Mine tire sidewall rubber and preparation method thereof

Abstract

The invention discloses mine tire sidewall rubber and a preparation method thereof, and relates to the technical field of tires. According to the technical scheme, the rubber comprises the following components in parts by weight: 100 parts of a rubber matrix, 40-55 parts of carbon black, 8-15 parts of basic aluminum sulfate, 3-5 parts of zinc oxide, 1-2 parts of stearic acid, 3-6 parts of a composite anti-aging agent, 1-2 parts of microcrystalline wax, 3-5 parts of tackifying resin, 1.8-2.2 parts of sulfur and 1.3-2.1 parts of an accelerant, the composite anti-aging agent is prepared from an anti-aging agent BXA, an anti-aging agent 3100 and an anti-aging agent 4020 according to the weight ratio of (1 to 2): (0.5 to 1.5): (1 to 1.5). According to the invention, the original ternary composite anti-aging agent is matched with the basic aluminum sulfate, so that the technical problem that high flex resistance and high tear resistance of traditional sidewall rubber are difficult to consider under mine working conditions is solved on the premise of not sacrificing processability and elasticity.

Description

Technical Field

[0001] This invention relates to the field of tire technology, specifically to the sidewall rubber of mining tires and its preparation method. Background Technology

[0002] The tire sidewall is the flexible support connecting the tread and the bead. Its main function is to withstand continuous, cyclical flexural deformation during vehicle operation. Therefore, the core concept of traditional tire sidewall compound formulation design has always revolved around "maximizing flexural fatigue resistance." To achieve this goal, a high proportion of natural rubber (NR) is typically used to provide excellent elasticity, while a portion of butadiene rubber (BR) is used to reduce dynamic heat generation and improve fatigue resistance. Simultaneously, conventional antioxidant systems (such as antioxidants 4020 and RD) are employed to delay the thermo-oxidative aging of the rubber during repeated flexing, preventing early crack formation.

[0003] However, with the expansion of global mining operations and the increasing complexity and severity of working conditions, the challenges faced by the sidewalls of mining tires have far exceeded the scope of traditional designs. While withstanding millions of flexural cycles, tire sidewalls are continuously exposed to direct impacts, cuts, and scratches from flying sharp ore, gravel, metal debris, and foreign objects such as branches in harsh conditions such as mines and construction sites. This necessitates that the sidewall rubber, in addition to possessing excellent flexural fatigue resistance, also has sufficiently high tear strength to resist mechanical damage and prevent severe scratches, chipping, or even tearing. Traditional sidewall rubbers, which focus solely on "flexural resistance," generally have low tear strength, which has become a weakness leading to premature tire failure, affecting equipment uptime, and impacting operational safety under current extreme mining conditions.

[0004] Currently, common techniques for improving the tear resistance of rubber in the industry have significant limitations: First, increasing the amount of reinforcing fillers such as carbon black to increase the hardness and strength of the rubber compound severely sacrifices its elasticity and significantly increases dynamic heat generation, thus accelerating flexural fatigue failure. Second, adding short fibers or rigid inorganic particles, such as the environmentally friendly, cut-resistant engineering machinery tire sidewall rubber disclosed in Chinese invention patent CN103642083A, which utilizes a reinforcing system of N115 carbon black and N330 carbon black combined with aramid short fibers to effectively enhance the cut resistance of the rubber compound. However, this method easily leads to uneven filler dispersion, the formation of stress concentration points, and a deterioration of fatigue life.

[0005] Therefore, in response to the new requirements of the mining tire market for the performance of sidewall rubber, there is an urgent need to develop an innovative formula and preparation technology that can fundamentally improve flexural fatigue life and tear strength, and ensure long-term durability. Summary of the Invention

[0006] The technical problem to be solved by this invention is to overcome the shortcomings of the prior art and provide a sidewall rubber for mining tires and its preparation method. By introducing an original composite antioxidant and combining it with basic aluminum sulfate, the sidewall rubber can be simultaneously and significantly improved in terms of flexural fatigue life and tear strength without compromising the processing performance, elasticity and dynamic heat generation characteristics of the rubber compound.

[0007] The technical solution of this invention is as follows: On one hand, the present invention provides a sidewall rubber for mining tires, comprising the following components by weight: 100 parts of rubber matrix, 40-55 parts of carbon black, 8-15 parts of basic aluminum sulfate, 3-5 parts of zinc oxide, 1-2 parts of stearic acid, 3-6 parts of composite antioxidant, 1-2 parts of microcrystalline wax, 3-5 parts of tackifying resin, 1.8-2.2 parts of sulfur, and 1.3-2.1 parts of accelerator; wherein the composite antioxidant is composed of antioxidant BXA, antioxidant 3100 and antioxidant 4020 in a weight ratio of (1-2):(0.5-1.5):(1-1.5).

[0008] Preferably, the rubber matrix is ​​composed of 55-70 parts of natural rubber and 30-45 parts of butadiene rubber.

[0009] Preferably, the carbon black is N550 carbon black.

[0010] Preferably, the tackifying resin is tackifying resin TKM, which is used to improve the adhesiveness and processing performance of the adhesive.

[0011] Preferably, the accelerator consists of 1-1.5 parts of accelerator CZ and 0.3-0.6 parts of accelerator DM.

[0012] On the other hand, the present invention provides a method for preparing the above-mentioned mining tire sidewall rubber, comprising the following steps: S1 First stage mixing: Rubber matrix, carbon black (accounting for 2 / 3 of the total amount), zinc oxide, stearic acid, composite antioxidant, and microcrystalline wax are put into an internal mixer for mixing. The mixing speed is 40-45 rpm. During the mixing process, the roller is lifted and pressed 3 times. The discharge temperature is controlled at 150-155℃ to obtain the first stage masterbatch. The first stage masterbatch is cooled and left to stand for 4-8 hours. S2 two-stage mixing: The first-stage masterbatch, the remaining carbon black, the tackifying resin, and the basic aluminum sulfate are put into the internal mixer for mixing. The mixing speed is 35-40 rpm. During the mixing process, the roller is lifted and pressed twice. The discharge temperature is controlled at 145-150℃ to obtain the second-stage masterbatch. The second-stage masterbatch is cooled and left to stand for 4-8 hours. S3 Final Mixing: The second-stage masterbatch, sulfur, and accelerator are put into an internal mixer for mixing. The mixing speed is 25-30 rpm, the mixing time is 90-110 s, and the discharge temperature is controlled at 95-100℃. After discharge, the sidewall rubber of the mining tire is obtained.

[0013] Compared with the prior art, the present invention has the following advantages: 1. This invention employs a highly efficient and synergistic ternary composite antioxidant: Antioxidant BXA serves as the "dynamic protection core" of this system. Its molecular structure specifically captures and eliminates free radicals generated by mechanical stress activation during repeated high-strain flexing of rubber, effectively inhibiting the resulting oxidative chain-scission reaction, thereby significantly extending the flexural fatigue life of the rubber compound. Antioxidant 3100's long-chain alkyl structure endows it with excellent mobility, continuously replenishing the rubber compound surface to form a dense and stable physicochemical protective film. This film effectively blocks ozone molecules from attacking the surface rubber molecular chains, fundamentally preventing the initiation of surface cracks. This is the first key line of defense for improving tear resistance, especially crack initiation resistance. Antioxidant 4020 provides resistance to thermo-oxidative aging, protecting the rubber matrix and cross-linked network to maintain stability under long-term high-temperature environments, preventing overall performance degradation.

[0014] 2. This invention discovers that the specific ratio of antioxidants BXA, 3100, and 4020 does not result in a simple functional additive effect, but rather produces a profound super-synergistic effect. This anti-aging system constructs a three-in-one, all-round, multi-level aging protection network. Its innovation lies in the fact that this protective network not only effectively delays pure flexural fatigue failure, but also provides immediate, efficient, and long-lasting protection during the high-stress, new surface-generating failure process of crack propagation. By stabilizing the molecular chains in the crack tip region and inhibiting the accelerated oxidative embrittlement caused by stress concentration and fresh surface exposure, crack propagation requires more energy, thus macroscopically manifesting as a substantial leap in tear strength. This achieves a functional leap for antioxidants from traditional "passive protection" to "active enhancement."

[0015] 3. This invention optimizes the reinforcing filler system to achieve synergistic performance. The invention controls the carbon black content within a moderate range of 40-55 parts, providing necessary reinforcement, ensuring hardness and modulus, while avoiding the loss of elasticity, rapid increase in dynamic heat generation, and negative impact on flexural life caused by excessive carbon black filler content. Furthermore, it innovatively introduces basic aluminum sulfate as a functional reinforcing filler, further increasing the tensile strength and tear resistance of the rubber compound.

[0016] 4. The sidewall rubber developed in this invention achieves significant improvements in key performance characteristics while ensuring excellent processing flowability, elasticity, and moderate hardness. Its tear resistance far exceeds that of traditional formulations, and its flexural fatigue life meets high-standard durability requirements. Simultaneously, the material exhibits excellent stability under long-term thermo-oxidative and ozone aging conditions, demonstrating reliable potential for long-term use. Detailed Implementation

[0017] To enable those skilled in the art to better understand the technical solutions of this invention, the technical solutions of this invention will be clearly and completely described below in conjunction with the embodiments of this invention.

[0018] The sources of some of the raw materials in the following embodiments are as follows: Basic aluminum sulfate: Shaanxi Didu Pharmaceutical Chemical Co., Ltd.; Anti-aging agent BXA: Lanxess Group, Germany.

[0019] To verify the unique effect of the composite antioxidant of the present invention, while keeping the basic formula of the tire sidewall rubber (60 parts natural rubber, 40 parts butadiene rubber, 50 parts carbon black N550, 15 parts basic aluminum sulfate, 4 parts zinc oxide, 1.5 parts stearic acid, 1.5 parts microcrystalline wax, 4 parts tackifying resin TKM, 2 parts sulfur, 1.2 parts accelerator CZ, and 0.4 parts accelerator DM) unchanged, only the composition and ratio of the composite antioxidant were changed. The following examples and comparative examples were designed, with a total addition amount of 3.5 parts, as shown in Table 1: Table 1. Composition and proportion of the composite antioxidants in Examples 1-2 and Comparative Examples 1-7

[0020] The preparation methods of the mining tire sidewall rubber in Examples 1-2 and Comparative Examples 1-7 include the following steps: S1 First stage mixing: Natural rubber NR, butadiene rubber BR, carbon black N550 (accounting for 2 / 3 of the total amount), zinc oxide, stearic acid, compound antioxidant, and microcrystalline wax are put into an internal mixer for mixing. The mixing speed is 42 rpm. During the mixing process, the roller is lifted and pressed 3 times. The discharge temperature is controlled at 152℃ to obtain the first stage masterbatch. The first stage masterbatch is cooled and left to stand for 6 hours. S2 two-stage mixing: The first-stage masterbatch, the remaining carbon black, the tackifying resin TKM, and the basic aluminum sulfate are put into the internal mixer for mixing. The mixing speed is 37 rpm. The grinding wheel is lifted and pressed twice during the mixing process. The discharge temperature is controlled at 148℃ to obtain the second-stage masterbatch. The second-stage masterbatch is cooled and left to stand for 6 hours. S3 Final Mixing: The second-stage masterbatch, sulfur, accelerator CZ, and accelerator DM are put into an internal mixer for mixing. The mixing speed is 28 rpm, the mixing time is 100 s, and the discharge temperature is controlled at 98℃. After discharge, the sidewall rubber of the mining tire is obtained.

[0021] The sidewall rubber of mining tires in Examples 1-2 and Comparative Examples 1-7 were vulcanized at 145℃ for 60 min to prepare test specimens, which were then subjected to physical property tests. The Shore A hardness was tested according to GB / T 531.1-2008 "Test Method for Indentation Hardness of Vulcanized Rubber or Thermoplastic Rubber Part 1: Shore Hardness Tester Method (Shore Hardness)". The 100% tensile stress, tensile strength, and elongation at break were tested according to GB / T 528-2009 "Determination of Tensile Stress-Strain Properties of Vulcanized Rubber or Thermoplastic Rubber". The flexural fatigue life was tested according to GB / T 13934-2006 "Determination of Flexural Cracking and Crack Growth of Vulcanized Rubber or Thermoplastic Rubber (Demercia Type)". Ozone aging rating: Static tensile tests were conducted on the samples according to GB / T 7762-2014 "Static Tensile Test for Ozone Cracking of Vulcanized Rubber or Thermoplastic Rubber". The ozone aging rating was then determined based on the crack condition of the samples after tensile testing. The test conditions were: ambient temperature 40℃, relative humidity 50%RH, ozone concentration 200pphm, static tensile strain 30%, and test time 150h. Ozone aging rating classification: No cracks in the sample, rated as level 0; crack density < 10 cracks / cm and crack width < 0.2mm, rated as level 1; 10 cracks / cm ≤ crack density < 20 cracks / cm and crack width < 0.2mm, rated as level 2; 20 cracks / cm ≤ crack density < 30 cracks / cm and crack width < 0.2mm, rated as level 3. Aging retention rate = (tensile strength after aging × elongation at break after aging) / (tensile strength before aging × elongation at break before aging) × 100%, thermo-oxidative aging test conditions: 100℃ × 48h.

[0022] The test results are shown in Table 2: Table 2. Physical property test results of vulcanized samples of mining tire sidewall rubber from Examples 1-2 and Comparative Examples 1-7

[0023] Table 2 shows that the ternary composite antioxidants in Examples 1-2 have a significant advantage in balancing the performance of the sidewall rubber. In Comparative Example 1, using antioxidant BXA alone, although the flexural fatigue life reached 451,000 cycles, the ozone aging level was only 2. In Comparative Example 2, using antioxidant 3100 alone, although the ozone aging level was 0, the flexural fatigue life was only 256,000 cycles. In Comparative Example 3, using antioxidant 4020 alone, although the aging retention rate reached 90%, the flexural fatigue life was only 318,000 cycles and the ozone aging level was 3. Therefore, the overall performance of the sidewall rubber in Comparative Examples 1-3, using only one antioxidant, still needs further improvement.

[0024] Compared to the binary compound antioxidant systems of Comparative Examples 4-6, Example 1 achieved a better synergistic balance in three key indicators: flexural fatigue life, ozone aging level, and aging retention rate. Comparative Example 4 had relatively low flexural fatigue life and aging retention rate; Comparative Example 5 had a high ozone aging level; and Comparative Example 6 had the lowest flexural fatigue life. Compared to Comparative Example 7, which used a conventional antioxidant system, Example 1 showed more significant overall advantages: flexural fatigue life increased by approximately 43.4%, the ozone aging level improved from level 3 (severe cracks) to level 0 (no cracks), and the aging retention rate increased from 82% to 88%.

[0025] The sidewall rubbers in Examples 1-2 used composite antioxidants composed of antioxidants BXA antioxidant 3100 and antioxidant 4020 in weight ratios of 1.5:1:1 and 1:1:1.5, respectively. This achieved a balance of performance, with a flexural fatigue life of 423,000 cycles, close to the optimal level. At the same time, it maintained a level 0 ozone aging rating and an aging retention rate of 88%. The overall performance was better than that of single antioxidant systems and binary compound antioxidant systems.

[0026] Based on the superior performance of the composite antioxidant in Example 1, Examples 3-5 and Comparative Examples 8-10 were designed to verify the effect of the basic aluminum sulfate of the present invention on the performance of the tire sidewall rubber.

[0027] Table 3. Tire sidewall compound formulations for Examples 3-5 and Comparative Examples 8-10

[0028] The preparation methods of the mining tire sidewall rubber in Examples 3-5 and Comparative Examples 8-10 are the same as those in Examples 1-2 and Comparative Examples 1-7.

[0029] The sidewall rubbers of mining tires in Examples 3-5 and Comparative Examples 8-10 were vulcanized at 145℃ for 60 min to prepare test specimens, which were then subjected to physical property tests. The 300% tensile stress, tensile strength, and elongation at break were tested according to GB / T 528-2009 "Determination of Tensile Stress-Strain Properties of Vulcanized Rubber or Thermoplastic Rubber"; the tear strength was tested according to GB / T 529-2008 "Determination of Tear Strength of Vulcanized Rubber or Thermoplastic Rubber". The test results are shown in Table 4. Table 4. Physical property test results of vulcanized samples of mining tire sidewall rubber from Examples 3-5 and Comparative Examples 8-10

[0030] As can be seen from Example 3 and Comparative Example 8 in Table 4, the rigidity of the rubber compound in Example 3 is significantly enhanced, with a hardness increase of 2 degrees and increases of 0.3 MPa and 1.5 MPa at 100% and 300% elongation, respectively. Most importantly, the tear strength of Example 3 increases dramatically from 56 kN / m to 75 kN / m. However, the elasticity and dynamic durability of the rubber compound in Example 3 are somewhat reduced, with the elongation at break decreasing from 530% to 500% and the flexural fatigue life decreasing from 410,000 cycles to 380,000 cycles. The tensile strength is slightly improved, while the aging performance (aging retention rate and ozone aging level) remains basically the same.

[0031] As can be seen from Table 4, the rubber compounds of Example 3 and Comparative Example 9 are similar in terms of hardness and stress at a given elongation. However, Example 3 is significantly superior in several key mechanical properties: its tear strength of 75 kN / m is much higher than that of Comparative Example 9 (62 kN / m), and its tensile strength is also higher. Simultaneously, the rubber compound of Example 3 exhibits better elasticity, with a higher elongation at break and better flexural fatigue life than Comparative Example 9; their aging properties are similar. This indicates that, under the premise of achieving similar rigidity, Example 3, using a composite antioxidant, provides higher tear strength and better maintains the toughness and fatigue life of the rubber compound than simply adding carbon black.

[0032] As can be seen from Example 3 and Comparative Example 10 in Table 4, the synergistic effect of basic aluminum sulfate and the composite antioxidant significantly improved the key properties of the rubber compound: tear strength increased from 55 kN / m to 75 kN / m, flexural fatigue life increased from 324,000 cycles to 380,000 cycles, and ozone aging level improved from level 1 (crack) to level 0 (no crack). Comparing Comparative Example 8 and Comparative Example 10, it can be seen that, without the addition of basic aluminum sulfate, Comparative Example 8, using the composite antioxidant, showed an increase in flexural fatigue life from 324,000 cycles to 410,000 cycles compared to Comparative Example 10, using the traditional antioxidant system, while the tear strength remained essentially the same, and the ozone aging level improved from level 1 to level 0. This indicates that the composite antioxidant is the core component for improving dynamic fatigue and ozone protection, while the addition of basic aluminum sulfate further significantly enhanced the tear resistance of the rubber compound.

[0033] The composite antioxidant of this invention is a compound of antioxidants BXA, 3100, and 4020 in a specific ratio. A synergistic effect occurs between the different antioxidants: antioxidants BXA and 3100 primarily provide excellent dynamic and static ozone protection, with antioxidant 3100 exhibiting excellent long-lasting protection; while antioxidant 4020 contributes to good resistance to flexural fatigue and thermo-oxidative aging. This ternary compound antioxidant, through the complementary effects of physical and chemical processes, covers a more comprehensive aging protection pathway, thereby achieving a balanced and high level of performance in ozone aging rating, flexural fatigue life, and aging retention that cannot be achieved by a single antioxidant.

[0034] Basic aluminum sulfate, as an inorganic reinforcing filler, significantly improves the modulus, hardness, and tear strength of rubber compounds, primarily by increasing the difficulty of crack propagation through its physical reinforcing effect. Its hard particles, uniformly dispersed in the rubber matrix, can pin and force crack tips to deflect and circumvent, significantly increasing the tear path length and required energy. Simultaneously, the localized debonding process at the particle-rubber interface under stress dissipates energy, and the matrix yielding deformation induced by debonding further absorbs tearing force. For natural rubber matrices, stress concentration around the filler can induce more significant strain crystallization, forming high-strength microcrystalline zones that reinforce the local area. These particles collectively construct a more effective three-dimensional stress dispersion network than traditional carbon black, making it difficult for external forces to concentrate locally and cause damage, thus significantly improving tear resistance macroscopically. However, the rigidity of its particles can also become stress concentration points, negatively impacting the elasticity and dynamic fatigue properties of the rubber compound.

[0035] By using the composite antioxidant of this invention in conjunction with basic aluminum sulfate, a synergistic enhancement of protective and mechanical properties is achieved. The powerful comprehensive aging protection capability of the composite antioxidant effectively buffers the risk of flexural fatigue and long-term aging performance degradation caused by stress concentration points introduced by basic aluminum sulfate, allowing the rubber compound to maintain good durability even under high reinforcement. Simultaneously, the significant improvement in tear strength and modulus by basic aluminum sulfate compensates for the shortcomings of high-performance antioxidant systems in mechanical reinforcement. The synergy between the two enables the rubber compound to achieve high levels in key indicators such as tear resistance, rigidity, ozone aging resistance, and flexural fatigue resistance, avoiding the drawbacks of using only a high-dose antioxidant (sacrificing mechanical properties) or only a high-reinforcing filler (sacrificing durability), achieving an optimized balance of comprehensive performance.

Claims

1. A sidewall rubber compound for mining tires, characterized in that, By weight, it includes the following components: 100 parts rubber matrix, 40-55 parts carbon black, 8-15 parts basic aluminum sulfate, 3-5 parts zinc oxide, 1-2 parts stearic acid, 3-6 parts composite antioxidant, 1-2 parts microcrystalline wax, 3-5 parts tackifying resin, 1.8-2.2 parts sulfur, and 1.3-2.1 parts accelerator; wherein, the composite antioxidant is composed of antioxidant BXA, antioxidant 3100 and antioxidant 4020 in a weight ratio of (1-2):(0.5-1.5):(1-1.5).

2. The sidewall rubber for mining tires as described in claim 1, characterized in that, The rubber matrix is ​​composed of 55-70 parts of natural rubber and 30-45 parts of butadiene rubber.

3. The sidewall rubber for mining tires as described in claim 1, characterized in that, The carbon black is N550 carbon black.

4. The sidewall rubber for mining tires as described in claim 1, characterized in that, The tackifying resin is tackifying resin TKM.

5. The sidewall rubber for mining tires as described in claim 1, characterized in that, The accelerator consists of 1-1.5 parts of accelerator CZ and 0.3-0.6 parts of accelerator DM.

6. The method for preparing the sidewall rubber of mining tires according to any one of claims 1-5, characterized in that, Includes the following steps: S1 First stage mixing: Rubber matrix, carbon black (accounting for 2 / 3 of the total amount), zinc oxide, stearic acid, composite antioxidant, and microcrystalline wax are put into an internal mixer for mixing. The mixing speed is 40-45 rpm. During the mixing process, the roller is lifted and pressed 3 times. The discharge temperature is controlled at 150-155℃ to obtain the first stage masterbatch. The first stage masterbatch is cooled and left to stand for 4-8 hours. S2 two-stage mixing: The first-stage masterbatch, the remaining carbon black, the tackifying resin, and the basic aluminum sulfate are put into the internal mixer for mixing. The mixing speed is 35-40 rpm. During the mixing process, the roller is lifted and pressed twice. The discharge temperature is controlled at 145-150℃ to obtain the second-stage masterbatch. The second-stage masterbatch is cooled and left to stand for 4-8 hours. S3 Final Mixing: The second-stage masterbatch, sulfur, and accelerator are put into an internal mixer for mixing. The mixing speed is 25-30 rpm, the mixing time is 90-110 s, and the discharge temperature is controlled at 95-100℃. After discharge, the sidewall rubber of the mining tire is obtained.

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