graphic information is presented to readers through paper. Therefore, the printability of newsprint directly affects the quality of the final printed newspaper. The smoothness, ink absorption, whiteness, mechanical properties, and dimensional stability of the paper can all affect the print quality of the newspaper.

First, the smoothness of newsprint

In printing, the first condition for obtaining prints faithful to the original is the smoothness of the newsprint. The smoothness of newsprint reflects the degree of microscopic geometrical unevenness on the surface of newsprint. Only with a certain degree of smoothness, can we ensure the reproduction of images and texts. The surface of newsprint has many pores and pores. To achieve the desired printing effect, that is, the print is clear, the ink is uniform, and the layers are rich, it must be ensured that the paper and the blanket are in good contact. If you want to get rich, colorful graphics, you must put four-color dots on paper as much as possible. The level of paper smoothness plays a decisive role. If the smoothness is small, the ink cannot fully contact with the paper, and the fine dots must be lost and have no layer. Therefore, the smoothness of the paper is an indispensable condition for determining the number of lines of the screen and obtaining a high quality dot. Highly flat paper can obtain enough ink, and the ink layer is uniform, the thickness is uniform, the ink transfer rate is high, the density of the printed matter is high, the dot enlargement value is small, the color is rich, and the reproducibility is strong. Paper with poor smoothness has incomplete dots, poor colors, and poor color reproducibility. Appropriately increasing the ink's fluidity, ink supply, and printing pressure can make up for the emptiness and falsehood caused by poor smoothness. However, the consequences of doing so is to cause the network to expand, dark tone paste, color cast, you can also print a lighter color, to achieve the purpose of the bottom. Therefore, newsprint must use newsprint with high smoothness.

Second, the whiteness of newsprint

Paper is the carrier of graphic information, and its whiteness directly affects the color of the print. When the light hits the paper, it is absorbed and the amount absorbed depends on its whiteness. The higher the whiteness, the more light is reflected. After the ink is transferred to the paper, the color is formed by the color subtracting method and the color light adding method. The low whiteness of the paper absorbs too much light, and the color of the ink cannot be fully exerted, affecting the hue, lightness, and saturation of the image color, resulting in dull colors, poor contrast, dullness of the picture, lack of vitality, and low levels.

Third, newsprint ink absorption

The ink absorbency of paper includes transfer and penetration of ink to paper. It depends not only on the newsprint's ability to absorb the ink binder, but also on the absorption of ink by newsprint under the imprinting conditions. Therefore, the ink absorbency should be paper. The comprehensive reflection of the performance of (newspaper) and ink under printing conditions, that is, the good or bad of ink absorption, does not depend entirely on the performance of newsprint, but also on the performance and printing conditions of the ink. When the newsprint is constant, changing ink properties or printing conditions will change ink absorption. The ink absorption directly affects the drying speed of the ink on the surface of the paper, and also affects the color effect and the film fastness of the ink. The essence of ink-absorption is the comprehensive reflection of ink absorption and adhesion during the printing process. It is not only related to the surface properties, porosity, compressibility, and adsorptivity of the paper, but also the composition and rheology of the ink. Dryness and other related, but also with the printing method, printing pressure and stamping time and so on.

Newsprint has a low degree of smoothness, and it is impossible to obtain a large amount of transfer under the condition of less ink supply. When the ink supply is large enough, the ink layer is in contact with the surface of the paper at the moment of imprinting to obtain a larger ink transfer amount. Therefore, the ink transfer amount differs depending on the nature of the paper surface. In order to achieve the desired printing effect, under the same conditions, the amount of ink supply must be determined according to the surface properties of the paper to meet the amount of solid ink required for different papers and the amount of free ink required to cover the surface is split on paper. The amount of ink.

During the transfer of the ink to the paper, the binder of the ink undergoes sorption and pressure infiltration, and the surface portion undergoes physical and chemical changes to form a solid dry ink film. When the ink absorption of the paper is too large, the amount of ink sucked is large, and too much of the binder and some of the pigment particles are sucked into the interior of the paper, so that the pigment particles are not effectively protected, causing the prints to be unstuck, from the powder, dried up, and the ink dark. Light, reducing the brightness of color, while saturation, hue are also affected. The low ink absorption results in thick ink film and high density in the field, which is beneficial to color reproduction. If the ink supply is too large, the back surface may be dirty. Web offset presses mostly use newsprint and have a high printing speed, so the ink absorption ability of the paper is strong.

Fourth, the surface efficiency of newsprint

The effect of color on the transfer of ink to paper depends mainly on the nature of the ink, but it is also inseparable from the nature of the paper. With the same ink printed on different paper, not only the color intensity and contrast are different, but also the difference in color and gray scale is also very large, even if printed on both sides of the same paper, the color effect is not the same. This is because the surface of the paper has different absorbency and gloss.

The surface efficiency of the paper is mainly about absorption and gloss. The absorptivity of the paper is mainly the strength of the liquid absorption capacity, and the absorption of the ink is mainly to absorb the link material in the ink. The color effect of the ink is formed after a certain amount of ink is solidified on the surface of the paper, but the degree of absorption of the binder in the ink or the ink layer is different by the paper, causing the gloss, color density and hue of the ink layer on the paper surface to change. Stronger ones have greater changes; lesser absorbances have less change. Gloss is the optical property of the paper surface - the degree of specular reflection. The degree of gloss depends mainly on the roughness of the surface of the paper and the properties of the materials that make up the paper. The ink is dry and color on the surface of the paper, and its continuity and uniformity after drying of the conjunctiva must be affected by the surface state of the paper, resulting in different color effects. The surface efficiency is high. Under the same conditions, the color intensity of the ink is the largest and the color shift and the gray scale are the minimum. Otherwise, the color intensity of the ink layer is low, the color deviation and the gray scale are relatively high, and the color overprint ash balance is difficult.

Paying attention to the surface efficiency of newsprint is of great help in improving the printing quality of color newspapers, because the surface efficiency of paper can provide powerful data for some quality problems, which is conducive to finding the cause of the problem. In the process of plate making and printing, according to the surface efficiency of the paper, it can effectively correct the color shift and gray scale of the ink color so as to achieve the gray balance of color overlay and reduce the factors that affect the color quality.

Fifth, the mechanical strength of newsprint

For web offset presses, due to newsprint slurry reasons. Its mechanical strength is an important factor affecting the printing quality. This is mainly manifested in two aspects: tensile strength and surface strength. The web path of the web offset press is generally long. In the high-speed printing process, the tension of each part of the paper path is different and the difference is large. Once the tension exceeds the tensile strength, the web break occurs, which affects normal printing. The surface strength of newsprint is another important technical indicator. In the printing process, when the ink is split between the paper and the blanket, the ink is peeled off due to the adhesion of the ink and the adhesion between the blanket and the paper. tension. When the peeling tension is greater than the surface strength (the internal binding force of the vertical paper surface), the paper strip is peeled from the middle and wound on the blanket cylinder, resulting in a web break and crushing the blanket. The surface of the paper is subjected to a peeling force to produce flakes, lint, and build up on the blanket. When a certain number of printing, the paper powder, paper piles are too thick to make the imprints false, small words off the pen, seriously affect the quality of the printing, but also due to increased pressure, resulting in grinding, reducing the life of the blanket . For color newspapers, the ink layer transferred to the surface of the paper is reduced. The dullness of color lacks a hierarchy, and dot-nets have been severely expanded. Because the ink is “wet and wet” during the printing process, the “wet-wet” transfer also exists. Therefore, in the printing color report, besides using high-surface-strength paper, corresponding technical measures must be taken to use the small-viscosity. The ink properly reduces printing pressure and printing speed.

Six, newsprint dimensional stability

Newsprint is made by intertwining plant fibers. The porous surface has hydrophilicity and hygroscopicity. Its water content has a great influence on its dimensional stability. It has to contact water several times in the printing process of color newspapers, causing dimensional stability to occur. Variety. The dimensional stability not only directly affects whether the printing production can proceed smoothly, but also affects the quality of the printed matter. Changes in dimensional stability include the expansion of the planar dimensions and changes in body shape. Newsprint is highly hygroscopic and therefore has poor dimensional stability. In different external conditions, the dimensional stability is not the same. For newsprint, due to its poor mechanical properties, dimensional stability is of great significance to the smooth progress of the printing process and to obtaining high-quality prints, otherwise it will cause problems such as paper breaks, wrinkle printing, and overprinting during the printing process. Newsprint must be controlled in temperature and humidity during transportation and storage to avoid significant changes, otherwise it will have a greater impact on dimensional stability.

In short, newsprint, as an indispensable printing material in the printing of newspapers and periodicals, must pay enough attention to its performance, and should provide adequate material protection for ensuring the normal production of printing and obtaining high quality printed matter.