Defects & Solutions in Winding Plastic Film

In flexible plastic film production, the final slitting results are affected by not only blowing and casting quality, but also the following process of slitting and rewinding. The precision slitting machines can provide smooth winding and less wrinkling of plastic film. Conversely, poor winding process may cause a series of problems such as film wrinkles, fuzzy ends, stretching problems, edge warps, etc. Below are some common quality defects and solutions summarized by Leap in processing plastic film.

Scratch defects on plastic films

The roller with smooth surface is critical, even a small burr or foreign matter attached to roller will cause crack on materials and result in tremendous economic loss. On the other hand, skidding issue may occur in many high-speed slitting machines, and the friction between roller and web materials can cause damage especially for some plastic films needing very high surface quality such as Aluminum coating films or laser films.

Therefore, before production, various guide rollers in slitting machines should be cleaned carefully and make sure there are no burrs. The better method is to cover the guiding roller with HNBR rubber or EPDM rubber to prevent scratch on film materials, moreover, it can also help to decrease the skid problems. Cork tape is another cost effective method, it’s easy to apply to rollers and provides good gripping property to transport plastic film materials. Self-adhesive backing ensures good adhesion to the surface of metal roller.

Wrinkling defects in plastic film winding

For winders with high speed, pressing rollers must be used to contact the outer surface of winding film roll to reduce vibration and prevent air entrainment. In the beginning of plastic film winding, the roll is small and more air is wound between layers of winding plastic roll to form vertical wrinkles due to the large wrap angle. With the increase of coil diameter, the wrap angle between pressing roller and film material tend to small, that means the less air involved and good quality of film coils. The solution is to choose the paper core with large diameter and reduce diameter of pressing roller as possible.

As the plastic rolls build larger in diameter, the rolling nip also induces in-wound tension into the roll, and the nip-pressure will increase with the increasing winding linear velocity. The inner layers will loosen and cause the roll to defects known as starring, telescoping and dish. That means the film rolls should be wound tight at paper core and then wound with less tightness as the rolls become larger in diameter. Therefore, the nip-pressure need to be tapered while winding to prevent wrinkle problems.

Vertical stripe issues mean that the surface of the plastic film roll form appearance of a ring of ribs or linear stripes. Large amount of air is entrained with the moving web film’s surface and further cause the poor tolerance of accumulated thickness. These defects often occurs on high-speed cutting machines, so the solution is simple to reduce the speed of winder. Besides, bad accuracy of equipment is another reason, the accuracy and efficiency of parts will decrease as long-term use. At this point, replacing parts and accessories for slitter rewinder machine is essential, while guarantee the high-level assemble accuracy.

Edge warping problems in rewinding process

Generally, edge warp problem occurs at the edge position of the thin film rewinding process, web materials tend to elongate along the cutting edges due to constant friction between film and the blade edge. As this elongation continues, the warping issues on film material can accumulate along the edges of rolls during the rewinding process. The common reason is that blades are too blunt and should be replaced in time.

For some light and thinner web materials, the film is easy to curl inward and result in edge warp. The solution is to change the radian of spreader roller or add a small amount of hygienic grade smoothing powder on crimping place. Besides, for some stretchable film materials such as PE, PP, Li battery separator, excessive winding tension or too fast winding speed is easy to cause stretching problems and result in poor uniformity of end face. The solution is to reduce the winding tension and adjust rewinding speed.