Magnetorheological elastomer composition and method for producing magnetorheological elastomer composition

Abstract

The present invention addresses the problem of providing a magnetorheological elastomer composition having excellent physical toughness. The means for solving the problem is a magnetorheological elastomer composition which comprises a viscoelastic elastomer and a magnetic powder dispersed in the viscoelastic elastomer, wherein the magnetic powder is surface-treated with a surface treatment agent comprising an alkylsilane coupling agent and an aminoalkylsilane coupling agent.

Description

MAGNETORHEISTIC ELASTOMER COMPOSITION AND METHOD FOR PRODUCING MAGNETORHEISTIC ELASTOMER COMPOSITION

[0001] This patent application claims the benefit of Patent Application No. 2024-23804, filed in Japan on February 20, 2024, the contents of which are incorporated herein by reference. The present invention relates to a magnetorheological elastomer composition, and more particularly to a magnetorheological elastomer composition comprising a viscoelastic elastomer and a magnetic powder.

[0002] Magnetically responsive materials, which are made by dispersing magnetic material such as iron in a resin material such as an elastomer, are known as materials that can be used as vibration-proof / damping materials and energy-transmitting materials.

[0003] Patent Document 1 describes a polyurethane elastomer composition containing a reaction product of a polyol compound and a polyisocyanate compound, and magnetic particles, in which the polyol compound includes a propylene oxide adduct of bisphenol A, etc., and the polyisocyanate compound is a polyisocyanate compound having an aromatic ring. The magnetically responsive material in Patent Document 1 is described as a highly elastic, magnetic field-responsive soft material with a large change in elastic modulus.

[0004] Patent Document 2 describes a magnetorheological elastomer composition containing a matrix resin and magnetic powder, wherein the magnetic powder accounts for 30 to 70 volume percent of the composition taken as 100 volume percent, and the magnetorheological elastomer composition has an Asker C hardness of 5 to 60 according to the Society of Rubber Industry Standards (SRIS0101) of the Japan Rubber Industry Association. Specifically, the magnetorheological elastomer composition is a silicone rubber sheet prepared by mixing a two-component room-temperature curing silicone rubber matrix resin with permalloy and carbonyl iron powder that have been surface-treated with a silane coupling agent, followed by heating and curing. It also describes that by surface-treating the magnetic powder in this manner, it is possible to prevent curing inhibition in the case of silicone rubber.

[0005] JP 2019-210311 A JP 2017-179338 A

[0006] Magnetically responsive materials are required to be highly elastic, magnetically responsive soft materials with large changes in elastic modulus, but also to have the physical toughness to withstand high loads, considering their application in vibration isolation / damping materials, energy transmission materials, tactile feedback devices, etc.

[0007] The present invention has been made to solve the above problems, and an object of the present invention is to provide a magnetorheological elastomer composition that has excellent physical toughness.

[0008] The present invention provides a magnetorheological elastomer composition comprising a viscoelastic elastomer and a magnetic powder dispersed in the viscoelastic elastomer, wherein the magnetic powder has been surface-treated using a surface treatment agent containing an alkylsilane coupling agent and an aminoalkylsilane coupling agent.

[0009] According to the present invention, a magnetorheological elastomer composition having high toughness is provided.

[0010] Hereinafter, embodiments of the present invention will be described in detail, but the scope of the present invention is not limited to the embodiments described herein, and various modifications can be made without departing from the spirit of the present invention. Furthermore, when multiple upper and lower limit values ​​are specified for a specific parameter, any upper and lower limit values ​​can be combined to form a suitable numerical range.

[0011] In this specification, a viscoelastic elastomer refers to a material that has both viscosity and elasticity, and can be distinguished based on the relaxation time of stress relaxation (change in stress over time) when a certain strain is applied. If the relaxation time is sufficiently short compared to the time scale of observation, it is considered to be a viscous material, if it is long, it is considered to be an elastic material, and if it is on the same scale, it is considered to be a viscoelastic material.

[0012] In this specification, the term "magnetorheological elastomer" refers to a viscoelastic elastomer containing magnetic particles, and preferably refers to a composite material in which magnetic particles are dispersed and fixed within a viscoelastic elastomer. The magnetorheological elastomer reversibly changes its apparent elastic modulus and damping characteristics in response to an external magnetic field.

[0013] Examples of the viscoelastic elastomer include a thermoplastic elastomer and a thermosetting elastomer.

[0014] The thermoplastic elastomer is not particularly limited, and examples thereof include polystyrene-based thermoplastic elastomers, polyvinyl chloride-based thermoplastic elastomers, polyolefin-based thermoplastic elastomers, polyurethane-based thermoplastic elastomers, polyester-based thermoplastic elastomers, polyamide-based thermoplastic elastomers, vinyl chloride-based thermoplastic elastomers, fluororubber-based thermoplastic elastomers, chlorinated polyethylene-based elastomers, and nitrile-based thermoplastic elastomers.

[0015] Among viscoelastic elastomers, thermosetting elastomers such as rubber and polyurethane elastomers are preferred, from the viewpoint that the change in elastic modulus of the magnetically responsive material increases before and after application of a magnetic field.

[0016] [Rubber] The rubber is not particularly limited, and examples thereof include natural rubber (NR), modified natural rubber, graft natural rubber, cyclized natural rubber, chlorinated natural rubber, synthetic natural rubber (IR); diene-based synthetic rubbers such as styrene-butadiene rubber (SBR), butadiene rubber (BR), chloroprene rubber (CR), nitrile rubber (NBR), and carboxylated nitrile rubber; mixtures of nitrile rubber and vinyl chloride resin, and mixtures of nitrile rubber and EPDM rubber; and non-diene-based synthetic rubbers such as butyl rubber (IIR), brominated butyl rubber, chlorinated butyl rubber, ethylene-vinyl acetate rubber, acrylic rubber, ethylene-acrylic rubber, chlorosulfonated polyethylene, chlorinated polyethylene (CM), epichlorohydrin rubber, epichlorohydrin-ethylene oxide rubber, methylsilicone rubber, vinyl-methylsilicone rubber, phenyl-methylsilicone rubber, fluorinated silicone rubber, ethylene propylene rubber (EPM, EPDM), urethane rubber, silicone rubber, chlorosulfonated polyethylene (CSM), and fluororubber. The rubber material may be in either a vulcanized or unvulcanized state, and may contain liquid substances such as oil, plasticizer, or softener.

[0017] [Polyurethane Elastomer] In this specification, the term "polyurethane elastomer" refers to an elastomer containing a urethane resin. Generally, the urethane resin corresponds to a component that forms the polymer skeleton of the polyurethane elastomer.

[0018] In this specification, urethane resin refers to a reaction product of a polyol and an isocyanate. A urethane bond is formed by reaction between a hydroxyl group contained in the polyol and an isocyanate group contained in the isocyanate, resulting in the formation of a urethane resin. The urethane resin may also be a reaction product of a reaction product of a polyol and an isocyanate with a chain extender and / or a terminal terminator, and all of these reaction products are included in the scope of the urethane resin. An example of a preferred urethane resin is the reaction product of a polyol compound and an isocyanate compound described in Patent Document 1.

[0019] The polyol refers to a compound having two or more hydroxyl groups in one molecule. The polyol preferably includes a triol.

[0020] A triol is a compound having three hydroxyl groups in one molecule. Each hydroxyl group in the triol reacts with an isocyanate group of a diisocyanate (described later) to form a urethane bond, and therefore the triol contains a branching point (crosslinking point) where three molecular chains are bonded to one atom.

[0021] The crosslinking points (branching points) in the triol can be introduced by a compound (initiator) having three or more active hydrogen atoms, and examples of such initiators include glycerol, trimethylolethane, trimethylolpropane, trimellitic acid, and diethylenetriamine.

[0022] In one embodiment, the number-average molecular weight of the triol is 1,000 or more, preferably 2,000 to 15,000, more preferably 3,000 to 10,000, and even more preferably 4,000 to 8,000. By having the number-average molecular weight of the triol within this range, the molecular weight of the molecular chains bonded to the crosslinking points can be maintained at a certain level or higher. As a result, when the magnetic field strength is changed, the orientation of the magnetic powder can be changed without restriction, which is thought to increase the change in the elastic modulus of the magnetorheological elastomer composition.

[0023] In the present invention, the number average molecular weight can be measured by gel permeation chromatography as a converted value using polystyrene as a standard sample.

[0024] The triol may be, for example, a polyether triol, a polyester triol, a polycarbonate triol, a polyolefin triol, a polyacrylic triol, or the like, and is preferably a polyether triol.

[0025] Polyether triol can typically be understood as a triol of a polymer having a unit containing an ether bond as a repeating unit, and the repeating unit preferably contains an oxyalkylene unit. Such units containing an ether bond include oxyalkylene units having from 2 to 4 carbon atoms, such as oxyethylene units, oxypropylene units, and oxytetramethylene units, and particularly include oxypropylene units and oxytetramethylene units. Polyether polyols may be homopolymers containing one type of oxyalkylene unit, or copolymers containing two or more types of oxyalkylene units. Examples of polyether polyols include polyethylene triol, polypropylene triol, polytetramethylene ether triol, and polyoxyethylene-polyoxypropylene triol.

[0026] The oxyalkylene units can be formed by ring-opening polymerization of cyclic ethers such as ethylene oxide, propylene oxide, tetrahydrofuran, and the like.

[0027] A polyester triol can be typically understood as a triol of a polymer having repeating units containing ester bonds. The units containing ester bonds can be formed by the reaction of a diol with a dicarboxylic acid or by ring-opening polymerization of a cyclic ester compound. A polyester polyol may be a homopolymer containing one type of repeating unit or a copolymer containing two or more types of repeating units.

[0028] The diol used as a raw material for the polyester triol may typically be a low-molecular-weight diol having a molecular weight of 50 or more and 300 or less, and specific examples thereof include linear or branched aliphatic diols such as ethylene glycol, propylene glycol, 1,3-butanediol, 1,4-butanediol, neopentyl glycol, 1,6-hexanediol, 3-methylpentane-1,5-diol, diethylene glycol, triethylene glycol, dipropylene glycol, and tripropylene glycol; bisphenol compounds such as bisphenol A and bisphenol F; alkylene oxide adducts of these bisphenol compounds; and alicyclic diols such as cyclohexanedimethanol. The alkylene oxide adducts of bisphenol compounds can be formed by ring-opening polymerization of a cyclic ether with a bisphenol compound, and examples of such cyclic ethers include ethylene oxide, propylene oxide, and tetrahydrofuran.

[0029] Examples of dicarboxylic acids that are raw materials for polyester triols include aliphatic dicarboxylic acids such as succinic acid, adipic acid, sebacic acid, and dodecanedicarboxylic acid; aromatic dicarboxylic acids such as phthalic acid, isophthalic acid, terephthalic acid, and naphthalenedicarboxylic acid; anhydrides of the aliphatic dicarboxylic acids or aromatic dicarboxylic acids; and esters of aliphatic dicarboxylic acids or aromatic dicarboxylic acids. The esters of aliphatic dicarboxylic acids or aromatic dicarboxylic acids can be formed by reacting an aliphatic dicarboxylic acid or aromatic dicarboxylic acid with an alcohol, and examples of such alcohols include aliphatic alcohols having from 1 to 4 carbon atoms, such as methanol, ethanol, propanol, and butanol.

[0030] Polycarbonate triol can be understood as a triol of a polymer having units containing carbonate bonds (-O-CO-O-) as repeating units. The units containing carbonate bonds (-O-CO-O-) can be formed by the reaction of a carbonate ester with a diol, or the reaction of phosgene with a diol, etc. Polycarbonate polyol may be a homopolymer containing one type of repeating unit, or a copolymer containing two or more types of repeating units.

[0031] Examples of carbonate esters that are raw materials for polycarbonate triol include methyl carbonate, dimethyl carbonate, ethyl carbonate, diethyl carbonate, cyclohexyl carbonate, dicyclohexyl carbonate, and diphenyl carbonate.

[0032] As the diol that is a raw material for the polycarbonate triol, typically, a low molecular weight diol having a molecular weight of 50 or more and 300 or less, or a high molecular weight diol having a number average molecular weight of more than 300 may be used.

[0033] Examples of low-molecular-weight diols include linear or branched aliphatic diols such as ethylene glycol, propylene glycol, 1,3-butanediol, 1,4-butanediol, neopentyl glycol, 1,6-hexanediol, 3-methylpentane-1,5-diol, diethylene glycol, triethylene glycol, dipropylene glycol, and tripropylene glycol; bisphenol compounds such as bisphenol A and bisphenol F; alkylene oxide adducts of the bisphenol compounds; and alicyclic diols such as cyclohexanedimethanol. The alkylene oxide adducts of bisphenol compounds can be formed by ring-opening polymerization of a bisphenol compound with a cyclic ether, and examples of such cyclic ethers include ethylene oxide, propylene oxide, and tetrahydrofuran.

[0034] Examples of high molecular weight diols include polyether diols such as polyethylene glycol and polypropylene glycol, polyester diols such as polyhexamethylene adipate, etc. The number average molecular weight of the high molecular weight diol is generally more than 300, preferably 400 to 5,000, more preferably 400 to 2,000.

[0035] Polyolefin triol can be understood as a triol of a polymer having a unit consisting of a divalent hydrocarbon group as a repeating unit. The unit consisting of a divalent hydrocarbon group can be formed by polymerization of an alkene or a diene. The polyolefin triol may be a homopolymer containing one type of repeating unit, or a copolymer containing two or more types of repeating units.

[0036] Examples of alkenes that are raw materials for polyolefin triols include ethylene, propylene, and isobutene, and examples of dienes that are raw materials for polyolefin triols include butadiene and isoprene.

[0037] The polyacrylic triol can be understood as a triol of a polymer having units derived from a (meth)acrylic monomer as repeating units. The polyacrylic triol may be a homopolymer containing one type of repeating unit, or a copolymer containing two or more types of repeating units.

[0038] The (meth)acrylic monomer may include a (meth)acrylic monomer having a hydroxyl group, other (meth)acrylic monomers and / or other vinyl monomers.

[0039] Examples of the (meth)acrylic monomer having a hydroxyl group include hydroxyethyl (meth)acrylate, hydroxypropyl (meth)acrylate, and hydroxybutyl (meth)acrylate.

[0040] Other (meth)acrylic monomers include (meth)acrylic acid esters such as methyl (meth)acrylate, ethyl (meth)acrylate, propyl (meth)acrylate, butyl (meth)acrylate, pentyl (meth)acrylate, hexyl (meth)acrylate, heptyl (meth)acrylate, octyl (meth)acrylate, nonyl (meth)acrylate, decyl (meth)acrylate, undecyl (meth)acrylate, and dodecyl (meth)acrylate; unsaturated carboxylic acids such as (meth)acrylic acid, maleic acid, and itaconic acid; and (meth)acrylamide monomers such as unsubstituted (meth)acrylamide, dimethyl(meth)acrylamide, N,N-methylenebis(meth)acrylamide, and diacetone(meth)acrylamide.

[0041] Other vinyl monomers include styrene and methylstyrene.

[0042] The content of triol contained in the polyol is, for example, 3% by mass or more, preferably 3% by mass or more and 70% by mass or less, more preferably 5% by mass or more and 60% by mass or less, and even more preferably 7% by mass or more and 55% by mass or less.

[0043] The polyol preferably contains a diol. A diol refers to a compound having two hydroxyl groups in one molecule. By containing a diol as the polyol, it may be easier to control the molecular weight of the molecular chains bonded to the crosslinking points.

[0044] The diol may be a low molecular weight diol having a molecular weight of 50 or more and 300 or less, or may be a high molecular weight diol having a number average molecular weight of more than 300. In one embodiment, a high molecular weight diol is preferred, and a polyether diol is more preferred.

[0045] Examples of low-molecular-weight diols include linear or branched aliphatic diols such as ethylene glycol, propylene glycol, 1,3-butanediol, 1,4-butanediol, neopentyl glycol, 1,6-hexanediol, 3-methylpentane-1,5-diol, diethylene glycol, triethylene glycol, dipropylene glycol, and tripropylene glycol; bisphenol compounds such as bisphenol A and bisphenol F; cyclic ether adducts of the bisphenol compounds; and alicyclic diols such as cyclohexanedimethanol. Alkylene oxide adducts of bisphenol compounds can be formed by ring-opening polymerization of a cyclic ether with a bisphenol compound, and examples of such cyclic ethers include ethylene oxide, propylene oxide, and tetrahydrofuran.

[0046] Examples of high molecular weight diols include polyether diols, polyester diols, polycarbonate diols, polyolefin diols, and polyacrylic diols.

[0047] Polyether diols can typically be understood as polymer diols having units containing ether bonds as repeating units, and the repeating units preferably contain oxyalkylene units. Such oxyalkylene units include oxyalkylene units having from 2 to 4 carbon atoms, such as oxyethylene units, oxypropylene units, and oxytetramethylene units, and particularly include oxypropylene units and oxytetramethylene units. Polyether polyols may be homopolymers containing one type of oxyalkylene unit, or copolymers containing two or more types of oxyalkylene units. Examples of polyether polyols include polyethylene triol, polypropylene triol, polytetramethylene ether triol, and polyoxyethylene-polyoxypropylene triol.

[0048] The oxyalkylene units can be formed by ring-opening polymerization of cyclic ethers such as ethylene oxide, propylene oxide, tetrahydrofuran, and the like.

[0049] A polyester diol can typically be understood as a polymer diol having a unit containing an ester bond as a repeating unit.

[0050] Polycarbonate diol can be typically understood as a polymer diol having units containing carbonate bonds (—O—CO—O—) as repeating units.

[0051] Polyolefin diols can be typically understood as polymeric diols having units consisting of divalent hydrocarbon groups as repeating units.

[0052] Polyacrylic diol can be typically understood as a polymeric diol having units derived from (meth)acrylic monomers as repeating units.

[0053] The number average molecular weight of the high molecular weight diol is generally more than 300, preferably 400 or more and 5,000 or less, and more preferably 400 or more and 3,000 or less.

[0054] The content of the diol is preferably 50 parts by mass or more and 2,000 parts by mass or less, more preferably 60 parts by mass or more and 1,500 parts by mass or less, and even more preferably 70 parts by mass or more and 1,200 parts by mass or less, based on 100 parts by mass of the triol.

[0055] In a preferred embodiment, the polyol includes a triol and a diol. The total content of the triol and the diol in 100% by mass of the polyol is, for example, 80% by mass or more and 100% by mass or less, preferably 90% by mass or more and 100% by mass or less, and more preferably 95% by mass or more and 100% by mass or less.

[0056] The polyol may contain other polyols in addition to the triol and diol, such as a triol having a molecular weight of less than 4,000 or a triol having four or more hydroxyl groups per molecule.

[0057] Isocyanate refers to a compound having two or more isocyanate groups in one molecule. The number of isocyanate groups contained in one molecule of isocyanate is typically 2 to 4, and particularly 2 to 3.

[0058] Examples of the isocyanate include aliphatic isocyanates, aromatic isocyanates, and alicyclic isocyanates.

[0059] Examples of the aliphatic isocyanate include tetramethylene diisocyanate, 1,6-hexamethylene diisocyanate, dodecamethylene diisocyanate, and trimethylhexamethylene diisocyanate.

[0060] Aromatic isocyanates include 1,3- and 1,4-phenylene diisocyanate, 1-methyl-2,4-phenylene diisocyanate, 1-methyl-2,6-phenylene diisocyanate, 1-methyl-2,5-phenylene diisocyanate, 1-methyl-2,6-phenylene diisocyanate, 1-methyl-3,5-phenylene diisocyanate, 1-ethyl-2,4-phenylene diisocyanate, 1-isopropyl-2,4-phenylene diisocyanate, 1,3-dimethyl-2,4-phenylene diisocyanate, 1,3-dimethyl-4,6-phenylene diisocyanate, 1,4-dimethyl-2,5-phenylene diisocyanate, diethylbenzene diisocyanate, diisopropylbenzene diisocyanate, 1-methyl-3,5-diethylbenzene diisocyanate, 3-methyl-4,6-phenylene diisocyanate, 3-methyl-5,5-diisocyanate, 5-methyl-6,6-diisocyanate, 5-methyl-7,6-diisocyanate, 5-methyl-8,6-diisocyanate, 5-methyl-9,6-diisocyanate, 5-methyl-10,10-diisocyanate, 1-methyl-11,12-diisocyanate, 1-methyl-12,13-diisocyanate, 1-methyl-13,14-diisocyanate, 1-methyl-14,15-diisocyanate, 1-methyl-15,16-diisocyanate, 1-methyl-15,17-diisocyanate, 1-methyl-16,18-diisocyanate, 1-methyl-17,19-diisocyanate, 1-methyl-18,19-diisocyanate, 1-methyl-19, -methyl-1,5-diethylbenzene-2,4-diisocyanate, 1,3,5-triethylbenzene-2,4-diisocyanate, naphthalene-1,4-diisocyanate, naphthalene-1,5-diisocyanate, 1-methyl-naphthalene-1,5-diisocyanate, naphthalene-2,6-diisocyanate, naphthalene-2,7-diisocyanate, 1,1-dinaphthyl-2,2'-diisocyanate isocyanate, biphenyl-2,4'-diisocyanate, biphenyl-4,4'-diisocyanate, 3,3'-dimethylbiphenyl-4,4'-diisocyanate, diphenylmethane-4,4'-diisocyanate, diphenylmethane-2,2'-diisocyanate, diphenylmethane-2,4-diisocyanate, toluene diisocyanate, xylylene diisocyanate, and the like.

[0061] Examples of alicyclic isocyanates include 1,3-cyclopentylene diisocyanate, 1,3-cyclohexylene diisocyanate, 1,4-cyclohexylene diisocyanate, 1,3-bis(isocyanatomethyl)cyclohexane, 1,4-bis(isocyanatomethyl)cyclohexane, lysine diisocyanate, isophorone diisocyanate, 4,4'-dicyclohexylmethane diisocyanate, 2,4'-dicyclohexylmethane diisocyanate, 2,2'-dicyclohexylmethane diisocyanate, and 3,3'-dimethyl-4,4'-dicyclohexylmethane diisocyanate.

[0062] When producing the urethane resin, the molar ratio [NCO / OH] of the isocyanate groups contained in the isocyanate to the hydroxyl groups contained in the polyol can be, for example, 0.1 or more and 5 or less, preferably 0.3 or more and 3 or less, and more preferably 0.4 or more and 1.5 or less.

[0063] A chain extender is a compound having two or more active hydrogen atoms in one molecule, and is typically used to further react with the reaction product of a polyol and an isocyanate. By further reacting the reaction product of a polyol and an isocyanate with a chain extender, it becomes easy to obtain a high-molecular-weight urethane resin.

[0064] Examples of the chain extender include a chain extender having an amino group and a chain extender having a hydroxyl group.

[0065] Examples of chain extenders having an amino group include ethylenediamine, 1,2-propanediamine, 1,6-hexamethylenediamine, piperazine, 2-methylpiperazine, 2,5-dimethylpiperazine, isophoronediamine, 4,4'-dicyclohexylmethanediamine, 3,3'-dimethyl-4,4'-dicyclohexylmethanediamine, 1,2-cyclohexanediamine, 1,4-cyclohexanediamine, aminoethylethanolamine, hydrazine, diethylenetriamine, and triethylenetetramine.

[0066] Examples of chain extenders having a hydroxyl group include aliphatic polyols such as ethylene glycol, diethylene glycol, triethylene glycol, propylene glycol, 1,3-propanediol, 1,3-butanediol, 1,4-butanediol, hexamethylene glycol, sucrose, methylene glycol, glycerin, and sorbitol; aromatic polyols such as bisphenol A, 4,4'-dihydroxydiphenyl, 4,4'-dihydroxydiphenyl ether, 4,4'-dihydroxydiphenyl sulfone, hydrogenated bisphenol A, and hydroquinone; and water.

[0067] When a chain extender is contained, the molar ratio [NCO / (H+OH)] of the isocyanate groups contained in the isocyanate to the sum of the hydroxyl groups contained in the polyol and the active hydrogen atoms contained in the chain extender can be, for example, 0.1 or more and 5 or less, preferably 0.3 or more and 3 or less, and more preferably 0.4 or more and 1 or less.

[0068] The terminal terminator is a compound having one active hydrogen atom per molecule, and is typically used to further react with the reaction product of the polyol isocyanate and the chain extender used as needed.

[0069] Examples of the end terminator include alcohols such as hexanol, heptanol, octanol, nonanol, and undecanol; and amines such as dibutylamine.

[0070] The amount of the terminal stopper may be preferably 0.01 parts by mass or more and 20 parts by mass or less, more preferably 0.1 parts by mass or more and 10 parts by mass or less, per 100 parts by mass of the reaction product of the polyol and the isocyanate.

[0071] The average molecular weight between crosslinks of the urethane resin may be preferably 9,300 or more and 30,000 or less, more preferably 9,500 or more and 27,000 or less, even more preferably 9,500 or more and 20,000 or less, and even more preferably 9,500 or more and 12,000 or less. The average molecular weight between crosslinks may be understood as the average value of the molecular weight of the molecular chain between two adjacent crosslinks (branch points). While not intended to be limited to a particular theory, it is believed that when the molecular weight between crosslinks of the urethane resin is within this range, the magnetic powder can change its orientation without restriction when a magnetic field is applied, thereby increasing the change in elastic modulus.

[0072] The average molecular weight between crosslinking points can be controlled by the number average molecular weight of the triol, or when a diol is used, the number average molecular weight of the diol, the amounts of the triol and diol used, and the like.

[0073] In one embodiment, the average molecular weight between crosslink points is determined by calculating the number average molecular weight of the i-functional polyol contained in the polyol as M ｉ The molar fraction of the polyol having the i-functionality in the total amount of polyol is C ｉ can be calculated based on the following formula:

[0074]

[0075] That is, assuming that the length of one polyol molecule is twice the number obtained by dividing the number average molecular weight of the polyol by the number of functional groups of the polyol, and that the number of crosslinking points contained in the polyol is the number obtained by subtracting 2 from the number of functional groups of the polyol, the above formula means that the total length of the polyol is divided by the total number of crosslinking points.

[0076] According to classical rubber theory, in crosslinked rubber that does not contain impurities, the molecular weight between crosslinking points of the crosslinked rubber is considered to correlate with the elastic modulus of the crosslinked rubber. That is, the molecular weight between crosslinking points of the crosslinked rubber is defined as Mc, the Poisson's ratio of the crosslinked rubber is defined as μ, and the density of the crosslinked rubber is defined as ρ (g / m ３ , the gas constant is R (J / (K·mol)), and the temperature is T (K), the elastic modulus E (Pa) of the crosslinked rubber is expressed by the following formula:

[0077]

[0078] That is, in a crosslinked rubber that does not contain impurities, the larger the molecular weight between crosslinks, the smaller the elastic modulus of the crosslinked rubber.

[0079] The urethane resin can be produced by reacting a polyol, an isocyanate, and optionally a chain extender and a terminal terminator. This reaction can be carried out in the absence of a solvent or in the presence of a reaction solvent. The reaction temperature can be 50°C or higher and 150°C or lower. Examples of reaction solvents include ketone solvents such as acetone and methyl ethyl ketone; ether solvents such as tetrahydrofuran and dioxane; acetate ester solvents such as ethyl acetate and butyl acetate; nitrile solvents such as acetonitrile; and amide solvents such as dimethylformamide and N-methylpyrrolidone.

[0080] The content of the urethane resin contained in the polyurethane elastomer is preferably 80% by mass or more and 100% by mass, more preferably 90% by mass or more and 100% by mass, and even more preferably 95% by mass or more and 100% by mass.

[0081] [Other Resins] The polyurethane elastomer may further contain a resin other than the urethane resin, such as an acrylic resin, a polyester resin, a polyamide resin, a polycarbonate resin, or a silicone resin.

[0082] [Plasticizer] The polyurethane elastomer may contain a plasticizer in addition to the urethane resin. Examples of the plasticizer include aromatic dicarboxylic acid plasticizers, aliphatic dicarboxylic acid plasticizers, phosphoric acid plasticizers, and trimellitic acid plasticizers.

[0083] Examples of aromatic dicarboxylic acid plasticizers include phthalate diesters such as dibutyl phthalate, dioctyl phthalate, di-2-ethylhexyl phthalate, diisononyl phthalate, diisodecyl phthalate, diundecyl phthalate, and ditridecyl phthalate; isophthalate diesters such as dioctyl isophthalate and di-2-ethylhexyl isophthalate; and terephthalate diesters such as dioctyl terephthalate and di-2-ethylhexyl terephthalate.

[0084] Examples of the aliphatic dicarboxylic acid plasticizer include adipic acid diesters such as dioctyl adipate, di-2-ethylhexyl adipate, isononyl adipate, and diisodecyl adipate; and sebacate diesters such as dioctyl sebacate, di-2-ethylhexyl sebacate, and diisononyl sebacate.

[0085] Examples of the phosphoric acid plasticizer include phosphate esters such as trioctyl phosphate, tri-2-ethylhexyl phosphate, and tricresyl phosphate.

[0086] Examples of trimellitic acid plasticizers include trimellitic acid triesters such as trioctyl trimellitate and tri-2-ethylhexyl trimellitate; and pyromellitic acid tetraesters such as tetraoctyl pyromellitate and tetra-2-ethylhexyl pyromellitate.

[0087] The plasticizer preferably includes an aromatic dicarboxylic acid plasticizer, more preferably includes a phthalic acid diester, and particularly preferably includes dioctyl phthalate or di-2-ethylhexyl phthalate.

[0088] The content of the plasticizer is 35 to 70 volume % of the total composition, preferably 40 to 60 volume %, and more preferably 45 to 50 volume %. When the content of the plasticizer is within this range, the magnetorheological elastomer composition has an appropriate viscosity, and the orientation of the magnetic powder is easily changed in response to changes in the magnetic field.

[0089] [Additives] The polyurethane elastomer may contain additives in addition to the urethane resin and plasticizer. Examples of such additives include urethane catalysts, antioxidants, light stabilizers, impact resistance agents, antistatic agents, flame retardants, preservatives, UV absorbers, viscosity modifiers, and colorants.

[0090] The urethanization catalyst is used in the reaction of a polyol and an isocyanate, and examples thereof include tin-based compounds such as tin octoate, dibutyltin dichloride, dibutyltin oxide, and dibutyltin dilaurate; titanium-based compounds such as dibutyltitanium dichloride, tetrabutyl titanate, and butoxytitanium trichloride; zinc-based compounds such as zinc naphthenate and zinc 2-ethylhexanoate; and tertiary amines such as triethylamine, triethylenediamine, and 1,8-diazabicyclo-(5,4,0)-undecene-7.

[0091] The content of the urethanization catalyst may be 0.01 parts by mass or more and 10 parts by mass or less relative to 100 parts by mass of the urethane resin.

[0092] [Magnetic Powder] The magnetic powder refers to a powder of a magnetic material whose magnetic moment can change in direction or magnitude in response to a change in an external magnetic field. The magnetic material may typically be a ferromagnetic material, and preferably a soft magnetic material.

[0093] The magnetic material may be, for example, Fe, or an alloy or oxide containing Fe; preferably, Fe, or an alloy or oxide containing Fe and at least one selected from the group consisting of B, C, N, O, Na, Mg, Al, Si, P, S, Cl, K, Ti, V, Cr, Mn, Co, Ni, Cu, Zn, As, Sr, Zr, Nb, Mo, Pd, Sn, Ba, La, Ta, and Bi; more preferably, Fe, or an alloy containing Fe and at least one selected from the group consisting of B, Al, Si, Cr, Co, and Ni.

[0094] Such magnetic materials include Fe, iron oxide, soft ferrites such as manganese zinc ferrite, nickel zinc ferrite, copper zinc ferrite, and sodium ferrite, and alloys such as FeNi alloys, FeCo alloys, FeSi alloys, FeSiCr alloys, FeSiAl alloys, and FeSiBCr alloys. Of these, preferred magnetic materials are Fe, iron oxide, FeCo alloys, and FeSiCr alloys.

[0095] The coercive force of the magnetic material is preferably 100 A / m or less, and the lower limit can be 0 A / m or more.

[0096] The saturation magnetic flux density of the magnetic material may be preferably 0.1 T or more and 3 T or less, more preferably 0.5 T or more and 2.5 T or less, and even more preferably 0.7 T or more and 2.3 T or less.

[0097] The magnetic permeability of the magnetic material measured under a magnetic field of 0.002 T may be preferably 0.0001 H / m or more and 1 H / m or less, more preferably 0.0005 H / m or more and 0.1 H / m or less, and even more preferably 0.001 H / m or more and 0.01 H / m or less.

[0098] The coercive force, saturation magnetic flux density and magnetic permeability of a magnetic material refer to the coercive force, saturation magnetic flux density and magnetic permeability measured in bulk, and can typically be measured by a vibrating sample magnetometer.

[0099] The magnetic powder has hydroxyl groups on its surface. Therefore, when the viscoelastic elastomer has active hydrogen groups, these bond with the hydroxyl groups on the surface of the magnetic powder, causing the magnetic powder to be uniformly dispersed within the viscoelastic elastomer and forming crosslinks. When many crosslinks centered around the magnetic powder exist within the viscoelastic elastomer, the hardness of the magnetorheological elastomer composition tends to increase, but on the other hand, the flexibility before application of a magnetic field decreases and the brittleness increases, making the composition more susceptible to breakage.

[0100] The hydroxyl groups on the surface of the magnetic powder can be blocked by, for example, surface treating the magnetic powder with an alkylsilane coupling agent. However, if the reactive sites on the surface of the magnetic powder are eliminated in this way, the viscoelastic elastomer will no longer bond to the surface of the magnetic powder, which will reduce the dispersibility of the magnetic powder and the toughness of the magnetorheological elastomer composition.

[0101] The magnetic powder used in the present invention is surface-treated using a surface treatment agent containing an alkylsilane coupling agent and an aminoalkylsilane coupling agent. This seals the hydroxyl groups present on the surface of the magnetic powder, generating amino groups instead. The amino groups on the surface of the magnetic powder bond with the active hydrogen groups of the viscoelastic elastomer. The amount of amino groups on the surface of the magnetic powder can be adjusted appropriately by changing the mixing ratio of the alkylsilane coupling agent and the aminoalkylsilane coupling agent in the surface treatment agent.

[0102] In other words, when the magnetic powder is surface-treated with the surface treatment agent, the amount of amino groups formed on the magnetic powder surface can be appropriately adjusted, thereby optimizing the number of cross-linking points within the viscoelastic elastomer. As a result, the magnetic powder can be uniformly dispersed within the viscoelastic elastomer, improving its toughness while maintaining its flexibility prior to application of the magnetic field.

[0103] The alkylsilane coupling agent may be, for example, a compound represented by the following formula: (R １ ) ａ Si(OR ２ ) ４－ａ (1)

[0104] In formula (1), R １ represents an alkyl group having 1 to 15 carbon atoms, preferably 1 to 10 carbon atoms, and more preferably 1 to 5 carbon atoms. １ If the number of carbon atoms in R exceeds 15, the frictional force between the magnetic powder particles when a magnetic field is applied decreases due to the large number (thickness) of alkyl groups covering the surface of the magnetic powder, making it difficult to increase the modulus of elasticity. ２ is eliminated when the coupling agent reacts, so its structure has little effect on the surface treatment state, and the structure is not limited, but generally represents an organic group, for example, an alkyl group having 1 to 15 carbon atoms, preferably 1 to 10 carbon atoms, and more preferably 1 to 5 carbon atoms. a represents an integer of 1 to 3, preferably 2.

[0105] R １ and R ２ Specific examples of the alkyl group include a methyl group, an ethyl group, an n-propyl group, an isopropyl group, an n-butyl group, an isobutyl group, a sec-butyl group, a tert-butyl group, an n-pentyl group, an n-hexyl group, an n-heptyl group, an n-octyl group, an n-nonyl group, an n-decyl group, an n-undecyl group, an n-dodecyl group, an n-tridecyl group, an n-tetradecyl group, and an n-pentadecyl group.

[0106] Specific examples of alkylsilane coupling agents include dimethyldimethoxysilane, dimethyldiethoxysilane, dimethoxydiphenylsilane, methyltrimethoxysilane, phenyltrimethoxysilane, n-propyltrimethoxysilane, hexyltrimethoxysilane, decyltrimethoxysilane, methyltriethoxysilane, phenyltriethoxysilane, n-propyltriethoxysilane, hexyltriethoxysilane, octyltriethoxysilane, etc. Among these, preferred is dimethyldimethoxysilane.

[0107] The aminoalkylsilane coupling agent may be, for example, a compound represented by the following formula: (NH ２ R ３ ) ｂ Si(OR ４ ) ４－ｂ (2) (NH ２ R ５ NHR ６ ) c Si(OR ７ ) ４－c (3)

[0108] In formula (2), R ３ represents an alkylene group having 1 to 15 carbon atoms, preferably 1 to 10 carbon atoms, and more preferably 1 to 5 carbon atoms. ３ If the carbon number of R exceeds 15, the amount of alkyl groups covering the surface of the magnetic powder will be large (thick), which will reduce the frictional force between the magnetic powder particles when a magnetic field is applied, making it difficult to increase the modulus of elasticity. ４ Since R is eliminated when the coupling agent reacts, its structure has little effect on the surface treatment state, but generally represents an organic group, for example, an alkyl group having 1 to 15 carbon atoms, preferably 1 to 10 carbon atoms, and more preferably 1 to 5 carbon atoms. b represents an integer of 1 to 3, preferably 1. In formula (3), R ５ represents an alkylene group having 1 to 15 carbon atoms, preferably 1 to 10 carbon atoms, and more preferably 2 to 6 carbon atoms. ６ represents an alkylene group having 1 to 10 carbon atoms, preferably 1 to 5 carbon atoms, and more preferably 2 to 3 carbon atoms. ７is eliminated when the coupling agent reacts, so its structure has little effect on the surface treatment state, and the structure is not limited, but generally represents an organic group, for example, an alkyl group having 1 to 15 carbon atoms, preferably 1 to 10 carbon atoms, and more preferably 1 to 5 carbon atoms. c represents an integer of 1 to 3, preferably 1.

[0109] R ３ Specific examples include a methylene group, an ethylene group, n-propylene, an isopropylene group, an n-butylene group, an isobutylene group, a sec-butylene group, a tert-butylene group, and an n-pentylene group.

[0110] R ５ Specific examples of R include a methylene group, an ethylene group, an n-propylene group, an isopropylene group, an n-butylene group, an isobutylene group, a sec-butylene group, a tert-butylene group, an n-pentylene group, an n-hexylene group, an n-heptylene group, an n-octylene group, an n-nonylene group, and an n-decylene group. ６ Specific examples include a methylene group, an ethylene group, n-propylene, an isopropylene group, an n-butylene group, an isobutylene group, a sec-butylene group, a tert-butylene group, and an n-pentylene group.

[0111] R ４ and R ７ Specific examples of ２ This is similar to what was described for

[0112] Specific examples of aminoalkylsilane coupling agents include 3-aminopropyltrimethoxysilane, 3-aminopropyltriethoxysilane, 3-(2-aminoethylamino)propyltrimethoxysilane, 3-(2-aminoethylamino)propyltriethoxysilane, [3-(6-aminohexylamino)propyl]trimethoxysilane, etc. Among these, 3-aminopropyltrimethoxysilane is preferred.

[0113] In the surface treatment agent, the ratio of alkylsilane coupling agent to aminoalkylsilane coupling agent is preferably 20 / 80 or more and 99 / 1 or less, expressed as a weight ratio of the alkylsilane coupling agent-derived product (hereinafter sometimes referred to as the "alkyl group portion") to the aminoalkylsilane coupling agent-derived product (hereinafter sometimes referred to as the "amino group portion") in the coating formed on the surface of the magnetic powder after surface treatment. If this ratio is less than 20 / 80, the amount of amino groups generated on the magnetic powder surface after surface treatment is too high, making the magnetorheological elastomer composition brittle and prone to fracture. If this ratio exceeds 99 / 1, the amount of amino groups is too low, reducing the dispersibility of the magnetic powder and reducing the toughness of the magnetorheological elastomer composition. The ratio is preferably 30 / 70 or more and 85 / 15 or less, more preferably 40 / 60 or more and 80 / 20 or less, and even more preferably 50 / 50 or more and 70 / 30 or less.

[0114] The surface treatment method for the magnetic powder may be a commonly used method, such as a dry method in which a surface treatment agent is added directly to the magnetic powder and uniformly dispersed using a ribbon mixer, Henschel mixer, etc., or a wet method in which the magnetic powder is dispersed in a solvent, a surface treatment agent is added thereto to cause a reaction, and then the solvent is removed. By performing the surface treatment, a coating having alkyl moieties and aminoalkyl moieties is formed on the surface of the magnetic powder.

[0115] The amount of surface treatment agent added is, for example, 0.1 to 10% by weight, preferably 1 to 6% by weight, and more preferably 1.5 to 3.5% by weight, based on the total weight of the magnetic powder and surface treatment agent. If the amount of surface treatment agent added is less than 0.1% by weight, based on the total weight of the magnetic powder and surface treatment agent, the toughness of the resulting magnetorheological elastomer composition is likely to be insufficient, while if it exceeds 10% by weight, reactions between the surface treatment agents occur preferentially, making it difficult for the magnetic powder surface to react with the surface treatment agent, making it difficult to obtain the desired magnetic powder surface composition.

[0116] When determined based on the amount of surface treatment agent added based on the total weight of the magnetic powder and the surface treatment agent, the ratio of alkyl silane coupling agent to amino alkyl silane coupling agent is, for example, 0.1 to 20, preferably 0.4 to 15, more preferably 2 to 13, and even more preferably 5 to 10.

[0117] The surface treatment agent used to treat the surface of the magnetic powder preferably contains at least one selected from the group consisting of tetraalkoxysilane and tetraalkoxytitanium. This strengthens the bond between the silane coupling agent (i.e., alkylsilane coupling agent and aminoalkylsilane coupling agent) and the magnetic powder surface, improving the toughness of the magnetorheological elastomer composition. In this specification, the term "silane coupling agent" refers to a silicon compound having a group that bonds to organic compounds and a group that bonds to inorganic compounds.

[0118] The tetraalkoxysilane or tetraalkoxytitanium may be, for example, a compound represented by the following formula: M(OR ８ ) ４ (4)

[0119] In the formula, M represents Si or Ti. ８ is eliminated when the coupling agent reacts, and therefore its structure has little effect on the surface treatment state, and the structure is not limited, but generally represents an organic group, for example, an alkyl group having 1 to 15 carbon atoms, preferably 1 to 10 carbon atoms, and more preferably 1 to 5 carbon atoms.

[0120] R ８ Specific examples of the alkyl group include a methyl group, an ethyl group, an n-propyl group, an isopropyl group, an n-butyl group, an isobutyl group, a sec-butyl group, a tert-butyl group, an n-pentyl group, an n-hexyl group, an n-heptyl group, an n-octyl group, an n-nonyl group, an n-decyl group, an n-undecyl group, an n-dodecyl group, an n-tridecyl group, an n-tetradecyl group, and an n-pentadecyl group.

[0121] Specific examples of tetraalkoxysilanes include tetraethoxysilane, tetramethoxysilane, tetrapropoxysilane, tetraisopropoxysilane, and tetrabutoxysilane. Among these, tetraethoxysilane is preferred. Specific examples of tetraalkoxytitaniums include tetraethoxytitanium, tetrapropoxytitanium, tetraisopropoxytitanium, tetrabutoxytitanium, and tetraisobutoxytitanium. Among these, tetraethoxytitanium is preferred.

[0122] In the surface treatment agent, the ratio of tetraalkoxysilane and / or tetraalkoxytitanium to the silane coupling agent (i.e., alkylsilane coupling agent and aminoalkylsilane coupling agent) is preferably 1 / 99 or more and 70 / 30 or less by weight, i.e., the ratio of the tetraalkoxysilane-derived product (hereinafter sometimes referred to as the "silicate portion") and / or tetraalkoxytitanium-derived product (hereinafter sometimes referred to as the "titanate portion") to the alkylsilane coupling agent-derived product and the aminoalkylsilane coupling agent-derived product in the coating formed on the surface of the magnetic powder after surface treatment. As this ratio decreases, the silane coupling agent tends to peel off from the magnetic powder surface, and the toughness of the magnetorheological elastomer composition tends to decrease. If this ratio exceeds 70 / 30, the amount of amino groups becomes too small, and the toughness of the magnetorheological elastomer composition tends to decrease. This ratio is preferably 10 / 90 or more and 70 / 30 or less, more preferably 30 / 70 or more and 60 / 40 or less.

[0123] When determined based on the amount of surface treatment agent added based on the total weight of the magnetic powder and the surface treatment agent, the ratio of tetraalkoxysilane or tetraalkoxytitanium to silane coupling agent is, for example, 0.1 to 20, preferably 0.5 to 10, more preferably 0.8 to 5, and even more preferably 1 to 2.5.

[0124] Average particle size of magnetic powder (D ５０From the viewpoint of improving the physical toughness of the magnetorheological elastomer composition, the thickness is, for example, 0.8 μm or more and 50 μm or less, preferably 1 μm or more and 30 μm or less, and more preferably 5 μm or more and 20 μm or less.

[0125] Average particle size of magnetic powder (D ５０ ) can be measured and calculated by a laser diffraction / scattering method based on the Mie scattering theory. Specifically, the particle size distribution of the magnetic powder is created on a volume basis using a laser diffraction / scattering particle size distribution measuring device, and the 50% particle size (average particle size) (D ５０ ) can be calculated. A measurement sample that can be preferably used is one in which magnetic powder is dispersed in pure water using ultrasonic waves. As a laser diffraction scattering type particle size distribution measuring device, "MT3000II" manufactured by Microtrackbell, "LA-960" manufactured by Horiba, Ltd., "SALD-2200" manufactured by Shimadzu Corporation, etc. can be used.

[0126] Unless otherwise specified, the particle size of the magnetic powder in this specification is the average particle size (D ５０ ) means

[0127] Known magnetic powders include those having spherical three-dimensional shapes and those having non-spherical three-dimensional shapes. Non-spherical magnetic powders are magnetic powders having a three-dimensional shape other than spherical. Examples of non-spherical magnetic powders include magnetic powders having three-dimensional shapes such as flat, flat spherical, plate-like, scale-like, needle-like, columnar, polygonal, and polyhedral. The magnetic powder may be spherical magnetic powder, or may be a mixture of spherical and non-spherical magnetic powders. In a preferred embodiment, the magnetic powder is a mixture of spherical magnetic powder and flat magnetic powder, or a mixture of spherical magnetic powder and polyhedral magnetic powder.

[0128] The aspect ratio of the spherical magnetic powder is preferably 1.5 or less, more preferably 1.3 or less, and even more preferably 1.2 or less. The lower limit can be 1, for example.

[0129] The aspect ratio of the flat magnetic powder is preferably 7 or more and 15 or less, more preferably 10 or more and 13 or less, and even more preferably 10 or more and 11 or less.

[0130] The aspect ratio of the magnetic powder referred to in this specification is the value (a / b) calculated by dividing the "average major axis length a (μm) of the magnetic powder" by the "average thickness b (μm) of the magnetic powder." The average major axis length of the magnetic powder is the average value of the major axis lengths of the magnetic powder. The average value of the major axis length of the magnetic powder can be, for example, the number average when the major axis lengths of, for example, 50 magnetic powder particles are measured based on a scanning electron microscope image. The major axis length of the magnetic powder refers to the length of the line segment connecting any two points on the outer surface of the magnetic powder particle that are the longest distance apart.

[0131] When the shape of the magnetic powder is spherical or flattened spherical, the aspect ratio of the magnetic powder is the value (a / b) calculated by dividing the "average radial length a (μm) of the magnetic powder" by the "average thickness b (μm) of the magnetic powder."

[0132] A polyhedron refers to a three-dimensional shape having four or more flat faces, a face-to-face angle greater than 0° but less than 180°, and an edge-to-edge angle greater than 0° but less than 180°. Specific examples of polyhedra include tetrahedrons, hexahedrons, octahedrons, decahedrons, dodecahedrons, and tetradecahedrons. Among these, preferred polyhedra are hexahedrons and octahedrons. Specific examples of hexahedrons include hexahedrons having face-to-face angles of approximately 90° and edge-to-edge angles of approximately 90°. Specific examples of octahedrons include octahedrons having face-to-face angles of approximately 109° and edge-to-edge angles of approximately 60°.

[0133] When the connecting portions between the faces of the polyhedron are formed by curved surfaces, the angle between the faces can be the angle of the intersection of straight lines extrapolated from both planes. In one embodiment, there may be a case where a depression exists in a part of the polyhedron, and the angle between the faces constituting the downward convex shape is x degrees, which is greater than 180 degrees. In such a case, the angle between the faces may be set to (360-x) degrees in order to specify the polyhedron shape as the overall outline supplementing the downward convex shape.

[0134] It is believed that when a magnetic field is applied to a magnetorheological elastomer composition, the magnetic powder in the viscoelastic elastomer aligns along the magnetic field lines and stacks up in chains, forming numerous magnetic powder pillars, thereby increasing the hardness in the direction of the magnetic field lines.

[0135] When flat magnetic powder or polyhedral magnetic powder is used as the magnetic powder, or when these are mixed with spherical magnetic powder, the flat magnetic powder or polyhedral magnetic powder has flat surfaces, so when a magnetic field is applied, it is easy to form a structure in which the flat surfaces face each other and support each other, and it is thought that the hardness of the magnetic viscoelastic elastomer composition is easy to increase after the magnetic field is applied.

[0136] The content of the magnetic powder in the magnetorheological elastomer composition of the present invention is, for example, 25 to 55 volume %, preferably 35 to 50 volume %, and more preferably 40 to 45 volume %. When the content of the magnetic powder is within this range, the change in elastic modulus in response to a change in magnetic field can be favorable.

[0137] The content of the magnetic powder can be determined by applying heat (500° C. or higher) to the magnetorheological elastomer to remove the organic components, and then measuring the weight of the remaining magnetic powder.

[0138] [Method for Producing the Composition] The magnetorheological elastomer composition of the present invention can be produced by mixing a viscoelastic elastomer and a magnetic powder. Mixing the viscoelastic elastomer and the magnetic powder can include, for example, directly mixing the viscoelastic elastomer and the magnetic powder, or mixing the raw materials for the viscoelastic elastomer with the magnetic powder and then reacting the raw materials to form the viscoelastic elastomer. When mixing the viscoelastic elastomer and the magnetic powder, catalysts, plasticizers, and additives may be used as needed.

[0139] When a polyurethane elastomer is used as the viscoelastic elastomer, the magnetorheological elastomer composition can be produced by mixing a polyol, a polyisocyanate, and a magnetic powder, followed by heating to obtain a reaction product of the polyol and the polyisocyanate. The heating temperature can be 50°C or higher and 150°C or lower, and the heating time can be 30 minutes or higher and 20 hours or lower. The heating can be carried out without a solvent or in the presence of a reaction solvent. Examples of such a reaction solvent include toluene, acetone, and n-methylpyrrolidone.

[0140] The order of mixing the polyol, polyisocyanate, and magnetic powder is not particularly limited. For example, the polyol, polyisocyanate, and magnetic powder may be mixed simultaneously, or the polyol and magnetic powder may be mixed together and then the mixture may be mixed with the polyisocyanate. When mixing the polyol, polyisocyanate, and magnetic powder, a urethane catalyst, resin, plasticizer, and additives, which are used as needed, may be present as appropriate.

[0141] [Characteristics of the Composition] The magnetorheological elastomer composition has viscosity and elasticity.

[0142] The magnetorheological elastomer composition of the present invention has excellent toughness and exhibits a high breaking strain rate. The breaking strain rate refers to the percentage of elongation a material undergoes before breaking. The magnetorheological elastomer composition of the present invention exhibits a breaking strain rate of, for example, 850% or more, preferably 970% or more, more preferably 1100% or more, and even more preferably 1250% or more.

[0143] Storage modulus G' of the magnetorheological elastomer composition measured under zero magnetic field ０ The storage modulus of the magnetorheological elastomer composition may be preferably 0.002 MPa or more and 0.020 MPa or less, more preferably 0.004 MPa or more and 0.015 MPa or less, and even more preferably 0.005 MPa or more and 0.010 MPa or less. When the storage modulus of the magnetorheological elastomer composition is within this range, the change in the elastic modulus when a magnetic field is applied can be favorable.

[0144] The magnetorheological elastomer composition of the present invention can have an increased storage modulus when a magnetic field is applied compared to when a magnetic field is not applied. Specifically, the storage modulus G' measured under the conditions used in the following examples can be expressed as １ The storage modulus after application of a magnetic field may be preferably 1.0 MPa or more, more preferably 1.5 MPa or more, and even more preferably 2.0 MPa or more. When the storage modulus after application of a magnetic field is within this range, the propagation speed of compressional waves, particularly sound waves and ultrasonic waves, passing through the magnetorheological elastomer composition may be increased.

[0145] The rate of change in storage modulus due to application of a magnetic field (hereinafter simply referred to as "rate of change in storage modulus due to a magnetic field") is defined as G' １ / G'０ In this case, the rate of change in storage modulus due to a magnetic field of the magnetorheological elastomer composition of the present invention is preferably 100 or more, more preferably 150 or more, and even more preferably 290 or more, and may be, for example, 1000 or less, 800 or less, or even 500 or less. When the rate of change in storage modulus due to a magnetic field is within this range, compressional waves, particularly sound waves and ultrasonic waves, passing through the magnetorheological elastomer composition can be highly deflected.

[0146] The magnetorheological elastomer composition of the present invention can increase its storage modulus by application of a magnetic field, and can be suitably used to change the propagation direction of compressional waves such as sound waves, ultrasonic waves, and vibration waves (to deflect compressional waves). The propagation velocity c (m / s) of compressional waves is proportional to the square root of the elastic modulus of the propagation medium, and specifically, when the density is ρ (kg / m ３ ), and the bulk modulus is κ (Pa), it is expressed by the following formula.

[0147]

[0148] Therefore, when the elastic modulus is high, the propagation velocity of the compressional wave is high, and when the elastic modulus is low, the propagation velocity of the compressional wave is low. Although not limited to a specific theory, when a magnetic field is applied to the magnetorheological elastomer composition of the present invention, the increase in the storage modulus correlates with the direction of the magnetic field, and typically, the storage modulus increases in the direction parallel to the direction of the magnetic field. Therefore, it is thought that the application of a magnetic field causes anisotropy in the storage modulus, which can change the propagation direction of the compressional wave.

[0149] The magnetorheological elastomer composition of the present invention is preferably used to deflect sound waves or ultrasonic waves, and is particularly suitable for use in acoustic devices such as speakers and ultrasonic devices such as ultrasonic sensors. The magnetorheological elastomer composition of the present invention can also be used in tactile feedback devices that utilize changes in elastic modulus.

[0150] The present invention provides the following aspects: [Aspect 1] A magnetorheological elastomer composition comprising a viscoelastic elastomer and a magnetic powder dispersed in the viscoelastic elastomer, wherein the magnetic powder is surface-treated with a surface treatment agent containing an alkylsilane coupling agent and an aminoalkylsilane coupling agent. [Aspect 2] The magnetorheological elastomer composition according to Aspect 1, wherein the alkylsilane coupling agent is a compound represented by formula (1), and the aminoalkylsilane coupling agent is a compound represented by formula (2) or (3). [Aspect 3] The magnetorheological elastomer composition according to Aspect 1 or 2, wherein the ratio of the content of the alkylsilane coupling agent to the content of the aminoalkylsilane coupling agent in the surface treatment agent is, in terms of the weight ratio of the product derived from the alkylsilane coupling agent to the product derived from the aminoalkylsilane coupling agent in the coating formed on the surface of the magnetic powder after surface treatment, from 20 / 80 to 99 / 1, preferably from 30 / 70 to 5 / 15, more preferably from 40 / 60 to 80 / 20, and even more preferably from 50 / 50 to 70 / 30. [Aspect 4] The magnetorheological elastomer composition according to any one of Aspects 1 to 3, wherein the surface treatment agent further contains a tetraalkoxysilane or a tetraalkoxytitanium. [Aspect 5] The magnetorheological elastomer composition according to Aspect 4, wherein the ratio of the content of the tetraalkoxysilane or tetraalkoxytitanium to the content of the silane coupling agent (i.e., alkylsilane coupling agent and aminoalkylsilane coupling agent) in the surface treatment agent is 1 / 99 or more and 70 / 30 or less, preferably 10 / 90 or more and 70 / 30 or less, and more preferably 30 / 70 or more and 60 / 40 or less, in terms of the weight ratio of the product derived from the tetraalkoxysilane or tetraalkoxytitanium to the product derived from the silane coupling agent in the coating formed on the surface of the magnetic powder after surface treatment. [Aspect 6] The magnetorheological elastomer composition according to any one of Aspects 1 to 5, wherein the magnetic powder has an average particle size of 0.8 μm or more and 50 μm or less, preferably 1 μm or more and 30 μm or more and 5 μm or more and 20 μm or less.[Aspect 7] The magnetorheological elastomer composition according to any one of Aspects 1 to 6, wherein the viscoelastic elastomer comprises a polyurethane elastomer. [Aspect 8] The magnetorheological elastomer composition according to Aspect 7, wherein the polyurethane elastomer comprises a urethane resin that is a reaction product of a polyol containing a triol having a number average molecular weight of 1,000 or more, preferably 2,000 to 15,000, more preferably 3,000 to 10,000, and even more preferably 4,000 to 8,000, with a polyisocyanate. [Aspect 9] A method for producing a magnetorheological elastomer composition comprising a viscoelastic elastomer and a magnetic powder dispersed in the viscoelastic elastomer, wherein the magnetic powder is surface-treated with a surface treatment agent containing an alkylsilane coupling agent and an aminoalkylsilane coupling agent. [Aspect 10] The method for producing a magnetorheological elastomer composition according to Aspect 9, wherein the surface treatment agent further comprises a tetraalkoxysilane or a tetraalkoxytitanium.

[0151] The present invention will be explained in more detail with reference to the following examples, but the present invention is not limited to these examples.

[0152] <Experimental Example 1> Polypropylene glycol having a number average molecular weight of 4000, triol type (PPT), polypropylene glycol having a number average molecular weight of 3000, diol type (PPG), tolylene diisocyanate (TDI), dioctyl phthalate, and tin octoate were prepared as components of a polyurethane elastomer and charged into a reaction vessel in the amounts shown in Table 1.

[0153]

[0154] As the magnetic powders, spherical FeSiCr powder (manufactured by Epson Atmix) with an average primary particle size of 10 μm and an aspect ratio of 1, spherical FeSiCr powder (manufactured by JFEM) with an average primary particle size of 0.8 μm and an aspect ratio of 1, and spherical FeSiCr powder (manufactured by Epson Atmix) with an average primary particle size of 30 μm and an aspect ratio of 1 were prepared.

[0155] 30 g of any of the magnetic powders described above was added to 25 g of an isopropyl alcohol solution containing 3.1 g of 28 wt% aqueous ammonia, and the mixture was stirred to uniformly disperse the powder. 0.8 g of a surface treatment agent was added to the dispersion, and the mixture was stirred at room temperature (20°C) for 90 minutes to perform a surface treatment on the magnetic powder. The surface-treated magnetic powder was filtered out of the reaction solution, washed with acetone, dried at 80°C for 60 minutes, and then further dried at 250°C for 30 minutes.

[0156] Several types of surface treatment agents were prepared, varying the type and content of the components. Commercially available components were used. The type and content of the components of each surface treatment agent are shown in Table 2. The structures of the components of each surface treatment agent are shown in Tables 3 to 6.

[0157] [Surface Structure Analysis] The surface structure of the surface-treated magnetic powder was analyzed. The surface structure of the magnetic powder can be determined by measuring the mass spectrum of the coating using gas chromatography mass spectrometry (GC / MS, device: GCMS-QP2010plus (manufactured by Shimadzu Corporation)). As a result of the analysis, the surface abundance (wt%) of silicate moieties, titanate moieties, methyl group moieties, and amino group moieties was determined.

[0158] The surface-treated magnetic powder was added to the same reaction vessel in an amount equivalent to 25% by volume of the total magnetorheological elastomer composition. The contents were mixed uniformly using a degassing stirrer to obtain a paste. The paste was then heated at 75°C for 2 hours on a hot plate to be thermally cured, producing a magnetorheological elastomer composition.

[0159] [Measurement of Breaking Strain Rate] The breaking strain rate of the magnetorheological elastomer composition was measured. The breaking strain rate is the rate at which the material is elongated until it breaks. The breaking strain rate is an index showing the toughness of the material. The length after breaking is defined as L ｆ , initial length is L ０ Then, the breaking strain rate δ is expressed by the following formula: δ (%) = {(L ｆ -L ０ ) / L ０} x 100

[0160] The magnetorheological elastomer composition was molded into a rod (5 mm x 20 mm x 1 mm thick) to prepare a sample. The sample was then placed in a dynamic viscoelasticity measuring device (TA Instruments, model: RSA-G2) and the strain until the sample broke was measured to determine the breaking strain rate. The results are shown in Table 2.

[0161] (Measurement conditions for fracture strain rate) Measurement temperature: 25°C Tensile speed: 0.2 mm / s

[0162] (Evaluation criteria for breaking strain rate) A (Excellent): 1100% or more B (Good): 970% or more and less than 1100% C (Acceptable): 800% or more and less than 970% D (Unacceptable): Less than 800%

[0163]

[0164]

[0165]

[0166]

[0167]

[0168] The experimental results shown in Table 3 confirm that the magnetorheological elastomer composition containing magnetic powder surface-treated with a surface treatment agent containing an alkylsilane coupling agent and an aminoalkylsilane coupling agent has a high breaking strain rate and excellent toughness.

Claims

1. A magnetorheological elastomer composition comprising a viscoelastic elastomer and a magnetic powder dispersed in the viscoelastic elastomer, wherein the magnetic powder is surface-treated with a surface treatment agent containing an alkylsilane coupling agent and an aminoalkylsilane coupling agent.

2. The alkylsilane coupling agent is represented by the formula (R １ ) ａ Si(OR ２ ) ４－ａ (1) [wherein, R １ represents an alkyl group having 1 to 15 carbon atoms, R ２ represents an organic group, and a represents an integer of 1 or more and 3 or less.], and the aminoalkylsilane coupling agent contains a compound represented by the formula (NH ２ R ３ ) ｂ Si(OR ４ ) ４－ｂ (2) [wherein, R ３ represents an alkylene group having 1 to 15 carbon atoms, R ４ represents an organic group, and b represents an integer of 1 or more and 3 or less. ], or a group represented by the formula (NH ２ R ５ NHR ６ ) ｃ Si(OR ７ ) ４－ｃ (3) [wherein, R ５ represents an alkylene group having 1 to 15 carbon atoms, R ６ represents an alkylene group having 1 to 10 carbon atoms, R ７ represents an organic group, and c represents an integer of 1 or more and 3 or less. The magnetorheological elastomer composition according to claim 1 , comprising a compound represented by the formula:

3. A magnetorheological elastomer composition according to claim 1 or 2, wherein the ratio of the content of alkylsilane coupling agent to the content of aminoalkylsilane coupling agent in the surface treatment agent is 20 / 80 or more and 99 / 1 or less in terms of the weight ratio of the product derived from the alkylsilane coupling agent to the product derived from the aminoalkylsilane coupling agent in the coating formed on the surface of the magnetic powder after surface treatment.

4. The magnetorheological elastomer composition according to any one of claims 1 to 3, wherein the surface treatment agent further comprises at least one selected from the group consisting of tetraalkoxysilane and tetraalkoxytitanium.

5. The magnetorheological elastomer composition according to claim 4, wherein the ratio of the content of tetraalkoxysilane or tetraalkoxytitanium to the content of silane coupling agent (i.e., alkylsilane coupling agent and aminoalkylsilane coupling agent) in the surface treatment agent is 1 / 99 or more and 70 / 30 or less in weight ratio of the product derived from tetraalkoxysilane or tetraalkoxytitanium to the product derived from the silane coupling agent in the coating formed on the surface of the magnetic powder after surface treatment.

6. The magnetorheological elastomer composition according to any one of claims 1 to 5, wherein the magnetic powder has an average particle size of 0.8 μm or more and 50 μm or less.

7. The magnetorheological elastomer composition according to any one of claims 1 to 6, wherein the viscoelastic elastomer comprises a polyurethane elastomer.

8. The magnetorheological elastomer composition according to claim 7, wherein the polyurethane elastomer comprises a urethane resin which is a reaction product of a polyol containing a triol having a number average molecular weight of 1,000 or more and a polyisocyanate.

9. A method for producing a magnetorheological elastomer composition comprising a viscoelastic elastomer and a magnetic powder dispersed in the viscoelastic elastomer, wherein the magnetic powder has been surface-treated using a surface treatment agent containing an alkylsilane coupling agent and an aminoalkylsilane coupling agent.

10. The method for producing a magnetorheological elastomer composition according to claim 9, wherein the surface treatment agent further contains tetraalkoxysilane or tetraalkoxytitanium.

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