Failure Analysis and Maintenance of Gravure Printing Process

During gravure printing, we often encounter some process failures. These processes not only occur in the printing process, but also occur in prepress and post-processing areas. The occurrence of these failures often results in the loss of processing costs, repair fees, and raw material costs; the order of printing operations is chaotic; efficient production is hindered and costs increase; valuable printed products cannot be provided, leading to a decline in market competitiveness.

In gravure printing, the problem of process failures is mainly manifested in the following aspects.

Prepress area: Incomplete product planning; poor print composition; incomplete design; bad platemaking;

Printing field: poor printing effect; inconsistent hue: inaccurate dimensions; poor print adaptability; poor printing conditions; inaccurate printing accuracy; incomplete press equipment; poor press operation; poor printing shop environment, etc.

Post-press processing: defective laminates; poor suitability for bag making; poor packing adaptability; poor post-processing performance (boiling, steam sterilization), poor light resistance, poor storage and adaptability, and poor flowability : Convenient for poor performance and so on.

Here are some examples of common failures in gravure printing.

The “pollution”, also called “non-graphic” phenomenon, refers to the phenomenon that the ink that has missed the doctor blade is transferred to the printing paper, and is a unique failure in gravure printing.

The unfavorable factors that produce stains are:

1, printing speed;

2, printing ink viscosity hard;

3, less diluent;

4. Extensive use of solvents other than No. 2 (standard) and No. 3 (slow drying) desiccants;

5, the ink drying is slow;

6, the blade is in a wavy state, the blade is too much, the blade pressure is too large, and the angle of the blade is not accurate;

7, the plate around the roller is too thin.

There is version pollution, we should analyze and adopt the corresponding solution.

1, reduce the printing speed, reduce the viscosity of the ink, in order to reduce the shear stress:

2, increase the amount of thinner resin, in order to improve the lubrication;

3, suspend the use of special speed drying, slow drying solvents, and try to improve the re-solubility;

4, to improve the 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 roller must be small;

2. The accuracy of the given blade, grinding angle, etc.;

3, too much force applied to the blade.

In short, one kind of factor can't cause the trouble to happen, should consider the comprehensive factor in many aspects, sum up the comprehensive countermeasure. Electrostatic trouble, this is the phenomenon that is most difficult to explain in most printing troubles, especially recent printing With the emergence of paper and the pursuit of higher speed printing, this phenomenon is more likely to occur. Static electricity mainly includes frictional electrification, flow electrification, discharge electrification, stripping electrification, smashing electrification, and stirring electrification and mixed electrification. Among them, friction and electrification, flow electrification and stripping electrification are the most important in relation to printing. Compared with other types of work, printing can be said to be very easy 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, air and film friction;

2, film and guide liquid, pressure roller friction, peeling;

3, the type of membrane is different, there are differences in chargeability;

4, due to the type of ink is not the same, there are differences in the chargeability;

5. The environmental conditions are different, and there is a difference in electrification;

6, the machine's power (ground) status is not the same so there are differences;

7. The difference in chargeability of printing speed.

corresponding strategy:

1. The angle of the pressure roller to the operating state of the printing paper is an obtuse angle to reduce the peeling electrification;

2, control the humidity, avoid 50% of the environmental humidity, should be controlled at 65% humidity, in order to reduce the flow of electricity;

3, check the static state of the machine to reduce friction and electrification;

4, reduce the printing speed, in order to reduce the stripping, flow friction and electrification.

The most commonly occurring phenomena in electrostatic faults are "beard," "splashing," and "moiré," and it is necessary to pay attention to the treatment of various phenomena.

1. Mustache

Phenomenon: Whisker-like ink flutters at the acute-angled positions of the printed body in black letters, letters, and solid prints.

Countermeasures: Generally improve the ink viscosity, reduce the printing speed can solve the problem. Now that the addition of an antistatic agent does not improve the results, the difference in influence of the printed film can be considered.

2, splash ink

Phenomenon: A few centimeters away from the pattern, fibrous ink flutters.

Solution: Reduce the viscosity of ink, and use a mixed solvent with fast and slow solvents.

3, moire

Phenomenon: In the printed part of the field there is no obvious haze or round appearance, especially the use of ink with toluene is prone to this phenomenon.

Countermeasures: This is not much related to the viscosity of the ink and the printing speed. Adding an antistatic agent and a small amount of alcohol are particularly effective.

Squeegee, it can be said that more than 70% of failures in gravure printing occur between the doctor blade and the plate roller.

Scraper failure is mainly manifested in:

1, scraper line

Phenomenon: There is an unrelated long line in the print and non-line.

Cause: There is a striated fouling line between the squeegee blade and the platen roller, or the squeegee is badly ground and damaged.

Fine Concentration Lines: There are hard inclusions that cause damage to the blade: Thick thick lines: There are soft inclusions, double lines appear in the center of the pattern.

Countermeasures: Before and after the use of ink to filter; scraper to re-grinding or a replacement; circulation pump to filter during use.

2. Scraper dust

Phenomenon: Filament lines appear at the end of the solid and bold characters.

Cause: A soft foreign material accumulates on the inside of the doctor blade, and foreign matter is left behind at the end of the pattern due to the transfer of the doctor blade.

Countermeasures: Remove impurities: Ink filter and cleaning of the inside of the blade; reduce the viscosity of the ink; to install the blade, it should pay attention to the length of the blade to avoid the blade too hard or too soft.

3, random painting marks

Phenomenon: Randomly generated 1-2cm high stain lines on the printed pattern and non-lined parts.

Cause: Fine and soft inclusions, resulting in dirt after escaping from the gap between the blade and plate roller.

Countermeasures: Ink filtration; environment re-cleaning; roll width before printing must be reset.

Squeegee failure, the inclusion of inclusions is the most common phenomenon, thoroughly filtered ink (150-200 mesh) to prevent dust mixed in the printing room. Always pay attention to the cleaning of the interior of the printing room is also an important link.

Schedule gravure common fault list

Factor Relations (● Large, Small Medium, Small Small)

No Fault Name Phenomenon Human Equipment Material Method Environment

1Scratches line stains △△○○●

2 scraper dust patterns tail thread ink △ - ● △ ○

3 circle planning traces of small lines △-○○ ●

4 After the rusty knife has been rusted for a period of time, the scraper blade tends to rust △ -● - ○

5 viscosity change after a period of time viscosity increase △ - ● △ ○

6 Ink failure, lack of gloss due to poor chromogenicity and adhesion - △ ● ○ ●

7 Foaming occurs in the ink fountain - △ ● ○ -

8 skin is difficult to flow in the ink fountain, dry ink appears △ ○ ● △ ○

9 Float color mixing ink separation in the ink fountain - ○ ● △ -

10 Precipitated on the ink roller with sludge-like non-decomposition material - ○ ● △ △

11 Non-graphical film-like oil film transfer to printing paper â–³ â—‹â—‹â—‹â–³
12 paste fine lines, small text breaks, off the bad phenomenon occurs △ ○ ● △ ●
13 mottled stripes appeared - â–³ â—‹ â–³
14 Ink film has a streamlined shade of dots appearing in the shaded area △—●○—`

15 Screening because of the same angle as the screen, there are spots with different shades of △—●○—

16 Poor tone reproduction The spots on the light-colored part of overprinting cannot be correctly reflected, and too thick and too thin misoperation occurs. △—●○○

17 letters are printed with thick ink, the small text is thickened, and the text is damaged △○△△—

18 Electrostatic gas barriers There are beard-like stain lines around the colored area, and the ink flies out. △○●○●

19 Residual solvent Residue of organic solvent, strong odor, plugging accident, poor processing of laminated sheets, etc. △●●○○

20 Print unevenness Because it is a multi-sided printing, the reproducibility of the top and bottom, left and right, and pattern reappears differently, especially the colored part—△—△—

The reproducibility of the wear pattern of the 21st version reflects the lack of â–³ - â—‹ -

22 Overprinting bad pattern position, bag size reflects insufficient △ ● ○ ○ -

23 Adhesion of printing surface and non-printing surface after agglomerating, ink detachment △○●○△

Change in the hue of the mixed ink in the residual ink stored in the 24-color change printing (mostly in the white ink mixture) △△●-

25 Leaving of the guide rail (defective point) Pinhole-shaped ink peels off in the colored and overlapping parts △●○○○

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