JP2014145064A - Rubber composition for clinch apex and pneumatic tire - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a rubber composition for clinch apex capable of improving low fuel consumption property and durability (rim chafing resistance) while maintaining or improving good processability even when replacing a material derived from an oil resource with a material derived from other than oil resource, and to provide a pneumatic tire using the same.SOLUTION: There is provided a rubber composition for clinch apex containing a modified natural rubber having the phosphorus content of 200 ppm or less, and a myrcene polymer, and having a weight average molecular weight of the myrcene polymer of 1000 to 500000.

Description

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

Since the clinch apex of a tire is in contact with the rim, the rubber composition for the clinch apex has conventionally had a phenomenon in which the portion that contacts the rim during running is scraped in addition to natural rubber (NR) exhibiting excellent tear strength (rim) In order to improve (chafing), butadiene rubber (BR) and carbon black have been blended to improve wear resistance and reinforcement.

However, in recent years, the reserves of petroleum resources themselves have decreased year by year, and the supply of petroleum resource-derived materials such as BR and carbon black is considered uneasy in the future. Efforts are being made to replace materials derived from petroleum resources with materials derived from resources other than petroleum, such as NR, silica, and softeners derived from resources other than petroleum.

In addition to this, environmental issues have become more important, and rubber compositions that improve rolling resistance characteristics (low fuel consumption) have been actively developed in order to suppress CO ₂ emissions during driving. The rubber composition for clinch apex is no exception.

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 in particular, tire rolling resistance increases (rolling resistance characteristics deteriorate) and fuel economy tends to deteriorate (low fuel consumption deteriorates). There is.

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 there is still room for improvement in processability, fuel efficiency and durability (rim-proofing resistance).

JP 2003-64222 A

The present invention solves the above-mentioned problems, and even when a material derived from petroleum resources is replaced with a material derived from non-petroleum resources, while maintaining or improving good processability, low fuel consumption and durability (resistance resistance) An object of the present invention is to provide a rubber composition for a clinch apex capable of improving the rim chafing property and a pneumatic tire using the same.

The present invention relates to a rubber composition for clinch apex comprising a modified natural rubber having a phosphorus content of 200 ppm or less and a myrcene polymer, wherein the myrcene polymer has a weight average molecular weight of 1,000 to 500,000.

The nitrogen content of the modified natural rubber is preferably 0.3% by mass or less, and the gel content measured as a toluene insoluble content is preferably 20% by mass or less.

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

The modified natural rubber is a step of saponifying natural rubber latex to prepare a saponified natural rubber latex (A), and a step of alkali-treating the agglomerated rubber obtained by agglomerating the saponified natural rubber latex ( B) and the step (C) of washing until the phosphorus content contained in the rubber is 200 ppm or less are preferred.

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

According to the present invention, the rubber composition for clinch apex includes a modified natural rubber having a phosphorus content of 200 ppm or less and a myrcene polymer, and the myrcene polymer has a weight average molecular weight of 1,000 to 500,000. Even if the material derived from petroleum resources is replaced with a material derived from non-oil resources, while maintaining or improving good processability, it is possible to improve fuel efficiency and durability (rim chafing resistance) It is possible to provide a pneumatic tire with excellent fuel efficiency and durability (rim chafing resistance). In addition, because it uses rubber components derived from non-petroleum resources (modified natural rubber) and softeners (myrcene polymer), it is environmentally friendly and prepares for future reductions in oil supply. A pneumatic tire having excellent performance can be provided.

The rubber composition for clinch apex of the present invention includes a modified natural rubber having a phosphorus content of 200 ppm or less and a myrcene polymer, and the weight average molecular weight of the myrcene polymer is 1000 to 500,000.

By using the modified natural rubber in which the phospholipids contained in the natural rubber are reduced and removed, the fuel efficiency can be improved. Moreover, the unvulcanized rubber composition containing the modified natural rubber is excellent in processability and can be sufficiently kneaded without performing a special kneading process. In addition to reducing not only phospholipids but also proteins and gels, these performances can be further improved. As described above, when the modified natural rubber is used, good processability and low fuel consumption can be obtained, but there is a problem that the rim chafing resistance is lowered as compared with the case where the natural rubber is used. Newly found. In response to this newly generated problem, in the present invention, by combining the modified natural rubber with a myrcene polymer having a specific molecular weight, which is a softener derived from non-petroleum resources, good processability can be obtained. While maintaining or improving, fuel economy and durability (rim chafing resistance) can be improved. In addition, because it uses rubber components derived from non-petroleum resources (modified natural rubber) and softeners (myrcene polymer) derived from non-petroleum resources, it is environmentally friendly and can prepare for future reductions in oil supply. .

The modified natural rubber has a phosphorus content of 200 ppm or less. If it exceeds 200 ppm, tan δ will increase and fuel efficiency will deteriorate, or the Mooney viscosity of unvulcanized rubber will increase and processability will tend to deteriorate. The phosphorus content is preferably 150 ppm or less, more preferably 100 ppm or less, and even more preferably 75 ppm or less. Here, the phosphorus content can be measured by a conventional method such as ICP emission analysis. Phosphorus is derived from phospholipids (phosphorus compounds).

In the modified natural rubber, the nitrogen content is preferably 0.3% by mass or less, more preferably 0.15% by mass or less, and further preferably 0.1% by mass or less. When the nitrogen content exceeds 0.3% by mass, the Mooney viscosity increases during storage and the processability tends to deteriorate, or the fuel efficiency tends to deteriorate. The nitrogen content can be measured by a conventional method such as Kjeldahl method. Nitrogen is derived from protein.

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

The modified natural rubber is preferably substantially free of phospholipids. “Substantially free of phospholipid” represents a state in which a natural rubber sample is extracted with chloroform and a peak due to phospholipid does not exist at −3 ppm to 1 ppm in ³¹ P-NMR measurement of the extract. The peak of phosphorus present at -3 ppm to 1 ppm is a peak derived from the phosphate structure of phosphorus in the phospholipid.

The modified natural rubber can be obtained, for example, by the production method described in JP 2010-138359 A. Among them, the process (A) of preparing a saponified natural rubber latex by saponifying the natural rubber latex, A production method comprising a step (B) of subjecting the agglomerated rubber obtained by agglomerating the saponified natural rubber latex to an alkali treatment and a step (C) of washing until the phosphorus content contained in the rubber is 200 ppm or less. What is prepared is preferred. By this manufacturing method, phosphorus content, nitrogen content, etc. can be reduced effectively. Further, by using the modified natural rubber obtained by the production method, the fuel economy and processability can be remarkably improved, and these performances can be obtained at a high level. Further, when the agglomeration with acid is performed, the remaining acid is neutralized with an alkali treatment, whereby deterioration of the rubber by the acid can be prevented.

In the production method described above, the saponification treatment can be performed by adding an alkali and, if necessary, a surfactant to natural rubber latex and allowing to stand at a predetermined temperature for a certain time. In addition, you may perform stirring etc. as needed. According to the above production method, the phosphorus content and nitrogen content of natural rubber can be suppressed.

As the natural rubber latex, conventionally known latexes such as raw latex, purified latex, and high ammonia latex can be used. Examples of the alkali used for the saponification treatment include sodium hydroxide, potassium hydroxide, calcium hydroxide, and amine compounds, and sodium hydroxide and potassium hydroxide are particularly preferable. As the surfactant, known anionic surfactants, nonionic surfactants, and amphoteric surfactants can be used. Of these, anionic surfactants are preferred, and sulfonic acid anions are preferred. A surfactant is more preferable.

In the saponification treatment, the amount of alkali added may be set as appropriate, but is preferably 0.1 to 10 parts by mass with respect to 100 parts by mass of the solid content of the natural rubber latex. The addition amount of the surfactant is preferably 0.01 to 6.0 parts by mass with respect to 100 parts by mass of the solid content of the natural rubber latex. The temperature and time of the saponification treatment may be set as appropriate, and is usually about 20 to 70 ° C. and about 1 to 72 hours.

After completion of the saponification reaction, the agglomerated rubber obtained by agglomerating the saponified natural rubber latex obtained by the reaction is crushed as necessary, and then the obtained agglomerated rubber or crushed rubber is brought into contact with an alkali. Perform alkali treatment. By the alkali treatment, the nitrogen content in the rubber can be efficiently reduced, and the effects of the present invention are further exhibited. Examples of the aggregation method include a method of adding an acid such as formic acid. The alkali treatment method is not particularly limited as long as it is a method in which rubber and alkali are brought into contact with each other, and examples thereof include a method in which agglomerated rubber and crushed rubber are immersed in alkali. Examples of the alkali that can be used for the alkali treatment include alkali metal carbonates such as potassium carbonate, sodium carbonate, sodium hydrogen carbonate, potassium hydrogen carbonate, lithium carbonate, lithium hydrogen carbonate, and ammonia in addition to the alkali in the saponification treatment described above. Water etc. are mentioned. Of these, alkali metal carbonates are preferable, and sodium carbonate and potassium carbonate are more preferable from the viewpoint of excellent effects of the present invention.

When the alkali treatment is performed by the above immersion, the treatment can be performed by immersing rubber (crushed rubber) in an alkaline aqueous solution having a concentration of preferably 0.1 to 5 mass%, more preferably 0.2 to 3 mass%. Thereby, the amount of nitrogen in the rubber can be further reduced.

When the alkali treatment is performed by the immersion, the temperature of the alkali treatment can be set as appropriate, but is usually preferably 20 to 70 ° C. The alkali treatment time depends on the treatment temperature, but is preferably 1 to 20 hours, more preferably 2 to 12 hours, considering sufficient treatment and productivity.

Phosphorus content can be reduced by performing a washing treatment after the alkali treatment. Examples of the washing treatment include a method of diluting a rubber component with water and washing, followed by a centrifugal separation treatment, and a method of leaving the rubber to stand and discharging the aqueous phase and taking out the rubber component. When centrifuging, it is first diluted with water so that the rubber content of the natural rubber latex is 5 to 40% by mass, preferably 10 to 30% by mass. Then, it may be centrifuged at 5000 to 10000 rpm for 1 to 60 minutes, and washing may be repeated until a desired phosphorus content is obtained. In addition, when the rubber is allowed to stand still, the addition of water and stirring may be repeated until the desired phosphorus content is obtained. The modified natural rubber in the present invention is obtained by drying after completion of the washing treatment.

The content of the modified natural rubber in 100% by mass of the rubber component contained in the rubber composition of the present invention is preferably 5% by mass or more, more preferably 20% by mass or more, still more preferably 40% by mass or more, particularly preferably. Is 60 mass% or more, and may be 100 mass%. If it is less than 5% by mass, the effect of blending the modified natural rubber may not be sufficiently obtained.

In addition to the modified natural rubber, examples of rubber components that can be used in the present invention include natural rubber (NR) (non-modified), isoprene rubber (IR), butadiene rubber (BR), styrene butadiene rubber (SBR), and styrene. Examples include diene rubbers such as isoprene butadiene rubber (SIBR), ethylene propylene diene rubber (EPDM), chloroprene rubber (CR), and acrylonitrile butadiene rubber (NBR).

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, along with the modified natural rubber, by blending a myrcene polymer having a specific molecular weight, which is a softener derived from non-petroleum resources, while maintaining or improving good processability, low fuel consumption, Durability (rim chafing resistance) can be improved. 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 softening agent such as oil conventionally blended in clinch apex 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 not particularly limited as long as it is 1000 or more, but is preferably 2000 or more, more preferably 3000 or more. If Mw is less than 1000, durability (rim chafing resistance) is significantly deteriorated. Mw is not particularly limited as long as it is 500,000 or less, more preferably 300,000 or less, still more preferably 150,000 or less, and particularly preferably 100,000 or less. When Mw exceeds 500,000, durability (rim chafing resistance) is greatly deteriorated and fuel efficiency is also deteriorated. 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 addition, in this specification, a weight average molecular weight (Mw) is obtained 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, the effect of blending the myrcene polymer tends to be insufficient. 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. If it exceeds 50 parts by mass, the fuel efficiency tends to decrease.

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.

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.

Silica is preferably blended in the rubber composition of the present invention. By blending silica together with the modified natural rubber and myrcene polymer, the fuel efficiency can be further improved while improving the processability and durability (rim chafing resistance), and the effects of the present invention are more suitable. Is obtained. 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 150 m ² / g or more. . If it is less than 10 m ² / g, sufficient reinforcement cannot be obtained, the mechanical strength and wear resistance necessary for use as a clinch apex cannot be ensured, and sufficient durability (rim chafing resistance) 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 is a possibility that the fuel efficiency is lowered.
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 3 parts by mass or more, more preferably 10 parts by mass or more, still more preferably 20 parts by mass or more, particularly preferably 40 parts by mass or more, and most preferably 100 parts by mass of the rubber component. It is 60 parts by mass or more. If it is less than 3 parts by mass, the effect of blending silica may not be sufficiently obtained. The content of the silica is preferably 150 parts by mass or less, more preferably 120 parts by mass or less, and still more preferably 100 parts by mass or less. If it exceeds 150 parts by mass, silica is difficult to disperse and processability may be deteriorated. Further, durability (rim chafing resistance) and fuel efficiency may be reduced.

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 the amount is less than 2 parts by mass, the dispersibility of silica cannot be improved, and there is a tendency that sufficient effects of improving fuel economy and durability (rim chafing resistance) cannot be obtained. 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, low fuel consumption and durability (rim chafing resistance) can be improved. As a silane compound, the compound represented by a following formula is mentioned, for example.
_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 (preferably an alkyl group having 1 to 10 carbon atoms). When Y is an alkyl group, for example, a methyl group (—CH ₃ ), for example, methyl triethoxysilane is flammable. When the point is 8 ° C. and a hexyl group (—CH ₂ (CH ₂ ) ₄ CH ₃ ), for example, hexyltriethoxysilane has a low flash point of 81 ° C., whereas when Y is a phenyl group, the flash point is 111 ° C. Therefore, a phenyl group is preferable because it is easy to handle.

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. If the content of the silane compound is less than 4 parts by mass, sufficient fuel economy and durability (rim chafing resistance) may not be improved. 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 increases meaninglessly or there is a concern that durability (rim chafing resistance) is lowered.

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

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, TBBS 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 7 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.

The rubber composition of the present invention can be produced by a general method. That is, it can be produced by a method of kneading the above components with a Banbury mixer, kneader, open roll or the like and then vulcanizing. Here, when producing a rubber composition containing natural rubber, a natural rubber mastication step is usually performed before a kneading step of each component such as a rubber component and a filler. In the present invention, since the modified natural rubber is used, the kneading step can be carried out satisfactorily without performing the kneading step, and a desired rubber composition can be produced.

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 can be produced by a usual method using the rubber composition.
That is, by extruding a rubber composition containing the above components in accordance with the shape of the clinch apex at an unvulcanized stage, and molding it on a tire molding machine together with other tire members. An unvulcanized 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 (particularly for passenger cars) such as for passenger cars, trucks, buses, heavy vehicles, etc.

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 Production Example 1 will be described together. In addition, the chemical | medical agent refine | purified according to the usual method as needed.
Natural rubber latex: Field latex surfactant obtained from Muhibah Lateks, Inc .: Emal-E27C (polyoxyethylene lauryl ether sodium sulfate) manufactured by Kao Corporation
NaOH: NaOH manufactured by Wako Pure Chemical Industries, Ltd.

(Production of saponified natural rubber)
<Production Example 1>
After adjusting solid content concentration (DRC) of natural rubber latex to 30% (w / v), 25 g of 10% Emal-E27C aqueous solution and 50 g of 40% NaOH aqueous solution are added to 1000 g of natural rubber latex (wet state), A saponification reaction was carried out at room temperature for 48 hours to obtain a saponified natural rubber latex. Water was added to the latex to dilute to DRC 15% (w / v), and then formic acid was added with slow stirring to adjust the pH to 4.0 for aggregation.
The agglomerated rubber was pulverized, dipped in a 1% aqueous sodium carbonate solution at room temperature for 5 hours, pulled up, repeatedly washed with 1000 ml of water, and then dried at 90 ° C. for 4 hours to obtain a solid rubber (HPNR).

With respect to the solid rubber (HPNR) and TSR obtained in Production Example 1, the nitrogen content, phosphorus content, and gel content were measured by the methods described below. The results are shown in Table 1.

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

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

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

As shown in Table 1, HPNR had a reduced nitrogen content, phosphorus content, and gel content as compared to TSR.
Further, in ³¹ P-NMR measurement, HPNR showed no peak due to phospholipid at -3 ppm to 1 ppm.

Hereinafter, various chemicals used in Production Example 2-5 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)
Dibutylhydroxytoluene: 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).

<Production Example 2 (Synthesis 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, 120 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 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 3 (synthesis of myrcene polymer 2)>
100 g of myrcene polymer 2 was obtained in the same manner as in Production Example 2 except that the amount of the catalyst solution (1) was changed to 6 ml.

<Production Example 4 (synthesis of myrcene polymer 3)>
100 g of myrcene polymer 3 was obtained in the same manner as in Production Example 2 except that the amount of the catalyst solution (1) was changed to 0.3 ml.

<Production Example 5 (synthesis of myrcene polymer 4)>
100 g of myrcene polymer 4 was obtained in the same manner as in Production Example 2 except that the amount of the catalyst solution (1) was changed to 0.09 ml.

The following evaluation was performed about the obtained myrcene polymers 1-4.

(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
HPNR: Modified natural rubber BR obtained in Production Example 1 above: 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)
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 2 using myrcene derived from natural resources (weight average molecular weight: 500)
Myrcene polymer 2: Myrcene polymer (softener derived from non-petroleum resources) obtained in Production Example 3 using myrcene derived from natural resources (weight average molecular weight: 10,000)
Myrcene polymer 3: Myrcene polymer (softener derived from non-petroleum resources) obtained in Production Example 4 using myrcene derived from natural resources (weight average molecular weight: 200,000)
Myrcene polymer 4: Myrcene polymer (softener derived from non-petroleum resources) obtained in Production Example 5 using myrcene derived from natural resources (weight average molecular weight: 650,000)
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.

Using a Banbury mixer, the amount of chemicals shown in Step 1 of Table 2 was charged, 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 amounts shown in Step 2 of Table 2 were added to the obtained kneaded product, and kneaded for about 3 minutes using a Banbury mixer so that the discharge temperature was 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.
In Comparative Examples 1 and 2 using NR, 0.4 parts by mass of a chelating agent was added to 100 parts by mass of NR, and then kneaded in advance. On the other hand, no mastication was performed in Comparative Examples 3-5 and Examples 1 and 2 using HPNR.

The following evaluation was performed about the obtained unvulcanized rubber composition, the vulcanized rubber composition, and the test tire. The results are shown in Table 2. The reference formulation in Table 2 was Comparative Example 1.

<Durability test>
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

<Rolling resistance test>
A rubber slab sheet (vulcanized rubber composition) measuring 2 mm × 130 mm × 130 mm was prepared, and a test piece for measurement was cut out from the rubber slab sheet. 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

<Processability index>
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 100 ° C., the small rotor was rotated, and the Mooney viscosity (ML _{1 +} 4/100 ° C.) of the unvulcanized rubber composition after 4 minutes was measured. The measurement result was set to 100 as the result of Comparative Example 1, and the Mooney viscosity of each formulation was indicated by an index according to the following formula. The larger the index, the lower the viscosity and the better the workability.
(Mooney viscosity index) = (Mooney viscosity of reference blend) / (Mooney viscosity of each blend) × 100

An embodiment including a modified natural rubber having a phosphorus content of 200 ppm or less and a myrcene polymer having a specific weight average molecular weight is a case where a material derived from petroleum resources is replaced with a material derived from resources other than petroleum, While maintaining or improving good processability, fuel economy and durability (rim chafing resistance) could be improved.

Claims (5)

A modified natural rubber having a phosphorus content of 200 ppm or less and a myrcene polymer;
A rubber composition for clinch apex, 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, wherein the nitrogen content of the modified natural rubber is 0.3% by mass or less and the gel content measured as a toluene insoluble content is 20% by mass or less. The rubber composition for clinch apex according to claim 1 or 2, wherein the modified natural rubber is obtained by saponifying natural rubber latex. The modified natural rubber is a step of saponifying natural rubber latex to prepare a saponified natural rubber latex (A), and a step of alkali treating the agglomerated rubber obtained by agglomerating the saponified natural rubber latex ( The rubber composition for clinch apex according to any one of claims 1 to 3, wherein the rubber composition is obtained by performing B) and a step (C) of washing until the phosphorus content in the rubber is 200 ppm or less. . The pneumatic tire which has the clinch apex produced using the rubber composition in any one of Claims 1-4.