JP2011084651A - Composite, rubber composition and pneumatic tire - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a composite in which silica is finely dispersed in a rubber component and a method for producing the same; to provide a rubber composition which exhibits excellent reinforcing properties and improves performances such as low heat buildup, grip performance and abrasion resistance with good balance because the composite is contained; and a pneumatic tire using the same. <P>SOLUTION: The composite is obtained from a compounded latex prepared by mixing a polar group-containing modified natural rubber latex and a fine particle silica dispersion having an average particle diameter of ≤100 nm produced from water glass. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

The present invention relates to a composite, a method for producing the same, a rubber composition containing the composite, and a pneumatic tire using the rubber composition.

Styrene butadiene rubber is widely used to ensure the grip performance of tires, but the use of epoxidized natural rubber is being studied because of environmental issues and limited petroleum resources. In addition, it has also been studied to obtain good low heat generation by blending silica as a filler for reducing the fuel consumption of a tire.

For this reason, combined use of epoxidized natural rubber and silica has been studied, but the wear resistance is not sufficient compared to the composition containing styrene butadiene rubber and carbon black, and it balances low rolling resistance, grip performance, and wear resistance. It is desired to improve it well. Generally, when fillers (fillers) are aggregated, the number of fillers per unit volume decreases, so that the reinforcing efficiency of the fillers deteriorates and the aggregates become starting points of destruction, so that the wear resistance tends to deteriorate. . Therefore, it is desirable that the filler is finely dispersed, and it is expected that various performances can be improved if the dispersibility of silica can be further improved even in a rubber composition containing epoxidized natural rubber and silica.

For the production of a rubber composition containing silica, a kneading method in which solid rubber and dry silica (particle size of about 20 to 60 nm) are kneaded with a Banbury mixer, an open roll, a kneader or the like is widely used. However, since silica has a silanol group on the surface and is hydrophilic, it generally has low affinity with rubber that exhibits hydrophobic properties and strong self-aggregation properties, so it can be easily dispersed uniformly in rubber. is not. In particular, when the particle size of silica is less than 20 nm, the surface area of the silica particles tends to increase, and further tends to aggregate.

Patent Document 1 discloses a rubber composition obtained by coagulating a compounded latex containing an epoxidized natural rubber and water glass, and in which silica is uniformly dispersed. Are difficult to form fine particles, and it is difficult to uniformly disperse the fine particle silica. Patent Document 2 discloses a method for producing a composite by mixing fine particle silica produced from water glass with rubber latex in a liquid state, but here, a substantially normal natural rubber latex is used. Only the manufacturing method was disclosed. Moreover, in the case of normal natural rubber latex, it is difficult to obtain a finely and uniformly dispersed state, particularly when the particle diameter of silica is 20 nm or less.

JP 2007-2177 A JP 2009-51955 A

An object of the present invention is to solve the above-mentioned problems and to provide a composite in which silica is finely dispersed in a rubber component and a method for producing the same. In addition, a rubber composition that exhibits excellent reinforcement by blending the composite and has improved performance such as low heat generation, grip performance, and wear resistance in a well-balanced manner, and a pneumatic tire using the rubber composition The purpose is to provide.

The present invention relates to a composite obtained from a blended latex in which a polar group-containing modified natural rubber latex and a fine particle silica dispersion having an average particle size of 100 nm or less produced from water glass are mixed.

In the composite, the polar group-containing modified natural rubber latex is preferably an epoxidized natural rubber latex. The fine particle silica dispersion is prepared by adjusting the pH of the water glass aqueous solution to 9 to 11 using an ion exchange resin, and the average particle size of silica in the dispersion is 15 nm or less. Preferably there is.

The present invention includes a step (I) of preparing a blended latex by mixing the polar group-containing modified natural rubber latex and a fine particle silica dispersion having an average particle size of 100 nm or less produced from the water glass, and the above step ( It is related with the manufacturing method of the said composite_body | complex containing process (II) which coagulates the mixing | blending latex obtained by I).

The present invention relates to a rubber composition containing the composite.
The rubber composition preferably further contains a fatty acid salt.
The present invention also relates to a pneumatic tire produced using the rubber composition.

According to the present invention, since it is produced from a compounded latex in which a polar group-containing modified natural rubber latex and a fine particle silica dispersion having an average particle size of 100 nm or less produced from water glass are mixed, fine silica is contained in the rubber component. A composite dispersed in can be provided. Therefore, since excellent reinforcement is exhibited in the rubber composition and pneumatic tire using the composite, performance such as low heat generation, grip performance, and wear resistance can be improved in a well-balanced manner.

Further, in the prior art, it was difficult to finely disperse silica fine particles of 10 nm or less in rubber, but in the present invention, such fine silica fine particles can be finely dispersed in rubber. Furthermore, tires using materials derived from resources other than petroleum are desired in the tire industry, and demand for natural rubber / silica composites is expected to increase in the future. It is expected that a composite dispersed in the resin is obtained, the contact area between silica and rubber is large, and the reinforcement is improved. Also, mixing the rubber latex and water-glass-derived fine particle silica dispersion at the initial stage of production is significantly more costly than the conventional process of drying the rubber and silica separately and mixing both components by rubber kneading. We can expect down.

A photograph of a composite using silica powder as a silica source (Comparative Example 7, left part of the photograph), and a photograph of a composite using a fine particle silica dispersion prepared from water glass as a silica source (Example 9, right part of the photograph) ) TEM photograph of Example 9 in FIG. 1 (section of sample cut out with microdome. Black part is silica and white part is rubber) TEM photograph of composite using natural rubber latex (Comparative Example 8)

<Composite>
The composite of the present invention is obtained from a compounded latex obtained by mixing a polar group-containing modified natural rubber latex and a dispersion containing fine particle silica having an average particle size of not more than a specific value produced from water glass. That is, firstly, a dispersion of fine particle silica having an average particle size of 100 nm or less is prepared from water glass, and then the blended latex (mixed solution) prepared by mixing the dispersion and polar group-containing modified natural rubber latex in a liquid state. Manufactured from. Since the compounded latex prepared in this way is used, a composite in which silica is finely dispersed in the polar group-containing modified natural rubber can be produced.

The composite of the present invention includes, for example, a step (I) of preparing a blended latex by mixing a polar group-containing modified natural rubber latex and a fine particle silica dispersion having an average particle size of 100 nm or less produced from water glass, and It is obtained by a production method including the step (II) of coagulating the compounded latex obtained in the step (I).

(Process (I))
In the polar group-containing modified natural rubber latex used in the step (I), examples of the polar group include an amino group, an imino group, a nitrile group, an ammonium group, an imide group, an amide group, a hydrazo group, an azo group, and a diazo group. Hydroxyl group, carboxyl group, carbonyl group, epoxy group, oxycarbonyl group, sulfide group, disulfide group, sulfonyl group, sulfinyl group, thiocarbonyl group, nitrogen-containing heterocyclic group, oxygen-containing heterocyclic group, alkoxysilyl group, etc. Can be mentioned. By having a polar group, the interaction between silica and rubber becomes strong, so that silica can be finely dispersed in the rubber matrix. These polar groups may be used alone or in combination of two or more. Among them, it is preferable to use an epoxy group, that is, an epoxidized natural rubber (ENR) latex.

In ENR latex, ENR can be produced by treating natural rubber with, for example, hydrogen peroxide and formic acid, or by treating with peracetic acid. This reaction epoxidizes the double bonds present in the natural rubber molecule. The structure of epoxidation can be clarified from proton nuclear magnetic resonance spectrum ( ¹ H-NMR) and infrared absorption spectrum (IR), and from the results of IR and elemental analysis, the content of epoxy group (epoxy group) Conversion rate) can be measured.

The epoxidation rate of ENR is preferably 1 mol% or more, more preferably 3 mol% or more, and further preferably 5 mol% or more. The epoxidation rate of ENR is preferably 70 mol% or less, more preferably 60 mol% or less, and still more preferably 50 mol% or less. When the amount is less than 1 mol%, the number of sites that interact with the silicic acid component generated from water glass decreases, and it becomes impossible to impart desired properties to the rubber composition, or the mechanical strength and dynamics of the rubber composition The effect of improving mechanical properties may be insufficient. On the other hand, when it exceeds 70 mol%, the glass transition point becomes too high, and the durability at low temperatures may be lowered, or the fuel efficiency may be deteriorated. In the present invention, two or more kinds of ENRs having an epoxidation rate in the above range may be mixed and used.

In the step (I), a fine particle silica dispersion having an average particle diameter of 100 nm or less produced from water glass is used. That is, silica is used by growing it as spherical fine particles, instead of using the raw water glass as it is. In this growth, it is more preferable to take a long ripening time and to make it spherical. When the spherical shape is obtained, the contact between the silica particles is minimized, the cohesive force is reduced, and the silica is easily dispersed.

The fine particle silica dispersion is preferably prepared by adjusting the pH of the aqueous water glass solution to 9-11.

The water glass is usually represented by a composition represented by the following formula.
Na ₂ O · nSiO ₂ · mH ₂ O
The coefficient n is a value represented by a molecular ratio of SiO ₂ / Na ₂ O, and is a range defined in JIS K 1408-1966 generally called a molar ratio. Although this coefficient n is not specifically limited, Preferably it is 2.1-3.3, More preferably, it is 3.1-3.3. When the coefficient n is 3.1 to 3.3, the silica component (in terms of SiO ₂ ) in the water glass increases, so that the efficiency of the composite treatment with rubber is improved.

In general, the water glass having the coefficient n of 3.1 to 3.3 is commercially available as Water Glass No. 3. The water glass which can be used for this invention is not limited to this, For example, No. 1-3 water glass prescribed | regulated to JISK1408, and other various grade products can be used.

By preparing an aqueous solution of water glass and adjusting the pH of the aqueous solution in the range of 9 to 11, a fine particle silica dispersion in which fine particle silica having an average particle diameter of 100 nm or less is dispersed can be prepared. When the pH is less than 9, gelation tends to occur, and when the pH exceeds 11, the fine particle silica tends to dissolve. More preferably, the pH is adjusted to a range of 9.5 to 10.5. The method for adjusting the pH to a range of 9 to 11 is not particularly limited, and can be carried out by a conventionally known method such as addition of an acid or alkali, use of an ion exchange resin, etc. Among them, a dispersion in which fine particle silica is more dispersed. From the point that can be obtained, it is preferable to use an ion exchange resin.

Examples of the pH adjustment method using an ion exchange resin include a method of bringing an aqueous solution of water glass into contact with a cation exchange resin. Specifically, an aqueous solution of water glass diluted to a predetermined concentration is brought into contact with a cation exchange resin to be dealkalized, and if necessary, brought into contact with an OH type strongly basic anion exchange resin to deanion. Can be done by. Examples of the contacting method include a batch method in which a cation exchange resin is directly put into an aqueous solution of water glass and stirred and contacted, and a method in which an aqueous solution of water glass is passed through a column filled with the cation exchange resin. . As the cation exchange resin, an H-type strong acid cation exchange resin, a weak acid cation exchange resin, or the like can be used. Amberlite IR120B, IR124, 200CT, IRC76, and FPC3500 manufactured by Organo Corporation are listed as commercial products. It is done. By the above method, sodium ions and the like in the water glass can be removed, so that silica particles in a more atomized state can be generated.

When adjusting the pH, the temperature of the aqueous solution of water glass is preferably adjusted to 10 to 90 ° C. If the temperature is less than 10 ° C., the production rate of fine-particle silica is slow, and if the temperature exceeds 90 ° C., water in the aqueous solution evaporates and the concentration of water glass in the aqueous solution tends to become unstable. What is necessary is just to adjust the temperature of the said aqueous solution suitably, and 15-40 degreeC and 60-80 degreeC are mentioned as a preferable range, for example.

The concentration of the silica component (SiO ₂ ) contained in the aqueous water glass solution is preferably in the range of 1 to 30% by mass. When the concentration is less than 1% by mass, a large amount of water glass aqueous solution is required for complexing with the rubber latex, and when it exceeds 30% by mass, silica aggregation tends to occur. The concentration of the silica component is more preferably in the range of 1.5 to 20% by mass, still more preferably 2 to 8% by mass. However, when water glass that has been subjected to desalting treatment is used, the upper limit is not particularly limited because silica aggregation is unlikely to occur.

The reaction time is preferably in the range of 1 to 72 hours. If it is less than 1 hour, the production of fine-particle silica is not sufficient, and even if it exceeds 72 hours, the reaction has already ended, and there is a tendency that there is no further change. When making it react at room temperature, it is suitable to carry out for 6 to 24 hours on stirring conditions. Further, in order to be as close to a true sphere as possible, aging at a high temperature and a long time is good, and a temperature of 60 to 80 ° C. for 24 hours or more is preferable.

The average particle diameter of silica contained in the fine particle silica dispersion is 100 nm or less, preferably 30 nm or less, more preferably 20 nm or less, still more preferably 15 nm or less, and particularly preferably 10 nm or less. Here, the size of the average particle diameter can be arbitrarily adjusted by adjusting the pH of the aqueous solution, the concentration of the silica component, the reaction temperature, the reaction time, and the like. In the present invention, by using a dispersion of polar group-containing modified natural rubber latex and spherical silica fine particles, a composite in which silica is finely dispersed can be obtained even with ultrafine silica.

In this specification, transmission electron microscope (TEM) observation is used as a method for measuring the average particle size of the fine particle silica. Specifically, the microparticles are photographed with a transmission electron microscope. If the shape of the microparticles is spherical, the diameter of the sphere is the particle diameter, and if it is needle-shaped or rod-shaped, the minor diameter is the particle diameter. In this case, the average particle diameter from the center is defined as the particle diameter, and the average value of the particle diameters of 100 fine particles is defined as the average particle diameter.

In step (I), the polar group-containing modified natural rubber latex and the fine-particle silica dispersion obtained by the above-mentioned production method are mixed by a known method, and then sufficiently stirred until the blended latex becomes a uniform solution. Thus, a compounded latex (mixed solution) is prepared. The polar group-containing modified natural rubber latex preferably has a rubber solid content of 10 to 70% by mass.

Further, in the mixing step, a polar group-containing modified natural rubber 100 parts by weight with respect to (the solid content), it is preferable that silica is mixed particulate silica dispersion such that 5 to 150 parts by weight (SiO ₂ conversion) . If the amount is less than 5 parts by mass, the amount of silica may be reduced when used as a master batch. When it exceeds 150 parts by mass, it is difficult to obtain uniform dispersion of silica in the rubber latex, and the uniform dispersion of silica in the rubber composition after coagulating the compounded latex tends to decrease. More preferably, it is 5-120 mass parts, More preferably, it is 10-100 mass parts.

(Process (II))
In step (II), the compounded latex obtained in step (I) is coagulated to produce a composite in which fine particle silica is uniformly dispersed in rubber. The coagulation of the compounded latex includes acid coagulation, salt coagulation, methanol coagulation, and the like. In order to coagulate the rubber latex and silica by uniform dispersion, acid coagulation, salt coagulation, or a combination thereof is preferable. Examples of the acid for coagulation include sulfuric acid, hydrochloric acid, formic acid, acetic acid and the like. Examples of the salt include monovalent to trivalent metal salts (such as calcium salts such as sodium chloride, magnesium chloride, calcium nitrate, and calcium chloride). When the amount of silica is small relative to the rubber latex, the type of metal salt is not limited, but when the amount of silica is large, monovalent and divalent metal salts such as sodium chloride and magnesium chloride are preferred. Here, when a trivalent metal salt is used, the cohesive force between silicas is too strong, and finally it is difficult to be finely dispersed.

Especially, coagulation | solidification of mixing | blending latex adjusts the pH of mixing | blending latex to 5-9 (preferably 6-8, more preferably 6.5-7.5) by addition of an acid or a salt, and solidifies solid content. It is preferable to be implemented. Thereby, a composite in which silica is finely dispersed can be suitably produced.

The coagulated compounded latex is usually dried by a known method (such as an oven). When the rubber is kneaded with a biaxial roll or Banbury after drying, a composite in which silica is uniformly dispersed in the rubber matrix can be obtained.
In addition, the composite_body | complex of this invention may contain another component in the range which does not inhibit the effect of this invention.

When natural rubber latex is used as rubber latex, it is difficult to finely disperse silica, but the reason why silica can be uniformly finely dispersed when polar group-containing modified natural rubber latex is used is presumed as follows. .
When ordinary natural rubber latex is used instead of the polar group-containing modified natural rubber latex, the silica is not uniformly dispersed even after the rubber kneading, and the form of the silica becomes like a bunch of straw. Generally, the rubber component in the latex has a spherical shape, and silica cannot penetrate into the rubber component in the latex. For this reason, when latex and silica coexist and solidify together, the latex-derived rubber component and the silica component tend to agglomerate separately. It is difficult to completely fray. On the other hand, when the polar group-containing modified natural rubber latex is used, it is presumed that separate agglomeration structures are less likely to be formed due to the strong interaction between the rubber component and the silica component. Further, it is assumed that the dispersion of the silica particles is promoted by the shearing force of the subsequent rubber kneading, and the silica is uniformly dispersed in the rubber.

<Rubber composition>
The rubber composition of the present invention contains the above composite. Thereby, the excellent reinforcement property is exhibited. The composite can be used as a master batch. Since the composite has the silica uniformly dispersed in the rubber, the silica can be uniformly dispersed in the rubber composition of the present invention obtained when mixed with other rubber components and a rubber compounding agent.

The composite contained in the rubber composition has a silica content (SiO ₂ conversion) of preferably 10 parts by mass or more with respect to 100 parts by mass (solid content) of the polar group-containing modified natural rubber in the composite. More preferably, it is 20 mass parts or more, More preferably, it is 30 mass parts or more. If the amount is less than 10 parts by mass, sufficient reinforcement may not be obtained. The silica content is preferably 120 parts by mass or less, more preferably 100 parts by mass or less, and still more preferably 80 parts by mass or less. If it exceeds 120 parts by mass, there is a possibility that sufficient low fuel consumption performance and wear resistance cannot be obtained.

The rubber composition of the present invention may contain other rubber components other than the polar group-containing modified natural rubber. Examples of other rubber components include natural rubber (NR), isoprene rubber (IR), butadiene rubber (BR), styrene butadiene rubber (SBR), styrene isoprene butadiene rubber (SIBR), ethylene propylene diene rubber (EPDM), Examples include chloroprene rubber (CR) and acrylonitrile butadiene rubber (NBR).

The rubber composition of the present invention preferably contains a fatty acid salt, particularly when ENR latex is used as the polar group-containing modified natural rubber latex. Thereby, performance, such as abrasion resistance, can be improved and heat resistance is also improved. Examples of fatty acid salts include metal salts of saturated fatty acids and metal salts of unsaturated fatty acids, and these fatty acid salts may be used alone or in combination of two or more. The fatty acid salt preferably has 6 or more carbon atoms, more preferably 8 or more. When the number of carbon atoms of the fatty acid salt is less than 6, there is a tendency that the improvement effect by adding the fatty acid salt cannot be confirmed. Specific examples of fatty acids that satisfy the above conditions include saturated fatty acids such as stearic acid, palmitic acid, myristic acid, and lauric acid, and unsaturated fatty acids such as oleic acid, linoleic acid, and linolenic acid. Among these, saturated fatty acids are preferable and stearic acid is more preferable because of excellent wear resistance, aging resistance, and heat resistance. Examples of the metal constituting the fatty acid salt include alkaline earth metals such as calcium, magnesium and barium, typical metals other than alkaline earth metals such as aluminum, sodium and potassium, and transition metals such as zinc. Among these, alkaline earth metals are preferable and calcium is more preferable because they are present in nature and have a low environmental load.

In the rubber composition of the present invention, the content of the fatty acid salt is preferably 2 parts by mass or more, more preferably 3 parts by mass or more with respect to 100 parts by mass of the rubber component. If it is less than 2 mass parts, there exists a possibility that the improvement effect by containing a fatty acid salt may not be acquired. The content of the fatty acid salt is preferably 15 parts by mass or less, more preferably 10 parts by mass or less, and still more preferably 8 parts by mass or less. If it exceeds 15 parts by mass, the wear resistance of the rubber may be reduced.

In addition to the above materials, the rubber composition of the present invention includes carbon black, silica, silane coupling agent, zinc oxide, stearic acid, anti-aging agent, sulfur, vulcanization, which are generally used in the tire industry. Various materials such as an accelerator may be appropriately blended.

In addition to the composite silica, general silica may be added during kneading. Examples of the silica include silica produced by a dry method or a wet method, but the method for producing silica is not particularly limited.

The nitrogen adsorption specific surface area (N ₂ SA) of silica is preferably 30 m ² / g or more, more preferably 50 m ² / g or more, and still more preferably 100 m ² / g or more. If it is less than 30 m ² / g, the reinforcing effect tends to be small. The _N 2 SA of the silica is 500m or less preferably ² / g, more preferably not more than 400 meters ² / g, more preferably not more than 250m ² / g. When the N ₂ SA of silica exceeds 500 m ² / g, the dispersibility tends to decrease and the exothermic property of the rubber composition tends to increase. In addition, the nitrogen adsorption specific surface area by the BET method of a silica can be measured by the method based on ASTM-D-4820-93.

In the rubber composition of the present invention, it is preferable to use a silane coupling agent in combination. Thereby, reinforcement can be further improved.
The silane coupling agent is not particularly limited, and those conventionally used in combination with silica in the tire industry can be used. For example, bis (3-triethoxysilylpropyl) tetrasulfide, bis (2-triethoxysilylethyl) Tetrasulfide, bis (4-triethoxysilylbutyl) tetrasulfide, bis (3-trimethoxysilylpropyl) tetrasulfide, bis (2-trimethoxysilylethyl) tetrasulfide, bis (4-trimethoxysilylbutyl) tetrasulfide Bis (3-triethoxysilylpropyl) trisulfide, bis (2-triethoxysilylethyl) trisulfide, bis (4-triethoxysilylbutyl) trisulfide, bis (3-trimethoxysilylpropyl) trisulfide, bis (2-G Methoxysilylethyl) trisulfide, bis (4-trimethoxysilylbutyl) trisulfide, bis (3-triethoxysilylpropyl) disulfide, bis (2-triethoxysilylethyl) disulfide, bis (4-triethoxysilylbutyl) Sulfide systems such as disulfide, bis (3-trimethoxysilylpropyl) disulfide, bis (2-trimethoxysilylethyl) disulfide, bis (4-trimethoxysilylbutyl) disulfide, and mercapto systems such as 3-mercaptopropyltrimethoxysilane Vinyl type such as vinyltriethoxysilane, amino type such as 3-aminopropyltriethoxysilane, glycidoxy type such as γ-glycidoxypropyltriethoxysilane, and 3-nitropropyltrimethoxysilane. Any nitro-based, chloro-based such as 3-chloropropyltrimethoxysilane, and the like can be mentioned.

In the rubber composition, the content of the silane coupling agent is preferably 4 parts by mass or more, and more preferably 6 parts by mass or more with respect to 100 parts by mass of the total amount of the composite and the silica contained therein. If it is less than 4 parts by mass, it does not sufficiently react with silica and the reinforcing property tends not to be improved. Further, the content of the silane coupling agent is preferably 20 parts by mass or less, and more preferably 15 parts by mass or less. If it exceeds 20 parts by mass, the effect of improving the rubber strength and wear resistance due to the blending of the silane coupling agent is not seen, and the cost tends to increase.

As a method for producing the rubber composition of the present invention, known methods can be used. For example, the above components are kneaded using a rubber kneader such as an open roll, a Banbury mixer, a closed kneader, and then added. It can be manufactured by a method of sulfurating.

The rubber composition can be applied to each member of a tire, and among them, it can be suitably used for a tread and a sidewall.

<Pneumatic tire>
The rubber composition of the present invention is suitably applied to a pneumatic tire. Since a composite in which silica is finely dispersed is used, excellent reinforcement is exhibited, and performance such as low heat generation, grip performance, and wear resistance can be improved in a well-balanced manner.

The pneumatic tire of the present invention is produced by a usual method using the rubber composition. That is, a rubber composition containing various additives as necessary is extruded in accordance with the shape of each member of the tire at an unvulcanized stage and molded by a normal method on a tire molding machine. After forming an unvulcanized tire by heating, the tire can be manufactured by heating and pressing in a vulcanizer.

Moreover, the pneumatic tire of the present invention can be suitably used for passenger cars, trucks and buses, and low-pollution vehicles (eco-cars) compatible with global environmental conservation.

The present invention will be specifically described based on examples, but the present invention is not limited to these examples.

Hereinafter, various chemicals used in Examples and Comparative Examples will be described together.
Natural rubber latex: high ammonia type (rubber solid content concentration 60 mass%)
Surfactant: Polyoxyethylene fatty acid alcohol (alcohol carbon number C _{12 to} C ₁₈ , cloud point 70 to 80 ° C.)
Glacial acetic acid: Concentration 98 mass% Reagent grade 1 hydrogen peroxide solution: Concentration 30 mass%
Water glass: Water glass No. 3 manufactured by Fuji Chemical Co., Ltd. (Na ₂ O.nSiO ₂ .mH ₂ O, n = 3.2, silica component (SiO ₂ equivalent) content: 28% by mass)
Composite: produced in the following examples and comparative examples ENR25: epoxidized natural rubber (epoxidation rate 25% mol) manufactured by Kumpulan Gathrie Berhad (Malaysia)
ENR50: Epoxidized natural rubber (epoxidation rate 50% mol) manufactured by Kumpulan Gathrie Berhad (Malaysia)
Silica (1): Ultrasil VN3 (N ₂ SA: 175 m ² / g) manufactured by EVONIK-DEGUSSA
Silica (2): Premium 200MP (N ₂ SA: 200 m ² / g) manufactured by Rhodia
Si69 (bis (3-triethoxysilylpropyl) tetrasulfide) manufactured by EVONIK-DEGUSSA, a silane coupling agent
Oil: Vegetable oil (soybean oil) manufactured by Nisshin Oilio Co., Ltd.
Calcium stearate: Zinc oxide manufactured by NOF Co., Ltd .: Zinc Hua No. 1 manufactured by Mitsui Mining & Smelting Co., Ltd. Stearate: Anti-aging agent manufactured by NOF CO., LTD. 6C (N- (1,3-dimethylbutyl) -N′-phenyl-p-phenylenediamine)
Sulfur: Powder sulfur vulcanization accelerator manufactured by Tsurumi Chemical Co., Ltd. NS: Noxera-NS (N-tert-butyl-2-benzothiazolylsulfenamide) manufactured by Ouchi Shinsei Chemical Co., Ltd.
Vulcanization accelerator D: Noxeller D (N, N′-diphenylguanidine) manufactured by Ouchi Shinsei Chemical Industry Co., Ltd.

The evaluation methods of the vulcanizates obtained in the examples and comparative examples are as follows.
<Rolling resistance>
Loss tangent (tan δ) of each compound (vulcanized product) using a viscoelastic spectrometer VES (manufactured by Iwamoto Seisakusho Co., Ltd.) under the conditions of a temperature of 50 ° C., an initial strain of 10%, a dynamic strain of 2%, and a frequency of 10 Hz. The loss tangent tan δ of Comparative Example 1, 4 or 7 was taken as 100, and the result was expressed as an index (rolling resistance index) by the following formula. The larger the index, the better the rolling resistance characteristics.
(Rolling resistance index) = (tan δ of Comparative Example 1) / (tan δ of Examples 1 to 4 and Comparative Examples 2 to 3) × 100
(Rolling resistance index) = (tan δ of Comparative Example 4) / (tan δ of Examples 5 to 8 and Comparative Examples 5 to 6) × 100
(Rolling resistance index) = (tan δ of Comparative Example 7) / (tan δ of Examples 9 to 11 and Comparative Example 8) × 100

<Abrasion test>
Using a Lambourn abrasion tester, the Lambourn abrasion amount was measured under the conditions of a temperature of 20 ° C., a slip ratio of 20% and a test time of 2 minutes. Furthermore, the volume loss amount was calculated from the measured lamborn wear amount, the lamborn wear index of Comparative Example 1, 4 or 7 was set to 100, and the volume loss amount of each compound (vulcanized product) was displayed as an index according to the following formula. . In addition, it shows that it is excellent in abrasion resistance, so that a Lambourn abrasion index is large.
(Lambourn wear index) = (volume loss amount of comparative example 1) / (volume loss amount of examples 1 to 4 and comparative examples 2 to 3) × 100
(Lambourn wear index) = (volume loss amount of comparative example 4) / (volume loss amount of examples 5 to 8 and comparative examples 5 to 6) × 100
(Lambourn wear index) = (volume loss amount of comparative example 7) / (volume loss amount of examples 9 to 11 and comparative example 8) × 100

<Grip performance>
Using a viscoelastic spectrometer manufactured by Iwamoto Seisakusho Co., Ltd., loss tangent (tan δ) of each compound (vulcanized product) under the conditions of temperature 0 ° C., initial strain 10%, dynamic strain 0.5%, and frequency 10 Hz. ), And the grip index index of Comparative Example 1, 4 or 7 was set to 100, and the index was displayed by the following formula. The larger the grip index index, the better the grip performance.
(Grip index index) = (tan δ of Examples 1-4 and Comparative Examples 2-3) / (tan δ of Comparative Example 1) × 100
(Grip index index) = (tan δ of Examples 5 to 8 and Comparative Examples 5 to 6) / (tan δ of Comparative Example 4) × 100
(Grip index index) = (tan δ of Examples 9 to 11 and Comparative Example 8) / (tan δ of Comparative Example 7) × 100

Examples 1-8 and Comparative Examples 1-6
(Production of epoxidized natural rubber latex)
Glacial acetic acid and 30% by mass hydrogen peroxide solution were added to a 300 ml Erlenmeyer flask in the formulation shown in Table 1, and after stirring, the mixture was allowed to stand for 24 hours while being kept at 40 ° C. in a thermostatic bath to prepare a peracetic acid solution. 150 g of natural rubber latex, 350 g of distilled water and 16 g of a 15% by weight surfactant aqueous solution were added to a 1 L glass container, cooled to 10 ° C., and the peracetic acid solution prepared while stirring was added dropwise over 10 minutes. After completion of dropping, the latex solution was stirred for 24 hours to obtain epoxidized natural rubber latex (1) to (3). As a result of H ¹ -NMR, the epoxidation rates as shown in Table 1 were obtained.

(Preparation of fine particle silica dispersion)
A water glass aqueous solution having a silica component content (concentration) of 2% by mass is prepared using water glass, adjusted to pH 10 and stirred at 25 ° C. for 10 to 24 hours to obtain a fine particle silica dispersion (1) and (2) was obtained. The pH was adjusted with sulfuric acid.
Observation of the TEM photograph confirmed that silica having an average particle size of about 10 nm (fine particle silica dispersion (1)) and silica having an average particle size of about 20 nm (fine particle silica dispersion (2)) were obtained.

(Preparation of compounded latex, coagulation, preparation of composite)
As shown in Table 2, an epoxidized natural rubber latex was mixed with the fine particle silica dispersion to prepare a compounded latex. Each was mixed so that the silica component was 50 g per 100 g of rubber latex (solid content). After sufficiently stirring until the blended latex became uniform, the blended latex was adjusted to pH 7 with sulfuric acid and coagulated. The obtained solid was filtered to recover the rubber, washed with pure water and dried to obtain composites (A) to (D).

Further, as shown in Table 3, the same procedure as above except that the epoxidized natural rubber latex was mixed with the fine particle silica dispersion and mixed so that the silica component was 75 g with respect to 100 g of rubber latex (solid content). Thus, composites (E) to (H) were obtained.

(Production of rubber test piece)
According to the formulations shown in Tables 4 to 5, chemicals other than sulfur and a vulcanization accelerator were kneaded using 1.7 L Banbury. Next, using a roll, sulfur and a vulcanization accelerator were added to the obtained kneaded product and kneaded to obtain an unvulcanized rubber composition.
The obtained unvulcanized rubber composition was press vulcanized at 150 ° C. for 30 minutes to obtain a vulcanized product. Each vulcanizate obtained was evaluated, and the results are shown in Tables 4-5.
In addition, the silica content of the used composites (A) to (H) is 50 parts by mass for (A) to (D) and 75 parts by mass for (E) to (H) with respect to 100 parts by mass of ENR. Yes (same as the amount charged).

From Table 4, in Examples 1-4 using the composites (A) to (D) (50 parts by mass of silica finely dispersed), the low rolling resistance, wear resistance, and grip performance were improved in a well-balanced manner. On the other hand, in Comparative Examples 1 to 3 in which ENR25 or ENR50 and silica were mixed by kneading, the performance was considerably inferior. Further, from Table 5, the same tendency was observed when the composites (E) to (H) (75 parts by mass of silica were finely dispersed) were used.

Examples 9-11
(Preparation of fine particle silica dispersion)
A water glass aqueous solution having a silica component content (concentration) of 2% by mass was prepared using water glass, adjusted to pH 10 and stirred at 80 ° C. for 24 hours to obtain a fine particle silica dispersion (3). .
The pH was adjusted using an H-type strongly acidic cation exchange resin (IR120B manufactured by Organo Corporation).
It was confirmed by observation of the TEM photograph that silica having an average particle diameter of about 10 nm was obtained.

(Preparation of compounded latex, coagulation, preparation of composite)
The fine particle silica dispersion (3) was mixed with the epoxidized natural rubber latex (2) obtained above to prepare a compounded latex. The mixture was mixed so that the silica component was 100 g with respect to 100 g of rubber latex, and stirred for 1 hour. Thereafter, sulfuric acid was added to the blended latex and coagulated by adjusting to pH 7. The obtained solid was filtered to recover the rubber, washed with pure water and dried. The obtained dried product was kneaded with rubber using a biaxial roll for 5 minutes to obtain a composite (I).

A photograph of the obtained complex (I) is shown in FIG. 1 (right part). It was clear that the composite was transparent, and that silica was uniformly finely dispersed. When the inorganic component was measured by thermogravimetric analysis, the charge ratio (rubber content: silica content) was 1: 1, but it was 1: 0.58, and the silica content was 37% by mass. The decrease in the silica component was thought to be because some of the silica passed through the filter paper during the filtration operation due to the fine particles of silica.

Furthermore, the TEM photograph of the obtained complex (I) is shown in FIG. A large silica aggregate exceeding several μm was not formed, and it was observed that silica having a particle size of 10 nm or less was uniformly dispersed in the rubber without forming a large aggregate.
From the above, it has been clarified that the present invention can uniformly disperse fine particle silica having an average particle diameter of 10 nm or less in rubber.

Comparative Example 7
Silica (1) (VN3) was used as the silica. Then, in place of the fine particle silica dispersion (3), a composite (a) was obtained in the same manner as in Example 9, except that a silica dispersion in which silica (1) was dispersed in water was used. In addition, when the inorganic component was measured by thermogravimetric analysis, it was rubber part: silica part = 1: 0.57, and silica content was 36 mass.
A photograph of the resulting composite (a) is shown in FIG. 1 (left part). It was revealed that the obtained rubber sheet was not transparent and silica was agglomerated.

Comparative Example 8
A composite (b) was obtained in the same manner as in Example 9 except that natural rubber latex was used instead of the epoxidized natural rubber latex (2). When the inorganic component was measured by thermogravimetric analysis, the silica content was 30 mass.
A photograph of the obtained complex (b) is shown in FIG. It was revealed that the obtained rubber sheet was not transparent and silica was agglomerated.

(Production of rubber test piece)
For Example 9 and Comparative Examples 7 to 8, a vulcanizate was obtained in the same manner as above except that the obtained composites (I), (a) and (b) were used and the composition shown in Table 6 was followed. Evaluation was performed. The results are shown in Table 6.

From Table 6, also in Examples 9 to 11 using the composite (I) obtained by adjusting the pH with a cation exchange resin, the low rolling resistance, wear resistance, and grip performance were improved in a well-balanced manner. On the other hand, in Comparative Example 7 in which ENR latex and silica were mixed and in Comparative Example 8 in which natural rubber latex was used, the performance was considerably inferior.

Claims (7)

A composite obtained from a blended latex obtained by mixing a polar group-containing modified natural rubber latex and a fine particle silica dispersion having an average particle size of 100 nm or less produced from water glass. The composite according to claim 1, wherein the polar group-containing modified natural rubber latex is an epoxidized natural rubber latex. The fine particle silica dispersion is prepared by adjusting the pH of a water glass aqueous solution to 9 to 11 using an ion exchange resin, and the average particle diameter of silica in the dispersion is 15 nm or less. The complex according to 1 or 2. The polar group-containing modified natural rubber latex and the fine particle silica dispersion having an average particle size of 100 nm or less produced from water glass are mixed to prepare a compounded latex (I), and obtained in the step (I). The manufacturing method of the composite_body | complex in any one of Claims 1-3 including the process (II) which coagulate | blends mixing | blending latex. The rubber composition containing the composite_body | complex in any one of Claims 1-3. The rubber composition according to claim 5, further comprising a fatty acid salt. A pneumatic tire produced using the rubber composition according to claim 5.