JP2011017013A - Modified natural rubber and method for producing the same, rubber composition, and tire - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide modified natural rubber producible at a low cost and capable of improving low loss properties, abrasion resistance, and breaking properties of a rubber composition by being used as a rubber component in the rubber composition.SOLUTION: The modified natural rubber is obtained when an alkoxysilyl group-containing mercapto compound is added to at least one natural rubber raw material selected from the group consisting of natural rubber, a coagulum of natural rubber latex, and a natural rubber cup lump by being applied with mechanical shear force. A twin screw kneading extruder and a dry prebreaker are preferable as a means for applying the mechanical shear force.

Description

  The present invention relates to a modified natural rubber, a method for producing the same, and a rubber composition and a tire using the modified natural rubber, and particularly relates to a rubber composition excellent in low loss property, wear resistance, and fracture resistance.

  In recent years, demands for reducing fuel consumption of automobiles are increasing, and tires with low rolling resistance are required. Therefore, as a rubber composition used for tire treads or the like, a rubber composition having a low tan δ (hereinafter referred to as low loss property) and excellent in low heat generation properties is required. In addition, a rubber composition for a tread is required to have excellent wear resistance and fracture characteristics in addition to low loss. On the other hand, in order to improve the low loss property, wear resistance and fracture characteristics of the rubber composition, it is necessary to improve the affinity between the rubber component and the filler such as carbon black and silica in the rubber composition. It is valid.

  For example, in order to improve the affinity between the filler and the rubber component in the rubber composition and to improve the reinforcing effect by the filler, synthetic rubber or functional group having improved affinity with the filler by terminal modification Synthetic rubbers and the like have been developed in which the monomers are copolymerized to improve the affinity with the filler.

  On the other hand, although natural rubber is used in large quantities by taking advantage of its excellent physical properties, it is a technology that improves the natural rubber itself to improve the affinity with the filler and greatly enhance the reinforcing effect of the filler. There is no.

  For example, a technology for epoxidizing natural rubber has been proposed. However, since this technology cannot sufficiently improve the affinity between the natural rubber and the filler, the reinforcing effect of the filler can be sufficiently improved. Can not. In addition, a technique (see Patent Documents 1 to 6) in which a vinyl monomer is added to natural rubber latex and graft polymerization is known, and the grafted natural rubber obtained by the technique has already been used as MG latex or the like. Is being produced. However, in order to achieve high grafting efficiency by this method, it is necessary to use a high-purity latex, so that it is necessary to separately perform an operation such as centrifugation, and there is a problem that the manufacturing cost increases.

JP-A-5-287121 JP-A-6-329702 Japanese Patent Laid-Open No. 9-25468 JP 2000-319339 A JP 2002-138266 A JP 2002-348559 A

  Therefore, the object of the present invention is to solve the above-mentioned problems of the prior art, and can be manufactured at a low cost. By using it as a rubber component of a rubber composition, the low loss property, wear resistance and destruction of the rubber composition are achieved. An object of the present invention is to provide a modified natural rubber capable of improving the properties and a method for producing the modified natural rubber. Another object of the present invention is to provide a rubber composition using the modified natural rubber and a tire using the rubber composition.

  As a result of diligent studies to achieve the above object, the present inventor has obtained a rubber composition by grafting or adding a polar group-containing compound to a solid natural rubber raw material that can be obtained at low cost by applying a mechanical shearing force. The present inventors have found that a modified natural rubber capable of improving the low loss property, wear resistance and fracture characteristics of the product can be obtained, and the present invention has been completed.

  That is, the modified natural rubber of the present invention applies a mechanical shearing force to a polar group-containing compound on at least one natural rubber raw material selected from the group consisting of natural rubber, natural rubber latex coagulum, and natural rubber cup lamp. It is characterized by graft polymerization or addition.

  In a preferred example of the modified natural rubber of the present invention, the means for applying the mechanical shearing force is a twin-screw extrusion kneader or a dry prebreaker.

  In another preferred embodiment of the modified natural rubber of the present invention, the graft amount or addition amount of the polar group-containing compound is 0.01 to 5.0% by mass with respect to the solid rubber component in the natural rubber raw material.

  In another preferred embodiment of the modified natural rubber of the present invention, the polar group of the polar group-containing compound is an amino group, imino group, nitrile group, ammonium group, imide group, amide group, hydrazo group, azo group, diazo group, It is at least one selected from the group consisting of a hydroxyl group, a carboxyl group, a carbonyl group, an epoxy group, an oxycarbonyl group, a nitrogen-containing heterocyclic group, an oxygen-containing heterocyclic group, a tin-containing group and an alkoxysilyl group.

  In addition, the method for producing a modified natural rubber of the present invention comprises adding a polar group-containing compound to at least one natural rubber raw material selected from the group consisting of natural rubber, natural rubber latex coagulated material, and natural rubber cup lamp. And graft polymerization or addition.

  Furthermore, the rubber composition of the present invention is characterized by using the above-mentioned modified natural rubber, and the tire of the present invention is characterized by using the rubber composition for any of tire members.

  According to the present invention, low loss property, wear resistance and fracture of a rubber composition obtained by graft-polymerizing or adding a polar group-containing compound to a solid natural rubber raw material which can be obtained at low cost by applying mechanical shearing force. A modified natural rubber capable of improving the properties and a method for producing the modified natural rubber can be provided. Moreover, the rubber composition and tire which were excellent in the low loss property, abrasion resistance, and a fracture | rupture characteristic using this modified natural rubber can be provided.

  The present invention is described in detail below. The modified natural rubber of the present invention is obtained by graft polymerization by applying a mechanical shearing force to a polar group-containing compound on at least one natural rubber raw material selected from the group consisting of natural rubber, natural rubber latex coagulum and natural rubber cup lamp. Or the rubber composition of the present invention uses the modified natural rubber, and the tire of the present invention uses the rubber composition for any of the tire members. It is characterized by. Since the polar group of the polar group-containing compound is excellent in affinity with various fillers such as carbon black and silica, the modified natural rubber has a higher affinity for various fillers than unmodified natural rubber. . Therefore, the rubber composition of the present invention using the modified natural rubber as a rubber component has a high dispersibility of the filler with respect to the rubber component, and the reinforcing effect of the filler is sufficiently exhibited, resulting in fracture characteristics and wear resistance. In addition to being excellent, the low heat build-up (low loss) is also greatly improved. Further, by using the rubber composition for a tire, particularly a tread of the tire, it is possible to remarkably improve fracture resistance and wear resistance while greatly reducing rolling resistance.

  As raw materials of the modified natural rubber of the present invention, various solid natural rubbers after drying, various natural rubber latex coagulates (including unsmoked sheets) or natural rubber cup lamps can be used. These natural rubber raw materials are: You may use individually by 1 type and may be used in combination of 2 or more type. Since the production of the modified natural rubber of the present invention does not require the use of a natural rubber latex having a high purity, the modified natural rubber can be produced at a relatively low cost. Among the natural rubber raw materials, cup lamps and the like can be obtained at a low cost, so that there is a great merit in terms of cost. Note that when cup lamps or the like are used as raw materials, the modification efficiency of natural rubber may be slightly reduced, but the merit is superior in terms of the overall cost and modification efficiency.

  In the present invention, when a polar group-containing compound is graft-polymerized to a natural rubber molecule in a natural rubber raw material, the polar group-containing compound preferably has a carbon-carbon double bond in the molecule. A monomer is preferred. On the other hand, when a polar group-containing compound is subjected to an addition reaction with a natural rubber molecule in a natural rubber raw material, the polar group-containing compound preferably has a mercapto group in the molecule, and is preferably a polar group-containing mercapto compound.

  As means for imparting mechanical shearing force to the mixture of the natural rubber raw material and the polar group-containing compound, a twin-screw extrusion kneader and a dry prebreaker are preferable. Here, in the case where the polar group-containing compound is graft-polymerized to the natural rubber molecule in the natural rubber raw material, the natural rubber raw material and the polar group-containing compound (preferably, the polar group-containing vinyl are contained in the apparatus to which the mechanical shearing force is applied. By introducing a polymerization initiator together with a system monomer) and applying a mechanical shearing force, a polar group-containing compound can be introduced into the natural rubber molecule in the natural rubber raw material by graft polymerization. In addition, when a polar group-containing compound is subjected to an addition reaction with a natural rubber molecule in a natural rubber raw material, the natural rubber raw material and the polar group-containing compound (preferably, a polar group-containing mercapto compound are contained in the above-described mechanical shear force device. ) And, if necessary, organic peroxides and the like are further added to give mechanical shearing force, so that a polar group-containing compound is added to the double bond of the main chain of the natural rubber molecule in the natural rubber raw material. An addition reaction can be performed.

  Specific examples of polar groups of the polar group-containing vinyl monomer suitable for graft polymerization to natural rubber molecules in the natural rubber raw material include amino groups, imino groups, nitrile groups, ammonium groups, imide groups, amides. Group, hydrazo group, azo group, diazo group, hydroxyl group, carboxyl group, carbonyl group, epoxy group, oxycarbonyl group, nitrogen-containing heterocyclic group, oxygen-containing heterocyclic group, tin-containing group, alkoxysilyl group, etc. Can be mentioned. These polar group-containing vinyl monomers may be used alone or in combination of two or more.

  Examples of the vinyl 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, tertiary amino group-containing vinyl monomers such as dialkylaminoalkyl (meth) acrylate are particularly preferable. These amino group-containing vinyl monomers may be used alone or in a combination of two or more.

  Here, the primary amino group-containing vinyl monomers include acrylamide, methacrylamide, 4-vinylaniline, aminomethyl (meth) acrylate, aminoethyl (meth) acrylate, aminopropyl (meth) acrylate, aminobutyl. Examples include (meth) acrylate.

  Secondary vinyl group-containing vinyl 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) 1-anilinophenyl-1,3-butadiene, 1-anilinophenyl-3-methyl-1,3-butadiene, 1-anilinophenyl-3-chloro-1,3-butadiene, 3 -Anilinophenyl-2-methyl-1,3-butadiene, 1-a Linophenyl-2-chloro-1,3-butadiene, 2-anilinophenyl-1,3-butadiene, 2-anilinophenyl-3-methyl-1,3-butadiene, 2-anilinophenyl-3-chloro- Anilinophenylbutadienes such as 1,3-butadiene, (3) N-methyl (meth) acrylamide, N-ethyl (meth) acrylamide, N-methylolacrylamide, N- (4-anilinophenyl) methacrylamide, etc. N-mono substituted (meth) acrylamides and the like can be mentioned.

  Furthermore, examples of the tertiary amino group-containing vinyl 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-dioctyl 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-dioctylaminoethyl (meth) Particularly preferred are acrylate, N-methyl-N-ethylaminoethyl (meth) acrylate, and the like.

  Examples of the N, N-disubstituted aminoalkyl (meth) acrylamide include N, N-dimethylaminomethyl (meth) acrylamide, N, N-dimethylaminoethyl (meth) acrylamide, N, N-dimethylaminopropyl ( (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-dihexylaminoethyl ( Data) acrylamide, N, N-dihexyl-aminopropyl (meth) acrylamide, N, N-acrylamide compounds such as dioctyl aminopropyl (meth) acrylamide or methacrylamide compounds and the like. 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 vinyl monomer containing a nitrile group include (meth) acrylonitrile and vinylidene cyanide. These nitrile group-containing vinyl monomers may be used alone or in a combination of two or more.

  Examples of the vinyl 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 vinyl monomer include 2-hydroxyethyl (meth) acrylate, 2-hydroxypropyl (meth) acrylate, 3-hydroxypropyl (meth) acrylate, 2-hydroxybutyl (meta ) Acrylate, 3-hydroxybutyl (meth) acrylate, hydroxyalkyl (meth) acrylates such as 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 Hydroxyl group-containing unsaturated amides such as o- Contains hydroxyl groups such as loxystyrene, m-hydroxystyrene, p-hydroxystyrene, o-hydroxy-α-methylstyrene, m-hydroxy-α-methylstyrene, p-hydroxy-α-methylstyrene, p-vinylbenzyl alcohol And vinyl aromatic compounds. 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 vinyl monomers may be used alone or in a combination of two or more.

  Examples of the vinyl 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 vinyl monomers may be used alone or in a combination of two or more.

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

  In the vinyl monomer containing the nitrogen-containing heterocyclic group, the nitrogen-containing heterocyclic ring includes 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 vinyl monomer containing a pyridyl group as a nitrogen-containing heterocyclic group, 2-vinylpyridine, 3-vinylpyridine, 4-vinylpyridine, 5-methyl-2-vinylpyridine, 5-ethyl- 2-vinylpyridine and the like can be mentioned, among which 2-vinylpyridine, 4-vinylpyridine and the like are particularly preferable. These nitrogen-containing heterocyclic group-containing vinyl monomers may be used alone or in a combination of two or more.

  Examples of the vinyl monomer having a tin-containing group include allyltri-n-butyltin, allyltrimethyltin, allyltriphenyltin, allyltri-n-octyltin, (meth) acryloxy-n-butyltin, (meth) acryloxy Tin-containing monomers such as trimethyltin, (meth) acryloxytriphenyltin, (meth) acryloxy-n-octyltin, vinyltri-n-butyltin, vinyltrimethyltin, vinyltriphenyltin, vinyltri-n-octyltin Can be mentioned. These tin-containing vinyl monomers may be used alone or in a combination of two or more.

  Examples of the vinyl monomer containing the alkoxysilyl group include (meth) acryloxymethyltrimethoxysilane, (meth) acryloxymethylmethyldimethoxysilane, (meth) acryloxymethyldimethylmethoxysilane, (meth) acryloxy. Methyltriethoxysilane, (meth) acryloxymethylmethyldiethoxysilane, (meth) acryloxymethyldimethylethoxysilane, (meth) acryloxymethyltripropoxysilane, (meth) acryloxymethylmethyldipropoxysilane, (meth) Acryloxymethyldimethylpropoxysilane, γ- (meth) acryloxypropyltrimethoxysilane, γ- (meth) acryloxypropylmethyldimethoxysilane, γ- (meth) acryloxypropyldimethylmethoxysilane, γ- (meth) acryloxy Propyltriethoxy Lan, γ- (meth) acryloxypropylmethyldiethoxysilane, γ- (meth) acryloxypropyldimethylethoxysilane, γ- (meth) acryloxypropyltripropoxysilane, γ- (meth) acryloxypropylmethyldipropoxy Silane, γ- (meth) acryloxypropyldimethylpropoxysilane, γ- (meth) acryloxypropylmethyldiphenoxysilane, γ- (meth) acryloxypropyldimethylphenoxysilane, γ- (meth) acryloxypropylmethyldibenzyl Examples include loxysilane, γ- (meth) acryloxypropyldimethylbenzyloxysilane, trimethoxyvinylsilane, triethoxyvinylsilane, 6-trimethoxysilyl-1,2-hexene, and p-trimethoxysilylstyrene. These alkoxysilyl group-containing vinyl monomers may be used alone or in a combination of two or more.

  The polymerization initiator used for graft polymerization of the polar group-containing compound to natural rubber molecules in the natural rubber raw material is not particularly limited, and various polymerization initiators for emulsion polymerization can be used. There is also no particular restriction on. 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. In the redox polymerization initiator, examples of the reducing agent to be combined with the peroxide include tetraethylenepentamine, mercaptans, acidic sodium sulfite, reducing metal ion, 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 the low loss and wear resistance without lowering the processability of the rubber composition by adding a filler such as carbon black or silica to the modified natural rubber, the polar group is added to each natural rubber molecule. Since it is important that the contained compound 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 polar group-containing compound. preferable.

  The above-described components are charged into an apparatus that can be given mechanical shearing force, and mechanical shearing force is applied to obtain a modified natural rubber in which the polar group-containing compound is graft copolymerized with natural rubber molecules. In this case, the modification reaction of the natural rubber molecule may be carried out by heating, preferably at a temperature of 30 to 160 ° C., more preferably 50 to 130 ° C., so that the modified natural rubber has sufficient reaction efficiency. Can be obtained.

  On the other hand, specific examples of the polar group of the polar group-containing mercapto compound suitable for addition reaction with the natural rubber molecule in the natural rubber raw material include amino group, imino group, nitrile group, ammonium group, imide group, amide group. Preferred examples include hydrazo group, azo group, diazo group, hydroxyl group, carboxyl group, carbonyl group, epoxy group, oxycarbonyl group, nitrogen-containing heterocyclic group, oxygen-containing heterocyclic group, tin-containing group and alkoxysilyl group. be able to. These polar group-containing mercapto compounds may be used alone or in combination of two or more.

  Examples of the mercapto compound containing an amino group include mercapto compounds having at least one amino group selected from primary, secondary and tertiary amino groups in one molecule. Among the mercapto compounds having an amino group, a tertiary amino group-containing mercapto compound is particularly preferable. Here, as the primary amino group-containing mercapto compound, 4-mercaptoaniline, 2-mercaptoethylamine, 2-mercaptopropylamine, 3-mercaptopropylamine, 2-mercaptobutylamine, 3-mercaptobutylamine, 4-mercaptobutylamine Etc. The secondary amino group-containing mercapto compounds include N-methylaminoethanethiol, N-ethylaminoethanethiol, N-methylaminopropanethiol, N-ethylaminopropanethiol, N-methylaminobutanethiol, N- And ethylaminobutanethiol. Further, the tertiary amino group-containing mercapto compounds include N, N-dimethylaminoethanethiol, N, N-diethylaminoethanethiol, N, N-dimethylaminopropanethiol, N, N-diethylaminopropanethiol, N, N N, N-disubstituted aminoalkyl mercaptans such as -dimethylaminobutanethiol and N, N-diethylaminobutanethiol. Among these amino group-containing mercapto compounds, 2-mercaptoethylamine, N, N-dimethylaminoethanethiol and the like are preferable. These amino group-containing mercapto compounds may be used alone or in combination of two or more.

  Examples of the mercapto compound having a nitrile group include 2-mercaptopropane nitrile, 3-mercaptopropane nitrile, 2-mercaptobutane nitrile, 3-mercaptobutane nitrile, 4-mercaptobutane nitrile, and the like. These nitrile group-containing mercapto compounds May be used individually by 1 type, and may be used in combination of 2 or more type.

  Examples of the mercapto compound containing a hydroxyl group include mercapto compounds having at least one primary, secondary, or tertiary hydroxyl group in one molecule. Specific examples of the hydroxyl group-containing mercapto compound include 2-mercaptoethanol, 3-mercapto-1-propanol, 3-mercapto-2-propanol, 4-mercapto-1-butanol, 4-mercapto-2-butanol, 3 -Mercapto-1-butanol, 3-mercapto-2-butanol, 3-mercapto-1-hexanol, 3-mercapto-1,2-propanediol, 2-mercaptobenzyl alcohol, 2-mercaptophenol, 4-mercaptophenol, etc. Among these, 2-mercaptoethanol and the like are preferable. These hydroxyl group-containing mercapto compounds may be used alone or in a combination of two or more.

  Examples of the mercapto compound containing a carboxyl group include mercaptoacetic acid, mercaptopropionic acid, thiosalicylic acid, mercaptomalonic acid, mercaptosuccinic acid, mercaptobenzoic acid and the like. Among these, mercaptoacetic acid is preferred. These carboxyl group-containing mercapto compounds may be used individually by 1 type, and may be used in combination of 2 or more type.

  In the mercapto compound containing the nitrogen-containing heterocyclic group, the nitrogen-containing heterocyclic ring includes pyrrole, histidine, imidazole, triazolidine, triazole, triazine, pyridine, pyrimidine, pyrazine, indole, quinoline, purine, phenazine, pteridine, melamine. Etc. The nitrogen-containing heterocycle may contain other heteroatoms in the ring. Here, as a mercapto compound containing a pyridyl group as a nitrogen-containing heterocyclic group, 2-mercaptopyridine, 3-mercaptopyridine, 4-mercaptopyridine, 5-methyl-2-mercaptopyridine, 5-ethyl-2-mercapto Examples of mercapto compounds containing other nitrogen-containing heterocyclic groups include 2-mercaptopyrimidine, 2-mercapto-5-methylbenzimidazole, 2-mercapto-1-methylimidazole, and 2-mercapto. Examples include benzimidazole and 2-mercaptoimidazole. Among these, 2-mercaptopyridine and 4-mercaptopyridine are preferable. These nitrogen-containing heterocyclic group-containing mercapto compounds may be used alone or in combination of two or more.

  Examples of the mercapto compound having a tin-containing group include 2-mercaptoethyltri-n-butyltin, 2-mercaptoethyltrimethyltin, 2-mercaptoethyltriphenyltin, 3-mercaptopropyltri-n-butyltin, and 3-mercaptopropyl. Mention may be made of tin-containing mercapto compounds such as trimethyltin and 3-mercaptopropyltriphenyltin. These tin-containing mercapto compounds may be used individually by 1 type, and may be used in combination of 2 or more type.

  Examples of the mercapto compound containing an alkoxysilyl group include 3-mercaptopropyltrimethoxysilane, 3-mercaptopropyltriethoxysilane, 3-mercaptopropylmethyldimethoxysilane, 3-mercaptopropyldimethylmethoxysilane, and 2-mercaptoethyltrimethoxysilane. Examples include silane, 2-mercaptoethyltriethoxysilane, mercaptomethylmethyldiethoxysilane, mercaptomethyltrimethoxysilane, and the like. Among these, 3-mercaptopropyltrimethoxysilane is preferable. These alkoxysilyl group-containing mercapto compounds may be used alone or in a combination of two or more.

  The above-mentioned components are charged into a device that can be applied with mechanical shearing force, and mechanical shearing force is applied within the device to obtain a modified natural rubber in which the polar group-containing compound is added to a natural rubber molecule. In this case, the modification reaction of the natural rubber molecule may be carried out by heating, preferably 30 to 160 ° C., more preferably 50 to 130 ° C., so that the modified natural rubber has sufficient addition efficiency. Can be obtained.

  In the modified natural rubber of the present invention, the graft amount or addition amount of the polar group-containing compound is preferably in the range of 0.01 to 5.0% by mass, and in the range of 0.02 to 3.0% by mass with respect to the solid rubber component in the natural rubber raw material. Is more preferable, and a range of 0.03 to 2.0% by mass is even more preferable. If the grafting amount or addition amount of the polar group-containing compound is less than 0.01% by mass, the low loss and wear resistance of the rubber composition may not be sufficiently improved. Moreover, if the grafting amount or addition amount of the polar group-containing compound exceeds 5.0% by mass, the physical properties inherent to natural rubber such as viscoelasticity and SS characteristics (stress-strain curve in a tensile tester) are greatly changed. In addition, the physical properties inherent to natural rubber are impaired, and the processability of the rubber composition may be greatly deteriorated.

  The rubber composition of the present invention is characterized by using the modified natural rubber, and preferably further contains a filler. Here, the blending amount of the filler is not particularly limited, but is preferably in the range of 5 to 100 parts by mass, more preferably in the range of 10 to 70 parts by mass with respect to 100 parts by mass of the modified natural rubber. If the blending amount of the filler is less than 5 parts by mass, sufficient reinforcement may not be obtained, and if it exceeds 100 parts by mass, the workability may be deteriorated.

Examples of the filler used in the rubber composition of the present invention include carbon black and inorganic filler. Here, as the inorganic filler, silica and the following formula (I):
nM · xSiO _y · zH ₂ O (I)
[Wherein, M is a metal selected from the group consisting of aluminum, magnesium, titanium, calcium and zirconium, an oxide or hydroxide of these metals, and a hydrate thereof, or a carbonate of these metals. And n, x, y, and z are each an integer of 1 to 5, an integer of 0 to 10, an integer of 2 to 5, and an integer of 0 to 10]. Is mentioned. These fillers may be used alone or in a combination of two or more.

Examples of the carbon black include GPF, FEF, SRF, HAF, ISAF, and SAF grades, and examples of the silica include wet silica, dry silica, and colloidal silica. Furthermore, the inorganic compound of the above formula (I) includes alumina (Al ₂ O ₃ ) such as γ-alumina and α-alumina; alumina monohydrate such as boehmite and diaspore (Al ₂ O ₃ .H ₂ O). Aluminum hydroxide [Al (OH) ₃ ] such as gibbsite and bayerite; aluminum carbonate [Al ₂ (CO ₃ ) ₃ ], magnesium hydroxide [Mg (OH) ₂ ], magnesium oxide (MgO), magnesium carbonate ( MgCO ₃ ), talc (3MgO · 4SiO ₂ · H ₂ O), attapulgite (5MgO · 8SiO ₂ · 9H ₂ O), titanium white (TiO ₂ ), titanium black (TiO _2n-1 ), calcium oxide (CaO), calcium hydroxide [Ca (OH) _2], magnesium aluminum oxide _{(MgO · Al 2 O 3)} , clay _{(Al 2 O 3 · 2SiO 2} ), kaolin _{(Al 2 O 3 · 2SiO 2} · 2 ₂ O), pyrophyllite _{(Al 2 O 3 · 4SiO 2} · H 2 O), bentonite _{(Al 2 O 3 · 4SiO 2} · 2H 2 O), aluminum silicate _{(Al 2 SiO 5, Al 4} · 3SiO 4・ 5H ₂ O etc.), magnesium silicate (Mg ₂ SiO ₄ , MgSiO ₃ etc.), calcium silicate (Ca ₂ SiO ₄ etc.), aluminum calcium silicate (Al ₂ O ₃ · CaO · 2SiO ₂ etc.), silica Magnesium calcium oxide (CaMgSiO ₄ ), calcium carbonate (CaCO ₃ ), zirconium oxide (ZrO ₂ ), zirconium hydroxide [ZrO (OH) ₂ .nH ₂ O], zirconium carbonate [Zr (CO ₃ ) ₂ ], various zeolites Examples thereof include crystalline aluminosilicates containing hydrogen, alkali metals, or alkaline earth metals that correct electric charges.

  In addition to the above modified natural rubber and filler, the rubber composition of the present invention includes compounding agents commonly used in the rubber industry, such as anti-aging agents, softeners, silane coupling agents, stearic acid, zinc white. Further, a vulcanization accelerator, a vulcanizing agent, and the like can be appropriately selected and blended within a range that does not impair the object of the present invention. As these compounding agents, commercially available products can be suitably used. The rubber composition of the present invention can be produced by blending various modified additives appropriately selected as necessary with the modified natural rubber, kneading, heating, extruding and the like.

  The tire of the present invention is characterized by using the rubber composition, and the rubber composition is preferably used for a tread. A tire using the rubber composition as a tread is excellent in fuel efficiency, fracture characteristics, and wear resistance. The tire of the present invention is not particularly limited except that the rubber composition described above is used for any of the tire members, and can be produced according to a conventional method. Moreover, as gas with which this tire is filled, inert gas, such as nitrogen, argon, helium other than normal or the air which adjusted oxygen partial pressure, can be used.

  Hereinafter, the present invention will be described in more detail with reference to examples. However, the present invention is not limited to the following examples.

<Production Example 1>
Formic acid was added to the field latex to adjust the pH to 4.7, the latex was coagulated, and the obtained solid was treated 5 times with a creper and crushed through a shredder. Next, the dry rubber content of the obtained coagulum was determined, and 600 g of coagulum, 3.0 g of N, N-diethylaminoethyl methacrylate, tert-butyl hydroperoxide (t-BHPO) 1.2 in terms of dry rubber. were kneaded in a kneader at room temperature at 30 rpm for 2 minutes to be uniformly dispersed. Next, while uniformly adding 1.2 g of tetraethylenepentamine (TEPA) to the obtained mixture, a twin-screw kneading extruder made of Kobe Steel [same-direction rotating screw diameter = 30 mm, L / D = 35, three vent holes The modified modified natural rubber A was obtained by extrusion while applying mechanical shearing force at a barrel temperature of 120 ° C. and a rotation speed of 100 rpm.

  Further, based on the mass of the resulting modified natural rubber A, the conversion rate of N, N-diethylaminoethyl methacrylate added as a monomer was 83%. Further, when the modified natural rubber A was extracted with petroleum ether and further extracted with a 2: 1 mixed solvent of acetone and methanol, homopolymer was separated, and 7% of the charged monomer amount was detected. . Accordingly, the graft amount of N, N-diethylaminoethyl methacrylate in the modified natural rubber A is 0.39% by mass with respect to the solid rubber component in the natural rubber raw material.

<Production Examples 2-7>
Instead of 3.0 g of N, N-diethylaminoethyl methacrylate, 2.1 g of 2-hydroxyethyl methacrylate was added in Production Example 2, 1.7 g of 4-vinylpyridine was added in Production Example 3, and 1.4 g of methacrylic acid was added in Production Example 4. In Production Example 5, 1.7 g of acrylonitrile is added, 2.3 g of glycidyl methacrylate is added in Production Example 6, 2.8 g of methacrylamide is added in Production Example 7, and other than that, the modified natural rubber B˜ G was obtained. Further, in the same manner as in the modified natural rubber A, the graft amount of the polar group-containing compound added as a monomer in the modified natural rubbers B to G was analyzed, and the results shown in Table 1 were obtained.

<Production Example 8>
Other than using 1.7 g of N, N-dimethylaminoethanethiol instead of 3.0 g of N, N-diethylaminoethyl methacrylate without adding tert-butyl hydroperoxide (t-BHPO) and tetraethylenepentamine (TEPA) Obtained modified natural rubber H in the same manner as in Production Example 1 above. Moreover, when the addition amount of dimethylaminomethanethiol in the obtained modified natural rubber H was analyzed using a pyrolysis gas chromatograph-mass spectrometer, it was 0.22% by mass with respect to the solid rubber component in the natural rubber raw material. .

<Production Examples 9-12>
Instead of 1.7 g of N, N-dimethylaminoethanethiol, 1.8 g of 4-mercaptopyridine was added in Production Example 9, 1.3 g of mercaptoethanol was added in Production Example 10, and 1.5 g of mercaptoacetic acid was added in Production Example 11. In Example 12, modified natural rubbers I to L were obtained in the same manner as in Production Example 8 except that 3.3 g of 3-mercaptopropyltrimethoxysilane was added. Further, in the same manner as the modified natural rubber H, the addition amount of the mercapto compound in the modified natural rubbers I to L was analyzed, and the results shown in Table 1 were obtained.

<Production Example 13>
Formic acid was added to the field latex to adjust the pH to 4.7, the latex was coagulated, and the obtained solid was treated 5 times with a creper, passed through a shredder and crushed, and then heated at 110 ° C. with a hot air dryer. And dried for 210 minutes to obtain natural rubber M.

<Production Examples 14 to 26>
In Production Examples 1 to 13, in place of the solidified product obtained by adding formic acid to the field latex, a cup lamp (obtained by natural coagulation of latex obtained from a natural rubber tree) was used as a natural rubber raw material. Modified natural rubbers N to Y and natural rubber Z were obtained in the same manner as in Production Examples 1 to 13 except that they were used. Further, in the same manner as in the modified natural rubber A or the modified natural rubber H, the graft amount or addition amount of the polar group-containing compound in the modified natural rubbers N to Y was analyzed, and the results shown in Table 1 were obtained.

  Next, a rubber composition having the formulation shown in Table 2 was prepared by kneading with a plast mill, and the Mooney viscosity, tensile strength (Tb), tan δ, and abrasion resistance were measured for the rubber composition by the following methods. Measured and evaluated. The results of the rubber composition according to Formula 1 are shown in Table 3, and the results of the rubber composition according to Formula 2 are shown in Table 4.

(1) Mooney viscosity The Mooney viscosity ML _{1 + 4} (130 ° C.) of the rubber composition was measured at 130 ° C. according to JIS K6300-1994.

(2) Tensile strength The vulcanized rubber obtained by vulcanizing the rubber composition at 145 ° C for 33 minutes was subjected to a tensile test according to JIS K6301-1995, and the tensile strength (Tb) was measured. . It shows that fracture resistance is so favorable that tensile strength is large.

(3) tanδ
Using a viscoelasticity measuring device [manufactured by Rheometrics Co., Ltd.] for the vulcanized rubber obtained by vulcanizing the rubber composition at 145 ° C. for 33 minutes, loss tangent (tan δ) at a temperature of 50 ° C., a strain of 5%, and a frequency of 15 Hz. ) Was measured. It shows that it is excellent in low-loss property, so that tan-delta is small.

(4) Abrasion resistance For the vulcanized rubber obtained by vulcanizing the above rubber composition at 145 ° C for 33 minutes, the amount of wear at a slip rate of 60% at room temperature was measured using a Lambone type abrasion tester. For Examples 1 to 11 and Comparative Example 1 in Table 3, the reciprocal of the wear amount of Comparative Example 1 was set to 100, and for Examples 12 to 22 and Comparative Example 2 of Table 3 the reciprocal of the wear amount of Comparative Example 2 was set to 100. For Examples 23 to 34 and Comparative Example 3 in Table 4, the reciprocal of the wear amount of Comparative Example 3 is set to 100, and for Examples 35 to 46 and Comparative Example 4 of Table 4 are the reciprocal of the wear amount of Comparative Example 4. The index was expressed as 100. The larger the index value, the smaller the wear amount and the better the wear resistance.

* 1 The types of rubber components used are shown in Table 3 and Table 4.
* 2 “Nipsil AQ” manufactured by Nippon Silica Kogyo.
* 3 Degussa “Si69”, bis (3-triethoxysilylpropyl) tetrasulfide.
* 4 N- (1,3-Dimethylbutyl) -N'-phenyl-p-phenylenediamine.
* 5 N, N'-dicyclohexyl-2-benzothiazolylsulfenamide.
* 6 Diphenylguanidine.
* 7 Dibenzothiazyl disulfide.
* 8 Nt-butyl-2-benzothiazylsulfenamide.

  From the comparison between Examples and Comparative Examples in Table 3 and Table 4, by using a modified natural rubber modified with a polar group-containing compound in place of natural rubber, the fracture characteristics, low loss and abrasion resistance of the rubber composition are used. It can be seen that the sex can be greatly improved.

Claims (6)

  A modified natural rubber obtained by adding a mechanical shearing force to an alkoxysilyl group-containing mercapto compound to at least one natural rubber raw material selected from the group consisting of natural rubber, natural rubber latex coagulum, and natural rubber cup lamp.   The modified natural rubber according to claim 1, wherein the means for applying the mechanical shearing force is a twin-screw extrusion kneader or a dry prebreaker.   2. The modified natural rubber according to claim 1, wherein the addition amount of the alkoxysilyl group-containing mercapto compound is 0.01 to 5.0 mass% with respect to the solid rubber component in the natural rubber raw material.   A modification characterized in that an alkoxysilyl group-containing mercapto compound is added with mechanical shearing force to at least one natural rubber raw material selected from the group consisting of natural rubber, natural rubber latex coagulum, and natural rubber cup lamp. A method for producing natural rubber.   A rubber composition using the modified natural rubber according to claim 1.   A tire using the rubber composition according to claim 4 for any tire member.