Collection of common technical problems of gravure printing machine

- Apr 17, 2020-

Overprint error

Overprint errors are mostly common defects in the printing of gravure printing machines.The phenomenon is that in the multi-color overprint process, each color cannot completely overlap, and there is a certain error.


The first aspect: personnel quality

Because the color registration error exists objectively, it requires employees to have a strong working ability. Printing is a meticulous job, and it must be attentive, careful and responsible. Self-inspection and self-inspection should be done during work, and observations should be made by multiple parties to find problems in time.


Second aspect: equipment factor

The precision and performance of the entire equipment, the tension control of the overprint, the heating and air supply system, the cooperation of the imprinting rubber roller, plate roller, plate shaft, guide roller and other systems, these conditions determine the temperature, pressure, parallelism, stretch Long rate, winding, etc., and the color registration system itself limits its accuracy.

The increase of the plate roller is not suitable, and it is easy to produce longitudinal color registration inaccuracy, 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 setting of the substrate is unreasonable, the tension is too small, the substrate is slack, and the color registration in the vertical and horizontal directions is inaccurate; if the tension is too large, the substrate shrinks laterally and the color registration in the vertical direction is unstable.

The temperature is not suitable, especially if the temperature of the oven is too high, and the temperature of the cooling roller is too high to deform the film. For a film that is not flat, the temperature of the preheating box should be appropriately increased.

The intake and exhaust air flow in the oven is unbalanced, which causes the film to shake in the oven. The anemometer should be used to measure the intake and exhaust air flow and control it.

The plate roller is not installed properly. If eccentricity occurs, the ink on the plug must be cleaned before the plate roller is installed.

Scraper line

Causes

1. No ink marks. The main reason is that hard impurities such as sand are mixed into the ink. These hard particles are embedded in the blade edge of the scraper. Sometimes such scraper line marks are also dashed lines, and such scraper line marks can easily damage the printing and the scraper.

2. Thick continuous ink scrape line marks with ink. This is mainly caused by some coarse soft particles or impurities pushing up the doctor blade, or the blade edge damage. This is the simplest and most common scraper line mark.

3. "Meteor" -like scratch marks. This type of scraper line marks generally appear on the printing plate roller with very shallow dots or unengraved dots, which appear and disappear from time to time, which is extremely harmful to product quality. The causes of this type of scraper line marks are relatively complicated. For years, people have been explaining from the aspects of ink, plate-making, and printing environment, but so far, no one has been more complete. Better is the "active particle hypothesis".

4. Filamentous continuous scraper line marks. This type of squeegee line is as small as a hairline, and it often appears in the printing process, and it is difficult to observe on the printing machine. When it is discovered, a large number of products have been printed, so the quality is greatly damaged. This type of line 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 that the hair is silky at first, and then slowly distributed in a band shape It cannot be wiped off with a bamboo knife. The reasons for its occurrence are very complicated. It involves ink, plate-making, environmental temperature, humidity, and softness of the blade. It needs specific analysis and treatment. In general, there are probably the following aspects: a. Plate roller. The surface finish of the roller is not good, 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. Ink. The ink is not fine enough, the pigment particles are too large, and particulate impurities are mixed during the use of the ink; the dilution of the ink is not standardized, resulting in a solvent impact phenomenon; the ink has poor antistatic performance and poor lubrication performance. The use of high-hardness pigments produces lines. c. Environmental aspects. The temperature, humidity and cleanliness of the air in the printing shop will also be affected. d. Scraper. Hard scrapers produce more line marks than soft scrapers. In addition, if the scraper line marks cannot be processed in time, a large bundle of scraper line marks will be generated around the line marks as the scraper swings back and forth.

Countermeasures

When installing the knife, it must be smooth and careful. Before installing the knife, check whether the scraper blade has a gap. After the knife is installed, it must be carefully ground. If there is a knife wire during the printing process, it must be stopped and then carefully ground.

The environment must be governed to reduce dust before troubleshooting. 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 in the part of the shallow net, such as rough version, excessive uneven gradient, and unsuitable net depth. Generally, the metallographic sandpaper should be used to grind the plate. Pay attention to the uniform force when grinding the plate, and especially return it to the platemaking factory for processing.

Reduce the viscosity of the ink. If the viscosity is too high, the printing surface ink dries too quickly, which relatively increases the friction between the printing plate cylinder and the doctor blade, making it difficult for the doctor blade to scrape the wire formed by the printing ink.

If the knife wire is caused by ink, it is generally caused by garbage in the ink or uneven dissolution of the ink. Filter ink or reselect a solvent with strong dissolving power or change the ink.