pneumatic tires

Abstract

To provide a pneumatic tire having high life performance in which temporal change of rubbers is sufficiently suppressed.SOLUTION: In the pneumatic tire, grooves are formed on a surface of a tread part. Rubber compositions constituting the tread part are rubber compositions in which a ratio V(%) of monosulfide bond in a total cross-linking form by sulfide bond is 50% or higher and further a land ratio L(%) in the tread part of the tire mounted on a normal rim and filled with normal inner pressure is 70% or less.SELECTED DRAWING: None

Description

[Technical Field]

[0001] This disclosure relates to pneumatic tires, and more specifically, to pneumatic tires with high lifespan. [Background technology]

[0002] The pneumatic tires fitted to vehicles (hereinafter simply referred to as "tires") deteriorate over time due to factors such as increased mileage and the effects of ultraviolet rays. This aging process of the rubber leads to accelerated wear due to friction with the road surface, the formation of cracks in the tread, and the occurrence of cut chips where the corners of the tread pattern are broken off. As a result, the wear performance gradually decreases, and the tire's lifespan is reduced, eventually leading to the need to replace the tires.

[0003] Therefore, various technologies have been proposed to improve tire wear performance by modifying the compound of tread rubber and other materials, thereby suppressing the deterioration of the rubber over time and extending tire life, i.e., improving life performance (for example, Patent Document 1).

[0004] However, considering the increasing demands for safety in recent years, where long-distance travel on expressways is common, as well as demands for environmental protection and economic efficiency, the conventional technologies mentioned above are insufficient, and further improvements in lifespan are desired. [Prior art documents] [Patent Documents]

[0005] [Patent Document 1] Japanese Patent Publication No. 2008-31244 [Overview of the project] [Problems that the invention aims to solve]

[0006] In view of the above problems, an object of the present disclosure is to provide a pneumatic tire with high life performance in which the change over time of rubber is sufficiently suppressed.

Means for Solving the Problems

[0007] The present inventors have earnestly studied to solve the above problems, and have found that the above problems can be solved by the disclosure described below, and have completed the present disclosure.

[0008] The present disclosure is a pneumatic tire having grooves on the surface of the tread portion, where the rubber composition constituting the tread portion contains 50 parts by mass or more of natural rubber in 100 parts by mass of the rubber component, and the ratio V (%) of monosulfide bonds in the total crosslinked form by sulfide bonds is 50% or more The rubber component contains 20 parts by mass or more of carbon black with an average primary particle diameter of 5 nm or more and 20 nm or less, per 100 parts by mass. is a rubber composition, furthermore, when incorporated into a standard rim and set to the standard internal pressure, the land ratio L (%) in the tread portion of the tire is 70% or less, the ratio V / L (%) of the ratio V (%) of the monosulfide bonds to the land ratio L (%) is 140% or more, also, the tread portion has one or more circumferential grooves extending continuously in the tire circumferential direction in each of two regions sandwiching the tire equatorial plane, when the land ratio in one region is La (%) and the land ratio in the other region is Lb (%), La and Lb are different from each other, and the pneumatic tire is characterized in that La (%) and Lb (%) satisfy the following formula. |La - Lb|>20

Advantages of the Invention

[0009] According to the present disclosure, it is possible to sufficiently suppress the change over time of rubber and provide a pneumatic tire with high life performance.

Embodiments for Carrying Out the Invention

[0010] [1] Features of the Tire of the Present Disclosure 1. Outline The pneumatic tire of this disclosure has the following features:

[0011] The pneumatic tire of this disclosure is a pneumatic tire having grooves on the surface of the tread portion, wherein the rubber composition constituting the tread portion contains 50 parts by mass or more of natural rubber per 100 parts by mass of rubber component, and the ratio V(%) of monosulfide bonds in the total crosslinking configuration by sulfide bonds is 50% or more. The rubber component contains 20 parts by mass or more of carbon black with an average primary particle diameter of 5 nm or more and 20 nm or less, per 100 parts by mass. It is a rubber composition. When assembled onto a standard rim and subjected to standard internal pressure, the land ratio L(%) of the tire tread is 70% or less. Furthermore, the ratio V(%) of monosulfide bonds to the land ratio L(%) is 140% or more. Furthermore, the tread portion has one or more circumferential grooves extending continuously in the circumferential direction of the tire, in each of the two regions flanking the tire's equatorial plane, and when the land ratio in one region is La (%) and the land ratio in the other region is Lb (%), La and Lb are different from each other, and La (%) and Lb (%) satisfy the following equation. |La-Lb|>20

[0012] By using a tire with such a tread section, the deterioration of the rubber over time is sufficiently suppressed, as will be explained in the following sections, and a pneumatic tire with high lifespan performance can be provided.

[0013] In the above description, "standard rim" refers to the rim specified for each tire in the standard system that includes the standard on which the tire is based. For example, in the case of JATMA (Japan Automobile Tire Manufacturers Association), it refers to the standard rim for the applicable size listed in the "JATMA YEAR BOOK," in the case of ETRTO (The European Tyre and Rim Technical Organisation), it refers to the "Measuring Rim" listed in the "STANDARDS MANUAL," and in the case of TRA (The Tire and Rim Association, Inc.), it refers to the "Design Rim" listed in the "YEAR BOOK." In the case of tires not specified in the standard, it refers to the rim with the smallest diameter and the narrowest rim width among rims that can be mounted on and can maintain internal pressure, i.e., rims that do not cause air leakage from between the rim and tire.

[0014] Furthermore, "standard internal pressure" refers to the air pressure specified for each tire by the aforementioned standards. For JATMA, it refers to the maximum air pressure; for TRA, it refers to the maximum value listed in the table "TIRE LOAD LIMITS AT VARIOUS COLD INFLATION PRESSURES"; and for ETRTO, it refers to "INFLATION PRESSURE."

[0015] 2. Mechanism of action of the pneumatic tire of this disclosure The mechanism by which the pneumatic tire of this disclosure exhibits its effect, that is, the mechanism by which the deterioration of the rubber over time is sufficiently suppressed, thereby providing a pneumatic tire with high lifespan performance, is thought to be as follows.

[0016] (1) Ratio of monosulfide bonds As described above, in the pneumatic tire according to this disclosure, the rubber composition used to constitute the tread portion is a rubber composition in which the ratio V (%) of monosulfide bonds in the total crosslinking configuration by sulfide bonds is 50% or more.

[0017] Tires are generally manufactured by crosslinking unvulcanized tires, which are made using various tire components, with sulfur. The crosslinking forms can be classified into monosulfide bonds, in which only one sulfur molecule is involved, and polysulfide bonds, in which two or more sulfur molecules are involved between the crosslinking points.

[0018] Of these, polysulfide bonds are weak because multiple sulfur molecules are interposed between the crosslinking points. Therefore, the crosslinking chains are easily broken by heat generated during operation, leading to an increase in crosslinking density and a decrease in lifespan. On the other hand, monosulfide bonds have only one sulfur molecule interposed between the crosslinking points, making the crosslinking chains less likely to break and suppressing an increase in crosslinking density. Therefore, it is thought that increasing the proportion of monosulfide bonds in the overall crosslinking configuration can suppress the decrease in lifespan.

[0019] Based on this idea, the Discloser conducted various experiments and studies and found that when the tread portion is formed from a rubber composition in which the ratio V(%) of monosulfide bonds in the total crosslinking configuration by sulfide bonds is 50% or more, it is possible to sufficiently suppress the deterioration of the rubber over time and provide a tire with high life performance. Furthermore, it was found that this ratio V(%) of monosulfide bonds is more preferably 60% or more, and even more preferably 70% or more. There is no particular upper limit, but from the viewpoint of cut chip performance, it is preferable to be 90% or less.

[0020] The ratio V (%) of monosulfide bonds described above can be calculated using the known method shown in Japanese Patent Publication No. 2019-35013, Japanese Patent Publication No. 2019-45196, Japanese Patent Publication No. 2020-111674, etc., by dividing the crosslinking density of monosulfide bonds by the total crosslinking density of sulfide bonds.

[0021] (2) Rand ratio Furthermore, in the pneumatic tire relating to this disclosure, the land ratio L(%) in the tread portion of the tire, when mounted on a regular rim and at regular internal pressure, is set to 70% or less.

[0022] The "land ratio" is the ratio of the actual contact area to the hypothetical contact area created by filling all the grooves on the surface of the tread.

[0023] While driving, tires generate heat in the tread due to friction with the road surface, but the air passing through the grooves cools the tread, thus suppressing the rise in temperature. However, if the land ratio is large, the contact area with the road surface increases, and the volume of the groove space decreases. As a result, efficient cooling cannot occur in the groove space, the tread is more prone to overheating, and this is thought to easily lead to a decrease in tire lifespan.

[0024] Based on this idea, the Discloser conducted various experiments and studies and found that in the case of tires with a land ratio L(%) of 70% or less, the area in contact with the road surface can be appropriately reduced, and the volume of the groove space can be appropriately secured, so that cooling can be efficiently performed in the groove space, the temperature rise of the tread part is sufficiently suppressed, and a decrease in life performance is unlikely to occur. Furthermore, it was found that a land ratio L(%) of 60% or less is more preferable, and 50% or less is even more preferable. There is no particular lower limit, but from the viewpoint of grip performance during driving, it is preferable to have a land ratio of 40% or more.

[0025] The above-mentioned land ratio can be determined from the contact patch shape under normal rim, normal internal pressure, and normal load conditions.

[0026] Specifically, the tire is mounted on a standard rim, the standard internal pressure is applied, and it is left to stand at 25°C for 24 hours. Then, ink is applied to the surface of the tire tread, and the standard load is applied and it is pressed onto cardboard (camber angle is 0°). By transferring the image to the paper, the contact shape can be obtained. The tire is rotated 72° in the circumferential direction, and the image is transferred at 5 locations. In other words, the contact shape is obtained 5 times. At this time, for the 5 contact shapes, S is the average value (simple average) of the maximum length in the axial direction of the tire, and W is the average value (simple average) of the length in the direction perpendicular to the axial direction.

[0027] The land ratio can then be calculated from (average area of ​​the five contact shapes (inked areas) transferred to the cardboard / (S × W) × 100 (%).

[0028] "Regular load" refers to the load specified for each tire by each standard in the standards system, including the standard on which the aforementioned tire is based, and indicates the maximum mass that the tire is allowed to be loaded with. For JATMA, this is the maximum load capacity; for TRA, it is the maximum value listed in the table "TIRE LOAD LIMITS AT VARIOUS COLD INFLATION PRESSURES"; and for ETRTO, it is "LOAD CAPACITY".

[0029] In summary, in the tire according to this disclosure, the effects of composing the tread portion with a rubber composition having a monosulfide bond ratio V(%) of 50% or more, and the effects of setting the land ratio L(%) of the tread portion to 70% or less, work together to synergistically suppress the deterioration of the rubber over time, thereby providing a tire with high lifespan performance.

[0030] [2] More preferred embodiments of the tire relating to the present disclosure The tire relating to this disclosure can achieve even greater effects by adopting the following configurations.

[0031] 1. Relationship between monosulfide bond ratio V (%) and land ratio L (%) As described above, the tire relating to this disclosure has a tread made of a rubber composition with a monosulfide bond ratio V(%) of 50% or more, and a land ratio L(%) of the tread is 70% or less. However, after further experiments and studies conducted by the Discloser, it was found that a more significant effect can be obtained when both V and L are controlled to a certain relationship.

[0032] Specifically, it was found that if V / L(%) is 75% or higher, more preferably 100% or higher, and even more preferably 140% or higher, the change over time is further suppressed and the life performance is further improved.

[0033] In other words, it was found that when the land ratio L(%) is constant, a larger monosulfide bond ratio V(%) leads to better life performance, and when the monosulfide bond ratio V(%) is constant, a smaller land ratio L(%) leads to better life performance.

[0034] 2. Land ratio L (%) in the two regions straddling the tire's equatorial plane. When a vehicle is driving straight, the inner part of the tread of the tire makes contact with the road surface, while when turning, the outer part of the tread tends to make contact with the road surface. Generally, the rubber changes over time differently in the inner and outer parts of the tread.

[0035] Therefore, in the tire according to this disclosure, the tread portion has one or more circumferential grooves extending continuously in the circumferential direction of the tire, in each of the two regions flanking the tire's equatorial plane, and it is preferable that when the land ratio in one region is La (%) and the land ratio in the other region is Lb (%), La and Lb are different from each other. This makes it possible to equalize the change in rubber over time in the two regions of the tread portion, and is therefore thought to further improve life performance.

[0036] Specifically, it is preferable that the land ratios La(%) and Lb(%) in each region satisfy the relationship |La-Lb|>20.

[0037] [3] Embodiment The present disclosure will be described in detail below based on embodiments.

[0038] 1. Rubber composition that forms the tread (tread rubber composition) In this disclosure, the tread rubber composition can be obtained by appropriately adjusting the types and amounts of the various compounding materials described below, specifically, rubber components, fillers, softeners, vulcanizing agents, and vulcanization accelerators.

[0039] (1) Compounding materials (a) Rubber component In the tread rubber composition, the rubber component is not particularly limited, and various rubbers (polymers) commonly used in tire manufacturing can be used, such as isoprene rubber, styrene-butadiene rubber (SBR), butadiene rubber (BR), diene rubbers such as nitrile rubber (NBR), and butyl rubbers such as butyl rubber. However, from the viewpoint of obtaining good wear resistance, it is preferable to use a mixture of isoprene-based rubber, such as natural rubber (NR), with styrene-butadiene rubber (SBR) and / or butadiene rubber (BR).

[0040] (i) Isoprene rubber Examples of isoprene-based rubbers include natural rubber (NR), isoprene rubber (IR), modified NR, modified NR, and modified IR, but NR is preferred from the viewpoint of abrasion resistance.

[0041] For NR, common types used in the tire industry can be used, such as SIR20, RSS#3, and TSR20. For IR, there are no particular limitations, and common types used in the tire industry can be used, such as IR2200. Examples of modified NR include deproteinized natural rubber (DPNR) and high-purity natural rubber (UPNR). Examples of modified NR include epoxidized natural rubber (ENR), hydrogenated natural rubber (HNR), and grafted natural rubber. Examples of modified IR include epoxidized isoprene rubber, hydrogenated isoprene rubber, and grafted isoprene rubber. These may be used individually or in combination of two or more types.

[0042] The natural rubber content in 100 parts by mass of rubber components is preferably 25 parts by mass or more, more preferably 50 parts by mass or more, and even more preferably 75 parts by mass or more. On the other hand, there is no particular upper limit, but it is preferably 85 parts by mass or less. By using such a content, good wear resistance can be obtained.

[0043] (b) SBR The weight-average molecular weight of SBR is, for example, more than 100,000 and less than 2,000,000. The styrene content of SBR is preferably 10% by mass or more, more preferably 20% by mass or more, and even more preferably 30% by mass or more. On the other hand, it is preferably 50% by mass or less, more preferably 45% by mass or less, and even more preferably 40% by mass or less. Furthermore, the amount of vinyl bonded to SBR (amount of 1,2-bonded butadiene units) is preferably more than 5 mol% and less than 70 mol%.

[0044] By using SBR with such styrene content and vinyl bonding amount, good wear resistance can be obtained. The structure of SBR (measurement of styrene content and vinyl bonding amount) can be performed, for example, using the JNM-ECA series equipment manufactured by JEOL Ltd.

[0045] The SBR is not particularly limited; for example, emulsion-polymerized styrene-butadiene rubber (E-SBR), solution-polymerized styrene-butadiene rubber (S-SBR), etc., can be used. The SBR may be either unmodified SBR or modified SBR.

[0046] Modified SBRs can be any SBR having a functional group that interacts with a packing material such as silica. Examples include terminally modified SBRs (terminally modified SBRs having the functional group at the terminal) in which at least one end of the SBR is modified with a compound having the functional group (modifying agent), main-chain modified SBRs having the functional group in the main chain, main-chain terminally modified SBRs having the functional group in both the main chain and the terminal (for example, main-chain terminally modified SBRs having the functional group in the main chain and at least one end modified with the modifying agent), and terminally modified SBRs that are modified (coupled) with a polyfunctional compound having two or more epoxy groups in the molecule, and in which hydroxyl groups or epoxy groups are introduced.

[0047] Examples of the functional group include an amino group, an amide group, a silyl group, an alkoxysilyl group, an isocyanate group, an imino group, an imidazole group, a urea group, an ether group, a carbonyl group, an oxycarbonyl group, a mercapto group, a sulfide group, a disulfide group, a sulfonyl group, a sulfinyl group, a thiocarbonyl group, an ammonium group, an imide group, a hydrazo group, an azo group, a diazo group, a carboxyl group, a nitrile group, a pyridyl group, an alkoxy group, a hydroxyl group, an oxy group, an epoxy group, etc. These functional groups may have substituents.

[0048] As the modified SBR, for example, SBR modified with a compound (modifying agent) represented by the following formula can be used.

[0049]

Chemical formula

[0050] In the formula, R 4 , R 2 and R 3 are the same or different and represent an alkyl group, an alkoxy group, a silyloxy group, an acetal group, a carboxyl group (-COOH), a mercapto group (-SH) or derivatives thereof. R 4 and R 5 are the same or different and represent a hydrogen atom or an alkyl group. R 4 and R 5 may combine to form a ring structure together with the nitrogen atom. n represents an integer.

[0051] Examples of the modified SBR modified with the compound (modifying agent) represented by the above formula include SBR in which the polymerization terminal (active terminal) of solution-polymerized styrene-butadiene rubber (S-SBR) is modified with the compound represented by the above formula (modified SBR described in JP-A-2010-111753), etc.

[0052] R 1 , R 2 and R 3A suitable alkoxy group is used (preferably an alkoxy group having 1 to 8 carbon atoms, more preferably an alkoxy group having 1 to 4 carbon atoms). 4 and R 5 A suitable alkyl group (preferably an alkyl group having 1 to 3 carbon atoms) is used. n is preferably 1 to 5, more preferably 2 to 4, and even more preferably 3. Also, R 4 and R 5 When the alkoxy group is bonded to form a ring structure with the nitrogen atom, it is preferably a 4- to 8-membered ring. Note that the alkoxy group also includes cycloalkoxy groups (such as cyclohexyloxy groups) and aryloxy groups (such as phenoxy and benzyloxy groups).

[0053] Specific examples of the above-mentioned denaturing agents include 2-dimethylaminoethyltrimethoxysilane, 3-dimethylaminopropyltrimethoxysilane, 2-dimethylaminoethyltriethoxysilane, 3-dimethylaminopropyltriethoxysilane, 2-diethylaminoethyltrimethoxysilane, 3-diethylaminopropyltrimethoxysilane, 2-diethylaminoethyltriethoxysilane, and 3-diethylaminopropyltriethoxysilane. These may be used individually or in combination of two or more.

[0054] Furthermore, modified SBR can also be modified using the following compounds (modifying agents): For example, polyglycidyl ethers of polyhydric alcohols such as ethylene glycol diglycidyl ether, glycerin triglycidyl ether, trimethylolethane triglycidyl ether, and trimethylolpropane triglycidyl ether; polyglycidyl ethers of aromatic compounds having two or more phenol groups such as diglycidyl bisphenol A; polyepoxy compounds such as 1,4-diglycidylbenzene, 1,3,5-triglycidylbenzene, and polyepoxylated liquid polybutadiene; epoxy group-containing tertiary amines such as 4,4'-diglycidyl-diphenylmethylamine and 4,4'-diglycidyl-dibenzylmethylamine; diglycidylaniline, N,N'-diglycidyl-4-glycidyloxyaniline, Diglycidylamino compounds such as diglycidyl orthotoluidine, tetraglycidylmetoxylendiamine, tetraglycidylaminodiphenylmethane, tetraglycidyl-p-phenylenediamine, diglycidylaminomethylcyclohexane, and tetraglycidyl-1,3-bisaminomethylcyclohexane; amino group-containing acid chlorides such as bis-(1-methylpropyl)carbamate chloride, 4-morpholine carbonyl chloride, 1-pyrrolidinecarbonyl chloride, N,N-dimethylcarbamate chloride, and N,N-diethylcarbamate chloride; epoxy group-containing silane compounds such as 1,3-bis-(glycidyloxypropyl)-tetramethyldisiloxane and (3-glycidyloxypropyl)-pentamethyldisiloxane;(Trimethylsilyl)[3-(trimethoxysilyl)propyl]sulfide, (Trimethylsilyl)[3-(triethoxysilyl)propyl]sulfide, (Trimethylsilyl)[3-(tributoxysilyl)propyl]sulfide, (Trimethylsilyl)[3-(methyldimethoxysilyl)propyl]sulfide, (Trimethylsilyl)[3-(methyldiethoxysilyl)propyl]sulfide, (Trimethylsilyl)[3-(methyldipropoxysilyl)propyl]sulfide Sulfide group-containing silane compounds such as [sisilyl)propyl]sulfide and (trimethylsilyl)[3-(methyldibutoxysilyl)propyl]sulfide; N-substituted aziridine compounds such as ethyleneimine and propyleneimine; methyltriethoxysilane, N,N-bis(trimethylsilyl)-3-aminopropyltrimethoxysilane, N,N-bis(trimethylsilyl)-3-aminopropyltriethoxysilane, N,N-bis(trimethylsilyl)aminoethyltrimethoxysilane, N,N-bis(trimethylsilyl)aminoethyl Alkoxysilanes such as tiltriethoxysilane; (thio)benzophenone compounds having an amino group and / or a substituted amino group, such as 4-N,N-dimethylaminobenzophenone, 4-N,N-di-t-butylaminobenzophenone, 4-N,N-diphenylaminobenzophenone, 4,4'-bis(dimethylamino)benzophenone, 4,4'-bis(diethylamino)benzophenone, 4,4'-bis(diphenylamino)benzophenone, and N,N,N',N'-bis-(tetraethylamino)benzophenone; 4-N,N- Benzaldehyde compounds having an amino group and / or a substituted amino group, such as dimethylaminobenzaldehyde, 4-N,N-diphenylaminobenzaldehyde, and 4-N,N-divinylaminobenzaldehyde; N-substituted pyrrolidones such as N-methyl-2-pyrrolidone, N-vinyl-2-pyrrolidone, N-phenyl-2-pyrrolidone, Nt-butyl-2-pyrrolidone, and N-methyl-5-methyl-2-pyrrolidone; N-substituted piperidones such as N-methyl-2-piperidone, N-vinyl-2-piperidone, and N-phenyl-2-piperidone;In addition to N-substituted lactams such as N-methyl-ε-caprolactam, N-phenyl-ε-caprolactam, N-methyl-ω-laurylolactam, N-vinyl-ω-laurylolactam, N-methyl-β-propiolactam, and N-phenyl-β-propiolactam, other examples include N,N-bis-(2,3-epoxypropoxy)-aniline, 4,4-methylene-bis-(N,N-glycidylaniline), and tris-(2,3-epoxypropyl)-1,3,5-triazine-2,4,6-triones. Examples include N,N-diethylacetamide, N-methylmaleimide, N,N-diethylurea, 1,3-dimethylethyleneurea, 1,3-divinylethyleneurea, 1,3-diethyl-2-imidazolidinone, 1-methyl-3-ethyl-2-imidazolidinone, 4-N,N-dimethylaminoacetophene, 4-N,N-diethylaminoacetophenone, 1,3-bis(diphenylamino)-2-propanone, and 1,7-bis(methylethylamino)-4-heptanone. Modification using the above compounds (modifiers) can be carried out by known methods.

[0055] Furthermore, the SBR content in 100 parts by mass of rubber components is preferably 10 parts by mass or more, more preferably 15 parts by mass or more, and even more preferably 20 parts by mass or more, when combined with BR.

[0056] For example, SBR manufactured and sold by companies such as Sumitomo Chemical Co., Ltd., JSR Corporation, Asahi Kasei Corporation, and Nippon Zeon Co., Ltd. can be used. SBR may be used alone or in combination of two or more types.

[0057] (H)BR The weight-average molecular weight of BR is between 100,000 and 2,000,000. The vinyl bond content of BR is between 1% and 30% by mass, the cis content is between 1% and 98% by mass, and the trans content is between 1% and 60% by mass. The cis content can be measured by infrared absorption spectroscopy.

[0058] The BR is not particularly limited, and can be high-cis content (cis content of 90% or more), low-cis content, or BR containing syndiotactic polybutadiene crystals. The BR can be either unmodified or modified, and modified BR can be modified BR into which the aforementioned functional groups have been introduced. These may be used individually or in combination of two or more.

[0059] For example, tin-modified BR can be used. Tin-modified BR is obtained by polymerizing 1,3-butadiene with a lithium initiator, followed by the addition of a tin compound, and it is preferable that the terminal ends of the tin-modified BR molecule are linked by tin-carbon bonds.

[0060] Examples of lithium initiators include lithium-based compounds such as alkyllithium, aryllithium, vinyllithium, organotinlithium, and organonitrogenlithium compounds, as well as lithium metal. By using the aforementioned lithium initiator as the initiator for tin-modified BR, tin-modified BR with high vinyl and low cis content can be produced.

[0061] Examples of tin compounds include tin tetrachloride, butyltin trichloride, dibutyltin dichloride, dioctyltin dichloride, tributyltin chloride, triphenyltin chloride, diphenyldibutyltin, triphenyltin ethoxide, diphenyldimethyltin, dityltin chloride, diphenyltin dioctanoate, divinyldiethyltin, tetrabenzyltin, dibutyltin distearate, tetraalyltin, and p-tributyltin styrene.

[0062] Furthermore, the tin atom content in tin-modified BR is preferably 50 ppm or more, more preferably 60 ppm or more. On the other hand, it is preferably 3000 ppm or less, more preferably 2500 ppm or less, and even more preferably 250 ppm or less.

[0063] Furthermore, the molecular weight distribution (Mw / Mn) of tin-modified BR is preferably 2 or less, and more preferably 1.5 or less.

[0064] Furthermore, the amount of vinyl bonded in tin-modified BR is preferably 5% by mass or more, and more preferably 7% by mass or more. On the other hand, the amount of vinyl bonded in tin-modified BR is preferably 50% by mass or less, and more preferably 20% by mass or less.

[0065] The S-modified BR and tin-modified BR mentioned above may be used individually or in combination of two or more types.

[0066] As mentioned above, the BR content in 100 parts by mass of rubber components is preferably 10 parts by mass or more, more preferably 15 parts by mass or more, and even more preferably 20 parts by mass or more, when combined with SBR.

[0067] For example, BR manufactured and sold by companies such as Ube Industries, Ltd., JSR Corporation, Asahi Kasei Corporation, and Nippon Zeon Co., Ltd. can be used. BR may be used alone or in combination of two or more types.

[0068] (ii) Other rubber components In addition, other rubber components may include, if necessary, nitrile rubber (NBR) or other rubbers (polymers) commonly used in tire manufacturing.

[0069] (b) Compounding materials other than rubber components (i) Filling agent In this embodiment, the tread rubber composition preferably contains a filler. Specific fillers include, for example, carbon black, silica, graphite, calcium carbonate, talc, alumina, clay, aluminum hydroxide, and mica.

[0070] (i) Carbon Black The tread rubber composition preferably contains carbon black. From the viewpoint of wear resistance, the particle size (average primary particle size) of the carbon black is preferably 20 nm or less, more preferably 17 nm or less, and even more preferably 15 nm or less. On the other hand, there is no particular lower limit, but from the viewpoint of dispersibility, it is preferably 5 nm or more, and more preferably 10 nm or more.

[0071] The average primary particle diameter described above can be calculated by directly observing carbon black extracted from the rubber composition cut from a tire using an electron microscope (TEM), calculating the equicross-sectional area diameter from the area of ​​the obtained carbon black particles, and then determining the average value.

[0072] The specific surface area of ​​carbon black CTAB (Cetyl Tri-methyl Ammonium Bromide) is 130 m² from the perspective of abrasion resistance. 2 It is preferable that it be 140m or more / g. 2 It is more preferable that it is 150m or more per gram. 2 It is even more preferable if it is 1 / g or more. On the other hand, there is no particular upper limit, but from the viewpoint of variability, etc., 250m 2 It is preferable that it be less than / g, and 200m 2 It is more preferable that it be less than or equal to / g, and 180m 2 It is even more preferable if it is less than or equal to / g. Note that the CTAB specific surface area is a value measured in accordance with JIS K6217-3:2001.

[0073] The nitrogen adsorption specific surface area (N2SA) of carbon black is 125 m², from the perspective of abrasion resistance. 2 It is preferable that it be 145m or more / g 2 It is more preferable to be 155m or more per g. 2 It is even more preferable if it is 1 / g or more. On the other hand, there is no particular upper limit, but from the viewpoint of variability, etc., 250m 2 It is preferable that it be less than / g, and 200m 2 It is more preferable that it be less than or equal to / g, and 180m 2It is even more preferable if the amount is less than or equal to / g. The specific surface area for nitrogen adsorption of carbon black is a value measured in accordance with JIS K6217-2:2001.

[0074] The iodine adsorption capacity (IA) of carbon black is 120 m from the perspective of abrasion resistance. 2 It is preferable that it be 130m or more. 2 It is more preferable that it is 140m or more / g. 2 It is even more preferable if it is 1 / g or more. On the other hand, there is no particular upper limit, but from the viewpoint of variability, etc., 200m 2 It is preferable that it be less than or equal to / g, and 180m 2 It is more preferable that it be less than or equal to / g, and 160m 2 It is even more preferable if the amount is less than or equal to / g. The iodine adsorption amount (IA) of carbon black is a value measured in accordance with JIS K6217-1:2001.

[0075] Carbon black is not particularly limited and can include furnace blacks (furnace carbon blacks) such as SAF, ISAF, HAF, MAF, FEF, SRF, GPF, APF, FF, CF, SCF, and ECF; acetylene black (acetylene carbon black); thermal blacks (thermal carbon blacks) such as FT and MT; and channel blacks (channel carbon blacks) such as EPC, MPC, and CC. These may be used individually or in combination of two or more types.

[0076] There are no specific limitations on the carbon blacks used, but examples include N110, N115, N120, N121, N125, N134, N135, N219, N220, N231, N234, N293, N299, N326, N330, N335, N339, N343, N347, N351, N356, N358, N375, N539, N550, N582, N630, N642, N650, N660, N683, N754, N762, N765, N772, N774, N787, N907, N908, N990, N991, etc.

[0077] Commercially available products include those from Asahi Carbon Co., Ltd., Cabot Japan Co., Ltd., Tokai Carbon Co., Ltd., Mitsubishi Chemical Corporation, Lion Corporation, Shin-Nippon Carbon Co., Ltd., and Columbia Carbon Corporation, but it is also possible to use carbon black that has been synthesized independently. These can be used individually or in combination of two or more types.

[0078] From the viewpoint of wear resistance, the carbon black content is preferably 10 parts by mass or more, more preferably 20 parts by mass or more, and even more preferably 30 parts by mass or more, per 100 parts by mass of rubber component. On the other hand, from the viewpoint of dispersibility, it is preferably 100 parts by mass or less, more preferably 70 parts by mass or less, and even more preferably 60 parts by mass or less.

[0079] (ii) Silica The tread rubber composition may also contain silica, if necessary. The BET specific surface area of ​​silica is 140 m² from the viewpoint of obtaining good durability. 2 Preferably more than / g, 160m 2 A value greater than / g is preferable. On the other hand, from the viewpoint of obtaining good low rolling resistance, 250m 2 Preferably less than / g, 220m 2 It is more preferable that the value be less than / g.

[0080] Furthermore, the silica content per 100 parts by mass of rubber component is preferably 3 parts by mass or more, and more preferably 5 parts by mass or more, when not used in combination with a silane coupling agent. On the other hand, it is preferably 25 parts by mass or less, and more preferably 15 parts by mass or less. When used in combination with a silane coupling agent, it is preferably 25 parts by mass or more. On the other hand, it is preferably 50 parts by mass or less, more preferably 40 parts by mass or less, and even more preferably 30 parts by mass or less. The BET specific surface area mentioned above is the N2SA value measured by the BET method in accordance with ASTM D3037-93.

[0081] Examples of silica include dry-process silica (anhydrous silica) and wet-process silica (hydrated silica). Among these, wet-process silica is preferred because it contains a large number of silanol groups. Silica made from hydrated glass or silica made from biomass materials such as rice husks may also be used.

[0082] For example, silica products from companies such as Degussa, Rhodia, Tosoh Silica Co., Ltd., Solvay Japan Co., Ltd., and Tokuyama Corporation can be used.

[0083] (iii) Silane coupling agents When using silica, it is also possible to use a silane coupling agent in combination. The silane coupling agent is not particularly limited and includes, for example, bis(3-triethoxysilylpropyl)tetrasulfide, bis(2-triethoxysilylethyl)tetrasulfide, bis(4-triethoxysilylbutyl)tetrasulfide, bis(3-trimethoxysilylpropyl)tetrasulfide, bis(2-trimethoxysilylethyl)tetrasulfide, bis(2-triethoxysilylethyl) trisulfide, bis(4-trimethoxysilylbutyl) trisulfide, bis(3-triethoxysilylpropyl) disulfide, bis(2-triethoxysilylethyl) disulfide, bis(4-triethoxysilylbutyl) disulfide, bis(3-trimethoxysilylpropyl) disulfide, bis(2-trimethoxysilylethyl) disulfide, bis(4-trimethoxysilylbutyl) disulfide, 3-trimethoxysilylpropyl-N,N-dimethylthioca Examples include sulfide compounds such as rubamoyl tetrasulfide, 2-triethoxysilylethyl-N,N-dimethylthiocarbamoyl tetrasulfide, and 3-triethoxysilylpropyl methacrylate monosulfide; mercapto compounds such as 3-mercaptopropyltrimethoxysilane, 2-mercaptoethyltriethoxysilane, and Momentive's NXT and NXT-Z; vinyl compounds such as vinyltriethoxysilane and vinyltrimethoxysilane; amino compounds such as 3-aminopropyltriethoxysilane and 3-aminopropyltrimethoxysilane; glycidoxy compounds such as γ-glycidoxypropyltriethoxysilane and γ-glycidoxypropyltrimethoxysilane; nitro compounds such as 3-nitropropyltrimethoxysilane and 3-nitropropyltriethoxysilane; and chloro compounds such as 3-chloropropyltrimethoxysilane and 3-chloropropyltriethoxysilane. These may be used individually or in combination of two or more.

[0084] Examples of silane coupling agents that can be used include products from companies such as Degussa, Momentive, Shin-Etsu Silicone Co., Ltd., Tokyo Chemical Industry Co., Ltd., Azumax Co., Ltd., and Toray Dow Corning Co., Ltd.

[0085] The silane coupling agent content is, for example, more than 3 parts by mass and less than 15 parts by mass per 100 parts by mass of silica.

[0086] (iv) Other fillers In addition to the carbon black and silica mentioned above, the sidewall rubber composition may further contain fillers commonly used in the tire industry, such as graphite, calcium carbonate, talc, alumina, clay, aluminum hydroxide, and mica. The amount of these fillers is, for example, more than 0.1 parts by mass and less than 200 parts by mass per 100 parts by mass of the rubber component.

[0087] (b) Resin components The tread rubber composition preferably contains a resin component that functions as a tackifier and plasticizer, if necessary. The resin component may be solid or liquid at room temperature. Specific examples of resin components include rosin resins, styrene resins, coumarone resins, terpene resins, C5 resins, C9 resins, C5C9 resins, and acrylic resins, with terpene resins being preferred among these. Two or more types may be used in combination. The content of the resin component is preferably 5 parts by mass or more, more preferably 10 parts by mass or more, and even more preferably 15 parts by mass or more, per 100 parts by mass of the rubber component. On the other hand, it is preferably 45 parts by mass or less, more preferably 40 parts by mass or less, and even more preferably 35 parts by mass or less.

[0088] Rosin resins are resins whose main component is rosin acid, obtained by processing pine resin. These rosin resins (rosins) can be classified according to whether or not they are modified, and can be classified into unmodified rosin and rosin derivatives. Examples of unmodified rosin include tall rosin (also known as tall oil rosin), gum rosin, wood rosin, disproportionate rosin, polymerized rosin, hydrogenated rosin, and other chemically modified rosins. Rosin derivatives are modified forms of unmodified rosin and include rosin esters, unsaturated carboxylic acid-modified rosins, unsaturated carboxylic acid-modified rosin esters, rosin amide compounds, and rosin amine salts.

[0089] Styrene resins are polymers that use styrene monomers as constituent monomers, and include polymers polymerized with styrene monomers as the main component (50% by mass or more). Specifically, examples include homopolymers obtained by polymerizing styrene monomers (styrene, o-methylstyrene, m-methylstyrene, p-methylstyrene, α-methylstyrene, p-methoxystyrene, p-tert-butylstyrene, p-phenylstyrene, o-chlorostyrene, m-chlorostyrene, p-chlorostyrene, etc.) individually, copolymers obtained by copolymerizing two or more styrene monomers, and copolymers of styrene monomers and other monomers that can copolymerize with them.

[0090] Examples of the aforementioned other monomers include acrylonitriles such as acrylonitrile and methacrylonitrile, unsaturated carboxylic acids such as acrylics and methacrylic acid, unsaturated carboxylic acid esters such as methyl acrylate and methyl methacrylate, dienes such as chloroprene and butadiene isoprene, olefins such as 1-butene and 1-pentene; and α,β-unsaturated carboxylic acids such as maleic anhydride or their acid anhydrides.

[0091] Among coumarone-based resins, coumarone-indene resin is preferred. Coumarone-indene resin is a resin that contains coumarone and indene as monomer components that constitute the resin's backbone (main chain). Other monomer components that can be included in the backbone besides coumarone and indene include styrene, α-methylstyrene, methylindene, and vinyltoluene.

[0092] The coumaron indene resin content is, for example, more than 1.0 part by mass and less than 50.0 parts by mass per 100 parts by mass of rubber component.

[0093] The hydroxyl value (OH value) of coumarone indene resin is, for example, greater than 15 mg KOH / g and less than 150 mg KOH / g. The OH value is expressed in milligrams as the amount of potassium hydroxide required to neutralize the acetic acid bonded to the hydroxyl groups when acetylating 1 g of resin, and is measured by potentiometric titration (JIS K 0070:1992).

[0094] The softening point of coumarone indene resin is, for example, above 30°C and below 160°C. The softening point is determined by measuring the softening point as specified in JIS K 6220-1:2001 using a ring-type softening point measuring device, and it is the temperature at which the sphere descends.

[0095] Examples of terpene resins include polyterpenes, terpene phenols, and aromatically modified terpene resins. Polyterpenes are resins obtained by polymerizing terpene compounds and their hydrogenated products. Terpene compounds are (C5H8) n A hydrocarbon represented by the following composition and its oxygen-containing derivative, a monoterpene (C 10 H 16 ), sesquiterpenes (C 15 H 24 ), diterpene (C 20 H 32These are compounds with a terpene as their basic skeleton, classified as such, and examples include α-pinene, β-pinene, dipentene, limonene, myrcene, allocimene, ocimene, α-phellandrene, α-terpinene, γ-terpinene, terpinolene, 1,8-cineole, 1,4-cineole, α-terpineol, β-terpineol, and γ-terpineol.

[0096] Polyterpenes include terpene resins such as α-pinene resin, β-pinene resin, limonene resin, dipentene resin, and β-pinene / limonene resin, which are made from the terpene compounds mentioned above, as well as hydrogenated terpene resins obtained by hydrogenating these terpene resins. Terpene phenols include resins obtained by copolymerizing the above terpene compounds with phenolic compounds, and resins obtained by hydrogenating these resins. Specifically, resins obtained by condensing the above terpene compounds, phenolic compounds, and formalin are included. Examples of phenolic compounds include phenol, bisphenol A, cresol, and xylenol. Aromatically modified terpene resins include resins obtained by modifying terpene resins with aromatic compounds, and resins obtained by hydrogenating these resins. The aromatic compounds are not particularly limited as long as they are compounds having an aromatic ring, but examples include phenol compounds such as phenol, alkylphenol, alkoxyphenol, and phenol containing an unsaturated hydrocarbon group; naphthol compounds such as naphthol, alkylnaphthol, alkoxynaphthol, and naphthol containing an unsaturated hydrocarbon group; styrene derivatives such as styrene, alkylstyrene, alkoxystyrene, and styrene containing an unsaturated hydrocarbon group; coumarone, indene, and others.

[0097] "C5 resin" refers to a resin obtained by polymerizing a C5 fraction. Examples of C5 fractions include petroleum fractions with 4 to 5 carbon atoms, such as cyclopentadiene, pentene, pentadiene, and isoprene. Dicyclopentadiene resin (DCPD resin) is preferably used as a C5-based petroleum resin.

[0098] "C9 resin" refers to a resin obtained by polymerizing a C9 fraction, and may be hydrogenated or modified. Examples of C9 fractions include petroleum fractions with 8 to 10 carbon atoms, such as vinyltoluene, alkylstyrene, indene, and methylindene. Specific examples include coumarone indene resin, coumarone resin, indene resin, and aromatic vinyl resins, which are suitably used. As aromatic vinyl resins, homopolymers of α-methylstyrene or styrene, or copolymers of α-methylstyrene and styrene are preferred, and copolymers of α-methylstyrene and styrene are more preferred, due to their economical nature, ease of processing, and excellent heat generation properties. Aromatic vinyl resins that are commercially available from companies such as Kraton and Eastman Chemical can be used.

[0099] "C5C9 resin" refers to a resin obtained by copolymerizing the C5 fraction and the C9 fraction, and may be hydrogenated or modified. Examples of the C5 and C9 fractions include the petroleum fractions mentioned above. As for the C5C9 resin, commercially available products from companies such as Tosoh Corporation and LUHUA can be used.

[0100] While there are no particular limitations on the acrylic resin used, for example, a solvent-free acrylic resin can be used.

[0101] Solvent-free acrylic resins include (meth)acrylic resins (polymers) synthesized by high-temperature continuous polymerization (high-temperature continuous mass polymerization) (methods described in U.S. Patent No. 4,414,370, Japanese Patent Publication No. 59-6207, Japanese Patent Publication No. 5-58005, Japanese Patent Publication No. 1-313522, U.S. Patent No. 5,010,166, Toa Gosei Research Annual Report TREND2000 No. 3 pp. 42-45, etc.) with minimal use of polymerization initiators, chain transfer agents, organic solvents, etc. as auxiliary raw materials. In this disclosure, (meth)acrylic means methacrylic and acrylic.

[0102] Examples of monomer components constituting the above-mentioned acrylic resin include (meth)acrylic acid, (meth)acrylic acid esters (alkyl esters, aryl esters, aralkyl esters, etc.), (meth)acrylamide, and (meth)acrylic acid derivatives such as (meth)acrylamide derivatives.

[0103] Furthermore, as monomer components constituting the above-mentioned acrylic resin, aromatic vinyls such as styrene, α-methylstyrene, vinyltoluene, vinylnaphthalene, divinylbenzene, trivinylbenzene, and divinylnaphthalene may be used along with (meth)acrylic acid and (meth)acrylic acid derivatives.

[0104] The above-mentioned acrylic resin may be a resin composed solely of (meth)acrylic components, or a resin that also contains components other than (meth)acrylic components. Furthermore, the above-mentioned acrylic resin may have hydroxyl groups, carboxyl groups, silanol groups, etc.

[0105] As resin components, products from companies such as Maruzen Petrochemical Co., Ltd., Sumitomo Bakelite Co., Ltd., Yasuhara Chemical Co., Ltd., Tosoh Corporation, Rutgers Chemicals, BASF, Arizona Chemical Company, Nippon Paint Chemical Co., Ltd., Nippon Shokubai Co., Ltd., JX Energy Corporation, Arakawa Chemical Industries, Ltd., and Taoka Chemical Industries, Ltd. can be used.

[0106] (h) Plasticizer components The tread rubber composition may optionally contain plasticizer components such as oil (including stretching oil) or liquid rubber as components that soften the rubber. The plasticizer components are those that can be extracted from vulcanized rubber with acetone. The total content of plasticizer components is preferably more than 5 parts by mass, more preferably more than 10 parts by mass, per 100 parts by mass of rubber components. On the other hand, it is preferably less than 70 parts by mass, more preferably less than 50 parts by mass, and even more preferably less than 30 parts by mass. The oil content also includes the amount of oil contained in the rubber (oil-expanded rubber).

[0107] (i) oil Examples of oils include mineral oil (generally called process oil), vegetable oils, or mixtures thereof. Examples of mineral oils (process oils) include paraffinic process oil, aromatic process oil, and naphthenic process oil. Examples of vegetable oils include castor oil, cottonseed oil, linseed oil, rapeseed oil, soybean oil, palm oil, coconut oil, peanut oil, rosin, pine oil, pine tar, tall oil, corn oil, rice oil, safflower oil, sesame oil, olive oil, sunflower oil, palm kernel oil, camellia oil, jojoba oil, macadamia nut oil, and tung oil. These may be used individually or in combination of two or more.

[0108] Specific examples of process oils (mineral oils) that can be used include products from Idemitsu Kosan Co., Ltd., Sankyo Yuka Kogyo Co., Ltd., Japan Energy Co., Ltd., Orisoy Inc., H&R Inc., Toyokuni Oil Co., Ltd., Showa Shell Sekiyu K.K., Fuji Kosan Co., Ltd., and others.

[0109] (ii) Liquid rubber The liquid rubber mentioned as a plasticizer is a polymer that is in a liquid state at room temperature (25°C) and is a rubber component that can be extracted from vulcanized tires by acetone extraction. Examples of liquid rubber include farnesene polymers, liquid diene polymers, and their hydrogenated derivatives.

[0110] Farnesene polymers are polymers obtained by polymerizing farnesene and have constituent units based on farnesene. Farnesene has isomers such as α-farnesene ((3E,7E)-3,7,11-trimethyl-1,3,6,10-dodecatetraene) and β-farnesene (7,11-dimethyl-3-methylene-1,6,10-dodecatriene).

[0111] The farnesene polymer may be a farnesene homopolymer (farnesene homopolymer) or a farnesene-vinyl monomer copolymer (farnesene-vinyl monomer copolymer).

[0112] Examples of liquid diene polymers include liquid styrene-butadiene copolymer (liquid SBR), liquid butadiene polymer (liquid BR), liquid isoprene polymer (liquid IR), and liquid styrene-isoprene copolymer (liquid SIR).

[0113] The liquid diene polymer has a weight-average molecular weight (Mw) on a polystyrene basis, measured by gel permeation chromatography (GPC), for example, 1.0 × 10⁻⁶. 3 Super, 2.0×10 5 It is less than. In this specification, the Mw of the liquid diene polymer is the polystyrene equivalent value measured by gel permeation chromatography (GPC).

[0114] The liquid rubber content (total content of liquid farnesene polymers, liquid diene polymers, etc.) is, for example, more than 1 part by mass and less than 100 parts by mass per 100 parts by mass of rubber components.

[0115] As for liquid rubber, products from companies such as Kuraray Co., Ltd. and Clay Valley Corporation can be used.

[0116] (ii) Anti-aging agents The tread rubber composition preferably contains an anti-aging agent. The amount of anti-aging agent is, for example, more than 1 part by mass and less than 10 parts by mass per 100 parts by mass of the rubber component.

[0117] Examples of anti-aging agents include naphthylamine-based anti-aging agents such as phenyl-α-naphthylamine; diphenylamine-based anti-aging agents such as octylated diphenylamine and 4,4′-bis(α,α′-dimethylbenzyl)diphenylamine; N-isopropyl-N′-phenyl-p-phenylenediamine, N-(1,3-dimethylbutyl)-N′-phenyl-p-phenylenediamine, and N,N′-di-2-naphthyl-p-phenylenediamine. Examples include p-phenylenediamine-based antioxidants such as 2,2,4-trimethyl-1,2-dihydroquinoline polymers and other quinoline-based antioxidants; monophenol-based antioxidants such as 2,6-di-t-butyl-4-methylphenol and styrenated phenol; and bis-, tris-, and polyphenol-based antioxidants such as tetrakis-[methylene-3-(3′,5′-di-t-butyl-4′-hydroxyphenyl)propionate]methane. These may be used individually or in combination of two or more types.

[0118] Furthermore, as an anti-aging agent, products from companies such as Seiko Chemical Co., Ltd., Sumitomo Chemical Co., Ltd., Ouchi Shinko Chemical Co., Ltd., and Flexis Co., Ltd. can be used.

[0119] (Ho) Stearic Acid The tread rubber composition may optionally contain stearic acid. The stearic acid content is, for example, more than 0.5 parts by mass and less than 10.0 parts by mass per 100 parts by mass of the rubber component. Conventional known stearic acid can be used, such as products from NOF Corporation, Kao Corporation, Fujifilm Wako Pure Chemical Corporation, Chiba Fatty Acid Co., Ltd., etc.

[0120] (H) Zinc oxide The tread rubber composition may optionally contain zinc oxide. The zinc oxide content is, for example, more than 0.5 parts by mass and less than 15 parts by mass per 100 parts by mass of the rubber component. Conventionally known zinc oxides can be used, such as products from Mitsui Mining & Smelting Co., Ltd., Toho Zinc Co., Ltd., Hakusui Tech Co., Ltd., Seido Chemical Industry Co., Ltd., Sakai Chemical Industry Co., Ltd., etc.

[0121] (t) Crosslinking agents and vulcanization accelerators The tread rubber composition preferably contains a crosslinking agent such as sulfur. The crosslinking agent content is, for example, more than 0.1 parts by mass and less than 10.0 parts by mass per 100 parts by mass of the rubber component.

[0122] Examples of sulfur commonly used in the rubber industry include powdered sulfur, precipitated sulfur, colloidal sulfur, insoluble sulfur, highly dispersible sulfur, and soluble sulfur. These may be used individually or in combination of two or more types.

[0123] For sulfur, products from companies such as Tsurumi Chemical Industries, Karuizawa Sulfur Co., Ltd., Shikoku Chemicals Co., Ltd., Flexis Co., Ltd., Nippon Dry Distillation Co., Ltd., and Hosoi Chemical Industries, Ltd. can be used.

[0124] Other crosslinking agents besides sulfur include, for example, sulfur-containing vulcanizing agents such as Tackyrol V200 manufactured by Taoka Chemical Industries, Ltd., Duralink HTS (1,6-hexamethylene-dithiosulfate sodium dihydrate) manufactured by Flexis, and KA9188 (1,6-bis(N,N'-dibenzylthiocarbamoyldithio)hexane) manufactured by Lanxess, as well as organic peroxides such as dicumyl peroxide.

[0125] The tread rubber composition preferably contains a vulcanization accelerator. The vulcanization accelerator content is, for example, more than 0.3 parts by mass and less than 10.0 parts by mass per 100 parts by mass of the rubber component.

[0126] Examples of vulcanization accelerators include thiazole-based vulcanization accelerators such as 2-mercaptobenzothiazole, di-2-benzothiazolyl disulfide, and N-cyclohexyl-2-benzothiadylsulfenamide; thiuram-based vulcanization accelerators such as tetramethylthiuram disulfide (TMTD), tetrabenzylthiuram disulfide (TBzTD), and tetrakis(2-ethylhexyl)thiuram disulfide (TOT-N); and N-cyclohexyl-2-benzothiazole sulfenamide and Nt-butyl-2-benzothiazolyl sulfenamide. Examples of sulfenamide-based vulcanization accelerators include phenamide, N-oxyethylene-2-benzothiazole sulfenamide, N-oxyethylene-2-benzothiazole sulfenamide, and N,N'-diisopropyl-2-benzothiazole sulfenamide; guanidine-based vulcanization accelerators include diphenylguanidine, diortotrilguanidine, and orthotrilbiguanidine; and dithiocarbamate-based vulcanization accelerators include zinc dibenzyldithiocarbamate and zinc N-pentamethylenedithiocarbamate. These may be used individually or in combination of two or more.

[0127] (Chi) Others In addition to the above-mentioned components, the tread rubber composition may further contain additives commonly used in the tire industry, such as fatty acid metal salts, carboxylate metal salts, and organic peroxides. The content of these additives is, for example, more than 0.1 parts by mass and less than 200 parts by mass per 100 parts by mass of the rubber component.

[0128] (2) Manufacturing of tread rubber composition and production of tread components Tread rubber compositions can be manufactured by a general method, for example, a manufacturing method that includes a base mixing step of mixing rubber components with fillers such as carbon black, and a finish mixing step of mixing the mixture obtained in the base mixing step with a crosslinking agent.

[0129] Mixing can be carried out using known (closed) mixers such as Banbury mixers, kneaders, and open roll mixers.

[0130] The mixing temperature in the base mixing process is, for example, more than 50°C and less than 200°C, and the mixing time is, for example, more than 30 seconds and less than 30 minutes. In the base mixing process, in addition to the above components, compounding agents conventionally used in the rubber industry, such as plasticizer components such as oil, stearic acid, zinc oxide, antioxidants, waxes, and vulcanization accelerators, may be added and mixed as needed.

[0131] In the final mixing step, the mixture obtained in the base mixing step and the crosslinking agent are mixed together. The mixing temperature in the final mixing step is, for example, above room temperature but below 80°C, and the mixing time is, for example, more than 1 minute but less than 15 minutes. In the final mixing step, in addition to the above components, vulcanization accelerators, zinc oxide, etc., may be added and mixed as needed.

[0132] The obtained tread rubber composition can then be extruded into a predetermined shape using an extrusion molding machine to produce a tread component.

[0133] 2. Manufacturing of pneumatic tires The pneumatic tire of this embodiment can be manufactured as an unvulcanized tire by molding the tread member obtained above together with other tire members on a tire molding machine in a conventional manner.

[0134] Specifically, an inner liner, which is a component to ensure the airtightness of the tire, a carcass, which is a component to withstand the load, impact, and air pressure the tire receives, and a belt component, which is a component to tighten the carcass and increase the rigidity of the tread, are wound onto a molding drum. The ends of the carcass are fixed to both side edges, and a bead portion is placed as a component to fix the tire to the rim. After forming it into a toroid shape, a tread component is bonded to the center of the outer circumference, and a sidewall component is bonded to the radially outer side to form the sidewall portion, thereby producing an unvulcanized tire.

[0135] Subsequently, the prepared unvulcanized tire is heated and pressurized in a vulcanizing machine to obtain a tire. The vulcanization process can be carried out by applying known vulcanization methods. The vulcanization temperature is, for example, above 120°C and below 200°C, and the vulcanization time is, for example, above 5 minutes and below 15 minutes. At this time, the surface of the vulcanization mold is processed so that a tread portion with a predetermined land ratio is formed.

[0136] The scope of application of the tires described herein is not particularly limited and can be applied to any type of tire, such as those for passenger cars, trucks / buses, or motorcycles. However, it is preferable to apply the tires to pneumatic tires for passenger cars, where aesthetics are of particular importance, that is, tires mounted on four-wheeled vehicles with a maximum load capacity of 1000 kg or less.

[0137] The maximum load capacity mentioned above is not particularly limited as long as it is 1000 kg or less. However, generally, as the maximum load capacity increases, the tire weight tends to increase, and consequently, the heat generation of the tire tends to increase. Therefore, it is preferable that the maximum load capacity be 900 kg or less, more preferably 800 kg or less, and even more preferably 700 kg or less.

[0138] Furthermore, the tire weight mentioned above is preferably 20 kg or less, more preferably 15 kg or less, and even more preferably 12 kg or less, 10 kg or less, or 8 kg or less, from the viewpoint of reducing the heat generation of the tire. Note that the tire weight referred to here is the weight of the entire tire, and if the tire's inner surface is equipped with sealant, sponge, three-dimensional mesh structure, electronic components, etc., then the weight includes these components. [Examples]

[0139] The present disclosure will be further explained in detail below with reference to examples. In these examples, a tire with a tire size of 205 / 55R16 was manufactured and evaluated.

[0140] 1. Manufacturing of tread rubber composition First, the tread rubber composition was manufactured.

[0141] (1) Compounding materials First, the following ingredients were prepared.

[0142] (a) Rubber component (i) NR: TSR20 (b) BR: UBEPOL-BR150B (High-Sys BR) manufactured by Ube Industries, Ltd. (Cis content 97% by mass, trans content 2% by mass, vinyl content 1% by mass) (h) SBR: HPR850 (solution polymerized SBR) manufactured by JSR Corporation (Styrene content: 27.5% by mass, Vinyl bond content: 58.5% by mass)

[0143] (b) Compounding materials other than rubber components (i) Carbon Black: Show Black N220 manufactured by Cabot Japan Co., Ltd. (N2SA:115m 2 / g, CTAB specific surface area: 111m 2 / g) (b) Silica: Ultrasil VN3 manufactured by Evonik Degussa (N2SA:175m 2 / g, average primary particle diameter: 17nm) (h) Silane coupling agent: Si266 manufactured by Evonik DeGussa (Bis(3-triethoxysilylpropyl) disulfide) (ii) Resin: YS Polystar T160 manufactured by Yasuhara Chemical Co., Ltd. (Terpene phenol resin, softening point: 160°C) (e) Anti-aging agent: Nocrack 6C (6PPD) manufactured by Ouchi Shinko Chemical Industry Co., Ltd. (N-phenyl-N'-(1,3-dimethylbutyl)-p-phenylenediamine) (H) Zinc oxide: Zinc oxide No. 1 manufactured by Mitsui Mining & Smelting Co., Ltd. (T) Stearic acid: Beads stearic acid "Tsubaki" manufactured by NOF Corporation (C) Sulfur: HK-200-5 (5% oil-containing powdered sulfur) manufactured by Hosoi Chemical Industry Co., Ltd. (R) Vulcanization accelerator-1: Noxellar CZ (CBS) manufactured by Ouchi Shinko Chemical Industry Co., Ltd. (N-cyclohexyl-2-benzothiazolyl sulfenamide) (Nu) Vulcanization accelerator-2: Noxellar DM-P (DM) manufactured by Ouchi Shinko Chemical Industry Co., Ltd. (Di-2-benzothiazolyl disulfide) (L) Vulcanization accelerator-3: Noxellar ZTC manufactured by Ouchi Shinko Chemical Industry Co., Ltd. (Zinc dibenzyl dithiocarbamate)

[0144] (2) Manufacturing of tread rubber composition According to the formulations shown in Tables 1 and 2, the materials other than sulfur and vulcanization accelerator were mixed in a 3L Banbury mixer for 5 minutes under conditions of 150°C to obtain a mixture. The amounts of each ingredient are in parts by mass.

[0145] Next, sulfur and a vulcanization accelerator were added to the resulting mixture, and the mixture was kneaded using an open roll at 80°C for 5 minutes to obtain a tread rubber composition.

[0146] Next, a tread component was fabricated using the obtained tread rubber composition.

[0147] 2. Tire manufacturing The tread members obtained above were bonded together with other tire members to form an unvulcanized tire, which was then press-vulcanized at 140°C for 50 minutes to produce each test tire. At this time, the tread portion was molded to have the land ratio shown in Tables 1 and 2. In Example 7, the land ratio was changed in the region of the tread portion that straddles the equatorial plane.

[0148] 3. Measurement of various parameters Next, the following parameters were measured using each test tire.

[0149] (1) Ratio of monosulfide bonds V (%) Using sample test pieces (2cm x 2cm, 1mm thick) cut from the tread of each test tire, the ratio V (%) of monosulfide bonds was calculated in accordance with the method described in Japanese Patent Publication No. 2019-45196. The results are shown in Tables 1 and 2.

[0150] (2) Land ratio L (%) Using each test tire, the land ratio L(%) was measured based on the method described in "1. Overview" of "[1] Characteristics of the Tires Related to This Disclosure" above. The results are shown in Tables 1 and 2.

[0151] (3) V / L (%) Based on the V(%) and L(%) values ​​obtained above, the V / L(%) ratio for each test tire was calculated. The results are shown in Tables 1 and 2.

[0152] 4. Evaluation (1) Changes in rubber over time Using No. 3 dumbbell-shaped test specimens prepared from the tread area of ​​each test tire before installation on a vehicle, tensile tests were performed in accordance with JIS K6251 (2010) using a Shimadzu Autograph (test temperature: 23°C) to determine the 300% elongation stress (M300A) before aging.

[0153] Next, each test tire was aged by being left in an oven at a temperature of 80°C and an oxygen concentration of 20% for 168 hours. The stress at 300% tensile strength (M300B) after aging was then determined in the same manner.

[0154] Next, the percentage change in M300 before and after aging was calculated as the rate of change over time based on the following formula, and this was used as an indicator of the rubber's change over time. The results are shown in Tables 1 and 2. A smaller value indicates that the change over time of the rubber is suppressed. Rate of change over time = [(M300B - M300A) / M300A] × 100 (%)

[0155] (2) Wear performance at the end of the lifespan Each test tire was mounted on all wheels of a vehicle (a domestically produced front-wheel-drive car with a 2000cc engine), and after inflating it to an internal pressure of 250kPa (the standard internal pressure for passenger cars), the vehicle was driven at 50km / h on a dry test course, and the distance traveled until the tires were replaced with new ones was measured.

[0156] Next, the results in Comparative Example 1 were set to 100 and indexed based on the following formula to evaluate the wear performance at the end of the life cycle. The results are shown in Tables 1 and 2. A higher numerical value indicates better wear performance at the end of the life cycle. End-of-life wear performance = [(Results of test tire) / (Results of comparative example 1)] × 100

[0157] [Table 1]

[0158] [Table 2]

[0159] Tables 1 and 2 show that tires with a monosulfide bond ratio V (%) of 50% or more in the tread area and a land ratio L (%) of 70% or less in the tread area can sufficiently suppress the deterioration of the rubber over time and provide tires with high lifespan performance.

[0160] Furthermore, it is evident that even greater effects can be achieved by appropriately controlling the compounding of the tread rubber, V / L (%), etc., and by changing the land ratio in the tread area.

[0161] Although the present disclosure has been described above based on embodiments, the present disclosure is not limited to the embodiments described above. Various modifications can be made to the embodiments described above within the same and equivalent scope as the present disclosure.

[0162] This disclosure (1) is, A pneumatic tire having grooves on the surface of the tread portion, The rubber composition constituting the tread portion contains 50 parts by mass or more of natural rubber per 100 parts by mass of rubber components, and the ratio V(%) of monosulfide bonds in the total crosslinking configuration by sulfide bonds is 50% or more. The rubber component contains 20 parts by mass or more of carbon black with an average primary particle diameter of 5 nm or more and 20 nm or less, per 100 parts by mass. It is a rubber composition, Furthermore, the land ratio L(%) of the tread portion of the tire, when mounted on a standard rim and subjected to standard internal pressure, is 70% or less. The ratio V(%) of the monosulfide bond to the land ratio L(%) is 140% or more, Furthermore, the tread portion has one or more circumferential grooves extending continuously in the circumferential direction of the tire, in each of the two regions flanking the tire's equatorial plane. A pneumatic tire characterized in that, when the land ratio in one region is La (%) and the land ratio in the other region is Lb (%), La and Lb are different from each other, and La (%) and Lb (%) satisfy the following formula. |La-Lb|>20

[0166] This disclosure ( 2 )teeth, The present disclosure (1) is characterized in that the ratio V (%) of the monosulfide bond is 60% or more. Described It is a pneumatic tire.

[0167] This disclosure ( 3 )teeth, The present disclosure is characterized in that the ratio V (%) of the monosulfide bond is 70% or more. 2 These are pneumatic tires as described above.

[0168] This disclosure ( 4 )teeth, The aforementioned land ratio L(%) is characterized by being 60% or less, as described in this disclosure (1) to ( 3 It is a pneumatic tire in any combination of any of the following:

[0169] This disclosure ( 5 )teeth, The aforementioned land ratio L(%) is characterized by being 50% or less, and this disclosure ( 4 These are pneumatic tires as described above.

[0171] This disclosure ( 6 )teeth, The rubber composition constituting the tread portion is characterized in that it contains 20 parts by mass or more of styrene-butadiene rubber and butadiene rubber in total per 100 parts by mass of rubber components, and the present disclosure (1) to ( 5 It is a pneumatic tire in any combination of any of the following:

[0172] Book Disclosure ( 7 )teeth, The rubber composition constituting the tread portion is characterized in that, in addition to the carbon black, it further contains 25 parts by mass or more of silica per 100 parts by mass of the rubber component, together with a silane coupling agent, and this disclosure Any combination of (1) through (6) It is a pneumatic tire.

[0173] This disclosure ( 8 )teeth, The rubber composition constituting the tread portion is characterized in that it contains 5 parts by mass or more of resin component per 100 parts by mass of rubber component, and the present disclosure (1) to ( 7 It is a pneumatic tire in any combination of any of the following:

[0174] This disclosure ( 9 )teeth, The present disclosure is characterized in that the aforementioned resin component is a terpene-based resin. 8 These are pneumatic tires as described above.

[0177] This disclosure ( 10 )teeth, It is characterized as a tire for passenger cars, and as described in this disclosure (1) to ( 9 It is a pneumatic tire in any combination of any of the following:

Claims

1. A pneumatic tire having grooves on the surface of the tread portion, The rubber composition constituting the tread portion contains 50 parts by mass or more of natural rubber per 100 parts by mass of rubber component, the ratio V (%) of monosulfide bonds in the total crosslinking configuration by sulfide bonds is 50% or more, and the rubber composition contains 20 parts by mass or more of carbon black with an average primary particle diameter of 5 nm or more and 20 nm or less per 100 parts by mass of the rubber component. Furthermore, the land ratio L (%) of the tread portion of the tire, when mounted on a standard rim and subjected to standard internal pressure, is 70% or less. The ratio V (%) of the monosulfide bond to the land ratio L (%) is 140% or more. Furthermore, the tread portion has one or more circumferential grooves extending continuously in the circumferential direction of the tire, in each of the two regions flanking the tire's equatorial plane. A pneumatic tire characterized in that, when the land ratio in one region is La (%) and the land ratio in the other region is Lb (%), La and Lb are different from each other, and La (%) and Lb (%) satisfy the following formula. |La-Lb|>20

2. The pneumatic tire according to claim 1, characterized in that the ratio V (%) of the monosulfide bonds is 60% or more.

3. The pneumatic tire according to claim 2, characterized in that the ratio V (%) of the monosulfide bonds is 70% or more.

4. The pneumatic tire according to any one of claims 1 to 3, characterized in that the land ratio L (%) is 60% or less.

5. The pneumatic tire according to claim 4, characterized in that the land ratio L (%) is 50% or less.

6. The pneumatic tire according to any one of claims 1 to 5, characterized in that the rubber composition constituting the tread portion contains 20 parts by mass or more of styrene-butadiene rubber and butadiene rubber in total, per 100 parts by mass of rubber components.

7. The pneumatic tire according to any one of claims 1 to 6, characterized in that the rubber composition constituting the tread portion further contains, in addition to the carbon black, 25 parts by mass or more of silica per 100 parts by mass of the rubber component, together with a silane coupling agent.

8. The pneumatic tire according to any one of claims 1 to 7, characterized in that the rubber composition constituting the tread portion contains 5 parts by mass or more of resin component per 100 parts by mass of rubber component.

9. The pneumatic tire according to claim 8, characterized in that the resin component is a terpene-based resin.

10. A pneumatic tire according to any one of claims 1 to 9, characterized in that it is a tire for a passenger car.

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