Functions and Dosage of various PVC Lubricants-2
3. Fischer Tropsch Wax
Fischer Tropsch synthetic wax has a linear structure which gives high-temperature resistance, lower viscosity and softening points between 65-105°C. It increases the fusion time and stability of PVC while decreasing the fusion torque required for the processing of PVC. Its linear structure provides an excellent metal release effect and reducing the formation of hot spots resulting in thermal degradation, which further reduces scrap. Due to its low viscosity, the speed of production increases and also improves the gloss. As compared to PE and paraffin waxes, the dosage of FT wax required is less. This makes FT wax an excellent external lubricant for use during PVC processing.
B. Internal Lubricant
Internal lubricant promotes inter-molecular flow via chain slippage and decreases the melt viscosity. It reduces the friction between the particles before the melting of PVC, which reduces shear burn-in injection moulding. It reduces back pressure in extrusion and allows easier, faster and better mould filling (including reduced tendency to sink marks, better part-size control and surface finish). It improves the dispersion of fillers, eliminates crease whitening and imparts good clarity.
1. Oxidized PE wax
The chain ends of the low molecular weight PE waxes are oxidized to acid groups under controlled conditions and are called oxidized polythene waxes. This improves the solubility parameter of PE wax. OPE wax is multifunctional, it acts as both internal as well as external lubricant. It is useful in filler treatment and dispersion of colorants in PVC processing and masterbatches. It gives the product good transparency and gloss. The general dosage for OPE wax is 0.1-1.0 PHR.
2. Ester wax
Ester waxes are multifunctional, i.e. these are lubricating and moderately co-stabilizing. Being of the same family, these are highly compatible with plasticizers and resist fogging in transparent applications. The increase in the chain length of esters may increase the fusion time. Fatty acid diesters are excellent internal lubricants, promote flow, and resist plate out. Penta-erythritol based esters are particularly used for high-speed extrusions, in wires and cables for improving output and providing a smooth surface without bloom.