JP5216045B2 - 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.

In order to improve fuel efficiency in tires (particularly heavy duty tires), a method using natural rubber or butadiene rubber as a rubber component is common. As a method for further improving the low fuel consumption performance, a method of using silica as a filler, a method of reducing the amount of filler, and the like are known. However, when these methods are used, the rubber strength may be lowered and good wear resistance performance may not be maintained. In particular, it is difficult to use the above method because a rubber composition used for a heavy duty tire requires high rubber strength. In addition, the conventional silane coupling agent used in combination with silica may adversely affect workability, such as an increase in viscosity during kneading and a tendency to shorten the scorch time. Therefore, a method for improving the fuel efficiency performance, wear resistance performance and workability in a well-balanced manner is desired.

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 still room for improvement in terms of improving fuel efficiency, wear resistance, and workability in a well-balanced manner.

JP 2007-169431 A

An object of the present invention is to solve the above-mentioned problems and to provide a tire rubber composition that can improve fuel economy performance, wear resistance performance and processability in a well-balanced manner, and a heavy duty tire having a tread produced using the rubber composition. And

（式中、ｘ、ｙはそれぞれ１以上の整数である。Ｒ^１は水素、ハロゲン、分岐若しくは非分岐の炭素数１〜３０のアルキル基若しくはアルキレン基、分岐若しくは非分岐の炭素数２〜３０のアルケニル基若しくはアルケニレン基、分岐若しくは非分岐の炭素数２〜３０のアルキニル基若しくはアルキニレン基、又は該アルキル基若しくは該アルケニル基の末端の水素が水酸基若しくはカルボキシル基で置換されたものを示す。Ｒ^２は水素、分岐若しくは非分岐の炭素数１〜３０のアルキレン基若しくはアルキル基、分岐若しくは非分岐の炭素数２〜３０のアルケニレン基若しくはアルケニル基、又は分岐若しくは非分岐の炭素数２〜３０のアルキニレン基若しくはアルキニル基を示す。Ｒ^１とＲ^２とで環構造を形成してもよい。） The present invention includes a rubber component, silica and a silane coupling agent, and the rubber component includes a modified natural rubber having a phosphorus content of 200 ppm or less and a butadiene rubber synthesized using a rare earth element-based catalyst. The content of the modified natural rubber is 60 to 95% by mass in 100% by mass of the rubber component, and the content of butadiene rubber synthesized using the rare earth element-based catalyst is 5 to 40% by mass. The silica content is 10 to 60 parts by mass with respect to 100 parts by mass of the rubber component, and the silane coupling agent includes a bonding unit A represented by the following formula (1) and a coupling unit B represented by the following formula (2). It is related with the rubber composition for tires which is what copolymerized the bond unit B in the ratio of 1-70 mol% with respect to the total amount.

(In the formula, x and y are each an integer of 1 or more. R ¹ is hydrogen, halogen, branched or unbranched alkyl group or alkylene group having 1 to 30 carbon atoms, branched or unbranched carbon atoms 2 to 30. Or an alkenyl group or alkenylene group, a branched or unbranched alkynyl group or alkynylene group having 2 to 30 carbon atoms, or a hydrogen atom substituted at the terminal of the alkyl group or the alkenyl group with a hydroxyl group or a carboxyl group. ² is hydrogen, a branched or unbranched alkylene group or alkyl group having 1 to 30 carbon atoms, a branched or unbranched alkenylene group or alkenyl group having 2 to 30 carbon atoms, or a branched or unbranched carbon group having 2 to 30 carbon atoms. R represents an alkynylene group or an alkynyl group, and R ¹ and R ² may form a ring structure.)

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 synthesized using the rare earth element-based catalyst preferably has a cis content of 95% by mass or more and a vinyl content of 1.0% by mass or less.

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, as the rubber component, a predetermined amount of a modified natural rubber having a low phosphorus content and a butadiene rubber synthesized using a rare earth element-based catalyst are used, and a specific silane coupling agent is used. Since this is a tire rubber composition containing a predetermined amount of silica, the fuel composition, wear resistance, and processability are improved in a balanced manner by using the rubber composition in a tread for a heavy duty tire. Heavy duty tires can be provided.

The rubber composition for tires of the present invention includes a modified natural rubber (HPNR) having a low phosphorus content, a butadiene rubber (rare earth BR) synthesized using a rare earth element-based catalyst, silica, and a specific silane cup. Including a ring agent. By using HPNR in which proteins, gels, and phospholipids contained in natural rubber (NR) are reduced and removed, fuel consumption can be further reduced as compared with the use of NR. In addition, Mooney viscosity is reduced and good processability is also obtained.

However, when HPNR is synthesized by saponification of NR or the like, the degradation preventing component in NR is also removed during the synthesis, resulting in faster rubber degradation, resulting in poor performance such as wear resistance. . In addition, when HPNR and silica are used in combination, the wear resistance performance tends to be reduced, although greater fuel efficiency can be realized. The use of butadiene rubber can suppress a decrease in wear resistance performance to some extent, but the effect is not sufficient in a silica compounded system.

On the other hand, in this invention, since the rare earth type | system | group BR with a high cis content and a small vinyl content is used as a rubber component with HPNR, favorable abrasion resistance performance is securable. In addition, since silica and a specific silane coupling agent are used together with the rubber component, good dispersibility of silica can be obtained, and fuel resistance performance and wear resistance performance can be improved. . Furthermore, since good processability is also obtained, low fuel consumption performance, wear resistance performance and processability can be improved in a 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, 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.

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 6.0 parts by mass or less, more preferably 5.0 parts by mass or less, and further preferably 3.5 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 6.0 parts by mass, the natural rubber latex may be overstabilized and coagulation may be difficult. 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.

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. If it is less than 60% by mass, the fuel efficiency may not be sufficiently improved. The content of the modified natural rubber is 95% by mass or less, more preferably 92% by mass or less. If it exceeds 95% by mass, the content of rare earth BR tends to decrease, and the wear resistance tends to deteriorate.

In the rubber composition of the present invention, a butadiene rubber (rare earth-based BR) synthesized using a rare earth element-based catalyst is used. As the rare earth element-based catalyst, a known one can be used, for example, a lanthanum series Examples include rare earth element compounds, organoaluminum compounds, aluminoxanes, halogen-containing compounds, and catalysts containing a Lewis base as necessary. Among these, an Nd-based catalyst using a neodymium (Nd) -containing compound as a lanthanum series rare earth element compound is particularly preferable.

Examples of the lanthanum series rare earth element compounds include halides, carboxylates, alcoholates, thioalcolates, amides, and the like of rare earth metals having an atomic number of 57 to 71. Of these, as described above, the use of an Nd-based catalyst is preferable in that a BR having a high cis content and a low vinyl content can be obtained.

The organoaluminum compound is represented by AlR ^a R ^b R ^c (wherein R ^a , R ^b and R ^c are the same or different and represent hydrogen or a hydrocarbon group having 1 to 8 carbon atoms). Things can be used. Examples of aluminosans include chain aluminoxanes and cyclic aluminoxanes. As the halogen-containing compound, AlX _k R ^d _3-k (wherein X is a halogen, R ^d is an alkyl group having 1 to 20 carbon atoms, an aryl group or an aralkyl group, k is 1, 1.5, 2 or 3) Aluminum halides represented by: Me ₃ SrCl, Me ₂ SrCl ₂ , strontium halides such as MeSrHCl ₂ , MeSrCl ₃ ; metal halides such as silicon tetrachloride, tin tetrachloride, titanium tetrachloride, etc. . The Lewis base is used for complexing a lanthanum series rare earth element compound, and acetylacetone, ketone, alcohol and the like are preferably used.

The rare earth element-based catalyst may be used in the state of being dissolved in an organic solvent (n-hexane, cyclohexane, n-heptane, toluene, xylene, benzene, etc.) during the polymerization of butadiene, silica, magnesia, magnesium chloride, etc. These may be used by being supported on a suitable carrier. The polymerization conditions may be either solution polymerization or bulk polymerization. The preferable polymerization temperature is -30 to 150 ° C, and the polymerization pressure may be arbitrarily selected depending on other conditions.

The rare earth BR has a Mooney viscosity ML _{1 + 4} (100 ° C.) of preferably 35 or more, more preferably 40 or more, and still more preferably 44 or more. If it is less than 35, the viscosity of the unvulcanized rubber composition is low, and there is a possibility that an appropriate thickness cannot be ensured after vulcanization. The Mooney viscosity is preferably 55 or less, more preferably 50 or less. If it exceeds 55, the unvulcanized rubber composition becomes too hard and it may be difficult to extrude with a smooth edge.
The Mooney viscosity is measured according to ISO 289 and JIS K6300.

In the rare earth BR, the ratio (Mw / Mn) of the weight average molecular weight (Mw) to the number average molecular weight (Mn) is preferably 1.2 or more, more preferably 1.5 or more, still more preferably 2.5 or more. It is. If it is less than 1.2, the workability tends to deteriorate significantly. The Mw / Mn is preferably 5 or less, more preferably 4 or less, and even more preferably 3 or less. If it exceeds 5, the effect of improving the wear resistance tends to decrease.

The Mw of the rare earth BR is preferably 300,000 or more, more preferably 500,000 or more, still more preferably 550,000 or more, and preferably 1.5 million or less, more preferably 1.2 million or less. Further, the Mn of the rare earth-based BR is preferably 100,000 or more, more preferably 150,000 or more, and preferably 1,000,000 or less, more preferably 800,000 or less. When Mw and Mn are less than the lower limit, the wear resistance and fuel efficiency tends to deteriorate. When the upper limit is exceeded, there is a concern about deterioration of workability.
In the present invention, Mw and Mn are values converted from standard polystyrene using a gel permeation chromatograph (GPC).

The cis content of the rare earth BR is preferably 95% by mass or more, more preferably 96% by mass or more, and still more preferably 97% by mass or more. If it is less than 95% by mass, the effect of improving the wear resistance tends to be reduced. The upper limit of the cis content of the rare earth BR is not particularly limited, and may be 100% by mass.

The vinyl content of the rare earth BR is preferably 1.0% by mass or less, more preferably 0.8% by mass or less, still more preferably 0.6% by mass or less, and particularly preferably 0.5% by mass or less. If it exceeds 1.0% by mass, the effect of improving the wear resistance tends to decrease. The lower limit of the vinyl content of the rare earth BR is not particularly limited, and may be 0% by mass.
In the present invention, the vinyl content (1,2-bonded butadiene unit amount) and cis content (cis-1,4-bonded butadiene unit amount) of the rare earth BR can be measured by infrared absorption spectrum analysis.

The content of rare earth 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 wear resistance may not be sufficiently improved. The rare earth BR content is 40% by mass or less, preferably 35% by mass or less, more preferably 32% by mass or less. When it exceeds 40% by mass, the content of HPNR decreases and the fuel efficiency tends to deteriorate.

The total content of HPNR and rare earth 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, the fuel efficiency, wear resistance and processability 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).

The rubber composition of the present invention contains silica. By containing silica, the reinforcing property is enhanced and the fuel efficiency is improved, and the effects of the present invention can be obtained satisfactorily. Examples of silica include dry process silica (anhydrous silica), wet process silica (hydrous silica), and wet process silica is preferred because it has many silanol groups.

The average primary particle diameter of silica is preferably 10 nm or more, more preferably 15 nm or more. When it is less than 10 nm, silica is difficult to disperse, and there is a tendency that low fuel consumption performance and processability are lowered. The average primary particle diameter of silica is preferably 40 nm or less, more preferably 30 nm or less. If it exceeds 40 nm, the rubber strength tends to decrease and the wear resistance performance tends to deteriorate.
In addition, the average primary particle diameter of silica can be calculated | required from the average value which observes a silica with an electron microscope, measures a particle diameter about 50 arbitrary particles, for example.

The nitrogen adsorption specific surface area (N ₂ SA) of silica is preferably 120 m ² / g or more, more preferably 140 m ² / g or more, and further preferably 150 m ² / g or more. There exists a tendency for sufficient reinforcement property not to be acquired as it is less than 120 m < ² > / g. Further, N ₂ SA of silica is preferably 250 m ² / g or less, more preferably 200 m ² / g or less. When it exceeds 250 m < ² > / g, the viscosity of an unvulcanized rubber composition will become high and there exists a tendency for workability to fall.
The _N 2 SA of silica is a value measured by the BET method in accordance with ASTM D3037-81.

The content of silica is 10 parts by mass or more, preferably 12 parts by mass or more with respect to 100 parts by mass of the rubber component. If the amount is less than 10 parts by mass, the effect of incorporating silica tends to be insufficient. The content of the silica is 60 parts by mass or less, preferably 45 parts by mass or less, more preferably 35 parts by mass or less. When it exceeds 60 parts by mass, the viscosity of the unvulcanized rubber composition increases, and the processability tends to decrease.

In the rubber composition of the present invention, as the silane coupling agent, 1 bonding unit B is used with respect to the total amount of the bonding unit A represented by the above formula (1) and the bonding unit B represented by the above formula (2). It contains what is copolymerized at a ratio of ˜70 mol%. By blending the silane coupling agent having the above structure, low fuel consumption and wear resistance can be improved while ensuring good processability.

The silane coupling agent having the above structure has an increased viscosity during processing as compared with polysulfide silanes such as bis- (3-triethoxysilylpropyl) tetrasulfide because the molar ratio of the bond unit A to the bond unit B satisfies the above conditions. Is suppressed. This is presumably because the increase in Mooney viscosity is small because the sulfide portion of the bond unit A is a C—S—C bond and is thermally stable compared to tetrasulfide and disulfide.

Moreover, when the molar ratio of the bond unit A and the bond unit B satisfies the above condition, the shortening of the scorch time is suppressed as compared with mercaptosilane such as 3-mercaptopropyltrimethoxysilane. This is because the bonding unit B has a structure of mercaptosilane, but the —C ₇ H ₁₅ portion of the bonding unit A covers the —SH group of the bonding unit B, so that it is difficult to react with the polymer. As a result, the scorch time is unlikely to be shortened and the viscosity is unlikely to increase.

Examples of the halogen for R ¹ include chlorine, bromine, and fluorine.

Examples of the branched or unbranched alkyl group having 1 to 30 carbon atoms of R ¹ and R ² include a methyl group, an ethyl group, an n-propyl group, an isopropyl group, an n-butyl group, an iso-butyl group, and a sec-butyl group. Tert-butyl group, pentyl group, hexyl group, heptyl group, 2-ethylhexyl group, octyl group, nonyl group, decyl group and the like. The number of carbon atoms of the alkyl group is preferably 1-12.

Examples of the branched or unbranched alkylene group having 1 to 30 carbon atoms of R ¹ and R ² include ethylene group, propylene group, butylene group, pentylene group, hexylene group, heptylene group, octylene group, nonylene group, decylene group, Examples include an undecylene group, a dodecylene group, a tridecylene group, a tetradecylene group, a pentadecylene group, a hexadecylene group, a heptadecylene group, and an octadecylene group. The alkylene group preferably has 1 to 12 carbon atoms.

Examples of the branched or unbranched alkenyl group having 2 to 30 carbon atoms of R ¹ and R ² include a vinyl group, 1-propenyl group, 2-propenyl group, 1-butenyl group, 2-butenyl group, 1-pentenyl group, 2-pentenyl group, 1-hexenyl group, 2-hexenyl group, 1-octenyl group and the like can be mentioned. The alkenyl group preferably has 2 to 12 carbon atoms.

Examples of the branched or unbranched C 2-30 alkenylene group of R ¹ and R ² include vinylene group, 1-propenylene group, 2-propenylene group, 1-butenylene group, 2-butenylene group, 1-pentenylene group, 2-pentenylene group, 1-hexenylene group, 2-hexenylene group, 1-octenylene group and the like can be mentioned. The alkenylene group preferably has 2 to 12 carbon atoms.

Examples of the branched or unbranched alkynyl group having 2 to 30 carbon atoms of R ¹ and R ² include ethynyl group, propynyl group, butynyl group, pentynyl group, hexynyl group, heptynyl group, octynyl group, noninyl group, decynyl group, An undecynyl group, a dodecynyl group, etc. are mentioned. The alkynyl group preferably has 2 to 12 carbon atoms.

Examples of the branched or unbranched alkynylene group having 2 to 30 carbon atoms represented by R ¹ and R ² include ethynylene group, propynylene group, butynylene group, pentynylene group, hexynylene group, heptynylene group, octynylene group, noninylene group, decynylene group, An undecynylene group, a dodecynylene group, etc. are mentioned. The alkynylene group preferably has 2 to 12 carbon atoms.

In the silane coupling agent having the above structure, the total repeating number (x + y) of the repeating number (x) of the bonding unit A and the repeating number (y) of the bonding unit B is preferably in the range of 3 to 300. Within this range, since the mercaptosilane of the bond unit B is covered by —C ₇ H ₁₅ of the bond unit A, it is possible to suppress the scorch time from being shortened and to have good reactivity with silica and rubber components. Can be secured.

As the silane coupling agent having the above structure, for example, NXT-Z30, NXT-Z45, NXT-Z60 manufactured by Momentive, etc. can be used. These may be used alone or in combination of two or more.

The content of the silane coupling agent having the above structure is preferably 2 parts by mass or more, more preferably 4 parts by mass or more, and further preferably 6 parts by mass or more with respect to 100 parts by mass of silica. If the amount is less than 2 parts by mass, rolling resistance tends to increase, and the fuel efficiency tends to deteriorate. The content is preferably 20 parts by mass or less, more preferably 16 parts by mass or less, still more preferably 12 parts by mass or less, and particularly preferably 10 parts by mass or less. When it exceeds 20 parts by mass, there is a tendency that an effect commensurate with the increase in cost cannot be obtained.

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, the reinforcing property is enhanced and the effects of the present invention can be obtained satisfactorily.

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 10 parts by mass or more, and still more preferably 15 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 60 parts by mass or less, still more preferably 45 parts by mass or less, and particularly preferably 40 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.

In the rubber composition of the present invention, the total content of carbon black and silica is preferably 15 parts by mass or more, more preferably 30 parts by mass or more, and further preferably 45 parts by mass or more with respect to 100 parts by mass of the rubber component. is there. The total content is preferably 100 parts by mass or less, more preferably 80 parts by mass or less, still more preferably 65 parts by mass or less, and particularly preferably 55 parts by mass or less. By setting it within the above range, good wear resistance can be obtained. In addition, good fuel efficiency can be obtained without reducing the total content.

In the rubber composition of the present invention, the oil content is preferably 5 parts by mass or less, more preferably 1 part by mass or less, still more preferably 0 parts by mass (substantially not contained) with respect to 100 parts by mass of the rubber component. ). The rubber composition of the present invention can reduce Mooney viscosity by using HPNR as compared to NR, and therefore can reduce oil and improve fuel efficiency while maintaining good processability.

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 (Polyoxyethylene lauryl ether sodium sulfate) manufactured by Kao Corporation
NaOH: NaOH manufactured by Wako Pure Chemical Industries, Ltd.
NR: TSR
HPNR (saponified natural rubber): Production Example 1 below
Co-based BR1: BR150B manufactured by Ube Industries, Ltd. (BR synthesized using a Co-based catalyst, cis content: 97.0% by mass, vinyl content: 1.5% by mass, ML _{1 + 4} (100 ° C.):
40, Mw: 52.0 × 10 ⁴ , Mn: 15.0 × 10 ⁴ , Mw / Mn: 3.3)
Co-based BR2: BR150L manufactured by Ube Industries, Ltd. (BR synthesized using a Co-based catalyst, cis content: 98.2% by mass, vinyl content: 1.0% by mass, ML _{1 + 4} (100 ° C.):
43, Mw: 54.2 × 10 ⁴ , Mn: 22.1 × 10 ⁴ , Mw / Mn: 2.4)
Nd-based BR: Buna CB24 manufactured by LANXESS (BR synthesized using an Nd-based catalyst, cis content: 97.6% by mass, vinyl content: 0.4% by mass, ML _{1 + 4} (100 ° C.):
45 ,: Mw: 59.7 × 10 ⁴ , Mn: 22.2 × 10 ⁴ , Mw / Mn: 2.7)
Carbon Black: Show Black N220 (N ₂ SA: 111 m ² / g) manufactured by Cabot Japan
Silica: ULTRASIL VN3 manufactured by Degussa (average primary particle size: 15 nm, N ₂ SA: 175 m ² / g)
Silane coupling agent 1: Si266 (sulfide silane) manufactured by Degussa
Silane coupling agent 2: A1891 (Mercaptosilane) manufactured by Momentive
Silane coupling agent 3: NXT-Z45 manufactured by Momentive (copolymer of bonding unit A and bonding unit B (bonding unit A: 55 mol%, bonding unit B: 45 mol%))
Silane coupling agent 4: NXT-Z15 manufactured by Momentive (copolymer of bonding unit A and bonding unit B (bonding unit A: 85 mol%, bonding unit B: 15 mol%))
Silane coupling agent 5: NXT-Z60 manufactured by Momentive (copolymer of bond unit A and bond unit B (bond unit A: 40 mol%, bond unit B: 60 mol%))
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 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. A treated 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).
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 saponified natural rubber (HPNR) had a reduced nitrogen content, phosphorus content, and gel content as compared to TSR. Further, in the ³¹ P NMR measurement of an extract obtained by extracting from the modified natural rubber obtained in Production Example 1 it did not detect the peak due to phospholipids -3Ppm～1ppm.

<Examples 1-9, Comparative Examples 1-13>
In accordance with the formulation shown in Tables 2 and 3, 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 conducted using the obtained unvulcanized rubber composition and vulcanized rubber composition.

(Heat generation performance index)
Using a viscoelastic spectrometer VES (manufactured by Iwamoto Seisakusho Co., Ltd.), tan δ of the vulcanized rubber composition was measured under 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 2) × 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 amount of Lambourn wear, and the volume loss amount of Comparative Example 2 was taken as 100, and the volume loss amount of each formulation was displayed as an index according to the following 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 2) / (volume loss amount of each formulation) × 100

(Mooney viscosity index)
Based on JIS K6300, the Mooney viscosity of the unvulcanized rubber composition was measured at 100 ° C. Then, the Mooney viscosity of Comparative Example 2 was set to 100, and the Mooney viscosity of each formulation was indicated by an index according to the following calculation formula. It shows that Mooney viscosity is so low that a numerical value is large, and it is excellent in workability.
(Mooney viscosity index) = (Mooney viscosity of Comparative Example 2) / (Mooney viscosity of each formulation) × 100

(Scorch time index)
Based on JIS K6300, the time until the vulcanization degree of the unvulcanized rubber composition reached 10% (T ₁₀ ) was measured at 160 ° C. Then, the _{T 10} of Comparative Example 2 as 100, was displayed by indices by the following calculation formula. The larger the value, the longer the scorch time and the better the workability.
_{(T 10} of Comparative Example 2) (scorch time index) = _(T 10 of each formulation) / × 100

From Tables 2 and 3, in Examples using HPNR, Nd-based BR and silica, and using any of the silane coupling agents 3 to 5, low fuel consumption performance and wear resistance performance can be improved in a well-balanced manner. It was. Moreover, the workability was also good, and these performances were obtained with a good balance. On the other hand, the comparative example which does not use the said component together was inferior in performance compared with the Example.

Claims (8)

Contains rubber component, silica and silane coupling agent,
The rubber component includes a modified natural rubber having a phosphorus content of 200 ppm or less, and a butadiene rubber synthesized using a rare earth element-based catalyst,
In 100% by mass of the rubber component, the content of the modified natural rubber is 60 to 95% by mass, and the content of butadiene rubber synthesized using the rare earth element-based catalyst is 5 to 40% by mass.
The silica content relative to 100 parts by mass of the rubber component is 10 to 60 parts by mass,
The silane coupling agent is a proportion of 1 to 70 mol% of the binding unit B with respect to the total amount of the binding unit A represented by the following formula (1) and the binding unit B represented by the following formula (2). A rubber composition for a tire which is a copolymer.

(In the formula, x and y are each an integer of 1 or more. R ¹ is hydrogen, halogen, branched or unbranched alkyl group or alkylene group having 1 to 30 carbon atoms, branched or unbranched carbon atoms 2 to 30. Or an alkenyl group or alkenylene group, a branched or unbranched alkynyl group or alkynylene group having 2 to 30 carbon atoms, or a hydrogen atom substituted at the terminal of the alkyl group or the alkenyl group with a hydroxyl group or a carboxyl group. ² is hydrogen, a branched or unbranched alkylene group or alkyl group having 1 to 30 carbon atoms, a branched or unbranched alkenylene group or alkenyl group having 2 to 30 carbon atoms, or a branched or unbranched carbon group having 2 to 30 carbon atoms. R represents an alkynylene group or an alkynyl group, and R ¹ and R ² may form a ring structure.) 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 modified natural rubber is obtained by saponifying natural rubber latex with an alkali, repeatedly washing the agglomerated rubber after saponification, and washing and removing the phosphorus compound separated by saponification. The tire rubber composition according to any one of the above. The rubber composition for a tire according to any one of claims 1 to 5, wherein the butadiene rubber synthesized using the rare earth element-based catalyst has a cis content of 95% by mass or more and a vinyl content of 1.0% by mass or less. . The tire rubber composition according to any one of claims 1 to 6, which is used for a tread of a heavy load tire. A heavy duty tire having a tread produced using the rubber composition according to claim 1.