JP4776215B2 - Pneumatic tire - Google Patents

Description

  The present invention relates to a pneumatic tire, particularly a run flat tire having high run flat durability and low rolling resistance.

  Conventionally, a tire that can safely travel a certain distance even in a state where the internal pressure of the tire has decreased due to puncture or the like, a so-called run-flat tire, a substantially crescent-shaped cross section on the innermost side of the carcass in the sidewall portion of the tire A side reinforcing type run flat tire is known in which the side reinforcing rubber layer is arranged to improve the rigidity of the side wall portion. However, in the so-called run-flat running in a state where the internal pressure of the tire is reduced, the deformation of the side reinforcing rubber layer increases as the deformation of the sidewall portion of the tire increases. In some cases, the rubber component itself in the side reinforcing rubber layer is cut or crosslinked between the rubber components formed by vulcanization. The part may be cut. In this case, the elastic modulus of the side reinforcing rubber layer decreases, the deflection of the tire further increases, the heat generation of the side wall portion proceeds, and finally the side reinforcing rubber layer exceeds its failure limit, and the tire is compared. There is a risk of failure at an early stage.

  As one of means for delaying the time until failure, there is a method for increasing the breaking strength of the side reinforcing rubber layer at a high temperature. For example, natural rubber has higher breaking strength at high temperatures than synthetic rubbers such as styrene-butadiene copolymer rubber (SBR) and polybutadiene rubber (BR). It is possible to increase the ratio of natural rubber.

  On the other hand, as another means for delaying the time to failure, a rubber composition having as small a loss tangent (tanδ) is applied to the side reinforcing rubber layer to suppress heat generation of the side reinforcing rubber layer. There is also a technique for suppressing a decrease in the elastic modulus of the side reinforcing rubber layer. Here, as for the synthetic rubbers such as SBR and BR, synthetic rubbers having low heat generation have been developed by various modification techniques and the like, but there is no natural rubber that has been reduced in heat generation, and side reinforcing rubbers. In order to increase the breaking strength at high temperature of the layer, the heat generation increases as the ratio of natural rubber in the rubber composition used for the side reinforcing rubber layer increases, so the heat generation at low temperature is reduced while improving the breaking strength at high temperature. I couldn't.

  In addition, as a technique for modifying natural rubber, a technique of adding a vinyl monomer to natural rubber latex and performing graft polymerization (see Patent Documents 1 to 6) is known. Since a large amount (20 to 50% by mass) of a vinyl compound is grafted as a monomer in order to change the characteristics of the natural rubber itself, it does not have the excellent physical properties inherent to natural rubber.

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

  Accordingly, an object of the present invention is to provide a pneumatic tire that solves the above-described problems of the prior art, has high run-flat durability, and low rolling resistance.

  As a result of intensive studies to achieve the above-mentioned object, the present inventor uses a rubber composition containing a specific modified natural rubber in at least one of the bead filler and the side reinforcing rubber layer. The inventors have found that the rolling resistance can be reduced and the heat generation of the tire can be suppressed while improving the invention, and the present invention has been completed.

That is, the first pneumatic tire of the present invention has a pair of bead portions and a pair of sidewall portions, and a tread portion connected to both sidewall portions, and extends in a toroidal shape between the pair of bead portions. In a pneumatic tire provided with a carcass that reinforces each of these parts, and a bead filler that is disposed outside the bead core in the tire radial direction, each embedded in the bead part,
To the bead filler, as a rubber component, a polar group-containing monomer is added to natural rubber latex, the polar group-containing monomer is graft-polymerized to natural rubber molecules in the natural rubber latex, and further solidified and dried. The rubber composition containing the modified natural rubber is used.

The second pneumatic tire of the present invention has a pair of bead portions, a pair of sidewall portions, and a tread portion connected to both sidewall portions, and extends in a toroidal shape between the pair of bead portions. In a pneumatic tire provided with a carcass for reinforcing these parts, and a pair of side reinforcing rubber layers arranged inside the carcass of the sidewall part,
To the side reinforcing rubber layer, as a rubber component, a polar group-containing monomer is added to natural rubber latex, and the polar group-containing monomer is graft-polymerized to natural rubber molecules in the natural rubber latex, and further solidified and dried. A rubber composition containing a modified natural rubber is used.

Furthermore, the third pneumatic tire of the present invention has a pair of bead portions and a pair of sidewall portions, and a tread portion connected to both sidewall portions, and extends in a toroidal shape between the pair of bead portions. A carcass that reinforces each of these parts, a bead filler that is disposed outside the bead core in the tire radial direction, and a pair of side reinforcing rubber layers that are disposed inside the carcass of the sidewall part. In the provided pneumatic tire,
To the bead filler and the side reinforcing rubber layer, as a rubber component, a polar group-containing monomer is added to natural rubber latex, and the polar group-containing monomer is graft-polymerized to natural rubber molecules in the natural rubber latex, Further, a rubber composition containing a modified natural rubber obtained by coagulation and drying is used.

  In a preferred example of the pneumatic tire of the present invention, the rubber component of the rubber composition contains 10% by mass or more of the modified natural rubber.

  In another preferred embodiment of the pneumatic tire of the present invention, the polar group of the polar group-containing monomer is an amino group, imino group, nitrile group, ammonium group, imide group, amide group, hydrazo group, azo group, diazo group. Group, hydroxyl group, carboxyl group, carbonyl group, epoxy group, oxycarbonyl group, sulfide group, disulfide group, sulfonyl group, sulfinyl group, thiocarbonyl group, nitrogen-containing heterocyclic group, oxygen-containing heterocyclic group, tin-containing group and It is at least one selected from the group consisting of alkoxysilyl groups.

  Moreover, in the other suitable example of the pneumatic tire of this invention, the graft amount of the said polar group containing monomer is 0.01-5.0 mass% with respect to the rubber component in the said natural rubber latex.

  According to the present invention, there is provided a pneumatic tire having a high run-flat durability and a low rolling resistance using a rubber composition containing a specific modified natural rubber in at least one of a bead filler and a side reinforcing rubber layer. Can do.

  Hereinafter, the present invention will be described in detail with reference to the drawings. FIG. 1 is a cross-sectional view of one embodiment of the pneumatic tire of the present invention. The tire shown in FIG. 1 has a pair of left and right bead portions 1 and a pair of sidewall portions 2 and a tread portion 3 connected to both sidewall portions 2, and extends in a toroidal shape between the pair of bead portions 1. A radial carcass 4 that reinforces each of these parts 1, 2, 3, a belt 5 composed of two belt layers arranged on the outer side in the tire radial direction of the crown part of the carcass 4, and the bead part 1 A bead filler 7 disposed on the outer side in the tire radial direction of each of the ring-shaped bead cores 6 embedded therein and a pair of side reinforcing rubber layers 8 disposed on the inside of the carcass 4 of the sidewall portion 2 are provided.

  In the illustrated tire, the radial carcass 4 includes a main body portion extending in a toroid shape between the bead cores 6 embedded in the pair of bead portions 1, and a radial direction around the bead core 6 from the inner side to the outer side in the tire width direction. However, the structure of the carcass and the number of plies of the tire according to the present invention are not limited to this. Further, the bead filler 7 is disposed between the carcass main body portion and the folded portion of the bead core 6 on the outer side in the tire radial direction. In addition, although the shape of the side reinforcing rubber layer 8 in the illustrated example has a crescent-shaped cross section, the cross-sectional shape is not particularly limited as long as it has a side reinforcing function.

  Further, in the tire shown in FIG. 1, a belt 5 composed of two belt layers is arranged on the outer side in the tire radial direction of the crown portion of the radial carcass 4, and the belt layer is usually on the tire equatorial plane. The belt 5 is composed of a rubberized layer of cords extending obliquely with respect to each other, and the two belt layers are laminated so that the cords constituting the belt layers intersect with each other across the equator plane. The belt 5 in FIG. 1 is composed of two belt layers, but in the tire of the present invention, the number of belt layers constituting the belt 5 is not limited to this. Further, the pneumatic tire of the present invention may include a belt reinforcing layer made of a rubberized layer of cords arranged substantially parallel to the tire circumferential direction on the outer side in the tire radial direction of the belt 5.

  In the pneumatic tire of the present invention, a polar group-containing monomer is added to natural rubber latex to at least one of the bead filler 7 and the side reinforcing rubber layer 8, and the polar group-containing monomer is added to the natural rubber latex. It is necessary to use a rubber composition containing, as a rubber component, a modified natural rubber obtained by graft polymerization to natural rubber molecules therein and further solidified and dried. Although the illustrated tire includes both the bead filler 7 and the side reinforcing rubber layer 8, the tire of the present invention uses a bead filler and / or a side reinforcing rubber in which the rubber composition containing the modified natural rubber is used. What is necessary is just to provide a layer.

  Since the polar group of the polar group-containing monomer used in the modified natural rubber has excellent affinity for various fillers such as carbon black and silica, the modified natural rubber is more various than the unmodified natural rubber. High affinity for fillers. Therefore, the rubber composition using the modified natural rubber as a rubber component has high dispersibility of the filler with respect to the rubber component, the reinforcing effect of the filler is sufficiently exhibited, the breaking strength is high, and the low exothermic property. (Low loss) is also greatly improved. Therefore, by using the rubber composition for at least one of the bead filler 7 and the side reinforcing rubber layer 8 of the tire, while significantly reducing the rolling resistance of the tire, the breaking strength of the sidewall portion 2 is greatly increased. The run flat durability of the tire can be remarkably improved.

  The natural rubber latex used for the production of the modified natural rubber is not particularly limited. For example, field latex, ammonia-treated latex, centrifugal concentrated latex, deproteinized latex treated with a surfactant or an enzyme, and a combination thereof. A thing etc. can be used.

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

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

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

  The secondary amino group-containing monomer includes (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-anilino Anilinostyrenes such as styrene, 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-aniline Linophenyl-2-methyl-1,3-butadiene, 1-anilinov Nyl-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 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 nitrile group-containing monomer include (meth) acrylonitrile, vinylidene cyanide, and the like. These nitrile group-containing monomers may be used alone or in a combination of two or more.

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

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

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

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

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

  Examples of the monomer containing the alkoxysilyl group include (meth) acryloxymethyltrimethoxysilane, (meth) acryloxymethylmethyldimethoxysilane, (meth) acryloxymethyldimethylmethoxysilane, (meth) acryloxymethyltrimethoxysilane. Ethoxysilane, (meth) acryloxymethylmethyldiethoxysilane, (meth) acryloxymethyldimethylethoxysilane, (meth) acryloxymethyltripropoxysilane, (meth) acryloxymethylmethyldipropoxysilane, (meth) acryloxy Methyldimethylpropoxysilane, γ- (meth) acryloxypropyltrimethoxysilane, γ- (meth) acryloxypropylmethyldimethoxysilane, γ- (meth) acryloxypropyldimethylmethoxysilane, γ- (meth) acryloxypropyltri Ethoxysilane, γ -(Meth) acryloxypropylmethyldiethoxysilane, γ- (meth) acryloxypropyldimethylethoxysilane, γ- (meth) acryloxypropyltripropoxysilane, γ- (meth) acryloxypropylmethyldipropoxysilane, γ -(Meth) acryloxypropyldimethylpropoxysilane, γ- (meth) acryloxypropylmethyldiphenoxysilane, γ- (meth) acryloxypropyldimethylphenoxysilane, γ- (meth) acryloxypropylmethyldibenzyloxysilane, γ- (meth) acryloxypropyldimethylbenzyloxysilane, trimethoxyvinylsilane, triethoxyvinylsilane, 6-trimethoxysilyl-1,2-hexene, p-trimethoxysilylstyrene and the like can be mentioned. These alkoxysilyl group-containing monomers may be used alone or in a combination of two or more.

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

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

  In order to improve the low loss and breaking strength without reducing the processability of the rubber composition by blending the modified natural rubber with a filler such as carbon black or silica, the natural rubber contains the above polar group. Since it is important that the monomer is introduced in a small amount and uniformly, the addition amount of the polymerization initiator is preferably in the range of 1 to 100 mol%, preferably 10 to 100 mol% with respect to the polar group-containing monomer. A range is more preferred.

  Each component described above is charged into a reaction vessel and reacted at 30 to 80 ° C. for 10 minutes to 7 hours, whereby a modified natural rubber latex in which the polar group-containing monomer is graft copolymerized with a natural rubber molecule is obtained. The modified natural rubber latex is coagulated, washed, and then dried using a dryer such as a vacuum dryer, an air dryer, a drum dryer or the like to obtain a modified natural rubber. Here, the coagulant used for coagulating the modified natural rubber latex is not particularly limited, and examples thereof include acids such as formic acid and sulfuric acid, and salts such as sodium chloride.

  In the modified natural rubber, the graft amount of the polar group-containing monomer is preferably in the range of 0.01 to 5.0% by mass, more preferably in the range of 0.02 to 3.0% by mass, relative to the rubber component in the natural rubber latex, 0.03 The range of -2.0 mass% is still more preferable. When the graft amount of the polar group-containing monomer is less than 0.01% by mass, the low loss property and breaking strength of the rubber composition may not be sufficiently improved. Moreover, when the graft amount of the polar group-containing monomer exceeds 5.0% by mass, the natural physical properties of natural rubber such as viscoelasticity and SS characteristics (stress-strain curve in a tensile tester) are greatly changed. The inherent physical properties of natural rubber are impaired, and the processability of the rubber composition may be greatly deteriorated.

  The rubber composition used for the bead filler 7 and / or the side reinforcing rubber layer 8 of the pneumatic tire according to the present invention includes the modified natural rubber as a rubber component, and 10% by mass or more of the rubber component is the modified natural rubber. A rubber is preferable. The rubber composition may contain other rubber as a rubber component. For example, unmodified natural rubber (NR), styrene-butadiene copolymer rubber (SBR), polybutadiene rubber (BR), poly Various synthetic rubbers such as isoprene rubber (IR) can be included.

  The rubber composition 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 rubber component. 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 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.), 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 the rubber composition, in addition to the rubber component and filler, a compounding agent usually used in the rubber industry, such as anti-aging agent, softener, silane coupling agent, stearic acid, zinc white, vulcanized Accelerators, vulcanizing agents, 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 can be produced by blending various compounding agents appropriately selected as necessary with a rubber component containing at least a modified natural rubber, and kneading, heating, extruding or the like.

  The pneumatic tire of the present invention can be manufactured by a conventional method by applying the above modified natural rubber-containing rubber composition to at least one of the bead filler 7 and the side reinforcing rubber layer 8. In the pneumatic tire of the present invention, as the gas filled in the tire, normal or air with a changed oxygen partial pressure, or an inert gas such as nitrogen 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>
(Natural rubber latex modification reaction process)
The field latex was centrifuged using a latex separator (manufactured by Saito Centrifugal Industries Co., Ltd.) at a rotational speed of 7500 rpm to obtain a concentrated latex having a dry rubber concentration of 60%. 1000 g of this concentrated latex is put into a stainless steel reaction vessel equipped with a stirrer and a temperature control jacket, and 10 mL of water and 90 mg of emulsifier [Emulgen 1108, manufactured by Kao Corporation] are added in advance to 3.0 g of N, N-diethylaminoethyl methacrylate. The emulsified product was added with 990 mL of water, and the mixture was stirred at room temperature for 30 minutes while purging with nitrogen. Next, as a polymerization initiator, 1.2 g of tert-butyl hydroperoxide and 1.2 g of tetraethylenepentamine were added and reacted at 40 ° C. for 30 minutes to obtain a modified natural rubber latex.

(Coagulation and drying process)
Next, formic acid was added to the modified natural rubber latex to adjust the pH to 4.7 to coagulate the modified natural rubber latex. The solid material thus obtained was treated with a creper five times, passed through a shredder and crushed, and then dried at 110 ° C. for 210 minutes with a hot air drier to obtain modified natural rubber A. From the mass of the modified natural rubber A thus obtained, it was confirmed that the conversion rate of N, N-diethylaminoethyl methacrylate added as a monomer was 100%. In addition, the modified natural rubber A was extracted with petroleum ether and further extracted with a 2: 1 mixed solvent of acetone and methanol, but when the extract was analyzed, no homopolymer was detected. It was confirmed that 100% of the added monomer was introduced into the natural rubber molecule. Therefore, the graft amount of the monomer in the resulting modified natural rubber A is 0.5% by mass with respect to the rubber component in the natural rubber latex.

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

<Production Example 3>
Natural rubber C was prepared by directly coagulating and drying the natural rubber latex without undergoing a modification reaction step.

  Next, a rubber composition having a formulation shown in Table 1 was prepared by kneading with a plast mill, and the dynamic storage elastic modulus of the obtained rubber composition was measured by the following method. The results of the rubber composition according to Formula 1 are shown in Table 2, and the results of the rubber composition according to Formula 2 are shown in Table 3.

(1) Dynamic storage elastic modulus A sheet having a width of 5 mm and a length of 40 mm was cut out from a slab sheet having a thickness of 2 mm obtained by vulcanizing the rubber composition under the conditions of 160 ° C. and 12 minutes, and used as a sample. . Using a spectrometer manufactured by Ueshima Seisakusho Co., Ltd., the distance between chucks is 10 mm, the initial strain is 200 μm, the dynamic strain is 1%, the frequency is 52 Hz, the measurement start temperature is 25 ° C., the temperature rise rate is 3 ° C./min, and the measurement end temperature. The dynamic storage elastic modulus was measured under the measurement condition of 250 ° C. Moreover, the ratio of the minimum value of the dynamic storage elastic modulus in the region of 200 to 250 ° C. to the dynamic storage elastic modulus at 50 ° C. was expressed as an index. It shows that the fall of the dynamic storage elastic modulus by high temperature is so small that this index | exponent is large.

* 1 Blends of any of the above (modified) natural rubbers A to C and polybutadiene rubber [BR, manufactured by Ube Industries, 150L] are used. The compositions of the rubber components used are shown in Tables 2 and 3.
* 2 Asahi Carbon, "Asahi # 65".
* 3 Made by Idemitsu Kosan, “Diana Processing Oil NP-24”.
* 4 N- (1,3-Dimethylbutyl) -N'-phenyl-p-phenylenediamine.
* 5 N-t-butyl-2-benzothiazylsulfenamide.

  Next, a radial tire for a passenger car having a size of 205 / 55R16 is used by using the rubber composition according to Formula 1 only for the side reinforcing rubber layer or using the rubber composition according to Formula 2 for both the side reinforcing rubber layer and the bead filler. Was prepared according to a conventional method. Tables 2 and 3 show the maximum thickness of the side reinforcing rubber layer of the tire (reinforcing rubber layer gauge) and the height of the bead filler. The test tire was assembled with a rim of size 6.5JJ-16, and the run-flat durability and rolling resistance of the tire were evaluated by the following methods. Table 2 shows the results of tires using the rubber composition according to Formula 1 only for the side reinforcing rubber layer, and Table 3 shows the results of tires using the rubber composition according to Formula 2 for both the side reinforcing rubber layer and the bead filler. .

(2) Run Flat Durability Each prototype tire is assembled with a rim at normal pressure, filled with an internal pressure of 200 kPa, left in a room at 38 ° C for 24 hours, then the valve core is removed and the internal pressure is set to atmospheric pressure. 3 and Comparative Examples 1 and 2 for tires with a load of 4.32 kN (440 kgf), Examples 4 to 6 and Comparative Examples 3 to 4 with a load of 4.06 kN (414 kgf), speed 89 km / h, temperature The drum running test was conducted at 38 ° C. The distance traveled until the failure occurred at this time was measured. For the tires of Examples 1 to 3 and Comparative Examples 1 and 2, the distance traveled until the failure occurred in Comparative Example 1 was displayed as an index, and Examples 4 to For the tires of No. 6 and Comparative Examples 3 to 4, the mileage until the occurrence of the failure of Comparative Example 3 was taken as 100 and indicated as an index. The larger the index value, the longer the distance traveled until the failure occurs, indicating better run-flat durability.

(3) Rolling resistance Under the conditions of tire internal pressure: 1.7 kg / cm ² , load: JIS 100% load, coasting start speed: 100 km / hr, the rolling resistance of the test tire was measured by the coasting method. For the tires of No. 3 and Comparative Examples 1-2, the rolling resistance of Comparative Example 1 is indicated as an index, and for the tires of Examples 4-6 and Comparative Examples 3-4, the rolling resistance of Comparative Example 3 is taken as 100. The index was displayed. The smaller the index value, the smaller the rolling resistance and the better.

  From the comparison between Comparative Example 1 and Comparative Example 2 in Table 2 and the comparison between Comparative Example 3 and Comparative Example 4 in Table 3, the proportion of natural rubber in the rubber composition used for the side reinforcing rubber layer and bead filler is increased. It can be seen that the rolling resistance is increased although the run-flat durability of the tire can be slightly improved by simply making it.

  On the other hand, from the comparison between Examples and Comparative Examples in Tables 2 and 3, dynamic rubber due to high temperature of the rubber composition was obtained by using modified natural rubber modified with a polar group-containing monomer instead of natural rubber. Reduction in storage elastic modulus can be suppressed, and by using the rubber composition only in the side reinforcing rubber layer or in both the side reinforcing rubber layer and the bead filler, the rolling resistance is improved while improving the run flat durability. It can be seen that it can be reduced.

It is sectional drawing of one embodiment of the pneumatic tire of this invention.

Explanation of symbols

1 Bead part 2 Side wall part 3 Tread part 4 Radial carcass 5 Belt 6 Bead core 7 Bead filler 8 Side reinforcement rubber layer

Claims (6)

A carcass having a pair of bead portions and a pair of sidewall portions, and a tread portion connected to both sidewall portions, extending in a toroidal shape between the pair of bead portions, and reinforcing each of these portions; and in the bead portion In a pneumatic tire provided with a bead filler disposed outside the bead core in the radial direction of the tire,
To the bead filler, as a rubber component, a polar group-containing monomer is added to natural rubber latex, the polar group-containing monomer is graft-polymerized to natural rubber molecules in the natural rubber latex, and further solidified and dried. A pneumatic tire characterized by using a rubber composition containing a modified natural rubber. A carcass having a pair of bead portions and a pair of sidewall portions, and a tread portion connected to both sidewall portions, and extending in a toroidal shape between the pair of bead portions to reinforce these portions; and the sidewall In a pneumatic tire provided with a pair of side reinforcing rubber layers disposed inside the carcass of the part,
To the side reinforcing rubber layer, as a rubber component, a polar group-containing monomer is added to natural rubber latex, and the polar group-containing monomer is graft-polymerized to natural rubber molecules in the natural rubber latex, and further solidified and dried. A pneumatic tire comprising a rubber composition containing a modified natural rubber. A carcass having a pair of bead portions and a pair of sidewall portions, and a tread portion connected to both sidewall portions, extending in a toroidal shape between the pair of bead portions, and reinforcing each of these portions; and in the bead portion In a pneumatic tire provided with a bead filler disposed on the outer side in the tire radial direction of each bead core embedded in the tire and a pair of side reinforcing rubber layers disposed on the inner side of the carcass of the sidewall portion,
To the bead filler and the side reinforcing rubber layer, as a rubber component, a polar group-containing monomer is added to natural rubber latex, and the polar group-containing monomer is graft-polymerized to natural rubber molecules in the natural rubber latex, A pneumatic tire comprising a rubber composition containing a modified natural rubber obtained by further solidification and drying.   The pneumatic tire according to any one of claims 1 to 3, wherein the rubber component of the rubber composition contains 10% by mass or more of the modified natural rubber.   The polar group of the polar group-containing monomer is amino group, imino group, nitrile group, ammonium group, imide group, amide group, hydrazo group, azo group, diazo group, hydroxyl group, carboxyl group, carbonyl group, epoxy group, It is at least one selected from the group consisting of oxycarbonyl group, sulfide group, disulfide group, sulfonyl group, sulfinyl group, thiocarbonyl group, nitrogen-containing heterocyclic group, oxygen-containing heterocyclic group, tin-containing group and alkoxysilyl group The pneumatic tire according to any one of claims 1 to 4, wherein:   The pneumatic tire according to any one of 1 to 5, wherein the graft amount of the polar group-containing monomer is 0.01 to 5.0 mass% with respect to the rubber component in the natural rubber latex.

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