Lubricants are a class of additives used to improve the processability and apparent properties of polymers such as plastics and rubber. In addition to reducing friction in the general sense and improving fluidity and mold release during resin or rubber processing, the function of the lubricant can be extended to increase the surface finish of the product and prevent interfacial adhesion between the products. aspect. In terms of processing modification, the lubricant mainly reduces the mutual friction between the resin or the compound and the processing equipment and between the polymer molecules in the polymer processing process, thereby reducing the torque, saving energy, promoting flow and improving quality. the goal of.
Lubricants can be divided into internal and external lubricants. The distinction between internal and external lubricants depends mainly on their compatibility with the resin.
The internal lubricant has a large affinity with the resin, and its function is to reduce the force between the macromolecules;
The external lubricant has a low affinity with the resin, and its function is to reduce the friction between the tree and the processing machine.
The internal and external lubricants are only relatively speaking and there is no strict classification criteria. In resins with different polarities, the effects of internal and external lubricants may change.
First, the role of lubricants
The role of the internal lubricant is as follows:
(1) Stabilizing the resin to prevent a sharp increase in torque during plasticization;
(2) reducing the melt viscosity of the resin, increasing the fluidity, reducing the screw torque, increasing the extrusion amount and the production amount;
(3) Improve processing capacity, reduce equipment load, and improve energy efficiency.
The role of external lubricants is as follows:
(1) preventing decomposition and coloration of the resin due to frictional heat between the resin and the surface of the molding metal;
(2) preventing sintering on the surface of the forming machine;
(3) improving the peeling performance of the roller surface;
(4) Improve the release property;
(5) Improve the smoothness of the finished surface.
Second, the type of lubricant
Saturated hydrocarbons - saturated hydrocarbons can be classified into non-polar hydrocarbons (such as polyethylene wax and polypropylene wax) and polar hydrocarbons (such as chlorinated paraffin and oxidized polyethylene). Mainly used for PVC non-toxic external lubricants.
Liquid paraffin - commonly known as white oil, is a colorless transparent liquid, can be used as a transparent internal lubricant for PVC, the dosage is about 0.5 parts. In the extrusion process, the initial lubricity of the liquid paraffin is good and does not affect the thermal stability;
Solid paraffin wax, also known as natural paraffin wax, white solid, can be used as an external lubricant for PVC. The dosage is 0.1~1.0 parts. If the dosage is too large, it will affect the transparency;
Microcrystalline paraffin, also known as high melting paraffin, has a white or light yellow solid appearance and is called microcrystalline paraffin because of its fine crystallinity. Lubrication and thermal stability are better than other paraffin waxes. The amount used in PVC is small, generally 0.1~0.2 parts;
Low molecular weight polyethylene, also known as polyethylene wax, has a self-colored or light yellow solid appearance and poor transparency. It can be used for PVC extrusion and calendering, and the dosage is generally less than 0.5 parts;
Oxidized polyethylene wax - is a product of partial oxidation of polyethylene wax, the appearance is white powder; has excellent internal and external lubrication, good transparency and low price; the dosage is 0.1~1.0 parts;
Chlorinated paraffin - good compatibility with PVC, poor transparency, and good effect with other lubricants. The dosage of 0.3 or less is suitable.
Metal soaps - both excellent heat stabilizers and lubricants, have both internal and external lubrication, and the different varieties have slightly different weights.
Commonly used metal soaps are used in lubricants 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.
Aliphatic phenolamines - including two major classes of mono-fatty acid amides and di-fatty amides.
Mono-fatty amide - mainly for internal lubrication, specific varieties are stearic acid amine, erucic acid amide and ricinoleic acid amide;
Bis fatty acid guanamine - mainly for external lubrication, specific varieties are N, N-ethylene bis-stearic acid amine and N, N-ethylene bis-ricinoleic acid amine.
Fatty acid esters
Butyl stearate - the appearance of a colorless or light yellow oily liquid, mainly in the internal lubrication of PVC and external lubrication, the amount of 0.5 ~ 1.5 parts;
Glyceryl monostearate - code GMS, the appearance of a white waxy solid, is an excellent internal lubricant for PVC. It has little effect on transparency, and the amount added is less than 1.5 parts, which can be used together with stearic acid.
Fatty alcohols
Stearyl alcohol - the appearance of white fine beads, from the internal lubrication, transparent, 0.2 ~ 0.5 parts in PVC, in addition, can also be used in PS;
Pentaerythritol - PVC high temperature lubricant, the amount of 0.2 ~ 0.5 parts.
Third, the selection criteria of lubricants
1, according to different processing methods
a, calendering - the purpose is to prevent sticking rolls, reduce melt viscosity and improve fluidity. Lubricant application of internal lubricant and external lubricants, the common varieties are mainly metal soap, and appropriate with stearic acid;
b. Extrusion and injection molding - the purpose is to reduce viscosity, improve fluidity and ease demoulding. Lubricants are generally based on internal lubricants, and the main lubricants are generally used in combination with esters and waxes;
c, molding and laminating - mainly lubricants, the common varieties are wax lubricants;
d. Forming of paste products - the amount of lubricant is small, and the lubricant is mainly used, and liquid lubricant is preferred.
2, according to different products
Soft products (soft products contain large plasticizers, and plasticizers have excellent lubricity, so the amount of lubricant is small.)
a. In the transparent film formula, metal soap and liquid compound stabilizer are selected, and stearic acid is used (the amount is less than 0.5 parts);
b. For blown film, in order to prevent adhesion, stearic acid monoglyceride may be used;
c. In the cable material formulation, if adding filler, 0.3~0.5 parts of high melting point wax can be used as lubricant.
Hard products (lubricants are used in larger quantities than soft products, which require higher lubrication performance.)
a, transparent non-toxic products, such as blown bottles and transparent sheets, etc., commonly used OP wax and E wax, etc., the amount of addition is 0.3 ~ 0.5 parts, can also be combined with 0.5 parts of n-butyl stearate or 0.5 parts hard Fatty acid combination.
b, opaque products such as plates and pipes, etc., commonly used in combination with metal soap, paraffin and stearic acid. The amount of metal soap added is 1-2 parts, and the paraffin and stearic acid are added to the wall from 0.3 to 0.5 parts.
3. The effect of blending resin
a. In order to improve the impact properties of PVC, resins such as aBS, CPE and MBS are often blended; however, since these blended resins have great compatibility with lubricants, it is necessary to increase the amount of lubricant used accordingly.
b. In order to improve the surface gloss of PVC, a vinyl chloride-vinyl acetate copolymer is often added, and the amount of lubricant is also required to be increased accordingly.
4. Relationship between lubricants and other additives
a. The heat stabilizer in PVC has a certain lubricating effect. The lubricity of different heat stabilizers is as follows: metal soap>liquid composite metal soap>lead salt>tin laurate>tin maleate, thiol organotin. Therefore, for the lubrication of the heat stabilizer, the amount of the lubricant can be correspondingly reduced in the formulation. The organic thiol tin-based heat stabilizer lacks external lubricity, and the external lubricant should be appropriately added in the formulation; while the external lubrication of the dibutyltin carboxylate heat stabilizer is prominent, and the amount of the external lubricant can be appropriately reduced in the formulation.
b. Most of the processing aids have external lubrication function, which can reduce the amount of lubricant added.
c. When the formula contains a large amount of non-lubricating filler, the amount of internal and external lubricants should be increased accordingly.
5, the amount of lubricant
In a formulation, the internal and external lubricants should generally be used together. The amount of lubricant used will vary with the processing method.
Calendering: internal lubricants - 0.3 ~ 0.8 parts, external lubricants - 0.2 ~ 0.8 parts;
Extrusion and injection molding: internal lubricant - 0.5 ~ 1.0 parts, external lubricant - 0.2 ~ 0.4 parts.
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