JP2011079961A - Rubber composition for tire, and pneumatic tire - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a rubber composition for a tire, satisfying both of low fuel consumption performance and crack growth resistant performance, and a pneumatic tire by using the same at each of the members (especially at a side wall) of the tire. <P>SOLUTION: This rubber composition for the tire is provided by containing a crystalline rubber component and at least 1 kind selected from the group consisting of a sorbitol derivative, a saturated fatty acid and a benzoic acid metal salt. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

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

For tire sidewalls, crystalline rubbers such as butadiene rubber and natural rubber and blend compositions containing these as one of the components are used in order to achieve both fracture resistance and low fuel consumption performance. The surface of the sidewall is repeatedly bent and deformed as the tire rolls, and the energy loss generated from the rubber during the deformation deteriorates the fuel efficiency. Further, by repeating the deformation, the crack growth of the rubber is promoted. Therefore, in the rubber composition for a sidewall, it is an important issue to achieve both low fuel consumption performance and crack growth resistance.

Patent Document 1 discloses a rubber composition excellent in low fuel consumption performance by blending a diene rubber with an inorganic filler, a silane coupling agent, and a specific vegetable oil. There is room for improvement in terms of achieving both crack growth resistance.
Patent Document 2 discloses a rubber composition for a sidewall containing a composite component composed of starch and a plasticizer in a rubber component composed of natural rubber and / or isoprene rubber and butadiene rubber. When added, the viscoelastic properties of the rubber composition are remarkably changed and the low fuel consumption performance is deteriorated. Therefore, there is room for improvement in terms of both low fuel consumption performance and crack growth resistance.

As described above, conventionally, attempts have been made to reduce the elastic modulus of a rubber composition by adding a blend of rubber components or an oil or plasticizer, and to improve the crack growth resistance performance. If it decreases, the rolling resistance increases, so the fuel efficiency is deteriorated, and it is not sufficient in terms of both the fuel efficiency and the crack growth resistance.

Further, Patent Document 3 uses a predetermined vegetable oil and a modified natural rubber latex, and manufactures an oil-extended rubber for a tire by a predetermined manufacturing method, thereby suppressing the molecular chain breakage of the natural rubber and bending resistance. It is described that crack growth can be improved. However, there is room for improvement in achieving both low fuel consumption performance and crack growth resistance.
Patent Document 4 describes that by adding a crystal nucleating agent and a plasticizer to diene rubber, crystallization is promoted and mechanical properties are improved. The use of a sorbitol derivative as a base material and application to a rubber composition for a sidewall that requires both low fuel consumption performance and crack growth resistance performance have not been studied.

JP 2003-64222 A JP 2005-53944 A JP 2007-291347 A JP-A-9-31248

The present invention solves the above-mentioned problems, and provides a rubber composition for a tire that can achieve both low fuel consumption performance and crack growth performance, and a pneumatic tire using the same for each member (particularly, sidewall) of the tire. With the goal.

The present inventors paid attention to the crack growth process of rubber in order to achieve both low fuel consumption performance and crack growth resistance.
In the crack growth process, it is known that a large deformation occurs at the crack tip compared to the deformation of the entire sidewall. Since it is considered that the crack grows when the amount of deformation at the crack tip exceeds the rupture limit (breaking strength) of the rubber molecule, the deformation of the molecular chain at the crack tip plays an important role in resistance to crack growth. Presumed to be.
Generally, polymer crystals do not exist under temperature conditions higher than the melting point, but in the case of crystalline rubber, even if the temperature is higher than the melting point, it is crystallized by stretching the molecule. For this reason, it is considered that rubber molecules are crystallized (stretched crystallization) at the crack tip during repeated deformation. Conventionally, rubber crystallization has been mainly studied for this stretch crystallization, and rubber crystallization is composed of a generation process of crystal origin and a growth process, and the generation process of crystal origin is usually the rate-limiting process. It is known.

Therefore, the present inventors have come up with the following hypothesis as a result of intensive studies.
Since the generation process of the crystal origin is the rate-limiting process, if a small number of origins are generated, the generated origin will grow, and a small number of large crystals will be generated. The size of the crystal generated at the crack tip and its spatial arrangement Becomes heterogeneous. Then, the stress was concentrated in a portion where the distance between crystals was close, and a portion where deformation was concentrated due to the stress concentration was generated, which led to the idea that the crack growth resistance would be degraded. On the other hand, if fine crystals are generated uniformly at the crack tip, stress concentration does not occur and the stress is dispersed, so the portion exceeding the fracture threshold is reduced and crack growth performance is improved. I came up with the idea that it might be. Then, by uniformly dispersing the crystal nucleating agent in the rubber, crystallization based on the crystal nucleating agent is caused to generate a large number of fine crystals, and a homogeneous stress field in which the spatial arrangement and size of the crystals are uniform. The inventors have come up with the idea that the crack growth performance can be improved.

Therefore, the present inventors have confirmed through experiments that the crack growth resistance can be improved by adding a crystal nucleating agent to the rubber based on the above hypothesis. As described above, the present inventors can control the crystallization in the elongation process and improve the crack growth resistance performance by actively controlling the crystal state of the unstretched state with the crystal nucleating agent. I found.
That is, this invention relates to the rubber composition for tires containing a crystalline rubber component and at least 1 sort (s) selected from the group which consists of a sorbitol derivative, a saturated fatty acid, and a benzoic acid metal salt.

In the rubber composition, the sorbitol derivative is preferably a dibenzylidene sorbitol represented by the following formula (1).

（式（１）において、Ｒ^１ 及びＲ^２ は、同一又は異なって、炭素数１〜５のアルキル基、炭素数１〜５のアルコキシ基又はハロゲン原子を表す。ｍ及びｎは０〜３の整数を表す。）

In (Equation (1), ^{R 1} and ^{R 2} are the same or different, an alkyl group having 1 to 5 carbon atoms, .m and n is from 0 to 3 represents an alkoxy group or a halogen atom having 1 to 5 carbon atoms Represents an integer.)

In the rubber composition, the sorbitol derivative is preferably a compound represented by the following formula (2).

Moreover, it is preferable that the said rubber composition contains 0.03-1.2 mass part of sorbitol derivatives with respect to 100 mass parts of rubber components.

Moreover, it is preferable that the said benzoic acid metal salt is sodium benzoate.

Moreover, it is preferable that the said rubber composition is used as a rubber composition for sidewalls.

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

According to the present invention, the tire rubber composition includes a crystalline rubber component and at least one crystal nucleating agent selected from the group consisting of a sorbitol derivative, a saturated fatty acid, and a metal salt of benzoic acid. Both performance and crack growth resistance can be achieved, and it can be suitably applied to each member (particularly, sidewall) of a pneumatic tire. In the present invention, it is presumed that by adding a crystal nucleating agent to the crystalline rubber component, the spatial arrangement and size of crystals can be controlled, and the crack growth performance of the rubber composition can be improved. The Furthermore, even if a crystal nucleating agent is added, the elastic modulus in the frequency region related to low fuel consumption performance does not change, so it is estimated that crack growth resistance can be improved while maintaining low fuel consumption performance. This is presumed to be because the crystal structure corresponds to fast molecular motion and thus does not affect dynamic viscoelasticity in a high temperature region related to low fuel consumption performance.

It is a figure which shows the relationship between the compounding quantity of gel oar D, and J integral value (Ji) at the time of a crack start.

The rubber composition for tires of the present invention includes a crystalline rubber component and at least one selected from the group consisting of a sorbitol derivative, a saturated fatty acid, and a metal benzoate. A sorbitol derivative is highly compatible with a rubber component (crystalline rubber component), and has a high intermolecular cohesive force, so it has a high melting point of 210 ° C. or higher and good thermal stability. Can be suitably used.
Saturated fatty acids can be suitably used because they promote crystallization of the rubber component in order to plasticize the rubber component and increase molecular mobility.
Moreover, since a metal salt of benzoate has a layer structure and exhibits a high melting point, it acts as a crystal plane and can be used as a crystal nucleating agent.

Examples of the crystalline rubber component include natural rubber (NR), isoprene rubber (IR), butadiene rubber (BR), chloroprene rubber (CR), and the like. A crystalline rubber component may be used independently and may use 2 or more types together. Of these, NR, BR, and the combined use of NR and BR are preferable because the crack growth resistance is good as a rubber component for the sidewall.

The NR is not particularly limited, and for example, those commonly used in the tire industry such as SIR20, RSS # 3, TSR20, epoxidized natural rubber (ENR) can be used. In recent years, with the growing awareness of environmental conservation, the use of non-oil resources is urgently needed. NR is a non-petroleum resource, but its crack growth performance is low, so improving the crack growth performance is the biggest challenge for practical application. In the present invention, by using NR as the crystalline rubber, the above-mentioned problem that the crack growth performance of NR is low can be solved (both low fuel consumption performance and crack growth performance can be achieved). The use of a certain NR can be promoted and the environment can be considered. Among these, ENR is preferable because it has a high glass transition temperature (Tg) and excellent mechanical strength and wear resistance.

As the ENR, a commercially available ENR may be used, or natural rubber may be epoxidized. Examples of the method for epoxidizing natural rubber include chlorohydrin method, direct oxidation method, hydrogen peroxide method, alkyl hydroperoxide method, peracid method and the like.

The BR is not particularly limited. For example, BR1220 manufactured by Nippon Zeon Co., Ltd., BR130B manufactured by Ube Industries, Ltd., BR150B and other high cis content BR, VCR412 manufactured by Ube Industries, Inc., VCR617, etc. BR containing syndiotactic polybutadiene crystals can be used. Among these, BR having a cis content of 95% by mass or more is preferable because of excellent crack growth resistance.

In addition to the crystalline rubber, those that can be used as the rubber component (non-crystalline rubber component) include styrene butadiene rubber (SBR), ethylene propylene diene rubber (EPDM), and the like. An amorphous rubber component may be used independently and may use 2 or more types together. Among these, SBR is preferable because it exhibits high grip performance.
In addition, in this invention, when only describing as a rubber component, both a crystalline rubber component and an amorphous rubber component shall be represented collectively.

80 mass% or more is preferable, as for content of the crystalline rubber in 100 mass% of rubber components, 90 mass% or more is more preferable, and it is still more preferable that it is 100 mass%. If it is less than 80% by mass, crystal defects occur and become inhomogeneous, so that stress concentration tends to occur.

Examples of the sorbitol derivative include dibenzylidene sorbitol, ditrilidene sorbitol, asymmetric dialkylbenzylidene sorbitol, and derivatives thereof.

Among sorbitol derivatives, dibenzylidene sorbitols represented by the following formula (1) are preferable because they form a three-dimensional network structure by self-organization in a molten matrix at a high temperature.

（式（１）において、Ｒ^１ 及びＲ^２ は、同一又は異なって、炭素数１〜５のアルキル基、炭素数１〜５のアルコキシ基又はハロゲン原子を表す。ｍ及びｎは０〜３の整数を表す。）

In (Equation (1), ^{R 1} and ^{R 2} are the same or different, an alkyl group having 1 to 5 carbon atoms, .m and n is from 0 to 3 represents an alkoxy group or a halogen atom having 1 to 5 carbon atoms Represents an integer.)

The substitution position of R ¹ and R ² may be any of the ortho position, the meta position, and the para position, and is not particularly limited. Examples of the alkyl group having 1 to 5 carbon atoms include linear or branched ones such as a methyl group, an ethyl group, an isopropyl group, an n-butyl group, and an n-pentyl group. 1-3 alkyl groups are preferred. Examples of the alkoxy group having 1 to 5 carbon atoms include linear or branched groups such as a methoxy group, an ethoxy group, an n-propoxy group, an isopropoxy group, and an n-butoxy group. An alkoxy group having 1 to 3 carbon atoms is preferable. Examples of the halogen atom include chlorine and bromine.

Specific examples of the compound represented by the above formula (1) include 1,3: 2,4-dibenzylidene sorbitol, 1,3: 2,4-bis (p-methylbenzylidene) sorbitol, 1,3: 2. , 4-bis (o-methylbenzylidene) sorbitol, 1,3: 2,4-bis (p-ethylbenzylidene) sorbitol, 1,3: 2,4-bis (p-chlorobenzylidene) sorbitol, 1,3: 2,4-bis (p-methoxybenzylidene) sorbitol, 1,3: 2,4-bis (2,4-dimethylbenzylidene) sorbitol, 1,3: 2,4-bis (3,4-dimethylbenzylidene) sorbitol , 1,3: 2,4-bis (2,4,5-trimethylbenzylidene) sorbitol and the like, a compound having the same type of substituted or unsubstituted benzylidene group, 1,3-benzylidene -2,4-p-methylbenzylidene sorbitol, 1,3-p-methylbenzylidene-2,4-benzylidene sorbitol, 1,3-benzylidene-2,4-p-ethylbenzylidene sorbitol, 1,3-p-ethyl Benzylidene-2,4-benzylidenesorbitol, 1,3-benzylidene-2,4- (3,4-dimethylbenzylidene) sorbitol, 1,3- (3,4-dimethylbenzylidene) -2,4-benzylidenesorbitol, 1 , 3-benzylidene-2,4- (2,4-dimethylbenzylidene) sorbitol, 1,3- (2,4-dimethylbenzylidene) -2,4-benzylidenesorbitol and the like, which have different substituted or unsubstituted benzylidene groups Compounds and the like. The compound represented by the above formula (1) may be used alone or in combination of two or more. Among them, dibenzylidene sorbitols having the same kind of substituted or unsubstituted benzylidene groups are preferable because of good dispersibility and easy to form a three-dimensional network structure. 1,3: 2,4-dibenzylidene sorbitol, 1 , 3: 2,4-bis (p-methylbenzylidene) sorbitol, 1,3: 2,4-bis (o-methylbenzylidene) sorbitol, 1,3: 2,4-bis (p-ethylbenzylidene) sorbitol, 1,3: 2,4-bis (3,4-dimethylbenzylidene) sorbitol and 1,3: 2,4-bis (2,4,5-trimethylbenzylidene) sorbitol are more preferable. Furthermore, among the compounds described above, a compound represented by the following formula (2) (1,3: 2,4-dibenzylidenesorbitol) is particularly preferably used.

The compounds represented by the above formula (1) or (2) are known and easily available, or Japanese Patent Publication Nos. 48-43748, 53-5156, 57-185287. Can be produced according to known methods such as JP-A No. 2-231488. These crystal forms are not particularly limited as long as the effects of the present invention are obtained, and any crystal form such as hexagonal crystal, monoclinic crystal, and cubic crystal can be used. Examples of commercially available compounds represented by the above formula (1) or (2) include, for example, Gelol D (1,3: 2,4-dibenzylidene sorbitol), Gelol MD (1) manufactured by Shin Nippon Rika Co., Ltd. , 3: 2,4-bis (p-methylbenzylidene) sorbitol) and Millad 3988 (1,3: 2,4-bis (3,4-dimethylbenzylidene) sorbitol) manufactured by Milliken.

The content of the sorbitol derivative is preferably 0.03 parts by mass or more, more preferably 0.05 parts by mass or more, and further preferably 0.1 parts by mass or more with respect to 100 parts by mass of the rubber component. If the amount is less than 0.03 parts by mass, the effect of blending the crystal nucleating agent is small, so that the crack growth performance tends not to be sufficiently improved. The content of the sorbitol derivative is preferably 1.2 parts by mass or less, more preferably 0.5 parts by mass or less, and still more preferably 0.3 parts by mass or less. When the amount exceeds 1.2 parts by mass, the growth of crystals is promoted to generate agglomerates and the crack growth resistance tends to deteriorate.

Examples of the saturated fatty acid include myristic acid, stearic acid, palmitic acid, lauric acid, margaric acid and the like. Of these, saturated fatty acids having 8 to 24 carbon atoms (preferably 12 to 17 carbon atoms) are preferred because higher fatty acids are higher for higher fatty acids and lower are unsaturated, and myristic acid, palmitic acid, stearin are preferred. Acid is more preferred.
When BR is used as the crystalline rubber component, saturated fatty acid can be suitably used as a crystal nucleating agent because it has high crystallinity and can promote crystallization of BR.

The content of the saturated fatty acid is preferably 0.01 parts by mass or more, more preferably 0.1 parts by mass or more, and further preferably 0.5 parts by mass or more with respect to 100 parts by mass of the rubber component. If the amount is less than 0.01 parts by mass, the effect of blending the crystal nucleating agent is small, so that the crack growth performance tends not to be sufficiently improved. Further, the content of the saturated fatty acid is preferably 25 parts by mass or less, more preferably 20 parts by mass or less, still more preferably 15 parts by mass or less, and particularly preferably 10 parts by mass or less. When the amount exceeds 25 parts by mass, the growth of crystals is promoted to generate agglomerates, which tends to deteriorate the crack growth resistance.

Examples of the benzoic acid metal salt include monovalent metal salts such as sodium benzoate, potassium benzoate and lithium benzoate, and divalent metal salts such as calcium benzoate and magnesium benzoate. Of these, monovalent metal salts are preferable, and sodium benzoate and potassium benzoate are more preferable because of their low molecular weight and high molecular mobility. The benzoic acid in the present invention includes benzoic acid induction. Examples of the benzoic acid derivative include those in which a functional group such as a hydrocarbon group (alkyl group, alkoxy group, etc.) or a hydroxyl group is introduced into benzoic acid. Specifically, p-methylbenzoic acid, p- Examples include methoxybenzoic acid, p-chlorobenzoic acid, p-nitrobenzoic acid, and salicylic acid.

The content of the benzoic acid metal salt is preferably 0.05 parts by mass or more, more preferably 0.1 parts by mass or more, and further preferably 0.2 parts by mass or more with respect to 100 parts by mass of the rubber component.
If the amount is less than 0.05 parts by mass, the effect of blending the crystal nucleating agent is small, and thus the crack growth resistance tends to be insufficiently improved. Further, the content of the benzoic acid metal salt is preferably 15 parts by mass or less, more preferably 10 parts by mass or less, and still more preferably 5 parts by mass or less. When the amount exceeds 15 parts by mass, the growth of crystals is promoted to generate agglomerates and the crack growth resistance tends to deteriorate.

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

The nitrogen adsorption specific surface area (N ₂ SA) of carbon black is preferably 10 m ² / g or more, and more preferably 20 m ² / g or more. If it is less than 10 m ² / g, a balanced effect cannot be obtained in terms of wear resistance and reinforcing effect. Further, the nitrogen adsorption specific surface area of carbon black is preferably 130 m ² / g or less, and more preferably 70 m ² / g or less. If it exceeds 130 m ² / g, the dispersibility of the carbon black is deteriorated and the workability may be lowered.
In addition, the nitrogen adsorption specific surface area of carbon black is calculated | required by A method of JISK6217.

When the rubber composition contains carbon black, the content of carbon black is preferably 40 parts by mass or more, more preferably 50 parts by mass or more with respect to 100 parts by mass of the rubber component. If it is less than 40 parts by mass, the wear resistance may be deteriorated. The carbon black content is preferably 80 parts by mass or less, more preferably 70 parts by mass or less. If it exceeds 80 parts by mass, the exothermic property may deteriorate.

The rubber composition of the present invention preferably contains silica. The silica is not particularly limited, and examples thereof include dry process silica (anhydrous silicic acid), wet process silica (hydrous silicic acid), and the like, but wet process silica is preferable because of its large number of silanol groups. Silica may be used alone or in combination of two or more.

The nitrogen adsorption specific surface area (N ₂ SA) of the silica is preferably 140 m ² / g or more, more preferably 170 m ² / g or more. If it is less than 140 m < ² > / g, there exists a possibility that reinforcement and abrasion resistance may not fully be acquired. Further, N ₂ SA of silica is preferably 280 m ² / g or less, more preferably 250 m ² / g or less. When it exceeds 280 m < ² > / g, there exists a possibility that workability may deteriorate.
The nitrogen adsorption specific surface area of silica is a value measured by the BET method according to ASTM D3037-81.

The content of silica is preferably 5 parts by mass or more, more preferably 10 parts by mass or more with respect to 100 parts by mass of the rubber component. If the amount is less than 5 parts by mass, the effect of improving wear resistance and reinforcement may be small. Content of this silica becomes like this. Preferably it is 50 mass parts or less, More preferably, it is 40 mass parts or less, More preferably, it is 30 mass parts or less. If it exceeds 50 parts by mass, the rubber composition becomes hard and the processability may be deteriorated.

The rubber composition of the present invention preferably contains a silane coupling agent together with silica.
As the silane coupling agent, any silane coupling agent conventionally used in combination with silica can be used in the rubber industry. For example, bis (3-triethoxysilylpropyl) tetrasulfide, bis (2-tri Ethoxysilylethyl) tetrasulfide, bis (4-triethoxysilylbutyl) tetrasulfide, bis (3-trimethoxysilylpropyl) tetrasulfide, bis (2-trimethoxysilylethyl) tetrasulfide, bis (4-trimethoxysilyl) Butyl) tetrasulfide, bis (3-triethoxysilylpropyl) trisulfide, bis (2-triethoxysilylethyl) trisulfide, bis (4-triethoxysilylbutyl) trisulfide, bis (3-trimethoxysilylpropyl) Trisulfi Bis (2-trimethoxysilylethyl) trisulfide, bis (4-trimethoxysilylbutyl) trisulfide, bis (3-triethoxysilylpropyl) disulfide, bis (2-triethoxysilylethyl) disulfide, bis (4 -Triethoxysilylbutyl) disulfide, bis (3-trimethoxysilylpropyl) disulfide, bis (2-trimethoxysilylethyl) disulfide, bis (4-trimethoxysilylbutyl) disulfide, 3-trimethoxysilylpropylbenzothiazoli And sulfide systems such as tetratetrasulfide and 3-triethoxysilylpropylbenzothiazole tetrasulfide. Moreover, mercapto type, vinyl type, glycidoxy type, nitro type, chloro type and the like can also be mentioned. Especially, it is preferable to use a sulfide type | system | group from the point that the scorch at the time of kneading | mixing the thing of 4 or less sulfur contained in 1 molecule can be avoided. These silane coupling agents may be used alone or in combination of two or more.

1 mass part or more is preferable with respect to 100 mass parts of silica content, and, as for content of a silane coupling agent, 2 mass parts or more is more preferable. If it is less than 1 part by mass, the effect of silica blending may not be sufficiently obtained. Further, the content of the silane coupling agent is preferably 20 parts by mass or less, and more preferably 15 parts by mass or less. If it exceeds 20 parts by mass, an effect commensurate with the increase in the amount of the silane coupling agent cannot be obtained, and the cost may increase.

The rubber composition of the present invention preferably contains zinc oxide. When the rubber composition contains zinc oxide, the content of zinc oxide is preferably 1 part by mass or more, more preferably 2 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, the effect of blending zinc oxide cannot be obtained. Further, the content of zinc oxide is preferably 6 parts by mass or less, more preferably 5 parts by mass or less. If it exceeds 6 parts by mass, the strength and wear may be reduced.

In addition to the above components, the rubber composition of the present invention includes compounding agents conventionally used in the rubber industry, for example, inorganic and organic fillers such as clay, vulcanization acceleration aids such as stearic acid, and various anti-aging agents. Further, an ozone deterioration inhibitor, a vulcanizing agent such as wax, oil, sulfur or a sulfur compound, a vulcanization accelerator, and the like can be appropriately blended as necessary.

The rubber composition of the present invention is produced by a general method. That is, it can be produced by a method of kneading the above components with a Banbury mixer, a kneader, an open roll or the like and then vulcanizing.

The rubber composition of the present invention can be suitably used for each member (particularly, sidewall) of a pneumatic tire.

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 the sidewall or the like at an unvulcanized stage, molded by a normal method on a tire molding machine, and bonded together with other tire members, and an unvulcanized tire Form. 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 together.
NR: TSR20
BR: Ubepol 150B manufactured by Ube Industries, Ltd. (cis content: 96% by mass)
ENR: ENR25 (Epoxidation rate: 25 mol%) manufactured by Kungpu Langurs
Carbon black: Seast S0 FEF (N ₂ SA: 42 m ² / g) manufactured by Tokai Carbon Co., Ltd.
Stearic acid: “Nada” made by NOF Corporation
Zinc oxide: Zinc Hua 1 anti-aging agent manufactured by Mitsui Mining & Smelting Co., Ltd .: NOCRACK 6C (N- (1,3-dimethylbutyl) -N'-phenyl-p- Phenylenediamine) (6PPD)
Silica: Ultrazil VN3 manufactured by Degussa (N ₂ SA: 175 m ² / g)
Silane coupling agent: Si266 manufactured by Degussa
Gelol D: Gelall D (1,3: 2,4-dibenzylidenesorbitol (compound of the above formula (2))) manufactured by Shin Nippon Rika Co., Ltd.
Myristic acid: myristic acid (M3128-500G) manufactured by Aldrich (carbon number: 14)
Sodium benzoate: Sodium benzoate (109169-1KG) manufactured by Aldrich
Sulfur: Powder sulfur vulcanization accelerator manufactured by Tsurumi Chemical Industry Co., Ltd .: Noxeller NS manufactured by Ouchi Shinsei Chemical Industry Co., Ltd.

Examples 1 to 23 and Comparative Examples 1 to 3
According to the blending contents shown in Tables 1 to 4, materials other than sulfur and a vulcanization accelerator were kneaded for 5 minutes at 150 ° C. using a 1.7 L Banbury mixer to obtain a kneaded product. Next, sulfur and a vulcanization accelerator were added to the obtained kneaded product, and kneaded for 5 minutes under the condition of 80 ° C. using an open roll to obtain an unvulcanized rubber composition. The obtained unvulcanized rubber composition was press vulcanized with a 0.5 mm thick mold at 150 ° C. for 35 minutes to obtain a vulcanized rubber composition (sheet having a thickness of about 1 mm).

The following evaluation was performed using the obtained vulcanized rubber composition. Each test result is shown in Tables 1-4. The results shown in Table 1 are further shown in FIG.

(Crack growth resistance)
The crack growth resistance was evaluated by the J integral value (Ji) at the start of cracking. In order to evaluate Ji, a strip-shaped test piece having a width (W) of about 15 mm and a thickness (B) of about 1 mm having an initial crack (a) of 3 mm at one end was used. The initial crack was made using a razor, and talc was sprayed on the initial crack portion. The height was adjusted so that the initial crack was in the center, and it was installed in a tensile tester (Shimadzu Corporation autograph) so that the distance between chucks was 40 mm. The stress-strain relationship was measured until the sample broke at a tensile rate of 25 mm / min. The initial crack portion was observed with a CCD camera, and the crack start point di was determined. The area U (di) up to the stress σ (di) corresponding to di in the stress-strain curve was determined, and Ji was calculated by the following equation. The larger Ji, the better the crack growth resistance.
Ji = U (di) / (B × (W−a))

(Low fuel consumption performance)
Using a viscoelastic spectrometer VA-4000 (manufactured by Metraviv), tan δ of each compounding (vulcanized rubber sheet) under the conditions of frequency 10 Hz, temperature 70 ° C., initial strain 10%, dynamic strain 0.5% It was measured. The smaller tan δ, the better the fuel efficiency.

FIG. 1 is a diagram showing the relationship between the amount of gelol D and the J integral value (Ji) at the start of cracking. As shown in FIG. 1, it was confirmed that by adding Gelol D, which is a crystal nucleating agent, Ji increased, crack growth resistance could be improved. Moreover, it turned out that Ji has taken the maximum value, when the compounding quantity of gelol D is 0.2 mass part vicinity. Moreover, from Table 1, compared with the comparative example 1 which does not mix | blend gelol D, the fuel-efficient performance of Examples 1-5 which mix | blended 0.4 mass parts or less of gelol D is equivalent, 0.5 The fuel efficiency performance of Examples 6 and 7 in which Gelol D of not less than part by mass was blended was excellent. From the above, it has been found that when NR is used as the crystalline rubber component, by adding Gelol D, the crack growth resistance can be improved while maintaining or improving the low fuel consumption performance.

From Table 2, Examples 8-10 which mix | blended myristic acid are equivalent to a low fuel consumption performance compared with the comparative example 1 (refer Table 1) which is not mix | blending the crystal nucleating agent, and crack growth performance is good. It was confirmed that it could be improved. From the above, it has been found that when NR is used as the crystalline rubber component, crack growth resistance can be improved while maintaining low fuel consumption by blending myristic acid.
Moreover, Examples 11-13 which mix | blended sodium benzoate confirmed that low-fuel-consumption performance and crack-proof growth performance can be improved compared with the comparative example 1 (refer Table 1) which is not mix | blending the crystal nucleating agent. . From the above, it has been found that when NR is used as the crystalline rubber component, low fuel consumption performance and crack growth resistance performance can be improved by adding sodium benzoate.

From Table 3, when BR is used as the crystalline rubber component, Examples 15 to 17 in which myristic acid is blended maintain low fuel consumption performance as compared with Comparative Example 2 in which no crystal nucleating agent is blended. While improving, it was confirmed that crack growth performance could be improved. From the above, it was found that when BR is used as the crystalline rubber component, by adding myristic acid, the crack growth resistance can be improved while maintaining or improving the low fuel consumption performance.

From Table 4, when NR and ENR are used as the crystalline rubber component, Examples 18 to 23 in which any of gelol D, myristic acid, and sodium benzoate are blended are comparative examples in which no crystal nucleating agent is blended. Compared to 3, it was confirmed that the crack growth performance could be maintained or improved while improving fuel efficiency. From the above, when NR and ENR are used as the crystalline rubber component, by adding any of gelol D, myristic acid and sodium benzoate, the fuel economy performance is improved and the crack growth resistance performance is maintained. It turns out that it can improve.

Claims (7)

A rubber composition for a tire comprising a crystalline rubber component and at least one selected from the group consisting of a sorbitol derivative, a saturated fatty acid, and a metal benzoate. The tire rubber composition according to claim 1, wherein the sorbitol derivative is a dibenzylidene sorbitol represented by the following formula (1).

In (Equation (1), ^{R 1} and ^{R 2} are the same or different, an alkyl group having 1 to 5 carbon atoms, .m and n is from 0 to 3 represents an alkoxy group or a halogen atom having 1 to 5 carbon atoms Represents an integer.) The tire rubber composition according to claim 1 or 2, wherein the sorbitol derivative is a compound represented by the following formula (2).

The rubber composition for a tire according to any one of claims 1 to 3, comprising 0.03 to 1.2 parts by mass of a sorbitol derivative with respect to 100 parts by mass of the rubber component. The tire rubber composition according to claim 1, wherein the metal salt of benzoic acid is sodium benzoate. The tire rubber composition according to any one of claims 1 to 5, which is used as a rubber composition for a sidewall. A pneumatic tire using the rubber composition according to claim 1.

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