Lubricant is a kind of additives used to improve processing performance and appearance performance of polymers such as plastics and rubber. In addition to reducing friction in general sense and improving fluidity and release properties of resin or rubber during processing, function of lubricants can also be extended to increase surface finish of products and prevent products from sticking to each other.
As far as processing modification is concerned, lubricants in polymer processing process mainly reduce friction between resin or rubber material, processing equipment and polymer molecules, thereby achieving purpose of reducing torque, saving energy, promoting flow and improving quality.

 

Lubricants can be divided into internal and external lubricants. Distinction between internal and external lubricants is mainly based on their compatibility with resins.
Internal lubricant has a high affinity with resin, its function is to reduce force between macromolecules;
External lubricant has a small affinity with resin, its role is to reduce friction between tree and processing machinery.
Distinction between internal and external lubricants is only relative, and there is no strict division standard. In resins with different polarities, role of internal and external lubricants may change.

Role of internal lubricants has the following three aspects:
(1) Stably plasticize resin to prevent torque from increasing sharply during plasticization;
(2) Reduce melt viscosity of resin, increase fluidity, reduce screw torque, increase extrusion volume and production volume;
(3) Improve processing capacity, reduce equipment load, and improve energy efficiency.
Role of external lubricants has following five aspects:
(1) Prevent resin from decomposing and coloring due to friction and heat between resin and molded metal surface;
(2) Prevent sintering on the surface of forming machine;
(3) Improve peeling performance of drum surface;
(4) Improve demouldability;
(5) Improve smoothness of surface of finished product.

Saturated hydrocarbons-Saturated hydrocarbons can be divided into non-polar hydrocarbons (such as polyethylene wax and polypropylene wax) and polar hydrocarbons (such as chlorinated paraffin and oxidized polyethylene) according to their polarity. Mainly used for PVC non-toxic external lubricant.
Liquid paraffin-commonly known as white oil, it is a colorless and transparent liquid. It can be used as a transparent internal lubricant for PVC. Dosage is about 0.5 parts. In extrusion process, liquid paraffin has good initial lubricity and does not affect thermal stability;
Paraffin wax-also known as natural paraffin, white solid, can be used as an external lubricant for PVC, dosage is 0.1~1.0 parts, too much dosage will affect transparency;
Microcrystalline paraffin-also known as high melting point paraffin, it is white or light yellow solid in appearance. It is called microcrystalline paraffin because of its fine crystals. Lubricating effect and thermal stability are better than other paraffin waxes. Amount used in PVC is small, generally 0.1~0.2 parts;
Low-molecular-weight polyethylene-also known as polyethylene wax, its appearance is self-colored or light yellow solid, and its transparency is poor. It can be used for PVC extrusion and calendering processing, dosage is generally less than 0.5 parts;
Oxidized polyethylene wax-is product of partial oxidation of polyethylene wax, and appearance is white powder; it has excellent internal and external lubrication, good transparency, and low price; dosage is 0.1~1.0 parts;
Chlorinated paraffin-good compatibility with PVC, poor transparency, good effect when used with other lubricants. Dosage is less than 0.3.
Metal soaps-both an excellent heat stabilizer and a lubricant, have both internal and external lubrication effects, different varieties have slightly different emphasis.
Commonly used metal soaps used in lubricants are added in amounts such as: PbSt-0.2 to 1.0 parts; LiSt-0.6 parts; CaSt-0.2 to 1.5 parts; ZnSt-0.15; BaSt-0.2 to 1.0 parts.

Butyl stearate—It is a colorless or light yellow oily liquid in appearance. It is mainly used for internal lubrication and external lubrication in PVC. Dosage is 0.5~1.5 parts;
Glyceryl monostearate-code-named GMS, white waxy solid in appearance, is an excellent internal lubricant for PVC. It has little effect on transparency, addition amount is less than 1.5 parts, and it can be used together with stearic acid.

Stearyl Alcohol-Appearance is white fine beads, with internal lubrication, good transparency, 0.2~0.5 part in PVC, in addition, it can also be used in PS;
Pentaerythritol —— PVC high temperature lubricant, dosage is 0.2~0.5 parts.

a. Calendering-purpose is to prevent sticking to roll, reduce melt viscosity and improve fluidity. Lubricants should be used in conjunction with internal lubricants and external lubricants. Commonly used varieties are mainly metal soaps, and stearic acid is suitably used;
b. Extrusion and injection molding-purpose is to reduce viscosity, improve fluidity and easy demoulding. Lubricants are generally internal lubricants, and main lubricants are generally used in combination with esters and waxes;
c. Moulding and lamination forming-mainly other lubricants, and commonly used varieties are wax lubricants;
d. Molding of paste products-amount of lubricant is less, mainly internal lubricant, and liquid lubricant is suitable.

Soft products (Because soft products contain Dali plasticizers, and most plasticizers have excellent lubricity, amount of lubricants is less.)
a. In transparent film formula, use metal soaps and liquid composite stabilizers to match stearic acid (amount is less than 0.5 parts);
b. For blown film, in order to prevent adhesion, stearic acid monoglyceride can be used;
c. In cable material formula, if filler is added, 0.3~0.5 parts of high melting point wax can be used as lubricant.
Hard products (Amount of lubricant used is greater than that of soft products, which requires higher lubrication performance.)
a. Transparent and non-toxic products, such as blow-molded bottles and transparent sheets, commonly used are OP wax and E wax, etc., addition amount is 0.3~0.5 parts, and it can also be mixed with 0.5 parts of n-butyl stearate or 0.5 parts of hard Fatty acid coordination.
b. Opaque products such as plates and pipes are commonly used in combination with metal soap, paraffin wax and stearic acid. Amount of metal soap is 1~2 parts, amount of paraffin and stearic acid is 0.3~0.5 parts.

a. In order to improve impact performance of PVC, resins such as ABS, CPE and MBS are often blended; however, since these blended resins are highly compatible with lubricants, amount of lubricant used should be increased accordingly.
b. In order to improve surface gloss of PVC, vinyl chloride-vinyl acetate copolymer is often added, and amount of lubricant needs to be increased accordingly.

a. Heat stabilizer in PVC has a certain lubricating effect. Lubricity of different heat stabilizers is as follows: metal soap>liquid composite metal soap>lead salt>tin laurate>tin maleate, organotin mercaptan.
Therefore, for heat stabilizers with great lubricating effect, amount of lubricant can be correspondingly reduced in their formulations. Organic tin mercaptan heat stabilizer lacks external lubricity, and external lubricant should be appropriately added in formulation; while dibutyl tin carboxylate heat stabilizer has outstanding external lubrication effect, and amount of external lubricant can be appropriately reduced in formulation.
b. Most processing aids have external lubrication functions, which can reduce amount of lubricant added accordingly.
c. When formula contains a large amount of non-lubricating fillers, amount of internal and external lubricants added should be increased accordingly.

In a formula, internal and external lubricants should generally be used together. Amount of lubricant varies with processing method.