A tire cushion layer low deformation rubber composition based on bimodal ssbr, mixing method and tire

Abstract

This invention relates to the field of tire manufacturing technology, and more particularly to a low-deformation rubber composition for tire buffer layers based on bimodal SSBR, 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, 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. The mixing process is optimized to achieve efficient reaction and uniform distribution of SiO2 with the rubber. Experiments have shown that, without sacrificing hardness and handling performance, this composition can achieve tanδ (60℃) ≤0.071, M300 controlled at 6.8-7.2 MPa, and DIN abrasion ≤99 mm. 3 Compression permanent deformation ≤30%, flexural life >2.0×10 5 Its overall performance is significantly better than existing oil-filled buffer layer formulations, and it has excellent fuel efficiency, comfort, and process adaptability.

Description

Technical Field

[0001] This invention relates to the field of tire manufacturing technology, and in particular to a low deformation rubber composition for tire buffer layers based on bimodal SSBR, a mixing method, and a tire. Background Technology

[0002] The buffer layer (also known as the tread cushion or belt buffer) is located between the belt layer and the carcass ply. Its main function is to homogenize abrupt changes in belt layer stiffness, absorb radial impacts, and suppress stress concentration in the gaps. As vehicle operating conditions shift from traditional passenger cars to high-torque electric vehicles (EVs), the buffer layer must simultaneously withstand higher frequency compression-shear cycles and greater instantaneous deformation. EV tire compound engineers therefore face three major technical challenges: 1) Low heat generation: In long-range scenarios, the temperature rise of the buffer layer must be suppressed to protect the belt layer adhesive; 2) Low permanent deformation: High compression resilience can reduce the thickness decay of the cushion and maintain the tread profile; 3) Processing and green requirements: Reduce plasticizers and high-density fillers to lower VOCs and reduce weight.

[0003] An early published Chinese invention patent application, CN101735498A, disclosed the introduction of 7-50 phr of silica into a NR and modified BR system, which can reduce rolling loss and enhance fracture strength, and is suitable for multiple parts such as "buffer pads, tread base, and carcass bonding rubber". However, this solution relies on a high BR content to achieve fracture toughness, resulting in a compression set exceeding 35%, which does not meet the requirements of EVs for lateral stability and lightweighting.

[0004] Chinese invention patent application CN110466287A improves heat dissipation and puncture resistance by layering a multi-material buffer layer of "low-heat-generating rubber + nylon cloth" at the bottom of the tire crown. Although this structure reduces the crown temperature, most of the rubber still uses the NR / NBR + N330 carbon black system, and the tanδ (60℃) is still greater than 0.085. Moreover, the multi-layer lamination increases manufacturing complexity. Chinese invention patent application CN116144084B uses N-(carboxymethyl)maleic acid in synergy with TESPT to improve the dispersion of silica in the sidewall rubber, reducing tanδ to around 0.080. However, its rubber skeleton is a two-rubber system of 40-60 phr NR + 40-60 phr BR. The high glass transition temperature of BR (-50℃) results in a low dynamic modulus, and the compression set is still relatively large. Furthermore, maleic acid has a significant impact on scorch time, leading to poor batch stability.

[0005] In summary, existing Chinese patents still face the following common bottlenecks in achieving the triangular balance of "low heat generation - high elasticity - low permanent deformation" in buffer layer rubber compounds: 1) Filler oil migration - Most low heat generation formulations still rely on aromatics / paraffin oils to reduce viscosity. The oil phase is prone to migrating into the tire carcass under compression-shear, leading to a hysteresis-rebound increase; 2) Single-peak or low-vinyl polymers - The high Mw or low-vinyl S-SBR modulus-heat generation balance is limited, and there is insufficient synergy with silica; 3) High permanent deformation rate - The deformation of NR / BR-dominated systems after long-term compression at 70℃ is often >35%, which can easily lead to tire crown collapse and stress relaxation. Summary of the Invention

[0006] To address the aforementioned technical problems, the present invention aims to provide a low-deformation rubber composition for tire buffer layers based on bimodal SSBR. This composition achieves a breakthrough in all dimensions of "low heat generation, low deformation, and high elasticity" without the use of plasticizers or special high-priced fillers. Furthermore, it features a simple formulation, a wide process window, and is environmentally friendly, exhibiting significant advantages for industrialization.

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

[0008] A low-deformation rubber composition for tire buffer layers based on bimodal SSBR is prepared by compounding raw materials comprising the following components, based on 100 parts by weight of the rubber component:

[0009] 20–50 parts natural rubber;

[0010] 15–35 parts of first solution-polymerized styrene-butadiene rubber;

[0011] 15–35 parts of second solution-polymerized styrene-butadiene rubber;

[0012] 10–30 parts of high cis polybutadiene;

[0013] 15–35 parts of silica;

[0014] 10–30 parts carbon black;

[0015] 1–4 parts of silane coupling agent;

[0016] 3–8 parts of α-methylstyrene resin;

[0017] The mass ratio of the first solution-polymerized styrene-butadiene rubber (SBR) to the second solution-polymerized SBR is 1.5:1 to 1:1.5, and both are unoil-extended high-vinyl solution-polymerized SBRs. 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 .

[0018] Preferably, it is prepared by mixing raw materials comprising the following components in parts by weight:

[0019] 30–40 parts natural rubber;

[0020] 20–30 parts of first solution-polymerized styrene-butadiene rubber;

[0021] 20–30 parts of second solution-polymerized styrene-butadiene rubber;

[0022] 15–25 parts of high cis polybutadiene rubber;

[0023] 20–30 parts of silica;

[0024] 15–25 parts carbon black;

[0025] 2–3 parts of silane coupling agent;

[0026] 4–6 parts of α-methylstyrene resin.

[0027] 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 1.2:1–0.8:1.

[0028] Preferably, highly dispersed silica has a specific surface area (CTAB) ≥ 160 m². 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.

[0029] 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.

[0030] Preferably, the α-methylstyrene resin has a softening point of 95–120°C and a number-average molecular weight of 1000–3000.

[0031] 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.

[0032] Furthermore, the present invention also provides a mixing method for preparing the rubber composition, the method comprising the following steps:

[0033] (1) At 110–125℃, natural rubber, first solution polymerized styrene-butadiene rubber, second solution polymerized styrene-butadiene rubber, high cis polybutadiene, and all silica, carbon black, and silane coupling agent are put into a mixer at once and mixed for 50 seconds.

[0034] (2) Raise the mixing temperature to 145–148℃, continue mixing for 40 seconds, add α-methylstyrene resin and discharge to obtain masterbatch.

[0035] (3) Cool the masterbatch to 95–100°C, add sulfur and accelerator, and finally mix in an internal mixer or open mill for 60 seconds.

[0036] (4) Press and vulcanize at 165–175℃ for 12–18 min.

[0037] Furthermore, the present invention also provides the use of the rubber composition in the manufacture of tire cushioning layers.

[0038] Furthermore, the present invention also provides a tire in which the tire cushioning layer is obtained by vulcanizing the rubber composition.

[0039] This invention, by employing the aforementioned technical solution, utilizes BF2055H / BF2055L series solution-polymerized styrene-butadiene rubber with a bimodal molecular weight structure, a vinyl content of 55%, and no filler oil, combined with highly dispersed silica, carbon black, appropriate amounts of α-methylstyrene resin, and silane coupling agent Si69, to construct a low-deformation rubber composition for tire cushioning layers. Its specific technical effects are as follows:

[0040] 1. Heat generation is significantly reduced, and rolling energy consumption decreases accordingly.

[0041] By using a completely unoiled bimodal SSBR with a vinyl content of 55% (Mw_H≈400 kg·mol⁻¹) -1 / Mw_L≈300kg·mol -1 In addition, it is synergistically reinforced with silica. The hysteresis factor tanδ of the buffer adhesive of this invention under RPA 60℃ and 10Hz conditions is only 0.068–0.071. Goodrich test (100℃, 0.7MPa, 30min) shows that the steady-state temperature rise is significantly lower than that of the traditional oil-extended system.

[0042] 2. The compression set is significantly reduced, and the tire crown profile remains stable over the long term.

[0043] The bimodal segment distribution allows the high-Mw segments to form the skeleton and the low-Mw segments to fully wet the filler. The 300% constant tensile stress M300 can be stabilized at 6.0–7.2 MPa. Under ASTM D395-B conditions (70℃, 24h), the compression set is controlled at 28–30%, which significantly inhibits pad collapse and stress relaxation compared to rubber compounds using unimodal star-shaped SSBR or NR / BR systems.

[0044] 3. Low initial modulus ensures comfort, while high dynamic modulus ensures stable handling.

[0045] The initial modulus M10 of the buffer rubber of this invention is only 0.37–0.39 MPa, which can absorb the impact of the tire crown and reduce tire noise; while the α-methylstyrene resin and high Mw SSBR jointly build a high-frequency modulus platform, so that the dynamic support does not decrease but increases, and meets the geometric stability of the tire crown under high-speed conditions.

[0046] 4. Significantly improved flexural fatigue life

[0047] De-Mattia crack propagation tests show that the average lifespan of the buffer adhesive of this invention is >2.2 × 10⁻⁶. 5 Secondly, it improves tire life by at least 35% compared to oil-filled / monotropic rubber systems.

[0048] In summary, this invention achieves a comprehensive performance breakthrough in low heat generation, low deformation, high resilience, high fatigue life, and environmentally friendly manufacturing without increasing processing viscosity or manufacturing costs. It solves the industry pain point of existing buffer layer rubber materials that are difficult to balance "heat generation, deformation, and processing". It can be directly applied to high-end product lines for passenger car tires, SUV tires, and tires for new energy vehicles, and has significant energy-saving and safety value. Detailed Implementation

[0049] 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.

[0050] I. Main Raw Materials and Models

[0051]

[0052] II. Formulation Design (PHR)

[0053] The following provides formulations for 3 examples (E-1 to E-3) and 5 comparative examples (C-1 to C-5), with the oil-extended raw materials subtracted from the oil-extended content (unit: phr).

[0054] Components E-1 E-2 E-3 C-1 C-2 C-3 C-4 C-5 SMR-20 40 45 30 40 40 40 40 40 BF2055H 22 20 23 20 — — — — BF2055L 18 15 17 20 — — — — Star-V55 — — — — 40 — — — OS-4712 — — — — — 40 — — OS-3720 — — — — — — 40 — Milk Polymer 1502 — — — — — — — 40 BR-9000 20 20 30 20 20 20 20 20 Processing oil — — — 25 — — — — Ultrasil 7800 25 30 22 25 25 25 25 25 Carbon Black N330 25 20 28 25 25 25 25 25 Si69 3 3 3 3 3 3 3 3 α-MPS resin 5 6 7 5 5 5 5 5

[0055] In addition to the listed components, ZnO (3 phr), stearic acid (2 phr), 6PPD (2 phr), TMQ (1 phr), TBBS (1 phr), DPG (0.3 phr), and insoluble sulfur OT-20HD (1.3 phr) are the same in all rubber compounds and are not included in the rubber 100 phr.

[0056] Comparison of different types

[0057] C-1 (Old-style oil diffuser): Oil-free SSBR + 25 phr paraffin oil plus

[0058] C-2 (Single-peak star configuration): Star-V55 only, no BF2055L.

[0059] C-3 (Oil-filled, high-vinyl): All OS-4712 (55% vinyl, comes with 25 phr oil)

[0060] C-4 (Low Vinyl Filled): All OS-3720 (37% Vinyl, comes with 22 phr oil)

[0061] C-5 (Emulsion Polymer SBR): Solution Polymer SBR is replaced with 1502.

[0062] III. The mixing process adopts a two-stage mixing process.

[0063]

[0064] IV. Test Methods and Conditions

[0065]

[0066]

[0067] Unified vulcanization and temperature control conditions: ① All rubber compounds are vulcanized on a flat plate at 170℃±2℃ for 15min; ② After vulcanization, the samples are placed in an environment of 23℃±2℃ and 50%±5%RH for 24h, and then the samples are prepared and tested according to the table above.

[0068] V. Test Experiment Data

[0069] The table below lists the complete mechanical and dynamic test data for three examples (E-1 to E-3) and five comparative examples (C-1 to C-5). All data are average values ​​obtained from testing 3-5 samples (3 205 / 55R16 solid tires for rolling resistance) from the same batch of formulations, with the standard deviation in parentheses being 1σ.

[0070]

[0071]

[0072] Note: "Lifetime" refers to the number of cycles required for a crack to extend to 1 mm.

[0073] VI. Conclusions of Experimental Data Analysis

[0074] 1. Low heat generation advantage

[0075] In the example, tanδ was reduced to 0.068–0.071, which is at least about 27% lower than that of the old oil-expanded C-1 and oil-filled high-vinyl C-3, and the Goodrich temperature rise was reduced by at least 6–10°C.

[0076] 2. Elastic-deformation equilibrium

[0077] In the examples, M10 maintained 0.37–0.39 MPa (compliance and noise reduction), while M300 maintained 6.8–7.2 MPa; the compression set was ≤30%. Although Comparative Example C-5 had the highest hardness, it had the worst M300 and durability due to the loose network of the emulsion polymer structure.

[0078] 3. Durability and wear resistance

[0079] Example: DIN wear < 100mm3 E-1 showed an improvement of 2.9–13.5% compared to the comparative formulation; the flexural life of the examples was >2.0 × 10⁻⁶. 5 E-1 improves the ratio by 35–64% compared to the control, significantly enhancing the crack resistance and fatigue resistance of the buffer layer.

[0080] 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-deformation rubber composition for tire buffer layers based on bimodal SSBR, characterized in that, It is prepared by mixing raw materials comprising the following components, based on 100 parts by weight of rubber component: 20–50 parts natural rubber; 15–35 parts of first solution-polymerized styrene-butadiene rubber; 15–35 parts of second solution-polymerized styrene-butadiene rubber; 10–30 parts of high cis polybutadiene; 15–35 parts of silica; 10–30 parts carbon black; 1–4 parts of silane coupling agent; 3–8 parts of α-methylstyrene resin; The mass ratio of the first solution-polymerized styrene-butadiene rubber (SBR) to the second solution-polymerized SBR is 1.5:1 to 1:1.5, and both are unoil-extended high-vinyl solution-polymerized SBRs with a styrene content of 20±1wt%, a vinyl content of 55±3wt%, a glass transition temperature of −35±2℃, and a weight-average molecular weight of 380–420 kg·mol⁻¹. -1 With 280–320 kg·mol -1 .

2. The low-deformation rubber composition for tire buffer layers based on bimodal SSBR according to claim 1, characterized in that, It is prepared by mixing raw materials comprising the following components in parts by weight: 30–40 parts natural rubber; 20–30 parts of first solution-polymerized styrene-butadiene rubber; 20–30 parts of solution-polymerized styrene-butadiene rubber; 15–25 parts of high-cis polybutadiene rubber; 20–30 parts of silica; 15–25 parts carbon black; 2–3 parts of silane coupling agent; 4–6 parts of α-methylstyrene resin.

3. The low-deformation rubber composition for tire buffer layers based on bimodal SSBR 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 1.2:1–0.8:

1.

4. The low-deformation rubber composition for tire buffer layers based on bimodal SSBR according to claim 1, characterized in that, Highly dispersed silica with a specific surface area (CTAB) ≥ 160 m² 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-deformation rubber composition for tire buffer layers based on bimodal SSBR 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-deformation rubber composition for tire buffer layers based on bimodal SSBR 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-deformation rubber composition for tire buffer layers based on bimodal SSBR 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) At 110–125°C, natural rubber, first solution-polymerized styrene-butadiene rubber, second solution-polymerized styrene-butadiene rubber, high cis polybutadiene, and all silica, carbon black, and silane coupling agent are added to a mixer and mixed for 50 seconds; (2) The mixing temperature is raised to 145–148°C and mixed for another 40 seconds. After adding α-methylstyrene resin, the mixture is discharged to obtain the masterbatch; (3) The masterbatch is cooled to 95–100°C, sulfur and accelerator are added, and the mixture is finally mixed in a mixer or open mill for 60 seconds; (4) The mixture is pressed into sheets and vulcanized at 165–175°C for 12–18 minutes.

9. Use of the rubber composition of any one of claims 1–7 in the manufacture of a tire cushioning layer.

10. A tire, characterized in that, The tire cushioning layer is obtained by vulcanizing the rubber composition described in any one of claims 1–7.

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