pneumatic tires

Abstract

To provide a pneumatic tire which sufficiently improves stability on a wet road surface at high speed traveling.SOLUTION: A pneumatic tire in which a circumferential direction main groove is arranged at a tread part is given. An outermost layer of the tread part consists of rubber composition containing vulcanized rubber powder. Area ratio S(%) of vulcanized rubber powder to the cross section of the outermost layer is 5% or more and 50% or less. Loss tangent (30°Ctanδ) is 0.15 or less in a condition of 30°C of temperature, 10 Hz of frequency, 5% of initial strain, and 1% of dynamic strain of the rubber composition, and it is measured at deformation mode of tension. Groove depth D (mm) of the circumferential direction main groove is more than 6 mm, and S / D>0.85 is satisfied.SELECTED DRAWING: None

Description

[Technical Field]

[0001] The present disclosure relates to a pneumatic tire, and more particularly to a pneumatic tire that has excellent steering stability on wet road surfaces when traveling at high speeds. [Background technology]

[0002] Pneumatic tires (hereinafter simply referred to as "tires") are required to have high braking performance (grip performance) for safety reasons, and various technologies have been proposed to improve grip performance and steering stability (for example, Patent Documents 1 to 3). [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Application Laid-Open No. 2016-043709 [Patent Document 2] Japanese Patent Application Publication No. 2018-135436 [Patent Document 3] Patent Publication No. 2021-167401 Summary of the Invention [Problem to be solved by the invention]

[0004] However, with the recent development of expressways, it is not uncommon for people to travel long distances on expressways, and there is an increasing demand for improved grip performance on wet roads (wet grip performance) and handling stability.

[0005] In view of the above-described current situation, an object of the present disclosure is to provide a pneumatic tire with sufficiently improved steering stability on wet road surfaces during high-speed driving. [Means for solving the problem]

[0006] The present inventors have conducted extensive research into solving the above problems and have found that the above problems can be solved by the disclosure described below.

[0007] The present disclosure provides: A pneumatic tire having a circumferential main groove in a tread portion, the outermost layer of the tread portion is formed using a rubber composition containing vulcanized rubber powder, In the cross section of the outermost layer, the area ratio S (%) occupied by the vulcanized rubber powder is 5% or more and 50% or less, the loss tangent (30°C tanδ) of the rubber composition measured in a tensile deformation mode under conditions of 30°C, a frequency of 10 Hz, an initial strain of 5%, and a dynamic strain rate of 1% is 0.15 or less; The groove depth D (mm) of the circumferential main groove is greater than 6 mm, Furthermore, the pneumatic tire is characterized in that S / D>0.85. [Effects of the Invention]

[0008] According to the present disclosure, it is possible to provide a pneumatic tire with sufficiently improved steering stability on wet road surfaces during high-speed driving. DETAILED DESCRIPTION OF THE INVENTION

[0009] [1] Characteristics of the pneumatic tire according to the present disclosure First, the features of the tire according to the present disclosure will be described.

[0010] 1. Overview A pneumatic tire according to the present disclosure is a pneumatic tire having a circumferential main groove in a tread portion, and the outermost layer (hereinafter also referred to as a "cap rubber layer") of the tread portion is formed using a rubber composition (hereinafter also referred to as a "tread rubber composition") containing vulcanized rubber powder. The area ratio (exclusive area ratio) S (%) of the vulcanized rubber powder in a cross section of the cap rubber layer is 5% or more and 50% or less. The loss tangent (30°C tanδ) of the rubber composition measured in a tensile deformation mode under conditions of 30°C, a frequency of 10 Hz, an initial strain of 5%, and a dynamic strain rate of 1% is 0.15 or less. The groove depth D (mm) of the circumferential main groove is greater than 6 mm, and S / D > 0.85.

[0011] By having these characteristics, it is possible to provide a pneumatic tire with sufficiently improved steering stability on wet roads during high-speed driving, as will be described later.

[0012] 2. Mechanism of effect manifestation in pneumatic tires according to the present disclosure In the pneumatic tire according to the present disclosure, the contact patch is in sufficient contact with the road surface even on a wet road surface, and the steering stability performance on wet road surfaces during high-speed driving is sufficiently improved. The mechanism by which this effect is achieved is thought to be as follows.

[0013] (1) Content of vulcanized rubber powder in tread rubber composition As described above, in the present disclosure, the cap rubber layer is formed using a rubber composition containing vulcanized rubber powder, and the area ratio S (%) of the vulcanized rubber powder in its cross section is 5% or more and 50% or less.

[0014] By incorporating a certain amount of vulcanized rubber powder, specifically, by making the area ratio S (%) of vulcanized rubber powder in the cross section of the cap rubber layer 5% or more, unevenness is created on the surface of the tread portion, making it easier for the tire contact patch to grip the road surface, thereby achieving an anchoring effect on the road surface and improving steering stability on wet roads during high-speed driving. 6% or more is more preferable, 9% or more is even more preferable, and 20% or more is particularly preferable.

[0015] However, if too much vulcanized rubber powder is contained in the cap rubber layer, the area ratio S occupied by the vulcanized rubber powder will become too large. Specifically, if it exceeds 50%, the reinforcing properties will decrease, which may lead to a decrease in tire durability. Therefore, the area ratio S occupied by the vulcanized rubber powder is preferably 50% or less, more preferably 48% or less, even more preferably 45% or less, and particularly preferably 40% or less.

[0016] The above-mentioned "area ratio S occupied by vulcanized rubber powder" can be obtained by cutting a sample into the tread portion so that a plane parallel to the tread surface becomes the cross section for observation, photographing the sample with, for example, a scanning electron microscope, determining the area of ​​the domain occupied by the vulcanized rubber powder, and calculating the ratio of this area to the area of ​​the entire cross section.

[0017] (2) Loss tangent of tread rubber composition In the present disclosure, the tread rubber composition has a loss tangent (30°C tan δ) of 0.15 or less, measured under conditions of 30°C, a frequency of 10 Hz, an initial strain of 5%, and a dynamic strain rate of 1%, in a deformation mode of tension.

[0018] By reducing 30°C tan δ to 0.15 or less, the phase difference between input and response to the rubber layer is reduced, which speeds up the transmission of force from the contact patch to the inside of the tread portion and ensures good responsiveness even during high-speed driving. It is more preferably 0.12 or less, and even more preferably 0.10 or less. On the other hand, the lower limit is not particularly limited, but is preferably 0.03 or more, more preferably 0.05 or more, and even more preferably 0.07 or more.

[0019] The above-mentioned "loss tangent (30°C tan δ)" can be measured using a viscoelasticity measuring device such as "IPLEXER (registered trademark)" manufactured by GABO.

[0020] (3) Depth of circumferential main groove In the present disclosure, the groove depth D (mm) of the circumferential main groove is greater than 6 mm. By making the groove depth D of the circumferential main groove greater than 6 mm, the drainage function between the contact patch and the road surface is sufficiently ensured, making it easier for the tread surface to come into contact with the road surface and ensuring good responsiveness during high-speed driving.

[0021] In this disclosure, the term "circumferential main groove" refers to a groove with a groove width of more than 3 mm that is continuous in the tire circumferential direction and is closest to the tire equatorial plane. The term "groove depth D" refers to the height from the groove bottom to the opening in the tire radial direction under normal conditions and no load, where normal conditions refer to a state in which the tire is mounted on a normal rim and pressurized to the normal internal pressure.

[0022] Here, "genuine rim" refers to a rim specified for each tire by a standard system that includes the standard on which the tire is based, such as the standard rim for the applicable size listed in the "JATMA YEAR BOOK" for JATMA (Japan Automobile Tire Manufacturers Association), the "Measuring Rim" listed in the "STANDARDS MANUAL" for ETRTO (The European Tyre and Rim Technical Organization), or the "Design Rim" listed in the "YEAR BOOK" for TRA (The Tire and Rim Association, Inc.). For tires not specified by a standard, this refers to a rim that can be mounted on a rim and can maintain internal pressure, i.e., the rim with the smallest rim diameter and the next narrowest rim width, among rims that do not leak air between the rim and tire.

[0023] "Normal internal pressure" refers to the air pressure specified for each tire by the standard, and in the case of JATMA it refers to the maximum air pressure, in the case of TRA it refers to the maximum value listed in the table "TIRE LOAD LIMITS AT VARIOUS COLD INFLATION PRESSURES", and in the case of ETRTO it refers to "INFLATION PRESSURE".

[0024] (4) Collaboration between (1) and (3) In the present disclosure, the above-mentioned (1) to (3) work together to ensure that the contact patch is in sufficient contact with the road surface, even on wet roads, ensuring sufficient grip and enabling quick response, which is believed to improve steering stability when driving at high speeds on wet roads.

[0025] (5) Relationship between the area ratio S (%) occupied by vulcanized rubber powder and groove depth D (mm) However, if the groove depth is too large, while the drainage function is improved, it also leads to a decrease in the rigidity of the tread portion, which reduces the reaction force generated in the tread portion, and therefore, the grip force also decreases, which may lead to a decrease in steering stability.

[0026] Therefore, in the present disclosure, the area ratio S (%) occupied by the vulcanized rubber powder is set to a certain value or more relative to the groove depth D (mm), specifically, S / D > 0.85, thereby obtaining a sufficiently large anchoring effect from the vulcanized rubber powder relative to the groove depth of the tread portion, thereby preventing a decrease in steering stability. It is more preferably 1.0 or more, and even more preferably 3.5 or more. On the other hand, the upper limit is not particularly limited, but is preferably 8.0 or less, more preferably 7.0 or less, and even more preferably 6.0 or less.

[0027] [2] More preferred embodiments of the tire according to the present disclosure The tire according to the present disclosure can achieve even greater effects by adopting the following aspects.

[0028] 1. Rubber component in tread rubber composition In the present disclosure, the tread rubber composition contains, as rubber components, natural rubber (NR), butadiene rubber (BR), and styrene-butadiene rubber (SBR) having a styrene ratio of 30% by mass or less, and the total content RR in 100 parts by mass of the rubber component is preferably 90 parts by mass or more, and more preferably 95 parts by mass or more.

[0029] This makes it possible to lower the glass transition temperature Tg of the rubber component, ensuring the flexibility of the rubber surface at low temperatures required for high-speed driving, while also reducing the 30°C tan δ and enabling the force to be transmitted from the contact patch to the tread more quickly, which is thought to further improve steering stability on wet roads when driving at high speeds.

[0030] 2. Inclusion of silica in the tread rubber composition In the present disclosure, the tread rubber composition contains silica as a filler in an amount of preferably 65 parts by mass or less, more preferably 60 parts by mass or less, per 100 parts by mass of the rubber component. On the other hand, although there is no particular lower limit, it is preferably 35 parts by mass or more, and more preferably 40 parts by mass or more.

[0031] By incorporating silica, the 30°C tan δ can be reduced and the force can be transmitted from the contact patch to the tread more quickly, which is thought to further improve steering stability on wet roads when driving at high speeds.

[0032] In this case, it is preferable to use a silane coupling agent together with the silica, which improves the dispersibility of the silica in the tread rubber composition, reduces the 30°C tan δ, and enables the force to be transmitted from the contact patch to the tread portion more quickly, which is thought to further improve the steering stability on wet roads when driving at high speeds.

[0033] Specifically, the silane coupling agent is preferably a silane coupling agent having a thiocarbonyl group.

[0034] 3. Modified groups in SBR In the present disclosure, the SBR preferably has a modifying group capable of reacting with silica, which improves the dispersibility of silica and the bonding between polymers, reduces 30°C tan δ, and accelerates the transmission of force from the contact patch to the tread, thereby further improving wet grip performance and steering stability.

[0035] 4. Relationship between occupancy rate and tread gauge In the present disclosure, when the thickness (gauge) of the tread portion on the equatorial plane is G (mm), it is preferable that the area ratio S (%) occupied by the vulcanized rubber powder satisfies S / G≧0.6. It is more preferable that it is 0.9 or more, and even more preferable that it is 2.0 or more. On the other hand, although there is no particular upper limit, it is preferably 7.0 or less, more preferably 6.0 or less, and even more preferably 5.0 or less.

[0036] The thicker the tread, the easier it is for the rubber to penetrate into the road surface, but on the other hand, the rigidity of the tread decreases, making it more difficult to obtain a reaction force. Therefore, in the present disclosure, it is preferable to increase the area of ​​the vulcanized rubber powder as the gauge becomes thicker, specifically, to make S / G≧0.6, thereby improving the grip on the tread surface and making it easier to obtain a large reaction force.

[0037] In the above, "tread gauge G" refers to the thickness of the tread on the tire equatorial plane, but if there are circumferential grooves on the equatorial plane, it refers to the thickness of the tread at the point closest to the equatorial plane, excluding the circumferential grooves. Also, "tread gauge G" is the linear distance from the outermost surface of the tread to the interface of the innermost layer of the tread, and in the case of a tire having a belt layer, a belt reinforcing layer, and a carcass layer, it is the distance to the outermost layer of these.

[0038] 5. Relationship between 30℃ tanδ and tread gauge G As mentioned above, by reducing 30°C tan δ, force is transmitted from the contact patch to the tread portion more quickly. On the other hand, the thicker the tread portion, the more difficult it is to obtain reaction force. Therefore, in the present disclosure, it is preferable that the relationship between 30°C tan δ and the gauge G of the tread portion satisfies (30°C tan δ × G) ≦ 1.30. It is more preferable that it is 1.10 or less, and even more preferable that it is 1.00 or less. This results in better steering stability on wet roads during high-speed driving. On the other hand, although there is no particular limitation on the lower limit, it is preferably 0.30 or more, more preferably 0.40 or more, and even more preferably 0.50 or more.

[0039] 6. Particle size of vulcanized rubber powder In the present disclosure, the vulcanized rubber powder preferably has a particle size finer than 30 mesh pass and coarser than 250 mesh pass using a test sieve specified in JIS Z8801-1. By using a particle size larger than 250 mesh pass, the anchor effect is fully exerted, better wet grip performance can be obtained, and handling stability can be improved. On the other hand, by using a particle size finer than 30 mesh pass, uniform dispersion in the rubber composition forming the cap rubber layer can be easily achieved, making it easier to obtain sufficient durability.

[0040] [3] Implementation form Hereinafter, the present disclosure will be specifically described based on embodiments.

[0041] 1. Tread rubber composition (1) Compounding materials In the present disclosure, the tread rubber composition forming the cap rubber layer can be obtained from the rubber components described below and other compounding materials, excluding vulcanized rubber powder.

[0042] (a) Rubber component The rubber component is not particularly limited, and rubbers (polymers) commonly used in tire production can be used, such as isoprene-based rubber, diene-based rubbers such as BR, SBR, and nitrile rubber (NBR), and butyl-based rubbers such as butyl rubber, among which diene-based rubbers are preferably used. These may be used alone, but it is preferable to include any one of isoprene-based rubber, BR, and SBR, more preferably to include two or more of these, and even more preferably to include three of isoprene-based rubber, BR, and SBR.

[0043] (a) Isoprene rubber Examples of isoprene-based rubber include natural rubber (NR), isoprene rubber (IR), modified NR, modified NR, and modified IR, with NR being preferred due to its excellent strength.

[0044] Examples of NR that can be used include SVR-L, SIR20, RSS#3, and TSR20, which are commonly used in the tire industry. IR is not particularly limited, and examples of IR that can be used include IR2200 and other commonly used NRs. Modified NRs include deproteinized natural rubber (DPNR) and highly purified natural rubber (UPNR). Modified NRs include epoxidized natural rubber (ENR), hydrogenated natural rubber (HNR), and grafted natural rubber. Modified IRs include epoxidized isoprene rubber, hydrogenated isoprene rubber, and grafted isoprene rubber. These may be used alone or in combination of two or more.

[0045] From the viewpoint of improving the responsiveness of the rubber composition, the content of the isoprene-based rubber in 100 parts by mass of the rubber component is preferably 30 parts by mass or more, more preferably 35 parts by mass or more, while the upper limit is preferably 50 parts by mass or less, more preferably 45 parts by mass or less.

[0046] (b) SBR The amount of SBR in 100 parts by mass of the rubber component is preferably 20 parts by mass or more, and more preferably 25 parts by mass or more. Although there is no particular upper limit, it is preferably 40 parts by mass or less, and more preferably 35 parts by mass or less.

[0047] 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 not particularly limited, but as described above, it is preferably 30% by mass or less. It is more preferably 25% by mass or less, and even more preferably 20% by mass or less. On the other hand, the lower limit is preferably 3% by mass or more, more preferably 5% by mass or more, and even more preferably 8% by mass or more. The vinyl bond content (amount of 1,2-bonded butadiene units) of SBR is, for example, preferably more than 5 mol%, more preferably more than 10 mol%, and even more preferably more than 15 mol%, relative to the butadiene portion of SBR. On the other hand, the upper limit is preferably less than 70 mol%, more preferably less than 40 mol%, and even more preferably less than 30 mol%. SBR structural identification (measurement of styrene content and vinyl bond content) can be performed using, for example, a JNM-ECA series instrument manufactured by JEOL Ltd.

[0048] The SBR is not particularly limited, and examples thereof include emulsion-polymerized styrene-butadiene rubber (E-SBR) and solution-polymerized styrene-butadiene rubber (S-SBR). The SBR may be either unmodified or modified. Hydrogenated SBR, which is obtained by hydrogenating the butadiene portion of SBR, may also be used. Hydrogenated SBR may be obtained by subsequently hydrogenating the BR portion of SBR, or a similar structure may be obtained by copolymerizing styrene, ethylene, and butadiene.

[0049] As described above, the modified SBR is preferably an SBR having a functional group that interacts with a filler such as silica. Examples of such SBR include terminal-modified SBR in which at least one terminal of the SBR has been modified with a compound (modifier) ​​having the above functional group (terminal-modified SBR having the above functional group at the terminal), main-chain-modified SBR in which the main chain has the above functional group, main-chain terminal-modified SBR in which the main chain and the terminals have the above functional group (for example, main-chain terminal-modified SBR in which the main chain has the above functional group and at least one terminal has been modified with the above modifier), and terminal-modified SBR in which the SBR has been modified (coupled) with a polyfunctional compound having two or more epoxy groups in the molecule and in which a hydroxyl group or epoxy group has been introduced.

[0050] 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 a substituent.

[0051] Furthermore, as the modified SBR, for example, SBR modified with a compound (modifying agent) represented by the following formula can be used.

[0052] [ka]

[0053] In the formula, R 1 , R 2 and R 3 R may be 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 a derivative thereof. 4 and R 5 are the same or different and represent a hydrogen atom or an alkyl group. 4and R 5 may bond to form a ring structure together with the nitrogen atom, and n represents an integer.

[0054] As the modified SBR modified with a compound (modifier) ​​represented by the above formula, SBR in which the polymerization terminals (active terminals) of solution-polymerized styrene-butadiene rubber (S-SBR) have been modified with a compound represented by the above formula (such as the modified SBR described in JP 2010-111753 A).

[0055] R 1 , R 2 and R 3 R is preferably an alkoxy group (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 is preferably an alkyl group (preferably an alkyl group having 1 to 3 carbon atoms). n is preferably 1 to 5, more preferably 2 to 4, and even more preferably 3. In addition, R 4 and R 5 When the groups bond to form a ring structure together with the nitrogen atom, the ring is preferably a 4- to 8-membered ring. The alkoxy group also includes a cycloalkoxy group (such as a cyclohexyloxy group) and an aryloxy group (such as a phenoxy group or a benzyloxy group).

[0056] Specific examples of the modifying agent include 2-dimethylaminoethyltrimethoxysilane, 3-dimethylaminopropyltrimethoxysilane, 2-dimethylaminoethyltriethoxysilane, 3-dimethylaminopropyltriethoxysilane, 2-diethylaminoethyltrimethoxysilane, 3-diethylaminopropyltrimethoxysilane, 2-diethylaminoethyltriethoxysilane, 3-diethylaminopropyltriethoxysilane, etc. These may be used alone or in combination of two or more.

[0057] Modified SBR may also be modified with the following compounds (modifiers): Examples of the modifier include 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 diglycidylated bisphenol A; polyepoxy compounds such as 1,4-diglycidylbenzene, 1,3,5-triglycidylbenzene, and polyepoxidized liquid polybutadiene; epoxy group-containing tertiary amines such as 4,4'-diglycidyl-diphenylmethylamine and 4,4'-diglycidyl-dibenzylmethylamine; diglycidylaniline, N,N'-diglycidyl-4-glycidyloxyaniline; Diglycidyl amino compounds such as diglycidyl orthotoluidine, tetraglycidyl meta-xylenediamine, tetraglycidyl aminodiphenylmethane, tetraglycidyl-p-phenylenediamine, diglycidyl aminomethylcyclohexane, and tetraglycidyl-1,3-bisaminomethylcyclohexane; amino group-containing acid chlorides such as bis-(1-methylpropyl)carbamic acid chloride, 4-morpholinecarbonyl chloride, 1-pyrrolidinecarbonyl chloride, N,N-dimethylcarbamic acid chloride, and N,N-diethylcarbamic acid 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-(trippropoxysilyl)propyl]sulfide, (trimethylsilyl)[3-(tributoxysilyl)propyl]sulfide, (trimethylsilyl)[3-(methyldimethoxysilyl)propyl]sulfide, (trimethylsilyl)[3-(methyldiethoxysilyl)propyl]sulfide, (trimethylsilyl)[3-(methyldipropoxy sulfide group-containing silane compounds such as (trimethylsilyl)[3-(methyldibutoxysilyl)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)aminoethyltrimethoxysilane, Alkoxysilanes such as thyltriethoxysilane; (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; and N-substituted piperidones such as N-methyl-2-piperidone, N-vinyl-2-piperidone, and N-phenyl-2-piperidone;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; as well as 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-trione , 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-dimethylaminoacetophen, 4-N,N-diethylaminoacetophenone, 1,3-bis(diphenylamino)-2-propanone, 1,7-bis(methylethylamino)-4-heptanone, etc. Modification with the above compounds (modifiers) can be carried out by known methods.

[0058] As the SBR, for example, SBR manufactured and sold by Sumitomo Chemical Co., Ltd., JSR Corporation, Asahi Kasei Corporation, Nippon Zeon Co., Ltd., etc. can be used. The SBR may be used alone or in combination of two or more types.

[0059] (C)BR The amount of BR in 100 parts by mass of the rubber component is preferably 20 parts by mass or more, and more preferably 25 parts by mass or more. Although there is no particular upper limit, it is preferably 40 parts by mass or less, and more preferably 35 parts by mass or less.

[0060] The weight-average molecular weight of the BR is, for example, more than 100,000 and less than 2,000,000. The vinyl bond amount (amount of 1,2-bonded butadiene units) of the BR is, for example, more than 1% by mass and less than 30% by mass. The cis content of the BR is, for example, more than 1% by mass and less than 98% by mass. The trans content of the BR is, for example, more than 1% by mass and less than 60% by mass.

[0061] The BR is not particularly limited, and examples thereof include BR with a high cis content (cis content of 90% or more), BR with a low cis content, and BR containing syndiotactic polybutadiene crystals (SPB-containing BR). BR may be either unmodified or modified, and the modified BR may be, for example, tin-modified BR. Tin-modified BR is preferably obtained by polymerizing 1,3-butadiene with a lithium initiator and then adding a tin compound, and the terminals of the tin-modified BR molecule are preferably bonded via a tin-carbon bond.

[0062] Examples of the lithium initiator include lithium compounds such as alkyllithium, aryllithium, vinyllithium, organotinlithium, and organonitrogen lithium compounds, as well as lithium metal. By using the lithium initiator as the initiator for the tin-modified BR, a tin-modified BR with a high vinyl and low cis content can be produced.

[0063] Examples of tin compounds include tin tetrachloride, butyltin trichloride, dibutyltin dichloride, dioctyltin dichloride, tributyltin chloride, triphenyltin chloride, diphenyldibutyltin, triphenyltin ethoxide, diphenyldimethyltin, ditolyltin chloride, diphenyltin dioctanoate, divinyldiethyltin, tetrabenzyltin, dibutyltin distearate, tetraallyltin, and p-tributyltin styrene.

[0064] The tin atom content in the tin-modified BR is preferably 50 ppm or more, more preferably 60 ppm or more, and is preferably 3000 ppm or less, more preferably 2500 ppm or less, and even more preferably 250 ppm or less.

[0065] The molecular weight distribution (Mw / Mn) of the tin-modified BR is preferably 2 or less, and more preferably 1.5 or less.

[0066] The vinyl bond content in the tin-modified BR is preferably 5% by mass or more, more preferably 7% by mass or more, while the vinyl bond content in the tin-modified BR is preferably 50% by mass or less, more preferably 20% by mass or less.

[0067] The above-mentioned S-modified BR and tin-modified BR may be used alone or in combination of two or more kinds.

[0068] As the BR, for example, products from Ube Industries, Ltd., JSR Corporation, Asahi Kasei Corporation, Nippon Zeon Corporation, etc. can be used.

[0069] (d) Other rubber components Furthermore, as other rubber components, rubbers (polymers) that are generally used in the production of tires, such as nitrile rubber (NBR), may be included as necessary.

[0070] (b) Compounding materials other than rubber components (a) Filler In the present embodiment, the rubber composition preferably contains a filler. Specific examples of the filler include silica, carbon black, graphite, calcium carbonate, talc, alumina, clay, aluminum hydroxide, and mica. Among these, silica is preferably contained in combination with a silane coupling agent, and carbon black may also be contained as necessary.

[0071] The total amount of filler blended per 100 parts by mass of the rubber component is preferably 40 parts by mass or more, more preferably 45 parts by mass or more, and even more preferably 50 parts by mass or more, while from the viewpoint of dispersibility in the rubber composition, it is preferably 150 parts by mass or less, more preferably 110 parts by mass or less, and even more preferably 70 parts by mass or less.

[0072] (i) Silica If the average primary particle diameter of silica is too small, processability will be poor, so silica having an average primary particle diameter of more than 8 nm is preferably used. 9 nm or more is more preferable, and 10 nm or more is even more preferable. On the other hand, from the viewpoint of ensuring the reinforcement of rubber and ensuring steering stability on wet roads during high-speed driving, the average primary particle diameter is preferably 25 nm or less, more preferably 20 nm or less, and even more preferably 17 nm or less.

[0073] The average primary particle size of silica refers to the average value of the diameter of the circle measured by observing the smallest particle unit of silica constituting the aggregate structure as a circle and measuring the absolute maximum length of the smallest particle. The average primary particle size of silica can be determined by observing with a transmission or scanning electron microscope, measuring 400 or more primary particles of silica observed within the field of view, and averaging the measured values.

[0074] The BET specific surface area of ​​silica is 100m 2 / g, and preferably greater than 130m 2 / g. On the other hand, it is more preferable that the 2 / g, and preferably less than 200m 2 / g or less. The BET specific surface area is the N2SA value measured by the BET method in accordance with ASTM D3037-93.

[0075] Examples of silica include dry process silica (anhydrous silica) and wet process silica (hydrated silica). Among them, wet process silica is preferred because it has a large number of silanol groups. Silica made from hydrous glass or silica made from biomass materials such as rice husks may also be used.

[0076] As silica, products available from Evonik Degussa, Rhodia, Tosoh Silica Corporation, Solvay Japan, Tokuyama Corporation, etc. can be used.

[0077] In the present disclosure, the amount of silica per 100 parts by mass of the rubber component is preferably 35 parts by mass or more, more preferably 40 parts by mass or more, and even more preferably 45 parts by mass or more, while from the viewpoint of dispersibility in the rubber composition, it is preferably 65 parts by mass or less, and more preferably 60 parts by mass or less.

[0078] (ii) Silane coupling agent When using silica, it is preferable to use silane coupling agent together.Silane coupling agent is not particularly limited, 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 tetrasulfide, 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-dimethylthiocarbamoyl tetrasulfide, 2-triethoxysilylethyl- Examples of suitable silane coupling agents include sulfide-based silanes such as N,N-dimethylthiocarbamoyl tetrasulfide and 3-triethoxysilylpropyl methacrylate monosulfide, mercapto-based silanes such as 3-mercaptopropyltrimethoxysilane, 2-mercaptoethyltriethoxysilane, and Momentive's NXT and NXT-Z, vinyl-based silanes such as vinyltriethoxysilane and vinyltrimethoxysilane, amino-based silanes such as 3-aminopropyltriethoxysilane and 3-aminopropyltrimethoxysilane, glycidoxy-based silanes such as γ-glycidoxypropyltriethoxysilane and γ-glycidoxypropyltrimethoxysilane, nitro-based silanes such as 3-nitropropyltrimethoxysilane and 3-nitropropyltriethoxysilane, and chloro-based silanes such as 3-chloropropyltrimethoxysilane and 3-chloropropyltriethoxysilane. As mentioned above, among these, silane coupling agents having a thiocarbonyl group such as the above-mentioned NXT are preferred. These may be used alone or in combination of two or more.

[0079] As the silane coupling agent, for example, products from Degussa, Momentive, Shin-Etsu Silicone Co., Ltd., Tokyo Chemical Industry Co., Ltd., Azumax Co., Ltd., Dow Corning Toray Co., Ltd., etc. can be used.

[0080] The content of the silane coupling agent is, for example, preferably more than 3 parts by mass and less than 15 parts by mass, and more preferably 5 parts by mass or more and 10 parts by mass or less, relative to 100 parts by mass of silica.

[0081] (iii) Carbon black The rubber composition preferably contains carbon black. When silica is not used in combination, the amount of carbon black is preferably 50 parts by mass or more, more preferably 55 parts by mass or more, per 100 parts by mass of the rubber component, and is preferably 70 parts by mass or less, more preferably 65 parts by mass or less.

[0082] When used in combination with silica, the amount of carbon black is preferably 1 part by mass or more, more preferably 3 parts by mass or more, per 100 parts by mass of the rubber component, and is preferably 9 parts by mass or less, more preferably 7 parts by mass or less.

[0083] The carbon black is not particularly limited, and examples thereof 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 alone or in combination of two or more.

[0084] The nitrogen adsorption specific surface area (N2SA) of carbon black is, for example, 30m 2 / g over 250m 2The dibutyl phthalate (DBP) absorption of carbon black is, for example, more than 50 ml / 100 g and less than 250 ml / 100 g. The nitrogen adsorption specific surface area of ​​carbon black is measured in accordance with ASTM D4820-93, and the DBP absorption is measured in accordance with ASTM D2414-93.

[0085] Specific carbon blacks are not particularly limited, and examples include N134, N110, N220, N234, N219, N339, N330, N326, N351, N550, and N762. Commercially available carbon blacks include those from Asahi Carbon Co., Ltd., Cabot Japan Co., Ltd., Tokai Carbon Co., Ltd., Mitsubishi Chemical Corporation, Lion Corporation, Shin-Nichika Carbon Co., Ltd., and Columbia Carbon Co., Ltd. These may be used alone or in combination of two or more.

[0086] (iv) Other fillers In addition to the above-mentioned silica and carbon black, the rubber composition may further contain fillers commonly used in the tire industry, such as graphite, calcium carbonate, talc, alumina, clay, aluminum hydroxide, mica, magnesium sulfate, etc. The content of these fillers is, for example, more than 0.1 part by mass and less than 150 parts by mass per 100 parts by mass of the rubber component.

[0087] (b) Vulcanized rubber powder As described above, in the present disclosure, the tread rubber composition contains vulcanized rubber powder. The vulcanized rubber powder may be a commercially available vulcanized rubber powder obtained by pulverizing used tires using a roller or grinder, and then sieving the pulverized rubber to a predetermined particle size. Alternatively, if necessary, a vulcanized rubber powder obtained by vulcanizing a separately formulated rubber composition, pulverizing it, and sieving it may be used. As described above, the particle size of the vulcanized rubber powder is preferably finer than 30 mesh pass and coarser than 250 mesh pass using a test sieve specified in JIS Z8801-1.

[0088] The inclusion of vulcanized rubber powder may reduce the reinforcing properties of the tire and lead to a decrease in tire durability. Therefore, the content of vulcanized rubber powder per 100 parts by mass of the rubber component is, for example, preferably 5 parts by mass or more, more preferably 20 parts by mass or more, and even more preferably 40 parts by mass or more. On the other hand, the content is preferably 100 parts by mass or less, more preferably 90 parts by mass or less, and even more preferably 80 parts by mass or less.

[0089] Furthermore, if the vulcanized rubber powder also contains silica, a further decrease in 30°C tan δ of the entire rubber layer is expected, and therefore it is preferable to use vulcanized rubber powder containing silica.

[0090] The silica content of the vulcanized rubber powder is preferably the same as that of the parts other than the vulcanized rubber powder, but since the degree of contribution to the entire cap rubber layer is lower than that of the parts other than the vulcanized rubber powder, it is also possible to use vulcanized rubber powder with a lower silica content than that of the parts other than the vulcanized rubber powder.

[0091] The content of the vulcanized rubber powder is appropriately adjusted so that the occupied area ratio falls within the above range.

[0092] (c) Plasticizer component The rubber composition preferably contains a plasticizer component as needed. The content of the plasticizer component per 100 parts by mass of the rubber component is preferably 20 parts by mass or more, more preferably 30 parts by mass or more, and even more preferably 40 parts by mass or more. On the other hand, although there is no particular upper limit, it is preferably 70 parts by mass or less, more preferably 60 parts by mass or less, and even more preferably 50 parts by mass or less. This allows the vulcanized rubber powder to be properly dispersed during mixing. Here, the plasticizer component refers to a component that plasticizes the rubber composition, such as process oil, rubber component extender oil, liquid rubber, or resin component.

[0093] (i) Oil Examples of oils include mineral oil (commonly referred to as process oil), vegetable oil, and mixtures thereof. Among these, vegetable oil is preferably used because it has a high molecular weight, which makes it easier to suppress migration at the rubber layer interface, etc., and makes it easier to maintain grip performance on the tread surface.

[0094] Examples of mineral oils (process oils) include paraffin-based process oils, aromatic process oils, naphthenic process oils, etc. 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 bran oil, safflower oil, sesame oil, olive oil, sunflower oil, palm kernel oil, camellia oil, jojoba oil, macadamia nut oil, tung oil, etc. These may be used alone or in combination of two or more.

[0095] From the viewpoint of life cycle assessment, lubricating oils used in the mixers and engines of rubber mixers, waste cooking oils used in restaurants, etc. may be appropriately refined and used as these oils.

[0096] As the mineral oil (process oil), for example, products from Idemitsu Kosan Co., Ltd., Sankyo Yuka Kogyo Co., Ltd., Japan Energy Co., Ltd., Orisoi Co., Ltd., H&R Co., Ltd., Toyokuni Oil Mills Co., Ltd., Showa Shell Sekiyu K.K., Fuji Kosan Co., Ltd., etc. can be used.

[0097] (ii) Liquid rubber Liquid rubber is a polymer that is in a liquid state at room temperature (25°C) and is a rubber component that can be extracted by acetone extraction from a vulcanized tire. Examples of liquid rubber include farnesene-based polymers, liquid diene-based polymers, and hydrogenated products thereof.

[0098] Farnesene polymers are polymers obtained by polymerizing farnesene, which has structural 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).

[0099] The farnesene-based polymer may be a homopolymer of farnesene (farnesene homopolymer) or a copolymer of farnesene and a vinyl monomer (farnesene-vinyl monomer copolymer).

[0100] 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).

[0101] The liquid diene polymer has a weight average molecular weight (Mw) of, for example, 1.0 × 10 in terms of polystyrene measured by gel permeation chromatography (GPC). 3 Super, 2.0×10 5 In this specification, the Mw of the liquid diene polymer is a polystyrene-equivalent value measured by gel permeation chromatography (GPC).

[0102] The amount of the liquid rubber (total amount of the liquid farnesene polymer, liquid diene polymer, etc.) is, for example, more than 1 part by mass and less than 100 parts by mass per 100 parts by mass of the rubber component.

[0103] As the liquid rubber, for example, products of Kuraray Co., Ltd., Cray Valley Co., Ltd., etc. can be used.

[0104] (iii) Resin component The resin component also functions as a tackifier and may be solid or liquid at room temperature. Specific examples of the resin component include rosin resins, styrene resins, coumarone resins, terpene resins, C5 resins, C9 resins, C5C9 resins, and acrylic resins. Two or more of these may be used in combination. The content of the resin component is preferably more than 2 parts by mass and less than 45 parts by mass, and more preferably less than 30 parts by mass, per 100 parts by mass of the rubber component.

[0105] Rosin-based resins are resins whose main component is rosin acid, which is obtained by processing pine resin. These rosin-based resins (rosins) can be classified based on whether they are modified or not, and can be divided into unmodified rosin (unmodified rosin) and modified rosin (rosin derivatives). Examples of unmodified rosins include tall rosin (also known as tall oil rosin), gum rosin, wood rosin, disproportionated rosin, polymerized rosin, hydrogenated rosin, and other chemically modified rosins. Modified rosin is a modification of unmodified rosin, and examples include rosin esters, unsaturated carboxylic acid-modified rosin esters, unsaturated carboxylic acid-modified rosin esters, rosin amide compounds, and rosin amine salts.

[0106] Styrenic resins are polymers that use styrene monomers as constituent monomers, and examples thereof include polymers obtained by polymerizing styrene monomers as the main component (50% by mass or more).Specific 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 be copolymerized with them.

[0107] Examples of the 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, α,β-unsaturated carboxylic acids such as maleic anhydride or acid anhydrides thereof, and the like.

[0108] Among the coumarone resins, coumarone-indene resins are preferred. Coumarone-indene resins are resins containing coumarone and indene as monomer components that constitute the resin skeleton (main chain). Monomer components contained in the skeleton other than coumarone and indene include styrene, α-methylstyrene, methylindene, vinyltoluene, etc.

[0109] The amount of the coumarone-indene resin per 100 parts by mass of the rubber component is, for example, more than 1.0 part by mass and less than 50.0 parts by mass.

[0110] The hydroxyl value (OH value) of the coumarone-indene resin is, for example, more than 15 mgKOH / g and less than 150 mgKOH / g. The OH value is the amount of potassium hydroxide, expressed in milligrams, required to neutralize acetic acid bonded to hydroxyl groups when acetylating 1 g of the resin, and is a value measured by potentiometric titration (JIS K 0070:1992).

[0111] The softening point of the coumarone-indene resin is, for example, more than 30° C. and less than 160° C. The softening point is the temperature at which the ball drops when the softening point specified in JIS K 6220-1:2001 is measured using a ring and ball softening point tester.

[0112] Terpene resins include polyterpenes, terpene phenols, and aromatic modified terpene resins. Polyterpenes are resins obtained by polymerizing terpene compounds and their hydrogenated products. Terpene compounds are (C5H8) n The hydrocarbons and their oxygen-containing derivatives are represented by the following composition: monoterpenes (C10 H 16 ), sesquiterpenes (C 15 H 24 ), diterpenes (C 20 H 32 ), and examples thereof include α-pinene, β-pinene, dipentene, limonene, myrcene, alloocimene, ocimene, α-phellandrene, α-terpinene, γ-terpinene, terpinolene, 1,8-cineole, 1,4-cineole, α-terpineol, β-terpineol, and γ-terpineol.

[0113] Examples of 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 above-mentioned terpene compounds, as well as hydrogenated terpene resins obtained by hydrogenating the terpene resins. Examples of terpene phenols include resins obtained by copolymerizing the above-mentioned terpene compounds with phenolic compounds, and resins obtained by hydrogenating the above-mentioned resins. Specific examples include resins obtained by condensing the above-mentioned terpene compounds, phenolic compounds, and formalin. Examples of phenolic compounds include phenol, bisphenol A, cresol, and xylenol. Examples of aromatic-modified terpene resins include resins obtained by modifying terpene resins with aromatic compounds, and resins obtained by hydrogenating the above-mentioned resins. The aromatic compound is not particularly limited as long as it is a compound having an aromatic ring, and examples thereof include phenolic compounds such as phenol, alkylphenol, alkoxyphenol, and unsaturated hydrocarbon group-containing phenol; naphthol compounds such as naphthol, alkylnaphthol, alkoxynaphthol, and unsaturated hydrocarbon group-containing naphthol; styrene derivatives such as styrene, alkylstyrene, alkoxystyrene, and unsaturated hydrocarbon group-containing styrene; coumarone, indene, and the like.

[0114] "C5 resin" refers to a resin obtained by polymerizing a C5 fraction. Examples of C5 fractions include petroleum fractions having 4 to 5 carbon atoms, such as cyclopentadiene, pentene, pentadiene, and isoprene. Dicyclopentadiene resin (DCPD resin) is preferably used as a C5 petroleum resin.

[0115] "C9 resin" refers to a resin obtained by polymerizing a C9 fraction, and may be a hydrogenated or modified version. Examples of C9 fractions include petroleum fractions having 8 to 10 carbon atoms, such as vinyltoluene, alkylstyrene, indene, and methylindene. Specific examples of suitable aromatic vinyl resins include coumarone-indene resins, coumarone resins, indene resins, and aromatic vinyl resins. Preferred aromatic vinyl resins are α-methylstyrene (AMS resin), styrene homopolymers, and copolymers of α-methylstyrene and styrene, with copolymers of α-methylstyrene and styrene being more preferred, due to their economical efficiency, ease of processing, and excellent heat generation. Examples of aromatic vinyl resins that can be used include those commercially available from Kraton, Eastman Chemical, and the like.

[0116] "C5C9 resin" refers to a resin obtained by copolymerizing the C5 fraction and the C9 fraction, and may be a hydrogenated or modified resin. Examples of C5 fractions and C9 fractions include the petroleum fractions mentioned above. As the C5C9 resin, for example, commercially available products from Tosoh Corporation, LUHUA, etc. can be used.

[0117] The acrylic resin is not particularly limited, but for example, a solventless acrylic resin can be used.

[0118] Examples of solvent-free acrylic resins include (meth)acrylic resins (polymers) synthesized by high-temperature continuous polymerization (high-temperature continuous bulk polymerization) (methods described in U.S. Pat. No. 4,414,370, JP-A-59-6207, JP-B-5-58005, JP-A-1-313522, U.S. Pat. No. 5,010,166, and Toa Gosei Kenkyusho TREND 2000 Vol. 3, pp. 42-45, etc.), with minimal use of secondary raw materials such as polymerization initiators, chain transfer agents, and organic solvents. In this disclosure, (meth)acrylic refers to both methacrylic and acrylic.

[0119] Examples of the monomer components constituting the 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.

[0120] Furthermore, aromatic vinyls such as styrene, α-methylstyrene, vinyltoluene, vinylnaphthalene, divinylbenzene, trivinylbenzene, and divinylnaphthalene may be used together with (meth)acrylic acid or a (meth)acrylic acid derivative as a monomer component constituting the acrylic resin.

[0121] The acrylic resin may be a resin composed solely of a (meth)acrylic component, or a resin containing components other than a (meth)acrylic component, and may have a hydroxyl group, a carboxyl group, a silanol group, or the like.

[0122] As the resin component, for example, products from Maruzen Petrochemical Co., Ltd., Sumitomo Bakelite Co., Ltd., Yasuhara Chemical Co., Ltd., Tosoh Corporation, Rutgers Chemicals, BASF, Arizona Chemical Company, Nitto Chemical Co., Ltd., Nippon Shokubai Co., Ltd., JX Nippon Energy Corporation, Arakawa Chemical Industries, Ltd., Taoka Chemical Co., Ltd., etc. can be used.

[0123] (D) Wax The rubber composition preferably contains wax. The content of the wax per 100 parts by mass of the rubber component is, for example, 0.5 to 20 parts by mass, preferably 1.0 to 15 parts by mass, and more preferably 1.5 to 10 parts by mass.

[0124] The wax is not particularly limited, and examples thereof include petroleum waxes such as paraffin wax and microcrystalline wax; natural waxes such as plant wax and animal wax; and synthetic waxes such as polymers of ethylene, propylene, etc. These may be used alone or in combination of two or more.

[0125] As the wax, for example, products from Ouchi Shinko Chemical Industry Co., Ltd., Nippon Seiro Co., Ltd., Seiko Chemical Co., Ltd., etc. can be used.

[0126] (e) Antiaging agents The rubber composition preferably contains an antioxidant. The content of the antioxidant 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.

[0127] Examples of the antioxidant include naphthylamine-based antioxidants such as phenyl-α-naphthylamine; diphenylamine-based antioxidants 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 of antioxidants include p-phenylenediamine antioxidants such as quinolone; quinoline antioxidants such as polymers of 2,2,4-trimethyl-1,2-dihydroquinoline; monophenol antioxidants such as 2,6-di-t-butyl-4-methylphenol and styrenated phenol; and bis-, tris-, and polyphenol antioxidants such as tetrakis-[methylene-3-(3',5'-di-t-butyl-4'-hydroxyphenyl)propionate]methane. These antioxidants may be used alone or in combination of two or more.

[0128] As the antioxidant, for example, products available from Seiko Chemical Co., Ltd., Sumitomo Chemical Co., Ltd., Ouchi Shinko Chemical Industry Co., Ltd., Flexis, etc. can be used.

[0129] (f) Lubricants The rubber composition may contain a lubricant. The lubricant is preferably a lubricant based on a fatty acid derivative such as stearic acid. Specific examples of stearic acid that can be used include products from NOF Corporation, NOF Corporation, Kao Corporation, Fujifilm Wako Pure Chemical Industries, Ltd., Chiba Fatty Acid Co., Ltd., and the like. Struktol WB16 manufactured by Struktol Co., Ltd. can also be used. The content of the vulcanization activator is preferably 0.1 to 3 parts by mass, more preferably 0.5 to 2.5 parts by mass, and even more preferably 1.0 to 2.0 parts by mass, per 100 parts by mass of the rubber component.

[0130] (g) Zinc oxide The rubber composition may contain zinc oxide. The content of zinc oxide 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. As the zinc oxide, a conventionally known product 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.

[0131] (H) Crosslinking agents and vulcanization accelerators The rubber composition preferably contains a crosslinking agent such as sulfur, etc. The content of the crosslinking agent 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.

[0132] Examples of sulfur include powdered sulfur, precipitated sulfur, colloidal sulfur, insoluble sulfur, highly dispersible sulfur, soluble sulfur, etc., which are commonly used in the rubber industry. These may be used alone or in combination of two or more.

[0133] As sulfur, for example, products from Tsurumi Chemical Industry Co., Ltd., Karuizawa Iso Co., Ltd., Shikoku Chemical Industry Co., Ltd., Flexis Corporation, Nippon Kanzuri Kogyo Co., Ltd., Hosoi Chemical Industry Co., Ltd., etc. can be used.

[0134] The tread rubber composition preferably contains a vulcanization accelerator. The content of the vulcanization accelerator 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.

[0135] Examples of the vulcanization accelerator include thiazole-based vulcanization accelerators such as 2-mercaptobenzothiazole, di-2-benzothiazolyl disulfide, and N-cyclohexyl-2-benzothiazyl sulfenamide; thiuram-based vulcanization accelerators such as tetramethylthiuram disulfide (TMTD), tetrabenzylthiuram disulfide (TBzTD), and tetrakis(2-ethylhexyl)thiuram disulfide (TOT-N); sulfenamide-based vulcanization accelerators such as N-cyclohexyl-2-benzothiazole sulfenamide, Nt-butyl-2-benzothiazolyl sulfenamide, N-oxyethylene-2-benzothiazole sulfenamide, N-oxyethylene-2-benzothiazole sulfenamide, and N,N'-diisopropyl-2-benzothiazole sulfenamide; and guanidine-based vulcanization accelerators such as diphenyl guanidine, di-orthotolyl guanidine, and orthotolyl biguanidine. These may be used alone or in combination of two or more.

[0136] (R) Other In addition to the above components, the tread rubber composition may further contain additives commonly used in the tire industry, such as fatty acid metal salts, carboxylic acid metal salts, organic peroxides, etc. The content of these additives is, for example, more than 0.1 parts by mass and less than 50 parts by mass per 100 parts by mass of the rubber component.

[0137] (2) Preparation of tread rubber composition The tread rubber composition is produced by a general method, for example, a manufacturing method including a base kneading step in which a rubber component, vulcanized rubber powder, and a filler such as silica are kneaded together, and a finish kneading step in which the kneaded product obtained in the base kneading step is kneaded with a crosslinking agent.

[0138] The kneading can be carried out using a known (internal) kneading machine such as a Banbury mixer, a kneader, or an open roll.

[0139] The kneading temperature in the base kneading step is, for example, higher than 50° C. and lower than 200° C., and the kneading time is, for example, higher than 30 seconds and lower than 30 minutes. In the base kneading step, in addition to the above components, compounding agents conventionally used in the rubber industry, for example, plasticizers such as oil, stearic acid, zinc oxide, antioxidants, waxes, vulcanization accelerators, etc., may be appropriately added and kneaded as needed.

[0140] In the final kneading step, the kneaded product obtained in the base kneading step is kneaded with a crosslinking agent. The kneading temperature in the final kneading step is, for example, higher than room temperature and lower than 80°C, and the kneading time is, for example, longer than 1 minute and shorter than 15 minutes. In the final kneading step, in addition to the above components, a vulcanization accelerator, zinc oxide, etc. may be appropriately added and kneaded as necessary.

[0141] The resulting rubber composition is then extruded into a predetermined shape to form a tread.

[0142] 2. Tire manufacturing The tire of the present disclosure is first produced by molding in a conventional manner on a tire building machine to produce an unvulcanized tire.

[0143] Specifically, an inner liner as a component for ensuring the airtightness of the tire, a carcass as a component for withstanding the load, impact, and inflation pressure to which the tire is subjected, and a belt component as a component for tightly fastening the carcass and increasing the rigidity of the tread are wound around a forming drum, and both ends of the carcass are fixed to both side edges, and bead portions as components for fixing the tire to the rim are arranged. After forming into a toroidal shape, a tread is attached to the center of the outer periphery and sidewalls are attached to the radially outer sides to form side portions, thereby producing an unvulcanized tire.

[0144] The unvulcanized tire is then heated and pressurized in a vulcanizer to obtain a tire. The vulcanization process can be carried out by using a known vulcanization method. The vulcanization temperature is, for example, greater than 120°C and less than 200°C, and the vulcanization time is, for example, greater than 5 minutes and less than 15 minutes.

[0145] As described above, the obtained tire has sufficiently improved grip performance and responsiveness on wet road surfaces, and can therefore exhibit excellent steering stability on wet road surfaces when traveling at high speeds. [Example]

[0146] The present disclosure will be described in more detail below with reference to examples. In the examples, tires having a tread portion formed of a single layer of cap rubber and a size of 205 / 55R16 are manufactured, and steering stability performance on wet roads during high-speed driving is evaluated.

[0147] 1. Production of tread rubber composition Prior to the production of a tire, a tread rubber composition for forming a cap rubber layer is first produced.

[0148] (1) Compounding materials First, the following ingredients are prepared. (a) Rubber component (i) NR:SVR-L (B-1) SBR1: Tufuden 3830 (S-SBR) manufactured by Asahi Kasei Corporation (Styrene content: 33% by mass, vinyl bond amount: 31% by mass, 37.5% oil extended product) (Ro-2) SBR2: SBR1502 (E-SBR) manufactured by JSR (Styrene content: 24% by mass, vinyl bond content: 16% by mass, non-oil extended) (Ro-3) SBR3: JSR HPR840 (styrene ratio 10% by mass, vinyl bond content: 42% by mass, modified, non-oil extended) (c) BR: Ube Industries BR150B (high-sys BR) (cis content 97% by mass, trans content 2% by mass, vinyl content 1% by mass)

[0149] (b) Compounding materials other than rubber components (a) Carbon black: Show Black N220 manufactured by Cabot Japan (N2SA:111m 2 / g) (B-1) Silica-1: Ultrasil VN3 manufactured by Evonik Degussa (N2SA:175m 2 / g, average primary particle diameter: 18nm) (B-2) Silica-2: Ultrasil 9100Gr manufactured by Evonik Degussa (N2SA:230m 2 / g, average primary particle diameter: 15nm) (H-1) Silane coupling agent-1: Si266 manufactured by Evonik Degussa (Bis(3-triethoxysilylpropyl)disulfide) (H-2) Silane coupling agent-2: NXT manufactured by Momentive (Thiocarbonyl-containing mercapto silane coupling agent) (d) Vulcanized rubber powder: Vulcanized rubber powder containing 40% silica by weight (see next item (c) for manufacturing method) (E) Oil: Idemitsu Kosan Diana Process Oil NH-70S (Aromatic processed oil) (F) Vegetable oil: Sunflower oil manufactured by Nisshin Oillio Group Co., Ltd. (glycerol fatty acid triester) (g) Liquid BR: Ricon 130 manufactured by Cray Valley (Number average molecular weight: 2500) (H) Resin: Syltraxx 4401 manufactured by Arizona Chemical Company (α-methylstyrene resin, softening point 85°C) (i) Zinc oxide: Zinc oxide No. 1 manufactured by Mitsui Mining & Smelting Co., Ltd. (Nu-1) Antioxidant 1: Nocrac 6C manufactured by Ouchi Shinko Chemical Industry Co., Ltd. (N-phenyl-N'-(1,3-dimethylbutyl)-p-phenylenediamine) (Nu-2) Antioxidant 2: Nocrac FR manufactured by Ouchi Shinko Chemical Industry Co., Ltd. (2,2,4-trimethyl-1,2-dihydroquinoline polymer) (k) Stearic acid: NOF Corporation's "Tsubaki" stearic acid (L) Wax: Ozoace 0355 manufactured by Nippon Seiro Co., Ltd. (W) Sulfur: 5% oil-treated powder sulfur manufactured by Tsurumi Chemical Industry Co., Ltd. (Ka-1) Vulcanization accelerator-1: Noccela D (DPG) manufactured by Ouchi Shinko Chemical Industry Co., Ltd. (3-diphenylguanidine) (Ka-2) Vulcanization accelerator-2: Noccela CZ manufactured by Ouchi Shinko Chemical Industry Co., Ltd. (N-cyclohexyl-2-benzothiazolylsulfenamide)

[0150] (c) Manufacture of vulcanized rubber powder The vulcanized rubber powder described above is produced according to the following procedure.

[0151] First, according to the composition shown in Table 1, materials other than sulfur and vulcanization accelerator are kneaded for 5 minutes at 150°C using a Banbury mixer, and then sulfur and vulcanization accelerator are added, followed by kneading for 5 minutes at 80°C using an open roll to obtain a kneaded mixture. The amounts of each ingredient are in parts by mass.

[0152] The resulting kneaded material is then vulcanized at 170°C for 20 minutes to obtain a rubber plate, which is then roll-pulverized and passed through a 30-mesh sieve to obtain a vulcanized rubber powder with a silica content of 40 wt%.

[0153] [Table 1]

[0154] (2) Manufacturing of tread rubber composition According to the formulations shown in Tables 2 to 4, materials other than sulfur and vulcanization accelerator are kneaded for 5 minutes at 150°C using a Banbury mixer to obtain a kneaded mixture. Each blend amount is in parts by mass.

[0155] Next, sulfur and a vulcanization accelerator are added to the obtained kneaded mixture, and the mixture is kneaded for 5 minutes at 80°C using an open roll to obtain each tread rubber composition.

[0156] 2. Manufacturing of cap rubber and tires Each of the obtained tread rubber compositions is extruded into a predetermined shape to produce a cap rubber, which is then laminated together with other tire components to form an unvulcanized tire, and press-vulcanized at 170°C for 10 minutes to produce test tires for Examples 1 to 16 and Comparative Examples 1 to 9.

[0157] 3. Calculation of parameters Next, the following parameters are determined for each test tire.

[0158] (1) Area ratio S occupied by vulcanized rubber powder First, a sample for observation is cut out from the cap rubber layer of each test tire so that the plane parallel to the tread surface becomes the cross section for observation.

[0159] Next, the cross section for observation of each sample is photographed using a scanning electron microscope (Teneo manufactured by ThermoFisher) at an acceleration voltage of 15 kV to obtain an electron microscope image at a magnification of 50 times.

[0160] Next, the area of ​​the domain corresponding to the vulcanized rubber powder is calculated within a 2.54 mm × 1.69 mm range of the obtained electron microscope image, and the ratio of this area to the total area of ​​the cross section is calculated. This is done for three fields of view per sample, and the average value is taken as the area ratio S (%) occupied by the vulcanized rubber powder.

[0161] The results are shown in Tables 2 to 4. Note that for test tires using the same compounding, the same measurements were carried out for each, and the obtained results were again averaged to obtain the area ratio of the vulcanized rubber powder for each compounding.

[0162] (2) Loss tangent (30℃tanδ) A rubber test specimen for measurement was prepared by cutting a piece 20 mm long x 4 mm wide x 1 mm thick from the cap rubber layer of each test tire, with the long side aligned in the tire circumferential direction. The loss tangent (30°C tanδ) of each rubber test specimen was measured using a GABO Iplexer series under the conditions of 30°C, a frequency of 10 Hz, an initial strain of 5%, and a dynamic strain rate of 1%, in a tensile deformation mode.

[0163] The results are shown in Tables 2 to 4. Note that for test tires using the same formulation, the same measurements were carried out for each, and the results were averaged to obtain the 30°C tan δ for each formulation.

[0164] (3) Groove depth Each test tire was placed in a normal state, and the height from the groove bottom to the opening of the circumferential main groove was measured under no load, and this was taken as the groove depth D (mm). The results are shown in Tables 2 to 4.

[0165] (4) Tread gauge Each test tire was cut in the tire radial direction, and the thickness of the tread portion at the equatorial plane of the cut surface was measured and recorded as the tread gauge G (mm). The results are shown in Tables 2 to 4.

[0166] (5) Other parameters Next, (S / D), (S / G), and (30°C tan δ×G) were calculated using the area ratio S (%), 30°C tan δ, groove depth D (mm), and tread gauge G (mm) obtained above. The total rubber amount RR (parts by mass) of NR, SBR with a styrene content of 30% or less, and BR per 100 parts by mass of the rubber component was also calculated according to the following formula. The results are shown in Tables 2 to 4. RR = {NR amount + BR amount + SBR (Sty: ≦ 30) amount} / rubber component amount × 100

[0167] 4.Performance Evaluation Each test tire was fitted to all wheels of a vehicle (a domestically produced FR vehicle with an engine displacement of 2000cc), and the front tires were inflated to an internal pressure of 230kPa and the rear tires to 220kPa. After that, the vehicle was driven around the track at a speed of 100km / h with water being sprayed on the road surface, and the handling stability was evaluated by the driver on a sensory scale of 1 to 5. Similar evaluations were carried out by 20 drivers, and the total scores obtained were calculated.

[0168] The evaluation was carried out by indexing the steering stability performance of each test tire on wet roads when traveling at high speeds based on the following formula, with the total score of Comparative Example 9 being set to 100. A larger value indicates better steering stability performance on wet roads when traveling at high speeds. The results are shown in Tables 2 to 4. Steering stability on wet roads at high speeds = (total score of Comparative Example 9 / total score of test tires) × 100

[0169] [Table 2]

[0170] [Table 3]

[0171] [Table 4]

[0172] Tables 2 to 4 show that examples in which the area ratio of vulcanized rubber powder in the cap rubber layer is 5% or more and 50% or less, the 30°C tan δ is 0.15 or less, the groove depth of the circumferential main groove is greater than 6 mm, and the ratio of the area ratio of vulcanized rubber powder to groove depth (occupancy area ratio / groove depth) is greater than 0.85 (% / mm) have excellent steering stability on wet roads when driving at high speeds.

[0173] Furthermore, by appropriately controlling various parameters, such as the total rubber amount of NR, SBR with a styrene content of 30% or less, and BR being 90 parts by mass or more per 100 parts by mass of the rubber component, the inclusion of 60 parts by mass or less of silica in the cap rubber, the use of a thiocarbonyl group-containing silane coupling agent, an S / D of 1.0% / mm or more, and an S / G of 0.6 or more, even better steering stability on wet roads when driving at high speeds can be achieved.

[0174] Although the present disclosure has been described above based on the embodiments, the present disclosure is not limited to the above embodiments. Various modifications can be made to the above embodiments within the scope of the same or equivalent to the present disclosure.

[0175] This disclosure (1) A pneumatic tire having a circumferential main groove in a tread portion, the outermost layer of the tread portion is formed using a rubber composition containing vulcanized rubber powder, In the cross section of the outermost layer, the area ratio S (%) occupied by the vulcanized rubber powder is 5% or more and 50% or less, the loss tangent (30°C tanδ) of the rubber composition measured in a tensile deformation mode under conditions of 30°C, a frequency of 10 Hz, an initial strain of 5%, and a dynamic strain rate of 1% is 0.15 or less; The groove depth D (mm) of the circumferential main groove is greater than 6 mm, Furthermore, the pneumatic tire is characterized in that S / D>0.85.

[0176] This disclosure (2) The pneumatic tire according to the present disclosure (1) is characterized in that the area ratio S (%) is 20% or more and 40% or less.

[0177] This disclosure (3) The pneumatic tire is characterized in that the 30° C. tan δ is 0.12 or less, as described in the present disclosure (1) or (2).

[0178] This disclosure (4) The pneumatic tire is characterized in that the S / D is 1.0 or more, and is any combination with any of the present disclosures (1) to (3).

[0179] This disclosure (5) The rubber composition contains, as rubber components, natural rubber (NR), butadiene rubber (BR), and styrene-butadiene rubber (SBR) having a styrene ratio of 30% by mass or less, in a total content of 90 parts by mass or more in 100 parts by mass of the rubber components, and is a pneumatic tire in any combination with any of the present disclosures (1) to (4).

[0180] This disclosure (6) The pneumatic tire is characterized in that the rubber composition contains 60 parts by mass or less of silica per 100 parts by mass of the rubber component, and is any combination with any of the present disclosures (1) to (5).

[0181] This disclosure (7) The pneumatic tire is characterized in that the rubber composition contains a silane coupling agent having a thiocarbonyl group, and is any combination with any of the present disclosures (1) to (6).

[0182] This disclosure (8) When the thickness (gauge) of the tread portion on the equatorial plane is G (mm), the area ratio S (%) satisfies S / G≧0.6, and the pneumatic tire is any combination with any of the present disclosures (1) to (7).

[0183] This disclosure (9) The pneumatic tire is characterized in that, in the tread portion, the 30°C tan δ and the thickness (gauge) G (mm) of the tread portion on the equatorial plane satisfy the following formula, and is any combination with any of the present disclosures (1) to (8). (30℃ tanδ×G)≦1.30

[0184] The present disclosure (10) The pneumatic tire according to the present disclosure (9) is characterized in that the (30° C. tan δ×G) is 1.10 or less.

[0185] This disclosure (11) The particle size of the vulcanized rubber powder is finer than 30 mesh pass and coarser than 250 mesh pass using a test sieve specified in JIS Z8801-1, and the pneumatic tire is any combination with any of the present disclosures (1) to (10).

[0186] This disclosure (12) The pneumatic tire is characterized in that the rubber composition contains a liquid rubber, and is any combination with any of the present disclosures (1) to (11).

[0187] This disclosure (13) The pneumatic tire according to the present disclosure (12) is characterized in that the liquid rubber is a liquid butadiene polymer (liquid BR).

[0188] This disclosure (14) The pneumatic tire is characterized in that the rubber composition contains a resin component, and is any combination with any of the present disclosures (1) to (13).

[0189] This disclosure (15) The pneumatic tire is characterized in that the rubber composition contains vegetable oil, and is any combination with any of the present disclosures (1) to (14).

[0190] This disclosure (16) The vulcanized rubber powder is characterized by containing silica, and is a pneumatic tire in any combination with any of the present disclosures (1) to (15).

Claims

1. A pneumatic tire having a circumferential main groove in a tread portion, the outermost layer of the tread portion is formed using a rubber composition containing vulcanized rubber powder, an area ratio S (%) of the vulcanized rubber powder in a cross section of the outermost layer is 5% or more and 50% or less; the rubber composition has a loss tangent (30°C tanδ) of 0.15 or less, measured in a tensile deformation mode under conditions of 30°C, a frequency of 10 Hz, an initial strain of 5%, and a dynamic strain rate of 1%; The groove depth D (mm) of the circumferential main groove is greater than 6 mm, The pneumatic tire is further characterized in that S / D>0.

85.

2. 2. The pneumatic tire according to claim 1, wherein the area ratio S (%) is 20% or more and 40% or less.

3. 3. The pneumatic tire according to claim 1, wherein the 30° C. tan δ is 0.12 or less.

4. 4. The pneumatic tire according to claim 1, wherein the S / D ratio is 1.0 or greater.

5. 5. The pneumatic tire according to claim 1, wherein the rubber composition contains, as rubber components, natural rubber (NR), butadiene rubber (BR), and styrene-butadiene rubber (SBR) having a styrene ratio of 30% by mass or less, in a total content of 90 parts by mass or more per 100 parts by mass of the rubber components.

6. 6. The pneumatic tire according to claim 1, wherein the rubber composition contains 60 parts by mass or less of silica per 100 parts by mass of the rubber component.

7. 7. The pneumatic tire according to claim 1, wherein the rubber composition contains a silane coupling agent having a thiocarbonyl group.

8. 8. The pneumatic tire according to claim 1, wherein when the thickness (gauge) of the tread portion on the equatorial plane is G (mm), the area ratio S (%) satisfies S / G≧0.

6.

9. 9. The pneumatic tire according to claim 1, wherein the 30° C. tan δ and a thickness (gauge) G (mm) of the tread portion on the equatorial plane satisfy the following formula: (30°C tan δ × G)≦1.30

10. The pneumatic tire according to claim 9, wherein the (30° C. tan δ×G) is 1.10 or less.

11. The pneumatic tire according to any one of claims 1 to 10, characterized in that the particle size of the vulcanized rubber powder is finer than 30 mesh pass and coarser than 250 mesh pass, when measured using a test sieve specified in JIS Z8801-1.

12. 12. The pneumatic tire according to claim 1, wherein the rubber composition contains a liquid rubber.

13. 13. The pneumatic tire according to claim 12, wherein the liquid rubber is a liquid butadiene polymer (liquid BR).

14. 14. The pneumatic tire according to claim 1, wherein the rubber composition contains a resin component.

15. 15. The pneumatic tire according to claim 1, wherein the rubber composition contains vegetable oil.

16. 16. The pneumatic tire according to claim 1, wherein the vulcanized rubber powder contains silica.

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