WO2025005131A1 - Rubber composition for tires, and tire - Google Patents

Abstract

The purpose of the present invention is to provide: a rubber composition for tires which exhibit excellent resistance to thermal sagging, resistance to wear in circuit running, wet performance, and rolling performance; and a tire produced using the rubber composition. This rubber composition for tires comprises: a rubber component A including a modified conjugated-diene rubber A1; silica B; and a softener C comprising at least one member selected from the group consisting of thermoplastic resins and oils. The A1 is a conjugated-diene rubber satisfying a specific expression and having a modification group including a nitrogen atom, a silicon atom, and an oxygen atom adjacent thereto and accounts for 25 mass% or more of the A. The A as a whole has a glass transition temperature higher than -80°C but not higher than -45°C. The content of the B is 80-160 parts by mass per 100 parts by mass of the A. The content of the thermoplastic resin(s) is 30-80 parts by mass, excluding 80 parts by mass, per 100 parts by mass of the A, and the proportion of the thermoplastic resin(s) to the sum of the thermoplastic resin(s) and the oil(s) is 50 mass% or higher.

Description

Rubber composition for tires and tires

The present invention relates to a rubber composition for tires and a tire.

　Conventionally, rubber compositions for tires that contain silica in order to improve performance have been known (for example, Patent Document 1).

JP 2014-28902 A

Recently, from the viewpoint of safety, etc., there is a demand for further improvements in heat sagging resistance, circuit wear resistance (wear resistance under high severity conditions such as circuit driving), wet performance, etc. In addition, from the viewpoint of environmental issues, etc., there is also a demand for further improvements in rolling performance.
Under these circumstances, the present inventors have studied the rubber composition for tires described in Patent Document 1 and the like, and have found that further improvement is desirable in consideration of future expected increases in demand.

In view of the above circumstances, the present invention aims to provide a rubber composition for tires that exhibits excellent heat sagging resistance, circuit abrasion resistance, wet performance, and rolling performance when made into a tire, as well as a tire manufactured using the rubber composition for tires.

As a result of intensive research into the above-mentioned problems, the present inventors have found that the above-mentioned problems can be solved by using a specific modified conjugated diene rubber as the rubber component and optimizing the contents of silica and thermoplastic resin, etc., and have arrived at the present invention.
That is, the present inventors have found that the above problems can be solved by the following configuration.

(1) A rubber composition comprising a rubber component (A) containing a modified conjugated diene rubber (A1), silica (B), and a softener (C) made of at least one selected from the group consisting of a thermoplastic resin and an oil,
The modified conjugated diene rubber (A1) satisfies the following formula (1) and the following formula (2) and has a modifying group containing a nitrogen atom, a silicon atom and an oxygen atom adjacent thereto,
The proportion of the modified conjugated diene rubber (A1) in the rubber component (A) is 25% by mass or more,
The glass transition temperature of the entire rubber component (A) is higher than −80° C. and not higher than −45° C.,
an amount of the silica (B) per 100 parts by mass of the rubber component (A) is 80 parts by mass or more and 160 parts by mass or less;
the content of the thermoplastic resin per 100 parts by mass of the rubber component (A) is 30 parts by mass or more and less than 80 parts by mass,
A rubber composition for tires, wherein a ratio of the thermoplastic resin to a total of the thermoplastic resin and the oil is 50 mass % or more.
IVw _10% ≦3.1×10 ^-6 ×Mw _10% -2.77 (1)
St+Vn≦50 (2)
Mw _10% and IVw _10% in formula (1) are as follows.
The modified conjugated diene rubber is subjected to gel permeation chromatography measurement using a differential refractive index detector and a viscosity detector as detectors. The weight average molecular weight obtained using the high molecular weight side portion of the peak of the chromatogram obtained by the differential refractive index detector, which is 10% of the total peak area, is defined as Mw _10% . The weight average intrinsic viscosity obtained using the high molecular weight side portion of the peak of the chromatogram obtained by the viscosity detector, which is 10% of the total peak area, is defined as IVw _10% . The unit of weight average intrinsic viscosity is dL/g.
In formula (2), St represents the proportion (mass%) of repeating units derived from styrene to the entire modified conjugated diene rubber, and Vn represents the proportion (mass%) of repeating units of 1,2-vinyl structure derived from conjugated diene to the entire modified conjugated diene rubber.
(2) The modified conjugated diene rubber (A1) is
a star structure having three or more branches, at least one branch of which has a moiety derived from a vinyl monomer containing an alkoxysilyl group or a halosilyl group;
The rubber composition for a tire according to the above (1), further comprising a main chain branched structure in the above portion.
(3) The rubber composition for tires according to (1) or (2) above, wherein the thermoplastic resin comprises at least one selected from the group consisting of a terpene resin, a C5/C9 resin, a C9 resin, a DCPD resin, a DCPD/C9 resin, a hydrogenated C5/C9 resin, a hydrogenated C9 resin, a hydrogenated DCPD resin, and a hydrogenated DCPD/C9 resin.
(4) The rubber composition for a tire according to any one of (1) to (3) above, further comprising 0.2 parts by mass or more and 3.0 parts by mass or less of a thiuram vulcanization accelerator per 100 parts by mass of the rubber component (A).
(5) The content of the thermoplastic resin per 100 parts by mass of the rubber component (A) is 50 parts by mass or more and less than 80 parts by mass,
The rubber composition for tires according to any one of (1) to (4), wherein a ratio of the thermoplastic resin to a total of the thermoplastic resin and the oil is 80 mass % or more.
(6) The rubber composition for tires according to any one of (1) to (5) above, wherein the softener (C) contains two or more thermoplastic resins.
(7) A tire produced using the rubber composition for tires according to any one of (1) to (6) above.

As described below, the present invention can provide a rubber composition for tires that exhibits excellent heat sagging resistance, circuit abrasion resistance, wet performance, and rolling performance when made into a tire, as well as a tire manufactured using the rubber composition for tires.

1 is an example of a GPC chromatogram. 1 is a partial cross-sectional schematic view showing an example of an embodiment of a tire of the present invention.

The rubber composition for tires and the like of the present invention will be described below.
In this specification, a numerical range expressed using "to" means a range that includes the numerical values before and after "to" as the lower and upper limits.
In addition, each component may be used alone or in combination of two or more. When two or more components are used in combination, the content of the components refers to the total content unless otherwise specified.
In addition, with regard to a rubber composition for tires, the heat sagging resistance, circuit abrasion resistance, wet performance, and rolling performance when made into a tire are also simply referred to as "heat sagging resistance,""circuit abrasion resistance,""wetperformance," and "rolling performance," respectively.
In addition, in this specification, a power of 10 may be represented as E. For example, E+5 represents 10 to the fifth power.

[I] Rubber Composition for Tires The rubber composition for tires of the present invention (hereinafter also referred to as the "composition of the present invention") is
The rubber composition contains a rubber component (A) containing a modified conjugated diene rubber (A1), silica (B), and a softener (C) made of at least one selected from the group consisting of a thermoplastic resin and an oil,
The modified conjugated diene rubber (A1) satisfies the formula (1) described below and the formula (2) described below, and has a modifying group containing a nitrogen atom, a silicon atom, and an oxygen atom adjacent thereto,
The proportion of the modified conjugated diene rubber (A1) in the rubber component (A) is 25% by mass or more,
The glass transition temperature of the entire rubber component (A) is higher than −80° C. and not higher than −45° C.,
an amount of the silica (B) per 100 parts by mass of the rubber component (A) is 80 parts by mass or more and 160 parts by mass or less;
the content of the thermoplastic resin per 100 parts by mass of the rubber component (A) is 30 parts by mass or more and less than 80 parts by mass,
The rubber composition for tires has a ratio of the thermoplastic resin to the total of the thermoplastic resin and the oil of 50 mass % or more.

It is believed that the composition of the present invention, having such a structure, can solve the above-mentioned problems. Although the reason for this is not clear, it is speculated to be as follows.
The composition of the present invention contains, as a rubber component, a conjugated diene rubber (hereinafter also referred to as a "specific conjugated diene rubber") that satisfies the formula (1) and formula (2) described below and has a modified group (hereinafter also referred to as a "specific modified group") containing a nitrogen atom, a silicon atom, and an oxygen atom adjacent thereto. Formula (1) specifies the relationship between the weight average intrinsic viscosity on the high molecular weight side and the weight average molecular weight on the high molecular weight side, and the inventors have found that rubber that satisfies formula (1) has excellent processability. In addition, it is believed that the specific modified group of the specific conjugated diene rubber interacts with silica. Therefore, in the composition of the present invention, the dispersibility of silica is extremely high, which is believed to lead to excellent effects (heat sagging resistance, circuit wear resistance, wet performance, rolling performance). Furthermore, since the composition of the present invention contains a specific amount of thermoplastic resin, it is believed that an extremely high level of modulus (heat sagging resistance) and circuit wear resistance is achieved.

The components contained in the composition of the present invention are explained below.

[1] Rubber Component The composition of the present invention contains a rubber component containing a specific conjugated diene rubber.
The composition of the present invention may contain a rubber component other than the specific conjugated diene rubber.

[Specific conjugated diene rubber]
The specific conjugated diene rubber is a conjugated diene rubber that satisfies the formula (1) described below and the formula (2) described below and has a modifying group (specific modifying group) containing a nitrogen atom, a silicon atom, and an oxygen atom adjacent thereto.

[Skeleton]
The skeleton of the specific conjugated diene rubber is a polymer having repeating units derived from a conjugated diene.

<Conjugated dienes>
Specific examples of the conjugated diene include butadiene (particularly 1,3-butadiene), isoprene, chloroprene, etc. The diene is preferably butadiene (particularly 1,3-butadiene) or isoprene, and more preferably butadiene (particularly 1,3-butadiene), because the effects of the present invention are more excellent.

<Other Monomers>
The skeleton of the specific conjugated diene rubber may have a repeating unit other than the repeating unit derived from the conjugated diene. Examples of the monomer (other monomer) that becomes such a repeating unit include vinyl monomers, alkenes (e.g., ethylene, propylene, butene), etc. Examples of the vinyl monomer include aromatic vinyl (e.g., styrene), acrylonitrile, and the specific branching agent described later.

<Specific examples>
Specific examples of the skeleton include natural rubber (NR), butadiene rubber (BR), aromatic vinyl-conjugated diene copolymer rubber, isoprene rubber (IR), acrylonitrile-butadiene copolymer rubber (NBR), butyl rubber (IIR), halogenated butyl rubber (Br-IIR, Cl-IIR), chloroprene rubber (CR), etc. Examples of the aromatic vinyl-conjugated diene copolymer rubber include styrene-butadiene rubber (SBR), styrene-isoprene copolymer rubber, etc.
The conjugated diene rubber is preferably SBR because the effects of the present invention are more excellent.

[Specific modifying group]
As described above, the specific conjugated diene rubber has a modifying group (specific modifying group) containing a nitrogen atom, a silicon atom, and an oxygen atom adjacent to the silicon atom.
The specific modifying group may be present at any one of the terminals, main chain, or side chain of the conjugated diene rubber.
For the reason that the effect of the present invention is more excellent, the specific modifying group preferably contains a silicon atom and an oxygen atom adjacent thereto as an alkoxysilyl group. The alkoxysilyl group is a group represented by -Si(OR1) _n (R2) _3-n (wherein R1 is an alkyl group, R2 is a hydrogen atom or an alkyl group, and n is an integer of 1 to 3).
The specific modifying group preferably contains a nitrogen atom as an amino group (primary to tertiary amino group) because this provides better effects of the present invention.
The specific modifying group is preferably a group derived from a specific modifying agent described below, because the effects of the present invention are more excellent.

[Formula (1)]
The specific conjugated diene rubber satisfies the following formula (1).
Formula (1) specifies the relationship between the weight-average intrinsic viscosity on the high molecular weight side and the weight-average molecular weight on the high molecular weight side, and polymers having a small molecular size relative to their molecular weight, such as those having branches, tend to satisfy formula (1). The reason for limiting the molecular weight side is that it has a large effect on the physical properties of the entire polymer.

IVw _10% ≦3.1×10 ^-6 ×Mw _10% -2.77 (1)

The Mw _10% and IVw _10% in formula (1) are determined as follows.
The modified conjugated diene rubber is subjected to gel permeation chromatography measurement using a differential refractive index detector (RI detector) and a viscosity detector as detectors. The weight average molecular weight obtained using the high molecular weight side portion of the peak of the chromatogram obtained by the differential refractive index detector, which is 10% of the total peak area, is defined as Mw _10% . In addition, the weight average intrinsic viscosity obtained using the high molecular weight side portion of the peak of the chromatogram obtained by the viscosity detector, which is 10% of the total peak area, is defined as IVw _10% . However, the unit of weight average intrinsic viscosity is dL/g.

Hereinafter, Mw _10% and IVw _10% in formula (1) will be explained in more detail.

As described above, the modified conjugated diene rubber is subjected to gel permeation chromatography (GPC) measurement using a differential refractive index detector and a viscosity detector as detectors. The specific method of GPC measurement is as follows.

Toluene containing 5 mmol/L triethylamine is used as the eluent. Three columns packed with polystyrene gel (product names "TSKgel G4000HXL", "TSKgel G5000HXL", and "TSKgel G6000HXL" manufactured by Tosoh Corporation) are connected together and used. The measurement sample is dissolved in toluene to a concentration of 1 mg/mL to prepare the measurement solution, and 100 μL of the measurement solution is injected into the GPC measurement device and measured under conditions of an oven temperature of 40°C and a toluene flow rate of 1 mL/min.

Among the peaks (peaks attributable to the modified conjugated diene rubber) in the chromatogram (horizontal axis: elution time, vertical axis: signal intensity) obtained by the differential refractive index detector, the weight average molecular weight is determined using the portion on the high molecular weight side (the side with the shorter elution time) that accounts for 10% of the total peak area. The weight average molecular weight obtained is designated as Mw _10% .

In addition, the weight-average intrinsic viscosity is calculated by using the portion of the high molecular weight side (the portion with the shorter elution time) that accounts for 10% of the total area of the peaks (peaks derived from the modified conjugated diene rubber) in the chromatogram (horizontal axis: elution time, vertical axis: signal intensity) obtained by the viscosity detector. The weight-average intrinsic viscosity thus obtained is designated as IVw10 _% .
The weight average intrinsic viscosity is defined as (Σ(ηi×Mi×Ni))/(Σ(Mi×Ni)), where Ni is the number of molecules and ηi is the intrinsic viscosity at molecular weight Mi.

An example of a GPC chromatogram (horizontal axis: elution time, vertical axis: signal intensity) is shown in Figure 1. Mw _10% and IVw _10% are calculated using P1, which is a portion on the high molecular weight side (shorter elution time) that has an area of 10% of the area of P0, which is the entire peak.

As a method for making the modified conjugated diene rubber satisfy formula (1), for example, a method of changing the type and amount of the specific modifier and the type and amount of the specific branching agent in the production method of the present invention described later can be mentioned.

Mw _10% is preferably from 100,000 to 10,000,000, and more preferably from 1,000,000 to 5,000,000, because the effects of the present invention are more excellent.

The IVw _10% is preferably 2 to 8, and more preferably 4 to 6, because the effects of the present invention are more excellent.

[Formula (2)]
The specific conjugated diene rubber satisfies the following formula (2).

St+Vn≦50 (2)

In formula (2), St represents the ratio (mass%) of repeating units derived from styrene to the entire specific conjugated diene rubber (hereinafter also referred to as the "styrene amount"), and Vn represents the ratio (mass%) of repeating units of 1,2-vinyl structure derived from conjugated diene (e.g., butadiene) to the entire specific conjugated diene rubber (hereinafter also referred to as the "vinyl amount").

St+Vn is preferably 10 to 45, and more preferably 25 to 45, because this provides a better effect of the present invention.

St is preferably 5 to 40, more preferably 10 to 35, and even more preferably 15 to 30, because this provides a better effect of the present invention.

Vn is preferably 5 to 30, and more preferably 10 to 20, because this provides a better effect of the present invention.

[Molecular weight]
The weight average molecular weight (Mw) of the specific conjugated diene rubber is preferably from 100,000 to 2,000,000, and more preferably from 200,000 to 1,300,000, because the effects of the present invention are more excellent.
The method for measuring the weight average molecular weight (Mw) of the specific conjugated diene rubber is the same as that for the above-mentioned Mw _10% , except that the entire peak is used.

[Glass transition temperature]
The glass transition temperature (Tg) of the specific conjugated diene rubber is not particularly limited, but is preferably from -100°C to -30°C, and more preferably from -80°C to -45°C, for reasons of better effects of the present invention.
The glass transition temperature can be adjusted, for example, by the amount of styrene or vinyl.
In this specification, the glass transition temperature (Tg) is measured using a differential scanning calorimeter (DSC) at a temperature rise rate of 10° C./min and calculated by the midpoint method.

[Preferred embodiment 1]
The specific conjugated diene rubber preferably has a star structure having three or more branches, more preferably has a star structure having three or more branches with a specific modifying group as a branch point, and further preferably is a conjugated diene rubber represented by the following formula (A), because the effects of the present invention are more excellent.

In formula (A), X represents an n-valent group (specific modifying group) containing a nitrogen atom, a silicon atom, and an oxygen atom adjacent thereto, P represents a conjugated diene polymer chain, and n represents an integer of 3 or more.

As described above, X represents an n-valent group (specific modifying group) containing a nitrogen atom, a silicon atom and an oxygen atom adjacent thereto.
X preferably contains a silicon atom and an oxygen atom adjacent thereto as an alkoxysilyl group, because this provides a better effect of the present invention.
X preferably contains a nitrogen atom as an amino group because the effect of the present invention is more excellent.

As described above, P represents a conjugated diene polymer chain. A plurality of P's may be the same or different.
The definition, specific examples and preferred embodiments of the conjugated diene polymer chain are the same as those of the skeleton of the specific conjugated diene rubber described above.

As mentioned above, n represents an integer of 3 or more. There is no particular upper limit to n, but it is preferably 30 or less because the effects of the present invention are superior.

[Preferred embodiment 2]
When the specific conjugated diene rubber has a star structure having three or more branches, at least one branched chain (conjugated diene polymer chain) of the star structure preferably has a portion derived from a specific branching agent described later, and the portion preferably has a further main chain branched structure, for reasons of better effects of the present invention.
The main chain branched structure refers to a structure in which a branched chain (conjugated diene polymer chain) forms a branch point at a portion derived from a vinyl monomer containing an alkoxysilyl group or a halosilyl group, and a polymer chain (e.g., another conjugated diene polymer chain) extends from the branch point.

[Content]
The proportion of the specific conjugated diene rubber in the rubber component is 25% by mass or more.
The above ratio is preferably 30% by mass or more, more preferably 40% by mass or more, and even more preferably 50% by mass or more, because the effects of the present invention are more excellent.
The upper limit of the above proportion is not particularly limited, and is 100% by mass.

[Method of producing specific conjugated diene rubber]
The method for producing the specific conjugated diene rubber is not particularly limited, but because the effects of the present invention are superior, a method including the following steps (1) and (2) (hereinafter also referred to as the "production method of the present invention") is preferred.
(1) a polymerization step in which a monomer containing a conjugated diene is polymerized by anionic polymerization to obtain a conjugated diene polymer; (2) a modification step in which the conjugated diene polymer obtained in the polymerization step is reacted with a compound containing a nitrogen atom and an alkoxysilyl group (hereinafter also referred to as a "specific modifier") to obtain a conjugated diene rubber having a specific modifying group.

[Polymerization step]
The polymerization step is a step of obtaining a conjugated diene-based polymer by polymerizing a monomer containing a conjugated diene by anionic polymerization.

<Anionic Polymerization>
The anionic polymerization is not particularly limited, but anionic polymerization using an organolithium compound as an initiator is preferred because the effects of the present invention are more excellent.

The organolithium compound is not particularly limited, but specific examples include mono-organolithium compounds such as n-butyllithium (n-BuLi), sec-butyllithium, tert-butyllithium, n-propyllithium, iso-propyllithium, and benzyllithium; and polyfunctional organolithium compounds such as 1,4-dilithiobutane, 1,5-dilithiopentane, 1,6-dilithiohexane, 1,10-dilithiodecane, 1,1-dilithiodiphenylene, dilithiopolybutadiene, dilithiopolyisoprene, 1,4-dilithiobenzene, 1,2-dilithio-1,2-diphenylethane, 1,4-dilithio-2-ethylcyclohexane, 1,3,5-trilithiobenzene, and 1,3,5-trilithio-2,4,6-triethylbenzene. Among these, mono-organolithium compounds such as n-butyllithium, sec-butyllithium, and tert-butyllithium are preferred because they provide better effects for the present invention, with n-butyllithium being more preferred.

The amount of the organolithium compound used is not particularly limited, but it is preferably 0.001 to 10 mol% relative to the monomer, because this provides a better effect of the present invention.

<Monomer>
Specific examples and preferred embodiments of the conjugated diene-containing monomer used in the polymerization step are the same as those of the conjugated diene and other monomers in the skeleton of the specific conjugated diene-based rubber described above.

(Specific branching agent)
The monomer preferably contains a vinyl monomer containing an alkoxysilyl group or a halosilyl group (hereinafter also referred to as a "specific branching agent") because this provides a superior effect of the present invention.
The specific branching agent is preferably an aromatic vinyl (particularly styrene) containing an alkoxysilyl group or a halosilyl group, more preferably an aromatic vinyl containing an alkoxysilyl group, and even more preferably an aromatic vinyl containing a trialkoxysilyl group, for reasons that the effects of the present invention are more excellent.

(1) Specific Examples Specific examples of aromatic vinyls containing an alkoxysilyl group include 1-(trimethoxysilyl)-4-vinylbenzene, 1,1-bis(4-trimethoxysilylphenyl)ethylene, and the like.
Examples of aromatic vinyls containing a halosilyl group include trichloro(4-vinylphenyl)silane and 1,1-bis(4-trichlorosilylphenyl)ethylene.

(2) Amount Used The amount of the specific branching agent used is preferably 0.001 to 0.1% by mass, and more preferably 0.005 to 0.05% by mass, based on the conjugated diene, because this provides a better effect of the present invention.

<Polar Compounds>
In the polymerization step, a polar compound may be added. This allows the monomers to be randomly copolymerized. In addition, polar compounds tend to be usable as vinylating agents for controlling the microstructure of conjugated dienes. In addition, polar compounds tend to be effective in promoting polymerization reactions.

Examples of the polar compound that can be used include ethers such as tetrahydrofuran, diethyl ether, dioxane, dimethoxybenzene, and 2,2-bis(2-oxolanyl)propane; tertiary amine compounds such as tetramethylethylenediamine, dipiperidinoethane, trimethylamine, triethylamine, pyridine, and quinuclidine; alkali metal alkoxide compounds such as potassium tert-amylate and sodium tert-butylate; and phosphine compounds such as triphenylphosphine.
These polar compounds may be used alone or in combination of two or more.

(Amount used)
The amount of the polar compound used is preferably 0.01 moles or more and 100 moles or less per mole of the initiator, because the effects of the present invention are more excellent.

[Modification step]
The modification step is a step of obtaining a conjugated diene rubber having a specific modifying group by reacting the conjugated diene polymer obtained in the polymerization step with a modifier (specific modifier) containing a nitrogen atom, a silicon atom and an oxygen atom adjacent thereto.

In the modification step, it is considered that the active terminal of the conjugated diene polymer obtained in the polymerization step is bonded to the silicon atom of the specific modifier. For example, when the specific modifier contains an alkoxysilyl group, it is considered that the active terminal is bonded to the silicon atom of the alkoxysilyl group, and the alkoxy group is eliminated.
In addition, when the conjugated diene polymer obtained in the polymerization step has a portion derived from a specific branching agent, in addition to the above-mentioned active terminal, the alkoxysilyl group or halosilyl group of the above-mentioned portion is also considered to react with the specific modifying agent (e.g., alkoxysilyl group). In addition, the alkoxysilyl group or halosilyl group of the above-mentioned portion is also considered to react with the active terminal of another conjugated diene polymer. As a result, the conjugated diene polymer having a portion derived from a specific branching agent has a main chain branched structure (another conjugated diene polymer chain) in the above-mentioned portion.

<Specific Modifier>
The specific modifier is a compound containing a nitrogen atom, a silicon atom and an oxygen atom adjacent thereto.
For the reason that the effect of the present invention is more excellent, the specific modifier preferably contains a silicon atom and an oxygen atom adjacent thereto as an alkoxysilyl group (particularly a trialkoxysilyl group) or a group containing a silazane structure (particularly a cyclic silazane structure) in which an alkoxy group is bonded to a silicon atom of the silazane structure. Here, the silazane structure refers to a structure in which a silicon atom and a nitrogen atom are directly bonded (a structure having a Si-N bond).
The specific modifying agent preferably contains a nitrogen atom as a group containing an amino group (primary to tertiary amino group) or a silazane structure (particularly a cyclic silazane structure) because the effects of the present invention are more excellent.
The specific modifying agent preferably has two or more (preferably three or more) sites capable of reacting with an active terminal such as an alkoxysilyl group. When the specific modifying agent has a plurality of such sites, the specific modifying agent functions as a coupling agent that connects conjugated diene polymers together.

(Specific example)
Specific examples of the specific modifying agent include tertiary amines having an alkoxysilyl group, such as tris(3-trimethoxysilylpropyl)amine and tetrakis(3-trimethoxysilylpropyl)-1,3-propanediamine; cyclic silazanes having an alkoxysilyl group, such as 2,2-dimethoxy-1-(3-trimethoxysilylpropyl)-1-aza-2-silacyclopentane; tertiary amines having a group containing an alkoxysilyl group-containing cyclic silazane structure, such as tris[3-(2,2-dimethoxy-1-aza-2-silacyclopentane)propyl]amine and tetrakis[3-(2,2-dimethoxy-1-aza-2-silacyclopentane)propyl]-1,3-propanediamine; bis(3-trimethoxysilylpropyl)-[3-(2,2-dimethoxy-1-aza-2-silacyclopentane)propyl]amine; bis[3 tertiary amines having an alkoxysilyl group and a group containing a cyclic silazane structure, such as -(2,2-dimethoxy-1-aza-2-silacyclopentane)propyl]-(3-trimethoxysilylpropyl)amine, tris(3-trimethoxysilylpropyl)-[3-(2,2-dimethoxy-1-aza-2-silacyclopentane)propyl]-1,3-propanediamine, bis(3-trimethoxysilylpropyl)-[3-(2,2-dimethoxy-1-aza-2-silacyclopentane)propyl]-[3-(1-methoxy-2-trimethylsilyl-1-sila-2-azacyclopentane)propyl]-1,3-propanediamine, and bis(2-trimethoxysilylpropyl)-[3-(2,2-dimethoxy-1-aza-2-silacyclopentane)propyl]-methyl-1,3-propanediamine.

(Amount used)
The amount of the specific modifier used is preferably 0.01 to 1% by mass, and more preferably 0.02 to 0.2% by mass, based on the conjugated diene, because this provides a better effect of the present invention.

[Other steps]
The manufacturing method of the present invention may include steps (other steps) other than the steps described above.
Other steps include a polymerization terminating step in which a polymerization terminator (e.g., methanol) is added, and a solvent removal step in which the solvent is removed by steam stripping.

[Other rubber components]
The rubber component may contain a rubber component (rubber component) other than the specific conjugated diene rubber. Examples of such other rubber components include natural rubber (NR), butadiene rubber (BR), aromatic vinyl-conjugated diene copolymer rubber, isoprene rubber (IR), acrylonitrile-butadiene copolymer rubber (NBR), butyl rubber (IIR), halogenated butyl rubber (Br-IIR, Cl-IIR), chloroprene rubber (CR), etc. Examples of the aromatic vinyl-conjugated diene copolymer rubber include styrene butadiene rubber (SBR), styrene isoprene copolymer rubber, etc.

[Average Tg]
The glass transition temperature (hereinafter also referred to as "average Tg") of the entire rubber component is higher than -80°C and equal to or lower than -45°C.
The average Tg of the rubber component is preferably −75° C. or more and −45° C. or less, and more preferably −70° C. or more and −50° C. or less, because the effects of the present invention are more excellent.
The average Tg of the rubber components is the sum of the glass transition temperatures (Tg) of the individual rubber components multiplied by the mass fraction of each rubber component (weighted average value of the glass transition temperatures).

[Molecular weight]
The preferred embodiment of the weight average molecular weight (Mw) of the rubber component is the same as that of the specific conjugated diene rubber described above.

[2] Silica The composition of the present invention contains silica.
The silica is not particularly limited, and any conventionally known silica can be used.
Examples of silica include wet silica, dry silica, fumed silica, diatomaceous earth, etc. Silica derived from biomass such as rice husk may also be used. The above silica may be used alone or in combination of two or more kinds.

[CTAB]
The cetyltrimethylammonium bromide (CTAB) adsorption specific surface area of silica (hereinafter, "CTAB adsorption specific surface area" may be simply referred to as "CTAB") is not particularly limited, but is preferably 100 to 300 ^{m 2} /g, and more preferably 150 to 200 m ² /g, for reasons of superior effects of the present invention.
Here, the CTAB adsorption specific surface area is a value measured in accordance with JIS K6430:2008 Annex G.

[Content]
In the composition of the present invention, the content of silica is 80 parts by mass or more and 160 parts by mass or less per 100 parts by mass of the above-mentioned rubber component. The content of silica is preferably 100 parts by mass or more and 140 parts by mass or less per 100 parts by mass of the above-mentioned rubber component because the effect of the present invention is more excellent.

[3] Softener The composition of the present invention contains a softener comprising at least one type selected from the group consisting of thermoplastic resins and oils.

[Thermoplastic resin]
The softener contains a thermoplastic resin.
The softener preferably contains two or more thermoplastic resins because the effects of the present invention are more excellent.

[Specific examples]
Examples of the thermoplastic resin include coumarone resins (e.g., coumarone resin, coumarone-indene resin, coumarone-indene-styrene resin), phenol resins (e.g., phenol resin, phenol-acetylene resin, phenol-formaldehyde resin), xylene resins (e.g., xylene resin, xylene-acetylene resin, xylene-formaldehyde resin), rosin resins (e.g., rosin, rosin ester, hydrogenated rosin derivative), terpene resins (e.g., terpene resin, modified rosin ... Examples of the resins include aromatic terpene resins (such as aromatic modified terpene resins), terpene phenol resins, hydrogenated terpene resins, α-pinene resins, β-pinene resins, limonene resins, hydrogenated limonene resins, dipentene resins, and terpene styrene resins), styrene-based resins, petroleum-based resins (for example, C5/C9-based resins, C9-based resins, DCPD (dicyclopentadiene)-based resins, DCPD/C9-based resins, hydrogenated C5/C9-based resins, hydrogenated C9-based resins, hydrogenated DCPD-based resins, and hydrogenated DCPD/C9-based resins), and aliphatic saturated hydrocarbon-based resins.

The thermoplastic resin preferably contains at least one selected from the group consisting of terpene resins, C5/C9 resins, C9 resins, DCPD resins, DCPD/C9 resins, hydrogenated C5/C9 resins, hydrogenated C9 resins, hydrogenated DCPD resins, and hydrogenated DCPD/C9 resins, because this provides a better effect for the present invention.

[Content]
In the composition of the present invention, the content of the thermoplastic resin is 30 parts by mass or more and less than 80 parts by mass per 100 parts by mass of the above-mentioned rubber component.
In the composition of the present invention, the content of the thermoplastic resin is preferably 50 parts by mass or more and less than 80 parts by mass per 100 parts by mass of the rubber component described above, because the effects of the present invention are more excellent.

In the composition of the present invention, the content of the thermoplastic resin is preferably 40 to 120% by mass relative to the specific conjugated diene rubber described above, because this provides a better effect of the present invention.

[oil]
The softener may include an oil.

[Content]
In the composition of the present invention, the content of the oil is preferably 0 to 40 parts by mass, and more preferably 5 to 35 parts by mass, per 100 parts by mass of the rubber component, because the effects of the present invention are more excellent.

[Resin ratio]
In the composition of the present invention, the ratio of the thermoplastic resin to the total of the thermoplastic resin and the oil (hereinafter also referred to as the "resin ratio") is 50 mass % or more.
The resin ratio is preferably 80% by mass or more because the effects of the present invention are more excellent.
The upper limit of the resin ratio is not particularly limited, and is 100% by mass.

[4] Optional Components The composition of the present invention may contain components (optional components) other than the above-mentioned components, as necessary.
Examples of such components include various additives commonly used in rubber compositions, such as fillers other than silica (preferably carbon black), silane coupling agents, thermally expandable microcapsules, zinc oxide (zinc white), stearic acid, antioxidants, waxes, processing aids, liquid polymers, thermosetting resins, vulcanizing agents (e.g., sulfur), vulcanization accelerators (accelerators), and vulcanization activators.

[Silane coupling agent]
The composition of the present invention preferably contains a silane coupling agent because the effects of the present invention are more excellent.

The silane coupling agent is not particularly limited as long as it is a silane compound having a hydrolyzable group and an organic functional group.
The hydrolyzable group is not particularly limited, and examples thereof include an alkoxy group, a phenoxy group, a carboxyl group, and an alkenyloxy group. Of these, an alkoxy group is preferable because the effects of the present invention are more excellent. When the hydrolyzable group is an alkoxy group, the number of carbon atoms in the alkoxy group is preferably 1 to 16, and more preferably 1 to 4, because the effects of the present invention are more excellent. Examples of the alkoxy group having 1 to 4 carbon atoms include a methoxy group, an ethoxy group, and a propoxy group.

The organic functional group is not particularly limited, but is preferably a group capable of forming a chemical bond with an organic compound. Examples of the organic functional group include an epoxy group, a vinyl group, an acryloyl group, a methacryloyl group, an amino group, a sulfide group, a mercapto group, and a blocked mercapto group (protected mercapto group) (e.g., an octanoylthio group). Of these, a sulfide group (particularly a disulfide group or a tetrasulfide group), a mercapto group, and a blocked mercapto group are preferred because they provide better effects of the present invention.
The silane coupling agents may be used alone or in combination of two or more kinds.

The above silane coupling agent is preferably a sulfur-containing silane coupling agent, since this provides a better effect of the present invention.

Specific examples of the silane coupling agent include bis(3-triethoxysilylpropyl)tetrasulfide, bis(3-trimethoxysilylpropyl)tetrasulfide, bis(3-triethoxysilylpropyl)disulfide, mercaptopropyltrimethoxysilane, mercaptopropyltriethoxysilane, 3-trimethoxysilylpropyl-N,N-dimethylthiocarbamoyl-tetrasulfide, trimethoxysilylpropyl-mercaptobenzothiazole tetrasulfide, triethoxysilylpropyl-methacrylate-monosulfide, dimethoxymethylsilylpropyl-N,N-dimethylthiocarbamoyl-tetrasulfide, 3-octanoylthio-1-propyltriethoxysilane, and the like. One of these may be used alone, or two or more may be used in combination.

[Content]
In the composition of the present invention, the content of the silane coupling agent is not particularly limited. However, in order to obtain better effects of the present invention, the content is preferably 2 to 20 parts by mass per 100 parts by mass of the rubber component described above.

In addition, in the composition of the present invention, the content of the silane coupling agent is preferably 1 to 20 mass % relative to the above-mentioned silica content, and more preferably 5 to 15 mass %, because this provides a better effect of the present invention.

[Carbon black]
The composition of the present invention preferably contains carbon black because the effects of the present invention are more excellent. The carbon black may be used alone or in combination of two or more kinds.
The carbon black is not particularly limited, and various grades such as SAF-HS, SAF, ISAF-HS, ISAF, ISAF-LS, IISAF-HS, HAF-HS, HAF, HAF-LS, FEF, GPF, and SRF can be used.

[ _N2SA ]
The nitrogen adsorption specific surface area (N ₂ SA) of the carbon black is not particularly limited, but in order to obtain a superior effect of the present invention, it is preferably 50 to 200 m ² /g, and more preferably 70 to 150 m ² /g.
The nitrogen adsorption specific surface area (N ₂ SA) is the amount of nitrogen adsorbed on the surface of carbon black measured according to JIS K6217-2:2001 "Part 2: Determination of specific surface area - Nitrogen adsorption method - Single point method".

[Content]
In the composition of the present invention, the content of carbon black is not particularly limited. However, in order to obtain better effects of the present invention, the content of carbon black is preferably 1 to 100 parts by mass, and more preferably 2 to 30 parts by mass, per 100 parts by mass of the rubber component described above.

[Vulcanization accelerator]
The composition of the present invention preferably contains a vulcanization accelerator because the effect of the present invention is more excellent.
Examples of the vulcanization accelerator include sulfenamide-based, thiuram-based, and guanidine-based accelerators.

[Content]
In the composition of the present invention, the content of the vulcanization accelerator is preferably 1 to 10 parts by mass, more preferably 2 to 8 parts by mass, and further preferably 3 to 6 parts by mass, per 100 parts by mass of the rubber component, because the effects of the present invention are more excellent.

[Preferred embodiment]
The vulcanization accelerator preferably contains a thiuram-based vulcanization accelerator because the effects of the present invention are more excellent.

In the composition of the present invention, the content of the thiuram vulcanization accelerator is preferably 0.2 parts by mass or more and 3.0 parts by mass or less per 100 parts by mass of the rubber component, because the effects of the present invention are more excellent.
In the composition of the present invention, the content of the thiuram vulcanization accelerator is preferably 0.1 to 10 mass %, more preferably 0.2 to 5 mass %, and even more preferably 0.5 to 2 mass %, relative to the above-mentioned specific conjugated diene rubber, because the effects of the present invention are more excellent.

[5] Method for preparing rubber composition for tires The method for producing the composition of the present invention is not particularly limited, and specific examples thereof include a method of kneading the above-mentioned components using a known method or device (e.g., a Banbury mixer, a kneader, a roll, etc.) When the composition of the present invention contains sulfur or a vulcanization accelerator, it is preferable to first mix the components other than the sulfur and the vulcanization accelerator at a high temperature (preferably 100 to 160°C), cool the mixture, and then mix the sulfur or the vulcanization accelerator.
The composition of the present invention can be vulcanized or crosslinked under conventionally known vulcanization or crosslinking conditions.

[II] Tire The tire of the present invention is a tire manufactured using the above-mentioned composition of the present invention. The tire of the present invention is preferably a pneumatic tire, and can be filled with air, an inert gas such as nitrogen, or other gases.

FIG. 2 shows a schematic partial cross-sectional view of a tire that represents one example of an embodiment of a tire of the present invention. However, the tire of the present invention is not limited to the embodiment shown in FIG. 2.

In FIG. 2, reference numeral 1 denotes a bead portion, reference numeral 2 denotes a sidewall portion, and reference numeral 3 denotes a tire tread portion.
Between the pair of left and right bead portions 1, a carcass layer 4 having fiber cords embedded therein is installed, and the ends of this carcass layer 4 are folded back and wrapped around the bead cores 5 and bead fillers 6 from the inside to the outside of the tire.
In the tire tread portion 3, a belt layer 7 is disposed on the outer side of the carcass layer 4 around one circumference of the tire.
In addition, a rim cushion 8 is disposed in the bead portion 1 at a portion that comes into contact with the rim.
At least one of the components 2, 3, 5, 6 and 8 (preferably the component 3) is made of the composition of the present invention.

The tire of the present invention can be manufactured, for example, according to a conventionally known method. In addition, the gas to be filled into the tire can be normal air or air with an adjusted oxygen partial pressure, or an inert gas such as nitrogen, argon, or helium.

The present invention will be explained in more detail below with reference to examples, but the present invention is not limited to these.

[Synthesis of conjugated diene rubber]
Each conjugated diene rubber was synthesized as follows.

[Conjugated diene rubber 1]

<Polymerization step>
In a stirrer-equipped autoclave, cyclohexane 1000 g/h (hour), tetramethylethylenediamine 0.023 g/h, 1,3-butadiene 176.4 g/h, 1-butene 0.406 g/h, and styrene 23.6 g/h were charged under a nitrogen atmosphere, and n-butyllithium was continuously added at 1.43 mmol/h to initiate polymerization at 70° C. When the polymerization was sufficiently stabilized, 1-(trimethoxysilyl)-4-vinylbenzene (branching agent) was added at 0.02 g/h and reacted with stirring. The branching agent corresponds to the specific branching agent described above.

<Modification step>
To the solution flowing out from the reactor outlet, bis(3-trimethoxysilylpropyl)-[3-(2,2-dimethoxy-1-aza-2-silacyclopentane)propyl]amine (modifier) was added at 0.08 g/h, and the mixture was stirred to react.

Then, methanol was added as a polymerization terminator to obtain a solution containing conjugated diene rubber.

To the resulting solution, 1.14 parts by mass of Irganox 1520L (manufactured by BASF) was added as an anti-aging agent per 100 parts by mass of conjugated diene rubber, after which the solvent was removed by steam stripping and the mixture was vacuum dried at 60°C for 24 hours to obtain a solid conjugated diene rubber. The resulting conjugated diene rubber is also referred to as conjugated diene rubber 1.

The conjugated diene rubber 1 is a reaction product of a conjugated diene polymer, which is a copolymer of butadiene, styrene, and a branching agent, with a modifier, and is a modified conjugated diene rubber having a modifying group (specific modifying group) derived from the modifier, which includes a nitrogen atom, a silicon atom, and an oxygen atom adjacent thereto.
The conjugated diene rubber 1 has a star structure with three or more branches, with the modifying group as a branching point, and the branched chain bonded to the modifying group has a portion derived from a branching agent, and the portion derived from the branching agent has a further main chain branched structure (conjugated diene polymer chain).

[Conjugated diene rubber 2]
A solid conjugated diene rubber was obtained in the same manner as for the conjugated diene rubber 1, except that the amount of each component was changed as shown in Table 1. The obtained conjugated diene rubber is also referred to as conjugated diene rubber 2.

The conjugated diene rubber 2 is a reaction product of a conjugated diene polymer, which is a copolymer of butadiene, styrene, and a branching agent, with a modifier, and is a modified conjugated diene rubber having a modifying group (specific modifying group) containing a nitrogen atom, a silicon atom, and an oxygen atom adjacent thereto, which is derived from the modifier.
The conjugated diene rubber 2 has a star structure with three or more branches, with the modifying group as a branching point, and the branched chain bonded to the modifying group has a portion derived from a branching agent, and the portion derived from the branching agent has a further main chain branched structure (conjugated diene polymer chain).

[Conjugated diene rubber 3]
A solid conjugated diene rubber was obtained in the same manner as for the conjugated diene rubber 1, except that the amount of each component was changed as shown in Table 1. The obtained conjugated diene rubber is also referred to as conjugated diene rubber 3.

The conjugated diene rubber 3 is a reaction product of a conjugated diene polymer, which is a copolymer of butadiene, styrene and a branching agent, with a modifier, and is a modified conjugated diene rubber having a modifying group (specific modifying group) containing a nitrogen atom, a silicon atom and an oxygen atom adjacent thereto, which is derived from the modifier.
The conjugated diene rubber 3 has a star structure with three or more branches, with the modifying group as a branching point, and the branched chain bonded to the modifying group has a portion derived from a branching agent, and the portion derived from the branching agent has a further main chain branched structure (conjugated diene polymer chain).

[Comparative conjugated diene rubber]
Into a nitrogen-substituted autoclave reactor having an internal volume of 5 liters, 2,000 g of cyclohexane, 31.6 g of tetrahydrofuran, 122 g of styrene, and 320 g of 1,3-butadiene were charged. After adjusting the temperature of the contents of the reactor to 10°C, 4.75 mmol of n-butyllithium was added as a polymerization initiator to start polymerization. The polymerization was carried out under adiabatic conditions, and the maximum temperature reached 85°C. When the polymerization conversion rate reached 99% (20 minutes after the start of polymerization), 10 g of 1,3-butadiene was added over 2 minutes, and then 2.12 mmol of a compound (modifier) represented by the following formula (4) was added and the reaction was carried out for 15 minutes. The modifier corresponds to the specific modifier described above.
To the resulting solution, 3.96 g of 2,6-di-tert-butyl-p-cresol was added. Next, the solvent was removed by steam stripping, and the mixture was dried with a heated roll adjusted to 110° C. to obtain a solid conjugated diene rubber. The obtained conjugated diene rubber is also referred to as a comparative conjugated diene rubber.

Equation (4)

In formula (4), R ¹ is a hydrocarbyl group having 1 to 20 carbon atoms, R ² is a hydrocarbyloxy group having 1 to 20 carbon atoms, R ³ is an alkanediyl group having 1 to 20 carbon atoms, and A ² is a group "*-C(R ⁵ )=N-" or a group "*-N=C(R ⁵ )-" (wherein R ⁵ is a hydrogen atom or a hydrocarbyl group, and "*" indicates a bond bonded to R ⁴ ). ^{R 4} is an m-valent hydrocarbyl group having 1 to 20 carbon atoms, or an m-valent group having 1 to 20 carbon atoms that has at least one atom selected from the group consisting of nitrogen atoms, oxygen atoms, and sulfur atoms and does not have active hydrogen. n is an integer of 1 to 3, and m is an integer of 2 to 10. In the formula, multiple R ¹ , R ² , R ³ , A ² , and n may be the same or different.

The comparative conjugated diene rubber is a reaction product between a conjugated diene polymer, which is a copolymer of butadiene and styrene, and a modifier, and is a modified conjugated diene rubber having a modifying group (specific modifying group) that contains a nitrogen atom, a silicon atom, and an oxygen atom adjacent to the nitrogen atom, which is derived from the modifier.

[Weight average molecular weight, weight average intrinsic viscosity, styrene content, vinyl content, glass transition temperature]
For the conjugated diene rubbers synthesized as described above (conjugated diene rubbers 1 to 3, comparative conjugated diene rubbers), Mw, Mw10 _% , IVw, IVw10 _% , St, Vn, and glass transition temperature (Tg) are shown in Table 2. The same is true for E581 and NS612, which will be described later.
In Table 2, the "right side" of formula (1) represents the value of the right side of formula (1), which is "3.1×10 ^-6 ×Mw _10% -2.77".
In addition, in Table 2, "Suitable" of formula (1) indicates whether formula (1) is satisfied or not, and specifically, "A" indicates that formula (1) is satisfied, and "B" indicates that formula (1) is not satisfied.
In addition, in Table 2, "St+Vn" in formula (2) represents the above-mentioned St+Vn.

As shown in Table 2, all of the conjugated diene rubbers 1 to 3 satisfy the formula (1) and the formula (2). As described above, all of the conjugated diene rubbers 1 to 3 are modified conjugated diene rubbers having a specific modifying group. Therefore, all of the conjugated diene rubbers 1 to 3 correspond to the above-mentioned specific conjugated diene rubber.
As shown in Table 2, the comparative conjugated diene rubber satisfies formula (1). As described above, the comparative conjugated diene rubber is a modified conjugated diene rubber having a specific modifying group. However, as shown in Table 2, the comparative conjugated diene rubber does not satisfy formula (2), and therefore does not fall under the above-mentioned specific conjugated diene rubber.
Furthermore, as shown in Table 2, neither E581 nor NS612 satisfies formula (1), and therefore does not fall under the category of the above-mentioned specific conjugated diene rubber.

[Preparation of rubber composition for tires]
The components in Tables 3 and 4 below were mixed in the compositions (parts by mass) shown in the tables.
Specifically, first, the components other than sulfur and the vulcanization accelerator in Tables 3 and 4 were mixed in a 1.8 L internal mixer at 160°C or less for 5 minutes, and a master batch was discharged. Thereafter, sulfur and the vulcanization accelerator were added to the master batch, and the mixture was mixed at 100°C or less using an open roll to produce each rubber composition for tires.

[evaluation]
The following evaluations were carried out for each of the obtained rubber compositions for tires.

[Heat resistance]
Using each of the obtained rubber compositions for tires, each test tire was produced with a tire size of 245/40R19. The tires were mounted on a front-wheel drive vehicle with an engine displacement of 2300cc via the applicable rim, and the front-wheel drive vehicle was driven for two laps on a test course with a lap length of 10km. The test driver evaluated the controllability during steering by a sensory evaluation, and the standard example was indexed with 100. The results are shown in Tables 3 and 4. In this evaluation, the higher the index, the higher the dry steering stability performance and its heat sagging resistance. For practical purposes, the index is preferably 105 or more.

[Circuit abrasion resistance]
Using each of the obtained rubber compositions for tires, each test tire was produced with a tire size of 245/40R19. The tires were mounted on a front-wheel drive vehicle with an engine displacement of 2300cc via the applicable rim, and a test driver drove the front-wheel drive vehicle for five laps on a circuit with a lap length of 3.6km. The tire profile was measured before and after the run, and the amount of wear was calculated from the difference, and the reciprocal was expressed as an index with the standard example being 100. The results are shown in Tables 3 and 4. In this evaluation, the higher the index, the higher the circuit wear resistance. In practice, the index is preferably 105 or more.

[Wet performance]
Using each of the obtained rubber compositions for tires, test tires were prepared with a tire size of 245/40R19 and subjected to a braking test. The braking test was performed by mounting four test tires on a passenger car with an engine displacement of 2300cc. The wet braking test was performed by measuring the braking distance from an initial speed of 100km/h on an asphalt road surface on which water was sprayed. The reciprocal of the distance was indexed with the standard example being 100, and is shown in Tables 3 and 4. The larger the value, the better the performance. In practice, the index is preferably 103 or more.

[Rolling performance]
Each of the obtained rubber compositions for tires was press-vulcanized in a mold (15 cm x 15 cm x 0.2 cm) at 160°C for 40 minutes to produce each vulcanized rubber sheet. Then, for the obtained vulcanized rubber sheets, tan δ (60°C) was measured under conditions of an elongation deformation rate of 10% ± 2%, a frequency of 20 Hz, and a temperature of 60°C in accordance with JIS K6394:2007 using a viscoelasticity spectrometer (manufactured by Toyo Seiki Seisakusho, Ltd.), and the reciprocal of tan δ (60°C) was calculated.
The results are shown in Tables 3 and 4. The results are expressed as an index, with the reciprocal of tan δ (60° C.) of the standard example taken as 100. A higher index indicates better rolling performance (low rolling resistance). For practical purposes, an index of 102 or more is preferable.

Details of each component in Tables 3 and 4 are as follows.
Conjugated diene rubbers 1 to 3: Conjugated diene rubbers 1 to 3 synthesized as described above
Comparative conjugated diene rubber: Comparative conjugated diene rubber synthesized as described above. E581: Asahi Kasei Corporation's E581 (terminally modified solution-polymerized SBR having a hydroxyl group at the end, Tg: -27°C) (does not satisfy formula (1) and therefore does not fall under the above-mentioned specific conjugated diene rubber).
NS612: NS612 manufactured by Zeon Corporation (solution polymerization SBR, Tg: -60°C) (does not satisfy formula (1) and therefore does not fall under the above-mentioned specific conjugated diene rubber)
BR: Nipol BR1220 (butadiene rubber, Tg: -106°C) manufactured by Nippon Zeon Co., Ltd. (does not fall under the above-mentioned specific conjugated diene rubber because it does not have a specific modifying group)
Carbon black: Seast 3 manufactured by Tokai Carbon Co., Ltd. (HAF carbon black, nitrogen adsorption specific surface area (N ₂ SA): 79 m ² /g)
Silica: ZEOSIL 1165MP manufactured by Solvay (CTAB adsorption specific surface area: 160 m ² /g)
Terpene resin: YS Resin TO125 manufactured by Yasuhara Chemical Co., Ltd. (aromatic modified terpene resin, softening point: 125°C)
C5/C9 resin: HC-3100 manufactured by Guangzhou Ecopower New Material Co., Ltd.
Oil: Showa Shell Sekiyu Extract No. 4 S
Silane coupling agent (Si69): Si69 manufactured by Evonik
・Zinc oxide: Three types of zinc oxide (manufactured by Seido Chemical Industry Co., Ltd.)
Stearic acid: Beads Stearic Acid YR (manufactured by NOF Corporation)
Anti-aging agent: Nocrac 6C (manufactured by Ouchi Shinko Chemical Industry Co., Ltd.)
Wax: Sunnock (Ouchi Shinko Chemical Industry Co., Ltd.)
Vulcanization accelerator (CZ): Sancerer CM-G (sulfenamide type) manufactured by Sanshin Chemical Industry Co., Ltd.
Vulcanization accelerator (TBzTD): Sancerer TBZTD (thiuram type) manufactured by Sanshin Chemical Industry Co., Ltd.
・Vulcanization accelerator (DPG): Sumitomo Chemical Co., Ltd. Soxinol D-G (guanidine type)
Sulfur: Shikoku Chemical Industry Co., Ltd. Myucron OT-20

In Tables 3 and 4, "average Tg" represents the glass transition temperature of the entire rubber component.
In addition, in Tables 3 and 4, "resin ratio" represents the resin ratio described above.

As can be seen from Tables 3 and 4, all of Examples 1 to 12, which contain a rubber component with an average Tg in a specific range containing a specific amount of a specific conjugated diene rubber, a specific amount of silica, and a specific amount of a thermoplastic resin, and have a resin ratio in a specific range, exhibited excellent heat sagging resistance, circuit abrasion resistance, wet performance, and rolling performance.
Comparing Examples 1 to 4 (comparison between embodiments differing only in the type of rubber component), Examples 1 to 2 and Example 4, in which the St+Vn of the specific conjugated diene rubber was 30 or more, showed better wet performance. Among them, Examples 1 and 4, in which the IVw _10% of the specific conjugated diene rubber was 4.5 or more, showed better circuit wear resistance.
In addition, comparing Examples 4 to 6 (comparison between embodiments differing only in the content of carbon black and silica), Examples 4 and 6, in which the content of silica per 100 parts by mass of the rubber component is 100 parts by mass or more, showed better wet performance and rolling performance.
In addition, comparing Examples 4 to 6 (comparison between embodiments differing only in the carbon black and silica contents), Examples 4 to 5, in which the silica content per 100 parts by mass of the rubber component is 140 parts by mass or less, exhibited superior heat sagging resistance and circuit abrasion resistance.
In addition, comparing Example 4 with Example 7 (comparison between embodiments in which only the type of thermoplastic resin is different), Example 4, in which the thermoplastic resin contains a terpene resin, exhibited superior circuit wear resistance, wet performance, and rolling performance.
In addition, in comparison between Example 4 and Example 8 (comparison between embodiments in which only the vulcanization accelerator is different), Example 8, which contains 0.2 parts by mass or more and 3.0 parts by mass or less of a thiuram vulcanization accelerator per 100 parts by mass of the rubber component, exhibited better heat sagging resistance, circuit wear resistance, and rolling performance. Similarly, in comparison between Example 11 and Example 12 (comparison between embodiments in which only the vulcanization accelerator is different), Example 12, which contains 0.2 parts by mass or more and 3.0 parts by mass or less of a thiuram vulcanization accelerator per 100 parts by mass of the rubber component, exhibited better heat sagging resistance, circuit wear resistance, and rolling performance.
In addition, comparing Example 4, Example 9, and Example 10 (comparison between embodiments with different resin ratios), Examples 9 to 10, in which the resin ratio was 60% by mass or more, showed better wet performance. Among them, Example 9, in which the resin ratio was 90% by mass or less, showed better heat sagging resistance, circuit wear resistance, and rolling performance.
In addition, comparing Example 9 with Example 11 (comparison between embodiments in which only the type of thermoplastic resin is different), Example 11, in which the thermoplastic resin contains a terpene resin and a C5/C9 resin, exhibited superior circuit wear resistance, wet performance, and rolling performance.

On the other hand, the standard example that does not contain the specific conjugated diene rubber, Comparative Example 1 that contains the specific conjugated diene rubber but the content of the specific conjugated diene rubber in the rubber component is less than 25% by mass, Comparative Example 2 that contains a comparative conjugated diene rubber that is a modified diene rubber other than the specific conjugated diene rubber instead of the specific conjugated diene rubber, Comparative Example 3 in which the average Tg of the rubber component exceeds -45°C, Comparative Example 4 in which the average Tg of the rubber component is -80°C or lower, Comparative Example 5 in which the content of the thermoplastic resin per 100 parts by mass of the rubber component is less than 30 parts by mass, Comparative Example 6 in which the content of the thermoplastic resin per 100 parts by mass of the rubber component is 80 parts by mass or more, Comparative Example 7 in which the content of silica per 100 parts by mass of the rubber component is less than 80 parts by mass, and Comparative Example 8 in which the content of silica per 100 parts by mass of the rubber component exceeds 160 parts by mass were insufficient in at least one of the heat sagging resistance, circuit abrasion resistance, wet performance, and rolling performance.

Reference Signs List 1 Bead portion 2 Sidewall portion 3 Tire tread portion 4 Carcass layer 5 Bead core 6 Bead filler 7 Belt layer 8 Rim cushion

Claims (7)

The rubber composition contains a rubber component (A) containing a modified conjugated diene rubber (A1), silica (B), and a softener (C) made of at least one selected from the group consisting of a thermoplastic resin and an oil,
The modified conjugated diene rubber (A1) satisfies the following formula (1) and the following formula (2) and has a modifying group containing a nitrogen atom, a silicon atom, and an oxygen atom adjacent thereto,
The proportion of the modified conjugated diene rubber (A1) in the rubber component (A) is 25% by mass or more,
The glass transition temperature of the entire rubber component (A) is higher than −80° C. and not higher than −45° C.,
The content of the silica (B) relative to 100 parts by mass of the rubber component (A) is 80 parts by mass or more and 160 parts by mass or less,
The content of the thermoplastic resin relative to 100 parts by mass of the rubber component (A) is 30 parts by mass or more and less than 80 parts by mass,
A rubber composition for tires, wherein a ratio of the thermoplastic resin to a total of the thermoplastic resin and the oil is 50 mass % or more.
IVw _10% ≦3.1×10 ^-6 ×Mw _10% -2.77 (1)
St+Vn≦50 (2)
Mw _10% and IVw _10% in formula (1) are as follows.
The modified conjugated diene rubber is subjected to gel permeation chromatography measurement using a differential refractive index detector and a viscosity detector as detectors. The weight average molecular weight obtained using the high molecular weight side portion of the peak of the chromatogram obtained by the differential refractive index detector, which is 10% of the total peak area, is defined as Mw _10% . The weight average intrinsic viscosity obtained using the high molecular weight side portion of the peak of the chromatogram obtained by the viscosity detector, which is 10% of the total peak area, is defined as IVw _10% . The unit of weight average intrinsic viscosity is dL/g.
In formula (2), St represents the proportion (mass%) of repeating units derived from styrene to the entire modified conjugated diene rubber, and Vn represents the proportion (mass%) of repeating units of 1,2-vinyl structure derived from conjugated diene to the entire modified conjugated diene rubber. The modified conjugated diene rubber (A1) is
a star-shaped structure having three or more branches, at least one branch of which has a moiety derived from a vinyl monomer containing an alkoxysilyl group or a halosilyl group;
The rubber composition for a tire according to claim 1 , wherein the portion further has a main chain branched structure. The rubber composition for tires according to claim 1, wherein the thermoplastic resin comprises at least one selected from the group consisting of terpene resins, C5/C9 resins, C9 resins, DCPD resins, DCPD/C9 resins, hydrogenated C5/C9 resins, hydrogenated C9 resins, hydrogenated DCPD resins, and hydrogenated DCPD/C9 resins. The rubber composition for tires according to claim 1 further contains 0.2 parts by mass or more and 3.0 parts by mass or less of a thiuram vulcanization accelerator per 100 parts by mass of the rubber component (A). The content of the thermoplastic resin relative to 100 parts by mass of the rubber component (A) is 50 parts by mass or more and less than 80 parts by mass,
The rubber composition for tires according to claim 1 , wherein a ratio of the thermoplastic resin to a total of the thermoplastic resin and the oil is 80% by mass or more. The rubber composition for tires according to claim 1, wherein the softener (C) contains two or more types of thermoplastic resins. A tire manufactured using the rubber composition for tires according to any one of claims 1 to 6.

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