High-strength high-elongation low-hardness natural rubber and preparation method thereof

Abstract

This invention discloses a high-strength, high-elongation, low-hardness natural rubber and its preparation method. By weight, the high-strength, high-elongation, low-hardness natural rubber comprises the following components: 100 parts natural rubber, 1.5-3 parts crosslinking agent, 0.8-2 parts accelerator, 10-20 parts reinforcing agent, 5-15 parts softener, 1-3 parts antioxidant, and 3-8 parts activator. The high-strength, high-elongation, low-hardness natural rubber has a tensile strength ≥20 MPa, an elongation ≥700%, and a Shore A hardness of 35-45. Under normal operating conditions of -20℃ to 80℃, the fluctuation range of the tensile strength and elongation is controlled within ±5%, and the Shore A hardness fluctuation is ≤±2. This invention solves the technical problem of achieving a balance between high strength, high elongation, and low hardness in existing natural rubber formulations. The formulation components of this invention are widely available, the preparation process is simple, and the production cost is controllable. It can be widely applied in multiple fields and has extremely high practical value and promising prospects for promotion.

Description

Technical Field

[0001] This invention relates to the field of natural rubber materials technology, and in particular to a high-strength, high-elongation, low-hardness natural rubber and its preparation method. Background Technology

[0002] Natural rubber possesses excellent elasticity, toughness, fatigue resistance, and processing properties, making it an extremely widely used polymer material. It is extensively applied in rubber products, industrial seals, medical supplies, and daily necessities. In practical applications, the performance requirements for natural rubber vary significantly depending on the specific scenario. Some scenarios (such as flexible seals, human contact products, and elastic cushioning components) not only require high tensile strength and elongation to ensure structural stability and fracture resistance during use, but also low hardness to meet the needs for flexibility, conformability, or cushioning and shock absorption.

[0003] Currently, in existing natural rubber formulations, increasing the amount of reinforcing agent is usually required to improve tensile strength. However, excessive reinforcing agent can lead to increased rubber hardness and decreased elongation. To reduce hardness, it is often necessary to increase the amount of softener, which in turn reduces tensile strength. It is difficult to achieve a balance between high tensile strength, high elongation, and low hardness. In existing technologies, most low-hardness natural rubbers have a tensile strength of less than 15 MPa and an elongation of less than 600%, while high-tensile-strength natural rubbers typically have a hardness of over 50. This fails to meet the demands of scenarios requiring high comprehensive material performance, creating a technical bottleneck where strength, elongation, and hardness are mutually exclusive. For example, the low-hardness natural rubber formulation of around 40 degrees disclosed in patent CN102417618B has a tensile strength that does not exceed 20 MPa, and the elongation is not mentioned and is estimated to be less than 600% based on conventional formulations. In various wear-resistant and high-strength modified patents (including graphene modification and organic polymer reinforcement), the hardness of high-tensile-strength (≥20 MPa) formulations is ≥50 and the elongation is ≤650%. However, high-elongation (≥700%) formulations rely on a large amount of softener, resulting in a tensile strength ≤15 MPa and large fluctuations in hardness.

[0004] Meanwhile, existing high-performance natural rubber patents, such as graphene modification (patent CN115073826B), latex pretreatment (patent CN113929977B), and bio-fermentation modification patents, all rely on special raw materials (graphene, special modifiers) or complex pretreatment processes (latex ammonia / hydrogen peroxide modification, microbial fermentation and maturation) to achieve performance improvement. These patents suffer from high raw material costs, complex processes, difficulty in industrialization, and poor mass production stability. Graphene modification requires the addition of compatibilizers to solve the agglomeration problem, further increasing the number of process steps and costs. Special working condition-specific formulations (such as patent CN113150405B, a low-hardness formulation adapted to the space environment) require the compounding of special antioxidants and accelerators. They are highly targeted in performance but have poor versatility, and their mechanical properties fluctuate greatly, with tensile strength not reaching 20MPa, making them unsuitable for general applications.

[0005] Furthermore, existing natural rubber formulations suffer from poor performance stability and insufficient versatility: general-purpose formulations offer balanced performance but lack outstanding advantages, failing to consistently achieve core performance indicators such as tensile strength ≥20MPa, elongation ≥700%, and hardness ≈40, with hardness fluctuations ≥±8 (Shore A), affecting product consistency; special-condition formulations are limited to single scenarios and cannot meet the diverse general requirements of being both "soft and tough." Simultaneously, existing low-hardness natural rubber formulations generally suffer from the shortcoming of "excessive softener leading to poor aging resistance and weak deformation resistance." Adding large amounts of softener to reduce hardness results in loose rubber molecular chains, making it difficult to improve tensile strength and causing a decrease in aging resistance and an increase in permanent deformation (typically ≥15%). Existing aging-resistant formulations often improve aging resistance by increasing the amount of antioxidants, leading to increased hardness and failing to meet the requirements for low hardness.

[0006] Therefore, developing a natural rubber formulation that can simultaneously achieve a tensile strength of over 20 MPa, an elongation of over 700%, and a hardness of around 40, without requiring special modification, with a simple process, controllable cost, stable performance, and adaptability to multiple scenarios, would fill existing technological gaps, break through inherent industry bottlenecks, and expand the application scope of natural rubber, and has significant practical significance and market value. Summary of the Invention

[0007] The purpose of this invention is to provide a high-strength, high-elongation, low-hardness natural rubber and its preparation method. The rubber material prepared by this formula has a tensile strength ≥20MPa, an elongation ≥700%, and a Shore hardness controlled at around 40. It has excellent comprehensive performance, requires no special modified raw materials, has a simple preparation process, controllable cost, stable performance, and outstanding aging resistance and deformation resistance.

[0008] To achieve the above objectives, the present invention adopts the following technical solution: In a first aspect, the present invention provides a high-strength, high-elongation, low-hardness natural rubber, comprising the following components by weight: 100 parts of natural rubber, 1.5-3 parts of crosslinking agent, 0.8-2 parts of accelerator, 10-20 parts of reinforcing agent, 5-15 parts of softener, 1-3 parts of antioxidant, and 3-8 parts of activator. The high-strength, high-elongation, low-hardness natural rubber has a tensile strength ≥20MPa, an elongation ≥700%, and a Shore A hardness of 35-45. Under normal operating conditions of -20℃ to 80℃, the fluctuation range of the tensile strength and elongation is controlled within ±5%, and the fluctuation of the Shore A hardness is ≤±2.

[0009] In some possible implementations, the natural rubber includes one or more of STR20, SCR20, RSS3, SCR5, SIR20, SMR20, and RSS1.

[0010] In some possible embodiments, the crosslinking agent includes one or more of sulfur, dicumyl peroxide, 2,5-dimethyl-2,5-bis(tert-butylperoxy)hexane, di-tert-butyl peroxide, benzoyl peroxide, and di-tert-butyl peroxide.

[0011] In some possible implementations, the promoter includes one or more of dibenzothiazole disulfide, N-cyclohexyl-2-benzothiazole sulfenamide, N-tert-butyl-2-benzothiazole sulfenamide, and tetramethylthiuram disulfide.

[0012] In some possible implementations, the reinforcing agent includes one or more of N330, N550, N660, N220, N234, fumed silica, precipitated silica, and carbon nanotubes.

[0013] In some possible implementations, the softener includes one or more of aromatic oils, paraffin oils, dioctyl phthalate, dioctyl terephthalate, dibutyl phthalate, diisononyl phthalate, and trioctyl trimellitate.

[0014] In some possible embodiments, the antioxidant includes one or more of N-isopropyl-N'-phenyl-p-phenylenediamine, N,N'-diphenyl-p-phenylenediamine, N-(1,3-dimethylbutyl)-N'-phenyl-p-phenylenediamine, 2,6-di-tert-butyl-p-methylphenol, pentaerythritol tetrakis[β-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate], 2,2'-methylenebis(4-methyl-6-tert-butylphenol), and 2-thiolbenzimidazole.

[0015] In some possible implementations, the activator includes one or more of zinc oxide, stearic acid, diphenylguanidine, magnesium oxide, 2-mercaptobenzimidazole, zinc stearate, and calcium stearate.

[0016] In a second aspect, the present invention also provides a method for preparing high-strength, high-elongation, low-hardness natural rubber as described in any one of the first aspects, comprising the following steps: Plasticizing: The natural rubber is fed into a two-roll mill, the first roll temperature is set to 50-60℃, the roll gap is 0.5-1mm, and plasticizing is carried out for 5-10 minutes to obtain plasticized rubber. Mixing: Add the activator, antioxidant, reinforcing agent, and softener to the plasticized rubber in sequence, set the second roller temperature to 50-60℃, and mix for 8-15 minutes; then add the crosslinking agent and accelerator, set the third roller temperature to 40-50℃, and mix for 3-5 minutes to obtain the initial compound; the roller temperature needs to be controlled during the mixing process to prevent the crosslinking agent from crosslinking prematurely; Storage: Place the initial compound in a constant temperature environment, set the temperature to 23±2℃ and the humidity to 50±5%, and store for 8-12 hours to obtain the compound. Crosslinking: The compound is placed in a flat crosslinking machine, the crosslinking temperature is set to 140-150℃, the crosslinking pressure is 5-10MPa, the crosslinking time is 10-30min, and it is cooled to room temperature to obtain the high-strength, high-elongation, low-hardness natural rubber.

[0017] It should be noted that the order of adding each component must be strictly controlled during the preparation process. First, add the reinforcing agent and softener, then add the activator and antioxidant, and finally add the crosslinking agent and accelerator. This is to avoid premature contact between the crosslinking agent and the accelerator, which could lead to scorching and affect the rubber properties. This further ensures the stability of the product performance and guarantees that each batch of products can consistently achieve the core indicators of tensile strength ≥20MPa, elongation ≥700%, and hardness 35-45, with hardness fluctuation ≤±2 Shore A.

[0018] Compared with the prior art, the beneficial effects of the present invention are as follows: 1. This invention overcomes the bottleneck of mutual exclusion among strength, elongation and hardness by optimizing the precise synergistic ratio of conventional components, achieving synergistic performance of low hardness (35-45), high strength (≥20MPa), and high elongation (≥700%). It does not require special modified raw materials or complex pretreatment processes, and takes into account both low cost and industrial feasibility. At the same time, it has outstanding performance stability, excellent aging resistance and deformation resistance, and can be adapted to a variety of general scenarios, filling the gap in existing technology. Its practicality and promotion value are significant. It is different from existing natural rubber formulation patents and effectively solves the related technical pain points in the industry.

[0019] 2. The preparation method of this invention requires no additional steps such as latex pretreatment or component modification. The steps are simple, the parameters are easy to control, and existing natural rubber production lines can be directly used without adding new production equipment. This solves the pain point of existing high-performance formulations being "feasible in the laboratory but difficult to implement in industrialization." Compared with the preparation methods of existing modified and pretreated patents, the process steps are simplified by more than 30%, the mass production stability is significantly improved, large-scale stable production can be achieved, and energy consumption and labor costs are reduced. Attached Figure Description

[0020] Figure 1 The flowchart illustrates the preparation method of high-strength, high-elongation, and low-hardness natural rubber provided by this invention. Detailed Implementation

[0021] The technical solutions of the embodiments of this application will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only a part of the embodiments of this application, and not all of the embodiments. Based on the embodiments of this application, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this application. At the same time, in the description of the embodiments of this application, the terms "first," "second," etc., are only used to distinguish descriptions and should not be construed as indicating or implying relative importance. Thus, features defined with "first" and "second" may explicitly or implicitly include one or more features. In the description of the embodiments of this application, "multiple" means two or more, unless otherwise explicitly specified.

[0022] Example 1 This embodiment provides a high-strength, high-elongation, low-hardness natural rubber, comprising the following components by weight: STR20 100 parts, sulfur 2 parts, dibenzothiazole disulfide (DM) 0.5 parts, N-cyclohexyl-2-benzothiazole sulfenamide (CZ) 0.5 parts, N330 carbon black 12 parts, precipitated silica 3 parts, paraffin oil 8 parts, N-isopropyl-N'-phenyl-p-phenylenediamine 1.2 parts, 2,2'-methylenebis(4-methyl-6-tert-butylphenol) 0.8 parts, zinc oxide 5 parts, and stearic acid 1 part; Preparation methods of high-strength, high-elongation, and low-hardness natural rubber, such as Figure 1 As shown, it includes the following steps: Plasticizing: Natural rubber (STR20) is put into a two-roll mill, the first roll temperature is set to 55℃, the roll gap is 0.6mm, and plasticizing is carried out for 7 minutes, during which the rubber is turned over once every 2 minutes until the rubber is softened and uniform without lumps, thus obtaining plasticized rubber. Mixing: In the plasticized rubber, add the activator (zinc oxide and stearic acid), antioxidant (N-isopropyl-N'-phenyl-p-phenylenediamine and 2,2'-methylenebis(4-methyl-6-tert-butylphenol)), reinforcing agent (N330 carbon black and precipitated silica), and softener (paraffin oil) in sequence. Set the second roller temperature to 55℃ and mix for 10 minutes. Then add the crosslinking agent (sulfur) and accelerator (dibenzothiazole disulfide and N-cyclohexyl-2-benzothiazole sulfenamide). Set the third roller temperature to 45℃ and mix for 4 minutes to obtain the initial compound. During the mixing process, the roller temperature needs to be controlled to prevent the crosslinking agent from crosslinking prematurely. Storage: Place the initial compound in a constant temperature environment, set at 23±2℃ and 50±5%, and let it stand for 10 hours to allow the components to fully diffuse and stabilize, thus obtaining the compound. Crosslinking: The compounded rubber is placed in a flat crosslinking machine, the crosslinking temperature is set to 145℃, the crosslinking pressure is 7MPa, the crosslinking time is 20min, and it is cooled to room temperature to obtain high-strength, high-elongation, and low-hardness natural rubber.

[0023] Example 2 This embodiment provides a high-strength, high-elongation, low-hardness natural rubber, which, by weight, comprises the following components: 100 parts of STR20, 2.5 parts of 2,5-dimethyl-2,5-bis(tert-butylperoxy)hexane, 1.8 parts of N-tert-butyl-2-benzothiazole sulfenamide (NS), 10 parts of N550 carbon black, 5 parts of fumed silica, 12 parts of di(2-ethylhexyl) terephthalate, 2.5 parts of N-(1,3-dimethylbutyl)-N'-phenyl-p-phenylenediamine, 4 parts of zinc oxide, and 2 parts of stearic acid; The preparation method of high-strength, high-elongation, and low-hardness natural rubber includes the following steps: Plasticizing: Natural rubber (STR20) is put into a two-roll mill, the first roll temperature is set to 50℃ and the roll gap is 0.5mm, and plasticizing is carried out for 5 minutes. During this period, the rubber is turned over once every 2 minutes until it is softened and uniform without lumps, and plasticized rubber is obtained. Mixing: In the plasticized rubber, add the activator (zinc oxide and stearic acid), antioxidant (N-(1,3-dimethylbutyl)-N'-phenyl-p-phenylenediamine), reinforcing agent (N550 carbon black and fumed silica), and softener (di(2-ethylhexyl) terephthalate) in sequence. Set the second roller temperature to 50°C and mix for 8 minutes. Then add the crosslinking agent (2,5-dimethyl-2,5-bis(tert-butylperoxy)hexane) and accelerator (N-tert-butyl-2-benzothiazole sulfenamide (NS)). Set the third roller temperature to 40°C and mix for 3 minutes to obtain the initial compound. During the mixing process, the roller temperature needs to be controlled to prevent the crosslinking agent from crosslinking prematurely. Storage: Place the initial compound in a constant temperature environment, set at 23±2℃ and 50±5%, and let it stand for 8 hours to allow the components to fully diffuse and stabilize, thus obtaining the compound. Crosslinking: The compounded rubber is placed in a flat crosslinking machine, the crosslinking temperature is set to 140℃, the crosslinking pressure is 5MPa, the crosslinking time is 30min, and it is cooled to room temperature to obtain high-strength, high-elongation, and low-hardness natural rubber.

[0024] Example 3 This embodiment provides a high-strength, high-elongation, low-hardness natural rubber, which, by weight, comprises the following components: 100 parts RSS3, 1.5 parts dicumyl peroxide, 0.8 parts tetramethylthiuram disulfide (TMTD), 18 parts N660 carbon black, 2 parts carbon nanotubes, 5 parts aromatic oil, 1 part N,N'-diphenyl-p-phenylenediamine, 1 part 2,6-di-tert-butyl-p-methylphenol, 3 parts zinc oxide, and 2 parts stearic acid; The preparation method of high-strength, high-elongation, and low-hardness natural rubber includes the following steps: Plasticizing: Natural rubber (RSS3) is put into a two-roll mill, the first roll temperature is set to 60℃, the roll gap is 1.0mm, and plasticizing is carried out for 10 minutes. During this period, the rubber is turned over once every 3 minutes until it is softened and uniform without lumps, and plasticized rubber is obtained. Mixing: In the plasticized rubber, add the activator (zinc oxide and stearic acid), antioxidant (N,N'-diphenyl-p-phenylenediamine and 2,6-di-tert-butyl-p-methylphenol), reinforcing agent (N660 carbon black and carbon nanotubes), and softener (aromatic oil) in sequence. Set the second roller temperature to 60°C and mix for 15 minutes. Then add the crosslinking agent (diisopropylbenzene peroxide) and accelerator (tetramethylthiuram disulfide (TMTD)). Set the third roller temperature to 50°C and mix for 5 minutes to obtain the initial compound. During the mixing process, the roller temperature needs to be controlled to prevent the crosslinking agent from crosslinking prematurely. Storage: Place the initial compound in a constant temperature environment, set the temperature to 23±2℃ and the humidity to 50±5%, and store for 12 hours to allow the components to fully diffuse and stabilize, thus obtaining the compound. Crosslinking: The compounded rubber is placed in a flat crosslinking machine, the crosslinking temperature is set to 150℃, the crosslinking pressure is 10MPa, the crosslinking time is 10min, and it is cooled to room temperature to obtain high-strength, high-elongation, and low-hardness natural rubber.

[0025] Comparative Example 1 This comparative example uses an over-proportioning reinforcing agent. The only difference between this comparative example and Example 1 is that 30 parts of reinforcing agent N330 carbon black and 10 parts of precipitated silica are used.

[0026] Comparative Example 2 This comparative example uses an over-proportion of softener. The only difference between this comparative example and Example 1 is that the softener is 30 parts of paraffin oil.

[0027] Comparative Example 3 This comparative example is a formulation with insufficient accelerator dosage. The only difference between this comparative example and Example 1 is that the accelerators are 0.2 parts of dibenzothiazole disulfide (DM) and 0.2 parts of N-cyclohexyl-2-benzothiazole sulfenamide (CZ).

[0028] The natural rubbers prepared in Examples 1-3 and Comparative Examples 1-3 were subjected to performance tests according to conventional testing standards for rubber materials. Tensile strength and elongation at break were tested according to GB / T528-2009, Shore A hardness according to GB / T531.1-2008, performance fluctuations under normal operating conditions (-20℃-80℃) were measured as the rate of change relative to the 23℃ baseline value, compression set (70℃×22h, 25% compression ratio) was tested according to GB / T7759-2015, and tensile strength retention after heat aging (70℃×72h) was tested according to GB / T528-2009. The results are shown in Table 1. Table 1 Performance Test Data Table 1 shows that the tensile strength, elongation at break, and hardness of the natural rubber prepared in Examples 1-3 consistently meet the preset core indicators, and their performance fluctuates little in an environment ranging from -20℃ to 80℃. They also exhibit excellent aging resistance and deformation resistance. Comparative Examples 1-3 further confirm that deviations from the formulation range of this invention will lead to performance imbalances. This invention uses readily available raw materials, employs a simple process, and has controllable costs. It can be widely applied in fields such as flexible seals and elastic buffers, possessing significant practical value and industrialization prospects, and demonstrating outstanding substantive characteristics and significant progress.

[0029] Obviously, those skilled in the art can make various modifications and variations to the embodiments of the present invention without departing from the spirit and scope of the invention. Therefore, if these modifications and variations fall within the scope of the claims of the present invention and their equivalents, the present invention also intends to include these modifications and variations.

Claims

1. A high-strength, high-elongation, low-hardness natural rubber, characterized in that, By weight, it includes the following components: 100 parts natural rubber, 1.5-3 parts crosslinking agent, 0.8-2 parts accelerator, 10-20 parts reinforcing agent, 5-15 parts softener, 1-3 parts antioxidant, and 3-8 parts activator; The high-strength, high-elongation, low-hardness natural rubber has a tensile strength ≥20MPa, an elongation ≥700%, and a Shore A hardness of 35-45. Under normal operating conditions of -20℃ to 80℃, the fluctuation range of the tensile strength and elongation is controlled within ±5%, and the fluctuation of the Shore A hardness is ≤±2.

2. The high-strength, high-elongation, low-hardness natural rubber according to claim 1, characterized in that, The natural rubber includes one or more of STR20, SCR20, RSS3, SCR5, SIR20, SMR20, and RSS1.

3. The high-strength, high-elongation, low-hardness natural rubber according to claim 1, characterized in that, The crosslinking agent includes one or more of sulfur, dicumyl peroxide, 2,5-dimethyl-2,5-bis(tert-butylperoxy)hexane, di-tert-butyl peroxide, benzoyl peroxide, and di-tert-butyl peroxide.

4. The high-strength, high-elongation, low-hardness natural rubber according to claim 1, characterized in that, The accelerator includes one or more of dibenzothiazole disulfide, N-cyclohexyl-2-benzothiazole sulfenamide, N-tert-butyl-2-benzothiazole sulfenamide, and tetramethylthiuram disulfide.

5. The high-strength, high-elongation, low-hardness natural rubber according to claim 1, characterized in that, The reinforcing agent includes one or more of N330, N550, N660, N220, N234, fumed silica, precipitated silica, and carbon nanotubes.

6. The high-strength, high-elongation, low-hardness natural rubber according to claim 1, characterized in that, The softener includes one or more of the following: aromatic oil, paraffin oil, dioctyl phthalate, dioctyl terephthalate, dibutyl phthalate, diisononyl phthalate, and trioctyl trimellitate.

7. The high-strength, high-elongation, low-hardness natural rubber according to claim 1, characterized in that, The antioxidant includes one or more of N-isopropyl-N'-phenyl-p-phenylenediamine, N,N'-diphenyl-p-phenylenediamine, N-(1,3-dimethylbutyl)-N'-phenyl-p-phenylenediamine, 2,6-di-tert-butyl-p-methylphenol, pentaerythritol tetrakis[β-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate], 2,2'-methylenebis(4-methyl-6-tert-butylphenol), and 2-thiol-benzimidazole.

8. The high-strength, high-elongation, low-hardness natural rubber according to claim 1, characterized in that, The activator includes one or more of zinc oxide, stearic acid, diphenylguanidine, magnesium oxide, 2-mercaptobenzimidazole, zinc stearate, and calcium stearate.

9. The method for preparing high-strength, high-elongation, low-hardness natural rubber according to any one of claims 1-8, characterized in that, Includes the following steps: Plasticizing: The natural rubber is fed into a two-roll mill, the first roll temperature is set to 50-60℃, the roll gap is 0.5-1mm, and plasticizing is carried out for 5-10 minutes to obtain plasticized rubber. Mixing: Add the activator, antioxidant, reinforcing agent and softener to the plasticized rubber in sequence, set the second roller temperature to 50-60℃ and mix for 8-15 minutes; then add the crosslinking agent and accelerator, set the third roller temperature to 40-50℃ and mix for 3-5 minutes to obtain the initial mixed rubber; Storage: Place the initial compound in a constant temperature environment, set the temperature to 23±2℃ and the humidity to 50±5%, and store for 8-12 hours to obtain the compound. Crosslinking: The compound is placed in a flat crosslinking machine, the crosslinking temperature is set to 140-150℃, the crosslinking pressure is 5-10MPa, the crosslinking time is 10-30min, and it is cooled to room temperature to obtain the high-strength, high-elongation, low-hardness natural rubber.

Images