JP2014114414A - Rubber composition for tread, and pneumatic tire - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a rubber composition for a tread in which while a used amount of a raw material derived from an oil resource can be reduced, and favorable grip performance is maintained or improved, processability, a high mileage property, and a fracture characteristic can be improved; and a pneumatic tire using the same.SOLUTION: A rubber composition for a tread includes: 25-60 pts.mass of silica; at most 5 pts.mass of carbon black; and 1-100 pts.mass of a myrcene polymer based on 100 pts.mass of a rubber constituent including a natural rubber and/or a modified natural rubber.

Description

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

In recent years, environmental issues have become more important and regulations on CO ₂ emissions have been strengthened. In addition, oil resources are limited, and in the future, it may become difficult to supply raw materials derived from petroleum resources such as carbon black, and oil prices are expected to rise due to a decrease in supply volume year by year. The Therefore, it is required to replace raw materials derived from petroleum resources with raw materials derived from resources other than petroleum.

At present, in the tires that are generally marketed, more than half of the total mass is composed of raw materials derived from petroleum resources. For example, a general tire for a passenger car contains about 20% by mass of synthetic rubber, about 20% by mass of carbon black, a softening agent, synthetic fiber, etc., so that about 50% by mass or more of the entire tire is a raw material derived from petroleum resources. It is composed of Thus, development of rubber for tires using raw materials derived from natural resources, which are raw materials derived from resources other than petroleum, is desired. However, for example, the tread rubber constituting the tread portion of the tire is required to maintain grip performance while reducing the rolling resistance of the tire. As in the case of using the above raw materials, the tire rubber is required to have basic performance according to the applied member.

On the other hand, while reducing the amount of raw materials derived from petroleum resources, it suppresses the increase in tire rolling resistance caused by increased hysteresis loss, specifically loss tangent (tan δ), due to heat generated during running. For the purpose of improving fuel economy, it has also been proposed to replace carbon black, which is blended in a large amount as a reinforcing filler, with silica.

Even if carbon black is replaced with silica, a rubber having relatively good durability can be obtained. However, when silica is blended, there is a tendency that a problem of deterioration in workability due to an increase in viscosity tends to occur when a rubber composition is prepared. is there. On the other hand, there is a method of using a surfactant-based processing aid for silica for improving processability, but there is a problem that such processing aid is derived from petroleum resources.

As a rubber composition containing silica, for example, Patent Document 1 discloses that 30 parts by mass or more of silica having a BET specific surface area of less than 150 m ² / g and 100% by mass of carbon black with respect to 100 parts by mass of a rubber component made of natural rubber. A rubber composition for an inner liner containing 5 parts by mass or less has been proposed. However, this technique aims to improve the fuel efficiency of the inner liner, and no consideration is given to the tread rubber and the performance required for it. Further, Patent Document 2 shows an example in which the same rubber composition is applied to the tread formulation, but there is room for improvement in terms of low fuel consumption and improvement in fracture characteristics necessary for tires.

JP 2006-249147 A JP 2009-1665 A

The present invention solves the above-described problems, and can reduce the amount of raw materials derived from petroleum resources, and can maintain or improve good grip performance while improving processability, fuel efficiency, and fracture characteristics. It is an object to provide a product and a pneumatic tire using the same.

The present invention relates to a tread containing 25 to 60 parts by mass of silica, 5 parts by mass or less of carbon black, and 1 to 100 parts by mass of a myrcene polymer with respect to 100 parts by mass of a rubber component containing natural rubber and / or modified natural 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 the softening agent containing the myrcene polymer is preferably 1 to 30 parts by mass with respect to 100 parts by mass of the rubber component.

It is preferable that the rubber composition for tread does not substantially contain carbon black.

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

According to the present invention, 25 to 60 parts by mass of silica, 5 parts by mass or less of carbon black, and 1 to 100 parts by mass of myrcene polymer with respect to 100 parts by mass of a rubber component containing natural rubber and / or modified natural rubber. Since it is a rubber composition for treads, the amount of raw materials derived from petroleum resources can be reduced, and while maintaining or improving good grip performance, processability, fuel efficiency, fracture characteristics can be improved, grip performance, It is possible to provide a pneumatic tire excellent in fuel efficiency and breaking characteristics.

The rubber composition for a tread of the present invention has 25 to 60 parts by mass of silica, 5 parts by mass or less of carbon black, and 1 myrcene polymer with respect to 100 parts by mass of a rubber component containing natural rubber and / or modified natural rubber. Contains 100 parts by mass.

In the present invention, by blending a rubber component containing natural rubber and / or modified natural rubber with a predetermined amount of silica and myrcene polymer, the amount of raw material derived from petroleum resources can be reduced and good grip performance ( In particular, it is possible to improve workability, fuel efficiency, and fracture characteristics (breaking strength, elongation at break) while maintaining or improving wet grip performance. In the present invention, natural rubber and / or modified natural rubber, which is a raw material derived from resources other than petroleum, silica, and myrcene polymer, and the blending amount of carbon black, which is a raw material derived from petroleum resources, is a predetermined amount or less. Since it is suppressed, the amount of raw materials derived from petroleum resources can be reduced. Here, the predetermined amount or less of carbon black is a concept including a case where carbon black is not blended.

In the present invention, natural rubber (NR) and / or modified natural rubber (modified NR) is used as the rubber component. Thereby, while being able to reduce the usage-amount of the raw material derived from a petroleum resource, workability, a fuel-consumption property, and a destructive characteristic can be improved, maintaining or improving favorable grip performance. In addition, NR and modified | denatured NR may be used independently and may use 2 or more types together.

As the NR, for example, those commonly used in the tire industry such as SIR20, RSS # 3, TSR20 can be used. Further, deproteinized natural rubber (DPNR) may be used as NR.

The content of NR in 100% by mass of the rubber component is preferably 60% by mass or more, more preferably 80% by mass or more, and may be 100% by mass. If the amount is less than 60% by mass, the amount of raw materials derived from petroleum resources cannot be sufficiently reduced, and processability, fuel efficiency, and fracture characteristics cannot be sufficiently improved while maintaining or improving good grip performance. There is a fear.

The modified NR is not particularly limited as long as it is a modified NR, and examples thereof include epoxidized natural rubber (ENR), grafted natural rubber, and hydrogenated natural rubber. Among these, ENR is preferable because the effects of the present invention (particularly, the effect of improving processability, wet grip performance, and fuel efficiency) can be obtained more suitably.

As ENR, a commercially available product may be used, or an NR epoxidized product may be used. The method for epoxidizing NR is not particularly limited, and examples thereof include a chlorohydrin method, a direct oxidation method, a hydrogen peroxide method, an alkyl hydroperoxide method, and a peracid method. Examples of the peracid method include a method of reacting an organic peracid such as peracetic acid or performic acid as an epoxidizing agent with an emulsion of natural rubber.

The epoxidation rate of ENR is preferably 5 mol% or more, and more preferably 10 mol% or more. When the epoxidation rate is less than 5 mol%, the glass transition temperature of ENR is low, so that wet grip performance and fracture characteristics tend to be reduced. The epoxidation rate of the epoxidized natural rubber (ENR) is preferably 60 mol% or less, and more preferably 50 mol% or less. When the epoxidation rate exceeds 60 mol%, the tread rubber composition tends to be too hard and the fracture characteristics tend to be lowered.
Here, 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 the modified NR (particularly ENR) in 100% by mass of the rubber component is preferably 60% by mass or more, more preferably 80% by mass or more, and may be 100% by mass. If the amount is less than 60% by mass, the amount of raw materials derived from petroleum resources cannot be sufficiently reduced, and processability, fuel efficiency, and fracture characteristics cannot be sufficiently improved while maintaining or improving good grip performance. There is a fear.

The total content of NR and modified NR in 100% by mass of the rubber component is preferably 60% by mass or more, more preferably 80% by mass or more, and may be 100% by mass. If the amount is less than 60% by mass, the amount of raw materials derived from petroleum resources cannot be sufficiently reduced, and processability, fuel efficiency, and fracture characteristics cannot be sufficiently improved while maintaining or improving good grip performance. There is a fear.

In addition to NR and modified NR, rubber components that can be used in the present invention include, for example, butadiene rubber (BR), styrene butadiene rubber (SBR), styrene isoprene butadiene rubber (SIBR), ethylene propylene diene rubber (EPDM), chloroprene rubber ( CR), acrylonitrile butadiene rubber (NBR), diene rubber such as butyl rubber (IIR). A rubber component may be used independently and may use 2 or more types together.

In the present invention, a myrcene polymer is used. 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). However, in the present invention, simply referring to myrcene means β-myrcene (a compound having the following structure).

In the present invention, by blending a myrcene polymer as a softening agent, processability, fuel efficiency, and fracture characteristics can be improved while maintaining or improving good grip performance. In addition, since myrcene, which is a monomer component, is an organic compound that exists in nature, the amount of raw material derived from petroleum resources can be reduced by blending a myrcene polymer. The myrcene polymer is preferably blended in place of a softening agent such as oil that has been blended in conventional tread rubber. 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 3000 or more, and still more preferably 10,000 or more. If Mw is less than 1000, the polymer tends to be a liquid polymer with particularly high fluidity, and the fuel efficiency tends to deteriorate due to the increased mobility of the molecular chain terminal of the polymer. Mw is preferably 500,000 or less, more preferably 350,000 or less, still more preferably 250,000 or less, and particularly preferably 150,000 or less. When Mw exceeds 500,000, the viscosity of the rubber composition increases and the processability and fracture characteristics (particularly processability) 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.

The weight average molecular weight (Mw) / number average molecular weight (Mn) of the myrcene polymer is preferably 20.0 or less, more preferably 10.0 or less. When Mw / Mn exceeds 20.0, wet grip performance tends to deteriorate due to a decrease in the hardness of the rubber composition. On the other hand, there is no restriction | limiting in particular about the lower limit of Mw / Mn, For example, if it is 1.0 or more, there will be no trouble. In addition, in this specification, a weight average molecular weight (Mw) and a number average molecular weight (Mn) can be measured by the method as described in an Example.

The Mooney viscosity ML _{1 + 4} (130 ° C.) of the myrcene polymer is lower than that of the same molecular weight polymer in which the myrcene constituting the polymer is replaced with a conjugated diene compound (for example, butadiene). As long as the processability is improved, the processability is not particularly limited, but is generally preferably 15 or more, and more preferably 20 or more. If the Mooney viscosity is less than 15, the fluidity becomes too high, and the wet grip performance and fracture characteristics of the rubber composition tend to be lowered. On the other hand, the Mooney viscosity is preferably 160 or less, more preferably 150 or less, still more preferably 100 or less, particularly preferably 60 or less, and most preferably 40 or less. If the Mooney viscosity exceeds 160, the processability tends to decrease.
In addition, in this specification, Mooney viscosity ML1 _{+ 4} (130 degreeC) can be 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 1 part by mass or more, preferably 3 parts by mass or more, more preferably 8 parts by mass or more, and further preferably 12 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, the workability, fuel efficiency and fracture characteristics cannot be sufficiently improved while maintaining or improving good grip performance. The content of the myrcene polymer is 100 parts by mass or less, preferably 50 parts by mass or less, more preferably 40 parts by mass or less, and still more preferably 25 parts by mass or less. If it exceeds 100 parts by mass, fuel efficiency and destructive properties will be reduced.

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 30 parts by mass, more preferably 5 to 25 parts by mass, and 12 to 20 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 compounded by replacing part or all of a softening agent such as oil that is conventionally blended in the tread rubber as a softening agent. The content of the myrcene polymer is preferably 25% by mass or more, more preferably 50% by mass or more, still more preferably 80% by mass or more, and may be 100% by mass. Thereby, the effect of this invention is acquired more suitably.

The rubber composition of the present invention contains silica. As a result, the amount of raw materials derived from petroleum resources can be reduced, reinforcement can be improved, fuel economy can be improved, and good grip performance can be maintained or improved while improving workability, fuel efficiency, and fracture characteristics. Can improve.

Examples of the silica include, but are not limited to, dry process silica (anhydrous silicic acid), wet process silica (hydrous silicic acid), and wet process silica is preferable because of its large number of silanol groups.

The nitrogen adsorption specific surface area (N ₂ SA) of silica is preferably 100 m ² / g or more, more preferably 150 m ² / g or more. If it is less than 100 m < ² > / g, there exists a tendency for elongation at break and fracture strength to fall. The N ₂ SA is preferably 220 m ² / g or less, more preferably 200 m ² / g or less. If it exceeds 220 m ² / g, fuel economy and processability tend to be reduced.
The _N 2 SA of silica is a value determined by the BET method in accordance with ASTM D3037-93.

The content of silica is 25 parts by mass or more, preferably 30 parts per 100 parts by mass of the rubber component.
More than part by mass. If the amount is less than 25 parts by mass, sufficient grip performance, low fuel consumption and breaking characteristics cannot be obtained. Further, the content of silica is 60 parts by mass or less, preferably 50 parts by mass or less. If it exceeds 60 parts by mass, the processability, fuel efficiency, and fracture characteristics are degraded.

The rubber composition of the present invention 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 fracture characteristics tend to be greatly reduced. Further, the content of the silane coupling agent is preferably 20 parts by mass or less, more 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.

The rubber composition of the present invention may contain carbon black. Although it does not specifically limit as carbon black, GPF, FEF, HAF, ISAF, SAF, etc. can be used.

Carbon black is a raw material derived from petroleum resources, and it is desirable to reduce the amount of use, and there is a risk of deteriorating fuel economy, so the carbon black content is based on 100 parts by mass of the rubber component. It is further preferably 5 parts by mass or less, preferably 3 parts by mass or less, more preferably 0.5 parts by mass or less, and substantially no blending (0 parts by mass).

The content of silica in 100% by mass of silica and carbon black is preferably 85% by mass or more, more preferably 90% by mass or more, and may be 100% by mass. Thereby, the effect of this invention is acquired more suitably.

The rubber composition of the present invention preferably contains a vulcanization accelerator. Examples of the vulcanization accelerator include sulfenamide, thiazole, thiuram, thiourea, guanidine, dithiocarbamic acid, aldehyde-amine or aldehyde-ammonia, imidazoline, or xanthate vulcanization accelerators. Etc. These vulcanization accelerators may be used alone or in combination of two or more. Of these, sulfenamide-based vulcanization accelerators are preferable because the effects of the present invention can be obtained more suitably.

Examples of the sulfenamide vulcanization accelerator include N-tert-butyl-2-benzothiazolylsulfenamide (TBBS), N-cyclohexyl-2-benzothiazolylsulfenamide (CBS), N, N -Dicyclohexyl-2-benzothiazolylsulfenamide (DCBS) and the like. Among these, CBS is preferable because the effects of the present invention can be obtained more suitably.

The content of the vulcanization accelerator is preferably 0.3 parts by mass or more, more preferably 1 part by mass or more with respect to 100 parts by mass of the rubber component. The content is preferably 5 parts by mass or less, more preferably 3 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.

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.

In addition to the above components, the rubber composition of the present invention includes compounding agents commonly used in the production of rubber compositions, such as zinc oxide, stearic acid, various anti-aging agents, tackifiers, waxes, sulfur and the like. Vulcanizing agents and the like can be appropriately blended.

As a method for producing the rubber composition of the present invention, a known method can be used. For example, the above components are kneaded using a rubber kneader such as an open roll or a Banbury mixer, and then vulcanized. Can be manufactured.

The rubber composition of the present invention can be suitably used for a tire tread (cap tread).

The pneumatic tire of the present invention can be produced by a usual method using the rubber composition.
That is, the rubber composition containing the above components is extruded in accordance with the shape of the tread at an unvulcanized stage and molded together with other tire members on a tire molding machine by a normal method. A vulcanized tire can be formed. A tire is obtained by heating and pressurizing the unvulcanized tire 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 usual 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)
Isoprene: Isoprene butylhydroxytoluene manufactured by Wako Pure Chemical Industries, Ltd .: Dibutylhydroxytoluene isopropanol manufactured by Tokyo Chemical Industry Co., Ltd .: Isopropanol manufactured by Kanto Chemical Co., Ltd. (special grade)
Butadiene: 1,3-butadiene produced by Takachiho Chemical Co., Ltd.

<Preparation of catalyst solution (1)>
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 catalyst solution (1).

<Preparation of catalyst solution (2)>
In the above <Preparation of catalyst solution (1)>, except that myrcene was replaced with isoprene, the same treatment as in the above <Preparation of catalyst solution (1)> was performed to obtain catalyst solution (2).

<Production Example 1 (Synthesis of 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 (1) 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 methanol separately prepared, and the precipitate thus obtained was air-dried overnight and further dried under reduced pressure for 2 days to obtain 100 g of polymer 1. The polymerization conversion rate (percentage of “dry weight / charge amount”) was almost 100%.

<Production Example 2 (Synthesis of Polymer 2)>
100 g of polymer 2 was obtained in the same manner as in Production Example 1, except that 100 g of butadiene was used instead of 100 g of myrcene and catalyst solution (1) was used as catalyst solution (2). The polymerization conversion was almost 100%.

The obtained polymers 1 and 2 were evaluated as follows.

(Measurement of weight average molecular weight (Mw), number average molecular weight (Mn))
Mw and Mn are based on values measured by gel permeation chromatograph (GPC) (GPC-8000 series manufactured by Tosoh Corporation, detector: differential refractometer, column: TSKGEL SUPERMALTPORE HZ-M manufactured by Tosoh Corporation). Was obtained by standard polystyrene conversion.

(Mooney viscosity)
In accordance with JIS K 6300-1 “Unvulcanized rubber—physical properties—Part 1: Determination of viscosity and scorch time using Mooney viscometer”, it was heated by preheating for 1 minute using a Mooney viscosity tester. Under the temperature condition of 130 ° C., the small rotor was rotated, and the Mooney viscosity (ML _{1 + 4} , 130 ° C.) of the polymer after 4 minutes was measured. The numbers after the decimal point are rounded off.

Mw, Mw / Mn, and ML _{1 + 4} (130 ° C.) of Polymer 1 were 56000, 3.8, and 21, respectively. Mw, Mw / Mn, and ML _{1 + 4} (130 ° C.) of Polymer 2 were 57000, 3.8, and 22, respectively.

Hereinafter, various chemicals used in Examples and Comparative Examples will be described together.
NR: TSR20
ENR: ENR-25 manufactured by MRB (Malaysia) (epoxidation rate: 25 mol%)
BR: BR150B manufactured by Ube Industries, Ltd. (cis content: 97% by mass, ML1 + 4 (100 ° C.): 40, 5% toluene solution viscosity at 25 ° C .: 48 cps, Mw / Mn: 3.3)
Silica: ULTRASIL VN3 manufactured by Degussa (N ₂ SA: 175 m ² / g)
Carbon Black: Show Black N220 (N ₂ SA: 125 m ² / g) manufactured by Cabot Japan
Silane coupling agent: Si69 (bis (3-triethoxysilylpropyl) tetrasulfide) manufactured by Tegussa
Polymers 1 and 2: Polymers 1 and 2 obtained in Production Examples 1 and 2 above
Vegetable oil: Process X-140 manufactured by Japan Energy Co., Ltd.
Oil: Mineral oil PW-380 manufactured by Idemitsu Kosan Co., Ltd.
Anti-aging agent: NOCRACK 6C (N-1,3-dimethylbutyl-N′-phenyl-p-phenylenediamine) manufactured by Ouchi Shinsei Chemical Co., Ltd.
Stearic acid: Zinc stearate oxide made by NOF Corporation: Zinc Hua No. 1 made by Mitsui Mining & Smelting Co., Ltd. Wax: Sunnock wax N made by Ouchi Shinsei Chemical Co., Ltd.
Sulfur: Powder sulfur vulcanization accelerator manufactured by Tsurumi Chemical Co., Ltd .: Noxeller CZ (N-cyclohexyl-2-benzothiazolylsulfenamide) manufactured by Ouchi Shinsei Chemical Industry Co., Ltd.

In accordance with the formulation shown in Table 1, using a 1.7L Banbury mixer manufactured by Kobe Steel, the components other than sulfur and vulcanization accelerator were filled so that the filling rate would be 58%, and the rotational speed was 80 rpm. And kneading for 3 minutes until reaching 140 ° C. Next, sulfur and a vulcanization accelerator were added to the obtained kneaded material in the amounts shown in Table 1, and then kneaded at 80 ° C. for 5 minutes using an open roll to obtain an unvulcanized rubber composition. . The obtained unvulcanized rubber composition was press vulcanized at 170 ° C. for 12 minutes to obtain a vulcanized rubber composition.

The unvulcanized rubber composition and the vulcanized rubber composition were evaluated as follows, and the results are shown in Table 1.

(Mooney viscosity)
According to JIS K6300-1, the Mooney viscosity of the unvulcanized rubber composition was measured at 130 ° C., and the Mooney viscosity of Comparative Example 1 was taken as 100, and the index was expressed by the following calculation formula. The larger the index, the lower the viscosity and the easier the processing (excellent processability).
Mooney viscosity index = (Mooney viscosity of Comparative Example 1) / (Mooney viscosity of each example) × 100

(Wet grip performance)
Wet grip performance was evaluated using a flat belt friction tester (FR5010 type) manufactured by Ueshima Seisakusho. A cylindrical rubber test piece having a width of 20 mm and a diameter of 100 mm made of the above vulcanized rubber composition was used as a sample, and the slip ratio of the sample with respect to the road surface was 0 to 0 at a speed of 20 km / hour, a load of 4 kgf, and a road surface temperature of 20 ° C. The maximum value of the friction coefficient detected at that time was read up to 70%. And the measurement result was displayed as an index according to the following formula. A larger index indicates better wet grip performance.
(Wet grip performance index) = (maximum friction coefficient of each formulation) / (maximum friction coefficient of Comparative Example 1) × 100

(Low fuel consumption)
Using a spectrometer manufactured by Ueshima Seisakusho, tan δ of the vulcanized rubber composition was measured at a dynamic strain amplitude of 1%, a frequency of 10 Hz, and a temperature of 50 ° C. And the measurement result was displayed as an index according to the following formula. The larger the index, the lower the rolling resistance and the better the fuel efficiency.
(Low fuel consumption index) = (tan δ of Comparative Example 1) / (tan δ of each formulation) × 100

(Destructive properties)
A test piece was cut out from the vulcanized rubber composition, and subjected to a tensile test using a No. 3 dumbbell according to JIS K6251 “Vulcanized rubber and thermoplastic rubber—How to obtain tensile properties”. TB) and elongation at break (EB) were measured, and the results of Comparative Example 1 were indicated as 100, respectively. The larger the index, the better the fracture characteristics.

Examples that contain 25-60 parts by mass of silica, 5 parts by mass or less of carbon black, and 1-100 parts by mass of myrcene polymer with respect to 100 parts by mass of the rubber component containing natural rubber and / or modified natural rubber are petroleum In addition to reducing the amount of resource-derived raw materials used, it was possible to improve processability, fuel efficiency and fracture characteristics while maintaining or improving good grip performance.

Claims (5)

A rubber composition for a tread containing 25 to 60 parts by mass of silica, 5 parts by mass or less of carbon black, and 1 to 100 parts by mass of a myrcene polymer with respect to 100 parts by mass of a rubber component containing natural rubber and / or modified natural rubber. . The rubber composition for a tread according to claim 1, wherein the myrcene polymer has a weight average molecular weight of 1,000 to 500,000. The rubber composition for a tread according to claim 1 or 2, wherein a total content of the softening agent containing the myrcene polymer is 1 to 30 parts by mass with respect to 100 parts by mass of the rubber component. The rubber composition for a tread according to any one of claims 1 to 3, which contains substantially no carbon black. The pneumatic tire which has a tread produced using the rubber composition in any one of Claims 1-4.