Lubricants can be divided into two types, and the role of external lubricants is mainly. It is less compatible with polymers and easily migrates from the melt to the outside, so it can form a thin layer of lubrication at the interface between the plastic melt and the metal. Internal lubricants have good compatibility with polymers, and they play a role in reducing the cohesion between polymer molecules inside the polymer, thereby improving the internal frictional heat generation of the plastic melt and the fluidity of the melt. The commonly used external lubricants are stearic acid and its salts, and the internal lubricants are low molecular weight polymers. Some lubricants have other functions. In fact, each lubricant has a role that can achieve a certain requirement, and it always works together with internal and external lubrication, but it is more prominent in a certain aspect. The same lubricant will exhibit different lubricating effects in different polymers or under different processing conditions, such as at high temperature and high pressure, the internal lubricant will be extruded to become an external lubricant.
In the production of plastic films, we also encounter some sticking phenomena, such as in the production of plastic films, the two layers of film are not easy to separate, which brings difficulties to automatic high-speed packaging. To overcome it, a small amount of additives that increase surface lubricity can be added to the resin to increase external lubricity, generally known as anti-blocking agents or slip agents. In general, in the molecular structure of lubricants, there will be two parts of the long chain of non-polar groups and polar groups, and their compatibility in different polymers is different, thus showing different internal and external lubrication functions. According to the chemical composition, commonly used lubricants can be divided into the following categories: fatty acids and their esters, fatty acid amides, metal soaps, hydrocarbons, organosilicon compounds, etc.