A low heat build-up rubber composition, a method for preparing the same and use thereof

Abstract

The application discloses a low-heat rubber composition and a preparation method and application thereof, and relates to the technical field of rubber. The low-heat rubber composition comprises the following components in mass fraction: 60-80 parts of natural rubber, 20-40 parts of butadiene-styrene rubber, 40-55 parts of N774 carbon black, 5-15 parts of attapulgite, 1-3 parts of polytetrafluoroethylene micro powder, 2-4 parts of zinc stearate, 3-5 parts of zinc oxide, 1-2 parts of stearic acid, 2-4 parts of antioxidant, 0.8-1.2 parts of sulfur and 1.2-1.8 parts of accelerator. The three-stage mixing can prepare the rubber composition with good tensile strength, tear strength and processing safety while keeping low heat, and the rubber composition can meet the actual use requirements of tire shoulder cushion rubber.

Description

Technical Field

[0001] This application relates to the field of rubber technology, and in particular to a low-heat-generating rubber composition, its preparation method, and its application. Background Technology

[0002] Rubber products accumulate heat due to hysteresis loss during dynamic use, especially in areas subjected to large cyclic deformations such as tire shoulders. Excessive heat generation can lead to decreased material properties, accelerated aging, and even premature damage such as shoulder voids and cracks. Therefore, developing low-heat-generating rubber compositions has always been an important research direction in this field.

[0003] To reduce the dynamic heat generation of rubber, existing technologies mainly focus on the following aspects: First, using solution-polymerized styrene-butadiene rubber or preparing special low-heat-generating polymers such as trans-polyisoprene (TPI), as exemplified by Chinese patents CN112521554A and CN107522924A; second, optimizing the reinforcing filler system, such as using a compound of silica and silane coupling agents, as exemplified by CN113861533A; and third, adjusting the vulcanization system, as exemplified by CN 112662021A. While these solutions can reduce heat generation to some extent, they generally suffer from high overall costs, complex processing techniques, and an inability to balance dynamic heat generation and mechanical properties, thus limiting their application in large-scale industrial products such as ordinary tires.

[0004] In addition, there have been attempts to add inorganic fillers (such as silicates, calcium carbonate, etc.) to rubber to reduce costs. However, conventional inorganic fillers have poor compatibility with rubber and are prone to agglomeration, which often leads to increased dynamic heat generation or decreased mechanical properties. It is also difficult to meet the comprehensive requirements of low heat generation, low cost, easy processing, and good mechanical properties.

[0005] Therefore, there is an urgent need to develop a low-heat-generating rubber composition that can further reduce the dynamic heat generation of rubber while maintaining better mechanical properties, while keeping costs low and simplifying the process. Summary of the Invention

[0006] To solve at least one of the above-mentioned technical problems, this application provides a low-heat-generating rubber composition, its preparation method and application. The low-heat-generating rubber composition can effectively reduce dynamic heat generation, and overcomes the problems of poor compatibility between inorganic fillers and rubber matrix and easy agglomeration. It has good processing performance and mechanical properties.

[0007] In a first aspect, this application provides a low-heat-generating rubber composition, comprising the following components by mass fraction: 60-80 parts of natural rubber, 20-40 parts of styrene-butadiene rubber, 40-55 parts of N774 carbon black, 5-15 parts of attapulgite, 1-3 parts of polytetrafluoroethylene micro powder, 2-4 parts of zinc stearate, 3-5 parts of zinc oxide, 1-2 parts of stearic acid, 2-4 parts of antioxidant, 0.8-1.2 parts of sulfur, and 1.2-1.8 parts of accelerator.

[0008] The low-heat-generating rubber composition provided in this application, through the compounding of attapulgite clay, polytetrafluoroethylene (PTFE) micro powder, zinc stearate, and N774 carbon black, forms a synergistic effect in a natural rubber and styrene-butadiene rubber blend system. This significantly reduces the dynamic heat generation of the rubber composition, keeping the compression fatigue temperature rise of the vulcanized rubber below 30°C, while maintaining excellent mechanical properties and processability. The raw materials for this composition are readily available and cost-effective, making it suitable for components with stringent dynamic heat generation requirements, such as tire shoulder pad rubber, effectively reducing internal heat accumulation and extending product service life.

[0009] In some embodiments, attapulgite is needle-shaped crystal with an aspect ratio of 30 to 100:1 and an average crystal length of 0.5 to 5 μm.

[0010] By adopting the above technical solution, the natural needle-shaped attapulgite clay with a specific aspect ratio and size can easily align along the stress direction during rubber mixing and vulcanization, forming a physical isolation skeleton, effectively reducing direct friction and hysteretic heat generation between rubber molecular chains, thereby further reducing dynamic temperature rise and maintaining good processing performance and mechanical strength of the rubber compound.

[0011] In some embodiments, the average particle size of the polytetrafluoroethylene micropowder is 3~10 μm.

[0012] By adopting the above technical solution, PTFE micro powder in this particle size range can not only achieve uniform dispersion in the rubber matrix, but also form an effective lubrication interface between the filler and the rubber by utilizing its ultra-low friction characteristics, thereby significantly reducing dynamic heat generation, while avoiding damage to the mechanical properties of the rubber compound by excessively coarse particles or increased costs by excessively fine particles.

[0013] In some embodiments, the nitrogen adsorption specific surface area of ​​N774 carbon black is 25~35m². 2 / g, oil absorption value is 55~65ml / 100g.

[0014] By adopting the above technical solution, the soft carbon black with low specific surface area and low structure has less filler network structure and lower binder content in rubber, which can significantly reduce the frictional heat generated between materials during dynamic deformation, while ensuring reinforcing performance and processing dispersibility. It can also achieve a lower compression fatigue temperature rise in synergy with attapulgite clay and polytetrafluoroethylene micro powder.

[0015] In some embodiments, the accelerator is a mixture of N-cyclohexyl-2-benzothiazole sulfenamide (CZ) and tetramethylthiuram disulfide (TT) in any ratio; and / or, the mass ratio of N-cyclohexyl-2-benzothiazole sulfenamide to tetramethylthiuram disulfide is 5 to 10:1.

[0016] By adopting the above technical solution and using a accelerator system combining CZ and TT, effective vulcanization can be achieved with low sulfur content, forming a moderate and uniform crosslinked network, thereby reducing dynamic hysteresis heat generation. Furthermore, this specific ratio of CZ / TT can achieve an optimal balance between vulcanization rate and crosslinking density, further compressing fatigue temperature rise while maintaining excellent mechanical properties, avoiding increased dynamic heat generation caused by over-crosslinking or under-crosslinking, while also providing moderate vulcanization time and good process stability.

[0017] In some embodiments, the antioxidant is selected from antioxidant 4020 and / or antioxidant RD.

[0018] By adopting the above technical solutions, the thermo-oxidative aging of rubber materials caused by dynamic fatigue and heat accumulation can be effectively suppressed, thereby effectively maintaining the integrity of the cross-linked network and the stability of the interface, delaying the heat recovery caused by aging, and thus maintaining low heat generation characteristics for a long time under high temperature dynamic conditions such as tire shoulder pad rubber, extending the service life of the product.

[0019] Secondly, this application relates to a method for preparing the above-mentioned low-heat-generating rubber composition, comprising the following steps: S1. According to the corresponding mass parts, shear and disperse N774 carbon black, attapulgite clay, polytetrafluoroethylene micro powder, and zinc stearate, and premix for 3~6 minutes to obtain a premix. S2. According to the corresponding mass parts, natural rubber, styrene-butadiene rubber, premix, zinc oxide, stearic acid and antioxidant are mixed and then discharged in one step to obtain masterbatch. S3. After cooling the masterbatch to room temperature, it is mixed with sulfur and accelerator, and after a second degassing, a low-heat rubber composition is obtained.

[0020] By adopting the above technical solution, the uniform dispersion of low-heat-generating functional fillers is achieved, enabling each component to work synergistically to reduce heat generation. At the same time, the premature reaction between sulfur and accelerator at high temperatures is avoided. The process is simple, has good repeatability, and the resulting composition exhibits high dynamic heat generation consistency and batch stability.

[0021] In some embodiments, in step S2, after mixing natural rubber, styrene-butadiene rubber, premix, zinc oxide, stearic acid, and antioxidant, the mixture is discharged once to obtain masterbatch, specifically including: Natural rubber, styrene-butadiene rubber, the premix, zinc oxide, stearic acid, and antioxidant are mixed together. When the mixing temperature reaches 130°C, the rotor speed is adjusted so that the temperature rises to the first discharge temperature within 3-5 minutes. The temperature of the first glue discharge is 140~150℃.

[0022] By adopting the above technical solution, local overheating and uneven packing dispersion caused by excessively rapid heating are avoided. At the same time, a suitable time window is provided for the directional arrangement of the needle-like structure of attapulgite and the full coating of the packing by zinc stearate, thereby further reducing dynamic heat generation while ensuring mixing efficiency.

[0023] In some embodiments, in step S3, the secondary glue removal temperature does not exceed 95°C.

[0024] By adopting the above technical solution, the secondary degassing temperature is limited to below 95℃, which can effectively prevent sulfur and accelerator from scorching or volatilizing prematurely due to overheating during the mixing process. This ensures that the vulcanizing agent is evenly dispersed in the rubber compound, thereby guaranteeing the formation of a stable and uniform low-heat crosslinking network during subsequent vulcanization, while maintaining good fluidity and processing safety of the rubber compound.

[0025] Thirdly, this application also relates to the application of the above-mentioned low heat-generating rubber composition in tire shoulder pad rubber, wherein the tire shoulder pad rubber is obtained by vulcanization molding of the above-mentioned low heat-generating rubber composition, and the average temperature rise of the tire shoulder pad rubber during compression fatigue does not exceed 30°C.

[0026] By adopting the above technical solution, when the vulcanized rubber of this application is used as tire shoulder pad rubber, the average temperature rise during compression fatigue does not exceed 30°C, which is significantly lower than the 35~40°C of conventional tire shoulder pad rubber. This can effectively reduce the heat accumulation in the shoulder during tire driving, reduce the risk of early damage such as shoulder voids and shoulder cracks, extend tire service life and retreading times, while maintaining excellent mechanical strength and adhesion performance.

[0027] The advantages of the technical solution in this application compared to the prior art are: 1. The low heat-generating rubber composition of this application achieves a temperature rise of no more than 30°C without increasing costs through the synergistic effect of physical isolation by natural needle-shaped attapulgite, ultra-low friction lubrication by PTFE, and interfacial coating by zinc stearate.

[0028] 2. The preparation method of this application adopts conventional internal mixing equipment and three-stage mixing process, which does not require special equipment or extreme conditions and is easy to industrialize.

[0029] 3. The rubber composition prepared in this application can maintain good tensile strength, tear strength and processing safety while generating low heat, thus meeting the actual application requirements of tire shoulder pad rubber. Detailed Implementation

[0030] The present application will be further described in detail below with reference to the embodiments.

[0031] In the embodiments of this application, N774 carbon black is a low-structure, large-particle-size soft carbon black, whose nitrogen adsorption specific surface area is typically 25~35 m². 2 / g, with an oil absorption value of 55~65 ml / 100g. Soft carbon blacks with similar properties (low specific surface area, low structure) can be used in this application, such as N550 and N762, but considering dispersibility and heat generation control, N774 carbon black is preferred in this application.

[0032] In the implementation scheme of this application, the attapulgite is natural needle-shaped attapulgite, which has not undergone surface modification treatment. Before use, it needs to be dried to remove crystal water and adsorbed water. The drying conditions are baking at 100~120℃ for 1.5~2.5 hours, and controlling the moisture content to ≤1.5%.

[0033] In this embodiment, the PTFE micro powder has an extremely low coefficient of friction, approximately 0.04 to 0.10, which is far lower than the surface friction coefficients of conventional rubber and carbon black fillers. The average particle size of the PTFE micro powder is 3 to 10 μm, and it is in the form of regular spheres or irregular shapes. It is chemically inert, does not participate in the vulcanization reaction, and maintains a solid state within the rubber processing temperature range.

[0034] In this embodiment, zinc stearate has a melting point of 120-130°C and is mainly used as a filler surface modifier and internal lubricant. It should be noted that the zinc stearate added directly in this application preferentially adheres to the filler surface and subsequently coats it to reduce friction between materials, thereby reducing heat generation during mixing and promoting dispersion; while stearic acid and zinc oxide focus on their activation function during the vulcanization stage.

[0035] In this embodiment, step S1, the shear dispersion specifically refers to high-speed shear dispersion, with the linear velocity of the stirring paddle edge controlled at 8~15 m / s. Simultaneously, the mixing temperature can be controlled to not exceed 80℃ via cooling water. This linear velocity range is independent of equipment size and can be converted to the corresponding rotational speed based on the diameter of the mixer's stirring paddle. Therefore, it is applicable to different specifications of equipment, such as laboratory high-speed mixers, industrial-grade kneaders, or horizontal mixers. It should be noted that if the linear velocity is below 8 m / s, it is difficult to effectively disperse PTFE micropowder, and agglomeration is likely to occur; if it is above 15 m / s, excessive shearing may damage the needle-like crystal structure of attapulgite, reducing its aspect ratio and thus affecting the low heat generation effect.

[0036] In the implementation scheme of this application, in step S3, the total time from adding sulfur and accelerator to desiccant removal is controlled within 2 minutes.

[0037] In this embodiment, the final rubber compound needs to be placed in a constant temperature and humidity environment for 12-24 hours before vulcanization. The constant temperature and humidity environment is defined as a temperature of 23±2℃ and a relative humidity of 50±10%. During the placement period, the final rubber compound should be laid flat on a clean metal tray or plastic mat and covered with a plastic film to prevent surface crusting or contamination. After placement, if further improvement in compound uniformity is required, 1-2 low-temperature thin passes can be performed on an open mill with a roll gap of 0.5-1mm and a roll temperature ≤50℃, followed by vulcanization molding.

[0038] In the embodiments of this application, no processing oil or plasticizer is added to the composition to avoid the increase in dynamic heat generation caused by its plasticizing effect.

[0039] In the embodiments of this application, other conventional processing aids, including but not limited to homogenizers, may be added in appropriate amounts without compromising the purpose of the present invention.

[0040] In this embodiment, the cooling water temperature should be controlled below 25°C during the mixing process to effectively remove shear heat and prevent the rubber compound temperature from becoming too high. Industrial circulating water can be used for cooling, ensuring sufficient flow and good heat exchange efficiency. In actual production, the heat dissipation effect can be judged by monitoring the temperature difference between the inlet and outlet of the cooling water. If necessary, additional cooling devices can be added or the rotor speed can be reduced to control the rate of temperature rise of the rubber compound.

[0041] This application provides a low-heat-generating rubber composition. This product, through the physical isolation effect of natural needle-shaped attapulgite, the ultra-low friction lubrication effect of polytetrafluoroethylene micro powder, and the interfacial coating and dispersion-promoting effect of zinc stearate, works synergistically with N774 soft carbon black and an effective vulcanization system. It can solve the problems of high cost and complex processing caused by relying solely on special polymers or modified fillers in related technologies, as well as the poor compatibility between conventional inorganic fillers and rubber, easy agglomeration, and difficulty in effectively controlling dynamic heat generation. It achieves a compression fatigue temperature rise of ≤30℃ while maintaining a low cost, and also takes into account good mechanical properties and processability.

[0042] Specifically, the low-heat-generating rubber composition of this application comprises, by mass fraction, the following components: 60-80 parts of natural rubber, 20-40 parts of styrene-butadiene rubber, 40-55 parts of N774 carbon black, 5-15 parts of attapulgite, 1-3 parts of polytetrafluoroethylene powder, 2-4 parts of zinc stearate, 3-5 parts of zinc oxide, 1-2 parts of stearic acid, 2-4 parts of antioxidant, 0.8-1.2 parts of sulfur, and 1.2-1.8 parts of accelerator.

[0043] In this application, the base rubber system is composed of natural rubber and styrene-butadiene rubber in a certain proportion, taking into account the low heat generation characteristics of natural rubber and the wear resistance and anti-slip properties of styrene-butadiene rubber. The reinforcing system uses N774 soft carbon black, combined with natural needle-shaped attapulgite, to form a composite reinforcement of soft carbon black and inorganic mineral fillers. To further reduce internal friction, a small amount of polytetrafluoroethylene micro powder is added to the composition, along with zinc stearate as a dispersant and lubricant. The vulcanization system employs a high-efficiency vulcanization system combining low sulfur and accelerators, with monosulfide and disulfide bonds as the main crosslinking bond types. In addition, the composition also contains zinc oxide and stearic acid as vulcanization activators, as well as antioxidants to ensure heat aging resistance. The components are used in proportion according to the stated mass ratio range, so that the composition can achieve low dynamic heat generation after mixing and vulcanization while maintaining excellent mechanical properties and processability. Among them, the high aspect ratio attapulgite needle-like crystals can effectively reduce the direct contact and friction between rubber molecular chains during dynamic deformation of rubber; polytetrafluoroethylene micro powder can further reduce the internal friction between materials due to its ultra-low friction coefficient; zinc stearate is physically attached to the filler surface in solid micro powder form during the premixing stage to achieve pre-dispersion; after the masterbatch is mixed and heated to its melting point, zinc stearate melts into a liquid state and forms a dense lubricating isolation layer on the filler surface under shear action, thereby reducing the interfacial friction between filler materials, reducing dynamic heat generation, and promoting uniform dispersion of filler; N774 soft carbon black ensures basic reinforcement and low hysteresis heat generation. Under the synergistic effect of each component, the average temperature rise of the finally prepared vulcanized rubber can be controlled below 30℃ in the compression fatigue temperature rise test, which is far lower than the 35-40℃ of conventional formulations, while maintaining excellent tensile strength and tear strength. The raw materials used in this application are all commercially available products, with controllable costs, simple processes, and easy industrial production. They are especially suitable for components with harsh dynamic heat generation, such as tire shoulder pads, and can significantly reduce the risk of shoulder gaps and cracks, and extend tire service life.

[0044] Meanwhile, the low-heat-generating rubber composition of this application is prepared by the following steps: S1. According to the corresponding mass parts, shear and disperse N774 carbon black, attapulgite clay, polytetrafluoroethylene micro powder, and zinc stearate, and premix for 3~6 min to obtain a premix. S2. According to the corresponding mass parts, natural rubber, styrene-butadiene rubber, premix, zinc oxide, stearic acid and antioxidant are mixed and then discharged in one step to obtain masterbatch. S3. After cooling the masterbatch to room temperature, it is mixed with sulfur and accelerator, and after a second degassing, the low heat-generating rubber composition is obtained.

[0045] In step S1 of this application, during the premixing stage, high-speed shear dispersion can break down solid zinc stearate and polytetrafluoroethylene micro powder and mix them evenly onto carbon black and attapulgite, preventing their self-aggregation and providing a good spatial distribution basis for melt coating in subsequent steps, thereby significantly improving the dispersibility of fillers in the rubber matrix.

[0046] In step S2 of this application, the one-time mixing can fully combine the filler and the rubber. At the same time, it can melt the zinc stearate that is uniformly attached to the surface of the filler, thereby achieving full coating and internal lubrication of the inorganic filler interface. In addition, controlling the discharge temperature avoids premature vulcanization and ensures that the masterbatch has good processing performance.

[0047] In step S3 of this application, secondary mixing can effectively prevent scorching, ensure uniform dispersion of the vulcanizing agent, and provide a guarantee for the formation of a stable low-heat crosslinking network.

[0048] The technical solutions provided in this application will be described in detail below with reference to the embodiments. Unless otherwise specified, the materials used in the embodiments and comparative examples are all commercially available conventional products.

[0049] Example 1

[0050] This embodiment provides a low-heat-generating rubber composition, which, by mass fraction, comprises the following components: 70 parts natural rubber, 30 parts styrene-butadiene rubber, 50 parts N774 carbon black, 10 parts attapulgite, 2 parts polytetrafluoroethylene micro powder, 3 parts zinc stearate, 4 parts zinc oxide, 1.5 parts stearic acid, 3 parts antioxidant 4020, 1 part sulfur, and 1.5 parts accelerator; Among them, attapulgite should be dried at 110℃ for 2 hours before use, and then cooled to room temperature before use, with a moisture content of ≤1.5%; The accelerator is a mixture of CZ and TT in a mass ratio of 7:1; This low-heat-generating rubber composition is prepared by the following steps: S1. Add N774 carbon black, attapulgite, polytetrafluoroethylene powder, and zinc stearate to a high-speed shear mill and premix them at a stirring paddle speed of 10 m / s for 5 minutes to obtain a uniform premix. S2. After preheating the internal mixer to 50°C, add natural rubber and styrene-butadiene rubber into it and press and plasticize for 1 minute. Then add the premix from step S1, as well as zinc oxide, stearic acid, and antioxidant, and continue mixing. When the mixing temperature reaches 130°C, control the temperature to slowly rise to 140°C within 4 minutes, and then discharge the rubber to obtain the masterbatch. S3. After cooling the masterbatch from step S2 to room temperature, put it into an internal mixer, add sulfur and accelerator for mixing, and then control the discharge temperature to not exceed 95°C to obtain a low-heat rubber composition.

[0051] Example 2

[0052] This embodiment provides a low-heat-generating rubber composition, which, by mass fraction, comprises the following components: 60 parts natural rubber, 20 parts styrene-butadiene rubber, 40 parts N774 carbon black, 5 parts attapulgite, 1 part polytetrafluoroethylene micro powder, 2 parts zinc stearate, 3 parts zinc oxide, 1 part stearic acid, 2 parts antioxidant RD, 0.8 parts sulfur, and 1.2 parts accelerator. Among them, attapulgite should be dried at 110℃ for 2 hours before use, and then cooled to room temperature before use, with a moisture content of ≤1.5%; The accelerator is a mixture of CZ and TT in a mass ratio of 7:1; This low-heat-generating rubber composition is prepared by the following steps: S1. Add N774 carbon black, attapulgite, polytetrafluoroethylene powder, and zinc stearate to a high-speed shear mill and premix them at a stirring paddle speed of 10 m / s for 5 minutes to obtain a uniform premix. S2. After preheating the internal mixer to 50°C, add natural rubber and styrene-butadiene rubber into it and press and plasticize for 1 minute. Then add the premix from step S1, as well as zinc oxide, stearic acid, and antioxidant, and continue mixing. When the mixing temperature reaches 130°C, control the temperature to slowly rise to 150°C within 4 minutes, and then discharge the rubber to obtain the masterbatch. S3. After cooling the masterbatch from step S2 to room temperature, put it into an internal mixer, add sulfur and accelerator for mixing, and then control the discharge temperature to not exceed 95°C to obtain a low-heat rubber composition.

[0053] Example 3

[0054] This embodiment provides a low-heat-generating rubber composition, which, by mass fraction, comprises the following components: 80 parts natural rubber, 40 parts styrene-butadiene rubber, 55 parts N774 carbon black, 15 parts attapulgite, 3 parts polytetrafluoroethylene micro powder, 4 parts zinc stearate, 5 parts zinc oxide, 2 parts stearic acid, 4 parts antioxidant 4020, 1.2 parts sulfur, and 1.8 parts accelerator. Among them, attapulgite should be dried at 110℃ for 2 hours before use, and then cooled to room temperature before use, with a moisture content of ≤1.5%; The accelerator is a mixture of CZ and TT in a mass ratio of 7:1; This low-heat-generating rubber composition is prepared by the following steps: S1. Add N774 carbon black, attapulgite, polytetrafluoroethylene powder, and zinc stearate to a high-speed shear mill and premix them at a stirring paddle speed of 10 m / s for 5 minutes to obtain a uniform premix. S2. After preheating the internal mixer to 50°C, add natural rubber and styrene-butadiene rubber into it and press and plasticize for 1 minute. Then add the premix from step S1, as well as zinc oxide, stearic acid, and antioxidant, and continue mixing. When the mixing temperature reaches 130°C, control the temperature to slowly rise to 150°C within 4 minutes, and then discharge the rubber to obtain the masterbatch. S3. After cooling the masterbatch from step S2 to room temperature, put it into an internal mixer, add sulfur and accelerator for mixing, and then control the discharge temperature to not exceed 95°C to obtain a low-heat rubber composition.

[0055] Example 4

[0056] The difference from Example 1 is that the accelerator is a mixture of CZ and TT in a mass ratio of 6:1, while the other components and preparation steps remain unchanged.

[0057] Example 5

[0058] The difference from Example 1 is that the accelerator is a mixture of CZ and TT in a mass ratio of 8:1, while the other components and preparation steps remain unchanged.

[0059] Example 6

[0060] The difference from Example 1 is that the accelerator is a mixture of CZ and TT in a mass ratio of 5:1, while the other components and preparation steps remain unchanged.

[0061] Example 7

[0062] The difference from Example 1 is that the accelerator is a mixture of CZ and TT in a mass ratio of 10:1, while the other components and preparation steps remain unchanged.

[0063] Example 8

[0064] The difference from Example 1 is that 3 parts of antioxidant 4020 are replaced with 1.5 parts of antioxidant 4020 and 1.5 parts of antioxidant RD.

[0065] Comparative Example 1 The difference from Example 1 is that no PTFE micro powder is added, while the remaining components and preparation steps remain unchanged.

[0066] Comparative Example 2 The difference from Example 1 is that zinc stearate is not added, while the remaining components and preparation steps remain unchanged.

[0067] Comparative Example 3 The difference from Example 1 is that commercially available needle-shaped wollastonite powder of equal mass is used to replace attapulgite, while the other components and preparation steps remain unchanged.

[0068] Comparative Example 4 The difference from Example 1 is that an equal mass fraction of commercially available N330 carbon black is used instead of N774 carbon black, while the remaining components and preparation steps remain unchanged.

[0069] Comparative Example 5 The difference from Example 1 is that no attapulgite clay is added, and the amount of N774 carbon black added is adjusted to 60 parts.

[0070] Comparative Example 6 The difference from Example 1 is that step S1 is omitted, and the materials are directly mixed together in step S2. The components and other preparation steps remain unchanged.

[0071] Comparative Example 7 The difference from Example 1 is that the only accelerator is accelerator CZ. The remaining components and preparation steps remain unchanged.

[0072] After the final rubber compounds (i.e., rubber compositions) prepared in Examples 1-8 and Comparative Examples 1-7 were allowed to stand for a certain period of time, they were re-milled twice on an open mill, with a roll gap of 0.5-1 mm and a roll temperature ≤50℃. Then, they were vulcanized using a flat vulcanizing machine under the following conditions: temperature 150±2℃, pressure 12 MPa, and time equal to the positive vulcanization time (t90) measured by a rotorless vulcanizing apparatus plus 8 min. After vulcanization, the test pieces were allowed to stand at room temperature for 20 h, and then the samples were cut according to the corresponding standards for relevant performance tests.

[0073] This includes the following performance tests: (1) Compression fatigue temperature rise: According to GB / T 1687.3-2016 standard, the compression flexure tester was used for testing. The stroke was 4.45 mm, the load was 1 MPa, the constant temperature was 55℃, the test time was 25 min, and the equilibrium temperature rise (℃) was recorded.

[0074] (2) Tensile strength: According to GB / T 528-2009 standard, the test was conducted using an electronic tensile testing machine with dumbbell-shaped specimens, tensile speed of 500 mm / min, and room temperature.

[0075] (3) Tear strength: According to GB / T 529-2008 standard, the test was conducted using an electronic tensile testing machine with right-angled specimens, tensile speed of 500 mm / min, and room temperature.

[0076] (4) Vulcanization characteristics: According to GB / T 9869.3-2025 standard, a rotorless vulcanizer was used for testing at a temperature of 150℃ and a time of 30 min. The scorching time (t10) and positive vulcanization time (t90) were recorded.

[0077] (5) Resilience: Tested using an impact elasticity testing machine according to GB / T 1681-2009 standard at room temperature.

[0078] (6) Hot air aging: The aging process was carried out in a hot air aging chamber according to GB / T 3512-2014 standard, with an aging temperature of 100℃ and a time of 72 h. After removal, the tensile strength after aging was tested according to GB / T 528-2009, and the percentage of the tensile strength before aging was calculated, i.e., the tensile strength retention rate (%).

[0079] Record the above performance test results in the table below.

[0080] Table 1 Performance Test Results

[0081] As shown in Table 1, the compression fatigue temperature rise of the rubber compositions prepared in this application examples does not exceed 30.0℃, which is significantly better than the compression fatigue temperature rise values ​​of the comparative examples. Furthermore, the tensile strength, tear strength, and resilience of Examples 1-7 are all superior to those of the comparative examples, and their vulcanization characteristics meet the processing safety and vulcanization efficiency requirements for tire shoulder pad rubber. The tensile strength retention rate of the rubber compositions prepared in this application examples after aging is not less than 80%, which demonstrates that the rubber compositions of this application not only have low initial heat generation but also excellent heat aging resistance, and can maintain low heat generation characteristics for a long time.

[0082] Based on Table 1, Examples 1-3, and Examples 4-7, it can be seen that when the mass ratio of CZ to TT is in the range of 5:1 to 10:1, as the relative proportion of TT increases, the vulcanization speed accelerates, and t10 and t90 shorten. However, an excessively high TT proportion leads to excessively high crosslinking density, an increase in polysulfide bonds, increased dynamic heat generation, and decreased resilience. Conversely, as the relative proportion of CZ increases, the vulcanization speed slows down, and processing safety improves. However, when the TT proportion is too low, vulcanization is insufficient, and the proportion of monosulfide bonds in the crosslinking network is insufficient, which is also not conducive to reducing heat generation. Therefore, the applicant suggests controlling the mass ratio of CZ to TT between 6 and 8:1 to obtain a comprehensive effect of moderate vulcanization speed, reasonable monosulfide / disulfide bond ratio, lowest dynamic heat generation, and best resilience.

[0083] Meanwhile, considering Table 1, Example 1, and Comparative Example 7, the accelerator system using CZ and TT together exhibits significant advantages in vulcanization characteristics, dynamic heat generation, and resilience compared to using CZ alone. The reason for this may be that when CZ is used alone, the lack of the synergistic effect of the super-accelerator TT significantly slows down the vulcanization rate and results in insufficient crosslinking density. This leads to the formation of more unstable polysulfide bonds or incomplete crosslinking networks within the vulcanized rubber, resulting in greater hysteresis loss during dynamic deformation, increased heat generation, and decreased resilience. However, when CZ and TT are used together, the addition of TT accelerates the vulcanization reaction, forming a highly efficient crosslinking network dominated by monosulfide and disulfide bonds even with low sulfur content. This network has a moderate crosslinking density and a stable structure, effectively reducing dynamic heat generation and improving resilience.

[0084] Combining Table 1, Example 1, and Example 8: Although Example 1, using antioxidant 4020 alone, could meet the initial low heat generation requirement, after hot air aging, the tensile strength retention rate of Example 8 was significantly higher than that of Example 1. This demonstrates that using two antioxidants can produce a certain synergistic effect, enabling the product of this application to continuously maintain low heat generation characteristics and mechanical properties during long-term use.

[0085] Based on Table 1, Example 1, and Comparative Examples 1-5, it can be seen that Example 1 has superior overall performance. This may be because: Comparative Example 1 lacks PTFE micro powder, thus losing its lubricating effect and failing to effectively reduce hysteresis heat generation; Comparative Example 2 lacks zinc stearate, resulting in poor filler dispersibility, which affects the mechanical properties and low heat generation effect of the product; Comparative Example 3, after replacing the attapulgite with ordinary wollastonite of the present application with attapulgite of a specific aspect ratio and crystal length, cannot effectively reduce the direct contact and friction between rubber molecular chains due to the weakened physical isolation effect; Comparative Example 4, after replacing N774 carbon black with high-structure N330 carbon black, increases the hysteresis loss of the filler network, which is not conducive to reducing heat generation; Comparative Example 5 does not contain attapulgite, and simply increasing the amount of N774 carbon black not only increases the temperature rise but also leads to the deterioration of the product's resilience. This indicates that the present application can effectively reduce the dynamic heat generation of rubber through the synergistic effect of the ultra-low friction lubrication of PTFE micro powder, the interfacial coating and dispersion promotion of zinc stearate, the needle-like physical isolation of attapulgite, and the low hysteresis characteristics of N774 carbon black, while maintaining good mechanical properties and processability, and achieving a compression fatigue temperature rise of ≤30℃.

[0086] As shown in Table 1, Example 1, and Comparative Example 6, directly mixing the powder with rubber results in uneven dispersion of the PTFE micropowder and ineffective coating of the filler surface by zinc stearate, leading to increased product temperature rise and decreased resilience. This indicates that the premixing step of this application can achieve uniform dispersion of the filler and interfacial lubrication.

[0087] The above are all preferred embodiments of this application, and are not intended to limit the scope of protection of this application. Therefore, all equivalent changes made in accordance with the structure, shape and principle of this application should be covered within the scope of protection of this application.

Claims

1. A low-heat-generating rubber composition, characterized in that, The composition, by mass fraction, includes the following components: 60-80 parts natural rubber, 20-40 parts styrene-butadiene rubber, 40-55 parts N774 carbon black, 5-15 parts attapulgite, 1-3 parts polytetrafluoroethylene powder, 2-4 parts zinc stearate, 3-5 parts zinc oxide, 1-2 parts stearic acid, 2-4 parts antioxidant, 0.8-1.2 parts sulfur, and 1.2-1.8 parts accelerator. The accelerator is a mixture of N-cyclohexyl-2-benzothiazole sulfenamide and tetramethylthiuram disulfide in a mass ratio of 5 to 10:1; The preparation method includes the following steps: S1. According to the stated mass fractions, N774 carbon black, attapulgite clay, polytetrafluoroethylene micro powder, and zinc stearate are sheared and dispersed, and premixed for 3-6 minutes to obtain a premix. S2. According to the stated mass proportions, natural rubber, styrene-butadiene rubber, the premix, zinc oxide, stearic acid, and antioxidant are mixed and then discharged in one step to obtain masterbatch. S3. After cooling the masterbatch to room temperature, it is mixed with sulfur and accelerator, and after a second degassing, the low heat-generating rubber composition is obtained.

2. The low-heat-generating rubber composition according to claim 1, characterized in that, The attapulgite clay consists of needle-like crystals with an aspect ratio of 30 to 100:1 and an average crystal length of 0.5 to 5 μm.

3. The low-heat-generating rubber composition according to claim 1, characterized in that, The average particle size of the polytetrafluoroethylene micro powder is 3~10μm.

4. The low-heat-generating rubber composition according to claim 1, characterized in that, The nitrogen adsorption specific surface area of ​​the N774 carbon black is 25~35m². 2 / g, oil absorption value is 55~65ml / 100g.

5. The low-heat-generating rubber composition according to claim 1, characterized in that, The antioxidant is selected from antioxidant 4020 and / or antioxidant RD.

6. The low-heat-generating rubber composition according to claim 1, characterized in that, In step S2, the process of mixing natural rubber, styrene-butadiene rubber, the premix, zinc oxide, stearic acid, and antioxidant, followed by a single discharge to obtain the masterbatch, specifically includes: Natural rubber, styrene-butadiene rubber, the premix, zinc oxide, stearic acid, and antioxidant are mixed together. When the mixing temperature reaches 130°C, the rotor speed is adjusted so that the temperature rises to the first discharge temperature within 3-5 minutes. The temperature of the first glue discharge is 140~150℃.

7. The low-heat-generating rubber composition according to claim 1, characterized in that, In step S3, the temperature of the secondary glue removal does not exceed 95°C.

8. The use of the low-heat-generating rubber composition according to any one of claims 1 to 7 in tire shoulder pad rubber, characterized in that, The tire shoulder pad rubber is obtained by vulcanization molding of the low heat-generating rubber composition according to any one of claims 1 to 7, and the average temperature rise of the tire shoulder pad rubber during compression fatigue does not exceed 30°C.

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