A constant viscosity natural rubber, its preparation method and application, and unfilled and filled rubber composites

Abstract

The present application relates to the technical field of natural rubber processing, and particularly relates to constant viscosity natural rubber, a preparation method and application thereof, and unfilled and filled rubber composite materials. Through a multi-stage processing mode of "constant viscosity agent soaking + smoking + spraying constant viscosity agent + hot air drying + spraying constant viscosity agent again during fast drying", the constant viscosity agent is uniformly distributed in the rubber matrix and continuously acts, effectively inhibits the rebound of the Mooney viscosity, and significantly improves the viscosity stability of the natural rubber. The constant viscosity natural rubber prepared by the present application can significantly improve the dispersion uniformity of the filler in the rubber compound, the long-chain branched natural rubber with reduced long-chain branching degree and widened molecular weight distribution has significantly reduced processing viscosity and greatly improved flowability, which provides a good processing basis for the uniform dispersion of fillers such as carbon black in the rubber compound, and further improves the comprehensive mechanical properties of the rubber product, such as tensile strength, flex resistance and wear resistance.

Description

Technical Field

[0001] This invention relates to the field of natural rubber processing technology, and in particular to a constant viscosity natural rubber, its preparation method and application, and unfilled and filled rubber composite materials. Background Technology

[0002] Natural rubber, as an important industrial raw material, is widely used in tires, hoses, seals, and medical latex products. Its Mooney viscosity is a crucial indicator of processing performance. However, during storage and processing, natural rubber is prone to increased Mooney viscosity and unstable processing performance due to changes in molecular chain structure and increased gel content, affecting the consistency of subsequent product quality.

[0003] To improve the viscosity stability of natural rubber, existing technologies often employ viscosity-stabilizing agents, such as hydroxylamine hydrochloride and hydroxylamine sulfate, which inhibit molecular chain cross-linking reactions by blocking the aldehyde groups in the rubber molecules, thus achieving a constant viscosity. However, traditional viscosity-stabilizing treatments result in uneven agent distribution and limited effectiveness, making it difficult to achieve precise control over Mooney viscosity. Therefore, developing a constant-viscosity natural rubber preparation method that can effectively stabilize Mooney viscosity, offers controllable processing, and is easy to operate is of great significance. Summary of the Invention

[0004] In view of this, the purpose of this invention is to provide a constant viscosity natural rubber, its preparation method and application, and unfilled and filled rubber composite materials. The constant viscosity natural rubber prepared by this invention maintains a constant Mooney viscosity over a long period without rebounding or fluctuating, while also retaining high strength and high wear resistance.

[0005] To achieve the above-mentioned objectives, the present invention provides the following technical solution: This invention provides a method for preparing constant viscosity natural rubber, comprising the following steps: Natural rubber latex is coagulated, pressed, and air-dried in sequence to obtain rubber sheets; The film is immersed in a constant viscosity solution to obtain a first-processed film. The first-processed film is then subjected to a smoking treatment to obtain a smoked film; The smoked film is subjected to a first tack-fixing agent spraying treatment to obtain a secondary treated film. The secondary-treated film is dried with hot air until the moisture content is 10-20%, then subjected to a second constant tack spray treatment, and dried further until constant weight is obtained to obtain constant tack natural rubber.

[0006] Preferably, the viscosity constant agent solution is a hydroxylamine hydrochloride solution or a hydroxylamine sulfate solution; the mass concentration of the viscosity constant agent solution is 0.1-1.0%; and the soaking treatment time is 2-12 hours.

[0007] Preferably, the coagulation method includes at least one of formic acid coagulation, acetic acid coagulation, microbial coagulation, and enzyme coagulation.

[0008] Preferably, the fumigation conditions include: a temperature of 40~100℃, a time of 0.5~10h, and a smoke concentration of 0.5~1.5g / m³. 3 The smoke velocity is 0.2~2m / s.

[0009] Preferably, the viscosity-fixing agent solution used in the first and second viscosity-fixing agent spraying treatments has a mass concentration of 0.05–0.5% and a spraying volume of 0.5–2 L / m³. 2 .

[0010] Preferably, the temperature of the hot air drying is 60~100℃.

[0011] This invention provides a constant viscosity natural rubber prepared by the preparation method described above.

[0012] This invention provides the application of the constant-viscosity natural rubber described above in natural rubber products.

[0013] The present invention provides an unfilled rubber composite material comprising the following components in parts by weight: 100 parts of constant-viscosity natural rubber as described above (based on dry rubber), 5-7 parts of zinc oxide, 0.4-0.6 parts of stearic acid, 0.4-0.6 parts of 2-mercaptobenzothiazole, and 3-4 parts of sulfur.

[0014] The present invention provides a filled rubber composite material comprising the following components in parts by weight: 100 parts of the constant-viscosity natural rubber as described in claim 7 (based on dry rubber), 4-6 parts of zinc oxide, 1-3 parts of stearic acid, 0.5-0.8 parts of N-tert-butyl-2-benzothiazole sulfinamide, 2-3 parts of sulfur, and 10-60 parts of filler.

[0015] This invention provides a method for preparing constant-viscosity natural rubber, comprising the following steps: coagulating, pressing, and air-drying natural rubber latex sequentially to obtain a rubber sheet; immersing the rubber sheet in a constant-viscosity agent solution to obtain a first-treated rubber sheet; subjecting the first-treated rubber sheet to smoking treatment to obtain a smoked rubber sheet; subjecting the smoked rubber sheet to a first constant-viscosity agent spray treatment to obtain a second-treated rubber sheet; subjecting the second-treated rubber sheet to hot air drying until the moisture content is 10-20%, subjecting it to a second constant-viscosity agent spray treatment, and continuing drying to constant weight to obtain constant-viscosity natural rubber.

[0016] This invention employs a segmented processing technology combining tackifier immersion, fumigation, multi-stage spraying, and hot air drying to achieve uniform distribution and sustained effectiveness of the tackifier in the rubber matrix. This effectively curbs Mooney viscosity rebound and improves the storage viscosity stability of natural rubber. Fumigation creates a synergistic effect with the tackifier: the phenolic and carbonyl compounds in the fumigation gas react with rubber proteins and phospholipids, breaking down branching nodes, reducing the degree of long-chain branching, and disassembling the network of ultra-long branches into linear main chains and short branches, widening the molecular weight range and optimizing processing characteristics. Furthermore, the fumigation environment promotes deep penetration of the tackifier, significantly enhancing the tack stabilization effect.

[0017] The constant viscosity natural rubber prepared by this invention can significantly improve the dispersion uniformity of fillers in the rubber compound. The natural rubber with reduced long chain branching degree and broadened molecular weight distribution has significantly reduced processing viscosity and greatly improved fluidity, providing a good processing basis for the uniform dispersion of fillers such as carbon black in the rubber compound, thereby improving the comprehensive mechanical properties of rubber products such as tensile strength, flexural strength, and abrasion resistance. Detailed Implementation

[0018] This invention provides a method for preparing constant viscosity natural rubber, comprising the following steps: Natural rubber latex is coagulated, pressed, and air-dried in sequence to obtain rubber sheets; The film is immersed in a constant viscosity solution to obtain a first-processed film. The first-processed film is then subjected to a smoking treatment to obtain a smoked film; The smoked film is subjected to a first tack-fixing agent spraying treatment to obtain a secondary treated film. The secondary-treated film is dried with hot air until the moisture content is 10-20%, then subjected to a second constant tack spray treatment, and dried further until constant weight is obtained to obtain constant tack natural rubber.

[0019] Unless otherwise specified, all raw materials used in this invention are commercially available products well known in the art.

[0020] This invention involves sequentially coagulating, pressing, and air-drying natural rubber latex to obtain a rubber sheet.

[0021] In this invention, the dry rubber content of the natural rubber latex is preferably 20-40%, and in specific embodiments it can be 20%, 25%, 30%, 35%, or 40%; the particle size of the natural rubber latex is preferably ≤80 mesh (i.e., the mesh size is 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 is preferably 80 mesh; the dilution is preferably performed using deionized water.

[0022] In this invention, the coagulation method preferably includes at least one of formic acid coagulation, acetic acid coagulation, microbial coagulation, and enzyme coagulation. In 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 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 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 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.

[0023] The present invention does not impose any special limitations on the pressing process, and any process well known to those skilled in the art can be used. In the present invention, the preferred size of the film is (500~900) mm × (200~500) mm × (900~1000) mm.

[0024] In this invention, the air-drying temperature is preferably 25~40℃, specifically 25, 26, 28, 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.

[0025] After obtaining the film, the present invention immerses the film in a constant viscosity solution to obtain a first-processed film.

[0026] In this invention, the viscosity stabilizer solution is preferably an aqueous solution of hydroxylamine hydrochloride or hydroxylamine sulfate; the mass concentration of the viscosity stabilizer solution is preferably 0.1-1.0%, and in specific embodiments it can be 0.1%, 0.2%, 0.3%, 0.4%, 0.5%, 0.6%, 0.7%, 0.8%, 0.9%, or 1.0%; in this invention, the soaking time is preferably 2-12 hours, and in specific embodiments it can be 2, 4, 6, 8, 10, or 12 hours. This invention, through soaking in the viscosity stabilizer solution, pre-penetrates the hydroxylamine-based viscosity stabilizer uniformly into the rubber matrix, completing the initial uniform loading of the viscosity stabilizer within the matrix; this not only pre-constructs an internal antioxidant stabilizing system, inhibiting the Mooney viscosity rebound caused by the oxidative branching of rubber molecular chains during subsequent storage, but also improves the dense structure of the rubber surface, facilitating better penetration of subsequent smoke components and surface-sprayed viscosity stabilizers into the rubber compound, achieving a complete coordination of the internal-external viscosity stabilizer system.

[0027] After obtaining the first-processed film, the present invention performs a smoking treatment on the first-processed film to obtain a smoked film.

[0028] In this invention, the preferred conditions for the fumigation treatment include: a temperature of 40~100℃, specifically 40, 50, 60, 70, 80, 90, or 100℃ in specific embodiments; a time of 0.5~10h, specifically 0.5, 1, 2, 3, 4, 5, 6, 7, or 8h in specific embodiments; and a smoke concentration of 0.5~1.5g / m³. 3 In specific embodiments, the concentration can be 0.5, 0.6, 0.7, 0.8, 0.9, 1.0, 1.1, 1.2, 1.3, 1.4, or 1.5 g / m³; the smoke flow rate is 0.2~2 m / s, and in specific embodiments, it can be 0.2, 0.4, 0.6, 0.8, 1.0, 1.2, 1.4, 1.6, 1.8, or 2 m / s. In this invention, the smoking treatment is preferably carried out in a smokehouse or a drying box with flue gas. During the smoking process, the phenols and carbonyl compounds in the smoke react with the proteins and phospholipids in the rubber, reducing the long-chain branching degree and improving the processing performance of natural rubber. In addition, the smoking treatment also promotes the penetration of the tackifier and enhances the tack-consistency effect.

[0029] After obtaining the smoked film, the present invention subjectes the smoked film to a first constant viscosity agent spraying treatment to obtain a secondary treated film.

[0030] In this invention, the mass concentration of the viscosity-fixing agent solution used in the first viscosity-fixing agent spraying treatment is preferably 0.05-0.5%, and in specific embodiments it can be 0.05%, 0.1%, 0.2%, 0.3%, 0.4%, or 0.5%; the spraying volume is preferably 0.5-2 L / m³. 2In specific embodiments, the concentration can be 0.5, 0.8, 1.0, 1.2, 1.5, 1.8, or 2 L / m³. 2 In this invention, the type of viscosity stabilizer solution is the same as that used in the aforementioned immersion treatment, and will not be repeated here. In the first viscosity stabilizer spraying treatment, after the branching regulation is completed in the fumigation process, a viscosity stabilizer is uniformly added to the rubber surface to replenish the surface additive content. This works in conjunction with the internal viscosity stabilizer pre-embedded in the immersion process to bidirectionally inhibit the oxidative cross-linking of rubber molecular chains. The low-concentration spray solution can gently penetrate to the near-surface layer of the rubber without causing excessive precipitation of additives. The surface additives are pre-loaded before hot air drying, ensuring the effectiveness of the subsequent secondary spraying film formation.

[0031] After obtaining the secondary treated film, the present invention performs hot air drying on the secondary treated film until the moisture content is 10~20%, then performs a second constant tack spray treatment, and continues to dry until constant weight, to obtain constant tack natural rubber.

[0032] In this invention, the preferred temperature for hot air drying is 60-100℃, specifically 60, 65, 70, 75, 80, 85, 90, or 100℃. When the moisture content reaches 10%, 12%, 14%, 16%, 18%, or 20%, a second tackifier spraying treatment is performed. This second tackifier spraying treatment is performed when the moisture content reaches 10-20% after hot air drying because: during this rapid drying stage, the film still retains a suitable amount of residual moisture and residual heat from drying; the micropores on the rubber surface are not completely closed, allowing the sprayed tackifier solution to moderately penetrate the surface pores, ensuring the stabilizer is firmly embedded in the rubber surface; simultaneously, the residual heat of the film rapidly evaporates the solvent, promoting the uniform curing of the tackifier components into a continuous and dense surface protective film. This film, together with the tackifier previously soaked and embedded within the substrate and initially sprayed and loaded onto the near-surface layer, forms a three-layer gradient stabilizing system from the inside out, effectively blocking oxygen and capturing active free radicals. If the rubber is sprayed only after it has completely dried to a constant weight, the rubber surface will shrink due to water loss, and the pores will be completely closed. The liquid can only float on the surface, making it easy to fall off and form an uneven film. At the same time, cold-dry rubber is prone to internal stress cracking when it comes into contact with water, which will greatly reduce the viscosity stabilization effect and the quality of the finished rubber.

[0033] In this invention, the mass concentration of the viscosity-fixing agent solution used in the second viscosity-fixing agent spraying treatment is preferably 0.05-0.5%, and in specific embodiments it can be 0.05%, 0.1%, 0.2%, 0.3%, 0.4%, or 0.5%; the spraying volume is preferably 0.5-2 L / m³. 2 In specific embodiments, the concentration can be 0.5, 0.8, 1.0, 1.2, 1.5, 1.8, or 2 L / m³. 2In this invention, the type of viscosity-regulating agent solution is the same as that used in the aforementioned immersion treatment, and will not be repeated here. The present invention sprays the viscosity-regulating agent again during the rapid drying stage, which can form a protective layer on the rubber surface, further delaying viscosity changes and improving product storage stability.

[0034] This invention employs a multi-stage treatment method involving "immersion in a tackifier + fumigation + spraying the tackifier + hot air drying + spraying the tackifier again during rapid drying" to ensure that the tackifier is evenly distributed and continuously acts within the rubber matrix, effectively suppressing Mooney viscosity rebound and significantly improving the viscosity stability of natural rubber.

[0035] This invention provides a constant viscosity natural rubber prepared by the preparation method described above.

[0036] This invention provides the application of the constant-viscosity natural rubber described above in natural rubber products. In this invention, the natural rubber products preferably include aircraft tires, engineering tires, rubber hoses, seals, medical latex products, or shoe soles.

[0037] The present invention provides an unfilled rubber composite material comprising the following components in parts by weight: 100 parts of constant-viscosity natural rubber as described above (based on dry rubber), 5-7 parts of zinc oxide, 0.4-0.6 parts of stearic acid, 0.4-0.6 parts of 2-mercaptobenzothiazole, and 3-4 parts of sulfur.

[0038] In a specific embodiment, the zinc oxide may be in the amount of 5, 5.5, 6, 6.5 or 7 parts by mass; the stearic acid may be in the amount of 0.4, 0.5 or 0.6 parts by mass; the 2-mercaptobenzothiazole may be in the amount of 0.4, 0.5 or 0.6 parts by mass; and the sulfur may be in the amount of 3, 3.5 or 4 parts by mass.

[0039] This invention provides a method for preparing the unfilled rubber composite material described above, preferably comprising the following steps: mixing the components to obtain a compound; allowing the compound to stand for 12 hours, measuring the optimal vulcanization time T90, and then vulcanizing. In this invention, the mixing temperature is preferably 50~70℃, and the mixing time is preferably 8~12 min; the vulcanization temperature is preferably 143℃.

[0040] The present invention provides a filled rubber composite material comprising the following components in parts by weight: 100 parts of the above-mentioned constant viscous natural rubber on a dry basis, 4-6 parts of zinc oxide, 1-3 parts of stearic acid, 0.5-0.8 parts of N-tert-butyl-2-benzothiazole sulfinamide, 2-3 parts of sulfur, and 10-60 parts of filler.

[0041] In a specific embodiment, the zinc oxide may be in the amount of 4, 4.5, 5, 5.5, 6, 6.5 or 7 parts by mass; the N-tert-butyl-2-benzothiazole sulfinamide may be in the amount of 0.5, 0.6, 0.7 or 0.8 parts by mass; the sulfur may be in the amount of 2, 2.5 or 3 parts by mass; and the filler may be in the amount of 10, 20, 30, 40, 50 or 60 parts by mass.

[0042] In this invention, the filler is preferably carbon black, silica, or montmorillonite, more preferably carbon black. In this invention, the carbon black is preferably carbon black N330.

[0043] In this invention, the preparation method of the filled rubber composite material is the same as the preparation method of the unfilled rubber composite material described above, and will not be repeated here.

[0044] The following detailed description, in conjunction with embodiments, illustrates the constant-viscosity natural rubber, its preparation method, its application, and unfilled and filled rubber composite materials provided by the present invention. However, these descriptions should not be construed as limiting the scope of protection of the present invention.

[0045] Example 1 Fresh natural latex (26wt% dry latex content) was filtered through an 80-mesh screen to remove impurities and diluted to a dry latex content of 20%. Formic acid was used for coagulation. After coagulation, the latex was pressed into sheets using a crepe press and air-dried at 30°C for 120 hours. Soak the film in a 0.5% hydroxylamine hydrochloride solution for 6 hours, then remove and drain. The soaked film was placed in a smoking oven at 60°C and a smoke concentration of 1.0 g / m³. 3 Under the conditions of fumigation for 4 hours and a smoke flow rate of 0.2 m / s, fumigated film was obtained; The surface of the smoked film was sprayed with a 0.1% hydroxylamine hydrochloride solution at a spraying rate of 1.0 L / m². 2 ; The sprayed rubber sheet was dried with hot air at 80°C. When the moisture content dropped to 15%, the same concentration of constant tack solution was sprayed again, and the drying continued until constant weight was obtained to obtain constant tack natural rubber.

[0046] Application Example 1 An unfilled rubber composite material comprises: 100 parts of the constant-viscosity natural rubber product obtained in Example 1 (based on 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 min), and the optimal vulcanization time T90 is measured to be 16.89 min after the resulting compound is left to stand for 12 h. Vulcanization is then performed on a flat vulcanizing machine at 143°C. T90); Application Example 2 A carbon black rubber, comprising: 100 parts of the natural rubber product obtained in Example 1 (by dry rubber 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 were mixed (at 50°C for 12 min), and the optimal vulcanization time T90 was measured to be 13.53 min after the resulting compound was left to stand for 12 h. Vulcanization was then performed on a flat vulcanizing machine at 143°C. T90).

[0047] Example 2 Fresh natural rubber latex (dry rubber content 42wt%) is filtered through an 80-mesh screen to remove impurities and diluted to a dry rubber content of 20%. Microbial coagulation is employed, wherein the microorganisms are lactic acid bacteria; the preferred mass ratio of the natural rubber latex to the microorganisms is 100:0.3 based on the dry rubber mass; after coagulation, the latex is pressed into sheets using a crepe press and air-dried at 40℃ for 5 hours. Soak the film in a 0.3% hydroxylamine hydrochloride solution for 12 hours, then remove and drain. The soaked film was placed in a smoking oven at 80°C and a smoke concentration of 1.5 g / m³. 3 Under the conditions of fumigation for 0.5 hours, the smoke flow rate was 2 m / s; Spray the smoked film surface with a 0.2% hydroxylamine hydrochloride solution at a rate of 0.8 L / m. 2 ; The sprayed rubber sheet was dried with hot air at 90°C. When the moisture content dropped to 12%, the same concentration of constant tack solution was sprayed again, and the drying continued until constant weight was obtained to obtain constant tack natural rubber. Unfilled rubber composites and carbon black rubber were obtained according to the methods of Application Example 1 and Application Example 2, respectively.

[0048] Example 3 Fresh natural latex (35wt% dry latex content) was filtered through an 80-mesh screen to remove impurities and diluted to a dry latex content of 22%. Coagulation was carried out using a combination of microbial coagulation and formic acid coagulation. After coagulation, the latex was pressed into sheets using a crepe press and air-dried at 40℃ for 5 hours. Soak the film in a 0.3% hydroxylamine hydrochloride solution for 12 hours, then remove and drain. The soaked film was placed in a smoking oven at 80°C and a smoke concentration of 1.5 g / m³. 3 Smoke treatment for 0.5 hours at a smoke flow rate of 1.6 m / s; Spray the smoked film surface with a 0.2% hydroxylamine hydrochloride solution at a rate of 0.8 L / m. 2 ; The sprayed rubber sheet was dried with hot air at 90°C. When the moisture content dropped to 12%, the same concentration of constant viscosity agent solution was sprayed again, and the drying continued until constant weight was obtained to obtain a constant viscosity natural rubber product. Unfilled rubber composites and carbon black rubber were obtained according to the methods of Application Example 1 and Application Example 2, respectively.

[0049] Example 4 Fresh natural latex (32wt% dry rubber content) was filtered through an 80-mesh screen to remove impurities and diluted to a dry rubber content of 24%. Enzymatic coagulation was used, with papain as the enzyme; the mass ratio of natural rubber latex to enzyme was 100:1.0 based on the dry rubber mass. After coagulation, the latex was pressed into sheets using a crepe press and air-dried at 32℃ for 6 hours. Soak the film in a 0.3% hydroxylamine hydrochloride solution for 9 hours, then remove and drain. The soaked film was placed in a fumigation oven at 70°C and a smoke concentration of 1.2 g / m³. 3 Fumigation treatment for 2 hours under a smoke flow rate of 1.2 m / s; Spray the smoked film surface with a 0.2% hydroxylamine hydrochloride solution at a rate of 0.8 L / m. 2 ; The sprayed rubber sheet was dried with hot air at 90°C. When the moisture content dropped to 12%, it was sprayed with the same concentration of constant tack solution again and dried until constant weight was obtained to obtain constant tack natural rubber. Unfilled rubber composites and carbon black rubber were obtained according to the methods of Application Example 1 and Application Example 2, respectively.

[0050] Example 5 Freshly extracted natural latex (dry rubber content 31wt%) 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 rubber sheets by a crepe press and air-dried at 30°C for 7 hours. Soak the film in a 0.4% hydroxylamine sulfate solution for 7.5 hours, then remove and drain. The soaked film was placed in a fumigation oven at 70°C and a smoke concentration of 1.2 g / m³. 3 Smoke treatment for 2.5 hours at a smoke flow rate of 1.3 m / s; Spray the smoked film surface with a 0.2% hydroxylamine hydrochloride solution at a rate of 0.8 L / m. 2 ; The sprayed rubber sheet is dried with hot air at 90℃. When the moisture content drops to 12%, it is sprayed with the same concentration of constant viscosity agent solution again and dried until constant weight is obtained to obtain constant viscosity natural rubber product. Unfilled rubber composites and carbon black rubber were obtained according to the methods of Application Example 1 and Application Example 2, respectively.

[0051] Comparative Example 1 The natural rubber product prepared according to Example 1, wherein no smoking treatment is performed; Unfilled rubber composites and carbon black rubber were prepared according to the methods of Application Example 1 and Application Example 2, respectively.

[0052] Comparative Example 2 The traditional one-time immersion constant viscosity process is adopted, and the specific steps are as follows: Fresh natural latex raw material completely identical to that in Example 4 was used: fresh natural latex (dry latex content 32wt%) was filtered through an 80-mesh screen to remove impurities and diluted to a dry latex content of 24%; papain was used for coagulation, and the mass ratio of latex to papain was 100:1.0 based on the dry latex mass; it was pressed into film of the same specifications and air-dried at 32°C for 6 hours.

[0053] The traditional one-time soaking constant tack process was adopted: the air-dried rubber sheet was directly soaked in a 0.3% hydroxylamine hydrochloride constant tack agent aqueous solution for 9 hours (the soaking concentration and time were completely consistent with those in the example). After soaking, the excess liquid on the surface was drained and the sheet was directly sent to 90°C hot air drying to constant weight. The whole process was without smoke treatment and without two spraying of constant tack agent, thus obtaining a traditional constant tack modified natural rubber control sample.

[0054] Subsequently, following the same formulation and vulcanization process as in Example 4, unfilled rubber composite materials and carbon black filled rubber compounds were prepared for simultaneous performance testing.

[0055] Comparative Example 3 The only difference between this comparative example and Example 1 is that the second constant viscosity agent spraying process at the quick-drying moisture content node is omitted, and a control natural rubber sample is obtained. Subsequently, following the exact same formulation, mixing, and vulcanization process as Application Example 1 and Application Example 2, unfilled rubber composites and carbon black filled rubber compounds were prepared for simultaneous performance testing.

[0056] 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.

[0057] 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 accelerated storage hardening values ​​of the rubbers in Examples 1-5 and Comparative Examples 1-3 were determined according to the method in GB / T 18013-2008 (Determination of Accelerated Storage Hardening Value of Natural Raw Rubber).

[0058] 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).

[0059] 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 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.

[0060] Table 1. Properties of the rubber materials obtained in the examples and comparative examples.

[0061] As shown in Table 1, the natural rubber raw rubber prepared by the method provided by this invention has lower Mooney viscosity, initial plasticity P0, and long-chain branching degree than the untreated rubber. Furthermore, the number of times the Mooney viscosity decreases to 50 MU is lower than that of the untreated rubber, indicating that the plasticizing efficiency of the constant-viscosity natural rubber prepared by the method provided by this invention is higher than that of the untreated rubber. The accelerated storage hardening value of the constant-viscosity natural rubber prepared in Examples 1-5 is lower than that of the constant-viscosity natural rubber prepared in Comparative Examples 1-3, indicating that the constant-viscosity natural rubber prepared in Examples 1-5 has better long-term stability of Mooney viscosity. In addition, the 500% tensile stress and tear strength of the unfilled natural rubber prepared using the constant-viscosity natural rubber of this invention are greater than those of the untreated rubber; simultaneously, the 100% tensile stress and tear strength of the carbon black rubber prepared in Examples 1-5 are greater than those of the untreated rubber, and the abrasion resistance is improved.

[0062] As can be seen from the above embodiments and comparative examples, the present invention utilizes a multi-stage treatment method of "immersion in tackifier + fumigation + spraying tackifier + hot air drying + spraying tackifier again during rapid drying" to ensure that the tackifier is evenly distributed and continuously acts in the rubber matrix, effectively suppressing the Mooney viscosity rebound and significantly improving the viscosity stability of natural rubber.

[0063] The above description is only a preferred embodiment of the present invention. It should be noted that for those skilled in the art, several improvements and modifications can be made without departing from the principle of the present invention, and these improvements and modifications should also be considered within the scope of protection of the present invention.

Claims

1. A method for preparing constant-viscosity 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 film is immersed in a constant viscosity solution to obtain a first-processed film. The first-processed film is then subjected to a smoking treatment to obtain a smoked film; The smoked film is subjected to a first tack-fixing agent spraying treatment to obtain a secondary treated film. The secondary-treated film is dried with hot air until the moisture content is 10-20%, then subjected to a second constant tack spray treatment, and dried further until constant weight is obtained to obtain constant tack natural rubber.

2. The preparation method according to claim 1, characterized in that, The viscosity constant agent solution is a hydroxylamine hydrochloride solution or a hydroxylamine sulfate solution; the mass concentration of the viscosity constant agent solution is 0.1-1.0%; the soaking treatment time is 2-12 hours.

3. The preparation 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 preparation method according to claim 1, characterized in that, The fumigation conditions include: a temperature of 40~100℃, a time of 0.5~10h, and a smoke concentration of 0.5~1.5g / m³. 3 The smoke velocity is 0.2~2m / s.

5. The preparation method according to claim 1, characterized in that, The viscosity-fixing agent solution used in the first and second viscosity-fixing agent spraying treatments has a mass concentration of 0.05–0.5% and a spraying volume of 0.5–2 L / m³, respectively. 2 .

6. The preparation method according to claim 1, characterized in that, The preferred temperature for hot air drying is 60~100℃.

7. The constant-viscosity natural rubber prepared by the preparation method according to any one of claims 1 to 6.

8. The application of the constant-viscosity natural rubber of claim 7 in natural rubber products.

9. An unfilled rubber composite material, characterized in that, The components include the following parts by mass: The constant-viscosity natural rubber of claim 7 comprises 100 parts by dry weight, 5-7 parts by zinc oxide, 0.4-0.6 parts by stearic acid, 0.4-0.6 parts by 2-mercaptobenzothiazole, and 3-4 parts by sulfur.

10. A rubber-filled composite material, characterized in that, The components include the following parts by mass: The constant-viscosity natural rubber of claim 7 comprises 100 parts by dry weight, 4-6 parts by zinc oxide, 1-3 parts by stearic acid, 0.5-0.8 parts by N-tert-butyl-2-benzothiazole sulfinamide, 2-3 parts by sulfur, and 10-60 parts by filler.

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