Print is a kind of visually judged goods and artwork. Its quality depends on many factors. Paper characteristics are undoubtedly an important factor. The paper with excellent performance can completely complete the transfer of ink and make the picture clearly and plumply reproduced on the paper so as to obtain a satisfactory copying effect. However, due to limitations of paper and other materials and process technologies, most color continuous tone images cannot be faithfully copied and reproduced, but only the printed image can be as close to the original as possible.
The effect of paper properties on the gloss of the print During the printing process, the ink film is transferred to the surface of the paper and fills the unevenness of the paper surface, making the surface of the printed product quite smooth. The specular reflection of light on the surface of the printed ink film determines the gloss of the printed matter, and the surface of the ink film is closely related to the characteristics of the paper.
Ink film thickness The thickness of the ink film is the main factor affecting the gloss of the print. After the paper absorbs the ink binder to the maximum extent, the remaining binder remains in the ink film, which can effectively improve the gloss of the print. The thicker the ink film, the more the remaining linking material, the more conducive to improving the gloss of the print. Studies have found that the tendency of gloss to increase with ink film thickness varies from paper to paper. Figure 1 is a graph of the relationship between gloss and ink film thickness of prints printed on the same ink on four different papers. As can be seen from the figure, although the inks are the same, the tendency of the gloss of prints formed by different papers varies with the ink film thickness is different. When the ink film is thin, the glossiness of the printed matter of the high-gloss coating paper decreases as the thickness of the ink film increases. This is because the ink film masks the original higher glossiness of the paper itself, and the ink film itself forms a glossiness due to the paper. Absorbed and lower. As the ink film thickness increases, the original higher gloss of the paper itself is more difficult to reflect through the ink film. When the ink film thickness reaches 1.5 μm, the absorption of the web by the paper is substantially saturated. Afterwards, as the thickness of the ink film continues to increase, the more link material remains, the more the gloss increases. The gloss of coated cardboard prints increases rapidly with the increase of the ink film thickness. After the ink film thickness increases to 3.8 μm, the gloss does not increase with the increase of ink film thickness. However, regardless of the type of paper, the amount of gloss increase with the increase of ink film thickness has a certain limit.
The effect of paper properties on the gloss of printed paper The paper forms a capillary network structure due to the interweaving of fibers, which causes the paper to have a large number of pores and become the basis for its absorption of ink. The balance between the absorption time of the ink binder material and the rounding time of the binder material by the paper capillary network determines the degree of penetration of the binder during gloss formation of the printed product. The gloss of general prints decreases with the increase of paper absorption capacity.
Paper smoothness and its own gloss affect print gloss. High smoothness is conducive to the formation of a uniform and smooth ink film, thereby improving the gloss of prints. The good gloss of the paper itself can increase the reflectance of the ink film, especially for transparent inks. Figure 2 shows the results of printing two inks on four different gloss coated papers. It can be seen from the figure that the gloss of the two inks increases with the improvement of the gloss of the paper itself. There is an excellent correlation between the gloss of the printed matter and the gloss of the paper itself, which is better than the correlation between the gloss of the printed matter and the absorptive capacity of the paper.
From the above discussion, it can be found that there is also a correlation between paper smoothness, gloss, and absorptive capacity. This is easily explained from the papermaking process. For example, calendering can improve paper smoothness and gloss while also reducing the amount of paper porosity, thereby reducing the paper's absorbency. In addition, the PH value of the paper surface is also a non-negligible factor in the glossiness of the printed matter. The high PH value is beneficial to the drying of the ink, which helps to improve the gloss of the printed matter.
The effect of paper properties on the reproduction of the printed image is ideal. Toner reproduction is the most important process for obtaining high-quality printed images. Most of the bad prints are caused by problems with the reproduction of the tone.
The most obvious requirement for image copying is that the copied image is visually matched to the original. However, in most cases it is impossible. Obviously, in most cases, the density of the original document is greater than the density range of the printed image, and as the quality of the paper decreases, the range of the reproducible density is smaller, as is the case with saturation and color. The characteristics of the paper are the initial conditions that restrict the quality of the image reproduction, and are decoupled from the actual paper material, and the reproduction of the gradation has no high quality. The solution is to compress the gradation range of the original so that it matches the reproducible density range such as paper.
The effect of paper characteristics on dot gain The dot gain on dot gain has a greater effect on copy hue change than any other variable. The amount of ink printed on the paper will affect the dot gain, while the dot gain will affect the print contrast. When printing black-and-white or color halftoning images, dot gain can change the contrast of the picture and cause loss of image detail and sharpness. In multi-color printing, dot gain can result in loss of contrast, dark images, dead spots, and sudden color changes.
The effect of paper properties on the dot gain The smooth surface of the ink produces the best on-site density on higher quality paper. When the quality of the paper is reduced, the density of the solid ink decreases, resulting in a certain dot gain that affects the quality of the print. Obviously absorbed ink does not produce a smooth printing surface.
The higher the number of screen lines, the smaller the dot diameter, and the tiny pits on the paper that can distort or miss the small plate dots. Therefore, the finer prints with the highest number of screens require higher paper smoothness. This is a principle of using paper. However, in practice, some properties of the ink may be properly adjusted or the process parameters may be changed to adapt to the characteristics of the paper.
The effect of paper properties on the overprint accuracy of printed products For fine prints, the registration requirements are high, and the general tolerance is within 0.05 mm. In multi-color printing, there are many reasons for overprinting, but the paper deformation caused by changes in the water content during the printing process is an important factor.
It is well-known that changes in the water content of the paper not only lead to the expansion or contraction of the paper, but also changes in the local size of the paper due to changes in the water content, thereby forming other forms of deformation, such as curling, wrinkling, and the like. This deformation seriously affects the quality of the print.
Printers are concerned with the effect of relative humidity on the moisture content of paper. Figure 3 shows the relationship between relative humidity and water content. Learn from the curve:
(1) When the room temperature is certain, when the humidity is high, the rate of change of the water content caused by the change in relative humidity is much greater than the rate of change of the water content caused by changes in the relative humidity of the medium humidity; the same is true under low humidity conditions. From this point of view, printing is best performed in moderate humidity conditions.
2 In the figure, A and B are the relative humidity and moisture content curves of the process of moisture absorption and desorption, respectively. The two do not coincide and form a closed hysteresis loop. This phenomenon is called hysteretic hysteresis of the paper. The performance is: if the paper reaches equilibrium water in a certain relative humidity condition, if it is reabsorbed (dehumidified) and then returned to the original relatively humid ambient air, its water content is increased (reduced) compared with the original. .
In order to keep the moisture content of the paper uniform on the entire paper surface, and to adapt to the temperature and humidity of the printing shop, and to reduce the sensitivity of the paper to the environmental humidity, and to improve the stability of the paper size, generally before printing , to conduct humidity control (hanging) processing.
Conclusion Paper is an important basic material used by the printing industry. The quality of paper directly affects the quality of printed matter. Due to the different characteristics of the paper used, there are obvious differences in printability. In the printing process, the characteristics of the paper that affect the print quality include the whiteness of the paper, the ink absorption of the paper, the smoothness of the surface, the pH, the dimensional stability of the paper, and the surface strength of the paper. In order to achieve a color balance between the color separation sheets, the color rendering effect of the ink on the paper surface must be taken into account when performing color adjustment and layer adjustment. Similarly, proofing should also use papers with similar hue and structural characteristics in order to simulate printing effects.
The effect of paper properties on the gloss of the print During the printing process, the ink film is transferred to the surface of the paper and fills the unevenness of the paper surface, making the surface of the printed product quite smooth. The specular reflection of light on the surface of the printed ink film determines the gloss of the printed matter, and the surface of the ink film is closely related to the characteristics of the paper.
Ink film thickness The thickness of the ink film is the main factor affecting the gloss of the print. After the paper absorbs the ink binder to the maximum extent, the remaining binder remains in the ink film, which can effectively improve the gloss of the print. The thicker the ink film, the more the remaining linking material, the more conducive to improving the gloss of the print. Studies have found that the tendency of gloss to increase with ink film thickness varies from paper to paper. Figure 1 is a graph of the relationship between gloss and ink film thickness of prints printed on the same ink on four different papers. As can be seen from the figure, although the inks are the same, the tendency of the gloss of prints formed by different papers varies with the ink film thickness is different. When the ink film is thin, the glossiness of the printed matter of the high-gloss coating paper decreases as the thickness of the ink film increases. This is because the ink film masks the original higher glossiness of the paper itself, and the ink film itself forms a glossiness due to the paper. Absorbed and lower. As the ink film thickness increases, the original higher gloss of the paper itself is more difficult to reflect through the ink film. When the ink film thickness reaches 1.5 μm, the absorption of the web by the paper is substantially saturated. Afterwards, as the thickness of the ink film continues to increase, the more link material remains, the more the gloss increases. The gloss of coated cardboard prints increases rapidly with the increase of the ink film thickness. After the ink film thickness increases to 3.8 μm, the gloss does not increase with the increase of ink film thickness. However, regardless of the type of paper, the amount of gloss increase with the increase of ink film thickness has a certain limit.
The effect of paper properties on the gloss of printed paper The paper forms a capillary network structure due to the interweaving of fibers, which causes the paper to have a large number of pores and become the basis for its absorption of ink. The balance between the absorption time of the ink binder material and the rounding time of the binder material by the paper capillary network determines the degree of penetration of the binder during gloss formation of the printed product. The gloss of general prints decreases with the increase of paper absorption capacity.
Paper smoothness and its own gloss affect print gloss. High smoothness is conducive to the formation of a uniform and smooth ink film, thereby improving the gloss of prints. The good gloss of the paper itself can increase the reflectance of the ink film, especially for transparent inks. Figure 2 shows the results of printing two inks on four different gloss coated papers. It can be seen from the figure that the gloss of the two inks increases with the improvement of the gloss of the paper itself. There is an excellent correlation between the gloss of the printed matter and the gloss of the paper itself, which is better than the correlation between the gloss of the printed matter and the absorptive capacity of the paper.
From the above discussion, it can be found that there is also a correlation between paper smoothness, gloss, and absorptive capacity. This is easily explained from the papermaking process. For example, calendering can improve paper smoothness and gloss while also reducing the amount of paper porosity, thereby reducing the paper's absorbency. In addition, the PH value of the paper surface is also a non-negligible factor in the glossiness of the printed matter. The high PH value is beneficial to the drying of the ink, which helps to improve the gloss of the printed matter.
The effect of paper properties on the reproduction of the printed image is ideal. Toner reproduction is the most important process for obtaining high-quality printed images. Most of the bad prints are caused by problems with the reproduction of the tone.
The most obvious requirement for image copying is that the copied image is visually matched to the original. However, in most cases it is impossible. Obviously, in most cases, the density of the original document is greater than the density range of the printed image, and as the quality of the paper decreases, the range of the reproducible density is smaller, as is the case with saturation and color. The characteristics of the paper are the initial conditions that restrict the quality of the image reproduction, and are decoupled from the actual paper material, and the reproduction of the gradation has no high quality. The solution is to compress the gradation range of the original so that it matches the reproducible density range such as paper.
The effect of paper characteristics on dot gain The dot gain on dot gain has a greater effect on copy hue change than any other variable. The amount of ink printed on the paper will affect the dot gain, while the dot gain will affect the print contrast. When printing black-and-white or color halftoning images, dot gain can change the contrast of the picture and cause loss of image detail and sharpness. In multi-color printing, dot gain can result in loss of contrast, dark images, dead spots, and sudden color changes.
The effect of paper properties on the dot gain The smooth surface of the ink produces the best on-site density on higher quality paper. When the quality of the paper is reduced, the density of the solid ink decreases, resulting in a certain dot gain that affects the quality of the print. Obviously absorbed ink does not produce a smooth printing surface.
The higher the number of screen lines, the smaller the dot diameter, and the tiny pits on the paper that can distort or miss the small plate dots. Therefore, the finer prints with the highest number of screens require higher paper smoothness. This is a principle of using paper. However, in practice, some properties of the ink may be properly adjusted or the process parameters may be changed to adapt to the characteristics of the paper.
The effect of paper properties on the overprint accuracy of printed products For fine prints, the registration requirements are high, and the general tolerance is within 0.05 mm. In multi-color printing, there are many reasons for overprinting, but the paper deformation caused by changes in the water content during the printing process is an important factor.
It is well-known that changes in the water content of the paper not only lead to the expansion or contraction of the paper, but also changes in the local size of the paper due to changes in the water content, thereby forming other forms of deformation, such as curling, wrinkling, and the like. This deformation seriously affects the quality of the print.
Printers are concerned with the effect of relative humidity on the moisture content of paper. Figure 3 shows the relationship between relative humidity and water content. Learn from the curve:
(1) When the room temperature is certain, when the humidity is high, the rate of change of the water content caused by the change in relative humidity is much greater than the rate of change of the water content caused by changes in the relative humidity of the medium humidity; the same is true under low humidity conditions. From this point of view, printing is best performed in moderate humidity conditions.
2 In the figure, A and B are the relative humidity and moisture content curves of the process of moisture absorption and desorption, respectively. The two do not coincide and form a closed hysteresis loop. This phenomenon is called hysteretic hysteresis of the paper. The performance is: if the paper reaches equilibrium water in a certain relative humidity condition, if it is reabsorbed (dehumidified) and then returned to the original relatively humid ambient air, its water content is increased (reduced) compared with the original. .
In order to keep the moisture content of the paper uniform on the entire paper surface, and to adapt to the temperature and humidity of the printing shop, and to reduce the sensitivity of the paper to the environmental humidity, and to improve the stability of the paper size, generally before printing , to conduct humidity control (hanging) processing.
Conclusion Paper is an important basic material used by the printing industry. The quality of paper directly affects the quality of printed matter. Due to the different characteristics of the paper used, there are obvious differences in printability. In the printing process, the characteristics of the paper that affect the print quality include the whiteness of the paper, the ink absorption of the paper, the smoothness of the surface, the pH, the dimensional stability of the paper, and the surface strength of the paper. In order to achieve a color balance between the color separation sheets, the color rendering effect of the ink on the paper surface must be taken into account when performing color adjustment and layer adjustment. Similarly, proofing should also use papers with similar hue and structural characteristics in order to simulate printing effects.
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