Fault Analysis and Maintenance Countermeasures of Gravure Process
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A factor is unlikely to lead to failures, taking into account multiple factors. Electrostatic failure, which is the most difficult to explain in most printing failures, especially the recent emergence of a variety of printing paper and the pursuit of high speed printing, this phenomenon is more likely to occur. Electrostatics are mainly triboelectrically charged, flow charged, ejected and charged, stripped and charged, pulverized and charged, and agitated and charged. The most important relationship with printing is triboelectric charging, flowing charging and stripping charging. Compared with other types of work, printing can be said to be a very easy job to generate static electricity. In the future, research on countermeasures against static electricity will become an important management project.
In gravure printing, the main causes of static electricity are:
1. Friction of air and film;
2. Friction and peeling of film and guiding liquid and pressure roller;
3. The type of film is different, the chargeability is different;
4. Due to different types of ink, there are differences in chargeability;
5. The environmental conditions are different, there are differences in electrification;
6. The machine's power (ground) state is not the same, so there are differences;
7. The difference in printing speed chargeability.
Corresponding strategy:
1. The angle of the pressure roller to the running state of the printing paper is an obtuse angle to reduce the stripping electrification;
2. Control the humidity, avoid 50% of the ambient humidity, should be controlled above 65% humidity to reduce the flow of electricity;
3. Check the static state of the machine to reduce frictional charging;
4. Reduce the printing speed to reduce stripping, flow friction and charging.
The most common phenomena in electrostatic failure are "beard", "splashing" and "moire". It is necessary to pay attention to the treatment of various phenomena.
1. Beard
Phenomenon: The black-faced characters, the letter box, and the printed area of the printed object have a whisker-like ink flying at an acute angle.
Countermeasure: Generally improve the viscosity of the ink and reduce the printing speed to solve the problem. Now that the addition of the antistatic agent does not improve the results, the differential effects of the printed film can be considered.
2. Splashing ink
Phenomenon: A few centimeters from the pattern, a fibrous ink flying occurs.
Countermeasure: Reduce the viscosity of the ink and use a solvent mixture of fast and slow solvents.
3. Moire
Phenomenon: There is an inconspicuous fog or round appearance in the printed part of the field, especially in the case of inks with toluene.
Countermeasure: This has little to do with the viscosity and printing speed of the ink. It is especially effective to add an antistatic agent and a small amount of alcohol.
Scraper, it can be said that more than 70% of the faults in gravure printing occur between the doctor blade and the plate roller. The main manifestations of the blade failure are:
1. Scraper line
Phenomenon: Unrelated long lines appear in printed matter and non-lined parts.
Cause: There is a grainy dirt line between the scraper and the plate roller, which is contaminated with foreign matter, or the blade is poorly ground and damaged. Thin thick lines: There are hard inclusions, causing blade damage: thick thick lines: soft inclusions, double lines appear in the center of the pattern.
Countermeasure: The ink should be filtered before and after use; the scraper should be ground or replaced; the circulating pump should be filtered during use.
2. Scraper dust
Phenomenon: The solid part, the end of the bold type, has a silky dirty line.
Cause: There is a soft foreign matter accumulation on the inside of the scraper. Due to the transfer of the scraper at the end of the pattern, the foreign matter is left behind and a dirty line is generated.
Countermeasure: remove debris: ink filtration and cleaning the inside of the scraper; reduce the viscosity of the ink; when installing the scraper, you should pay attention to the length of the scraper to avoid the scraper is too hard or too soft.
3. Random traces
Phenomenon: In the printed and non-lined parts of the printed matter, a dirty line of 1-2 cm is randomly generated.
Cause: Small and soft inclusions are dirty after flowing out of the gap between the scraper and the plate roll.
Countermeasure: filtration of the ink; re-cleaning of the environment; the width of the roll before printing must be reset.
In the case of scraper failure, the phenomenon of inclusions is the most common. It is also an important part to thoroughly filter the ink (150-200 mesh) to prevent environmental cleaning in the printing room.