Lubricant is in the plastic processing and product releasability, to prevent the machine or the mold due to sticky and produce defects. Generally added to the molding compound or coated on the cavity surface. Commonly used lubricants are fatty acids and their salts, long-chain aliphatic hydrocarbons. According to the different mechanism of the role of lubricant can be divided into external lubricant and internal lubricant.
(1) Outer lubricant: This lubricant has poor compatibility with the molding resin and is therefore commonly used in forming machines or molds to form a lubricating layer between the resin and the resin to facilitate resin flow and product release , Such as paraffin.
(2) Lubricants: Such lubricants and resin compatibility, often incorporated into the resin, reducing the melt viscosity of the resin to improve its mobility. Such as butyl stearate, lead stearate and the like. Stearic acid salts are both good lubricants and effective stabilizers.
(1) Calcium stearate:
White powder, the melting point of 148-155 ℃, non-toxic, excellent lubricity and processability, no sulfide pollution, and lead lead salts and lead soap with alkali, can increase the rate of gelation, dosage is generally 0.1-0.4PHR.
(2) oxidized polyethylene wax
White or light yellow powder or particles, although the polyethylene oxide wax contains a small amount of polar groups, is still incompatible with PVC, but higher lubrication efficiency, can improve the lubricity between polymer and metal, improve the extrusion efficiency, improve Dispersibility of the colorant gives the article good transparency and gloss. Amount of 0.1-0.5PHR.
(3) Stearic acid
White or yellowish particles, melting point 70-71 ℃. Slowly volatilized at 90-100 ℃, in the hard PVC processing for external lubricants, the dosage is generally 0.2-0.5PHR, and prevent the effect of chromatography and scaling, but the amount of too easy to blooming cream.
(4) Glyceryl stearate
Powder, melting point 85-87 ℃, with excellent heat resistance and fluidity, can increase the amount of filler, and can promote plasticization. Used in combination with waxes to improve the thermal stability of PVC-U. The general amount of 0.2-0.6PHR.
In practice, it has been found that when two or more lubricants are used in combination, a different effect occurs when used alone. Form in the profile, most of the use of complex ways
Melting point 57-63 ℃, does not contain polar groups, is a typical external lubricant. Because of its low melting point, easy to evaporate, melt viscosity is small, only in a narrow range from the role of lubrication, suitable for single and twin-screw extruder, the general amount of 0.1-0.8PHR. This product is poor transparency, easy to white.
(6) polyethylene wax
White powder, softening point of about 100-117 ℃, due to its relatively high molecular mass, high melting point, low volatility and thus at higher temperatures and shear rates, also showed significant lubrication effect. For hard PVC single, twin-screw extrusion, the commonly used amount of 0.1-0.5PHR.