Method for improving processability of natural rubber, unfilled rubber composite material and carbon black rubber

Abstract

The invention belongs to the technical field of natural rubber processing, and particularly relates to a method for improving the processing performance of natural rubber, an unfilled rubber composite material and carbon black rubber. Before the natural rubber is dried by hot air, the rubber sheet is smoked, on one hand, in the smoking process, smoke mainly contains ash, phenolic compounds and carbonyl compounds, and the phenolic compounds, the carbonyl compounds and proteins or phospholipids in the natural rubber are subjected to chemical reaction, so that the content of the natural rubber is reduced; the carbon black filler is added into the natural rubber, so that the long-chain branching degree and Mooney viscosity of the natural rubber are reduced, meanwhile, molecular chains with small molecular weights are generated, and rubber hydrocarbon with small molecular weights and ash (tar) in smoke have a very good plasticizing effect on the carbon black filler, so that the carbon black filler is more uniformly dispersed in a natural rubber matrix; the stress at definite elongation, the tear resistance and the wear resistance of the natural rubber / carbon black composite material are improved.

Description

Technical Field

[0001] This invention belongs to the field of natural rubber processing technology, specifically relating to a method for improving the processing performance of natural rubber, an unfilled rubber composite material, and carbon black rubber. Background Technology

[0002] Natural rubber, as an important industrial raw material, is widely used in tires, hoses, seals, and medical latex products. Its processing performance directly determines production efficiency, product quality stability, and the service performance of the final product. However, traditional processing methods often result in poor rubber processing performance and poor bonding with carbon black, affecting the wear resistance and service life of the final product. While existing processes can partially improve performance by adjusting coagulation or drying conditions, they still suffer from complex processes, large quality fluctuations, or difficulties in simultaneously achieving both processing performance and wear resistance. Therefore, developing a simple process that provides stable product quality and comprehensively improves the processing performance of natural rubber is of great significance. Summary of the Invention

[0003] The purpose of this invention is to provide a method for improving the processing performance of natural rubber, an unfilled rubber composite material, and carbon black rubber.

[0004] To achieve the above objectives, the present invention provides the following technical solution: This invention provides a method for improving the processing properties of natural rubber, comprising the following steps: Natural rubber latex is coagulated, pressed, and air-dried in sequence to obtain rubber sheets; The rubber sheet was subjected to smoking and hot air drying in sequence to obtain natural rubber with excellent processing properties.

[0005] Preferably, the dry rubber content of the natural rubber latex is 20-25%; and the particle size of the natural rubber latex is not less than 80 mesh.

[0006] Preferably, the coagulation method includes at least one of formic acid coagulation, acetic acid coagulation, microbial coagulation, and enzyme coagulation.

[0007] Preferably, the air-drying temperature is 30~40℃ and the time is 0.5~120h.

[0008] Preferably, the fumigation conditions include: a temperature of 40-80°C, a time of 0.5-8 hours, and a smoke concentration of 0.5-1.5 g / m³. 3 ; The smoking process is carried out in a smokehouse or a drying box vented with flue gas.

[0009] Preferably, the hot air drying temperature is 60~90℃ and the time is 12~48h.

[0010] The present invention also provides natural rubber with excellent processing properties obtained by the method described in the above technical solution.

[0011] The present invention also provides the application of natural rubber with excellent processing performance as described in the above technical solution in natural rubber products; the natural rubber products include tires, hoses, seals, medical latex products or shoe soles.

[0012] The present invention also provides an unfilled rubber composite material comprising the following components in parts by weight: 100 parts natural rubber, 5-7 parts zinc oxide, 0.4-0.6 parts stearic acid, 0.4-0.6 parts 2-mercaptobenzothiazole, and 3-4 parts sulfur; The natural rubber mentioned above is the natural rubber with excellent processing performance described in the above technical solution; The quality of the natural rubber is measured in dry rubber mass.

[0013] The present invention also provides a carbon black rubber comprising the following components in parts by weight: 100 parts natural rubber, 4-6 parts zinc oxide, 1-3 parts stearic acid, 0.5-0.8 parts N-tert-butyl-2-benzothiazolyl sulfinamide, 2-3 parts sulfur, and 30-40 parts carbon black N330; The natural rubber mentioned above is the natural rubber with excellent processing performance described in the above technical solution; The quality of the natural rubber is measured in dry rubber mass.

[0014] This invention provides a method for improving the processing performance of natural rubber, comprising the following steps: coagulating, pressing and air-drying natural rubber latex in sequence to obtain rubber sheets; subjecting the rubber sheets to smoking and hot air drying in sequence to obtain natural rubber with excellent processing performance.

[0015] Compared with the prior art, the beneficial effects of the present invention include: Before hot air drying of natural rubber, the rubber sheets are treated by smoking. During the smoking process, the smoke mainly contains ash, phenolic compounds, and carbonyl compounds. These phenolic compounds and carbonyl compounds react chemically with the proteins or phospholipids in natural rubber, resulting in a decrease in the long-chain branching degree and Mooney viscosity of natural rubber. At the same time, some small molecular weight chains are generated. These small molecular weight rubber hydrocarbons and the ash (tar) in the smoke have a good plasticizing effect on carbon black fillers, making the carbon black fillers more uniformly dispersed in the natural rubber matrix, and improving the tensile stress, tear resistance and abrasion resistance of natural rubber / carbon black composite materials.

[0016] Natural rubber treated by the method of the present invention has the following significant effects: a. Improved the processing performance of natural rubber, mainly reflected in the reduction of Mooney viscosity of raw rubber, the reduction of initial plasticity P0, and the high plasticizing efficiency: The Mooney viscosity of untreated raw rubber is 99.05~103.65MU, the initial plasticity P0 is 39.0~45.1, and the number of times it takes to masticate to Mooney viscosity 50 is 20.54~25.18.

[0017] The Mooney viscosity of the smoked raw rubber is 73.57~78.11MU, the initial plasticity P0 is 32.0~35.0, and the number of times it takes to masticate to Mooney viscosity 50 is 11.96~18.17.

[0018] b. Improved tensile stress and tear strength of unfilled rubber composites: The 500% tensile stress of the unsmoked, unfilled rubber composite material is 2.61~2.71 MPa, and the tear strength is 24.1~25.5 N / mm.

[0019] The 500% tensile stress of the smoked unfilled rubber composite material is 3.11~3.50MPa, and the tear strength is 26.9~28.9N / mm.

[0020] c. Improved the tensile stress, tear strength, and abrasion resistance of carbon black rubber: The tensile stress of untreated carbon black rubber is 2.09~2.18 MPa, the tear strength is 70.3~88.9 N / mm, and the abrasion volume is 146~158 mm². 3 .

[0021] The tensile stress of carbon black rubber treated with smoke is 2.32~2.50 MPa, the tear strength is 92.1~101.3 N / mm, and the abrasion volume is 130~140 mm². 3 . Attached Figure Description

[0022] Figure 1 The performance results of the rubber materials obtained in the examples and comparative examples are as follows; Figure 2 The images show the microstructure of the carbon black adhesive obtained in Example 2 (a) and Comparative Example 2 (b). Detailed Implementation

[0023] This invention provides a method for improving the processing properties of natural rubber, comprising the following steps: Natural rubber latex is coagulated, pressed, and air-dried in sequence to obtain rubber sheets; The rubber sheet was subjected to smoking and hot air drying in sequence to obtain natural rubber with excellent processing properties.

[0024] This invention involves sequentially coagulating, pressing, and air-drying natural rubber latex to obtain a rubber sheet.

[0025] In this invention, the dry rubber content of the natural rubber latex is preferably 20-25%; the particle size of the natural rubber latex is preferably not less than 80 mesh. In this invention, the natural rubber latex is preferably obtained by sequentially removing impurities and diluting freshly extracted natural latex; the dry rubber content of the freshly extracted natural latex is preferably 26-42%; the impurity removal method is preferably filtration, and the sieve used for filtration preferably has an 80-mesh aperture; the dilution is preferably performed using deionized water.

[0026] In this invention, the coagulation method preferably includes at least one of formic acid coagulation, acetic acid coagulation, microbial coagulation, and enzyme coagulation. In the formic acid coagulation, the mass ratio of natural rubber latex to formic acid, based on the dry rubber mass, is preferably 100:0.8~1.2. In the acetic acid coagulation, the mass ratio of natural rubber latex to acetic acid, based on the dry rubber mass, is preferably 100:0.8~1.2. In the microbial coagulation, the microorganisms preferably include at least one of lactic acid bacteria and Bacillus; the mass ratio of natural rubber latex to microorganisms, based on the dry rubber mass, is preferably 100:0.3~0.4. In the enzyme coagulation, the enzyme preferably includes at least one of papain and alkaline protease; the mass ratio of natural rubber latex to enzyme, based on the dry rubber mass, is preferably 100:0.5~2.0. This invention does not impose any particular limitation on the coagulation process; any process well-known to those skilled in the art can be used.

[0027] The present invention does not impose any particular limitation on the pressing process; any process well known to those skilled in the art can be used. In the present invention, the preferred size of the film is 500~900mm × 200~500mm × 900~1000mm.

[0028] In this invention, the air-drying temperature is preferably 30~40℃, specifically 30℃, 31℃, 32℃, 33℃, 34℃, 35℃, 36℃, 37℃, 38℃, 39℃, or 40℃, and the drying time is preferably 0.5~120h, specifically 0.5h, 2h, 4h, 6h, 10h, 20h, 30h, 40h, 50h, 60h, 70h, 80h, 90h, 100h, 110h, or 120h.

[0029] After obtaining the rubber sheet, the present invention sequentially subjectes the rubber sheet to smoking and hot air drying to obtain natural rubber with excellent processing performance.

[0030] In this invention, the preferred conditions for the fumigation treatment include: a temperature of 40~80℃, specifically 40℃, 50℃, 60℃, 70℃, and 80℃; a time of 0.5~8h, specifically 0.5h, 1h, 2h, 3h, 4h, 5h, 6h, 7h, and 8h; and a smoke concentration of 0.5~1.5g / m³. 3 Specifically, it can be 0.5g / m 3 0.6g / m 3 0.7g / m 3 0.8g / m 3 0.9g / m 3 1.0g / m 3 1.1g / m 3 1.2g / m 3 1.3g / m 3 1.4g / m 3 1.5g / m 3 The smoking process is preferably carried out in a smokehouse or a drying box with flue gas.

[0031] In this invention, the preferred temperature for hot air drying is 60~90℃, specifically 60℃, 65℃, 70℃, 75℃, 80℃, 85℃, or 90℃, and the preferred time is 12~48h, specifically 12h, 18h, 24h, 30h, 36h, 42h, or 48h.

[0032] The present invention also provides natural rubber with excellent processing properties obtained by the method described in the above technical solution.

[0033] The present invention also provides the application of natural rubber with excellent processing performance as described in the above technical solution in natural rubber products; the natural rubber products include tires, hoses, seals, medical latex products or shoe soles.

[0034] The present invention also provides an unfilled rubber composite material comprising the following components in parts by weight: 100 parts natural rubber, 5-7 parts zinc oxide, 0.4-0.6 parts stearic acid, 0.4-0.6 parts 2-mercaptobenzothiazole, and 3-4 parts sulfur; The natural rubber mentioned above is the natural rubber with excellent processing performance described in the above technical solution; The quality of the natural rubber is measured in dry rubber mass.

[0035] In this invention, the preparation method of the unfilled rubber composite material preferably includes the following steps: mixing the included components, and after the obtained compound is left to stand for 12 hours, the optimal vulcanization time T90 is measured and then vulcanized; the mixing temperature is preferably 50~70℃, the mixing time is preferably 8~12min; and the vulcanization temperature is preferably 143℃.

[0036] The present invention also provides a carbon black rubber comprising the following components in parts by weight: 100 parts natural rubber, 4-6 parts zinc oxide, 1-3 parts stearic acid, 0.5-0.8 parts N-tert-butyl-2-benzothiazolyl sulfinamide, 2-3 parts sulfur, and 30-40 parts carbon black N330; The natural rubber mentioned above is the natural rubber with excellent processing performance described in the above technical solution; The quality of the natural rubber is measured in dry rubber mass.

[0037] In this invention, the preparation method of the carbon black adhesive is preferably the same as the preparation method of the unfilled rubber composite material described above, and will not be repeated here.

[0038] Unless otherwise specified, the materials and equipment used in this invention are all commercially available products in the field.

[0039] The technical solutions of this invention will be clearly and completely described below with reference to the embodiments thereof. Obviously, the described embodiments are only a part of the embodiments of this invention, and not all of them. All other embodiments obtained by those skilled in the art based on the embodiments of this invention without creative effort are within the scope of protection of this invention.

[0040] Example 1 Freshly extracted natural latex (dry rubber content 26wt%) was filtered through an 80-mesh filter to remove impurities, and then diluted with deionized water to obtain natural rubber latex with a dry rubber content of 20wt%. The obtained natural rubber latex is coagulated by formic acid coagulation, wherein the mass ratio of the natural rubber latex to formic acid is preferably 100:0.8 based on the dry rubber mass; after coagulation, it is pressed into a sheet by a crepe press, and the size of the sheet is 500mm×200mm×900mm. Hang the film in a drying oven at 30°C for 120 hours to air dry; The film, after being hung, is placed in a smoking oven at a temperature of 40℃ and a smoke concentration of 0.5g / m³. 3 Under the conditions of fumigation for 4 hours; The smoked rubber sheets were transferred to a hot air drying oven and dried at 60°C for 48 hours to obtain the finished natural rubber product. An unfilled rubber composite material comprises: 100 parts of the above-obtained natural rubber product (by dry rubber weight), 6 parts of zinc oxide, 0.5 parts of stearic acid, 0.5 parts of 2-mercaptobenzothiazole, and 3.5 parts of sulfur. The above components are mixed (at 50°C for 12 minutes). After the resulting compound is left to stand for 12 hours, the optimal vulcanization time T90 is measured to be 15.65 minutes. A carbon black rubber comprises: 100 parts of the above-obtained natural rubber product (by dry weight), 5 parts of zinc oxide, 2 parts of stearic acid, 0.7 parts of N-tert-butyl-2-benzothiazole sulfinamide, 2.5 parts of sulfur, and 35 parts of carbon black N330. The above components are mixed (at 50°C for 12 minutes). After the resulting compound is left to stand for 12 hours, the optimal vulcanization time T90 is measured to be 13.06 minutes. Example 2 Freshly extracted natural latex (dry rubber content 42wt%) was filtered through an 80-mesh filter to remove impurities, and then diluted with deionized water to obtain natural rubber latex with a dry rubber content of 25wt%. The obtained natural rubber latex is coagulated by microbial coagulation, wherein the microorganism is lactic acid bacteria; the mass ratio of the natural rubber latex to the microorganism is preferably 100:0.3 based on the dry rubber mass; after coagulation, it is pressed into a sheet by a crepe press, and the sheet size is 900mm×500mm×1000mm. Hang the film in a drying oven at 40℃ for 0.5 hours to air dry; The film, after being hung, is placed in a smoking oven at a temperature of 80℃ and a smoke concentration of 1.5g / m³. 3 Under the conditions of fumigation for 0.5 hours; The smoked rubber sheets were transferred to a hot air drying oven and dried at 90°C for 12 hours to obtain the finished natural rubber product. Unfilled rubber composite material and carbon black rubber were obtained according to the method in Example 1.

[0041] Example 3 Freshly extracted natural latex (35wt% dry rubber content) was filtered through an 80-mesh filter to remove impurities, and then diluted with deionized water to obtain natural rubber latex with a dry rubber content of 23wt%. The obtained natural rubber latex was coagulated using a combination of microbial coagulation and formic acid coagulation, wherein the microorganisms were lactic acid bacteria; based on the dry rubber mass, the mass ratio of the natural rubber latex to the microorganisms was 100:0.3, and the mass ratio of the microorganisms to the formic acid was 3:1; after coagulation, it was pressed into a sheet using a crepe press, and the sheet size was 700mm×400mm×950mm; Hang the film in a drying oven at 35°C for 6 hours to air dry; The film, after being hung, is placed in a smoking oven at a temperature of 60℃ and a smoke concentration of 1.0 g / m³. 3 Under the conditions of fumigation for 3 hours; The smoked rubber sheets were transferred to a hot air drying oven and dried at 90°C for 12 hours to obtain the finished natural rubber product. Unfilled rubber composite material and carbon black rubber were obtained according to the method in Example 1.

[0042] Example 4 Freshly extracted natural latex (dry rubber content 38wt%) was filtered through an 80-mesh filter to remove impurities, and then diluted with deionized water to obtain natural rubber latex with a dry rubber content of 20wt%. The obtained natural rubber latex was coagulated using a combination of enzyme coagulation and acetic acid coagulation, wherein the enzyme was an alkaline protease; based on the dry rubber mass, the mass ratio of the natural rubber latex to the enzyme was 100:0.5, and the mass ratio of natural rubber to acetic acid was 100:0.8; after coagulation, it was pressed into a sheet using a crepe press, and the sheet size was 750mm×450mm×940mm. Hang the film in a drying oven at 38°C for 80 hours to air dry; The film, after being hung, is placed in a smoking oven at a temperature of 50℃ and a smoke concentration of 0.7g / m³. 3 Under the conditions of fumigation for 5 hours; The smoked rubber sheets were transferred to a hot air drying oven and dried at 70°C for 30 hours to obtain the finished natural rubber product. Unfilled rubber composite material and carbon black rubber were obtained according to the method in Example 1.

[0043] Example 5 Freshly extracted natural latex (dry rubber content 36wt%) was filtered through an 80-mesh filter to remove impurities, and then diluted with deionized water to obtain natural rubber latex with a dry rubber content of 23wt%. The obtained natural rubber latex was coagulated by enzyme coagulation, wherein the enzyme was papain; the mass ratio of the natural rubber latex to the enzyme was 100:2.0 based on the dry rubber mass; after coagulation, it was pressed into a sheet by a crepe press, and the size of the sheet was 650mm×480mm×920mm. Hang the film in a drying oven at 34℃ for 50 hours to air dry; The film, after being hung, is placed in a smoking oven at a temperature of 50℃ and a smoke concentration of 1.1 g / m³. 3 Under the conditions of fumigation for 4 hours; The smoked rubber sheets were transferred to a hot air drying oven and dried at 65°C for 40 hours to obtain the finished natural rubber product. Unfilled rubber composite material and carbon black rubber were obtained according to the method in Example 1.

[0044] Comparative Example 1 The natural rubber product prepared according to Example 1, wherein no smoking treatment is performed; Unfilled rubber composite material and carbon black rubber were prepared according to the method in Example 1.

[0045] Comparative Example 2 The natural rubber product prepared according to Example 2, wherein no smoking treatment is performed; Unfilled rubber composite material and carbon black rubber were prepared according to the method in Example 2.

[0046] Comparative Example 3 The natural rubber product prepared according to Example 3, wherein no smoking treatment is performed; Unfilled rubber composite material and carbon black rubber were prepared according to the method in Example 4.

[0047] Performance testing The Mooney viscosity of raw rubber (i.e., the natural rubber products obtained in the examples and comparative examples) was tested in accordance with GB / T 1232.1-2016 (Determination of unvulcanized rubber by disc shear viscometer - Part 1: Determination of Mooney viscosity). The plasticizing efficiency of natural rubber raw rubber is represented by the number of thin passes when the Mooney viscosity drops to 50 MU. The fewer the number of thin passes when the Mooney viscosity drops to 50 MU, the higher the plasticizing efficiency of the rubber. Figure 1 This is a graph showing the relationship between the Mooney viscosity of raw natural rubber and the number of thin-pass tests. From... Figure 1 The number of thin passes can be obtained when the Mooney viscosity drops to 50 MU.

[0048] The initial plasticity value P0 of raw rubber was tested according to GB / T 3510-2023 (Determination of plasticity of unvulcanized rubber by rapid plasticizer method); The degree of long-chain branching of natural rubber was characterized using a rubber processing analyzer. The specific method can be found in the literature (Kautschuk Gummi Kunststoffe, 2005, 58, 423-431).

[0049] The tensile stress and tear strength of the rubber compound were tested in accordance with GB / T 528-2009 (Determination of tensile stress-strain properties of vulcanized rubber or thermoplastic rubber) and GB / T529-2008 (Determination of tear strength of vulcanized rubber or thermoplastic rubber (trouser-shaped, right-angled and crescent-shaped specimens)). The microstructure of carbon black adhesive was analyzed using scanning electron microscopy. The abrasion resistance of the obtained rubber compound was tested according to GB / T 9867-2008 (Determination of abrasion resistance of vulcanized rubber or thermoplastic rubber (rotary roller abrasion tester method)); the test results are shown in Table 1. Table 1. Properties of the rubber materials obtained in the examples and comparative examples.

[0050] Depend on Figure 1 It can be seen that the natural rubber raw rubber prepared by the method provided by the present invention has lower Mooney viscosity, initial plasticity P0, and long chain branching degree than that of the untreated rubber. At the same time, the number of times the Mooney viscosity is reduced to 50MU is less than that of the untreated rubber, indicating that the plasticizing efficiency of the natural rubber prepared by the method provided by the present invention is higher than that of the untreated rubber.

[0051] As can be seen from Table 1, the natural rubber unfilled rubber prepared by the method provided by the present invention has a 500% tensile stress and tear strength greater than that of the untreated natural rubber; the natural rubber filled rubber prepared by the method provided by the present invention has a 100% tensile stress and tear strength greater than that of the untreated natural rubber, while also having improved wear resistance. Moreover, the preparation method is simple, low in cost, and easy to scale up for production.

[0052] Figure 2 These are microscopic morphology images (a) of the carbon black adhesive obtained in Example 2 and (b) of the carbon black adhesive obtained in Comparative Example 2; Figure 2 It can be seen that the carbon black dispersion of the natural rubber filler prepared by the method provided by the present invention is more uniform than that of the untreated natural rubber.

[0053] As can be seen from the above embodiments, the present invention provides a method for improving the processing performance of natural rubber. This method utilizes fumigation treatment of the rubber sheet. During the fumigation process, the smoke mainly contains ash, phenolic compounds, and carbonyl compounds. These phenolic and carbonyl compounds react chemically with the proteins or phospholipids in the natural rubber, leading to a decrease in the long-chain branching degree and Mooney viscosity of the natural rubber. Simultaneously, some low-molecular-weight molecular chains are generated. These low-molecular-weight rubber hydrocarbons and the ash (tar) in the smoke have a good plasticizing effect on the carbon black filler, making the carbon black filler more uniformly dispersed in the natural rubber matrix, thereby improving the tensile stress, tear resistance, and abrasion resistance of the natural rubber / carbon black composite material. The natural rubber obtained by this invention possesses excellent processing performance, high tensile stress, tear resistance, and abrasion resistance, and can be widely used in natural rubber products such as tires, hoses, medical latex products, and shoe soles.

[0054] Although the above embodiments have provided a detailed description of the present invention, they are only some embodiments of the present invention, and not all embodiments. Other embodiments can be obtained based on these embodiments without creative effort, and these embodiments all fall within the protection scope of the present invention.

Claims

1. A method for improving the processing properties of natural rubber, characterized in that, Includes the following steps: Natural rubber latex is coagulated, pressed, and air-dried in sequence to obtain rubber sheets; The rubber sheet was subjected to smoking and hot air drying in sequence to obtain natural rubber with excellent processing properties.

2. The method according to claim 1, characterized in that, The dry rubber content of the natural rubber latex is 20-25%; the particle size of the natural rubber latex is not less than 80 mesh.

3. The method according to claim 1, characterized in that, The coagulation method includes at least one of formic acid coagulation, acetic acid coagulation, microbial coagulation, and enzyme coagulation.

4. The method according to claim 1, characterized in that, The air-drying temperature is 30~40℃, and the time is 0.5~120h.

5. The method according to claim 1, characterized in that, The fumigation treatment conditions include: temperature of 40~80℃, time of 0.5~8h, and smoke concentration of 0.5~1.5g / m³. 3 ; The smoking process is carried out in a smokehouse or a drying box vented with flue gas.

6. The method according to claim 1, characterized in that, The hot air drying temperature is 60~90℃, and the time is 12~48h.

7. The natural rubber with excellent processing properties obtained by the method according to any one of claims 1 to 6.

8. The application of the natural rubber with excellent processing properties as described in claim 7 in natural rubber products; the natural rubber products include tires, hoses, seals, medical latex products, or shoe soles.

9. An unfilled rubber composite material, characterized in that, The composition includes the following components in parts by weight: 100 parts natural rubber, 5-7 parts zinc oxide, 0.4-0.6 parts stearic acid, 0.4-0.6 parts 2-mercaptobenzothiazole, and 3-4 parts sulfur; The natural rubber is the natural rubber with excellent processing properties as described in claim 7; The quality of the natural rubber is measured in dry rubber mass.

10. A carbon black adhesive, characterized in that, The composition includes the following components in parts by weight: 100 parts natural rubber, 4-6 parts zinc oxide, 1-3 parts stearic acid, 0.5-0.8 parts N-tert-butyl-2-benzothiazole sulfinamide, 2-3 parts sulfur, and 30-40 parts carbon black N330. The natural rubber is the natural rubber with excellent processing properties as described in claim 7; The quality of the natural rubber is measured in dry rubber mass.

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