Flame-retardant sidewall rubber composition, mixing method thereof and tire

Abstract

The invention relates to the technical field of rubber manufacturing, and discloses a flame-retardant sidewall rubber composition, a mixing method thereof and a tire. In a common diene rubber system, chlorinated polyethylene is added with a small amount of zinc salt flame retardant and ceramic microbeads, so that the flame retardant property of the rubber composition can be effectively improved, the use of high-toxicity hazardous chemicals containing halogen compounds such as bromine and chlorine is avoided, and the emission of VOC (Volatile Organic Compounds) is reduced; meanwhile, the lubricity of natural paraffin and the polarity and elasticity of chlorinated polyethylene are used as polymer compatilizers, so that the dispersity of the zinc salt flame retardant and the ceramic microbeads in the rubber is effectively improved, and the process dispersion problem caused by the use of inorganic flame retardants such as high-content antimony trioxide and the problem of performance degradation of the rubber composition are avoided; therefore, the flame-retardant rubber composition which is low in smoke, low in toxicity and efficient in flame retardance is comprehensively realized, and industrialization can be realized.

Description

Technical Field

[0001] This invention relates to the field of tire rubber manufacturing technology, and more specifically, to a flame-retardant sidewall rubber composition, its mixing method, and a tire. Background Technology

[0002] As a key component of a vehicle that contacts the road surface and bears the load, the tire sidewall is subjected to a coupled condition of "alternating flexure - thermo-oxygen environment - external oxygen supply" during its service life. On the one hand, the tire sidewall repeatedly bends and deforms during rolling, generating hysteretic heat. Especially in scenarios such as heavy loads, high speeds, continuous braking on long downhill slopes, high-temperature roads in summer, and mining / hazardous chemical transportation, the local temperature rise of the tire sidewall is more likely to accumulate. On the other hand, the tire sidewall is directly exposed to the air, and the combined effect of oxygen and heat can accelerate the thermo-oxygen aging of rubber and crack propagation. In extreme cases, it may also induce combustion or smoldering under external fire sources, friction sparks, electric arcs, or abnormal overheating conditions. Traditional tire sidewall rubbers mostly use diene rubbers such as natural rubber (NR) and butadiene rubber (BR) as the main body, reinforced with carbon black and vulcanized with sulfur system. This system has mature advantages in terms of flexural resistance, tear resistance, and dynamic fatigue. However, diene rubber itself has high flammability, and carbon black easily produces sparks and smoke when burning, resulting in insufficient safety redundancy of the tire sidewall under fire or thermal runaway conditions. Therefore, improving flame retardancy / self-extinguishing ability without significantly sacrificing the dynamic fatigue, mechanical and processing properties of the sidewall rubber, and meeting the consistency and environmental compliance requirements of industrial continuous mixing, has become an important research direction in the field of tire materials.

[0003] In existing technologies, flame retardant modification of tire rubber typically employs the following approaches: First, introducing halogenated flame retardants in conjunction with synergists such as antimony trioxide to improve flame retardancy through gas-phase blocking and condensed-phase charring / insulation; second, using borates (such as zinc borate) in synergy with halogenated flame retardants and antimony trioxide to improve smoke suppression and charring; and third, improving the material's flame retardancy through highly polar or bulk-flame-retardant elastomers / rubbers (such as chlorinated or fluorinated elastomers), or achieving flame retardancy through the endothermic decomposition of a large amount of inorganic flame-retardant fillers. However, in engineering applications of the above solutions in the high-dynamic-fatigue part of tire sidewall rubber, multiple objectives often conflict, including flame retardant efficiency, mechanical / fatigue properties, processing dispersion, environmental compliance, and cost, making it difficult to balance comprehensive performance with large-scale manufacturing.

[0004] For example, existing patent document CN104311909A discloses a fire-resistant and flame-retardant tire rubber composition. The idea is to use an additional amount of flame retardant compared to ordinary tire rubber compounds to improve fire resistance and flame retardancy. In the examples, a flame-retardant coating / flame-retardant system composed of decabromodiphenyl ether, antimony trioxide, and zinc borate is used. Simultaneously, the raw rubber system, filler system, and protective system are adjusted to meet tire performance requirements. The advantages of this type of solution are the maturity of the flame-retardant system and the direct improvement in oxygen index and flame retardancy rating. However, its engineering application often has two potential risks: First, halogenated flame retardants and antimony trioxide systems may bring high smoke density and corrosive products during combustion or thermal decomposition, and some halogenated flame-retardant systems are more sensitive to environmental regulations and supply chain management. Second, the use of flame retardants with multiple inorganic powders places higher demands on mixing and dispersion. Uneven dispersion can easily form stress concentration points, thus adversely affecting the flexural crack resistance and dynamic fatigue life of the sidewall rubber. In other words, although this type of solution can improve flame retardancy, its long-term reliability and batch consistency still need further optimization in the application scenarios of "high flexibility and high durability" of tire sidewall rubber.

[0005] For example, the existing patent document CN117801387A discloses a sidewall rubber for a flame-retardant tire used in underground coal mines and its preparation method. In addition to NR and BR, its formulation system may also include styrene-butadiene rubber and MCSM rubber, and uses flame-retardant materials such as chlorinated paraffin, decabromodiphenyl ether, antimony trioxide, and zinc borate. The preparation process of masterbatch mixing and final mixing is given, aiming to increase the oxygen index of the sidewall rubber to more than 22% while taking into account properties such as ozone aging resistance and flexural crack resistance. This technology targets scenarios with higher flame retardant requirements, such as underground coal mines, and enhances the superposition and synergy of flame retardant materials. However, it can also be observed that it is dependent on halogenated flame retardants (such as decabromodiphenyl ether) and chlorinated paraffin systems. The formulation contains a variety of flame retardant components with a wide range of dosages, which may lead to fluctuations in the viscoelastic properties of the rubber compound, increased difficulty in controlling odor / VOC, and a narrowing of the mixing and dispersion window. In addition, the superposition of multiple powders and plasticizing components may also cause increased dispersion of mechanical properties and fatigue properties under different batches or equipment conditions, thereby increasing the difficulty of industrial-scale stable control.

[0006] For example, existing patent document CN104927110B discloses a flame-retardant rubber composition and its application. Without using decabromodiphenyl ether, it employs decabromodiphenyl ethane, antimony trioxide, and red phosphorus to synergistically enhance the flame-retardant properties of rubber. It proposes that this flame-retardant rubber can be used in tire manufacturing, enabling the prepared rubber to self-extinguish upon contact with open flame. This approach involves some adjustments to the material selection compared to the decabromodiphenyl ether route, but it still falls within the typical flame-retardant framework of "halogenated flame retardant + antimony synergist (and the introduction of phosphorus-based synergists)". While such systems may achieve high flame-retardant efficiency for tire sidewall rubber, red phosphorus components typically require higher standards in terms of processing safety, stability, and dispersion control. Furthermore, without specific interface control and dispersion strategies for dynamic fatigue of the sidewall, the halogen / antimony / phosphorus multi-component synergistic system may still cause problems such as decreased flexural performance or accelerated crack propagation, which is detrimental to the long-term service reliability of the sidewall.

[0007] In summary, the existing technologies closest to this invention generally adopt the route of "halogenated flame retardants, antimony trioxide, and borates" or superimposed with chlorinated paraffin and phosphorus-based flame retardant components to improve the flame retardant performance of tire rubber compounds (especially sidewall rubber). Although this route has a more direct flame retardant effect, it may still face the following technical challenges in the industrial application of tire sidewalls: (1) It is difficult to balance environmental protection with low smoke and low toxicity goals: Halogen / antimony systems have potential disadvantages in terms of smoke density, corrosive gases, odor, and compliance management, making it difficult to meet the development trend of "low smoke, low toxicity, low corrosion, and low VOC"; (2) The contradiction between dispersion and fatigue durability is prominent: Sidewall rubber is extremely sensitive to dynamic flexure, and the superposition of multiple inorganic powders and flame retardants can easily cause agglomeration and stress concentration, leading to a reduction in fatigue life. 1. Increased risk of cracking and increased difficulty in batch stability control; (3) Narrowing processing window and challenges to industrial consistency: There are many types of flame retardant systems and the complex combination of fillers and plasticizers, which makes the mixing temperature, stage sequence, discharge temperature and final mixing temperature more sensitive, and performance dispersion is more likely to occur when scaled up to different machines and different production lines; (4) Cost and compatibility issues: High flame retardant rating often means higher flame retardant dosage and more complex formulation structure, which may cause material cost to rise and affect the matching of vulcanization system and comprehensive physical property balance of tire sidewall rubber.

[0008] Therefore, the industry urgently needs a safer and industrially feasible flame-retardant reinforcement strategy in traditional general-purpose diene rubber systems such as NR / BR. This strategy aims to reduce dependence on typical high-halogen / high-antimony systems while further resolving the contradiction between the dispersion stability of flame-retardant fillers and the maintenance of sidewall flexural fatigue performance. Furthermore, it requires a matching method for controlling the mixing sequence and temperature window in continuous internal / open mixing production to achieve the comprehensive goal of "significant flame retardant effect, no significant decrease in mechanical / fatigue properties, controllable process, and environmental friendliness" for tire sidewall rubber. These problems and needs constitute the technical background and improvement direction of this invention. Summary of the Invention

[0009] The purpose of this invention is to provide an industrially prepared flame-retardant sidewall rubber composition and its mixing method, and to apply it to the sidewall of all-steel radial tires. In a conventional sidewall rubber system mainly composed of natural rubber / butadiene rubber, by combining CPE, zinc salt flame retardant and ceramic microspheres with a segmented mixing process, the flame retardant performance is significantly improved without significantly reducing the mechanical properties and flexural fatigue performance of the sidewall rubber, and the dependence on smoke toxicity and harmful flame retardants is reduced, thereby improving the safety and reliability of tires under high temperature, open flame or high-risk transportation conditions.

[0010] To achieve the above objectives, the present invention adopts the following technical solution: A flame-retardant tire sidewall rubber composition, said rubber composition is prepared by mixing raw materials comprising the following components based on 100 parts by weight of raw rubber: Natural rubber 40-60 phr Butadiene rubber 40-60 phr Carbon black 10-20 phr 30-40 phr of silica Silane 2.0-4.0 phr, Chlorinated polyethylene (CPE) 20-80 phr Natural paraffin wax 1.0-5.0 phr Ceramic microspheres 2.0-10 phr Zinc salt flame retardant 5.0-10 phr.

[0011] Preferably, the rubber composition is prepared by mixing raw materials comprising the following components based on 100 parts by weight of raw rubber: Natural rubber 45-55 phr Butadiene rubber 45-55 phr Carbon black 10-20 phr 30-40 phr of silica Silane 2.0-4.0 phr, Chlorinated polyethylene (CPE) 40-80 phr Natural paraffin wax 1.0-5.0 phr Ceramic microspheres 2.0-10 phr Zinc salt flame retardant 5.0-10 phr.

[0012] Furthermore, the rubber composition is prepared by mixing the following components: Softener 10.0-13.0 phr, Protective wax 1.5-2.5 phr Anti-aging agent 2.5-6.0 phr, Activator 4.0-6.0 phr, Vulcanizing agent 1.0-2.0 phr, Accelerator 0.6-1.8 phr.

[0013] Preferably, the zinc salt flame retardant is a mixture of boron trioxide and zinc oxide in a ratio of 2:1 to 1:1.

[0014] Preferably, the ceramic microspheres are made of silica-alumina ceramic with a D50 ≤ 10 μm.

[0015] Preferably, the chlorinated polyethylene (CPE) has a chlorine content of 25%-45%; more preferably, it has a chlorine content of 30%-40%.

[0016] Preferably, the carbon black is N3 series or N2 series carbon black; N330 or N375 carbon black is preferred.

[0017] Preferably, the silica is silica 165, silica 175, or highly dispersed silica.

[0018] Preferably, the raw materials for the rubber products of the present invention also include silane coupling agents. Examples of silane coupling agents include sulfide-based, polysulfide-based, thioester-based, thiol-based, olefin-based, epoxy-based, amino-based, and alkyl-based silane coupling agents. These can be used individually or in combination of two or more. Among these, sulfide-based silane coupling agents and amino-based silane coupling agents are preferred.

[0019] Examples of silane coupling agents based on sulfide systems include: bis(3-triethoxysilylpropyl)tetrasulfide, bis(3-trimethoxysilylpropyl)tetrasulfide, bis(3-methyldimethoxysilylpropyl)tetrasulfide, bis(2-triethoxysilylethyl)tetrasulfide, bis(3-triethoxysilylpropyl)disulfide, bis(3-trimethoxysilylpropyl)disulfide, bis(3-methyldimethoxysilylpropyl)disulfide, bis(2-triethoxysilylethyl)disulfide, bis(3-triethoxysilylpropyl)trisulfide, bis(3-triethoxysilylpropyl)trisulfide, bis(3-trimethoxysilylpropyl)trisulfide, and bis(3-methyldimethoxysilylpropyl)tetrasulfide. Bis(2-triethoxysilylethyl) trisulfide, bis(3-monoethoxydimethylsilylpropyl) tetrasulfide, bis(3-monoethoxydimethylsilylpropyl) trisulfide, bis(3-monoethoxydimethylsilylpropyl) disulfide, bis(3-monoethoxydimethylsilylpropyl) tetrasulfide, bis(3-monoethoxydimethylsilylpropyl) trisulfide, bis(3-monoethoxydimethylsilylpropyl) disulfide, bis(3-monoethoxydimethylsilylpropyl) disulfide, bis(2-monoethoxydimethylsilylethyl) tetrasulfide, bis(2-monoethoxydimethylsilylethyl) trisulfide, bis(2-monoethoxydimethylsilylethyl) disulfide, etc. Among these, bis(3-triethoxysilylpropyl) tetrasulfide is preferred.

[0020] Examples of thioester-based silane coupling agents include 3-hexanoylthiopropyltriethoxysilane, 3-octanoylthiopropyltriethoxysilane, 3-decanoylthiopropyltriethoxysilane, 3-lauroylthiopropyltriethoxysilane, 2-hexanoylthioethyltriethoxysilane, 2-octanoylthioethyltriethoxysilane, 2-decanoylthioethyltriethoxysilane, and 2-lauroylthio... Ethyltriethoxysilane, 3-hexanoylthiopropyltrimethoxysilane, 3-octanoylthiopropyltrimethoxysilane, 3-decanoylthiopropyltrimethoxysilane, 3-lauroylthiopropyltrimethoxysilane, 2-hexanoylthioethyltrimethoxysilane, 2-octanoylthioethyltrimethoxysilane, 2-decanoylthioethyltrimethoxysilane, 2-lauroylthioethyltrimethoxysilane, etc.

[0021] Examples of thiol-based silane coupling agents include 3-mercaptopropyltrimethoxysilane, 3-mercaptopropyltriethoxysilane, and 3-mercaptopropylmethyldimethoxysilane.

[0022] Examples of olefin-based silane coupling agents include dimethoxymethylvinylsilane, vinyltrimethoxysilane, dimethylethoxyvinylsilane, diethoxymethylvinylsilane, triethoxyvinylsilane, vinyltris(2-methoxyethoxy)silane, allyltrimethoxysilane, allyltriethoxysilane, p-styryltrimethoxysilane, 3-(methoxydimethoxydimethylsilyl)propyl acrylate, 3-(trimethoxysilyl)propyl acrylate, 3-[dimethoxy(methyl)silyl]propyl methacrylate, 3-(trimethoxysilyl)propyl methacrylate, 3-[dimethoxy(methyl)silyl]propyl methacrylate, 3-[triethoxysilyl]propyl methacrylate, and 3-[tris(trimethylsiloxy)silyl]propyl methacrylate.

[0023] Examples of epoxy-based silane coupling agents include 3-epoxypropoxypropyl(dimethoxy)methylsilane, 3-epoxypropoxypropyltrimethoxysilane, diethoxy(3-epoxypropoxypropyl)methylsilane, triethoxy(3-epoxypropoxypropyl)silane, and 2-(3,4-epoxycyclohexyl)ethyltrimethoxysilane.

[0024] Examples of amino-based silane coupling agents include N-2-(aminoethyl)-3-aminopropylmethyldimethoxysilane, N-2-(aminoethyl)-3-aminopropyltrimethoxysilane, 3-aminopropyltrimethoxysilane, 3-aminopropyltriethoxysilane, 3-ethoxysilyl-N-(1,3-dimethylbutylene)propylamine, N-phenyl-3-aminopropyltrimethoxysilane, and N-(vinylbenzyl)-2-aminoethyl-3-aminopropyltrimethoxysilane. Among these, 3-aminopropyltriethoxysilane is preferred.

[0025] Examples of alkyl-based silane coupling agents include methyltrimethoxysilane, dimethyldimethoxysilane, trimethylmethoxysilane, methyltriethoxysilane, ethyltrimethoxysilane, n-propyltrimethoxysilane, isobutyltrimethoxysilane, isobutyltriethoxysilane, n-hexyltrimethoxysilane, n-hexyltriethoxysilane, cyclohexylmethyldimethoxysilane, n-octyltriethoxysilane, and n-decyltrimethoxysilane.

[0026] Among these silane coupling agents, one or more of Si69, Si-75, and mercaptosilanes are particularly preferred.

[0027] Preferably, the softener is one or two of aromatic oil, tert-butylphenol resin, and octylphenol resin.

[0028] Preferably, the activator is stearic acid and zinc oxide.

[0029] Preferably, the raw materials for the rubber products of the present invention also include a vulcanizing agent, which can be combined with an organic peroxide or a sulfur-based vulcanizing agent. Examples of organic peroxides include benzoyl peroxide, dicumyl peroxide, di-tert-butyl peroxide, tert-butylcumyl peroxide, methyl ethyl ketone peroxide, cumene hydroperoxide, 2,5-dimethyl-2,5-di(tert-butylperoxide)hexane, 2,5-dimethyl-2,5-di(benzoyl peroxide)hexane, 2,5-dimethyl-2,5-di(tert-butylperoxide)hexyn-3, 1,3-bis(tert-butylperoxidepropyl)benzene, di-tert-butylperoxide diisopropylbenzene, tert-butylperoxidebenzene, 2,4-dichlorobenzoyl peroxide, 1,1-di-tert-butylperoxide-3,3,5-trimethylsiloxane, and 4,4-di-tert-butylperoxyvalerate n-butyl ester. Among these organic peroxides, dicumyl peroxide, tert-butyl peroxide, and di-tert-butyl peroxide diisopropylbenzene are preferred. Additionally, sulfur, morpholine disulfide, etc., can be used as sulfur-based vulcanizing agents. Sulfur is preferred among these sulfur-based vulcanizing agents.

[0030] Preferably, the raw materials of the rubber products of the present invention also include accelerators that can be combined with sulfenamide, thiazole, thiuram, thiourea, guanidine, dithiocarbamate, aldehyde-amine, or aldehyde-amine systems, etc.

[0031] Examples of sulfonamide compounds include CBS (N-cyclohexyl-2-benzothiazolyl sulfonamide), TBBS (N-tert-butyl-2-benzothiazolyl sulfonamide), N,N-dicyclohexyl-2-benzothiazolyl sulfonamide, N-oxodiethylidene-2-benzothiazolyl sulfonamide, and N,N-diisopropyl-2-benzothiazolyl sulfonamide.

[0032] Examples of thiazole derivatives include MBT (2-mercaptobenzothiazole), MBTS (dibenzothiazolium disulfide), sodium salts, zinc salts, copper salts, cyclohexylamine salts of 2-mercaptobenzothiazole, 2-(2,4-dinitrophenyl)mercaptobenzothiazole, and 2-(2,6-diethyl-4-morpholinothio)benzothiazole.

[0033] Examples of thiuram derivatives include TMTD (tetramethylthiuram disulfide), tetraethylthiuram disulfide, tetramethylthiuram monosulfide, diamylenethiuram disulfide, diamylenethiuram monosulfide, diamylenethiuram tetrasulfide, diamylenethiuram hexasulfide, tetrabutylthiuram disulfide, and diamylenethiuram tetrasulfide.

[0034] Examples of thiourea compounds include thiourea compounds such as thiouramide, diethylthiourea, dibutylthiourea, trimethylthiourea, and di-o-tolylthiourea.

[0035] Examples of guanidine compounds include diphenylguanidine, di-o-toluidine, triphenylguanidine, o-toluidine, and diphenylguanidine phthalate.

[0036] Examples of dithiocarbamate compounds include zinc ethylphenyl dithiocarbamate, zinc butylphenyl dithiocarbamate, sodium dimethyl dithiocarbamate, zinc dimethyl dithiocarbamate, zinc diethyl dithiocarbamate, zinc dibutyl dithiocarbamate, zinc dipentyl dithiocarbamate, zinc dipropyl dithiocarbamate, a coordination salt of zinc pentamethylene dithiocarbamate and piperidine, zinc hexadecyl isopropyl dithiocarbamate, zinc octadecyl isopropyl dithiocarbamate, zinc dibenzyl dithiocarbamate, sodium diethyl dithiocarbamate, piperidine pentamethylene dithiocarbamate, selenium dimethyl dithiocarbamate, tellurium diethyl dithiocarbamate, and cadmium dipentyl dithiocarbamate.

[0037] Examples of aldehyde-amine or aldehyde-amine compounds include acetaldehyde-aniline reactants, butyraldehyde-aniline condensates, hexamethylenetetramine, and acetaldehyde-amine reactants.

[0038] Among these accelerators, accelerator NS, accelerator CZ, or a mixture of the two are particularly preferred.

[0039] Furthermore, the present invention also provides a method for preparing the rubber composition, comprising the following steps: 1) First stage of mixing: Add natural rubber, zinc salt flame retardant, ceramic microspheres, and 1 / 2 chlorinated polyethylene, press and hold for 30-40 seconds, lift and clean, add carbon black, press and mix again, and discharge the glue at 145-155℃. 2) Second stage mixing: Add the first stage compound, butadiene rubber, the remaining chlorinated polyethylene, natural paraffin, silica and silane, press and mix to 120℃-130℃, add softener and other compounding agents (except vulcanizing agent and accelerator), press and mix for 25-35s, lift and clean, then press and mix again to 145℃-155℃ to discharge the rubber; 3) Third stage mixing: Add the second stage compound, vulcanizing agent, and accelerator, press and hold for 30-40 seconds, lift and clean, press and hold for another 30-40 seconds, lift and clean, and then press and mix to 105-115℃ for discharge.

[0040] Preferably, the first, second, and third mixing stages are completed in an internal mixer, and after each stage of rubber discharge, the mixture is passed through a two-roll mill, pressed into sheets, and cooled before entering the next mixing stage.

[0041] Preferably, the vulcanization conditions of the rubber composition are 140-160°C for 15-30 minutes.

[0042] Furthermore, the present invention also provides an all-steel radial tire, comprising a crown, a shoulder, a sidewall, a belt layer, a crown belt layer, and a ply layer, wherein the sidewall is prepared by vulcanization of the rubber composition described above.

[0043] This invention, by synergistically introducing chlorinated polyethylene (CPE), zinc salt flame retardants (such as boron trioxide / zinc oxide systems), and fine-particle-size silica-alumina ceramic microspheres into a conventional NR / BR sidewall rubber system, and combining this with a three-stage mixing process and temperature window control, achieves more uniform and stable dispersion and interfacial bonding of the flame-retardant components in the rubber compound. This significantly improves the flame-retardant self-extinguishing ability and oxygen index (in the examples, the oxygen index can be increased to approximately 25%–26% or more) of the sidewall rubber without relying on highly toxic or heavily regulated halogenated flame retardants or antimony trioxide and other traditional systems. Furthermore, it maintains mechanical properties comparable to ordinary sidewall rubber in terms of constant tensile stress and tensile strength. The strength and elongation at break are high, while ensuring excellent dynamic flexural fatigue resistance (achieving 1 million flexes without cracking within a reasonable CPE content window), avoiding fatigue degradation and processing fluctuations caused by relying solely on high CPE content or high filler for flame retardancy. In addition, the polarity / lubrication synergy of natural paraffin and CPE reduces the difficulty of mixing and dispersion, improves the processing stability and batch consistency of the rubber compound, and helps reduce smoke and harmful volatile emissions, enabling the prepared flame-retardant sidewall rubber to meet the requirements of continuous industrial tire production, significantly improving the safety and reliability of all-steel radial tires under heavy load, high temperature, open flame, or high-risk transportation conditions. Detailed Implementation

[0044] The following examples and comparative examples illustrate the implementability and repeatability of the technical solution of the present invention. Those skilled in the art can use this information to complete formula selection, mixing, vulcanization, and performance verification without any inventive effort. It should be understood that the examples described are for illustrative purposes only and do not constitute a limitation on the scope of protection; equivalent substitutions or conventional adjustments (e.g., minor adjustments to rotation speed and filling coefficient due to differences in equipment volume) made within the raw material range and process window defined by the present invention should all fall within the scope of protection of the present invention.

[0045] I. Explanation of Terms and Parameters phr: A unit of measurement for the amount of raw rubber used in a compounding process based on 100 parts by weight of raw rubber (natural rubber + butadiene rubber totals 100 phr).

[0046] CPE: Chlorinated polyethylene. The chlorine content of the CPE used in the examples / comparative examples is 30%–40%.

[0047] Zinc salt flame retardant: a mixture of boron trioxide (B2O3) and zinc oxide (ZnO); in this embodiment, B2O3:ZnO = 2:1 (by weight).

[0048] Ceramic microspheres: silica alumina ceramic microspheres, with particle size characterized by D50. In the examples, D50 ≤ 10 μm was used.

[0049] Carbon Black N375: The carbon black in Table 1 is uniformly N375 (belonging to the N3 series).

[0050] Silanes: Silanes in Table 1 are 2.0–3.0 phr (which may correspond to Si69, Si-75 or mercaptosilane, etc.).

[0051] Accelerators: The amount of accelerators in Table 1 is 0.8–1.6 phr (NS, CZ or a combination thereof can be selected).

[0052] II. Raw Materials and Compounding Agents Except for the quantities specified in Table 1, all other materials are from conventional industrial sources and only need to meet the requirements for tire adhesives. Natural rubber (NR): such as SCR5 / 10 tire grade; Butadiene rubber (BR): such as the BR9000 series and other tire grades; Silica: such as silica 165 / 175 or highly dispersed silica (specific dosages are given in Table 1); Softener: 2–12.5 phr in Table 1 (can be aromatic oil or phenolic resin softening system); Antioxidant: Antioxidant 4020 and antioxidant RD are used in combination (dosage given in Table 1); Activator: stearic acid + zinc oxide (dosage given in Table 1); Vulcanization system: sulfur + accelerator (dosage given in Table 1).

[0053] III. Formulations of Examples and Comparative Examples (I) Explanation of Formulation Design Principles Comparative Example 1: Ordinary tire sidewall rubber (without CPE / without flame retardant synergistic system) as the baseline; Comparative Examples 2–5: Used to separate and verify the individual / synergistic effects of CPE, natural paraffin, zinc salt flame retardant and ceramic microspheres; Comparative Example 6: CPE dosage reached 80 phr, used to illustrate the boundary effect that "excessive CPE improves flame retardancy but significantly impairs flexural fatigue"; Examples 1–4: falling within the scope defined by this invention, the synergistic combination of “CPE + natural paraffin + zinc salt flame retardant + ceramic microspheres” achieves both flame retardancy and mechanical / fatigue performance.

[0054] The formulations of the examples and comparative examples are shown in Table 1.

[0055] Table 1 Formula

[0056] CPE: Chlorine content is 30%-40%.

[0057] Zinc salt flame retardant: the ratio of boron trioxide to zinc oxide is 2:1.

[0058] IV. Preparation method of rubber composition (mixing process) This invention employs a "three-stage mixing" approach to take into account: the pre-dispersion of zinc salt flame retardant / ceramic microspheres in the polar phase; temperature window control of the silica-silane coupling reaction; and the addition of the vulcanization system at the low-temperature end to avoid early scorching.

[0059] 1) First stage of mixing (high temperature dispersion stage, sheeting temperature 145–155℃) Feeding sequence: Add natural rubber → zinc salt flame retardant → ceramic microspheres → 1 / 2 CPE; press and hold for 30–40 seconds; lift and clean; add carbon black; press and mix again.

[0060] Endpoint control: Mix until the glue temperature reaches 145–155℃ and then discharge the glue.

[0061] Key points: First, establish a "polar dispersion environment" by combining zinc salt flame retardant and ceramic microspheres in a CPE-containing system, and then introduce carbon black, which helps reduce the agglomeration of inorganic components; compaction / lifting cleaning ensures the recovery of fallen powder and wall adhesive, reducing batch fluctuations.

[0062] 2) Second stage mixing (white carbon black-silane reaction section, sheeting temperature 145–155℃) Feeding sequence: Add the first stage of compound rubber → butadiene rubber → the remaining 1 / 2 CPE → natural paraffin wax → silica and silane; press and mix to a rubber temperature of 120–130℃; add softener and other compounding agents (except vulcanizing agents and accelerators); press and mix for 25–35 seconds; lift and clean the rubber; press and mix again to a rubber temperature of 145–155℃ and discharge the rubber.

[0063] Key points: Introducing silica and silane at 120–130℃ facilitates the initiation of the coupling reaction and controls exothermic reactions; adding natural paraffin at this stage provides lubrication and aids in dispersibility during processing, synergistically improving the dispersion stability of the inorganic flame retardant system with CPE; vulcanizing agents / accelerators are not added at this stage to avoid the risk of early vulcanization or scorching due to high temperatures.

[0064] 3) Third stage mixing (final sulfur addition stage, sheeting temperature 105–115℃) Feeding sequence: Add the second stage of compound rubber → vulcanizing agent → accelerator; press and hold for 30–40 seconds; lift and clean; press and hold for 30–40 seconds again; lift and clean; press and mix again.

[0065] Endpoint control: Mix until the glue temperature reaches 105–115℃ and then discharge the glue.

[0066] Key points: By using "low-temperature final grinding + multiple pressing / cleaning", the vulcanization system is uniformly dispersed without excessively rapid heating, ensuring the safety of subsequent vulcanization and the consistency of the finished product.

[0067] V. Vulcanization conditions and sample preparation Vulcanization conditions: Vulcanization temperature 140–160℃, time 15–30 min. In this embodiment, 150℃×20 min can be selected as the median condition for sample vulcanization (which is a conventional implementation method within the above window).

[0068] Sample preparation: After the third stage of compound rubber has been left to warm up, it is vulcanized and molded under the above conditions using a flat vulcanizing machine, and dumbbell-shaped samples / hardness samples / flexural samples are cut according to the corresponding standards.

[0069] VI. Performance Testing Methods 1. Stress at a constant elongation, tensile strength (Tb) and elongation at break (Eb) of M100, M200 and M300: Refer to GB / T528-2009.

[0070] 2. Shore hardness: Refer to GB / T531.1-2008.

[0071] 3. Flexion fatigue: Refer to GB / T13934-2012.

[0072] 4. Oxygen index: Refer to GB / T2406.2-2009.

[0073] VII. Test Results and Comparative Analysis (a) The test results are shown in Table 2.

[0074] Table 2

[0075] (II) Combustion Verification (Description of Whole Tire Verification) Further combustion tests were conducted on a standard tire with sidewall rubber (Comparative Example 1) and a tire with flame-retardant sidewall rubber (Example 1). Under safe conditions and with a dedicated fire extinguisher, the sidewall was continuously heated and burned at a fixed point using a flame gun. The results showed that the standard tire spontaneously combusted within 1 minute and 31 seconds with an unextinguished flame; the flame-retardant tire burned continuously for 2 minutes and 18 seconds without any visible flame, demonstrating a significant flame-retardant effect.

[0076] (III) Summary of technical effects (proof relationship between corresponding proportions / examples) 1. Balancing flame retardancy enhancement and mechanical integrity: Examples 1–4 are generally comparable to Comparative Example 1 in terms of M100 / M200 / M300, Tb, Eb, etc., indicating that the introduction of CPE and flame retardant synergistic system within the formulation window of this invention has not caused unacceptable mechanical degradation. At the same time, the oxygen index is increased to more than 25%, reflecting enhanced flame retardancy.

[0077] 2. Comparative proof of the synergistic flame retardant mechanism: Comparing Comparative Example 2 (with CPE + microbeads but no zinc salt) and Comparative Example 3 (with CPE + zinc salt but no microbeads), the oxygen indices were 21.8% and 22.5%, respectively. 3. Comparing Comparative Example 4 / 5 (with zinc salt and microbeads but different CPE / paraffin conditions) with Example 3 (which simultaneously contains CPE, paraffin, zinc salt, and microbeads), the oxygen index was significantly improved (26.2% in Example 3), indicating that there is a synergistic effect between CPE / natural paraffin and zinc salt flame retardant / ceramic microbeads.

[0078] 4. Boundary effect of the upper limit of CPE usage: Although the oxygen index of Comparative Example 6 reached 27.3%, "Grade 1" cracks appeared in flexural fatigue, indicating that excessive CPE will significantly impair the flexural resistance of the tire sidewall; while Example 4 can still achieve 1 million cycles without cracks when CPE=60phr, achieving a balance between flame retardancy and fatigue performance.

[0079] 5. Dispersion and processing stability: By comparing Comparative Example 4 / 5 with Example 3, it can be seen that the combination of natural paraffin and CPE is beneficial to the dispersion of the flame-retardant inorganic system in rubber, thereby avoiding excessive deterioration of mechanical properties and improving flame retardant consistency.

[0080] VIII. Tire Application Implementation Methods In an all-steel radial tire structure (including the crown, shoulder, sidewall, belt layer, crown belt layer, and ply layer), the sidewall portion uses any of the flame-retardant sidewall rubber compositions described in Examples 1–4 above. After extrusion molding and bonding with other tire components, it is vulcanized at 140–160°C for 15–30 minutes to obtain a flame-retardant sidewall all-steel radial tire. This tire significantly improves sidewall flame resistance while meeting conventional sidewall mechanical and fatigue requirements.

[0081] 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 flame-retardant tire sidewall rubber composition, characterized in that, The rubber composition is prepared by mixing raw materials comprising the following components based on 100 parts by weight of raw rubber: Natural rubber 40-60 phr Butadiene rubber 40-60 phr Carbon black 10-20 phr 30-40 phr of silica Silane 2.0-4.0 phr, Chlorinated polyethylene (CPE) 20-60 phr Natural paraffin wax 1.0-5.0 phr Ceramic microspheres 2.0-10 phr Zinc salt flame retardant 5.0-10 phr.

2. The flame-retardant tire sidewall rubber composition according to claim 1, characterized in that, The rubber composition is prepared by mixing raw materials comprising the following components based on 100 parts by weight of raw rubber: Natural rubber 45-55 phr Butadiene rubber 45-55 phr Carbon black 10-20 phr 30-40 phr of silica Silane 2.0-4.0 phr, Chlorinated polyethylene (CPE) 40-60 phr Natural paraffin wax 1.0-5.0 phr Ceramic microspheres 2.0-10 phr Zinc salt flame retardant 5.0-10 phr; Furthermore, the rubber composition is prepared by mixing the following components: Softener 10.0-13.0 phr, Protective wax 1.5-2.5 phr Anti-aging agent 2.5-6.0 phr, Activator 4.0-6.0 phr, Vulcanizing agent 1.0-2.0 phr, Accelerator 0.6-1.8 phr.

3. A flame-retardant tire sidewall rubber composition according to claim 1 or 2, characterized in that, The zinc salt flame retardant is a mixture of boron trioxide and zinc oxide in a ratio of 2:1 to 1:

1.

4. A flame-retardant tire sidewall rubber composition according to claim 1 or 2, characterized in that, The ceramic microspheres are made of silica-alumina ceramic with a D50 ≤ 10 μm.

5. A flame-retardant tire sidewall rubber composition according to claim 1 or 2, characterized in that, The chlorinated polyethylene (CPE) has a chlorine content of 25%-45%; more preferably, it has a chlorine content of 30%-40%.

6. A flame-retardant tire sidewall rubber composition according to claim 1 or 2, characterized in that, The carbon black is selected from N3 series or N2 series carbon black; preferably N330 or N375 carbon black. And / or, the silica is selected from silica 165, silica 175, or highly dispersed silica; And / or, the silane is selected from one or more of Si69, Si-75, and mercaptosilane; And / or, the softener is one or two of aromatic oil, tert-butylphenol resin, and octylphenol resin; And / or, the activator is stearic acid and zinc oxide; And / or, the vulcanizing agent is sulfur; And / or, the accelerator is accelerator NS, accelerator CZ, or a mixture of the two.

7. The method for preparing the rubber composition according to any one of claims 1-6, characterized in that, Includes the following steps: 1) First stage of mixing: Add natural rubber, zinc salt flame retardant, ceramic microspheres, and 1 / 2 chlorinated polyethylene, press and hold for 30-40 seconds, lift and clean, add carbon black, press and mix again, and discharge the glue at 145-155℃. 2) Second stage mixing: Add the first stage compound, butadiene rubber, the remaining chlorinated polyethylene, natural paraffin, silica and silane, press and mix to 120℃-130℃, add softener and other compounding agents (except vulcanizing agent and accelerator), press and mix for 25-35s, lift and clean, then press and mix again to 145℃-155℃ to discharge the rubber; 3) Third stage mixing: Add the second stage compound, vulcanizing agent, and accelerator, press and hold for 30-40 seconds, lift and clean, press and hold for another 30-40 seconds, lift and clean, and then press and mix to 105-115℃ for discharge.

8. The preparation method according to claim 7, characterized in that, The first, second, and third mixing stages are completed in an internal mixer, and after each stage of rubber discharge, the mixture is passed through a two-roll mill, pressed into sheets, and cooled before entering the next mixing stage.

9. The method for preparing the rubber composition according to claim 7, characterized in that, The vulcanization conditions for the rubber composition are 140-160℃ for 15-30 minutes.

10. An all-steel radial tire, comprising a crown, shoulder, sidewall, belt layer, crown belt layer, and ply layer, characterized in that, The sidewall is prepared by vulcanization of the rubber composition according to any one of claims 1-6.

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