Flame-retardant seam allowance protective rubber composition, mixing method thereof and tire

Abstract

The invention relates to the technical field of rubber manufacturing, and discloses a flame-retardant seam allowance protection 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 bead protector rubber composition, its mixing method, and a tire. Background Technology

[0002] As a key component of a vehicle responsible for bearing and transmitting driving and braking forces, tires generate significant heat under high-speed, heavy-load, and frequent braking conditions. This is especially true for all-steel radial tires, where the tire-rim assembly area (typically including the bead, bead, and bead protector) is subjected to long-term cyclic compression, shearing, and flexing, resulting in significant stress concentration. During continuous braking on long downhill slopes, emergency braking, or abnormal overheating of the wheel ends (brake drum / disc, hub), external heat sources can rapidly transfer to the tire through the rim-bead area. This, combined with the rubber's own delayed heat generation, exacerbates the temperature rise in the bead area. The bead protector is typically a diene rubber system containing reinforcing fillers, and is a flammable organic material. When the wheel end temperature rises suddenly or localized heat accumulation reaches critical conditions, there is a risk of ignition, smoldering spread, and smoke generation. For special scenarios such as heavy-duty oil tankers, hazardous chemical transport vehicles, express delivery vehicles, mining vehicles, and fire and rescue vehicles, the requirements for heat resistance and flame retardancy safety in the tire bead area are higher, prompting the industry to continuously carry out research on flame retardant rubber materials for tires and their mixing processes.

[0003] In existing technologies, the main approaches to improving the flame retardancy of tire rubber include: introducing flame retardants (halogen-based, antimony-based, boron-based, phosphorus-based, etc.) into the conventional rubber matrix, or selecting intrinsically flame-retardant halogen / fluorine-containing rubbers (such as chloroprene rubber, fluororubber, etc.) to improve flame retardancy, supplemented by appropriate formulations and processing controls. However, tire rubbers are subject to strict constraints on mechanical properties (tensile strength, elongation), flexural fatigue resistance, heat aging resistance, processing safety (scorching, roller sticking / sticking, extrusion stability), and cost. The introduction of flame-retardant systems often leads to problems such as dispersion difficulties, decreased compatibility, deterioration of dynamic performance, increased smoke density, or environmental compliance pressures. Therefore, achieving a balance among multiple objectives of "flame retardancy, mechanical properties, processing, and cost" has been a long-standing engineering challenge in this field.

[0004] Taking specialized tires designed for high-risk scenarios such as fire trucks as an example, Chinese patent application (CN105949537A) proposes a wear-resistant rubber composition for fire truck tire beads. The formulation uses a base rubber reinforced with carbon black, while introducing flame-retardant systems such as antimony trioxide, chlorinated paraffin-70, and zinc borate. It also controls the discharge temperature through three-stage mixing to balance flame retardancy and processing performance. This approach is representative: relying on the synergistic effect of a chlorinated synergistic system (chlorinated paraffin) and antimony- and boron-based flame retardants to enhance flame retardancy and corrosion resistance. Although this type of solution can improve flame resistance to some extent, the chlorinated paraffin and antimony-based flame-retardant components used in the formulation often raise environmental and smoke toxicity controversies, material odor / VOC issues, and regulatory compliance pressures. Furthermore, high-filler / multi-component flame-retardant systems can increase rubber viscosity, exacerbate dispersion difficulties and batch stability fluctuations, and may adversely affect dynamic fatigue and permanent deformation, thus impacting long-term tire durability and high-speed safety.

[0005] Chinese patent application (CN105061832A) discloses a sidewall rubber composition for fire truck tires. This composition combines natural rubber and chloroprene rubber in the sidewall rubber, using chlorinated paraffin-70 and antimony trioxide as a flame-retardant system to achieve flame retardancy and acid / alkali resistance. This document reflects another common approach: using halogenated rubber (such as chloroprene rubber) to obtain a certain intrinsic flame retardancy, and then supplementing it with halogenated / antimony-based synergistic flame retardants to further enhance the flame-retardant effect. However, in the tire industry, blending highly polar materials such as chloroprene rubber with commonly used diene rubbers often faces compatibility and processing window limitations. For example, high heat generation during mixing, increased scorching tendency, roller sticking, and poor extrusion stability are common problems. Furthermore, the combination of halogenated rubber and halogenated flame retardants may also bring subsequent constraints regarding smoke corrosivity, odor, and environmental compliance, affecting its large-scale application on more vehicle platforms.

[0006] Besides special-purpose vehicle tires, there is also considerable research on flame-retardant tire compounds for general heavy-duty or special transportation scenarios. Chinese patent application CN104311909A discloses a fire-resistant and flame-retardant tire rubber composition, which introduces flame-retardant components such as zinc borate, antimony trioxide, and decabromodiphenyl ether into the NR / BR matrix to achieve fire-resistant and flame-retardant effects. The anti-aging system and filler system are adjusted to meet the requirements for aging resistance and flexural performance. This type of solution embodies the classic flame-retardant technology framework of "bromine-based flame retardant + antimony-based synergist + boron-based smoke suppressant / charring agent," exhibiting high flame-retardant efficiency and a long history of application. However, from the perspective of tire application, the constraints of bromine-based flame retardants (such as decabromodiphenyl ether) and antimony-based synergists in terms of toxicology, smoke toxicity, and environmental regulations are continuously increasing. Simultaneously, the addition of large amounts of low-molecular-weight or inorganic flame-retardant components can easily lead to an increase in the specific gravity of the rubber compound, a decrease in dynamic performance, interface weakening, and processing fluctuations, thereby affecting the overall performance of the tire, including rolling resistance, heat generation, and durability.

[0007] In summary, while existing flame-retardant rubber compounds for tires (especially those targeting high-temperature risk areas such as the sidewall / bead) can achieve certain flame-retardant effects through pathways such as halogen-antimony-boron or a combination of halogenated rubbers, they generally still have the following areas requiring improvement: First, some flame-retardant systems involve halogenated flame retardants, chlorinated paraffins, and antimony synergists, which present uncertainties regarding smoke toxicity, corrosiveness, odor, and regulatory compliance, putting pressure on large-scale applications. Second, multi-component inorganic flame-retardant systems are prone to manufacturing problems such as uneven dispersion, narrow mixing process windows, and large batch-to-batch fluctuations, affecting product consistency. Third, the introduction of flame-retardant components often leads to a decline in mechanical and dynamic properties (such as increased permanent deformation, decreased flexural / fatigue life, and increased heat generation), which contradicts the comprehensive requirements of tire bead protectors for "wear resistance, flexural resistance, heat resistance, and processing stability." Fourth, the use of specialized rubbers (such as chloroprene rubber and fluororubber) may be constrained by cost, supply, and processing compatibility, making it difficult to promote on a wider range of product platforms. Therefore, there is still a need for a flame-retardant rubber material and matching mixing process for tire bead protection that can take into account flame retardant safety, mechanical / dynamic performance and industrial processing stability, while also being easier to meet environmental protection and low smoke and low toxicity requirements. Summary of the Invention

[0008] This invention addresses the shortcomings of existing technologies. The technical objective of this invention is to provide a flame-retardant rubber composition and its mixing method suitable for the bead protector of all-steel radial tires. In a conventional diene rubber system primarily composed of natural rubber / butadiene rubber, this invention combines chlorinated polyethylene (CPE), zinc salt flame retardants, ceramic microspheres, and a system of natural paraffin and silanes. This achieves a low-smoke, low-toxicity, highly efficient flame-retardant bead protector material that can be stably produced industrially, without significantly sacrificing the mechanical properties and processing stability of the bead protector. This material is then applied to all-steel radial tires to improve the flame-retardant safety of the tire bead area.

[0009] To achieve the above objectives, the present invention adopts the following technical solution: A flame-retardant rubber composition for the bezel protector, wherein the rubber composition is prepared by mixing raw materials comprising the following components based on 100 parts by weight of raw rubber: Natural rubber 45-65 phr Butadiene rubber 35-55 phr Carbon black 25-35 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.

[0010] 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) 40-60 phr Natural paraffin wax 1.0-5.0 phr Ceramic microspheres 2.0-10 phr Zinc salt flame retardant 5.0-10 phr.

[0011] Furthermore, the rubber composition is prepared by mixing the following components: Softener 4.0-12.0 phr, Protective wax 0.5-1.5 phr, Anti-aging agent 2.5-4.5 phr, Activator 4.0-6.0 phr, Vulcanizing agent 2.5-3.5 phr, Accelerator 3.0-4.0 phr.

[0012] Preferably, the zinc salt flame retardant is a mixture of boron trioxide and zinc oxide in a ratio of 2:1 to 1:1.

[0013] Preferably, the ceramic microspheres are made of silica-alumina ceramic with a D50 ≤ 10 μm.

[0014] Preferably, the chlorinated polyethylene (CPE) has a chlorine content of 25%-45%; more preferably, it has a chlorine content of 30%-40%.

[0015] Preferably, the carbon black is N3 series or N2 series carbon black; N375 carbon black is preferred.

[0016] Preferably, the silica is silica 165, silica 175, or highly dispersed silica.

[0017] 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.

[0018] 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.

[0019] 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.

[0020] Examples of thiol-based silane coupling agents include 3-mercaptopropyltrimethoxysilane, 3-mercaptopropyltriethoxysilane, and 3-mercaptopropylmethyldimethoxysilane.

[0021] 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.

[0022] 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.

[0023] 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.

[0024] 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.

[0025] Among these silane coupling agents, one or more of Si69, Si-75, and mercaptosilanes are particularly preferred.

[0026] Preferably, the softener is one or two of aromatic oil, tert-butylphenol resin, and octylphenol resin.

[0027] Preferably, the activator is stearic acid and zinc oxide.

[0028] 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.

[0029] 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.

[0030] 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.

[0031] 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.

[0032] 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.

[0033] Examples of thiourea compounds include thiourea compounds such as thiocarbamate, diethylthiourea, dibutylthiourea, trimethylthiourea, and di-o-tolylthiourea.

[0034] Examples of guanidine compounds include diphenylguanidine, di-o-toluidine, triphenylguanidine, o-toluidine, and diphenylguanidine phthalate.

[0035] 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.

[0036] Examples of aldehyde-amine or aldehyde-amine compounds include acetaldehyde-aniline reactants, butyraldehyde-aniline condensates, hexamethylenetetramine, and acetaldehyde-amine reactants.

[0037] Among these accelerators, one or two of accelerators NS, CZ, and HMT are particularly preferred.

[0038] 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 the mixture into a ball and hold for 30-40 seconds. Remove the ball, clean it, and then press and mix it again until the rubber is discharged at 140-150℃. 2) Second stage mixing: Add the first stage compound rubber, carbon black, silica and silane, press and mix for 10-20 seconds, then add butadiene rubber, the remaining chlorinated polyethylene and natural paraffin, press and mix to 120℃-130℃, add softener and other compounding agents (except vulcanizing agent and accelerator), press and mix for 20-30 seconds, lift and clean, then press and mix 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.

[0039] Preferably, the vulcanization conditions of the rubber composition are 140-160°C for 15-30 minutes.

[0040] 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, a ply layer, and a bead protector, wherein the bead protector is prepared by vulcanization of the rubber composition described above.

[0041] This invention achieves a comprehensive technical effect of improved flame retardancy, maintained mechanical properties, and stable processing without relying on highly toxic halogenated flame retardants, brominated flame retardants, or high-dosage antimony flame retardants, by synergistically introducing chlorinated polyethylene (CPE), zinc salt flame retardant, and fine-particle ceramic microspheres into a conventional diene rubber system (natural rubber / butadiene rubber), combined with natural paraffin wax lubrication and plasticization and a silane coupling dispersion system. On one hand, the polar phase and elastic compatibility of CPE improve the wetting and interfacial bonding of zinc salt flame retardant and ceramic microspheres in the rubber. Natural paraffin wax further reduces powder agglomeration and heat generation during mixing. Combined with a two-stage silanization and a three-stage low-temperature final mixing process, the flame retardant components form a more uniform and stable dispersion network in the rubber compound, thereby significantly improving the oxygen index and enhancing the self-extinguishing ability after flame removal. The tire bead protector remains visibly extinguished under continuous flame. It significantly delays spontaneous combustion and extinguishes quickly or without open flame after flameout, demonstrating outstanding flame-retardant effects. On the other hand, the constructed synergistic system avoids the problem of rapid deterioration in strength / elongation caused by traditional high-filler inorganic flame retardants. It keeps key mechanical indicators such as tensile stress, tensile strength, and elongation at break on the same order of magnitude as conventional bead protectors, with controllable hardness changes. It only causes a slight increase in permanent deformation within an acceptable range without affecting the structural service requirements of the bead area. At the same time, the temperature window and feeding sequence of the three-stage mixing suppress scorching, improve mixing uniformity and batch stability, and are conducive to the consistency of extrusion molding and tire vulcanization. It comprehensively achieves a bead protector rubber compound system that is low in smoke and toxicity, highly efficient in flame retardancy, has balanced performance, and can be mass-produced. This significantly improves the flame-retardant safety and application reliability of the bead area of ​​all-steel radial tires under extreme thermal conditions such as heavy load, high speed, and emergency braking. Detailed Implementation

[0042] 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.

[0043] I. Terminology and Measurement Explanation phr: "parts per hundred rubber" based on the total amount of raw rubber. In this invention, "based on 100 parts by weight of raw rubber" has the same meaning as phr.

[0044] Bead protector: A protective / wear-resistant rubber compound used in the bead area of ​​the tire (near the rim seat and bead area). It is usually applied to the relevant structure of the tire body in the form of extruded rubber strips and is integrally formed with the tire vulcanization. It is used to improve the wear resistance, heat resistance and flame retardancy of the bead area.

[0045] Zinc salt flame retardant: The preferred embodiment of the present invention is a mixture of boron trioxide (B2O3) and zinc oxide (ZnO) in a mass ratio of 2:1 to 1:1; 2:1 is used in the examples.

[0046] Ceramic microspheres: The present invention preferably uses silica alumina ceramic microspheres with a median particle size D50 ≤ 10 μm.

[0047] CPE: Chlorinated polyethylene, preferably with a chlorine content of 25% to 45%, more preferably 30% to 40%.

[0048] II. Raw Materials and Scope of Selection The following raw materials are all commonly used or commercially available materials in the tire industry, and their sources are not limited: Natural rubber (NR): such as SMR, RSS, etc.; Butadiene rubber (BR): such as high cis BR; Carbon black: N3 series or N2 series, N375 preferred; Silica: Silica 165, Silica 175 or Highly Dispersible Silica; Silane coupling agent: preferably one or more of Si69, Si-75 or mercaptosilane; CPE: CPE with a chlorine content of 30% to 40%; Natural paraffin wax: serves as a lubricant, improves processing, and enhances compatibility; Softener: one or two of aromatic oil, tert-butylphenol resin, and octylphenol resin; Protective wax: such as tire protective wax; Antioxidants: such as antioxidant 4020, RD, etc.; Activators: stearic acid and zinc oxide; Vulcanizing agent: sulfur; Accelerator: One or two of accelerators NS, CZ, and HMT (NS is used as an example in the embodiments).

[0049] III. Equipment and Tooling The mixing method of this invention can be implemented in a conventional tire rubber compound mixing production line. Example equipment is as follows (equipment models are for illustrative purposes only and do not constitute a limitation): Internal mixer: such as 160L~270L internal mixer (either tangential or meshing rotors are acceptable); Open mill: such as 18-22 inch open mill, used for thin sheet processing, vulcanization systems, and sheet production; Film cooling and storage: cooling conveyor line, storage rack; Vulcanizing machine: Flat vulcanizing machine or drum vulcanizing equipment, used for vulcanizing test pieces or tires.

[0050] IV. Preparation Method of Rubber Composition This invention employs a three-stage mixing process to balance the dispersion of flame-retardant fillers, silanization reaction, and the safety of the vulcanization system.

[0051] 1) First stage of mixing (master rubber I) Feeding sequence: Add natural rubber (NR), zinc salt flame retardant, ceramic microspheres, and about 1 / 2 of the amount of CPE; Mixing method: Press the lump and hold for 30-40 seconds, lift the lump and clean it, then press the lump again and mix; Discharge temperature: Discharge the lump when the rubber temperature reaches 140-150℃.

[0052] Objective: To pre-wet and disperse zinc salt flame retardant and ceramic microspheres in NR / CPE matrix to form stable masterbatch, thereby reducing the risk of powder agglomeration and uneven dispersion during subsequent mixing.

[0053] 2) Second stage mixing (Masterbatch II, containing silanization) Feeding sequence: Add the first stage of compound rubber, carbon black, silica and silane; press and mix for 10-20 seconds; then add butadiene rubber (BR), the remaining CPE and natural paraffin wax; mid-stage control: after pressing and mixing to a rubber temperature of 120-130℃, add softener and other compounding agents (except vulcanizing agent and accelerator); press and mix for 20-30 seconds; lift and clean the rubber, then press and mix again; discharge temperature: discharge the rubber when the rubber temperature reaches 145-155℃.

[0054] Objective: To achieve effective dispersion and silane coupling reaction (silanization) of carbon black / silica, and to improve the dispersion uniformity of flame retardant system and ceramic microspheres in diene rubber by leveraging the polarity of CPE and the lubricating dispersion of natural paraffin, while taking into account both processing flowability and mechanical properties.

[0055] 3) Third stage mixing (addition of final rubber / vulcanization system) Feeding sequence: Add the second stage of compound rubber, vulcanizing agent, and accelerator; Key operating points: Press the lump and hold for 30-40 seconds, then lift and clean it; press the lump again and hold for 30-40 seconds, then lift and clean it; press the lump again and mix. Discharge temperature: Discharge adhesive when the adhesive temperature reaches 105-115℃.

[0056] Objective: To add the vulcanization system at a lower adhesive temperature to avoid early vulcanization (scorching) and ensure processing safety and vulcanization uniformity.

[0057] 4) Vulcanization conditions The vulcanization conditions after molding the rubber sample or the end cap protector can be selected as follows: 140-160℃, 15-30min.

[0058] V. Examples and Comparative Examples (I) Formula Design Principles Comparative examples were used to verify the changes in flame retardant properties and / or overall performance in the absence of CPE, zinc salt flame retardant, or ceramic microspheres. Examples are provided to demonstrate that, within the raw material range defined in this invention, the synergy between CPE / natural paraffin and zinc salt flame retardant / ceramic microspheres can significantly improve the oxygen index and combustion performance while maintaining mechanical properties.

[0059] (II) Formulations of the Examples and Comparative Examples (Table 1) In Table 1, all components are listed in phr (based on 100 parts of raw rubber). The chlorine content of CPE is 30%–40%; the zinc salt flame retardant is a mixture of B2O3 and ZnO in a mass ratio of 2:1; and the ceramic microspheres have a D50 ≤ 10 μm.

[0060] The formulations of the examples and comparative examples are shown in Table 1.

[0061] Table 1 Formula

[0062] CPE: Chlorine content is 30%-40%.

[0063] Zinc salt flame retardant: the ratio of boron trioxide to zinc oxide is 2:1.

[0064] (III) The preparation steps of the rubber composition are as follows: 1) First stage of mixing: Add natural rubber, zinc salt flame retardant, ceramic microspheres, and 1 / 2 chlorinated polyethylene. Press the mixture into a ball and hold for 30-40 seconds. Remove the ball, clean it, and then press and mix it again until the rubber is discharged at 140-150℃. 2) Second stage mixing: Add the first stage compound rubber, carbon black, silica and silane, press and mix for 10-20 seconds, then add butadiene rubber, the remaining chlorinated polyethylene and natural paraffin, press and mix to 120℃-130℃, add softener and other compounding agents (except vulcanizing agent and accelerator), press and mix for 20-30 seconds, lift and clean, then press and mix 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.

[0065] VI. Vulcanization Sample Preparation and Testing Methods Vulcanization conditions: 140-160℃, 15-30min (the test pieces can be selected according to the normal vulcanization time t90 of the rubber compound, which is a routine test condition selection).

[0066] 1. Stress at a constant elongation, tensile strength (Tb) and elongation at break (Eb) of M100, M200 and M300: Refer to GB / T528-2009.

[0067] 2. Shore hardness: Refer to GB / T531.1-2008.

[0068] 3. Permanent deformation: Refer to GB / T7759.1-2015.

[0069] 4. Oxygen index: Refer to GB / T2406.2-2009.

[0070] VII. Test Results The test results are shown in Table 2.

[0071] Table 2

[0072] VIII. Results Analysis and Technical Effect Description 1. Significantly improved flame retardant performance: The oxygen index of Comparative Example 1 (ordinary diene rubber system) was only 18%; the oxygen index of Examples 1 to 5 was all increased to over 24%, with the highest reaching 26.8%, indicating that in diene rubber systems, the combination of CPE + zinc salt flame retardant + ceramic microspheres can significantly improve the self-extinguishing and flame-retardant capabilities of the material.

[0073] 2. The synergistic effect can be verified: Comparative Example 2 (with CPE + ceramic microspheres, without zinc salt flame retardant) had an oxygen index of 20.4%; Comparative Example 3 (with CPE + zinc salt flame retardant, without ceramic microspheres) had an oxygen index of 20.9%; Comparative Example 4 (with zinc salt flame retardant + ceramic microspheres, no CPE) had an oxygen index of 21.1%. Example 1 (CPE + zinc salt flame retardant + ceramic microspheres combined) Oxygen index 24.7%.

[0074] The above comparison shows that the combination of CPE, zinc salt flame retardant and ceramic microspheres results in a more significant improvement in flame retardancy compared to any combination of two or the system lacking CPE, demonstrating synergistic effects.

[0075] 3. Mechanical properties remain at a usable level: M100, M200, M300 and Tb, Eb of Examples 1-5 are generally comparable to or better than those of Comparative Example 1, indicating that unacceptable mechanical degradation was not introduced while improving flame retardancy, and the overall requirements of the ferrule sealant for strength, hardness and elongation were met.

[0076] 4. Industrial feasibility of processing and dispersion: Comparative Example 5 (without natural paraffin) still has a certain oxygen index in the presence of flame retardant components. However, compared with Example 1, the combination of natural paraffin and CPE is more conducive to the wetting, dispersion and processing stability of flame retardant fillers and ceramic microspheres in the adhesive. Thus, a low-smoke, low-toxicity and industrially scalable flame retardant sealant system can be achieved without increasing the amount of highly toxic halogenated flame retardants.

[0077] As can be seen from the examples and comparative examples, in a common diene rubber system, the present invention, through the synergistic dispersion of flame-retardant fillers and ceramic microspheres by CPE / natural paraffin and the synergistic flame retardancy of zinc salt flame retardant / ceramic microspheres, can significantly improve the oxygen index and self-extinguishing performance of the bead protector while maintaining the necessary mechanical properties of the bead protector. This results in a low-toxicity, low-smoke, industrially scalable flame-retardant bead protector rubber composition and its application in all-steel radial tires.

[0078] IX. Examples of Tire Application Tire trials were conducted using the rubber compound from Example 1 as the bead protector compound: Bead protector molding: The final compound of Example 1 is extruded into bead protector strips using an extruder (the size is determined according to the target tire specifications and process card, which is standard in the industry). Tire forming: During the forming process of all-steel radial tires, the bead protector strip is attached to the relevant parts of the bead area according to the design position, and is integrally formed with the tire body, belt layer, crown belt layer and other structures; Tire vulcanization: Vulcanize according to the target tire specifications and vulcanization process conditions (temperature is usually in the range of 140-160℃, and time is determined according to the positive vulcanization curve of the tire, which is a conventional setting).

[0079] Further combustion comparison verification was conducted (under conditions where dedicated fire extinguishers were available and safety was ensured): A regular tire (comparative example 1 bead rubber system) spontaneously combusted after being continuously sprayed with flame at a fixed point on the sidewall for about 1 minute and 31 seconds. After the flame gun was removed, the open flame did not extinguish and spread to the bead rubber protection area. The flame-retardant tire (Example 1 Bead Protection System) was continuously sprayed with flame at a fixed point on the bead protection for about 3 minutes and 15 seconds. After the flame gun was removed, there was no open flame at the bead protection, which showed obvious flame-retardant advantages.

[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 flame-retardant rubber composition for the bezel seal, 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 45-65 phr Butadiene rubber 35-55 phr Carbon black 25-35 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.

2. The flame-retardant ferrule protector 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) 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.

3. The flame-retardant ferrule protector rubber composition according to claim 1 or 2, characterized in that, The rubber composition is further prepared by mixing the following raw materials: Softener 4.0-12.0 phr, Protective wax 0.5-1.5 phr, Anti-aging agent 2.5-4.5 phr, Activator 4.0-6.0 phr, Vulcanizing agent 2.5-3.5 phr, Accelerator 3.0-4.0 phr.

4. The flame-retardant ferrule protector 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.

5. A flame-retardant bezel protector 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.

6. A flame-retardant ferrule protector 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%.

7. A flame-retardant bezel protector rubber composition according to claim 1 or 2, characterized in that, The carbon black is selected from N3 series or N2 series carbon black; N375 carbon black is preferred. 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 one or two of accelerator NS, accelerator CZ, and accelerator HMT.

8. The method for preparing the rubber composition according to any one of claims 1-7, 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 the mixture into a ball and hold for 30-40 seconds. Remove the ball, clean it, and then press and mix it again until the rubber is discharged at 140-150℃. 2) Second stage mixing: Add the first stage compound rubber, carbon black, silica and silane, press and mix for 10-20 seconds, then add butadiene rubber, the remaining chlorinated polyethylene and natural paraffin, press and mix to 120℃-130℃, add softener and other compounding agents (except vulcanizing agent and accelerator), press and mix for 20-30 seconds, lift and clean, then press and mix 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.

9. The method for preparing the rubber composition according to claim 8, characterized in that, The vulcanization conditions for the rubber composition are 140-160℃ for 15-30 minutes.

10. A type of all-steel radial tire, comprising a crown, shoulder, sidewall, belt layer, crown belt layer, ply layer, and bead protector, characterized in that, The ferrule is prepared by vulcanization of the rubber composition according to any one of claims 1-7.

Images