JP2011225735A - Pneumatic tire - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a pneumatic tire in which low rolling resistance, elastic modulus and wear resistance are made highly compatible.SOLUTION: The pneumatic tire uses a rubber composition in its tire member, which contains a hydrazone compound and carbon black having a nitrogen adsorption specific surface area (NSA) of >130 and ≤160 m/g and a dibutyl phthalate (DBP) oil absorption amount of 60-170 mL/100g to 100 pts.mass of a rubber component containing modified natural rubber obtained by adding a polar group-containing monomer to a natural rubber latex, then subjecting the monomer to graft polymerization with the natural rubber in the natural rubber latex, and coagulating and drying the resulting rubber.

Description

  The present invention relates to a pneumatic tire, and more particularly, to a pneumatic tire that achieves both low rolling resistance, elastic modulus, and wear resistance at a high level.

  Conventionally, as means for improving the rolling resistance of tires, there are methods such as reducing the amount of carbon black compounded in the rubber composition constituting the tire or replacing part of the carbon black with silica. Although employed, such a method has a problem that it is difficult to ensure wear resistance.

  In order to ensure the dispersion of the filler and reduce the hysteresis loss, a method using a synthetic rubber in which the end of the synthetic rubber is modified with carbon or silane is also used (for example, refer to Patent Document 1) and has a certain effect. However, in a blend mainly composed of natural rubber such as a pneumatic tire, the filler dispersion in the natural rubber portion cannot be said to be sufficient, and further improvement is desired.

  On the other hand, the applicant of the present invention adds the polar group-containing monomer to the natural rubber latex, grafts the monomer to the natural rubber in the natural rubber latex, solidifies and dries the natural characteristics of the natural rubber. A modified natural rubber (see, for example, Patent Document 2) excellent in odor reduction and freezing resistance during storage while being maintained is proposed.

  Further, in order to provide a low heat-generating rubber composition with improved low heat-generating properties, 100 parts by weight of a rubber component composed of at least one rubber selected from the group consisting of natural rubber and synthetic rubber is reinforced. Low exothermic rubber composition formed by blending 20 to 150 parts by weight of the filler and 0.05 to 20 parts by weight of at least one selected from the group consisting of a specific hydrazone compound (for example, see Patent Document 3) In addition, in order to provide a pneumatic tire having high elasticity, low heat generation, and improved wear resistance, silica and a specific reactive group for the rubber component in the same molecule are added to the rubber component. And a compound having two or more specific adsorption groups for silica and a hydrazone compound, and the rubber component is added to a natural rubber latex with a polar group-containing monomer or alkoxysilane. And a modified natural rubber obtained by grafting the monomer to a natural rubber molecule in a natural rubber latex and further coagulating and drying the rubber component. A rubber composition characterized in that it is 0.5 to 20 parts by mass with respect to 100 parts by mass, and the compounding amount of the hydrazone compound is 0.1 to 10 parts by mass with respect to 100 parts by mass of the rubber component. A pneumatic tire used for a tire member (for example, see Patent Document 4) has been proposed.

  However, the rubber compositions and pneumatic tires shown in the above Patent Documents 2 to 4 have performances such as low heat generation, which are unprecedented, but pneumatic tires having further low rolling resistance are anxious. Has been.

Further, when carbon black is used for the modified natural rubber, the dispersibility of the carbon black is improved and the rolling resistance is low.
However, the improvement in the dispersibility of carbon black has the problem of simultaneously lowering the elastic modulus and deteriorating riding comfort and handling stability.

JP 2001-131230 A (Claims, Examples, etc.) JP-A-2004-359717 (Claims, Examples, etc.) JP-A-10-139934 (Claims, Examples, etc.) JP 2006-143830 A (Claims, Examples, etc.)

  In view of the above-described conventional problems and current situation, the present invention aims to solve this problem, and an object of the present invention is to provide a pneumatic tire that is highly compatible with low rolling resistance, elastic modulus, and wear resistance. To do.

  As a result of intensive studies on the above-described conventional problems, the present inventor has obtained a rubber composition containing a specific hydrazone compound and carbon black having specific physical properties for a rubber component including a specific modified natural rubber. It has been found that a pneumatic tire of the above-mentioned purpose can be obtained by applying to a member, and the present invention has been completed.

That is, the present invention resides in the following (1) to (6).
(1) 100 parts by mass of a rubber component containing a modified natural rubber obtained by adding a polar group-containing monomer to natural rubber latex, graft-polymerizing the monomer to natural rubber in natural rubber latex, coagulating and drying In contrast, a hydrazone compound, a carbon black having a nitrogen adsorption specific surface area (N ₂ SA) of more than 130 m ² / g and 160 m ² / g and a dibutyl phthalate (DBP) oil absorption of 60 to 170 mL / 100 g A pneumatic tire comprising a tire composition containing a rubber composition.
(2) The polar group of the polar group-containing monomer is an amino group, imino group, nitrile group, ammonium group, imide group, amide group, hydrazo group, azo group, diazo group, hydroxyl group, carboxyl group, carbonyl group, It is at least one selected from the group consisting of epoxy groups, oxycarbonyl groups, sulfide groups, disulfide groups, sulfonyl groups, sulfinyl groups, thiocarbonyl groups, nitrogen-containing heterocyclic groups, and oxygen-containing heterocyclic groups. The pneumatic tire according to (1) above.
(3) The above (1) or (1), wherein the amount of the monomer grafted in the modified natural rubber is 0.01 to 5.0% by mass with respect to the rubber component in the natural rubber latex. The pneumatic tire as described in 2).
(4) The pneumatic tire according to any one of (1) to (3), wherein the rubber component of the rubber composition contains 20 parts by mass or more of the modified natural rubber in 100 parts by mass. .
(5) The pneumatic tire according to any one of (1) to (4), wherein the content of the hydrazone compound is 0.1 to 5.0 parts by mass.
(6) The pneumatic tire according to any one of (1) to (5), wherein the carbon black content is 20 to 80 parts by mass.

  According to the present invention, even when used in carbon black as a rubber component containing a specific modified natural rubber, a pneumatic material that achieves a high level of both low rolling resistance, elastic modulus and wear resistance without lowering the elastic modulus. Tires are provided.

Hereinafter, embodiments of the present invention will be described in detail.
The pneumatic tire of the present invention includes a modified natural rubber obtained by adding a polar group-containing monomer to a natural rubber latex, graft-polymerizing the monomer to the natural rubber in the natural rubber latex, and coagulating and drying. With respect to 100 parts by mass of the rubber component, the hydrazone compound, the nitrogen adsorption specific surface area (N ₂ SA) is more than 130 m ² / g and not more than 160 m ² / g, and the dibutyl phthalate (DBP) oil absorption is 60 to 170 mL / 100 g. A rubber composition containing carbon black to be used is used for a tire member.

The modified natural rubber used in the present invention is obtained by adding a polar group-containing monomer to natural rubber latex, graft-polymerizing the monomer to natural rubber in the natural rubber latex, solidifying and drying.
The natural rubber latex used for the modified natural rubber is not particularly limited. For example, field latex, ammonia-treated latex, centrifugal concentrated latex, deproteinized latex treated with a surfactant or an enzyme, and combinations thereof. At least one of the above can be used.

The polar group-containing monomer added to the natural rubber latex is not particularly limited as long as it has at least one polar group in the molecule and can be graft-polymerized with the natural rubber molecule.
The polar group-containing monomer used preferably has a carbon-carbon double bond in the molecule for graft polymerization with the natural rubber molecule. Specific examples of the polar group include amino group, imino group, nitrile group, ammonium group, imide group, amide group, hydrazo group, azo group, diazo group, hydroxyl group, carboxyl group, carbonyl group, epoxy group, oxycarbonyl Preferred examples include groups, sulfide groups, disulfide groups, sulfonyl groups, sulfinyl groups, thiocarbonyl groups, nitrogen-containing heterocyclic groups, and oxygen-containing heterocyclic groups. These monomers containing a polar group may be used alone or in combination of two or more.

  Examples of the monomer containing an amino group include polymerizable monomers containing at least one amino group selected from primary, secondary and tertiary amino groups in one molecule. . Among the polymerizable monomers having an amino group, a tertiary amino group-containing monomer such as dialkylaminoalkyl (meth) acrylate is particularly preferable. These amino group-containing monomers may be used alone or in a combination of two or more.

  Examples of the primary amino group-containing monomer include acrylamide, methacrylamide, 4-vinylaniline, aminomethyl (meth) acrylate, aminoethyl (meth) acrylate, aminopropyl (meth) acrylate, aminobutyl (meth) ) Acrylate and the like.

  Examples of secondary amino group-containing monomers include (1) anilinostyrene, β-phenyl-p-anilinostyrene, β-cyano-p-anilinostyrene, β-cyano-β-methyl. -p-anilinostyrene, β-chloro-p-anilinostyrene, β-carboxy-p-anilinostyrene, β-methoxycarbonyl-p-anilinostyrene, β- (2-hydroxyethoxy) carbonyl-p- Anilinostyrene such as anilinostyrene, β-formyl-p-anilinostyrene, β-formyl-β-methyl-p-anilinostyrene, α-carboxy-β-carboxy-β-phenyl-p-anilinostyrene (2) Anilinophenylbutadiene, 1-anilinophenyl-1,3-butadiene, 1-anilinophenyl-3-methyl-1,3-butadiene, 1-anilinophenyl-3-chloro-1, 3-butadiene, 3-anilinophenyl-2-me Cyl-1,3-butadiene, 1-anilinophenyl-2-chloro-1,3-butadiene, 2-anilinophenyl-1,3-butadiene, 2-anilinophenyl-3-methyl-1,3- Anilinophenylbutadienes such as butadiene, 2-anilinophenyl-3-chloro-1,3-butadiene, (3) N-methyl (meth) acrylamide, N-ethyl (meth) acrylamide, N-methylolacrylamide, N And N-monosubstituted (meth) acrylamides such as-(4-anilinophenyl) methacrylamide.

  Furthermore, examples of the tertiary amino group-containing monomer include N, N-disubstituted aminoalkyl (meth) acrylate and N, N-disubstituted aminoalkyl (meth) acrylamide.

  Examples of the N, N-disubstituted aminoalkyl (meth) acrylate include N, N-dimethylaminomethyl (meth) acrylate, N, N-dimethylaminoethyl (meth) acrylate, N, N-dimethylaminopropyl ( (Meth) acrylate, N, N-dimethylaminobutyl (meth) acrylate, N, N-diethylaminoethyl (meth) acrylate, N, N-diethylaminopropyl (meth) acrylate, N, N-diethylaminobutyl (meth) acrylate, N -Methyl-N-ethylaminoethyl (meth) acrylate, N, N-dipropylaminoethyl (meth) acrylate, N, N-dibutylaminoethyl (meth) acrylate, N, N-dibutylaminopropyl (meth) acrylate, N, N-dibutylaminobutyl (meth) acrylate, N, N-dihexylaminoethyl (meth) acrylate, N, N- Octyl aminoethyl (meth) acrylate, esters of acrylic acid or methacrylic acid such as acryloyl morpholine and the like. Among these, N, N-dimethylaminoethyl (meth) acrylate, N, N-diethylaminoethyl (meth) acrylate, N, N-dipropylaminoethyl (meth) acrylate, N, N-diocleaminoethyl (meta) ) Acrylate, N-methyl-N-ethylaminoethyl (meth) acrylate and the like are particularly preferred.

  Examples of the N, N-disubstituted aminoalkyl (meth) acrylamide include N, N-dimethylaminomethyl (meth) acrylamide, N, N-dimethylaminoethyl (meth) acrylamide, and N, N-dimethylamino. Propyl (meth) acrylamide, N, N-dimethylaminobutyl (meth) acrylamide, N, N-diethylaminoethyl (meth) acrylamide, N, N-diethylaminopropyl (meth) acrylamide, N, N-diethylaminobutyl (meth) acrylamide N-methyl-N-ethylaminoethyl (meth) acrylamide, N, N-dipropylaminoethyl (meth) acrylamide, N, N-dibutylaminoethyl (meth) acrylamide, N, N-dibutylaminopropyl (meth) Acrylamide, N, N-dibutylaminobutyl (meth) acrylamide, N, N-dihexylamino Examples include acrylamide compounds such as ethyl (meth) acrylamide, N, N-dihexylaminopropyl (meth) acrylamide, N, N-dioctylaminopropyl (meth) acrylamide, and methacrylamide compounds. Among these, N, N-dimethylaminopropyl (meth) acrylamide, N, N-diethylaminopropyl (meth) acrylamide, N, N-dioctylaminopropyl (meth) acrylamide and the like are particularly preferable.

  Examples of the nitrile group-containing monomer include (meth) acrylonitrile, vinylidene cyanide, and the like. These nitrile group-containing monomers may be used alone or in a combination of two or more.

  Examples of the monomer containing a hydroxyl group include polymerizable monomers having at least one primary, secondary, and tertiary hydroxyl group in one molecule. Examples of such monomers include hydroxyl group-containing unsaturated carboxylic acid monomers, hydroxyl group-containing vinyl ether monomers, hydroxyl group-containing vinyl ketone monomers, and the like. Here, specific examples of the hydroxyl group-containing monomer include 2-hydroxyethyl (meth) acrylate, 2-hydroxypropyl (meth) acrylate, 3-hydroxypropyl (meth) acrylate, and 2-hydroxybutyl (meth) acrylate. Hydroxyalkyl (meth) acrylates such as 3-hydroxybutyl (meth) acrylate and 4-hydroxybutyl (meth) acrylate; polyalkylene glycols such as polyethylene glycol and polypropylene glycol (the number of alkylene glycol units is, for example, 2 to 23 Mono (meth) acrylates; N-hydroxymethyl (meth) acrylamide, N- (2-hydroxyethyl) (meth) acrylamide, N, N-bis (2-hydroxymethyl) (meth) acrylamide, etc. Hydroxyl group-containing unsaturated amides; o-hydroxy Hydroxyl group-containing vinyl such as tylene, m-hydroxystyrene, p-hydroxystyrene, o-hydroxy-α-methylstyrene, m-hydroxy-α-methylstyrene, p-hydroxy-α-methylstyrene, p-vinylbenzyl alcohol Aromatic compounds etc. are mentioned. Among these, hydroxyl group-containing unsaturated carboxylic acid monomers, hydroxyalkyl (meth) acrylates, and hydroxyl group-containing vinyl aromatic compounds are preferable, and hydroxyl group-containing unsaturated carboxylic acid monomers are particularly preferable. Here, examples of the hydroxyl group-containing unsaturated carboxylic acid-based monomer include esters such as acrylic acid, methacrylic acid, itaconic acid, fumaric acid, maleic acid, amides, and anhydrides. Among these, Particularly preferred are esters such as acrylic acid and methacrylic acid. These hydroxyl group-containing monomers may be used alone or in a combination of two or more.

  Examples of the monomer containing a carboxyl group include unsaturated carboxylic acids such as (meth) acrylic acid, maleic acid, fumaric acid, itaconic acid, tetraconic acid, cinnamic acid; phthalic acid, succinic acid, adipic acid, etc. Non-polymerizable polyvalent carboxylic acids and free carboxyl group-containing esters such as monoesters of hydroxyl-containing unsaturated compounds such as (meth) allyl alcohol and 2-hydroxyethyl (meth) acrylate, and salts thereof It is done. Of these, unsaturated carboxylic acids are particularly preferred. These carboxyl group-containing monomers may be used alone or in a combination of two or more.

  Examples of the monomer containing an epoxy group include (meth) allyl glycidyl ether, glycidyl (meth) acrylate, 3,4-oxycyclohexyl (meth) acrylate, and the like. These epoxy group-containing monomers may be used alone or in combination of two or more.

  In the nitrogen-containing heterocyclic group-containing monomer, examples of the nitrogen-containing heterocyclic ring include pyrrole, histidine, imidazole, triazolidine, triazole, triazine, pyridine, pyrimidine, pyrazine, indole, quinoline, purine, phenazine, Examples include pteridine and melamine. The nitrogen-containing heterocycle may contain other heteroatoms in the ring. Here, as a monomer containing a pyridyl group as a nitrogen-containing heterocyclic group, 2-vinylpyridine, 3-vinylpyridine, 4-vinylpyridine, 5-methyl-2-vinylpyridine, 5-ethyl-2- Examples include vinyl compounds containing a pyridyl group such as vinyl pyridine, among which 2-vinyl pyridine, 4-vinyl pyridine and the like are particularly preferable. These nitrogen-containing heterocyclic group-containing monomers may be used alone or in a combination of two or more.

  In the modified natural rubber used in the present invention, graft polymerization of the polar group-containing monomer onto the natural rubber molecule is performed by, for example, emulsion polymerization. Here, in the emulsion polymerization, generally, the above-mentioned monomer is added to a solution obtained by adding water and, if necessary, an emulsifier to natural rubber latex, and a polymerization initiator is further added at a predetermined temperature. It is preferred to polymerize the monomer by stirring. In addition, in the addition of the monomer to the natural rubber latex, an emulsifier may be added to the natural rubber latex in advance, or the monomer may be added to the natural rubber latex after being emulsified with the emulsifier. In addition, it does not specifically limit as an emulsifier which can be used for emulsification of a natural rubber latex and / or a monomer, Nonionic surfactants, such as polyoxyethylene lauryl ether, are mentioned.

There is no restriction | limiting in particular as said polymerization initiator, The polymerization initiator for various emulsion polymerization can be used, and there is no restriction | limiting in particular also about the addition method. Examples of commonly used polymerization initiators include benzoyl peroxide, hydrogen peroxide, cumene hydroperoxide, tert-butyl hydroperoxide, di-tert-butyl peroxide, 2,2-azobisisobutyronitrile, 2,2-azobis (2-diaminopropane) hydrochloride, 2,2-azobis (2-diaminopropane) dihydrochloride, 2,2-azobis (2,4-dimethylvaleronitrile), potassium persulfate, sodium persulfate And ammonium persulfate.
In order to lower the polymerization temperature, it is preferable to use a redox polymerization initiator. Examples of the reducing agent to be combined with the peroxide in the redox polymerization initiator include tetraethylenepentamine, mercaptans, acidic sodium sulfite, reducing metal ions, ascorbic acid and the like. A preferred combination of a peroxide and a reducing agent in the redox polymerization initiator includes a combination of tert-butyl hydroperoxide and tetraethylenepentamine.

  In order to improve low loss and wear resistance without lowering the processability of the rubber composition by blending carbon black and the like described later with the rubber component containing the modified natural rubber, each natural rubber molecule Since it is important that the monomer is introduced in a small amount and uniformly, the addition amount of the polymerization initiator is preferably in the range of 1 to 100 mol%, more preferably in the range of 10 to 100 mol% with respect to the monomer. Further preferred.

  The modified natural rubber used in the present invention is a modified natural rubber in which the above-mentioned components are graft-copolymerized to natural rubber molecules by charging the above-described components in a reaction vessel and reacting at 30 to 80 ° C. for 10 minutes to 7 hours. Latex is obtained. The modified natural rubber latex is coagulated, washed, and then dried using a dryer such as a vacuum dryer, air dryer, drum dryer or the like to obtain the desired modified natural rubber. Here, the coagulant used for coagulating the modified natural rubber latex is not particularly limited, and examples thereof include acids such as formic acid and sulfuric acid, and salts such as sodium chloride.

In the modified natural rubber latex and the modified natural rubber, the graft amount of the monomer is preferably in the range of 0.01 to 5.0% by mass with respect to the rubber component in the natural rubber latex, and 0.1 to 3. The range of 0% by mass is further preferable, and the range of 0.2 to 1.0% by mass is even more preferable.
By making the graft amount of this monomer 0.01% by mass or more, it becomes possible to sufficiently improve the low loss property and wear resistance of the rubber composition, while the graft amount of the monomer is 5%. By setting the content to 0.0 mass% or less, the physical properties inherent to natural rubber can be improved without greatly changing the physical properties inherent to natural rubber such as viscoelasticity and SS characteristics (stress-strain curve in a tensile tester). Since it can be utilized, the processability of the rubber composition can be kept good.

The rubber component used in the present invention preferably contains the above modified natural rubber in an amount of 20 parts by mass or more per 100 parts by mass of the rubber component.
If the modified natural rubber is 20 parts by mass or more in 100 parts by mass of the rubber component, the dispersibility between the rubber component and the carbon black to be used is greatly improved, and the reinforcing effect of the carbon black is sufficiently exhibited. The wear resistance and low-loss property can be greatly improved.
Examples of rubber components that can be used other than the above-described modified natural rubber include unmodified natural rubber (NR), polyisoprene rubber (IR), polybutadiene rubber (BR), and styrene-butadiene copolymer rubber (SBR). The diene-based synthetic rubber can be used.

The hydrazone compound contained in the rubber composition used in the pneumatic tire of the present invention suppresses the vulcanization return of the rubber composition and reduces the elastic modulus of the rubber composition and reduces the elasticity of the rubber composition. The synergistic effect can further reduce the heat generation of the rubber composition.
As the hydrazone compound that can be used, hydrazone compounds represented by the following formulas (I) to (III) are preferable.

In the above formulas (I) to (III), A is a divalent aromatic ring group (any of the ortho-position, meta-position, and para-position, regardless of the position of the bond), hydantoin ring group, or carbon number It represents 0-18 saturated or unsaturated linear hydrocarbon group (ethylene group, tetramethylene group, heptamethylene group, octamethylene group, octadecamethylene group, 7,11-octadecadienylene group, etc.). B represents an aromatic group (such as a phenyl group or a naphthyl group). X represents a hydroxy group or an amino group. Y represents a pyridyl group or a hydrazino group. R ^{1 to} R ⁴ are a hydrogen atom, an alkyl group having 1 to 18 carbon atoms, a cycloalkyl group, and an aromatic ring (which may have a substituent, and the position of the substituent in that case does not matter). Yes, they may be the same as or different from each other.

  Examples of the hydrazone compound represented by the above formula (I) include isophthalic acid dihydrazide, adipic acid hydrazide derivative isophthalic acid di (1-methylethylidene) hydrazide, adipic acid di (1-methylethylidene) hydrazide, and isophthalic acid. Acid di (1-methylpropylidene) hydrazide, adipic acid di (1-methylpropylidene) hydrazide, isophthalic acid di (1,3-dimethylpropylidene) hydrazide, adipic acid di (1,3-dimethylpropylidene) hydrazide And isophthalic acid di (1-phenylethylidene) hydrazide, adipic acid di (1-phenylethylidene) hydrazide, and the like. Other than these, for example, terephthalic acid dihydrazide, azelaic acid dihydrazide, succinic acid dihydrazide, icosanoic dicarboxylic acid dihydrazide and the like can also be mentioned. Among these, a derivative of isophthalic acid dihydrazide is preferable in that Mooney viscosity can be reduced without deteriorating exothermic property.

  Examples of the hydrazone compound represented by the above formula (II) include 3-hydroxy-2-naphthoic acid hydrazide derivatives, N ′-(1,3-dimethylbutylidene) salicylic acid hydrazide, and 4-hydroxybenzoic acid. Examples thereof include hydrazide, anthranilic acid hydrazide, and 1-hydroxy-2-naphthoic acid hydrazide derivatives. Examples of derivatives of 3-hydroxy-2-naphthoic acid hydrazide include 3-hydroxy-2-naphthoic acid (1-methylethylidene) hydrazide, 3-hydroxy-2-naphthoic acid (1-methylpropylidene) hydrazide, 3 And 3-hydroxy-2-naphthoic acid hydrazide such as 3-hydroxy-2-naphthoic acid (1,3-dimethylpropylidene) hydrazide and 3-hydroxy-2-naphthoic acid (1-phenylethylidene) hydrazide. Among these, derivatives of 3-hydroxy-2-naphthoic acid hydrazide and derivatives of N ′-(1,3-dimethylbutylidene) salicylic acid hydrazide can keep Mooney viscosity low without deteriorating exothermicity. 3-hydroxy-2-N ′-(1,3-dimethylbutylidene) -2-naphthoic acid hydrazide, which is a derivative of 3-hydroxy-2-naphthoic acid hydrazide, is particularly preferable because of its remarkable effect. .

  Examples of the hydrazone compound represented by the above formula (III) include isonicotinic acid (1-methylethylidene) hydrazide, isonicotinic acid (1-methylpropylidene) hydrazide, isonicotinic acid (1,3-dimethylpropylidene). In addition to derivatives of isonicotinic acid hydrazide such as hydrazide and isonicotinic acid (1-phenylethylidene) hydrazide, derivatives of carbonic acid dihydrazide and the like can be mentioned. Among these, isonicotinic acid hydrazide derivatives are preferable in that the Mooney viscosity can be reduced without deteriorating exothermic properties.

  The hydrazone compound represented by the above formulas (I) to (III) is excellent in the effect of suppressing reversion of the rubber composition, and contains a modified natural rubber as the rubber component without reducing the elastic modulus. Therefore, the performance is hardly lowered even under high temperature vulcanization conditions. The hydrazone compound may be used alone or in combination of two or more. The hydrazone compounds represented by the above formulas (I) to (III) are described in the documents of Pant, UC; Ramchandran, Reena; Joshi, BC Rev. Roum. Chim. (1979) 24 (3), 471-82. It can be produced on the basis of the described method.

The content of the hydrazone compound represented by the formulas (I) to (III) is preferably 0.1 to 5.0 parts by mass with respect to 100 parts by mass of the rubber component.
If the content of this hydrazone compound is less than 0.1 parts by mass, the effect of suppressing reversion of the rubber composition and the effect of reducing heat generation are small. On the other hand, if it exceeds 5.0 parts by mass, the cost increases. The effect will be saturated.

The carbon black used in the rubber composition used in the pneumatic tire of the present invention is used as a reinforcing filler, and has a nitrogen adsorption specific surface area (N ₂ SA) of 130 m ² / from the point of exerting the effects of the present invention. g is over 160 m ² / g, and the dibutyl phthalate (DBP) oil absorption is 60 to 150 mL / 100 g.
When the N ₂ SA of the carbon black is 130 m ² / g or less or the DBP oil absorption is less than 60 mL / 100 g, although the heat generation of the tire is excellent, the fracture characteristics such as wear resistance are remarkably lowered, while the N ₂ SA Is over 160 m ² / g or the DBP oil absorption is over 150 mL / 100 g, the workability during kneading of the rubber composition will be significantly reduced.

The carbon black content is preferably in the range of 20 to 80 parts by mass, more preferably in the range of 30 to 60 parts by mass with respect to 100 parts by mass of the rubber component.
By making the content of carbon black 20 parts by mass or more, it becomes possible to achieve both low heat generation and wear resistance of the tire, while by making it 80 parts by mass or less, without increasing the heat generation of the tire. The workability during kneading of the rubber composition can be improved.

  The rubber composition used in the pneumatic tire of the present invention includes a rubber component including the modified natural rubber, a hydrazone compound, carbon black, a compounding agent commonly used in the rubber industry, such as silica, softener, and aging. An inhibitor, a vulcanizing agent, a vulcanization accelerator and the like can be appropriately blended depending on the purpose. As these compounding agents, commercially available products can be suitably used. The rubber composition is prepared by blending a rubber component containing at least the modified natural rubber with a hydrazone compound, carbon black, and various compounding agents appropriately selected as necessary, kneading, heating, extruding, and the like. Can be manufactured.

The rubber composition for use in the pneumatic tire of the present invention is not only for the modified natural rubber and hydrazone compound contained in the rubber component to be firmly bonded to carbon black, but also between the functional groups of the modified natural rubber and hydrazone compound. As a result, the dispersibility and reinforcing effect of carbon black are improved, and not only low rolling resistance but also elastic modulus and wear resistance (destructive resistance) are improved, and low rolling resistance, elastic modulus and wear resistance are improved. This effect is achieved when the nitrogen adsorption specific surface area (N ₂ SA) exceeds 130 m ² / g and 160 m ² / g, and the dibutyl phthalate (DBP) oil absorption is 60 to 150 mL / 100 g. This can be achieved when carbon black is used.

The pneumatic tire of the present invention is a tire member, for example, a tread member, a sidewall, and the like, which has a low rolling resistance, an elastic modulus and a high wear resistance without reducing the elastic modulus as described above. Since it is applied to a member, preferably a tread member, it is suitable as a pneumatic tire, particularly as a pneumatic tire for heavy loads. The tire is also suitable as an off-road tire for traveling on rough roads.
In addition, as gas with which the pneumatic tire of this invention is filled, inert gas, such as nitrogen, argon, helium other than the air which adjusted normal or oxygen partial pressure, can be used.

  EXAMPLES Next, although an Example and a comparative example are given and this invention is demonstrated in more detail, this invention is not limited to the following Example at all.

[Production Example 1 of Modified Natural Rubber (Natural Rubber-A)]
(Natural rubber latex modification reaction process)
The field latex was centrifuged at a rotational speed of 7500 rpm using a latex separator (manufactured by Saito Centrifugal Co., Ltd.) to obtain a concentrated latex having a dry rubber concentration of 60%. 1000 g of this concentrated latex is put into a stainless steel reaction vessel equipped with a stirrer and a temperature control jacket, and 10 mL of water and 90 mg of emulsifier [Emulgen 1108, manufactured by Kao Corporation] are added in advance to N, N-diethylaminoethyl methacrylate. What was emulsified in addition to 0 g was added together with 990 mL of water, and these were stirred at room temperature for 30 minutes while purging with nitrogen. Next, modified natural rubber latex is prepared by adding 1.2 g of tert-butyl hydroperoxide (t-BHPO) and 1.2 g of tetraethylenepentamine (TEPA) as a polymerization initiator and reacting at 40 ° C. for 30 minutes. Got.

(Coagulation and drying process)
Formic acid was added to the modified natural rubber latex to adjust the pH to 4.7 to coagulate the modified natural rubber latex. The solid material thus obtained was treated with a creper five times, passed through a shredder and crushed, and then dried at 110 ° C. for 210 minutes with a hot air dryer to obtain modified natural rubber-1. From the mass of the modified natural rubber-1 thus obtained, it was confirmed that the conversion rate of N, N-diethylaminoethyl methacrylate added as a monomer was 100%. In addition, the modified natural rubber-1 was extracted with petroleum ether and further extracted with a 2: 1 mixed solvent of acetone and methanol, and the homopolymer was separated by analysis of the extract. It was confirmed that 100% of the added monomer was introduced into the natural rubber molecule.
Therefore, the graft amount of the monomer in the obtained modified natural rubber (natural rubber-A) is 0.5% by mass with respect to the rubber component in the natural rubber latex.

[Production Example 2 of Modified Natural Rubber (Natural Rubber-B)]
A modified natural rubber (natural rubber-B) was obtained in the same manner as in Production Example 1 except that 1.7 g of 4-vinylpyridine was added instead of 3.0 g of N, N-diethylaminoethyl methacrylate as a monomer. . Further, when the modified natural rubber (natural rubber-B) was analyzed in the same manner as the modified natural rubber (natural rubber-A), it was found that 100% of the added monomer was introduced into the natural rubber molecule. confirmed.
Therefore, the graft amount of the monomer in the obtained modified natural rubber (natural rubber B) is 0.28% by mass with respect to the rubber component in the natural rubber latex.

[Production example of natural rubber for comparison (natural rubber-C)]
The natural rubber latex of Production Example 1 was coagulated and dried directly in the same manner as Production Example 1 without modification to obtain solid natural rubber (natural rubber-C).

The outline of the modified natural rubber (natural rubber-A, B) and natural rubber (natural rubber-C) is shown in Table 1 below.

Next, using the modified natural rubber (natural rubber-A, B) and natural rubber (natural rubber-C) obtained above, rubber compositions having the compounding formulations shown in Tables 2 and 3 below were prepared, The elastic modulus was evaluated by the following method. Further, the rubber composition was used as a tread and vulcanized under ordinary vulcanization conditions to produce a tire of size 3700R57 (off-road tire), and the heat generation property and wear resistance were evaluated by the following methods.
These results are shown in Tables 2 and 3 below.

(Measurement method of elastic modulus)
The samples obtained by vulcanizing each rubber composition were measured for dynamic storage elastic modulus (E ′) at a strain of 1%, 50 Hz, and a measurement temperature of 25 ° C. using a spectrometer manufactured by Toyo Seiki Co., Ltd., Comparative Example 1 or 4 Is shown as an index with 100 being 100. A larger index value indicates a higher elastic modulus and higher rigidity.

(Method of measuring exothermicity)
A drum test under constant speed and step load conditions was performed on each test tire, the temperature at a constant depth position inside the tire tread was measured, and indexed with Comparative Example 1 or 4 as 100. The smaller the index value, the lower the temperature and the greater the effect of reducing heat generation.

(Abrasion resistance measurement method)
After mounting each test tire on four wheels of an off-road car and running for 2000 hours, the running distance / (groove depth before running of the tread−groove depth after running) was calculated, and Comparative Example 1 or 4 was taken as 100. The index was displayed. The larger the index value, the higher the wear resistance and the better.

  As is apparent from the results of Table 2 above, Examples 1 and 2 that are within the scope of the present invention are less exothermic (low rolling resistance) and elastic modulus than Comparative Examples 1 to 3 that are outside the scope of the present invention. It has also been found that a pneumatic tire with a high degree of both wear resistance and wear resistance can be obtained. Further, as is clear from the results of Table 3 above, Examples 3 and 4 that are within the scope of the present invention are less exothermic (low rolling resistance) than Comparative Examples 4 to 12 that are outside the scope of the present invention. It has been found that a pneumatic tire having a high degree of both elastic modulus and wear resistance can be obtained.

  It is suitable for a heavy-duty pneumatic tire that has both low rolling resistance, elastic modulus, and wear resistance.

Claims (6)

To 100 parts by mass of a rubber component containing a modified natural rubber obtained by adding a polar group-containing monomer to natural rubber latex, graft-polymerizing the monomer to natural rubber in natural rubber latex, coagulating and drying And a hydrazone compound and carbon black having a nitrogen adsorption specific surface area (N ₂ SA) of more than 130 m ² / g and 160 m ² / g and a dibutyl phthalate (DBP) oil absorption of 60 to 170 mL / 100 g. A pneumatic tire characterized by using a rubber composition as a tire member.   The polar group of the polar group-containing monomer is amino group, imino group, nitrile group, ammonium group, imide group, amide group, hydrazo group, azo group, diazo group, hydroxyl group, carboxyl group, carbonyl group, epoxy group, 2. The oxycarbonyl group, the sulfide group, the disulfide group, the sulfonyl group, the sulfinyl group, the thiocarbonyl group, the nitrogen-containing heterocyclic group, and the oxygen-containing heterocyclic group. Pneumatic tire described in 2.   The air according to claim 1 or 2, wherein a graft amount of the monomer in the modified natural rubber is 0.01 to 5.0 mass% with respect to a rubber component in the natural rubber latex. Tires.   The pneumatic tire according to any one of claims 1 to 3, wherein the rubber component of the rubber composition contains 20 parts by mass or more of the modified natural rubber in 100 parts by mass.   The pneumatic tire according to any one of claims 1 to 4, wherein the content of the hydrazone compound is 0.1 to 5.0 parts by mass.   The pneumatic tire according to any one of claims 1 to 5, wherein a content of the carbon black is 20 to 80 parts by mass.