WO2024232139A1 - Magnetorheological elastomer composition - Google Patents

Abstract

The present invention addresses the problem of providing a magnetorheological elastomer composition having a large change in storage elastic modulus before and after the application of a magnetic field and a large storage elastic modulus after application of the magnetic field. The problem is resolved by a magnetorheological elastomer composition containing a viscoelastic elastomer and 25-55 vol% of magnetic powder dispersed in the viscoelastic elastomer, wherein the magnetic powder contains spherical magnetic powder and aspherical magnetic powder, and 3-60 mass% of the aspherical magnetic powder is contained based on the whole magnetic powder.

Description

Magnetorheological elastomer composition

The present invention relates to a magnetorheological elastomer composition.

Magnetic responsive materials, which are resin materials in which magnetic bodies are dispersed, are known as materials that can be used as vibration-proofing and damping materials and energy transmission materials.

Patent Document 1 describes a polyurethane elastomer composition that contains a reaction product of a polyol compound and a polyisocyanate compound, and magnetic particles, in which the polyol compound contains a propylene oxide adduct of bisphenol A, and the polyisocyanate compound is a polyisocyanate compound having an aromatic ring. It is described that the magnetically responsive material in Patent Document 1 is a highly elastic magnetic field responsive soft material with a large change in elastic modulus.

Patent Document 2 describes a magnetically responsive material in which non-spherical magnetic particles are dispersed in a viscoelastic material, and the non-spherical magnetic particles are oriented in the viscoelastic material. The non-spherical particles referred to here are particles having a shape other than a perfect sphere, and examples include plate-shaped and scale-shaped particles. It is described that the magnetically responsive material in Patent Document 2 has the property that the elastic modulus is significantly reduced after the application of a magnetic field compared to before the application.

JP 2019-210311 A JP 2008-195826 A

When considering using magnetically responsive materials as vibration-proofing and damping materials or energy transmission materials, taking advantage of the property that their elastic modulus changes depending on the strength of the applied magnetic field, there is a demand for the change in elastic modulus of magnetic material depending on the strength of the applied magnetic field, and for the elastic modulus itself to be increased when a magnetic field is applied.

The present invention aims to provide a magnetorheological elastomer composition (hereinafter sometimes referred to as an "MRE composition") that exhibits a large change in storage modulus before and after the application of a magnetic field. The present invention also aims to provide a magnetorheological elastomer composition that exhibits a large storage modulus after the application of a magnetic field.

The present invention provides a magnetorheological elastomer composition comprising a viscoelastic elastomer and a magnetic powder dispersed in the viscoelastic elastomer, the magnetic powder comprising a spherical magnetic powder and a non-spherical magnetic powder.

The present invention provides a magnetorheological elastomer composition that exhibits a large change in storage modulus before and after the application of a magnetic field. The present invention also provides a magnetorheological elastomer composition that exhibits a large storage modulus after the application of a magnetic field.

The following describes in detail an embodiment of the present invention, but the scope of the present invention is not limited to the embodiment described here, and various modifications can be made without departing from the spirit of the present invention. Furthermore, when multiple upper and lower limit values are listed for a particular parameter, any of these upper and lower limit values can be combined to create a suitable numerical range.

In this specification, viscoelastic elastomer means 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 understood to be a viscous material, if it is long, it is an elastic material, and if it is on the same scale, it is a viscoelastic material.

In addition, in this specification, a 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 inside a viscoelastic elastomer. The magnetorheological elastomer reversibly changes its apparent elastic modulus and damping characteristics in response to an external magnetic field.

Examples of viscoelastic elastomers include rubber, thermoplastic elastomers, and thermosetting elastomers such as polyurethane elastomers.

The rubber is not particularly limited, and examples thereof include natural rubber (NR), modified natural rubber, grafted 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; 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, methyl silicone rubber, vinyl-methyl silicone rubber, phenyl-methyl silicone 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, plasticizers, and softeners.

Thermoplastic elastomers are not particularly limited, and examples 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.

Among viscoelastic elastomers, thermosetting elastomers such as polyurethane elastomers are preferred from the viewpoint of increasing the change in elastic modulus of the magnetically responsive material before and after the application of a magnetic field. In this specification, polyurethane elastomer refers to an elastomer that contains a urethane resin. In general, urethane resin corresponds to the component that forms the polymer skeleton of polyurethane elastomers.

[Urethane resin]
In this specification, the urethane resin refers to a reaction product of a polyol and a polyisocyanate. A hydroxyl group contained in a polyol reacts with an isocyanate group contained in a polyisocyanate to form a urethane bond, thereby forming a urethane resin. The urethane resin may be a reaction product of a reaction product of a polyol and a polyisocyanate, and 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 a reaction product of a polyol compound and a polyisocyanate compound described in Patent Document 1.

Polyol means a compound having two or more hydroxyl groups in one molecule. It is preferable that the polyol includes a triol.

Triol refers to a compound that has three hydroxyl groups in one molecule. Each hydroxyl group in a triol reacts with the isocyanate group of a diisocyanate (described below) to form a urethane bond, so a triol contains a branching point (crosslinking point) where three molecular chains are bonded to one atom.

The cross-linking points (branching points) in the triol can be introduced by a compound (initiator) having three or more active hydrogen atoms. Examples of such initiators include glycerol, trimethylolethane, trimethylolpropane, trimellitic acid, and diethylenetriamine.

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 the above range, the molecular weight of the molecular chains bonded to the crosslinking points can be equal to or greater than a certain level. As a result, when the magnetic field strength is changed, the orientation of the magnetic powder can change without restriction, and it is believed that the change in the elastic modulus of the magnetorheological elastomer composition increases.

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

The triol may be, for example, a polyether triol, a polyester triol, a polycarbonate triol, a polyolefin triol, a polyacrylic triol, etc., and is preferably a polyether triol.

Polyether triol can be typically 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 2 to 4 carbon atoms, such as oxyethylene units, oxypropylene units, and oxytetramethylene units, and in particular, 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, polyoxyethylene-polyoxypropylene triol, and the like.

Oxyalkylene units can be formed by ring-opening polymerization of cyclic ethers such as ethylene oxide, propylene oxide, and tetrahydrofuran.

A polyester triol can be typically understood as a triol of a polymer having a repeating unit containing an ester bond. The unit containing an ester bond 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 can be a homopolymer containing one type of repeating unit, or a copolymer containing two or more types of repeating units.

The diol used as the raw material for polyester triol is typically a low molecular weight diol having a molecular weight of 50 or more and 300 or less. Specific examples 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 cyclic ethers to bisphenol compounds, and examples of such cyclic ethers include ethylene oxide, propylene oxide, and tetrahydrofuran.

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 the aliphatic dicarboxylic acids or aromatic dicarboxylic acids can be formed by reacting the aliphatic dicarboxylic acids or aromatic dicarboxylic acids with alcohols, and examples of such alcohols include aliphatic alcohols having 1 to 4 carbon atoms, such as methanol, ethanol, propanol, and butanol.

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 can be a homopolymer containing one type of repeating unit, or a copolymer containing two or more types of repeating units.

Carbonate esters, which are the raw materials for polycarbonate triol, include methyl carbonate, dimethyl carbonate, ethyl carbonate, diethyl carbonate, cyclohexyl carbonate, dicyclohexyl carbonate, diphenyl carbonate, etc.

The diol used as the raw material for polycarbonate triol may typically be a low molecular weight diol with a molecular weight of 50 to 300, or a high molecular weight diol with a number average molecular weight of more than 300.

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. Alkylene oxide adducts of bisphenol compounds can be formed by ring-opening polymerization of cyclic ethers to bisphenol compounds, and examples of such cyclic ethers include ethylene oxide, propylene oxide, and tetrahydrofuran.

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 high molecular weight diols is generally more than 300, preferably 400 to 5,000, more preferably 400 to 2,000.

Polyolefin triol can be understood as a triol of a polymer having units consisting of divalent hydrocarbon groups as repeating units. The units consisting of divalent hydrocarbon groups can be formed by polymerization of alkenes and dienes. Polyolefin triol can be a homopolymer containing one type of repeating unit, or a copolymer containing two or more types of repeating units.

Alkenes that are raw materials for polyolefin triols include ethylene, propylene, isobutene, etc., and dienes that are raw materials for polyolefin triols include butadiene, isoprene, etc.

Polyacrylic triol can be understood as a triol of a polymer having units derived from (meth)acrylic monomers as repeating units. Polyacrylic triol may be a homopolymer containing one type of repeating unit, or a copolymer containing two or more types of repeating units.

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

Examples of (meth)acrylic monomers having a hydroxyl group include hydroxyethyl (meth)acrylate, hydroxypropyl (meth)acrylate, and hydroxybutyl (meth)acrylate.

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.

Other vinyl monomers include styrene and methylstyrene.

The triol content 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.

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

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.

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 cyclic ethers to bisphenol compounds, and examples of such cyclic ethers include ethylene oxide, propylene oxide, and tetrahydrofuran.

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

Polyether diols can be typically understood as polymer diols having units containing ether bonds as repeating units, and the repeating units preferably contain oxyalkylene units. Examples of such oxyalkylene units include oxyalkylene units having 2 to 4 carbon atoms, such as oxyethylene units, oxypropylene units, and oxytetramethylene units, and in particular, 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, polyoxyethylene-polyoxypropylene triol, and the like.

Oxyalkylene units can be formed by ring-opening polymerization of cyclic ethers such as ethylene oxide, propylene oxide, and tetrahydrofuran.

A polyester diol can typically be understood as a polymer diol that has units containing ester bonds as repeating units.

Polycarbonate diol can typically be understood as a polymer diol that has units containing carbonate bonds (-O-CO-O-) as repeating units.

Polyolefin diols can typically be understood as polymer diols that have repeating units consisting of divalent hydrocarbon groups.

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

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 3,000.

The diol content 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, per 100 parts by mass of triol.

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.

In addition to triols and diols, the polyol may contain other polyols. Such other polyols may include triols with a molecular weight of less than 4,000, triols with four or more hydroxyl groups in one molecule, etc.

Polyisocyanate refers to a compound that has two or more isocyanate groups in one molecule. The number of isocyanate groups contained in one molecule of polyisocyanate is typically 2 to 4, and in particular 2 to 3.

Polyisocyanates include aliphatic polyisocyanates, aromatic polyisocyanates, alicyclic polyisocyanates, etc.

Aliphatic polyisocyanates include tetramethylene diisocyanate, 1,6-hexamethylene diisocyanate, dodecamethylene diisocyanate, trimethylhexamethylene diisocyanate, etc.

Aromatic polyisocyanates 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, and 1-methyl-3,5-diethylbenzene diisocyanate. , 3-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'-di Examples of isocyanates include 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, and xylylene diisocyanate.

Alicyclic polyisocyanates 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, 3,3'-dimethyl-4,4'-dicyclohexylmethane diisocyanate, etc.

When producing a urethane resin, the molar ratio [NCO/OH] of the isocyanate groups contained in the polyisocyanate 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.

A chain extender is a compound that has two or more active hydrogen atoms in one molecule, and is typically used to further react with the reaction product of a polyol and a polyisocyanate. By further reacting the reaction product of a polyol and a polyisocyanate with a chain extender, it becomes easier to obtain a high molecular weight urethane resin.

Chain extenders include chain extenders with amino groups and chain extenders with hydroxyl groups.

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, triethylenetetramine, etc.

Chain extenders having hydroxyl groups 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.

When a chain extender is included, the molar ratio [NCO/(H+OH)] of the isocyanate groups contained in the polyisocyanate 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.

A terminal terminator is a compound that has one active hydrogen atom per molecule, and is typically used to further react the reaction product of a polyol, a polyisocyanate, and an optional chain extender.

Terminator agents include alcohols such as hexanol, heptanol, octanol, nonanol, and undecanol; and amines such as dibutylamine.

The amount of the terminal terminator 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 polyisocyanate.

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 (branching points). Although it should not be interpreted as being limited to a particular theory, it is believed that when the molecular weight between crosslinks of the urethane resin is in this range, the magnetic powder can change its orientation without restriction when a magnetic field is applied, and the change in elastic modulus is increased.

The average molecular weight between crosslinking points can be controlled by the number average molecular weight of the triol, or if a diol is used, the number average molecular weight of the diol, the amount of triol and diol used, etc.

In one embodiment, the average molecular weight between crosslinking points can be calculated based on the following formula (1), where _M is the number average molecular weight of the i-functional polyol contained in the polyol, and _C is the molar fraction of the i-functional polyol in the total amount of the polyol.

In other words, if we assume 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 of functional groups of the polyol minus 2, then in the above formula (1), the total length of the polyol is divided by the total number of crosslinking points.

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. In other words, when the molecular weight between crosslinking points of the crosslinked rubber is Mc, the Poisson's ratio of the crosslinked rubber is μ, the density of the crosslinked rubber is 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:

In other words, in crosslinked rubber that does not contain impurities, the higher the molecular weight between crosslinks, the lower the elastic modulus of the crosslinked rubber.

The urethane resin can be produced by reacting a polyol, a polyisocyanate, and, if necessary, a chain extender and a terminal terminator. This reaction can be carried out without 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.

The content of 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.

[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.

[Plasticizer]
The polyurethane elastomer may contain a plasticizer in addition to the urethane resin, such as an aromatic dicarboxylic acid plasticizer, an aliphatic dicarboxylic acid plasticizer, a phosphoric acid plasticizer, or a trimellitic acid plasticizer.

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.

Aliphatic dicarboxylic acid plasticizers include adipic acid diesters such as dioctyl adipate, di-2-ethylhexyl adipate, isononyl adipate, and diisodecyl adipate; and sebacic acid diesters such as dioctyl sebacate, di-2-ethylhexyl sebacate, and diisononyl sebacate.

Phosphate-based plasticizers include phosphate esters such as trioctyl phosphate, tri-2-ethylhexyl phosphate, and tricresyl phosphate.

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.

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.

The plasticizer content is 35% by volume or more and 70% by volume or less, preferably 40% by volume or more and 60% by volume or less, and more preferably 45% by volume or more and 50% by volume or less, based on the entire composition. When the plasticizer content is within this range, the magnetorheological elastomer composition has an appropriate viscosity, and the orientation of the magnetic powder is more likely to change in response to changes in the magnetic field.

[Additives]
The polyurethane elastomer may contain additives in addition to the urethane resin and plasticizer, such as a urethane catalyst, an antioxidant, a light stabilizer, an impact resistance agent, an antistatic agent, a flame retardant, a preservative, an ultraviolet absorber, a viscosity modifier, a colorant, etc.

Urethanization catalysts are used in the reaction of polyols and polyisocyanates, and include tin compounds such as tin octoate, dibutyltin dichloride, dibutyltin oxide, and dibutyltin dilaurate; titanium compounds such as dibutyltitanium dichloride, tetrabutyl titanate, and butoxytitanium trichloride; zinc 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.

The amount of the urethane catalyst contained may be 0.01 parts by mass or more and 10 parts by mass or less per 100 parts by mass of the urethane resin.

[Magnetic powder]
The magnetic powder refers to a powder of a magnetic material that can change the direction or magnitude of its magnetic moment in response to a change in an external magnetic field. The magnetic material is typically a ferromagnetic material, and preferably a soft magnetic material.

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.

Such magnetic materials include Fe; 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.

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.

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.

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.

The coercivity, saturation magnetic flux density, and permeability of a magnetic material refer to the coercivity, saturation magnetic flux density, and permeability measured in bulk, and can typically be measured using a vibrating sample magnetometer.

Magnetic powders are known that have, for example, a spherical shape and a non-spherical shape. Non-spherical magnetic powders are magnetic powders that have a shape other than spherical. Examples of non-spherical magnetic powders include magnetic powders that have shapes such as flat, flattened spheres, plates, scales, needles, columns, and polygons. In the magnetic viscoelastic elastomer composition of the present invention, spherical magnetic powders and non-spherical magnetic powders are mixed and used.

When a magnetic field is applied to a magnetorheological elastomer composition, it is believed that the magnetic powder in the viscoelastic elastomer aligns itself along the magnetic field lines, stacking up in chains and forming numerous magnetic powder pillars, thereby increasing the hardness in the direction of the magnetic field lines.

If the magnetic powder consists only of spherical particles, the frictional force between the stacked magnetic powder particles is small and they move easily, and the pillars formed when a magnetic field is applied are easily distorted, and there is a limit to how much the hardness of the magnetorheological elastomer composition can be increased. On the other hand, if the magnetic powder consists only of non-spherical particles, the frictional force between the magnetic powder particles is large in the non-spherical parts and they move less easily, and when a magnetic field is applied, they are less likely to align in a chain shape, resulting in many incomplete pillars, and the hardness of the magnetorheological elastomer composition does not increase sufficiently.

In contrast, when the magnetic powder contains spherical magnetic powder and non-spherical magnetic powder, the spherical magnetic powder can be sandwiched between the non-spherical portions of multiple non-spherical magnetic powders, and the individual non-spherical magnetic powder particles move easily and tend to align in chains when a magnetic field is applied, forming many pillars containing non-spherical magnetic powder. Since the non-spherical magnetic powder has a large mutual frictional force, the pillars are less likely to distort, and as a result, it is believed that the hardness of the magnetic viscoelastic elastomer composition is sufficiently increased.

Among the non-spherical magnetic powders, flat magnetic powders, which have a large frictional force between the non-spherical portions, are preferred from the viewpoint of increasing the storage modulus after the application of a magnetic field. Among the flat magnetic powders, flat spherical magnetic powders are more preferred because they increase the change in storage modulus before and after the application of a magnetic field.

Flattened refers to a flat shape in which one dimension is smaller than the other dimensions. Flattened spherical refers to the shape obtained when a sphere is flattened. When viewed from the flattening direction, the flattened spherical shape is a rectangle of a certain thickness with rounded edges, and when viewed from a direction perpendicular to the flattening direction, it is a circle. In reality, the shape viewed from the flattening direction may have uneven thickness and variation, and the shape viewed from the flattening direction may be approximately circular or approximately elliptical with minute irregularities on the outer periphery. For example, WO 2020/179535 describes the properties, characteristics, and manufacturing method of flattened spherical magnetic powder. The descriptions in this publication regarding flattened spherical magnetic powder are incorporated herein by reference.

The average particle size (D ₅₀ ) of the spherical magnetic powder is, for example, 0.5 μm to 50 μm, preferably 1 μm to 25 μm, and more preferably 3 μm to 10 μm, from the viewpoint of increasing the storage modulus after application of a magnetic field.

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, and the lower limit can be, for example, 1.

The average particle size (D ₅₀ ) of the flat magnetic powder is, for example, 2 μm to 100 μm, preferably 5 μm to 70 μm, and more preferably 10 μm to 40 μm, from the viewpoint of increasing the storage modulus after application of a magnetic field.

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.

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

Unless otherwise specified, the particle size of the magnetic powder referred to in this specification means the average particle size (D ₅₀ ).

The aspect ratio of magnetic powder as referred to in this specification is the value (a/b) calculated by dividing the "average major axis length a (μm) of magnetic powder" by the "average thickness b (μm) of magnetic powder." The average major axis length of magnetic powder is the average value of the major axis lengths of magnetic powder. The average value of the major axis length of 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 magnetic powder refers to the length of the line segment connecting any two points on the outer surface of a magnetic powder particle that are the longest distance apart.

If 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 of the magnetic powder a (μm)" by the "average thickness of the magnetic powder b (μm)."

The mixing ratio of the spherical magnetic powder to the non-spherical magnetic powder is such that the non-spherical magnetic powder accounts for 3% by mass or more and 60% by mass or less, preferably 5% by mass or more and 45% by mass or less, and more preferably 10% by mass or more and 30% by mass or less, based on the total magnetic powder. By adjusting the mixing ratio of the spherical magnetic powder to the non-spherical magnetic powder within the above range, it becomes easier to increase the storage modulus of the magnetorheological elastomer composition after application of a magnetic field.

The magnetic powder may be a powder having an insulating coating on its surface. Examples of such insulating coatings include inorganic glass coatings, organic polymer coatings, organic-inorganic hybrid coatings, and inorganic insulating coatings formed by the sol-gel reaction of metal alkoxides.

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

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

[Production method of the composition]
The magnetic viscoelastic elastomer composition of the present invention can be produced by mixing a viscoelastic elastomer and a magnetic powder. The mixing of the viscoelastic elastomer and the magnetic powder can include, for example, mixing the viscoelastic elastomer and the magnetic powder as they are, or mixing the raw materials of 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, a catalyst, a plasticizer, and an additive used as necessary may be appropriately present.

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, and then heating the mixture 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 reaction solvents include toluene, acetone, and n-methylpyrrolidone.

The order in which the polyol, polyisocyanate and magnetic powder are mixed 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 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 necessary, may be appropriately present.

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

The storage modulus _G'0 of the magnetorheological elastomer composition measured under zero magnetic field can 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 in this range, the change in modulus when a magnetic field is applied can be favorable.

The magnetorheological elastomer composition of the present invention may have an increased storage modulus when a magnetic field is applied, compared to when no magnetic field is applied. Specifically, the storage modulus _G'1 measured under the conditions used in the following examples 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.

When the rate of change in storage modulus due to application of a magnetic field (hereinafter also simply referred to as "rate of change in storage modulus due to a magnetic field") is taken as _G'1 / _G'0 , the rate of change in storage modulus due to a magnetic field of the magnetorheological elastomer composition of the present invention is preferably at least 100, more preferably at least 150, even more preferably at least 290, and may be, for example, at most 1000, or at most 800, or even at most 500. 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.

The magnetorheological elastomer composition of the present invention can increase its storage modulus by application of a magnetic field, and can be suitably used for changing the propagation direction of compressional waves (deflecting compressional waves) such as sound waves, ultrasonic waves, vibration waves, etc. The propagation speed c (m/s) of a compressional wave 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 (2):

Therefore, when the elastic modulus is high, the propagation speed of the compressional wave is high, and when the elastic modulus is low, the propagation speed of the compressional wave is low. Although it should not be interpreted as being 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 a 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 result in a change in the propagation direction of the compressional wave.

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.

The present invention provides the following aspects:

[1] A magnetorheological elastomer composition comprising a viscoelastic elastomer and 25% by volume or more and 55% by volume or less, preferably 35% by volume or more and 50% by volume or less, more preferably 40% by volume or more and 45% by volume or less, of a magnetic powder dispersed in the viscoelastic elastomer,
The magnetic powder includes spherical magnetic powder and non-spherical magnetic powder,
The non-spherical magnetic powder is contained in an amount of 3% by mass or more and 60% by mass or less, preferably 5% by mass or more and 45% by mass or less, and more preferably 10% by mass or more and 30% by mass or less, based on the total amount of the magnetic powder.
Magnetorheological elastomer composition.

[2] The magnetorheological elastomer composition of embodiment [1], wherein the non-spherical magnetic powder includes a flat magnetic powder.

[3] The flat magnetic powder has an aspect ratio a/b, which indicates the ratio of the average radial length a to the average thickness b in the thickness direction, of 10 to 20, preferably 7 to 15, more preferably 10 to 13, and even more preferably 10 to 11. The magnetorheological elastomer composition of embodiment [2].

[4] The magnetic viscoelastic elastomer composition of aspect [2] or [3], wherein the spherical magnetic powder has an average particle size of 0.5 μm or more and 50 μm or less, preferably 1 μm or more and 25 μm or less, more preferably 3 μm or more and 10 μm or less, and the flat spherical magnetic powder has an average particle size of 2 μm or more and 100 μm or less, preferably 5 μm or more and 70 μm or less, more preferably 10 μm or more and 40 μm or less.

[5] The magnetorheological elastomer composition according to any one of embodiments [1] to [4], wherein the viscoelastic elastomer comprises a polyurethane elastomer.

[6] The magnetorheological elastomer composition of aspect [5], wherein the polyurethane elastomer comprises a urethane resin that is a reaction product of a polyol, including 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, and a polyisocyanate.

[7] A method for producing a magnetorheological elastomer composition comprising a viscoelastic elastomer and 25% by volume or more and 55% by volume or less, preferably 35% by volume or more and 50% by volume or less, more preferably 40% by volume or more and 45% by volume or less of a magnetic powder dispersed in the viscoelastic elastomer, comprising the steps of:
The magnetic powder contains spherical magnetic powder and non-spherical magnetic powder, and the non-spherical magnetic powder is contained in an amount of 3 mass% to 60 mass%, preferably 5 mass% to 45 mass%, and more preferably 10 mass% to 30 mass%, based on the total amount of the magnetic powder.
A method for producing a magnetorheological elastomer composition comprising:

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

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

As the magnetic powder, spherical FeSiCr powder (manufactured by Epson Atomics, no product name) with a particle size of 10 μm and an aspect ratio of 1 was prepared and filled into the same reaction vessel in an amount that was 25% by volume based on the total magnetic viscoelastic elastomer composition.

The filling materials were mixed uniformly using a degassing mixer to obtain a paste. The resulting paste was heated to 75°C for 2 hours using a hot plate and thermally cured to produce a magnetorheological elastomer composition.

<Experimental Examples 2 to 10>
As the magnetic powder, FeSiCr powder of the type shown in Table 2 was prepared.

A magnetic viscoelastic elastomer composition was produced in the same manner as in Experimental Example 1, except that spherical FeSiCr powder and flat spherical FeSiCr powder of the specified particle sizes shown in Table 2 were used in the specified ratio instead of the spherical FeSiCr powder.

The storage modulus was measured for the magnetorheological elastomer compositions of Experimental Examples 1 to 10.

[Measurement of storage modulus]
The magnetorheological elastomer composition was molded into a disk shape with a diameter of 2 cm and a thickness of 1 mm to prepare a sample. The sample was then set in a viscoelasticity measuring device (Anton Paar, model: MCR301), and the storage modulus was measured before and after application of a magnetic field using a magnetic field generator (Anton Paar, model: PS-MRD). The measurement was performed with the rotation axis of the viscoelasticity measuring device parallel to the direction of the magnetic field. The results are shown in Table 3.

(Conditions for viscoelasticity measurement)
Measurement temperature: 25°C
Load applied to the sample from the terminal: 0.3 N
Frequency: 1Hz
Strain: 0.01%
Magnetic field strength when applying magnetic field: 500 mT

The experimental results shown in Table 3 confirmed that the magnetorheological elastomer composition satisfying the constituent requirements of the present invention exhibited a larger change in storage modulus before and after application of a magnetic field, and a larger storage modulus after application of a magnetic field, compared to experimental examples that did not satisfy the requirements.

Claims (7)

A magnetorheological elastomer composition comprising a viscoelastic elastomer and 25% by volume or more and 55% by volume or less of a magnetic powder dispersed in the viscoelastic elastomer,
The magnetic powder includes spherical magnetic powder and non-spherical magnetic powder,
The non-spherical magnetic powder is contained in an amount of 3% by mass or more and 60% by mass or less based on the total amount of the magnetic powder.
A magnetorheological elastomer composition. The magnetorheological elastomer composition according to claim 1, wherein the non-spherical magnetic powder includes a flat magnetic powder. The magnetic viscoelastic elastomer composition according to claim 1 or 2, wherein the flat magnetic powder has an aspect ratio a/b, which indicates the ratio of the average major axis length a to the average thickness b, of 10 or more and 20 or less. The magnetic viscoelastic elastomer composition according to any one of claims 1 to 3, wherein the spherical magnetic powder has an average particle size of 0.5 μm or more and 50 μm or less, and the flat magnetic powder has an average particle size of 2 μm or more and 100 μm or less. The magnetorheological elastomer composition according to any one of claims 1 to 4, wherein the viscoelastic elastomer comprises a polyurethane elastomer. The magnetorheological elastomer composition according to claim 5, wherein the polyurethane elastomer contains 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 and a polyisocyanate. A method for producing a magnetorheological elastomer composition comprising a viscoelastic elastomer and 25% by volume or more and 55% by volume or less of a magnetic powder dispersed in the viscoelastic elastomer, comprising:
The magnetic powder contains spherical magnetic powder and non-spherical magnetic powder, and the non-spherical magnetic powder is contained in an amount of 3% by mass or more and 60% by mass or less based on the total amount of the magnetic powder.
A method for producing a magnetorheological elastomer composition comprising: