Process failure problems in gravure
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In the gravure process, we often encounter some process failures. These processes not only occur in the printing process, but also in the pre-press and post-processing areas. The occurrence of these failures often results in: loss of processing costs, repair costs, and raw material costs; confusion in the order of printing operations; efficient production is hindered, costs increase; and valuable printed products cannot be provided, resulting in a decline in market competitiveness.
In gravure, the problem of process failure occurs mainly in the following aspects
Pre-press field: incomplete product planning; poor composition of printed materials; incomplete design; poor plate making; poor printing materials, etc.
Printing field: poor printing effect; hue does not match: size is not accurate; poor printing adaptability; poor printing conditions; inaccurate printing precision; incomplete printing equipment; poor printing operation; poor printing workshop environment, etc.
Post-press processing: poor lamination; poor adaptability of bag making; poor adaptability to filling; poor post-processing performance (boiling, steam sterilization); poor light resistance; poor storage and storage performance; : Convenient performance and so on.
The following are some common fault examples in gravure
The smear, also called the non-pattern phenomenon, refers to the phenomenon that the ink that has passed through the squeegee is transferred to the printing paper, which is a special malfunction in gravure printing.
The main disadvantages of producing a stain are:
1, printing speed is fast;
2, printing ink viscosity is hard;
3. Less use of thinner;
4, a large number of solvents other than No. 2 (standard), No. 3 (dry slow) desiccant;
5. The drying of the ink is slow;
6. The scraper is in a wave state, the blade is too probing, the blade pressure is too large, and the scraper angle is not allowed;
7, the plate around the roller is too thin.
In the case of a smear, we should analyze and adopt a corresponding solution.
1. Reduce the speed of printing and reduce the viscosity of the ink to reduce the shear stress:
2. Increase the amount of diluent resin to improve lubricity;
3. Suspend the use of ultra-fast drying and slow drying solvents in an effort to improve resolubility;
4. Improve drying performance.
Among the above solutions, the first one 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 blade setting, grinding angle, etc.;
3. Excessive force applied to the scraper.
In short, a factor can not lead to the occurrence of failures, taking into account the comprehensive factors of many aspects, summing up comprehensive countermeasures. Electrostatic failure, which is the most difficult to explain in most printing failures, especially the recent printing The appearance of paper and the pursuit of high speed printing are 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 the film and the guiding liquid and the 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 word 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, moiré
Phenomenon: There is an inconspicuous fog or round appearance in the printed part of the field, especially in the case of using ink 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 performance of the blade failure is:
1, scraper line
Phenomenon: Unrelated long lines appear in printed matter and non-lined parts.
Cause: There is a smudge line between the scraper and the plate roller with foreign matter, or the scraper is poorly ground and damaged.
Thin thick line: 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 part 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 too hard or too soft on the scraper.
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 blade failure, the phenomenon of inclusions is the most common. The thorough filtration of the ink (150-200 mesh) can prevent dust from entering the printing room. It is also an important part to pay attention to the cleaning of the environmental hygiene in the printing room.