Factors affecting the uneven color of the product:
1. The uneven thickness of the ink layer caused by the printing bar marks. The so-called printing "bar mark", also known as "back glue shadow", commonly known as "rubber roll mark". It is also a common process defect in the process of plate printing, that is, there are one or more stripes shadow traces with obvious differences in the color shade in the horizontal position of the printed product, which greatly affects the aesthetic sense of the product. There are many reasons for the printing bar marks, including operational technical reasons and technological factors. Such as uneven or too high plate pad, printing pressure is too heavy, the inking roller is hard and easy to slip or its height is not adjusted well, the inking roller is not enough, the amount of ink is insufficient, or the rubber roll head wear gap is the source of printing bar marks. In addition, factors such as ink hue, ink shade difference, and poor adjustment of ink viscosity are also one of the reasons for printing bar marks. Therefore, all aspects of the printing technology should be effectively done to effectively prevent the printing defects of uneven ink layers.
2. The lack of the amount of ink in the series leads to the uneven color of the ink strip. The difference in the thickness of the ink layer caused by the longitudinal position of the printing is also a common situation in plate printing. This is because of the defects in the ink hopper structure, it can not be adjusted into a very accurate longitudinal ink delivery uniformity, for this reason, there are several groups of iron rollers that play the role of ink, and the size of the string stroke can be adjusted at will, when printing products with large amounts of ink, the string stroke of the iron roller should also be adjusted to ensure the uniform distribution of ink.
3. The printing area is too large, and the structure and performance of the equipment are not suitable for the uneven ink layer. The larger the printing layout, the stronger the adhesion between the ink layer and the printing plate, so when embossed, due to the imbalance between the adhesion of the ink and the printing plate and the adsorption force of the paper on the ink, it is inevitable to be locally produced, so the ink layer is broken, and therefore cannot be uniformly and completely transferred to the paper. Therefore, to print large-area plate products, it is appropriate to use a rotary platform press with a circular flattening structure or a rotary press with a circular press, so that the printing ink color is uniform.
4. Uneven printing pressure or plate support is not solid, so that the page ink layer can not be uniformly transferred to the substrate. When the printing pressure is uneven or insufficient, the ink layer on the page can not be uniformly or completely transferred to the substrate, so that the ink layer of the printing product is concentrated or inked. In addition, if the letterpress process uses a wooden base to print a larger area of the plate, because the base is easy to produce compression deformation, and the firmness is insufficient, the ink layer of the printing is often false and uneven, and the batch of products are also prone to ink concentration and inconsistency. Therefore, the letterpress process should use the gold plate plate to ensure the printing quality.
5. Ink viscosity is too large and the ink layer is too thick caused by uneven ink color. When the stroke of the iron roller is too small, and the gap between the steel sheet and the iron roller is too large, then the ink layer of the ink hopper is thick, and it is not easy to be evenly coated, and after being transferred to the plate, there are often fine scale spots, which is due to the adsorption force of the paper on the ink is less than the adhesion of the ink on the printing plate.
6. Inker iron roller grinding loss circle and steel sheet edge curve serious, resulting in inking quantity imbalance resulting in uneven ink layer. In these cases, appropriate repair measures must be taken to keep the iron roller as close to the concentricity as possible and to grind the edge of the steel sheet into a straight line, so that the amount of ink produced by the ink roller on the ink hopper can be controlled flexibly, so as to avoid uneven color in the printing.
7. Poor roller precision, improper roller position adjustment and too hard colloid cause uneven ink distribution. When the rubber roller head is worn or the rubber roller is in poor contact with the iron roller, the more uniform ink distribution and ink transfer can not be achieved. In addition, when the colloid of the inking roller is hard, it is easy to slip in the process of layout inking, causing the defects of printing bar marks and uneven inking, affecting the printing quality of the layout.
