What may cause defects in PVC film?

Qualified PVC Film demand that the surface should be free from specks, dots, pin holes and hard particles. It is important to find out the causes of such defects and eliminate them to ensure the quality.

Various sources of hard particles are:

1. Resin

2. Other solid ingredients in the formulation

3. Processing condition

4. Contamination like dirt and dust

Resin:

Fish eyes appearing on the surface of product can be particles from the resin itself that do not get fused under a given set of processing conditions.

These fish eyes do not absorb plasticizes and do not fuse readily. They appear on the surface of the extruded Rigid PVC Sheet and even puncture the film or appear on PVC product.

Other solid ingredients in the formulation:

During mixing, sequence of addition of additives like lubricants, processing aids, impact modifiers etc. plays an important role.

Non-uniform absorption of ingredients especially like plasticizer by PVC, results in fish eyes.

Coarser particles of non melting ingredients like CaCO3, TiO2, carbon black etc contributes to hard particles.

Processing condition:

Gel formation during processing is generally related to extent of shear and or heat that the compound is subjected to. If gels are from resin, it would appear on the product surface in random location and non linear form, while aligned defects are always caused on the production line.

Contamination like dirt and dust: