Trouble shooting process
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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 the gravure printing, 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 operation of printing press;
Post-press processing field: poor lamination film; poor adaptability of bag making; poor adaptability of filling; poor post-processing performance (boiling, steam sterilization); good light resistance; poor storage and storage performance; : Convenient performance and so on.
The following are some examples of common faults in gravure.
The smear, also called the non-pattern part phenomenon, refers to the phenomenon that the ink that has passed through the squeegee is transferred to the printing paper, which is a kind of malfunction unique to gravure printing.
The main disadvantages of the resulting pollution are:
1. printing speed is fast;
2. printing ink viscosity is hard;
3. less amount of thinner;
4. Use a large amount of solvents other than No. 2 (standard) and 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:
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, should take into account the comprehensive factors of many aspects, summed up comprehensive countermeasures.
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, moiré
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 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. Keeping an eye on the cleaning of the environmental hygiene in the printing room is also an important part.
Schedule gravure common fault table
Factor relationship (● large, ○ medium, △ small)
No fault name phenomenon person equipment material method environment
1 Scratch Line-shaped dirt line △ △ ○ ○ ●
2 Scraper dust There is a silky ink at the end of the pattern △ — ● △ ○
3 Round plan marks Rain line-like small spots △ — ○ ○ ●
4 Ink knife rust After a period of time, the blade is easy to rust. △ — ● — ○
5 Viscosity change After a period of time, the viscosity increases △ — ● △ ○
6 Ink failure Color development, poor adhesion, resulting in insufficient gloss — △ ● ○ ●
7 Foaming Bubbles appear in the fountain — △ ● ○ —
8 peeling in the ink fountain is difficult to flow, there is dry ink skin △ ○ ● △ ○
9 Floating color The mixed color ink is separated in the ink fountain — ○ ● △ —
10 Precipitation There is a sludge-like non-decomposed substance on the ink roller. ○ ● △ △
11 Non-image part The film-like oil film is transferred to the printing paper △ ○ ○ ○ △
12 Paste plate The appearance of fine lines, small text breaks, and falling off occurs △ ○ ● △ ●
13 Moiré appears with markings — △ ○ △
14 Ink film In the shaded part, there are streamlined spots with different shades. △ — ● ○ —`
15 Screening Because of the same angle as the screen, there are spots of different shades △ — ● ○ —
16 Poor tone reproduction The spots in the light color part of the overprint printing cannot be correctly reflected, and the operation is too thick and too fine. △ — ● ○ ○
17 The text is thick and the solid ink is printed, the small text becomes thicker, and the text is damaged. △ ○ △ ● —
18 Electrostatic gas barrier There is a whisker-like stain around the colored part, and the ink flies out △ ○ ● ○ ●
19 Residual solvent Residual organic solvent, odor is very strong, blockage accident, poor processing of laminated sheets, etc. △ ● ● ○ ○
20 Uneven printed matter Because it is multi-faceted printing, there are differences in the reproducibility of up and down, left and right, and pattern, especially the colored part — △ — △ —
Type 21 wear Pattern reproducibility, insufficient reflection of all concentrations △ — ○ ○ —
22 Poor printing The position of the pattern, the size of the bag is not reflected △ ● ○ ○ —
23 Agglomeration Attached to the printed and non-printed surfaces after winding, the ink falls off △ ○ ● ○ △
24 color change The hue of the mixed ink in the residual ink stored in the printing changes (most of the mixture in the white ink) △ △ ● — —
25 Rail off (疵 point) There is a pinhole-like ink peeling off in the colored and overlapping parts △ ● ○ ○ ○
26 Pulling the ink of the previous unit adheres to the plate △ △ ● ○
27 sets of inaccuracies The reproducibility of the pattern is unstable △ ● — ○ —
28 Paper fluffing Embossing rubber roller/unit wrinkle △ ○ ○ ○ ○