JP5123342B2 - Tire rubber composition and heavy duty tire - Google Patents

Description

The present invention relates to a tire rubber composition and a heavy duty tire using the same for a tread.

In recent years, due to soaring fuel costs and the introduction of environmental regulations, the demand for lower fuel consumption of vehicles has become stronger, and among the tire components, the rubber composition for producing treads with a high occupation ratio in tires. Therefore, excellent fuel efficiency is required.

As a method for improving the low fuel consumption performance, a method of reducing the amount of filler such as carbon black is known. However, when the amount of the filler is reduced, the rubber strength tends to decrease and the wear resistance performance tends to deteriorate, and it is difficult to achieve both low fuel consumption performance and wear resistance performance at a high level. In addition to the low fuel consumption performance and wear resistance performance, the rubber composition is also required to have deterioration resistance performance, and there is a method for achieving both low fuel consumption performance and wear resistance performance while maintaining good deterioration resistance performance. It was desired.

Patent Documents 1 to 3 propose to reduce rolling resistance using modified diene rubbers such as modified butadiene rubber and modified styrene butadiene rubber. Patent Documents 4 and 5 propose improving natural rubber strength using natural rubber subjected to protein removal treatment. However, there is still room for improvement in terms of achieving both low fuel consumption and wear resistance while maintaining good deterioration resistance.

JP 2001-114939 A JP 2005-126604 A JP 2005-325206 A JP-A-8-12814 Japanese Patent Laid-Open No. 11-12306

The present invention solves the above-mentioned problems and provides a tire rubber composition capable of achieving both low fuel consumption and wear resistance while maintaining good deterioration resistance, and a heavy duty tire having a tread produced using the rubber composition. The purpose is to provide.

The present invention contains a rubber component including a modified natural rubber having a phosphorus content of 200 ppm or less and a butadiene rubber, and the content of the modified natural rubber is 60 to 95% by mass in 100% by mass of the rubber component. Further, the present invention relates to a tire rubber composition in which the content of the butadiene rubber is 5 to 40% by mass.

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 modified natural rubber is preferably obtained by saponifying natural rubber latex.

The butadiene rubber is preferably a modified butadiene rubber.

（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 modified butadiene rubber is preferably modified with a compound represented by the following formula (1).

(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 rubber composition preferably contains carbon black.

The rubber composition is preferably used for a tread of a heavy duty tire.

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

According to the present invention, since the rubber composition for a tire uses a predetermined amount of a modified natural rubber and a butadiene rubber having a low phosphorus content as a rubber component, the rubber composition is used for a tread of a heavy duty tire. Thus, it is possible to provide a heavy duty tire that achieves both low fuel consumption and wear resistance while maintaining good deterioration resistance.

The rubber composition for tires of the present invention contains modified natural rubber (HPNR) having a low phosphorus content and butadiene rubber (BR). By using the modified natural rubber (HPNR) in which the protein, gel, and phospholipid contained in the natural rubber (NR) are reduced and removed, fuel consumption can be further reduced as compared with the use of NR. However, when HPNR is synthesized by saponification of NR, etc., the deterioration-preventing components in NR are also removed during the synthesis, resulting in faster rubber degradation, resulting in performance such as degradation resistance and wear resistance. It is inferior to. On the other hand, in the present invention, since BR is used together with HPNR as a rubber component, it is possible to improve wear resistance performance as well as low fuel consumption performance, and these can be satisfactorily achieved. In addition, since good deterioration resistance can be maintained, low fuel consumption performance, wear resistance performance and deterioration resistance performance can be obtained in a well-balanced manner.

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, and more preferably 10% 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.

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.

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 the upper limit is preferably 6 parts by mass or less with respect to 100 parts by mass of the solid content of the natural rubber latex. 5 mass parts or less are more preferable, 3.5 mass parts or less are more preferable, and 3 mass parts or less are especially preferable. 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.

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 cause 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 sufficient treatment and improvement of productivity, depending on the treatment temperature when the treatment is performed with the 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 10,000 rpm for 1 to 60 minutes. 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.

The content of the modified natural rubber in 100% by mass of the rubber component is 60% by mass or more, preferably 65% by mass or more, and more preferably 68% by mass or more. If it is less than 60% by mass, the rubber strength tends to decrease and the wear resistance tends to deteriorate. The content of the modified natural rubber is 95% by mass or less, preferably 92% by mass or less. If it exceeds 95% by mass, the BR content tends to decrease, and the fuel efficiency, wear resistance and deterioration resistance tend to deteriorate.

The rubber composition of the present invention contains BR. The BR is not particularly limited. For example, BR having a high cis content, BR containing a syndiotactic polybutadiene crystal, and the like can be used. In addition, BR obtained by polymerization using a catalyst containing a lanthanum series rare earth-containing compound described in JP-T-2003-514078 can also be used. Of these, BR having a high cis content is preferable.

As BR, it is more preferable to use butadiene rubber (modified BR) modified with a modifier. By using the modified BR, the Tg (glass transition temperature) of the polymer can be lowered, and the dispersibility of fillers such as carbon black can be improved. As a result, low fuel consumption performance and wear resistance performance can be improved while maintaining good deterioration resistance performance. Preferable examples of the modified BR include butadiene rubber (S-modified BR) modified with the compound represented by the above formula (1).

In the compound represented by the above formula (1), R ¹ , R ² and R ³ 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 derivatives thereof.

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 an alkoxy group having 1 to 8 carbon atoms (preferably 1 to 6 carbon atoms) such as a methoxy group, an ethoxy group, an n-propoxy group, an isopropoxy group, an n-butoxy group, and a t-butoxy group. More preferably, C1-C4) etc. are mentioned. Examples of the alkoxy group include a cycloalkoxy group (such as a cycloalkoxy group having 5 to 8 carbon atoms such as a cyclohexyloxy group) and an aryloxy group (an aryloxy group having 6 to 8 carbon atoms such as a phenoxy group and a 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, and more preferably methoxy groups. Thereby, the improvement effect of the dispersibility of a filler can be heightened.

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 for R ⁴ and R ⁵ 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 R ⁴ and R ⁵ , an alkyl group (preferably having 1 to 3 carbon atoms, more preferably 1 to 2 carbon atoms) is preferable, and an ethyl group is more preferable. Thereby, the improvement effect of the dispersibility of a filler can be heightened.

As n (integer), 2-5 are preferable. Thereby, the improvement effect of the dispersibility of a filler can be heightened. Furthermore, n is more preferably 2 to 4, and most preferably 3. If n is 1 or less, the denaturation reaction may be inhibited, and if n is 6 or more, the effect as a denaturing agent 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 (2) to ( 9) and the like. These may be used alone or in combination of two or more. Of these, 3-diethylaminopropyltrimethoxysilane, 3-dimethylaminopropyltrimethoxysilane, and a compound represented by the following formula (2) are preferable because the effect of improving the dispersibility of the filler is great.

Methods for modifying butadiene rubber with the compound represented by the above formula (1) (modifier) are described in JP-B-6-53768, JP-B-6-57767, JP-T2003-514078, and the like. Conventionally known methods such as the above method can be used. For example, the butadiene rubber may be brought into contact with the modifying agent, the butadiene rubber is polymerized, and a predetermined amount of the modifying agent is added to the polymer rubber solution, and the modifying agent is added to the butadiene rubber solution and reacted. The method etc. are mentioned.

As BR to be modified, the same material as BR described above can be used.

The content of BR (including modified BR) in 100% by mass of the rubber component is 5% by mass or more, preferably 8% by mass or more. If it is less than 5% by mass, the fuel efficiency and wear resistance may not be improved sufficiently, and deterioration of the deterioration resistance may be a concern. The BR content is 40% by mass or less, preferably 35% by mass or less, and more preferably 32% by mass or less. When it exceeds 40% by mass, the HPNR content is decreased, and the rubber strength may be insufficient.

The total content of HPNR and BR in 100% by mass of the rubber component is preferably 70% by mass or more, more preferably 80% by mass or more, still more preferably 90% by mass or more, and particularly preferably 100% by mass. If it is less than 70% by mass, there is a possibility that low fuel consumption performance, wear resistance performance and deterioration resistance performance may not be obtained in a well-balanced manner.

Other rubber components that can be used in the rubber composition of the present invention include natural rubber (NR), isoprene rubber (IR), styrene butadiene rubber (SBR), acrylonitrile butadiene rubber (NBR), chloroprene rubber (CR), butyl rubber. And diene rubbers such as (IIR).

In the rubber composition, in addition to the above components, compounding agents conventionally used in the rubber industry, for example, fillers such as carbon black, oils or plasticizers, antioxidants, anti-aging agents, zinc oxide, sulfur, You may contain vulcanizing agents, such as a sulfur-containing compound, a vulcanization accelerator, etc.

The rubber composition of the present invention preferably contains carbon black. Examples of carbon black that can be used include GPF, FEF, HAF, ISAF, and SAF, but are not particularly limited. By blending carbon black, it is possible to enhance the reinforcement. For this reason, the effect of this invention is acquired favorably by using with HPNR and BR.

The nitrogen adsorption specific surface area _(N 2 SA) of carbon black is preferably not less than ^{20 m} 2 / g, more preferably at least ^35m 2 / g, more preferably ^{70m 2 / g, 100m 2 /} g or more is particularly preferable. If it is less than 20 m < ² > / g, there exists a possibility that sufficient reinforcement may not be acquired. Further, the nitrogen adsorption specific surface area of the carbon black is preferably 200 meters ² / g or less, more preferably 150m ² / g. If it exceeds 200 m ² / g, it tends to be difficult to disperse carbon black well.
In addition, the nitrogen adsorption specific surface area of carbon black is calculated | required by A method of JISK6217.

When the rubber composition contains carbon black, the carbon black content is preferably 5 parts by mass or more, more preferably 20 parts by mass or more, and still more preferably 30 parts by mass or more with respect to 100 parts by mass of the rubber component. It is. If it is less than 5 mass parts, there exists a possibility that reinforcing property cannot fully be improved. The carbon black content is preferably 100 parts by mass or less, more preferably 80 parts by mass or less, and still more preferably 60 parts by mass or less. When it exceeds 100 parts by mass, it tends to be difficult to disperse carbon black well. Moreover, there exists a tendency for workability to fall.

The rubber composition of the present invention is produced by a general method. That is, it can be produced by a method of kneading each component with a kneader such as a Banbury mixer, a kneader, or an open roll, and then vulcanizing. The rubber composition of the present invention is suitably used as a tread (cap tread) for heavy duty tires (especially for trucks and buses).

The heavy duty tire of the present invention is produced by a usual method using the rubber composition.
That is, a rubber composition containing the above components is extruded in accordance with the shape of a tire member such as a tread at an unvulcanized stage, and is molded together with other tire members by a normal method on a tire molding machine. Thus, an unvulcanized tire is formed. By heating and pressurizing this unvulcanized tire in a vulcanizer, the heavy duty tire of the present invention can be produced.

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

Hereinafter, various chemicals used in Examples and Comparative Examples will be described.
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.
NR: TSR
HPNR (saponified natural rubber): Production Example 1 below
Non-modified BR: BR150B manufactured by Ube Industries, Ltd.
Modified BR: Modified butadiene rubber manufactured by Sumitomo Chemical Co., Ltd. (S-modified BR (terminal modified), vinyl content: 15% by mass, R ¹ , R ² and R ³ = —OCH ₃ , R ⁴ and R ⁵ = —CH ₂ CH ₃ , n = 3)
Carbon Black: Show Black N220 (N ₂ SA: 111 m ² / g) manufactured by Cabot Japan
Wax: Sannoc Wax anti-aging agent manufactured by Ouchi Shinsei Chemical Industry Co., Ltd .: Anti-aging agent 6C (SANTOFLEX 6PPD) manufactured by FLEXSYS Co., Ltd.
Stearic acid: Stearic acid “椿” manufactured by NOF Corporation
Zinc oxide: Zinc Hua 2 types manufactured by Mitsui Mining & Smelting Co., Ltd. Sulfur: Powdered sulfur vulcanization accelerator manufactured by Tsurumi Chemical Co., Ltd .: Noxeller NS manufactured by Ouchi Shinsei Chemical Co., Ltd.

(Production of saponified natural rubber with alkali)
Production Example 1
After adjusting the solid rubber latex solid content 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 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 (saponified natural rubber).

With respect to the solid rubber and TSR obtained in Production Example 1, the nitrogen content, phosphorus content, and gel content were measured by the methods described below. 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 sample obtained in the production example was weighed, and the 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).

(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 saponification natural rubber (HPNR) had a reduced nitrogen content, phosphorus content, and gel content as compared with TSR.

<Examples 1-4, Comparative Examples 1-3>
According to the formulation shown in Table 2, using a 1.7 L Banbury mixer, chemicals other than sulfur and a vulcanization accelerator were kneaded to obtain a kneaded product. Next, using an open roll, sulfur and a vulcanization accelerator were kneaded into the obtained kneaded material to obtain an unvulcanized rubber composition. The obtained unvulcanized rubber composition was pressed with a 2 mm-thick mold at 150 ° C. for 30 minutes to obtain a vulcanized rubber composition.
The following tests were performed using the obtained vulcanized rubber composition.

(Heat generation performance index)
Using a viscoelastic spectrometer VES (manufactured by Iwamoto Seisakusho Co., Ltd.), tan δ of the above vulcanized rubber composition was measured under the conditions of a temperature of 70 ° C., an initial strain of 10%, and a dynamic strain of 2%. Using tan δ as 100, tan δ of each formulation was displayed as an index according to the following formula. A smaller value indicates less heat generation and better fuel efficiency.
(Heat generation performance index) = (tan δ of each formulation) / (tan δ of Comparative Example 1) × 100

(Abrasion resistance index)
Using a Lambone abrasion tester manufactured by Iwamoto Seisakusho Co., Ltd., Lambbone abrasion of the above vulcanized rubber composition under 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 was measured. Then, the volume loss amount was calculated from the measured lamborn wear amount, and the volume loss amount of Comparative Example 1 was set as 100, and the volume loss amount of each formulation was indicated by an index according to the following calculation formula. It shows that it is excellent in abrasion resistance performance, so that a numerical value is large.
(Abrasion resistance index) = (Volume loss amount of Comparative Example 1) / (Volume loss amount of each formulation) × 100

(Deterioration resistance)
The vulcanized rubber composition was thermally deteriorated in an oven at 80 ° C. for 7 days to obtain a deteriorated product. Next, a tensile test was performed according to JIS K6251, and the elongation at break of the deteriorated product was measured. And the breaking elongation of the comparative example 1 was set to 100, and the breaking elongation of each formulation was indicated by an index by the following calculation formula. It shows that it is excellent in deterioration-resistant performance, so that a numerical value is large.
(Deterioration resistance index) = (breaking elongation of each formulation) / (breaking elongation of Comparative Example 1) × 100

From Table 2, in Examples using HPNR and BR in combination, low fuel consumption performance and wear resistance performance were obtained in a well-balanced manner while maintaining good deterioration resistance performance. In particular, in Example 4 using modified BR, excellent performance was obtained. On the other hand, Comparative Examples 1 and 2 in which HPNR and BR were not used together and Comparative Example 3 in which the HPNR content and the BR content were outside the predetermined range were inferior in performance to the Examples.

Claims (11)

Containing a rubber component including a modified natural rubber having a phosphorus content of 200 ppm or less and a butadiene rubber;
A tire rubber composition in which the content of the modified natural rubber is 60 to 95% by mass and the content of the butadiene rubber is 5 to 40% by mass in 100% by mass of the rubber component. 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 rubber composition for a tire according to any one of claims 1 to 4, wherein the modified natural rubber is obtained by saponifying natural rubber latex. 6. The modified natural rubber is obtained by saponifying natural rubber latex with alkali, repeatedly washing the saponified and agglomerated rubber, and washing away the phosphorus compound separated by saponification. Rubber composition for tires. The tire rubber composition according to any one of claims 1 to 6 , wherein the butadiene rubber is a modified butadiene rubber. The tire rubber composition according to claim 7 , wherein the modified butadiene rubber is modified with a compound represented by the following formula (1).

(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 rubber composition for tires according to any one of claims 1 to 8 , containing carbon black. The tire rubber composition according to any one of claims 1 to 9 , which is used for a tread of a heavy load tire. Heavy duty tire having a tread produced from the rubber composition according to any one of claims 1-10.