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PVC lubricants are divided into two categories, internal and external lubricants, but the internal and external lubrication is only relatively speaking, there is no strict classification standards, the main distinction is based on lubricants and resin compatibility.
Internal lubrication has a high affinity with resin, its role is to reduce intermolecular force, improve the dispersion of raw materials components; external lubricant and resin affinity is small, its role is to reduce the friction between resin and metal surface.
Due to the different polarity of resin, the effect of internal and external lubricants may change. Generally, the highly polar lubricants, such as stearic alcohol, stearic amide, butyl stearate and stearic monoglyceride, are listed as internal lubricants, while the less polar lubricants, such as paraffin and PE wax, are listed as external lubricants；This is for PVC and PA resins with extremely strong polarity. For non-polar resins, such as PE and PP, the results are just the opposite. For example, paraffin wax and PE wax are non-polar substances with PE and PP resins, which have good compatibility, so they are typical internal lubricants.
The compatibility between lubricant and resin is not invariable, but varies with the processing temperature. For example, stearic acid and stearic alcohol are used in the initial stage of PVC extrusion, because of the low melt temperature and poor compatibility with PVC resin, they mainly play the role of external lubrication; When the temperature increases, the compatibility with PVC increases, and the small molecule lubricant is easy to enter between the molecular chains, then it becomes an internal lubricant.
The change of lubricant properties is also related to the amount of lubricant added. When the lubricant content is less than its compatibility, it does not wash out the external lubrication effect of PVC secondary particles. When the lubricant addition is greater than the compatibility, a part of the lubricant is excluded from the macro particles and secondary particles of PVC and the external lubrication effect. Stearic acid is a widely used lubricant after metal soap. It is a typical external lubricant in soft products, which can reduce the friction heat between resin and processing equipment, and prevent the adhesion of molten resin to metal surface. However, in PVC-U, when the amount of PVC-U is small, it plays an internal lubricating role, can obviously promote plasticization and reduce melt viscosity; When the dosage is large, it can obviously delay the plasticizing speed and play the role of external lubrication.
In view of the fact that the compatibility of lubricants, especially metal soap lubricants, with PVC resin changes under certain temperature, pressure and shear heat. In fact, there are few lubricants that are simple internal or external. It means that the internal or external lubrication is the main or internal lubrication of a lubricant according to the normal conditions.
Alkoxywax is generally used as an external sliding agent, because it has little polarity and has little compatibility with extremely polar resin. Before plasticizing, the PVC particles were coated on the surface of PVC particles evenly, which made the particles slide each other and hindered the mutual expansion, adhesion and delay plasticizing of the segments; After plasticization, it is rejected on the outer surface of the melt and forms a liquid lubrication film, which reduces the adhesion and friction between the PVC melt and the metal surface of the processing equipment, thus reducing the local overheating phenomenon and improving the thermal stability and fluidity of PVC resin.
Qingdao Sainuo Chemical Co.,Ltd. We are manufacturer for PE wax, PP wax, OPE wax, EVA wax, PEMA, EBS, Zinc/Calcium Stearate…. Our products have passed the REACH, ROHS, PAHS, FDA testing.
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