The main problems during film blowing are tendency blocking, abrasion, and delamination. Films with tendency blocking are not suitable for applications requiring low-density film. To mitigate negative effects on the end product, manufacturers should measure the tendency of the film to block. There are different test methods to measure tendency blocking. Simple manual tests are usually used in production. To measure tendency blocking, two layers of blown film are placed on top of each other, and the film layers are separated by the thumb and index fingers.

Imperfections in the film can be caused by the takeoff systems or the die lip area. Burrs and degraded resin can also cause a streaking effect on the blown film. Additionally, black specks in film can be the result of something being added to the feedstock, such as regrind. Listed below are the most common problems and their solutions. If you're having trouble producing films, contact our service team or visit your local Davis marketing office for assistance.

Uneven melt cooling or excessive tension from the winder are other common problems. Uneven heat exchange and misaligned nip rolls can also cause a film to stretch. In addition, the bubble should be centered in the air ring and oriented properly between the nip and die to minimize differential shrinkage. If there is an issue, the gauge profile of the bubble can help you identify its cause.

A good reference for the film blowing process is Butler et al., which has an excellent description of the process. Calhoun and Vlachopoulos also cover the process in their SPE Plastics Technicians Toolbox Book 6: Blown Film Extrusion
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