Causes of paper wrinkles and solutions (1)

When the paper enters the drum and is subjected to pressure, it forms curved or irregular folds on the surface of the paper, known as folds, which are commonly called pleats. A flat sheet of paper that is wrinkled after being rolled by rollers is a common type of failure, which seriously affects the accuracy of registration.

There are two reasons for paper creases: one is the improper adjustment of machine parts, and the other is the physical and chemical nature of the paper itself.

Improper adjustment of a machine part

1 Imprinting roller uneven bite force

When the paper is bitten by the impression roller, the paper bite is not even. In one case, two or more teeth on one side of a row of teeth on one side of the teeth are too loose. When the roller is pressed, the paper is pressed. Due to the squeezing force and the peeling force between the rollers, the part of the paper where the nip is too loose is pulled out, resulting in wrinkles under the action of the roller pressing force, as shown in Figure 1(A).

(A) It is called a scattered wrinkle.

In the other case, the biting force of two adjacent teeth in a row of biting teeth is greater than the biting force of the other teeth. After the drum is pressed together, it is subjected to the squeezing force and the peeling force, and the edge of the teeth where the teeth are light is pulled. Out, produce a convergent fold Figure 1 (B)

There is also a situation in which several teeth in the middle position have too little biting force, or the diamond pattern of the teeth pad wears, resulting in a small friction force. Under the effect of peeling tension, the middle part of the paper bite is pulled out to cause roundness. The arc fold is shown in Fig. 1(C). It is common on two-color and multi-color offset presses.

2. The position of the side regulation position is not proper. When the paper arrives at the predetermined position, the corner of the paper collides with the gap of the feed tooth pad and the iron plate of the tooth plate, or the corner of the paper or the paper itself is curled upwards, causing the paper to not be fed straight. The teeth pass to the impression cylinder teeth, or the edge of the paper is far from the teeth at the end of the teething axis, especially when the paper is full, the paper corners are easy to flutter, and the impressions may not be properly bitten by the impression teeth. Post-printing will produce skewed folds as shown in Figure 1(D). In some cases, inconsistency of wrinkles may occur due to the fact that the lateral force is slightly slower or the outermost biting force of the delivery tooth near the side scale is too light.

(to be continued)