1.Film Slitting TechnologyWrinkles
1; The impact of wrinkles on usage quality
BOPP film, commonly known as "glass paper", reflects the characteristics of high stiffness and good gloss. The appearance of wrinkles indicates that the flatness of the film has been compromised to a certain extent, which is not allowed for any purpose of the film. It not only affects the appearance of deep-processed products but also causes quality defects in usage.

2; Causes of wrinkles and countermeasures
Wrinkles caused by film slitting can be categorized into various forms: bottom wrinkles, longitudinal wrinkles, transverse wrinkles, line wrinkles, etc., each with different causes, briefly described as follows:
1) Bottom wrinkles: Also known as initial wrinkles, these occur in the section of the film initially wound on the paper core. Since bottom wrinkles are often irregular dead wrinkles, users generally treat the film as waste once it reaches the bottom wrinkle position. The degree of bottom wrinkles is an important indicator of a BOPP film company's slitting technology level. The length of bottom wrinkles in films produced by different companies can range from several meters to hundreds of meters. The more severe the bottom wrinkles, the greater the loss to the company and users. Bottom wrinkles can be resolved through adjustments in process parameters and equipment, including:
A; Wrinkles near the paper core cannot be smoothed out, which is largely related to the pressure of the contact rollers of the slitting machine. Practice has shown that increasing the pressure of the contact rollers leads to more wrinkles, while reducing the pressure results in fewer wrinkles. Increasing the amount of air inside the film roll enlarges the gaps between the films, thereby reducing friction and helping to decrease bottom wrinkles;
B; A lower winding pressure results in fewer bottom wrinkles, but too low a pressure can cause the film roll to deviate. Therefore, it is crucial to set a reasonable pressure curve. A smaller pressure should be set at the start, and once the length prone to bottom wrinkles has passed, the pressure should be quickly increased to avoid deviation;
C; When improving bottom wrinkles, it is necessary to consider the control of winding tension. If only winding pressure is considered, the initial pressure setting must be very low. In special situations, reducing speed midway can cause defects like deviation due to low pressure. Therefore, the tension curve setting is also very important, and winding pressure and tension must be appropriately coordinated.
D; The pressure near the paper core cannot be reduced indefinitely, as too low a pressure can cause the film roll to be wound too loosely, resulting in star-shaped ends and transverse wrinkles. Therefore, when setting the pressure curve, adjustments should be made to ensure that the film roll ends are free of star shapes while minimizing bottom wrinkles.
E; The degree of bottom wrinkles varies with the thickness of the film. Thicker films have better stiffness and fewer bottom wrinkles, while thinner films tend to have more bottom wrinkles. Therefore, for thinner films, greater adjustments in parameters should be made to overcome the occurrence of bottom wrinkles, and different thickness films require different slitting process parameters.
F; Products slitting on the inside and outside of the slitting machine may have different degrees of bottom wrinkles due to the angle (wrap angle) at which they enter the winding pressure rollers. Attention should be paid to comparing the differences in bottom wrinkles on the inner and outer sides of each slitting machine.Slitting machineIf the differences are significant, during the slitting process, specifications prone to bottom wrinkles should be placed on the side that is less likely to produce wrinkles.
G; Adjusting the exhaust properties of the pressure rollers and improving the stability of the winding arms can also help reduce bottom wrinkles.
With the continuous improvement of slitting technology, the length of bottom wrinkles has been decreasing. It is worth noting that sometimes the appearance of bottom wrinkles is not due to unreasonable settings of slitting parameters but rather due to the lack of responsibility from the operators, who do not properly align the film on the paper tube and instead casually place the film on the tube before starting the slitting process, artificially creating quality issues with bottom wrinkles. This must be taken seriously to eliminate human-induced quality defects and improve the quality of product slitting.