Analysis of Wrinkle in Offset Printing Process (I)

Wrinkling (pleating or wrinkling) is a serious quality problem in printing, and wrinkled prints are generally unacceptable. Sometimes wrinkling in printing is a very vexing thing! The following are some of the analysis and discussion of the wrinkle phenomenon.

The root cause of wrinkle is generally nothing less than uneven paper entering the embossed area and the paper being compressed by the pressure of the impression cylinder. When this amount of compression exceeds the compressibility limit of the paper, it will wrinkle. In the process of imprinting, the paper bears two forces: the pressure perpendicular to the paper surface and the backward rolling force tangential to the paper surface, so that the plain paper may also bite against the paper during the imprinting process due to the roller teething. Less than the calendering force causes the paper to slip backwards and cause wrinkles.

One is the flat service of the material itself, and the other is that the plain paper has become unfair before entering the embossing area due to the machine itself. Below we do some empirical analysis of the situation that may cause wrinkling of printed products, and list some of the most likely causes of wrinkling in actual printing:

First, the material:

1. The stiffness of the paper is too bad; most of the wrinkling conditions are based on the premise that the stiffness of the paper is small and the gram number is small. Even if the quality of the paper is good, no wrinkles will be generated even if the machine has some defects. In general, the paper is limited to papers with a weight less than 90 G/m2, especially paper with poor stiffness.

Root cause: Paper stiffness is poor, rigid transfer is not effective when the front edge of the paper (mouth) or the side of the paper is stressed, especially if the paper is stressed locally or suddenly subjected to stress. Deformation is serious.

Solution: (a) Paper change, "although thorough but often out of cost considerations is not very practical."

(b) do paper indentation processing, press the fan-shaped ridge line on the paper (Figure 1), can properly improve the stiffness of the paper, <however this will often affect the overprint>

Figure 1

2, the paper surface roughness is not good, there are lotus leaf (or tight edge)

Source: Due to the uneven moisture content on the surface of the paper, resulting in surface deformation, the modified paper will cause wrinkles if it enters the imprint.

Solution: (a) cool paper, do the paper surface humidity treatment.

(b) try to put a large deformation as a drag.

(3) Distribute the paper-feeding roller and the paper-feeding belt on the paper-feeding board into an inverted figure eight shape, and try to make the paper entering the embossing area be flat.