No need to fear wrinkling of printing paper; there are solutions!

No need to fear wrinkling of printing paper; there are solutions!

Our unit's Northern 05 model printing press has been in use for many years, and often experiences paper wrinkling during printing, which severely affects print quality. Based on my years of experience with equipment operation and understanding of the machinery, after making appropriate adjustments in the following areas, the occurrence of paper wrinkling has significantly decreased, and both print quality and production efficiency have greatly improved. I would like to share these adjustment methods with everyone in the hope of helping colleagues in the industry.

Strictly Control Workshop Temperature and Humidity

Under normal circumstances, paper needs to be stored in the warehouse for a period of time after being delivered. Three to four days before printing, the paper should be placed in the workshop, with strict control over temperature and humidity. The temperature should be maintained at 20–25°C, and the humidity at 50%–60%.

To achieve this, our unit improved the workshop's enclosure by installing partition walls and ceiling panels, used high-power air conditioners to regulate temperature, and during dry seasons, adjusted humidity by sprinkling water inside the workshop.

Cut Paper as Printing Proceeds

Paper wrinkling in our unit often occurs with cardboard, coated paper, and some lighter-weight paper. The cause is uneven moisture content in these papers during printing, resulting in wrinkling at the edges, which affects print registration or causes inconsistency in trimming, delaying production tasks.

To minimize this issue, our unit adopted the practice of not pre-cutting paper, but cutting it as printing proceeds, which avoids tension caused by air exposure. If paper has already developed tension along its edges, tapping the paper at the gripper location can reduce the degree of wrinkling.

Adjust the Feed Belt and Impression Roller Tension

Since paper moves forward under the action of the feed belt and impression rollers, the tension of these parts affects the flatness of the paper. Paper only enters the oscillating mechanism in a flat state can wrinkling be minimized. Therefore, it is necessary to correctly adjust the tension of the feed belt and impression rollers.

Adjust the Oscillator Gripper Pads

Oscillator gripper pads can become uneven due to wear. When this happens, the gripper row on the oscillator can cause localized unevenness in the paper. When the paper is transferred to the impression roller, the uneven areas can easily form fixed-point wrinkles under the pressure of the rubber roller. Therefore, machine operators should often check whether the oscillator gripper pads are level.

Adjust the Impression Cylinder Gripper Bars

With long-term use, the impression cylinder gripper bars may grip paper unevenly, causing irregular wrinkles at the trailing edge under pressure. To solve this, the gripper teeth on the impression cylinder can be replaced and the gripper bar tension adjusted to ensure uniformity.

Regulate Printing Pressure

During the operation of the printing press, if paper wrinkling occurs, the printing pressure should be reduced as much as possible, which can lessen the degree of wrinkling.