In the process of gravure printing, we often encounter some process failures. These processes not only occur in the printing process, but also appear in the field of pre-press production and post-processing. The occurrence of these failures often results in the loss of processing costs, repair costs, and raw material costs; the chaotic sequence of printing operations; efficient production is hindered and costs rise; and the inability to provide valuable printed products leads to a decline in market competitiveness.
In gravure printing, the problems of process failures are mainly manifested in the following aspects
Prepress area: incomplete product planning; poor composition of printed matter; incomplete design; poor platemaking; poor printing materials, etc.
Printing field: poor printing effect; inconsistent color: inaccurate size; poor printing adaptability; poor printing conditions; inaccurate printing precision; incomplete printing machine equipment; poor printing machine operation; poor printing workshop environment, etc.
Post-press processing field: poor lamination; poor adaptability of bag making; poor adaptability of filling; poor post-processing performance (boiling, steam sterilization); small light resistance; poor storage adaptability; good circulation performance : Convenient performance and so on.
The following are some examples of common faults in gravure
Plate fouling, also known as non-patterning phenomenon, refers to the phenomenon that the ink that has leaked through the doctor blade is transferred to the printing paper, and is a unique fault in gravure printing.
The unfavorable factors that cause plate contamination are:
1. Fast printing speed;
2. The printing ink has a hard viscosity;
3. Less dosage of thinner;
4. Use a lot of solvents other than No. 2 (standard) and No. 3 (slow drying) desiccant;
5. The drying of ink is slow;
6. The scraper is in a wavy state, the blade is protruding too much, the pressure of the scraper is too large, and the angle of the scraper is not accurate;
7. The plate roller is too thin.
If there is plate contamination, we should analyze and adopt corresponding solutions.
1. Reduce the printing speed and the viscosity of the ink to reduce the shear stress:
2. Increase the amount of thinner resin to improve lubricity;
3. Discontinue the use of ultra-drying and slow-drying solvents in an effort to improve resolubility;
4. Improve drying performance.
Of the above solutions, the first is the most effective strategy. In addition, we should also pay attention to the following matters:
1. The circumference of the plate roller should be small;
2. The accuracy of the given scraper, grinding angle, etc .;
3. Excessive force applied to the scraper.
In short, one kind of factor can not lead to the occurrence of failures, we must consider the comprehensive factors of various aspects, and summarize the comprehensive countermeasures. Electrostatic failure, which is the most difficult phenomenon to explain clearly in most printing failures, especially recently The emergence of paper and the pursuit of high-speed printing are more prone to this phenomenon. Static electricity mainly includes frictional charging, flow charging, ejection charging, peeling charging, crushing charging, stirring charging and mixed charging, among which the most relevant to printing are frictional charging, flow charging and peeling charging. Compared with other types of work, printing can be said to be very easy to generate static electricity. Future research on countermeasures against static electricity obstacles will become an important management project.
In gravure printing, the main causes of static electricity are:
1. Friction between air and membrane;
2. Friction and peeling of the film and the guide fluid and pressure roller;
3. Different types of membranes have different charging properties;
4. Due to the different types of ink, the chargeability is different;
5. With different environmental conditions, the chargeability is different;
6. The machine's static electricity removal (ground) status is different, so there are differences;
7. The difference in the chargeability of the printing speed.
1. The angle of the pressing roller to the running state of the printing paper is obtuse to reduce the peeling charge;
2. Control the humidity, avoid the ambient humidity of 50% or less, and control the humidity above 65% to reduce the flow of electricity;
3. Check the static-removal status of the machine to reduce frictional charging;
4. Reduce the printing speed to reduce peeling and flow frictional charging.
The most common phenomena in electrostatic faults are "beard", "splashing ink" and "cloud pattern". It is necessary to pay attention to the countermeasures for various phenomena.
Phenomenon: the black ink, the letter frame of the printed matter, and the sharp corners of the solid printed part have whisker-like ink flying.
Countermeasures: Generally increase the viscosity of the ink and reduce the printing speed to solve the problem. At present, the addition of static electricity preventive agent has not improved the results, so we can consider the different influence of the printed film.
2. Splashing ink
Phenomenon: A few centimeters away from the pattern, fibrous ink flying occurs.
Countermeasure: To reduce the viscosity of ink, it is effective to use a mixed solvent of fast and slow solvents.
Phenomenon: There is no obvious fog or circle in the printed part of the field, especially when using ink with toluene.
Countermeasure: This has nothing to do with the viscosity of the ink and the printing speed. Adding a static preventive agent and a small amount of alcohol is particularly effective.
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 performance of the scraper failure is:
1. Scraper line
Phenomenon: Unrelated long lines appear in the printed matter and non-line drawing parts.
Cause: Striated dirt lines with foreign objects between the blade and the plate roller are generated, or the blade is poorly ground and damaged.
Thin thick lines: There are hard inclusions that cause damage to the blade: Thick thick lines: There are soft inclusions, and double patterns appear in the central part of the pattern.
Countermeasures: Ink should be filtered before and after use; the scraper should be reground or replaced; the filter should be filtered during the use of the circulating pump.
2. Scraper dust
Phenomenon: The solid part and the end part of the bold type have silky dirt lines.
Cause: There is a buildup of soft foreign objects on the inside of the scraper. Due to the transfer of the scraper at the end of the pattern, the foreign objects are left out and produce stains.
Countermeasure: Remove debris: Ink filtering and cleaning the inside of the blade; reduce the viscosity of the ink; when installing the blade, you should pay attention to the length of the blade to avoid the blade being too hard or too soft.
3. Random drawing marks
Phenomenon: In the pattern and non-line drawing part of the printed matter, a dirt line with a height of 1-2cm is randomly generated.
Cause: Small and soft inclusions, after flowing out from the gap between the doctor blade and the plate roller, become dirty.
Countermeasures: Ink filtration; environment re-cleaning; the roll width of the printing plate must be reset before printing.
In the case of squeegee failure, the inclusion of inclusions is the most common phenomenon. Thoroughly filtering the ink (150-200 mesh) can prevent the mixing of dust in the printing room. It is also an important part to pay attention to the cleaning of the environmental hygiene of the printing room at any time.
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