If it is center winding (also known as hanging winding), it may be because the winding tension is set too high.
If it is surface center winding (also known as pressure winding), it may be because the pressure is set too high.
Of course, it may also be that you did not adjust the tension or film threading method during the unwinding and stretching process, causing the film to wrinkle, or it may be that the unwinding film itself is already wrinkled and has formed dead wrinkles.
