JP5466567B2 - Rubber composition for tire and pneumatic tire - Google Patents

Description

The present invention relates to a tire rubber composition and a pneumatic tire using the same.

In the transportation industry, tires with excellent fuel efficiency are desired because of the increase in costs associated with soaring oil prices. From the viewpoint of improving low fuel consumption performance (low heat generation performance), natural rubber and silica are often blended.

However, since natural rubber contains an unsaturated bond, heat resistance (deterioration resistance) tends to be inferior to that of non-diene rubber. In addition, silica blending can improve fuel efficiency, but has low reinforcement and wear resistance. Therefore, it has been difficult to achieve both low fuel consumption performance and deterioration resistance performance while obtaining good wear resistance performance with conventional silica blends.

Patent Document 1 discloses a rubber composition using natural rubber and epoxidized natural rubber in order to increase the content ratio of non-petroleum resources. However, there is room for improvement in terms of achieving both low fuel consumption and deterioration resistance while obtaining good wear resistance.

JP 2007-169431 A

The present invention solves the above-described problems, and provides a rubber composition for a tire that can achieve both low fuel consumption and deterioration resistance while having good wear resistance, and a pneumatic tire using the rubber composition. For the purpose.

The present invention includes a rubber component containing a modified natural rubber having a phosphorus content of 200 ppm or less and a diene rubber synthesized by solution polymerization, silica, and zinc oxide having an average primary particle size of 200 nm or less. It is related with the rubber composition for tires whose content of the said zinc oxide is 0.3-5 mass parts with respect to 100 mass parts of components.

The modified natural rubber preferably has a gel content measured as a toluene insoluble content of 20% by mass or less.
The modified natural rubber is preferably substantially free of phospholipids and has no peak due to phospholipid at -3 ppm to 1 ppm in ³¹ P NMR measurement of the chloroform extract.
The modified natural rubber preferably has a nitrogen content of 0.3% by mass or less.
The zinc oxide content is preferably 0.3 to 3 parts by mass with respect to 100 parts by mass of the rubber component.

（式中、Ｒ^１、Ｒ^２及びＲ^３は、同一若しくは異なって、アルキル基、アルコキシ基、シリルオキシ基、アセタール基、カルボキシル基、メルカプト基又はこれらの誘導体を表す。Ｒ^４及びＲ^５は、同一若しくは異なって、水素原子、アルキル基又は環状エーテル基を表す。ｎは整数を表す。） The diene rubber is preferably modified with a compound represented by the following formula (1) or a polyfunctional compound having two or more epoxy groups in the molecule.

(Wherein R ¹ , R ² and R ³ are the same or different and each represents an alkyl group, an alkoxy group, a silyloxy group, an acetal group, a carboxyl group, a mercapto group or a derivative thereof. R ⁴ and R ⁵ are (The same or different and represents a hydrogen atom, an alkyl group or a cyclic ether group. N represents an integer.)

The present invention also relates to a pneumatic tire having a tread produced using the rubber composition.

The tire rubber composition of the present invention includes a rubber component containing the modified natural rubber and a diene rubber synthesized by solution polymerization, silica, and a specific amount of the zinc oxide. It has excellent fuel efficiency performance and high anti-degradation performance, and can improve these performances in a well-balanced manner.

The rubber composition for tires of the present invention includes a rubber component containing a modified natural rubber having a phosphorus content of 200 ppm or less and a diene rubber synthesized by solution polymerization, silica, and zinc oxide having an average primary particle size of 200 nm or less. The content of the zinc oxide is 0.3 to 5 parts by mass with respect to 100 parts by mass of the rubber component.
Hereinafter, the modified natural rubber is also referred to as HPNR, and the diene rubber synthesized by solution polymerization is also referred to as solution polymerization diene rubber.

According to the present invention, by using modified natural rubber (HPNR) in which proteins, gels, and phospholipids contained in natural rubber (NR) are reduced and removed, fuel consumption can be further reduced compared to the use of NR. Can be achieved. On the other hand, when HPNR is synthesized by saponification of NR or the like, deterioration preventing components in NR are also removed at the time of synthesis. Therefore, when HPNR is blended with a tire rubber composition, it is more durable than blending NR. Tend to be deteriorated and the deterioration resistance performance tends to be inferior. In the present invention, since fine zinc oxide having a specific average primary particle size is blended and the specific surface area is large, it effectively functions as a vulcanization accelerator and can vulcanize rubber more uniformly. Therefore, the effect of the present invention can be obtained by blending HPNR, diene rubber and a specific amount of fine zinc oxide in the silica blend.

The modified natural rubber (HPNR) has a phosphorus content of 200 ppm or less. When it exceeds 200 ppm, the amount of gel increases during storage, and the tan δ of the vulcanized rubber tends to increase. The phosphorus content is preferably 150 ppm or less, and more preferably 100 ppm or less. Here, the phosphorus content can be measured by a conventional method such as ICP emission analysis. Phosphorus is derived from phospholipids (phosphorus compounds).

The gel content in the modified natural rubber is preferably 20% by mass or less, more preferably 10% by mass or less, and still more preferably 7% by mass or less. If it exceeds 20% by mass, the processability tends to decrease, for example, the Mooney viscosity increases. The gel content means a value measured as an insoluble content with respect to toluene which is a nonpolar solvent, and may be simply referred to as “gel content” or “gel content” below. The measuring method of the content rate of a gel part is as follows. First, a natural rubber sample is soaked in dehydrated toluene, light-shielded in the dark and left for 1 week, and then the toluene solution is centrifuged at 1.3 × 10 ⁵ rpm for 30 minutes to obtain an insoluble gel content and a toluene soluble content. Isolate. Methanol is added to the insoluble gel and solidified, and then dried, and the gel content is determined from the ratio between the mass of the gel and the original mass of the sample.

The modified natural rubber is preferably substantially free of phospholipids. “Substantially no phospholipid is present” represents a state in which a natural rubber sample is extracted with chloroform and a peak due to phospholipid does not exist at −3 ppm to 1 ppm in ³¹ P NMR measurement of the extract. The peak of phosphorus present at -3 ppm to 1 ppm is a peak derived from the phosphate structure of phosphorus in the phospholipid.

In the modified natural rubber, the nitrogen content is preferably 0.3% by mass or less, and more preferably 0.15% by mass or less. When the nitrogen content exceeds 0.3% by mass, the Mooney viscosity tends to increase during storage. Nitrogen is derived from proteins. The nitrogen content can be measured by a conventional method such as Kjeldahl method.

In the tire rubber composition of the present invention, the content of the modified natural rubber in 100% by mass of the rubber component is preferably 10% by mass or more, more preferably 20% by mass or more, and further preferably 30% by mass or more. It is. If it is less than 10% by mass, a sufficient fuel efficiency effect tends not to be obtained. The content of the modified natural rubber is preferably 90% by mass or less, more preferably 80% by mass or less, still more preferably 60% by mass or less, and particularly preferably 40% by mass or less. If it exceeds 90% by mass, sufficient wet skid performance may not be ensured.

Examples of the method for producing the modified natural rubber include a method of producing natural rubber latex by saponification with alkali, washing the saponified and agglomerated rubber, and then drying. The saponification treatment is performed by adding an alkali and, if necessary, a surfactant to natural rubber latex and allowing to stand at a predetermined temperature for a predetermined time. In addition, you may perform stirring etc. as needed. According to the above production method, the phosphorus compound separated by saponification is washed away, so that the phosphorus content of the natural rubber can be suppressed. Moreover, since the protein in natural rubber is decomposed by the saponification treatment, the nitrogen content of the natural rubber can be suppressed. In the present invention, alkali can be added to natural rubber latex for saponification, but by adding it to natural rubber latex, there is an effect that saponification can be efficiently performed.

Natural rubber latex is collected as sap of heavy trees and contains rubber, water, proteins, lipids, inorganic salts, etc., and the gel content in rubber is thought to be based on the complex presence of various impurities. . In the present invention, raw latex produced by tapping a heavy tree or purified latex concentrated by centrifugation can be used. Furthermore, high ammonia latex to which ammonia is added by a conventional method may be used in order to prevent the progress of decay due to bacteria present in the raw rubber latex and to avoid coagulation of the latex.

Examples of the alkali used for the saponification treatment include sodium hydroxide, potassium hydroxide, calcium hydroxide, and an amine compound. From the viewpoint of the effect of the saponification treatment and the influence on the stability of the natural rubber latex, it is particularly hydroxylated. Sodium or potassium hydroxide is preferably used.

The amount of alkali added is not particularly limited, but the lower limit is preferably 0.1 parts by mass or more, more preferably 0.3 parts by mass or more, and the upper limit is 12 parts by mass or less with respect to 100 parts by mass of the solid content of natural rubber latex. Is preferably 10 parts by mass or less, more preferably 7 parts by mass or less, and particularly preferably 5 parts by mass or less. If the amount of alkali added is less than 0.1 parts by mass, saponification may take time. Conversely, if the amount of alkali added exceeds 12 parts by mass, the natural rubber latex may be destabilized.

As the surfactant, an anionic surfactant, a nonionic surfactant, and an amphoteric surfactant can be used. Examples of the anionic surfactant include carboxylic acid-based, sulfonic acid-based, sulfate ester-based and phosphate ester-based anionic surfactants. Examples of nonionic surfactants include nonionic surfactants such as polyoxyalkylene ethers, polyoxyalkylene esters, polyhydric alcohol fatty acid esters, sugar fatty acid esters, and alkyl polyglycosides. Examples of the amphoteric surfactant include amphoteric surfactants such as amino acid type, betaine type, and amine oxide type. Among these, an anionic surfactant is preferable, and a sulfonic acid anionic surfactant is more preferable.

The addition amount of the surfactant is preferably 0.01 parts by mass or more, more preferably 0.1 parts by mass or more, and even more preferably 1.1 parts by mass or more with respect to 100 parts by mass of the solid content of the natural rubber latex. The upper limit is preferably 6 parts by mass or less, more preferably 5 parts by mass or less, still more preferably 3.5 parts by mass or less, and particularly preferably 3 parts by mass or less. If the addition amount of the surfactant is less than 0.01 parts by mass, the natural rubber latex may become unstable during the saponification treatment. On the other hand, if the amount of the surfactant added exceeds 6 parts by mass, the natural rubber latex is too stabilized and it may be difficult to coagulate. Moreover, when it is 1.1 mass parts or more, the phosphorus content, the nitrogen content, and the gel content in the natural rubber can be further reduced.

The temperature of the saponification treatment can be appropriately set within a range where the saponification reaction with alkali can proceed at a sufficient reaction rate and within a range where the natural rubber latex does not undergo alteration such as coagulation, but is usually 20 to 70 ° C. Preferably, 30-70 degreeC is more preferable. Further, the treatment time is 3 to 48 hours in consideration of both sufficient treatment and productivity improvement, depending on the treatment temperature when the treatment is performed with natural rubber latex standing. Is preferable, and 3 to 24 hours is more preferable.

After completion of the saponification reaction, the agglomerated rubber is crushed and washed. Examples of the aggregation method include a method of adjusting pH by adding an acid such as formic acid. Examples of the washing treatment include a method of diluting the rubber with water and washing it, and then performing a centrifugal separation treatment to take out the rubber. When centrifuging, it is first diluted with water so that the rubber content of the natural rubber latex is 5 to 40% by mass, preferably 10 to 30% by mass. Then, it may be centrifuged at 5000 to 10000 rpm for 1 to 60 minutes, and washing may be repeated until a desired phosphorus content is obtained. After completion of the washing treatment, a saponified natural rubber latex is obtained. The modified natural rubber according to the present invention is obtained by drying the saponified natural rubber latex.

In the above production method, the saponification, washing and drying steps are preferably completed within 15 days after collecting the natural rubber latex. More preferably, it is within 10 days, and more preferably within 5 days. This is because the gel content increases if the sample is left for more than 15 days without solidification after collection.

In the present invention, a diene rubber synthesized by solution polymerization is used as the rubber component. By using solution polymerization diene rubber together with HPNR, sufficient wet skid performance can be secured.

Diene rubbers synthesized by solution polymerization include styrene butadiene rubber (S-SBR), butadiene rubber (BR), isoprene rubber (IR), chloroprene rubber (CR), and nitrile rubber (NBR) synthesized by solution polymerization. Etc. and mixtures thereof may be used. A modified diene rubber modified with a modifying agent can also be used. Among them, a modified diene rubber is preferable and a modified S-SBR is more preferable because sufficient abrasion resistance and wet skid performance are ensured.

As the modifier used for modifying the solution-polymerized diene rubber, the compound represented by the above formula (1) and 2 in the molecule from the viewpoint of good binding property with the polymer and high affinity with the filler. A polyfunctional compound having at least one epoxy group is preferred, and a polyfunctional compound having at least two epoxy groups in the molecule is more preferred. The modified solution polymerized diene rubber is preferably one obtained by reacting a modifier with the terminal of the solution polymerized diene rubber.

R ¹ , R ² and R ³ in the above formula (1) are the same or different and are an alkyl group, an alkoxy group, a silyloxy group, an acetal group, a carboxyl group (—COOH), a mercapto group (—SH) or a derivative thereof. Represents. As said alkyl group, C1-C4 alkyl groups, such as a methyl group, an ethyl group, n-propyl group, isopropyl group, n-butyl group, t-butyl group, etc. are mentioned, for example. Examples of the alkoxy group include alkoxy groups having 1 to 8 carbon atoms such as methoxy group, ethoxy group, n-propoxy group, isopropoxy group, n-butoxy group and t-butoxy group (preferably having 1 to 6 carbon atoms). More preferably, C1-C4) etc. are mentioned. The alkoxy group includes a cycloalkoxy group (cycloalkoxy group having 5 to 8 carbon atoms such as cyclohexyloxy group) and an aryloxy group (aryloxy group having 6 to 8 carbon atoms such as phenoxy group and benzyloxy group). ) Is also included.

Examples of the silyloxy group include a silyloxy group substituted with an aliphatic group having 1 to 20 carbon atoms and an aromatic group (trimethylsilyloxy group, triethylsilyloxy group, triisopropylsilyloxy group, diethylisopropylsilyloxy group, t- Butyldimethylsilyloxy group, t-butyldiphenylsilyloxy group, tribenzylsilyloxy group, triphenylsilyloxy group, tri-p-xylylsilyloxy group, etc.).

Examples of the acetal group include groups represented by -C (RR ')-OR "and -O-C (RR')-OR". Examples of the former include a methoxymethyl group, an ethoxymethyl group, a propoxymethyl group, a butoxymethyl group, an isopropoxymethyl group, a t-butoxymethyl group, and a neopentyloxymethyl group. The latter includes a methoxymethoxy group, an ethoxy group, and the like. Methoxy group, propoxymethoxy group, i-propoxymethoxy group, n-butoxymethoxy group, t-butoxymethoxy group, n-pentyloxymethoxy group, n-hexyloxymethoxy group, cyclopentyloxymethoxy group, cyclohexyloxymethoxy group, etc. Can be mentioned. R ¹ , R ² and R ³ are preferably alkoxy groups. Thereby, the outstanding low exothermic property (low fuel consumption) can be obtained.

In the compound represented by the above formula (1), R ⁴ and R ⁵ are the same or different and each represents a hydrogen atom, an alkyl group or a cyclic ether group.

Examples of the alkyl group of R ⁴ and R ^{5 in} the above formula (1) include the same groups as the above alkyl group.

Examples of the cyclic ether group of R ⁴ and R ⁵ include one ether bond such as an oxirane group, an oxetane group, an oxolane group, an oxane group, an oxepane group, an oxocan group, an oxonan group, an oxecan group, an oxet group, and an oxole group. A cyclic ether group having two ether bonds such as a cyclic ether group, a dioxolane group, a dioxane group, a dioxepane group and a dioxecan group, and a cyclic ether group having three ether bonds such as a trioxane group. Among these, a C2-C7 cyclic ether group having one ether bond is preferable, and a C3-C5 cyclic ether group having one ether bond is more preferable. The cyclic ether group preferably has no unsaturated bond in the ring skeleton.

As n (integer) of said Formula (1), 1-5 are preferable. Thereby, the outstanding low exothermic property (low fuel consumption) can be obtained. Furthermore, n is more preferably 2 to 4, and most preferably 3. When n is 0, it is difficult to bond a silicon atom and a nitrogen atom, and when n is 6 or more, the effect as a modifier is reduced.

Specific examples of the compound represented by the above formula (1) include 3-aminopropyldimethylmethoxysilane, 3-aminopropylmethyldimethoxysilane, 3-aminopropylethyldimethoxysilane, 3-aminopropyltrimethoxysilane, 3-aminopropyltrimethoxysilane, Aminopropyldimethylethoxysilane, 3-aminopropylmethyldiethoxysilane, 3-aminopropyltriethoxysilane, 3-aminopropyldimethylbutoxysilane, 3-aminopropylmethyldibutoxysilane, dimethylaminomethyltrimethoxysilane, 2-dimethyl Aminoethyltrimethoxysilane, 3-dimethylaminopropyltrimethoxysilane, 4-dimethylaminobutyltrimethoxysilane, dimethylaminomethyldimethoxymethylsilane, 2-dimethylaminoethyldimethoxy Methylsilane, 3-dimethylaminopropyldimethoxymethylsilane, 4-dimethylaminobutyldimethoxymethylsilane, dimethylaminomethyltriethoxysilane, 2-dimethylaminoethyltriethoxysilane, 3-dimethylaminopropyltriethoxysilane, 4-dimethylaminobutyl Triethoxysilane, dimethylaminomethyldiethoxymethylsilane, 2-dimethylaminoethyldiethoxymethylsilane, 3-dimethylaminopropyldiethoxymethylsilane, 4-dimethylaminobutyldiethoxymethylsilane, diethylaminomethyltrimethoxysilane, 2- Diethylaminoethyltrimethoxysilane, 3-diethylaminopropyltrimethoxysilane, 4-diethylaminobutyltrimethoxysilane, diethylamino Tildimethoxymethylsilane, 2-diethylaminoethyldimethoxymethylsilane, 3-diethylaminopropyldimethoxymethylsilane, 4-diethylaminobutyldimethoxymethylsilane, diethylaminomethyltriethoxysilane, 2-diethylaminoethyltriethoxysilane, 3-diethylaminopropyltriethoxysilane 4-diethylaminobutyltriethoxysilane, diethylaminomethyldiethoxymethylsilane, 2-diethylaminoethyldiethoxymethylsilane, 3-diethylaminopropyldiethoxymethylsilane, 4-diethylaminobutyldiethoxymethylsilane, the following formulas (3) to ( 10) and the like. Among these, 3-aminopropyltrimethoxysilane and a compound represented by the following formula (3) are preferable from the viewpoints of good binding properties with the polymer and high affinity with the filler. These may be used alone or in combination of two or more.

A polyfunctional compound having two or more epoxy groups in the molecule is suitable as the modifier used for modifying the solution polymerization diene rubber.

The polyfunctional compound having two or more epoxy groups in the molecule is not particularly limited as long as it is a compound having two or more epoxy groups in the molecule. For example, ethylene glycol diglycidyl ether, glycerin triglycidyl ether, etc. Polyglycidyl ether of polyhydric alcohol, polyglycidyl ether of aromatic compound having two or more phenol groups such as diglycidylated bisphenol A, 1,4-diglycidylbenzene, 1,3,5-triglycidylbenzene, poly Polyepoxy compounds such as epoxidized liquid polybutadiene, tertiary amines containing epoxy groups such as 4,4′-diglycidyl-diphenylmethylamine, 4,4′-diglycidyl-dibenzylmethylamine, diglycidylaniline, diglycidyl orthotoluidine, Tetraglycidylme Xylene diamine, tetraglycidyl diaminodiphenylmethane, tetraglycidyl -p- phenylenediamine, diglycidyl aminomethyl cyclohexane, polyglycidyl amino compound such as tetraglycidyl-1,3-bis-aminomethyl cyclohexane. Especially, the polyfunctional compound which has 2 or more epoxy groups and 1 or more nitrogen-containing group in a molecule | numerator is preferable, and the polyfunctional compound shown by following formula (2) is more preferable.

式（２）中、Ｒ^６及びＲ^７は、同一又は異なって、炭素数１〜１０の炭化水素基を表し、該炭化水素基は、エーテル、及び３級アミンからなる群より選択される少なくとも１種の基を有してもよい。Ｒ^８及びＲ^９は、同一若しくは異なって、水素原子、又は炭素数１〜２０の炭化水素基を表し、該炭化水素基は、エーテル、及び３級アミンからなる群より選択される少なくとも１種の基を有してもよい。Ｒ^１０は、炭素数１〜２０の炭化水素基を表し、該炭化水素基は、エーテル、３級アミン、エポキシ、カルボニル、及びハロゲンからなる群より選択される少なくとも１種の基を有してもよい。ｚは１〜６（好ましくは１〜４）の整数を表す。

In the formula (2), R ⁶ and R ⁷ are the same or different and represent a hydrocarbon group having 1 to 10 carbon atoms, and the hydrocarbon group is at least selected from the group consisting of ether and tertiary amine You may have 1 type of group. R ⁸ and R ⁹ are the same or different and each represents a hydrogen atom or a hydrocarbon group having 1 to 20 carbon atoms, and the hydrocarbon group is at least one selected from the group consisting of ethers and tertiary amines. You may have group of. R ¹⁰ represents a hydrocarbon group having 1 to 20 carbon atoms, and the hydrocarbon group has at least one group selected from the group consisting of ether, tertiary amine, epoxy, carbonyl, and halogen. Also good. z represents an integer of 1 to 6 (preferably 1 to 4).

The polyfunctional compound is more preferably a polyfunctional compound having a diglycidylamino group. Further, the number of epoxy groups in the molecule of the polyfunctional compound is 2 or more, more preferably 3 or more, and further preferably 4 or more.

As a method for modifying a diene polymer with a modifier, conventionally known methods such as those described in JP-B-6-53768 and JP-B-6-57767 can be used. For example, a diene polymer and a modifying agent may be brought into contact with each other, and a method of adding a modifying agent to a diene polymer solution and reacting them may be mentioned.

The styrene content of the solution-polymerized diene rubber is preferably 5% by mass or more, more preferably 15% by mass or more. If it is less than 5% by mass, the wet skid performance tends to deteriorate. Moreover, this styrene content becomes like this. Preferably it is 45 mass% or less, More preferably, it is 40 mass% or less. If it exceeds 45 mass%, the low heat generation performance tends to deteriorate.
In the present specification, the styrene content is calculated by H ¹ -NMR measurement.

The content of the solution-polymerized diene rubber in 100% by mass of the rubber component is preferably 10% by mass or more, more preferably 20% by mass or more, still more preferably 40% by mass or more, and particularly preferably 60% by mass or more. If it is less than 10% by mass, sufficient wet skid performance may not be ensured. The content of the solution-polymerized diene rubber is preferably 90% by mass or less, more preferably 80% by mass or less, and still more preferably 70% by mass or less. If it exceeds 90% by mass, the low heat generation performance may not be sufficiently improved.

The rubber component that can be used in the present invention other than the modified natural rubber and the solution-polymerized diene rubber is not particularly limited, and examples thereof include diene rubbers such as natural rubber (NR) and epoxidized natural rubber (ENR).

In the present invention, silica is used. By blending silica together with the rubber component, the fuel efficiency is improved. Further, the silica compound has a problem of low wear resistance, but this problem can be improved by using HPNR and solution-polymerized diene rubber as the rubber component, and the effects of the present invention can be obtained satisfactorily. The silica is not particularly limited, and examples thereof include dry process silica (anhydrous silicic acid), wet process silica (hydrous silicic acid), and the like, but wet process silica is preferable because of its large number of silanol groups.

The nitrogen adsorption specific surface area (N ₂ SA) of silica is preferably 100 m ² / g or more, more preferably 130 m ² / g or more, and still more preferably 160 m ² / g or more. If it is less than 100 m < ² > / g, there exists a possibility that the effect of this invention cannot fully be acquired. Further, N ₂ SA of silica is preferably 220 m ² / g or less, and more preferably 200 m ² / g or less. If it exceeds 220 m ² / g, the low heat build-up tends to decrease.
The nitrogen adsorption specific surface area of silica is a value measured by the BET method according to ASTM D3037-81.

The content of silica is preferably 10 parts by mass or more, more preferably 20 parts by mass or more, still more preferably 30 parts by mass or more, and particularly preferably 50 parts by mass or more with respect to 100 parts by mass of the rubber component. When the amount is less than 10 parts by mass, there is a tendency that a sufficient effect due to silica blending cannot be obtained. The content of the silica is preferably 150 parts by mass or less, more preferably 120 parts by mass or less, and still more preferably 100 parts by mass or less. When the amount exceeds 150 parts by mass, it is difficult to disperse silica in rubber, and the processability of rubber tends to deteriorate.

In the present invention, it is preferable to use a silane coupling agent together with silica. Examples of the silane coupling agent include sulfide, mercapto vinyl, amino, glycidoxy, nitro, and chloro silane coupling agents. Among them, bis (3-triethoxysilylpropyl) tetrasulfide, bis (2-triethoxysilylethyl) tetrasulfide, bis (3-triethoxysilylpropyl) disulfide, bis (2-triethoxysilylethyl) disulfide, etc. Sulfide systems are preferred, with bis (3-triethoxysilylpropyl) disulfide being particularly preferred.

When the silane coupling agent is contained, the content of the silane coupling agent is preferably 5 parts by mass or more and more preferably 8 parts by mass or more with respect to 100 parts by mass of silica. If it is less than 5 parts by mass, the fracture strength is lowered and the performance such as wear resistance may be lowered.
Moreover, 15 mass parts or less are preferable, and, as for content of this silane coupling agent, 10 mass parts or less are more preferable. When it exceeds 15 parts by mass, there is a tendency that effects such as an increase in fracture strength and a reduction in heat generation due to the incorporation of the silane coupling agent cannot be obtained.

In the present invention, zinc oxide having a specific average primary particle size is used. Uniform vulcanization can be achieved by blending such fine zinc oxide. Compared to NR (unmodified) and emulsion polymerized diene rubbers, HPNR and solution polymerized diene rubbers are less likely to trap zinc oxide than necessary, and even a small amount is effective as a vulcanization accelerator. Since it is demonstrated, the compounding quantity of a zinc oxide can be reduced. Thereby, fracture nuclei are reduced and good wear resistance can be obtained. Moreover, low heat generation can be achieved.

The average primary particle diameter of the zinc oxide is 15 nm or more, preferably 30 nm or more, more preferably 50 nm or more, and further preferably 60 nm or more. If it is less than 15 nm, it is difficult to uniformly disperse zinc oxide in the rubber composition, and there is a tendency that the effect of improving the durability performance cannot be obtained. The average primary particle diameter of zinc oxide is 200 nm or less, preferably 150 nm or less, more preferably 100 nm or less, and still more preferably 70 nm or less. If it exceeds 200 nm, the effects of the present invention may not be sufficiently obtained.

In the present invention, the average primary particle diameter of zinc oxide is the primary particle diameter when converted from a specific surface area measured by the BET method to a true spherical particle model.
Here, the primary particle diameter when converted from the specific surface area to the true spherical particle model can be calculated by the following relational expression. When the primary particles are regarded as ideal spheres, the relationship represented by the following formula is established between the surface area S, volume V, density ρ, and specific surface area SSA of each particle.
SSA = 1 / (V · ρ) × S
Here, since V and S are physical quantities that are uniquely determined by the particle diameter, the particle diameter can be obtained from the specific surface area and density. The density can be easily determined by, for example, a commercially available pycnometer.

The content of the zinc oxide (zinc oxide having a specific average primary particle size) is preferably 0.3 parts by mass or more, more preferably 0.5 parts by mass or more, further preferably 100 parts by mass of the rubber component. 0.7 parts by mass or more, particularly preferably 0.9 parts by mass or more. If it is less than 0.3 part by mass, the vulcanization acceleration effect may not be obtained. The zinc oxide content is preferably 5 parts by mass or less, more preferably 3 parts by mass or less, still more preferably 1.5 parts by mass or less, and particularly preferably 1.0 part by mass or less. When it exceeds 5 parts by mass, the fracture nuclei increase and the wear resistance tends to deteriorate.

The rubber composition of the present invention preferably contains carbon black as the filler. Thereby, reinforcement property can be improved and abrasion resistance performance can be improved more.

The nitrogen adsorption specific surface area (N ₂ SA) of carbon black is preferably 50 m ² / g or more, more preferably 100 m ² / g or more. If it is less than 50 m < ² > / g, there exists a tendency for sufficient reinforcement property not to be acquired. Also, _N 2 SA of carbon black is preferably not more than 200 meters ² / g, more preferably at most 150m ² / g. When it exceeds 200 m ² / g, it becomes difficult to disperse the carbon black into the rubber, and the processability tends to deteriorate.
In addition, the nitrogen adsorption specific surface area of carbon black is calculated | required by A method of JISK6217.

The content of carbon black is preferably 2 parts by mass or more, more preferably 3 parts by mass or more, and further preferably 5 parts by mass or more with respect to 100 parts by mass of the rubber component. If the amount is less than 2 parts by mass, sufficient reinforcing properties tend not to be obtained. The carbon black content is preferably 15 parts by mass or less, more preferably 10 parts by mass or less, and still more preferably 6 parts by mass or less with respect to 100 parts by mass of the rubber component. If it exceeds 15 parts by mass, the effect of improving the low heat build-up tends to decrease.

In addition to the above components, the rubber composition of the present invention contains compounding agents generally used in the production of rubber compositions, such as stearic acid, various anti-aging agents, ozone degradation inhibitors, oils, waxes, and vulcanizing agents. Further, a vulcanization accelerator and the like can be appropriately blended.

The rubber composition of the present invention is produced by a general method. That is, it can be produced by a method of kneading the above components with a Banbury mixer, a kneader, an open roll or the like and then vulcanizing.

The rubber composition of the present invention can be suitably used for each member of a tire. In particular, it is preferably used for a tread (cap tread) that requires wear resistance, low fuel consumption and deterioration resistance.

The pneumatic tire of the present invention is produced by a usual method using the rubber composition.
That is, the rubber composition containing the above components is extruded in accordance with the shape of the tread at an unvulcanized stage and molded together with other tire members on a tire molding machine by a normal method. Form a vulcanized tire. The unvulcanized tire is heated and pressurized in a vulcanizer to obtain a tire.

The present invention will be specifically described based on examples, but the present invention is not limited to these examples.

The various chemicals used in the examples are described below.
Natural rubber: TSR20
Modified natural rubber 1: Solid rubber modified natural rubber obtained from the following production example 1: Solid rubber HPR355 obtained from the following production example 2 (solution polymerization diene rubber 1): HPR355 manufactured by JSR Corporation ( S-SBR modified with 3-aminopropyltrimethoxysilane represented by the above formula (1), styrene content: 27% by mass)
E15 (solution polymerization diene rubber 2): modified by Asaprene E15 (polyfunctional compound having two or more epoxy groups in the molecule (polyfunctional compound represented by the above formula (2)) manufactured by Asahi Kasei Chemicals Corporation (Coupled S-SBR, styrene content: 23 mass%, vinyl content: 63 mass%)
Carbon black: N220 (N ₂ SA: 111 m ² / g) manufactured by Cabot Japan
Silica: Ultrasil VN3 manufactured by Evonik Degussa (N ₂ SA: 175 m ² / g)
Silane coupling agent: Si266 (Bis (3-triethoxysilylpropyl) disulfide) manufactured by Evonik Degussa
Aroma oil: Process X-140 manufactured by Japan Energy Co., Ltd.
Wax: Sannox wax anti-aging agent manufactured by Ouchi Shinsei Chemical Industry Co., Ltd .: Anti-aging agent 6C (SANTOFLEX 6PPD) manufactured by FLEXSYS Co., Ltd.
Zinc oxide: 2 types of zinc oxide manufactured by Mitsui Mining & Smelting Co., Ltd. (average primary particle size: 400 nm)
F-2 fine particle zinc white: manufactured by Hakusuitec Co., Ltd., trade name: fine particle zinc oxide F-2 (average primary particle size: 65 nm)
Stearic acid: Stearic acid “椿” manufactured by NOF Corporation
Sulfur: Powder sulfur noxeller NS (vulcanization accelerator) manufactured by Tsurumi Chemical Co., Ltd .: Noxera-NS (Nt-butyl-2-benzothiazylsulfenamide) manufactured by Ouchi Shinsei Chemical Industry Co., Ltd.
Natural rubber latex: Field latex obtained from Taitex Co., Ltd. Surfactant: Emal-E manufactured by Kao Corporation
NaOH: NaOH manufactured by Wako Pure Chemical Industries, Ltd.

(Production of saponified natural rubber with alkali)
Production Example 1
After adjusting the solid rubber latex solids concentration (DRC) to 30% (w / v), 1000 g of natural rubber latex was added with 10 g of Emal-E and 20 g of NaOH, followed by saponification at room temperature for 48 hours. Natural rubber latex was obtained. Water was added to the latex to dilute to DRC 15% (w / v), and then formic acid was added with slow stirring to adjust the pH to 4.0 to 4.5 to cause aggregation. The agglomerated rubber was pulverized, washed repeatedly with 1000 ml of water, and then dried at 110 ° C. for 2 hours to obtain a solid rubber (modified natural rubber 1).
Production Example 2
After adjusting the solid rubber latex solids concentration (DRC) to 30% (w / v), 1000 g of natural rubber latex was added with 10 g of Emal-E and 15 g of NaOH, followed by a saponification reaction at room temperature for 48 hours. Natural rubber latex was obtained. Water was added to the latex to dilute to DRC 15% (w / v), and then formic acid was added with slow stirring to adjust the pH to 4.0 to 4.5 to cause aggregation. The agglomerated rubber was pulverized, washed repeatedly with 1000 ml of water, and then dried at 110 ° C. for 2 hours to obtain a solid rubber (modified natural rubber 2).

With respect to the solid rubber and TSR obtained in Production Examples 1 and 2, the nitrogen content, phosphorus content, and gel content were measured by the following methods. The results are shown in Table 1.

(Measurement of nitrogen content)
The nitrogen content was measured using CHN CORDER MT-5 (manufactured by Yanaco Analytical Industries). For the measurement, first, a calibration curve for determining the nitrogen content was prepared using antipyrine as a standard substance. Next, about 10 mg of the modified natural rubber or TSR obtained in each production example was weighed, and an average value was obtained from the measurement results of three times to obtain the nitrogen content of the sample.

(Measurement of phosphorus content)
The phosphorus content was determined using an ICP emission spectrometer (ICPS-8100, manufactured by Shimadzu Corporation).
In addition, ³¹ P-NMR measurement of phosphorus uses an NMR analyzer (400 MHz, AV400M, manufactured by Nippon Bruker Co., Ltd.), and uses a measurement peak of P atom in an 80% aqueous phosphoric acid solution as a reference point (0 ppm), and raw rubber with chloroform. More extracted components were purified, dissolved in CDCl ₃ and measured.

(Measurement of gel content)
A raw rubber sample 70.00 mg cut to 1 mm × 1 mm was weighed, 35 mL of toluene was added thereto, and the mixture was allowed to stand in a cool dark place for 1 week. Subsequently, centrifugation was performed to precipitate a gel component insoluble in toluene, the soluble component of the supernatant was removed, and only the gel component was solidified with methanol, and then dried and the mass was measured. The gel content (%) was determined by the following formula.
Gel content (mass%) = [mass mg after drying / mg of initial sample] × 100

As shown in Table 1, the modified natural rubbers 1 and 2 had a reduced nitrogen content, phosphorus content, and gel content as compared with TSR.
Further, in the ³¹ P NMR measurement of an extract obtained by extracting from the modified natural rubber 1 and 2, it did not detect the peak due to phospholipids -3Ppm～1ppm.

<Examples and Comparative Examples>
(Production of rubber test piece)
In accordance with the formulation shown in Table 2, 1.7 L Banbury was used to knead chemicals other than sulfur and a vulcanization accelerator. The resulting kneaded product was kneaded with sulfur and a vulcanization accelerator using a roll to obtain an unvulcanized rubber composition. This was pressed with a 2 mm thick mold at 170 ° C. for 12 minutes to obtain a vulcanized rubber composition (vulcanized rubber sheet).
The obtained vulcanized rubber sheet was evaluated as follows.

(Rubber heat generation performance index)
For the vulcanized rubber sheet, tan δ of each formulation was measured under the conditions of a temperature of 70 ° C., an initial strain of 10%, and a dynamic strain of 2% using a viscoelastic spectrometer VES (manufactured by Iwamoto Seisakusho Co., Ltd.). The tan δ of 1 was set to 100, and the index was expressed by the following calculation formula. The lower the index, the lower the heat generation.
(Rubber exothermic performance index) = (tan δ of each formulation) / (tan δ of Comparative Example 1) × 100

(Wear performance index)
Using a Lambourne Abrasion Tester manufactured by Iwamoto Seisakusho, the test piece (vulcanized rubber sheet) was tested under the conditions of a surface rotation speed of 50 m / min, a load load of 3.0 kg, a sandfall amount of 15 g / min, and a slip rate of 20%. The amount of lamborn wear was measured. The volume loss amount was calculated from the measured amount of Lambourn wear, and the volume loss amount of each formulation was expressed as an index according to the following formula, with the volume loss amount of Comparative Example 1 being 100. It shows that it is excellent in abrasion resistance performance, so that a numerical value is large.
(Wear performance index) = (Volume loss amount of Comparative Example 1) / (Volume loss amount of each formulation) × 100

(Degradation resistance index)
A vulcanized rubber sheet (new article) was thermally deteriorated in an oven at 80 ° C. for 7 days to obtain a deteriorated product. A new article and a deteriorated article were subjected to a tensile test according to JIS K6251 to measure elongation at break. The measurement results were expressed as an index as the anti-deterioration performance of each formulation by the following formula. The smaller the index, the greater the degree of deterioration.
(Deterioration resistance index) = (Breaking elongation of deteriorated product) / (Breaking elongation of new product) × 100

In the compounding of silica, HPNR and solution polymerization modified diene rubber as rubber components and fine particle zinc oxide as a vulcanization accelerating aid were able to improve the wear resistance, fuel efficiency and deterioration resistance in a well-balanced manner. On the other hand, in the comparative example, the fuel efficiency performance and the deterioration resistance performance were not improved in a well-balanced manner. Further, the comparative example had a tendency to be inferior in wear resistance performance as compared with the example.

Claims (7)

A rubber component containing a modified natural rubber having a phosphorus content of 200 ppm or less and a diene rubber synthesized by solution polymerization, silica, and zinc oxide having an average primary particle size of 200 nm or less,
The rubber composition for tires whose content of the said zinc oxide is 0.3-5 mass parts with respect to 100 mass parts of said rubber components. The rubber composition for a tire according to claim 1, wherein the modified natural rubber has a gel content measured as a toluene insoluble content of 20% by mass or less. 3. The tire rubber composition according to claim 1, wherein the modified natural rubber has no phospholipid peak at -3 ppm to 1 ppm and substantially no phospholipid in ³¹ P NMR measurement of a chloroform extract. object. The rubber composition for a tire according to any one of claims 1 to 3, wherein the modified natural rubber has a nitrogen content of 0.3 mass% or less. The tire rubber composition according to any one of claims 1 to 4, wherein a content of the zinc oxide is 0.3 to 3 parts by mass with respect to 100 parts by mass of the rubber component. The tire according to any one of claims 1 to 5, wherein the diene rubber is modified with a compound represented by the following formula (1) or a polyfunctional compound having two or more epoxy groups in a molecule. Rubber composition.

(Wherein R ¹ , R ² and R ³ are the same or different and each represents an alkyl group, an alkoxy group, a silyloxy group, an acetal group, a carboxyl group, a mercapto group or a derivative thereof. R ⁴ and R ⁵ are (The same or different and represents a hydrogen atom, an alkyl group or a cyclic ether group. N represents an integer.) The pneumatic tire which has a tread produced using the rubber composition in any one of Claims 1-6.