How to solve the problem of wrinkling during die cutting and slitting of thin films?

There are several types of folds, including wrinkling, longitudinal folds, transverse folds, and line folds.

The occurrence of folds in thin films indicates a certain degree of damage to the flatness of the film, which is not allowed for any purpose. It not only affects the appearance of deep-processed products, but also causes quality defects in use, such as missing coating or printing.

Wrinkling, also known as bottom fold or initial fold, refers to the folds that appear at the beginning of the film winding on the core. Since wrinkles are often irregular and permanent, the film is generally scrapped at the location of the wrinkle.

The severity of wrinkles is an important indicator of the slitting technology level of a film company. Different companies produce films with different lengths of wrinkles, ranging from a few meters to hundreds of meters. The more severe the wrinkles, the greater the losses to the company and the users. Therefore, every film company is dedicated to improving the research on slitting wrinkles.

Here are some methods to solve bottom folds:

1. The occurrence of folds near the core is largely related to the pressure of the contact roller of the slitting machine. It has been proven that increasing the pressure of the contact roller leads to more folds, while reducing the pressure leads to fewer folds. Increasing the amount of air between the film rolls increases the gap between the films, thereby reducing friction and minimizing wrinkling.

2. The control of winding tension should be considered when improving wrinkles. If only the winding pressure is considered, the setting value of the initial pressure must be very small. In special cases, defects such as deviation may occur due to low pressure during deceleration. Therefore, the setting of the tension curve is also very important, and the winding pressure and tension should be well coordinated.

3. The pressure near the core should not be reduced indefinitely, as too small pressure will cause the inner winding of the film roll to be too loose and result in star-shaped defects on the end face, leading to transverse wrinkles. Therefore, when setting the pressure curve, it should be adjusted to minimize wrinkles while ensuring that the end face of the film roll does not have star-shaped defects.

4. Under the same parameter conditions, film rolls with longer specifications are more prone to wrinkles than shorter ones, indicating that the longer the specification, the worse the exhaust effect. In addition, due to the relatively poor strength of the middle part of the paper tube for long specifications, slight bending of the paper tube during the slitting process can cause long-lasting wrinkles in the middle of the film roll. Moreover, when the paper core is longer, as the axis for winding the film, its straightness, concentricity, strength, and surface smoothness are the most important indicators. Generally, the longer the paper core, the more difficult it is to ensure straightness and concentricity.

Therefore, the quality of the paper core is very important. The inspection of the paper core should be improved, and if any abnormality is found during the slitting process, the paper tube should be replaced in a timely manner. Furthermore, under the same parameter conditions, film rolls with shorter specifications are more prone to deviation and require greater winding pressure. Therefore, in adjusting wrinkles, the pressure can be appropriately reduced for long specifications to reduce wrinkles, while increased pressure is needed for short specifications to prevent deviation.

5. Products cut on the inner and outer sides of the slitting machine may have transverse folds due to different entry angles (included angles) into the winding pressure roller. Generally, reducing the pressure to reduce wrinkles during the slitting process may cause transverse folds. Effective adjustments of the cutting tension and pressure for different product models can effectively eliminate the occurrence of transverse wrinkles.

6. The degree of wrinkles on the inner and outer sides of the slitting machine may also differ. It is important to compare the differences in wrinkles between each slitting machine. If the differences are significant, the easy-to-wrinkle specifications should be cut on the side that is less prone to wrinkles during the slitting process.