In the plastic industry, PVC plastic lubricant is especially suitable for plastic foam products, as an internal lubricant in the production of PVC products, and as a modifier for alkyd resins, and as a plasticizer for nitrocellulose.
The function of PVC plastic lubricant is to prevent the defects caused by adhesion in the machine or mold in the plastic processing and release of the products. Generally added in the mold plastic or coated on the surface of the mold cavity. Commonly used lubricants are fatty acids and their salts, long chain aliphatic hydrocarbons. According to the different mechanism of lubricant action, it can be divided into external lubricant and internal lubricant.
1, External lubricant: this kind of lubricant is less compatible with the resin used for molding, so it is often used in the molding processing machinery or mold, which forms a lubricating layer with the resin to facilitate the flow of resin and the demolding of products, such as paraffin.
2, Internal lubricant: this kind of lubricant has good compatibility with resin, and is often mixed with resin to reduce the melt viscosity of resin and improve its fluidity.
Commonly used PVC lubricants Main properties are as follows.
1, Calcium stearate
White powder, melting point 148-155 ℃, non-toxic, has excellent lubricity and processability, no sulfur pollution, and alkali lead salt and lead soap, can improve the gelation speed, the amount is generally 0.1-0.4 PHR.
2, oxidized polyethylene wax solubility
White or light yellow powder or granules, oxidized polyethylene wax, although containing a small number of polar groups, still incompatible with PVC, but the lubrication efficiency is high, can improve the lubrication between the polymer and metal, improve the efficiency of extrusion, improve the dispersion of colorants, give the product good transparency and gloss. Dosage 0.1-0.5PHR.
3, Stearic acid
White or slightly yellow granules, melting point 70-71℃. Slowly volatilizing at 90-100℃, it is used as external lubricant in hard PVC processing, the dosage is generally 0.2-0.5 PHR, and has the effect of preventing laminar scaling, but the dosage is too large and easy to spray frost.
4, Glyceryl stearate
Powder, melting point 85-87 ℃, has excellent heat resistance and fluidity, can increase the amount of filler, and can promote plasticization. Used with waxes, can improve the thermal stability of PVC-U. The general dosage is 0.2-0.6PHR.
In practice people find that when two or more lubricants are used together, different effects appear than when they are used alone. In the profile formulation, most of them are used in compounding
5, Paraffin wax
Melting point 57-63℃, without polar group, it is a typical external lubricant. Because of its low melting point, easy to evaporate and small melt viscosity, it can only play the role of lubrication in a narrow range, suitable for single and twin-screw extruder extrusion, the general dosage is 0.1-0.8 PHR.
6, Polyethylene wax
White powder, softening point of about 100-117 ℃, due to its large relative molecular mass, high melting point, low volatility and therefore at higher temperatures and shear rates, also show obvious lubrication effect. It is suitable for hard PVC single and twin screw extrusion, and the common amount is 0.1-0.5 PHR.
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