Noise reduction agent, resin composition for friction material, and friction material

Abstract

The present invention addresses the problem of providing a novel noise reduction agent with which it is possible to provide a resin composition for a friction material capable of providing a friction material with reduced noise. Provided is a noise reduction agent containing polymer fine particles (A) having a specific tan delta peak top or a noise reduction agent containing polymer fine particles (A) having a specific configuration and a specific volume-average particle size.

Description

Noise reducing agent, resin composition for friction material, and friction material

[0001] The present invention relates to a noise reducing agent, a resin composition for a friction material, and a friction material.

[0002] Friction materials used in brake pads, clutches, and the like are produced by curing a thermosetting resin composition (friction material resin composition). Resin compositions for friction materials that use a phenolic resin as a binder are widely known. Furthermore, a technique for blending (adding) core-shell particles into friction materials used in brake pads, clutches, and the like to enhance impact resistance and flexibility is known (see, for example, Patent Document 1).

[0003] Also known is a technique of compounding (adding) a core-shell type graft copolymer to binders for friction materials such as disc pads and drum brake linings (see, for example, Patent Document 2).

[0004] Japanese Patent Application Publication No. 2004-182845 International Publication No. WO2018 / 105682

[0005] However, the friction materials of the above-described prior art have room for further improvement in view of the loud noise (brake squeal) generated by braking operations.

[0006] One embodiment of the present invention has been made in consideration of the above-mentioned problems, and an object of the present invention is to provide a novel noise reducing agent that can provide a resin composition for a friction material that can provide a friction material with reduced noise.

[0007] The present inventors have conducted extensive research to solve the above problems and have completed the present invention.

[0008] A noise reducing agent according to one embodiment of the present invention comprises polymer fine particles (A), the polymer fine particles (A) comprising a core portion and a graft portion grafted to the core portion, the noise reducing agent having a tan δ peak top in a temperature range of 10° C. or higher, and the maximum value of the tan δ peak height in a temperature range of 10° C. or higher is 0.70 or higher. Another embodiment of the present invention comprises polymer fine particles (A), the polymer fine particles (A) comprising a core portion and a graft portion grafted to the core portion, the proportion of the graft portion in the polymer fine particles (A) being 20% ​​to 90% by weight based on 100% by weight of the polymer fine particles (A), and the proportion of unsubstituted vinyl aromatic units and / or vinyl-substituted aromatic units in the graft portion being more than 70% by weight and not more than 100% by weight based on 100% by weight of the graft portion.

[0009] According to one embodiment of the present invention, it is possible to provide a resin composition for a friction material that can provide a friction material with reduced noise, and it is possible to provide a novel noise reducing agent.

[0010] An embodiment of the present invention will be described below, but the present invention is not limited thereto. The present invention is not limited to the respective configurations described below, and various modifications are possible within the scope of the claims. Furthermore, embodiments or examples obtained by combining the technical means disclosed in different embodiments or examples are also included in the technical scope of the present invention. Furthermore, new technical features can be formed by combining the technical means disclosed in each embodiment. All academic literature and patent documents described in this specification are incorporated herein by reference. Furthermore, unless otherwise specified in this specification, the term "A to B" representing a numerical range means "greater than or equal to A (including and greater than A) and less than or equal to B (including and less than B)."

[0011] In this specification, the term "X unit" contained in a polymer, copolymer, or resin refers to a "structural unit derived from an X monomer" or a "structural unit derived from an X compound." For example, the term "styrene unit" refers to a "structural unit derived from a styrene monomer."

[0012] In this specification, the "noise reducing agent according to one embodiment of the present invention" may be referred to as the "noise reducing agent." Furthermore, in this specification, the "resin composition for a friction material" may be referred to as the "composition," and the "resin composition for a friction material according to one embodiment of the present invention" may be referred to as the "composition." Furthermore, in this specification, the "friction material according to one embodiment of the present invention" may be referred to as the "friction material."

[0013] [1. Technical Concept of One Embodiment of the Invention] As described above, a technique of compounding (adding) core-shell particles to friction materials used in brake pads, clutches, and the like to improve impact resistance and flexibility has been known. However, in the conventional technique described above, there is room for further improvement in terms of the large amount of noise (brake squeal) generated by braking. Therefore, the present inventors have conducted extensive research with the aim of providing a novel noise-reducing agent that can provide a resin composition for a friction material that can provide a friction material with reduced noise.

[0014] As a result, the present inventors independently discovered the following novel findings, which led to the completion of the present invention: (1) A noise-reducing agent containing polymer fine particles (A) including a core portion and a graft portion graft-bonded to the core portion, which has a tan δ peak top in a temperature range of 10°C or higher and a maximum value of the tan δ peak height in a temperature range of 10°C or higher of 0.70, can provide a resin composition for a friction material that can provide a friction material with reduced noise; (2) A noise-reducing agent containing polymer fine particles (A) including a core portion and a graft portion graft-bonded to the core portion, which has a proportion of the graft portion of 20 to 90% by weight based on 100% by weight of the polymer fine particles (A), and which has a proportion of unsubstituted vinyl aromatic units and / or vinyl-substituted aromatic units in the graft portion of more than 70% by weight but not more than 100% by weight based on 100% by weight of the graft portion, can provide a resin composition for a friction material that can provide a friction material with reduced noise.

[0015] [2. Noise Reducing Agent] A noise reducing agent according to one embodiment of the present invention comprises polymer fine particles (A), the polymer fine particles (A) comprising a core portion and a graft portion graft-bonded to the core portion, and having a tan δ peak top in a temperature range of 10°C or higher, and the maximum value of the tan δ peak height in a temperature range of 10°C or higher is 0.70 or higher.

[0016] Alternatively, according to another embodiment of the present invention, there is provided a noise reducing agent comprising polymer fine particles (A), the polymer fine particles (A) comprising a core portion and a graft portion graft-bonded to the core portion, the proportion of the graft portion in the polymer fine particles (A) being 20% ​​by weight to 90% by weight based on 100% by weight of the polymer fine particles (A), and the proportion of unsubstituted vinyl aromatic units and / or vinyl-substituted aromatic units in the graft portion being more than 70% by weight and not more than 100% by weight based on 100% by weight of the graft portion.

[0017] The noise reducing agent has the above-described structure, and therefore has high vibration absorption capacity, making it possible to provide a resin composition for friction materials that can reduce noise.

[0018] The present noise reducing agent can also be said to be a noise reducing agent for producing a resin composition for a friction material.

[0019] (2-1. Polymer Fine Particles (A)) The polymer fine particles (A) include a core portion and a graft portion graft-bonded to the core portion.

[0020] (2-1-1. Core Portion) In one embodiment of the present invention, the core portion preferably contains at least one material selected from the group consisting of diene-based rubbers, (meth)acrylate-based rubbers, and organosiloxane-based rubbers.

[0021] The case where the core portion contains a diene rubber (Case A) will be described. In Case A, the resulting resin composition can provide a cured product having excellent toughness and impact resistance. A cured product having excellent toughness and / or impact resistance can also be said to have excellent durability.

[0022] The diene rubber is a core portion containing, as structural units, structural units derived from a diene monomer. The diene monomer can also be referred to as a conjugated diene monomer. In Case A, the diene rubber may have one of the following structures (i) to (vii): (i) A structure containing, out of 100% by weight of structural units, 50% to 100% by weight of structural units derived from a diene monomer and 0% to 50% by weight of structural units derived from a vinyl monomer other than a diene monomer copolymerizable with the diene monomer; (ii) A structure containing, out of 100% by weight of structural units, more than 50% to 100% by weight of structural units derived from a diene monomer and 0% to less than 50% by weight of structural units derived from a vinyl monomer other than a diene monomer copolymerizable with the diene monomer. (iii) A composition containing, out of 100% by weight of structural units, 60% by weight to 100% by weight of structural units derived from diene monomers and 0% by weight to 40% by weight of structural units derived from vinyl monomers other than diene monomers copolymerizable with diene monomers. (iv) A composition containing, out of 100% by weight of structural units, 70% by weight to 100% by weight of structural units derived from diene monomers and 0% by weight to 30% by weight of structural units derived from vinyl monomers other than diene monomers copolymerizable with diene monomers. (v) A composition containing, out of 100% by weight of structural units, 80% by weight to 100% by weight of structural units derived from diene monomers and 0% by weight to 20% by weight of structural units derived from vinyl monomers other than diene monomers copolymerizable with diene monomers. (vi) A composition containing, out of 100% by weight of structural units, 90% by weight to 100% by weight of structural units derived from diene monomers and 0% by weight to 10% by weight of structural units derived from vinyl monomers other than diene monomers copolymerizable with diene monomers. (vii) A composition consisting solely of structural units derived from diene monomers out of 100% by weight of structural units.

[0023] In Case A, the diene rubber may contain, as structural units, structural units derived from (meth)acrylate monomers in an amount less than the amount of structural units derived from diene monomers.

[0024] Examples of the diene monomer include 1,3-butadiene, isoprene (2-methyl-1,3-butadiene), 2-chloro-1,3-butadiene, etc. These diene monomers may be used alone or in combination of two or more.

[0025] Examples of vinyl monomers other than diene monomers copolymerizable with diene monomers (hereinafter also referred to as vinyl monomer A) include vinyl arenes such as styrene, α-methylstyrene, monochlorostyrene, and dichlorostyrene; vinyl carboxylic acids such as acrylic acid and methacrylic acid; vinyl cyanides such as acrylonitrile and methacrylonitrile; vinyl halides such as vinyl chloride, vinyl bromide, and chloroprene; vinyl acetate; alkenes such as ethylene, propylene, butylene, and isobutylene; and polyfunctional monomers such as diallyl phthalate, triallyl cyanurate, triallyl isocyanurate, and divinylbenzene. The above-mentioned vinyl monomer A may be used alone or in combination of two or more. Among the above-mentioned vinyl monomers A, styrene is particularly preferred. In the diene rubber in Case A, the structural unit derived from the vinyl monomer A is an optional component. In case A, the diene rubber may be composed solely of structural units derived from diene monomers.

[0026] In Case A, the core preferably contains butadiene rubber (hereinafter also referred to as polybutadiene rubber) consisting of structural units derived from 1,3-butadiene, and / or butadiene-styrene rubber (hereinafter also referred to as polystyrene-butadiene), which is a copolymer of 1,3-butadiene and styrene, and it is particularly preferable that the core contains polybutadiene rubber. According to this configuration, the desired effects of including a diene rubber in the polymer microparticles (A) can be more effectively exhibited. Furthermore, it is more preferable that the core contains butadiene-styrene rubber, since the transparency of the resulting cured product can be improved by adjusting the refractive index.

[0027] The butadiene-styrene rubber may have any of the following structures (i) to (v): (i) a structure in which, based on 100% by weight of the butadiene-styrene rubber, more than 50% by weight and 100% by weight or less of structural units derived from butadiene and 0% by weight or more but less than 50% by weight of structural units derived from styrene; (ii) a structure in which, based on 100% by weight of the butadiene-styrene rubber, 60% by weight to 100% by weight of structural units derived from butadiene and 0% by weight to 40% by weight of structural units derived from styrene; (iii) a structure in which, based on 100% by weight of the butadiene-styrene rubber, 70% by weight to 100% by weight of structural units derived from butadiene and 0% by weight to 30% by weight of structural units derived from styrene; (iv) a structure in which, based on 100% by weight of the butadiene-styrene rubber, 80% by weight to 100% by weight of structural units derived from butadiene and 0% by weight to 20% by weight of structural units derived from styrene. (v) A composition containing 90% by weight to 100% by weight of structural units derived from butadiene and 0% by weight to 10% by weight of structural units derived from styrene, based on 100% by weight of butadiene-styrene rubber.

[0028] The case where the core portion contains a (meth)acrylate rubber (Case B) will be described. In Case B, a wide range of polymer designs for the core portion are possible by combining a variety of monomers.

[0029] The (meth)acrylate rubber is a core portion that includes, as structural units, structural units derived from (meth)acrylate monomers. In Case B, the (meth)acrylate rubber may have one of the following structures (i) to (vii): (i) A structure that includes, out of 100% by weight of structural units, 50% to 100% by weight of structural units derived from (meth)acrylate monomers and 0% to 50% by weight of structural units derived from vinyl monomers other than (meth)acrylate monomers that are copolymerizable with (meth)acrylate monomers. (ii) A structure that includes, out of 100% by weight of structural units, more than 50% to 100% by weight of structural units derived from (meth)acrylate monomers and 0% to less than 50% by weight of structural units derived from vinyl monomers other than (meth)acrylate monomers that are copolymerizable with (meth)acrylate monomers. (iii) A composition containing, out of 100% by weight of structural units, 60% by weight to 100% by weight of structural units derived from (meth)acrylate monomers and 0% by weight to 40% by weight of structural units derived from vinyl monomers other than (meth)acrylate monomers copolymerizable with (meth)acrylate monomers. (iv) A composition containing, out of 100% by weight of structural units, 70% by weight to 100% by weight of structural units derived from (meth)acrylate monomers and 0% by weight to 30% by weight of structural units derived from vinyl monomers other than (meth)acrylate monomers copolymerizable with (meth)acrylate monomers. (v) A composition containing, out of 100% by weight of structural units, 80% by weight to 100% by weight of structural units derived from (meth)acrylate monomers and 0% by weight to 20% by weight of structural units derived from vinyl monomers other than (meth)acrylate monomers copolymerizable with (meth)acrylate monomers. (vi) A composition containing, out of 100% by weight of structural units, 90% by weight to 100% by weight of structural units derived from (meth)acrylate monomers and 0% by weight to 10% by weight of structural units derived from vinyl monomers other than (meth)acrylate monomers copolymerizable with (meth)acrylate monomers. (vii) A composition consisting exclusively of structural units derived from (meth)acrylate monomers.

[0030] In Case B, the (meth)acrylate rubber may contain, as structural units, structural units derived from diene monomers in an amount less than the amount of structural units derived from (meth)acrylate monomers.

[0031] Examples of the (meth)acrylate monomer include alkyl (meth)acrylates such as methyl (meth)acrylate, ethyl (meth)acrylate, butyl (meth)acrylate, 2-ethylhexyl (meth)acrylate, octyl (meth)acrylate, dodecyl (meth)acrylate, stearyl (meth)acrylate, and behenyl (meth)acrylate; aromatic ring-containing (meth)acrylates such as phenoxyethyl (meth)acrylate and benzyl (meth)acrylate; 2-hydroxyethyl (meth)acrylate, 4-hydroxybutyl (meth)acrylate; Examples of the (meth)acrylate monomer include hydroxyalkyl (meth)acrylates such as acrylate; glycidyl (meth)acrylates such as glycidyl (meth)acrylate and glycidyl alkyl (meth)acrylate; alkoxyalkyl (meth)acrylates; allyl alkyl (meth)acrylates such as allyl (meth)acrylate and allyl alkyl (meth)acrylate; and polyfunctional (meth)acrylates such as monoethylene glycol di(meth)acrylate, triethylene glycol di(meth)acrylate, and tetraethylene glycol di(meth)acrylate. These (meth)acrylate monomers may be used alone or in combination of two or more. Among these (meth)acrylate monomers, ethyl (meth)acrylate, butyl (meth)acrylate, and 2-ethylhexyl (meth)acrylate are preferred, with butyl (meth)acrylate being more preferred.

[0032] In Case B, the (meth)acrylate rubber is preferably one or more selected from the group consisting of ethyl (meth)acrylate rubber, butyl (meth)acrylate rubber, and 2-ethylhexyl (meth)acrylate rubber, and more preferably butyl (meth)acrylate rubber. The ethyl (meth)acrylate rubber is a rubber composed of structural units derived from ethyl (meth)acrylate. The butyl (meth)acrylate rubber is a rubber composed of structural units derived from butyl (meth)acrylate. The 2-ethylhexyl (meth)acrylate rubber is a rubber composed of structural units derived from 2-ethylhexyl (meth)acrylate. This configuration lowers the glass transition temperature (Tg) of the core portion, and as a result, (i) the resulting composition can provide a cured product with excellent toughness, and (ii) the viscosity of the resin composition can be further reduced.

[0033] Examples of vinyl monomers other than (meth)acrylate monomers copolymerizable with (meth)acrylate monomers (hereinafter also referred to as vinyl monomer B) include the monomers listed for vinyl monomer A. Only one type of vinyl monomer B may be used, or two or more types may be used in combination. Among the vinyl monomers B, styrene is particularly preferred. In the (meth)acrylate rubber in Case B, the structural unit derived from vinyl monomer B is an optional component. In Case B, the (meth)acrylate rubber may be composed only of structural units derived from (meth)acrylate monomers.

[0034] The case where the core contains an organosiloxane rubber (Case C) will now be described. In Case C, the resulting composition has sufficient heat resistance and can provide a cured product that has excellent impact resistance at low temperatures.

[0035] Examples of organosiloxane rubbers include (i) organosiloxane polymers composed of alkyl or aryl di-substituted silyloxy units, and (ii) organosiloxane polymers composed of alkyl or aryl mono-substituted silyloxy units. Examples of the alkyl or aryl di-substituted silyloxy units include dimethylsilyloxy, diethylsilyloxy, methylphenylsilyloxy, diphenylsilyloxy, and dimethylsilyloxy-diphenylsilyloxy. Examples of the alkyl or aryl mono-substituted silyloxy units include organohydrogensilyloxy in which some of the alkyl groups in the side chains are substituted with hydrogen atoms. These organosiloxane polymers may be used alone or in combination of two or more.

[0036] In this specification, a polymer composed of dimethylsilyloxy units is referred to as a dimethylsilyloxy rubber. In this specification, a polymer composed of methylphenylsilyloxy units is referred to as a methylphenylsilyloxy rubber. In this specification, a polymer composed of dimethylsilyloxy units and diphenylsilyloxy units is referred to as a dimethylsilyloxy-diphenylsilyloxy rubber. In Case C, the organosiloxane rubber is preferably one or more selected from the group consisting of dimethylsilyloxy rubber, methylphenylsilyloxy rubber, and dimethylsilyloxy-diphenylsilyloxy rubber, because (i) the resulting composition can provide a cured product with excellent heat resistance, and (ii) dimethylsilyloxy rubber is more preferred because it is easily available and economical.

[0037] The core may further contain a rubber other than diene rubber, (meth)acrylate rubber, and organosiloxane rubber, such as natural rubber.

[0038] In one embodiment of the present invention, the core is preferably one or more selected from the group consisting of butadiene rubber, butadiene-styrene rubber, butadiene-(meth)acrylate rubber, ethyl (meth)acrylate rubber, butyl (meth)acrylate rubber, 2-ethylhexyl (meth)acrylate rubber, dimethylsilyloxy rubber, methylphenylsilyloxy rubber, and dimethylsilyloxy-diphenylsilyloxy rubber, more preferably one or more selected from the group consisting of butadiene rubber, butadiene-styrene rubber, butyl (meth)acrylate rubber, and dimethylsilyloxy rubber, and even more preferably one or more selected from the group consisting of butadiene rubber, butadiene-styrene rubber, and butyl acrylate rubber.

[0039] (Crosslinked Structure of Core Portion) From the viewpoint of maintaining the dispersion stability of the polymer microparticles (A) in the thermosetting resin, it is preferable that a crosslinked structure be introduced into the core portion. As a method for introducing a crosslinked structure into the core portion, a commonly used method can be adopted, and examples thereof include the following methods. In producing the core portion, a method in which a crosslinkable monomer such as a polyfunctional monomer and / or a mercapto group-containing compound is mixed with a monomer capable of constituting the core portion, and then polymerized. In this specification, producing a polymer such as a core portion is also referred to as polymerizing a polymer.

[0040] Other methods for introducing a crosslinked structure into organosiloxane rubber include the following: (a) a method of using a polyfunctional alkoxysilane compound in combination with other materials when polymerizing organosiloxane rubber; (b) a method of introducing reactive groups (e.g., (i) mercapto groups and (ii) reactive vinyl groups) into organosiloxane rubber, and then adding (i) an organic peroxide or (ii) a polymerizable vinyl monomer to the resulting reaction product to cause a radical reaction; or (c) a method of mixing a crosslinkable monomer such as a polyfunctional monomer and / or a mercapto group-containing compound with other materials when polymerizing organosiloxane rubber, and then polymerizing the resultant product.

[0041] A polyfunctional monomer is a monomer having two or more polymerizable unsaturated bonds in the molecule. The polymerizable unsaturated bond is preferably a carbon-carbon double bond. Examples of polyfunctional monomers include (meth)acrylates having an ethylenically unsaturated double bond, such as allyl alkyl (meth)acrylates and allyloxy alkyl (meth)acrylates, and do not include butadiene. Examples of monomers having two (meth)acrylic groups include ethylene glycol di(meth)acrylate, butylene glycol di(meth)acrylate, butanediol di(meth)acrylate, hexanediol di(meth)acrylate, cyclohexanedimethanol di(meth)acrylate, and polyethylene glycol di(meth)acrylates. Examples of the polyethylene glycol di(meth)acrylates include triethylene glycol di(meth)acrylate, tripropylene glycol di(meth)acrylate, tetraethylene glycol di(meth)acrylate, and polyethylene glycol (600) di(meth)acrylate. Examples of monomers having three (meth)acrylic groups include alkoxylated trimethylolpropane tri(meth)acrylates, glycerol propoxy tri(meth)acrylate, pentaerythritol tri(meth)acrylate, and tris(2-hydroxyethyl)isocyanurate tri(meth)acrylate. Examples of the alkoxylated trimethylolpropane tri(meth)acrylates include trimethylolpropane tri(meth)acrylate and trimethylolpropane triethoxy tri(meth)acrylate. Further, examples of monomers having four (meth)acrylic groups include pentaerythritol tetra(meth)acrylate and ditrimethylolpropane tetra(meth)acrylate.Further, examples of monomers having five (meth)acrylic groups include dipentaerythritol penta(meth)acrylate.Further, examples of monomers having six (meth)acrylic groups include ditrimethylolpropane hexa(meth)acrylate.Other examples of polyfunctional monomers include diallyl phthalate, triallyl cyanurate, triallyl isocyanurate, divinylbenzene, etc. The term "polymerizable unsaturated bond" can also be referred to as "unsaturated bond having polymerizability," and refers to an unsaturated bond that can serve as a starting point for a polymerization reaction by radicals or the like.

[0042] Among the above-mentioned polyfunctional monomers, polyfunctional monomers that can be preferably used for polymerization of the core portion include allyl methacrylate, ethylene glycol di(meth)acrylate, butylene glycol di(meth)acrylate, butanediol di(meth)acrylate, hexanediol di(meth)acrylate, cyclohexanedimethanol di(meth)acrylate, and polyethylene glycol di(meth)acrylates. These polyfunctional monomers may be used alone or in combination of two or more.

[0043] Examples of mercapto group-containing compounds include alkyl group-substituted mercaptans, allyl group-substituted mercaptans, aryl group-substituted mercaptans, hydroxy group-substituted mercaptans, alkoxy group-substituted mercaptans, cyano group-substituted mercaptans, amino group-substituted mercaptans, silyl group-substituted mercaptans, acid group-substituted mercaptans, halo group-substituted mercaptans, and acyl group-substituted mercaptans. As alkyl group-substituted mercaptans, alkyl group-substituted mercaptans having 1 to 20 carbon atoms are preferred, and alkyl group-substituted mercaptans having 1 to 10 carbon atoms are more preferred. As aryl group-substituted mercaptans, phenyl group-substituted mercaptans are preferred. As alkoxy group-substituted mercaptans, alkoxy group-substituted mercaptans having 1 to 20 carbon atoms are preferred, and alkoxy group-substituted mercaptans having 1 to 10 carbon atoms are more preferred. The acid group-substituted mercaptan is preferably an alkyl group-substituted mercaptan having a carboxyl group and 1 to 10 carbon atoms, or an aryl group-substituted mercaptan having a carboxyl group and 1 to 12 carbon atoms. These mercapto group-containing compounds may be used alone or in combination of two or more.

[0044] (Glass Transition Temperature of Core Portion) The glass transition temperature of the core portion is preferably 0° C. or lower, more preferably less than 0° C., more preferably −20° C. or lower, more preferably −40° C. or lower, more preferably −50° C. or lower, more preferably −55° C. or lower, more preferably −60° C. or lower, more preferably −65° C. or lower, more preferably −70° C. or lower, even more preferably −75° C. or lower, and particularly preferably −80° C. or lower. The lower limit of the glass transition temperature of the core portion is not particularly limited, but may be, for example, −120° C. or higher, or −100° C. or higher.

[0045] In this specification, "glass transition temperature" may also be referred to as "Tg." This configuration allows for the production of polymer microparticles (A) having a low Tg and a composition having a low Tg. As a result, the resulting composition can provide a cured product having excellent toughness. Furthermore, this configuration allows for the viscosity of the resulting composition to be further reduced.

[0046] When the monomer used for producing (polymerizing) the core portion is known, the glass transition temperature (Tg) of the core portion can be calculated using the FOX formula (Formula 1) shown below: 1 / Tg=w １ / Tg １ +w ２ / Tg ２ +...+w ｎ / Tg ｎ (Formula 1); where Tg １ , Tg ２ , ..., Tg ｎ are the Tg (K) of the homopolymer of the components constituting the core part (i.e., the monomers used in the production of the core part) 1, 2, ..., n, respectively. １ , w ２ ,...,w ｎ are the weight fractions of the components constituting the core portion (i.e., the monomers used in producing the core portion) 1, 2, ..., n, respectively. The Tg of the homopolymer can be, for example, the value described in "Polymer Handbook Fourth Edition" (edited by J. Brandup et al., J. Wiley & Sons, Inc.).

[0047] Furthermore, when the monomer used in the production (polymerization) of the core portion is unknown, viscoelasticity measurement (shear method, measurement frequency: 1 Hz) is performed using a flat plate made of polymer fine particles (A), a loss tangent (tan δ) graph is obtained, and the peak temperature in the obtained graph is used as Tg. Here, when multiple peaks are obtained in the tan δ graph, the glass transition temperature of the core portion can be determined by combining them with other analytical data such as composition analysis.

[0048] The Tg of the core portion can be determined by the composition of the structural units contained in the core portion, etc. In other words, the Tg of the obtained core portion can be adjusted by changing the composition of the monomers used when producing (polymerizing) the core portion.

[0049] (Volume Average Particle Diameter of Core Portion) The volume average particle diameter of the core portion is preferably 0.03 μm to 10.00 μm, more preferably 0.05 μm to 10.00 μm, more preferably 0.08 μm to 2.00 μm, even more preferably 0.10 μm to 1.00 μm, even more preferably 0.10 μm to 0.80 μm, and particularly preferably 0.10 μm to 0.50 μm. When the volume average particle diameter of the core portion is 0.03 μm or more, core portions having the desired volume average particle diameter can be stably obtained. When the volume average particle diameter of the core portion is 10.00 μm or less, the heat resistance and impact resistance of the resulting cured product are good. The volume average particle diameter of the core portion can be measured using a dynamic light scattering particle size distribution analyzer or the like, using an aqueous latex containing the core portion as a sample.

[0050] (Proportion of Core Portion) The proportion of core portions in the polymer microparticles (A) is preferably 10% by weight to 80% by weight, more preferably 10% by weight to 70% by weight, and even more preferably 10% by weight to 60% by weight, based on 100% by weight of the polymer microparticles (A). When the proportion of core portions is 10% by weight or more, the resulting composition can provide a cured product with excellent toughness and impact resistance. When the proportion of core portions is 80% by weight or less, the polymer microparticles (A) do not easily aggregate, so the composition does not become highly viscous, and as a result, the resulting composition can have excellent handleability.

[0051] (Gel Content of Core Portion) The core portion is preferably one that can swell in an appropriate solvent but is substantially insoluble in the thermosetting resin used.

[0052] The gel content of the core portion is preferably 30% by weight to 100% by weight, more preferably 40% by weight to 100% by weight, more preferably 50% by weight to 100% by weight, even more preferably 60% by weight to 100% by weight, still more preferably 70% by weight to 100% by weight, even more preferably 80% by weight to 100% by weight, particularly preferably 90% by weight to 100% by weight, and most preferably 95% by weight to 100% by weight. When the gel content of the core portion is within the above range, the resulting composition can provide a cured product with excellent toughness.

[0053] In this specification, the gel content is calculated as follows. First, an aqueous latex containing core portions is obtained, and then a powder of core portions is obtained from the aqueous latex. The method for obtaining a powder of core portions from the aqueous latex is not particularly limited, but examples thereof include (i) agglomerating the core portions in the aqueous latex, (ii) dehydrating the obtained agglomerates, and (iii) further drying the agglomerates to obtain a powder of core portions. Next, 2.0 g of the powder of core portions is dissolved in 50 mL of methyl ethyl ketone (MEK). Thereafter, the obtained MEK solution is separated into a component soluble in MEK (MEK-soluble component) and a component insoluble in MEK (MEK-insoluble component). Specifically, the obtained MEK dissolved material is centrifuged using a centrifuge (CP60E, manufactured by Hitachi Koki Co., Ltd.) at a rotation speed of 30,000 rpm for 1 hour to separate the dissolved material into MEK-soluble and MEK-insoluble components. Three sets of centrifugation are performed in total. The weights of the obtained MEK-soluble and MEK-insoluble components are measured, and the gel content is calculated using the following formula: Gel content (%) = (weight of methyl ethyl ketone-insoluble component) / {(weight of methyl ethyl ketone-insoluble component) + (weight of methyl ethyl ketone-soluble component)} × 100.

[0054] In one embodiment of the present invention, the "core portion" of the polymer microparticle (A) may be composed of only one type of core portion having the same composition of structural units. In this case, the "core portion" of the polymer microparticle (A) is preferably one type selected from the group consisting of diene rubber, (meth)acrylate rubber, and organosiloxane rubber.

[0055] In one embodiment of the present invention, the "core portion" of the polymer microparticles (A) may be composed of multiple types of core portions each having a different constitutional unit composition. In this case, the "core portion" of the polymer microparticles (A) may be one type or two or more types selected from the group consisting of diene rubber, (meth)acrylate rubber, and organosiloxane rubber. In other words, the "core portion" of the polymer microparticles (A) may be multiple types of diene rubber, (meth)acrylate rubber, or organosiloxane rubber each having a different constitutional unit composition.

[0056] In one embodiment of the present invention, the case where the "core part" of the polymer microparticle (A) is composed of a plurality of types of core parts each having a different composition of structural units will be described. In this case, each of the plurality of types of core parts is referred to as a core part. １ , core part ２ , ..., and the core part ｎ Here, n is an integer of 2 or more. The "core portion" of the polymer fine particles (A) is a core portion that is polymerized separately. １ , core part ２ , ..., and the core part ｎ The "core portion" of the polymer fine particles (A) may contain a composite of the following: １ , core part ２ , ..., and the core ｎ The polymerizable composition may include one core part obtained by sequentially polymerizing each of the above. Such sequential polymerization of multiple core parts (polymers) is also referred to as multistage polymerization. One core part obtained by multistage polymerization of multiple types of core parts is also referred to as a multistage-polymerized core part. The method for producing the multistage-polymerized core part will be described in detail later.

[0057] Core １ , core part ２, ..., and the core ｎ In the multistage polymerization core part, the core part ｎ is the core part ｎ－１ At least a part of the core may be coated. ｎ－１ In the multi-stage polymerization core part, ｎ Part of the core ｎ－１ Sometimes it penetrates inside the

[0058] In the multi-stage polymerization core part, each of the plurality of core parts may form a layer structure. For example, the multi-stage polymerization core part may be １ , core part ２ , and the core part ３ If it consists of １ forms the innermost layer, and the core １ The core part on the outside ２ A layer of ２ The outer layer of the core ３ An embodiment in which the above layer is formed as the outermost layer of the core part is also one aspect of the present invention. In this way, a multistage polymerization core part in which each of the multiple core parts forms a layer structure can also be called a multilayer core part. That is, in one embodiment of the present invention, the "core part" of the polymer microparticle (A) may contain (i) a composite of multiple types of core parts, (ii) a multistage polymerization core part, and / or (iii) a multilayer core part.

[0059] (2-1-2. Graft Portion) In this specification, the polymer grafted to the core portion is referred to as the graft portion. In one embodiment of the present invention, the graft portion preferably contains one or more structural units selected from the group consisting of an aromatic vinyl unit, a vinyl cyan unit, and a (meth)acrylate unit. When the graft portion has the above-described structure, it has the advantage that the polymer fine particles (A) do not easily aggregate.

[0060] Specific examples of the aromatic vinyl unit include structural units derived from monomers or compounds such as unsubstituted vinyl aromatic compounds such as styrene and 2-vinylnaphthalene; vinyl-substituted aromatic compounds such as α-methylstyrene, 3-methylstyrene, 4-methylstyrene, 2,4-dimethylstyrene, 2,5-dimethylstyrene, 3,5-dimethylstyrene, and 2,4,6-trimethylstyrene; ring-alkoxylated vinyl aromatic compounds such as 4-methoxystyrene and 4-ethoxystyrene; ring-halogenated vinyl aromatic compounds such as 2-chlorostyrene and 3-chlorostyrene; ring-ester-substituted vinyl aromatic compounds such as 4-acetoxystyrene; ring-hydroxylated vinyl aromatic compounds such as 4-hydroxystyrene; aromatic methacrylates such as phenyl methacrylate; and aromatic monomers such as acenaphthalene and indene.

[0061] Specific examples of the vinylcyan unit include structural units derived from monomers such as acrylonitrile and methacrylonitrile.

[0062] Specific examples of the (meth)acrylate unit include structural units derived from monomers such as methyl (meth)acrylate, ethyl (meth)acrylate, butyl (meth)acrylate, hydroxyethyl (meth)acrylate, and hydroxybutyl (meth)acrylate.

[0063] The one or more structural units selected from the group consisting of the aromatic vinyl unit, the vinylcyan unit, and the (meth)acrylate unit may be used alone or in combination of two or more.

[0064] The graft portion preferably contains, as structural units, aromatic vinyl units, vinylcyan units, and (meth)acrylate units in a total amount of 10 to 95% by weight, more preferably 30 to 92% by weight, even more preferably 50 to 90% by weight, particularly preferably 60 to 87% by weight, and most preferably 70 to 85% by weight, based on 100% by weight of the polymer contained in the graft portion. This configuration has the advantage that the polymer fine particles (A) do not easily aggregate.

[0065] The graft portion (i) preferably contains one or more structural units selected from the group consisting of unsubstituted vinyl aromatic units and vinyl-substituted aromatic units, and may be composed solely of one or more structural units selected from this group; (ii) more preferably contains one or more structural units selected from the group consisting of styrene units, 2-vinylnaphthalene units, α-methylstyrene units, 3-methylstyrene, 4-methylstyrene, 2,4-dimethylstyrene, 2,5-dimethylstyrene, 3,5-dimethylstyrene, and 2,4,6-trimethylstyrene, and may be composed solely of one or more structural units selected from this group; (iii) even more preferably contains one or more structural units selected from the group consisting of styrene units and α-methylstyrene units, and may be composed solely of one or more structural units selected from this group; and (iv) particularly preferably contains a styrene unit, and may be composed solely of a styrene unit. This configuration has the advantage of increasing the peak height of tan δ of the noise reducing agent in the temperature range of 10°C or higher.

[0066] In one embodiment of the present invention, the total amount of unsubstituted vinyl aromatic units and vinyl-substituted aromatic units in the graft portion is preferably more than 70% by weight and not more than 100% by weight, more preferably 75% by weight to 100% by weight, even more preferably 80% by weight to 100% by weight, and particularly preferably 85% by weight to 100% by weight. This configuration has the advantage of increasing the peak height of tan δ in the temperature range of 10°C or higher of the noise reducing agent.

[0067] The graft moiety may further contain, as a structural unit, a structural unit derived from a monomer having a reactive group. The monomer having a reactive group is preferably a monomer having one or more reactive groups selected from the group consisting of an epoxy group, an oxetane group, a hydroxyl group, an amino group, an imide group, a carboxylic acid group, a carboxylic anhydride group, a cyclic ester, a cyclic amide, a benzoxazine group, and a cyanate ester group, more preferably a monomer having one or more reactive groups selected from the group consisting of an epoxy group, a hydroxyl group, and a carboxylic acid group, and most preferably a monomer having an epoxy group. This allows the polymer fine particles (A) to be maintained in a well-dispersed state in the composition or in a molded product thereof without agglomerating.

[0068] Specific examples of the monomer having an epoxy group include glycidyl group-containing vinyl monomers such as glycidyl (meth)acrylate, 4-hydroxybutyl (meth)acrylate glycidyl ether, and allyl glycidyl ether.

[0069] Specific examples of monomers having a hydroxyl group include: (a) linear hydroxy alkyl (meth)acrylates such as 2-hydroxyethyl (meth)acrylate, hydroxypropyl (meth)acrylate, and 4-hydroxybutyl (meth)acrylate (particularly preferred are linear C1-6 hydroxy alkyl (meth)acrylates); (b) caprolactone-modified hydroxy (meth)acrylates; (c) branched hydroxy alkyl (meth)acrylates such as methyl α-(hydroxymethyl)acrylate and ethyl α-(hydroxymethyl)acrylate; and (d) hydroxyl group-containing (meth)acrylates such as mono(meth)acrylates of polyester diols (particularly preferred are saturated polyester diols) obtained from divalent carboxylic acids (such as phthalic acid) and dihydric alcohols (such as propylene glycol). Note that "linear C1-6 alkyl" refers to linear alkyls having 1 to 6 carbon atoms.

[0070] Specific examples of the monomer having a carboxylic acid group include (a) monocarboxylic acids such as acrylic acid, methacrylic acid, and crotonic acid, and (b) dicarboxylic acids such as maleic acid, fumaric acid, and itaconic acid. The above-mentioned monocarboxylic acids are preferably used as the monomer having a carboxylic acid group.

[0071] The above-mentioned monomers having a reactive group may be used alone or in combination of two or more.

[0072] The graft portion preferably contains 0.5 wt% to 90 wt%, more preferably 1 wt% to 50 wt%, even more preferably 2 wt% to 35 wt%, and particularly preferably 3 wt% to 20 wt% of structural units derived from a monomer having a reactive group, based on 100 wt% of the polymer contained in the graft portion. When the graft portion contains 0.5 wt% or more of structural units derived from a monomer having a reactive group, based on 100 wt% of the polymer contained in the graft portion, the resulting composition has the advantage of being capable of providing molded articles having sufficient impact resistance. When the graft portion contains 90 wt% or less of structural units derived from a monomer having a reactive group, based on 100 wt% of the polymer, the resulting composition has the advantage of being capable of providing molded articles having sufficient impact resistance, and the storage stability of the composition is excellent.

[0073] The structural unit derived from a monomer having a reactive group is preferably contained in the graft portion, and more preferably contained only in the graft portion.

[0074] From the viewpoint of ease of dispersion of the polymer fine particles (A) in the matrix resin, it is preferable that the graft portion does not contain a structural unit derived from a monomer having a reactive group. From the viewpoint of ease of dispersion of the polymer fine particles (A) in the matrix resin, the amount of structural units derived from a monomer having a reactive group in 100% by weight of the polymer contained in the graft portion is preferably 10% by weight or less, more preferably 5% by weight or less, more preferably 3% by weight or less, even more preferably 1% by weight or less, and particularly preferably 0% by weight.

[0075] The graft moiety may contain a structural unit derived from a polyfunctional monomer as a structural unit. When the graft moiety contains a structural unit derived from a polyfunctional monomer, it has the following advantages: (a) swelling of the polymer fine particles (A) in the composition can be prevented, (b) the viscosity of the composition is reduced, which tends to improve the handleability of the composition, and (c) the dispersibility of the polymer fine particles (A) in the composition is improved.

[0076] When the graft portion does not contain a structural unit derived from a polyfunctional monomer, the resulting composition can provide a molded article having superior toughness and impact resistance, compared to when the graft portion contains a structural unit derived from a polyfunctional monomer.

[0077] Examples of the polyfunctional monomer having two or more polymerizable unsaturated bonds in the molecule include the polyfunctional monomers exemplified in the section (Crosslinked structure of the core portion) above.

[0078] Among the above-mentioned polyfunctional monomers, polyfunctional monomers that can be preferably used for polymerization of the graft portion include allyl methacrylate, ethylene glycol di(meth)acrylate, butylene glycol di(meth)acrylate, butanediol di(meth)acrylate, hexanediol di(meth)acrylate, cyclohexanedimethanol di(meth)acrylate, and polyethylene glycol di(meth)acrylates. These polyfunctional monomers may be used alone or in combination of two or more.

[0079] The graft portion preferably contains 1% by weight to 20% by weight, and more preferably 5% by weight to 15% by weight, of structural units derived from polyfunctional monomers, based on 100% by weight of the polymer contained in the graft portion.

[0080] In the polymerization of the graft portion, the above-mentioned monomers may be used alone or in combination of two or more. Furthermore, the graft portion may contain, as a constituent unit, a constituent unit derived from another monomer in addition to the constituent units derived from the above-mentioned monomers.

[0081] (Glass Transition Temperature of Graft Portion) The glass transition temperature of the graft portion is preferably 0° C. or higher, more preferably 10° C. or higher, more preferably 20° C. or higher, more preferably 30° C. or higher, more preferably 40° C. or higher, more preferably 50° C. or higher, more preferably 60° C. or higher, more preferably 70° C. or higher, more preferably 80° C. or higher, even more preferably 90° C. or higher, and particularly preferably 100° C. or higher. The upper limit of the glass transition temperature of the graft portion is not particularly limited, but may be, for example, 120° C. or lower, or 110° C. or lower.

[0082] The Tg of the graft portion can be determined by the composition of the structural units contained in the graft portion, etc. In other words, the Tg of the resulting graft portion can be adjusted by changing the composition of the monomers used when producing (polymerizing) the graft portion.

[0083] When the monomer used for producing (polymerizing) the grafted portion is known, the glass transition temperature (Tg) of the grafted portion can be calculated using the FOX formula (Formula 1) shown below: 1 / Tg=w １ / Tg １ +w ２ / Tg ２ +...+w ｎ / Tg ｎ (Formula 1); where Tg １ , Tg ２ , ..., Tg ｎ are the Tg (K) and w of the homopolymers of the components constituting the graft portion (i.e., the monomers used in the production of the graft portion) 1, 2, ..., n, respectively. １ , w ２ ,...,w ｎ are the weight fractions of the components constituting the graft portion (i.e., the monomers used in producing the graft portion) 1, 2, ..., n, respectively. The Tg of the homopolymer can be, for example, the value described in "Polymer Handbook Fourth Edition" (edited by J. Brandup et al., Jphn Wiley & Sons, Inc.).

[0084] Furthermore, when the monomer used in the production (polymerization) of the graft moiety is unknown, viscoelasticity measurement (shear method, measurement frequency: 1 Hz) is performed using a flat plate made of polymer fine particles (A), a loss tangent (tan δ) graph is obtained, and the peak temperature in the obtained graph may be used as Tg. Here, when multiple peaks are obtained in the tan δ graph, the glass transition temperature of the graft moiety can be determined by combining this with other analytical data such as composition analysis.

[0085] (Graft Ratio of Graft Moiety) In preparing the graft moiety in the production of polymer microparticles (A), when the monomer mixture used to prepare the graft moiety is polymerized in the presence of the core moiety, a polymer having the same structure as the graft moiety but not graft-bonded to the core moiety may be produced. In preparing the graft moiety in the production of polymer microparticles (A), when the monomer mixture used to prepare the graft moiety is polymerized in the presence of the core moiety, at least a portion of the polymer obtained from the monomer mixture may be graft-bonded to the core moiety. In this specification, a "polymer having the same structure as the graft moiety but not graft-bonded to the core moiety" is also referred to as a non-graft polymer. The non-graft polymer may or may not be removed from the aqueous latex of the obtained polymer microparticles (A). In other words, in one embodiment of the present invention, the noise reducing agent may contain a polymer having the same structure as the graft moiety but not graft-bonded to the core moiety (non-graft polymer). The non-graft polymer contained in the noise reducing agent corresponds to polymer (B) described below.

[0086] In this specification, the proportion of the polymer grafted to the core portion, i.e., the proportion of the graft portion, among the polymers produced in the production (polymerization) of the graft portion, is referred to as the graft ratio. The graft ratio can also be expressed as (weight of the graft portion) / {(weight of the graft portion)+(weight of the non-grafted polymer)}×100.

[0087] In the production (polymerization) of the grafted portion, soluble components are present in addition to the grafted portion and the non-grafted polymer. The soluble components include unpolymerized monomers and secondary raw materials such as initiators.

[0088] As a method for determining whether a particle is polymer fine particles (A), a non-graft polymer, or a soluble component, for example, a method for determining based on solubility / insolubility in a solvent can be mentioned, such as (i) determining that the particle is insoluble in MEK as polymer fine particles (A), (ii) determining that the particle is soluble in MEK and insoluble in methanol as a non-graft polymer, or (iii) determining that the particle is soluble in MEK and soluble in methanol as a soluble component.

[0089] In this specification, the graft ratio was calculated by the following method using an aqueous latex immediately after the production of polymer microparticles (A). First, an amount of aqueous latex corresponding to 2 g of solids in the aqueous latex immediately after the production of polymer microparticles (A) was mixed with 50 ml of methyl ethyl ketone (MEK) to prepare an MEK solution. Alternatively, a powder of polymer microparticles (A) was obtained from the aqueous latex immediately after the production of polymer microparticles (A), and 2 g of the obtained powder was mixed with 50 mL of MEK to prepare an MEK solution. Specific methods for obtaining powder of polymer microparticles (A) from aqueous latex include (i) coagulating the polymer microparticles (A) in the aqueous latex, (ii) dehydrating the obtained coagulate, and (iii) further drying the coagulate to obtain powder of polymer microparticles (A). The resulting MEK solution is then separated into a MEK-soluble component (MEK-soluble fraction) and a MEK-insoluble component (MEK-insoluble fraction). Specifically, the following steps (1) to (3) are performed: (1) the resulting MEK solution is centrifuged using a centrifuge (Hitachi Koki Co., Ltd., CP60E) at 30,000 rpm for 1 hour to separate the solution into a MEK-soluble fraction and a MEK-insoluble fraction; (2) the resulting MEK-soluble fraction and MEK are mixed, and the resulting MEK mixture is centrifuged using the above-mentioned centrifuge at 30,000 rpm for 1 hour to separate the MEK mixture into a MEK-soluble fraction and a MEK-insoluble fraction; and (3) the step (2) is repeated once more (i.e., the centrifugation process is performed three times in total). A concentrated MEK-soluble fraction is obtained by these steps. Next, 20 ml of the concentrated MEK-soluble fraction was mixed with 200 ml of methanol. An aqueous calcium chloride solution prepared by dissolving 0.01 g of calcium chloride in water was added to the resulting mixture, and the resulting mixture was stirred for 1 hour. The resulting mixture was then separated into a methanol-soluble fraction and a methanol-insoluble fraction.

[0090] The graft ratio was calculated using the following formula: Graft ratio (%) = 100 - [(weight of methanol insoluble matter) / {(weight of methanol insoluble matter) + (weight of MEK insoluble matter)}] / (total amount of monomer mixture used in production (polymerization) of the graft portion) × 10,000.

[0091] In the above-mentioned method for calculating the graft ratio, (a) the MEK-insoluble matter corresponds to the polymer fine particles (A), and (b) the MEK-soluble matter and methanol-insoluble matter corresponds to the non-grafted polymer.

[0092] The lower limit of the graft ratio of the graft portion is preferably 5% or more, more preferably 10% or more, more preferably 15% or more, more preferably 20% or more, more preferably 25% or more, more preferably 30% or more, more preferably 35% or more, more preferably 40% or more, more preferably 45% or more, more preferably 50% or more, more preferably 55% or more, more preferably 60% or more, more preferably 65% ​​or more, more preferably 70% or more, more preferably 75% or more, more preferably 80% or more, more preferably 85% or more, more preferably 90% or more, and more preferably 95% or more. A graft ratio of 5% or more has the advantage that the viscosity of the composition does not become too high. The upper limit of the graft rate of the graft portion is preferably 100% or less, more preferably 95% or less, more preferably 90% or less, more preferably 85% or less, more preferably 80% or less, more preferably 75% or less, more preferably 70% or less, more preferably 65% ​​or less, more preferably 60% or less, more preferably 55% or less, more preferably 50% or less, more preferably 45% or less, more preferably 40% or less, more preferably 35% or less, more preferably 30% or less, more preferably 25% or less, more preferably 20% or less, more preferably 15% or less, and more preferably 10% or less.

[0093] The graft ratio of the grafted portion can be appropriately adjusted by changing the amount of chain transfer agent used during preparation of the grafted portion.

[0094] (Proportion of Graft Moiety) In one embodiment of the present invention, the proportion of the graft moiety in the polymer fine particles (A) is preferably 20% by weight to 90% by weight, more preferably 30% by weight to 90% by weight, and even more preferably 40% by weight to 90% by weight, based on 100% by weight of the polymer fine particles (A).

[0095] (Modifications of the Graft Portion) In one embodiment of the present invention, the graft portion may consist of only one type of graft portion having structural units of the same composition. In one embodiment of the present invention, the graft portion may consist of multiple types of graft portions each having a structural unit of a different composition.

[0096] In one embodiment of the present invention, the graft portion is composed of a plurality of types of graft portions. In this case, each of the plurality of types of graft portions is １ , graft part ２ , ..., graft part ｎ (n is an integer of 2 or more). The graft portions are each polymerized separately. １ , graft part ２ , ..., and the graft portion ｎ The graft portion may comprise a composite of １ , graft part ２ , ..., and the graft portion ｎ The polymer may contain a single polymer obtained by sequentially polymerizing each of the above. Such sequential polymerization of multiple polymerization portions (graft portions) is also referred to as multistage polymerization. A single polymer obtained by multistage polymerization of multiple types of graft portions is also referred to as a multistage polymerization graft portion. A method for producing a multistage polymerization graft portion will be described in detail later.

[0097] When the graft moiety is composed of multiple types of graft moieties, not all of these multiple types of graft moieties need to be graft-bonded to the core moiety. When the graft moiety is composed of multiple types of graft moieties, it is sufficient that at least a portion of at least one type of graft moiety is graft-bonded to the core moiety, and the other types (multiple other types) of graft moieties may be graft-bonded to graft moieties that are graft-bonded to the core moiety. Furthermore, when the graft moiety is composed of multiple types of graft moieties, it may have multiple types of polymers (multiple types of polymers (B)) that have the same structure as the multiple types of graft moieties and are not graft-bonded to the core moiety.

[0098] Graft area １ , graft part ２ , ..., and the graft portion ｎ In the multi-stage polymerization graft portion, ｎ is the graft area ｎ－１ or a graft portion. ｎ－１ In the multi-stage polymerization graft portion, ｎ Part of the graft ｎ－１ Sometimes it penetrates inside the

[0099] In the multi-stage polymerization graft portion, each of the plurality of graft portions may form a layer structure. For example, the multi-stage polymerization graft portion may be １ , graft part ２ , and the graft portion ３ If it consists of １ forms the innermost layer of the graft portion, １ The graft part is located on the outside of the ２ A layer of graft tissue is formed. ２ The graft area is located on the outside of the layer. ３An embodiment in which the layer (a) is formed as the outermost layer is also one aspect of the present invention. In this way, a multi-stage polymerization graft portion in which each of a plurality of graft portions forms a layer structure can also be called a multi-layer graft portion. That is, in one embodiment of the present invention, the graft portion may include (a) a composite of a plurality of types of graft portions, (b) a multi-stage polymerization graft portion, and / or (c) a multi-layer graft portion.

[0100] When the core portion and the graft portion are polymerized in this order in the production of polymer microparticles (A), at least a portion of the graft portion can cover at least a portion of the core portion in the resulting polymer microparticles (A). Polymerization of the core portion and the graft portion in this order can be said to be multistage polymerization of the core portion and the graft portion. The polymer microparticles (A) obtained by multistage polymerization of the core portion and the graft portion can also be said to be a multistage polymer.

[0101] When the polymer microparticles (A) are multistage polymers, the graft moieties may cover at least a portion of the core moieties, or may cover the entire core moieties. When the polymer microparticles (A) are multistage polymers, some of the graft moieties may penetrate into the inside of the core moieties. It is preferable that at least a portion of the graft moieties cover at least a portion of the core moieties. In other words, it is preferable that at least a portion of the graft moieties is present at the outermost portion of the polymer microparticles (A).

[0102] When the polymer microparticles (A) are multistage polymers, the core portion and the graft portion may form a layer structure. For example, one embodiment of the present invention is one in which the core portion forms the innermost layer (also referred to as the core layer) and a layer of the graft portion is formed as the outermost layer (also referred to as the shell layer) outside the core portion. A structure in which the core portion forms the core layer and the graft portion forms the shell layer can also be referred to as a core-shell structure. Thus, polymer microparticles (A) in which the core portion and the graft portion form a layer structure (core-shell structure) can also be referred to as a multilayer polymer or a core-shell polymer. That is, in one embodiment of the present invention, the polymer microparticles (A) may be multistage polymers and / or may be multilayer polymers or core-shell polymers. However, as long as they have core portions and graft portions, the polymer microparticles (A) are not limited to the above structure.

[0103] (2-1-4. Volume Average Particle Diameter (Mv) of Polymer Microparticles (A)) The volume average particle diameter (Mv) of the polymer microparticles (A) is preferably 0.10 μm to 10.00 μm, more preferably 0.10 μm to 1.00 μm, even more preferably 0.10 μm to 0.80 μm, and particularly preferably 0.10 μm to 0.50 μm, because this allows for the production of a composition having the desired viscosity and high stability. When the volume average particle diameter (Mv) of the polymer microparticles (A) is within the above range, there is also the advantage that the dispersibility of the polymer microparticles (A) in the composition is improved. In this specification, the term "volume average particle diameter (Mv) of the polymer microparticles (A)" refers to the volume average particle diameter of the primary particles of the polymer microparticles (A), unless otherwise specified. The volume average particle diameter of the polymer microparticles (A) can be measured using a dynamic light scattering particle size distribution analyzer or the like, using an aqueous latex containing the polymer microparticles (A) as a sample.

[0104] (2-1-5. Production method of polymer microparticles (A)) An example of a production method of polymer microparticles (A) will be described below. The polymer microparticles (A) can be produced, for example, by polymerizing the core portion and then graft-polymerizing a polymer constituting the graft portion onto the core portion in the presence of the core portion.

[0105] The polymer microparticles (A) can be produced by known methods, such as emulsion polymerization, suspension polymerization, and microsuspension polymerization. Specifically, the polymerization of the core portion and the polymerization (graft polymerization) of the graft portion in the polymer microparticles (A) can be carried out by known methods, such as emulsion polymerization, suspension polymerization, and microsuspension polymerization. Among these, emulsion polymerization is particularly preferred as a method for producing the polymer microparticles (A). The emulsion polymerization method has the following advantages: (i) the composition of the polymer microparticles (A) can be easily designed, (ii) the polymer microparticles (A) can be easily produced industrially, and (iii) an aqueous latex suitable for use in the production method described below can be easily obtained. Hereinafter, methods for producing the core portion and graft portion that can be contained in the polymer microparticles (A) will be described.

[0106] (Method for Producing Core Portion) The core portion is preferably produced by polymerizing one or more monomers selected from the group consisting of diene-based monomers, (meth)acrylate-based monomers, and organosiloxane-based monomers.

[0107] Consider a case where the core portion contains at least one selected from the group consisting of diene rubbers and (meth)acrylate rubbers. In this case, the core portion can be produced by polymerizing one or more monomers selected from the group consisting of diene monomers and (meth)acrylate monomers. In this case, the polymerization of the monomers can be carried out by, for example, emulsion polymerization, suspension polymerization, microsuspension polymerization, or the like, and examples of such methods include the method described in WO 2005 / 028546.

[0108] The "core portion" of the polymer fine particles (A) is a plurality of types of core portions (for example, １ , core part ２ , ..., core part ｎ In this case, the core part １ , core part ２ , ..., core part ｎAlternatively, the core parts may be polymerized separately by the above-mentioned method, and then mixed and composited to produce a composite comprising a plurality of types of core parts. １ , core part ２ , ..., core part ｎ may be sequentially polymerized in multiple stages to produce one core part consisting of multiple types of core parts.

[0109] The multi-stage polymerization of the core part will be specifically described. For example, the multi-stage polymerization core part can be obtained by carrying out the following steps (1) to (4) in order: (1) Core part １ Polymerize the core １ (2) Then, the core part is obtained. １ In the presence of ２ The two-stage core part is made by stacking １＋２ (3) Then, the core part is obtained. １＋２ In the presence of ３ The three-stage core part is made by stacking １＋２＋３ (4) After the same procedure, the core part is obtained in the presence of core part 1+2+...+(n-1). ｎ The multi-stage polymerization core １＋２＋・・・＋ｎ get.

[0110] (Method for Producing Graft Portion) The graft portion can be formed, for example, by polymerizing the monomer used to form the graft portion by known radical polymerization in the presence of the core portion. When the core portion is obtained as an aqueous latex, the polymerization of the graft portion is preferably carried out by emulsion polymerization. The graft portion can be produced, for example, according to the method described in WO2005 / 028546.

[0111] The graft portion is a graft portion of multiple types (e.g., graft portion １ , graft part ２ , ..., graft part ｎ In this case, the graft portion is made of １ , graft part ２ , ..., graft part ｎmay be polymerized separately by the above-mentioned method, and then mixed and composited to produce a graft portion (composite) consisting of a plurality of types of graft portions. １ , graft part ２ , ..., graft part ｎ may be sequentially polymerized in multiple stages to produce one graft moiety consisting of multiple types of graft moieties.

[0112] The multi-stage polymerization of the graft portion will be specifically described. For example, the multi-stage polymerization graft portion can be obtained by carrying out the following steps (1) to (4) in order: (1) Graft portion １ is polymerized to form the grafted portion. １ (2) Then, the graft portion is obtained. １ In the presence of ２ Polymerization to form a two-stage grafted portion １＋２ (3) Then, the graft portion is obtained. １＋２ In the presence of ３ Polymerization to form a three-stage graft section １＋２＋３ (4) After the same procedure, the grafted portion 1+2+...+(n-1) is obtained. ｎ is polymerized to form a multi-stage grafted portion. １＋２＋・・・＋ｎ get.

[0113] When the graft moiety is composed of a plurality of types of graft moieties, the graft moieties having a plurality of types of graft moieties may be polymerized and then graft polymerized onto the core moieties to produce the polymer microparticles (A).The polymer microparticles (A) may also be produced by sequentially graft polymerizing the plurality of types of polymers constituting the graft moieties onto the core moieties in the presence of the core moieties in multiple stages.

[0114] When emulsion polymerization is used as the method for producing polymer microparticles (A), known emulsifiers (dispersants) can be used to produce the polymer microparticles (A). Examples of emulsifiers include anionic emulsifiers, nonionic emulsifiers, polyvinyl alcohol, alkyl-substituted cellulose, polyvinylpyrrolidone, and polyacrylic acid derivatives. Examples of anionic emulsifiers include sulfur-based emulsifiers, phosphorus-based emulsifiers, sarcosinic acid-based emulsifiers, and carboxylic acid-based emulsifiers. Examples of sulfur-based emulsifiers include sodium dodecylbenzenesulfonate (abbreviated as SDBS). Examples of phosphorus-based emulsifiers include sodium polyoxyethylene lauryl ether phosphate.

[0115] When emulsion polymerization is used as the method for producing the polymer microparticles (A), a thermally decomposable initiator can be used to produce the polymer microparticles (A). Examples of the thermally decomposable initiator include known initiators such as (i) 2,2'-azobisisobutyronitrile and (ii) peroxides such as organic peroxides and inorganic peroxides. Examples of the organic peroxides include t-butylperoxyisopropyl carbonate, paramenthane hydroperoxide, cumene hydroperoxide, dicumyl peroxide, t-butyl hydroperoxide, di-t-butyl peroxide, and t-hexyl peroxide. Examples of the inorganic peroxides include hydrogen peroxide, potassium persulfate, and ammonium persulfate.

[0116] A redox initiator can also be used to produce the polymer microparticles (A). The redox initiator is an initiator that combines (i) a peroxide such as an organic peroxide or an inorganic peroxide with (ii) a transition metal salt such as iron (II) sulfate, or a reducing agent such as sodium formaldehyde sulfoxylate or glucose. If necessary, a chelating agent such as disodium ethylenediaminetetraacetate and, if necessary, a phosphorus-containing compound such as sodium pyrophosphate may also be used in combination.

[0117] When a redox initiator is used, polymerization can be carried out even at a low temperature where the peroxide does not substantially decompose thermally, and the polymerization temperature can be set over a wide range. Therefore, it is preferable to use a redox initiator. Among redox initiators, redox initiators using organic peroxides such as cumene hydroperoxide, dicumyl peroxide, paramenthane hydroperoxide, and t-butyl hydroperoxide as the peroxide are preferred. The amount of the initiator used, and when a redox initiator is used, the amounts of the reducing agent, transition metal salt, chelating agent, etc. used can be within known ranges.

[0118] When a polyfunctional monomer is used in polymerization of the core or graft portion for the purpose of introducing a crosslinked structure into the core or graft portion, a known chain transfer agent can be used in a known amount range. By using the chain transfer agent, the molecular weight and / or degree of crosslinking of the resulting core or graft portion can be easily adjusted.

[0119] In addition to the above-mentioned components, a surfactant may be used in the production of the polymer microparticles (A). The type and amount of the surfactant used are within known ranges.

[0120] In the production of the polymer fine particles (A), conditions within known numerical ranges can be appropriately applied as polymerization conditions such as polymerization temperature, pressure, and deoxidation.

[0121] An aqueous latex containing the polymer fine particles (A) can be obtained by the above-mentioned method for producing the polymer fine particles (A). That is, the description in the section (2-1-5. Method for producing the polymer fine particles (A)) can be cited as the description regarding the method for preparing the aqueous latex in the method for producing the present composition.

[0122] [3. Polymer (B)] The present noise reducing agent may contain a polymer (B). The polymer (B) may be mixed in mainly during the process of producing the polymer microparticles (A). Specifically, during the production (polymerization) of the graft portion in the production of the polymer microparticles (A), a polymer that is not bonded to the core portion (a non-grafted polymer) may be generated. If the non-grafted polymer is not removed from the aqueous latex of the obtained polymer microparticles (A), the non-grafted polymer may become the polymer (B) in the obtained noise reducing agent. Note that the polymer (B) is not limited to the polymer mixed in during the production process of the polymer microparticles (A) described above, but also includes a polymer that is added separately.

[0123] The noise reducing agent contains a polymer (B) derived only from a non-grafted polymer generated during the production process of the polymer fine particles (A). In this case, the lower the graft ratio of the polymer fine particles (A), the greater the amount of polymer (B).

[0124] (3-1. Proportion of polymer (B)) In one embodiment of the present invention, the proportion of polymer (B) in the noise reducing agent is not particularly limited. The proportion of polymer (B) in the noise reducing agent may be 1.0 wt% to 50.0 wt%, 3.0 wt% to 45.0 wt%, or 5.0 wt% to 40.0 wt% relative to 100 wt% of the total of polymer fine particles (A) and polymer (B). The proportion of polymer (B) in the noise reducing agent is preferably 7.0 wt% to 40.0 wt%, more preferably 10.0 wt% to 40.0 wt%, even more preferably 15.0 wt% to 40.0 wt%, and particularly preferably 20.0 wt% to 40.0 wt% relative to 100 wt% of the total of polymer fine particles (A) and polymer (B). Since a resin composition for a friction material having low viscosity and easy handling can be provided, the proportion of the polymer (B) in the noise reducing agent is preferably 5.0% by weight to 30.0% by weight, more preferably 5.0% by weight to 20.0% by weight, even more preferably 5.0% by weight to 15.0% by weight, particularly preferably 5.0% by weight to 12.0% by weight, and most preferably 5.0% by weight to 10.0% by weight, relative to 100% by weight of the total of the polymer fine particles (A) and the polymer (B).

[0125] When the noise reducing agent contains a polymer (B) derived only from a non-grafted polymer generated during the production process of the polymer fine particles (A), the composition of the polymer (B) may be the same as the composition of the graft portion of the polymer fine particles (A). Therefore, except for the matters described above regarding the polymer (B), the description in the above section (2-1-2. Graft portion) can be appropriately cited.

[0126] 4. Noise Reducing Agent 4-1. Peak Height of Noise Reducing Agent The tan δ of the polymer fine particles (A) is a value calculated by the following formula (1): tan δ of polymer fine particles (A) = loss modulus E'' / storage modulus E' (1).

[0127] In one embodiment of the present invention, the noise reducing agent has at least one tan δ peak top in a temperature range of 10° C. or higher. The noise reducing agent may have two or more tan δ peak tops in a temperature range of 10° C. or higher.

[0128] In one embodiment of the present invention, the lower limit of the maximum value of the peak height of tan δ of the noise reducing agent in a temperature range of 10°C or higher is 0.70 or higher, preferably 0.75 or higher, more preferably 0.80 or higher, even more preferably 0.85 or higher, and particularly preferably 0.90 or higher. The larger the maximum value of the peak height of tan δ of the noise reducing agent in a temperature range of 10°C or higher, the more preferable it is. The upper limit of the maximum value of the peak height of tan δ of the noise reducing agent in a temperature range of 10°C or higher may be, for example, 3.00 or lower. If the maximum value of the peak height of tan δ of the noise reducing agent in a temperature range of 10°C or higher is within the above range, there is an advantage that a friction material having high vibration absorption ability and reduced noise generation can be obtained. Note that when the noise reducing agent has two or more peak tops of tan δ in a temperature range of 10°C or higher, the height of the highest peak top is defined as the "peak height of tan δ of the noise reducing agent in a temperature range of 10°C or higher."

[0129] The noise reducing agent may have at least one tan δ peak top in a temperature range of 15°C or higher, may have at least one tan δ peak top in a temperature range of 20°C or higher, may have at least one tan δ peak top in a temperature range of 25°C or higher, may have at least one tan δ peak top in a temperature range of 30°C or higher, may have at least one tan δ peak top in a temperature range of 35°C or higher, may have at least one tan δ peak top in a temperature range of 40°C or higher, may have at least one tan δ peak top in a temperature range of 45°C or higher, may have at least one tan δ peak top in a temperature range of 50°C or higher, may have at least one tan δ peak top in a temperature range of 55°C or higher. It may have at least one peak top of tan δ in a temperature range of 60°C or higher, at least one peak top of tan δ in a temperature range of 65°C or higher, at least one peak top of tan δ in a temperature range of 70°C or higher, at least one peak top of tan δ in a temperature range of 75°C or higher, at least one peak top of tan δ in a temperature range of 80°C or higher, at least one peak top of tan δ in a temperature range of 85°C or higher, at least one peak top of tan δ in a temperature range of 90°C or higher, or at least one peak top of tan δ in a temperature range of 95°C or higher.

[0130] Furthermore, the noise reducing agent may have at least one tan δ peak top in a temperature range of 250°C or less, may have at least one tan δ peak top in a temperature range of 200°C or less, may have at least one tan δ peak top in a temperature range of 150°C or less, or may have at least one tan δ peak top in a temperature range of 100°C or less.

[0131] (4-2. Method for Producing Noise-Reducing Agent) In one embodiment of the present invention, the method for producing the noise-reducing agent is not particularly limited. In one embodiment of the present invention, the method for producing the noise-reducing agent comprises a preparation step of preparing an aqueous latex containing polymer microparticles (A), an aggregation step of preparing aggregates containing the polymer microparticles (A) using the obtained aqueous latex, and a recovery step of recovering the aggregates. In this specification, the terms "aggregation," "coagulation," and "coagulation" have the same meaning and are interchangeable.

[0132] The preparation step is a step of obtaining an aqueous latex containing polymer fine particles (A). The specific method for preparing the aqueous latex containing polymer fine particles (A) is not particularly limited, and examples thereof include emulsion polymerization and suspension polymerization.

[0133] The aggregation step is a step for aggregating the polymer microparticles (A) in the aqueous latex. In the aggregation step, aggregates containing the polymer microparticles (A) can be obtained. The method for aggregating the polymer microparticles (A) is not particularly limited, but for example, a method using a solvent, a method using an aggregating agent (also referred to as a coagulant or a coagulant), a method of spraying the aqueous latex containing the polymer microparticles (A), etc. can be used.

[0134] The aggregating step preferably includes a step of preparing aggregates containing polymer fine particles (A) using a flocculant. This configuration eliminates the need for a solvent, making it possible to obtain powders and granules for friction materials with a low environmental impact. Furthermore, this configuration does not require special facilities for spraying, making it possible to easily obtain powders and granules for friction materials.

[0135] The recovery step is a step of removing water from the aqueous latex to obtain aggregates containing polymer microparticles (A). The recovery step can also be described as a step of separating the aggregates containing polymer microparticles (A) from the water component from the aqueous latex. The water component is a mixture containing water as the main component but also containing an emulsifier, non-aggregated polymer microparticles (A), etc. The method for recovering the aggregates containing polymer microparticles (A) is not particularly limited, and examples thereof include filtration, centrifugation, etc.

[0136] The aggregate obtained through the above-described aggregation step and recovery step can be used as a noise reducing agent.

[0137] In one embodiment of the present invention, the method for producing a noise reducing agent may further include a washing step.

[0138] The washing step is a step of washing the aggregates containing the polymer fine particles (A) obtained in the recovery step. By washing the aggregates, powder particles for friction materials with a low content of impurities can be obtained. In the washing step, the aggregates are preferably washed with water, and more preferably washed with ion-exchanged water or pure water.

[0139] The washing step may be any step for washing the aggregates, and the specific method is not particularly limited. Examples include a method of mixing the aggregates with water and stirring them with a stirrer, a method of kneading the aggregates with water using a kneader, a method of mixing the aggregates with water using a planetary mixer, a method of spraying water onto the aggregates, and a method of washing the cake with a pressure filter. Various kneaders can be used, such as a batch kneader, a continuous kneader, an extrusion kneader, and an extruder.

[0140] The objects to be washed include all impurities contained in the aggregates, and are not particularly limited. Examples include impurities derived from emulsifiers (e.g., phosphorus-based emulsifiers, sulfonic acid-based emulsifiers), and, when a flocculant described below is used, impurities derived from the flocculant.

[0141] In one embodiment of the present invention, the method for producing a noise reducing agent may further include a drying step. By drying the noise reducing agent obtained by the above-mentioned method, a powder or granular noise reducing agent can be obtained. In other words, the noise reducing agent may be in the form of a powder or granular material.

[0142] The drying step is a step of drying the aggregates containing the polymer fine particles (A) obtained in the recovery step or the washing step to obtain a powder or granule. The method for drying the aggregates is not particularly limited, and examples thereof include a method of drying the aggregates using a dryer, a method of placing the aggregates in a container and heating and reducing the pressure in the container, and a method of placing the aggregates in a container and bringing a dry gas into countercurrent contact with the aggregates in the container.

[0143] In the above-mentioned method for producing a noise reducing agent including the preparation step, aggregation step, and recovery step, a case will be described in which the non-grafted polymer obtained during the production of polymer microparticles (A) is not removed from the aqueous latex of the polymer microparticles (A) and no separately prepared polymer is blended (hereinafter also referred to as "Case D"). In Case D, the obtained noise reducing agent may contain polymer (B) derived only from the non-grafted polymer. In case D, the amounts of polymer fine particles (A) and polymer (B) in the noise reducing agent can be measured by the following method: (1) mixing the noise reducing agent with 50 mL of MEK to prepare an MEK solution; (2) subsequently separating the obtained MEK solution into an MEK-soluble fraction and an MEK-insoluble fraction; (3) further mixing the MEK-soluble fraction with methanol to obtain a mixture; (4) then adding an aqueous calcium chloride solution prepared by dissolving 0.01 g of calcium chloride in water to the obtained mixture, and stirring the resulting mixture for 1 hour; (5) thereafter separating the resulting mixture into a methanol-soluble fraction and a methanol-insoluble fraction. The amount of MEK-insoluble fraction in the noise reducing agent thus obtained can represent the amount of polymer fine particles (A) in the noise reducing agent. The amount of methanol-insoluble fraction (both MEK-soluble and methanol-insoluble fraction) in the noise reducing agent thus obtained can represent the amount of polymer (B) in the noise reducing agent.

[0144] 5. Resin Composition for Friction Material A resin composition for friction material containing the noise-reducing agent described above is also one embodiment of the present invention. This composition can provide a friction material with reduced noise.

[0145] (5-1. Resin) The present composition may contain a resin in addition to the noise reducing agent described above. The resin in the present composition can function as a binder.

[0146] The resin is not particularly limited, and examples thereof include thermosetting resins, thermoplastic resins, and any combination of thermosetting and thermoplastic resins. Because of their heat resistance, the resin is preferably a thermosetting resin such as a phenolic resin, an epoxy resin, a polyimide resin, or an oxetane resin, or a thermoplastic resin such as a polycarbonate resin.

[0147] The resin preferably contains at least a phenolic resin. The phenolic resin is not particularly limited, and various phenolic resins can be used. Specific examples of the phenolic resin include: (i) novolac-type phenolic resins (e.g., novolac-type cresol-modified phenolic resins and novolac-type bisphenol-modified phenolic resins) obtained by condensing or co-condensing phenols and / or naphthols with a compound having an aldehyde group under an acidic catalyst; and (ii) resol-type phenolic resins (e.g., resol-type cresol-modified phenolic resins and resol-type bisphenol-modified phenolic resins) obtained by condensing or co-condensing phenols and / or naphthols with a compound having an aldehyde group under an alkaline acidic catalyst. (iii) aralkyl-type phenolic resins synthesized from phenols and / or naphthols and dimethoxyparaxylene or bis(methoxymethyl)biphenyl (e.g., phenol-aralkyl resins, naphthol-aralkyl resins, and biphenyl-type phenol-aralkyl resins), biphenyl-modified phenolic resins, melamine-modified phenolic resins, and guanamine-modified phenolic resins; and (iv) thermosetting resins having a benzoxazine ring synthesized from phenols, aldehydes, and aromatic amines. Examples of phenols include phenol, cresol, resorcinol, catechol, bisphenol A, bisphenol F, phenylphenol, and aminophenol. Examples of naphthols include α-naphthol, β-naphthol, and dihydroxynaphthalene. Examples of compounds having an aldehyde group include formaldehyde. These phenolic resins may be used alone or in combination of two or more. Among these phenolic resins, novolac type phenolic resins are preferred from the viewpoints of production stability and cost.

[0148] The softening point of the phenolic resin is preferably 80 to 120°C, more preferably 90 to 110°C.

[0149] The resin preferably contains 50% by weight or more of a phenolic resin, more preferably 60% by weight or more, even more preferably 70% by weight or more, still more preferably 80% by weight or more, even more preferably 90% by weight or more, and particularly preferably 95% by weight or more, based on 100% by weight of the resin.

[0150] (5-2. Ratio of Content of Noise Reducing Agent to Resin) In the present composition, when the total of the noise reducing agent and the resin is taken as 100% by weight, the ratio (content ratio) of the content of the noise reducing agent to the resin is usually preferably 0.5% by weight to 50.0% by weight and 50.0% by weight to 99.5% by weight of the resin, more preferably 1.0% by weight to 40.0% by weight and 60.0% by weight to 99.0% by weight of the resin, still more preferably 1.0% by weight to 25.0% by weight and 75.0% by weight to 99.0% by weight of the resin, and particularly preferably 2.5% by weight to 20.0% by weight and 80.0% by weight to 97.5% by weight of the noise reducing agent.

[0151] The content ratio of the noise reducing agent to the resin can be appropriately set depending on (a) the content and water content of components other than the polymer microparticles (A) contained in the noise reducing agent, and (b) the method of mixing the noise reducing agent and the resin, so as to achieve a desired content ratio of the polymer microparticles (A) to the resin in the resulting composition.

[0152] In the present composition, the ratio (content ratio) of the polymer microparticles (A) to the resin, when the total of the polymer microparticles (A) and the resin is taken as 100% by weight, is usually preferably 0.5% by weight to 50.0% by weight of the polymer microparticles (A) and 50.0% by weight to 99.5% by weight of the resin, more preferably 1.0% by weight to 40.0% by weight of the polymer microparticles (A) and 60.0% by weight to 99.0% by weight of the resin, still more preferably 1.0% by weight to 25.0% by weight of the polymer microparticles (A) and 75.0% by weight to 99.0% by weight of the resin, and particularly preferably 2.5% by weight to 20.0% by weight of the polymer microparticles (A) and 80.0% by weight to 97.5% by weight of the resin.

[0153] (5-3. Other Optional Components) The present composition may contain other optional components in addition to the components described above, as necessary. Examples of other optional components include reinforcing materials (steel, wool, aramid fiber, acrylic fiber, ceramic wool, copper, brass fiber, asbestos, etc.), friction modifiers (rubber (NBR, SBR, etc.), cashew-based dust, metal powder (copper, brass, etc.), abrasives, inorganic fillers (barium sulfate, mica, etc.)), lubricants (graphite, antimony sulfide, tin sulfide, composite metal sulfides, molybdenum disulfide, etc.), curing agents, coloring agents such as pigments and dyes, etc. Examples of the other optional components include body pigments, pigment dispersants, ultraviolet absorbers, the above-mentioned antioxidants, heat stabilizers (antigelling agents), plasticizers, leveling agents, antifoaming agents, silane coupling agents, antistatic agents, flame retardants, viscosity reducers, viscosity modifiers, thixotropy-imparting agents, low-shrinkage agents, organic fillers, thermoplastic resins, drying agents, dispersants, thermal conductivity improvers, water binding agents, anti-sagging agents, color separation inhibitors, anti-settling agents, coating wear adjusters, surface conditioners, monobasic organic acids, camphor, castor oil, etc. One type of the other optional components may be used alone, or two or more types may be used in combination.

[0154] (5-4. Method for producing a friction material resin composition) A method for producing a friction material resin composition according to one embodiment of the present invention is a method for producing a friction material resin composition, which includes a step of mixing a noise reducing agent containing polymer fine particles (A) with, optionally, a resin and other optional components. The noise reducing agent containing the polymer fine particles (A) can be produced by the production method described above in the section (2-1-5. Method for producing polymer fine particles (A)).

[0155] The method for producing the present composition is not particularly limited as long as it includes a step of mixing a noise reducing agent containing polymer fine particles (A) with, optionally, a resin and other optional components. Examples of the method for producing the present composition include a method in which the noise reducing agent and the thermosetting resin are mixed, and then the other optional components described above are added to the resulting mixture as needed, and the mixture is mixed using a mixer or the like. The order in which the noise reducing agent, the thermosetting resin, and the other optional components are added is not limited to the order described above, and any order may be used.

[0156] The method for producing a friction material resin composition according to one embodiment of the present invention is more preferably a method for producing a friction material resin composition comprising a step of mixing a noise reducing agent containing polymer fine particles (A) with a phenolic resin. Even in the production method comprising a step of mixing a noise reducing agent containing polymer fine particles (A) with a phenolic resin, the order in which the noise reducing agent, the phenolic resin, and other optional components are added may be any order. Examples of the above-mentioned mixing method include a method in which the noise reducing agent and the phenolic resin are mixed, and then the other optional components are added as needed, and the mixture is mixed using a mixer or the like.

[0157] The temperature at which the noise reducing agent and the resin are mixed is generally set to a temperature at which the resin can flow.

[0158] [6. Friction Material] The friction material according to one embodiment of the present invention contains the noise-reducing agent or composition described above. Because the friction material according to one embodiment of the present invention contains the composition having the above-described configuration, it has the advantage of being able to reduce noise.

[0159] The present friction material is not particularly limited, but examples thereof include brake pads and clutches.

[0160] The present friction material can be produced using the noise reducing agent or composition. The method for producing the present friction material is not particularly limited, and known methods can be used.

[0161] One embodiment of the present invention includes the inventions described in the following [1] to

[13] . [1] A noise reducing agent comprising polymer fine particles (A), wherein the polymer fine particles (A) comprise a core portion and a graft portion graft-bonded to the core portion, and wherein the polymer fine particles (A) have a tan δ peak top in a temperature range of 10°C or higher, and the maximum value of the tan δ peak height in a temperature range of 10°C or higher is 0.70 or higher. [2] The noise reducing agent according to [1], wherein the core portion comprises one or more rubbers selected from the group consisting of diene rubbers, (meth)acrylate rubbers, and organosiloxane rubbers. [3] The noise reducing agent according to [1] or [2], wherein the core portion is one or more rubbers selected from the group consisting of butadiene rubbers, butadiene-styrene rubbers, and butyl acrylate rubbers. [4] The noise reducing agent according to any one of [1] to [3], wherein the graft portion comprises one or more structural units selected from the group consisting of aromatic vinyl units, vinylcyan units, and (meth)acrylate units. [5] The noise reducing agent according to any one of [1] to [4], wherein the proportion of the graft moiety in the polymer fine particles (A) is 20% by weight to 90% by weight, based on 100% by weight of the polymer fine particles (A). [6] The noise reducing agent according to any one of [1] to [5], wherein the proportion of unsubstituted vinyl aromatic units and / or vinyl-substituted aromatic units in the graft moiety is more than 70% by weight and 100% by weight or less, based on 100% by weight of the graft moiety. [7] The noise reducing agent according to any one of [1] to [6], wherein the volume average particle diameter of the polymer fine particles (A) is 0.10 μm to 10.00 μm. [8] A noise reducing agent comprising polymer fine particles (A), the polymer fine particles (A) comprising a core portion and a graft portion graft-bonded to the core portion, the proportion of the graft portion in the polymer fine particles (A) being 20% ​​by weight to 90% by weight based on 100% by weight of the polymer fine particles (A), and the proportion of unsubstituted vinyl aromatic units and / or vinyl-substituted aromatic units in the graft portion being more than 70% by weight and not more than 100% by weight based on 100% by weight of the graft portion. [9] The noise reducing agent according to [8], wherein the core portion comprises one or more rubbers selected from the group consisting of diene-based rubbers, (meth)acrylate-based rubbers, and organosiloxane-based rubbers.

[10] The noise reducing agent according to [8] or [9], wherein the core part is one or more selected from the group consisting of butadiene rubber, butadiene-styrene rubber, and butyl acrylate rubber.

[11] A resin composition for a friction material, comprising the noise reducing agent according to [1] or [8].

[12] The resin composition for a friction material according to

[11] , further comprising a phenolic resin.

[13] A friction material, comprising the resin composition for a friction material according to

[11] or

[12] .

[0162] The present invention will be described in more detail with reference to the following examples and comparative examples. However, the present invention is not limited to these examples, and examples obtained by appropriately combining the technical means disclosed in each example are also included in the scope of the present invention.

[0163] [Measurement and Evaluation Methods] 1. Volume Average Particle Diameter of Polymer Microparticles (A) The volume average particle diameter (Mv) of the polymer microparticles (A) dispersed in the aqueous latex was measured using a Nanotrac Wave II-EX150 (manufactured by Microtrackbell Co., Ltd.). Aqueous latex diluted with deionized water was used as the measurement sample. The measurement was performed by inputting the refractive index of water and each polymer microparticle, measuring for 120 seconds, and adjusting the sample concentration so that the loading index was within the range of 1 to 10.

[0164] 2. Tan δ Peak Temperature and Peak Height of Noise Reducing Agent The tan δ peak temperature and peak height were measured by the following method: (1) each powder (noise reducing agent) was pressed under conditions that would yield a uniform flat plate to form a 1 mm thick flat plate; (2) the obtained flat plate was subjected to dynamic viscoelasticity measurement under tensile conditions using a dynamic viscoelasticity measuring device (for example, DVA-200, manufactured by IT Measurement Control Co., Ltd.) to obtain a tan δ graph; (3) from the obtained graph, the tan δ peak temperature and peak height for each sample in the range of 0°C to 200°C were calculated.

[0165] 3. Thermal decomposition characteristics The thermal decomposition characteristics were determined by analyzing each powder (noise reducing agent) using a simultaneous differential thermal analysis - thermogravimetry (TG-DTA) (e.g., STA-700 manufactured by Hitachi High-Technologies Corporation), and the temperature at which the weight decreased by 5% was recorded.

[0166] 4. Measurement of Noise of Brake Pad and Noise-Reducing Effect of Noise-Reducing Agent Friction materials (brake pads) were produced using the resin composition for friction material obtained in the above section "4. Peak Height of Tan δ of Resin Composition for Friction Material." The noise of the obtained brake pads was measured, and the noise-reducing effect of the noise-reducing agent was evaluated on a three-point scale as follows: "2" indicates an excellent noise-reducing effect, "1" indicates a good noise-reducing effect, and "0" indicates a poor noise-reducing effect.

[0167] [Noise Reducing Agent] [Example 1: Production Method of Powder (P-1)] (Production Example 1-1: Preparation of Aqueous Latex (R-1)) 233 parts by mass of deionized water, 0.006 parts by mass of EDTA, 0.0015 parts by mass of ferrous sulfate heptahydrate, 0.2 parts by mass of SFS, and 0.15 parts by mass of SDBS were placed in a glass reactor. The glass reactor was equipped with a thermometer, a stirrer, a reflux condenser, a nitrogen inlet, and devices for adding monomers and an emulsifier. The raw materials placed in the glass reactor were stirred at 60°C while the gas in the glass reactor was replaced with nitrogen (i.e., in a nitrogen stream). Next, a mixture of 79 parts by mass of butyl acrylate (BA), 2 parts by mass of allyl methacrylate (ALMA), and 0.021 parts by mass of cumene hydroperoxide (CHP) was continuously added dropwise to the glass reactor over a period of 175 minutes. After the addition was completed, the mixture in the glass reactor was stirred for an additional 0.5 hours to complete the polymerization. Through the above operations, core portions were formed, and an aqueous latex (R-1) containing core portions was obtained. Since the amount of allyl methacrylate used in the obtained core portions was small and its effect on the glass transition temperature of the core portions was minimal, it could be ignored in determining the glass transition temperature. Therefore, the glass transition temperature of the core portions of the aqueous latex (R-1) can be considered to be −54°C, the same as the glass transition temperature of a butyl acrylate homopolymer.

[0168] (Production Example 2-1: Preparation of Aqueous Latex (L-1)) A mixture of 18.9 parts by mass of methyl methacrylate (MMA), 2.1 parts by mass of BA, and 0.05 parts by mass of CHP was continuously added over 200 minutes to a glass reactor containing the aqueous latex (R-1) obtained in Production Example 1-1. After completion of the addition, 0.04 parts by mass of CHP was added to the glass reactor, and the mixture in the glass reactor was continuously stirred for an additional hour to complete the polymerization. Through the above operations, graft moieties graft-bonded to the crosslinked core moieties were formed, and an aqueous latex (L-1) containing polymer fine particles (A) was obtained. The polymerization conversion rate of the monomer components was 99% or more. The volume average particle diameter of the polymer fine particles (A) contained in the obtained aqueous latex (L-1) was 0.25 μm.

[0169] (Production Example 3-1: Production of powdery material (P-1)) 333 parts by weight of the obtained aqueous latex (L-1) and 2 parts by weight of Irganox 1135 were mixed. The obtained mixture was poured into 600 parts by weight of ion-exchanged water in which 4 parts by weight of calcium chloride had been dissolved and the temperature had been adjusted to 70°C, to aggregate the polymer fine particles (A). The obtained mixture was then filtered to obtain a wet powder. Furthermore, the obtained wet powder was subjected to a total of two cycles of an operation of pouring the wet powder into 500 parts by weight of ion-exchanged water and an operation of filtering the wet powder poured into the ion-exchanged water, and finally dried in a dryer at 50°C for 48 hours to obtain powdery material (P-1) (noise reducing agent).

[0170] Example 2: Method for Producing Powder (P-2) (Production Example 1-2: Preparation of Aqueous Latex (R-2)) 200 parts by mass of deionized water, 0.03 parts by mass of tripotassium phosphate, 0.002 parts by mass of disodium ethylenediaminetetraacetate (EDTA), 0.001 parts by mass of ferrous sulfate heptahydrate, and 1.55 parts by mass of sodium dodecylbenzenesulfonate (SDBS) as an emulsifier were charged into a pressure-resistant polymerization vessel. Next, while stirring the charged raw materials, the gas inside the pressure-resistant polymerization vessel was replaced with nitrogen, thereby thoroughly removing oxygen from inside the pressure-resistant polymerization vessel. Thereafter, 100 parts by mass of butadiene (Bd) was charged into the pressure-resistant polymerization vessel, and the temperature inside the pressure-resistant polymerization vessel was raised to 45°C. Thereafter, 0.03 parts by mass of paramenthane hydroperoxide (PHP) was charged into the pressure-resistant polymerization reactor, followed by 0.1 parts by mass of sodium formaldehyde sulfoxylate (SFS) to initiate polymerization. Fifteen hours after the start of polymerization, volatilization was performed under reduced pressure to remove remaining monomers not used in the polymerization, thereby completing the polymerization. During the polymerization, PHP, EDTA, and ferrous sulfate heptahydrate were each added to the pressure-resistant polymerization reactor in desired amounts and at desired times. Through the above operations, a core portion was formed, yielding a polybutadiene rubber latex (R-2) primarily composed of polybutadiene rubber. The volume average particle diameter of the polybutadiene rubber contained in the resulting polybutadiene rubber latex (R-2) was 0.08 μm. The glass transition temperature of the core portion of the polybutadiene rubber latex (R-2) is −80° C., which is the same as the glass transition temperature of the butadiene homopolymer.

[0171] (Production Example 2-2: Preparation of Aqueous Latex (L-2)) 132 parts by mass of the polybutadiene rubber latex (R-2) obtained in Production Example 1-2 (containing 44 parts by mass of polybutadiene rubber particles) and 145 parts by mass of deionized water were charged into a glass reactor. The glass reactor was equipped with a thermometer, a stirrer, a reflux condenser, a nitrogen inlet, and a monomer addition device. While the gas in the glass reactor was replaced with nitrogen, the charged raw materials were stirred at 60°C. Next, 0.004 parts by mass of EDTA, 0.001 parts by mass of ferrous sulfate heptahydrate, and 0.2 parts by mass of SFS were added to the glass reactor. Then, a mixture of 56 parts by mass of styrene (St) and 0.04 parts by mass of CHP was continuously added to the glass reactor over 85 minutes. After the addition was completed, 0.065 parts by mass of CHP was added to the glass reactor, and the mixture in the glass reactor was further stirred for 1 hour to complete the polymerization. By the above operations, graft moieties grafted to the crosslinked core moieties were formed, and an aqueous latex (L-2) containing polymer fine particles (A) was obtained. The polymerization conversion rate of the monomer components was 99% or more. The volume average particle diameter of the polymer fine particles (A) contained in the obtained aqueous latex (L-2) was 0.10 μm.

[0172] (Production Example 3-2: Production of powder / granule (P-2)) 333 parts by weight of the obtained aqueous latex (L-2) and 2 parts by weight of Irganox 1135 were mixed. The obtained mixture was poured into 600 parts by weight of ion-exchanged water in which 4 parts by weight of calcium chloride had been dissolved and the temperature had been adjusted to 70°C, to aggregate the polymer fine particles (A). The obtained mixture was then filtered to obtain a wet powder. Furthermore, the obtained wet powder was subjected to a total of two cycles of an operation of pouring the wet powder into 500 parts by weight of ion-exchanged water and an operation of filtering the wet powder poured into the ion-exchanged water, and finally dried in a dryer at 50°C for 48 hours to obtain powder / granule (P-2) (noise reducing agent).

[0173] Example 3: Method for producing powder (P-3) (Production Example 1-3: Preparation of polybutadiene rubber latex (R-3)) 21 parts by mass of the polybutadiene rubber latex (R-2) obtained in Production Example 1-2 (containing 7 parts by mass of polybutadiene rubber), 185 parts by mass of deionized water, 0.03 parts by mass of tripotassium phosphate, 0.002 parts by mass of EDTA, and 0.001 parts by mass of ferrous sulfate heptahydrate were charged into a pressure-resistant polymerization vessel. Next, while stirring the charged raw materials, the gas inside the pressure-resistant polymerization vessel was replaced with nitrogen, thereby thoroughly removing oxygen from inside the pressure-resistant polymerization vessel. Thereafter, 93 parts by mass of Bd were charged into the pressure-resistant polymerization vessel, and the temperature inside the pressure-resistant polymerization vessel was raised to 45°C. Thereafter, 0.02 parts by mass of PHP was charged into the pressure-resistant polymerization vessel, followed by 0.1 parts by mass of SFS, to initiate polymerization. Thirty hours after the start of polymerization, devolatilization was carried out under reduced pressure to remove the remaining monomers not used in the polymerization, thereby completing the polymerization. During the polymerization, PHP, EDTA, ferrous sulfate heptahydrate, and SDBS were each added to the pressure-resistant polymerization reactor in desired amounts and at desired times. By the above operations, a core portion was formed, and a polybutadiene rubber latex (R-3) containing a core portion composed mainly of polybutadiene rubber was obtained. The volume average particle diameter of the core portion contained in the obtained polybutadiene rubber latex (R-3) was 0.19 μm. The glass transition temperature of the core portion in this aqueous latex was −80° C.

[0174] (Production Example 2-3: Preparation of Aqueous Latex (L-3)) 132 parts by mass of the polybutadiene rubber latex (R-3) obtained in Production Example 1-3 (containing 44 parts by mass of polybutadiene rubber particles) and 145 parts by mass of deionized water were charged into a glass reactor. The glass reactor was equipped with a thermometer, a stirrer, a reflux condenser, a nitrogen inlet, and a monomer addition device. While the gas in the glass reactor was replaced with nitrogen, the charged raw materials were stirred at 60°C. Next, 0.004 parts by mass of EDTA, 0.001 parts by mass of ferrous sulfate heptahydrate, and 0.2 parts by mass of SFS were added to the glass reactor. Thereafter, a mixture of 56 parts by mass of styrene (St) and 0.04 parts by mass of CHP was continuously added to the glass reactor over 85 minutes. After the addition was completed, 0.065 parts by mass of CHP was added to the glass reactor, and the mixture in the glass reactor was further stirred for 1 hour to complete the polymerization. By the above operations, graft moieties grafted to the crosslinked core moieties were formed, and an aqueous latex (L-3) containing polymer fine particles (A) was obtained. The polymerization conversion rate of the monomer components was 99% or more. The volume average particle diameter of the polymer fine particles (A) contained in the obtained aqueous latex (L-3) was 0.20 μm.

[0175] (Production Example 3-3: Production of powder / granule (P-3)) ​​333 parts by weight of the obtained aqueous latex (L-3) and 2 parts by weight of Irganox 1135 were mixed. The obtained mixture was poured into 600 parts by weight of ion-exchanged water in which 4 parts by weight of calcium chloride had been dissolved and the temperature had been adjusted to 70°C, to aggregate the polymer fine particles (A). Thereafter, the obtained mixture was filtered to obtain a wet powder. Furthermore, the obtained wet powder was subjected to a total of two cycles of an operation of pouring the wet powder into 500 parts by weight of ion-exchanged water and an operation of filtering the wet powder poured into the ion-exchanged water, and finally dried in a dryer at 50°C for 48 hours to obtain powder / granule (P-3) (noise reducing agent).

[0176] Example 4: Method for Producing Powder (P-4) (Production Example 2-4: Preparation of Aqueous Latex (L-4)) 90 parts by mass of the polybutadiene rubber latex (R-3) obtained in Production Example 1-3 (containing 30 parts by mass of polybutadiene rubber particles) and 173 parts by mass of deionized water were charged into a glass reactor. The glass reactor was equipped with a thermometer, a stirrer, a reflux condenser, a nitrogen inlet, and a monomer addition device. While the gas in the glass reactor was replaced with nitrogen, the charged raw materials were stirred at 60°C. Next, 0.004 parts by mass of EDTA, 0.001 parts by mass of ferrous sulfate heptahydrate, and 0.2 parts by mass of SFS were added to the glass reactor. Thereafter, a mixture of 70 parts by mass of styrene (St) and 0.04 parts by mass of CHP was continuously added to the glass reactor over 85 minutes. After the addition was completed, 0.065 parts by mass of CHP was added to the glass reactor, and the mixture in the glass reactor was further stirred for 1 hour to complete the polymerization. By the above operations, graft moieties grafted to the crosslinked core moieties were formed, and an aqueous latex (L-4) containing polymer fine particles (A) was obtained. The polymerization conversion rate of the monomer components was 99% or more. The volume average particle diameter of the polymer fine particles (A) contained in the obtained aqueous latex (L-4) was 0.20 μm.

[0177] (Production Example 3-4: Production of powder / granule (P-4)) 333 parts by weight of the obtained aqueous latex (L-4) and 2 parts by weight of Irganox 1135 were mixed. The obtained mixture was poured into 600 parts by weight of ion-exchanged water in which 4 parts by weight of calcium chloride had been dissolved and the temperature had been adjusted to 70°C, to aggregate the polymer fine particles (A). Thereafter, the obtained mixture was filtered to obtain a wet powder. Furthermore, the obtained wet powder was subjected to a total of two cycles of an operation of pouring the wet powder into 500 parts by weight of ion-exchanged water and an operation of filtering the wet powder poured into the ion-exchanged water, and finally dried in a dryer at 50°C for 48 hours to obtain powder / granule (P-4) (noise reducing agent).

[0178] Example 5: Method for Producing Powder (P-5) (Production Example 2-5: Preparation of Aqueous Latex (L-5)) 60 parts by mass of the polybutadiene rubber latex (R-3) obtained in Production Example 1-3 (containing 20 parts by mass of polybutadiene rubber particles) and 193 parts by mass of deionized water were charged into a glass reactor. The glass reactor was equipped with a thermometer, a stirrer, a reflux condenser, a nitrogen inlet, and a monomer addition device. The charged raw materials were stirred at 60°C while the gas in the glass reactor was replaced with nitrogen. Next, 0.004 parts by mass of EDTA, 0.001 parts by mass of ferrous sulfate heptahydrate, and 0.2 parts by mass of SFS were added to the glass reactor. Thereafter, a mixture of 80 parts by mass of styrene (St) and 0.04 parts by mass of CHP was continuously added to the glass reactor over 85 minutes. After the addition was completed, 0.065 parts by mass of CHP was added to the glass reactor, and the mixture in the glass reactor was further stirred for 1 hour to complete the polymerization. By the above operations, graft moieties grafted to the crosslinked core moieties were formed, and an aqueous latex (L-5) containing polymer fine particles (A) was obtained. The polymerization conversion rate of the monomer components was 99% or more. The volume average particle diameter of the polymer fine particles (A) contained in the obtained aqueous latex (L-5) was 0.20 μm.

[0179] (Production Example 3-5: Production of powder (P-5)) 333 parts by weight of the obtained aqueous latex (L-5) and 2 parts by weight of Irganox 1135 were mixed. The obtained mixture was poured into 600 parts by weight of ion-exchanged water in which 4 parts by weight of calcium chloride had been dissolved and the temperature had been adjusted to 70°C, to aggregate the polymer fine particles (A). The obtained mixture was then filtered to obtain a wet powder. Furthermore, the obtained wet powder was subjected to a total of two cycles of pouring the wet powder into 500 parts by weight of ion-exchanged water and filtering the wet powder poured into the ion-exchanged water, and finally dried in a dryer at 50°C for 48 hours to obtain powder (P-5) (noise reducer).

[0180] Example 6: Method for Producing Powder (P-6) (Production Example 2-6: Preparation of Aqueous Latex (L-6)) 132 parts by mass of the polybutadiene rubber latex (R-3) obtained in Production Example 1-3 (containing 44 parts by mass of polybutadiene rubber particles) and 145 parts by mass of deionized water were charged into a glass reactor. The glass reactor was equipped with a thermometer, a stirrer, a reflux condenser, a nitrogen inlet, and a monomer addition device. The charged raw materials were stirred at 60°C while the gas in the glass reactor was replaced with nitrogen. Next, 0.004 parts by mass of EDTA, 0.001 parts by mass of ferrous sulfate heptahydrate, and 0.2 parts by mass of SFS were added to the glass reactor. Thereafter, a mixture of 53.2 parts by mass of styrene (St), 2.8 parts by mass of butyl acrylate, and 0.04 parts by mass of CHP was continuously added to the glass reactor over 85 minutes. After completion of the addition, 0.065 parts by mass of CHP was added to the glass reactor, and the mixture in the glass reactor was further stirred for 1 hour to complete the polymerization. Through the above operations, graft moieties graft-bonded to the crosslinked core moieties were formed, and an aqueous latex (L-6) containing polymer fine particles (A) was obtained. The polymerization conversion rate of the monomer components was 99% or more. The volume average particle diameter of the polymer fine particles (A) contained in the obtained aqueous latex (L-6) was 0.20 μm.

[0181] (Production Example 3-6: Production of powder / granule (P-6)) 333 parts by weight of the obtained aqueous latex (L-6) and 2 parts by weight of Irganox 1135 were mixed. The obtained mixture was poured into 600 parts by weight of ion-exchanged water in which 4 parts by weight of calcium chloride had been dissolved and the temperature had been adjusted to 70°C, to aggregate the polymer fine particles (A). Thereafter, the obtained mixture was filtered to obtain a wet powder. Furthermore, the obtained wet powder was subjected to a total of two cycles of an operation of pouring the wet powder into 500 parts by weight of ion-exchanged water and an operation of filtering the wet powder poured into the ion-exchanged water, and finally dried in a dryer at 50°C for 48 hours to obtain powder / granule (P-6) (noise reducing agent).

[0182] [Example 7: Method for Producing Powder (P-7)] (Production Example 2-7: Preparation of Aqueous Latex (L-7)) 90 parts by mass of the polybutadiene rubber latex (R-3) obtained in Production Example 1-3 (containing 30 parts by mass of polybutadiene rubber particles) and 173 parts by mass of deionized water were charged into a glass reactor. The glass reactor was equipped with a thermometer, a stirrer, a reflux condenser, a nitrogen inlet, and a monomer addition device. The charged raw materials were stirred at 60°C while the gas in the glass reactor was replaced with nitrogen. Next, 0.004 parts by mass of EDTA, 0.001 parts by mass of ferrous sulfate heptahydrate, and 0.2 parts by mass of SFS were added to the glass reactor. Thereafter, a mixture of 32.5 parts by mass of styrene (St), 32.5 parts by mass of BA, and 0.04 parts by mass of CHP was continuously added to the glass reactor over 85 minutes. After the addition was completed, 0.065 parts by mass of CHP was added to the glass reactor, and the mixture in the glass reactor was continued to be stirred for an additional hour to complete the polymerization. Thereafter, a mixture of 5 parts by mass of styrene (St) and 0.01 parts by mass of CHP was continuously added to the glass reactor over 15 minutes. After the addition was completed, 0.065 parts by mass of CHP was added to the glass reactor, and the mixture in the glass reactor was continued to be stirred for an additional hour to complete the polymerization. By the above operations, a graft moiety graft-bonded to the crosslinked core moiety was formed, and an aqueous latex (L-7) containing polymer fine particles (A) was obtained. The polymerization conversion rate of the monomer component was 99% or more. The volume average particle diameter of the polymer fine particles (A) contained in the obtained aqueous latex (L-7) was 0.20 μm.

[0183] (Production Example 3-7: Production of powder (P-7)) 333 parts by weight of the obtained aqueous latex (L-7) and 2 parts by weight of Irganox 1135 were mixed. The obtained mixture was poured into 600 parts by weight of ion-exchanged water in which 4 parts by weight of calcium chloride had been dissolved and the temperature had been adjusted to 70°C, to aggregate the polymer fine particles (A). Thereafter, the obtained mixture was filtered to obtain a wet powder. Furthermore, the obtained wet powder was subjected to a total of two cycles of an operation of pouring the wet powder into 500 parts by weight of ion-exchanged water and an operation of filtering the wet powder poured into the ion-exchanged water, and finally dried in a dryer at 50°C for 48 hours to obtain powder (P-7) (noise reducer).

[0184] Example 8: Method for Producing Powder (P-8) (Production Example 2-8: Preparation of Aqueous Latex (L-8)) 90 parts by mass of the polybutadiene rubber latex (R-3) obtained in Production Example 1-3 (containing 30 parts by mass of polybutadiene rubber particles) and 173 parts by mass of deionized water were charged into a glass reactor. The glass reactor was equipped with a thermometer, a stirrer, a reflux condenser, a nitrogen inlet, and a monomer addition device. The charged raw materials were stirred at 60°C while the gas in the glass reactor was replaced with nitrogen. Next, 0.004 parts by mass of EDTA, 0.001 parts by mass of ferrous sulfate heptahydrate, and 0.2 parts by mass of SFS were added to the glass reactor. Thereafter, a mixture of 26 parts by mass of styrene (St), 39 parts by mass of BA, and 0.04 parts by mass of CHP was continuously added to the glass reactor over 85 minutes. After the addition was completed, 0.065 parts by mass of CHP was added to the glass reactor, and the mixture in the glass reactor was continued to be stirred for an additional hour to complete the polymerization. Thereafter, a mixture of 5 parts by mass of styrene (St) and 0.01 parts by mass of CHP was continuously added to the glass reactor over 15 minutes. After the addition was completed, 0.065 parts by mass of CHP was added to the glass reactor, and the mixture in the glass reactor was continued to be stirred for an additional hour to complete the polymerization. By the above operations, a graft moiety graft-bonded to the crosslinked core moiety was formed, and an aqueous latex (L-8) containing polymer microparticles (A) was obtained. The polymerization conversion rate of the monomer component was 99% or more. The volume average particle diameter of the polymer microparticles (A) contained in the obtained aqueous latex (L-8) was 0.20 μm.

[0185] (Production Example 3-8: Production of powder (P-8)) 333 parts by weight of the obtained aqueous latex (L-8) and 2 parts by weight of Irganox 1135 were mixed. The obtained mixture was poured into 600 parts by weight of ion-exchanged water in which 4 parts by weight of calcium chloride had been dissolved and the temperature had been adjusted to 70°C, to aggregate the polymer fine particles (A). Thereafter, the obtained mixture was filtered to obtain a wet powder. Furthermore, the obtained wet powder was subjected to a total of two cycles of an operation of pouring the wet powder into 500 parts by weight of ion-exchanged water and an operation of filtering the wet powder poured into the ion-exchanged water, and finally dried in a dryer at 50°C for 48 hours to obtain powder (P-8) (noise reducing agent).

[0186] Example 9: Method for Producing Powder (P-9) (Production Example 2-9: Preparation of Aqueous Latex (L-9)) 90 parts by mass of the polybutadiene rubber latex (R-3) obtained in Production Example 1-3 (containing 30 parts by mass of polybutadiene rubber particles) and 173 parts by mass of deionized water were charged into a glass reactor. The glass reactor was equipped with a thermometer, a stirrer, a reflux condenser, a nitrogen inlet, and a monomer addition device. The charged raw materials were stirred at 60°C while the gas in the glass reactor was replaced with nitrogen. Next, 0.004 parts by mass of EDTA, 0.001 parts by mass of ferrous sulfate heptahydrate, and 0.2 parts by mass of SFS were added to the glass reactor. Thereafter, a mixture of 29.5 parts by mass of styrene (St), 30.5 parts by mass of BA, and 0.04 parts by mass of CHP was continuously added to the glass reactor over 85 minutes. After the addition was completed, 0.065 parts by mass of CHP was added to the glass reactor, and the mixture in the glass reactor was continued to be stirred for an additional hour to complete the polymerization. Thereafter, a mixture of 10 parts by mass of styrene (St) and 0.01 parts by mass of CHP was continuously added to the glass reactor over 15 minutes. After the addition was completed, 0.065 parts by mass of CHP was added to the glass reactor, and the mixture in the glass reactor was continued to be stirred for an additional hour to complete the polymerization. By the above operations, a graft moiety graft-bonded to the crosslinked core moiety was formed, and an aqueous latex (L-9) containing polymer microparticles (A) was obtained. The polymerization conversion rate of the monomer component was 99% or more. The volume average particle diameter of the polymer microparticles (A) contained in the obtained aqueous latex (L-9) was 0.20 μm.

[0187] (Production Example 3-9: Production of powder (P-9)) 333 parts by weight of the obtained aqueous latex (L-9) and 2 parts by weight of Irganox 1135 were mixed. The obtained mixture was poured into 600 parts by weight of ion-exchanged water in which 4 parts by weight of calcium chloride had been dissolved and the temperature had been adjusted to 70°C, to aggregate the polymer fine particles (A). Thereafter, the obtained mixture was filtered to obtain a wet powder. Furthermore, the obtained wet powder was subjected to a total of two cycles of an operation of pouring the wet powder into 500 parts by weight of ion-exchanged water and an operation of filtering the wet powder poured into the ion-exchanged water, and finally dried in a dryer at 50°C for 48 hours to obtain powder (P-9) (noise reducer).

[0188] Example 10: Method for Producing Powder (P-10) (Production Example 2-10: Preparation of Aqueous Latex (L-10)) 90 parts by mass of the polybutadiene rubber latex (R-3) obtained in Production Example 1-3 (containing 30 parts by mass of polybutadiene rubber particles) and 173 parts by mass of deionized water were charged into a glass reactor. The glass reactor was equipped with a thermometer, a stirrer, a reflux condenser, a nitrogen inlet, and a monomer addition device. The charged raw materials were stirred at 60°C while the gas in the glass reactor was replaced with nitrogen. Next, 0.004 parts by mass of EDTA, 0.001 parts by mass of ferrous sulfate heptahydrate, and 0.2 parts by mass of SFS were added to the glass reactor. Thereafter, a mixture of 36 parts by mass of styrene (St), 24 parts by mass of BA, and 0.04 parts by mass of CHP was continuously added to the glass reactor over 85 minutes. After the addition was completed, 0.065 parts by mass of CHP was added to the glass reactor, and the mixture in the glass reactor was continued to be stirred for an additional hour to complete the polymerization. Thereafter, a mixture of 10 parts by mass of styrene (St) and 0.01 parts by mass of CHP was continuously added to the glass reactor over 15 minutes. After the addition was completed, 0.065 parts by mass of CHP was added to the glass reactor, and the mixture in the glass reactor was continued to be stirred for an additional hour to complete the polymerization. Through the above operations, a graft moiety grafted to the crosslinked core moiety was formed, and an aqueous latex (L-10) containing polymer microparticles (A) was obtained. The polymerization conversion rate of the monomer components was 99% or more. The volume average particle diameter of the polymer microparticles (A) contained in the obtained aqueous latex (L-10) was 0.20 μm.

[0189] (Production Example 3-10: Production of powder (P-10)) 333 parts by weight of the obtained aqueous latex (L-10) and 2 parts by weight of Irganox 1135 were mixed. The obtained mixture was poured into 600 parts by weight of ion-exchanged water in which 4 parts by weight of calcium chloride had been dissolved and the temperature had been adjusted to 70°C, to aggregate the polymer fine particles (A). Thereafter, the obtained mixture was filtered to obtain a wet powder. Furthermore, the obtained wet powder was subjected to a total of two cycles of an operation of pouring the wet powder into 500 parts by weight of ion-exchanged water and an operation of filtering the wet powder poured into the ion-exchanged water, and finally dried in a dryer at 50°C for 48 hours to obtain powder (P-10) (noise reducing agent).

[0190] Example 11: Method for Producing Powder (P-11) (Production Example 2-11: Preparation of Aqueous Latex (L-11)) 90 parts by mass of the polybutadiene rubber latex (R-3) obtained in Production Example 1-3 (containing 30 parts by mass of polybutadiene rubber particles) and 173 parts by mass of deionized water were charged into a glass reactor. The glass reactor was equipped with a thermometer, a stirrer, a reflux condenser, a nitrogen inlet, and a monomer addition device. The charged raw materials were stirred at 60°C while the gas in the glass reactor was replaced with nitrogen. Next, 0.004 parts by mass of EDTA, 0.001 parts by mass of ferrous sulfate heptahydrate, and 0.2 parts by mass of SFS were added to the glass reactor. Thereafter, a mixture of 45 parts by mass of styrene (St), 15 parts by mass of BA, and 0.04 parts by mass of CHP was continuously added to the glass reactor over 85 minutes. After the addition was completed, 0.065 parts by mass of CHP was added to the glass reactor, and the mixture in the glass reactor was continued to be stirred for an additional hour to complete the polymerization. Thereafter, a mixture of 10 parts by mass of styrene (St) and 0.01 parts by mass of CHP was continuously added to the glass reactor over 15 minutes. After the addition was completed, 0.065 parts by mass of CHP was added to the glass reactor, and the mixture in the glass reactor was continued to be stirred for an additional hour to complete the polymerization. By the above operations, a graft moiety graft-bonded to the crosslinked core moiety was formed, and an aqueous latex (L-11) containing polymer microparticles (A) was obtained. The polymerization conversion rate of the monomer components was 99% or more. The volume average particle diameter of the polymer microparticles (A) contained in the obtained aqueous latex (L-11) was 0.20 μm.

[0191] (Production Example 3-11: Production of powder (P-11)) 333 parts by weight of the obtained aqueous latex (L-11) and 2 parts by weight of Irganox 1135 were mixed. The obtained mixture was poured into 600 parts by weight of ion-exchanged water in which 4 parts by weight of calcium chloride had been dissolved and the temperature had been adjusted to 70°C, to aggregate the polymer fine particles (A). Thereafter, the obtained mixture was filtered to obtain a wet powder. Furthermore, the obtained wet powder was subjected to a total of two cycles of an operation of pouring the wet powder into 500 parts by weight of ion-exchanged water and an operation of filtering the wet powder poured into the ion-exchanged water, and finally dried in a dryer at 50°C for 48 hours to obtain powder (P-11) (noise reducer).

[0192] For the noise reducing agents and friction material resin compositions containing the noise reducing agents obtained in each Example and Comparative Example, the volume average particle diameter of the polymer fine particles (A), the amount of the core and shell portions, the tan δ peak temperature and peak height of the polymer fine particles (A), thermal decomposition characteristics, and the tan δ peak height of the friction material resin composition were measured using the methods described above. The results are shown in Table 1. Note that Nippol 1411 (NBR) manufactured by Nippon Zeon Co., Ltd. was used as Comparative Example 1.

[0193] Furthermore, brake pads were manufactured using the above method and the noise reduction effect was evaluated. The results are shown in Table 1.

[0194]

[0195] An embodiment of the present invention can provide a noise reducing agent for a resin composition for a friction material, which can reduce noise. Therefore, the noise reducing agent according to an embodiment of the present invention can be particularly suitably used as a material for friction materials, adhesives, molded composites, laminates, etc.

Claims

1. A noise reducer comprising polymer fine particles (A), wherein the polymer fine particles (A) include a core part and a graft part graft-bonded to the core part, have a peak top of tanδ in a temperature range of 10°C or higher, and the maximum value of the peak height of tanδ in a temperature range of 10°C or higher is 0.70 or higher.

2. The noise reducer according to claim 1, wherein the core part includes one or more selected from the group consisting of diene rubbers, (meth)acrylate rubbers, and organosiloxane rubbers.

3. The noise reducer according to claim 1, wherein the core part is one or more selected from the group consisting of butadiene rubber, butadiene-styrene rubber, and butyl acrylate rubber.

4. The noise reducer according to claim 1, wherein the graft part includes one or more constitutional units selected from the group consisting of aromatic vinyl units, vinyl cyanide units, and (meth)acrylate units.

5. The noise reducer according to claim 1, wherein the proportion of the graft part in the polymer fine particles (A) is 20% by weight to 90% by weight in 100% by weight of the polymer fine particles (A).

6. The noise reducer according to claim 1, wherein the graft part includes one or more constitutional units selected from the group consisting of unsubstituted vinyl aromatic units and vinyl-substituted aromatic units, and the total amount of the unsubstituted vinyl aromatic units and vinyl-substituted aromatic units in the graft part is more than 70% by weight and 100% by weight or less in 100% by weight of the graft part.

7. The noise reducer according to claim 1, wherein the volume average particle diameter of the polymer fine particles (A) is 0.10 µm to 10.00 µm.

8. A noise reducer comprising polymer fine particles (A), wherein the polymer fine particles (A) include a core part and a graft part graft-bonded to the core part, the proportion of the graft part in the polymer fine particles (A) is 20% by weight to 90% by weight in 100% by weight of the polymer fine particles (A), the graft part includes one or more constitutional units selected from the group consisting of unsubstituted vinyl aromatic units and vinyl-substituted aromatic units, and the total amount of the unsubstituted vinyl aromatic units and vinyl-substituted aromatic units in the graft part is more than 70% by weight and 100% by weight or less in 100% by weight of the graft part.

9. The noise reducer according to claim 8, wherein the core part contains one or more selected from the group consisting of diene-based rubber, (meth)acrylate-based rubber, and organosiloxane-based rubber.

10. The noise reducer according to claim 8, wherein the core part is one or more selected from the group consisting of butadiene rubber, butadiene-styrene rubber, and butyl acrylate rubber.

11. A resin composition for a friction material, comprising the noise reducer according to claim 1 or 8.

12. The resin composition for a friction material according to claim 11, further comprising a phenolic resin.

13. A friction material, comprising the resin composition for a friction material according to claim 11.

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