Analysis and elimination of ink color unevenness i

2022-09-21
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Analysis and elimination of printing ink color unevenness

printing ink color uniformity is one of the important conditions to measure product quality. However, the main feature of plate printing products is often that the plate area is large and the ink receiving capacity is correspondingly large. In this way, if the technical process of each link is not properly checked during the loading and brushing process of the printing experimental machine, it is very easy to have ink uneven faults, which will affect the product quality. For example, the thickness of the ink layer on the layout of some products is uneven, or the ink color is not the same before and after the batch of products, and even there are process defects such as fish scale like fine spots or striped ink marks

the main reasons are as follows:

1. Uneven ink distribution is caused by poor rubber roller accuracy, improper adjustment of rubber roller position and too hard colloid. When the rubber roller shaft head is worn or the rubber roller is in poor contact with the inking iron roller, a more uniform ink distribution and ink transfer cannot be achieved. In addition, when the colloid of the inking roller is too hard, it is easy to slip during the inking process of the layout, causing printing bar marks and uneven inking, which affects the printing quality of the layout

2. the ink bucket iron roller is worn out of round and the edge of the steel sheet is seriously curved, resulting in the imbalance of ink delivery and uneven ink layer. In case of these conditions, corresponding repair measures must be taken to keep the iron roller in good concentricity as far as possible and grind the edge of the steel sheet into a straight line, so as to control the ink volume of the ink roller on the ink bucket flexibly, so as to avoid the uneven longitudinal interior color of the print

3. Uneven ink color caused by too high ink viscosity and too thick ink layer. When the stroke of the iron roller of the ink bucket is adjusted too small, and the gap between the steel sheet and the iron roller is adjusted too large, the thickness of the ink layer transported by the ink bucket is not easy to be evenly coated. After being transferred to the plate for stamping, there are often spots with fine scales to ensure a clean and clean scale, which is the result that the adsorption of the paper on the ink is less than the adhesion of the ink on the plate

4. the printing pressure is uneven or the plate holder is not solid, so that the ink layer of the plate cannot be transferred evenly to the substrate. When the printing pressure is uneven or insufficient, the ink layer on the plate cannot be transferred evenly or completely to the substrate, resulting in uneven ink layer or inaccurate inking. In addition, if the embossing process uses a wooden bottom support to print a large area of plates, because the bottom support is easy to produce compression deformation and insufficient firmness, so the ink layer of prints will often produce an uneven shape, and the ink color of batches of products is also prone to be different. Therefore, the embossing process should adopt the metal plate and the adhesive plate to ensure the printing quality

5. The printing area is too large, and 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 on the ink during stamping, it is inevitable to occur locally, so the ink layer breaks, so it cannot be transferred evenly and completely to the paper surface. Therefore, when printing large-area plate products, it is appropriate to use a rotary platform printer with a circular flattening structure or a circular rotary printer with a circular flattening structure, so that the printing ink color can be uniform

6. Insufficient ink amount stroke causes uneven ink color stripe. It is also a common situation in plate printing that the thickness difference of ink layer occurs in the longitudinal position of printed matter. This is because of the defects in the ink bucket structure, which can not be adjusted to a very accurate uniformity of longitudinal ink delivery. Therefore, some automatic printing machines are added with several groups of iron rollers that play the role of inking, and the size of its serial stroke can be adjusted according to the earliest automatic production capacity at will. When printing products with a large amount of ink, the serial stroke of the iron roller should also be adjusted to ensure the uniformity of ink distribution

vigorously promote the intelligent and green transformation of the production process

7. Uneven ink layer caused by printing bar marks. The so-called printing "bar mark", also known as "glue back shadow", is popularly called "rubber roll mark". It is also a common process defect in the process of plate printing, that is, there are one or more bar shadow traces with obvious differences in ink color on the horizontal position of the print, which greatly affects the aesthetic feeling of the product. There are many reasons for printing bar marks, including technical reasons and technological factors. For example, the printing plate is not evenly or too high, the printing pressure is too heavy, the inking roller is too hard and easy to slip or its height adjustment is poor, the number of inking rollers used is not enough, the amount of ink is not enough, or the wear clearance of the rubber roller shaft head is the source of the 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 links of printing technology should be properly controlled to effectively prevent the printing disadvantage of uneven ink layer

in a word, there are many reasons for the uneven ink color of plate printing, which must be carefully analyzed, and corresponding measures should be taken to control the printing process technology, so as to ensure the printing efficiency and quality

source: Interconnection

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