其现象是 , 在多色套印过程 , 每一色不能完全重叠 , 有一定的误差 . Overprint errors are mostly common defects in gravure printing.The phenomenon is that in the multi-color overprint process , each color cannot completely overlap , and there is a certain error .
人员素质 The first aspect : the quality of personnel
就要求员工要有极强的工作能力 . 印刷是一项细致的工作 , 必须做到用心、细心、责任心。 Because the registration error exists objectively , employees are required to have a strong working ability . Printing is a meticulous job , which must be carefully, carefully and responsible. Do self-inspection and self-inspection while working, observe from multiple parties, and discover problems in time.
Second aspect: equipment factors
The accuracy and performance of the entire equipment, the tension control of the overprint, the heating air supply system, the rubber roller, plate roller, plate shaft, guide roller and other systems cooperate. These conditions determine the temperature, pressure, parallelism, and extension of the overprint. Length rate, winding, etc., and the color registration system itself limits its accuracy.
The increment of the plate roller is not suitable, and it is easy to cause inaccurate longitudinal color registration. The rubber of the impression roller is deformed and the elasticity is insufficient. Keep the pressure roller in good condition.
The third aspect: operation process
The tension of the substrate is not set properly, the tension is too small, the substrate is loose, and the color registration is inaccurate both vertically and horizontally; if the tension is too large, the substrate shrinks horizontally and the vertical color registration is unstable, and the tension is adjusted accordingly.
The temperature is not suitable, especially the temperature of the oven is too high, and the temperature of the cooling roller is too high to deform the film . For the film that is not flat, the temperature of the preheating box should be appropriately raised. The air intake and exhaust air volume in the oven is unbalanced, causing the film to shake in the oven. An anemometer is used to measure the air intake and exhaust air volume to control it.
The plate roller is not properly installed. If eccentricity occurs, the ink on the plug must be cleaned before the plate roller is installed.
1. No ink marks. It is mainly caused by hard impurities such as sand mixed in the ink. These hard particles are embedded in the blade edge of the scraper. Sometimes such scraper line marks are also dotted lines. Such scraper line marks can easily damage the printing and scraper.
2. Thicker continuous scraper line marks with ink. This is mainly caused by some thicker soft particles or impurities lifting the doctor blade, or the blade edge damage. This is the simplest and most common scraper line mark.
3. "Meteor" shaped scraper line marks. This kind of scraper line marks usually appear on the printing plate roller's screen dots are very shallow or unengraved screen dots, appearing from time to time, which is extremely harmful to product quality. The cause of this type of scraper line marks is more complicated. For many years, people have explained it from the aspects of ink, plate making, and printing environment, but so far, no one is relatively complete. The better one is the "active particle hypothesis".
4. Filament-like continuous scraper line marks. This kind of scraper line marks are as small as hair silk, they often appear in the printing process, and it is difficult to observe on the printing machine. When they are found, a large number of products have been printed, which is extremely harmful to quality. This kind of thread marks can be divided into two types, one is soft and can be gently wiped off with a bamboo knife, mainly caused by impurities; and the other is a silky hair at first, and then gradually distributed in a band shape It ca n’t be wiped away with a bamboo knife. The reasons for this are very complicated. They involve ink, plate making, ambient temperature, humidity, and the hardness of the scraper. Specific problems need to be analyzed. In general, there are probably the following aspects:
a. Plate roller. The surface of the roller is not smooth, the hardness of the chrome layer on the surface of the roller is not enough, the plate roller is too smooth, and it is easy to produce without lubrication.
b. In terms of ink. The ink fineness is not enough, the pigment particles are too large, and the particulate impurities are mixed during the use of the ink;
Ink dilution is not standardized, resulting in the impact of solvents; the ink has poor antistatic properties and poor ink lubrication properties. The use of high hardness pigments can create lines.
c. Environmental aspects. The temperature, humidity and cleanliness of the air in the print shop can also have an effect.
d. In terms of scraper. Hard scrapers produce more line marks than soft scrapers. In addition, if the scraper line marks are not processed in time, a large bunch of scraper line marks will be generated around the line marks with the back and forth swinging of the scraper.
When installing the knife, it must be smooth and careful. Before installing the knife, check whether the scraper blade has a gap. After grinding, carefully grind it. If any wire appears during the printing process, stop the machine and grind it carefully.
You must manage the environment and reduce dust to troubleshoot. The color printing environment should be kept as closed as possible. Air filters can be installed and the dust content can be checked. Otherwise, it is difficult to produce high-quality products.
The knife wire caused by the plate roller generally appears on the part of the shallow screen, such as the plate is rough, the gradation is excessively uneven, and the screen depth is not suitable. Generally, it should be processed by metallographic sandpaper grinding. Pay attention to the uniform force during grinding, and return it to the platemaking factory to deal with it.
Reduce the viscosity of the ink. If the viscosity is too high, the ink on the plate will dry too fast, which will increase the friction between the plate roller and the scraper, making it difficult for the scraper to scrape the wire formed by the ink on the plate. If the knife wire is caused by ink, it is usually caused by garbage in the ink or uneven dissolution of the ink. Filter the ink or re-select a solvent with strong dissolving power or change the ink.