WO2010055919A1

WO2010055919A1 - Rubber compositions and tires

Info

Publication number: WO2010055919A1
Application number: PCT/JP2009/069376
Authority: WO
Inventors: 基之間宮
Original assignee: 株式会社ブリヂストン
Priority date: 2008-11-13
Filing date: 2009-11-13
Publication date: 2010-05-20

Abstract

The rubber compositions comprise natural rubber and a reinforcing filler made of carbon black or carbon black and silica, and the product of the specific surface area expressed as the specific surface area of the filler to which cetyltrimethylammonium bromide is adsorbed (CTAB: m²/g), and the parts by mass of the filler B (phr) per 100 parts by mass of the natural rubber component satisfies equation (1) relative to the rebound resilience of the rubber composition. A master batch, obtained from natural rubber latex and carbon black, and a polar group-containing modified natural rubber are preferably used for the natural rubber component. Blending of agents that confer low heat build-up and processing to improve low heat build-up or abrasion resistance are also performed. (1) Rebound resistance > -0.0019 x A + 77.5 Herein, A = CTAB x B

Description

Rubber composition and tire

The present invention relates to a rubber composition suitable for use in a tire tread, and more particularly, a low heat generation suitable for use in a tire having improved wear resistance and improved tread heat generation, particularly a large tire such as an off-road tire. The present invention relates to a rubber composition having excellent wear resistance and a tire using the same.

In recent years, demands for reducing the fuel consumption of automobiles are becoming more severe in connection with the movement of global carbon dioxide emission regulations due to the social demand for energy saving and the increasing interest in environmental problems. In order to meet such demands, tires with low heat build-up with reduced rolling resistance have been demanded. In particular, for heavy-duty pneumatic tires used for trucks, buses, etc., improved heat generation is required to be reduced. Further, in a large tire such as an off-road tire, the tread rubber has a large volume so that the internal rubber is likely to store heat and deteriorates remarkably. Therefore, low hysteresis loss (low rolling resistance) and wear resistance of the tread rubber are required.
As a technique for reducing the rolling resistance of the tire, although a technique by optimizing the tire structure has been studied, the most common technique is to use a material having lower heat generation as the rubber composition. In general, in order to improve low heat buildup, it is preferable to suppress deformation of the tread rubber and lower tan δ in a high temperature range.

Especially for off-road tires, in order to improve the wear resistance, synthetic rubber components such as SBR have been used in the tread rubber composition to improve the cutting performance and the fatigue resistance. In order to improve low hysteresis loss and low heat generation, it has also been proposed to add a modified conjugated diene polymer such as a modified styrene-butadiene copolymer (see, for example, Patent Document 1). . However, if the amount of the modified conjugated diene polymer is excessively increased, the wear resistance cannot be sufficiently improved, and the fracture resistance is deteriorated.

Up to now, as a method for obtaining a rubber composition having low exothermic properties, improvement of a reinforcing filler and improvement of a rubber component have been performed.
Conventionally, carbon black has been used as a reinforcing filler for rubber. This is because carbon black can impart high wear resistance to the rubber composition. When trying to reduce heat generation, there are methods such as reducing the carbon black filling amount and using a large particle size, but rolling resistance is improved when using a large particle size carbon black. Inevitably, wear resistance is reduced. On the other hand, in order to improve the wear resistance, carbon black is atomized, the filling amount is increased, or the carbon black is made to have a high structure or have pores, thereby strengthening the interaction with the polymer and increasing the resistance. Although wear resistance is improved, there is a problem that the rolling resistance of the tire increases. Therefore, in order to solve these problems, a rubber composition in which carbon black having colloidal characteristics in a specific relationship is combined with natural rubber and / or diene synthetic rubber has been proposed (for example, Patent Document 2).

Further, silica is known as a filler for improving low heat build-up (for example, Patent Documents 3 to 6), but silica tends to aggregate particles and has wettability with rubber. Inferior, not well dispersed in rubber. If the silica is not sufficiently dispersed in the rubber, the rubber composition has a high Mooney viscosity, and there is a problem that the processability such as extrusion is poor.

On the other hand, as a method for improving the rubber component, many technological developments have been made on modified rubbers that interact with fillers such as carbon black and silica. For synthetic rubber, a method in which the polymerization active terminal of a conjugated diene polymer is modified with an alkoxysilane derivative containing a functional group that interacts with a filler has been proposed (for example, Patent Documents 7 and 8). . As for natural rubber, modified natural rubber is obtained by graft polymerizing a polar group-containing simple substance to natural rubber molecules in natural rubber latex, improving affinity with fillers and improving low loss and wear resistance. However, recently, there is a demand for further improving the low loss and wear resistance of the rubber for treads.

JP-A-9-316132 JP-A-6-157822 JP-A-6-248116 Japanese Patent Laid-Open No. 7-70369 JP-A-8-245838 JP-A-3-252431 Japanese Patent Publication No. 6-57767 Japanese Examined Patent Publication No. 6-53763 International Publication No. 2004/106397 Pamphlet

The present invention has been made in view of such circumstances, and is prepared by applying a treatment method that can achieve low heat resistance and low rolling resistance while ensuring wear resistance by the colloidal characteristics of the reinforcing filler. It is an object of the present invention to provide a rubber composition and a tire excellent in both low heat buildup and wear resistance using the rubber composition.

The present invention is a rubber composition using a reinforcing filler that meets specific conditions, and further a rubber composition that is improved in low heat buildup and wear resistance by applying another treatment method.
Conventionally, it is generally known that the product of the specific surface area and the filling amount of a filler such as carbon black or silica is inversely proportional to the resilience of the rubber composition.
The present invention relates to a specific surface area (hereinafter referred to as CTAB) (m ² / g) expressed as a cetyltrimethylammonium bromide adsorption specific surface area as a filler and a filler mass part B (phr) of the filler per 100 parts by mass of a rubber component. Is a rubber composition using a filler satisfying the following formula.
Rebound resilience> −0.0019 × A + 77.5 (1)
Where A = CTAB × B

The present invention is also a rubber composition which is processed by using one or more of the following processing methods in combination with the filler having the above characteristics.
1. Use natural rubber masterbatch.
2. Use modified natural rubber.
3. Use a low heat build-up agent.
4). A hydrazide compound is used.
5). Dipolar nitrogen and a compound having a nitrogen-containing heterocyclic ring containing oxygen or sulfur are used.
6). Increase the amount of stearic acid.
7). Perform a remill.
8). Vulcanize at low temperature.

When the rubber composition of the present invention is applied to tread rubber, a tire having both low heat buildup and wear resistance can be obtained, and is particularly suitable for large tires such as off-road tires.

In addition to using carbon black of specific conditions, or carbon black and silica as a reinforcing filler, the present invention may further contain other additives and / or various rubber components and resulting rubber compositions. This is a rubber composition that has been processed such as
In general, it is known that the product of the specific surface area and the filling amount of a filler such as carbon black or silica is inversely proportional to the resilience of the rubber composition.
In the present invention, the product of a specific surface area (CTAB) (m ² / g) expressed as an adsorption specific surface area of cetyltrimethylammonium bromide as a filler and a filler mass part B (phr) of the filler per 100 parts by mass of the rubber component It is a rubber composition using a filler satisfying the following formula.
Rebound resilience> −0.0019 × A + 77.5 (1)
Where A = CTAB × B
Here, CTAB is a value measured according to ISO6810, and rebound resilience is a value measured according to JIS K6255 (25 ° C.).

In the present invention, carbon black or carbon black and silica are used as the filler, and any filler can be appropriately selected from those usually used in the rubber industry as long as the above conditions are satisfied. Examples of carbon black include SAF, HAF, and ISAF. Examples of silica include wet silica (hydrous silicic acid), dry silica (anhydrous silicic acid), calcium silicate, aluminum silicate, and the like. And commercially available products can be used. Of these, wet silica is particularly preferred.

Next, treatments performed on the rubber composition and additives will be described.
(1) Natural rubber masterbatch In the present invention, natural rubber can be used as a masterbatch as a natural rubber component.
The masterbatch of natural rubber used in the present invention is a mixture of natural rubber latex and carbon black. The production method is preferably such that after decomposing the amide bond in the latex, natural rubber latex and carbon black in water are mixed. And a step of mixing, coagulating and drying a water slurry solution in which is dispersed.

(Preparation of aqueous dispersion slurry solution)
Prior to mixing the natural rubber latex and the water-dispersed slurry solution, a slurry solution in which carbon black is previously dispersed in water is produced. The manufacturing method of this slurry can use a well-known method, and is not specifically limited.
The water dispersion slurry of carbon black can be prepared, for example, by putting a predetermined amount of carbon black and water in a homomixer and stirring for a certain time. The concentration of carbon black in the slurry solution is preferably from 0.5 to 30% by weight, particularly preferably from 1 to 15% by weight, based on the slurry.

Carbon black has a cetyltrimethylammonium bromide (CTAB) adsorption specific surface area (m ² / g) in the range of more than 70 and less than 150. If the CTAB specific surface area is 70 or less, sufficient abrasion resistance is not ensured, and if it is 150 or more, the heat generation deteriorates. The compressed DBP oil absorption (24M4DBP, ml / 100g) is more than 50 and less than 100. If it is 50 or less, the effect of improving the wear resistance cannot be obtained, and if it is 100 or more, the wear resistance is lowered. Preferably it is 55 to 95, more preferably 70 to 95.

Regarding the particle size distribution of the carbon black in the water-dispersed slurry solution, the volume average particle size (mv) is preferably 25 μm or less and the 90% by volume particle size (D90) is preferably 30 μm or less. When the volume average particle size is 25 μm or less and the 90% by volume particle size is 30 μm or less, the carbon black dispersion in the rubber is further improved, and the reinforcing property and wear resistance are further improved.
If excessive shearing force is applied to the slurry to reduce the particle size of the carbon black, the structure of the carbon black is destroyed and the reinforcing property is lowered. Therefore, 24M4DBP oil absorption of the carbon black recovered by drying from the aqueous dispersion slurry solution The amount is preferably mixed so as to maintain 93% or more, more preferably 96% or more of the 24M4DBP oil absorption before being dispersed in water.

(Mixing process)
The mixing amount of the carbon black when mixing the natural rubber latex and the water-dispersed slurry solution is 10 to 100 parts by mass with respect to 100 parts by mass of the natural rubber component in the natural rubber latex. If it is less than 10 parts by mass, sufficient wear resistance cannot be obtained, and if it exceeds 100 parts by mass, the low heat build-up is reduced. The mixing amount of carbon black is preferably 20 to 80 parts by mass, and more preferably 30 to 60 parts by mass.
Through this mixing step, a natural rubber wet masterbatch is obtained.

(Coagulation process)
The natural rubber wet masterbatch obtained through the mixing step is preferably coagulated in the coagulation step.
As a method for coagulating the wet masterbatch, an acid such as formic acid or sulfuric acid or a salt coagulant such as sodium chloride is used as usual. Alternatively, coagulation may be performed by adding natural rubber latex and the slurry solution without adding a coagulant.

(Drying process)
It is preferable to perform a drying process as the final step of master batch production. As the dryer, ordinary dryers such as vacuum dryers, air dryers, drum dryers, band dryers, etc. can be used, but in order to further improve the dispersibility of carbon black, while applying mechanical shearing force It is preferable to dry. Thereby, rubber excellent in processability and reinforcement can be obtained. Although this drying can be performed using a general kneader, it is preferable to use a continuous kneader. Furthermore, it is more preferable to use a multi-axis kneading extruder that rotates in the same direction or in different directions.
In the step of drying while applying a shearing force, the moisture in the masterbatch before the drying step is preferably 10% or more. This is because when the water content is less than 10%, the dispersion improvement width of the carbon black in the drying process is reduced.

(Amide bond decomposition process)
The natural rubber latex used in the mixing step may be subjected to a step of decomposing the amide bond in the latex. If the amide bond is decomposed in advance, molecules are entangled by the hydrogen bondability of the amide bond, the viscosity increase of the rubber is small, and the processability can be improved.
In the amide bond decomposition step, it is preferable to use a protease and / or an aromatic polycarboxylic acid derivative. Proteases have the property of hydrolyzing amide bonds present in the surface layer components of natural rubber latex particles, and examples include acidic proteases, neutral proteases, and alkaline proteases. In the present invention, alkaline protease is particularly preferred from the viewpoint of effect. When the amide bond is decomposed by a protease, it may be carried out under conditions suitable for the enzyme to be mixed. For example, when mixing Alvarase 2.5L type DX manufactured by Novozyme with natural rubber latex, it is usually 20 to 80 ° C. It is desirable to process with a range. The pH at this time is usually in the range of 6.0 to 12.0. The amount of protease added is usually in the range of 0.01 to 2% by mass, preferably 0.02 to 1% by mass, based on the natural rubber latex.

In the method using an aromatic polycarboxylic acid derivative, the addition amount of the aromatic polycarboxylic acid derivative is preferably 0.01 to 30% by mass with respect to the natural rubber latex. If the addition amount is less than 0.01% by mass, the Mooney viscosity may not be sufficiently reduced. On the other hand, if it exceeds 30% by mass, not only the effect corresponding to the increase is obtained but also the vulcanized rubber is destroyed. May adversely affect properties. The addition amount varies within the above range depending on the type and grade of the natural rubber latex used, but it is preferably in the range of 0.05 to 20% by mass from the physical properties and cost.
The aromatic polycarboxylic acid derivative is preferably a derivative of phthalic acid, trimellitic acid, pyromellitic acid and its anhydride, specifically, monostearyl phthalate, monodecyl phthalate, monophthalic acid Examples include octylamide, polyoxyethylene lauryl phthalate, monodecyl trimellitic acid, monostearyl trimellitic acid, monostearyl pyromellitic acid, and distearyl pyromellitic acid.

In the amide bond decomposition step, it is desirable to add a surfactant for the purpose of improving the stability of the latex. As the surfactant, anionic, cationic, nonionic and amphoteric surfactants can be used, and anionic and nonionic surfactants are particularly preferable. The addition amount of the surfactant can be appropriately adjusted according to the properties of the natural rubber latex, but is usually 0.01 to 2% by mass, preferably 0.02 to 1% by mass with respect to the natural rubber latex. . The addition of the surfactant is preferably performed in the amide bond decomposition step, but is not particularly limited as long as it is at least before the mixing step.

(2) Modified natural rubber In the present invention, a modified natural rubber containing a polar group in a natural rubber molecule can be used as a natural rubber component. Modified natural rubber has a higher affinity for reinforcing fillers than unmodified natural rubber.
Examples of polar groups to be introduced include amino group, imino group, nitrile group, ammonium group, imide group, amide group, hydrazo group, azo group, diazo group, hydroxyl group, carboxyl group, carbonyl group, epoxy group, oxycarbonyl group, It is at least one selected from the group consisting of sulfide groups, disulfide groups, sulfonyl groups, sulfinyl groups, thiocarbonyl groups, nitrogen-containing heterocyclic groups, oxygen-containing heterocyclic groups, alkoxysilyl groups, and tin-containing groups.
As a natural rubber modification method, for example, a modification method described in JP-A-2007-326990 can be applied.

In the production of modified natural rubber, natural rubber latex may be used as a raw material, or at least one solid natural rubber raw material selected from the group consisting of natural rubber, natural rubber latex coagulum and natural rubber cup lamp is used. May be.
The natural rubber latex is not particularly limited, and for example, a field latex, an ammonia-treated latex, a centrifugal concentrated latex, a deproteinized latex treated with a surfactant or an enzyme, and a combination thereof can be used.
When natural rubber latex is used as a raw material, a polar group-containing modified natural rubber can be obtained by producing a polar group-containing modified natural rubber latex and further coagulating and drying.

The production method of the polar group-containing modified natural rubber latex is not particularly limited, for example,
1) A method of adding a polar group-containing monomer to natural rubber latex and graft polymerizing the polar group-containing monomer to natural rubber molecules in natural rubber latex,
2) A method of adding a polar group-containing mercapto compound to natural rubber latex and adding the polar group-containing mercapto compound to natural rubber molecules in the natural rubber latex,
3) A method of adding a polar group-containing olefin and a metathesis catalyst to natural rubber latex and reacting the polar group-containing olefin with a natural rubber molecule in the natural rubber latex using the metathesis catalyst.

The polar group-containing monomer added to the natural rubber latex is not particularly limited as long as it has at least one polar group in the molecule and can be graft-polymerized with the natural rubber molecule. Here, the polar group-containing monomer preferably has a carbon-carbon double bond in the molecule for graft polymerization with a natural rubber molecule, and is preferably a polar group-containing vinyl monomer. . These monomers containing polar groups may be used alone or in combination of two or more.

When the polar group-containing monomer is graft-polymerized to the natural rubber molecule in the natural rubber latex, the graft polymerization of the polar group-containing monomer to the natural rubber molecule is performed by emulsion polymerization. In emulsion polymerization, in general, a polar group-containing monomer is added to a solution of natural rubber latex with water and, if necessary, an emulsifier, a polymerization initiator is added, and the mixture is stirred at a predetermined temperature. It is preferable to polymerize the polar group-containing monomer. In addition, in the addition of the polar group-containing monomer to the natural rubber latex, an emulsifier may be added to the natural rubber latex in advance, or the polar group-containing monomer is emulsified with the emulsifier and then added to the natural rubber latex. May be. The emulsifier that can be used for emulsifying the natural rubber latex and / or the polar group-containing monomer is not particularly limited, and examples thereof include nonionic surfactants such as polyoxyethylene lauryl ether.

There is no restriction | limiting in particular as a polymerization initiator, The polymerization initiator for various emulsion polymerization can be used, and there is no restriction | limiting in particular also about the addition method. Examples of generally used polymerization initiators include benzoyl peroxide, hydrogen peroxide, cumene hydroperoxide, tert-butyl hydroperoxide, ditert-butyl peroxide, 2,2-azobisisobutyronitrile, , 2-azobis (2-diaminopropane) hydrochloride, 2,2-azobis (2-diaminopropane) dihydrochloride, 2,2-azobis (2,4-dimethylvaleronitrile), potassium persulfate, sodium persulfate, Examples thereof include ammonium persulfate. In order to lower the polymerization temperature, it is preferable to use a redox polymerization initiator. Examples of the reducing agent to be combined with the peroxide in the redox polymerization initiator include tetraethylenepentamine, mercaptans, acidic sodium sulfite, reducing metal ions, ascorbic acid and the like. A preferred combination of a peroxide and a reducing agent in the redox polymerization initiator includes a combination of tert-butyl hydroperoxide and tetraethylenepentamine.
In order to improve the low loss and wear resistance without reducing the processability of the rubber composition using a modified natural rubber, a small amount and a uniform amount of a polar group-containing monomer is introduced into each natural rubber molecule. Therefore, the addition amount of the polymerization initiator is preferably in the range of 1 to 100 mol%, more preferably in the range of 10 to 100 mol% with respect to the polar group-containing monomer.

Each component described above is charged into a reaction vessel and reacted at 30 to 80 ° C. for 10 minutes to 7 hours to obtain a modified natural rubber latex in which a polar group-containing monomer is graft copolymerized with a natural rubber molecule. The modified natural rubber latex is coagulated, washed, and then dried using a dryer such as a vacuum dryer, air dryer, drum dryer or the like to obtain a modified natural rubber. Here, the coagulant used for coagulating the modified natural rubber latex is not particularly limited, and examples thereof include acids such as formic acid and sulfuric acid, and salts such as sodium chloride.

Next, the polar group-containing mercapto compound which is added to the natural rubber latex and undergoes an addition reaction with the natural rubber molecule in the natural rubber latex has at least one mercapto group and the polar group other than the mercapto group in the molecule. There is no particular limitation. The mercapto compound containing a polar group may be used alone or in combination of two or more.

When the polar group-containing mercapto compound is added to the natural rubber molecule in the natural rubber latex, the polar group-containing mercapto compound is generally added to a solution obtained by adding water and, if necessary, an emulsifier to the natural rubber latex. By stirring at a temperature of 1, the polar group-containing mercapto compound is subjected to an addition reaction with the double bond of the main chain of the natural rubber molecule in the natural rubber latex. In addition, in the addition of the polar group-containing mercapto compound to the natural rubber latex, an emulsifier may be added to the natural rubber latex in advance, or the polar group-containing mercapto compound may be added to the natural rubber latex after emulsifying with the emulsifier. . Moreover, an organic peroxide can also be added as needed. In addition, it does not specifically limit as an emulsifier which can be used for emulsification of natural rubber latex and / or a polar group containing mercapto compound, Nonionic surfactants, such as polyoxyethylene lauryl ether, are mentioned.

In order to improve the low loss and wear resistance without reducing the processability of the rubber composition, it is important that the polar group-containing mercapto compound is introduced in a small amount and uniformly into each natural rubber molecule. The modification reaction is preferably carried out with stirring. For example, the above components such as natural rubber latex and polar group-containing mercapto compound are charged in a reaction vessel and reacted at 30 to 80 ° C. for 10 minutes to 24 hours. A modified natural rubber latex in which the polar group-containing mercapto compound is added to the molecule is obtained.

Next, the polar group-containing olefin added to the natural rubber latex has at least one polar group in the molecule, and also has a carbon-carbon double bond for cross-metathesis reaction with the natural rubber molecule. A polar group containing olefin may be used individually by 1 type, and may be used in combination of 2 or more type.

When a polar group-containing olefin is reacted with a natural rubber molecule in a natural rubber latex by a metathesis catalyst, the polar group-containing olefin is generally added to a solution obtained by adding water and, if necessary, an emulsifier to a natural rubber latex. A metathesis catalyst is added and stirred at a predetermined temperature to cause a metathesis reaction between the natural rubber molecule and the polar group-containing olefin. Here, in the addition of the polar group-containing olefin to the natural rubber latex, an emulsifier may be added to the natural rubber latex in advance, or the polar group-containing olefin may be added to the natural rubber latex after emulsification with the emulsifier. . In addition, it does not specifically limit as an emulsifier which can be used for emulsification of natural rubber latex and / or a polar group containing olefin, Nonionic surfactants, such as polyoxyethylene lauryl ether, are mentioned.

The metathesis catalyst is not particularly limited as long as it has a catalytic action on the metathesis reaction between the natural rubber molecule and the polar group-containing olefin, and various metathesis catalysts can be used. The metathesis catalyst contains a transition metal, but since it is used in a natural rubber latex, it is preferable that the stability to water is high. Therefore, the transition metal constituting the metathesis catalyst is preferably any one of ruthenium, osmium, and iridium. Specific examples of the metathesis catalyst include bis (tricyclohexylphosphine) benzylideneruthenium dichloride [RuCl ₂ (═CHPh) (PCy ₃ ) ₂ ], and RuCl ₂ (═CH—CH═CPh ₂ ) (PPh ₃ ) _2. RuCl ₂ (= CHPh) (PCp ₃ ) ₂ , RuCl ₂ (= CHPh) (PPh ₃ ) ₂ , RuCl ₂ (= CHPh) [Cy ₂ PCH ₂ CH ₂ N (CH ₃ ) ₃ ⁺ Cl] ₂ etc. Can be mentioned. In the chemical formula, Cy represents a cyclohexyl group, and Cp represents a cyclopentyl group. The addition amount of the metathesis catalyst is preferably in the range of 1 to 500 mol%, more preferably in the range of 10 to 100 mol% with respect to the polar group-containing olefin.

The above-mentioned components are charged into a reaction vessel and reacted at 30 to 80 ° C. for 10 minutes to 24 hours to obtain a modified natural rubber latex in which the polar group is introduced into natural rubber molecules.

Further, when using at least one natural rubber raw material selected from the group consisting of natural rubber, natural rubber latex coagulum and natural rubber cup lamp as a raw material, the polar group-containing compound is given a mechanical shearing force, A modified natural rubber can be obtained by graft polymerization or addition to a rubber raw material.

As a means for applying a mechanical shearing force to the mixture of the natural rubber raw material and the polar group-containing compound, a twin-screw extrusion kneader and a dry prebreaker are preferable. Here, in the case where the polar group-containing compound is graft-polymerized to the natural rubber molecule in the natural rubber raw material, the natural rubber raw material and the polar group-containing compound (preferably, the polar group-containing compound are contained in an apparatus capable of applying mechanical shearing force. By introducing a polymerization initiator together with a vinyl monomer) and applying a mechanical shearing force, a polar group-containing compound can be introduced into the natural rubber molecule in the natural rubber raw material by graft polymerization. In addition, when a polar group-containing compound is subjected to an addition reaction with a natural rubber molecule in a natural rubber raw material, the natural rubber raw material and the polar group-containing compound (preferably, a polar group-containing compound are contained in the apparatus capable of applying the mechanical shearing force. Mercapto compound), and if necessary, organic peroxide, etc., is added to provide mechanical shearing force, so that polar groups are contained in the double bond of the main chain of natural rubber molecules in natural rubber raw materials. The compound can be subjected to an addition reaction. Examples of the polar group-containing compound used here include the above-described polar group-containing monomers, polar group-containing mercapto compounds, polar group-containing olefins, and the like.

The modified natural rubber in which the above polar group-containing compound is graft-polymerized or added to the natural rubber molecule is obtained by charging the above-described components into an apparatus that can be applied with a mechanical shearing force and applying the mechanical shearing force. At this time, the modification reaction of the natural rubber molecule may be carried out by heating, and preferably at 30 to 160 ° C., more preferably 50 to 130 ° C., the modified natural rubber with sufficient reaction efficiency. Can be obtained.

The polar group content of the modified natural rubber is preferably in the range of 0.001 to 0.5 mmol / g, more preferably in the range of 0.002 to 0.3 mmol / g, based on the rubber component in the modified natural rubber. The range of 0.003 to 0.2 mmol / g is even more preferable. If the polar group content of the modified natural rubber is less than 0.001 mmol / g, the low loss and wear resistance of the rubber composition may not be sufficiently improved. Also, if the polar group content of the modified natural rubber exceeds 0.5 mmol / g, the physical properties inherent to natural rubber such as viscoelasticity and SS characteristics (stress-strain curve in a tensile testing machine) will be greatly changed. In addition, the physical properties inherent to natural rubber are impaired, and the processability of the rubber composition may be greatly deteriorated.

(3) Low exothermic property imparting agent The low exothermic property imparting agent is blended in the rubber composition in order to realize low heat generation and high reinforcement of the tread rubber. As such a representative compound, a nitrosoquinoline compound is known (for example, see JP-A-60-82406). Specifically, 5-nitroso-8-hydroxyquinoline, 7-nitroso-8-hydroxy-5-methylquinoline, 5-nitroso-8-hydroxy-6-methylquinoline, 8-nitroso-5-hydroxy-6- Examples thereof include methylquinoline, 5-nitroso-8-hydroxy-7-methylquinoline, and 6-nitroso-5-hydroxy-8-methylquinoline. Among them, 5-nitroso-8-hydroxyquinoline is preferable.
The low heat build-up agent is blended in an amount of 0.1 to 10 parts by mass with respect to 100 parts by mass of the rubber component.

(4) Hydrazide compound When a hydrazide compound is blended in a rubber composition suitable for a tread rubber of a heavy duty pneumatic tire, it suppresses a decrease in elastic modulus caused by overvulcanization due to reversion, thereby reducing low heat buildup and resistance. It is known to have an action of suppressing a decrease in wear (see, for example, JP-A-2002-146102).

Examples of the hydrazide compound that can be used in the present invention include 1-hydroxy-N ′-(1-methylethylidene) -2-naphthoic acid hydrazide, 1-hydroxy-N ′-(1-methylpropylidene) -2-naphthoyl. Acid hydrazide, 1-hydroxy-N ′-(1-methylbutylidene) -2-naphthoic acid hydrazide, 1-hydroxy-N ′-(1,3-dimethylbutylidene) -2-naphthoic acid hydrazide, 1-hydroxy -N '-(2,6-dimethyl-4-heptylidene) -2-naphthoic acid hydrazide, 2-hydroxy-N'-(1-methylethylidene) -3-naphthoic acid hydrazide, 2-hydroxy-N '-( 1-methylpropylidene) -3-naphthoic acid hydrazide, 2-hydroxy-N ′-(1-methylbutylidene) -3-naphthoic acid hydrazide 2-hydroxy-N ′-(1,3-dimethylbutylidene) -3-naphthoic acid hydrazide, 2-hydroxy-N ′-(2,6-dimethyl-4-heptylidene) -3-naphthoic acid hydrazide, isophthal Di (1-methylethylidene) hydrazide, di (1-methylpropylidene) hydrazide, isophthalic acid di (1-methylbutylidene) hydrazide, di (1,3-dimethylbutylidene) hydrazide, isophthalic acid Di (2,6-dimethyl-4-heptylidene) hydrazide, isonicotinic acid (1-methylethylidene) hydrazide, isonicotinic acid (1-methylpropylidene) hydrazide, isonicotinic acid (1-methylbutylidene) hydrazide, iso Nicotinic acid (2,6-dimethyl-4-heptylidene) hydrazide, isoni Tinic acid (1,3-dimethylbutylidene) hydrazide, N ′-(1-methylethylidene) -salicylic acid hydrazide, N ′-(1-methylpropylidene) -salicylic acid hydrazide, N ′-(1-methylbutylidene) -Salicylic acid hydrazide, N '-(1,3-dimethylbutylidene) -salicylic acid hydrazide, N'-(2,6-dimethyl-4-heptylidene) -salicylic acid hydrazide and the like.

Among them, preferred hydrazide compounds are 2-hydroxy-N ′-(1-methylethylidene) -3-naphthoic acid hydrazide, 2-hydroxy-N ′-(1-methylpropylidene) -3-naphthoic acid hydrazide, 2- Hydroxy-N ′-(1-methylbutylidene) -3-naphthoic acid hydrazide, 2-hydroxy-N ′-(1,3-dimethylbutylidene) -3-naphthoic acid hydrazide, 2-hydroxy-N ′-( 2,6-dimethyl-4-heptylidene) -3-naphthoic acid hydrazide, N ′-(1-methylethylidene) -salicylic acid hydrazide, N ′-(1-methylpropylidene) -salicylic acid hydrazide, N ′-(1- Methylbutylidene) -salicylic acid hydrazide, N ′-(1,3-dimethylbutylidene) -salicylic acid hydrazide, N ′-(2,6-dimethyl-4) -Heptylidene) -salicylic acid hydrazide and the like.
The hydrazide compound is blended in an amount of 0.05 to 5 parts by mass with respect to 100 parts by mass of the rubber component.

(5) Compound having dipolar nitrogen and nitrogen-containing heterocycle containing oxygen or sulfur In the present invention, the dispersibility of carbon black is improved to give low heat build-up, and the interaction between polymers is strengthened. Thus, a compound having a dipolar nitrogen-containing portion having an effect of improving wear resistance and a 4- to 6-membered nitrogen-containing heterocyclic portion containing oxygen or sulfur can be blended.

The above compound is included in the compound used in the present invention as long as it contains a dipolar nitrogen moiety. Specific examples of particularly preferred dipolar nitrogen moieties include A1-C (A2) = N (A3) → O (nitrone system), A1-C≡N → O (nitrile oxide system), and A1-C≡. N → N—A4 (nitrile imine type) can be mentioned. These dipolar nitrogen portions are bonded to double bond portions in a polymer such as a rubber component.

The groups A1 to A4 in the nitrone, nitrile oxide, and nitrileimine dipolar nitrogen moieties are preferably hydrogen, a group having 20 or less carbon atoms, or a connecting chain. When the number of carbon atoms exceeds 20, the molecular weight of the compound itself increases, and the reactivity with the rubber component becomes worse.

Since the above compound has a nitrogen-containing heterocyclic moiety, A1 to A4 can be a connecting chain connecting the nitrogen-containing heterocyclic moieties. Specific groups or linking chains of A1 to A4 of the above compound include hydrogen, an alkyl group having 1 to 20 carbon atoms, and an aryl group having 6 to 20 carbon atoms (provided that aromatic The group ring may be a group selected from any one of nitro group, cyano group, chloro group, bromo group, acyl group, carbonylalkyl group, alkyl group and alkoxyl group), or a connecting chain. . The alkyl group, acyl group, carbonylalkyl group and alkoxyl group may have a branched chain and may have a cyclo ring. A1 to A4 may be different from each other.

The nitrogen-containing heterocyclic moiety of the above compound is an oxetine-type, thiozetin-type, oxazoline-type, thiazoline-type, tetrahydrooxazine-type or tetrahydrothoxazine-type nitrogen-containing heterocycle, particularly a 4- to 6-membered nitrogen. Containing heterocycle. Of these, oxazoline and thiozoline are preferable. The nitrogen-containing heterocyclic moiety undergoes a binding reaction with carbon black and white carbon (silica), and these can be uniformly incorporated into the polymer of the rubber component.

Specific examples of the dipolar nitrogen and the compound having a nitrogen-containing heterocyclic ring containing oxygen or sulfur include 4- (2-oxazolyl) -phenyl-N-methyl-nitrone, 4- (2-thiazolyl)- Phenyl-N-methyl-nitrone, 4- (2-oxazolyl) -phenyl-N-phenyl-nitrone, 4- (2-thiazolyl) -phenyl-N-phenyl-nitrone, phenyl-N-4- (2-oxazolyl) ) -Phenyl-nitrone, phenyl-N-4- (2-thiazolyl) -phenyl-nitrone, 4-tolyl-N-4- (2-oxazolyl) -phenyl-nitrone, 4-tolyl-N-4- (2 -Thiazolyl) -phenyl-nitrone, 4-methoxyphenyl-N-4- (2-oxazolyl) -phenyl-nitrone, 4-methoxyphenyl-N-4- (2-thi Azolyl) -phenyl-nitrone, 4- (2-oxazolyl) -phenyl-nitrile oxide, 4- (2-thiazolyl) -phenyl-nitrile oxide, 4- (2-oxazolyl) -phenyl-N-methyl-nitrileimine, 4- (2-thiazolyl) -phenyl-N-methyl-nitrileimine, 4- (2-oxazolyl) -phenyl-N-phenyl-nitrileimine, 4- (2-thiazolyl) -phenyl-N-phenyl-nitrileimine And phenyl-N-4- (2-oxazolyl) -phenyl-nitrileimine, phenyl-N-4- (2-thiazolyl) -phenyl-nitrileimine, and the like.

In such compounds, 4- (2-oxazolyl) -phenyl-N-methyl-nitrone (hereinafter referred to as “4OPMN”) and 4- (2-oxazolyl) -phenyl-N-phenyl-nitrone (hereinafter referred to as “4OPPN”). Can be preferably used.

The method for producing the above compound can be produced without undue experimentation. For example, with respect to 4OPPN, a manufacturing method thereof will be shown in an example described later.
Also, other compounds can be produced by typical production methods by appropriately selecting other starting materials and intermediate materials.

The above compound is blended in the range of 0.1 to 30 parts by mass with respect to 100 parts by mass of the rubber component. In particular, it is preferably included in the range of 0.1 to 5 parts by mass. If the compounding amount is less than 0.1, the effects of low heat generation and low hysteresis loss are not sufficient. When the compounding amount of the compound exceeds 30 parts by mass, the cost is significantly increased, which is not preferable.
In the present invention, when a natural rubber masterbatch is used, a compound having a nitrogen-containing heterocyclic ring containing dipolar nitrogen and oxygen or sulfur is used together with carbon black in the production process of the natural rubber wet masterbatch or the wet rubber. You may mix | blend during the drying process of a masterbatch.
(6) Increased amount of stearic acid Stearic acid has the functions of improving the dispersibility of carbon black and increasing the wear resistance of rubber, and is used in many rubbers as a compounding agent. It is used more frequently and is added to 4 phr.

(7) Remill Usually, vulcanizing agents and vulcanization accelerators are added to the non-pro rubber obtained by non-pro kneading and non-pro kneading to ensure the reinforcing property of the rubber and the filler without adding the rubber to the rubber and to promote the dispersion of the filler. There is a professional kneading that also contains a vulcanizing agent and a vulcanization accelerator, but remilling is a non-pro kneading and before the pro kneading before non-pro kneading, that is, strengthening the reinforcing property of the filler to improve dispersion. Therefore, it refers to the process of only kneading.

(8) Low-temperature vulcanization The rubber composition is vulcanized at a low temperature to suppress reversion and prevent deterioration of physical properties. Usually, vulcanization is performed in the range of about 130 to 200 ° C., but the vulcanization temperature is set to a low temperature in the range of 80 to 120 ° C. and vulcanization is performed for a long time.

In addition to the components used for the above treatment, the rubber composition of the present invention includes vulcanizing agents such as sulfur, vulcanization accelerators, softeners, anti-aging agents, zinc oxide, stearin, which are usually used in the rubber industry. A compounding agent such as an acid can be blended.

The method for producing the tire rubber composition of the present invention is not particularly limited, and can be prepared by adding a compounding agent to the rubber component and kneading by a commonly performed method. Moreover, when using a masterbatch as a rubber component, this compounding agent can be added in the process of manufacturing a masterbatch.

The tire of the present invention can be manufactured by vulcanization molding using the rubber composition as a tread rubber. The tire of the present invention is excellent in low heat buildup and has high wear resistance. In addition, air or inert gas, such as nitrogen, is used for the gas with which the tire of the present invention is filled.

The present invention will be described in more detail with reference to the following examples. However, the present invention is not limited to the following examples.
In the following examples and comparative examples, wear resistance was measured and evaluated by the following methods as CTAB as a filler, resilience (rebound resilience) as a rubber composition, and tire performance.

(1) CTAB
Measured according to ISO 6810.
(2) Resilience Measured according to JIS K6255-1996 (room temperature 25 ° C.).
(3) Abrasion resistance Each rubber composition was applied to a tire tread to produce tires each having a size of 1000R20 14PR. After running on a rough road for 6000 km, the following formula was calculated according to the running distance per 1 mm of tire wear. From this, the wear resistance index was calculated. The higher the value, the better the wear resistance.
Abrasion resistance index = 100 × (travel distance / amount of wear) (each tire) / (travel distance / amount of wear) (Comparative Example 1)

The various processing methods performed with respect to the rubber composition of an Example are as follows.
(A) Production of Master Batch Natural rubber field latex (rubber content 24.2%) was diluted with deionized water to give a rubber content of 20%. To 100 parts by weight of this natural rubber latex, 0.5 part by weight of an anionic surfactant (Demol N made by Kao Corporation) and 0.1 part by weight of alkaline protease (Alkalase 2.5L type DX made by Novozyme) were added, By stirring at 40 ° C. for 8 hours, the amide bond in the natural rubber was decomposed.
On the other hand, 1425 g of deionized water and 75 g of carbon black were put into a colloid mill with a rotor diameter of 50 mm, and stirred for 10 minutes at a rotor-stator interval of 0.3 mm and a rotational speed of 5000 rpm to produce an aqueous dispersion slurry.
Next, natural rubber latex and water-dispersed slurry were mixed so that the mass ratio of the natural rubber component and carbon black was the ratio shown in Table 1 to produce a natural rubber wet masterbatch. While stirring the obtained natural rubber wet masterbatch, formic acid was added until the pH reached 4.5 to coagulate the natural rubber wet masterbatch. The natural rubber wet masterbatch after coagulation was collected, washed with water, and dehydrated until the water content was about 40%. Then, using a twin-screw kneading extruder (Kobe Steel: Co-directional rotating screw diameter 30 mm, L / D = 35, 3 vent holes), dried at a barrel temperature of 120 ° C. and a rotation speed of 100 rpm, and a natural rubber master batch Manufactured.
In the following examples, the natural rubber component is used in an amount corresponding to the amount of natural rubber shown in Table 1.

(B) Production of modified natural rubber The field latex was centrifuged at a rotational speed of 7500 rpm using a latex separator (manufactured by Saito Centrifugal Co., Ltd.) to obtain a concentrated latex having a dry rubber concentration of 60%. 1000 g of this concentrated latex is put into a stainless steel reaction vessel equipped with a stirrer and a temperature control jacket, and 10 ml of water and 90 mg of emulsifier (Emulgen 1108, manufactured by Kao Corporation) are added in advance to N, N-diethylaminoethyl methacrylate. What was emulsified in addition to 0 g was added together with 990 ml of water, and these were stirred at room temperature for 30 minutes while purging with nitrogen. Next, 1.2 g of tert-butyl hydroperoxide and 1.2 g of tetraethylenepentamine were added as polymerization initiators and reacted at 40 ° C. for 30 minutes to obtain a modified natural rubber latex.
Next, the modified natural rubber latex was coagulated by adding formic acid to adjust the pH to 4.7. The solid material thus obtained was treated with a creper five times, passed through a shredder and crushed, and then dried at 110 ° C. for 210 minutes with a hot air dryer to obtain a modified natural rubber. From the mass of the modified natural rubber thus obtained, it was confirmed that the conversion rate of N, N-diethylaminoethyl methacrylate added as a monomer was 100%. In addition, the modified natural rubber was extracted with petroleum ether and further extracted with a 2: 1 mixed solvent of acetone and methanol, but when the extract was analyzed, the homopolymer was not detected. It was confirmed that 100% of the added monomer was introduced into the natural rubber molecule. Accordingly, the polar group content of the resulting modified natural rubber is 0.027 mmol / g with respect to the rubber component in the natural rubber latex.
In the following examples, the modified natural rubber is used in an amount corresponding to the amount of natural rubber shown in Table 1.

(C) Addition of hydrazide compound 1.0 part by mass of 2-hydroxy-N '-(1,3-dimethylbutylidene) -3-naphthoic acid hydrazide (BMH) is added per 100 parts by mass of the natural rubber.
(D) Addition of low exothermic property-imparting agent 1.0 part by mass of 5-nitroso-8-hydroxyquinoline (NQ58) is added per 100 parts by mass of natural rubber.
(E) Addition of a nitrogen-containing heterocyclic compound containing dipolar nitrogen

Preparation of 4- (2-oxazolyl) -phenyl-N-phenyl-nitrone (4OPPN) 10.9 g of 4-formyl-benzoyl chloride (1 equivalent) in 300 ml of chloroform was stirred and mixed with 10.9 g of 200 ml of chloroform. A solution of 2-aminoethanol (2 equivalents) was added dropwise at -10 ° C. The solution was placed at 25 ° C. for 2 hours and then the white precipitate was removed by filtration. The filtrate was dried on a rotary evaporator to give 17.4 g of yellow liquid 4-formyl-N- (2-hydroxyethyl) -benzamide.
Subsequently, 17.4 g of 4-formyl-N- (2-hydroxyethyl) -benzamide was added dropwise to 50 ml of concentrated sulfuric acid with stirring, and the mixture was heated at 100 ° C. for 1 hour. To this solution, 500 ml of 20% sodium hydroxide and chloroform were added dropwise with stirring and mixing, and the temperature was maintained at 15 ° C. or lower. The product layer was separated and dried to give 6.3 g of 4- (2-oxazolyl) -benzaldehyde.
A mixture of 4- (2-oxazolyl) -benzaldehyde (1 eq, 6.3 g) and N-phenyl-hydroxyamine (1 eq, 3.9 g) was refluxed in 100 ml ethanol for 30 min to a volume of 50 ml. Concentrated. An equal amount of 50 ml of water was added and the mixture was cooled overnight at 5 ° C. in a refrigerator. Filtration and drying gave white crystals, yielding 6.7 g of 4- (2-oxazolyl) -phenyl-N-phenyl-nitrone (4OPPN).
The 4- (2-oxazolyl) -phenyl-N-phenyl-nitrone thus obtained is added in an amount of 1.0 part by mass per 100 parts by mass of the natural rubber.

(F) Stearic acid increase When stearic acid in the rubber composition is not subjected to this treatment, the amount of 2.0 parts by mass is increased to 4.0 parts by mass per 100 parts by mass of the natural rubber.
(G) Remill After non-pro-kneading to promote the dispersion of reinforcing fillers (carbon black, silica) on natural rubber, before reinforcing the pro-kneading, to enhance the reinforcing properties of the filler and improve dispersion, Non-pro-kneading once for 3 minutes.
(H) Low-temperature vulcanization The vulcanization is usually carried out at 150 ° C./30 minutes, but at 120 ° C./120 minutes.

Examples 1 to 8 and Comparative Examples 1 to 8
As rubber components, natural rubber masterbatch or modified natural rubber is used in the examples, and natural rubber obtained by coagulating and drying natural comb latex is used in the comparative examples. Carbon black or carbon black and silica are added to various natural rubbers. A rubber composition was prepared by adding an agent and kneading with a Banbury mixer.
Rubber composition (parts by mass)
Natural rubber 100
Carbon black variable silica variable wax 2
Stearic acid 2 (normal), 4 (when increased)
Anti-aging agent 6C 1
Zinc flower 3
Vulcanization accelerator CZ 1.4
(N-cyclohexyl-2-benzothiazylsulfenamide)
Sulfur 1.8
Compounds 1-3 3 1.0
Tables 1 and 2 show the types and properties of the rubber components, carbon black, and silica used, the treatments performed, and the evaluation results of the resilience and tire performance of each rubber composition.
In Tables 1 and 2, ◯ indicates that the processing was performed.

Table 1

Table 2

Note CB: Carbon black 1) Natural rubber obtained by coagulating and drying natural rubber latex, natural rubber masterbatch with carbon black or modified natural rubber 2) Nipseal AQ: manufactured by Tosoh Silica Co. 3) Y = -0. 0019 × CTAB × filler amount + 77.5
4) 5-nitroso-8-hydroxyquinoline 5) 2-hydroxy-N '-(1,3-dimethylbutylidene) -3-naphthoic acid hydrazide 6) 4- (2-oxazolyl) -phenyl-N-phenyl- Nitron

In comparison with the comparative examples that do not satisfy the value of resilience> Y, which is a requirement of the present invention, and in which none of the treatments A to H is performed, the resilience is higher in Examples 1 to 8 and the tire wear resistance is higher. Equivalent or significantly improved.

The rubber composition of the present invention can be suitably used for tire treads.

Claims

In a rubber composition containing a reinforcing filler made of natural rubber and carbon black, or carbon black and silica, the specific surface area (CTAB) represented by the cetyltrimethylammonium bromide adsorption specific surface area measured according to ISO 6810 of the filler. m 2 / g) and the impact resilience of the rubber composition in which the product of the filler mass part B (phr) of the filler per 100 parts by mass of the natural rubber component is measured according to JIS K6255 (25 ° C.) A rubber composition satisfying the following formula (1).
Rebound resilience> −0.0019 × A + 77.5 (1)
Where A = CTAB × B
The rubber composition according to claim 1, wherein the natural rubber component and carbon black are used as a natural rubber masterbatch produced from natural rubber latex and carbon black.
The rubber composition according to claim 1, wherein the natural rubber component is a polar group-containing modified natural rubber.
A rubber composition obtained by blending any one of the hydrazide compound, the nitrosoquinoline compound, and a compound having a nitrogen-containing heterocyclic ring containing oxygen or sulfur with a hydrazide compound, a nitrosoquinoline compound, or the rubber composition according to any one of claims 1 to 3.
The rubber composition according to claim 4, wherein a hydrazide compound is blended.
The rubber composition according to claim 4, wherein a nitrosoquinoline compound is blended.
The rubber composition according to claim 4, wherein a compound having a nitrogen-containing heterocyclic ring containing dipolar nitrogen and oxygen or sulfur is blended.
The rubber composition according to any one of claims 2 to 7, wherein a blending amount of stearic acid is added by 2.0 parts by mass or more per 100 parts by mass of the natural rubber component, further kneading is added after non-pro kneading, and low temperature vulcanization The rubber composition which performed at least 1 process of these.
A tire using the rubber composition according to any one of claims 1 to 8 as a tread rubber.