Preparation method of a lubricant for plastic processing

Abstract

The present invention provides a preparation method of a lubricant for plastic processing, belonging to the technical field of lubricants, and comprising the following steps: mixing stearic acid, D-mannitol and other additives, performing a high-temperature reaction, performing vacuum drying, and grinding to obtain mannitol stearate; mixing bis(4-tert-butylcyclohexyl) peroxydicarbonate, butyl acrylate, vinyl acetate and n-hexane, deoxidizing, adding vinyl chloride, performing a high-temperature reaction, and performing vacuum drying to obtain a terpolymer; after kneading the terpolymer, adding polydimethylsiloxane raw rubber, continuing to knead, discharging, and performing normal-temperature cooling to obtain a semi-finished masterbatch; putting the semi-finished masterbatch into a twin-screw extruder, extruding, cutting, and vibrating to obtain modified silicone particles; and mixing mannitol stearate with the modified silicone particles to obtain the lubricant. The present invention can achieve a multifunctional lubricating effect, can not only improve the fluidity of PVC materials but also reduce the friction between PVC materials and equipment.

Description

Technical Field

[0001] The present invention relates to the technical field of lubricants, and particularly relates to a preparation method of a lubricant for plastic processing. Background Art

[0002] Due to the inherent molecular structure characteristics of polyvinyl chloride, when directly used as a raw material for extrusion processing to produce plastic products, its chemical properties have many defects. People usually add a certain amount of processing aids to polyvinyl chloride resin powder to change the chemical properties of the polyvinyl chloride material, so as to meet the process requirements of PVC resin forming processing and the technical indicators of different PVC products. In actual use, stabilizers, lubricants, auxiliary processing agents, colorants, impact modifiers and other additives are often added to PVC materials. The produced PVC materials have certain thermal stability, high strength, resistance to climate change and excellent geometric stability.

[0003] Among them, the lubricant plays a crucial role in the processing technology of PVC and the performance of its products. The function of the PVC lubricant is to improve the fluidity of the resin and the demoulding property of the product during plastic processing, and prevent defects caused by adhesion in the machine or the mold. Commonly used lubricants include fatty acids and their salts, and long-chain aliphatic hydrocarbons. According to their action mechanisms, they can be divided into external lubricants and internal lubricants. External lubricant: This kind of lubricant has poor compatibility with the molding resin. It forms a lubricating layer between the resin, facilitating the resin flow and product demoulding, such as paraffin wax. Internal lubricant: mainly polar, has good compatibility with the resin, reduces the melt viscosity of the resin, and improves its fluidity, such as butyl stearate, lead stearate, etc.

[0004] However, the current various lubricants are not suitable for producing PVC products with better quality. The patent document with the publication number of CN102504442B discloses a PVC external lubricant for PVC extrusion processing, and its composition includes: hydroxy stearic acid, 30% - 80%, octadecanol, 10% - 35%, adipic acid, 9.7% - 40%, phosphoric acid, 0.1% - 0.7%. It realizes certain lubricating performance and fluidity, but the structure of the PVC lubricant product produced by this production method is relatively simple, the product performance is single, and the product is prone to precipitation, resulting in uneven melt dispersion during the processing process, unstable internal structure, and poor thermal stability, bringing inconvenience to the production of customers and increasing the production cost.

[0005] Therefore, it is necessary to provide a preparation method of a lubricant for plastic processing to solve the problems existing in the above-mentioned prior art. Summary of the Invention

[0006] In view of this, the present invention provides a preparation method of a lubricant for plastic processing, which can achieve multiple functions, can not only improve the fluidity of PVC materials but also reduce the friction between PVC materials and equipment, provide good lubrication performance and have a certain thermal stability.

[0007] To achieve the above object, the specific solutions provided by the present invention are as follows:

[0008] A preparation method of a lubricant for plastic processing, comprising the following steps:

[0009] S1. Mix stearic acid, D-mannitol, and p-toluenesulfonic acid, add cyclohexane, react at high temperature under a nitrogen atmosphere, vacuum dry, and grind into powder to obtain stearic acid mannitol ester;

[0010] S2. Mix bis(4-tert-butylcyclohexyl) peroxydicarbonate, butyl acrylate, vinyl acetate, and n-hexane, deoxygenate, add vinyl chloride, react at high temperature, and vacuum dry to obtain a terpolymer;

[0011] S3. After kneading the terpolymer, add polydimethylsiloxane raw rubber, continue kneading, discharge, and cool at room temperature to obtain a semi-finished masterbatch; put the semi-finished masterbatch into a twin-screw extruder, extrude, cut, and vibrate to obtain modified silicone particles; mix stearic acid mannitol ester with the modified silicone particles to obtain a lubricant.

[0012] The present invention prepares stearic acid mannitol ester. Through an esterification reaction, stearic acid and D-mannitol react under the action of an acid catalyst p-toluenesulfonic acid to form stearic acid mannitol ester. The stearic acid molecule is long and hydrophobic, while the mannitol part contains multiple hydroxyl groups and has a certain hydrophilicity. This esterified product combines the hydrophobicity of stearic acid and the hydrophilicity of mannitol to form a molecule with certain polar and non-polar characteristics. During the PVC processing, the polar part (from the hydroxyl group of mannitol) of stearic acid mannitol ester has a certain interaction with the polar groups in PVC, enhancing its compatibility with PVC. The long alkyl chain of stearic alcohol interacts with the hydrocarbon chain part in the resin, enabling it to be embedded between the resin chains, forming a lubricating film, reducing the friction and adhesion between resin molecules, and further improving the fluidity of the resin during processing. Among them, the esterification reaction process is as follows:

[0013]

[0014] The present invention prepares a terpolymer by precipitation polymerization. In this reaction system, bis(4-tert-butylcyclohexyl) peroxydicarbonate generates free radicals through thermal decomposition to initiate the polymerization reaction. Butyl acrylate and vinyl acetate monomers have good polarity, while vinyl chloride has strong chemical activity. Therefore, the terpolymer can have good compatibility with the PVC matrix. The main chain of silicone is very flexible, and the intermolecular force is much weaker than that of hydrocarbons. Therefore, compared with hydrocarbons of the same molecular weight, it has a lower viscosity, weaker surface tension, smaller surface energy, and stronger film-forming ability. This low surface tension and low surface energy endow it with excellent hydrophobic, lubricating, and glazing properties. At the same time, due to the extremely low surface energy of the silicone material, the silicone macromolecules migrating to the surface of the matrix material well isolate the friction surface and reduce the friction force between the resin and the equipment. However, when directly using silicone particles, uneven or agglomerated silicone particles may occur. Therefore, the present invention prepares modified silicone particles, using butyl acrylate-vinyl acetate-vinyl chloride terpolymer as a carrier to help disperse the silicone particles, making the lubricating effect more uniform and stable, enabling it to form a more stable lubricating film during the processing, reducing the friction force between the resin and the equipment, and improving the lubricity and brightness of the plastic product surface. In addition, butyl acrylate also endows the material with more flexibility. Therefore, using this terpolymer as a carrier can effectively improve the impact strength and elongation at break of PVC, thereby enhancing its mechanical properties. In addition, the silicone particles themselves have good thermal stability, which can delay the degradation of PVC at high temperatures and increase the heat resistance.

[0015] In the present invention, mannitol stearate is used as a lubricant component, which can reduce the viscosity of PVC, reduce the friction between particles, and promote fluidity. In addition, the n-butyl acrylate and vinyl acetate parts in the terpolymer contain polar groups, and these polar groups can interact with the chlorine atoms of the PVC chain to reduce the friction between polymer chains. The Si-O bond in the modified silicone particles also has partial compatibility with the C-C bond in the PVC plastic matrix, and thus has a certain lubricating effect. Using it as an external lubricant during the plastic processing can better mix with the PVC plastic, ensure the fluidity of the melt and the molding quality, reduce the friction between the melt and the mold, improve the surface quality, and help with demolding.

[0016] Optionally, in step S1, after adding cyclohexane, a high-temperature reaction is carried out for 4-6 h under a nitrogen atmosphere. After evaporating cyclohexane, vacuum drying is carried out for 12-15 h, and then it is ground into powder to obtain mannitol stearate.

[0017] Optionally, the temperature of the high-temperature reaction in step S1 is 170-200 °C, and the temperature of the vacuum drying is 45-60 °C.

[0018] Optionally, in step S2, bis(4-tert-butylcyclohexyl) peroxydicarbonate, butyl acrylate, vinyl acetate and n-hexane are added to a reactor and mixed. After deoxidization through 3 freeze-pump-thaw cycles, vinyl chloride is added, the reactor is sealed, and then transferred to a preheated water bath for high-temperature reaction. After that, tetrahydrofuran is added to dissolve the unreacted monomers, the solid polymerization product is separated, washed 3 - 5 times with a large amount of n-hexane, and dried under vacuum to obtain a terpolymer.

[0019] The present invention uses tetrahydrofuran to dissolve some soluble impurities and unreacted monomers in the reaction system, and washes 3 - 5 times with a large amount of n-hexane to remove the residual unpolymerized monomers, thereby improving the purity of the finally obtained terpolymer.

[0020] Optionally, in step S2, the temperature of the high-temperature reaction is 60 - 80 °C and the time is 24 h, and the temperature of the vacuum drying is 40 - 60 °C and the time is 48 - 72 h.

[0021] The present invention controls the polymerization reaction temperature at 60 - 80 °C so that bis(4-tert-butylcyclohexyl) peroxydicarbonate can decompose to generate free radicals to initiate the polymerization reaction.

[0022] Optionally, in step S3, the kneading time is 2 - 5 min and the temperature is 170 - 200 °C, the continuous kneading time is 3 - 10 min, and the normal-temperature cooling time is 24 - 36 h.

[0023] Optionally, in step S3, the mass ratio of the terpolymer to the polydimethylsiloxane raw rubber is (2 - 3):2.

[0024] Optionally, in step S3, the melt temperature of the twin-screw extruder is set at 170 °C, the cutting is carried out in an underwater pelletizing device, and the modified silicone particles are the same size as ordinary PVC plastic particles.

[0025] The present invention prepares the modified silicone particles to be the same size as ordinary PVC plastic particles, enabling better physical mixing of the two and reducing the risk of migration and precipitation.

[0026] Optionally, in step S3, the mass ratio of mannitol stearate to the modified silicone particles during plastic processing is 1:2.

[0027] Optionally, the lubricant comprises raw materials in the following weight parts: 25 - 30 parts of stearic acid, 15 - 20 parts of D-mannitol, 20 - 30 parts of the terpolymer, 20 parts of polydimethylsiloxane raw rubber; wherein, the terpolymer comprises raw materials in the following weight parts: 1 - 1.5 parts of bis(4-tert-butylcyclohexyl) peroxydicarbonate, 15 - 30 parts of butyl acrylate, 15 - 30 parts of vinyl acetate, 10 - 30 parts of vinyl chloride.

[0028] The above technical solutions of the present invention have at least the following beneficial effects:

[0029] 1. The present invention prepares mannitol stearate. This ester combines the hydrophobicity of stearic acid and the hydrophilicity of mannitol to form a molecule with certain polar and non-polar characteristics. The polar part of mannitol stearate interacts with the polar groups in PVC, enhancing its compatibility with PVC. The long alkyl chain of stearyl alcohol interacts with the hydrocarbon chain part in the resin to form a lubricating film, further improving the fluidity of PVC resin during processing.

[0030] 2. The present invention uses precipitation polymerization to prepare a terpolymer. Butyl acrylate and vinyl acetate monomers have good polarity, while vinyl chloride has strong chemical activity. Therefore, the terpolymer can have good compatibility with the PVC matrix. Using the terpolymer as a carrier helps disperse silicone particles, making the lubricating effect more uniform and stable, reducing the friction between the resin and the equipment, and improving the lubricity and brightness of the plastic product surface. The silicone particles have good thermal stability, which can delay the degradation of PVC at high temperatures and increase heat resistance.

[0031] 3. The present invention uses mannitol stearate as a lubricant component to reduce the friction between particles and promote fluidity. The addition of modified silicone particles can ensure the fluidity of the melt and the molding quality, reduce the friction between the melt and the mold, improve the surface quality, and help with demolding.

[0032] 4. The n-butyl acrylate and vinyl acetate parts in the terpolymer contain polar groups. These polar groups can interact with the chlorine atoms of the PVC chain, reducing the friction between polymer chains, and thus also having a certain lubricating effect. In addition, butyl acrylate also endows the material with more flexibility, which can effectively improve the impact strength and elongation at break of PVC, and thus enhance its mechanical properties. Specific Embodiments

[0033] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions of the embodiments of the present invention will be clearly and completely described below in conjunction with the embodiments of the present invention. Obviously, the described embodiments are part of the embodiments of the present invention, rather than all of the embodiments. Based on the described embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art belong to the scope of protection of the present invention.

[0034] Example 1

[0035] After mixing 25 parts of stearic acid, 15 parts of D-mannitol and 0.3 part of p-toluenesulfonic acid in a mixer, 10 parts of cyclohexane was added. Under a nitrogen atmosphere, the mixture was reacted at a high temperature of 170 °C for 6 h. After evaporating cyclohexane, it was vacuum dried at 60 °C for 12 h and then ground into powder to obtain mannitol stearate.

[0036] 1 part of bis(4-tert-butylcyclohexyl) peroxydicarbonate, 15 parts of butyl acrylate, 5 parts of vinyl acetate and 100 parts of n-hexane were added to a reactor. Deoxygenation was carried out through 3 freeze-pump-thaw cycles, and then 10 parts of vinyl chloride was added. After the reactor was sealed and transferred to a preheated water bath, the reaction was maintained at 60 °C for 24 h. Then, 20 parts of tetrahydrofuran was added to dissolve the unreacted monomers. The solid polymerization product was separated, washed 3 times with a large amount of n-hexane, and vacuum dried at 60 °C for 48 h to obtain a terpolymer.

[0037] 20 parts of the terpolymer was put into an internal mixer at 170 °C and kneaded for 5 min. 20 parts of polydimethylsiloxane raw rubber was added and kneading continued for 10 min. Then the material was discharged and cooled at room temperature for 24 h to obtain a semi-finished masterbatch. The semi-finished masterbatch was put into a twin-screw extruder, the melt temperature was set at 170 °C, and after extrusion, it was cut by an underwater pelletizing device. After passing through a vibrating screen, modified silicone particles of uniform size were obtained, which were the same size as ordinary PVC plastic particles. Mannitol stearate and the modified silicone particles were mixed according to a mass ratio of 1:2 to obtain a lubricant.

[0038] Example 2

[0039] After mixing 30 parts of stearic acid, 20 parts of D-mannitol and 0.5 part of p-toluenesulfonic acid in a mixer, 20 parts of cyclohexane was added. Under a nitrogen atmosphere, the mixture was reacted at a high temperature of 200 °C for 4 h. After evaporating cyclohexane, it was vacuum dried at 45 °C for 15 h and then ground into powder to obtain mannitol stearate.

[0040] 1.5 parts of bis(4-tert-butylcyclohexyl) peroxydicarbonate, 30 parts of butyl acrylate, 10 parts of vinyl acetate and 150 parts of n-hexane were added to a reactor. Deoxygenation was carried out through 3 freeze-pump-thaw cycles, and then 30 parts of vinyl chloride was added. After the reactor was sealed and transferred to a preheated water bath, the reaction was maintained at 80 °C for 24 h. Then, 25 parts of tetrahydrofuran was added to dissolve the unreacted monomers. The solid polymerization product was separated, washed 5 times with a large amount of n-hexane, and vacuum dried at 40 °C for 72 h to obtain a terpolymer.

[0041] Put 30 parts of the terpolymer into a mixer at 200 °C and knead for 2 min. Add 20 parts of polydimethylsiloxane raw rubber, continue kneading for 3 min, discharge the material, and cool at room temperature for 36 h to obtain a semi-finished masterbatch. Put the semi-finished masterbatch into a twin-screw extruder, set the melt temperature at 170 °C, extrude and then cut through an underwater pelletizing device. After passing through a vibrating screen, uniform-sized modified silicone particles are obtained, which are the same size as ordinary PVC plastic particles. Mix stearic acid mannitol ester and the modified silicone particles in a mass ratio of 1:2 to obtain a lubricant.

[0042] Example 3

[0043] Mix 28 parts of stearic acid, 17 parts of D-mannitol and 0.4 part of p-toluenesulfonic acid in a mixer, add 15 parts of cyclohexane, react at 180 °C under a nitrogen atmosphere for 5 h, evaporate cyclohexane, and vacuum dry at 50 °C for 13 h and then grind into powder to obtain stearic acid mannitol ester.

[0044] Add 1.2 parts of bis(4-tert-butylcyclohexyl) peroxydicarbonate, 20 parts of butyl acrylate, 7 parts of vinyl acetate and 130 parts of n-hexane to a reactor, deoxygenate through 3 freeze-pump-thaw cycles, then add 20 parts of vinyl chloride, seal the reactor and transfer it to a preheated water bath and keep reacting at 70 °C for 24 h. Add 22 parts of tetrahydrofuran to dissolve the unreacted monomers, separate and take the solid polymerization product, wash it 4 times with a large amount of n-hexane, and vacuum dry at 50 °C for 60 h to obtain the terpolymer.

[0045] Put 25 parts of the terpolymer into a mixer at 190 °C and knead for 3 min. Add 20 parts of polydimethylsiloxane raw rubber, continue kneading for 8 min, discharge the material, and cool at room temperature for 30 h to obtain a semi-finished masterbatch. Put the semi-finished masterbatch into a twin-screw extruder, set the melt temperature at 170 °C, extrude and then cut through an underwater pelletizing device. After passing through a vibrating screen, uniform-sized modified silicone particles are obtained, which are the same size as ordinary PVC plastic particles. Mix stearic acid mannitol ester and the modified silicone particles in a mass ratio of 1:2 to obtain a lubricant.

[0046] Example 4

[0047] Mix 27 parts of stearic acid, 18 parts of D-mannitol and 0.35 part of p-toluenesulfonic acid in a mixer, add 15 parts of cyclohexane, react at 190 °C under a nitrogen atmosphere for 4.5 h, evaporate cyclohexane, and vacuum dry at 55 °C for 14 h and then grind into powder to obtain stearic acid mannitol ester.

[0048] Add 1.2 parts of bis(4-tert-butylcyclohexyl) peroxydicarbonate, 18 parts of butyl acrylate, 6 parts of vinyl acetate and 110 parts of n-hexane to the reactor. Deoxygenate through 3 freeze-pump-thaw cycles, then add 17 parts of vinyl chloride. Seal the reactor and transfer it to a preheated water bath. Keep the reaction at 65 °C for 24 h, then add 23 parts of tetrahydrofuran to dissolve the unreacted monomers. Separate and collect the solid polymerization product, wash it 3 times with a large amount of n-hexane, and dry it under vacuum at 55 °C for 72 h to obtain the terpolymer.

[0049] Place 26 parts of the terpolymer into a mixer at 180 °C and knead for 4 min. Add 20 parts of polydimethylsiloxane raw rubber and continue to knead for 8 min. Discharge the material and cool it at room temperature for 36 h to obtain the semi-finished masterbatch. Put the semi-finished masterbatch into a twin-screw extruder, set the melt temperature at 170 °C, extrude it and then cut it through an underwater pelletizing device. After passing through a vibrating screen, obtain uniformly sized modified silicone particles similar in size to ordinary PVC plastic particles. Mix stearic acid mannitol ester and the modified silicone particles in a mass ratio of 1:2 to obtain the lubricant.

[0050] Example 5

[0051] Mix 30 parts of stearic acid, 20 parts of D-mannitol and 0.5 part of p-toluenesulfonic acid in a mixer, then add 20 parts of cyclohexane. Under a nitrogen atmosphere, react at a high temperature of 200 °C for 5 h. Evaporate cyclohexane and then dry it under vacuum at 50 °C for 13 h and grind it into powder to obtain stearic acid mannitol ester.

[0052] Add 1.5 parts of bis(4-tert-butylcyclohexyl) peroxydicarbonate, 25 parts of butyl acrylate, 7 parts of vinyl acetate and 130 parts of n-hexane to the reactor. Deoxygenate through 3 freeze-pump-thaw cycles, then add 20 parts of vinyl chloride. Seal the reactor and transfer it to a preheated water bath. Keep the reaction at 75 °C for 24 h, then add 25 parts of tetrahydrofuran to dissolve the unreacted monomers. Separate and collect the solid polymerization product, wash it 5 times with a large amount of n-hexane, and dry it under vacuum at 40 °C for 72 h to obtain the terpolymer.

[0053] Place 30 parts of the terpolymer into a mixer at 190 °C and knead for 2 - 5 min. Add 20 parts of polydimethylsiloxane raw rubber and continue to knead for 7 min. Discharge the material and cool it at room temperature for 30 h to obtain the semi-finished masterbatch. Put the semi-finished masterbatch into a twin-screw extruder, set the melt temperature at 170 °C, extrude it and then cut it through an underwater pelletizing device. After passing through a vibrating screen, obtain uniformly sized modified silicone particles similar in size to ordinary PVC plastic particles. Mix stearic acid mannitol ester and the modified silicone particles in a mass ratio of 1:2 to obtain the lubricant.

[0054] Example 6

[0055] Mix 27 parts of stearic acid, 15 parts of D-mannitol and 0.4 part of p-toluenesulfonic acid in a mixer, then add 15 parts of cyclohexane. Under a nitrogen atmosphere, react at a high temperature of 170 °C for 4 h. After evaporating cyclohexane, vacuum dry at 60 °C for 12 h and then grind into powder to obtain mannitol stearate.

[0056] Add 1.5 parts of bis(4-tert-butylcyclohexyl) peroxydicarbonate, 30 parts of butyl acrylate, 7 parts of vinyl acetate and 120 parts of n-hexane into a reactor. Deoxygenate through 3 freeze-pump-thaw cycles, then add 20 parts of vinyl chloride. Seal the reactor and transfer it to a preheated water bath, and keep reacting at 70 °C for 24 h. Then add 23 parts of tetrahydrofuran to dissolve the unreacted monomers, separate and take the solid polymerization product, wash it 3 times with a large amount of n-hexane, and vacuum dry at 60 °C for 72 h to obtain a terpolymer.

[0057] Put 25 parts of the terpolymer into a mixer at 170 - 200 °C and knead for 4 min, add 20 parts of polydimethylsiloxane raw rubber, continue to knead for 7 min, discharge the material, and cool at room temperature for 30 h to obtain a semi-finished masterbatch. Put the semi-finished masterbatch into a twin-screw extruder, set the melt temperature at 170 °C, extrude and then cut through an underwater pelletizing device. After passing through a vibrating screen, obtain uniformly sized modified silicone particles similar in size to ordinary PVC plastic particles. Mix mannitol stearate and modified silicone particles according to a mass ratio of 1:2 to prepare a lubricant.

[0058] The present invention also carried out comparative examples and related tests.

[0059] Comparative Example 1

[0060] Compared with Example 1, the difference is that mannitol stearate was not prepared, and stearic acid and modified silicone particles were directly mixed, and other components and preparation steps were exactly the same, and a lubricant was prepared.

[0061] Comparative Example 2

[0062] Compared with Example 1, the difference is that mannitol stearate was not prepared, and only modified silicone particles were used as the lubricant, and other components and preparation steps were exactly the same, and a lubricant was prepared.

[0063] Comparative Example 3

[0064] Compared with Example 1, the difference is that the terpolymer was not added to prepare the modified silicone particles, and other components and preparation steps were exactly the same, and a lubricant was prepared.

[0065] Comparative Example 4

[0066] Compared with Example 1, the difference is that modified silicone particles were not prepared, and only mannitol stearate was prepared as a lubricant, while other components and preparation steps were exactly the same.

[0067] Performance detection test

[0068] The lubricants obtained in Examples 1 to 6 and Comparative Examples 1 to 4 were respectively added to the PVC resin system, and the addition amount as the lubricant was 1.5% of the overall material of the PVC resin system. After being thoroughly mixed in a high-speed mixer, melt blending and extrusion were carried out using an extruder of model SHJ-20B, and the middle zone temperature was set at 180 °C. The current values, melt pressure values, and MFRs of each group are recorded in Table 1.

[0069] Table 1

[0070]

[0071] As can be seen from Table 1, the current values and melt pressure values used in the tests of Examples 1 to 6 are both smaller than those of Comparative Examples 1 to 4, and the MFRs of the test groups of Examples 1 to 6 are all higher than those of Comparative Examples 1 to 4. It can be seen that the lubricants prepared in Examples 1 to 6 play a more excellent lubricating role compared to the lubricants prepared in Comparative Examples 1 to 4 during the plastic processing process, significantly improving the fluidity of the material during the plastic processing process.

[0072] Combined with Table 1, since mannitol stearate was not prepared in Comparative Example 1, and a lubricant directly obtained by mixing stearic acid and modified silicone particles was used, its compatibility with PVC plastic was reduced, thereby affecting the fluidity during the plastic processing process and significantly decreasing the MFR.

[0073] After the lubricants prepared using Examples 1 to 6 and Comparative Examples 1 to 4 were processed and extruded with PVC resin, they were injection molded into standard samples with a thickness of 2.0 mm. The friction coefficient of the material was tested according to the ASTM G-115 standard, and the rheological curves recorded by the computer and the surface finish of the plasticized standard samples were observed and compared. The impact strength and tensile strength of the plastic standard samples were detected using an impact testing machine and a tensile testing machine, and the test results are shown in Table 2.

[0074] Table 2

[0075]

[0076] As can be seen from Table 2, the surface smoothness and surface finish of the standard samples injection-molded with the lubricants prepared in Examples 1 to 6 are significantly better than those of Comparative Examples 1 to 4. The surface finish and smoothness of Comparative Example 4 do not meet the standards because no modified silicone particles are added, and the surface is relatively rough and no longer smooth, which also reduces the friction coefficient of the standard samples. In addition, since no ternary polymer is added as the carrier of the silicone particles in Comparative Example 3, the tensile strength of the overall standard samples decreases significantly.

[0077] The above are the preferred embodiments of the present invention. It should be noted that for those of ordinary skill in the art, without departing from the principle of the present invention, several improvements and refinements can be made, and these improvements and refinements should also be regarded as the protection scope of the present invention.

Claims

1. A method for preparing a lubricant for plastic processing, characterized in that: The steps include: S1, after mixing stearic acid, D-mannitol and p-toluenesulfonic acid, adding cyclohexane, reacting at high temperature, vacuum drying, grinding into powder to obtain stearic acid mannitol ester; S2, mixing bis(4-tert-butylcyclohexyl) peroxydicarbonate, butyl acrylate, vinyl acetate and n-hexane, deoxygenating, adding vinyl chloride, reacting at high temperature, and vacuum drying to obtain a terpolymer; S3, after kneading the terpolymer, adding polydimethylsiloxane raw rubber, continuing to knead, discharging, cooling at room temperature, and obtaining a masterbatch semi-finished product; placing the masterbatch semi-finished product into a twin-screw extruder, extruding, cutting, and vibrating to obtain modified silicone particles; mixing mannitol stearate with the modified silicone particles to obtain a lubricant; In step S3, the mass ratio of the terpolymer to the polydimethylsiloxane raw rubber is (2-3):2; the mass ratio of mannitol stearate to the modified silicone particles used in plastic processing is 1:

2.

2. The method for preparing a lubricant for plastic processing according to claim 1, characterized in that: In the step S1, after adding cyclohexane, the mixture is reacted at high temperature for 4 to 6 hours under a nitrogen atmosphere, and after evaporating the cyclohexane, the mixture is vacuum dried for 12 to 15 hours and then ground into powder to obtain mannitol stearate.

3. The method for preparing a lubricant for plastic processing according to claim 1, characterized in that: In step S1, the temperature of the high temperature reaction is 170-200°C, and the temperature of the vacuum drying is 45-60°C.

4. The method for preparing a lubricant for plastic processing according to claim 1, characterized in that: In the step S2, bis(4-tert-butylcyclohexyl) peroxydicarbonate, butyl acrylate, vinyl acetate and n-hexane are added to a reactor and mixed, and deoxygenated by three freeze-pump-thaw cycles. After adding vinyl chloride, the reactor is sealed and transferred to a preheated water bath for high-temperature reaction. After that, tetrahydrofuran is added to dissolve unreacted monomers, and the solid polymer product is separated and washed with a large amount of n-hexane for 3 to 5 times, and vacuum dried to obtain a terpolymer.

5. The method for preparing a lubricant for plastic processing according to claim 1, characterized in that: In step S2, the temperature of the high temperature reaction is 60-80° C. and the time is 24 h, and the temperature of the vacuum drying is 40-60° C. and the time is 48-72 h.

6. The method for preparing a lubricant for plastic processing according to claim 1, characterized in that: In step S3, the mixing time is 2-5 minutes, the temperature is 170-200° C., the mixing time is continued for 3-10 minutes, and the cooling time at room temperature is 24-36 hours.

7. The method for preparing a lubricant for plastic processing according to any one of claims 1 to 6, characterized in that: The lubricant comprises the following raw materials in parts by weight: 25-30 parts of stearic acid, 15-20 parts of D-mannitol, 20-30 parts of terpolymer, and 20 parts of polydimethylsiloxane raw rubber; The terpolymer includes the following raw materials in parts by weight: 1-1.5 parts of bis(4-tert-butylcyclohexyl)peroxydicarbonate, 15-30 parts of butyl acrylate, 15-30 parts of vinyl acetate, and 10-30 parts of vinyl chloride.

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