JP7626307B2 - Rubber composition for tires and pneumatic tire - Google Patents

Description

The present invention relates to a rubber composition for tires and a pneumatic tire using the same.

In recent years, the performance requirements for tires have been increasing, and improvements in tread wear resistance and wet skid performance are being called for. As a method for satisfying these performance requirements, Patent Document 1 discloses a rubber composition for tires that can improve wet skid performance by compounding silica, but the steering stability has not been studied in detail, and there is still room for improvement.

In addition, attempts are being made to improve wet skid performance by utilizing the property that when aluminum hydroxide is blended into a rubber composition, the rubber composition becomes soft at low temperatures and with low strain. However, there is a problem in that the tire temperature rises when driven for a long time, and handling stability deteriorates.

JP 2008-31244 A

The present invention aims to solve the above problems and provide a rubber composition for tires that can achieve both wet skid performance (initial stage) and handling stability (particularly handling stability during long-term driving), and a pneumatic tire using the same.

The inventors discovered that by combining silica having a CTAB specific surface area and BET specific surface area equal to or greater than a specific value with aluminum hydroxide, it is possible to achieve both wet skid performance (initial stage) and handling stability (particularly handling stability during long driving periods), and thus completed the present invention.

The present invention relates to a rubber composition for tires, which comprises aluminum hydroxide and silica, the silica having a CTAB specific surface area of 180 m ² /g or more and a BET specific surface area of 185 m ² /g or more.

The silica preferably has an aggregate size of 30 nm or more.

It is preferable that the average particle size of the aluminum hydroxide is 10 μm or less.

The rubber composition is preferably used in a tread.
The present invention also relates to a pneumatic tire using the above rubber composition.
The pneumatic tire is preferably a racing tire.

According to the present invention, since the rubber composition for tires contains aluminum hydroxide and silica having a CTAB specific surface area and BET specific surface area of a specific value or more, a pneumatic tire can be provided that can achieve both wet skid performance (initial stage) and steering stability (particularly, steering stability during long-term driving). This is presumably because, even when aluminum hydroxide is blended, the complex modulus (E ^* ) and loss tangent (tan δ) at 40°C are improved by blending silica having a CTAB specific surface area and BET specific surface area of a specific value or more, and the stability of the rubber composition is improved.

FIG. 2 is a diagram showing a pore distribution curve.

The rubber composition for tires of the present invention contains aluminum hydroxide and silica having a CTAB specific surface area and a BET specific surface area equal to or greater than a specific value.

Examples of the rubber component include diene rubbers such as natural rubber (NR), isoprene rubber (IR), butadiene rubber (BR), styrene butadiene rubber (SBR), epoxidized natural rubber (ENR), acrylonitrile butadiene rubber (NBR), chloroprene rubber (CR), butyl rubber (IIR), and styrene-isoprene-butadiene copolymer rubber (SIBR). These diene rubbers may be used alone or in combination of two or more. Among these, SBR is preferred because of its excellent rigidity (high glass transition temperature).

Examples of SBR include emulsion-polymerized styrene-butadiene rubber (E-SBR) and solution-polymerized styrene-butadiene rubber (S-SBR).

The amount of bound styrene in the SBR is preferably 50% by mass or less, more preferably 40% by mass or less. If it exceeds 50% by mass, it may be too hard at low temperatures, and the wet skid performance (wet grip performance) may deteriorate. In addition, the amount of bound styrene in the SBR is preferably 5% by mass or more, more preferably 10% by mass or more, and even more preferably 20% by mass or more. If it is less than 5% by mass, sufficient rigidity may not be obtained, and sufficient steering stability may not be obtained.
The amount of bound styrene is calculated by H ¹ -NMR measurement.

Modified SBR is also suitable for use because it can improve breaking strength. This can prevent the deterioration of abrasion resistance caused by the addition of aluminum hydroxide.

Modified SBR includes emulsion polymerization modified SBR (modified E-SBR) and solution polymerization modified SBR (modified S-SBR). Generally, it is easier to control the molecular weight with solution polymerization. On the other hand, with emulsion polymerization, it is difficult to control the molecular weight, and tan δ tends to be high.

The amount of bound styrene in the modified SBR is preferably 50% by mass or less, more preferably 40% by mass or less. If it exceeds 50% by mass, it may be too hard at low temperatures, and the wet skid performance (wet grip performance) may deteriorate. In addition, the amount of bound styrene in the modified SBR is preferably 5% by mass or more, more preferably 10% by mass or more. If it is less than 5% by mass, sufficient rigidity may not be obtained, and sufficient steering stability may not be obtained.
The amount of bound styrene is calculated by H ¹ -NMR measurement.

The modified SBR preferably used is one that is coupled with tin or silicon. The coupling method for modified SBR is, for example, a method in which an alkali metal (such as Li) or an alkaline earth metal (such as Mg) at the molecular chain end of the modified SBR is reacted with a tin halide or a silicon halide according to a conventional method.

The modified SBR is a copolymer of styrene and butadiene, and preferably has a primary amino group or an alkoxysilyl group. The primary amino group may be bonded to the polymerization initiation end, polymerization termination end, polymer main chain, or side chain, but it is preferable that it is introduced to the polymerization initiation end or polymerization termination end, since this can suppress energy loss from the polymer end and improve hysteresis loss characteristics.

Among the modified SBRs produced by solution polymerization, styrene butadiene rubber (SBR) modified with a compound represented by the following formula (1) (modified S-SBR) is particularly suitable. This makes it easier to control the molecular weight of the polymer, reduces the amount of low molecular weight components that increase tan δ, and strengthens the bond between the silica and the polymer chain, improving abrasion resistance and providing sufficient rigidity.

（式中、Ｒ^１、Ｒ^２及びＲ^３は、同一若しくは異なって、アルキル基、アルコキシ基、シリルオキシ基、アセタール基、カルボキシル基、メルカプト基又はこれらの誘導体を表す。Ｒ^４及びＲ^５は、同一若しくは異なって、水素原子又はアルキル基を表す。ｎは整数を表す。）

(In the formula, R ¹ , R ² and R ³ are the same or different and each represents an alkyl group, an alkoxy group, a silyloxy group, an acetal group, a carboxyl group, a mercapto group, or a derivative thereof. R ⁴ and R ⁵ are the same or different and each represents a hydrogen atom or an alkyl group. n is an integer.)

In the compound represented by the above formula (1), R ¹ , R ² and R ³ are the same or different and represent an alkyl group, an alkoxy group, a silyloxy group, an acetal group, a carboxyl group (-COOH), a mercapto group (-SH) or a derivative thereof. Examples of the alkyl group include alkyl groups having 1 to 4 carbon atoms, such as a methyl group, an ethyl group, an n-propyl group, an isopropyl group, an n-butyl group, and a t-butyl group. Examples of the alkoxy group include alkoxy groups having 1 to 8 carbon atoms (preferably having 1 to 6 carbon atoms, more preferably having 1 to 4 carbon atoms), such as a methoxy group, an ethoxy group, an n-propoxy group, an isopropoxy group, an n-butoxy group, and a t-butoxy group. The alkoxy group also includes cycloalkoxy groups (cycloalkoxy groups having 5 to 8 carbon atoms, such as a cyclohexyloxy group), and aryloxy groups (aryloxy groups having 6 to 8 carbon atoms, such as a phenoxy group and a benzyloxy group).

The above-mentioned silyloxy group includes, for example, an aliphatic group having 1 to 20 carbon atoms, and a silyloxy group substituted with an aromatic group (such as a trimethylsilyloxy group, a triethylsilyloxy group, a triisopropylsilyloxy group, a diethylisopropylsilyloxy group, a t-butyldimethylsilyloxy group, a t-butyldiphenylsilyloxy group, a tribenzylsilyloxy group, a triphenylsilyloxy group, and a tri-p-xylylsilyloxy group).

Examples of the acetal group include groups represented by -C(RR')-OR" and -O-C(RR')-OR". Examples of the former include methoxymethyl, ethoxymethyl, propoxymethyl, butoxymethyl, isopropoxymethyl, t-butoxymethyl, and neopentyloxymethyl groups, and examples of the latter include methoxymethoxy, ethoxymethoxy, propoxymethoxy, i-propoxymethoxy, n-butoxymethoxy, t-butoxymethoxy, n-pentyloxymethoxy, n-hexyloxymethoxy, cyclopentyloxymethoxy, and cyclohexyloxymethoxy. R ¹ , R ² , and R ³ are preferably alkoxy groups. This makes it possible to obtain excellent low heat buildup properties, fracture strength, crack growth resistance, and rigidity.

Examples of the alkyl group of ^R4 and ^R5 include the same groups as the alkyl groups described above.

n (an integer) is preferably 1 to 5. This allows for excellent low heat generation, fracture strength, crack growth resistance, and rigidity. Furthermore, n is more preferably 2 to 4, and most preferably 3. If n is 0, it is difficult for silicon atoms and nitrogen atoms to bond, and if n is 6 or more, the effect as a modifier is reduced.

Specific examples of the compound represented by the above formula (1) include 3-aminopropyldimethylmethoxysilane, 3-aminopropylmethyldimethoxysilane, 3-aminopropylethyldimethoxysilane, 3-aminopropyltrimethoxysilane, 3-aminopropyldimethylethoxysilane, 3-aminopropylmethyldiethoxysilane, 3-aminopropyltriethoxysilane, 3-aminopropyldimethylbutoxysilane, 3-aminopropylmethyldibutoxysilane, dimethylaminomethyltrimethoxysilane, 2-dimethylaminoethyltrimethoxysilane, 3-dimethylaminopropyltrimethoxysilane, 4-dimethylaminobutyltrimethoxysilane, dimethylaminomethyldimethoxymethylsilane, 2-dimethylaminoethyldimethoxymethylsilane, 3-dimethylaminopropyldimethoxymethylsilane, 4-dimethylaminobutyldimethoxymethylsilane, dimethylaminomethyltriethoxysilane, 2-dimethylaminoethyltriethoxysilane, 3-dimethylaminopropyltriethoxysilane, 4-dimethylaminobutyltriethoxysilane, xylsilane, dimethylaminomethyldiethoxymethylsilane, 2-dimethylaminoethyldiethoxymethylsilane, 3-dimethylaminopropyldiethoxymethylsilane, 4-dimethylaminobutyldiethoxymethylsilane, diethylaminomethyltrimethoxysilane, 2-diethylaminoethyltrimethoxysilane, 3-diethylaminopropyltrimethoxysilane, 4-diethylaminobutyltrimethoxysilane, diethylaminomethyldimethoxymethylsilane, 2-diethylaminoethyldimethoxymethylsilane, 3- Examples of the silane include diethylaminopropyl dimethoxymethylsilane, 4-diethylaminobutyl dimethoxymethylsilane, diethylaminomethyl triethoxysilane, 2-diethylaminoethyl triethoxysilane, 3-diethylaminopropyl triethoxysilane, 4-diethylaminobutyl triethoxysilane, diethylaminomethyl diethoxymethylsilane, 2-diethylaminoethyl diethoxymethylsilane, 3-diethylaminopropyl diethoxymethylsilane, and 4-diethylaminobutyl diethoxymethylsilane. These may be used alone or in combination of two or more.

The method of modifying styrene-butadiene rubber with the compound (modifier) represented by the above formula (1) can be a conventional method such as the methods described in JP-B-6-53768 and JP-B-6-57767. For example, it is sufficient to contact the styrene-butadiene rubber with the modifier, and examples of the method include a method of polymerizing the styrene-butadiene rubber and adding a predetermined amount of the modifier to the polymer rubber solution, and a method of adding the modifier to the styrene-butadiene rubber solution and reacting it.

The total content of SBR and modified SBR in 100% by mass of the rubber component is preferably 80% by mass or more, more preferably 90% by mass or more, and even more preferably 100% by mass. If it is less than 80% by mass, sufficient abrasion resistance and high rigidity may not be obtained.

The content of modified SBR in the total content of SBR and modified SBR (100% by mass) is preferably 40% by mass or more, and more preferably 50% by mass or more. If it is 40% by mass or more, abrasion resistance and high rigidity can be obtained more effectively. There is no particular upper limit to the content.

In the present invention, silica having a CTAB specific surface area of 180 ^m2 /g or more and a BET specific surface area of 185 ^m2 /g or more (hereinafter also referred to as "fine particle silica") is used. By blending such fine particle silica, even when aluminum hydroxide is blended, it is possible to achieve both wet skid performance (initial stage) and driving stability (particularly driving stability during long driving).

The CTAB (cetyltrimethylammonium bromide) specific surface area of the fine particle silica is preferably 190 ^m2 /g or more, more preferably 195 ^m2 /g or more, and even more preferably 197 ^m2 /g or more. If the CTAB specific surface area is less than 180 ^m2 /g, sufficient wet skid performance (wet grip performance) may not be obtained.
The CTAB specific surface area is preferably 500 m ² /g or less, more preferably 300 m ² /g or less, and even more preferably 250 m ² /g or less. If the CTAB specific surface area exceeds 500 m ² /g, dispersibility may deteriorate and sufficient abrasion resistance may not be obtained.
The CTAB specific surface area is measured in accordance with ASTM D3765-92.

The BET specific surface area of the finely divided silica is preferably 190 m ² /g or more, more preferably 195 m ² /g or more, and even more preferably 210 m ² /g or more. If the BET specific surface area is less than 185 m ² /g, sufficient abrasion resistance may not be obtained.
The BET specific surface area is preferably 500 m ² /g or less, more preferably 300 m ² /g or less, and even more preferably 260 m ² /g or less. If the BET specific surface area exceeds 500 m ² /g, the rubber is hard and may not provide sufficient wet skid performance (wet grip performance).
The BET specific surface area of silica is measured in accordance with ASTM D3037-81.

The aggregate size of the fine particle silica is 30 nm or more, preferably 35 nm or more, more preferably 40 nm or more, even more preferably 45 nm or more, particularly preferably 50 nm or more, and most preferably 55 nm or more. The aggregate size is preferably 100 nm or less, more preferably 80 nm or less, even more preferably 70 nm or less, and particularly preferably 65 nm or less. By having such an aggregate size, it is possible to provide excellent reinforcement, wet skid performance (initial stage), and handling stability (particularly handling stability when driving for long periods of time) while maintaining good dispersibility.

Aggregate size is also called the aggregate diameter or maximum frequency Stokes equivalent diameter, and corresponds to the particle diameter when a silica aggregate consisting of multiple primary particles is regarded as a single particle. Aggregate size can be measured using, for example, a disk centrifuge sedimentation type particle size distribution analyzer such as the BI-XDC (manufactured by Brookhaven Instruments Corporation).

Specifically, it can be measured by the following method using BI-XDC.
3.2 g of silica and 40 mL of deionized water are added to a 50 mL tall beaker, and the beaker containing the silica suspension is placed in an ice-filled crystallizer. The beaker is prepared by disintegrating the suspension for 8 minutes using an ultrasonic probe (1500 watt 1.9 cm VIBRACELL ultrasonic probe (Bioblock, used at 60% of maximum power)). 15 mL of the sample is introduced into the disk, stirred, and measured under the conditions of stationary mode, analysis time 120 minutes, and density 2.1.
On the recorder of the device, the values of the 16%, 50% (or median) and 84% mass passing diameters and the value of the mode are recorded. (The derivative of the cumulative granulometric curve gives the distribution curve its maximum abscissa, called the mode.)

（式中、ｍ_ｉは、Ｄ_ｉのクラスにおける粒子の全質量である。） This disk centrifuge sedimentation particle size analysis method can be used to measure the weight average diameter (aggregate size) of the particles (agglomerates), expressed as _Dw , after dispersing the silica in water by ultrasonic disintegration. After analysis (sedimentation for 120 minutes), the weight distribution of the particle size is calculated by a particle size distribution analyzer. The weight average diameter of the particle size, expressed as _Dw , is calculated by the following formula:

where m _i is the total mass of particles in class D _i .

The average primary particle size of the fine silica particles is preferably 25 nm or less, more preferably 22 nm or less, even more preferably 17 nm or less, and particularly preferably 14 nm or less. The lower limit of the average primary particle size is not particularly limited, but is preferably 3 nm or more, more preferably 5 nm or more, and even more preferably 7 nm or more. Although it has such a small average primary particle size, the dispersibility of silica can be further improved by the carbon black-like structure having the above aggregate size, and the reinforcement, abrasion resistance, wet skid performance (initial stage), and steering stability (especially steering stability when driving for a long time) can be further improved.
The average primary particle size of the finely divided silica particles can be determined by observing with a transmission or scanning electron microscope, measuring 400 or more primary silica particles observed within a visual field, and averaging the measurements.

The D50 of the fine silica particles is preferably 7.0 μm or less, more preferably 5.5 μm or less, and even more preferably 4.5 μm or less. If it exceeds 7.0 μm, there is a risk that sufficient rigidity cannot be obtained. The D50 of the fine silica particles is preferably 2.0 μm or more, more preferably 2.5 μm or more, and even more preferably 3.0 μm or more. If it is less than 2.0 μm, it is hard and there is a risk that sufficient wet skid performance (wet grip performance) cannot be obtained.
Here, D50 is the median diameter of the particulate silica, the median diameter being smaller than which 50% by weight of the particles are.

The proportion of finely divided silica particles having a particle size of more than 18 μm is preferably 6% by mass or less, more preferably 4% by mass or less, and even more preferably 1.5% by mass or less, which allows good dispersibility of the silica and desired performance to be obtained.
The D50 of the fine particle silica and the proportion of silica having a given particle size are measured by the following method.

The aggregation of aggregates is assessed by carrying out particle size measurements (using laser diffraction) on suspensions of previously ultrasonically disintegrated silica. This method measures the disintegrability of the silica (disintegration of silica from 0.1 to several tens of microns). Ultrasonic disintegration is carried out using a Bioblock VIBRACELL sound generator (600 W) equipped with a 19 mm diameter probe (operated at 80% of maximum power). Particle size measurements are carried out by laser diffraction on a Malvern Mastersizer 2000 particle size analyzer.

Specifically, it is measured by the following method.
1 gram of silica is weighed into a pillbox (height 6 cm and diameter 4 cm) and deionized water is added to make the mass 50 grams to prepare an aqueous suspension containing 2% silica, which is homogenized by magnetic stirring for 2 minutes. Then ultrasonic disintegration is carried out for 420 seconds, and after the entire homogenized suspension is introduced into the container of the particle size analyzer, a particle size measurement is carried out.

The pore volume distribution width W of the fine particle silica is preferably 1.0 or more, more preferably 1.5 or more, even more preferably 2.0 or more, and particularly preferably 2.5 or more. The pore distribution width W is preferably 5.0 or less, more preferably 4.5 or less, even more preferably 4.0 or less, and particularly preferably 3.5 or less. Such a broad pore distribution can improve the dispersibility of silica and obtain the desired performance.
The pore distribution width W of the pore volume of silica can be measured by the following method.

The pore volume of particulate silica is measured by mercury porosimetry. A sample of silica is pre-dried in an oven at 200°C for 2 hours, then removed from the oven and placed in a test vessel within 5 minutes of vacuum. The pore diameter (AUTOPORE III 9420 Powder Technology Porosimeter) is calculated by the Washburn equation at a contact angle of 140° and a surface tension γ of 484 dynes/cm (or N/m).

The pore distribution width W can be determined from a pore distribution curve as shown in Figure 1, which is a function of pore diameter (nm) and pore volume (mL/g). That is, the value of diameter Xs (nm) that gives the peak value Ys (mL/g) of the pore volume is recorded, and then a line of Y = Ys/2 is plotted, and points a and b where this line intersects with the pore distribution curve are determined. Then, when the abscissas (nm) of points a and b are Xa and Xb, respectively (Xa > Xb), the pore distribution width W corresponds to (Xa - Xb)/Xs.

The diameter Xs (nm) giving the peak value Ys of the pore volume in the pore distribution curve of the fine particle silica is preferably 10 nm or more, more preferably 15 nm or more, even more preferably 18 nm or more, and particularly preferably 20 nm or more, and is preferably 60 nm or less, more preferably 35 nm or less, even more preferably 28 nm or less, and particularly preferably 25 nm or less. If it is within the above range, fine particle silica with excellent dispersibility and reinforcing properties can be obtained.

The amount of the fine silica particles blended is preferably 5 parts by mass or more, more preferably 10 parts by mass or more, even more preferably 15 parts by mass or more, particularly preferably 20 parts by mass or more, and most preferably 30 parts by mass or more, per 100 parts by mass of the rubber component. If the amount is less than 5 parts by mass, sufficient rigidity may not be obtained. The amount of the fine silica particles blended is preferably 150 parts by mass or less, more preferably 100 parts by mass or less, and even more preferably 80 parts by mass or less. If the amount exceeds 150 parts by mass, dispersibility may deteriorate and sufficient abrasion resistance may not be obtained.

The rubber composition of the present invention may contain silica other than the above-mentioned fine particle silica. In this case, the total content of silica is preferably 30 parts by mass or more, more preferably 40 parts by mass or more, and even more preferably 45 parts by mass or more, per 100 parts by mass of the rubber component. The total content is preferably 200 parts by mass or less, more preferably 150 parts by mass or less, and even more preferably 100 parts by mass or less. When the content is less than the lower limit or exceeds the upper limit, the same tendency as the amount of fine particle silica mentioned above is observed.

In the rubber composition of the present invention, it is preferable to further compound a silane coupling agent. By compounding a silane coupling agent, it is possible to improve wear resistance. As the silane coupling agent, a conventionally known silane coupling agent can be used, for example, bis(3-triethoxysilylpropyl) tetrasulfide, bis(2-triethoxysilylethyl) tetrasulfide, bis(4-triethoxysilylbutyl) tetrasulfide, bis(3-trimethoxysilylpropyl) tetrasulfide, bis(2-trimethoxysilylethyl) tetrasulfide, bis(4-trimethoxysilylbutyl) tetrasulfide, bis(3-triethoxysilylpropyl) trisulfide, bis(2-triethoxysilylethyl) trisulfide, bis(4-triethoxysilylbutyl) trisulfide, bis(3-trimethoxysilylpropyl) trisulfide, bis(2-triethoxysilylethyl) trisulfide, bis(4-triethoxysilylbutyl) trisulfide, bis(3-trimethoxysilylpropyl) trisulfide, , bis(2-trimethoxysilylethyl)trisulfide, bis(4-trimethoxysilylbutyl)trisulfide, bis(3-triethoxysilylpropyl)disulfide, bis(2-triethoxysilylethyl)disulfide, bis(4-triethoxysilylbutyl)disulfide, bis(3-trimethoxysilylpropyl)disulfide, bis(2-trimethoxysilylethyl)disulfide, bis(4-trimethoxysilylbutyl)disulfide, 3-trimethoxysilylpropyl-N,N-dimethylthiocarbamoyltetrasulfide, 3-triethoxysilylpropyl-N,N-dimethylthiocarbamoyltetrasulfide, 2-triethoxysilylethyl-N,N-dimethylthio Sulfide-based compounds such as carbamoyl tetrasulfide, 2-trimethoxysilylethyl-N,N-dimethylthiocarbamoyl tetrasulfide, 3-trimethoxysilylpropyl benzothiazolyl tetrasulfide, 3-triethoxysilylpropyl benzothiazole tetrasulfide, and 3-trimethoxysilylpropyl methacrylate monosulfide; mercapto-based compounds such as 3-mercaptopropyl trimethoxysilane, 3-mercaptopropyl triethoxysilane, 2-mercaptoethyl trimethoxysilane, and 2-mercaptoethyl triethoxysilane; vinyl-based compounds such as vinyl triethoxysilane and vinyl trimethoxysilane; 3-aminopropyl triethoxysilane, 3-aminopropyl trimethysilane, and 3-aminopropyl trimethysilane; Examples of the silane coupling agents include amino-based silanes such as γ-glycidoxypropyl triethoxysilane, γ-glycidoxypropyl trimethoxysilane, γ-glycidoxypropyl methyl diethoxysilane, and γ-glycidoxypropyl methyl dimethoxysilane; nitro-based silanes such as 3-nitropropyl trimethoxysilane and 3-nitropropyl triethoxysilane; and chloro-based silanes such as 3-chloropropyl trimethoxysilane, 3-chloropropyl triethoxysilane, 2-chloroethyl trimethoxysilane, and 2-chloroethyl triethoxysilane. Among these, bis(3-triethoxysilylpropyl)tetrasulfide and bis(3-triethoxysilylpropyl)disulfide are preferred because of their good processability. These silane coupling agents may be used alone or in combination of two or more.

The content of the silane coupling agent is preferably 0.5 parts by mass or more, more preferably 1 part by mass or more, even more preferably 2 parts by mass or more, particularly preferably 5 parts by mass or more, and most preferably 10 parts by mass or more, per 100 parts by mass of silica. If the content is less than 0.5 parts by mass, sufficient abrasion resistance may not be obtained. The content is preferably 30 parts by mass or less, more preferably 25 parts by mass or less, and even more preferably 20 parts by mass or less. If the content exceeds 30 parts by mass, dispersibility may deteriorate.

In the present invention, aluminum hydroxide is used. In the present invention, aluminum hydroxide includes alumina hydrate.

The average particle size of the aluminum hydroxide is preferably 10 μm or less, more preferably 5 μm or less, and even more preferably 3 μm or less. If it exceeds 10 μm, there is a risk that sufficient wet skid performance (initial stage) and handling stability (particularly handling stability during long-term driving) may not be obtained. The average particle size of the aluminum hydroxide is preferably 0.05 μm or more, and more preferably 0.1 μm or more. If it is less than 0.05 μm, dispersibility may deteriorate and sufficient abrasion resistance may not be obtained.

In the present invention, the average particle size of aluminum hydroxide was measured using a transmission or scanning electron microscope. The average particle size means the long diameter, which is the longest length when the aluminum hydroxide powder is projected onto a projection plane while changing the direction of the aluminum hydroxide powder relative to the projection plane.

The content of aluminum hydroxide is preferably 1 part by mass or more, more preferably 2 parts by mass or more, even more preferably 10 parts by mass or more, and particularly preferably 20 parts by mass or more, per 100 parts by mass of the rubber component. If the content is less than 1 part by mass, sufficient wet skid performance (wet grip performance) may not be obtained. The content of aluminum hydroxide is preferably 60 parts by mass or less, more preferably 50 parts by mass or less. If the content exceeds 60 parts by mass, dispersibility may deteriorate and sufficient abrasion resistance may not be obtained.

In addition to the above components, the rubber composition of the present invention can be appropriately blended with compounding agents that are generally used in the manufacture of rubber compositions, such as reinforcing fillers such as carbon black and clay, zinc oxide, stearic acid, various antioxidants, vulcanizing agents such as oil, wax, sulfur, and sulfur-containing compounds, and vulcanization accelerators.

The rubber composition of the present invention preferably contains carbon black. Examples of carbon black that can be used include, but are not limited to, GPF, FEF, HAF, ISAF, and SAF. By blending carbon black, it is possible to increase the reinforcing properties and improve the abrasion resistance.

The nitrogen adsorption specific surface area ( _N2SA ) of carbon black is preferably 90 ^m2 /g or more, more preferably 100 ^m2 /g or more. If it is less than ^{90 m2} /g, sufficient rigidity may not be obtained. The nitrogen adsorption specific surface area of carbon black is preferably 200 ^m2 /g or less, more preferably 190 ^m2 /g or less. If it exceeds 200 ^m2 /g, wet skid performance (initial stage) may be deteriorated.
The nitrogen adsorption specific surface area of carbon black is determined by Method A of JIS K6217.

When the rubber composition contains carbon black, the carbon black content is preferably 5 parts by mass or more, more preferably 10 parts by mass or more, and even more preferably 15 parts by mass or more, per 100 parts by mass of the rubber component. If the carbon black content is less than 5 parts by mass, sufficient abrasion resistance and rigidity may not be obtained. In addition, the carbon black content is preferably 100 parts by mass or less, more preferably 90 parts by mass or less, even more preferably 70 parts by mass or less, particularly preferably 50 parts by mass or less, and most preferably 30 parts by mass or less. If the carbon black content exceeds 100 parts by mass, wet skid performance (initial stage) may be reduced.

In the present invention, examples of the antiaging agent that can be used include amine-based antiaging agents, quinoline-based antiaging agents, and monophenol-based antiaging agents. These antiaging agents may be used alone or in combination of two or more. Among them, amine-based antiaging agents and quinoline-based antiaging agents are preferably used because they can effectively exhibit heat resistance and fatigue resistance and can effectively suppress deterioration of steering stability during long-term driving, and it is more preferable to use an amine-based antiaging agent and a quinoline-based antiaging agent in combination.

Amine-based antioxidants include, for example, amine derivatives such as diphenylamine and p-phenylenediamine. Diphenylamine derivatives include, for example, p-(p-toluenesulfonylamido)-diphenylamine and octylated diphenylamine. p-phenylenediamine derivatives include, for example, N-(1,3-dimethylbutyl)-N'-phenyl-p-phenylenediamine (6PPD), N-phenyl-N'-isopropyl-p-phenylenediamine (IPPD), and N,N'-di-2-naphthyl-p-phenylenediamine.

Quinoline-based antioxidants include 2,2,4-trimethyl-1,2-dihydroquinoline polymers and 6-ethoxy-2,2,4-trimethyl-1,2-dihydroquinoline.

Examples of monophenol-based antiaging agents include 2,6-di-tert-butyl-4-methylphenol, 2,6-di-tert-butyl-4-ethylphenol, 2,6-di-tert-butylphenol, 1-oxy-3-methyl-4-isopropylbenzene, butylhydroxyanisole, 2,4-dimethyl-6-tert-butylphenol, n-octadecyl-3-(4'-hydroxy-3',5'-di-tert-butylphenyl)propionate, and styrenated phenol.

The content of the anti-aging agent is preferably 1 part by mass or more, more preferably 2 parts by mass or more, per 100 parts by mass of the rubber component. If it is less than 1 part by mass, there is a risk that the fracture properties cannot be improved and that the deterioration of the steering stability during long-term driving cannot be effectively suppressed. In addition, the content is preferably 15 parts by mass or less, more preferably 10 parts by mass or less. If it exceeds 15 parts by mass, there is a risk that blooming occurs on the surface.

When the rubber composition uses an amine-based antioxidant and a quinoline-based antioxidant in combination, the compounding ratio of the amine-based antioxidant to the quinoline-based antioxidant (amine-based antioxidant (parts by mass)/quinoline-based antioxidant (parts by mass)) is preferably at least 1, and more preferably at least 1.2. If the ratio is less than 1, sufficient fatigue resistance cannot be obtained, and there is a risk that deterioration of steering stability during long-term driving cannot be effectively suppressed.
The blending ratio is preferably not more than 5, more preferably not more than 2.5. If it exceeds 5, the heat resistance effect is not sufficiently exhibited, and there is a risk that the deterioration of the steering stability during long-term driving cannot be effectively suppressed.

The rubber composition of the present invention is produced by a general method. That is, it can be produced by kneading the above-mentioned components with a Banbury mixer, kneader, open roll, etc., and then vulcanizing the components. The rubber composition can be used for each component of a tire, and is particularly suitable for use in the tread.

The pneumatic tire of the present invention is produced by a conventional method using the above rubber composition.
That is, the rubber composition containing the above-mentioned components is extruded in an unvulcanized state to match the shape of each tire component such as the tread, and molded together with other tire components in a tire building machine by a normal method to form an unvulcanized tire. The unvulcanized tire is then heated and pressurized in a vulcanizer to obtain a tire.

The pneumatic tire of the present invention is suitable for use as a passenger car tire, a truck/bus tire, a motorcycle tire, a racing tire, etc., and is particularly suitable for use as a racing tire. Racing tires in the present invention are tires used in competitions such as karts. The pneumatic tire obtained by the present invention has excellent grip performance (wet skid performance (particularly initial wet skid performance)) on wet road surfaces and handling stability (particularly handling stability when driven for long periods of time), and is more suitable for use as a racing tire for driving on wet road surfaces.

The present invention will be specifically explained based on examples, but the present invention is not limited to these.

Various chemicals used in the Examples , Reference Examples and Comparative Examples will be collectively described below.
SBR: Tufuden 4350 manufactured by Asahi Kasei Corporation (bound styrene content: 39% by mass, containing 50 parts by mass of oil per 100 parts by mass of rubber solids)
Modified SBR: HPR355 manufactured by JSR Corporation (modified S-SBR, bound styrene content: 21% by mass, coupled with alkoxysilane to introduce it into the terminal, modified with a compound represented by formula (1) (in formula (1), R ¹ = methoxy group, R ² = methoxy group, R ³ = methoxy group, R ⁴ = hydrogen atom, R ⁵ = hydrogen atom, n = 3)).
Carbon black: Diablack A (N110) manufactured by Mitsubishi Chemical Corporation ( _N2SA : 142 ^m2 /g)
Silica 1: Nipsil VN3 manufactured by Nippon Silica Kogyo Co., Ltd. (CTAB specific surface area: 170 m ² /g, BET specific surface area: 191 m ² /g, average primary particle size: 19 nm, aggregate size: 33 nm)
Silica 2: Zeosil HRS 1200MP manufactured by Rhodia (CTAB specific surface area: 195 m ² /g, BET specific surface area: 200 m ² /g, average primary particle size: 15 nm, aggregate size: 40 nm, D50: 6.5 μm, proportion of particles larger than 18 μm: 5.0 mass%, pore distribution width W: 0.40, diameter Xs giving the pore volume peak value in the pore distribution curve: 18.8 nm)
Silica 3: Zeosil Premium 200MP manufactured by Rhodia (CTAB specific surface area 200 m ² /g, BET specific surface area: 220 m ² /g, average primary particle diameter 10: nm, aggregate size: 65 nm, D50: 4.2 μm, proportion of particles larger than 18 μm: 1.0 mass%, pore distribution width W: 1.57, diameter Xs giving the pore volume peak value in the pore distribution curve: 21.9 nm)
Antioxidant 6C: Santoflex 13 (N-(1,3-dimethylbutyl)-N'-phenyl-p-phenylenediamine (6PPD)) manufactured by Flexis Co., Ltd.
Antioxidant 224: Nocrac 224 (2,2,4-trimethyl-1,2-dihydroquinoline polymer) manufactured by Flexis Co., Ltd.
Stearic acid: Paulownia wood produced by NOF Corp. Zinc oxide: Zinc oxide type 2 produced by Mitsui Mining & Smelting Co., Ltd. Aroma oil: Process X-260 produced by Japan Energy Corp.
Silane coupling agent: Si69 (bis(3-triethoxysilylpropyl)tetrasulfide) manufactured by Degussa
Aluminum hydroxide: Showa Denko Hijilite H-43 (average particle size: 1 μm)
Sulfur: Powdered sulfur vulcanization accelerator manufactured by Tsurumi Chemical Industry Co., Ltd. NS: Noccela NS (N-tert-butyl-2-benzothiazolyl sulfenamide) manufactured by Ouchi Shinko Chemical Industry Co., Ltd.

Examples 1 to 2, 4, 5 , Reference Example 3 and Comparative Examples 1 to 4
According to the composition shown in Table 1, materials other than sulfur and vulcanization accelerator were kneaded for 3 minutes under the condition of 150°C using a BP type Banbury mixer to obtain a kneaded product. Next, sulfur and vulcanization accelerator were added to the kneaded product obtained, and the mixture was kneaded for 5 minutes under the condition of 50°C using an open roll to obtain an unvulcanized rubber composition.
The resulting unvulcanized rubber composition was press-vulcanized at 170° C. for 12 minutes to obtain a vulcanized rubber sheet.
The unvulcanized rubber composition thus obtained was molded into a tread shape, and was laminated with other tire components to form a tire. The tire was then vulcanized at 170° C. for 12 minutes to produce a test cart tire (tire size: 11×7.10-5).

The following evaluations were carried out using the resulting vulcanized rubber sheets and test cart tires. The test results are shown in Table 1.

(1) SWELL (crosslink density)
The obtained vulcanized rubber sheet was extracted with toluene, and the volume change rate (SWELL) before and after extraction was measured. The smaller the SWELL, the more the variation in crosslinking can be suppressed, which is preferable.

(2) Viscoelasticity Test Using a viscoelasticity spectrometer manufactured by Iwamoto Seisakusho Co., Ltd., the viscoelasticity (complex modulus E* and loss tangent tanδ ⁾ of the vulcanized rubber composition at 40°C was measured under the conditions of an initial strain of 10%, a dynamic strain of 2%, and a vibration frequency of 10 Hz.
Using a viscoelasticity spectrometer manufactured by Iwamoto Seisakusho Co., Ltd., the viscoelasticity (complex modulus E ^* and loss tangent tan δ) of the vulcanized rubber composition was measured at 0° C. under conditions of an initial strain of 10%, a dynamic strain of 0.5%, and a vibration frequency of 10 Hz.
In the viscoelasticity test at 40° C., a larger E ^* indicates higher rigidity and better handling stability.
In addition, in the viscoelasticity test at 0° C., a smaller E ^* indicates better initial grip performance (initial wet skid performance).

(3) Tensile Test According to JIS K 6251 "Vulcanized rubber and thermoplastic rubber - Determination of tensile properties", a tensile test was carried out using a No. 3 dumbbell-shaped rubber test piece made of the vulcanized rubber composition to measure the stress at 300% elongation (M300). The tensile strength index of Comparative Example 1 was set to 100, and the M300 of each compound was expressed as an index according to the following calculation formula. Note that a larger tensile strength index indicates better abrasion wear resistance.
(Tensile strength index) = (M300 of each formulation) / (M300 of Comparative Example 1) x 100

(4) Actual Vehicle Evaluation A test cart was fitted with the test cart tires and driven around a test course (wet road surface) of 2 km per lap for 8 laps. The initial wet skid performance of the tire of Comparative Example 1 was scored as 3 points, and the test driver performed a sensory evaluation on a 5-point scale. The initial wet skid performance indicates the wet skid performance on the 1st to 4th laps.
In addition, the test driver performed a sensory evaluation of the driving stability from the 5th to 8th laps on a 5-point scale. The higher the score, the better the driving stability.
In addition, the appearance of the tires after eight laps was evaluated on a scale of one to five for wear, with a higher score indicating better wear resistance.

As can be seen from Table 1, the examples and reference examples containing aluminum hydroxide and silica having a CTAB specific surface area and a BET specific surface area equal to or greater than a specific value were able to achieve both initial wet skid performance and steering stability during long-term driving. On the other hand, the comparative example not containing both could not achieve a good balance between the two performances.
In this way, the pneumatic tire obtained by the present invention has excellent initial wet skid performance on wet road surfaces and excellent handling stability when driven for long periods of time, and can effectively suppress the decrease in time associated with laps when driving on a circuit (wet road surfaces).

Claims (6)

Contains aluminum hydroxide, silica, amine-based antioxidants, and quinoline-based antioxidants.
The silica has a CTAB specific surface area of 180 m ² /g or more, a BET specific surface area of 185 m ² /g or more, and an aggregate size of 30 nm or more;
A rubber composition for tires, in which the total content of styrene-butadiene rubber and modified styrene-butadiene rubber is 90 mass % or more based on 100 mass % of the rubber component (excluding the case where modified styrene-butadiene rubber is contained) . The rubber composition for tires according to claim 1, wherein the average particle size of the aluminum hydroxide is 10 μm or less. The rubber composition for tires according to claim 1 or 2, wherein the content of aluminum hydroxide is 20 to 50 parts by mass per 100 parts by mass of the rubber component. The rubber composition for tires according to any one of claims 1 to 3 is used in a tread. A pneumatic tire using the rubber composition according to any one of claims 1 to 4. The pneumatic tire of claim 5 is a racing tire.

Images