JP2015040243A - Rubber composition for clinch apex, and pneumatic tire - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a rubber composition for a clinch apex, from which good degradation resistant performance, processability, durability (rim chafing resistance) and rolling resistance characteristics can be obtained even when a softening agent derived from a non-petroleum resource is used, and to provide a pneumatic tire manufactured by using the composition.SOLUTION: The rubber composition for a clinch apex contains a rubber component and a myrcene polymer, in which the rubber component contains at least one diene rubber selected from the group consisting of natural rubber, epoxidized natural rubber and butadiene rubber.

Description

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

Conventionally, rubber compositions for tire clinch apex are used to improve the phenomenon (rim chafing) in which the clinch apex rubber that contacts the rim during driving in addition to natural rubber (NR) exhibiting excellent tear strength is scraped. In addition, butadiene rubber (BR) and carbon black have been blended to improve rim chafing resistance and reinforcement.

On the other hand, in recent years, environmental issues have become more important, and CO ₂ emission regulations have been strengthened. In addition, oil resources are limited, and in the future, it may become difficult to supply raw materials derived from oil resources, and it is predicted that oil prices will rise due to a decrease in the supply amount year by year. Therefore, it is required to replace raw materials derived from petroleum resources with raw materials derived from resources other than petroleum.

In the tire rubber composition, aroma oil has been generally used as a softening agent. However, it is necessary to replace aroma oil due to its carcinogenic problems, etc., and tires are currently in the direction of changing to oil derived from various petroleum resources (alternative aroma oil) having a similar structure to aroma oil in Japan. Measures are being taken by each company.

However, alternative aroma oils still rely on petroleum resources. Furthermore, when oils derived from petroleum resources are blended with rubber compositions containing natural rubber or butadiene rubber in particular, tire rolling resistance increases (rolling resistance characteristics deteriorate) and fuel consumption worsens (low fuel consumption deteriorates). In addition, there is still room for improving performance in filler dispersibility and durability, particularly in rubber compositions containing natural rubber and butadiene rubber, even with aroma oils and alternative aroma oils.

On the other hand, for example, Patent Document 1 discloses a rubber composition containing a vegetable oil such as palm oil as a softener derived from a non-petroleum resource instead of an oil derived from a petroleum resource. This is excellent from the viewpoint of considering the environment, but the dispersibility and durability of the filler are greatly inferior to those in the case of blending an aroma oil. Thus, when a softener derived from non-petroleum resources is used, there is a problem that only a performance equal to or lower than the durability obtained when using a conventional softener derived from petroleum resources is obtained. .

JP 2003-066422 A

The present invention solves the above-mentioned problems, and even when a softener derived from a non-petroleum resource is used, good deterioration resistance, workability, durability (rim chafing resistance), and rolling resistance characteristics are obtained. It is an object of the present invention to provide a rubber composition for clinch apex and a pneumatic tire produced using the same.

The present invention relates to a clinch apex comprising a rubber component and a myrcene polymer, wherein the rubber component includes at least one diene rubber selected from the group consisting of natural rubber, epoxidized natural rubber, and butadiene rubber. The present invention relates to a rubber composition.

The myrcene polymer preferably has a weight average molecular weight of 1,000 to 500,000.

The total content of natural rubber and butadiene rubber in 100% by mass of the rubber component is preferably 50% by mass or more.
The total content of natural rubber and epoxidized natural rubber in 100% by mass of the rubber component is preferably 50% by mass or more.

（式中、Ｅは炭素数２〜１０のアルキレン基、Ｒ^１０１及びＲ^１０２は、同一若しくは異なって、窒素原子を含む１価の有機基を表す。） It is preferable to contain 0.5 to 10 parts by mass of a compound represented by the following formula (I) with respect to 100 parts by mass of the rubber component.

(In the formula, E represents an alkylene group having 2 to 10 carbon atoms, and R ¹⁰¹ and R ¹⁰² are the same or different and each represents a monovalent organic group containing a nitrogen atom.)

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

According to the present invention, a clinch comprising a rubber component and a myrcene polymer, wherein the rubber component comprises at least one diene rubber selected from the group consisting of natural rubber, epoxidized natural rubber, and butadiene rubber. Because it is a rubber composition for apex, good deterioration resistance, processability, durability (rim-chafing resistance), and rolling resistance characteristics can be obtained even when softeners derived from non-petroleum resources are used. And a pneumatic tire produced using the rubber composition. In addition, since a softener derived from non-petroleum resources is used, it is possible to provide a pneumatic tire that is environmentally friendly and that is excellent in the above performance even in such a situation, in preparation for a future reduction in the amount of oil supply.

The rubber composition for clinch apex of the present invention includes a rubber component and a myrcene polymer, and the rubber component is at least one selected from the group consisting of natural rubber, epoxidized natural rubber, and butadiene rubber. Includes diene rubber.

The rubber composition of the present invention contains at least one diene rubber selected from the group consisting of natural rubber, epoxidized natural rubber, and butadiene rubber as a rubber component, and therefore is necessary as a rubber composition for clinch apex. Durability (rim-proofing resistance) is obtained.
Furthermore, by blending this rubber component with a myrcene polymer as a softener derived from non-petroleum resources, good deterioration resistance, workability, durability (rim chafing resistance), and rolling resistance characteristics can be obtained. . It is also environmentally friendly and can be prepared for a future reduction in oil supply.
In the following, when simply described as durability, it means rim chafing resistance.

In the present invention, the rubber component includes at least one diene rubber selected from the group consisting of natural rubber (NR), epoxidized natural rubber (ENR), and butadiene rubber (BR). Among NR, ENR, and BR, it is preferable to use NR or NR and BR in combination.

The NR is not particularly limited, and for example, those commonly used in the tire industry such as SIR20, RSS # 3, TSR20, and the like can be used.

The content of NR in 100% by mass of the rubber component is preferably 20% by mass or more, more preferably 30% by mass or more, still more preferably 80% by mass or more, and may be 100% by mass. If it is less than 20% by mass, sufficient flex crack growth resistance, crack resistance, durability, and rolling resistance characteristics may not be obtained. In addition, the environment may not be fully considered, and there is a risk that it will not be possible to prepare for future reductions in oil supply.

As ENR, commercially available ENR may be used, or NR epoxidized one may be used. The method for epoxidizing NR is not particularly limited, and can be carried out using a method such as a chlorohydrin method, a direct oxidation method, a hydrogen peroxide method, an alkyl hydroperoxide method, or a peracid method. Examples of the peracid method include a method of reacting NR with an organic peracid such as peracetic acid or performic acid.

The epoxidation rate of ENR is preferably 5 mol% or more, more preferably 10 mol% or more, and further preferably 15 mol% or more. When the epoxidation rate of ENR is less than 5 mol%, the effect of epoxidation is small, and when blended with NR, the compatibility is too good, making it difficult to improve flex crack growth resistance and durability, and improve ozone resistance. It may be difficult to confirm the effect of. The epoxidation rate of ENR is preferably 60 mol% or less, more preferably 40 mol% or less, and further preferably 30 mol% or less. If the epoxidation rate of ENR exceeds 60 mol%, the rolling resistance characteristics may be deteriorated, or the workability when blended with NR may be too bad to deteriorate the durability.
The epoxidation rate means the ratio of the number of epoxidized out of the total number of carbon-carbon double bonds in the natural rubber before epoxidation. For example, by titration analysis or nuclear magnetic resonance (NMR) analysis Desired.

The content of ENR in 100% by mass of the rubber component is preferably 20% by mass or more, more preferably 30% by mass or more, still more preferably 80% by mass or more, and may be 100% by mass. If it is less than 20% by mass, sufficient flex crack growth resistance, crack resistance, durability, and rolling resistance characteristics may not be obtained. In addition, the environment may not be fully considered, and there is a risk that it will not be possible to prepare for future reductions in oil supply.

The total content of NR and ENR in 100% by mass of the rubber component is preferably 50% by mass or more, more preferably 75% by mass or more, still more preferably 90% by mass or more, and may be 100% by mass. If it is less than 50% by mass, there is a possibility that the bending crack growth resistance, durability, ozone resistance and crack generation resistance (particularly, bending crack growth resistance and durability) may not be sufficiently obtained. Moreover, there is a tendency that the environment cannot be fully considered and it is not possible to prepare for a future decrease in oil supply.

The BR is not particularly limited. For example, BR1220 manufactured by Nippon Zeon Co., Ltd., BR150B manufactured by Ube Industries, Ltd., high cis content BR, 1, VCR412, VCR617 manufactured by Ube Industries, etc. Commonly used in the tire industry such as BR containing 2-syndiotactic polybutadiene crystal (SPB) can be used. Among these, BR having a cis content of 80% by mass or more (more preferably 90% by mass or more, and further preferably 95% by mass or more) is preferable because it has excellent resistance to flex crack growth and durability.

The content of BR in 100% by mass of the rubber component is preferably 20% by mass or more, more preferably 30% by mass or more, still more preferably 40% by mass or more, and particularly preferably 50% by mass or more. If it is less than 20% by mass, the resistance to flex crack growth, crack resistance, durability, and rolling resistance may be deteriorated. The BR content is preferably 80% by mass or less, more preferably 70% by mass or less. If it exceeds 80% by mass, the bending crack growth resistance may be deteriorated, or sufficient mechanical strength may not be ensured.

The total content of NR and BR in 100% by mass of the rubber component is preferably 50% by mass or more, more preferably 75% by mass or more, still more preferably 90% by mass or more, and may be 100% by mass. If it is less than 50% by mass, sufficient resistance to bending crack growth, crack resistance, durability, and rolling resistance (particularly resistance to bending crack growth and durability) may not be obtained.

Examples of rubber components that can be used in addition to NR, ENR, and BR include isoprene rubber (IR), styrene butadiene rubber (SBR), styrene isoprene butadiene rubber (SIBR), chloroprene rubber (CR), acrylonitrile butadiene rubber (NBR), and the like. And diene rubber.

In the present invention, a myrcene polymer is used together with the rubber component. The myrcene polymer means a polymer obtained by polymerizing myrcene as a monomer component. Here, myrcene is a naturally occurring organic compound and is a kind of olefin belonging to monoterpene. Myrcene has two isomers, α-myrcene (2-methyl-6-methyleneocta-1,7-diene) and β-myrcene (7-methyl-3-methyleneocta-1,6-diene). Although it exists, “myrcene” in the present invention is β-myrcene having the following structure unless otherwise specified.

In the present invention, deterioration resistance, workability, durability, and rolling resistance characteristics can be improved by blending a myrcene polymer as a softener derived from non-petroleum resources together with the rubber component. In addition, since myrcene, which is a monomer component, is a naturally occurring organic compound, by using a myrcene polymer obtained by polymerizing the myrcene, it is possible to reduce the amount of raw material derived from petroleum resources, And can prepare for future reductions in oil supply. The myrcene polymer is preferably blended in place of a softener such as oil that has been blended in the conventional clinch apex. Thereby, while the usage-amount of the raw material derived from petroleum resources can be reduced more, the effect of this invention is acquired more suitably.

The weight average molecular weight (Mw) of the myrcene polymer is preferably 1000 or more, more preferably 2000 or more, and still more preferably 3000 or more. When Mw is less than 1000, deterioration resistance and durability tend to deteriorate. Mw is preferably 500,000 or less, more preferably 300,000 or less, still more preferably 150,000 or less, particularly preferably 100,000 or less, and most preferably 50,000 or less. When Mw exceeds 500,000, deterioration resistance performance, workability, and durability tend to deteriorate. A myrcene polymer having an Mw within the above range can be suitably used as a softening agent, and the effects of the present invention can be more suitably obtained. In particular, when the rubber composition of the present invention contains carbon black, durability can be remarkably improved by blending a myrcene polymer having an Mw of 150,000 or less (preferably 100,000 or less, more preferably 50,000 or less). .
In addition, in this specification, a weight average molecular weight (Mw) is measured by the method as described in an Example.

The myrcene polymer is obtained by polymerizing myrcene as a monomer component.

In the above polymerization, the polymerization procedure is not particularly limited, and for example, all the monomers may be polymerized at once, or the monomers may be sequentially added and polymerized. A monomer component other than myrcene may be used in combination as the monomer component, but the content of myrcene in 100% by mass of the monomer component is preferably 80% by mass or more, more preferably 90% by mass or more. It may be mass%.

The above polymerization can be carried out by a conventional method, for example, anionic polymerization, coordination polymerization or the like.

The polymerization method is not particularly limited, and any of a solution polymerization method, an emulsion polymerization method, a gas phase polymerization method, and a bulk polymerization method can be used. Among these, the solution polymerization method is preferable. Further, the polymerization format may be either a batch type or a continuous type.

Hereinafter, methods for preparing a myrcene polymer by anionic polymerization and coordination polymerization will be described.

<Anionic polymerization>
The anionic polymerization can be carried out in a suitable solvent in the presence of an anionic polymerization initiator. Any conventional anionic polymerization initiator can be suitably used. Examples of such an anionic polymerization initiator include a general formula RLix (where R represents one or more carbon atoms). An organic lithium compound having an aliphatic, aromatic or alicyclic group, and x is an integer of 1 to 20. Suitable organolithium compounds include methyllithium, ethyllithium, n-butyllithium, sec-butyllithium, tert-butyllithium, phenyllithium and naphthyllithium. Preferred organolithium compounds are n-butyllithium and sec-butyllithium. An anionic polymerization initiator can be used individually or in mixture of 2 or more types. The amount of the polymerization initiator used in the anionic polymerization is not particularly limited. For example, about 0.05 to 35 mmol is preferably used, and about 0.05 to 0.2 mmol is used per 100 g of all monomers to be subjected to polymerization. Is more preferable.

Moreover, as a solvent used for anionic polymerization, any solvent can be used suitably as long as it does not deactivate the anionic polymerization initiator or stop the polymerization reaction. Either a polar solvent or a nonpolar solvent can be used. Can be used. Examples of the polar solvent include ether solvents such as tetrahydrofuran, and examples of the nonpolar solvent include chain hydrocarbons such as hexane, heptane, octane and pentane, cyclic hydrocarbons such as cyclohexane, benzene and toluene. And aromatic hydrocarbons such as xylene. These solvents can be used alone or in admixture of two or more.

Anionic polymerization is preferably carried out in the presence of a polar compound. Examples of polar compounds include dimethyl ether, diethyl ether, ethyl methyl ether, ethyl propyl ether, tetrahydrofuran, dioxane, diphenyl ether, tripropylamine, tributylamine, trimethylamine, triethylamine, N, N, N ′, N′-tetramethylethylenediamine. (TMEDA). A polar compound can be used individually or in mixture of 2 or more types. This polar compound is useful for controlling the microstructure of the polymer. The amount of the polar compound used varies depending on the type of the polar compound and the polymerization conditions, but is preferably 0.1 or more as the molar ratio (polar compound / anionic polymerization initiator) to the anionic polymerization initiator. If the molar ratio with the anionic polymerization initiator (polar compound / anionic polymerization initiator) is less than 0.1, the effect of the polar substance on controlling the microstructure tends to be insufficient.

The reaction temperature during the anionic polymerization is not particularly limited as long as the reaction proceeds suitably, but it is usually preferably −10 ° C. to 100 ° C., more preferably 25 ° C. to 70 ° C. The reaction time varies depending on the charged amount, the reaction temperature, and other conditions, but usually, for example, about 3 hours is sufficient.

The anionic polymerization can be stopped by adding a reaction terminator usually used in this field. Examples of such a reaction terminator include polar solvents having active protons such as alcohols such as methanol, ethanol and isopropanol or acetic acid and mixtures thereof, or polar solvents and nonpolar solvents such as hexane and cyclohexane. A mixed solution is mentioned. The amount of the reaction terminator added is usually about the same molar amount or twice the molar amount relative to the anionic polymerization initiator.

After the termination of the polymerization reaction, the myrcene polymer can be easily removed by removing the solvent from the polymerization solution by a conventional method, or by pouring the polymerization solution into one or more times the amount of alcohol and precipitating the myrcene polymer. Can be separated.

<Coordination polymerization>
The coordination polymerization can be carried out by using a coordination polymerization initiator instead of the anionic polymerization initiator in the anionic polymerization. As the coordination polymerization initiator, any conventional one can be suitably used. Examples of such coordination polymerization initiator include transition metals such as lanthanoid compounds, titanium compounds, cobalt compounds, and nickel compounds. The catalyst which is a compound is mentioned. Further, if desired, an aluminum compound or a boron compound can be further used as a promoter.

The lanthanoid compound is not particularly limited as long as it contains any of the elements of atomic numbers 57 to 71 (lanthanoid), but among these lanthanoids, neodymium is particularly preferable. Examples of lanthanoid compounds include carboxylates, β-diketone complexes, alkoxides, phosphates or phosphites, halides, and the like of these elements. Of these, carboxylates, alkoxides, and β-diketone complexes are preferred because of easy handling. The titanium compound includes, for example, a cyclopentadienyl group, an indenyl group, a substituted cyclopentadienyl group, or a substituted indenyl group, and three substituents selected from a halogen, an alkoxyl group, and an alkyl group. Examples of the titanium-containing compound include compounds having one alkoxysilyl group from the viewpoint of catalyst performance. Examples of the cobalt compound include cobalt halides, carboxylates, β-diketone complexes, organic base complexes, and organic phosphine complexes. Examples of the nickel compound include nickel halides, carboxylates, β-diketone complexes, and organic base complexes. The catalyst used as the coordination polymerization initiator can be used alone or in combination of two or more. The amount of the catalyst used as the polymerization initiator in the coordination polymerization is not particularly limited. For example, the preferable amount used is the same as the amount of the catalyst used in the anionic polymerization.

Examples of the aluminum compound used as a cocatalyst include organic aluminoxanes, halogenated organoaluminum compounds, organoaluminum compounds, and hydrogenated organoaluminum compounds. Examples of organic aluminoxanes include alkylaluminoxanes (such as methylaluminoxane, ethylaluminoxane, propylaluminoxane, butylaluminoxane, isobutylaluminoxane, octylaluminoxane, hexylaluminoxane), and examples of halogenated organoaluminum compounds include alkyl halides. Aluminum compounds (dimethylaluminum chloride, diethylaluminum chloride, methylaluminum dichloride, ethylaluminum dichloride, etc.), and organic aluminum compounds such as alkylaluminum compounds (trimethylaluminum, triethylaluminum, triisopropylaluminum, triisobutylaluminum, etc.) , Hydrogenated organoaluminum The object, for example, hydrogenated alkylaluminum compounds (diethyl aluminum hydride, and diisobutyl aluminum hydride) and the like. Examples of the boron compound include compounds containing anionic species such as tetraphenylborate, tetrakis (pentafluorophenyl) borate, and (3,5-bistrifluoromethylphenyl) borate. These promoters can also be used alone or in combination of two or more.

Regarding the coordination polymerization, as the solvent and the polar compound, those described in the anionic polymerization can be used in the same manner. The reaction time and reaction temperature are also the same as those described in the anionic polymerization. Termination of the polymerization reaction and isolation of the myrcene polymer can be performed in the same manner as in the case of anionic polymerization.

The weight average molecular weight (Mw) of the myrcene polymer can be controlled by adjusting the amount of myrcene monomer and the amount of polymerization initiator charged during the polymerization. For example, if the total monomer / anionic polymerization initiator ratio or the total monomer / coordination polymerization initiator ratio is increased, Mw can be increased, and conversely, if it is decreased, Mw can be decreased. The same applies to the number average molecular weight (Mn) of the myrcene polymer.

The content of the myrcene polymer is preferably 1 part 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 it is less than 1 part by mass, durability and rolling resistance characteristics tend not to be sufficiently improved. Further, the content of the myrcene polymer is preferably 50 parts by mass or less, more preferably 30 parts by mass or less, and still more preferably 15 parts by mass or less. When it exceeds 50 mass parts, there exists a tendency for rolling resistance characteristics to deteriorate.

In the present invention, a softener may be blended in addition to the myrcene polymer. As the softener, for example, process oil, vegetable oil, and resin can be used. Examples of the process oil include paraffinic process oil, naphthenic process oil, aromatic process oil (aromatic process oil), and the like. Examples of vegetable oils include castor oil, cottonseed oil, sesame oil, rapeseed oil, soybean oil, palm oil, coconut oil, peanut hot water, rosin, pine oil, pine tar, tall oil, corn oil, rice bran oil, beet flower oil, sesame oil , Olive oil, sunflower oil, palm kernel oil, coconut oil, jojoba oil, macadamia nut oil, tung oil and the like. Examples of the resin include petroleum resins, coumarone indene resins, terpene resins, and the like. The total content of the softener (including the content of the myrcene polymer) is preferably 1 to 50 parts by mass, more preferably 3 to 30 parts by mass, and 5 to 15 parts by mass with respect to 100 parts by mass of the rubber component. Further preferred.

As described above, in the present invention, the myrcene polymer is preferably mixed with a part or all of a softener such as oil that has been blended as a softener in the conventional clinch apex rubber. The content of the myrcene polymer in the mass% is preferably 25 mass% or more, more preferably 50 mass% or more, still more preferably 80 mass% or more, and may be 100 mass%. Thereby, the effect of this invention is acquired more suitably.

The rubber composition of the present invention preferably contains carbon black. By blending carbon black together with the rubber component and myrcene polymer, durability, mechanical strength, UV resistance, resistance to flex crack growth, and crack resistance (particularly durability) can be further improved. As carbon black, SRF, GPF, FEF, HAF, ISAF, SAF, etc. can be used, for example.

The nitrogen adsorption specific surface area (N ₂ SA) of carbon black is preferably 50 m ² / g or more, and more preferably 70 m ² / g or more. When N ₂ SA is less than 50 m ² / g, sufficient reinforcement cannot be obtained, and sufficient durability, flex crack growth resistance, and crack resistance tend to be not obtained. Further, N ₂ SA of carbon black is preferably 120 m ² / g or less, more preferably 100 m ² / g or less, and still more preferably 90 m ² / g or less. When N ₂ SA exceeds 120 m ² / g, the viscosity of the unvulcanized becomes very high, processability tends to be deteriorated. Moreover, there exists a tendency for rolling resistance characteristics to deteriorate.
Incidentally, _N 2 SA of carbon black, JIS K 6217-2: determined by 2001.

In the rubber composition of the present invention, the carbon black content is preferably 3 parts by mass or more, more preferably 15 parts by mass or more, still more preferably 30 parts by mass or more, particularly preferably 100 parts by mass of the rubber component. It is 50 parts by mass or more. If the amount is less than 3 parts by mass, sufficient reinforcement and UV resistance cannot be obtained, and sufficient durability, mechanical strength, flex crack growth resistance, crack resistance and the like may not be obtained. Further, the carbon black content is preferably 100 parts by mass or less, more preferably 80 parts by mass or less, and still more preferably 70 parts by mass or less with respect to 100 parts by mass of the rubber component. When the amount exceeds 100 parts by mass, heat generation increases and rolling resistance characteristics tend to deteriorate.

Silica is preferably blended in the rubber composition of the present invention. By blending silica together with the rubber component and myrcene polymer, it is possible to improve rolling resistance characteristics while improving durability. It is also environmentally friendly and can be prepared for a future reduction in oil supply. Examples of the silica include dry method silica (anhydrous silica), wet method silica (hydrous silica), and the like. Of these, wet-process silica is preferred because it has many silanol groups.

The nitrogen adsorption specific surface area (N ₂ SA) of silica is preferably 10 m ² / g or more, more preferably 50 m ² / g or more, still more preferably 100 m ² / g or more, and particularly preferably 165 m ² / g or more. . If it is less than 10 m ² / g, sufficient reinforcement and mechanical strength cannot be secured, and sufficient durability may not be obtained. Further, N ₂ SA of silica is preferably 600 m ² / g or less, more preferably 300 m ² / g or less, still more preferably 260 m ² / g or less, and particularly preferably 200 m ² / g or less.
If it exceeds 600 m ² / g, silica is difficult to disperse and processability may be deteriorated. Moreover, there exists a possibility that a rolling resistance characteristic may 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 preferably 5 parts by mass or more, more preferably 10 parts by mass or more, still more preferably 20 parts by mass or more, particularly preferably 30 parts by mass or more, most preferably 100 parts by mass of the rubber component. It is 60 parts by mass or more. If it is less than 5 parts by mass, the effect of blending silica may not be sufficiently obtained. The silica content is preferably 150 parts by mass or less, more preferably 120 parts by mass or less, still more preferably 100 parts by mass or less, and particularly preferably 90 parts by mass or less. If it exceeds 150 parts by mass, silica is difficult to disperse and processability may be deteriorated. Moreover, there exists a possibility that a bending crack growth resistance and rolling resistance characteristic may fall.

The rubber composition preferably contains a silane coupling agent together with silica.
As the silane coupling agent, any silane coupling agent conventionally used in combination with silica can be used in the rubber industry. For example, sulfide systems such as bis (3-triethoxysilylpropyl) tetrasulfide, 3 -Mercapto type such as mercaptopropyltrimethoxysilane, vinyl type such as vinyltriethoxysilane, amino type such as 3-aminopropyltriethoxysilane, glycidoxy type of γ-glycidoxypropyltriethoxysilane, 3-nitropropyltri Examples thereof include nitro compounds such as methoxysilane, and chloro compounds such as 3-chloropropyltrimethoxysilane. Among these, sulfide type is preferable, and bis (3-triethoxysilylpropyl) tetrasulfide is more preferable.

The content of the silane coupling agent is preferably 2 parts by mass or more, more preferably 5 parts by mass or more with respect to 100 parts by mass of silica. If it is less than 2 parts by mass, the dispersibility of silica cannot be improved, and the durability tends to be greatly reduced. Further, the content of the silane coupling agent is preferably 15 parts by mass or less, more preferably 10 parts by mass or less. When it exceeds 15 parts by mass, there is a tendency that an effect commensurate with the increase in cost cannot be obtained.

In this invention, it is preferable that a silane compound is included with a silica. By containing a silane compound, the resistance to flex crack growth, durability, and rolling resistance can be improved. Examples of the silane compound include those represented by the following formula.
_Xn- Si-Y _4-n
(Wherein X is an alkoxy group having 1 to 5 carbon atoms, Y is a phenyl group or an alkyl group, and n is an integer of 1 to 3)

In the above formula, X is an alkoxy group having 1 to 5 carbon atoms, and is preferably a methoxy group or an ethoxy group because it easily reacts with silica, and more preferably an ethoxy group because it has a high flash point.

Y is a phenyl group or an alkyl group. When Y is an alkyl group, for example, a methyl group (—CH ₃ ), for example, methyltriethoxysilane has a flash point of 8 ° C., a hexyl group (—CH ₂ ( In the case of CH ₂ ) ₄ CH ₃ ), for example, hexyltriethoxysilane has a flash point as low as 81 ° C., whereas when Y is a phenyl group, the flash point is as high as 111 ° C. Groups are preferred.

n is an integer of 1 to 3. When n is 0, the silane compound does not have an alkoxy group and tends not to react with silica. Moreover, when n is 4, it tends to be difficult to be compatible with rubber. Note that n is preferably 3 because it is highly reactive with silica.

Examples of the silane compound satisfying the above formula include methyltrimethoxysilane (KBM13 manufactured by Shin-Etsu Chemical Co., Ltd.), dimethyldimethoxysilane (KBM22 manufactured by Shin-Etsu Chemical Co., Ltd.), phenyltrimethoxysilane (Shin-Etsu Chemical Co., Ltd.). KBM103 manufactured by Shin-Etsu Chemical Co., Ltd.), methyltriethoxysilane (KBE13 manufactured by Shin-Etsu Chemical Co., Ltd.), dimethyldiethoxysilane (KBE22 manufactured by Shin-Etsu Chemical Co., Ltd.) Etc.), phenyltriethoxysilane (KBE103 manufactured by Shin-Etsu Chemical Co., Ltd.), diphenyldiethoxysilane (KBE202 manufactured by Shin-Etsu Chemical Co., Ltd.), hexyltrimethoxysilane (KBM3063 manufactured by Shin-Etsu Chemical Co., Ltd.) , Hexyltriethoxysilane (manufactured by Shin-Etsu Chemical Co., Ltd.) BE3063 etc.), etc. KBM3103, KBM3103C made decyl trimethoxysilane (Shin-Etsu Chemical Co.) and the like, such as. Of these, phenyltriethoxysilane and phenyltrimethoxysilane are preferred, and phenyltriethoxysilane is more preferred because of its high reactivity with silica and high flash point.

4 mass parts or more are preferable with respect to 100 mass parts of silica, and, as for content of a silane compound, 6 mass parts or more are more preferable. When the content of the silane compound is less than 4 parts by mass, sufficient flex crack growth resistance, durability, and rolling resistance characteristics tend not to be obtained. Moreover, 16 mass parts or less are preferable and, as for content of a silane compound, 12 mass parts or less are more preferable. When the content of the silane compound exceeds 16 parts by mass, there is a tendency that only the cost is increased insignificantly or the durability is lowered.

When using ENR in the rubber composition of the present invention, an alkaline fatty acid metal salt may be blended. Since the alkaline fatty acid metal salt neutralizes the acid used during the ENR synthesis, it can prevent deterioration due to heat during ENR kneading and vulcanization. Also, reversion can be prevented.

Examples of the metal in the alkaline fatty acid metal salt include sodium, potassium, calcium, barium and the like. Among these, calcium and barium are preferable from the viewpoint of increasing the heat resistance improving effect and compatibility with the epoxidized natural rubber. Specific examples of alkaline fatty acid metal salts include sodium stearate, magnesium stearate, calcium stearate, barium stearate and other metal stearates, sodium oleate, magnesium oleate, calcium oleate, barium oleate and other oleic acids Examples thereof include metal salts. Of these, calcium stearate and calcium oleate are preferred because they have a large effect of improving heat resistance, high compatibility with epoxidized natural rubber, and relatively low cost.

The content of the alkaline fatty acid metal salt is preferably 1 part by mass or more, more preferably 1.5 parts by mass or more, still more preferably 3 parts by mass or more, particularly preferably 4.5 parts by mass or more with respect to 100 parts by mass of ENR. It is. If it is less than 1 part by mass, it is difficult to obtain sufficient effects with respect to heat resistance and reversion resistance. The content of the alkaline fatty acid metal salt is preferably 10 parts by mass or less, more preferably 8 parts by mass or less. When it exceeds 10 mass parts, there exists a tendency for fracture strength and durability to deteriorate.

（式中、Ｅは炭素数２〜１０のアルキレン基、Ｒ^１０１及びＲ^１０２は、同一若しくは異なって、窒素原子を含む１価の有機基を表す。） As a result of the study by the present inventors, when the total content of NR and ENR is increased in order to reduce the usage amount of materials derived from resources other than petroleum, for example, the total content of NR and ENR is 75% by mass or more. Then, the deterioration resistance tends to decrease, and a new problem has been clarified that sufficient deterioration resistance performance may not be obtained only by blending a myrcene polymer. As a result of intensive studies by the present inventors on this new problem, by containing a compound represented by the following formula (I) in addition to the myrcene polymer, the binding energy is high and the thermal stability is high. The present inventors have found that a high CC bond can be retained in a rubber composition, and that deterioration resistance performance, durability, and workability (particularly deterioration resistance performance) can be improved more suitably. Therefore, in this invention, it is preferable to contain the compound represented by a following formula (I).

(In the formula, E represents an alkylene group having 2 to 10 carbon atoms, and R ¹⁰¹ and R ¹⁰² are the same or different and each represents a monovalent organic group containing a nitrogen atom.)

The alkylene group for E is not particularly limited, and includes linear, branched, and cyclic groups. Among them, a linear alkylene group is preferable.

Carbon number of the alkylene group of E is 2-10, Preferably it is 4-8. When the number of carbon atoms in the alkylene group is 1, the thermal stability tends to be poor, and the effect of having an alkylene group tends to be insufficient. When the number of carbon atoms is 11 or more, -S-S-E-S- There is a tendency that formation of a crosslinked chain represented by S- becomes difficult.

Examples of the alkylene group satisfying the above conditions include ethylene group, trimethylene group, tetramethylene group, pentamethylene group, hexamethylene group, heptamethylene group, octamethylene group, decamethylene group and the like. Among these, a hexamethylene group is preferred because a cross-link represented by -S-S-E-SS-S is smoothly formed between the polymers and is thermally stable.

R ¹⁰¹ and R ¹⁰² are not particularly limited as long as they are monovalent organic groups containing a nitrogen atom, but those containing at least one aromatic ring are preferred, and N—C (═S) in which a carbon atom is bonded to a dithio group. )-Is more preferable. R ¹⁰¹ and R ¹⁰² may be the same or different from each other, but are preferably the same for reasons such as ease of production.

Examples of the compound represented by the formula (I) include 1,2-bis (N, N′-dibenzylthiocarbamoyldithio) ethane and 1,3-bis (N, N′-dibenzylthiocarbamoyldithio). Propane, 1,4-bis (N, N′-dibenzylthiocarbamoyldithio) butane, 1,5-bis (N, N′-dibenzylthiocarbamoyldithio) pentane, 1,6-bis (N, N ′) -Dibenzylthiocarbamoyldithio) hexane, 1,7-bis (N, N'-dibenzylthiocarbamoyldithio) heptane, 1,8-bis (N, N'-dibenzylthiocarbamoyldithio) octane, 1,9 -Bis (N, N′-dibenzylthiocarbamoyldithio) nonane, 1,10-bis (N, N′-dibenzylthiocarbamoyldithio) decane and the like. Among these, 1,6-bis (N, N′-dibenzylthiocarbamoyldithio) hexane is preferable because it is thermally stable and has excellent polarizability.

The content of the compound represented by the formula (I) is preferably 0.1 parts by mass or more, more preferably 0.5 parts by mass or more with respect to 100 parts by mass of the rubber component. If the amount is less than 0.1 part by mass, the effect obtained by blending the compound represented by formula (I) tends to be insufficient. The content is preferably 10 parts by mass or less, more preferably 5 parts by mass or less, and still more preferably 2 parts by mass or less. If it exceeds 10 parts by mass, the fracture strength tends to deteriorate.

In addition to the above components, the rubber composition of the present invention includes compounding agents generally used in the production of rubber compositions, such as reinforcing fillers such as clay, zinc oxide, stearic acid, various anti-aging agents, waxes Further, a vulcanizing agent such as sulfur, a vulcanization accelerator and the like can be appropriately blended.

Examples of the vulcanization accelerator include sulfenamide, thiazole, thiuram, thiourea, guanidine, dithiocarbamic acid, aldehyde-amine or aldehyde-ammonia, imidazoline, or xanthate vulcanization accelerator. Agents. Of these, sulfenamide vulcanization accelerators are preferred.

Examples of the sulfenamide vulcanization accelerator include N-tert-butyl-2-benzothiazolylsulfenamide (TBBS), N-cyclohexyl-2-benzothiazolylsulfenamide (CBS), N, N And '-dicyclohexyl-2-benzothiazolylsulfenamide (DZ). Of these, TBBS is preferable.

The content of the vulcanization accelerator is preferably 1 part by mass or more, more preferably 2 parts by mass or more with respect to 100 parts by mass of the rubber component. The content is preferably 8 parts by mass or less, more preferably 5 parts by mass or less. When the content of the vulcanization accelerator is within the above range, the effect of the present invention can be more suitably obtained.

As a method for producing the rubber composition of the present invention, known methods can be used. For example, each component excluding sulfur and a vulcanization accelerator is kneaded using a rubber kneading apparatus such as an open roll or a Banbury mixer. A base kneading step, a kneaded product obtained in the step, a finishing kneading step of kneading sulfur and a vulcanization accelerator, and a vulcanization method can be used. In particular, when NR and ENR are used in combination as the rubber component, the base kneading step includes the first base kneading step of kneading NR and a filler such as silica and carbon black, and the kneading obtained by the first base kneading step. And a second base kneading step of kneading the product, ENR, glycerol fatty acid triester, alkaline fatty acid metal salt and the like. In this case, it is easy to disperse silica in NR well, and glycerol fatty acid triester can easily enter ENR, so that the ENR phase that is an island phase can be softened, and the resistance to flex crack growth and crack resistance can be improved. Since it can improve further, the rubber composition in which the effect of the present invention is exhibited better can be manufactured.

The rubber composition of the present invention can be suitably used for tire clinch apex. The clinch apex is a rubber portion disposed on the inner end of the sidewall. Specifically, for example, FIG. 1 of Japanese Patent Application Laid-Open No. 2008-75066, FIG. 1 of Japanese Patent Application Laid-Open No. 2004-106796, and the like. It is a member shown by these.

The pneumatic tire of the present invention is produced by a usual method using the rubber composition. That is, if necessary, a rubber composition containing various additives is extruded in accordance with the shape of the tire clinch apex at an unvulcanized stage, and molded by a normal method on a tire molding machine. Then, after bonding together with other tire members to form an unvulcanized tire, the tire can be manufactured by heating and pressing in a vulcanizer.

The pneumatic tire of the present invention can be suitably used for various applications such as for passenger cars, trucks, buses, and heavy vehicles as “eco-tires” that are friendly to the global environment.

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 the production examples will be described together. In addition, the chemical | medical agent refine | purified according to the conventional method as needed.
Myrcene: Myrcene (myrcene derived from natural resources) manufactured by Wako Pure Chemical Industries, Ltd.
Cyclohexane: cyclohexane (special grade) manufactured by Kanto Chemical Co., Inc.
Neodymium 2-ethylhexanoate (III): Neodymium 2-ethylhexanoate (III) manufactured by Wako Pure Chemical Industries, Ltd.
PMAO: PMAO manufactured by Tosoh Finechem Co., Ltd.
Diisobutylaluminum hydride: Diisobutylaluminum hydride manufactured by Tokyo Chemical Industry Co., Ltd. Diethylaluminum chloride: Diethylaluminum hexane manufactured by Tokyo Chemical Industry Co., Ltd .: Normal hexane manufactured by Kanto Chemical Co., Ltd. (special grade)
Dibutylhydroxytoluene: dibutylhydroxytoluene isopropanol manufactured by Tokyo Chemical Industry Co., Ltd .: isopropanol manufactured by Kanto Chemical Co., Ltd. (special grade)

<Preparation of catalyst solution>
A 50 ml glass container was purged with nitrogen, 8 ml of cyclohexane solution (2.0 mol / L) of myrcene, 1 ml of neodymium (III) 2-ethylhexanoate / cyclohexane solution (0.2 mol / L), PMAO (Al: 6.8 mass) %) 8 ml was added and stirred. After 5 minutes, 5 ml of 1M-diisobutylaluminum hydride / hexane solution was added, and further 5 minutes later, 2 ml of 1M-diethylaluminum chloride / hexane solution was added and stirred to obtain a catalyst solution.

<Production Example 1 (Completion of Myrcene Polymer 1)>
The 3 L pressure-resistant stainless steel container was purged with nitrogen, and 1800 ml of cyclohexane and 100 g of myrcene were added and stirred for 10 minutes. Then, 6 ml of the catalyst solution was added, and stirring was performed while maintaining 30 ° C. After 3 hours, 10 ml of 0.01M-BHT (dibutylhydroxytoluene) / isopropanol solution was added dropwise to complete the reaction. After cooling, the reaction solution was added to 3 L of separately prepared methanol, and the precipitate thus obtained was air-dried overnight and further dried under reduced pressure for 2 days to obtain 100 g of myrcene polymer 1. The polymerization conversion rate (percentage of “dry weight / charge amount”) was almost 100%.

<Production Example 2 (synthesis of myrcene polymer 2)>
100 g of myrcene polymer 2 was obtained in the same manner as in Production Example 1 except that the amount of the catalyst solution was changed to 0.3 ml.

The obtained myrcene polymers 1 and 2 were evaluated as follows.

(Measurement of weight average molecular weight (Mw))
Mw is a standard based on a measurement value by gel permeation chromatograph (GPC) (GPC-8000 series manufactured by Tosoh Corporation, detector: differential refractometer, column: TSKGEL SUPERMALTPORE HZ-M manufactured by Tosoh Corporation). It calculated | required by polystyrene conversion.

Hereinafter, various chemicals used in Examples and Comparative Examples will be described together.
NR: TSR20
BR: BR150B manufactured by Ube Industries, Ltd. (cis content: 97% by mass, ML _{1 + 4} (100 ° C.): 40, 5% toluene solution viscosity at 25 ° C .: 48 cps, Mw / Mn: 3.3)
ENR: ENR-25 (Epoxidation rate: 28.1 mol%) manufactured by Malaysian Rubber Board
Silica: Ultrasil VN3 manufactured by Evonik Degussa (N ₂ SA: 175 m ² / g)
Carbon black: Dia Black H (N330, N ₂ SA: 81 m ² / g) manufactured by Mitsubishi Chemical Corporation
Silane coupling agent: Si69 (bis (3-triethoxysilylpropyl) tetrasulfide) manufactured by Evonik Degussa
Silane compound: KBE103 (phenyltriethoxysilane) manufactured by Shin-Etsu Chemical Co., Ltd.
Aroma oil: Process X-140 manufactured by Japan Energy Co., Ltd.
Petroleum resin: SP1068 resin (C9 resin) manufactured by Nippon Shokubai Co., Ltd.
Myrcene polymer (1): Myrcene polymer (softener derived from non-petroleum resource) obtained in Production Example 1 using myrcene derived from natural resources (weight average molecular weight: 10,000)
Myrcene polymer (2): Myrcene polymer (softener derived from non-petroleum resources) obtained in Production Example 2 using myrcene derived from natural resources (weight average molecular weight: 200,000)
Stearic acid: NOF made by NOF Corporation
Zinc oxide: Zinc oxide type 2 anti-aging agent manufactured by Mitsui Mining & Smelting Co., Ltd .: NOCRACK 6C (N- (1,3-dimethylbutyl) -N'-phenyl-p- manufactured by Ouchi Shinsei Chemical Co., Ltd.) Phenylenediamine)
Wax: Ozoace 0355 manufactured by Nippon Seiki Co., Ltd.
Sulfur: Powdered sulfur vulcanization accelerator manufactured by Tsurumi Chemical Industry Co., Ltd .: Noxeller NS (N-tert-butyl-2-benzothiazolylsulfenamide) manufactured by Ouchi Shinsei Chemical Industry Co., Ltd.
VP KA9188: VP KA9188 (1,6-bis (N, N′-dibenzylthiocarbamoyldithio) hexane manufactured by LANXESS

Using a Banbury mixer, the amount of chemicals shown in Step 1 of Table 1 was added, kneaded for 5 minutes so that the discharge temperature was about 150 ° C., and discharged (base kneading step).
Further, sulfur and a vulcanization accelerator in the blending amounts shown in Step 2 of Table 1 are added to the obtained kneaded product, and kneaded for about 3 minutes using a Banbury mixer so that the discharge temperature becomes 100 ° C. An unvulcanized rubber composition was obtained (finish kneading step).
The obtained unvulcanized rubber composition is molded into a clinch apex shape, bonded to another tire member, and vulcanized at 160 ° C. for 20 minutes to produce a test tire (size: 195 / 65R15). did. Moreover, the vulcanized rubber composition was produced by vulcanizing the obtained unvulcanized rubber composition at 160 ° C. for 20 minutes.

The following evaluation was performed about the obtained unvulcanized rubber composition, the vulcanized rubber composition, and the test tire. The results are shown in Tables 1 and 2. The reference formulations in Tables 1 and 2 were Comparative Examples 1 and 2, respectively.

(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. Then, the elongation at break of the deteriorated product of the reference comparative example was taken as 100, and the elongation at break of the deteriorated product of each formulation was indicated by an index according to the following formula. It shows that it is excellent in deterioration-resistant performance, so that a numerical value is large. If the degradation resistance index was 80 or more, it was judged that there was no practical problem.
(Degradation resistance index) = (Break elongation of deteriorated product of each formulation) / (Break elongation of deteriorated product of reference comparative example) × 100

(Processability)
Based on JIS K6300, the Mooney viscosity of the unvulcanized rubber composition was measured at 100 ° C. Then, with the Mooney viscosity of the reference comparative example as 100, the Mooney viscosity of each formulation was displayed as 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.
(Processability index) = (Mooney viscosity of reference comparative example) / (Mooney viscosity of each formulation) × 100

(Rolling resistance characteristics)
A rubber slab sheet (vulcanized rubber composition) of 2 mm × 130 mm × 130 mm was prepared, and a test piece for measurement was cut out from the rubber slab sheet, using a viscoelastic spectrometer VES (manufactured by Iwamoto Seisakusho Co., Ltd.), at a temperature of 50 ° C. Under the conditions of initial strain 10%, dynamic strain 2%, and frequency 10Hz, tan δ of each vulcanized rubber composition was measured, and the rolling resistance index of the standard blend was set to 100. displayed. The smaller the index, the lower the rolling resistance and the better the rolling resistance characteristics (low fuel consumption).
(Rolling resistance index) = (tan δ of each formulation / tan δ of the standard formulation) × 100

(durability)
Using a drum (outer diameter: 1.7 m), the manufactured test tire was subjected to rim (15 × 6.00 JJ), load (6.96 kN), internal pressure (250 kPa), speed (100 km / h). The tire was disassembled after running, and the surface shape of the bead portion (clinch apex rubber) was compared with a new tire to evaluate the scraping amount. The durability was indicated by an index according to the following calculation formula, with the amount of scraping of the reference blend as 100. (Average of 3 places on the circumference and 6 places on the left and right). It shows that it is excellent in durability (rim-proofing resistance), so that a numerical value is small.
(Durability index) = (Abrasion amount of each composition / Abrasion amount of the standard composition) × 100

From Tables 1 and 2, examples including at least one diene rubber selected from the group consisting of natural rubber, epoxidized natural rubber, and butadiene rubber, and myrcene polymer are used to reduce the amount of weight loss derived from petroleum resources. In addition to being able to reduce, degradation resistance, workability, durability, and rolling resistance characteristics could be improved.

Claims (6)

Including a rubber component and a myrcene polymer;
A rubber composition for clinch apex, wherein the rubber component comprises at least one diene rubber selected from the group consisting of natural rubber, epoxidized natural rubber, and butadiene rubber. The rubber composition for clinch apex according to claim 1, wherein the myrcene polymer has a weight average molecular weight of 1,000 to 500,000. The rubber composition for clinch apex according to claim 1 or 2, wherein the total content of natural rubber and butadiene rubber in 100% by mass of the rubber component is 50% by mass or more. The rubber composition for clinch apex according to any one of claims 1 to 3, wherein a total content of natural rubber and epoxidized natural rubber in 100% by mass of the rubber component is 50% by mass or more. The rubber composition for clinch apex according to any one of claims 1 to 4, comprising 0.5 to 10 parts by mass of a compound represented by the following formula (I) with respect to 100 parts by mass of the rubber component.

(In the formula, E represents an alkylene group having 2 to 10 carbon atoms, and R ¹⁰¹ and R ¹⁰² are the same or different and each represents a monovalent organic group containing a nitrogen atom.) The pneumatic tire which has a clinch apex produced using the rubber composition in any one of Claims 1-5.