Rubber compositions, reinforcing rubber, and run-flat tires

Abstract

The object of this invention is to provide a rubber composition that suppresses bloom and maintains tack while improving heat resistance. [Solution] A rubber composition comprising a rubber component, two or more sulfenamide-based vulcanization accelerators, and one or more thiram-based vulcanization accelerators, wherein the content of each of the two or more sulfenamide-based vulcanization accelerators is 3.7 parts by mass or less per 100 parts by mass of the rubber component, and the total content of the two or more sulfenamide-based vulcanization accelerators is 4 parts by mass or more per 100 parts by mass of the rubber component.

Description

Technical Field

[0001] The present invention relates to a rubber composition, a reinforcing rubber using the rubber composition, and a run-flat tire using the reinforcing rubber.

Background Art

[0002] Conventionally, from the viewpoints of vehicle safety and productivity improvement, heat resistance has been required due to durability and heat deterioration of rubber.

[0003] For example, in Patent Documents 1 to 3 below, the aim is to improve run-flat durability and the like. For example, in Patent Document 1, with respect to 100 parts by mass of a rubber component containing 20 to 80% by mass of a modified conjugated diene polymer, (B) 60 to 100 parts by mass of a filler, (C) 0.9 to 2.4 parts by mass of a phenolic resin, (D) 0.07 to 0.2 parts by mass of a methylene donor, (E) 1.5 to 2.1 parts by mass of a thiuram vulcanization accelerator, and (F) 3.2 to 4.5 parts by mass of a sulfenamide vulcanization accelerator are blended, and a tire characterized by using the rubber composition and the rubber composition for at least one member selected from a side reinforcing rubber layer and a bead filler is disclosed.

Prior Art Documents

[0006] Therefore, the object of the present invention is to solve the problems of the above-mentioned prior art and to provide a rubber composition that suppresses bloom and ensures tack while improving heat resistance. Furthermore, the present invention aims to provide a reinforcing rubber using such a rubber composition, and a run-flat tire equipped with the reinforcing rubber. [Means for solving the problem]

[0007] The gist of the rubber composition, reinforcing rubber, and run-flat tire of the present invention, which solve the above problems, is as follows.

[0008] [1] A rubber composition comprising a rubber component, two or more sulfenamide-based vulcanization accelerators, and one or more thiram-based vulcanization accelerators, The content of each of the two or more sulfenamide-based vulcanization accelerators is 3.7 parts by mass or less per 100 parts by mass of the rubber component. A rubber composition in which the total content of the two or more sulfenamide-based vulcanization accelerators is 4 parts by mass or more per 100 parts by mass of the rubber component. The rubber composition described in [1] above has improved heat resistance while suppressing bloom and ensuring tack.

[0009] [2] The rubber composition according to [1], wherein the content of each of the one or more thiram-based vulcanization accelerators is 0.8 parts by mass or less per 100 parts by mass of the rubber component. The rubber composition described in [2] above can ensure greater tack.

[0010] [3] The rubber composition comprises a vulcanizing agent, The rubber composition according to [1] or [2], wherein the total content (A) of the two or more sulfenamide-based vulcanization accelerators per 100 parts by mass of the rubber component is 1 or more, and the mass ratio (A / B) of the content of the vulcanizing agent per 100 parts by mass of the rubber component is 1 or more. The rubber composition described in [3] above has improved heat resistance.

[0011] [4] The rubber composition according to any one of [1] to [3], wherein the mass ratio (A / C) of the total content (A) of the two or more sulfenamide-based vulcanization accelerators per 100 parts by mass of the rubber component to the total content (C) of the one or more thiram-based vulcanization accelerators per 100 parts by mass of the rubber component is 6 or more and 9 or less. The rubber composition described in [4] above has improved heat resistance while suppressing a decrease in tack.

[0012] [5] The rubber composition according to any one of [1] to [4], wherein the rubber component is butadiene rubber and isoprene rubber. The rubber composition described in [5] above exhibits excellent tensile strength and fracture properties such as elongation at fracture.

[0013] [6] The rubber composition according to [5], wherein the butadiene rubber is a modified butadiene rubber. The rubber composition described above [6] has improved low heat generation properties.

[0014] [7] The rubber composition according to [5] or [6], wherein the content of the butadiene rubber is 20 parts by mass or more and 80 parts by mass or less per 100 parts by mass of the rubber component. The rubber composition described in [7] above has improved low heat generation properties.

[0015] [8] Furthermore, including fillers, The rubber composition according to any one of [1] to [7], wherein the content of the filler is 40 parts by mass or more and 70 parts by mass or less per 100 parts by mass of the rubber component. The rubber composition described in [8] above can improve the balance between the reinforcing properties and low loss properties of the reinforcing rubber using the rubber composition.

[0016] [9] The filler has a dibutylphthalate oil absorption capacity of 120 mL / 100 g or more, and a nitrogen adsorption specific surface area of ​​20 m². 2 / g or more 80m 2 The rubber composition according to [8], wherein the carbon black is less than or equal to / g. The rubber composition described in [9] above has improved low heat generation and compression resistance.

[0017]

[10] Reinforced rubber using any of the rubber compositions described in [1] to [9]. The reinforcing rubber described in

[10] above provides excellent heat resistance while ensuring tack.

[0018] A run-flat tire equipped with the reinforcing rubber described in

[11]

[10] . The above run-flat tires maintain tack while offering excellent heat resistance. [Effects of the Invention]

[0019] According to the present invention, it is possible to provide a rubber composition that suppresses bloom and maintains tack while improving heat resistance. Furthermore, according to the present invention, it is possible to provide a reinforcing rubber using such a rubber composition, and a run-flat tire equipped with the reinforcing rubber. [Brief explanation of the drawing]

[0020] [Figure 1] This is a schematic diagram showing a cross-section of one embodiment of the run-flat tire of this embodiment. [Modes for carrying out the invention]

[0021] The rubber composition of the present invention, the reinforcing rubber using the rubber composition, and the run-flat tire equipped with the reinforcing rubber will be described in detail below based on embodiments thereof.

[0022] <Definition> The compounds described herein may be derived in part or in whole from fossil resources, from biological resources such as plant resources, or from recycled resources such as used tires. They may also be derived from a mixture of two or more of fossil resources, biological resources, or recycled resources.

[0023] In this specification, the notation "a~b" in descriptions of numerical ranges means a or greater and b or less, unless otherwise specified.

[0024] In this specification, the "proportion of monosulfide bonds and disulfide bonds in the total sulfide bonds" may be referred to as the "amount of mono / disulfide bonds." In this specification, sulfide bonds are referred to as monosulfide bonds (-S-), disulfide bonds (-SS-), trisulfide bonds (-SSS-), etc., depending on the number of sulfur atoms bonded. In this specification, a sulfide bond (-[S]n-; 3≦n) consisting of three or more sulfur atoms may be referred to as a "polysulfide bond".

[0025] <Rubber composition> The rubber composition of this embodiment is a rubber composition comprising a rubber component, two or more sulfenamide-based vulcanization accelerators, and one or more thiram-based vulcanization accelerators, The content of each of the two or more sulfenamide-based vulcanization accelerators is 3.7 parts by mass or less per 100 parts by mass of the rubber component. The total content of the two or more sulfenamide-based vulcanization accelerators is characterized in that it is 4 parts by mass or more per 100 parts by mass of the rubber component.

[0026] Vulcanized rubber, obtained by vulcanizing a rubber composition, has a three-dimensional network structure formed by sulfur crosslinking of the rubber components. Depending on the bonding conditions of this network structure, its heat resistance may be low. Regarding the bonding state of the network structure described above, it is thought that the more sulfide bonds there are, the weaker the bonds become, as the polysulfide bonds consist of three or more sulfur atoms linked together, making the cross-linked network structure that cross-links the rubber components more prone to breaking. In other words, the more sulfide bonds there are linked together, the more easily they break with heat and the more susceptible they are to thermal degradation. Therefore, it is thought that reducing the amount of polysulfide bonds and increasing the proportion of monosulfide and disulfide bonds, for example, increasing the proportion of polysulfide bonds with fewer sulfide atoms (e.g., 7 or 8 sulfur atoms linked together), or decreasing the proportion of polysulfide bonds with fewer sulfur atoms (e.g., 3 or 4 sulfur atoms linked together), can reduce network failure in vulcanized rubber and improve its heat resistance.

[0027] The rubber composition of this embodiment improves heat resistance by using one or more thiram-based vulcanization accelerators and predetermined amounts of two or more sulfenamide-based vulcanization accelerators, thereby maintaining the proportion of monosulfide and disulfide bonds while reducing the proportion of polysulfide bonds with a large number of sulfur atoms (such as 7 or 8 linked sulfur atoms) and increasing the proportion of polysulfide bonds with a smaller number of linked sulfur atoms (such as 3 or 4). Furthermore, although the reason is unclear, by using multiple types of sulfenamide-based vulcanization accelerators in amounts below a predetermined level, it is possible to maintain the total amount of vulcanization accelerators necessary to improve heat resistance while reducing the amount of thiram-based vulcanization accelerators, which are also necessary to improve heat resistance but are thought to contribute to the formation of bloom. As a result, bloom can be suppressed and tack can be maintained. Therefore, the rubber composition of this embodiment suppresses bloom and ensures tack while improving heat resistance.

[0028] (Amount of mono / disulfide bonds) The amount of mono / disulfide bonds is calculated by the following equation (1). Mono / disulfide bond amount = 100 × [(monosulfide bond amount + disulfide bond amount) / total sulfide bond amount] ... (1) In addition, the total amount of sulfide bonds is calculated as the sum of the amount of monosulfide bonds, disulfide bonds, and polysulfide bonds. Note that the amount of mono / disulfide bonds, monosulfide bonds, disulfide bonds, and polysulfide bonds are all amounts relative to the total amount of sulfide bonds, and the unit is "%".

[0029] The amount of mono / disulfide bonds can be calculated by the swelling compression method. The swelling compression method is a method for measuring the amount of each sulfide bond by utilizing the chemical properties of lithium aluminum hydride (LiAlH4), propane-2-thiol, and piperidine (see Hideo Nakai, "Analysis of Cross-Linked Structure of Vulcanized Rubber by Swelling Compression Method", Journal of the Japan Rubber Association, Vol. 75, No. 2 (2002), pp. 73-78).

[0030] Lithium aluminum hydride (LiAlH4) selectively cleaves the disulfide bonds and polysulfide bonds of vulcanized rubber and does not cleave monosulfide bonds. On the other hand, propane-2-thiol and piperidine cleave only polysulfide bonds. Therefore, by utilizing the differences in these reagents, the ratio of each sulfide bond can be determined.

[0031] The ratio of monosulfide bonds in the total sulfide bonds (amount of monosulfide bonds) is obtained by converting the monosulfide network chain density (ν T ) to a percentage with the total sulfide network chain density (ν M ) as 100%. Similarly, the ratio of disulfide bonds in the total sulfide bonds (amount of disulfide bonds) is converted from the disulfide network chain density (ν D ), and the amount of polysulfide bonds is converted from the polysulfide network chain density (ν P ).

[0032] Note that the monosulfide network chain density is ν M [mol / cm 3 , the disulfide network chain density is ν D [mol / cm 3 , and the polysulfide network chain density is ν P [mol / cm3 ], the total sulfide network chain density is ν T [mol / cm 3 It is called ].

[0033] Total sulfide network chain density (ν T This can be determined by swelling the rubber composition with the same solvent, but without reagents. ν M and (ν M +ν D This is measured directly using the method described later. ν D is, (ν M +ν D )-ν M It can be calculated from this. ν P is, ν T -(ν M +ν D It can be calculated from ).

[0034] The amount of mono / disulfide bonds is calculated using equation (1) above.

[0035] ν T ν M , and (ν M +ν D The measurement method is as follows: First, a 2mm thick sheet is cut from the vulcanized rubber obtained by vulcanizing the rubber composition to obtain a vulcanized rubber sheet. The vulcanized rubber sheet is extracted with acetone for 24 hours, and then vacuum dried for 24 hours. The dried vulcanized rubber sheet is cut into 2mm x 2mm squares to form a cubic vulcanized rubber sample. Next, the dimensions of the vulcanized rubber sample in the length, width, and thickness directions are precisely measured.

[0036] Next, the total amount of sulfide bonds in vulcanized rubber (ν T ) For measurement, use solution (T), monosulfide bond amount (ν M ) For measurement, use solution (M), monosulfide bond amount + disulfide bond amount (ν M +ν D For measurement purposes, prepare the solution (M+D) as follows:

[0037] Benzene (or toluene) and tetrahydrofuran (THF) are dehydrated and deoxygenated, and the benzene (or toluene) and tetrahydrofuran (THF) are mixed in a 1:1 ratio by volume. The mixture is placed in a sealable container and nitrogen is purged to obtain solution (T). The container containing solution (T) is referred to as container (i). Lithium aluminum hydride (LiAlH4) powder is added to container (i) while purging with nitrogen, and left for 2-3 days. The supernatant of the solution is separated and designated as solution (M). The container from which solution (M) was separated is referred to as container (ii). The propane-2-thiol and piperidine are dehydrated and deoxygenated, and equimolar samples of the propane-2-thiol and piperidine are added to container (i) while purging with nitrogen. Solution (M+D) is obtained in this way. The vulcanized rubber samples, whose dimensions in three directions have been precisely measured, are placed in three separate airtight containers. Each container is then vacuum-dried for one hour, followed by nitrogen purging. Subsequently, solutions (T), (M), and (M+D) are added to the containers containing the vulcanized rubber samples, respectively. The containers are then sealed and left at 30°C for 24 hours to allow the vulcanized rubber samples to swell.

[0038] Next, under a nitrogen atmosphere, the vulcanized rubber samples are removed from each container, washed with solution (T), and the dimensions of the swollen vulcanized rubber samples are precisely measured. Furthermore, a thermomechanical analyzer (TMA) is used to apply loads ranging from 1 to 60 g in stages, depending on the degree of swelling of the vulcanized rubber samples, and the relationship between compressive stress and strain is determined.

[0039] The above data is input into Flory's theoretical formulas for swelling, compression, and network chain density (equations (2) or (3) below) to calculate the network chain density for each sulfide. If the vulcanized rubber sample is pure rubber without fillers, input the measurement data into the following formula (2) to calculate the density of each sulfide network chain. If the vulcanized rubber sample is a filled system containing fillers, input the measurement data into the following formula (3) to calculate the density of each sulfide network chain.

number

number

[0040] In equations (2) and (3) above, each symbol represents the following: f represents stress [N] and is obtained as the compressive stress measured by a thermomechanical analyzer. k represents a constant. T represents the measured temperature [K]. ν is the sulfide network chain density [mol / cm³] 3 ] and in the vulcanized rubber sample swollen with solution (M), ν M In the vulcanized rubber sample swollen with solution (T), ν T In vulcanized rubber samples swollen with solution (M+D), ν M +ν D That applies. V0 is the total volume [cm³] of the vulcanized rubber sample before swelling. 3 This represents [the value] and is determined from the dimensional measurement of the vulcanized rubber sample. α is the compression or elongation ratio of the vulcanized rubber sample after swelling, where α = L S / L S0 It will be found more. L0 represents the thickness [m] of the vulcanized rubber sample before swelling and is determined by measuring the dimensions of the vulcanized rubber sample. L S0 This represents the thickness [m] of the vulcanized rubber sample after swelling, and is determined by measuring the dimensions of the vulcanized rubber sample. L S This represents the thickness [m] of the vulcanized rubber sample after swelling, compression, or stretching, and is determined by measuring the dimensions of the vulcanized rubber sample. A0 is the cross-sectional area [m²] of the vulcanized rubber sample before swelling. 2 This represents [the value] and is determined from the dimensional measurement of the vulcanized rubber sample. φ represents the volume fraction [%] of the filler in the vulcanized rubber sample and is determined by measuring the dimensions of the vulcanized rubber sample and the filler.

[0041] (Rubber component) The rubber composition of this embodiment contains a rubber component. This rubber component may be a single type or a combination of two or more types. The rubber component is preferably a conjugated diene rubber, and examples of such conjugated diene rubbers include butadiene rubber and isoprene rubber. Including butadiene rubber and isoprene rubber as rubber components results in a rubber composition with excellent fracture properties such as tensile strength and elongation at fracture.

[0042] -Butadiene-based rubber- The aforementioned butadiene-based rubber is a polymer whose main units are butadiene units or butadiene derivative units. In this specification, polymers whose main units are isoprene units or isoprene derivative units are not included in butadiene-based rubber and are distinguished as isoprene-based rubber. The butadiene-based rubber may be a polymer of a single butadiene compound or a copolymer of two or more butadiene compounds, or a copolymer of a butadiene compound and an aromatic vinyl compound. Examples of butadiene-based rubbers include polybutadiene rubber (BR), styrene-butadiene copolymer rubber (SBR), butadiene-isoprene copolymer rubber, acrylonylitol-butadiene rubber (NBR), and styrene-isoprene-butadiene ternary copolymer rubber. These may be used individually or in combination of two or more.

[0043] The content of the butadiene-based rubber is preferably 20 parts by mass or more and 80 parts by mass per 100 parts by mass of the rubber component. When the content of the butadiene-based rubber is within the above range, the fracture characteristics such as tensile strength and elongation at break of the rubber composition can be improved. Furthermore, from a similar viewpoint, the content of the butadiene-based rubber is more preferably 40 parts by mass or more and 70 parts by mass per 100 parts by mass of the rubber component.

[0044] --Modified Butadiene Rubber-- The butadiene rubber is preferably a modified butadiene rubber. More preferably, the modified butadiene rubber is an amine-modified butadiene rubber. When the butadiene rubber is an amine-modified butadiene rubber, the low heat generation of the resulting rubber composition is improved. The amine-modified butadiene rubber is preferably one in which a primary amino group protected by a detachable group or a secondary amino group protected by a detachable group is introduced as a modifying amine-based functional group within the molecule, and more preferably one in which a functional group containing a silicon atom is introduced.

[0045] An example of a primary amino group protected by the aforementioned leaving group (also called a protected primary amino group) is the N,N-bis(trimethylsilyl)amino group, and an example of a secondary amino group protected by the leaving group is the N,N-(trimethylsilyl)alkylamino group. This N,N-(trimethylsilyl)alkylamino group-containing group may be either an acyclic residue or a cyclic residue. Among the amine-modified butadiene rubbers described above, primary amine-modified butadiene rubber modified with a protected primary amino group is preferred.

[0046] Examples of functional groups containing silicon atoms include hydrocarbyloxysilyl groups and / or silanol groups, which are formed by bonding a hydrocarbyloxy group and / or a hydroxyl group to a silicon atom. Such modifying functional groups may be present at the polymerization initiation end, side chain, or polymerization active end of butadiene rubber. However, in the present invention, it is preferable that the polymerization end has an amino group protected by a leaving group and one or more (e.g., 1 or 2) silicon atoms bonded to a hydrocarbyloxy group and a hydroxyl group, and it is more preferable that these be located at the same polymerization active end.

[0047] To modify the active end of the butadiene rubber by reacting it with a protected primary amine, it is preferable that the butadiene rubber has at least 10% of its polymer chains living or pseudo-living. Examples of polymerization reactions that produce such living rubber include anionic polymerization of a butadiene compound alone, or a butadiene compound and an aromatic vinyl compound, in an organic solvent using an organoalkali metal compound as an initiator, or coordination anionic polymerization of a butadiene compound alone, or a butadiene compound and an aromatic vinyl compound, in an organic solvent using a catalyst containing a lanthanum series rare earth element compound. The former is preferred because it can yield a higher vinyl bond content in the conjugated diene portion compared to the latter. By increasing the vinyl bond content, the heat resistance of the rubber composition can be improved.

[0048] As the organoalkali metal compound used as the initiator for the anionic polymerization described above, organolithium compounds are preferred. There are no particular restrictions on the organolithium compound, but lithium hydrocarbyl and lithium amide compounds are preferred. When the former, lithium hydrocarbyl, is used, a butadiene rubber is obtained in which a hydrocarbyl group is present at the polymerization initiation end and the other end is the polymerization active site. When the latter, lithium amide compound, is used, a butadiene rubber is obtained in which a nitrogen-containing group is present at the polymerization initiation end and the other end is the polymerization active site.

[0049] The aforementioned lithium hydrocarbyl is preferably one having a hydrocarbyl group with 2 to 20 carbon atoms. Examples of the aforementioned lithium hydrocarbyl include ethyllithium, n-propyllithium, isopropyllithium, n-butyllithium, sec-butyllithium, tert-octyllithium, n-decyllithium, phenyllithium, 2-naphthyllithium, 2-butylphenyllithium, 4-phenylbutyllithium, cyclohexyllithium, cyclopentyllithium, and reaction products of diisopropenylbenzene and butyllithium. Among these, n-butyllithium is particularly preferred as the aforementioned lithium hydrocarbyl.

[0050] On the other hand, examples of lithium amide compounds include lithium hexamethyleneimide, lithium pyrrolidide, lithium piperidide, lithium heptamethyleneimide, lithium dodecamethyleneimide, lithium dimethylamide, lithium diethylamide, lithium dibutylamide, lithium dipropylamide, lithium diheptylamide, lithium dihexylamide, lithium dioctylamide, lithium di-2-ethylhexylamide, lithium didecylamide, lithium-N-methylpiperazide, lithium ethylpropylamide, lithium ethylbutylamide, lithium ethylbenzylamide, and lithium methylphenethylamide. Among these, cyclic lithium amides such as lithium hexamethyleneimide, lithium pyrrolidide, lithium piperidide, lithium heptamethyleneimide, and lithium dodecamethyleneimide are preferred as lithium amide compounds in terms of their interaction effect with carbon black and polymerization initiation ability, with lithium hexamethyleneimide and lithium pyrrolidide being particularly preferred.

[0051] These lithium amide compounds can generally be prepared in advance from a secondary amine and a lithium compound and used for polymerization, but they can also be prepared in the polymerization system (in-situ). The amount of polymerization initiator used is preferably selected in the range of 0.2 to 20 mmol per 100 g of monomer.

[0052] There are no particular limitations on the method for producing butadiene rubber by anionic polymerization using the aforementioned organolithium compound as a polymerization initiator; conventionally known methods can be used. Specifically, butadiene rubber having the desired active end is obtained by anionic polymerization of a butadiene compound or a butadiene compound and an aromatic vinyl compound in a hydrocarbon solvent that is inert to the reaction, such as an aliphatic, alicyclic, and aromatic hydrocarbon compound, using the lithium compound as a polymerization initiator and in the presence of a randomizer, which can be used as desired.

[0053] Furthermore, when organolithium compounds are used as polymerization initiators, not only butadiene rubber with active ends, but also copolymers of butadiene compounds with active ends and aromatic vinyl compounds can be obtained more efficiently compared to when catalysts containing lanthanum-series rare earth element compounds are used.

[0054] The hydrocarbon solvents are preferably those having 3 to 8 carbon atoms, and examples include propane, n-butane, isobutane, n-pentane, isopentane, n-hexane, cyclohexane, propene, 1-butene, isobutene, trans-2-butene, cis-2-butene, 1-pentene, 2-pentene, 1-hexene, 2-hexene, benzene, toluene, xylene, ethylbenzene, etc. These may be used individually or in mixtures of two or more.

[0055] Furthermore, the monomer concentration in the solvent is preferably 5 to 50% by mass, more preferably 10 to 30% by mass. When copolymerization is carried out using a butadiene compound and an aromatic vinyl compound, the content of the aromatic vinyl compound in the starting monomer mixture is preferably in the range of 55% by mass or less.

[0056] Furthermore, the randomizer used as described above is a compound that controls the microstructure of butadiene rubber, for example, by increasing the 1,2 bonds in the butadiene portion of a butadiene-styrene copolymer or the 3,4 bonds in an isoprene polymer, or by controlling the compositional distribution of monomer units in a butadiene compound-aromatic vinyl compound copolymer, for example, by randomizing the butadiene units and styrene units in a butadiene-styrene copolymer.

[0057] There are no particular restrictions on the randomizer, and any known compound that has been commonly used as a randomizer can be appropriately selected and used. Specifically, examples of randomizers include dimethoxybenzene, tetrahydrofuran, dimethoxyethane, diethylene glycol dibutyl ether, diethylene glycol dimethyl ether, oxolanylpropane oligomers (especially those containing 2,2-bis(2-tetrahydrofuryl)-propane), triethylamine, pyridine, N-methylmorpholine, N,N,N',N'-tetramethylethylenediamine, ethers such as 1,2-dipiperidinoethane, and tertiary amines. Potassium salts such as potassium tert-amilate and potassium tert-butoxide, and sodium salts such as sodium tert-amilate can also be used as randomizers. These randomizers may be used individually or in combination of two or more. Furthermore, the amount of randomizer used is preferably selected within the range of 0.01 to 1000 molar equivalents per mole of lithium compound.

[0058] The temperature in the polymerization reaction is preferably selected within the range of 0 to 150°C, more preferably 20 to 130°C. The polymerization reaction can be carried out under the generated pressure, but it is usually desirable to operate at a pressure sufficient to keep the monomers substantially in the liquid phase. That is, the pressure depends on the individual substances being polymerized, the polymerization medium used, and the polymerization temperature, but higher pressures can be used if desired. Such pressures can be obtained by appropriate methods, such as pressurizing the reactor with a gas that is inert to the polymerization reaction.

[0059] The modified butadiene rubber has a Mooney viscosity (ML). 1+4 The viscosity (at 100°C) is preferably 10 to 150, more preferably 15 to 100. When the Mooney viscosity is 10 or higher, sufficient rubber properties, including fracture resistance, can be obtained, and when the Mooney viscosity is 150 or lower, workability is good and it can be kneaded together with compounding agents. Furthermore, the Mooney viscosity (ML) of the unvulcanized rubber composition according to this embodiment, which contains the modified butadiene rubber, is also specified.1+4 The temperature (130°C) is preferably 10 to 150°C, and more preferably 30 to 100°C.

[0060] The modified butadiene rubber preferably has a ratio of weight-average molecular weight (Mw) to number-average molecular weight (Mn) (Mw / Mn), i.e., a molecular weight distribution (Mw / Mn) of 1 to 3, and more preferably 1.1 to 2.7. By keeping the molecular weight distribution (Mw / Mn) of the modified butadiene rubber within the aforementioned range, the modified butadiene rubber can be incorporated into a rubber composition without reducing the workability of the rubber composition, making it easy to mix and significantly improving the physical properties of the rubber composition.

[0061] Furthermore, the modified butadiene rubber preferably has a number-average molecular weight (Mn) of 100,000 to 500,000, and more preferably 150,000 to 300,000. By keeping the number-average molecular weight of the modified butadiene rubber within the above range, a decrease in the elastic modulus of the vulcanized product and an increase in hysteresis loss can be suppressed, resulting in excellent fracture resistance, as well as excellent kneadability of the rubber composition containing the modified butadiene rubber.

[0062] The modified butadiene rubber preferably has a vinyl bond content of 10 to 60% by mass in the butadiene portion, and more preferably 12 to 60% by mass.

[0063] [Denaturant] In this embodiment, primary amine-modified butadiene rubber can be produced by reacting the active end of the butadiene rubber having an active end obtained as described above with a protected primary amine compound as a modifier. Alternatively, secondary amine-modified butadiene rubber can be produced by reacting the active end of the butadiene rubber having an active end obtained as described above with a protected secondary amine compound as a modifier. As the protected primary amine compound, an alkoxysilane compound having a protected primary amino group is preferred. As the protected secondary amine compound, an alkoxysilane compound having a protected secondary amino group is preferred.

[0064] Examples of alkoxysilane compounds having a protected primary amino group that can be used as the aforementioned modifying agent include N,N-bis(trimethylsilyl)aminopropylmethyldimethoxysilane, 1-trimethylsilyl-2,2-dimethoxy-1-aza-2-silacyclopentane, N,N-bis(trimethylsilyl)aminopropyltrimethoxysilane, N,N-bis(trimethylsilyl)aminopropyltriethoxysilane, N,N-bis(trimethylsilyl)aminopropylmethyldiethoxysilane, N,N-bis(trimethylsilyl)aminoethyltrimethoxysilane, N,N-bis(trimethylsilyl)aminoethyltriethoxysilane, N,N-bis(trimethylsilyl)aminoethylmethyldimethoxysilane, and N,N-bis(trimethylsilyl)aminoethylmethyldiethoxysilane. Among these, N,N-bis(trimethylsilyl)aminopropylmethyldimethoxysilane, N,N-bis(trimethylsilyl)aminopropylmethyldiethoxysilane, and 1-trimethylsilyl-2,2-dimethoxy-1-aza-2-silacyclopentane are preferred as the alkoxysilane compounds.

[0065] Furthermore, as denaturing agents, N-methyl-N-trimethylsilylaminopropyl(methyl)dimethoxysilane, N-methyl-N-trimethylsilylaminopropyl(methyl)diethoxysilane, N-trimethylsilyl(hexamethyleneimine-2-yl)propyl(methyl)dimethoxysilane, N-trimethylsilyl(hexamethyleneimine-2-yl)propyl(methyl)diethoxysilane, N-trimethylsilyl(pyrrolidine-2-yl)propyl N-(methyl)dimethoxysilane, N-trimethylsilyl(pyrrolidine-2-yl)propyl(methyl)diethoxysilane, N-trimethylsilyl(piperidine-2-yl)propyl(methyl)dimethoxysilane, N-trimethylsilyl(piperidine-2-yl)propyl(methyl)diethoxysilane, N-trimethylsilyl(imidazole-2-yl)propyl(methyl)dimethoxysilane, N-trimethylsilyl(imidazole-2-yl)propyl Alkoxysilane compounds having a protected secondary amino group, such as pyr(methyl)diethoxysilane, N-trimethylsilyl(4,5-dihydroimidazole-5-yl)propyl(methyl)dimethoxysilane, N-trimethylsilyl(4,5-dihydroimidazole-5-yl)propyl(methyl)diethoxysilane; N-(1,3-dimethylbutylidene)-3-(triethoxysilyl)-1-propanamine, N-(1-methylethylidene)-3- Alkoxysilane compounds having an imino group, such as (triethoxysilyl)-1-propanamine, N-ethylidene-3-(triethoxysilyl)-1-propanamine, N-(1-methylpropyridene)-3-(triethoxysilyl)-1-propanamine, N-(4-N,N-dimethylaminobenzylidene)-3-(triethoxysilyl)-1-propanamine, and N-(cyclohexylidene)-3-(triethoxysilyl)-1-propanamine;Examples include alkoxysilane compounds having an amino group, such as 3-dimethylaminopropyl(triethoxy)silane, 3-dimethylaminopropyl(trimethoxy)silane, 3-diethylaminopropyl(triethoxy)silane, 3-diethylaminopropyl(trimethoxy)silane, 2-dimethylaminoethyl(trimethoxy)silane, 2-dimethylaminoethyl(trimethoxy)silane, 3-dimethylaminopropyl(diethoxy)methylsilane, and 3-dibutylaminopropyl(triethoxy)silane. These modifying agents may be used individually or in combination of two or more. Furthermore, these modifying agents may be partial condensates. Here, a partial condensate refers to a product in which some (but not all) of the SiOR modifier has undergone condensation to form SiOSi bonds.

[0066] In the modification reaction with the aforementioned modifying agent, the amount of modifying agent used is preferably 0.5 to 200 mmol / kg·butadiene rubber. More preferably, the amount used is 1 to 100 mmol / kg·butadiene rubber, and particularly preferably 2 to 50 mmol / kg·butadiene rubber. Here, the aforementioned butadiene rubber refers to the mass of the polymer only, excluding additives such as antioxidants added during or after production. By setting the amount of modifying agent within the above range, the dispersibility of reinforcing fillers, especially carbon black, is improved, and the fracture resistance and low heat generation after vulcanization are enhanced. The method of adding the denaturing agent is not particularly limited and may include adding it all at once, adding it in stages, or adding it continuously. Among these, adding it all at once is preferred.

[0067] Furthermore, while the modifying agent can be attached to the polymer main chain or side chains in addition to the polymerization start or end ends, it is preferable that the modifying agent be introduced to the polymerization start or end ends, as this can suppress energy loss from the polymer ends and improve low heat generation.

[0068] [Condensation accelerator] In this embodiment, it is preferable to use a condensation accelerator to promote the condensation reaction involving the alkoxysilane compound having a protected primary amino group used as the modifying agent described above. Such condensation accelerators can include compounds containing a tertiary amino group, or organic compounds containing one or more elements belonging to groups 3, 4, 5, 12, 13, 14, and 15 of the periodic table (long-period type). Furthermore, it is preferable that the condensation accelerator is an alkoxide, carboxylate, or acetylacetonate complex salt containing at least one metal selected from the group consisting of titanium (Ti), zirconium (Zr), bismuth (Bi), aluminum (Al), and tin (Sn).

[0069] The condensation accelerator may be added before the denaturation reaction, but it is preferable to add it to the denaturation reaction system during and / or after the denaturation reaction. If added before the denaturation reaction, a direct reaction with the active end may occur, and a hydrocarbilloxy group having a protected primary amino group at the active end may not be introduced. The timing for adding the condensation accelerator is usually 5 minutes to 5 hours after the start of the denaturation reaction, preferably 15 minutes to 1 hour after the start of the denaturation reaction.

[0070] The aforementioned condensation accelerators include, specifically, tetramethoxytitanium, tetraethoxytitanium, tetra-n-propoxytitanium, tetraisopropoxytitanium, tetra-n-butoxytitanium, tetra-n-butoxytitanium oligomer, tetra-sec-butoxytitanium, tetra-tert-butoxytitanium, tetra(2-ethylhexyl)titanium, bis(octanediolate)bis(2-ethylhexyl)titanium, and tetra(octanediolate)titanium. Titanium, titanium lactate, titanium dipropoxybis(triethanolamine), titanium dibutoxybis(triethanolamine), titanium triphtoxystearate, titanium trippropoxystearate, titanium ethylhexyl diolate, titanium trippropoxyacetylacetonate, titanium dipropoxybis(acetylacetonate), titanium trippropoxyethylacetoacetate, titanium propoxyacetylacetonate bis(ethylacetonate) Titanium tributoxyacetylacetonate, titanium dibutoxybis(acetylacetonate), titanium tributoxyethylacetonate, titanium butoxyacetylacetonate bis(ethylacetonate), titanium tetrakis(acetylacetonate), titanium diacetylacetonate bis(ethylacetonate), bis(2-ethylhexanoate)titanium oxide, bis(laurate)titanium oxide, bis(laurate)titanium oxide, bis(2-ethylhexanoate Examples of titanium-containing compounds include s(naphthenate)titanium oxide, bis(stearate)titanium oxide, bis(oleate)titanium oxide, bis(linoleate)titanium oxide, tetrakis(2-ethylhexanoate)titanium, tetrakis(laurate)titanium, tetrakis(naphthenate)titanium, tetrakis(stearate)titanium, tetrakis(oleate)titanium, and tetrakis(linoleate)titanium. Furthermore, examples of condensation accelerators include tris(2-ethylhexanoate)bismuth, tris(laurate)bismuth, tris(naphthenate)bismuth, tris(stearate)bismuth, tris(oleate)bismuth, tris(linoleate)bismuth, tetraethoxyzirconium, tetra-n-propoxyzirconium, tetraisopropoxyzirconium, tetra-n-butoxyzirconium, tetra-sec-butoxyzirconium, tetra-tert-butoxyzirconium, tetra(2-ethylhexyl)zirconium, zirconium tributoxystearate, zirconium tributoxyacetylacetonate, zirconium dibutoxybis(acetylacetonate), zirconium tributoxyethylacetoacetate, zirconium butoxyacetyl Examples include acetonate bis(ethyl acetoacetate), zirconium tetrakis(acetylacetonate), zirconium diacetylacetonate bis(ethyl acetoacetate), bis(2-ethylhexanoate) zirconium oxide, bis(laurate) zirconium oxide, bis(naphthenate) zirconium oxide, bis(stearate) zirconium oxide, bis(oleate) zirconium oxide, bis(linoleate) zirconium oxide, tetrakis(2-ethylhexanoate) zirconium, tetrakis(laurate) zirconium, tetrakis(naphthenate) zirconium, tetrakis(stearate) zirconium, tetrakis(oleate) zirconium, and tetrakis(linoleate) zirconium.

[0071] Furthermore, examples of condensation accelerators include triethoxyaluminum, tri-n-propoxyaluminum, triisopropoxyaluminum, tri-n-butoxyaluminum, tri-sec-butoxyaluminum, tri-tert-butoxyaluminum, tri(2-1-ethylhexyl)aluminum, aluminum dibutoxystearate, aluminum dibutoxyacetylacetonate, aluminum butoxybis(acetylacetonate), aluminum dibutoxyethylacetoacetate, aluminum tris(acetylacetonate), aluminum tris(ethylacetoacetate), tris(2-ethylhexanoate)aluminum, tris(laurate)aluminum, tris(naphthenate)aluminum, tris(stearate)aluminum, tris(oleate)aluminum, and tris(linoleate)aluminum.

[0072] Among the condensation accelerators mentioned above, titanium compounds are preferred as condensation accelerators, and titanium metal alkoxides, titanium metal carboxylates, or titanium metal acetylacetonate complex salts are particularly preferred.

[0073] The amount of condensation accelerator used is preferably such that the molar ratio of the compound to the total amount of hydrocarbilloxy groups present in the reaction system is 0.1 to 10, and particularly preferably 0.5 to 5. By using the amount of condensation accelerator within this range, the condensation reaction proceeds efficiently.

[0074] The condensation reaction time is typically 5 minutes to 10 hours, preferably 15 minutes to 5 hours. By setting the condensation reaction time within this range, the condensation reaction can be completed smoothly. Furthermore, the pressure of the reaction system during the condensation reaction is typically 0.01 to 20 MPa, preferably 0.05 to 10 MPa.

[0075] -Isoprene-based rubber- The isoprene-based rubbers mentioned above are polymers whose main units are isoprene units or isoprene derivative units. Examples of isoprene-based rubbers include isoprene rubber (IR), epoxidized isoprene rubber, hydrogenated isoprene rubber, grafted isoprene rubber, natural rubber (NR), deproteinized natural rubber (DPNR), high-purity natural rubber (UPNR), epoxidized natural rubber (ENR), hydrogenated natural rubber (HNR), and grafted natural rubber. These may be used individually or in combination of two or more types.

[0076] When the isoprene-based rubber is used together with the butadiene-based rubber, the content of the isoprene-based rubber in the rubber composition is preferably 20 parts by mass or more and 80 parts by mass per 100 parts by mass of the rubber component. This is preferable because it can further improve the fracture characteristics of the rubber composition, such as tensile strength and elongation at fracture. From a similar viewpoint, it is more preferable that the content of the isoprene-based rubber is 30 parts by mass or more and 60 parts by mass per 100 parts by mass of the rubber component.

[0077] -Other rubber components- The rubber composition of this embodiment may contain other rubber components besides the butadiene-based rubber and isoprene-based rubber described above, to the extent that they do not interfere with the effects of the rubber composition of this embodiment. Examples of other rubber components include non-diene rubbers. Examples of such non-diene rubbers include ethylene propylene rubber (EPDM (also referred to as EPM)), maleic acid-modified ethylene propylene rubber (M-EPM), butyl rubber (IIR), copolymers of isobutylene and aromatic vinyl or diene monomers, acrylic rubber (ACM), ionomers, and the like.

[0078] (Vulcanizing agent) The rubber composition of this embodiment preferably contains a vulcanizing agent. There are no particular restrictions on the vulcanizing agent, and sulfur can usually be used. Examples of the sulfur include powdered sulfur, precipitated sulfur, colloidal sulfur, surface-treated sulfur, and insoluble sulfur.

[0079] From the viewpoint of improving heat resistance, the content of the vulcanizing agent is preferably the same as or less than the sulfenamide-based vulcanization accelerator described below. The content of the vulcanizing agent in the rubber composition is preferably 2.5 parts by mass or more and 4.2 parts by mass or less per 100 parts by mass of rubber component. A content of 2.5 parts by mass or more allows for sufficient vulcanization, and a content of 4.2 parts by mass or less improves the aging resistance of the vulcanized rubber. Also, from a similar viewpoint, the content of the vulcanizing agent in the rubber composition is more preferably 2.8 parts by mass or more, and more preferably 3.5 parts by mass or less, per 100 parts by mass of rubber component.

[0080] (Vulcanization accelerator) The rubber composition of this embodiment contains two or more sulfenamide-based vulcanization accelerators and one or more thiophene-based vulcanization accelerators. By including these vulcanization accelerators, it is possible to maintain the ratio of monosulfide bonds and disulfide bonds while reducing the proportion of polysulfide bonds with a large number of sulfur atoms, such as those with 7 or 8 sulfur atoms linked together, and increasing the proportion of polysulfide bonds with a smaller number of sulfur atoms, such as those with 3 or 4 sulfur atoms linked together, thereby improving heat resistance. Furthermore, in this embodiment, by using two or more sulfenamide-based vulcanization accelerators, the amount of each sulfenamide-based vulcanization accelerator is reduced while maintaining the total amount of sulfenamide-based vulcanization accelerators, thus reducing the amount of thiuram-based vulcanization accelerator, suppressing bloom formation, and ensuring tack.

[0081] In the rubber composition of this embodiment, it is preferable that the mass ratio (A / B) of the total content (A) of the two or more sulfenamide-based vulcanization accelerators per 100 parts by mass of the rubber component to the content (B) of the vulcanizing agent per 100 parts by mass of the rubber component is 1 or more. The higher the content of sulfenamide-based vulcanization accelerators relative to the content of the vulcanizing agent in the rubber composition, the more sulfur bonds are broken, increasing the proportion of sulfide bonds with fewer connected sulfur atoms and further improving heat resistance. From a similar viewpoint, the above mass ratio (A / B) is more preferably 1.2 or more, more preferably 1.4 or more, and even more preferably 1.5 or more. Furthermore, from the viewpoint of ensuring tack, the above mass ratio (A / B) is preferably 2.0 or less, and more preferably 1.9 or less.

[0082] In the rubber composition of this embodiment, the mass ratio (A / C) of the total content (A) of the two or more sulfenamide-based vulcanization accelerators per 100 parts by mass of the rubber component to the total content (C) of the one or more thiram-based vulcanization accelerators per 100 parts by mass of the rubber component is preferably 6 or more and 9 or less. When the mass ratio (A / C) is within the above range, it is possible to improve heat resistance while suppressing a decrease in tack. From the viewpoint of improving heat resistance, the mass ratio (A / C) is more preferably 6.2 or more, even more preferably 6.5 or more, even more preferably 6.8 or more, and particularly preferably 7.0 or more. Furthermore, from the viewpoint of ensuring tack, the mass ratio (A / C) is more preferably 8.5 or less, and even more preferably 8.0 or less.

[0083] -Sulfenamide-based vulcanization accelerator- The rubber composition of this embodiment is characterized by containing two or more sulfenamide-based vulcanization accelerators, wherein the content of each sulfenamide-based vulcanization accelerator is 3.7 parts by mass or less per 100 parts by mass of the rubber component, and the total amount of sulfenamide-based vulcanization accelerators is 4 parts by mass or more per 100 parts by mass of the rubber component. Although the detailed mechanism is unknown, it is thought that by including two or more sulfenamide-based vulcanization accelerators, the amount of each sulfenamide-based vulcanization accelerator can be reduced, thereby suppressing bloom and ensuring tack. Furthermore, even if the amount of each sulfenamide-based vulcanization accelerator is reduced, the total amount of the two or more sulfenamide-based vulcanization accelerators is sufficient, so it is thought that heat resistance can be improved.

[0084] Furthermore, the sulfenamide-based vulcanization accelerator has the function of cleaving sulfur network chains consisting of 7 and 8 sulfur atoms, resulting in sulfur network chains consisting of 3 to 6 sulfur atoms. Therefore, although the ratio of monosulfide bonds and disulfide bonds does not change, the proportion of polysulfide bonds in the sulfur network chains consisting of 7 and 8 sulfur atoms decreases, and the proportion of polysulfide bonds in the sulfur network chains consisting of shorter sulfur atoms increases, which is presumed to improve heat resistance.

[0085] The content of each of the two or more sulfenamide-based vulcanization accelerators is 3.7 parts by mass or less per 100 parts by mass of the rubber component. When the content of each of the two or more sulfenamide-based vulcanization accelerators is 3.7 parts by mass or less per 100 parts by mass of the rubber component, bloom can be suppressed and tack can be ensured. From the viewpoint of ensuring tack, the content of each of the two or more sulfenamide-based vulcanization accelerators is preferably 3.6 parts by mass or less, and more preferably 3.5 parts by mass or less, per 100 parts by mass of the rubber component. Furthermore, from the viewpoint of improving heat resistance, the content of each of the two or more sulfenamide-based vulcanization accelerators is preferably 1.0 part by mass or more, more preferably 1.2 parts by mass or more, and even more preferably 1.5 parts by mass or more, per 100 parts by mass of the rubber component.

[0086] Furthermore, the total content of the two or more sulfenamide-based vulcanization accelerators is 4 parts by mass or more per 100 parts by mass of the rubber component. When the total content of the two or more sulfenamide-based vulcanization accelerators is 4 parts by mass or more per 100 parts by mass of the rubber component, the heat resistance of the rubber composition can be improved. From a similar viewpoint, the total content of the two or more sulfenamide-based vulcanization accelerators is preferably 4.1 parts by mass or more, and more preferably 4.2 parts by mass or more, per 100 parts by mass of the rubber component. Also, from the viewpoint of ensuring tack, the total content of the two or more sulfenamide-based vulcanization accelerators is preferably 10 parts by mass or less, more preferably 8 parts by mass or less, even more preferably 6 parts by mass or less, even more preferably 5.5 parts by mass or less, and particularly preferably 5.2 parts by mass or less, per 100 parts by mass of the rubber component.

[0087] Examples of the sulfenamide-based sulfurization accelerators include N-cyclohexylbenzothiazole-2-sulfenamide, N,N-dicyclohexyl-2-benzothiazolyl sulfenamide, N-tert-butyl-2-benzothiazolyl sulfenamide, N-oxydiethylene-2-benzothiazolyl sulfenamide, N-methyl-2-benzothiazolyl sulfenamide, N-ethyl-2-benzothiazolyl sulfenamide, and N-propyl-2-benzothiazo Lyl sulfenamide, N-butyl-2-benzothiazolyl sulfenamide, N-pentyl-2-benzothiazolyl sulfenamide, N-hexyl-2-benzothiazolyl sulfenamide, N-heptyl-2-benzothiazolyl sulfenamide, N-octyl-2-benzothiazolyl sulfenamide, N-2-ethylhexyl-2-benzothiazolyl sulfenamide, N-decyl-2-benzothiazolyl sulfenamide, N-dodecyl-2-benzothiazo Rylsulfenamide, N-stearyl-2-benzothiazolylsulfenamide, N,N-dimethyl-2-benzothiazolylsulfenamide, N,N-diethyl-2-benzothiazolylsulfenamide, N,N-dipropyl-2-benzothiazolylsulfenamide, N,N-dibutyl-2-benzothiazolylsulfenamide, N,N-dipentyl-2-benzothiazolylsulfenamide, N,N-dihexyl-2-benzothiazolylsulfenamide, N, Examples include N-diheptyl-2-benzothiazolyl sulfenamide, N,N-dioctyl-2-benzothiazolyl sulfenamide, N,N-di-2-ethylhexylbenzothiazolyl sulfenamide, N,N-didecyl-2-benzothiazolyl sulfenamide, N,N-didodecyl-2-benzothiazolyl sulfenamide, N,N-distearyl-2-benzothiazolyl sulfenamide, and N-tert-butyl-2-benzothiazolyl sulfenamide.Among these, from the viewpoint of further improving heat resistance, the sulfenamide-based vulcanization accelerator is preferably N-tert-butyl-2-benzothiazolyl sulfenamide, and from the viewpoint of improving heat resistance while ensuring tack, it is preferably N-cyclohexylbenzothiazole-2-sulfenamide or N-tert-butyl-2-benzothiazolyl sulfenamide. Of the two sulfenamide-based vulcanization accelerators, the combination of N-cyclohexylbenzothiazole-2-sulfenamide and N-tert-butyl-2-benzothiazolyl sulfenamide is particularly preferred.

[0088] - Thiuram-based vulcanization accelerator - The rubber composition of this embodiment contains one or more thiram-based vulcanization accelerators. By including thiram-based vulcanization accelerators in the rubber composition, the heat resistance can be improved.

[0089] Thiuram-based vulcanization accelerators can improve heat resistance, but they are more polar than sulfenamide-based vulcanization accelerators. Therefore, thiram-based vulcanization accelerators are more prone to blooming than sulfenamide-based vulcanization accelerators. However, in this embodiment, since two or more sulfenamide-based vulcanization accelerators are used to ensure a sufficient total amount of vulcanization accelerators, the amount of thiram-based vulcanization accelerator, which is more polar and prone to blooming than sulfenamide-based vulcanization accelerators, can be reduced. By reducing the amount of thiram-based vulcanization accelerator, blooming can be suppressed, tack can be maintained, and heat resistance can be improved.

[0090] The content of each of the one or more thiram-based vulcanization accelerators is preferably 0.8 parts by mass or less per 100 parts by mass of the rubber component. When the content of each of the one or more thiram-based vulcanization accelerators is 0.8 parts by mass or less per 100 parts by mass of the rubber component, heat resistance can be improved while ensuring tack. From the viewpoint of ensuring tack, the content of each of the one or more thiram-based vulcanization accelerators is more preferably 0.75 parts by mass or less per 100 parts by mass of the rubber component, and even more preferably 0.7 parts by mass or less. Furthermore, from the viewpoint of improving heat resistance, the content of each of the one or more thiram-based vulcanization accelerators is preferably 0.01 parts by mass or more, more preferably 0.1 parts by mass or more, more preferably 0.2 parts by mass or more, more preferably 0.3 parts by mass or more, more preferably 0.4 parts by mass or more, and even more preferably 0.5 parts by mass or more per 100 parts by mass of the rubber component.

[0091] Furthermore, when two or more thiram-based vulcanization accelerators are included, the total content of thiram-based vulcanization accelerators per 100 parts by mass of rubber component is preferably 0.8 parts by mass or less per 100 parts by mass of rubber component. When the total content of thiram-based vulcanization accelerators is 0.8 parts by mass or less per 100 parts by mass of rubber component, heat resistance can be improved while ensuring tack. From the viewpoint of ensuring tack, the total content of thiram-based vulcanization accelerators is more preferably 0.75 parts by mass or less per 100 parts by mass of rubber component, and even more preferably 0.7 parts by mass or less. Furthermore, from the viewpoint of improving heat resistance, the total content of thiram-based vulcanization accelerators is preferably 0.01 parts by mass or more per 100 parts by mass of rubber component, more preferably 0.1 parts by mass or more, more preferably 0.2 parts by mass or more, more preferably 0.3 parts by mass or more, even more preferably 0.4 parts by mass or more, and even more preferably 0.5 parts by mass or more.

[0092] Examples of the thiuram-based vulcanization accelerators include tetrakis(2-ethylhexyl)thiuram disulfide, tetramethylthiuram disulfide, tetraethylthiuram disulfide, tetrapropylthiuram disulfide, tetraisopropylthiuram disulfide, tetrabutylthiuram disulfide, tetrapentylthiuram disulfide, tetrahexylthiuram disulfide, tetraheptylthiuram disulfide, tetraoctylthiuram disulfide, tetranonylthiuram disulfide, tetradecylthiuram disulfide, tetradodecylthiuram disulfide, tetrastearylthiuram disulfide, and tetrabenzylthiuram disulfide. Examples include tetramethylthiuram monosulfide, tetraethylthiuram monosulfide, tetrapropylthiuram monosulfide, tetraisopropylthiuram monosulfide, tetrabutylthiuram monosulfide, tetrapentylthiuram monosulfide, tetrahexylthiuram monosulfide, tetraheptylthiuram monosulfide, tetraoctylthiuram monosulfide, tetranonylthiuram monosulfide, tetradecylthiuram monosulfide, tetradodecylthiuram monosulfide, tetrastearylthiuram monosulfide, tetrabenzylthiuram monosulfide, and dipentamethylenethiuram tetrasulfide. Among these, tetrabenzylthiuram disulfide is preferred as a thiuram-based vulcanization accelerator.

[0093] -Other vulcanization accelerators- The rubber composition of this embodiment may contain, in addition to the sulfenamide-based and thiuram-based vulcanization accelerators mentioned above, other vulcanization accelerators such as thiazole-based vulcanization accelerators, thiourea-based vulcanization accelerators, guanidine-based vulcanization accelerators, dithiocarbamate-based vulcanization accelerators, and xanthogenic acid-based vulcanization accelerators.

[0094] (Filler) The rubber composition of this embodiment may further contain a filler. The filler is not limited to carbon black and silica, but carbon black is more preferred. The filler may be a single type or two or more types may be used in combination.

[0095] From the viewpoint of balancing the reinforcing properties and low loss properties of the reinforcing rubber using the rubber composition, the content of the filler in the rubber composition is preferably 40 parts by mass or more and 70 parts by mass or less per 100 parts by mass of the rubber component.

[0096] The aforementioned filler has a dibutyl phthalate (DBP) oil absorption capacity of 120 mL / 100 g or more, and a nitrogen adsorption specific surface area of ​​20 m². 2 / g or more 80m 2 It is preferable that the carbon black is less than or equal to [amount] / g. Using such carbon black improves the low heat generation and compression resistance of the rubber composition. Using carbon black with a dibutyl phthalate (DBP) oil absorption capacity of 120 mL / 100 g or more improves the tensile strength and compressive strength of the rubber composition. More preferably, the dibutyl phthalate (DBP) oil absorption capacity of the carbon black is 130 mL / 100 g or more, and even more preferably 160 mL / 100 g or more. Here, the amount of dibutyl phthalate (DBP) absorbed by carbon black is determined according to JIS K 6217-4:2017, and the specific surface area for nitrogen adsorption of carbon black is determined according to JIS K 6217-2:2017.

[0097] (Other ingredients) -Vulcanization retarder- The rubber composition of this embodiment may contain a vulcanization retarder. The inclusion of a vulcanization retarder in the rubber composition can suppress rubber burning caused by overheating of the rubber composition during its preparation. Furthermore, it improves the scorch stability of the rubber composition, making it easier to extrude the rubber composition from the kneader.

[0098] Examples of the vulcanization retarder include phthalic anhydride, benzoic acid, salicylic acid, N-nitrosodiphenylamine, N-(cyclohexylthio)-phthalimide (CTP), sulfonamide derivatives, diphenylurea, and bis(tridecyl)pentaerythritol-diphosphite. Commercial vulcanization retarders may also be used, such as Monsanto's "Santoguard PVI" (N-(cyclohexylthio)-phthalimide). Among these, N-(cyclohexylthio)-phthalimide (CTP) is preferably used as the vulcanization retarder.

[0099] When using a vulcanization retarder, from the viewpoint of suppressing rubber burning of the rubber composition without interfering with the vulcanization reaction and improving scorch stability, the content of the vulcanization retarder in the rubber composition is preferably 0.1 to 1.0 parts by mass per 100 parts by mass of the rubber component.

[0100] -Softeners, thermosetting resins- The rubber composition of this embodiment preferably contains substantially no softener and thermosetting resin. Specifically, the content of each softener and thermosetting resin is preferably 5 parts by mass or less per 100 parts by mass of rubber component, more preferably the total content of the softener and thermosetting resin is 5 parts by mass or less per 100 parts by mass of rubber component, even more preferably the total content is 1 part by mass or less, and it is particularly preferable that the composition contains neither a softener nor a thermosetting resin (the total content of the softener and thermosetting resin is 0 parts by mass per 100 parts by mass of rubber component). Because the rubber composition is substantially free of softening agents, the ratio of the elastic modulus at high temperatures (e.g., 180°C) to the elastic modulus at room temperature of the vulcanized rubber can be increased. Furthermore, because the rubber composition is substantially free of thermosetting resins, the vulcanized rubber becomes more flexible, and the static longitudinal spring constant of the run-flat tire using the rubber composition of this embodiment becomes smaller, resulting in improved ride comfort of the run-flat tire.

[0101] Examples of the softening agent include process oils and thermoplastic resins. Examples of process oils include mineral oil derived from minerals, aromatic oils derived from petroleum, paraffin oil, naphthenic oil, and palm oil derived from natural products.

[0102] Examples of the thermoplastic resin include resins that soften or become liquid at high temperatures, thereby making vulcanized rubber flexible. Specifically, examples of such resins include various petroleum-based resins such as C5 series (including cyclopentadiene resins and dicyclopentadiene resins), C9 series, and C5 / C9 mixed series, as well as terpene resins, terpene-aromatic compound resins, rosin resins, phenol resins, alkylphenol resins, and other tackifiers (excluding curing agents).

[0103] Examples of the thermosetting resin include phenolic resins, melamine resins, urea resins, and epoxy resins. Examples of curing agents for the phenolic resin include hexamethylenetetramine.

[0104] The rubber composition of this embodiment may contain, in addition to the above-mentioned components, compounding agents that are commonly used in conventional rubber compositions. Examples of such compounding agents include vulcanization accelerators (zinc oxide, stearic acid, etc.), anti-aging agents, compatibilizers, workability improvers, lubricants, tackifiers, dispersants, homogenizers, and other commonly used compounding agents.

[0105] The aforementioned antioxidant can be any known type and is not particularly limited, but examples include phenolic antioxidants, imidazole antioxidants, amine antioxidants, etc. The amount of these antioxidants added is usually 0.5 to 10 parts by mass, preferably 1 to 5 parts by mass, per 100 parts by mass of the rubber component.

[0106] (Method for manufacturing rubber composition) The rubber composition of this embodiment is obtained by kneading the components described above. The kneading method can be any method commonly practiced by those skilled in the art. For kneading, kneaders such as rolls, internal mixers, and Banbury rotors can be used. Furthermore, when forming the material into sheets, strips, etc., known molding machines such as extruders and presses can be used.

[0107] <Reinforcement rubber> The reinforcing rubber of this embodiment is a reinforcing rubber using the rubber composition of this embodiment. This reinforcing rubber has excellent heat resistance.

[0108] The aforementioned reinforcing rubber can be used, for example, in the side reinforcement rubber layer or bead filler of a run-flat tire.

[0109] <Run-flat tires> The run-flat tire of this embodiment is a run-flat tire equipped with the reinforcing rubber of this embodiment. The run-flat tire of this embodiment has excellent heat resistance.

[0110] Below, an example of the structure of a run-flat tire equipped with reinforcing rubber will be explained using Figure 1.

[0111] Figure 1 is a schematic diagram showing a cross-section of one embodiment of the run-flat tire of this embodiment, illustrating the arrangement of each component, such as the reinforcing rubber layer 8, that constitutes the run-flat tire 10 of this embodiment. In Figure 1, a preferred embodiment of the run-flat tire 10 of this embodiment (hereinafter sometimes simply referred to as "tire") comprises a carcass layer 2 consisting of at least one radial carcass ply that is connected in a toroidal shape between a pair of bead cores 1 and 1' (1' is not shown) and whose ends are wrapped around the bead core 1 from the inside to the outside of the tire; a side rubber layer 3 positioned on the axial side of the side region of the carcass layer 2 to form the outer portion; a tread rubber layer 4 positioned on the radial side of the crown region of the carcass layer 2 to form the contact portion; and the tread rubber layer 4 and the carcass layer 2 The tire comprises a belt layer 5 positioned between the crown regions to form a reinforcing belt, an inner liner 6 positioned across the entire inner surface of the carcass layer 2 to form an airtight film, a bead filler 7 positioned between the main body portion of the carcass layer 2 extending from one bead core 1 to the other bead core 1' and the rolled-up portion wrapped around the bead core 1, and at least one side reinforcing rubber layer 8, having a roughly crescent-shaped cross-section along the tire's rotation axis, positioned between the carcass layer 2 and the inner liner 6, extending from the side of the bead filler 7 in the side region of the carcass layer 2 to the shoulder region 9. The run-flat tire 10 of the present invention, which is equipped with reinforcing rubber using the rubber composition of this embodiment, has excellent heat resistance.

[0112] The carcass layer 2 of the run-flat tire 10 consists of at least one carcass ply, but there may be two or more carcass plies. The reinforcing cords of the carcass ply can be arranged at an angle substantially 90° with respect to the circumferential direction of the tire, and the number of reinforcing cords driven in can be 35 to 65 cords / 50 mm. The number of layers of the belt layer 5 on the radially outer side of the crown region of the carcass layer 2 may be one layer or two or more layers. If the belt layer 5 consists of two layers, for example, if each layer is a first belt layer 5a and a second belt layer 5b (5a and 5b are not shown), the first belt layer 5a and the second belt layer 5b can be made of multiple steel cords embedded in rubber, which are aligned in parallel in the tire width direction without being twisted together. For example, the first belt layer 5a and the second belt layer 5b may be arranged so as to intersect each other between layers to form a cross belt.

[0113] The run-flat tire 10 may have a belt reinforcement layer (not shown) arranged on the radially outer side of the belt layer 5. The purpose of the reinforcing cord of the belt reinforcement layer is to ensure tensile rigidity in the circumferential direction of the tire, so it is preferable to use an organic fiber cord made of highly elastic organic fibers. As the organic fiber cord, aromatic polyamide (aramid), polyethylene naphthalate (PEN), polyethylene terephthalate, rayon, Zylon® (poly(p-phenylenebenzobisoxazole (PBO) fiber), aliphatic polyamide (nylon), etc. can be used.

[0114] Furthermore, the run-flat tire 10 may have reinforcing members (not shown) such as inserts and flippers placed outside the side reinforcement layer. Here, an insert is a reinforcing material (not shown) made of multiple highly elastic organic fiber cords arranged in a rubber coating and positioned in the circumferential direction of the tire from the bead portion to the side portion. A flipper is a reinforcing material made of multiple highly elastic organic fiber cords arranged in a rubber coating and positioned between the main body portion of the carcass ply that extends between the bead cores 1 or 1' and the folded portion that is folded back around the bead cores 1 or 1', and encloses at least a part of the bead cores 1 or 1' and the bead filler 7 positioned radially outward of the tire. The angle of the insert and flipper is preferably 30 to 60° with respect to the circumferential direction.

[0115] A pair of bead cores 1 and 1' are embedded in each bead section, and the carcass layer 2 is folded back and secured around these bead cores 1 and 1' from the inside to the outside of the tire. However, the method of securing the carcass layer 2 is not limited to this. For example, at least one of the carcass plies constituting the carcass layer 2 may be folded back around the bead cores 1 and 1' from the inside to the outside in the tire width direction, with its folded end positioned between the belt layer 5 and the crown section of the carcass layer 2, forming a so-called envelope structure. Furthermore, a tread pattern may be formed on the surface of the tread rubber layer 4 as appropriate, and an inner liner 6 may be formed in the innermost layer. As the gas to be filled into the run-flat tire 10, ordinary air or air with altered oxygen partial pressure, or an inert gas such as nitrogen can be used.

[0116] The run-flat tire 10 of this embodiment is preferably manufactured by a conventional run-flat tire manufacturing method, using the reinforcing rubber made from the rubber composition of this embodiment in the bead filler 7 and the side reinforcing rubber layer 8, etc. Specifically, rubber compositions containing various chemicals are processed into individual components in an unvulcanized state, and then bonded and molded on a tire molding machine using a conventional method to form a green tire. This green tire is then heated and pressurized in a vulcanizing machine to obtain a run-flat tire 10. [Examples]

[0117] The present invention will be described in more detail below with reference to examples, but the present invention is not limited in any way to the following examples.

[0118] <Manufacturing of Modified Polybutadiene Rubber P> (1) Production of unmodified polybutadiene In a 5 L autoclave purged with nitrogen, 1.4 kg of cyclohexane, 250 g of 1,3-butadiene, and a cyclohexane solution of 2,2-ditetrahydrofurylpropane (0.285 mmol) were injected under nitrogen. 2.85 mmol of n-butyllithium (BuLi) was then added, and polymerization was carried out for 4.5 hours in a 50°C hot water bath equipped with a stirring device. The reaction conversion rate of 1,3-butadiene was approximately 100%. A portion of this polymer solution was withdrawn in a methanol solution containing 1.3 g of 2,6-di-tert-butyl-p-cresol to halt polymerization. The solvent was then removed by steam stripping, and the solution was dried on a roll at 110°C to obtain unmodified polybutadiene.

[0119] (2) Production of modified polybutadiene rubber P The polymer solution obtained in (1) above was kept at a temperature of 50°C without deactivating the polymerization catalyst, and 1129 mg (3,364 mmol) of N,N-bis(trimethylsilyl)aminopropylmethyldiethoxysilane with a protected primary amino group was added to carry out the denaturation reaction for 15 minutes. Next, 8.11 g of tetrakis(2-ethyl-1,3-hexanediolato)titanium, a condensation accelerator, was added, and the mixture was stirred for another 15 minutes. Finally, 242 mg of silicon tetrachloride was added as a metal halogen compound to the polymer solution after the reaction, and 2,6-di-tert-butyl-p-cresol was added. Then, the solvent was removed and the protected primary amino groups were deprotected by steam stripping, and the rubber was dried using a hot roll heated to 110°C to obtain primary amine-modified polybutadiene rubber P.

[0120] <Preparation of rubber composition> The rubber compositions of Comparative Examples 1-2 and Examples 1-6 were prepared by kneading each component according to the formulation shown in Table 1 below.

[0121] <Evaluation of rubber compositions> The rubber compositions prepared for Comparative Examples 1-2 and Examples 1-6 were evaluated according to the following (1)-(3).

[0122] (1) Amount of mono / disulfide bonds A 2 mm thick sheet was cut from the vulcanized rubber obtained by vulcanizing the rubber composition, and a vulcanized rubber sheet was obtained. The vulcanized rubber sheet was extracted with acetone for 24 hours and then vacuum dried for 24 hours. The dried vulcanized rubber sheet was cut into 2 mm x 2 mm squares to form a cubic vulcanized rubber sample. Next, the dimensions of the vulcanized rubber sample in the length, width, and thickness directions were precisely measured. Next, benzene and tetrahydrofuran (THF) were dehydrated and deoxygenated, and the mixture was then mixed by volume in a 1:1 ratio. The mixture was placed in a sealable container and purged with nitrogen to obtain solution (T). The container containing solution (T) was placed in container (i), and lithium aluminum hydride (LiAlH4) powder was added while purging with nitrogen, and the container was left to stand for 2 days. The supernatant of the solution was separated and designated as solution (M). Propane-2-thiol and piperidine were dehydrated and deoxygenated, and equimolar samples of the propane-2-thiol and piperidine were added to container (i) under nitrogen purging to obtain solution (M+D). The vulcanized rubber samples, whose dimensions in three directions had been precisely measured, were placed in three separate airtight containers. Each container was then vacuum-dried for one hour and followed by nitrogen purging. Subsequently, solutions (T), (M), and (M+D) were added to the containers containing the vulcanized rubber samples, respectively, and the containers were sealed. The containers were then left at 30°C for 24 hours to allow the vulcanized rubber samples to swell. Next, under a nitrogen atmosphere, the vulcanized rubber samples were removed from each container, washed with solution (T), and the dimensions of the swollen vulcanized rubber samples were precisely measured. Furthermore, a thermomechanical analyzer (NETZSCH, product name "TMA 4000SA") was used to apply loads ranging from 1 to 100 g in stages, depending on the degree of swelling of the vulcanized rubber samples, and the relationship between compressive stress and strain was determined. The obtained data is input into equation (3) described above, and the monosulfide network chain density (ν) is calculated. M )[mol / cm 3 ] and the total amount of monosulfide network chain density and disulfide network chain density (ν M +ν D )[mol / cm 3 ] was sought. Disulfide network chain density (ν D )[mol / cm 3 ] to (ν M +ν D )-ν M The polysulfide network chain density (ν) is calculated from this. P )[mol / cm 3 ] to ν T -(ν M +ν D ) was calculated from. Furthermore, the total sulfide network chain density (ν T Taking ) as 100%, the monosulfide network chain density (ν M ), disulfide network chain density (ν D ), polysulfide network chain density (ν P The amounts were converted to percentages to calculate the amount of monosulfide bonds, disulfide bonds, and polysulfide bonds. The obtained results were applied to equation (1) described above to calculate the amount of mono / disulfide bonds. The results are shown in Table 1 below.

[0123] (2) Evaluation of heat resistance The elastic modulus at 25% strain at room temperature (a) and the elastic modulus at 25% strain at room temperature after degradation at 100°C for 24 hours (b) were measured, and the ratio of (a) to (b) (a / b) was used to evaluate the heat resistance. In Table 1 below, a smaller value indicates better heat resistance. The elastic modulus at 25% strain at room temperature was measured at a frequency of 15 Hz using a viscoelasticity measuring device (manufactured by Rheometrics). The results are shown in Table 1 below.

[0124] (3) Evaluation of Tack Tack was evaluated using a Picma Tack Tester (manufactured by Toyo Seiki Co., Ltd.). The values ​​for Comparative Example 1 are expressed exponentially, with the value set to 100. In Table 1 below, a higher numerical value indicates better tack retention. The results are shown in Table 1 below.

[0125] [Table 1]

[0126] *1 Rubber component 1: Natural rubber (RSS#1) *2 Rubber component 2: Modified polybutadiene rubber P *3 Filler: DBP oil absorption: 120mL / 100g, nitrogen adsorption specific surface area: 28m 2 Carbon black / g *4 Sulfenamide-based vulcanization accelerator 1: N-cyclohexylbenzothiazole-2-sulfenamide (manufactured by Ouchi Shinko Chemical Industry Co., Ltd., product name "Noxellar CZ-G") *5 Sulfenamide-based vulcanization accelerator 2: N-tert-butyl-2-benzothiazolyl sulfenamide (manufactured by Ouchi Shinko Chemical Industry Co., Ltd., trade name "Noxellar NS") *6 Thiuram-based vulcanization accelerator: Tetrabenzyl thiuram disulfide (manufactured by Sanshin Chemical Industry Co., Ltd., product name "Sunceller TBzTD") *7 Vulcanizing agent: Powdered sulfur *8 Other ingredients: Alkylphenol-formaldehyde resin manufactured by Sumitomo Bakelite Co., Ltd., etc. *9 A / B: The mass ratio (A / B) of the total content of two or more sulfenamide-based vulcanization accelerators per 100 parts by mass of rubber component (A) to the content of the vulcanizing agent per 100 parts by mass of rubber component (B). *10 A / C: The mass ratio (A / C) of the total content (A) of two or more sulfenamide-based vulcanization accelerators per 100 parts by mass of the rubber component, and the total content (C) of one or more thiram-based vulcanization accelerators per 100 parts by mass of the rubber component.

[0127] Table 1 shows that the rubber compositions of Examples 1 to 6, which contain two or more sulfenamide-based vulcanization accelerators and one or more thiram-based vulcanization accelerators, and whose individual content and total content of sulfenamide-based vulcanization accelerators are within the range of the present invention, have improved heat resistance while maintaining tack. [Industrial applicability]

[0128] According to the present invention, it is possible to provide a rubber composition that suppresses bloom and maintains tack while improving heat resistance. Furthermore, according to the present invention, it is possible to provide a reinforcing rubber using such a rubber composition, and a run-flat tire equipped with the reinforcing rubber.

[0129] [Contribution to the United Nations-led Sustainable Development Goals (SDGs)] The SDGs have been proposed to realize a sustainable society. One embodiment of the present invention is considered to be a technology that can contribute to "No. 12: Responsible Consumption and Production" and "No. 13: Climate Action," among others. [Explanation of symbols]

[0130] 1: Bead core 2: Carcass layer 3: Side rubber layer 4: Tread rubber layer 5: Belt layer 6: Inner liner 7: Bead Filler 8: Side reinforcement rubber layer 9: Shoulder area 10: Run-flat tires

Claims

1. A rubber composition comprising a rubber component, two or more sulfenamide-based vulcanization accelerators, and one or more thiram-based vulcanization accelerators, The content of each of the two or more sulfenamide-based vulcanization accelerators is 3.7 parts by mass or less per 100 parts by mass of the rubber component. A rubber composition in which the total content of the two or more sulfenamide-based vulcanization accelerators is 4 parts by mass or more per 100 parts by mass of the rubber component.

2. The rubber composition according to claim 1, wherein the content of each of the one or more thiram-based vulcanization accelerators is 0.8 parts by mass or less per 100 parts by mass of the rubber component.

3. The rubber composition comprises a vulcanizing agent, The rubber composition according to claim 1, wherein the total content (A) of the two or more sulfenamide-based vulcanization accelerators per 100 parts by mass of the rubber component is 1 or more, and the mass ratio (A / B) of the content (B) of the vulcanizing agent per 100 parts by mass of the rubber component is 1 or more.

4. The rubber composition according to claim 1, wherein the mass ratio (A / C) of the total content (A) of the two or more sulfenamide-based vulcanization accelerators per 100 parts by mass of the rubber component to the total content (C) of the one or more thiram-based vulcanization accelerators per 100 parts by mass of the rubber component is 6 or more and 9 or less.

5. The rubber composition according to claim 1, wherein the rubber component is butadiene-based rubber and isoprene-based rubber.

6. The rubber composition according to claim 5, wherein the butadiene-based rubber is a modified butadiene rubber.

7. The rubber composition according to claim 5, wherein the content of the butadiene-based rubber is 20 parts by mass or more and 80 parts by mass or less per 100 parts by mass of the rubber component.

8. Furthermore, it includes a filler, The rubber composition according to claim 1, wherein the content of the filler is 40 parts by mass or more and 70 parts by mass or less per 100 parts by mass of the rubber component.

9. The aforementioned filler has a dibutyl phthalate oil absorption capacity of 120 mL / 100 g or more, and a nitrogen adsorption specific surface area of ​​20 m². ２ / g or more 80m ２ The rubber composition according to claim 8, wherein the carbon black is less than or equal to / g.

10. A reinforcing rubber using the rubber composition described in claim 1.

11. A run-flat tire comprising the reinforcing rubber described in claim 10.

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