JP5986368B2 - Modified natural rubber, method for producing the same, rubber composition and tire - Google Patents

Description

  The present invention relates to a modified natural rubber, a method for producing the same, a rubber composition, and a tire, and in particular, a modified natural rubber capable of improving low heat build-up (low loss) as compared with ordinary natural rubber, and a rubber composition thereof. The present invention relates to a production method, a rubber composition containing the modified natural rubber, and a tire using the rubber composition.

Conventionally, tire materials having excellent fuel efficiency (low loss) have been demanded and developed.
For example, a radical initiator and a radical polymerizable monomer are added to a diene rubber, and the radical polymerizable monomer is graft-modified to improve low heat build-up (low loss) (for example, There is still a market need to further improve the low-loss property.

Therefore, in order to further improve the low-loss property, natural rubber molecules are cross-linked (coupled) by graft polymerization of a polymerizable functional group-containing compound containing two or more polymerizable functional groups in the natural rubber molecule. ) To significantly improve the molecular weight.
For example, a technique of adding a vinyl compound to natural rubber latex and grafting it by emulsion polymerization (see, for example, Patent Documents 2 and 3) is known. Already, graft polymerization of monomethyl methacrylate is performed on natural rubber latex. Modified natural rubber latex (trade name: MG latex, manufactured by Regex Corp.), and the like.

  However, when the natural rubber in the natural rubber latex is grafted by emulsion polymerization, in order to increase the grafting efficiency, it is necessary to use a high-purity natural rubber latex obtained by performing centrifugation or the like, There is a problem that the cost cannot be reduced.

International Publication No. 08/004686 Pamphlet Japanese Patent Laid-Open No. 7-118446 JP 2003-12736 A

  An object of the present invention is to provide a modified natural rubber capable of improving low heat build-up (low loss) as compared with ordinary natural rubber, a method for producing the same, a rubber composition containing the modified natural rubber, and the The object is to provide a tire using a rubber composition.

  As a result of intensive studies to achieve the above object, the present inventors have found that at least one solid natural rubber raw material selected from the group consisting of natural rubber, natural rubber latex coagulum, and natural rubber cup lamp is 2 or more. Compared with normal natural rubber, it can improve the low heat build-up (low loss) by radical graft polymerization reaction of a polymerizable functional group-containing compound having a polymerizable functional group, and has an advanced network. The inventors have found that a modified natural rubber having a structure and a large molecular weight can be obtained, and the present invention has been completed.

That is, the modified natural rubber of the present invention is a modified natural rubber having a natural rubber molecule and a crosslinked portion formed by crosslinking the natural rubber molecules, and includes natural rubber, natural rubber latex coagulated product, and natural rubber cup lamp. At least one solid natural rubber raw material selected from the group consisting of: a radical functionalized graft polymerization reaction of a polymerizable functional group-containing compound having two or more polymerizable functional groups, wherein the polymerizable functional group-containing compound is a molecule. further comprising a polar group within the polar group, Ri amino der, a modified natural rubber further having a polar group-containing unit formed by grafted to the natural rubber molecules, the solid natural rubber raw material characterized by Rukoto such by a polar group-containing compound is further radical graft polymerization reaction with a polar group.

  The solid natural rubber raw material is preferably subjected to radical graft polymerization reaction of the polymerizable functional group-containing compound while imparting mechanical shearing force.

  The modified natural rubber of the present invention preferably has a number average molecular weight of 150,000 to 450,000.

The method for producing a modified natural rubber of the present invention is a method for producing a modified natural rubber having a natural rubber molecule and a cross-linked part formed by cross-linking the natural rubber molecules, and includes natural rubber, natural rubber latex coagulum and The polymerizable functional group is obtained by subjecting at least one solid natural rubber raw material selected from the group consisting of natural rubber cup lamps to a radical graft polymerization reaction with a polymerizable functional group-containing compound having two or more polymerizable functional groups. a containing compound polar groups further in the molecule, the polar group, Ri amino der, the modified natural rubber further has a polar group-containing unit formed by grafted natural rubber molecule, the solid natural rubber raw material, and wherein the Rukoto such by a polar group-containing compound is further radical graft polymerization reaction with a polar group.

  The method for producing a modified natural rubber according to the present invention is preferably obtained by subjecting the solid natural rubber raw material to a radical graft polymerization reaction with the polymerizable functional group-containing compound while imparting a mechanical shearing force.

  In the method for producing a modified natural rubber according to the present invention, the polymerizable functional group-containing compound is preferably added to the solid natural rubber raw material when mechanical shearing force is applied to the solid natural rubber raw material.

  The method for producing a modified natural rubber according to the present invention comprises adding 0.01 to 10.0 parts by mass of the polymerizable functional group-containing compound to 100 parts by mass of the solid rubber content in the solid natural rubber raw material. It is preferable.

  The method for producing a modified natural rubber of the present invention may comprise adding 0.01 parts by mass to 10.0 parts by mass of the polar group-containing compound with respect to 100 parts by mass of the solid rubber content of the solid natural rubber raw material. preferable.

  The rubber composition of the present invention includes the modified natural rubber of the present invention.

  In the rubber composition of the present invention, the content of the modified natural rubber in the rubber composition is preferably 15% by mass or more.

  The tire of the present invention is characterized by using the rubber composition of the present invention.

  According to the present invention, a modified natural rubber capable of improving low heat build-up (low loss) as compared with ordinary natural rubber, a method for producing the same, a rubber composition containing the modified natural rubber, and the A tire using the rubber composition can be provided.

(Modified natural rubber)
The modified natural rubber of the present invention has at least a natural rubber molecule and a cross-linked portion formed by cross-linking the natural rubber molecules, and, if necessary, a polarity formed by grafting to the natural rubber molecules. And a group-containing part.

<Natural rubber molecule>
There is no restriction | limiting in particular as a number average molecular weight of the said natural rubber molecule, Although it can select suitably according to the objective, 150,000-450,000 are preferable and 250,000-450,000 are more preferable.
If the number average molecular weight of the natural rubber molecule is less than 150,000, the exothermic property may be deteriorated due to the low molecular weight component, and if it exceeds 450,000, the viscosity becomes high and the compounding workability may be deteriorated. On the other hand, when the number average molecular weight of the natural rubber molecule is within the more preferable range, it is advantageous in terms of the balance between the molecular weight, the heat build-up, and the blending workability.
The number average molecular weight of the natural rubber molecule can be measured, for example, by gel permeation chromatography (GPC) of a natural rubber molecule obtained by dissolving in tetrahydrofuran.

-Polymerizable functional group-containing compound-
The polymerizable functional group-containing compound is not particularly limited as long as it has two or more polymerizable functional groups, and can be appropriately selected according to the purpose. For example, divinylbenzene, diallylbenzene, divinylsulfone, N , N′-methylenebisacrylamide, 2,2-bisacrylamideacetic acid, ethylene glycol di (meth) acrylate, diethylene glycol di (meth) acrylate, polyethylene glycol di (meth) acrylate, 1,3-divinyltetramethyldisiloxane, bis (2-methylallyl) carbonate, ethylene oxide-modified bisphenol A di (meth) acrylate, polymerizable functional group-containing compound having a polar group in the molecule other than the above compounds, and the like. These may be used individually by 1 type and may use 2 or more types together.
Among these, a polymerizable functional group-containing compound having a polar group in the molecule is preferable in that the affinity with a filler described later can be further improved.
The polymerizable functional group-containing compound having a polar group in the molecule is not particularly limited and may be appropriately selected depending on the intended purpose. Examples thereof include compounds represented by the following structural formulas.

  There is no restriction | limiting in particular as a commercial item of the polymerizable functional group containing compound which has a polar group in the said molecule | numerator, Although it can select suitably according to the objective, For example, diallylamine, N, N '-(1,2 -Dihydroxyethylene) bisacrylamide, 3,9-divinyl-2,4,8,10-tetraoxaspiro [5.5] undecane, triallylamine, bis (vinylsulfonyl) methane, 1,3-bis (vinylsulfonyl) -2-propanol, 1,3-divinyl-1,1,3,3-tetramethyldisilazane, 1,3-divinyltetramethyldisiloxane, 1,6-bis (acryloyloxy) hexane, N, N'- Bis (acryloyl) cystamine, bis (vinylsulfonyl) methane, 1,3-bis (vinylsulfonyl) -2-propanol, N, N'- (Vinylsulfonylacetyl) ethylenediamine, diallyl adipate, vinyl 10-undecenoate, trans, cis-2,6-nonadienal, divinyl adipate, cis-3-hexenoic acid, cis-3-hexenyl, 2-isopropenyl- 5-methyl-5-vinyltetrahydrofuran, (2,7-octadien-1-yl) succinic anhydride, diallyl 1,4-cyclohexanedicarboxylate (cis-, trans-mixture) (above, manufactured by Tokyo Chemical Industry Co., Ltd.) ); Divinyl glycol, divinyl sulfone, divinyl adipate, divinyl sebacate, diethylene glycol divinyl ether, triethylene glycol divinyl ether, diethylene glycol diacrylate, ethylene glycol diacrylate, bisacrylic acid 1 , 4-phenylene, polyethylene glycol diacrylate, N, N′-diacryloylethylenediamine, N, N′-hexamethylenebisacrylamide (manufactured by Wako Pure Chemical Industries, Ltd.); 1,4-butanediol diacrylate (Merck) Etc.);

--Polymerizable functional group--
There is no restriction | limiting in particular as said polymeric functional group, According to the objective, it can select suitably, For example, a vinyl group, an acryl group, etc. are mentioned. These may be used individually by 1 type and may use 2 or more types together.
Among these, an acrylic group is preferable in terms of polymerization reactivity.

-Polar group-
The polar group is not particularly limited as long as it has high affinity with the filler described later, and can be appropriately selected according to the purpose. For example, an amino group, imino group, nitrile group, ammonium group , Imide group, amide group, hydrazo group, azo group, diazo group, sulfide group, disulfide group, sulfonyl group, sulfinyl group, thiocarbonyl group, hydroxyl group, carboxyl group, carbonyl group, epoxy group, oxycarbonyl group, nitrogen-containing Heterocyclic groups, oxygen-containing heterocyclic groups, tin-containing groups, alkoxysilyl groups, and the like. These may be used individually by 1 type and may use 2 or more types together.
Among these, an amino group is preferable in that a modified natural rubber having high affinity with a filler and low loss (low rolling resistance) can be obtained.
The nitrogen-containing heterocyclic ring in the nitrogen-containing heterocyclic group is not particularly limited and can be appropriately selected depending on the purpose. For example, pyrrole, histidine, imidazole, triazolidine, triazole, triazine, pyridine, pyrimidine, pyrazine, Indole, quinoline, purine, phenazine, pteridine, melamine, and the like. The nitrogen-containing heterocycle may contain other heteroatoms in the ring.
There is no restriction | limiting in particular as an oxygen-containing heterocyclic ring in the said oxygen-containing heterocyclic group, According to the objective, it can select suitably. The oxygen-containing heterocycle may contain other heteroatoms in the ring.
There is no restriction | limiting in particular as said tin containing group, According to the objective, it can select suitably, For example, a tributyl vinyl tin etc. are mentioned.

<Polar group-containing part>
The polar group-containing part is not particularly limited as long as it is derived from a polar group-containing compound containing a polar group, and can be appropriately selected according to the purpose.

-Polar group-containing compound-
The polar group-containing compound is not particularly limited as long as it is a monomer containing at least one polar group in the molecule, and can be appropriately selected according to the purpose. 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, and oxycarbonyl group. , Sulfide groups, disulfide groups, sulfonyl groups, sulfinyl groups, thiocarbonyl groups, nitrogen-containing and oxygen-containing heterocyclic groups, tin-containing groups, alkoxysilyl groups, and the like. These monomers containing a polar group may be used alone or in combination of two or more.

Examples of the amino group-containing monomer include polymerizable monomers having at least one amino group selected from primary, secondary, and tertiary amino groups in one molecule. These may be used individually by 1 type and may use 2 or more types together.
Among these, tertiary amino group-containing monomers such as dialkylaminoalkyl (meth) acrylate are preferable.

  The primary amino group-containing monomer is not particularly limited and may be appropriately selected depending on the intended purpose. For example, acrylamide, methacrylamide, 4-vinylaniline, aminomethyl (meth) acrylate, aminoethyl (Meth) acrylate, aminopropyl (meth) acrylate, aminobutyl (meth) acrylate, etc. are mentioned.

  The secondary amino group-containing monomer is not particularly limited and may be appropriately selected depending on the intended purpose. Examples thereof 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-ani Linostyrene, β- (2-hydroxyethoxy) carbonyl-p-anilinostyrene, β-formyl-p-anilinostyrene, β-formyl-β-methyl-p-anilinostyrene, α-carboxy-β-carboxy Anilinostyrenes such as β-phenyl-p-anilinostyrene; (2) 1-anilinophenyl-1,3-butadiene, 1-anilinophenyl-3-me Til-1,3-butadiene, 1-anilinophenyl-3-chloro-1,3-butadiene, 3-anilinophenyl-2-methyl-1,3-butadiene, 1-anilinophenyl-2-chloro- 1,3-butadiene, 2-anilinophenyl-1,3-butadiene, 2-anilinophenyl-3-methyl-1,3-butadiene, 2-anilinophenyl-3-chloro-1,3-butadiene, etc. (3) N-monosubstituted (meta) such as N-methyl (meth) acrylamide, N-ethyl (meth) acrylamide, N-methylol acrylamide, N- (4-anilinophenyl) methacrylamide ) Acrylamides;

  The tertiary amino group-containing monomer is not particularly limited and may be appropriately selected depending on the intended purpose. Examples thereof include N, N-disubstituted aminoalkyl acrylate and N, N-disubstituted aminoalkylacrylamide. And vinyl compounds having a pyridyl group.

The N, N-disubstituted aminoalkyl acrylate is not particularly limited and may be appropriately selected depending on the intended purpose. Examples thereof include N, N-dimethylaminomethyl (meth) acrylate and 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) a Esters of acrylic acid or methacrylic acid such as relate, N, N-dibutylaminobutyl (meth) acrylate, N, N-dihexylaminoethyl (meth) acrylate, N, N-dioctylaminoethyl (meth) acrylate, acryloylmorpholine , Etc.
Among these, N, N-dimethylaminoethyl (meth) acrylate, N, N-diethylaminoethyl (meth) acrylate, N, N-dipropylaminoethyl (meth) acrylate, N, N-dioctylaminoethyl (meth) An acrylate, N-methyl-N-ethylaminoethyl (meth) acrylate is preferred.

The N, N-disubstituted aminoalkylacrylamide is not particularly limited and may be appropriately selected depending on the intended purpose. Examples thereof 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-dibutyla Nopropyl (meth) acrylamide, N, N-dibutylaminobutyl (meth) acrylamide, N, N-dihexylaminoethyl (meth) acrylamide, N, N-dihexylaminopropyl (meth) acrylamide, N, N-dioctylaminopropyl ( Examples include acrylamide compounds such as (meth) acrylamide or methacrylamide compounds.
Among these, N, N-dimethylaminopropyl (meth) acrylamide, N, N-diethylaminopropyl (meth) acrylamide, and N, N-dioctylaminopropyl (meth) acrylamide are preferable.

  Moreover, a nitrogen-containing heterocyclic group may be sufficient instead of an amino group. Examples of the nitrogen-containing heterocycle include pyrrole, histidine, imidazole, triazolidine, triazole, triazine, pyridine, pyrimidine, pyrazine, indole, quinoline, purine, phenazine, pteridine, melamine, and the like. The nitrogen-containing heterocycle may contain other heteroatoms in the ring.

The vinyl compound having a pyridyl group is not particularly limited and may be appropriately selected depending on the intended purpose. For example, 2-vinylpyridine, 3-vinylpyridine, 4-vinylpyridine, 5-methyl-2-vinyl Examples thereof include pyridine and 5-ethyl-2-vinylpyridine.
Among these, 2-vinylpyridine and 4-vinylpyridine are preferable.

  There is no restriction | limiting in particular as said nitrile group containing monomer, According to the objective, it can select suitably, For example, (meth) acrylonitrile, vinylidene cyanide, etc. are mentioned. These may be used individually by 1 type and may use 2 or more types together.

The hydroxyl group-containing monomer is not particularly limited and may be appropriately selected depending on the purpose. For example, the hydroxyl group-containing monomer has at least one primary, secondary, and tertiary hydroxyl group in one molecule. And polymerizable monomers. 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.
Specific examples of the hydroxyl group-containing monomer include, for example, 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) acrylate Hydroxyl group-containing unsaturated amides such as luamide; o-hydroxystyrene, m-hydroxystyrene, p-hydroxystyrene, o-hydroxy-α-methylstyrene, m-hydroxy-α-methylstyrene, p-hydroxy-α- And hydroxyl group-containing vinyl aromatic compounds such as methylstyrene and p-vinylbenzyl alcohol; (meth) acrylates, and the like.
Among these, a hydroxyl group-containing unsaturated carboxylic acid monomer, a hydroxyalkyl (meth) acrylate, and a hydroxyl group-containing vinyl aromatic compound are preferable, and a hydroxyl group-containing unsaturated carboxylic acid monomer is more preferable.
Examples of the hydroxyl group-containing unsaturated carboxylic acid monomer include esters such as acrylic acid, methacrylic acid, itaconic acid, fumaric acid and maleic acid, and derivatives such as amide and anhydride. These may be used individually by 1 type and may use 2 or more types together.
Among these, ester compounds such as acrylic acid and methacrylic acid are preferable.

The carboxyl group-containing monomer is not particularly limited and may be appropriately selected depending on the purpose. For example, (meth) acrylic acid, maleic acid, fumaric acid, itaconic acid, tetraconic acid, cinnamic acid, etc. Unsaturated carboxylic acids; monoesters of non-polymerizable polyvalent carboxylic acids such as phthalic acid, succinic acid, and adipic acid and hydroxyl-containing unsaturated compounds such as (meth) allyl alcohol and 2-hydroxyethyl (meth) acrylate Such free carboxyl group-containing esters and salts thereof. These may be used individually by 1 type and may use 2 or more types together.
Among these, unsaturated carboxylic acids are preferable.

  The epoxy group-containing monomer is not particularly limited and may be appropriately selected depending on the intended purpose. For example, (meth) allyl glycidyl ether, glycidyl (meth) acrylate, 3,4-oxycyclohexyl (meth) Acrylate, and the like. These may be used individually by 1 type and may use 2 or more types together.

  The tin-containing monomer is not particularly limited and may be appropriately selected depending on the intended purpose. Examples thereof include allyltri-n-butyltin, allyltrimethyltin, allyltriphenyltin, allyltri-n-octyltin, (meta ) Acryloxy-n-butyltin, (meth) acryloxytrimethyltin, (meth) acryloxytriphenyltin, (meth) acryloxy-n-octyltin, vinyltri-n-butyltin, vinyltrimethyltin, vinyltriphenyltin, And vinyl tri-n-octyltin. These may be used individually by 1 type and may use 2 or more types together.

  The alkoxysilyl group-containing monomer is not particularly limited and may be appropriately selected depending on the intended purpose. Examples thereof include (meth) acryloxymethyltrimethoxysilane, (meth) acryloxymethylmethyldimethoxysilane, ( (Meth) acryloxymethyldimethylmethoxysilane, (meth) acryloxymethyltriethoxysilane, (meth) acryloxymethylmethyldiethoxysilane, (meth) acryloxymethyldimethylethoxysilane, (meth) acryloxymethyltripropoxysilane, (Meth) acryloxymethylmethyldipropoxysilane, (meth) acryloxymethyldimethylpropoxysilane, γ- (meth) acryloxypropyltrimethoxysilane, γ- (meth) acryloxypropylmethyldimethoxysilane, γ- (meth) A Lilooxypropyldimethylmethoxysilane, γ- (meth) acryloxypropyltriethoxysilane, γ- (meth) acryloxypropylmethyldiethoxysilane, γ- (meth) acryloxypropyldimethylethoxysilane, γ- (meth) acryl Roxypropyltripropoxysilane, γ- (meth) acryloxypropylmethyldipropoxysilane, γ- (meth) acryloxypropyldimethylpropoxysilane, γ- (meth) acryloxypropylmethyldiphenoxysilane, γ- (meth) acryl Roxypropyldimethylphenoxysilane, γ- (meth) acryloxypropylmethyldibenzyloxysilane, γ- (meth) acryloxypropyldimethylbenzyloxysilane, trimethoxyvinylsilane, triethoxyvinylsilane, 6-trime Toxisilyl-1,2-hexene, p-trimethoxysilylstyrene, and the like can be given. These may be used individually by 1 type and may use 2 or more types together.

<Number average molecular weight of modified natural rubber>
There is no restriction | limiting in particular as a number average molecular weight of the said modified natural rubber, Although it can select suitably according to the objective, 150,000-450,000 are preferable and 250,000-450,000 are more preferable.
When the number average molecular weight of the modified natural rubber is less than 150,000, the heat build-up may be deteriorated due to the low molecular weight component, and when it exceeds 450,000, the viscosity becomes high and the blending workability may be deteriorated. On the other hand, when the molecular weight of the modified natural rubber is within the more preferable range, it is advantageous in terms of the balance between the molecular weight, the heat build-up, and the blending workability.
The number average molecular weight of the modified natural rubber can be measured, for example, by gel permeation chromatography (GPC) of natural rubber molecules obtained by dissolving in tetrahydrofuran.

(Method for producing modified natural rubber)
The method for producing the modified natural rubber of the present invention is not particularly limited as long as it is a method of subjecting a solid natural rubber raw material to a radical graft polymerization reaction of a polymerizable functional group-containing compound having two or more polymerizable functional groups. And can be appropriately selected according to the purpose.
For example, in a device capable of sufficiently imparting mechanical shearing force, the solid natural rubber raw material, the polymerizable functional group-containing compound, the polar group-containing compound, and a graft polymerization initiator described later are charged, By applying a mechanical shearing force, the natural rubber molecule can be crosslinked (coupled) and at the same time, a polar group can be introduced into the natural rubber molecule.
The addition of the polymerizable functional group-containing compound to the solid natural rubber raw material is preferably performed when mechanical shearing force is applied to the solid natural rubber raw material (when the solid natural rubber raw material is kneaded). Thereby, while being able to reduce a process further, the excessive reduction | decrease of molecular weight by provision (kneading) of a mechanical shear force can be suppressed.
The method for adding the polymerizable functional group-containing compound and the polar group-containing compound to the solid natural rubber raw material in the case of adding the polar group-containing compound is not particularly limited and may be appropriately selected depending on the purpose. For example, the polymerizable functional group-containing compound and the polar group-containing compound may be added to the solid natural rubber raw material at the same time, and either the polymerizable functional group-containing compound or the polar group-containing compound may be added first. It may be added to the solid natural rubber raw material, and then the other may be added to the solid natural rubber raw material.

The addition amount of the polymerizable functional group-containing compound with respect to 100 parts by mass of the solid rubber content in the solid natural rubber raw material is not particularly limited and may be appropriately selected depending on the intended purpose. 10.0 parts by mass is preferable, and 0.01 part by mass to 1.0 part by mass is more preferable.
If the addition amount of the polymerizable functional group-containing compound is less than 0.01 parts by mass, the modification effect may not be sufficiently exhibited. If the addition amount exceeds 10.0 parts by mass, gelation proceeds and workability deteriorates. There are things to do. On the other hand, when the addition amount of the polymerizable functional group-containing compound is within the more preferable range, it is advantageous in terms of the balance between the molecular weight, the exothermic property, and the blending workability.

There is no restriction | limiting in particular as an addition amount of the said polar group containing compound with respect to 100 mass parts of solid rubber components in the said solid natural rubber raw material, Although it can select suitably according to the objective, 0.01 mass part-10. 0 mass part is preferable and 0.01 mass part-1.0 mass part is more preferable.
When the addition amount of the polar group-containing compound is less than 0.01 parts by mass, the modification effect may not be sufficiently exhibited. When the addition amount exceeds 10.0 parts by mass, viscoelasticity, SS characteristics (in tensile tests) The physical properties inherent to natural rubber, such as stress-strain curves, may be greatly changed, and the physical properties inherent to natural rubber may be impaired, and the processability of the rubber composition may deteriorate. On the other hand, when the addition amount of the polar group-containing compound is within the more preferable range, it is advantageous in terms of balance between exothermic property and blending workability.

<Raw material of solid natural rubber>
The solid natural rubber raw material is not particularly limited and may be appropriately selected depending on the intended purpose. Examples thereof include various solid natural rubbers after drying, various natural rubber latex coagulates (including unsmoked sheets), natural Rubber cup lamps and the like. These may be used individually by 1 type and may use 2 or more types together.
There is no restriction | limiting in particular as said solid natural rubber, According to the objective, it can select suitably, For example, RSS (ribbed smoked sheet), TSR (technical specific driver), etc. are mentioned.
The natural rubber latex coagulated product is not particularly limited and may be appropriately selected depending on the intended purpose. Examples thereof include field latex, ammonia-treated latex, centrifugal concentrated latex, deproteinized latex treated with a surfactant and an enzyme. And those obtained by coagulating a natural rubber latex such as a combination thereof with an acid.
Specific coagulation conditions include a method of adjusting the pH to 4.7 by adding formic acid to natural rubber latex.
There is no restriction | limiting in particular as said natural rubber cup lamp, According to the objective, it can select suitably, For example, what solidified naturally, what solidified by adding acid, etc. are mentioned.

  By using the solid natural rubber raw material, it is not necessary to use high-purity natural rubber latex for the production of the modified natural rubber, and therefore 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 are great advantages 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.

<Mechanical shear force>
The mechanical shearing force means a force applied to the solid natural rubber raw material when the solid natural rubber raw material undergoes shear deformation in various kneading apparatuses.
The magnitude of the mechanical shearing force is not particularly limited and may be appropriately selected depending on the intended purpose. The shear rate is preferably in the range of 10 to 10,000 (1 / sec), and the shear rate is A range of 50 to 3000 (1 / sec) is more preferable.
When the shear rate is less than 10 (1 / sec), the mechanical shear force is insufficient and the radical graft polymerization reaction may not sufficiently proceed. When the shear rate exceeds 10,000 (1 / sec), the natural rubber molecule The molecular weight may decrease and the exothermic properties may deteriorate. On the other hand, when the shear rate is within the more preferable range, it is advantageous in terms of heat generation from the balance between the progress of the radical graft polymerization reaction and the decrease in molecular weight.
There is no restriction | limiting in particular as an apparatus which provides the said mechanical shear force, According to the objective, it can select suitably, For example, the closed-type twin-screw mixer represented by the Banbury type mixer, the twin-screw extrusion kneading apparatus , Dry prebreaker, and the like.

<Radical graft polymerization>
In the radical graft polymerization, the graft polymerization initiator is not particularly limited and may be appropriately selected depending on the intended purpose. Various initiators for emulsion polymerization can be used.
Moreover, there is no restriction | limiting in particular as the addition method of the said graft polymerization initiator, According to the objective, it can select suitably.

-Graft polymerization initiator-
The type of the graft polymerization initiator is not particularly limited and may be appropriately selected depending on the intended purpose. Examples thereof include benzoyl peroxide, hydrogen peroxide, cumene hydroperoxide, tert-butyl hydroperoxide, and 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, ammonium persulfate, and the like. In order to reduce the polymerization temperature, it is preferable to use a redox graft polymerization initiator.
The reducing agent combined with the peroxide used in the redox polymerization initiator is not particularly limited and can be appropriately selected depending on the purpose. For example, tetraethylenepentamine, mercaptans, acidic sodium sulfite, reducing property Examples include metal ions and ascorbic acid.
The redox initiator is not particularly limited and may be appropriately selected depending on the intended purpose. However, a combination of tert-butyl hydroperoxide and tetraethylenepentamine is preferable.
The amount of the graft polymerization initiator added to the natural rubber is not particularly limited and may be appropriately selected depending on the intended purpose. However, when a filler (carbon black, silica) is blended, the processability decreases. From the viewpoint of improving the low-loss characteristics without reducing the amount, the polymerizable functional group-containing compound (polar group-containing compound) is preferably 1 mol% to 100 mol%, more preferably 10 mol% to 100 mol%.
If the addition amount of the graft polymerization initiator is less than 1 mol%, the effect of adding the graft polymerization initiator may not be obtained, and if it exceeds 100 mol%, it is uniformly polymerizable functional group in each natural rubber molecule. The containing compound (polar group-containing compound) may not be introduced. On the other hand, when the addition amount of the graft polymerization initiator is within the more preferable range, a polymerizable functional group-containing compound (polar group-containing compound) is introduced into each natural rubber molecule in a uniform and sufficient amount, and the exothermic property is increased. This is advantageous in terms of improvement effect.

-Polymerization temperature-
The polymerization temperature is not particularly limited and can be appropriately selected depending on the purpose.
30 to 160 degreeC is preferable at the point from which sufficient efficiency is obtained, and 50 to 130 degreeC is more preferable.

(Rubber composition)
The rubber composition of the present invention is not particularly limited as long as it contains the modified natural rubber of the present invention, and can be appropriately selected according to the purpose, but rubber components other than the modified natural rubber of the present invention, fillers, It preferably contains a crosslinking agent, a vulcanization accelerator, an anti-aging agent, a softening agent and the like.

<Modified natural rubber>
There is no restriction | limiting in particular as content of the modified | denatured natural rubber of this invention in the said rubber composition, Although it can select suitably according to the objective, 15 mass% or more is preferable.
If the content of the modified natural rubber in the rubber composition is less than 15% by mass, the exothermic improvement effect may not be exhibited.

<Rubber component>
The rubber component is not particularly limited and can be appropriately selected according to the purpose. For example, the modified natural rubber, natural rubber, various butadiene rubbers, various styrene-butadiene copolymer rubbers, isoprene rubbers of the present invention, Butyl rubber, isobutylene and p-methylstyrene copolymer bromide, halogenated butyl rubber, acrylonitrile butadiene rubber, chloroprene rubber, ethylene-propylene copolymer rubber, ethylene-propylene-diene copolymer rubber, styrene-isoprene copolymer Polymer rubber, styrene-isoprene-butadiene copolymer rubber, isoprene-butadiene copolymer rubber, chlorosulfonated polyethylene, acrylic rubber, epichlorohydrin rubber, polysulfide rubber, silicone rubber, fluorine rubber, urethane rubber, etc. . These may be used individually by 1 type and may use 2 or more types together.
There is no restriction | limiting in particular as content of the modified natural rubber of this invention in the said rubber component, Although it can select suitably according to the objective, 20 mass% or more is preferable.
If the content of the modified natural rubber in the rubber component is less than 20% by mass, the exothermic improvement effect may not be exhibited.

<Filler>
The filler is not particularly limited and may be appropriately selected depending on the intended purpose. For example, carbon black, silica, aluminum hydroxide, clay, alumina, talc, calcium carbonate, magnesium carbonate, magnesium hydroxide, oxidation Examples thereof include magnesium and titanium oxide. These may be used individually by 1 type and may use 2 or more types together.
The carbon black is not particularly limited and may be appropriately selected depending on the intended purpose. However, SAF, ISAF, HAF, FEF, and GPF grade carbon black are preferable.
Moreover, there is no restriction | limiting in particular as said silica, Although it can select suitably according to the objective, Wet silica, dry-type silica, and colloidal silica are preferable.

There is no restriction | limiting in particular as content of the said filler, Although it can select suitably according to the objective, 5 mass parts-100 mass parts are preferable with respect to 100 mass parts of rubber components, and 10 mass parts-70 mass parts. A range of parts is more preferred.
When the content of the filler is less than 5 parts by mass, the effect of adding the filler may not be seen so much. When the content exceeds 100 parts by mass, the rubber component tends not to be mixed. .

<Crosslinking agent>
There is no restriction | limiting in particular as said crosslinking agent, According to the objective, it can select suitably, For example, sulfur etc. are mentioned.

There is no restriction | limiting in particular as content of the said crosslinking agent, Although it can select suitably according to the objective, 0.1 mass part-20 mass parts are preferable with respect to 100 mass parts of rubber components.
If the content of the cross-linking agent is less than 0.1 parts by mass, the effect of adding the cross-linking agent tends not to be obtained. If the content exceeds 20 parts by mass, cross-linking proceeds during kneading with some cross-linking agents. There is a tendency to become.

(tire)
The tire of the present invention is not particularly limited as long as the rubber composition of the present invention is used, and can be appropriately selected according to the purpose, but a pneumatic tire is preferable.
As a method for manufacturing the tire, a conventional method can be used. For example, on a tire molding drum, members usually used for manufacturing a tire such as a carcass layer, a belt layer, and a tread layer made of unvulcanized rubber are sequentially laminated, and the drum is removed to obtain a green tire. Next, the desired tire can be manufactured by heat vulcanizing the green tire according to a conventional method.
There is no restriction | limiting in particular as conditions for the said heat vulcanization, Although it can select suitably according to the objective, Temperature 100 to 200 degreeC and heating time 10 minutes-15 hours are preferable.

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. Below, the manufacturing method of natural rubber is shown.
Hereinafter, in this specification, Examples 1, 3, 5, 7, 9, 11, 13, 15, 17, 19, 21, 23 are referred to as Reference Examples 1, 3, 5, 7, 9, 11, respectively. , 13, 15, 17, 19, 21, 23.

(Production Example 1: Method for producing natural rubber A)
<Modification reaction process of natural rubber latex coagulum>
The pH was adjusted to 4.7 by adding formic acid to the field latex and coagulated. This solid was crumbized 5 times through a shredder. 60 g of the dried rubber obtained by drying this coagulated product at 110 ° C. for 210 minutes with a hot air dryer was used in a plast mill manufactured by Toyo Seiki Co., Ltd., 0.5 g of divinylbenzene, 0.15 g of tert-butyl hydroperoxide and 0. Natural rubber A was obtained by masticating with 15 g at 90 ° C. for 90 seconds.

(Production Example 2: Method for producing natural rubber B)
<Modification reaction process of natural rubber latex coagulum>
The pH was adjusted to 4.7 by adding formic acid to the field latex and coagulated. This solid was crumbized 5 times through a shredder. 60 g of the dried rubber obtained by drying this coagulated product with a hot air dryer at 110 ° C. for 210 minutes was subjected to a plast mill manufactured by Toyo Seiki Co., Ltd. 0.5 g of divinylbenzene, 0.75 g of N, N-diethylaminoethyl methacrylate, and tert-butyl hydroper Natural rubber B was obtained by masticating at 90 ° C. for 90 seconds together with 0.15 g of oxide and 0.15 g of tetraethylenepentamine.

(Production Example 3: Method for producing natural rubber C)
<Modification reaction process of natural rubber latex coagulum>
The pH was adjusted to 4.7 by adding formic acid to the field latex and coagulated. This solid was crumbized 5 times through a shredder. After determining the dry rubber content of the coagulated product, 600 g of coagulated rubber, 5.0 g of divinylbenzene and 1.5 g of tert-butyl hydroperoxide in terms of dry rubber were kneaded at 30 rpm for 2 minutes in a kneader. This was uniformly dispersed. Next, while uniformly adding 1.5 g of tetraethylenepentamine to this rubber, using a Kobe Steel twin-screw kneading extruder (same direction rotating screw diameter 30 mm, L / D = 35, three vent holes), Dry natural rubber C was obtained by extrusion while applying mechanical shearing force at a barrel temperature of 120 ° C. and a rotation speed of 100 rpm.

(Production Example 4: Method for producing natural rubber D)
<Modification reaction process of natural rubber latex coagulum>
The pH was adjusted to 4.7 by adding formic acid to the field latex and coagulated. This solid was crumbized 5 times through a shredder. After determining the dry rubber content of the coagulated product, 600 g of coagulated rubber, 5.0 g of divinylbenzene, 7.5 g of N, N-diethylaminoethyl methacrylate, and 1.5 g of tert-butyl hydroperoxide in terms of dry rubber were calculated. The mixture was kneaded at 30 rpm for 2 minutes in a kneader and dispersed uniformly. Next, while uniformly adding 1.5 g of tetraethylenepentamine to this rubber, using a Kobe Steel twin-screw kneading extruder (same direction rotating screw diameter 30 mm, L / D = 35, three vent holes), Dry natural rubber D was obtained by extrusion while applying mechanical shearing force at a barrel temperature of 120 ° C. and a rotation speed of 100 rpm.

(Production Examples 5 to 8: Method for producing natural rubber E, F, G, H)
In Production Examples 1 and 2, 0.6 g of N, N′-methylenebisacrylamide was added instead of adding 0.5 g of divinylbenzene, and in Production Examples 3 and 4, N, N′-methylene was added instead of adding 5.0 g of divinylbenzene. Natural rubber E, F, G, and H were obtained by adding 6.0 g of bisacrylamide and producing under the same conditions except that.

(Production Example 9: Method for producing natural rubber I)
<Modification reaction process of solid natural rubber>
60 g of natural rubber is masticated at 90 ° C. for 90 seconds with 0.5 g of divinylbenzene, 0.15 g of tert-butyl hydroperoxide and 0.15 g of tetraethylenepentamine in a plast mill manufactured by Toyo Seiki Co., Ltd. Obtained.

(Production Example 10: Method for producing natural rubber J)
<Modification reaction process of solid natural rubber>
60 g of natural rubber was used at 90 ° C. together with 0.5 g of divinylbenzene, 0.75 g of N, N-diethylaminoethyl methacrylate, 0.15 g of tert-butyl hydroperoxide and 0.15 g of tetraethylenepentamine at Toyo Seiki Co. Natural rubber J was obtained by masticating for 90 seconds.

(Production Example 11: Method for producing natural rubber K)
<Modification reaction process of solid natural rubber>
600 g of natural rubber, 5.0 g of divinylbenzene and 1.5 g of tert-butyl hydroperoxide were kneaded in a kneader at room temperature for 2 minutes at 30 rpm, and dispersed uniformly. Next, while uniformly adding 1.5 g of tetraethylenepentamine to this rubber, using a Kobe Steel twin-screw kneading extruder (same direction rotating screw diameter 30 mm, L / D = 35, three vent holes), Dry natural rubber K was obtained by extrusion while applying mechanical shearing force at a barrel temperature of 120 ° C. and a rotation speed of 100 rpm.

(Production Example 12: Method for producing natural rubber L)
<Modification reaction process of solid natural rubber>
600 g of natural rubber, 5.0 g of divinylbenzene, 7.5 g of N, N-diethylaminoethyl methacrylate and 1.5 g of tert-butyl hydroperoxide were kneaded in a kneader at room temperature for 2 minutes at 30 rpm and dispersed uniformly. Next, while uniformly adding 1.5 g of tetraethylenepentamine to this rubber, using a Kobe Steel twin-screw kneading extruder (same direction rotating screw diameter 30 mm, L / D = 35, three vent holes), Dry natural rubber L was obtained by extrusion while applying mechanical shearing force at a barrel temperature of 120 ° C. and a rotation speed of 100 rpm.

(Production Examples 13-16: Method for producing natural rubber M, N, O, P)
In Production Examples 9 to 10, 0.6 g of N, N'-methylenebisacrylamide was added instead of adding 0.5 g of divinylbenzene, and in Production Examples 11 to 12, N, N'- Natural rubber M, N, O, and P were obtained by adding 6.0 g of methylene bisacrylamide and manufacturing it on the same conditions other than that.

(Production Example 17: Method for producing natural rubber Q)
<Modification reaction process of natural rubber cup lamp>
A natural rubber cup lamp of 60 g in terms of dry rubber is used for 90 seconds at 90 ° C. with 0.5 g of divinylbenzene, 0.15 g of tert-butyl hydroperoxide and 0.15 g of tetraethylenepentamine in a plastmill manufactured by Toyo Seiki Co., Ltd. Natural rubber Q was obtained by kneading.

(Production Example 18: Method for producing natural rubber R)
<Modification reaction process of natural rubber cup lamp>
A natural rubber cup lamp of 60 g in terms of dry rubber was converted to 0.5 g of divinylbenzene, 0.75 g of N, N-diethylaminoethyl methacrylate, 0.15 g of tert-butyl hydroperoxide, and tetraethylenepenta using a plastmill manufactured by Toyo Seiki Co., Ltd. Natural rubber R was obtained by masticating at 90 ° C. for 90 seconds with 0.15 g of min.

(Production Example 19: Method for producing natural rubber S)
<Modification reaction process of natural rubber cup lamp>
600 g of natural rubber cup lamp, 5.0 g of divinylbenzene and 1.5 g of tert-butyl hydroperoxide were kneaded in a kneader at 30 rpm for 2 minutes in a kneader and dispersed uniformly. Next, while uniformly adding 1.5 g of tetraethylenepentamine to this rubber, using a Kobe Steel twin-screw kneading extruder (same direction rotating screw diameter 30 mm, L / D = 35, three vent holes), Dry natural rubber S was obtained by extrusion while applying mechanical shearing force at a barrel temperature of 120 ° C. and a rotation speed of 100 rpm.

(Production Example 20: Method for producing natural rubber T)
<Modification reaction process of natural rubber cup lamp>
Kneaded 600 g of natural rubber cup lamp, 5.0 g of divinylbenzene, 7.5 g of N, N-diethylaminoethyl methacrylate and 1.5 g of tert-butyl hydroperoxide in a kneader at room temperature for 30 rpm for 2 minutes, Evenly dispersed. Next, while uniformly adding 1.5 g of tetraethylenepentamine to this rubber, using a Kobe Steel twin-screw kneading extruder (same direction rotating screw diameter 30 mm, L / D = 35, three vent holes), Dry natural rubber T was obtained by extruding while applying mechanical shearing force at a barrel temperature of 120 ° C. and a rotational speed of 100 rpm.

(Production Examples 21 to 24: Method for producing natural rubber U, V, W, X)
In Production Examples 21 to 22, 0.6 g of N, N′-methylenebisacrylamide was added instead of adding 0.5 g of divinylbenzene, and in Production Examples 23 to 24, N, N′-methylene was added instead of adding 5.0 g of divinylbenzene. Natural rubbers U, V, W, and X were obtained by adding 6.0 g of bisacrylamide and producing under the same conditions.

(Production Examples 25-30: Method for producing natural rubber a, b, c, d, e, f)
In Production Example 1, Production Example 3, Production Example 9, Production Example 11, Production Example 17, and Production Example 19, natural rubber a, b, c, d, e, and f were obtained by processing without adding anything. .

  Table 1 summarizing Production Examples 1 to 30 is shown below.

  Next, rubber compositions 1 to 30 containing the natural rubbers A to X and a to f obtained in Production Examples 1 to 30 in the compounding formulation shown in Table 2 were prepared by kneading with a plast mill, “Mooney (ML1 + 4, 100 ° C.)”, “Number average molecular weight (Mn)” of natural rubber, “Mixed Mooney (ML1 + 4, 130 ° C.)” of rubber composition and “tan δ” of vulcanized rubber are measured by the following measurement methods. It was measured. The measurement results are shown in Tables 3-5.

（１）天然ゴム：製造例１〜３０で製造した天然ゴムＡ〜Ｘ及びａ〜ｆの各々
（２）カーボンブラックＮ３３９：東海カーボン社製「シーストＫＨ」
（３）老化防止剤６Ｃ：Ｎ−（１，３−ジメチルブチル）−Ｎ’−フェニル−ｐ−フェニレンジアミン
（４）加硫促進剤ＤＺ：Ｎ，Ｎ’−ジシクロヘキシル−２−ベンゾチアゾリルスルフェンアミド

(1) Natural rubber: each of natural rubbers A to X and a to f produced in Production Examples 1 to 30 (2) Carbon black N339: “Seast KH” manufactured by Tokai Carbon Co., Ltd.
(3) Anti-aging agent 6C: N- (1,3-dimethylbutyl) -N′-phenyl-p-phenylenediamine (4) Vulcanization accelerator DZ: N, N′-dicyclohexyl-2-benzothiazolylsulfur Fenamide

<Measurement method>
(1) Mooney viscosity of natural rubber (raw material Mooney (ML _{1 + 4} , 100 ° C.))
The Mooney viscosity ML _{1 + 4} (100 ° C.) of the (modified) natural rubber was measured at 100 ° C. in accordance with JIS K6300-1994. The measurement results are shown in Tables 3-5.
(2) Number average molecular weight of natural rubber Monodispersed by gel permeation chromatography [GPC: Tosoh HLC-8020, Column: Tosoh GMH-XL (two in series), Detector: Differential refractometer (RI)] Based on polystyrene, the number average molecular weight (Mn) in terms of polystyrene of each (modified) natural rubber was determined.
(3) Mooney viscosity of rubber composition (Mixed Mooney (ML _{1 + 4} , 130 ° C.)
Based on JIS K6300-1994, Mooney viscosity ML1 _{+ 4} (130 degreeC) of each said rubber composition was measured at 130 degreeC.
(4) Tan δ of vulcanized rubber
For each vulcanized rubber obtained by vulcanizing each rubber composition at 145 ° C. for 33 minutes, a loss tangent (with a temperature of 50 ° C., a strain of 5%, and a frequency of 15 Hz) was measured using a viscoelasticity measuring device (manufactured by Rheometrics). tan δ) was measured. It shows that it is excellent in low-loss property, so that tan-delta is small.

  From Tables 3 to 5, using the modified natural rubber of Examples 1 to 24 obtained by subjecting a solid natural rubber raw material to a radical graft polymerization reaction with a polymerizable functional group-containing compound having two or more polymerizable functional groups. It was found that the produced vulcanized rubber can improve the low heat buildup (low loss) as compared with the vulcanized rubber produced using the unmodified natural rubber of Comparative Examples 1-6.

  The modified natural rubber of the present invention can be used for elastomer products in general, particularly for tire members.

Claims (11)

A modified natural rubber having a natural rubber molecule and a crosslinked part formed by crosslinking between the natural rubber molecules,
Radical graft polymerization reaction of a polymerizable functional group-containing compound having two or more polymerizable functional groups onto at least one solid natural rubber raw material selected from the group consisting of natural rubber, natural rubber latex coagulum and natural rubber cup lamp Let me
The polymerizable functional group-containing compound further has a polar group in the molecule;
Said polar group, Ri amino der,
A modified natural rubber further having a polar group-containing part grafted to the natural rubber molecule,
Wherein the solid natural rubber raw material, the modified natural rubber, wherein Rukoto such by a polar group-containing compound is further radical graft polymerization reaction with a polar group.   The modified natural rubber according to claim 1, wherein the solid functional raw material is subjected to radical graft polymerization reaction of the polymerizable functional group-containing compound while imparting mechanical shearing force.   The modified natural rubber according to claim 1, wherein the number average molecular weight is 150,000 to 450,000. A method for producing a modified natural rubber having a natural rubber molecule and a cross-linked part formed by cross-linking the natural rubber molecules,
Radical graft polymerization reaction of a polymerizable functional group-containing compound having two or more polymerizable functional groups onto at least one solid natural rubber raw material selected from the group consisting of natural rubber, natural rubber latex coagulum and natural rubber cup lamp Let me
The polymerizable functional group-containing compound further has a polar group in the molecule;
Said polar group, Ri amino der,
The modified natural rubber further has a polar group-containing part formed by graft bonding to the natural rubber molecule,
Wherein the solid natural rubber raw material, the method for producing the modified natural rubber, wherein Rukoto such by a polar group-containing compound is further radical graft polymerization reaction with a polar group. The method for producing a modified natural rubber according to claim 4 , wherein the polymerizable functional group-containing compound is subjected to a radical graft polymerization reaction while imparting mechanical shearing force to the solid natural rubber raw material. 6. The process for producing a modified natural rubber according to claim 5 , wherein the polymerizable functional group-containing compound is added to the solid natural rubber raw material when a mechanical shearing force is applied to the solid natural rubber raw material. Wherein of the solid rubber component 100 parts by weight of a solid natural rubber raw material, according to claim 4, characterized by comprising the polymerizable functional group-containing compound is added to 10.0 parts by 0.01 parts by weight A method for producing modified natural rubber. The modified natural product according to claim 4 , wherein 0.01 parts by mass to 10.0 parts by mass of the polar group-containing compound is added to 100 parts by mass of the solid rubber content in the solid natural rubber raw material. Rubber production method.   A rubber composition comprising the modified natural rubber according to claim 1. The rubber composition according to claim 9 , wherein the content of the modified natural rubber in the rubber composition is 15% by mass or more. A tire comprising the rubber composition according to claim 9 .