JP2015196824A - Pneumatic tire - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a pneumatic tire that is excellent in both initial-stage gripping performance and late-stage gripping performance in not only an evaluation using a rubber test piece but also an evaluation using a real car.SOLUTION: A pneumatic tire comprises a tread made using a rubber composition comprising a rubber component, non-petroleum-based wax, and α-methyl styrenic resin.

Description

The present invention relates to a pneumatic tire.

Conventionally, it has been proposed to improve the initial grip performance of the tire by increasing the amount of plasticizer such as oil and softening the rubber hardness, and improving the late grip performance by adding a resin and increasing the glass transition temperature Tg. From the viewpoint of simplicity and the like, studies based on evaluation of rubber test pieces are being promoted.

However, there are cases in which the initial grip performance and late grip performance are poor and the expected performance cannot be obtained even if such rubber test pieces are used for the actual vehicle evaluation by applying the compounded rubber with good performance to the tire. For this reason, it is desired to provide a rubber composition that exhibits excellent performance in actual vehicles as well.

Patent Document 1 discloses a tread rubber composition using an α-methylstyrene resin or the like, but there is still room for improvement in terms of improving both initial grip performance and late grip performance in an actual vehicle. I'm leaving.

JP 2012-52028 A

An object of the present invention is to solve the above-mentioned problems and provide a pneumatic tire that is excellent not only in evaluation of rubber test pieces but also in initial grip performance and late grip performance even in an actual vehicle.

The present invention relates to a pneumatic tire having a tread manufactured using a rubber composition containing a rubber component, a non-petroleum wax, and an α-methylstyrene resin.

The non-petroleum wax is preferably a purified non-petroleum wax obtained by subjecting the non-petroleum wax to a treatment for removing at least one selected from the group consisting of free fatty acids, free alcohols and resins.

The non-petroleum wax is a refined candelilla wax containing 65% by mass or more of hydrocarbons having 28 to 33 carbon atoms and having a proportion of 31 hydrocarbons in the hydrocarbons of 60% by mass or more. It is preferable.

The non-petroleum wax is preferably a purified beeswax having a free fatty acid content of 17% by mass or less and a free alcohol content of less than 2.5% by mass.

In the rubber composition, the non-petroleum wax content is preferably 0.1 to 8 parts by mass with respect to 100 parts by mass of the rubber component.

According to the present invention, since it is a pneumatic tire having a tread produced using a rubber composition containing a rubber component, a non-petroleum wax, and an α-methylstyrene resin, not only the evaluation of the rubber test piece Even in actual vehicles, it is possible to obtain excellent initial grip performance and late grip performance.

The pneumatic tire of the present invention has a tread produced using a rubber composition containing a rubber component, a non-petroleum wax, and an α-methylstyrene resin.

In the present invention, by using a non-petroleum wax and an α-methylstyrene resin in combination, the initial grip performance and the late grip performance can be remarkably improved even in an actual vehicle. This is because, although the grip performance of the rubber test piece is improved by the blending of petroleum wax and resin, in the actual vehicle, the desired deposit is caused by deposits of chemicals such as petroleum wax deposited on the tire surface. In the present invention using a non-petroleum wax and an α-methylstyrene resin together, the initial grip performance is not exhibited, and the desired late grip performance is not obtained because the surface deposit does not peel off, Since the surface deposits are easily peeled off and the tire friction coefficient can be easily stabilized in a short time from the start of running, it is possible to obtain excellent initial grip performance and late grip performance even in an actual vehicle.

The rubber composition constituting the tread of the pneumatic tire of the present invention contains non-petroleum wax (non-petroleum-derived wax). The non-petroleum wax is not particularly limited as long as it is not a wax derived from petroleum. For example, plant waxes such as candelilla wax, carnauba wax, wood wax, rice wax, jojoba wax; beeswax, lanolin, whale wax, etc. Animal waxes; mineral waxes such as ozokerite, ceresin, petrolactam; natural fat-based hardened oils such as castor hardened oil, soybean hardened oil, rapeseed hardened oil, beef tallow hardened oil; and purified products thereof. Candelilla wax, beeswax and the like are preferred. In addition, non-petroleum waxes obtained from genetically modified plants and animals can also be used.

Further, among non-petroleum waxes, refined non-petroleum waxes obtained by subjecting non-petroleum-derived waxes to a treatment for removing at least one selected from the group consisting of free fatty acids, free alcohols and resins can be suitably used. Here, the removal treatment method is not particularly limited as long as it is a method capable of removing free alcohol, free fatty acid, and resin, and a known method can be used.

Specifically, the refined non-petroleum wax has a refined candelilla wax having a hydrocarbon content of 65% by mass or more, a free fatty acid content of 17% by mass or less, and / or a free alcohol content of 2.5% by mass. Less than purified beeswax or the like can be preferably used.

Refined candelilla wax, refined beeswax, etc. have a reduced amount of polar components such as free fatty acids, free alcohols, and resins compared to normal candelilla wax and beeswax, so the softening point distribution shifts or expands to lower temperatures. Has been. For this reason, ozone resistance especially at low temperatures is improved, and excellent ozone resistance is exhibited in a wide temperature range. In addition, the relative increase in the amount of hydrocarbons due to the weight loss improves compatibility with the low-polar rubber and uniformity of the film, and can suppress bloom, thereby preventing whitening of the rubber surface. Further, the precipitates such as wax are easily peeled off on the tire surface of the actual vehicle, and the initial grip performance and the late grip performance are sufficiently improved. In addition, it is environmentally friendly.

As described above, a suitable example of the non-petroleum wax includes a refined candelilla wax having a hydrocarbon content of 65% by mass or more (more preferably 75% by mass or more, and further preferably 80% by mass or more). Among them, a refined candelilla wax containing 65% by mass or more of hydrocarbons having 28 to 33 carbon atoms and having a proportion of 31 hydrocarbons in the hydrocarbons of 60% by mass or more is particularly preferable. Thereby, excellent ozone resistance (particularly at low temperatures) can be obtained, and whitening can be prevented. In addition, the rolling resistance can be reduced. Furthermore, even in an actual vehicle, the initial grip performance and the late grip performance are sufficiently improved.

The hydrocarbon content of 28 to 33 carbon atoms in 100% by mass of the purified candelilla wax is preferably 75% by mass or more, more preferably 80% by mass or more. If it is less than 65% by mass, ozone resistance, whitening countermeasures, initial grip performance, and late grip performance tend to be insufficient. The upper limit of the content is not particularly limited, but is preferably 95% by mass or less, more preferably 90% by mass or less.
In the refined candelilla wax, the proportion of the hydrocarbon having 31 carbon atoms in the hydrocarbon having 28 to 33 carbon atoms is preferably 60% by mass or more, and more preferably 65% by mass or more.

The content of free alcohol and free fatty acid in 100% by mass of the purified candelilla wax is preferably small, specifically 10% by mass or less and more preferably 7% by mass or less. If it exceeds 10% by mass, ozone resistance (particularly at low temperatures), initial grip performance, and late grip performance tend to deteriorate.

The content of the resin in 100% by mass of the purified candelilla wax is preferably small, specifically 15% by mass or less is preferable, 12% by mass or less is more preferable, 10% by mass or less is further preferable, and 7% by mass. The following are particularly preferred: If it exceeds 15% by mass, ozone resistance (particularly at low temperatures), initial grip performance, and late grip performance tend to deteriorate.

The content of the ester in 100% by mass of the purified candelilla wax is preferably 20% by mass or less, more preferably 15% by mass or less, still more preferably 10% by mass or less, and particularly preferably 5% by mass or less. As a result, good ozone resistance at low temperatures, initial grip performance, and late grip performance can be obtained.

In addition, as a non-petroleum-type wax in this invention, what contains the component which has a softening point of 40 degrees C or less is preferable. Here, the softening point distribution of the wax is examined by measuring the heat flow (mW / g) from a temperature of −30 ° C. to 100 ° C. at a rate of 5 ° C./min using a differential scanning calorimeter (DSC). It is done. Whether or not a component having a softening point at a predetermined temperature is included can be confirmed based on whether or not the temperature dependence curve of the heat flow at the predetermined temperature (for example, 40 ° C.) is lowered from the baseline in the endothermic direction. .

And as said refinement | purification candelilla wax, what satisfy | fills the relationship of (heat flow (mW / g) in 40 degreeC / heat flow (mW / g) of peak temperature) x100> = 0.1 is preferable, 0.2 What satisfy | fills the above relationship is more preferable, and what satisfy | fills the relationship of 0.5 or more is still more preferable. In this case, a component having a softening point of 40 ° C. or less can provide good low temperature ozone resistance, initial grip performance, and late grip performance.

The purified candelilla wax can be prepared by, for example, a production method described in JP-A-10-182500. That is, for example, non-petroleum wax is saponified and decomposed in the presence of alkali, extracted with petroleum ether, and the solid obtained by distillation of petroleum ether under reduced pressure is dissolved in an organic solvent such as n-hexane. Then, this is passed through a column packed with silica gel, eluted and developed with an organic solvent of n-hexane, divided into each fraction, and a desired fraction is collected.

Furthermore, as described above, preferred examples of the non-petroleum wax include purified beeswax having a free fatty acid content of 17% by mass or less and / or a free alcohol content of less than 2.5% by mass. It is desirable that the content of free fatty acid in the mass% is small, and specifically, it is more preferably 15 mass% or less. Further, it is desirable that the content of free alcohol in 100% by mass of the purified beeswax is also small. When the upper limit is exceeded, ozone resistance (particularly at low temperatures), initial grip performance, and late grip performance tend to deteriorate.

The hydrocarbon content in 100% by mass of the purified beeswax is preferably 10% by mass or more, more preferably 12% by mass or more. If it is less than 10% by mass, ozone resistance, whitening countermeasures, initial grip performance, and late grip performance tend to be insufficient. The upper limit of the content is not particularly limited, but is preferably 40% by mass or less, more preferably 20% by mass or less, in view of the cost required for purification.

The content of the ester in 100% by mass of the purified beeswax is preferably 65% by mass or more, more preferably 70% by mass or more. Although the upper limit of this content is not specifically limited, Preferably it is 90 mass% or less, More preferably, it is 85 mass% or less. As a result, good ozone resistance at low temperatures, initial grip performance, and late grip performance can be obtained.

The purified beeswax preferably satisfies the relationship of (heat flow at 40 ° C. (mW / g) / peak temperature heat flow (mW / g)) × 100 ≧ 10, more preferably satisfies the relationship of 11 or more. Preferably, those satisfying the relationship of 12 or more are more preferable, and those satisfying the relationship of 13 or more are particularly preferable. In this case, a component having a softening point of 40 ° C. or less can provide good low temperature ozone resistance, initial grip performance, and late grip performance.

The purified beeswax is obtained, for example, by removing beeswax from a beehive and removing dust and bee carcasses to obtain yellow wax, which is further decolorized and bleached to obtain beeswax. Furthermore, the exposed beeswax, yellow wax or the like can be obtained by heating or boiling treatment, or chemical treatment with an oxidizing agent or a reducing agent to reduce free alcohol, free fatty acid, resin content, or the like.

The contents of free alcohol, free fatty acid, resin, hydrocarbon and ester contained in purified non-petroleum wax such as refined candelilla wax and refined beeswax can be measured by conventional methods such as gas chromatography. The heat flow can be measured using a differential scanning calorimeter (DSC).

In the rubber composition, the content of the non-petroleum wax (total content of refined candelilla wax, refined beeswax, etc.) is preferably 0.1 parts by mass or more with respect to 100 parts by mass of the rubber component, More preferably, it is 0.5 mass part or more, More preferably, it is 1.5 mass part or more, Most preferably, it is 2.5 mass part or more. If the amount is less than 0.1 parts by mass, specific effects such as improvement in ozone resistance, initial grip performance, and late grip performance may not be confirmed. Moreover, this content becomes like this. Preferably it is 8 mass parts or less, More preferably, it is 5 mass parts or less. If the amount exceeds 8 parts by mass, the amount of bloom tends to increase and the tire tends to be white. In addition, the cost may increase.

The rubber composition contains an α-methylstyrene resin, and as the resin, a homopolymer of α-methylstyrene, a copolymer of α-methylstyrene and styrene, and the like are preferable.

As the α-methylstyrene resin, for example, commercially available products such as SA85, SA100, SA120, SA140 from Arizona Chemical Co., and R2336 from Eastman Chemical Co. can be suitably used.

The SP value of the α-methylstyrene resin is preferably 9-10. By using a resin having an SP value within the above range, compatibility with a rubber component such as SBR is improved, and initial grip performance and late grip performance can be improved.

The softening point of the α-methylstyrene resin is preferably 30 ° C or higher, more preferably 60 ° C or higher, and still more preferably 75 ° C or higher. The softening point is preferably 100 ° C. or lower, more preferably 92 ° C. or lower, and still more preferably 88 ° C. or lower. By using a resin having a softening point within the above range, compatibility with a rubber component such as SBR is improved, and initial grip performance and late grip performance can be improved.
The softening point is the temperature at which the sphere descends when the softening point specified in JIS K 6220 is measured with a ring and ball softening point measuring device.

The Tg of the α-methylstyrene resin is preferably 28 ° C. or higher, more preferably 38 ° C. or higher. The Tg is preferably 58 ° C. or lower, more preferably 48 ° C. or lower. By using a resin having a Tg within the above range, compatibility with a rubber component such as SBR is improved, and initial grip performance and late grip performance can be improved.

The Mw of the α-methylstyrene resin is preferably 500 or more, more preferably 800 or more. The Mw is preferably 3000 or less, more preferably 2000 or less. By using a resin having Mw within the above range, compatibility with a rubber component such as SBR is improved, and initial grip performance and late grip performance can be improved.

In the rubber composition, the content of the α-methylstyrene-based resin is preferably 2 parts by mass or more, more preferably 3 parts by mass or more with respect to 100 parts by mass of the rubber component. If it is less than 2 parts by mass, the desired wet grip performance may not be obtained. The content is preferably 30 parts by mass or less, more preferably 20 parts by mass or less. When it exceeds 30 parts by mass, the rubber becomes hard at low temperatures and the initial grip performance tends to deteriorate.

In the rubber composition, the rubber component includes natural rubber (NR), epoxidized natural rubber (ENR), isoprene rubber (IR), butadiene rubber (BR), styrene butadiene rubber (SBR), acrylonitrile butadiene rubber (NBR). ), Diene rubbers such as chloroprene rubber (CR), butyl rubber (IIR), styrene-isoprene-butadiene copolymer rubber (SIBR), and modified rubbers thereof, which are commonly used in the tire industry can be used. The rubber component may be appropriately selected according to the required performance. For example, NR, ENR, BR, SBR, modified rubbers thereof, and the like can be suitably used.

〔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（好ましくは炭素数１〜８、より好ましくは炭素数１〜６、更に好ましくは炭素数１〜４のアルコキシ基）、シリルオキシ基、アセタール基、カルボキシル基（−ＣＯＯＨ）、メルカプト基（−ＳＨ）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（好ましくは炭素数１〜４のアルキル基）を表す。ｎは整数（好ましくは１〜５、より好ましくは２〜４、更に好ましくは３）を表す。〕 As the modified rubber, known modified SBR and modified BR used in the tire industry can be used. For example, modified SBR and modified BR modified by a nitrogen-containing compound such as a compound represented by the following formula (1) Is mentioned.

[In formula, R < ¹ >, R < ² > and R < ³ > are the same or different, and are an alkyl group and an alkoxy group (preferably C1-C8, More preferably C1-C6, More preferably C1-C4 An alkoxy group), a silyloxy group, an acetal group, a carboxyl group (—COOH), a mercapto group (—SH) or a derivative thereof. R ⁴ and R ⁵ are the same or different and each represents a hydrogen atom or an alkyl group (preferably an alkyl group having 1 to 4 carbon atoms). n represents an integer (preferably 1-5, more preferably 2-4, still more preferably 3). ]

As R ¹ , R ² and R ³ , an alkoxy group is desirable, and as R ⁴ and R ⁵ , an alkyl group is desirable.

Specific examples of the compound represented by the above formula (1) include 3-aminopropyldimethylmethoxysilane, 3-aminopropylmethyldimethoxysilane, 2-dimethylaminoethyltrimethoxysilane, 3-diethylaminopropyltrimethoxysilane, 3 -Dimethylaminopropyltrimethoxysilane etc. are mentioned.

Methods for modifying BR and SBR with the compound represented by the above formula (1) (modifier) are described in JP-B-6-53768, JP-B-6-57767, JP-T2003-514078, and the like. A conventionally known method such as a known method can be used. For example, BR or SBR may be brought into contact with a modifying agent. After synthesizing BR or SBR by anionic polymerization, a predetermined amount of modifying agent is added to the polymer rubber solution, and the polymerization terminal (active activity of BR or SBR is activated). (Terminal) and a modifying agent, a method in which a modifying agent is added to a BR or SBR solution and reacted.

When NR and / or ENR is contained, the total content of NR and ENR in 100% by mass of the rubber component is preferably 5% by mass or more, more preferably 10% by mass or more. If it is less than 5% by mass, it may be difficult to obtain sufficient mechanical strength. The total content is preferably 90% by mass or less, more preferably 70% by mass or less. If it exceeds 90% by mass, the blending amount of other rubber becomes relatively low, and it may be difficult to improve crack growth resistance, ozone resistance, wear resistance, and the like.

When BR such as non-modified BR and modified BR is contained, the content of BR in 100% by mass of the rubber component is preferably 5% by mass or more, more preferably 10% by mass or more. If it is less than 5% by mass, it may be difficult to improve crack growth resistance, ozone resistance, wear resistance and the like. The content is preferably 70% by mass or less, more preferably 50% by mass or less. If it exceeds 70% by mass, the blending amount of other rubbers becomes relatively low, and it may be difficult to obtain sufficient mechanical strength.

When SBR such as non-modified SBR and modified SBR is contained, the content of SBR in 100% by mass of the rubber component is preferably 50% by mass or more, more preferably 70% by mass or more, and sufficient grip performance is obtained. 100 mass% is the most preferable from the point of being produced. If it is less than 50% by mass, the initial grip performance and the later grip performance tend to be lowered. Moreover, although the upper limit of this content is not specifically limited, When using together with NR and BR, it is preferable to set it as 90 mass% or less. In addition, when various rubber | gum, such as SBR, contains an oil component (it is an oil extended rubber | gum), content of this various rubber | gum means content of solid content (rubber component).

The bound styrene content of SBR is preferably 10% by mass or more, more preferably 20% by mass or more, further preferably 30% by mass or more, and particularly preferably 35% by mass or more. If it is less than 10 mass%, there is a tendency that a sufficient improvement effect of grip performance cannot be obtained under medium temperature (30 to 50 ° C.) and high temperature (around 100 ° C.) conditions. The amount of bound styrene of SBR is preferably 60% by mass or less, more preferably 50% by mass or less, and further preferably 45% by mass or less. When it exceeds 60% by mass, the rubber becomes hard, the contact area with the road surface is reduced, and there is a tendency that high grip performance cannot be obtained.

The rubber composition preferably contains carbon black. Thereby, a reinforcement effect and favorable grip performance are obtained.

The nitrogen adsorption specific surface area (N ₂ SA) of carbon black is preferably 15 × 10 ³ m ² / kg or more, and more preferably 25 × 10 ³ m ² / kg or more. If it is less than 15 × 10 ³ m ² / kg, a sufficient reinforcing effect may not be obtained. Further, N ₂ SA of carbon black is preferably 50 × 10 ³ m ² / kg or less, and more preferably 35 × 10 ³ m ² / kg or less. If it exceeds 50 × 10 ³ m ² / kg, the initial grip performance may be deteriorated.
In addition, the nitrogen adsorption specific surface area of carbon black is calculated | required by A method of JISK6217.

In the rubber composition, the content of carbon black is preferably 1 part by mass or more, more preferably 3 parts by mass or more with respect to 100 parts by mass of the rubber component. If it is less than 1 part by mass, there is a possibility that a sufficient reinforcing effect and an ultraviolet resistance improving effect cannot be obtained. The carbon black content is preferably 40 parts by mass or less, more preferably 30 parts by mass or less. If it exceeds 40 parts by mass, the fuel efficiency tends to deteriorate.

The rubber composition preferably contains silica. As a result, good grip performance can be obtained and a reinforcing effect can be obtained.

The nitrogen adsorption specific surface area by silica BET method is preferably 50 m ² / g or more, and more preferably 100 m ² / g or more. If it is less than 50 m ² / g, the rubber strength tends to decrease. Further, the nitrogen adsorption specific surface area by the BET method of the silica is preferably 250 meters ² / g or less, more preferably 200m ² / g. If it exceeds 250 m ² / g, the processability tends to deteriorate.
In addition, the nitrogen adsorption specific surface area by BET method of a silica can be measured by the method based on ASTM D3037-81.

In the rubber composition, the content of silica is preferably 10 parts by mass or more, more preferably 40 parts by mass or more with respect to 100 parts by mass of the rubber component. The content of the silica is preferably 150 parts by mass or less, more preferably 120 parts by mass or less, and still more preferably 100 parts by mass or less. By making it within the above range, good grip performance can be obtained and a reinforcing effect can also be obtained.

It is preferable to use a silane coupling agent together with silica. Examples of the silane coupling agent include sulfide, mercapto vinyl, amino, glycidoxy, nitro, and chloro silane coupling agents. Among them, bis (3-triethoxysilylpropyl) tetrasulfide, bis (2-triethoxysilylethyl) tetrasulfide, bis (3-triethoxysilylpropyl) disulfide, bis (2-triethoxysilylethyl) disulfide, etc. Sulfide systems are preferred, and bis (3-triethoxysilylpropyl) tetrasulfide is particularly preferred.

When the rubber composition contains a silane coupling agent, the content of the silane coupling agent is preferably 1 part by mass or more and more preferably 4 parts by mass or more with respect to 100 parts by mass of silica. The content is preferably 20 parts by mass or less, and more preferably 15 parts by mass or less. By setting it within the above range, good grip performance and reinforcement can be obtained.

The rubber composition preferably contains an anti-aging agent together with a non-petroleum wax and an α-methylstyrene resin. Thereby, ozone resistance can be improved.

As the anti-aging agent, amine-based, phenol-based, imidazole-based, quinoline-based compounds, carbamic acid metal salts, and the like can be appropriately selected and used. Of these, amines are preferable, and N- (1,3-dimethylbutyl) -N′-phenyl-p-phenylenediamine is more preferable. Here, in the said rubber composition, 0.5 mass part or more is preferable with respect to 100 mass parts of rubber components, 1 mass part or more is more preferable, and 2 mass parts or more is still more preferable. The content is preferably 8 parts by mass or less, and more preferably 5 parts by mass or less.

In addition to the above components, the rubber composition is appropriately combined with compounding agents generally used in the production of rubber compositions, such as zinc oxide, stearic acid, other waxes, vulcanizing agents, vulcanization accelerators, etc. can do.

The rubber composition is produced by a general method. That is, it can be produced by a method of kneading each component with a kneader such as a Banbury mixer, a kneader, or an open roll, and then vulcanizing. The rubber composition is suitably used as a rubber composition for producing a tread.

The pneumatic tire of the present invention is produced by a usual method using the rubber composition. That is, a rubber composition containing various additives as necessary is extruded according to the shape of a tire tread, etc. at an unvulcanized stage, and molded by a normal method on a tire molding machine, Bonding together with other tire members forms an unvulcanized tire. This unvulcanized tire can be heated and pressurized in a vulcanizer to produce a tire. Especially, it can be used conveniently as a tire for passenger cars.

The present invention will be specifically described based on examples, but the present invention is not limited to these examples.
The various chemicals used in the examples are described below.
SBR: Toughden 4350 manufactured by Asahi Kasei Corporation (bonded styrene content: 40% by mass, containing 50 parts by mass of oil with respect to 100 parts by mass of rubber solid content)
BR: BR150B manufactured by Ube Industries, Ltd. (cis 1,4 bond amount 97%, ML1 + 4 (100 ° C.) 40, 5% toluene solution viscosity at 25 ° C. 48 cps, Mw / Mn 3.3)
NR: RSS # 3
Carbon black: Niteron # 55S manufactured by Nippon Nisshin Carbon Co., Ltd. (carbon black made from coal-based heavy oil, N ₂ SA: 28 × 10 ³ m ² / kg)
α-methylstyrene resin: SA85 manufactured by Arizona Chemical Co., Ltd. (softening point: 85 ° C., Tg: 43 ° C., Mw: 1000, copolymer of α-methylstyrene and styrene)
Silica: Ultrazil VN3 manufactured by Degussa (N ₂ SA: 175 m ² / g)
Silane coupling agent: Si69 (bis (3-triethoxysilylpropyl) tetrasulfide) manufactured by Degussa
Anti-aging agent 6C: Nocrack 6C (N- (1,3-dimethylbutyl) -N-phenyl-p-phenylenediamine) manufactured by Ouchi Shinsei Chemical Co., Ltd.
Anti-aging agent 224: Nocrack 224 (2,2,4-trimethyl-1,2-dihydroquinoline polymer) manufactured by Flexis
Stearic acid: Stearic acid “paulownia” manufactured by NOF Corporation
Zinc oxide: Zinc oxide type 2 wax manufactured by Mitsui Mining & Smelting Co., Ltd. 1: Sunnock N (Ouchi Shinsei Chemical Petroleum Wax)
Wax 2: Purified candelilla wax MK-2 manufactured by Yokoseki Yushi Kogyo Co., Ltd. (constituent components: ester 22% by mass, free fatty acid 10% by mass, free alcohol 10% by mass, hydrocarbon 40% by mass, resin 18% by mass) (Softening point distribution: 42-73 ° C.) (heat flow at 40 ° C./heat flow at peak temperature × 100 = 0)
Wax 3: Purified candelilla wax MD-21 manufactured by Yokoseki Oil & Fat Co., Ltd. (components: 3% by mass of ester, 5% by mass of free fatty acid, 5% by mass of free alcohol, 82% by mass of hydrocarbon having 28 to 33 carbon atoms) (Ratio of about 31% by carbon number in the hydrocarbon), resin 5% by mass) (softening point distribution: 35 to 75 ° C.) (heat flow at 40 ° C./heat flow at peak temperature × 100 = 0. 6)
Wax 4: bleached beeswax (component: ester 66.5% by mass, free fatty acid 18% by mass, free alcohol 2.5% by mass, hydrocarbon 13% by mass) (softening point distribution: 20 to 70 ° C.) (at 40 ° C. Heat flow / heat flow at peak temperature × 100 = 9)
Wax 5: Purified beeswax BESWAXCO-100 (cosmetic specification) manufactured by Yokoseki Yushi Kogyo Co., Ltd. (constituent components: ester 70% by mass, free fatty acid 14% by mass, free alcohol 2% by mass, hydrocarbon 14% by mass) (softening point) Distribution: 0 to 75 ° C.) (heat flow at 40 ° C./heat flow of peak temperature × 100 = 13)
Aroma oil: JOMO process X140 manufactured by Japan Energy Co., Ltd.
Sulfur: Powder sulfur vulcanization accelerator DPG manufactured by Tsurumi Chemical Co., Ltd. DPG: Noxeller D manufactured by Ouchi Shinsei Chemical Industry Co., Ltd.
Vulcanization accelerator CZ: Noxeller CZ manufactured by Ouchi Shinsei Chemical Industry Co., Ltd.

For waxes 2 to 5, the contents of free alcohol, free fatty acid, resin, hydrocarbon, and ester were measured by gas chromatography.

Moreover, about softening point distribution, the heat flow (mW / g) was measured with the temperature increase rate of 5 degree-C / min from -30 degreeC to 100 degreeC using the differential scanning calorimeter (DSC).

As described above, with regard to the composition of each wax, the wax 3 had less resin component, ester component, free alcohol, and free fatty acid than the wax 2, and had a larger amount of hydrocarbon component. Further, the wax 5 has a smaller amount of free alcohol and free fatty acid and a larger amount of ester component than the wax 4, and from these results, the waxes 3 and 5 have many wax components effective for ozone resistance. Was confirmed. Furthermore, in the waxes 3 and 5, it was confirmed that the softening point distribution was shifted or expanded to the low temperature side and contained a component having a softening point of 40 ° C. or lower.

<Examples and Comparative Examples>
Using a Banbury mixer, the amount of chemicals shown in Step 1 of Table 1 was added, kneaded for 5 minutes so that the discharge temperature was about 150 ° C., and discharged. Further, sulfur and a vulcanization accelerator in the blending amounts shown in Step 2 of Table 1 were added, and kneaded for about 3 minutes using a Banbury mixer so that the discharge temperature was 100 ° C., to obtain an unvulcanized rubber composition. Obtained. The obtained unvulcanized rubber composition was vulcanized at 170 ° C. for 12 minutes to produce a vulcanized rubber sheet.

The following evaluation was performed using the obtained vulcanized rubber sheet. The results are shown in Tables 1-2.

(Grip evaluation)
"Evaluation of initial and late grip performance in lab tests"
A sample was prepared from the vulcanized rubber sheet, attached to a DF tester S type manufactured by Nippon Sangyo Co., Ltd., and repeatedly measured to show the second and tenth friction coefficients.
Initial grip performance: second coefficient of friction (sliding speed 7 km / h)
Late grip performance: 10th coefficient of friction (sliding speed 7 km / h)

It has been found that the number of continuous measurements of the DF tester is used as an index of the ease of removing tire deposits, and there is a correlation with the number of times it takes for the friction coefficient to stabilize in actual vehicle measurement. That is, the larger the second friction coefficient in the laboratory test, the better the initial grip performance in the actual vehicle, and the larger the tenth friction coefficient, the better the latter-stage grip performance.

In the formulation of Table 1 using SBR, BR, and NR, compared with Comparative Example 1 in which wax 1 (petroleum wax) and α-methylstyrene resin were used in combination, and Comparative Example 2 not including the resin, In the examples in which waxes 2 to 5 (non-petroleum wax) were used in combination, the initial grip performance and the late grip performance were excellent, and it was revealed that these performances were good even in the actual vehicle. The same effect was also seen in Table 2 using SBR and NR.
Further, the formulations of the examples were excellent in ozone resistance and discoloration resistance in outdoor exposure tests.

Claims (5)

A pneumatic tire having a tread produced using a rubber composition containing a rubber component, a non-petroleum wax, and an α-methylstyrene resin. The non-petroleum wax is a refined non-petroleum wax obtained by subjecting a non-petroleum wax to a treatment for removing at least one selected from the group consisting of free fatty acids, free alcohols and resins. Pneumatic tires. The non-petroleum wax is a refined candelilla wax containing 65% by mass or more of hydrocarbons having 28 to 33 carbon atoms and having a proportion of 31 hydrocarbons in the hydrocarbons of 60% by mass or more. The pneumatic tire according to claim 1 or 2. The pneumatic tire according to claim 1 or 2, wherein the non-petroleum wax is a purified beeswax having a free fatty acid content of 17% by mass or less and a free alcohol content of less than 2.5% by mass. The pneumatic tire according to any one of claims 1 to 4, wherein the rubber composition has a non-petroleum wax content of 0.1 to 8 parts by mass with respect to 100 parts by mass of the rubber component.