The impact of newsprint performance on color printing
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In the printing of color newspapers, newsprint is a substrate, and graphic information is finally presented to readers through paper. Therefore, the quality of newsprint printing directly affects the quality of the final color printing. The smoothness, ink absorption, whiteness, mechanical properties and dimensional stability of the paper will affect the print quality of the color newspaper.
First, the smoothness of newsprint
In printing, the first condition for obtaining a print that is faithful to the original is the smoothness of the newsprint. The smoothness of newsprint reflects the degree of unevenness of the microscopic geometric shape of the newsprint. Only with a certain degree of smoothness can the copying effect of the graphic and text be guaranteed. There are many pores and pores on the surface of the newsprint. In order to obtain the desired printing effect, that is, the imprint is clear, the ink is uniform, and the layers are rich, the paper must be in good contact with the blanket. If you want to get rich and vivid graphics, you must present the four-color dots on the paper as much as possible. The smoothness of the paper plays a decisive role. If the smoothness is small, the ink cannot be in full contact with the paper, and the small dots are inevitably lost and layerless. Therefore, the smoothness of the paper is an indispensable condition for determining the number of screen lines and obtaining high quality dots. The paper with high flatness can obtain enough ink, and the ink layer is uniform, the thickness is uniform, the ink transfer rate is high, the solid density of the printed matter is high, the dot gain value is small, the color is rich, and the reproducibility is strong. Papers with poor smoothness have incomplete dots, no vivid colors, and poor color reproducibility. Properly increasing the fluidity, ink supply and printing pressure of the ink can make up for the vacancy and falseness of the print due to the difference in smoothness. However, the consequence of this is that the outlets are enlarged, the dark adjustments are paste-printed, and the color casts. It is also possible to print a lighter color first to achieve the purpose of bottoming. Therefore, the color newspaper must use high-quality newsprint.
Second, the whiteness of newsprint
Paper is the carrier of graphic information, and its whiteness directly affects the color of printed matter. When light hits the paper, it is absorbed a part, and the amount of absorption 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 subtractive method and the color light addition method. If the whiteness of the paper is low, the excessive light is absorbed, and the color of the ink cannot be fully exerted, which affects the hue, brightness and saturation of the image color, resulting in dark color, poor contrast, dull picture, no vitality, and few levels.
Third, the ink absorption of news paper
The ink absorbency of the paper includes the transfer and penetration of the ink into the paper. It depends not only on the ability of the newsprint to absorb the ink binder, but also on the absorption of the ink by the newsprint under the imprinting conditions, so the ink absorbency should be paper. (News paper) and the performance of the ink under the printing conditions, that is, the quality of ink absorption, does not depend entirely on the performance of newsprint, but also depends on the performance of the ink and printing conditions. When the newsprint is fixed, changing the performance of the ink or the printing conditions will cause a change in ink absorbing properties. 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 fastness of the ink. The essence of ink absorption is a comprehensive reflection of the absorption and adhesion of paper during printing, not only related to paper surface properties, porosity, compressibility, adsorption, etc., but also with ink composition, rheology and Dryness and the like are also related to printing methods, printing pressure, and imprinting time.
The smoothness of newsprint is low, and it is impossible to obtain a large amount of transfer under a small amount of ink supply. When the ink supply amount is sufficiently large, the ink layer is brought into contact with the surface of the paper at the time of imprinting, and a large amount of ink transfer can be obtained. Therefore, the amount of ink transfer varies depending on the surface properties of the paper. 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 curing ink required for different papers and the amount of free ink required to cover the surface is split on the paper. The amount of ink.
During the transfer of the ink onto the paper, the binder of the ink penetrates through the sorption and pressure, and the surface portion undergoes physical and chemical changes to form a solid dry ink film. If the ink absorption of the paper is too large, the amount of ink absorption is large, and too much binder and part of the pigment particles are sucked into the interior of the paper, so that the pigment particles are not effectively protected, resulting in poor imprinting, powdering, drying, and darkening of the ink. Light, reduce the brightness of color, while saturation, hue is also affected. When the ink absorbing property is small, the ink film is thick, and the solid density is high, which is advantageous for color reproduction. If the ink supply amount is too large, the back surface is easily dirty. The web offset press mostly uses newsprint and has a fast printing speed, so the paper has a strong ink absorption capability.
Fourth, the surface efficiency of newsprint
The color effect produced by the transfer of ink onto paper depends mainly on the nature of the ink, but is also inseparable from the nature of the paper. Printing on different papers with the same ink not only has different color intensity and contrast, but also has a large difference in color deviation and gradation. Even if printed on both sides of the same sheet of paper, the color effect is different. This is because the surface of the paper has different absorbency and gloss.
The surface efficiency of paper mainly considers absorbency and gloss. The absorption of paper is mainly the ability to absorb liquid, and the absorption of ink is mainly to absorb the binder in the ink. The color effect of the ink is formed after a certain amount of ink is consolidated on the surface of the paper, but the degree of absorption of the binder in the ink or the ink layer is different, causing the gloss, color density and hue of the ink layer on the paper surface to be absorbed. Strong sex changes greatly; small absorption changes little. Gloss is the optical properties of the surface of the paper - the degree of specular reflection. The level of gloss depends mainly on the roughness of the surface of the paper and the nature of the material constituting the paper. The ink is dried and colored on the surface of the paper, and the continuity and uniformity after drying and 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 smallest. Otherwise, the color strength 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 to improve the quality of color printing, because the surface efficiency of paper can provide powerful data for some quality problems, which is helpful for finding the cause of the problem. In the plate making and printing process, according to the surface efficiency of the paper, the color shift and gray scale of the ink color are effectively corrected, thereby achieving the gray balance of the color overlap and reducing the factors affecting the color quality.
Fifth, the mechanical strength of newsprint
For web offset presses, due to newsprint paste. Its mechanical strength is an important factor affecting the quality of printing. This is mainly manifested in two aspects: tensile strength and surface strength. The paper path of the web offset press is generally long. During 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 paper breaks, which affects the normal printing. The surface strength of newsprint is another important technical indicator. During the printing process, when the ink splits between the paper and the blanket, it 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 bonding force of the vertical paper surface), the paper tape is peeled off from the middle and wound around the blanket cylinder, causing the paper to break and crushing the blanket. The surface of the paper is subjected to peeling tension to produce powder, lint, and buildup on the blanket. When a certain amount is printed, if the paper powder and paper wool are piled up too thick, the imprint is illusory, and the small text breaks the pen, which seriously affects the printing quality, and also causes the grinding plate to reduce the service life due to the pressure increase. . For color bullets, the ink layer transferred to the surface of the paper is reduced. The color is bleak and lacking in layers, and the outlets are seriously expanded. Since the ink is “wet-wet” transfer during the printing process of the color newspaper, there is also “wet hair loss”. Therefore, in the printing of the color report, in addition to the paper with high surface strength, corresponding technical measures must be taken, and the viscosity is small. The ink is appropriately reduced in printing pressure and printing speed.
Sixth, the dimensional stability of newsprint
Newsprint is made up of plant fibers. The surface is porous and hydrophilic and hygroscopic. Its water content has a great influence on its dimensional stability. In the process of color printing, it has to contact water several times, resulting in dimensional stability. Variety. Dimensional stability not only directly affects the smooth progress of printing production, but also affects the quality of printed matter. Variations in dimensional stability include telescopic and dimensional changes in planar dimensions. Newsprint is more hygroscopic and therefore has poor dimensional stability. Dimensional stability is different under different external conditions. For newsprint, due to its poor mechanical properties, dimensional stability is of great significance for the smooth progress of the printing process and the acquisition of high-quality printed matter, otherwise it will cause problems such as paper interruption, printing wrinkles, and overprinting in the printing process. Newsprint must control the temperature and humidity during transportation and storage to avoid large changes, otherwise it will have a greater impact on dimensional stability.
In short, newsprint as an indispensable printing material in newspaper printing, its performance.