JP7679168B2 - Manufacturing method of rubber-filler composite - Google Patents

Description

The present invention relates to a method for producing a rubber-filler composite, and a rubber-filler composite obtained by the method.

By blending fillers such as silica and microfibrillated vegetable fibers (such as cellulose fibers) into a rubber composition, it is possible to reinforce the rubber composition and improve its modulus (complex elastic modulus). However, for example, when adding a filler to a rubber latex and attempting to mix the rubber component with the filler, a problem occurs in which the added filler is not fully incorporated into the rubber component and remains in the solution.

In response to this, methods have been disclosed that chemically modify microfibrillated plant fibers to improve the compatibility between the rubber component and the microfibrillated plant fibers, that incorporate carboxyl group-containing cellulose fibers or finely modified cellulose fibers into rubber to improve the dispersibility of cellulose fibers in rubber, and that use composite cellulose fibers, which are made by graft-polymerizing polymers onto cellulose nanofibers, as a rubber reinforcing material to improve the affinity and dispersibility of rubber components (see Patent Documents 1 to 4).

However, even with the above-mentioned method, there is a problem in that some of the filler used is not sufficiently incorporated into the rubber component, making it difficult to obtain the desired rubber-filler composite.

Patent No. 4581116 specification JP 2013-18918 A JP 2014-125607 A JP 2009-263417 A

The present invention aims to solve the above problems and provide a method for producing a rubber-filler composite that can fully incorporate the filler used into the rubber component.

The present invention relates to a method for producing a rubber-filler composite, which includes a step of mixing rubber latex, a filler dispersion, and a surfactant, and which has a filler incorporation rate of 95% by mass or more in the rubber-filler composite.

The filler dispersion is preferably a silica dispersion and/or a microfibrillated plant fiber dispersion.

The surfactant is preferably a nonionic surfactant and/or an anionic surfactant.

The present invention also relates to a rubber-filler composite obtained by the above manufacturing method.

The present invention provides a method for producing a rubber-filler composite that includes a step of mixing rubber latex, a filler dispersion, and a surfactant, and has a filler incorporation rate of 95% by mass or more in the rubber-filler composite, thereby providing a method that can fully incorporate the filler used into the rubber component.

[Method for producing rubber-filler composite]
The present invention is a method for producing a rubber-filler composite, which includes a step of mixing a rubber latex, a filler dispersion, and a surfactant, and which has a filler incorporation rate of 95 mass% or more in the rubber-filler composite. Note that the production method of the present invention may include other steps as long as it includes the above steps, and each of the above steps may be performed once or repeatedly multiple times.

The mechanism by which the filler incorporation rate can be increased to 95% by mass or more is not entirely clear, but is presumed to be as follows.
For example, when a filler is added to rubber latex and the rubber component and the filler are mixed, the added filler is not fully incorporated into the rubber component and remains in the solution, but by using rubber latex as a rubber component source, a filler dispersion as a filler source, and at the same time using a surfactant, the hydrophilic group of the surfactant interacts with the functional group on the surface of the filler such as silica or microfibrillated plant fiber, and the hydrophobic group interacts with the rubber, so that the rubber and the filler become compatible and the filler is less likely to come out of the rubber. As a result, it is presumed that most of the filler used in producing the rubber-filler composite is incorporated into the rubber.

This is a manufacturing method in which the filler incorporation rate in the rubber-filler composite (the proportion (mass) of filler incorporated (contained) in the composite out of the total amount of filler used in the production of the rubber-filler composite (100 mass%)) is 95 mass% or more, but is preferably 96 mass% or more, and more preferably 98 mass% or more. There is no particular upper limit, and 100 mass% is most suitable.

The filler incorporation rate can be adjusted by the type and amount of the rubber latex source, the filler source, and the surfactant. For example, the incorporation rate can be adjusted by appropriately selecting the type and amount of the surfactant, and the incorporation rate tends to increase as a larger amount of surfactant that has a large interaction with the rubber latex type and filler type used is used. In addition, the incorporation rate can be adjusted by appropriately adjusting the concentration of the rubber latex and the filler dispersion.

Specific examples of methods for achieving a filler incorporation rate of 95% by mass or more include (a) using a nonionic surfactant as the surfactant when silica is used as the filler, (b) using an anionic surfactant and/or a nonionic surfactant as the surfactant when microfibrillated plant fiber is used as the filler, (c) adjusting the concentration of the rubber latex, (d) adjusting the concentration of the filler dispersion, and (e) first mixing the surfactant and the filler dispersion and then mixing the rubber latex, either alone or in combination as appropriate.

The filler incorporation rate (the incorporation rate (the proportion of filler incorporated in the rubber) per 100% by mass of the filler charge) can be measured by the method described in the Examples below. For example, a dispersion of a rubber-filler complex obtained from rubber latex, a filler dispersion, and a surfactant is solidified, and the rubber-filler complex thus produced is observed under an electron microscope such as a TEM. Next, the obtained image is binarized using image analysis software such as Image J, a threshold is set, the amount of filler is quantitatively analyzed, and the filler incorporation rate is calculated based on the amount of filler.

The step of mixing the rubber latex, filler dispersion, and surfactant is not particularly limited as long as it is a step of mixing the rubber latex, filler dispersion, and surfactant and adjusting the filler uptake rate in the rubber-filler composite to 95% by mass or more. In particular, it is preferable that the step includes a step of mixing the surfactant and the filler dispersion to prepare a mixed liquid (step (1)), and a step of mixing the mixed liquid and the rubber latex (step (2)).

(Step (1))
The surfactant has a hydrophobic group and a hydrophilic group, and examples thereof include nonionic surfactants, anionic surfactants, and cationic surfactants. Among them, from the viewpoint of filler incorporation rate, when silica is used as the filler, nonionic surfactants are preferred. When microfibrillated plant fibers are used as the filler, nonionic surfactants and anionic surfactants are preferred, and anionic surfactants are more preferred.

The nonionic surfactant is not particularly limited, and conventionally known surfactants can be used, such as polyoxyalkylene alkyl ethers such as polyoxyethylene alkyl ethers, polyoxyethylene polypropylene alkyl ethers, and polyoxyethylene polybutylene alkyl ethers; polyoxyalkylene alkenyl ethers such as polyoxyethylene alkenyl ethers; polyoxyethylene alkylphenyl ethers; and higher fatty acid alkanolamides. Of these, nonionic surfactants having a polyoxyethylene group as the hydrophilic group and a hydrocarbon group as the hydrophobic group can be preferably used.

As such a nonionic surfactant, compounds represented by the following formulas (I) to (III) can be preferably used. Among them, the compound represented by the following formula (I) is particularly preferably used.

R ¹ -O-(EO) _x -H (I)
(In formula (I), ^R1 represents an alkyl group having 3 to 50 carbon atoms or an alkenyl group having 3 to 50 carbon atoms. EO represents an oxyethylene group. The average number of moles added, x, is 3 to 100.)

The number of carbon atoms in ^R1 is preferably 5 to 30, and more preferably 8 to 20. The above x is preferably 5 to 50, and more preferably 8 to 30.

R ² -O-(AO) _y (EO) _z -H (II)
(In formula (II), ^R2 represents an alkyl group having 3 to 50 carbon atoms or an alkenyl group having 3 to 50 carbon atoms. AO represents an oxypropylene group or an oxybutylene group, and EO represents an oxyethylene group. The average number of moles added y is 3 to 100, and the average number of moles added z is 3 to 100.)

The number of carbon atoms in ^R2 is preferably 5 to 30, more preferably 8 to 20. The above y is preferably 5 to 50, more preferably 8 to 30. The above z is preferably 5 to 50, more preferably 8 to 30. The arrangement of EO and AO may be block or random.

In the above formula (III), R ³ to R ⁵ are the same or different and represent a hydrogen atom, an alkyl group having 1 to 30 carbon atoms, an alkenyl group having 1 to 30 carbon atoms, or an alkoxy group having 1 to 30 carbon atoms. R ⁶ represents an alkylene group having 1 to 30 carbon atoms. EO represents an oxyethylene group. The average number of moles added a is 0 to 50, the average number of moles added b is 0 to 50, and the average number of moles added c is 1 to 50.

The carbon number of ^R3 and ^R4 is preferably 1 to 25, and ^R5 is preferably a hydrogen atom or an alkyl group having 1 to 25 carbon atoms. The carbon number of ^R6 is preferably 3 to 8. The above a and b are preferably 0 to 30, more preferably 5 to 30, and the above c is preferably 1 to 30, more preferably 1 to 10.

The hydrophobic group of the anionic surfactant can be any hydrophobic functional group. Among these, a hydrocarbon group is preferred. The hydrocarbon group may be linear, branched, or cyclic, and examples thereof include an aliphatic hydrocarbon group, an alicyclic hydrocarbon group, and an aromatic hydrocarbon group. Among these, an aliphatic hydrocarbon group and an aromatic hydrocarbon group are preferred. The number of carbon atoms in the above-mentioned hydrocarbon group is preferably 4 to 20, more preferably 4 to 15, and even more preferably 4 to 12.

The aliphatic hydrocarbon group preferably has 1 to 20 carbon atoms, more preferably 1 to 10 carbon atoms, and even more preferably 1 to 6 carbon atoms. Preferred examples include alkyl groups having the above carbon numbers, specifically, for example, methyl, ethyl, n-propyl, isopropyl, n-butyl, isobutyl, sec-butyl, tert-butyl, pentyl, hexyl, heptyl, 2-ethylhexyl, octyl, nonyl, decyl, undecyl, dodecyl, tridecyl, tetradecyl, pentadecyl, and octadecyl groups. In addition, alkenyl and alkynyl groups having the above carbon numbers are also included, examples of which include alkenyl groups such as vinyl, allyl, 1-propenyl, 1-methylethenyl, and isobutylene groups, and alkynyl groups such as ethynyl and propargyl groups. Of these, the isobutylene group is preferred.

As the alicyclic hydrocarbon group, those having 3 to 8 carbon atoms are preferred, and specific examples include a cyclopropyl group, a cyclobutyl group, a cyclopentyl group, a cyclohexyl group, a cycloheptyl group, a cyclooctyl group, a cyclopropenyl group, a cyclobutenyl group, a cyclopentenyl group, a cyclohexenyl group, a cycloheptenyl group, and a cyclooctenyl group.

The aromatic hydrocarbon group preferably has 6 to 12 carbon atoms, and specific examples thereof include a phenyl group, a benzyl group, a phenethyl group, a tolyl group, a xylyl group, and a naphthyl group. Among these, a phenyl group, a benzyl group, and a phenethyl group are preferred, a phenyl group and a benzyl group are more preferred, and a phenyl group is particularly preferred. Note that the substitution position of the methyl group on the benzene ring in a tolyl group and a xylyl group may be any of the ortho, meta, and para positions.

As the hydrophilic group of the anionic surfactant, at least one selected from the group consisting of a carboxyl group, a sulfonic acid group, a sulfate group, and a phosphate group is preferred. Of these, a carboxyl group is particularly preferred.

Anionic surfactants can be specifically classified into carboxylic acid, sulfonic acid, sulfate, and phosphate surfactants.

Examples of carboxylic acid surfactants include fatty acid salts having 6 to 30 carbon atoms, polycarboxylic acid salts, rosin acid salts, dimer acid salts, polymer acid salts, tall oil fatty acid salts, polycarboxylic acid type polymer surfactants, etc., and preferably carboxylic acid salts having 10 to 20 carbon atoms, polycarboxylic acid salts, and polycarboxylic acid type polymer surfactants, and particularly preferably polycarboxylic acid type polymer surfactants. Examples of sulfonic acid surfactants include alkylbenzene sulfonates, alkyl sulfonates, alkylnaphthalene sulfonates, naphthalene sulfonates, diphenyl ether sulfonates, etc. Examples of the sulfate ester surfactants include alkyl sulfate esters, polyoxyalkylene alkyl sulfate esters, polyoxyalkylene alkylphenyl ether sulfates, tristyrenated phenol sulfate esters, distyrenated phenol sulfate esters, α-olefin sulfate esters, alkylsuccinic acid sulfate esters, polyoxyalkylene tristyrenated phenol sulfate esters, polyoxyalkylene distyrenated phenol sulfate esters, etc. Examples of phosphate ester surfactants include alkyl phosphate ester salts and polyoxyalkylene phosphate ester salts. Examples of salts of these compounds include metal salts (Na, K, Ca, Mg, Zn, etc.), ammonium salts, and amine salts (triethanolamine salts, etc.). The alkyl groups in these surfactants include alkyl groups having 4 to 30 carbon atoms. The polyoxyalkylene groups include those having alkylene groups having 2 to 4 carbon atoms, and those having an added mole number of ethylene oxide of about 1 to 50 moles can be used.

The anionic surfactant preferably has a weight average molecular weight (Mw) of 500 or more, more preferably 1000 or more. Also, it is preferably 50000 or less, more preferably 30000 or less. In this specification, Mw can be calculated based on the measured value obtained by gel permeation chromatography (GPC) (GPC-8000 series manufactured by Tosoh Corporation, detector: differential refractometer, column: TSKGEL SUPERMULTIPORE HZ-M manufactured by Tosoh Corporation) in terms of standard polystyrene.

As the cationic surfactant, a quaternary ammonium salt type, i.e., a surfactant represented by the following formula (IV) having a quaternary ammonium group and a hydrocarbon group, can be preferably used.

[R ⁷ R ⁸ R ⁹ R ¹⁰ N] ⁺ X ^- (IV)
(In formula (IV), R ⁷ and R ⁸ are the same or different and represent an alkyl group or alkenyl group having 1 to 22 carbon atoms, and at least one of R ⁷ and R ⁸ has 4 or more carbon atoms. ^{R 9} and R ¹⁰ represent an alkyl group having 1 to 3 carbon atoms. X represents a monovalent anion.)

In the above formula (IV), it is preferable that one of ^R7 and ^R8 is a methyl group and the other is an alkyl group having 6 to 18 carbon atoms. It is preferable that ^R9 and ^R10 are methyl groups. X includes a halogen ion such as a chloride ion or a bromide ion.

Specific examples of the cationic surfactant represented by the above formula (IV) include alkyltrimethylammonium salts such as hexyltrimethylammonium chloride, octyltrimethylammonium chloride, decyltrimethylammonium chloride, dodecyltrimethylammonium chloride, tetradecyltrimethylammonium chloride, hexadecyltrimethylammonium chloride, stearyltrimethylammonium chloride, and the corresponding bromides. Among these, hexadecyltrimethylammonium bromide is preferred.

Commercially available surfactants include those from Elementis, Kao Corporation, Daiichi Kogyo Seiyaku Co., Ltd., Sanyo Chemical Industries, Ltd., EVONIK-DEGUSSA Co., Ltd., Huntsman Co., Ltd., and others.

The filler dispersion is a dispersion (slurry) in which a filler is dispersed in a solvent. The filler is not particularly limited, and examples thereof include carbon black, silica, clay, talc, calcium carbonate, and microfibrillated plant fiber. For example, silica and microfibrillated plant fiber are preferably used. The solvent is not particularly limited, and examples thereof include water and organic solvents such as alcohol, and among these, water is preferred.

The silica is not particularly limited, and can be one normally used in the rubber industry, such as dry process silica (silicic anhydride) and wet process silica (silicic anhydride). Of these, wet process silica is preferred, and specific examples include Ultrasil VN3, 7000GR, and 9000GR manufactured by Degussa, Nipsil AQ manufactured by Tosoh Silica, and Zeosil 115GR manufactured by Rhodia Japan. These may be used alone or in combination of two or more types.

The nitrogen adsorption specific surface area (N ₂ SA) of silica is preferably 70 m ² /g or more, more preferably 140 m ² /g or more, and even more preferably 160 m ² /g or more. By making it equal to or more than the lower limit, good wet grip performance, breaking strength, etc. tend to be obtained. In addition, the upper limit of the N ₂ SA of silica is not particularly limited, but is preferably 500 m ² /g or less, more preferably 300 m ² /g or less, and even more preferably 250 m ² /g or less. By making it equal to or less than the upper limit, good dispersibility tends to be obtained.
The N ₂ SA of silica is a value measured by the BET method in accordance with ASTM D3037-93.

As the microfibrillated plant fiber, cellulose microfibrils are preferred because they provide good reinforcing properties. The cellulose microfibrils are not particularly limited as long as they are derived from natural products, and examples include those derived from resource biomass such as fruits, grains, and root vegetables, wood, bamboo, hemp, jute, and kenaf, as well as pulp, paper, cloth, agricultural waste, waste biomass such as food waste and sewage sludge obtained using these as raw materials, unused biomass such as rice straw, wheat straw, and thinning materials, as well as cellulose produced by sea squirts, acetic acid bacteria, and the like. These microfibrillated plant fibers may be used alone or in combination of two or more types.

In this specification, cellulose microfibrils typically refer to cellulose fibers having an average fiber diameter of 10 μm or less, and more typically refer to cellulose fibers having a microstructure formed by an assembly of cellulose molecules and an average fiber diameter of 500 nm or less. Typical cellulose microfibrils can be formed, for example, as an assembly of cellulose fibers having the above-mentioned average fiber diameter.

The method for producing the microfibrillated plant fiber is not particularly limited, but examples include a method in which the raw material for the cellulose microfibrils is chemically treated with an alkali such as sodium hydroxide as necessary, and then mechanically ground or beaten using a refiner, a twin-screw kneader (twin-screw extruder), a twin-screw kneading extruder, a high-pressure homogenizer, a media stirring mill, a stone mill, a grinder, a vibration mill, a sand grinder, or the like. In these methods, lignin is separated from the raw material by chemical treatment, so that microfibrillated plant fiber that is substantially free of lignin is obtained. Another example is a method in which the raw material for the cellulose microfibrils is subjected to ultra-high pressure treatment.

As the above-mentioned microfibrillated plant fiber, for example, products from Sugino Machine Ltd. can be used.

The microfibrillated plant fibers may be those obtained by the above-mentioned production method, which have been further subjected to oxidation treatment or various chemical modification treatments, or those obtained by using natural materials from which the above-mentioned cellulose microfibrils can be derived (e.g., wood, pulp, bamboo, hemp, jute, kenaf, agricultural waste, cloth, paper, sea squirt cellulose, etc.) as cellulose raw materials and subjecting them to oxidation treatment or various chemical modification treatments, followed by defibration treatment as necessary, or those obtained by subjecting the microfibrillated plant fiber dispersion to further oxidation treatment or various chemical modification treatments.

Examples of chemical modification of the microfibrillated plant fibers include, for example, esterification, etherification, and acetalization. More specifically, preferred examples include acylation such as acetylation, cyanoethylation, amination, sulfone esterification, phosphate esterification, alkyl esterification, alkyl etherification, complex esterification, β-keto esterification, alkylation such as butylation, and chlorination. Further examples include alkyl carbamate and aryl carbamate.

In other words, the microfibrillated plant fiber is a chemically modified microfibrillated plant fiber, and the chemical modification in the chemically modified microfibrillated plant fiber is preferably at least one selected from the group consisting of acetylation, amination, sulfone esterification, alkyl esterification, complex esterification, β-keto esterification, alkyl carbamate, and aryl carbamate. All of these chemical modification treatments are treatments that hydrophobize the microfibrillated plant fiber, and by using microfibrillated plant fiber that has been subjected to such chemical modification treatment, the dispersibility of the microfibrillated plant fiber can be further improved.

The chemically modified microfibrillated plant fiber is preferably chemically modified so that the degree of substitution is within the range of 0.2 to 2.5. Here, the degree of substitution means the average number of hydroxyl groups per glucose ring unit of cellulose that have been replaced with other functional groups by chemical modification, and the theoretical maximum value is 3. When the degree of substitution is 0.2 or more, the dispersibility of the chemically modified microfibrillated plant fiber is particularly good, and when the degree of substitution is 2.5 or less, the chemically modified microfibrillated plant fiber is particularly excellent in dispersibility and particularly excellent in flexibility. The degree of substitution is more preferably within the range of 0.3 to 2.5, even more preferably within the range of 0.4 to 2.3, and particularly preferably within the range of 0.4 to 2.0.

When the above-mentioned chemically modified microfibrillated plant fibers are a combination of two or more types, the above-mentioned degree of substitution is calculated as an average for the entire chemically modified microfibrillated plant fiber.

The degree of substitution in the above-mentioned chemically modified microfibrillated plant fibers can be confirmed, for example, by a titration method using 0.5N-NaOH and 0.2N-HCl, or by measurements such as NMR and infrared absorption spectroscopy.

When the chemically modified microfibrillated plant fiber is an acetylated microfibrillated plant fiber, the degree of substitution is preferably 0.3 to 2.5; when it is an aminated microfibrillated plant fiber, the degree of substitution is preferably 0.3 to 2.5; when it is a sulfone esterified microfibrillated plant fiber, the degree of substitution is preferably 0.3 to 1.8; when it is an alkyl esterified microfibril cellulose, the degree of substitution is preferably 0.3 to 1.8; when it is a complex esterified microfibril cellulose, the degree of substitution is preferably 0.4 to 1.8; when it is a β-keto esterified microfibril cellulose, the degree of substitution is preferably 0.3 to 1.8; when it is an alkyl carbamate microfibril cellulose, the degree of substitution is preferably 0.3 to 1.8; and when it is an aryl carbamate microfibril cellulose, the degree of substitution is preferably 0.3 to 1.8.

The acetylation can be carried out, for example, by adding acetic acid, concentrated sulfuric acid, or acetic anhydride to the microfibrillated plant fiber and reacting them. More specifically, the acetylation can be carried out by a conventional method, for example, by reacting the microfibrillated plant fiber with acetic anhydride in a mixed solvent of acetic acid and toluene in the presence of a sulfuric acid catalyst to cause the acetylation reaction to proceed, and then replacing the solvent with water.

The above amination can be carried out by known methods, such as a method in which the tosyl ester is converted, followed by reaction with an alkylamine in an alcohol to cause a nucleophilic substitution reaction.

The above-mentioned sulfone esterification can be carried out, for example, by a simple procedure of dissolving the microfibrillated plant fiber in sulfuric acid and then pouring it into water. It can also be carried out by other methods such as treatment with anhydrous sulfuric acid gas or treatment with chlorosulfonic acid and pyridine.

The above-mentioned phosphate esterification can be carried out, for example, by treating microfibrillated plant fibers that have been treated with dimethylamine or the like with phosphoric acid and urea.

The alkyl esterification can be carried out, for example, by the Schotten-Baumann method, in which microfibrillated plant fibers are reacted with a carboxylic acid chloride under basic conditions, and the alkyl etherification can be carried out by the Williamson method, in which microfibrillated plant fibers are reacted with an alkyl halide under basic conditions.

The above chlorination can be carried out, for example, by adding thionyl chloride in DMF (dimethylformamide) and heating.

The above complex esterification can be carried out, for example, by reacting microfibrillated plant fibers with two or more types of carboxylic acid anhydrides or carboxylic acid chlorides under basic conditions.

The above-mentioned β-ketoesterification can be carried out, for example, by reacting the microfibrillated plant fiber with diketene or alkyl ketene dimer, or by a transesterification reaction between the microfibrillated plant fiber and a β-ketoester compound such as an alkyl acetoacetate.

The alkyl carbamate formation can be carried out, for example, by reacting the microfibrillated plant fiber with an alkyl isocyanate in the presence of a basic catalyst or a tin catalyst.

The above-mentioned aryl carbamate formation can be carried out, for example, by reacting microfibrillated plant fibers with aryl isocyanate in the presence of a basic catalyst or a tin catalyst.

The oxidation treatment of the microfibrillated plant fibers may be, for example, an oxidation treatment using an N-oxyl compound.
The oxidation treatment using the above-mentioned N-oxyl compound can be carried out, for example, by using the N-oxyl compound as an oxidation catalyst in water and reacting a co-oxidant with the microfibrillated plant fiber.

Examples of the N-oxyl compound include 2,2,6,6-tetramethylpiperidine-1-oxyl (TEMPO) and its derivatives.
The co-oxidizing agent includes, for example, sodium hypochlorite.

The average fiber diameter of the microfibrillated plant fibers is preferably 4 to 100 nm. The average fiber diameter is preferably 90 nm or less, and more preferably 50 nm or less. In addition, because the microfibrillated plant fibers are difficult to disentangle and disperse, the average fiber diameter is preferably 10 nm or more, and more preferably 20 nm or more.

The average fiber length of the microfibrillated plant fibers is preferably 100 nm or more. More preferably, it is 300 nm or more, and even more preferably, it is 500 nm or more. In addition, it is preferably 5 mm or less, more preferably 1 mm or less, even more preferably 50 μm or less, particularly preferably 3 μm or less, and most preferably 2 μm or less.

When the microfibrillated plant fibers are a combination of two or more types, the average fiber diameter and average fiber length are calculated as the average for the entire microfibrillated plant fiber.

In this specification, the average fiber diameter and average fiber length of the microfibrillated plant fibers can be measured by image analysis using scanning electron microscope photographs, image analysis using transmission electron microscope photographs, image analysis using atomic force microscope photographs, analysis of X-ray scattering data, pore electrical resistance method (Coulter principle method), etc.

The filler dispersion can be produced by a known method, and the production method is not particularly limited. For example, it can be prepared by dispersing the filler in a solvent such as water using a high-speed homogenizer, an ultrasonic homogenizer, a colloid mill, a blender mill, or the like. The temperature and time during preparation can also be appropriately set within the ranges normally used so that the filler is sufficiently dispersed in the solvent such as water.

The filler content (solid content) in the filler dispersion is not particularly limited, but is preferably 0.2 to 20% by mass, more preferably 0.5 to 10% by mass, and even more preferably 0.5 to 7% by mass.

In the above step (1), the method of mixing the surfactant and the filler dispersion to prepare a mixture can be, for example, a method of mixing the surfactant and the filler dispersion using a known stirring device such as a high-speed homogenizer, an ultrasonic homogenizer, a colloid mill, or a blender mill, and the mixture can be obtained by stirring thoroughly until the surfactant and the filler dispersion are sufficiently dispersed. The temperature and time when preparing the mixture can be appropriately set within the range normally used until the surfactant and the filler dispersion are sufficiently dispersed, and for example, 10 to 40°C for 3 to 120 minutes are preferable, and 15 to 30°C for 5 to 90 minutes are more preferable.

The amount of surfactant added is preferably 1 to 50 parts by mass per 100 parts by mass of rubber latex (rubber solids) used in the rubber-filler composite. The amount added is more preferably 2 parts by mass or more, and even more preferably 3 parts by mass or more. Also, it is more preferably 25 parts by mass or less, even more preferably 20 parts by mass or less, and particularly preferably 15 parts by mass or less.

The amount of filler is preferably 1 to 50 parts by mass per 100 parts by mass of rubber latex (solid rubber content) used in the rubber-filler composite. The amount is more preferably 2 parts by mass or more, even more preferably 5 parts by mass or more, and particularly preferably 7 parts by mass or more. Also, it is more preferably 40 parts by mass or less, even more preferably 35 parts by mass or less, and particularly preferably 30 parts by mass or less. When microfibrillated vegetable fiber is used as the filler, the amount is preferably in the same range. When silica is used as the filler, the amount is preferably 5 to 50 parts by mass, more preferably 7 to 50 parts by mass, and even more preferably 7 to 40 parts by mass.

(Step (2))
In the present invention, the next step (step (2)) is to mix the mixture obtained in step (1) with rubber latex.

As the rubber latex, for example, diene-based rubber latex such as natural rubber latex, modified natural rubber latex (saponified natural rubber latex, epoxidized natural rubber latex, etc.), synthetic diene-based rubber latex (latex such as butadiene rubber (BR), styrene butadiene rubber (SBR), styrene isoprene butadiene rubber (SIBR), isoprene rubber, acrylonitrile butadiene rubber, ethylene vinyl acetate rubber, chloroprene rubber, vinylpyridine rubber, and butyl rubber) can be suitably used. These rubber latexes may be used alone or in combination of two or more. Among them, natural rubber latex, SBR latex, BR latex, and isoprene rubber latex are more preferable, and natural rubber latex is particularly preferable.

Natural rubber latex is collected as sap from natural rubber trees such as Hevea trees, and contains water, proteins, lipids, inorganic salts, etc. in addition to rubber components, and the gel content in the rubber is thought to be due to the presence of a complex of various impurities. In the present invention, the natural rubber latex that can be used includes raw latex (field latex) that comes out by tapping Hevea trees, concentrated latex concentrated by centrifugation or creaming methods (refined latex, high ammonia latex to which ammonia has been added by the usual method, LATZ latex stabilized with zinc oxide, TMTD, and ammonia, etc.), etc.

The pH of the rubber latex is preferably 8.5 or higher, more preferably 9.5 or higher. When the pH is 8.5 or higher, the rubber latex tends not to become unstable and not to coagulate. The pH of the rubber latex is preferably 12 or lower, more preferably 11 or lower. When the pH is 12 or lower, the rubber latex tends not to deteriorate.

Rubber latex can be prepared by a conventional method, and various commercially available products can also be used. It is preferable to use rubber latex with a rubber solids content of 10 to 80% by mass. More preferably, it is 20% by mass or more and 60% by mass or less.

In the above step (2), the mixed liquid obtained in step (1) and the rubber latex can be mixed, for example, in a known stirring device such as a high-speed homogenizer, ultrasonic homogenizer, colloid mill, or blender mill, by placing the rubber in the device and dropping the mixed liquid obtained in step (1) while stirring, or dropping the rubber latex into the mixed liquid obtained in step (1) while stirring. By stirring thoroughly until the rubber is sufficiently dispersed, a mixture of the mixed liquid obtained in step (1) and the rubber (compounded latex) can be obtained. The temperature and time for preparing the mixture can be appropriately set within the ranges normally used until the mixed liquid obtained in step (1) and the rubber are sufficiently dispersed, but for example, 10 to 40°C for 3 to 120 minutes are preferable, and 15 to 30°C for 5 to 90 minutes are more preferable.

The pH of the mixture (compounded latex) obtained in step (2) is preferably 9.0 or more, more preferably 9.5 or more. Also, it is preferably 12 or less, more preferably 11.5 or less. When the pH of the mixture (compounded latex) of the mixed liquid obtained in step (1) and rubber latex is in this range, deterioration can be suppressed and the mixture can be stabilized.

The mixture (compounded latex) obtained in step (2) above is coagulated as necessary, and the coagulated material (coagulated material containing coagulated rubber and filler) is filtered and dried by a known method. After further drying, rubber kneading is performed using a two-screw roll or Banbury roll to obtain a composite (rubber-filler composite) in which the filler is sufficiently dispersed in the rubber matrix. The rubber-filler composite may contain other components as long as they do not impair the effect.

The coagulation is usually carried out by adding an acid to the mixture (compounded latex) obtained in step (2) above. Examples of acids for coagulation include sulfuric acid, hydrochloric acid, formic acid, and acetic acid. The temperature during coagulation is preferably 10 to 40°C.

During the coagulation, it is preferable to adjust the pH of the mixture (compounded latex) obtained in step (2) to 3 to 5, and more preferably to 3 to 4.

Flocculants may also be added to control the state of coagulation (the size of the coagulated aggregated particles). Cationic polymers and the like can be used as flocculants.

Using such manufacturing methods, rubber-filler composites with a filler incorporation rate of 95% by mass or more can be produced.

[Rubber composition]
The rubber composition includes the rubber-filler complex. The rubber-filler complex can be used as a master batch. The rubber-filler complex has the filler sufficiently dispersed in the rubber, and the filler can be sufficiently dispersed even in a rubber composition mixed with other components. Therefore, it can exhibit effective reinforcing properties and can improve performance such as durability (breaking strength) and handling stability in a well-balanced manner.

The rubber composition may contain rubber components other than the rubber (rubber component) used in the rubber-filler complex.
As the other rubber component, for example, a diene rubber can be used.
Examples of the diene rubber include isoprene rubber, butadiene rubber (BR), styrene butadiene rubber (SBR), styrene isoprene butadiene rubber (SIBR), ethylene propylene diene rubber (EPDM), chloroprene rubber (CR), and acrylonitrile butadiene rubber (NBR). Examples of rubber components other than the above include butyl rubber and fluororubber. These may be used alone or in combination of two or more. As the rubber component, SBR, BR, and isoprene rubber are preferred, and SBR is more preferred.

Here, the other rubber component is preferably a rubber having a weight average molecular weight (Mw) of 200,000 or more, more preferably 350,000 or more. There is no particular upper limit for Mw, but it is preferably 4 million or less, more preferably 3 million or less.

In this specification, Mw and number average molecular weight (Mn) can be calculated based on the measured values obtained by gel permeation chromatography (GPC) (GPC-8000 series manufactured by Tosoh Corporation, detector: differential refractometer, column: TSKGEL SUPERMULTIPORE HZ-M manufactured by Tosoh Corporation) and converted into standard polystyrene.

The other rubber component may be a non-modified diene rubber or a modified diene rubber.
The modified diene rubber may be any diene rubber having a functional group that interacts with a filler such as silica. Examples of the modified diene rubber include terminal-modified diene rubber (terminal-modified diene rubber having the functional group at the terminal) in which at least one terminal of the diene rubber has been modified with a compound (modifier) having the functional group, main-chain modified diene rubber having the functional group in the main chain, main-chain terminal-modified diene rubber having the functional group in the main chain and at least one terminal (for example, main-chain terminal-modified diene rubber having the functional group in the main chain and at least one terminal modified with the modifier), and terminal-modified diene rubber modified (coupled) with a polyfunctional compound having two or more epoxy groups in the molecule and having a hydroxyl group or epoxy group introduced therein.

The above-mentioned functional groups include, for example, amino groups, amide groups, silyl groups, alkoxysilyl groups, isocyanate groups, imino groups, imidazole groups, urea groups, ether groups, carbonyl groups, oxycarbonyl groups, mercapto groups, sulfide groups, disulfide groups, sulfonyl groups, sulfinyl groups, thiocarbonyl groups, ammonium groups, imide groups, hydrazo groups, azo groups, diazo groups, carboxyl groups, nitrile groups, pyridyl groups, alkoxy groups, hydroxyl groups, oxy groups, and epoxy groups. These functional groups may have a substituent. Among them, amino groups (preferably amino groups in which the hydrogen atoms of the amino groups are substituted with alkyl groups having 1 to 6 carbon atoms), alkoxy groups (preferably alkoxy groups having 1 to 6 carbon atoms), and alkoxysilyl groups (preferably alkoxysilyl groups having 1 to 6 carbon atoms) are preferred.

The SBR is not particularly limited, and for example, emulsion-polymerized styrene-butadiene rubber (E-SBR), solution-polymerized styrene-butadiene rubber (S-SBR), etc. can be used. These may be used alone or in combination of two or more types.

The styrene content of SBR is preferably 5% by mass or more, more preferably 10% by mass or more, and even more preferably 15% by mass or more. The styrene content is preferably 60% by mass or less, more preferably 40% by mass or less, and even more preferably 30% by mass or less. When the styrene content is within the above range, the above-mentioned effects can be more suitably obtained.
In this specification, the styrene content of SBR is calculated by H ¹ -NMR measurement.

As SBR, for example, SBR manufactured and sold by Sumitomo Chemical Co., Ltd., JSR Corporation, Asahi Kasei Corporation, Nippon Zeon Co., Ltd., etc. can be used.

The SBR may be unmodified or modified. Examples of modified SBR include modified SBR into which functional groups similar to those of modified diene rubber have been introduced.

When SBR is contained, the content of SBR in 100% by mass of the rubber component is preferably 50% by mass or more, more preferably 70% by mass or more, and even more preferably 80% by mass or more, and may be 100% by mass. By keeping it within the above range, good tire performance tends to be obtained.

The BR is not particularly limited, and examples of the BR that can be used include high cis BR with a high cis content, BR containing syndiotactic polybutadiene crystals, and BR synthesized using a rare earth catalyst (rare earth BR). These may be used alone or in combination of two or more. Of these, high cis BR with a cis content of 90% by mass or more is preferred because it improves abrasion resistance.

The BR may be unmodified or modified. Examples of modified BR include modified BR into which functional groups similar to those of modified diene rubber have been introduced.

For example, products from Ube Industries, Ltd., JSR Corporation, Asahi Kasei Corporation, Zeon Corporation, etc. can be used as BR.

Isoprene-based rubbers include natural rubber (NR), isoprene rubber (IR), modified NR, modified NR, modified IR, etc. NR can be, for example, SIR20, RSS#3, TSR20, etc., which are common in the rubber industry. IR is not particularly limited, and can be, for example, IR2200, etc., which are common in the rubber industry. Modified NR can be, for example, deproteinized natural rubber (DPNR), high-purity natural rubber (UPNR), etc. Modified NR can be, for example, epoxidized natural rubber (ENR), hydrogenated natural rubber (HNR), grafted natural rubber, etc. Modified IR can be, for example, epoxidized isoprene rubber, hydrogenated isoprene rubber, grafted isoprene rubber, etc. These can be used alone or in combination of two or more.

In the rubber composition, the filler content (solid content) is preferably 2 parts by mass or more, more preferably 5 parts by mass or more, and even more preferably 10 parts by mass or more, per 100 parts by mass of the rubber component. Also, it is preferably 300 parts by mass or less, more preferably 250 parts by mass or less, and even more preferably 200 parts by mass or less.

When the rubber composition contains microfibrillated plant fibers, the content (solid content) is preferably 2 parts by mass or more, more preferably 5 parts by mass or more, and even more preferably 10 parts by mass or more, per 100 parts by mass of the rubber component. Also, it is preferably 45 parts by mass or less, more preferably 40 parts by mass or less, even more preferably 35 parts by mass or less, and particularly preferably 30 parts by mass or less. By keeping it within the above range, good dispersibility is obtained, and excellent rubber physical properties tend to be obtained.

When the rubber composition contains silica, the content is preferably 25 parts by mass or more, more preferably 30 parts by mass or more, and even more preferably 50 parts by mass or more, per 100 parts by mass of the rubber component. The upper limit of the content is not particularly limited, but is preferably 300 parts by mass or less, more preferably 200 parts by mass or less, even more preferably 170 parts by mass or less, particularly preferably 100 parts by mass or less, and most preferably 80 parts by mass or less. By keeping the content within the above range, good dispersibility is obtained, and excellent rubber physical properties tend to be obtained.

When the rubber composition contains silica, it is preferable that the rubber composition further contains a silane coupling agent.
The silane coupling agent is not particularly limited, and examples thereof include bis(3-triethoxysilylpropyl)tetrasulfide, bis(2-triethoxysilylethyl)tetrasulfide, bis(4-triethoxysilylbutyl)tetrasulfide, bis(3-trimethoxysilylpropyl)tetrasulfide, bis(2-trimethoxysilylethyl)tetrasulfide, bis(2-triethoxysilylethyl)trisulfide, bis(4-trimethoxysilylbutyl)trisulfide, bis(3-triethoxysilylpropyl)disulfide, bis(2-triethoxysilylethyl)disulfide, bis(4-triethoxysilylbutyl)disulfide, bis(3-trimethoxysilylpropyl)disulfide, bis(2-trimethoxysilylethyl)disulfide, bis(4-trimethoxysilylbutyl)disulfide, bis(3-trimethoxysilylpropyl)disulfide, bis(2-trimethoxysilylethyl)disulfide, bis(4-trimethoxysilylbutyl)disulfide, 3-trimethoxysilylpropyl-N,N-dimethylthiocarbamate, Examples of such silanes include sulfide-based silanes such as bamoyl tetrasulfide, 2-triethoxysilylethyl-N,N-dimethylthiocarbamoyl tetrasulfide, and 3-triethoxysilylpropyl methacrylate monosulfide; mercapto-based silanes such as 3-mercaptopropyltrimethoxysilane, 2-mercaptoethyltriethoxysilane, and Momentive's NXT and NXT-Z; vinyl-based silanes such as vinyltriethoxysilane and vinyltrimethoxysilane; amino-based silanes such as 3-aminopropyltriethoxysilane and 3-aminopropyltrimethoxysilane; glycidoxy-based silanes such as γ-glycidoxypropyltriethoxysilane and γ-glycidoxypropyltrimethoxysilane; nitro-based silanes such as 3-nitropropyltrimethoxysilane and 3-nitropropyltriethoxysilane; and chloro-based silanes such as 3-chloropropyltrimethoxysilane and 3-chloropropyltriethoxysilane. As commercially available products, products of Degussa, Momentive, Shin-Etsu Silicone Co., Ltd., Tokyo Chemical Industry Co., Ltd., Azumax Co., Ltd., Dow Corning Toray Co., Ltd., etc. can be used. These may be used alone or in combination of two or more kinds.

The content of the silane coupling agent is preferably 3 parts by mass or more, and more preferably 6 parts by mass or more, relative to 100 parts by mass of silica. When it is 3 parts by mass or more, good breaking strength and the like tend to be obtained. Furthermore, the content is preferably 20 parts by mass or less, and more preferably 15 parts by mass or less. When it is 20 parts by mass or less, an effect commensurate with the amount blended tends to be obtained.

The rubber composition may contain carbon black as a filler. Examples of carbon black include, but are not limited to, N134, N110, N220, N234, N219, N339, N330, N326, N351, N550, and N762. Commercially available products include those from Asahi Carbon Co., Ltd., Cabot Japan Co., Ltd., Tokai Carbon Co., Ltd., Mitsubishi Chemical Corporation, Lion Corporation, Shin-Nichika Carbon Co., Ltd., Columbia Carbon Co., Ltd., and the like. These may be used alone or in combination of two or more types.

The carbon black content is preferably 1 part by mass or more, and more preferably 3 parts by mass or more, per 100 parts by mass of the rubber component. By making it equal to or more than the lower limit, a good reinforcing effect tends to be obtained. In addition, the above content is preferably 20 parts by mass or less, and more preferably 15 parts by mass or less. By making it equal to or less than the upper limit, good processability tends to be obtained.

The nitrogen adsorption specific surface area ( _N2SA ) of carbon black is preferably 50 ^m2 /g or more, more preferably 80 ^m2 /g or more, and even more preferably 100 ^m2 /g or more. By making it equal to or more than the lower limit, a good reinforcing effect tends to be obtained. Moreover, the _N2SA is preferably 200 ^m2 /g or less, more preferably 150 ^m2 /g or less, and even more preferably 130 ^m2 /g or less. By making it equal to or less than the upper limit, a good dispersion of carbon black tends to be obtained.
The nitrogen adsorption specific surface area of carbon black is determined in accordance with JIS K6217-2:2001.

The rubber composition may contain fillers other than silica and carbon black. Examples of other fillers include the aforementioned clay.

The rubber composition may contain a plasticizer. The plasticizer is not particularly limited, but examples include plasticizers that are liquid at room temperature (25°C), such as oil and liquid resin. These plasticizers may be used alone or in combination of two or more.

When a plasticizer is contained, the content is preferably 1 part by mass or more, more preferably 3 parts by mass or more, and even more preferably 5 parts by mass or more, per 100 parts by mass of the rubber component. The content is preferably 100 parts by mass or less, more preferably 50 parts by mass or less, and even more preferably 30 parts by mass or less. Within the above range, good rubber physical properties tend to be obtained.

The oil is not particularly limited, and any conventionally known oil can be used, such as paraffin-based process oil, aromatic process oil, naphthenic process oil, low PCA (polycyclic aromatic) process oil such as TDAE and MES, vegetable oils, and mixtures thereof. Among them, aromatic process oils are preferred in terms of wear resistance and fracture properties. Specific examples of the aromatic process oil include the Diana Process Oil AH series manufactured by Idemitsu Kosan Co., Ltd.

Liquid resins are not particularly limited, but examples include liquid aromatic vinyl polymers, coumarone-indene resins, indene resins, terpene resins, rosin resins, and hydrogenated versions of these.

Liquid aromatic vinyl polymers are resins obtained by polymerizing α-methylstyrene and/or styrene, and examples of such liquid resins include homopolymers of styrene, homopolymers of α-methylstyrene, and copolymers of α-methylstyrene and styrene.

Liquid coumarone-indene resin is a resin that contains coumarone and indene as the main monomer components that make up the resin skeleton (main chain). Other monomer components that may be contained in the skeleton besides coumarone and indene include liquid resins such as styrene, α-methylstyrene, methylindene, and vinyltoluene.

Liquid indene resin is a liquid resin that contains indene as the main monomer component that makes up the resin's skeleton (main chain).

Liquid terpene resins are liquid terpene resins, such as those obtained by polymerizing terpene compounds such as α-pinene, β-pinene, camphor, and dipentene, and terpene phenol, which is a resin obtained from terpene compounds and phenolic compounds as raw materials.

Liquid rosin resin is a liquid rosin-based resin represented by natural rosin, polymerized rosin, modified rosin, ester compounds of these, or hydrogenated products of these.

The rubber composition may contain a solid resin (a polymer that is in a solid state at room temperature (25°C)).

When a solid resin is contained, the content is preferably 1 part by mass or more, more preferably 3 parts by mass or more, and even more preferably 5 parts by mass or more, per 100 parts by mass of the rubber component. The content is preferably 50 parts by mass or less, more preferably 30 parts by mass or less, and even more preferably 20 parts by mass or less. If it is within the above range, good wet grip performance tends to be obtained.

The solid resin is not particularly limited, but examples thereof include solid styrene-based resins, coumarone-indene resins, terpene-based resins, p-t-butylphenol acetylene resins, acrylic resins, dicyclopentadiene-based resins (DCPD-based resins), C5-based petroleum resins, C9-based petroleum resins, and C5C9-based petroleum resins. These may be used alone or in combination of two or more.

Solid styrene-based resins are solid polymers that use styrene-based monomers as constituent monomers, and examples thereof include polymers polymerized with styrene-based monomers as the main component (50% by mass or more). Specific examples include homopolymers obtained by polymerizing each of the styrene-based monomers (styrene, o-methylstyrene, m-methylstyrene, p-methylstyrene, α-methylstyrene, p-methoxystyrene, p-tert-butylstyrene, p-phenylstyrene, o-chlorostyrene, m-chlorostyrene, p-chlorostyrene, etc.) alone, copolymers obtained by copolymerizing two or more types of styrene-based monomers, and copolymers of a styrene-based monomer and another monomer that can be copolymerized with it.

Examples of the other monomers include acrylonitriles such as acrylonitrile and methacrylonitrile, unsaturated carboxylic acids such as acrylics and methacrylic acid, unsaturated carboxylic acid esters such as methyl acrylate and methyl methacrylate, dienes such as chloroprene and butadiene-isoprene, olefins such as 1-butene and 1-pentene, α,β-unsaturated carboxylic acids such as maleic anhydride or their acid anhydrides, etc.

Among these, solid α-methylstyrene resins (α-methylstyrene homopolymers, copolymers of α-methylstyrene and styrene, etc.) are preferred.

The solid coumarone-indene resin may be a solid resin having the same structural units as the liquid coumarone-indene resin described above.

Examples of solid terpene resins include polyterpene, terpene phenol, and aromatic modified terpene resins.
Polyterpenes are resins obtained by polymerizing terpene compounds and their hydrogenated products. Terpene compounds are hydrocarbons represented by the formula (C ₅ H ₈ ) _n and their oxygen-containing derivatives, and are compounds having a basic skeleton of a terpene classified into monoterpene (C ₁₀ H ₁₆ ), sesquiterpene (C ₁₅ H ₂₄ ), diterpene (C ₂₀ H ₃₂ ), etc. Examples of such compounds include α-pinene, β-pinene, dipentene, limonene, myrcene, alloocimene, ocimene, α-phellandrene, α-terpinene, γ-terpinene, terpinolene, 1,8-cineole, 1,4-cineole, α-terpineol, β-terpineol, and γ-terpineol.

Solid polyterpenes include terpene resins such as α-pinene resin, β-pinene resin, limonene resin, dipentene resin, and β-pinene/limonene resin, which are made from the above-mentioned terpene compounds, as well as solid resins such as hydrogenated terpene resins obtained by hydrogenating the terpene resins.

The solid terpene phenols include solid resins obtained by copolymerizing the above-mentioned terpene compounds with phenolic compounds, and solid resins obtained by hydrogenating the above-mentioned resins. Specifically, the solid resins include solid resins obtained by condensing the above-mentioned terpene compounds, phenolic compounds, and formalin. Examples of phenolic compounds include phenol, bisphenol A, cresol, and xylenol.

The solid aromatic modified terpene resin includes a solid resin obtained by modifying a terpene resin with an aromatic compound, and a solid resin obtained by hydrogenating the resin. The aromatic compound is not particularly limited as long as it is a compound having an aromatic ring, and examples thereof include phenolic compounds such as phenol, alkylphenol, alkoxyphenol, and unsaturated hydrocarbon group-containing phenol; naphthol compounds such as naphthol, alkylnaphthol, alkoxynaphthol, and unsaturated hydrocarbon group-containing naphthol; styrene derivatives such as styrene, alkylstyrene, alkoxystyrene, and unsaturated hydrocarbon group-containing styrene; coumarone, indene, etc.

An example of a solid p-t-butylphenol acetylene resin is a solid resin obtained by a condensation reaction between p-t-butylphenol and acetylene.

The solid acrylic resin is not particularly limited, but a solvent-free solid acrylic resin is preferably used because it has few impurities and produces a resin with a sharp molecular weight distribution.

Solid solvent-free acrylic resins include (meth)acrylic resins (polymers) synthesized by high-temperature continuous polymerization (high-temperature continuous bulk polymerization) (methods described in U.S. Pat. No. 4,414,370, JP-A-59-6207, JP-B-5-58005, JP-A-1-313522, U.S. Pat. No. 5,010,166, Toa Gosei Kenkyuu Nenpo TREND 2000 Vol. 3, pp. 42-45, etc.) with minimal use of secondary raw materials such as polymerization initiators, chain transfer agents, and organic solvents. In this specification, (meth)acrylic means methacryl and acrylic.

The solid acrylic resin preferably does not substantially contain auxiliary raw materials such as a polymerization initiator, a chain transfer agent, or an organic solvent. In addition, the acrylic resin is preferably one that has a relatively narrow composition distribution and molecular weight distribution obtained by continuous polymerization.

As described above, the solid acrylic resin is preferably one that does not substantially contain auxiliary raw materials such as polymerization initiators, chain transfer agents, and organic solvents, i.e., one with high purity. The purity of the solid acrylic resin (the proportion of resin contained in the resin) is preferably 95% by mass or more, more preferably 97% by mass or more.

Examples of monomer components constituting solid acrylic resins include (meth)acrylic acid, (meth)acrylic acid esters (alkyl esters, aryl esters, aralkyl esters, etc.), (meth)acrylamide, and (meth)acrylic acid derivatives such as (meth)acrylamide derivatives.

In addition, aromatic vinyls such as styrene, α-methylstyrene, vinyltoluene, vinylnaphthalene, divinylbenzene, trivinylbenzene, and divinylnaphthalene may be used together with (meth)acrylic acid or (meth)acrylic acid derivatives as monomer components constituting solid acrylic resins.

The solid acrylic resin may be a resin composed only of a (meth)acrylic component, or a resin containing components other than the (meth)acrylic component as constituent elements.
The solid acrylic resin may have a hydroxyl group, a carboxyl group, a silanol group, or the like.

As plasticizers and solid resins, for example, products from Maruzen Petrochemical Co., Ltd., Sumitomo Bakelite Co., Ltd., Yasuhara Chemical Co., Ltd., Tosoh Corporation, Rutgers Chemicals, BASF, Arizona Chemical Company, Nitto Chemical Co., Ltd., Nippon Shokubai Co., Ltd., JXTG Nippon Oil & Energy Corporation, Arakawa Chemical Industries Co., Ltd., Taoka Chemical Co., Ltd., etc. can be used.

The rubber composition preferably contains an antioxidant from the standpoint of crack resistance, ozone resistance, etc.

The anti-aging agent is not particularly limited, but may be naphthylamine-based anti-aging agents such as phenyl-α-naphthylamine; diphenylamine-based anti-aging agents such as octylated diphenylamine and 4,4'-bis(α,α'-dimethylbenzyl)diphenylamine; N-isopropyl-N'-phenyl-p-phenylenediamine, N-(1,3-dimethylbutyl)-N'-phenyl-p-phenylenediamine, N,N'-di-2-naphthyl-p-phenylenediamine, Examples of such antioxidants include p-phenylenediamine antioxidants such as amines; quinoline antioxidants such as polymerized 2,2,4-trimethyl-1,2-dihydroquinoline; monophenol antioxidants such as 2,6-di-t-butyl-4-methylphenol and styrenated phenol; and bis-, tris-, and polyphenol-based antioxidants such as tetrakis-[methylene-3-(3',5'-di-t-butyl-4'-hydroxyphenyl)propionate]methane. Among these, p-phenylenediamine antioxidants and quinoline antioxidants are preferred, and N-(1,3-dimethylbutyl)-N'-phenyl-p-phenylenediamine and polymerized 2,2,4-trimethyl-1,2-dihydroquinoline are more preferred. Commercially available products include those manufactured by Seiko Chemical Co., Ltd., Sumitomo Chemical Co., Ltd., Ouchi Shinko Chemical Co., Ltd., and Flexis Co., Ltd.

The content of the antioxidant is preferably 0.2 parts by mass or more, and more preferably 0.5 parts by mass or more, per 100 parts by mass of the rubber component. By making the content equal to or more than the lower limit, sufficient ozone resistance tends to be obtained. The content is preferably 7.0 parts by mass or less, and more preferably 4.0 parts by mass or less. By making the content equal to or less than the upper limit, a good appearance tends to be obtained.

The rubber composition preferably contains stearic acid. From the viewpoint of the above-mentioned performance balance, the content of stearic acid is preferably 0.5 to 10 parts by mass or more, and more preferably 0.5 to 5 parts by mass, per 100 parts by mass of the rubber component.

The stearic acid used may be any known product, such as products from NOF Corp., NOF Corporation, Kao Corp., Fujifilm Wako Pure Chemical Industries, Ltd., Chiba Fatty Acid Co., Ltd., etc.

The rubber composition preferably contains zinc oxide. From the viewpoint of the above-mentioned performance balance, the content of zinc oxide is preferably 0.5 to 10 parts by mass, more preferably 1 to 5 parts by mass, per 100 parts by mass of the rubber component.

As zinc oxide, any conventionally known product can be used, for example, products from Mitsui Mining & Smelting Co., Ltd., Toho Zinc Co., Ltd., Hakusui Tech Co., Ltd., Seido Chemical Industry Co., Ltd., Sakai Chemical Industry Co., Ltd., etc. can be used.

The rubber composition may contain wax. The wax is not particularly limited, and examples thereof include petroleum-based wax and natural wax. Synthetic waxes obtained by refining or chemically treating multiple waxes may also be used. These waxes may be used alone or in combination of two or more types.

Petroleum-based waxes include paraffin wax and microcrystalline wax. Natural waxes are not particularly limited as long as they are derived from resources other than petroleum, and examples include vegetable waxes such as candelilla wax, carnauba wax, Japan wax, rice wax, and jojoba wax; animal waxes such as beeswax, lanolin, and spermaceti; mineral waxes such as ozokerite, ceresin, and petrolactam; and refined products thereof. Commercially available products include, for example, products from Ouchi Shinko Chemical Industry Co., Ltd., Nippon Seiro Co., Ltd., and Seiko Chemical Co., Ltd. The wax content may be appropriately set in terms of ozone resistance and cost.

It is preferable to add sulfur to the above rubber composition, as this forms an appropriate amount of crosslinked chains in the polymer chains and imparts good rubber properties.

The sulfur content is preferably 0.1 parts by mass or more, more preferably 0.5 parts by mass or more, and even more preferably 0.7 parts by mass or more, per 100 parts by mass of the rubber component. The content is preferably 6.0 parts by mass or less, more preferably 4.0 parts by mass or less, and even more preferably 3.0 parts by mass or less.

Examples of sulfur include powdered sulfur, precipitated sulfur, colloidal sulfur, insoluble sulfur, highly dispersible sulfur, and soluble sulfur, which are commonly used in the rubber industry. Commercially available products include those from Tsurumi Chemical Industry Co., Ltd., Karuizawa Sulfur Co., Ltd., Shikoku Chemical Industry Co., Ltd., Flexis Corporation, Nippon Kanzuri Kogyo Co., Ltd., and Hosoi Chemical Industry Co., Ltd. These may be used alone or in combination of two or more types.

The rubber composition preferably contains a vulcanization accelerator.
The content of the vulcanization accelerator is not particularly limited and may be freely determined depending on the desired vulcanization speed and crosslink density, but is usually 0.3 to 10 parts by mass, preferably 0.5 to 7 parts by mass, per 100 parts by mass of the rubber component.

There are no particular restrictions on the type of vulcanization accelerator, and any commonly used accelerator can be used. Examples of the vulcanization accelerator include thiazole-based vulcanization accelerators such as 2-mercaptobenzothiazole, di-2-benzothiazolyl disulfide, and N-cyclohexyl-2-benzothiazyl sulfenamide; thiuram-based vulcanization accelerators such as tetramethylthiuram disulfide (TMTD), tetrabenzylthiuram disulfide (TBzTD), and tetrakis(2-ethylhexyl)thiuram disulfide (TOT-N); sulfenamide-based vulcanization accelerators such as N-cyclohexyl-2-benzothiazole sulfenamide, N-t-butyl-2-benzothiazolyl sulfenamide, N-oxyethylene-2-benzothiazole sulfenamide, N-oxyethylene-2-benzothiazole sulfenamide, and N,N'-diisopropyl-2-benzothiazole sulfenamide; and guanidine-based vulcanization accelerators such as diphenyl guanidine, di-orthotolyl guanidine, and orthotolyl biguanidine. These may be used alone or in combination of two or more. Among them, sulfenamide-based vulcanization accelerators and guanidine-based vulcanization accelerators are preferred.

In addition to the above components, the rubber composition may contain appropriate additives, such as release agents and pigments, that are commonly used in the application field.

The rubber composition can be produced by a known method, for example, by kneading the components using a rubber kneading device such as an open roll or a Banbury mixer, and then vulcanizing the mixture.

As for the kneading conditions, in the base kneading process where additives other than the vulcanizing agent and vulcanization accelerator are kneaded, the kneading temperature is usually 50 to 200°C, preferably 80 to 190°C, and the kneading time is usually 30 seconds to 30 minutes, preferably 1 minute to 30 minutes. In the finish kneading process where the vulcanizing agent and vulcanization accelerator are kneaded, the kneading temperature is usually 100°C or less, preferably room temperature to 80°C. Furthermore, the composition kneaded with the vulcanizing agent and vulcanization accelerator is usually subjected to a vulcanization treatment such as press vulcanization. The vulcanization temperature is usually 120 to 200°C, preferably 140 to 180°C.

The rubber composition can be used for tires, shoe sole rubber, flooring rubber, vibration-proof rubber, seismic isolation rubber, butyl frame rubber, belts, hoses, packing, drug stoppers, and other rubber industrial products. In particular, it is preferable to use it as a rubber composition for tires, since it can improve performance such as durability (breaking strength), steering stability, and fuel efficiency.

The rubber composition can be suitably used for pneumatic tires. The pneumatic tires are manufactured by a conventional method using the rubber composition. That is, the rubber composition, which is mixed with various materials as necessary, is extruded to fit the shape of the tire components while still unvulcanized, and molded together with other tire components in a conventional method on a tire building machine to form an unvulcanized tire, which is then heated and pressurized in the vulcanizer to manufacture the tire.

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

Various chemicals used in the examples and comparative examples will be collectively described below.
Natural rubber latex: Field latex obtained from Muhibbah LATEKS. Silica: Uratosil VN3 (N 2 SA 172 m ² /g) manufactured by Evonik Degussa.
Microfibrillated plant fiber: Biomass nanofiber manufactured by Sugino Machine Co., Ltd. (product name: "BiNFi-s Cellulose", average fiber length: about 2 μm, average fiber diameter: about 0.02 μm, solid content: 2% by mass)
Surfactant 1: teric 16A29 (CH ₃ (CH ₂ ) ₁₅ (OC ₂ H ₄ ) ₂₉ —OH, a nonionic surfactant manufactured by Huntsman Corporation
Surfactant 2: PD-430 manufactured by Kao Corporation (nonionic surfactant, R-(OC ₄ H ₈ ) _p (OC ₂ H ₄ ) _q -OH: R = long chain alkyl group, p = 3 to 100, q = 3 to 100)
Surfactant 3: Si363 manufactured by EVONIK-DEGUSSA (surfactant represented by the following formula, non-ionic surfactant)

界面活性剤４：エレメンティス社製のＮＵＯＳＰＥＲＳＥ ＦＸ ６００（陰イオン性界面活性剤、ポリカルボン酸アミン塩（疎水性基としてフェニル基、親水性基としてカルボキシル基を含有）、Ｍｗ２０００）
界面活性剤５：エレメンティス社製のＮＵＯＳＰＥＲＳＥ ＦＸ ６０５（陰イオン性界面活性剤、ポリカルボン酸ナトリウム塩（疎水性基としてフェニル基、親水性基としてカルボキシル基を含有）、Ｍｗ６０００）
界面活性剤６：花王（株）製のデモールＥＰ（陰イオン性界面活性剤、ポリカルボン酸ナトリウム塩（疎水性基としてイソブチレン基、親水性基としてカルボキシル基を含有）、Ｍｗ２００００）
界面活性剤７：第一工業製薬（株）製のＤＫＳディスコート Ｎ－１４（陰イオン性界面活性剤、ポリカルボン酸アンモニウム塩（疎水性基としてフェニル基、親水性基としてカルボキシル基を含有）、Ｍｗ７０００）
老化防止剤：大内新興化学工業（株）製のノクラック６Ｃ（Ｎ－（１，３－ジメチルブチル）－Ｎ’－フェニル－ｐ－フェニレンジアミン）
酸化亜鉛：三井金属鉱業（株）製の亜鉛華２種
ステアリン酸：日油（株）製の椿
硫黄：鶴見化学工業（株）製の粉末硫黄
加硫促進剤：大内新興化学工業（株）製のノクセラ－ＮＳ（Ｎ－ｔｅｒｔ－ブチル－２－ベンゾチアゾリルスルフェンアミド）

Surfactant 4: NUOSPERSE FX 600 manufactured by Elementis (anionic surfactant, polycarboxylate amine salt (containing a phenyl group as a hydrophobic group and a carboxyl group as a hydrophilic group), Mw 2000)
Surfactant 5: NUOSPERSE FX 605 manufactured by Elementis (anionic surfactant, sodium polycarboxylate (containing a phenyl group as a hydrophobic group and a carboxyl group as a hydrophilic group), Mw 6000)
Surfactant 6: Demol EP manufactured by Kao Corporation (anionic surfactant, sodium polycarboxylate (containing an isobutylene group as a hydrophobic group and a carboxyl group as a hydrophilic group), Mw 20,000)
Surfactant 7: DKS Discoat N-14 (anionic surfactant, polycarboxylate ammonium salt (containing a phenyl group as a hydrophobic group and a carboxyl group as a hydrophilic group), Mw 7000) manufactured by Daiichi Kogyo Seiyaku Co., Ltd.
Antioxidant: Nocrac 6C (N-(1,3-dimethylbutyl)-N'-phenyl-p-phenylenediamine) manufactured by Ouchi Shinko Chemical Industry Co., Ltd.
Zinc oxide: zinc oxide type 2 manufactured by Mitsui Mining & Smelting Co., Ltd. Stearic acid: camellia sulfur manufactured by NOF Corp. Powdered sulfur manufactured by Tsurumi Chemical Industry Co., Ltd. Vulcanization accelerator: Noccera-NS (N-tert-butyl-2-benzothiazolyl sulfenamide) manufactured by Ouchi Shinko Chemical Industry Co., Ltd.

(Preparation of Silica Dispersion)
190 g of pure water was added to 10 g of silica to prepare a 5% by mass (solid content) silica suspension, which was stirred and subjected to ultrasonic treatment for 10 minutes to obtain a silica dispersion.

(Preparation of Microfibrillated Plant Fiber Dispersion)
150 g of pure water was added to 50 g of microfibrillated plant fiber (2 wt%) to prepare a 0.5 mass % (solids concentration) suspension of microfibrillated plant fiber, which was then stirred and ultrasonicated for 10 minutes to obtain a microfibrillated plant fiber dispersion.

<Examples 1-1 to 1-7, 2-1 to 2-11 and Comparative Example 1-1>
(Preparation of Rubber-Filler Composite)
According to the compounding recipes in Tables 1 and 2, rubber-filler composites were produced.
Specifically, a surfactant was added to the prepared silica dispersion or microfibrillated plant fiber dispersion, and the mixture (mixture) of the silica dispersion or microfibrillated plant fiber dispersion and the surfactant was obtained using a high-speed homogenizer and stirred at room temperature (20 to 30°C) for 5 minutes. The mixture obtained was added to natural rubber latex, and the mixture was stirred at room temperature for 5 minutes using a high-speed homogenizer to obtain a compounded latex with a pH of 10.2. Next, a 2% by mass aqueous solution of formic acid was added at room temperature to adjust the pH to 3 to 4, and a coagulum was obtained. The coagulum obtained was filtered and dried to obtain a rubber-filler composite.

<Comparative Examples 1-2 and 2-1>
(Preparation of Rubber-Filler Composite)
According to the compounding recipes in Tables 1 and 2, rubber-filler composites were produced.
Specifically, natural rubber latex was added to a 0.5% by mass silica dispersion or a 0.5% by mass microfibrillated plant fiber dispersion, and the mixture was stirred at room temperature for 5 minutes using a high-speed homogenizer to obtain a compounded latex with a pH of 10.2. Next, a 2% by mass aqueous solution of formic acid was added at room temperature to adjust the pH to 3 to 4, and a coagulated product was obtained. The obtained coagulated product was filtered and dried to obtain a rubber-filler composite.

The rubber-filler composite obtained was evaluated as follows, and the results are shown in Tables 1 and 2. The standard formulations for hardness (Hs) in Tables 1 and 2 are Examples 1-1 and 2-1, respectively.

(Measurement of filler incorporation rate)
The coagulated products (rubber-filler composites) obtained in each example were subjected to TEM measurement to measure the amount of filler incorporated in the composites. Using Image J, the TEM measured images were binarized, a threshold value was set, the amount of filler was quantitatively analyzed, and the filler incorporation rate was calculated based on the amount of filler.

(Hardness (Hs))
The hardness of the obtained rubber-filler composite was measured at 25°C using a type A durometer in accordance with JIS K 6253-1:2012. The hardness of the standard formulation was set to 100, and the hardness of each formulation was expressed as an index. A larger index indicates a higher hardness.

As can be seen from Tables 1 and 2, in the rubber-silica composite, a high filler incorporation rate was obtained when a nonionic surfactant was used (filtrate: transparent), which allowed for the production of a composite with high hardness. In the rubber-microfibrillated plant fiber composite, a high filler incorporation rate was obtained when an anionic surfactant, a nonionic surfactant, and especially an anionic surfactant were used (filtrate: transparent), which allowed for the production of a composite with high hardness.

<Preparation of compounded rubber>
Chemicals other than sulfur and vulcanization accelerator were kneaded using a 1.7 L Banbury mixer according to the formulations shown in Tables 3 and 4. Next, sulfur and vulcanization accelerator were added to the kneaded mixture using a roll and kneaded to obtain an unvulcanized rubber composition. The unvulcanized rubber composition obtained was press-vulcanized at 170°C for 15 minutes to obtain a vulcanized product.

The obtained vulcanizates were evaluated as follows, and the results are shown in Tables 3 and 4. The reference formulations in Tables 3 and 4 are comparative formulations 1-2 and 2-1, respectively.

(Breaking strength)
Using the vulcanizate, No. 3 dumbbell-shaped rubber test pieces were prepared and subjected to a tensile test in accordance with JIS K6251 "Vulcanized rubber and thermoplastic rubber - Determination of tensile properties" to measure the breaking strength (TB). The TB index of the rubber test piece of the standard formulation was set to 100, and the TB of each formulation was expressed as an index according to the following formula. A higher TB index indicates a higher breaking strength and better reinforcement and durability.
(TB index) = (TB of each blend) / (TB of standard blend) x 100

(Handling stability)
Using a viscoelasticity spectrometer VES (manufactured by Iwamoto Seisakusho Co., Ltd.), the complex modulus E* of each compound (vulcanizate) was measured under conditions of a temperature of 50°C, an initial strain of 10%, a dynamic strain of 2%, and a frequency of 10 Hz, and expressed as an index according to the following calculation formula (elastic modulus index), with the E* of a rubber test piece of the standard compound being set at 100. The higher the index, the more excellent the handling stability.
(Elasticity index) = (E* of each formulation) / (E* of standard test piece) x 100

From Tables 3 and 4, it can be seen that the examples using high-hardness rubber-filler composites with a filler incorporation rate of 95% by mass or more had excellent breaking strength and elongation at break.

Claims (1)

A method for producing a rubber-filler composite, comprising the step of mixing a rubber latex, a filler dispersion, and a surfactant,
The filler incorporation rate in the rubber-filler composite is 95% by mass or more,
The rubber latex is natural rubber latex,
The filler dispersion is a microfibrillated plant fiber dispersion,
The surfactant is an anionic surfactant,
the surfactant is blended in an amount of 1 to 50 parts by mass relative to 100 parts by mass of a rubber solid content of the rubber latex,
The mixing step includes a step of mixing the surfactant and the filler dispersion to prepare a mixed liquid, and a step of mixing the mixed liquid with the rubber latex.