Influencing factors of printing color difference

Uniform ink color and bright color are the basic requirements for the quality of packaging products, and printing color difference is a common problem for the quality of printed products. Looking at the printing process, there are many reasons for the color difference in printing. There are adverse factors in the process technology and raw materials. Therefore, to correctly understand and understand the relationship between these printing conditions and ink color is of great significance to accurately control the quality of printing ink color and prevent the occurrence of printing color difference.

1. Printing color difference caused by bad ink

The process shows that the printing ink layer thickness and viscosity are not suitable for printing color difference. When printing, only a moderate and uniform printing ink layer can better ensure the ink color quality of the printed matter and effectively prevent the occurrence of printing stickiness. If the printing ink layer is too thick, its viscosity will increase accordingly, which will easily cause the paper surface to be powdered and fluffed during printing, which will affect the uniformity of the ink color of the printed product. However, if the printing ink layer is thin and the ink viscosity is too small, the ink color of the printed product will appear lighter, and the visual effect of the printed product will be poor. On the other hand, Shan Yu ink has thixotropic properties. As the operating time of the printing machine increases and the printing speed increases, the friction coefficient of the machine increases, and the temperature of the ink will gradually increase. It will decrease accordingly, so that the printing ink color will become lighter and lighter, so that the color of the ink is inconsistent before and after the batch of products to form a color difference. Therefore, these factors must be fully taken into account when withering ink, and the appropriate ink concentration should be adjusted according to the climate temperature and the characteristics of the printing machine to reduce the chance of color difference in printing and make the printing ink color relatively stable. However, in the actual printing process, the decrease in ink viscosity is inevitable. Often the prints that have just been printed are thicker in color, and then gradually faded. In this way, the amount of ink delivery can be gradually increased by appropriately adjusting the rotation angle of the transfer iron roller , So that the ink colors printed before and after are basically consistent. When mixing inter-color and multi-color inks, try to avoid mixing inks with large differences in specific gravity, so as to avoid the printing of the ink in the ink fountain due to the large difference in specific gravity, resulting in "layering" (that is, precipitation and suspension). Color difference. In order to keep the ink continuous and evenly transferred, the ink in the ink fountain should be stirred frequently with an ink knife. In addition, because the amount of ink in the ink fountain is significantly reduced during the printing process, it is easy to make the gap between the ink fountain steel sheet and the ink transfer iron roller smaller, which reduces the ink output and makes the ink color of the printed product lighter. In order to avoid this from happening, it should also be noted that the ink fountain is often refilled in production, so that the ink fountain always maintains a certain amount of ink. In order to prevent the ink viscosity from changing too much and affecting the balance of the ink color of the printed product, the contact between each rubber roller and the iron roller should not be too tight, and the rubber roller should not be too hard, to minimize the impact of friction heat on the thixotropy of the ink To reduce the fading of ink.

2. Printing color difference caused by uncomfortable pressure

Printing pressure is one of the conditions for ink transfer. Since the surface of the printing plate cannot be absolutely flat, the surface of the paper also inevitably has fine unevenness and uneven thickness. If the printing pressure is insufficient or uneven, the printing ink layer will be It is prone to uneven density. The ideal printing process is based on the "three flats", that is, the printing plate surface, the substrate and the liner surface must be relatively flat, so that the thin ink layer can obtain the printed products through the function of equalizing the printing pressure. More uniform ink color. When the printing pressure is insufficient or uneven, and there is a poor contact between the liner body and the printing plate surface, it is necessary to increase the amount of ink delivery to meet the visual effect of the printing plate, but this will not only increase the consumption of ink , It is easy to produce printing chromatic aberration and printing quality problems. Therefore, to prevent the occurrence of printing chromatic aberration, we should grasp the basic conditions of printing "three flats", and use uniform and constant pressure for printing. If you are printing a large-area plate product with a letterpress process (using a round flattening or flattening machine), it is best to use a metallic underlay material. In this way, the flatness and robustness of the material are better, and the printing pressure is more comparable. Stable, it is helpful to prevent the printing color difference caused by pressure variation.

3. Printing color difference caused by bad ink roller

For lithographic and letterpress printing processes, whether the printed product can obtain a uniform ink color, the quality of the rubber roller has a vital role. The machine that prints color printing crystals is generally equipped with three types of ink transfer roller, uniform ink roller and ink roller Among them, the ink transfer roller and the inking roller have the greatest influence on the color density of the ink. However, the elasticity, viscosity, center, hardness and surface finish of the ink roller largely determine the quality of the ink color of the printed product. If the ink roller has poor elasticity, insufficient viscosity, eccentric roller body, too hard colloid, and poor colloid finish, etc., it is easy to cause uneven or unstable ink brushing during the printing process, resulting in inconsistent printing ink colors. Therefore, when printing color products, rubber rollers with good quality should be used to ensure that the ink applied to the plate surface in each printing cycle remains basically the same. If printing large quantities of products, the rubber roller should be cleaned in time to ensure that the paper dust and impurities remaining on the rubber roller can be removed to ensure the uniform transmission of the ink and prevent the occurrence of printing chromatic aberration. On the other hand, the contact position of the ink roller and the ink-crossing iron roller should be adjusted. Generally, the automatic printing machine is provided with several groups of ink-crossing devices to achieve uniform ink delivery. However, if there is poor contact between the rubber roller and the ink-crossing iron roller, it will inevitably cause insufficient and uneven ink transfer, which will cause unevenness in the ink color of the horizontal layout of the printed product. In this regard, the shaft ends at both ends of the rubber roller should be adjusted to achieve uniform contact between the rubber roller and the iron roller. After adjustment, a steel sheet of Sichuan 5 wire can be inserted into the rubber roller and the iron roller for drawing inspection and drawing. The steel sheet has a degree of obvious resistance. In addition, the contact position between the ink roller and the printing plate surface should also be adjusted. If the inking roller is adjusted too high, the layout cannot get a uniform and sufficient amount of ink coating, and it is easy to produce printing streaks due to the inking roller slipping on the layout. If the inking roller is adjusted too low, the ink layer on the plate surface will be scraped to the trailing part of the printing plate, causing the color difference of the ink color of the printed product before and after the lightening, that is, the ink color of the mouth part is lighter, and the ink color of the trailing part is thicker . The inking roller and the printing plate surface should be adjusted into a parallel and uniform contact state. Only by accurately adjusting the contact position between the inking roller and the printing plate surface can the printing ink color be uniform.

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