Poor cot accuracy, improper cot position adjustment and too hard gel cause uneven ink distribution
When the rubber roller shaft head is worn or the rubber roller and the iron roller are in poor contact, the more uniform ink distribution and transfer can not be realized. In addition, when the colloid of inking roller is too hard, it is easy to slip in the process of layout, causing the defects of printing bar mark and uneven inking, which affect the printing quality of layout.
The iron roller of the ink bucket is seriously worn out of round and the edge of the steel sheet is curved
The ink layer is uneven due to the imbalance of ink delivery. When these conditions exist, we must take corresponding repair measures to keep the iron roll as concentric as possible, and grind the edge of the steel sheet into a straight line, so that the ink output of the ink roll on the ink hopper can be controlled flexibly, so as to avoid uneven vertical color of the printing.
Ink viscosity is too large and ink layer thickness caused by uneven ink
When the stroke of the iron roller is adjusted too small, and the gap between the steel plate and the iron roller is adjusted too large, the ink layer of the ink roller is thick, and it is not easy to be evenly coated. After being transferred to the layout, fine scale spots often appear, which is the result of the paper's less ink adsorption than the ink's adhesion on the printing plate.
The printing pressure is uneven or the plate holder is not solid
The ink layer of the layout cannot be transferred to the substrate evenly. When the printing pressure is uneven or insufficient, the ink layer on the layout can not be transferred to the substrate evenly or completely, resulting in uneven ink layer thickness or inking. In addition, if a large area of plate is printed with a wood base in the embossing process, the base is easy to produce compression deformation, and the firmness is insufficient, so that the ink layer of the printed products is often not solid and uniform, and the ink color of the batch products is easy to be different. Therefore, the embossing process should adopt the metal plate to support the adhesive plate, so as to ensure the printing quality.
The printing area is too large, the structure and performance of the equipment are not suitable, resulting in uneven ink layer
The larger the printing plate is, the stronger the adhesion between the ink layer and the printing plate is. In this way, due to the imbalance between the adhesion between the ink and the printing plate and the adsorption of the paper to the ink, it is inevitable that the ink layer will break up and cannot be transferred to the paper surface evenly and completely. Therefore, for printing large area plate products, it is better to use rotary platform printing machine with circular flattening structure or rotary printing machine with circular flattening type, so as to obtain even ink color.
Insufficient stroke of inking volume leads to uneven striped ink color
The difference of ink layer thickness caused by the vertical position of printing is also a common situation in plate printing. This is because of the structural defects of the ink hopper, it is impossible to adjust it to a very accurate uniformity of the longitudinal ink feeding. Therefore, some automatic printing machines are equipped with several groups of iron rollers which play the role of ink stringing, and the stroke size of the iron rollers can be adjusted at will. When printing products with a large amount of ink, the stroke of the iron rollers should also be adjusted to ensure the uniformity of ink distribution.
Uneven ink layer caused by printing mark
The so-called printing "bar mark", also known as "back glue shadow", commonly known as "cot mark". It is also a common process defect in the process of plate printing, that is, there are one or more stripes with obvious differences in ink color in the horizontal position of the printed product, which greatly affects the aesthetic feeling of the product. There are many reasons for printing bar marks, including technical reasons and technological factors.
Such as uneven or too high plate pad, heavy printing pressure, too hard roller easy to slip or poor height adjustment, insufficient number of inking roller, insufficient ink amount or roller head wear clearance, etc., are the sources of printing marks.
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