JP5747015B2 - Sidewall rubber composition and pneumatic tire - Google Patents

Description

The present invention relates to a rubber composition for a sidewall and a pneumatic tire having a sidewall manufactured using the rubber composition.

Conventionally, the sidewall of a pneumatic tire has been composed of a rubber composition containing a highly unsaturated rubber such as natural rubber or isoprene rubber having a high double bond content in the main chain. These double bonds in high-unsaturated rubber molecules react with ozone and depolymerize, so if you leave the tire in a place with strong ultraviolet rays or an atmosphere with high ozone concentration in the air, Cracks called so-called ozone cracks occur. In order to prevent this, the rubber composition for sidewalls is blended with an anti-ozone cracking agent such as an amine anti-aging agent or wax.

However, in a pneumatic tire having a sidewall composed of a rubber composition to which such an anti-ozone cracking agent is added, the anti-ozone cracking agent blooms on the surface of the sidewall during storage, as if dust adhered. It looks like this. Furthermore, since the amine-based anti-aging agent has the property of turning brown when exposed to air or sunlight, it has shifted to the surface of the side wall by bloom to change the side wall, thereby reducing the commercial value. On the other hand, when the amount of the anti-aging material is reduced in order to improve discoloration, cracks are quickly generated and durability is lowered.

Since ethylene-propylene-diene copolymer (EPDM) has few double bonds in the molecule and is not easily attacked by oxygen, ozone, etc., occurrence of cracks on the outer surface of the tire is caused by using EPDM for the sidewall. It is possible to provide a pneumatic tire that prevents the deterioration of the appearance due to discoloration and the like (see, for example, Patent Document 1).

However, when blended with EPDM and diene rubber, the reinforcing filler carbon black and silica are preferentially dispersed in the diene rubber, and the reinforcement at the EPDM portion is weakened. In addition, since the reinforcing filler gathers in the diene rubber portion, heat is likely to be generated, that is, tan δ increases, resulting in a deterioration in fuel efficiency (rolling resistance). Therefore, it is required to improve the weather resistance, the bending crack growth resistance and the low fuel consumption in a balanced manner.

JP 2002-284927 A

The present invention solves the above problems and provides a rubber composition for a sidewall capable of improving the weather resistance, flex crack growth resistance and fuel efficiency in a balanced manner, and a pneumatic tire having a sidewall produced using the rubber composition. For the purpose.

（式中、Ｒ^１、Ｒ^２は、同一又は異なって、水素原子、炭素数１〜２０のアルキル基、炭素数１〜２０のアルケニル基又は炭素数１〜２０のアルキニル基である。Ｍ^ｒ＋は金属イオンを示し、ｒはその価数を表す。） The present invention contains a rubber component, carbon black having a nitrogen adsorption specific surface area of 30 to 120 m ² / g, and a compound represented by the following formula (I), and the diene rubber in 100% by mass of the rubber component The content of the carbon black is 60 to 75% by mass, the content of the low-unsaturation copolymer is 25 to 40% by mass, and the content of the carbon black with respect to 100 parts by mass of the rubber component is 20 to 60 parts by mass. In addition, the present invention relates to a rubber composition for a sidewall, wherein the content of the compound represented by the following formula (I) with respect to 100 parts by mass of the carbon black is 0.5 to 20 parts by mass.

^(Wherein, R 1, ^{R 2} are the same or different, a hydrogen atom, an alkyl group having 1 to 20 carbon atoms, an alkenyl group or an alkynyl group having 1 to 20 carbon atoms having 1 to 20 carbon atoms ^{.M r +} Represents a metal ion, and r represents its valence.)

The copolymer is preferably an ethylene-propylene-diene copolymer (EPDM) and / or a brominated copolymer of isobutylene and p-methylstyrene.

The compound represented by the formula (I) is preferably a compound represented by the following formula (I-1), (I-2) or (I-3).

The metal ion is preferably sodium ion, potassium ion or lithium ion.

The present invention also relates to a pneumatic tire having a sidewall produced using the rubber composition.

According to the present invention, since the rubber composition for a sidewall contains a specific rubber component, a specific carbon black, and a compound represented by the formula (I) in predetermined amounts, the weather resistance, the flex crack resistance It is possible to provide a pneumatic tire with improved growth and low fuel consumption in a well-balanced manner.

The rubber composition of the present invention contains a specific rubber component, a specific carbon black, and a compound represented by the formula (I). The compound represented by the formula (I) can be bonded to carbon black by the reaction of the terminal nitrogen functional group with a functional group such as a carboxyl group present on the surface of the carbon black, and the carbon-carbon double The bonding portion can be bonded to the polymer by a reaction with a polymer radical or a reaction involving sulfur crosslinking. Therefore, the dispersibility of carbon black can be improved and the good dispersion state can be maintained even during use. Further, since the polymer restrains the carbon black through the compound represented by the formula (I), the exothermic property can be suppressed. By compounding the compound represented by the formula (I) having these functions with a specific carbon black and a rubber composition containing a specific rubber component, the fuel efficiency of the rubber composition is improved. Good weather resistance and flex crack growth resistance are also obtained.

The rubber composition of the present invention contains a diene rubber as a rubber component. Examples of the diene rubber include natural rubber (NR), isoprene rubber (IR), butadiene rubber (BR), styrene butadiene rubber (SBR), styrene isoprene butadiene rubber (SIBR), chloroprene rubber (CR), and acrylonitrile butadiene rubber. (NBR) etc. are mentioned, Preferably NR, IR, BR, More preferably, it is NR, BR. NR has a large molecular weight, and the polymer chain is broken during kneading to generate radicals. When the generated radical is captured by the compound represented by the formula (I), the polymer chain and the compound represented by the formula (I) can be efficiently bonded. Moreover, favorable bending crack growth resistance is obtained by blending BR.

The NR is not particularly limited, and for example, those commonly used in the tire industry such as SIR20, RSS # 3, TSR20, and the like can be used.
The BR is not particularly limited, and, for example, high cis content BR (high cis BR) such as BR130B and BR150B manufactured by Ube Industries, Ltd., and modified BR can be preferably used.

The content of NR in 100% by mass of the rubber component is preferably 20% by mass or more, more preferably 25% by mass or more. If it is less than 20% by mass, the fuel economy may not be sufficiently improved. The content is preferably 50% by mass or less, more preferably 45% by mass or less. If it exceeds 50% by mass, the flex crack growth resistance may be reduced.

The content of BR in 100% by mass of the rubber component is preferably 20% by mass or more, more preferably 25% by mass or more. If it is less than 20% by mass, the resistance to flex crack growth may be lowered. The content is preferably 50% by mass or less, more preferably 45% by mass or less. If it exceeds 50% by mass, fuel efficiency may be deteriorated.

The content (total content) of the diene rubber in 100% by mass of the rubber component is 60% by mass or more, preferably 65% by mass or more. If it is less than 60% by mass, the fuel economy may not be sufficiently improved. The content is 75% by mass or less, preferably 72% by mass or less. If it exceeds 75% by mass, the content of the low-unsaturation copolymer is decreased, and sufficient weather resistance may not be ensured.

The rubber composition of the present invention contains a low-unsaturated copolymer in addition to the diene rubber as a rubber component. Since a copolymer with a low degree of unsaturation does not have many double bonds in the molecule, good weather resistance can be obtained by blending.

Examples of the low unsaturated copolymer include ethylene-propylene rubber (EPM) and ethylene-propylene-diene rubber (EPDM). A brominated copolymer of isobutylene and p-methylstyrene can also be used. EPDM, a brominated copolymer of isobutylene and p-methylstyrene is preferred, and a combination thereof is more preferred.

The degree of unsaturation of EPDM was evaluated using the iodine value. The iodine value of EPDM is preferably 350 or less, more preferably 100 or less, and still more preferably 30 or less. Further, the degree of unsaturation of the brominated copolymer of isobutylene and p-methylstyrene was determined by 1H-NMR. The degree of unsaturation of the brominated copolymer of isobutylene and p-methylstyrene is preferably 0.6 mol% to 2.5 mol%.

EPDM is obtained by introducing a small amount of a third diene component into EPM which is a copolymer of ethylene and propylene. Examples of the third diene component include non-conjugated dienes having 5 to 20 carbon atoms. Examples of the non-conjugated dienes include 1,4-pentadiene, 1,4-hexadiene, 1,5-hexadiene, 2,5- Linear dienes such as dimethyl-1,5-hexadiene and 1,4-octadiene, cyclic dienes such as 1,4-cyclohexadiene, cyclooctadiene and dicyclopentadiene, 5-ethylidene-2-norbornene, 5-butylidene- Examples thereof include alkenyl norbornene such as 2-norbornene, 2-methallyl-5-norbornene and 2-isopropenyl-5-norbornene. Of these, alkenyl norbornene is preferable, and 5-ethylidene-2-norbornene is more preferable. The content of the third diene component is preferably 6 to 12% by mass.

The brominated copolymer of isobutylene and p-methylstyrene has no double bond in the molecule, so it has excellent weather resistance like butyl rubber, and since it has a styrene unit, it has a diene rubber compared to butyl rubber. Has the advantage of high compatibility. The brominated copolymer has an isobutylene unit amount / p-methylstyrene unit amount of 90/10 to 98/2 in terms of mass ratio and a bromine content of 0.5 to 5 mass in terms of excellent co-crosslinking properties. % Is preferred. Examples of commercially available brominated copolymers include EXXPRO 90-10 manufactured by ExxonMobil.

The content of EPDM 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, the weather resistance may not be improved. The content is preferably 30% by mass or less, more preferably 25% by mass or less. When it exceeds 30 mass%, there exists a possibility that low-fuel-consumption property may deteriorate.

The content of the brominated copolymer of isobutylene and p-methylstyrene in 100% by mass of the rubber component is preferably 5% by mass or more, more preferably 10% by mass or more. There exists a possibility that a weather resistance may become inadequate that it is less than 5 mass%. The content is preferably 30% by mass or less, more preferably 25% by mass or less. If it exceeds 30% by mass, the adhesion to other rubber layers may be inferior and the durability may deteriorate.

The content (total content) of the low-unsaturation copolymer in 100% by mass of the rubber component is 25% by mass or more, preferably 27% by mass or more, more preferably 30% by mass or more. If it is less than 25% by mass, sufficient weather resistance may not be obtained. The content is 40% by mass or less, preferably 38% by mass or less, more preferably 35% by mass or less. If it exceeds 40% by mass, the content of the diene rubber is reduced, and there is a possibility that sufficient fuel efficiency cannot be obtained.

The rubber composition of the present invention contains carbon black having a specific nitrogen adsorption specific surface area.

The nitrogen adsorption specific surface area (N ₂ SA) of carbon black is 30 m ² / g or more, preferably 35 m ² / g or more, more preferably 40 m ² / g or more. If it is less than 30 m < ² > / g, there exists a possibility that sufficient bending crack growth resistance cannot be ensured. The N ₂ SA is 120 m ² / g or less, preferably 100 m ² / g or less, more preferably 80 m ² / g or less. If it exceeds 120 m ² / g, the fuel economy may not be sufficiently improved.

Carbon black dibutyl phthalate (DBP) oil absorption is preferably 40 cm ^3/100 g or more, more preferably 70cm ^3/100 g or more. Is less than 40 cm ^3/100 g, it may not be possible to secure sufficient flex crack growth resistance. Intake oil amount is preferably 180cm ^3/100 g or less, and more preferably not more than 160cm ³ / 100g. Exceeds 180cm ³ / 100g, it may be impossible to ensure a minimum breaking elongation.

The pH of carbon black is preferably 7.9 or less, more preferably 7.8 or less, still more preferably 7.7 or less, and particularly preferably 7.6 or less. If it exceeds 7.9, the amount of acidic functional groups of carbon black is small, so the reactivity (interaction) with the compound represented by formula (I) is small, and there is a possibility that fuel economy and the like cannot be improved sufficiently. is there. Although the minimum of this pH is not specifically limited, Preferably it is 3.0 or more, More preferably, it is 3.5 or more. If it is less than 3.0, the pH of the rubber composition is lowered, whereby the activity of the vulcanizing agent is lowered and the crosslinking efficiency tends to be lowered.

The volatile content of carbon black is preferably 0.8% by mass or more, more preferably 0.9% by mass or more, and further preferably 1.0% by mass or more. If it is less than 0.8% by mass, the reactivity (interaction) with the compound represented by the formula (I) becomes small, and there is a possibility that the fuel efficiency cannot be sufficiently improved. Although the upper limit of this volatile matter is not specifically limited, Preferably it is 3.5 mass% or less, More preferably, it is 3.0 mass% or less. If it exceeds 3.5 mass%, it is necessary to volatilize most of the volatile components in the vulcanization process and continue vulcanization until porosity does not occur. There is a tendency to get worse.

In this specification, the DBP oil absorption, pH, and volatile content of carbon black are values measured by JIS K6221 (1982), and N ₂ SA of carbon black is a value measured by the method described by JIS K6217 (2001).

The content of carbon black is 20 parts by mass or more, preferably 30 parts by mass or more with respect to 100 parts by mass of the rubber component. If it is less than 20 parts by mass, sufficient flex crack growth resistance may not be ensured. The content is 60 parts by mass or less, preferably 55 parts by mass or less. When the amount exceeds 60 parts by mass, the rubber becomes too hard, and the flex crack growth resistance may be deteriorated. Moreover, there is a possibility that the fuel efficiency is deteriorated.

（式中、Ｒ^１、Ｒ^２は、同一又は異なって、水素原子、炭素数１〜２０のアルキル基、炭素数１〜２０のアルケニル基又は炭素数１〜２０のアルキニル基である。Ｍ^ｒ＋は金属イオンを示し、ｒはその価数を表す。） The rubber composition of the present invention contains a compound represented by the following formula (I).

^(Wherein, R 1, ^{R 2} are the same or different, a hydrogen atom, an alkyl group having 1 to 20 carbon atoms, an alkenyl group or an alkynyl group having 1 to 20 carbon atoms having 1 to 20 carbon atoms ^{.M r +} Represents a metal ion, and r represents its valence.)

Examples of the alkyl group for R ¹ and R ² include a methyl group, an ethyl group, an n-propyl group, an isopropyl group, an n-butyl group, a sec-butyl group, and a tert-butyl group.
Examples of the alkenyl group for R ¹ and R ² include a vinyl group, an allyl group, a 1-propenyl group, and a 1-methylethenyl group.
Examples of the alkynyl group for R ¹ and R ² include an ethynyl group and a propargyl group.

R ¹ and R ² are preferably a hydrogen atom or an alkyl group, more preferably a hydrogen atom or a methyl group, and still more preferably a hydrogen atom. That is, the compound represented by the above formula (I) is preferably a compound represented by the following formula (I-1), (I-2) or (I-3). It is more preferable that it is a compound represented by.

In the above formulas (I), (I-1), (I-2), and (I-3), examples of metal ions include sodium ions, potassium ions, and lithium ions, and sodium ions are preferable.

Content of the compound represented by Formula (I) is 0.5 mass part or more with respect to 100 mass parts of carbon black, Preferably it is 1 mass part or more, More preferably, it is 2 mass parts or more. If it is less than 0.5 parts by mass, the fuel economy may not be sufficiently improved. Content of the compound represented by Formula (I) is 20 mass parts or less, Preferably it is 15 mass parts or less, More preferably, it is 10 mass parts or less. If it exceeds 20 parts by mass, there is a possibility that sufficient bending crack growth resistance cannot be ensured.

In addition to the above components, the rubber composition of the present invention includes compounding agents generally used in the production of rubber compositions, for example, reinforcing fillers such as silica, zinc oxide, stearic acid, silane coupling agents, aging An inhibitor, oil, wax, sulfur, vulcanization accelerator, and the like can be appropriately blended.

Examples of the vulcanization accelerator include, for example, sulfenamide, thiazole, thiuram, thiourea, guanidine, dithiocarbamic acid, aldehyde-amine, aldehyde-ammonia, imidazoline, and xanthate vulcanization accelerators. Etc. Of these, sulfenamide vulcanization accelerators are preferred. Examples of the sulfenamide vulcanization accelerator include N-tert-butyl-2-benzothiazolylsulfenamide (TBBS), N-cyclohexyl-2-benzothiazolylsulfenamide (CBS), N, N And '-dicyclohexyl-2-benzothiazolylsulfenamide (DZ).

As a method for producing the rubber composition of the present invention, a known method, for example, a method of kneading each component with a known mixer such as a roll or Banbury can be used.

The rubber composition of the present invention can be used for tire sidewalls.

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 in accordance with the shape of the sidewall at an unvulcanized stage, molded by a normal method on a tire molding machine, Bonding together with the tire member forms an unvulcanized tire. This unvulcanized tire can be heated and pressurized in a vulcanizer to produce the pneumatic tire of the present invention.

The pneumatic tire of the present invention can be suitably used for passenger car tires.

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

酸化亜鉛：三井金属鉱業（株）製の酸化亜鉛
老化防止剤：精工化学（株）製のオゾノン６Ｃ（Ｎ−（１，３−ジメチルブチル）−Ｎ’−フェニル−ｐ−フェニレンジアミン）
ワックス：大内新興化学工業（株）製のサンノックワックス
オイル：ジャパンエナジー製のプロセスＰＸ−１４０
ステアリン酸：日油（株）製のステアリン酸「椿」
硫黄：鶴見化学工業（株）製の粉末硫黄
加硫促進剤：大内新興化学工業（株）製のノクセラーＮＳ（Ｎ−ｔｅｒｔ−ブチル−２−ベンゾチアゾリルスルフェンアミド） Below, various chemical | medical agents used by the Example and the comparative example are demonstrated.
NR: TSR20
BR: BR150B manufactured by Ube Industries, Ltd. (cis content: 97% by mass)
Low unsaturated copolymer (1): EP35 manufactured by JSR (EPDM containing 5-ethylidene-2-norbornene (ENB) as the third diene component, ENB content: 8.1% by mass, iodine Price: 26)
Low Unsaturation Copolymer (2): EXXPRO 90-10 manufactured by ExxonMobil (brominated copolymer of isobutylene and p-methylstyrene, p-methylstyrene unit amount: 7.5% by mass, containing bromine) (Rate: 2% by mass)
♯60 Asahi Carbon Co., Ltd. Asahi: carbon black ^{_{(N 2 SA: 40m 2 /}} g, DBP oil ^absorption: 114cm 3 ^{/100g,pH:6.8,} volatile matter: 1.0 wt%)
Compound (I): (2Z) -4-[(4-aminophenyl) amino] -4-oxo-2-butenoic acid sodium (compound represented by the following formula) manufactured by Sumitomo Chemical Co., Ltd.

Zinc oxide: Zinc oxide anti-aging agent manufactured by Mitsui Mining & Smelting Co., Ltd .: Ozonone 6C (N- (1,3-dimethylbutyl) -N′-phenyl-p-phenylenediamine) manufactured by Seiko Chemical Co., Ltd.
Wax: Sunnock wax oil manufactured by Ouchi Shinsei Chemical Co., Ltd .: Process PX-140 manufactured by Japan Energy
Stearic acid: Stearic acid “椿” manufactured by NOF Corporation
Sulfur: Powdered sulfur vulcanization accelerator manufactured by Tsurumi Chemical Industry Co., Ltd .: Noxeller NS (N-tert-butyl-2-benzothiazolylsulfenamide) manufactured by Ouchi Shinsei Chemical Industry Co., Ltd.

<Examples and Comparative Examples>
In accordance with the formulation shown in Table 1, various chemicals excluding sulfur and a vulcanization accelerator were kneaded with a Banbury mixer. Sulfur and a vulcanization accelerator were added to the obtained kneaded product and kneaded with an open roll to obtain an unvulcanized rubber composition. And the rubber sheet for a test was produced by vulcanizing an unvulcanized rubber composition for 12 minutes at 170 ° C, and the test shown below was done using the obtained rubber sheet for a test.

The following evaluation was performed about the obtained rubber sheet for a test. The results are shown in Table 1.

(Low fuel consumption)
Using a viscoelastic spectrometer VES (manufactured by Iwamoto Seisakusho Co., Ltd.), the loss tangent (tan δ) of each formulation was measured under conditions of a temperature of 70 ° C., an initial strain of 10%, a dynamic strain of 2%, and a frequency of 10 Hz. The loss tangent tan δ in Example 1 was set to 100, and an index was displayed by the following formula (low fuel consumption index). A larger index indicates lower rolling resistance and better fuel efficiency.
(Low fuel consumption index) = (tan δ of Comparative Example 1) / (tan δ of each formulation) × 100

(Flexible crack growth resistance)
A flex crack growth test was conducted using a sample made of a test rubber sheet prepared based on JIS K6260 “Vulcanized Rubber and Thermoplastic Rubber—Dematcher Flex Crack Test Method”. In the test, 70% elongation was repeated 1,000,000 times to bend the sample, and then the length of the crack that occurred was measured. And the measured value (length) of the comparative example 1 was set to 100, and it represented with the index | exponent by the following formula (flexural crack growth resistance index). The larger the index, the more the crack growth is suppressed and the better the resistance to flex crack growth.
(Bending crack resistance index) = (Measured value of Comparative Example 1) / (Measured value of each formulation) × 100

(crack)
In accordance with JIS K6259 (2004), an ozone deterioration test is performed under the conditions of a temperature of 40 ° C., an ozone concentration of 50 pphm, and an elongation of 20%. The deterioration state of the test rubber sheet after 50 hours is observed, and the presence or absence of cracks is visually confirmed. And weather resistance was evaluated.

Compared to Comparative Example 1 in which the low-unsaturated copolymer and Compound (I) are not blended, Comparative Example 2 in which a low-unsaturated copolymer is blended improves the weather resistance, but reduces fuel consumption. Sexually deteriorated.
On the other hand, in the examples in which a predetermined amount of the low-unsaturated copolymer and the compound (I) was blended, the fuel economy was improved while maintaining the weather resistance and flex crack growth resistance equivalent to those of Comparative Example 2.

In Comparative Example 3, a copolymer with a low degree of unsaturation and the compound (I) were blended, but since the content of the compound (I) was small, the fuel economy could not be sufficiently improved.
In Comparative Example 4, since the content of the compound (I) is large, the flex crack growth resistance was greatly deteriorated.

Claims (5)

A rubber component, a carbon black having a nitrogen adsorption specific surface area of 30 to 120 m ² / g, and a compound represented by the following formula (I):
In 100% by mass of the rubber component, the content of diene rubber is 60 to 75% by mass, and the content of ethylene-propylene-diene copolymer and / or brominated copolymer of isobutylene and p-methylstyrene is 25. ~ 40% by weight,
The content of the carbon black with respect to 100 parts by mass of the rubber component is 20 to 60 parts by mass,
A rubber composition for a sidewall, wherein the content of the compound represented by the following formula (I) with respect to 100 parts by mass of the carbon black is 0.5 to 20 parts by mass.

^(Wherein, R 1, ^{R 2} are the same or different, a hydrogen atom, an alkyl group having 1 to 20 carbon atoms, an alkenyl group or an alkynyl group having a carbon number of 2-20 of 2-20 carbon atoms ^{.M r +} Represents a metal ion, and r represents its valence.) The compound represented by formula (I) is the following formula (I-1), (I -2) or (I-3) a compound represented by the claims 1 Symbol placement of rubber composition for sidewalls.

The rubber composition for a sidewall according to claim 1 or 2 , wherein the metal ion is sodium ion, potassium ion or lithium ion. The rubber composition for a side wall according to any one of claims 1 to 3, comprising N-tert-butyl-2-benzothiazolylsulfenamide. The pneumatic tire which has a side wall produced using the rubber composition in any one of Claims 1-4.