Printing wrinkle analysis and elimination methods

Sheeting produces wrinkling, a common failure in the printing process. Its appearance has caused certain obstacles to normal printing, and at the same time it has affected the quality of the products. It must be promptly and accurately taken to eradicate it and ensure normal production.

The causes of creping of printed sheets are various: the moisture content of the paper, the layout structure defects, improper lining process, uneven printing pressure, excessive weight, misalignment of paper teeth or small amount of rinsing, and improper paper scoring. Therefore, correctly grasping the printing operation and the process technology can effectively prevent wrinkling of printed sheets.

Causes of 1 paper wrinkling

1.1 paper is not flat, edge curl

    Paper is very sensitive to changes in the temperature and humidity of the environment. Abnormal ambient temperature and humidity, easy to make paper moisture content variability. The moisture content of the paper is too low, and the paper is curled around. It is easy to wrinkle when printing. If the water content is too low, it is easy to generate static electricity and it is difficult to ensure normal printing. The high water content of the paper makes it easy to make the paper too soft and print wrinkles. Therefore, the paper storage room temperature should be controlled at 18 ~ 22 °C, relative humidity controlled at 60% ~ 70%. In addition, the paper stock time should not be too long, piles of paper piles have a certain distance from the ground. Keep away from the wall and avoid deforming the paper due to moisture absorption and moisture. In addition, the paper also needs sun protection, heat protection and anti-folding. After the paper bags are put into the warehouse, they should be flattened and stacked. Only the strict and scientific management of paper storage can effectively avoid wrinkling.

1.2 layout structure defects

Although the surface of some paper is flat, the printing also wrinkles. This is due to the structure of the layout. During printing, the contact between the printed sheet and the layout is prone to produce air resistance, causing the paper to partially bow and cause the printed product to wrinkle. In addition, the underplating of the wood-bottom plate is uneven, and the underlay is not solid, so that the printing pressure is heavy, and it is also easy to cause unevenness of the paper and wrinkling during printing. In this regard, it is necessary to strictly control the plate mounting operation and process technology to avoid wrinkling.

1.3 Improper lining

The lining pad is too soft, so that the lining of the lining contains imaginary and convex bulges, and the outer lining does not have enough tightness in the lining, or the surface has cracks and wanders. This can easily cause wrinkling of the printing. Therefore, pay attention to the lining process during printing to prevent wrinkling.

1.4 Loose Parts

When the parts (embossed parts) of the machine are worn out, the accuracy of the parts is lost, so that there is a slight amount of looseness and slippage at the moment of imprinting, resulting in wrinkling. Therefore, maintenance and repair of equipment should be strengthened at ordinary times, and the important parts of the equipment should be maintained in a good lubrication state. Reduce the chance of printing wrinkles.

2 eliminate the wrinkling of printed sheets

1) Knock paper to change the printability of the paper

In the absence of flatness and stiffness due to thinness or variation in the paper, and the downward curling of the edge of the printed sheet, it is easy to cause a misalignment with the teeth. By knocking the paper edge, the paper undergoes physical changes. The flatness and firmness of the edge of the printed sheet. There are bends in the paper. Horizontal knocking or vertical knocking can be used to restore the flatness of the paper and meet the printability requirements, so as to eliminate the wrinkling of printing.

2) Grasp the printing pressure and eliminate wrinkling caused by heavy printing pressure

For printing wrinkles, printing should be considered as possible to meet the requirements of the layout of the ink, in order to prevent the lack of ink due to misprint printing pressure, so that wrinkles appear Yinzhang phenomenon. In addition, the adjustment of the printing pressure should be achieved through the lower pad as much as possible, so as to avoid making a large-area affixation on the outer liner and repeatedly sticking the outer liner.

3) Adjust the pressure and position of the teeth and eliminate printing wrinkles caused by misalignment of printed sheets

When the pressure of the roller teether is uneven or the positioning of the paper is improper, the misalignment of the paper edge or the amount of the opening of the print sheet is too small, the paper is likely to wrinkle due to slipping or partial unevenness during the rolling process. For this reason, the pressure of the clenching teeth and the position of the printed sheets in the row of teeth should be adjusted so that the corners of the paper are given more teeth. If the amount of ink on the sheet is insufficient, the edge of the sheet is not pressed by the teeth, and the lack of flatness on the edge of the sheet causes wrinkling. To increase the amount of the sheet, the printed crease should be eliminated.

4) Adjust the machine support sheet parts

Automatic printing equipment To ensure the quality of printing overprint, a row of brushing mechanism is arranged at the position of the front line of the drum to support the function of the printed sheet to prevent the printed sheet from affecting the printing effect due to the fall. When printing thin paper, the brush is too tight or unable to support the printed sheet, and it is also very prone to wrinkling. Therefore, the position of the brush should be adjusted to eliminate the purpose of printing wrinkles. For an ordinary hand-panning platform machine, such as a TZ401 structure type printing machine, since there is no brush position on the machine, it is possible to add a curved iron plate to the paper support member on the paper holding support iron plate (ie, the front gauge part), and achieve Support the role of printed sheets. The curved support board can be made of tinplate material, the width of which should be controlled between 10 and 20 cm, one end of which is folded into a clamp, clamped on the front iron bar, and the other end is folded into an appropriate arc shape. After the arc-shaped iron plate is fitted into the proper place of the front gauge, its elastic arc-shaped lateral edge can be in contact with the surface of the roller, so that the printed sheet can be evenly pressed against the roller. Prevent printing wrinkles.

5) Adjust the lining to eliminate creases

Due to the lack of good flatness of the paper, wrinkling occurs during printing, and it is difficult to completely eliminate it by the above method. At this time, the blanking board corresponding to the blank space of the layout can be longitudinally pasted with white paper strips of appropriate thickness, length and width so that the loosened paper surface can be tightly rolled on the liner. If there are blank margins on both sides of the printed sheet, and each of the two corners has a bite to bite the edge of the sheet, a suitable size of cardboard strip can be attached to the lining corresponding to the blank space on both sides of the layout, which can better eliminate the printing. Wrinkling phenomenon.