JP2013082884A - Rubber composition for tire outer layer, and pneumatic tire - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide: a rubber composition for a tire outer layer, with which excellent ozone resistance is obtained in a wide environment temperature range, and discoloration can be satisfactorily suppressed; and a pneumatic tire manufactured using the rubber composition for a tire outer layer.SOLUTION: A rubber composition for a tire outer layer includes 20-32 C normal alkanes and a phenylene diamine-based antioxidant and/or quinone-based antioxidant. The total content of the 20-32 C normal alkanes is 0.7-3.5 pts.mass, and the total content of the phenylene diamine-based antioxidant and/or quinone-based antioxidant is 1.5-3 pts.mass, with respect to 100 pts.mass of diene-based rubber components.

Description

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

In rubber compositions such as tire treads and sidewalls, wax or the like is blended in order to prevent ozone deterioration, oxidation deterioration, and thermal decomposition deterioration. The blended wax oozes out to the rubber surface and forms a film on the rubber surface to physically protect the rubber from the stimulation of ozone, oxygen, and harmful gases.

In low-temperature regions and temperate regions, wax is difficult to bloom and it is difficult to ensure ozone resistance. For this reason, when a conventionally known wax is blended in an amount capable of suppressing discoloration, ozone resistance in a low temperature environment such as a temperate winter season may be insufficient. On the other hand, in a high temperature region, since the molecular motion of rubber is active, the wax tends to bloom and it is easy to ensure the ozone resistance, but the tire surface is likely to turn white. Thus, it is difficult to suppress white discoloration while obtaining excellent ozone resistance in a wide temperature range from the cold zone to the tropics.

In particular, in the case of tread rubber compounded with silica, compared to the state during vulcanization in the mold, after vulcanization and cooling to room temperature, the tread rubber tends to shrink in volume and before the tire pressure is filled in the tread groove bottom. Or after filling, tensile strain is likely to occur. When the rubber is pulled, it becomes susceptible to ozone attack, and tread groove cracks (TGC) are likely to occur. Therefore, it is important to achieve both ozone resistance and white discoloration.

Moreover, as a method for improving ozone resistance, a method using an anti-aging agent 3PPD is known, but it is easier to bloom than 6PPD and 6QDI and can improve ozone resistance in a low temperature environment. It is difficult to ensure ozone resistance for a long period of time because it decreases quickly and rapidly.

In Patent Document 1, it is proposed that a specific wax is blended. However, there is a large room for improvement in ozone resistance in a low temperature region and a temperate region winter season, while obtaining excellent ozone resistance in a wide temperature range, There is a demand for technology that can suppress discoloration.

JP 2011-116847 A

The present invention solves the above problems, and provides a rubber composition for a tire outer layer capable of satisfactorily suppressing discoloration while providing excellent ozone resistance in a wide environmental temperature range, and a pneumatic tire using the same. With the goal.

The present invention includes each normal alkane having 20 to 32 carbon atoms, a phenylenediamine-based antioxidant and / or a quinone-based antioxidant, and the carbon number of 20 to 32 with respect to 100 parts by mass of the diene rubber component. For the tire outer layer, the total content of each normal alkane is 0.7 to 3.5 parts by mass, and the total content of the phenylenediamine-based antioxidant and the quinone-based antioxidant is 1.5 to 3 parts by mass. The present invention relates to a rubber composition.

The tire outer layer rubber composition preferably contains a total of 0.1 parts by mass or less of each normal alkane having 48 or more carbon atoms with respect to 100 parts by mass of the diene rubber component.
The total content of each normal alkane having 20 to 32 carbon atoms is preferably 0.9 to 2.4 parts by mass with respect to 100 parts by mass of the diene rubber component. It is preferable that 15 parts by mass or less of process oil is included with respect to 100 parts by mass of the diene rubber component.

The rubber composition for a tire outer layer is preferably used as at least one selected from the group consisting of a tread, a sidewall, a wing, and a clinch apex.
The present invention also relates to a pneumatic tire produced using the rubber composition.

According to the present invention, each normal alkane having 20 to 32 carbon atoms and a phenylenediamine-based anti-aging agent and / or a quinone-based anti-aging agent, the total content of each normal alkane having 20 to 32 carbon atoms is Since it is a rubber composition for a tire outer layer having a specific amount and a total content of the phenylenediamine-based anti-aging agent and the quinone-based anti-aging agent, the ozone resistance is excellent in a wide environmental temperature range. As a result, discoloration can be satisfactorily suppressed.

It is a figure which shows carbon number distribution of wax.

The rubber composition for a tire outer layer according to the present invention includes each normal alkane having 20 to 32 carbon atoms, a phenylenediamine-based antioxidant and / or a quinone-based antioxidant, and has 20 to 20 carbon atoms relative to the diene rubber component. The total content of 32 normal alkanes is a specific amount, and the total content of the phenylenediamine-based anti-aging agent and the quinone-based anti-aging agent is also a specific amount.

The rubber composition of the present invention is used for tire outer layer members such as treads, sidewalls, wings, and clinch apex.

Examples of the diene rubber component include natural rubber (NR), highly purified natural rubber (Highly purified NR), epoxidized natural rubber (ENR), butadiene rubber (BR), styrene butadiene rubber (SBR), isoprene rubber ( IR), butyl rubber (IIR), acrylonitrile butadiene rubber (NBR), chloroprene rubber (CR), styrene isoprene butadiene rubber (SIBR), styrene isoprene rubber, isoprene butadiene rubber and the like, and these may be used alone, Two or more kinds may be used in combination.
Especially, when applying to a tread, it is preferable to use SBR and BR from the reason that grip performance and breaking strength are obtained satisfactorily. When applied to sidewalls and clinch apex, it is preferable to use BR from the reason that it is excellent in isoprene-based rubbers such as NR and IR, and crack growth property, because the breaking strength can be obtained satisfactorily.

The SBR is not particularly limited, and for example, those modified with a conventionally known modifier (modified SBR) can be suitably used.

The amount of bound styrene of SBR is preferably 10% by mass or more, more preferably 20% by mass or more from the viewpoint of improving grip performance. On the other hand, it is preferably 45% by mass or less, more preferably 40% by mass or less, from the viewpoint of improving wear resistance.
In the present invention, the styrene content of SBR is calculated by H ¹ -NMR measurement.

When the rubber composition of the present invention is applied to a tread, the content of SBR in 100% by mass of the diene rubber component is preferably 20% by mass or more, more preferably 60% by mass or more. If it is less than 20% by mass, the grip performance may not be sufficiently obtained. The content is preferably 90% by mass or less, more preferably 80% by mass or less. If it exceeds 90% by mass, sufficient wear resistance may not be obtained.

Although it does not specifically limit as BR, BR (high cis BR) whose cis content of a double bond part is 95 mol% or more is preferable.

When the rubber composition of the present invention is applied to a tread, the BR content in 100% by mass of the diene rubber component is preferably 10% by mass or more, more preferably 20% by mass or more. If it is less than 10% by mass, sufficient wear resistance may not be obtained. The content is preferably 80% by mass or less, more preferably 40% by mass or less. If it exceeds 80% by mass, sufficient grip performance may not be obtained.

When the rubber composition of the present invention is applied to sidewalls and clinch apex, the BR content in 100% by mass of the diene rubber component is preferably 10% by mass or more, more preferably 30% by mass or more. If it is less than 10% by mass, the crack growth property and the reversion property tend to be deteriorated. The content is preferably 80% by mass or less, more preferably 50% by mass or less. If it exceeds 80 mass%, there is a possibility that sufficient elongation at break and tearability may not be obtained.

The NR is not particularly limited, and for example, those commonly used in the tire industry such as SIR20, RSS # 3, TSR20, ENR25 can be used. Moreover, it does not specifically limit as IR, A general thing can be used in the tire industry.

When the rubber composition of the present invention is applied to sidewalls and clinch apex, the content of isoprene rubber in 100% by mass of the diene rubber component is preferably 20% by mass or more, more preferably 50% by mass or more. is there. If it is less than 20% by mass, the mechanical strength may not be sufficiently obtained. The content is preferably 90% by mass or less, more preferably 70% by mass or less. If it exceeds 90% by mass, crack growth and the like may be deteriorated.

The rubber composition of the present invention contains each normal alkane having 20 to 32 carbon atoms. Thereby, ozone resistance in a temperature range of about 0 to 20 ° C. can be obtained satisfactorily.
The total content of each normal alkane having 20 to 32 carbon atoms is 0.7 parts by mass or more, preferably 0.9 parts by mass or more with respect to 100 parts by mass of the diene rubber component. If it is less than 0.7 parts by mass, sufficient ozone resistance may not be obtained in a temperature range of 20 ° C. or lower. Further, the total content is 3.5 parts by mass or less, preferably 2.4 parts by mass or less. When it exceeds 3.5 parts by mass, the discoloration resistance and the adhesiveness during molding may be lowered.

The rubber composition of the present invention usually contains each normal alkane having 33 to 44 carbon atoms. Thereby, ozone resistance in the temperature range of about 40-50 degreeC is acquired favorably.
The total content of each normal alkane having 33 to 44 carbon atoms is preferably 0.45 parts by mass or more, more preferably 0.5 parts by mass or more with respect to 100 parts by mass of the diene rubber component. If the amount is less than 0.45 parts by mass, ozone resistance in a temperature range of about 40 to 50 ° C may not be sufficiently obtained. The total content is preferably 1.7 parts by mass or less, more preferably 1.6 parts by mass or less. When it exceeds 1.7 parts by mass, the amount of bloom precipitation of the normal alkane having 33 to 44 carbon atoms is large in the temperature range of about 40 to 50 ° C., and the color tends to be white.

The rubber composition of the present invention usually contains each normal alkane having 45 to 47 carbon atoms for the convenience of the purification and production process of wax described later.
The total content of each normal alkane having 45 to 47 carbon atoms is preferably 0.01 parts by mass or more, more preferably 0.05 parts by mass or more with respect to 100 parts by mass of the diene rubber component. If it is less than 0.01 parts by mass, the crack resistance in the temperature range of about 60 ° C. tends to be slightly deteriorated. The total content is preferably 1 part by mass or less, more preferably 0.15 part by mass or less. When the amount exceeds 1 part by mass, the discoloration resistance (white discoloration) in the temperature range of about 60 ° C. tends to deteriorate.

The rubber composition of the present invention preferably contains 0.1 part by mass or less of a normal alkane having 48 or more carbon atoms with respect to 100 parts by mass of the diene rubber component. Thereby, the discoloration resistance (white discoloration) in a temperature range of 60 ° C. or higher can be obtained satisfactorily. The content of the normal alkane having 48 or more carbon atoms is more preferably 0.08 parts by mass or less with respect to 100 parts by mass of the diene rubber component. If it exceeds 0.1 parts by mass, there is a risk of white discoloration.

In the present invention, the total content of each normal alkane having 25 to 27 carbon atoms is preferably a specific amount. The total content of each normal alkane having 25 to 27 carbon atoms is preferably 0.2 parts by mass or more, more preferably 0.5 parts by mass or more with respect to 100 parts by mass of the diene rubber component. If it is less than 0.2 parts by mass, sufficient ozone resistance may not be obtained in a temperature range of about 10 ° C. The total content is preferably 2 parts by mass or less, more preferably 1.8 parts by mass or less. If it exceeds 2 parts by mass, the color tends to change.

In order to set the total content of each normal alkane having 20 to 32 carbon atoms to a specific amount, for example, a wax containing each normal alkane having 20 to 32 carbon atoms may be blended.

The wax containing each normal alkane having 20 to 32 carbon atoms is not particularly limited, and a wax containing each normal alkane having 20 to 55 carbon atoms can be used. Among them, because the excellent ozone resistance can be obtained, those having a normal alkane content of 70% by mass or more in 100% by mass of the wax can be suitably used, and those having a mass of 80% by mass or more are more suitably used. it can.

In 100% by mass of the wax, the total content of each normal alkane having 20 to 32 carbon atoms is preferably 30% by mass or more, more preferably 35% by mass or more, and still more preferably 40% by mass or more. If it is less than 30% by mass, ozone resistance in a low temperature range of about 0 to 20 ° C. may not be sufficiently obtained. The content is preferably 90% by mass or less, and more preferably 65% by mass or less. When it exceeds 90 mass%, it tends to be easily white-discolored in a low temperature range of about 0 to 20 ° C.

In 100% by mass of the wax, the content of each normal alkane having 25 to 27 carbon atoms is preferably 4.1% by mass or more, and more preferably 5% by mass or more. If the amount is less than 4.1 mass, the effect of improving ozone resistance in a temperature range of about 10 ° C may not be sufficiently obtained. Although the upper limit of this content is not specifically limited, 50 mass% or less is preferable and 45 mass% or less is more preferable. When it exceeds 50 mass%, it tends to be white-discolored in a temperature range of about 10 ° C. Moreover, there exists a possibility that ozone resistance in the temperature range of about 30-50 degreeC may not be obtained sufficiently.

The wax containing each normal alkane having the carbon number distribution as described above can be prepared, for example, by appropriately mixing known waxes.

In the present invention, a phenylenediamine-based antioxidant and / or a quinone-based antioxidant is used. By blending a specific amount of each of these specific antioxidants and normal alkanes having a specific carbon number, excellent ozone resistance can be obtained in a wide temperature range, and discoloration can be well suppressed. On the other hand, with other anti-aging agents such as TMQ, the color of the anti-aging agent itself is thin and discoloration does not become a big problem, but there is a tendency that improvement effects such as ozone resistance cannot be sufficiently obtained.

Examples of the phenylenediamine antioxidant include N- (1,3-dimethylbutyl) -N′-phenyl-p-phenylenediamine, N-isopropyl-N′-phenyl-p-phenylenediamine, and N, N′-diphenyl. -P-phenylenediamine, N, N'-di-2-naphthyl-p-phenylenediamine, N-cyclohexyl-N'-phenyl-p-phenylenediamine, N, N'-bis (1-methylheptyl) -p -Phenylenediamine, N, N'-bis (1,4-dimethylpentyl) -p-phenylenediamine, N, N'-bis (1-ethyl-3-methylpentyl) -p-phenylenediamine, N-4- Methyl-2-pentyl-N′-phenyl-p-phenylenediamine, N, N′-diaryl-p-phenylenediamine, hindered diary -p- phenylenediamine, phenyl hexyl -p- phenylenediamine, and the like phenyloctyl -p- phenylenediamine. Of these, N- (1,3-dimethylbutyl) -N′-phenyl-p-phenylenediamine is preferable.

Examples of the quinone antioxidant include benzoquinone, hydroquinone, catechol, quinone diimine, quinomethane, and quinodimethane antioxidant, and quinone diimine antioxidant is preferable.

Examples of the quinonediimine antioxidant include N-isopropyl-N′-phenyl-p-quinonediimine, N- (1,3-dimethylbutyl) -N′-phenylquinonediimine, and N, N′-diphenyl-p-quinonediimine. N-cyclohexyl-N′-phenyl-p-quinone diimine, Nn hexyl-N′-phenyl-p-quinone diimine, N, N′-dioctyl-p-quinone diimine, and the like. Of these, N- (1,3-dimethylbutyl) -N′-phenylquinonediimine (6QDI) is preferable.

The total content of the phenylenediamine anti-aging agent and the quinone anti-aging agent is 1.5 parts by mass or more, preferably 2 parts by mass or more with respect to 100 parts by mass of the diene rubber component. If the amount is less than 1.5 parts by mass, sufficient ozone resistance may not be obtained. Moreover, this content is 3 mass parts or less, Preferably it is 2.8 mass parts or less. If it exceeds 3 parts by mass, the color tends to change (brown color).

The rubber composition of the present invention preferably contains carbon black. Thereby, the reinforcing effect and the ultraviolet ray preventing effect are obtained, and the effect of the present invention is obtained well.

When the rubber composition of the present invention is applied to a tread, the carbon black content is preferably 0.2 to 20 parts by mass, more preferably 2 to 20 parts by mass with respect to 100 parts by mass of the diene rubber component. is there. Within the above range, the reinforcing effect and the ultraviolet ray preventing effect can be obtained, and the effect of the present invention can be obtained well.

Moreover, when applying the rubber composition of this invention to a side wall and a clinch apex, content of carbon black becomes like this. Preferably it is 10-50 mass parts with respect to 100 mass parts of diene rubber components. Within the above range, a reinforcing effect can be obtained, and the effect of the present invention can be obtained satisfactorily.

The rubber composition of the present invention preferably contains silica. Thereby, favorable low fuel consumption is obtained.

The silica is not particularly limited, and for example, dry method silica (anhydrous silica), wet method silica (hydrous silica), and the like can be used. Wet silica (hydrous silica) is preferred because of the large number of silanol groups.

When applying the rubber composition of this invention to a tread, content of a silica becomes like this. Preferably it is 20 mass parts or more with respect to 100 mass parts of diene rubber components, More preferably, it is 60 mass parts or more. The content is preferably 120 parts by mass or less, more preferably 80 parts by mass or less. When the content is within the above range, good fuel economy and processability can be obtained.

When the rubber composition of the present invention is applied to sidewalls and clinch apex, the lower limit of the silica content is not particularly limited, but is preferably 0.1 parts by mass or more with respect to 100 parts by mass of the diene rubber component. is there. The content is preferably 30 parts by mass or less, more preferably 20 parts by mass or less. When the content is within the above range, good elongation at break, low fuel consumption and processability can be obtained.
In the present invention, when silica is used, it is preferable to use a silane coupling agent.

From the viewpoint of TGC and the like, the rubber composition of the present invention can be suitably used particularly as a silica-containing rubber composition. For example, when the rubber composition is applied to a tread, the total amount of silica and carbon black is 100% by mass. The silica content is preferably 60% by mass or more, more preferably 65% by mass or more, and still more preferably 70% by mass or more. In addition, an upper limit is not specifically limited, 100 mass% may be sufficient.

When the rubber composition of the present invention is applied to sidewalls and clinch apex, the content of silica in 100% by mass of silica and carbon black is preferably 5% by mass or more, more preferably 10% by mass. That's it. Although an upper limit is not specifically limited, Preferably it is 40 mass% or less, More preferably, it is 20 mass% or less.

In the present invention, process oil may be blended. As the process oil, for example, a paraffin process oil, an aroma process oil, a naphthenic process oil, or the like can be used.

The content of the process oil is preferably 15 parts by mass or less with respect to 100 parts by mass of the diene rubber component. When it exceeds 15 parts by mass, the color tends to change easily. Although the minimum of this content is not specifically limited, Preferably it is 2 mass parts or more, More preferably, it is 5 mass parts or more. If it is less than 2 mass parts, workability may be deteriorated.

In addition to the above components, the rubber composition of the present invention is polymerized with a compounding agent generally used in the production of rubber compositions, such as C5 petroleum resin, coumarone indene resin, α-methylstyrene and / or styrene. Aromatic vinyl polymers, stearic acid, zinc oxide, vulcanizing agents, vulcanization accelerators and the like obtained as described above can be appropriately blended.

As a method for producing the rubber composition of the present invention, known methods can be used. For example, the above components are kneaded using a rubber kneader such as an open roll or a Banbury mixer, and then vulcanized. Can be manufactured.

The rubber composition of the present invention can be used without particular limitation as long as it is an outer layer member of a tire, but as described above, it can be suitably used for treads, sidewalls, wings, and clinch apex.

The pneumatic tire of the present invention can be produced by a usual method using the rubber composition. That is, the rubber composition is extruded in accordance with the shape of each outer layer member (tread, sidewall, wing, clinch apex, etc.) of the tire at an unvulcanized stage, and is subjected to a normal method on a tire molding machine. And then bonded together with other tire members to form an unvulcanized tire. This unvulcanized tire can be heated and pressurized in a vulcanizer to produce a tire.

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

Hereinafter, various chemicals used in Examples and Comparative Examples will be described.
High cis BR (CB25): BUNA-CB25 manufactured by LANXESS (BR synthesized using Nd-based catalyst, cis content: 96%)
Modified SSBR (HPR355): HPR355 manufactured by JSR Corporation (modified S-SBR, styrene content: 27 mass%, vinyl content 55 mass%)
TSR20: NR (TSR20)
Carbon Black (N220): Show Black N220 (N ₂ SA: 120 m ² / g, DBP oil absorption: 115 ml / 100 g) manufactured by Cabot Japan
Carbon Black (N550): Show Black N550 manufactured by Cabot Japan Co., Ltd. (N ₂ SA: 42 m ² / g, DBP oil absorption: 115 ml / 100 g)
Silica: Ultrasil VN3 manufactured by Degussa (N ₂ SA: 175 m ² / g)
Coumarone indene resin: NOVARES C10 (coumarone indene resin, softening point: 5 to 15 ° C.) manufactured by Rutgers Chemicals
C5 petroleum resin: Marukaretsu T-100AS manufactured by Maruzen Petrochemical Co., Ltd. (C5 petroleum resin: aliphatic petroleum resin mainly composed of olefins and diolefins in C5 fraction obtained by naphtha cracking) ( (Softening point: 102 ° C)
Aromatic vinyl polymer (SA85): SYLVARES SA85 (copolymer of α-methylstyrene and styrene, softening point: 85 ° C., Mw: 1000) manufactured by Arizona chemical
Process oil: Vivatec 500 (TDAE) manufactured by H & R
Stearic acid: Stearic acid “椿” manufactured by NOF Corporation
Zinc flower: Toho Zinc Co., Ltd.
Silane coupling agent: Si75 (bis (3-triethoxysilylpropyl) disulfide) manufactured by Degussa
Powder sulfur containing 5% oil: HK-200-5 (oil content 5%) manufactured by Hosoi Chemical Co., Ltd.
10% oil-containing insoluble sulfur: Nippon Seimitsu Kogyo Co., Ltd. Seimisulfur (60% insoluble due to carbon disulfide, 10% oil)
Vulcanization accelerator (TBBS): Noxeller NS (N-tert-butyl-2-benzothiazolylsulfenamide) manufactured by Ouchi Shinsei Chemical Industry Co., Ltd.
Vulcanization accelerator (DPG): Noxeller D (N, N'-diphenylguanidine) manufactured by Ouchi Shinsei Chemical Co., Ltd.
Wax 1: Prototype 1 (normal alkane content: average 85% by mass)
Wax 2: Prototype 2 (normal alkane content: average 87% by mass)
Wax 3: Prototype 3 (normal alkane content: average 81% by mass)
Wax 4: Sorbitan monostearate (Glycomul S ^{™ from} Lonza Chemical Company)
6PPD: Antigen 6C (N- (1,3-dimethylbutyl) -N′-phenyl-p-phenylenediamine) manufactured by Sumitomo Chemical Co., Ltd.
6QDI: 6QDI (N- (1,3-dimethylbutyl) -N′-phenylquinonediimine) manufactured by Flexis
TMQ: Nocrack 224 (2,2,4-trimethyl-1,2-dihydroquinoline polymer) manufactured by Ouchi Shinsei Chemical Co., Ltd.

The carbon number distribution of the wax was measured by the following method. The results are shown in FIG.

Using a capillary GC as a measuring device and a capillary column coated with aluminum as a column, measurement was performed under conditions of carrier gas helium, a flow rate of 4 ml / min, a column temperature of 180 to 390 ° C., and a heating rate of 15 ° C./min.

(Examples and Comparative Examples)
According to the formulation shown in the upper part of Tables 1 to 3, chemicals other than sulfur and a vulcanization accelerator were kneaded using a 1.7L Banbury mixer manufactured by Kobe Steel Co., Ltd. Next, using an open roll, sulfur and a vulcanization accelerator were added to the kneaded product and kneaded to obtain an unvulcanized rubber composition.
By using the obtained unvulcanized rubber composition, members to be a tread portion, a sidewall portion and a clinch apex portion were produced to produce a raw tire, which was vulcanized at 170 ° C. to test tire (205 / 65R15). The performance of the obtained test tire was evaluated by the following test.

(Crack test)
A high-temperature area has been subjected to a road test in the Middle East and United Arab Emirates for about one year (including summer), and a sub-cold area has been subjected to a road test in Hokkaido for about one year (including winter). evaluated. The larger the number, the better the crack resistance performance.

(Standard)
1: Cracks or cuts of 3 mm or more are observed.
Deep cracks of 2: 1 mm or more and less than 3 mm are observed.
Deep and relatively large cracks less than 3: 1 mm are seen.
4: The naked eye can finally confirm cracks or cuts.
5: Although it cannot be confirmed with the naked eye, cracks or cuts can be confirmed with a magnifier (10x).

(Discoloration test)
Outdoor: Brown discoloration evaluation In Kobe, tires are left in the place exposed to the sun for 6 months (winter to summer), and a ^* and b ^* are measured using a color difference meter. The evaluation was divided into five stages according to the criteria of The higher the number, the less brown discoloration.

(Standard)
1: − (a ^* + b ^* ) × 10 ≦ −30
2: −30 <− (a ^* + b ^* ) × 10 ≦ −20
3: −20 <− (a ^* + b ^* ) × 10 ≦ −10
4: −10 <− (a ^* + b ^* ) × 10 ≦ 0
5:-(a ^* + b ^* ) × 10> 0
Indoors: White discoloration evaluation In Kobe, tires are left in an indoor warehouse for 6 months (winter-summer), L ^* is measured using a color difference meter, and five levels are determined according to the following criteria. It was divided and evaluated. The greater the number, the less white discoloration.

(Standard)
1: 100-L ^* ≦ 60
2: 60 <100-L ^* ≦ 65
3: 65 <100-L ^* ≦ 70
4: 70 <100-L ^* ≦ 75
5: 100-L ^* > 75

In the examples in which specific amounts of each normal alkane having 20 to 32 carbon atoms and a phenylenediamine-based anti-aging agent and / or a quinone-based anti-aging agent were blended, excellent ozone resistance was obtained in a wide temperature range. Moreover, discoloration was able to be suppressed favorably.
In particular, in Comparative Examples 5 to 8, 10, and 14 containing a large amount of a phenylenediamine-based anti-aging agent and a quinone-based anti-aging agent, brown discoloration occurred. In addition, when the compounding quantity of these anti-aging agents was reduced, there existed a tendency for ozone resistance to fall (Examples 9-11, 22).

Claims (6)

Each normal alkane having 20 to 32 carbon atoms, a phenylenediamine-based antioxidant and / or a quinone-based antioxidant,
The total content of each normal alkane having 20 to 32 carbon atoms is 0.7 to 3.5 parts by mass with respect to 100 parts by mass of the diene rubber component, the phenylenediamine antioxidant and the quinone antioxidant. The tire outer layer rubber composition having a total content of 1.5 to 3 parts by mass. The rubber composition for a tire outer layer according to claim 1, comprising 0.1 part by mass or less of a normal alkane having 48 or more carbon atoms with respect to 100 parts by mass of the diene rubber component. The rubber composition for a tire outer layer according to claim 1 or 2, wherein a total content of each normal alkane having 20 to 32 carbon atoms is 0.9 to 2.4 parts by mass with respect to 100 parts by mass of the diene rubber component. object. The rubber composition for a tire outer layer according to any one of claims 1 to 3, comprising 15 parts by mass or less of process oil with respect to 100 parts by mass of the diene rubber component. The rubber composition for a tire outer layer according to any one of claims 1 to 4, which is used as at least one selected from the group consisting of a tread, a sidewall, a wing and a clinch apex. The pneumatic tire produced using the rubber composition in any one of Claims 1-5.

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