The influence of the characteristics of the hottes

2022-08-16
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Paper characteristics on the quality of printed matter

printed matter is a kind of commodity and artwork judged by vision. Its quality depends on many factors, and paper characteristics are undoubtedly an important factor. The paper with excellent performance can complete the ink transfer completely, so that the pictures and texts can be clearly and fully reproduced on the paper, so as to obtain a satisfactory reproduction effect. However, due to the limitations of materials such as paper and process technology, most color continuous tone images cannot be faithfully copied and reproduced, and can only make the printed image close to the original as much as possible

influence of paper characteristics on the gloss of printed matter

in the printing process, the ink film is transferred to the surface of the paper and filled with the uneven surface of the paper, making the surface of the printed matter quite smooth. On the one hand, the printing ink film surface increases the melt temperature and reduces the activity resistance due to the shear heating of the plastic melt; On the other hand, it can also enter the pressure maintaining and feeding stage earlier when the melt temperature is still high and the activity resistance is small. The specular reflection of light determines the gloss of printed matter, and the surface of ink film is closely related to the characteristics of paper

ink film thickness

ink film thickness is the main factor affecting the gloss of printed matter. After the paper absorbs the binder of the ink to the maximum extent, the remaining binder remains in the ink film, which can effectively improve the gloss of the printed matter. The thicker the ink film, the more remaining binder, the more conducive to improving the gloss of the print. It is found that the gloss increases with the thickness of the ink film, which varies with different papers. Figure 1 shows the relationship between the gloss of printed matter and the thickness of ink film printed with the same ink on four different papers. It can be seen from the figure that although the inks are the same, the tendency of the gloss of printed matter formed by different papers to change with the thickness of the ink film is different. When the ink film of high gloss coated paper is thin, the gloss of its printed matter decreases with the increase of the ink film thickness, because the ink film masks the original high gloss of the paper itself, and the gloss formed by the ink film itself is low due to the absorption of the paper. With the increase of the thickness of the ink film, the original high gloss of the paper itself is more difficult to be reflected by the ink film. When the ink film thickness reaches 1.5 μ M, the absorption of the paper to the binder is basically saturated. After that, as the thickness of the ink film continues to increase, the more binder is retained, and the gloss continues to improve. The gloss of coated paperboard prints increases rapidly with the increase of ink film thickness, and the ink film thickness increases to 3.8 μ M later, the gloss will no longer increase with the increase of ink film thickness. But no matter what kind of paper, there is a certain limit to the amount of gloss that increases with the increase of ink film thickness

the influence of paper characteristics on the gloss of printed matter

paper forms capillary complex structure due to fiber interweaving, which makes the paper have a large number of pores, which becomes the basis for it to absorb ink. The balance between the absorption time of the ink binder by the capillary complex of the paper and the rounding time of the binder determines the penetration degree of the binder when the gloss of the printed matter is formed. Generally, the gloss of printed matter decreases with the enhancement of paper absorption capacity

the smoothness of paper and its own gloss affect the gloss of printed matter. High smoothness is conducive to the formation of a uniform and smooth ink film, thereby improving the gloss of printed matter. Good gloss of the paper itself can improve the reflectivity of the ink film, especially for transparent ink. Figure 2 is the result of printing two inks on four different gloss coated papers. It can be seen from the figure that the gloss of the printed matter of the two inks increases with the improvement of the gloss of the paper itself. There is an excellent correlation between the gloss of printed matter and the gloss of paper itself, which is better than the correlation between the gloss of printed matter and the absorption capacity of paper

from the above discussion, it can be found that there is also a correlation between paper smoothness, gloss and absorption capacity. It is easy to explain this from the papermaking process. For example, calendering can improve the smoothness and gloss of the paper, but also reduce the porosity of the paper, thereby reducing the absorption capacity of the paper. In addition, the pH value of the paper surface is also a factor that cannot be ignored in the formation of the gloss of the printed matter. High pH value is conducive to the drying of the ink, so it is conducive to improving the gloss of the printed matter

the influence of paper characteristics on the tone reproduction of printed images

ideal tone reproduction is the most important process to obtain high-quality printed images. Most bad prints are caused by the problems of tone reproduction

the most obvious requirement of image reproduction is that the copied image visually matches the original. But in fact, it is impossible in most cases. Obviously, in most cases, the density range of the original is larger than that of the printed image, and as the paper quality decreases, the smaller the reproducible density range, as well as for saturation and color. The characteristics of paper is the initial condition that restricts the quality of image reproduction. Without the actual paper material, the tone reproduction is not of high quality. The solution is to compress the gradient range of the original to match the reproducible density range of the paper, etc

the influence of paper characteristics on the amount of dot gain

dot gain

dot gain has a greater influence on the change of replication hue than any other variable. The amount of ink printed on the paper will affect the dot increase, and the dot increase will affect the printing contrast. When printing black-and-white or color eye tone images, point increase will change the contrast of the image and cause the loss of image detail and clarity. In multicolor printing, dot increase will lead to loss of contrast, dark image, dot paste and sharp color changes

the influence of paper characteristics on the amount of dot gain

the smooth surface of ink produces the best field density on high-quality paper. When the paper quality is reduced, the field ink density is reduced, resulting in a certain dot expansion, which affects the quality of printed matter. Obviously, the absorbed ink cannot produce a smooth printing surface

the higher the number of lines, the smaller the dot diameter, and the small pits on the paper can also distort or omit small printing plate dots. Therefore, the higher the number of lines, the higher the smoothness of the paper. This is a principle of choosing paper. However, in practice, some properties of ink can also be adjusted appropriately or process parameters can be changed to adapt to this characteristic of paper

the influence of paper characteristics on the overprint accuracy of printed matter

for fine printed matter, the registration requirements are high, and the general tolerance is within 0.05mm. In multicolor printing, there are many reasons for inaccurate overprint, but the paper deformation caused by the change of water content in the printing process is an important factor

as we all know, the change of water content in paper not only leads to the expansion or contraction of paper, but also changes the local size of paper due to the poor UV resistance of polyether sulfone, resulting in other forms of deformation, such as curling, wrinkling, etc. This deformation seriously affects the quality of printed matter

printers are concerned about the influence of relative humidity on the moisture content of paper. Figure 3 shows the relationship curve between relative humidity and water content. It is known from the curve that:

① when the room temperature is constant and the humidity is high, the change rate of water content caused by the change of relative humidity is much larger than that caused by the change of relative humidity at medium humidity; The same is true under low humidity conditions. From this point of view, printing is most advantageous under medium humidity conditions

② in the figure, a and B are the relative humidity and water content curves in the process of moisture absorption and dehumidification respectively, which do not coincide and form a closed hysteresis loop. This phenomenon is called the hysteresis phenomenon of paper humidity regulation. The performance is: if the paper reaches the equilibrium water content under a certain relative humidity condition, it will return to the original relatively wet ambient air after moisture absorption (dehumidification), and its water content will increase (decrease) compared with that of the original tape stripping experimental machine

in order to keep the moisture content of the paper uniform on the whole paper surface, and adapt to the temperature and humidity of the printing workshop, at the same time, in order to reduce the sensitivity of the paper to the environmental humidity and improve the stability of the paper size, it is generally necessary to adjust the humidity (hang) before printing

conclusion

paper is an important basic raw material used in the printing industry. The quality of paper directly affects the quality of centrally purchased prints. Due to the different characteristics of the paper used, its printability also has obvious differences. In the printing process, the paper characteristics that affect the printing quality include the whiteness of the paper, the ink absorption of the paper, the smoothness and pH of the surface, as well as the dimensional stability and surface strength of the paper. In order to achieve the color balance between the color separations, the color rendering effect of the ink on the paper must be considered when carrying out color correction and level adjustment. Similarly, proofing should also use paper with similar hue and structural characteristics in order to simulate the printing effect

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