A low heat build-up high elasticity sidewall rubber composition, a mixing method and a tire

Abstract

This invention relates to the field of tire manufacturing technology, and more particularly to a low-heat-generating, high-elasticity sidewall rubber composition, a mixing method, and a tire. Based on 100 parts by weight of the rubber components, it includes natural rubber, first and second non-oil-extended polystyrene-butadiene rubbers (BF2055H / L), polybutadiene rubber, and additives such as highly dispersed silica, a small amount of carbon black, silane coupling agents, and α-methylstyrene resin. BF2055H / L has a 20% styrene content, 55% vinyl content, and a bimodal molecular weight distribution, synergistically improving the dynamic modulus distribution of the rubber and the uniformity of filler dispersion. This invention, through the synergistic reinforcement of the bimodal high-vinyl SSBR-NR-BR system and silica / carbon black, significantly reduces sidewall heat generation and rolling energy consumption while maintaining a comfort hardness of 56–58A, thereby improving dynamic strength and flexural fatigue life, thus meeting the comprehensive requirements of electric vehicle tires for long range, lightweight, and high reliability.

Description

Technical Field

[0001] This invention relates to the field of tire manufacturing technology, and in particular to a low-heat-generating, high-elasticity sidewall rubber composition, a mixing method, and a tire. Background Technology

[0002] With the official implementation of the "Energy-Saving and New Energy Vehicle Technology Roadmap 2.0" and the "Passenger Car Tire Rolling Resistance Grading Evaluation Method (2023 Edition)," domestic and foreign OEMs have proposed a new indicator system for electric vehicle (EV) tires that emphasizes "low energy consumption, long mileage, lightweight design, and quietness." Among these, the tire sidewall, as a key component that bears torsional deformation, buffers vibration, and protects the tire cord, faces more stringent failure mechanisms under the multiple operating conditions of EVs—high-torque instantaneous acceleration, frequent energy recovery, and the relatively large curb weight of the vehicle—such as high-frequency flexing, heat accumulation, permanent deformation, and fatigue cracking. Therefore, developing a low-hysteresis and high-elasticity sidewall rubber composition has become another core technological hotspot after "low rolling resistance treads."

[0003] For example, Chinese invention CN116144084B provides a formulation for improving the interface between silica and rubber using chemical modifiers. In the NR / BR-silica system, N-(carboxymethyl)maleic acid is added to activate the coupling bond, which improves the filler dispersion and reduces the hysteresis at 60°C to 0.085. However, the rubber matrix is ​​composed entirely of NR and BR, lacking the dynamic reinforcement of high vinyl S-SBR. The hardness is >62A and M300 <6MPa, which is difficult to meet the dual requirements of softness and high-speed deformation rebound of electric vehicle tire sidewalls.

[0004] Chinese invention CN113136057A utilizes a thermally conductive filler approach for rapid heat dissipation. By introducing a mixture of high-thermal-transfer carbon black and nano-metal oxides into the tire sidewall rubber, the thermal conductivity is increased by 17%, reducing instantaneous temperature rise. However, this solution primarily uses N330 carbon black for reinforcement, resulting in a tanδ (60℃) still higher than 0.095. Furthermore, the thermally conductive micropowder increases the mixing viscosity and specific gravity, which is detrimental to lightweighting and energy consumption. Chinese invention CN114479206A employs hydrazide modifiers and low-structure carbon black to form a "soft-hard" layered network in NR / BR, significantly improving tear strength and suppressing heat generation. This technology requires a BR of 50 phr or higher to maintain modulus, leading to insufficient springback recovery. Additionally, hydrazide derivatives present VOC and cost pressures in passenger tire sidewalls.

[0005] Early solutions for low heat generation in precipitated silica tire sidewalls, such as Chinese invention patent CN107602948A, which uses rare earth butadiene rubber in combination with carbon black, can reduce the rolling resistance index to below 90% of that of traditional tire sidewalls. However, the formulation still contains processing oils above 15 phr, and oil migration during long-term service leads to hysteresis recovery and fatigue performance degradation. It is evident that the current technical challenges in this field are: 1. Migration of free plasticizer oil or high aromatic oil: Long-term dynamic flexing causes a gradual increase in sidewall hysteresis loss, making temperature rise difficult to control stably; 2. Insufficient viscoelastic balance of single-peak or low-vinyl polymers: Either excessive hardness affects comfort, or insufficient dynamic modulus weakens tread support; 3. Poor compatibility of high thermal conductivity / high filler systems: Improving heat dissipation often sacrifices processing fluidity and lightweighting; 4. Environmental friendliness and cost of compounded additives: Solutions containing hydroxyhydrazine, acylhydrazine, or high-valence metal oxides face environmental and cost barriers for large-scale application in passenger vehicles. Summary of the Invention

[0006] To address the aforementioned technical problems, the present invention aims to provide a low-heat-generating, high-elasticity sidewall rubber composition. Through the synergistic reinforcement of a bimodal high-vinyl SSBR-NR-BR system with silica / carbon black, it significantly reduces sidewall heat generation and rolling energy consumption while maintaining a comfortable hardness of 50–60A, thereby improving dynamic strength and flexural fatigue life. This meets the comprehensive requirements of electric vehicle tires for long range, lightweight design, and high reliability.

[0007] To achieve the above objectives, the present invention adopts the following technical solution:

[0008] A low-heat-generating, high-elasticity tire sidewall rubber composition is prepared by mixing raw materials comprising the following components, based on 100 parts by weight of the rubber component:

[0009] 10–30 parts natural rubber;

[0010] 20-40 parts of solution-polymerized styrene-butadiene rubber;

[0011] 50–70 parts of butadiene rubber;

[0012] 10–40 parts of silica;

[0013] 30–60 parts carbon black;

[0014] 1–5 parts of silane coupling agent;

[0015] 3–10 parts of α-methylstyrene resin;

[0016] The solution-polymerized styrene-butadiene rubber (SBR) is composed of a first SBR and a second SBR in a mass ratio of 1.5:1 to 1:1.5. Both the first and second SBRs are unoil-extended rubbers. The styrene content is 20±1wt%, the vinyl content is 55±3wt%, the glass transition temperature is -35±2℃, and the weight-average molecular weight is 380–420 kg·mol⁻¹. -1 With 280–320 kg·mol -1 .

[0017] Preferably, it is prepared by mixing raw materials comprising the following components in parts by weight:

[0018] 15–25 parts natural rubber;

[0019] 25-35 parts of solution-polymerized styrene-butadiene rubber;

[0020] 55–65 parts of butadiene rubber;

[0021] 20–30 parts of silica;

[0022] 35–50 parts carbon black;

[0023] 2–4 parts of silane coupling agent;

[0024] 4–8 parts of α-methylstyrene resin.

[0025] Preferably, the first and second solution-polymerized styrene-butadiene rubbers are BF2055H and BF2055L solution-polymerized styrene-butadiene rubbers produced by China Petroleum & Chemical Corporation (Sinopec), respectively. BF2055H has a styrene content of 20%, a vinyl content of 55%, is unextended with oil, has a Tg of -35℃, and a weight-average molecular weight of 380–420 kg·mol⁻¹. -1 BF2055L: 20% styrene, 55% vinyl, unoiled, Tg = -35℃, weight-average molecular weight 280–320 kg·mol⁻¹ -1 The preferred mass ratio is 1.2:1 to 1:1.2.

[0026] As a preferred option, highly dispersed silica with a specific surface area (CTAB) ≥ 160 m² is selected. 2 / g, preferably CTAB is 180–195m 2 / g, BET is 195–210m 2 / g; The preferred BET specific surface area of ​​carbon black particles is 20-160m². 2 / g, more preferably 40-130m 2 / g, further preferably 50-120m 2 / g; more preferably, the carbon black is one or more of N134, N220, N234, N375 or N375, N330, N339, N347, N326; more preferably, the carbon black is N234 or N330.

[0027] Preferably, the silane coupling agent has the structural formula YR-Si(OR)3, where Y is an organic functional group and SiOR is a silaneoxy group; preferably, the silane coupling agent is selected from one or more of vinyltriethoxysilane, vinyltrimethoxysilane, vinyltri(β-methoxyethoxy)silane, bis-[γ-(triethoxysilyl)propyl]tetrasulfide, bis-propyltriethoxysilane disulfide, 3-(octanoylthio)propyltriethoxysilane and n-octyltriethoxysilane.

[0028] Preferably, the α-methylstyrene resin has a softening point of 95–120°C and a number-average molecular weight of 1000–3000.

[0029] Preferably, the compounded raw materials also include an activator, an antioxidant, and a vulcanizing agent; preferably, the activator includes 2-5 parts zinc oxide and 1-3 parts stearic acid; 2-4 parts antioxidant; the vulcanizing agent includes 1.0-3.0 parts insoluble sulfur and 1.0-2.0 parts accelerator; more preferably, the accelerator includes one or more of N-tert-butyl-2-benzothiazole sulfenamide or N-cyclohexyl-2-benzothiazole sulfenamide, diphenylguanidine accelerators, hexamethylenetetramine, 4,4′-dithiodimorpholine, and dicaprolactam disulfide.

[0030] Furthermore, the present invention also provides a mixing method for preparing the rubber composition, the method comprising the following steps:

[0031] 1) The rubber, carbon black, silica and silane coupling agent are added to a mixer at 110–125℃ and mixed for 50 seconds.

[0032] 2) Heat to 145–148℃ and continue mixing for 40 seconds to form masterbatch;

[0033] 3) After cooling the masterbatch to 95–100°C, add sulfur and accelerator for final mixing.

[0034] Furthermore, the present invention also provides the use of the rubber composition in the manufacture of low-heat-generating, high-elasticity automotive tire sidewalls.

[0035] Furthermore, the present invention also provides a tire whose sidewall is obtained by vulcanizing the rubber composition.

[0036] By employing the aforementioned technical solution, this invention utilizes BF2055H / BF2055L series solution-polymerized styrene-butadiene rubber with a bimodal molecular weight structure, a vinyl content of 55%, and no filler oil to construct a low-heat-generating, high-elasticity tire sidewall rubber composition. Its specific technical effects are as follows:

[0037] 1) Significantly reduces heat generation and rolling energy consumption

[0038] By employing "BF2055H / LS-SBR with bimodal molecular weight, 55% vinyl content, and completely free of filler oil," and synergistically reinforcing it with medium specific surface area silica and medium structure carbon black, the free interface friction within the rubber was significantly reduced. The dynamic hysteresis factor tanδ decreased from 0.086-0.094 to 0.069 at 60℃, a reduction of approximately one-quarter. In the Goodrich flexural heat generation test, the steady-state temperature rise of the sidewall decreased from 67-71℃ to 61℃, with the peak temperature dropping by 6-10℃, thus significantly suppressing heat accumulation on the tire sidewall under long-range driving conditions for electric vehicles.

[0039] 2) Improve dynamic elasticity and fatigue life

[0040] Low molecular weight segments rapidly wet fillers, significantly reducing the initial modulus M10 and making the tire sidewalls more flexible, which helps reduce road noise input; high molecular weight segments and α-methylstyrene resin jointly construct a dense cross-linked network, significantly increasing the 300% tensile stress M300, ensuring the structural rigidity of the sidewalls and steering response at high speeds.

[0041] 3) Maintain comfortable firmness and low noise

[0042] ShoreA hardness is controlled at 56–58, and combined with low M10, it can reduce the lateral stiffness fluctuation of the tire sidewall; low molecular weight segment fast wetting filler significantly reduces the initial modulus M10, making the tire sidewall more flexible, which helps to reduce road noise input and meet the quiet requirements of mid-to-high-end EVs.

[0043] 4) Enhanced durability and wear resistance

[0044] In the DIN abrasion test, the abrasion volume of the formulation of this invention was ≥103 mm. 3 Reduced to ≤101mm 3 Wear resistance is significantly improved. Benefiting from lower hysteresis and higher network uniformity, the permanent deformation after 10 minutes of 100% tensile testing is reduced from 16-19% to 12-14%, the De-Mattia flexural crack life is increased from 140,000-170,000 cycles to over 200,000 cycles, and the sidewall's resistance to bulging and cracking is significantly enhanced.

[0045] 5) Green manufacturing and environmental friendliness

[0046] By eliminating filler oil, volatile organic compound emissions can be reduced by more than 90%; activated ultrafine zinc oxide only requires 3 phr to meet the sulfidation activation requirements, saving 40% of zinc usage compared to conventional systems, while also reducing the pressure of heavy metal emissions.

[0047] In summary, the sidewall rubber composition of the present invention achieves five major breakthroughs—low hysteresis, low temperature rise, high elasticity, long fatigue life, and green manufacturing—while maintaining comfortable hardness. It is significantly superior to existing traditional technologies such as oil-extended S-SBR, single-peak star-shaped S-SBR, low-vinyl S-SBR, and emulsion SBR, and fully meets the stringent requirements of electric vehicle tires for energy saving, quietness, and high reliability. Detailed Implementation

[0048] The technical solutions in the embodiments of the present invention will be clearly and completely described below. Obviously, the described embodiments are only a part of the embodiments of the present invention, and not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative effort are within the protection scope of the present invention.

[0049] I. Main Raw Materials and Models

[0050]

[0051]

[0052] II. Formulation Design (PHR)

[0053] 1. In the formulation of this invention, the oil-extended raw material is reduced by the amount of oil added (unit: phr).

[0054] Components (phr) E-1 E-2 E-3 Natural rubber 20 25 15 BF2055H 18 15 20 BF2055L 12 10 15 BR-9000 50 50 50 Ultrasil 7800 25 28 — Ultrasil 7000 — — 22 N234 Carbon Black 38 35 40 Si69 3 3 3 α-MPS resin 6 5 7 ZnO-AP5 3 3 3 stearic acid 2 2 2 Anti-aging agent 6PPD 2 2 2 Anti-aging agent TMQ 1 1 1 Accelerator TBBS 1 1 1 Accelerator DPG 0.3 0.3 0.3 Sulfur OT-20HD 1.2 1.2 1.2

[0055] 2. Comparative formulation, oil-extended raw materials minus oil extrusion (unit: phr)

[0056]

[0057]

[0058] III. The mixing process adopts a two-stage mixing process.

[0059] 1. Mother Refining (GK-160, 70rpm)

[0060] 1) 110–125℃ for 50 seconds: Add all rubber, silica, carbon black, Si69, zinc oxide and other additives at once;

[0061] 2) Continue at 145–148℃ for 40 seconds: After adding α-MPS resin, the discharged material is masterbatch.

[0062] 2. Final Refinement

[0063] Cool the masterbatch to 95–100°C, add sulfur and accelerator, and mix for 60 seconds.

[0064] 3. Vulcanization

[0065] 170℃×15min (flat vulcanizing machine).

[0066] IV. Test Methods and Conditions

[0067] The table below lists complete mechanical and dynamic test data for three examples (E-1 to E-3) and five comparative examples (C-1 to C-5). Standardized test methods and key test conditions for each test item are provided below the table. All data are average values ​​obtained from testing five samples (three 205 / 55R16 solid tires for rolling resistance) from the same batch of formulations. The values ​​in parentheses represent the 1σ standard deviation.

[0068]

[0069]

[0070] V. Test Experiment Data

[0071]

[0072] VI. Conclusions of Experimental Data Analysis

[0073] 1) ShoreA and M10: In the comparative example, the NR and oil-expanded S-SBR content are relatively high, and the BR content is fixed. The internal friction between chain segments is large, resulting in higher overall hardness and initial modulus than in the example. In the example, the "soft-hard" synergy of 55% vinyl oil-free S-SBR and high BR is achieved. ShoreA is controlled at 56-58, and M10 = 0.36-0.39 MPa, making the tire sidewall more flexible and having a certain degree of rigidity.

[0074] 2) tanδ and Goodrich ΔT: The example does not contain filler oil and the biphase reinforcement of silica-carbon black is more uniform with low internal loss, tanδ (60℃) = 0.069-0.071, ΔT ≤ 64℃; the comparative example contains oil or low vinyl / emulsion SBR, with large hysteresis loss, ΔT reaching 67–71℃.

[0075] 3) M300 and dynamic stiffness: The bimodal MwS-SBR and resin are co-networked, making the M300 of the example ≥ 7.0 MPa; C-5 has an M300 of only 5.8 MPa due to insufficient dynamic reinforcement of emulsion SBR.

[0076] 4) Wear, permanent deformation and crack life: Example DIN 97–101mm 3Permanent deformation 12–14%, De-Mattia > 2.1 × 10⁻⁶ 5 This result is significantly better than the other ratios, demonstrating the contribution of bimodal SSBR to durability.

[0077] The foregoing description of embodiments of the present invention, through which those skilled in the art are able to implement or use the present invention, will be readily apparent to those skilled in the art. Various modifications to these embodiments will be readily apparent to those skilled in the art. The general principles defined herein may be implemented in other embodiments without departing from the spirit or scope of the invention. Therefore, the present invention is not to be limited to the embodiments shown herein, but is to be accorded the widest scope consistent with the principles and novelty disclosed herein.

Claims

1. A low-heat-generating, high-elasticity tire sidewall rubber composition, characterized in that, It is prepared by mixing raw materials comprising the following components, based on 100 parts by weight of rubber component: 10–30 parts natural rubber; 20-40 parts of solution-polymerized styrene-butadiene rubber; 50–70 parts of butadiene rubber; 10–40 parts of silica; 30–60 parts carbon black; 1–5 parts of silane coupling agent; 3–10 parts of α-methylstyrene resin; The solution-polymerized styrene-butadiene rubber (SBR) is composed of a first SBR and a second SBR in a mass ratio of 1.5:1 to 1:1.

5. Both the first and second SBRs are unoil-extended rubbers. The styrene content is 20±1wt%, the vinyl content is 55±3wt%, the glass transition temperature is −35±2℃, and the weight-average molecular weight is 380–420 kg·mol⁻¹. -1 With 280–320 kg·mol -1 .

2. The low-heat-generating, high-elasticity tire sidewall rubber composition according to claim 1, characterized in that, It is prepared by mixing raw materials comprising the following components in parts by weight: 15–25 parts natural rubber; 25-35 parts of solution-polymerized styrene-butadiene rubber; 55–65 parts of butadiene rubber; 20–30 parts of silica; 35–50 parts carbon black; 2–4 parts of silane coupling agent; 4–8 parts of α-methylstyrene resin.

3. The low-heat-generating, high-elasticity tire sidewall rubber composition according to claim 1, characterized in that, The first and second solution-polymerized styrene-butadiene rubbers were BF2055H and BF2055L solution-polymerized styrene-butadiene rubbers produced by China Petroleum & Chemical Corporation (Sinopec). BF2055H: styrene content 20%, vinyl content 55%, unextended, Tg = -35℃, weight-average molecular weight 380–420 kg·mol⁻¹ -1 BF2055L: 20% styrene, 55% vinyl, unoiled, Tg = -35℃, weight-average molecular weight 280–320 kg·mol⁻¹ -1 The preferred mass ratio is 1.2:1 to 1:1.

2.

4. The low-heat-generating, high-elasticity tire sidewall rubber composition according to claim 1, characterized in that, Highly dispersed silica with a specific surface area (CTAB) ≥ 160 m² is selected. 2 / g, preferably CTAB is 180–195m 2 / g, BET is 195–210m 2 / g; The preferred BET specific surface area of ​​carbon black particles is 20-160m². 2 / g, more preferably 40-130m 2 / g, further preferably 50-120m 2 / g; more preferably, the carbon black is one or more of N134, N220, N234, N375 or N375, N330, N339, N347, N326; more preferably, the carbon black is N234 or N330.

5. The low-heat-generating, high-elasticity sidewall rubber composition according to claim 1, characterized in that, The silane coupling agent has the structural formula YR-Si(OR)3, where Y is an organic functional group and SiOR is a silaneoxy group; preferably, the silane coupling agent is selected from one or more of vinyltriethoxysilane, vinyltrimethoxysilane, vinyltri(β-methoxyethoxy)silane, bis-[γ-(triethoxysilyl)propyl]tetrasulfide, bis-propyltriethoxysilane disulfide, 3-(octanoylthio)propyltriethoxysilane and n-octyltriethoxysilane.

6. The low-heat-generating, high-elasticity sidewall rubber composition according to claim 1, characterized in that, The softening point of α-methylstyrene resin is 95–120℃, and the number average molecular weight is 1000–3000.

7. The low-heat-generating, high-elasticity tire sidewall rubber composition according to claim 1, characterized in that, The compounded raw materials also include activators, antioxidants, and vulcanizing agents; preferably, the activator includes 2-5 parts zinc oxide and 1-3 parts stearic acid; 2-4 parts antioxidant; the vulcanizing agent includes 1.0-3.0 parts insoluble sulfur and 1.0-2.0 parts accelerator; more preferably, the accelerator includes one or more of N-tert-butyl-2-benzothiazole sulfenamide or N-cyclohexyl-2-benzothiazole sulfenamide, diphenylguanidine accelerators, hexamethylenetetramine, 4,4′-dithiodimorpholine, and dicaprolactam disulfide.

8. A method for preparing the rubber composition according to any one of claims 1-7, characterized in that, The method includes the following steps: 1) The rubber, carbon black, silica and silane coupling agent are added to a mixer at 110–125°C and mixed for 50 seconds; 2) The temperature is raised to 145–148°C and the mixing continues for 40 seconds to form a masterbatch; 3) The masterbatch is cooled to 95–100°C and then sulfur and accelerator are added for final mixing.

9. Use of the rubber composition of any one of claims 1–7 in the manufacture of a low-heat-generating, highly elastic sidewall for automobile tires.

10. A tire, characterized in that, Its sidewall is obtained by vulcanization of the rubber composition described in any one of claims 1–7.

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