1. PVC external lubricant: The external lubricant has poor compatibility with PVC, and it is easy to migrate from the inside of the resin melt to the surface, forming a lubricant interface layer, thus reducing the mutual friction between particles before PVC melting and between the PVC melt and the contact surface of plastic machinery.

2. PVC internal lubricant: the internal lubricant contains polar groups and has good compatibility with PVC, which can reduce the intermolecular force of PVC, reduce the melt viscosity and improve the melt fluidity.

The distinction between internal and external lubricants is only relative, and there is no strict standard. In resins with different polarities, the functions of internal and external lubricants may change. There are many kinds of lubricants, and two or more lubricants are usually used to form PVC lubrication system to reduce its migration ability to the surface of products; Improve that dispersity of lubricant, and balance the functions of internal and external lubricant.