JP2016210834A - Rubber composition for tire - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a rubber composition for a tire, having improved low heat generation property and mechanical property.SOLUTION: Carbon black of 30 to 70 pts.wt. having nitrogen absorption specific surface area of 125 to 150 m/g is blended with 100 pts.wt. of a rubber composition composed of: 55 to 100 wt.% of a masticated natural rubber master batch in which 0.3 to 5.0 wt.% of a specific compound represented by the general formula (i) co-exists with 40 wt.% or more of a natural rubber and/or isoprene rubber and optionally 100 wt.% of a diene rubber containing butadiene rubber; and a butadiene rubber, a natural rubber and an isoprene rubber of 45 to 0 wt.% in total, the rubber composition containing the natural rubber and the isoprene rubber of 55 to 100 wt.% in total and optionally the butadiene rubber of 45 to 0 wt.% in total.SELECTED DRAWING: None

Description

  The present invention relates to a rubber composition for tires that is improved in low heat build-up and mechanical properties.

  In recent years, as a required performance for pneumatic tires, it has been demanded that fuel efficiency performance is excellent with increasing interest in global environmental problems. In order to improve fuel efficiency, it is necessary to reduce rolling resistance. For this reason, the rolling resistance of the tire is reduced by suppressing the heat generation of the rubber composition constituting the pneumatic tire. Generally, 60 ° C. tan δ by dynamic viscoelasticity measurement is used as an index of exothermic property of the rubber composition. The smaller the tan δ (60 ° C.) of the rubber composition, the smaller the exothermic property.

  As a method for reducing the tan δ (60 ° C.) of the rubber composition, for example, the amount of carbon black is decreased or the particle size of the carbon black is increased. However, in such a method, there is a problem that mechanical properties such as rubber hardness and tensile elongation at break of the rubber composition are lowered, and steering stability and wear resistance are lowered when the tire is formed.

  Patent Document 1 discloses that a rubber composition obtained by kneading a rubber component, (2Z) -4-aminophenylamino-4-oxo-2-butenoic acid, and a filler modifies the viscoelastic characteristics of the tire. It has been proposed to improve fuel economy performance. However, when this rubber composition is used for a cap tread of a heavy duty pneumatic tire, the required level of mechanical properties such as rubber hardness, tensile elongation at break and abrasion resistance, particularly rubber hardness and tensile elongation at break are sufficiently obtained. It could not be secured, and further improvement was demanded.

International Publication No. 2012/147984

  An object of the present invention is to provide a rubber composition for tires that is improved in low heat build-up and mechanical properties over conventional levels.

（式中、Ｒ¹は置換基を有してもよい炭素数６〜１２の２価の芳香族炭化水素基、Ｒ²，Ｒ³はそれぞれ独立に水素原子、ハロゲン原子、炭素数１〜６のアルキル基、炭素数６〜１２のアリール基、ヒドロキシ基または炭素数１〜６のアルコキシ基、Ｒ⁴はヒドロキシ基または−ＯＮａ、Ｘは−ＮＨ−または−Ｏ−を表す。） The rubber composition for tires of the present invention that achieves the above object is represented by the following general formula (i) in which 100% by weight of a natural rubber and / or isoprene rubber is 40% by weight or more and optionally a diene rubber containing butadiene rubber. A rubber component comprising 55 to 100% by weight of a kneaded rubber masterbatch in which 0.3 to 5.0% by weight of a compound coexists, and 45 to 0% by weight in total of butadiene rubber, natural rubber and isoprene rubber, Carbon black having a nitrogen adsorption specific surface area of 125 to 150 m ² / g based on 100 parts by weight of a rubber component containing 55 to 100% by weight of rubber and isoprene rubber, and optionally 45 to 0% by weight of butadiene rubber. 30 to 70 parts by weight of a rubber composition for tires.

(In the formula, R ¹ is an optionally substituted divalent aromatic hydrocarbon group having 6 to 12 carbon atoms, R ² and R ³ are each independently a hydrogen atom, a halogen atom, or 1 to 6 carbon atoms. An alkyl group, a C 6-12 aryl group, a hydroxy group or a C 1-6 alkoxy group, R ⁴ represents a hydroxy group or —ONa, and X represents —NH— or —O—.)

  The rubber composition for tires of the present invention is a rubber component containing a kneaded rubber masterbatch in which a compound represented by the above general formula (i) coexists in a diene rubber containing natural rubber and / or isoprene rubber. Since specific carbon black is blended and butadiene rubber is arbitrarily blended, tan δ (60 ° C.) of the rubber composition is reduced, and mechanical properties such as rubber hardness and tensile elongation at break are maintained and improved. be able to. As a result, when a pneumatic tire is used, the steering stability and the wear resistance can be improved to a level higher than the conventional level while improving the fuel efficiency.

In the compound represented by the general formula (i), R ⁴ may be a hydroxy group.

  This rubber composition is suitable for use in the cap tread of heavy duty pneumatic tires, while reducing rolling resistance and improving fuel economy performance of heavy duty pneumatic tires while improving handling stability and wear resistance. This can be improved as described above.

  The rubber composition for tires of the present invention comprises a kneaded rubber master batch and a reinforcing filler. The kneaded rubber master batch is obtained by reacting a specific compound with a diene rubber containing natural rubber and / or isoprene rubber and optionally butadiene rubber. As the natural rubber, isoprene rubber and butadiene rubber, those usually used for tire rubber compositions can be used.

  The kneaded rubber masterbatch includes at least one of natural rubber and isoprene rubber, and optionally includes butadiene rubber. If the kneaded rubber masterbatch does not have natural rubber and isoprene rubber, the desired effect of the present invention cannot be achieved.

  The content of natural rubber and isoprene rubber is preferably 40 to 100% by weight, more preferably 50 to 100% by weight, in 100% by weight of the diene rubber constituting the masticated rubber masterbatch. When the content of the natural rubber and isoprene rubber is less than 40% by weight, the compound of the general formula (i) cannot be sufficiently dispersed and mixed in the diene rubber.

  The diene rubber constituting the kneaded rubber masterbatch can optionally contain other diene rubbers other than natural rubber and isoprene rubber. Examples of other diene rubbers include butadiene rubber, styrene butadiene rubber, butyl rubber, and ethylene propylene diene rubber. Of these, butadiene rubber is preferred.

（式中、Ｒ¹は置換基を有してもよい炭素数６〜１２の２価の芳香族炭化水素基、Ｒ²，Ｒ³はそれぞれ独立に水素原子、ハロゲン原子、炭素数１〜６のアルキル基、炭素数６〜１２のアリール基、ヒドロキシ基または炭素数１〜６のアルコキシ基、Ｒ４はヒドロキシ基または−ＯＮａ、Ｘは−ＮＨ−または−Ｏ−を表す。） In the present invention, the kneaded rubber masterbatch is obtained by reacting 0.3% to 5.0% by weight of a compound represented by the following general formula (i) with 100% by weight of a diene rubber.

(In the formula, R ¹ is an optionally substituted divalent aromatic hydrocarbon group having 6 to 12 carbon atoms, R ² and R ³ are each independently a hydrogen atom, a halogen atom, or 1 to 6 carbon atoms. An alkyl group, a C6-C12 aryl group, a hydroxy group or a C1-C6 alkoxy group, R4 represents a hydroxy group or -ONa, and X represents -NH- or -O-.)

In general formula (i), R < ¹ > is a C6-C12 bivalent aromatic hydrocarbon group which may have a substituent. Examples of the divalent aromatic hydrocarbon group having 6 to 12 carbon atoms include a phenylene group, a naphthylene group, and a biphenylene group. Examples of the substituent include an alkyl group having 1 to 4 carbon atoms, an alkoxy group having 1 to 4 carbon atoms, a hydroxy group, a nitro group, a cyano group, a sulfo group, and a halogen atom. These substituents can arbitrarily substitute 0 to 4 hydrogen atoms of the aromatic hydrocarbon group. R ¹ is preferably a phenylene group.

R ² and R ³ are each independently a hydrogen atom, a halogen atom, an alkyl group having 1 to 6 carbon atoms, an aryl group having 6 to 12 carbon atoms, a hydroxy group, or an alkoxy group having 1 to 6 carbon atoms. Examples of the halogen atom in R ² and R ³ include fluorine, chlorine, bromine and iodine. Examples of the alkyl group having 1 to 6 carbon atoms include methyl, ethyl, n-propyl, isopropyl, n-butyl, isobutyl, sec-butyl, tert-butyl, n-pentyl, and isopentyl. Group, n-hexyl group and the like. As a C6-C12 aryl group, a C6-C12 monocyclic or condensed polycyclic aromatic hydrocarbon is shown, for example, a phenyl group, a naphthyl group, a biphenyl group etc. are mentioned. Examples of the alkoxy group having 1 to 6 carbon atoms include a methoxy group, an ethoxy group, an n-propoxy group, an isopropoxy group, an n-butoxy group, an isobutoxy group, a sec-butoxy group, a tert-butoxy group, and an n-pentoxy group. , Isopentoxy group, n-hexyloxy group and the like.

As R ² and R ^3, R ² is a hydrogen atom, it is preferred that R ³ is an alkyl group having 1 to 6 carbon hydrogen atom or atoms, more preferably R ² and R ³ are hydrogen atoms. R ⁴ is a hydroxy group or —ONa, preferably a hydroxy group. X is —NH— or —O—. X is preferably —NH—.

  Examples of the compound represented by the general formula (i) include (2Z) -4-[(4-aminophenyl) amino] -4-oxo-2-butenoic acid, (2Z) -4-[(3-amino Phenyl) amino] -4-oxo-2-butenoic acid, (2Z) -4-[(4-aminophenyl) amino] -2-methyl-4-oxo-2-butenoic acid, sodium (2Z) -4- Illustrative examples include [(4-aminophenyl) amino] -4-oxo-2-butenoic acid, sodium (2Z) -4-[(3-aminophenyl) amino] -4-oxo-2-butenoic acid, and the like. it can. Among them, (2Z) -4-[(4-aminophenyl) amino] -4-oxo-2-butenoic acid, sodium (2Z) -4-[(4-aminophenyl) amino] -4-oxo-2- Butenoic acid is preferred, and (2Z) -4-[(4-aminophenyl) amino] -4-oxo-2-butenoic acid is particularly preferred.

  In the kneaded rubber masterbatch, the content of the compound represented by the general formula (i) is 0.3 to 5.0% by weight, preferably 1.0 to 5.0% by weight based on 100% by weight of the diene rubber. It is. When the content of the compound represented by the general formula (i) is less than 0.3% by weight, the desired effect of the present invention cannot be achieved. On the other hand, if it exceeds 5.0% by weight, the tensile elongation at break of the rubber composition decreases.

  The kneaded rubber masterbatch should be free of reinforcing fillers. When the kneaded rubber masterbatch contains a reinforcing filler, the effects of reducing tan δ (60 ° C.) and improving mechanical properties such as tensile breaking strength, tensile breaking elongation, and rubber hardness are obtained by the present invention. It is inferior to the tire rubber composition obtained.

  In this masticated rubber masterbatch, natural rubber, isoprene rubber and optionally butadiene rubber coexist with the compound represented by the general formula (i) and are dispersed and mixed. Therefore, a reinforcing filler containing carbon black was blended later. When the rubber composition is used, the affinity between the diene rubber and the reinforcing filler containing carbon black can be improved.

  The rubber composition for tires of the present invention is obtained by blending a reinforcing filler containing 30 to 70 parts by weight of carbon black with respect to 100 parts by weight of a rubber component containing 55 to 100% by weight of the above-mentioned masticated rubber masterbatch. is there. The rubber component can optionally contain other diene rubbers in addition to the kneaded rubber masterbatch. The other diene rubber is an unmodified rubber and is selected from butadiene rubber, natural rubber and isoprene rubber.

  In the present invention, 100% by weight of the rubber component is comprised of 55-100% by weight of the kneaded rubber masterbatch and 45-0% by weight in total of butadiene rubber, natural rubber and isoprene rubber. The content of the kneaded rubber masterbatch is 55 to 100% by weight, preferably 75 to 100% by weight. The total of butadiene rubber, natural rubber and isoprene rubber is 45 to 0% by weight, preferably 25 to 0% by weight. When the content of the kneaded rubber masterbatch is less than 55% by weight, the affinity of the reinforcing filler containing the diene rubber and carbon black cannot be sufficiently increased.

  The rubber composition for tires of the present invention specifies the total of the natural rubber and isoprene rubber composing the kneaded rubber masterbatch in the rubber component and other diene rubbers to be added later. That is, a total of 55 to 100% by weight, preferably 75 to 100% by weight of the natural rubber and isoprene rubber to be added in 100% by weight of the rubber component, in the masticated rubber masterbatch and afterwards. By making the total of the natural rubber and isoprene rubber in the rubber component 55% by weight or more, the low heat build-up and the mechanical specification required for the cap tread of the heavy duty pneumatic tire can be obtained.

  The rubber component optionally contains butadiene rubber as another diene rubber added in the masticated rubber masterbatch and afterwards. Here, the butadiene rubber is another diene rubber that can be blended in the kneaded rubber masterbatch, and is optionally contained in the kneaded rubber masterbatch. The total amount of butadiene rubber is 45 to 0% by weight, preferably 30 to 0% by weight, based on 100% by weight of the rubber component. When the total amount of butadiene rubber exceeds 45% by weight, the tensile elongation at break decreases.

The rubber composition for tires of the present invention comprises 30 to 70 parts by weight, preferably 40 to 60 parts by weight of carbon black having a nitrogen adsorption specific surface area of 125 to 150 m ² / g with respect to 100 parts by weight of the rubber component described above. Including a reinforcing filler containing.

  If the blending amount of carbon black is less than 30 parts by weight, the effect of improving the mechanical properties of the rubber composition cannot be obtained sufficiently. When the compounding amount of carbon black exceeds 70 parts by weight, the heat generation property of the rubber composition is increased, and the rolling resistance is increased when the tire is formed.

The nitrogen adsorption specific surface area of carbon black is 125 to 150 m ² / g, preferably 130 to 140 m ² / g. When the nitrogen adsorption specific surface area of carbon black is less than 125 m ² / g, mechanical properties such as rubber strength and rubber hardness of the rubber composition are lowered. If the nitrogen adsorption specific surface area of carbon black exceeds 150 m ² / g, tan δ (60 ° C.) increases. In this specification, the nitrogen adsorption specific surface area of carbon black shall be measured according to JIS K6217-2.

  As the reinforcing filler, other reinforcing fillers other than carbon black can be blended, and examples thereof include silica, clay, aluminum hydroxide, calcium carbonate and the like. As the reinforcing filler, carbon black and silica are preferable, and carbon black is particularly preferable.

  The blending amount of carbon black is preferably 30% by weight or more, more preferably 55 to 100% by weight in 100% by weight of the reinforcing filler. By making carbon black 30% by weight or more in 100% by weight of the reinforcing filler, the affinity of the kneaded rubber masterbatch and the reinforcing filler can be further increased.

  The rubber composition of the present invention reduces the rolling resistance when the tan δ (60 ° C.) is reduced to form a pneumatic tire, and maintains and improves the mechanical properties such as rubber strength and tensile elongation at break. The handling stability and wear resistance of the entering tire can be improved over the conventional level.

（式中、Ｒ¹は置換基を有してもよい炭素数６〜１２の２価の芳香族炭化水素基、Ｒ²，Ｒ³はそれぞれ独立に水素原子、ハロゲン原子、炭素数１〜６のアルキル基、炭素数６〜１２のアリール基、ヒドロキシ基または炭素数１〜６のアルコキシ基、Ｒ⁴はヒドロキシ基または−ＯＮａ、Ｘは−ＮＨ−または−Ｏ−を表す。）
（２）前記素練りゴムマスターバッチ５５〜１００重量％、並びにブタジエンゴム、天然ゴムおよびイソプレンゴムの合計４５〜０重量％からなるゴム成分であると共に、素練りゴムマスターバッチ中および後添加する天然ゴムおよびイソプレンゴムの合計を５５〜１００重量％、並びに任意にブタジエンゴムの合計４５〜０重量％を含むゴム成分１００重量部に対し、窒素吸着比表面積が１２５〜１５０ｍ²／ｇであるカーボンブラックを３０〜７０重量部を配合し、混練することによりゴム混練物を得る第二混合工程、
（３）前記ゴム混練物に、加硫系配合剤を配合し、混合する第三混合工程。 The manufacturing method of the rubber composition for tires of this invention is good to include the process as described in following (1)-(3) at least.
(1) A natural rubber and / or isoprene rubber is added in an amount of 40% by weight or more and optionally a diene rubber containing a butadiene rubber in an amount of 100% by weight, and a compound represented by the following general formula (i) is added in an amount of 0.3 to 5.0% by weight. First mixing step to obtain a kneaded rubber masterbatch by blending and kneading in a state not containing a reinforcing filler,

(In the formula, R ¹ is an optionally substituted divalent aromatic hydrocarbon group having 6 to 12 carbon atoms, R ² and R ³ are each independently a hydrogen atom, a halogen atom, or 1 to 6 carbon atoms. An alkyl group, a C 6-12 aryl group, a hydroxy group or a C 1-6 alkoxy group, R ⁴ represents a hydroxy group or —ONa, and X represents —NH— or —O—.)
(2) 55-100% by weight of the kneaded rubber masterbatch, and a rubber component comprising a total of 45-0% by weight of butadiene rubber, natural rubber and isoprene rubber, and natural added in and after the masticated rubber masterbatch Carbon black having a nitrogen adsorption specific surface area of 125 to 150 m ² / g based on 100 parts by weight of a rubber component containing 55 to 100% by weight of rubber and isoprene rubber, and optionally 45 to 0% by weight of butadiene rubber. A second mixing step of blending 30 to 70 parts by weight and obtaining a rubber kneaded product by kneading,
(3) A third mixing step in which the rubber kneaded material is mixed with a vulcanizing compound and mixed.

  The rubber composition for tires of the present invention can be manufactured by a manufacturing method including at least three steps including a first mixing step (1), a second mixing step (2), and a third mixing step (3). If necessary, other kneading steps and / or mixing steps can be added. In this specification, mixing refers to the operation of mixing the blended ingredients to bring them into a homogeneous state, and kneading means distributing and dispersing the mixture in a homogeneous state, applying shearing force, and heating as necessary. The operation of kneading. The kneading and mixing can be performed using a commonly used means.

  The first mixing step (1) is a step of preparing a kneaded rubber master batch. The kneaded rubber masterbatch contains 100% by weight of a diene rubber containing natural rubber and / or isoprene rubber, and optionally butadiene rubber, and the compound represented by the general formula (i) is 0.3 to 5. It can be produced by blending 0% by weight and kneading in a state not containing a reinforcing filler. When the compounding amount of the compound represented by the general formula (i) is less than 0.3% by weight, the tan δ (60 ° C.) of the rubber composition is reduced, and the mechanical properties such as tensile breaking strength, tensile breaking elongation, rubber hardness, etc. The effect of improving the physical characteristics is not sufficiently obtained. On the other hand, if it exceeds 5.0% by weight, the tensile elongation at break of the rubber composition decreases.

In this production method, the kneaded rubber master batch needs to contain no reinforcing filler. If the kneaded rubber masterbatch contains a reinforcing filler, a tire rubber composition having the desired effect cannot be obtained. Moreover, as a compound represented by general formula (i), the compound whose R < ⁴ > is a hydroxy group is preferable.

  In the first mixing step (1), for example, in a natural rubber mastication step, the compound represented by the general formula (i) and optionally butadiene rubber are blended and kneaded in natural rubber and / or isoprene rubber. Can be implemented.

  Here, in 100% by weight of the diene rubber, the content of natural rubber and / or isoprene rubber is 40% by weight or more, preferably 50 to 100% by weight. When the content of the natural rubber and isoprene rubber is less than 40% by weight, the compound specified in the diene rubber cannot be sufficiently dispersed and mixed.

  In the first mixing step (1), the diene rubber and the compound represented by the general formula (i) are preferably kneaded at 150 to 180 ° C, more preferably 160 to 170 ° C. The kneading time is preferably 1 to 5 minutes, more preferably 2 to 4 minutes. By setting the kneading temperature and time in the first mixing step (1) within the above ranges, mechanical properties such as tensile breaking strength and tensile breaking elongation, particularly, tensile breaking elongation can be prevented from decreasing.

  In the second mixing step (2), the reinforcement containing 30 to 70 parts by weight of carbon black with respect to 100 parts by weight of the rubber component containing 55 to 100% by weight of the kneaded rubber masterbatch obtained in the first mixing step (1). A rubber kneaded product is obtained by blending and kneading compounding agents other than the conductive filler and the vulcanizing compound compounding agent. Carbon black is blended in an amount of 30 to 70 parts by weight, preferably 40 to 60 parts by weight, per 100 parts by weight of the rubber component. If the blending amount of carbon black is less than 30 parts by weight, the effect of improving mechanical properties such as tensile breaking strength and rubber hardness of the rubber composition cannot be obtained sufficiently. If the blending amount of carbon black exceeds 70 parts by weight, tan δ (60 ° C.) increases and tensile elongation at break decreases.

  As described above, examples of the reinforcing filler other than carbon black include silica, clay, aluminum hydroxide, and calcium carbonate. Of these, silica is preferable. The blending amount of the carbon black is preferably 30% by weight or more in 100% by weight of the reinforcing filler.

  In the second mixing step (2), the rubber kneaded material is mixed with a compounding agent other than the vulcanized compounding agent in addition to the kneaded rubber masterbatch and the reinforcing filler. Here, the vulcanizing compound includes a vulcanizing agent and a crosslinking agent, a vulcanization accelerator, a crosslinking accelerator, and a vulcanization retarder. Examples of additives other than vulcanizing additives include, for example, various additives generally used in tire rubber compositions such as zinc oxide, stearic acid, antioxidants, various oils, and plasticizers. Can do.

  In the second mixing step (2), the kneading operation is performed under the normal conditions in which the rubber kneaded material described above is applied to the mixture of the diene rubber and the reinforcing filler. The kneading temperature in the second mixing step is preferably 120 to 190 ° C, more preferably 140 to 180 ° C.

  The third mixing step (3) is a step of blending and mixing a vulcanizing compound with the rubber kneaded material obtained in the second mixing step. A vulcanization system compounding agent means the compounding agent mentioned above. In the third mixing step, mixing is performed by determining conditions so that the vulcanizing compound does not cause early vulcanization and crosslinking.

  The tire rubber composition obtained by the production method of the present invention is blended with 30 to 70 parts by weight of carbon black with respect to 100 parts by weight of the rubber component containing the kneaded rubber masterbatch. This carbon black is not blended in the kneaded rubber masterbatch produced in the first mixing step, but blended in the second mixing step. Thus, by not adding the reinforcing filler to the first mixing step, the reinforcing filler and the compound represented by the general formula (i) are prevented from agglomerating and the dispersibility of the carbon black is improved. The tan δ (60 ° C.) of the rubber composition can be reduced, and the mechanical strength, particularly the tensile elongation at break can be improved.

  The tire rubber composition of the present invention can be suitably used for a cap tread of a pneumatic tire for heavy loads. A heavy-duty pneumatic tire using the rubber composition of the present invention for the cap tread has low heat generation during running, so that rolling resistance can be reduced and fuel efficiency can be improved. At the same time, by improving the mechanical properties of the rubber composition, it is possible to maintain and improve the handling stability, wear resistance, and durability to the conventional level or higher.

  EXAMPLES Hereinafter, although an Example demonstrates this invention further, the scope of the present invention is not limited to these Examples.

  16 types of rubber compositions (Examples 1 to 8, Standard Examples, and Formulas 1 to 8 shown in Tables 1 to 3) were mixed as shown in Tables 1 to 3 in the three steps including the first mixing step, the second mixing step, and the third mixing step. Comparative Examples 1-7) were prepared. First, kneading is carried out under the conditions described in the column “First kneading condition of the first mixing step” and the following conditions of the first mixing step, with the compounding described in the column “Mixing of the first mixing step (kneaded rubber masterbatch)”. A kneaded rubber masterbatch was prepared. In addition, the compound of the comparative example which does not correspond to the kneaded rubber masterbatch of this invention is also considered as a kneaded rubber masterbatch for convenience. Using the resulting kneaded rubber masterbatch, kneading is carried out under the conditions of the following second mixing step with the formulation described in the column of “blending of the second mixing step (rubber kneaded product)” to prepare a rubber kneaded product did. Using the obtained rubber kneaded material, the rubber composition for tires was prepared by mixing under the conditions of the following third mixing step with the formulation described in the column of “3rd mixing step”.

  In addition, the description of the column of “kneaded rubber masterbatch (amount of rubber component)” in “mixture of second mixing step (rubber kneaded material)” in Tables 1 to 3 is the kneaded rubber master prepared in the first mixing step The amount of the rubber component described in the parenthesis represents the amount of the diene rubber contained therein. The description of “compounding agent (Table 4)” in “compounding of the second mixing step (rubber kneaded material)” in Tables 1 to 3 is the sum of compounding agents other than the vulcanizing compounding agent added in the second mixing step. The compounding agents other than the vulcanizing compounding agents are shown in Table 4 as common prescriptions.The amount of the compounding agent other than the vulcanizing compounding compound described in Table 4 is the tire described in Tables 1-3. Means parts by weight with respect to 100 parts by weight of the rubber component constituting the rubber composition.

<First mixing step>
After pre-mixing natural rubber for 1 minute (97 ° C.) using a 1.8 L Banbury mixer, add the compound described in the column of “Composition of first mixing step (kneaded rubber MB)” in Tables 1 to 3 And kneaded. In the table, a compound that does not correspond to the kneaded rubber masterbatch of the present invention is also described in the column of “Composition of the first mixing step (kneaded rubber MB)” for convenience. The total mixing time in the first mixing step was 4 minutes, and the filling rate was 72%. Tables 1 to 3 show the kneading temperature and the time for keeping the kneading temperature.

<Second mixing step>
Using a 1.8 L Banbury mixer, the kneaded rubber masterbatch obtained in the first mixing step and optionally the diene rubber blended in the second mixing step are premixed for 1 minute, and then carbon black or the like “ The compounding agents described in the column “Combination of two mixing steps (rubber kneaded product)” were mixed. In the table, the mixture obtained in the first mixing step that does not correspond to the kneaded rubber masterbatch of the present invention is also described in the column of “kneaded rubber MB (rubber component amount)” for convenience. The total mixing time of the second mixing step is 5 minutes 30 seconds, and the rubber temperature at that time is 162 ° C.

<Third mixing step>
The rubber kneaded material obtained in the second mixing step, the vulcanization accelerator, and sulfur at a temperature of 70 to 90 ° C. in an open roll machine are described in the column of “third mixing step” in Tables 1 to 3. The rubber composition for tires was obtained by blending with the composition.

  The obtained 16 kinds of rubber compositions were each vulcanized in a mold having a predetermined shape at 170 ° C. for 10 minutes to prepare test pieces. The rubber hardness, tensile properties and dynamic viscosity were determined by the following methods. Elasticity (tan δ at 60 ° C.) and wear resistance were evaluated.

Rubber hardness Using the obtained test piece, it was measured at a temperature of 20 ° C. with a durometer type A according to JIS K6253. The obtained results are shown in the column of “rubber hardness” with the value of the standard example being 100. The larger the rubber hardness index, the better the steering stability.

Tensile properties From the obtained test pieces, JIS No. 3 dumbbell-type test pieces (thickness 2 mm) were punched out in accordance with JIS K6251 and tested at a pulling rate of 500 mm / min at 100 ° C. to measure the tensile elongation at break. The obtained results are shown in the column of “Elongation at break” as an index with the value of the standard example as 100. The larger the elongation at break, the better the tire durability.

Dynamic viscoelasticity (tan δ at 60 ° C)
Based on JIS K6394, the obtained test piece was subjected to a loss tangent tan δ at a temperature of 60 ° C. under the conditions of an initial strain of 10%, an amplitude of ± 2%, and a frequency of 20 Hz, using a viscoelastic spectrometer manufactured by Toyo Seiki Seisakusho. It was measured. The obtained results are shown in the column of “tan δ (60 ° C.)” as an index with the value of the standard example as 100. The smaller the index of tan δ (60 ° C.), the smaller the heat generation, and the smaller the rolling resistance when the tire is made, the better the fuel efficiency.

In addition, the kind of raw material used in Tables 1-3 is shown below.
-NR: natural rubber, STR20
-BR: Butadiene rubber, NIPOL BR1220 manufactured by Nippon Zeon
-Carbon Black: Cabot Japan Show Black S118, nitrogen adsorption specific surface area of 140 m ² / g
-Sulfur: Flexex HS manufactured by Flexis
-Vulcanization accelerator: Nouchira NS

-Compound (i): (2Z) -4-[(4-aminophenyl) amino] -4-oxo-2-butenoic acid, prepared by the following method. Under a nitrogen atmosphere, a reaction vessel was charged with 25.17 g (0.233 mol) of 1,4-phenylenediamine and 230 ml of tetrahydrofuran. A solution prepared by dissolving 22.84 g (0.233 mol) of maleic anhydride in 50 ml of tetrahydrofuran was added dropwise thereto in about 1 hour under ice cooling, and the mixture was stirred overnight at room temperature. After completion of the reaction, the precipitated crystals were collected by filtration, washed twice with 40 ml of tetrahydrofuran, dried at 40 ° C. for 5 hours, and crude (2Z) -4-[(4-aminophenyl) amino] -4-oxo- 46.92 g of 2-butenoic acid was obtained as an orange powder. 250 ml of methanol was added to 46.92 g of crude (2Z) -4-[(4-aminophenyl) amino] -4-oxo-2-butenoic acid, stirred at 50 ° C. for 1 hour, cooled, filtered, and 20 ml of methanol. Washed twice. The obtained crystals were dried to obtain 42.67 g of (2Z) -4-[(4-aminophenyl) amino] -4-oxo-2-butenoic acid as a yellow-orange powder. The yield was 88.8%.

In addition, the kind of raw material used in Table 4 is shown below.
-Zinc oxide: 3 types of zinc oxide manufactured by Shodo Chemical Co., Ltd.-Stearic acid: Stearic acid YR manufactured by NOF Corporation
Anti-aging agent: SANTOFLEX 6PPD manufactured by FLEXSYS

  As is apparent from Tables 2 and 3, it was confirmed that the rubber compositions for tires of Examples 1 to 8 were improved in rubber hardness, tensile elongation at break and tan δ (60 ° C.) to the conventional level or more.

  As is clear from Table 1, the rubber composition of Comparative Example 1 did not perform the first mixing step and did not use the kneaded rubber master batch, so that the tensile elongation at break deteriorates. In the rubber composition of Comparative Example 2, since the kneaded rubber master batch produced in the first mixing step contains carbon black without containing the compound represented by the general formula (i), the rubber hardness is deteriorated.

  In the rubber composition of Comparative Example 3, since the kneaded rubber masterbatch produced in the first mixing step contains carbon black, the tensile elongation at break is deteriorated. In the rubber composition of Comparative Example 4, the kneaded rubber masterbatch produced in the first mixing step contains carbon black in an amount exceeding a predetermined amount (the compounding amount is 84 parts by weight), so that the tensile elongation at break is deteriorated. . In the rubber composition of Comparative Example 5, since the kneaded rubber masterbatch produced in the first mixing step does not contain the compound represented by the general formula (i), rubber hardness and tensile elongation at break are deteriorated.

  As is clear from Table 2, the rubber composition of Comparative Example 6 has a tensile elongation at break deteriorated because butadiene rubber exceeds 45% by weight in 100% by weight of the rubber component.

  As is apparent from Table 3, the rubber composition of Comparative Example 7 contains the compound represented by the general formula (i) in excess of a predetermined amount, so that the tensile elongation at break deteriorates.

Claims (3)

Natural rubber and / or isoprene rubber in an amount of 40% by weight or more and optionally 100% by weight of a diene rubber containing butadiene rubber coexisting with 0.3 to 5.0% by weight of a compound represented by the following general formula (i) It is a rubber component consisting of 55 to 100% by weight of a kneaded rubber masterbatch and a total of 45 to 0% by weight of butadiene rubber, natural rubber and isoprene rubber, and a total of 55 to 100% by weight of natural rubber and isoprene rubber. 30 to 70 parts by weight of carbon black having a nitrogen adsorption specific surface area of 125 to 150 m ² / g is blended with 100 parts by weight of a rubber component containing 45 to 0% by weight of butadiene rubber in total. Rubber composition.

(In the formula, R ¹ is an optionally substituted divalent aromatic hydrocarbon group having 6 to 12 carbon atoms, R ² and R ³ are each independently a hydrogen atom, a halogen atom, or 1 to 6 carbon atoms. An alkyl group, a C 6-12 aryl group, a hydroxy group or a C 1-6 alkoxy group, R ⁴ represents a hydroxy group or —ONa, and X represents —NH— or —O—.) The tire rubber composition according to claim 1, wherein in the general formula (i), R ⁴ is a hydroxy group.   A heavy-duty pneumatic tire using the tire rubber composition according to claim 1 or 2 for a cap tread.