Failure Analysis of Paper Bow and Wrinkle in Printing Process
In the printing process, paper bowing (pleating) is one of the most common failures, and the economic loss is relatively large. The reasons for such failures are mainly two aspects: One is caused by the paper itself (mostly in non-coatings) Paper), the second is the improper use of the machine adjustment, according to its shape to further analyze the cause and processing method.
1 small extruded pleats
Causes of such pleats
(1) The "lotus leaf edge" produced after the paper absorbs moisture (the paper itself has uneven moisture content or the workshop relative humidity is high, and the paper moisture content is low).
(2) The ink on the back of the printed piece on both sides is "stacked cylinder" (the accumulation of ink on the surface of the impression cylinder is too thick, resulting in changes in local pressure).
Treatment method: Hang the paper again; if it is printed on both sides, be sure to wash the impression cylinder frequently.
(Picture 2-2) Small casual pleats
2 Thin straight pleats that do not come out (the pleats are in the middle of the paper)
The main cause of such pleats is the deformation (tight edges) around the paper.
Treatment method: re-hang the paper, if some printing plants do not have the equipment to hang the paper, the uncut printing paper to be printed can be shaken a week in advance and placed in the printing workshop to adapt to the temperature and humidity around the machine. Then cut to machine.
(Figure 2-3) Thin straight pleats
3 large crooked pleats
Causes of such pleats
(1) The corners of Shuida paper are raised, and the paper teeth are not good.
(2) The gripping force of the paper gripper on one side of the paper is too light.
(3) The corner of the paper floats.
(4) The position of the side is not correct, and the corner of the paper touches the gap between the grippers of the paper.
Processing method: paper is knocked on and printed on the machine; readjustment is required for loose grippers, and the paper corners float mainly because the grippers cannot hold the paper.
(Figure 2-4) Large crooked pleats
[Case 2-7]
A factory J2105 machine printed middle school textbooks, color inserts. It was printed on 128g /? Coated paper, and shortly after the official printing, it was found that occasionally folds appeared on the outside. After observing the position on the outside, after careful observation, it was determined that the paper was pulled by the side rule and the paper was pulled. The gaps collide, causing pleats to appear.
Approach:
The side gauge is properly displaced to avoid the gap.
[Expert Tips]:
Similar to this phenomenon, the captain should deal with it in advance, and can not wait for the problem to appear and then deal with it.
4 Round pleats
The main reason for this kind of pleats is: the middle part of the gripper is too loose, which causes the phenomenon that the gripper cannot hold the paper, and it is pulled out during printing to produce folds.
Treatment method: Correct the grip of paper teeth. If the tooth pad is too smooth, you can replace it with a new one.
Figure 2-5 Circular pleats
[Case 2-8]
A factory used a four-color offset printing machine to print the advertising brochure of an enterprise, and found that circular folds (not every one) appeared in the place where the portraits were printed in the second half.
[case study]:
According to the conventional treatment method, it is necessary to check the gripping force of the gripper, but in this case, the gripper gripping force is good. Later, it was found that the black density of the folds is large, especially the density of the red ink is too large, resulting in here If the peeling force is increased and the gripper is slightly unsuitable, the above failure will occur.
Approach:
Re-make the plate, put the portrait of the person on the mouth or the first half of the paper, and the fault disappears.
[Expert Tips]:
General portraits or products with strict requirements for fitting, such as portraits or smaller pictures, are generally best placed in the first half of the mouth or printing paper during imposition. In addition, those with high ink density should not be printed in the second half.
5 big radiating pleats
Causes of such pleats
(1) Two or more gripper teeth of the impression cylinder are too loose in one place, and cannot even hold the paper.
(2) The unevenness of the delivery tooth pads causes the edge of the gripper paper not to be a straight line and becomes a wavy curve. When the impression roller grips the paper and presses the paper, the length of the paper is shortened. Pleat.
Treatment method: Check the gripping force of the gripper of the impression cylinder.
Figure 2-6 Large radiating pleats
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