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: loss of processing costs, repair costs, raw material costs; chaos in the printing operation sequence; efficient production is hindered and costs rise; unable to provide valuable printed products, resulting in 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 examples of common faults in gravure printing.
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. The printing speed is fast;
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. Around 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 special 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 elaborate in most printing failures, especially in recent printing The emergence of paper and the pursuit of high-speed printing are more prone to this phenomenon. Static electricity mainly includes friction charging, flow charging, ejection charging, peeling charging, crushing charging, stirring charging and mixed charging. Among them, the most relevant to printing are friction 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. The 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. Different environmental conditions have different electrification;
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.
corresponding strategy:
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 environmental humidity of 50% or less, and control the humidity above 65% to reduce the flow of electricity;
3. Check the static electricity removal state of the machine to reduce the friction and electrification;
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.
1. Beard phenomenon: beard-like ink flying in the black angles of the printed matter, the word frame, and the sharp corners of the solid printed part.
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. Ink splashing phenomenon: fibrous ink flying occurs a few centimeters away from the pattern.
Countermeasure: To reduce the viscosity of ink, it is effective to use a mixed solvent of fast and slow solvents.
3. Moiré phenomenon: There is no obvious fog or circle in the printed part on 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 on 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.
Countermeasure: Before and after the use of ink should be filtered; the scraper should be ground or replaced; the circulation pump should be filtered during use.
2. Squeegee dust phenomenon: there are filamentous dirt lines on the solid part and the end part of the bold type.
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.
Countermeasures: Remove debris: Ink filtration 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 soft.
3. Random drawing marks: 1-2cm high dirt lines are randomly generated in the pattern and non-line drawing parts of the printed matter.
Cause: Small and soft inclusions, after flowing out from the gap between the doctor blade and the plate roller, become dirty.
Countermeasures: Ink filtering; environment re-cleaning; the width of the plate roller 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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