Lubricant is a lubricating medium used to reduce the frictional resistance of the friction pair and slow down its wear. Lubricant can also play a role in cooling, cleaning and preventing contamination of friction pairs. The reason why lubricant can lubricate is that its addition reduces the friction of the plastic melt. This friction is divided into two categories: internal friction and external friction. Accordingly, there are internal lubricants and external lubricants, as shown below. Do you know about internal and external lubricants:
External lubricants:
Lubricant that reduces mutual friction between polymer solution and metal surface. The main function of the external lubricant is to improve the friction between the polymer melt and the hot metal surface of the processing equipment. It has poor compatibility with polymers and can form a lubricating thin layer at the interface between plastic melt and metal. Commonly used external lubricants are stearic acid, stearate, paraffin, etc.
Internal lubricant:
Internal lubricant refers to a lubricant that can reduce the friction between polymer molecules after the polymer is melted. . Generally speaking, the molecules of the internal lubricant have a high affinity with the polymer, and the compatibility between them is good. In this way, part of the lubricant molecules can enter between the polymer macromolecules, weaken the force between the polymer molecular chains, and cause the sliding and rotation of the polymer molecular chains. At the same time, it does not excessively reduce the Tg of the polymer and improve the polymerization. improve the fluidity of the product and improve the surface finish of the product. Internal lubricants are generally low molecular weight polymers.
The relationship between external lubricants and internal lubricants:
From the perspective of processing machinery, in molding processes such as mixing, calendering, and slush molding , external lubricant plays an important role, and in extrusion and injection molding, internal lubricant is more effective.
In fact, every lubricant can achieve a certain required function. Internal and external lubrication always work together, but it is more prominent in a certain aspect. The function of the lubricant depends on the type of polymer and processing equipment. , processing conditions and the type and dosage of other additives. The same lubricant will show different lubrication effects in different polymers or under different processing conditions. For example, under high temperature and high pressure, the internal lubricant will It is squeezed out and becomes external lubricant.
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