- Issue Time
Calcium stearate (CaSt₂) and stearic acid (HSt) in the formula in the presence of paraffin, PE wax conditions can effectively promote the resin plastic and reduce the melt viscosity, so they play from the internal lubrication, are internal lubricants. And in a certain range, the plasticizing time and the plasticizing torque decrease as the CaSt₂ and HSt additions increase.
In the absence of any additives to promote the plasticization of lubricants, only adding delayed plasticized paraffin, PE wax, according to common sense inferred that its plasticization time should be added to promote the plasticization of CaSt ₂ and HSt even longer, but the result is Than any addition to the internal lubricant CaSt ₂ and HSt plasticization time are shorter! It is recognized that the external lubricant mechanism of action: the external lubricant evenly coated outside the PVC particles, so that particles are easy to slide each other, reducing friction and delay the plasticization. But the question is whether it can be completely evenly coated on the PVC particles. Do not use the internal lubricant, only the use of external lubricants can not completely even cover all the RPVC particles, is due to paraffin, PE wax composition of the outer lubricating film tear strength and adhesion strength to the matrix is too small, easy to heat And shear damage caused by. Reason: on the one hand paraffin, PE wax outside the lubricant itself is a non-polar material, between them there is only a small force of the dispersion force (non-polar molecules close to each other, their instantaneous dipole moment will produce very Weak attraction), because the anti-tear strength of the lubricating film is small; on the other hand, the interaction between the polar resin molecules is much greater than that between the non-polar paraffin and the resin (interfacial tension) Together, accumulate in the local part of the resin, and thus can not even wet all the resin particles, so that the role of lubrication.
If there are CaSt₂ and HSt in the system, the polar groups are interconnected with the polar nodes on the surface of the PVC particles, while the non-polar long-chain alkyl moieties are wetted and coated The paraffin liquid film on the surface of the resin particles is miscible (similar to each other), and the wetting layers of adjacent paraffin layers can be thinned and diffused with each other. Polar internal lubricants like "rivets" as paraffin, PE wax wetting film evenly fixed on the metal surface and PVC resin particles on the surface. This "rivet" effect improves the strength of the paraffin, PE wax outside the lubricating film against high shear, maintains the integrity of the lubricating film, thereby delaying the plasticizing time more effectively than using only the external lubricant , And reduced the plasticizing torque.
Therefore, the internal lubricant can not only promote the plasticization, reduce the melt viscosity, and in combination with the external lubricant, and the external lubricant has a better synergistic effect, it can enhance the role of late lubricant lubricant lubrication.
Added: calcium stearate lubrication is stronger than stearic acid.