Expert advice: paper wrinkle phenomenon and elimination during printing
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During the printing process, paper wrinkles (pleats) are one of the most common failures, and the economic loss is relatively large. There are two main reasons for such failures: one is caused by the paper itself (mostly in non-coating). Paper), the second is the improper use of the machine, the shape and further analysis of the reasons and treatment methods.
During the printing process, paper wrinkles (pleats) are one of the most common failures, and the economic loss is relatively large. There are two main reasons for such failures: one is caused by the paper itself (mostly in non-coating). Paper), the second is the improper use of the machine, the shape and further analysis of the reasons and treatment methods.
1, small hair-shaped pleats
Reasons for producing such pleats:
(1) “Floating edge” produced after the paper absorbs moisture (the paper itself has uneven water content or the relative humidity of the workshop is high, and the water content of the paper is low).
(2) The ink on the back side of the printed on both sides of the print "stack roller" (the ink deposited on the surface of the impression cylinder is too thick, causing local pressure to change).
Approach:
Re-hang the paper; if it is printed on both sides, be sure to wash the impression cylinder.
2, straight and straight pleats (the pleats in the middle of the paper)
The main reason for the generation of such pleats is the deformation of the paper (tight side).
Approach:
Re-hang the paper, if some printing factory does not have the equipment to hang the paper, you can shake the uncut printing paper to be printed one week ahead of time, put it in the printing workshop to adapt to the temperature and humidity around the machine, and then cut it when printing. on board.
3, large pleats
Reasons for producing such pleats:
(1) The edge of the large paper is curled up, and the crepe paper is not good.
(2) The paper is too light at the side of the paper.
(3) The paper corner floats.
(4) The side is not properly positioned, and the paper corner touches the gap of the paper.
Approach:
After the paper is reversed, it is printed on the machine; for the looser crepe paper, it needs to be re-adjusted, and the paper angle floats mainly because the fangs cannot hold the paper.
[Case]:
A factory J2105 type printing middle school textbook, color inserts. Printed on 128g/m2 coated paper, shortly after the official printing, it was found that occasionally the pleats appeared outside, and after careful observation by the outer side, the paper angle and the paper feeding table were judged when the paper was pulled by the side gauge. The gaps collide, causing the pleats to appear.
Approach:
The side gauges are properly displaced to avoid the gap.
[Expert Tips]:
Similar to this phenomenon, the captain should handle it in advance, and can't wait for the problem to occur before processing it.
4, circular pleats
The main reason for the generation of such pleats is that the middle portion of the gripper is too loose, which causes the paper to be lost, and is pulled out to produce pleats during printing.
Approach:
Correct the force of the gripper. If the pad is too smooth, replace it with a new one.
[Case]:
A factory printed a corporate advertising brochure with a four-color offset press and found circular pleats (not every one) where the portraits were printed in the second half.
[case analysis]:
According to the conventional treatment method, it is necessary to check the force of the paper teeth, but in this case, the gripper teeth are good, and it is found that the black spots of the pleats are dense, especially the red ink density is too large, so that here The peeling force is increased, and the above-mentioned malfunction occurs when the gripper is slightly inappropriate.
Approach:
Re-plate, put the portrait of the person in the mouth or the front half of the paper, the fault disappears.
[Expert Tips]:
Most people's portraits or sets of products that require strict requirements, such as portraits or smaller pictures, are best placed in the front half of the mouth or printed paper. In addition, the ink density is not suitable for printing in the second half.
5, large hair-shaped pleats
Reasons for producing such pleats:
(1) The impression cylinder has more than two or more sheets of paper in one place, and even can not hold the paper.
(2) The height of the transfer paper pad is uneven, so that the edge of the paper is not in a straight line and becomes a wavy curve. When the embossing roller picks up the paper and presses the paper, the length of the paper is shortened and a large scatter is generated from the mouth. Pleats.
Treatment method: Check the pressure of the impression cylinder.