Internal and External Lubricants
Lubricants are divided into two areas, internal and external lubricants. The transition between external and internal lubricating effect is fluid, however, – internal lubricants often also have a certain external lubrication effect and vice versa. Lubricants having both effects are therefore called “combined lubricants”.
Internal lubricants reduce the frictional forces occurring between the PVC molecule chains, thus reducing melt viscosity. They are polar and thus are highly compatible with PVC. They help achieve excellent transparency even at high dosages and do not tend to exudate, which helps optimizing welding, gluing, and printing properties of the final product.
External lubricants reduce the adhesion between PVC and metal surfaces. They are mostly non-polar such as paraffin and polyethylene waxes. The external lubrication effect is largely determined by the length of the hydrocarbon chain, its branching and its functional group. At high dosages they can lead to cloudiness and exudation.