Grease is one of indispensable additives in modern plastics processing technology. Polymers usually have a high viscosity after melting. They must be added during processing to improve lubricity, reduce friction and reduce surface toughness. Target additive with performance, this additive is a lubricant. It can increase processing speed, reduce energy consumption, and improve quality of plastic products, especially the visible quality.
Picture 1 grease
1. Grease classification
There are many types of plastic lubricants, and there are two most commonly used classification methods. One is to classify lubricants according to their lubricating effect, as shown in Table 1-1. The other is that others are roughly divided into hydrocarbons, higher fatty acids, fatty acid amides, etc., according to chemical structure of lubricant.
Table 1-1 Types of Lubricants
Second, how grease works
The mechanism of action of external and internal lubrication is slightly different. Figure 2 shows different forms of internal and external lubrication.
Fig. 2. The form of action of lubricant
2.1 External lubrication mechanism
External lubrication is a plastic additive that can reduce friction between resin and surface of metalworking equipment and slow down plasticization of resin. External lubricants are typically non-polar organic compounds that have low compatibility with highly polar resins and are easily repelled from system interface by strong polar resins, forming a thin layer of external lubricating film. Before plasticizing resin, an external lubricant is applied to surface of resin particles to reduce friction between resin particles; After resin is plasticized, film formed by external lubricant on surface of resin melt can reduce friction. adhesion and friction of resin with a metal surface.
2.2 Internal lubrication mechanism
Internal lubricants are usually low molecular weight organic compounds with polar groups. It can penetrate into particles of each resin layer and particles. The internal lubricant has good compatibility with polar resin and reduces interaction force between molecular segments, thereby reducing "plasticizing moment". Before resin is plasticized, resin and internal lubricant form a complex bond after chemical adsorption, which weakens friction between resin segments, after resin is plasticized, polar group of internal lubricant weakens intermolecular and molecular interaction force. between segments of chain provides an easy flow of resin melt, reduces viscosity of melt, and plays role of internal lubrication.
3. Grease classification
3.1 Hydrocarbon grease
Hydrocarbon greases have a wide range of sources, low price, stable performance and good lubricating effect. By the principle of similar compatibility, this type of lubrication is internal lubrication in non-polar resins and external lubrication in polar resins.
Table 3-1 Hydrocarbon Plastic Lubricants
Table 3-2 Grease Greases
3.3 Combined lubrication
The direction to different applications and processing methods, mixing different lubricants with different properties into compound lubricants is direction of development of grease market today.
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