There are many influencing factors to print colorful prints with rich colors and rich layers. From the perspective of actual production, the performance of inks is also an important factor affecting the quality of prints. Paper serves as a carrier for printing and reproducing images, accepts ink, and mixes a color image on the surface of the paper. Under the effect of printing pressure, the combination of paper and ink determines the print reproduction quality of the screen.
Different types of paper have different color development capabilities for inks. Even if the same type of ink is used, the same ink layer thickness can be printed on different papers, and the resulting color effects are not the same. The physical and chemical properties of paper have a great influence on color reproduction. The whiteness, smoothness, absorbency, glossiness, opacity, pH, and water content of the paper can all affect the realization of the gray balance. Different papers, with different smoothness, glossiness, whiteness, absorbency, printing permeability, paper efficiency, etc., even if the same printing environment, the same printing parameters and other conditions, the amount of ink transferred to the paper The density of the ground generated will also be different, resulting in different dot gain rates, and the range of replicable density is not the same, and the effect on the reproduction of the final print is not the same. Therefore, the difference in color and tone reproduction caused by the paper difference is significant. In fact, these differences are mainly caused by the difference in the surface characteristics of the paper. The surface characteristics of the paper affect the printing process and restrict the reproduction effect of the printed image. The performance of a paper, which is generally associated with print quality, is generally referred to as the printability of the paper, and it includes the physical properties, chemical properties, optical properties, and the like of the paper. The surface properties of the paper are included in printability. The surface properties of the paper play a crucial role in the quality of the printed matter. It mainly includes the smoothness, gloss, whiteness, ink absorption, and the like of the paper. Let's talk about the effect of these surface properties on the quality of the printed matter.
1 Effect of smoothness
Paper smoothness is a very important printability, it is divided into apparent smoothness and print smoothness. Apparent smoothness refers to the flatness of the paper surface, which depends on the surface topography of the paper and describes the structural characteristics of the paper surface. The paper with high apparent smoothness is favorable for ink coverage and leveling, the formed ink film is glossy, and the reproducibility of print reproduction is good. The apparent smoothness of a paper has a certain relationship with its gloss, and paper with a high apparent smoothness has a high glossiness. Printing smoothness refers to the flatness of the paper under the effect of printing pressure in the printing mode that uses pressure to achieve ink transfer, and the printing smoothness is the comprehensive effect of the apparent smoothness and surface compressibility of the paper.
The smoothness of the paper has a direct impact on the quality of the printed matter. It determines the degree of contact between the surface of the paper and the surface of the printing plate or blanket at the moment of imprinting, which is an important factor influencing whether ink transfer is complete and whether the graphic is clear. High paper smoothness is conducive to the ink on the paper surface to form a uniform and smooth ink film, improve the gloss of prints, but also through the reflection characteristics of light affect the gloss of prints. Paper with high smoothness can maintain a relatively high and stable ink transfer rate when the thickness of the ink layer is slightly changed, and quickly forms a uniform dry ink film, with good gloss, bright colors, and bright, hierarchical rich. On the other hand, paper with low smoothness has uneven surface, voids, more ink penetration, poor gloss of the ink layer, and lower color saturation. The purpose of printing is to faithfully reproduce the manuscript, which includes the reproduction of colors and the reduction of dots, that is, it is required to restore the layered dot shapes to the original shape of the layout, and evenly distribute the ink within each dot. It is required that the paper have a good smoothness, and the finer printed matter with a higher number of screen lines requires a higher degree of smoothness of the paper. If the smoothness of the paper is not high, some small dots will fall on the surface of the paper when it is printed. This will result in poor print and picture clarity, and the hue levels of the color screen colors will be unclear. The smooth surface of the paper can be printed with the largest contact surface and the printing plate or blanket graphic contact, thereby achieving uniform and complete transfer of ink, so that the text and text clearly and plumply reproduced on the paper, to obtain satisfactory D. Although the smoothness of the paper is determined by the papermaking process, it is an effective way for the printer to understand the effect of smoothness on print quality and adjust the process parameters based on the smoothness of the paper.
2 Effect of gloss
Gloss is used to indicate a surface optical property of paper, which reflects the gloss of the paper and the gloss of the print, and also reflects the ability of the paper surface to display images. It refers to the degree of mirror reflection on the surface of the paper, which is the closeness of the paper's mirror reflection ability and the full specular reflection ability, expressed as a percentage. The higher the gloss of the paper, the more mirror-like the reflection of light on the surface, the more bright or glossy the appearance of the material. Since the surface of the paper cannot be as smooth as a mirror surface, there is diffuse reflection in addition to the specular reflection, thus reducing the glossiness of the paper.
The decisive factor in the gloss of the paper is the smoothness of the paper. Uneven paper surface, will reflect the light into all angles, showing a low gloss; the smoother the paper surface, the smaller the proportion of reflected light diffusion, the higher the gloss. The paper's ink receptivity is directly related to the gloss of the paper. When the same ink film thickness is printed, the high-gloss paper can obtain a higher printing density than the low-gloss paper.
For prints, glossiness is a very important quality indicator. In a sense, it determines the aesthetic beauty of prints. The gloss of the print is based on the high gloss of the paper. The smoother and delicate the surface of the paper, the higher the gloss, the higher the surface gloss of the ink after printing, the higher the color saturation. High-gloss paper can make the image clearer and brighter after printing, more reproducible layers, and more prominent visual effects. Low-gloss paper, printed with dull colors, layering and sharpness will be affected, making the entire screen appear dull. However, it is not the higher the gloss of paper, the better. Some printed papers with high gloss give people a feeling of flashiness, thinness and dullness, and some prints made of paper with low gloss give people With a deep, dignified and lively feeling. Therefore, the printer should select the paper with suitable glossiness according to the effect of the printing product, which is also a very important aspect of obtaining a good print. (to be continued)