Metal powder for magnetorheological elastomer and magnetorheological elastomer composition

Abstract

To provide a magneto-rheological elastomer composition having excellent dispersibility of magnetic metal particles and having a wide range of change in elastic modulus before and after application of a magnetic field, and a metal powder for a magneto-rheological elastomer capable of manufacturing the same.SOLUTION: A metal powder for a magneto-rheological elastomer includes magnetic metal particles with coercive force of 11 [Oe] (875 [A / m]) or less, and a coating film provided on the surface of the magnetic metal particles and containing a compound derived from a silane coupling agent composed of a branched silicone compound, and it is preferable to further have a silica film containing silicon oxide located between the magnetic metal particles and the coating film.SELECTED DRAWING: Figure 2

Description

Technical Field

[0001] The present invention relates to a metal powder for a magnetorheological elastomer and a magnetorheological elastomer composition.

Background Art

[0002] Patent Document 1 discloses a magnetorheological elastomer composition containing a matrix resin and magnetic powder. Among these, soft magnetic metal powder with an average particle diameter of 2 to 10 μm is used for the magnetic powder. Further, the surface of the magnetic powder is surface-treated with alkoxysilane.

[0003] According to such a magnetorheological elastomer composition, the change in the storage elastic modulus when a magnetic field is applied becomes large. Thereby, the vibration damping effect when the magnetorheological elastomer composition is used in a vibration absorber is enhanced.

Prior Art Documents

Patent Documents

[0004]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0005] In the magnetorheological elastomer composition described in Patent Document 1, when a magnetic field is applied, the magnetic powder is magnetized. And, considering its use, it is desirable that the magnetorheological elastomer composition exhibits magnetism when a magnetic field is applied and is substantially non-magnetic when no magnetic field is applied. However, in the magnetorheological elastomer composition described in Patent Document 1, even when a magnetic field is applied and then the application of the magnetic field is stopped, it is difficult to become a non-magnetic state. For this reason, the magnetorheological elastomer composition described in Patent Document 1 has a problem that the change width of the elastic modulus is not sufficient before and after the application of the magnetic field.

Means for Solving the Problems

[0006] The metal powder for a magnetorheological elastomer according to an application example of the present invention is magnetic metal particles having a coercive force of 11 [Oe] (875 [A / m]) or less, and a coating film provided on the surface of the magnetic metal particles and containing a compound derived from a silane coupling agent composed of a branched silicone compound, and is characterized by having the above.

[0007] The magnetorheological elastomer composition according to an application example of the present invention is the metal powder for a magnetorheological elastomer according to an application example of the present invention, and a matrix resin, and is characterized by having the above.

Brief Description of Drawings

[0008]

Figure 1

Figure 2

Figure 3

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Figure 8

Figure 9

Embodiments for Carrying out the Invention

[0009] Hereinafter, preferred embodiments of the metal powder for magnetorheological elastomers and the magnetorheological elastomer composition of the present invention will be described in detail with reference to the accompanying drawings.

[0010] First, the magnetorheological elastomer composition according to the embodiment will be described. FIG. 1 is a cross-sectional view schematically showing a magnetorheological elastomer composition 1 according to an embodiment. The magnetorheological elastomer composition 1 shown in FIG. 1 includes magnetic powder 2 and matrix resin 3. The magnetic powder 2 is dispersed in the matrix resin 3.

[0011] The magnetic powder 2 is the metal powder for magnetorheological elastomers according to the embodiment. FIG. 2 is a cross-sectional view schematically showing the particles of the magnetic powder 2 (the metal powder for magnetorheological elastomers according to the embodiment) shown in FIG. 1.

[0012] The magnetic powder 2 (the metal powder for magnetorheological elastomers according to the embodiment) shown in FIG. 2 includes magnetic metal particles 21 and a coating film 23. The magnetic metal particles 21 have a coercive force of 11 [Oe] (875 [A / m]) or less and are made of a soft magnetic metal material. The coating film 23 is provided on the surface of the magnetic metal particles 21 and contains a compound derived from a silane coupling agent composed of a branched silicone compound.

[0013] The magnetic powder 2 having particles with such a configuration contributes to the realization of the magnetorheological elastomer composition 1 having a large change width in elastic modulus before and after applying a magnetic field, which will be described in detail later. Further, in the magnetic powder 2, aggregation of the particles is suppressed by the coating film 23. Furthermore, the coating film 23 contains an organic compound 24 derived from a silane coupling agent composed of a branched silicone compound. Since the molecular structure of this organic compound 24 includes a branched structure, it has molecular chains protruding from the particle surface of the magnetic powder 2 and is likely to entangle with the matrix resin 3. As a result, the magnetic powder 2 is likely to be fixed to the matrix resin 3, and the dispersibility of the magnetic powder 2 is enhanced.

[0014] In addition, the magnetic powder 2 shown in FIG. 2 further has a silica film 22. The silica film 22 is provided between the magnetic metal particles 21 and the coating film 23 and is a film containing silicon oxide. Hereinafter, the magnetorheological elastomer composition 1 will be described in more detail.

[0015] 1. Magnetic powder As described above, each particle of the magnetic powder 2 has the magnetic metal particle 21 and the silica film 22 and the coating film 23 provided on its surface.

[0016] 1.1. Magnetic metal particles As described above, the coercive force of the magnetic metal particles 21 is 11 [Oe] (875 [A / m]) or less. Since such magnetic metal particles 21 with a low coercive force have a small residual magnetization, they are hardly magnetized when no magnetic field is applied, but are magnetized as the magnetic field is applied, so they have high followability of magnetization to changes in the magnetic field. Therefore, the magnetorheological elastomer composition 1 having the magnetic metal particles 21 is excellent in responsiveness to changes in the magnetic field. In addition, since such magnetic metal particles 21 with a low coercive force are less likely to aggregate when no magnetic field is applied, they are excellent in positional followability to changes in the magnetic field and can be dispersed in the matrix resin 3 at a high concentration and uniformly. Therefore, the magnetorheological elastomer composition 1 having the magnetic metal particles 21 has a large change width in elastic modulus before and after applying a magnetic field.

[0017] Such a magnetorheological elastomer composition 1 can be applied in various ways by utilizing a large change in elastic modulus accompanying a change in magnetic field. For example, the magnetorheological elastomer composition 1 can be used for a damper whose damping force can be adjusted. The magnetorheological elastomer composition 1 with a large change width in elastic modulus before and after applying a magnetic field contributes to widening the adjustment range of the damping force when used as a damper. Therefore, a damper with a wide dynamic range capable of switching the strength of the damping force can be realized.

[0018] The coercive force of the magnetic metal particles 21 is preferably 5 [Oe] (398 [A / m]) or less, more preferably 3 [Oe] (239 [A / m]) or less. Incidentally, the coercive force of the magnetic metal particles 21 is measured using, for example, a vibrating sample magnetometer (VSM).

[0019] Examples of the constituent material of the magnetic metal particles 21 include Fe-based metal materials, Ni-based metal materials, Co-based metal materials, etc., and a composite material of one or more of these is used. Also, a composite material of these metal-based magnetic materials and oxide-based magnetic materials may be used. Among these, an Fe-based metal material with a large saturation magnetization is preferably used as the constituent material of the magnetic metal particles 21.

[0020] The Fe-based metal material is a metal material mainly composed of Fe. The main component means that the content of Fe in the Fe-based metal material is 50% or more in atomic ratio. Such an Fe-based metal material has a larger saturation magnetization, toughness, and strength compared to ferrite, etc. Therefore, the Fe-based metal material is useful as the constituent material of the magnetic metal particles 21.

[0021] In addition to Fe, the Fe-based metal material may contain an element that exhibits ferromagnetism alone, such as Ni or Co, and may contain at least one selected from the group consisting of Cr, Nb, Cu, Al, Mn, Mo, Si, Sn, B, C, P, Ti, and Zr according to the target characteristics. Further, the Fe-based metal material may contain inevitable impurities as long as the effects of the embodiments are not impaired.

[0022] Inevitable impurities are impurities that are unintentionally mixed in during raw material or manufacturing. Examples of inevitable impurities include O, N, S, Na, Mg, K, etc.

[0023] Such Fe-based metal materials are not particularly limited, and examples include pure iron, carbonyl iron, and in addition, Fe-Si-Al-based alloys such as Sendust, Fe-Ni-based, Fe-Co-based, Fe-Ni-Co-based, Fe-Si-B-based, Fe-Si-B-C-based, Fe-Si-B-Cr-C-based, Fe-Si-Cr-based, Fe-B-based, Fe-P-C-based, Fe-Co-Si-B-based, Fe-Si-B-Nb-based, Fe-Si-B-Nb-Cu-based, Fe-Zr-B-based, Fe-Cr-based, Fe-Cr-Al-based Fe-based alloy materials, etc.

[0024] Also, the constituent material of the magnetic metal particles 21 may be an amorphous metal material, a crystalline metal material, or a microcrystalline (nanocrystalline) metal material. Among these, an amorphous metal material or a microcrystalline metal material is preferably used. Note that a microcrystalline metal material refers to a metal material in which microcrystals (nanocrystals) having a crystal grain size of 100 nm or less are present. Since these have higher toughness and strength than, for example, metal oxides, etc., wear, defects, etc. of the magnetic metal particles 21 can be effectively suppressed.

[0025] Examples of amorphous metal materials include binary or multi-component Fe-based amorphous alloys such as Fe-Si-B, Fe-Si-B-C, Fe-Si-B-Cr-C, Fe-Si-Cr, Fe-B, Fe-B-C, Fe-P-C, Fe-Co-Si-B, Fe-Si-B-Nb, and Fe-Zr-B; Ni-based amorphous alloys such as Ni-Si-B and Ni-P-B; Co-based amorphous alloys such as Co-Si-B; and the like.

[0026] Examples of microcrystalline metal materials include Fe-based nanocrystalline alloys such as Fe-Si-B-Nb-Cu, Fe-Zr-B, Fe-Hf-B, Fe-Nb-B, Fe-Zr-B-Co, Fe-Hf-B-Co, Fe-Nb-B-Co, and Fe-Si-B-P-Cu.

[0027] The magnetic metal particles 21 may be particles produced by any method. Examples of production methods include various atomization methods such as water atomization, gas atomization, and rotary water flow atomization, as well as pulverization methods and carbonyl methods. Among these, according to the atomization method, magnetic metal particles 21 with a particle shape closer to a perfect sphere can be obtained. Such magnetic metal particles 21 are less likely to aggregate.

[0028] The average particle diameter of the magnetic metal particles 21 is preferably 0.5 μm or more and 100 μm or less, more preferably 1.0 μm or more and 50 μm or less, and even more preferably 1.0 μm or more and 20 μm or less. If the average particle diameter of the magnetic metal particles 21 is within the above range, while suppressing the aggregation of the magnetic metal particles 21, the mass of the magnetic metal particles 21 can be made sufficiently small, so that the magnetic metal particles 21 can be prevented from sedimenting in the matrix resin 3 due to their own weight.

[0029] In addition, if the average particle diameter of the magnetic metal particles 21 is less than the lower limit value, depending on the constituent material of the magnetic metal particles 21, there is a risk that the magnetic powder 2 is likely to agglomerate. On the other hand, if the average particle diameter of the magnetic metal particles 21 exceeds the upper limit value, depending on the constituent material of the magnetic metal particles 21, there is a risk that the magnetic metal particles 21 settle and are unevenly distributed in the matrix resin 3.

[0030] The average particle diameter of the magnetic metal particles 21 is determined as the particle diameter D50 at which the cumulative value reaches 50% from the smaller diameter side in the volume-based particle size distribution obtained by the laser diffraction method.

[0031] 1.2. Silica film The silica film 22 is a film provided on the surface of the magnetic metal particles 21. The silica film 22 is interposed between the magnetic metal particles 21 and the coating film 23, and enhances the adhesion of the coating film 23 to the magnetic metal particles 21. In addition, by protecting the magnetic metal particles 21, the silica film 22 can enhance the moisture absorption resistance and rust prevention properties of the magnetic metal particles 21.

[0032] The constituent material of the silica film 22 may be any material containing silicon oxide. Examples of silicon oxide include SiO, SiO2, Si2O3, Si2O, Si3O, or a mixture of two or more of these. Specific materials include, for example, silica, silicon-containing glass, diatomaceous earth, and the like.

[0033] The average thickness of the silica film 22 is preferably 1 nm or more and 500 nm or less, more preferably 3 nm or more and 300 nm or less, and even more preferably 20 nm or more and 100 nm or less. If the average thickness of the silica film 22 is within the above range, while ensuring the effect of enhancing the adhesion of the coating film 23, it is possible to avoid the silica film 22 becoming thicker than necessary. Thereby, while suppressing the agglomeration of the magnetic powder 2, it is possible to suppress the deterioration of the magnetic properties of the magnetic powder 2.

[0034] The average thickness of the silica film 22 is a value obtained by observing the cross section of the particles of the magnetic powder 2 with an electron microscope and averaging the film thicknesses of the silica film 22 at 10 or more locations.

[0035] The method for forming the silica film 22 is not particularly limited, and examples thereof include wet film-forming methods such as the sol-gel method including the Stöber method, vapor-phase film-forming methods such as ALD (Atomic Layer Deposition), CVD (Chemical Vapor Deposition), and ion plating. Among these, the sol-gel method, particularly the Stöber method, is useful because the silica film 22 can be formed at low cost and uniformly.

[0036] The Stöber method is a technique for forming the silica film 22 by hydrolysis of silicon alkoxide. As the silicon alkoxide, for example, TEOS (tetraethoxysilane, Si(OC2H5)4) is preferably used.

[0037] Note that the silica film 22 may be provided as necessary and may be omitted. Further, instead of the silica film 22, a film made of various ceramic materials may be provided. As the ceramic material, for example, an oxide-based ceramic material containing one or more elements selected from the group consisting of Al, Ti, V, Nb, Cr, Mn, Sn, and Zr is preferably used. Oxides containing such elements can improve the moisture absorption resistance and rust prevention properties of the magnetic metal particles 21. Further, this film may be composed of a composite material of a plurality of ceramic materials, for example, a composite of silica and an oxide containing one or more elements selected from the group consisting of Al, Ti, V, Nb, Cr, Mn, Sn, and Zr.

[0038] As described above, the magnetic powder 2 (metal powder for the magnetorheological elastomer according to the embodiment) is located between the magnetic metal particles 21 and the coating film 23 and further has a silica film 22 containing silicon oxide.

[0039] According to such a configuration, the adhesion of the coating film 23 to the magnetic metal particles 21 can be enhanced. Thereby, the dispersibility of the magnetic powder 2 can be further enhanced. Further, the silica film 22 can enhance the moisture resistance and rust prevention properties of the magnetic metal particles 21 by protecting the magnetic metal particles 21. Thereby, the magnetic properties of the magnetic metal particles 21 can be stabilized over a long period of time.

[0040] 1.3. Coating film The coating film 23 covers the surface of the magnetic metal particles 21 via the silica film 22. Thereby, the dispersibility of the magnetic powder 2 in the matrix resin 3 can be enhanced.

[0041] The constituent material of the coating film 23 contains an organic compound 24 derived from a silane coupling agent containing a branched silicone compound. The silane coupling agent is an organosilicon compound having an organic reactive group and a hydrolyzable group. By using the silane coupling agent, an organic reactive group can be disposed on the surface of the silica film 22. By providing such a coating film 23, aggregation of the magnetic powder 2 particles can be suppressed. Thereby, it is possible to realize a magnetic powder 2 that is excellent in position followability with respect to changes in the magnetic field and can be dispersed uniformly at a high concentration in the matrix resin 3.

[0042] Further, since the branched silicone compound has a branched molecular chain, it has a characteristic that the molecular structure is bulky. Therefore, the organic compound 24 derived from the branched silicone compound is entangled with the matrix resin 3 at the branched site, so that the magnetic powder 2 is likely to be dispersed and held with respect to the molecular chain of the matrix resin 3. Thereby, uneven distribution of the magnetic powder 2 due to its own weight or the like is suppressed, and the dispersibility of the magnetic powder 2 in the matrix resin 3 is enhanced.

[0043] Furthermore, the coating film 23 also contributes to enhancing the moisture resistance, rust prevention property, etc. of the magnetic powder 2. By enhancing the moisture resistance and rust prevention property, deterioration of the magnetic powder 2 due to moisture absorption and rusting can be suppressed.

[0044] The branched silicone compound is not particularly limited as long as it is a compound having a silicone main chain and side chains branched from the silicone main chain.

[0045] For example, as the branched silicone compound, a compound represented by the following formula (1) is preferably used.

[0046] [Chemical formula] [In the formula, R 1 and R 2 are each independently an alkyl group having 1 to 8 carbon atoms, which may be the same or different from each other, and R 3 is a group represented by the following general formula (2)

[0047] [Chemical formula] (R 5 and R 6 are each independently an alkyl group having 1 to 8 carbon atoms, which may be the same or different from each other, and r and s are positive integers such that their sum is 1 or more and 1000 or less.) and R 4 is a group represented by the following general formula (3)

[0048] [Chemical formula] (R 7 each independently represents an alkyl group having 1 to 5 carbon atoms.) and n and m are integers such that their sum is 0 or more and 1000 or less, and p and q are each an integer of 1 or more and 1000 or less.] In addition, the general formulas (1) to (3) include not only the compounds and functional groups having the structures shown in the general formulas (1) to (3), but also their structural isomers and stereoisomers.

[0049] Since such a branched silicone compound has a particularly bulky molecular structure, the concentration of silicone in the vicinity of the surface of the particles of the magnetic powder 2 can be further increased. As a result, molecular chains can be arranged at a high density on the surface of the particles of the magnetic powder 2. Consequently, the dispersibility of the magnetic powder 2 in the matrix resin 3 can be particularly enhanced. Further, since the side chains branching from the silicone main chain, particularly the side chains represented by the general formula (2), are rich in hydrophobicity, the affinity between the magnetic powder 2 and the matrix resin 3 is increased. Thereby, the dispersibility of the magnetic powder 2 in the matrix resin 3 can be further enhanced.

[0050] In the general formula (1), the sum of n and m is preferably 0 or more and 500 or less. Further, in the general formula (1), p and q are each preferably 1 or more and 500 or less. Furthermore, in the general formula (2), the sum of r and s is preferably 1 or more and 500 or less.

[0051] Specific examples of the branched silicone compound represented by the general formula (1) include triethoxysilylethylpolydimethylsiloxylethyldimethylcon, triethoxysilylethylpolydimethylsiloxylethylhexyldimethylcon, and the like. Specific examples of other such branched silicone compounds include acrylates / tridecyl acrylate / triethoxysilylpropyl methacrylate / dimethylcon methacrylate) copolymer), triethoxycaprylylsilane, and the like.

[0052] The weight-average molecular weight of the branched silicone compound is not particularly limited, but is preferably 150 or more and 1800 or less, more preferably 300 or more and 1200 or less, and even more preferably 450 or more and 900 or less. If the weight-average molecular weight of the branched silicone compound is within the above range, the coating film 23 coats the surface of the magnetic metal particles 21 more uniformly, and a necessary and sufficient length is ensured for the side chains. As a result, the branched silicone compound and the matrix resin 3 included in the magnetic powder 2 are more likely to be intertwined, and it is possible to suppress the excessive bulkiness of the branched silicone compound, so that the molecular chains of the branched silicone compound can easily enter the gaps between the molecular chains of the matrix resin 3. As a result, the dispersibility of the magnetic powder 2 in the matrix resin 3 can be ensured.

[0053] If the weight-average molecular weight of the branched silicone compound is less than the lower limit value, the entanglement between the branched silicone compound and the matrix resin 3 may decrease, and the dispersibility of the magnetic powder 2 in the matrix resin 3 may decrease. On the other hand, if the weight-average molecular weight of the branched silicone compound exceeds the upper limit value, the molecular structure of the branched silicone compound becomes too bulky, and it becomes difficult for the molecular chains of the branched silicone compound to enter the gaps between the molecular chains of the matrix resin 3, and there is a risk that the magnetic powder 2 becomes difficult to be fixed to the matrix resin 3.

[0054] The weight-average molecular weight of the branched silicone compound can be measured using gel permeation chromatography (GPC).

[0055] In addition, when the volume of the magneto-viscoelastic elastomer composition 1 is 100 parts by volume, the content of the magnetic powder 2 is preferably 5 parts by volume or more and 80 parts by volume or less, more preferably 10 parts by volume or more and 70 parts by volume or less, and even more preferably 20 parts by volume or more and 60 parts by volume or less. As a result, when a magnetic field is applied to the magneto-viscoelastic elastomer composition 1, the change range of the storage elastic modulus becomes sufficiently large.

[0056] 2. Matrix resin The matrix resin 3 is a polymer material that serves as a matrix for dispersing the magnetic powder 2. Therefore, the matrix resin 3 contains, for example, polymer chains forming a three-dimensional network structure. Then, the molecular chains of the coating film 23 of the magnetic powder 2 are intertwined with the polymer chains, whereby the magnetic powder 2 is retained with respect to the matrix resin 3. Thereby, the dispersibility of the magnetic powder 2 can be ensured.

[0057] FIG. 3 is a partially enlarged view of the magnetorheological elastomer composition 1 shown in FIG. 1. The magnetorheological elastomer composition 1 shown in FIG. 3 has polymer chains 31 contained in the matrix resin 3 and magnetic powder 2 provided between the polymer chains 31.

[0058] As shown in FIG. 3, the polymer chains 31 are crosslinked with each other to form a three-dimensional network structure. The coating film 23 of the magnetic powder 2 contains an organic compound 24 derived from a bulky branched silicone compound. Since the organic compound 24 has side chains extending so as to rise from the surface as shown in FIG. 2, the probability of entanglement with the polymer chains 31 becomes high as shown in FIG. 3. Thereby, the magnetic powder 2 is easily retained by the polymer chains 31, and the dispersibility of the magnetic powder 2 in the matrix resin 3 becomes high.

[0059] Examples of the matrix resin 3 include thermosetting resins, thermoplastic resins, photocurable resins, elastomers, rubbers, gels, and the like. And it is preferable that the matrix resin 3 has rubber elasticity like so-called elastomers and rubbers. Rubber elasticity refers to the property of greatly stretching when a force is applied and stretching, and returning to about the original length when the force is removed. Since the matrix resin 3 has such rubber elasticity, the magnetorheological elastomer composition 1 can exhibit various viscoelasticities in response to the application of a magnetic field. Thereby, applications such as a damping force adjustment damper become possible.

[0060] Examples of the elastomer used as the matrix resin 3 include various thermoplastic elastomers such as styrene-based thermoplastic elastomer (TPE), olefin-based TPE, vinyl chloride-based TPE, urethane-based TPE, ester-based TPE, amide-based TPE, chlorinated polyethylene-based TPE, Syn-1,2-polybutadiene-based TPE, Trans-1,4-polyisoprene-based TPE, and fluorine-based TPE. A mixture of one or more of these is used. Note that the above "based" refers to a homopolymer or copolymer.

[0061] Examples of the rubber used as the matrix resin 3 include natural rubber, isoprene rubber (IR), butadiene rubber (BR), 1,2-polybutadiene (1,2-BR), styrene-butadiene (SBR), chloroprene rubber (CR), nitrile rubber (NBR), butyl rubber (IIR), ethylene-propylene rubber (EPM, EPDM), chlorosulfonated polyethylene (CSM), acrylic rubber (ACM, ANM), epichlorohydrin rubber (CO, ECO), polysulfide rubber (T), silicone rubber, fluorine rubber (FKM), urethane rubber (U), etc. A mixture of one or more of these is used.

[0062] In addition, the following thickeners may be added to the matrix resin 3. As a result, the matrix resin 3 gels and becomes a state called a so-called elastomer gel. Examples of the thickener include plant-based polymers such as gum arabic, tragacanth, galactan, carob gum, guar gum, karaya gum, carrageenan, pectin, agar, quince seed, starch, algin colloid, trant gum, locust bean gum; microbial-based polymers such as xanthan gum, dextran, succinoglucan, pullulan; animal-based polymers such as collagen, casein, albumin, gelatin; starch-based polymers such as carboxymethyl starch, methyl hydroxypropyl starch; cellulose-based polymers such as methyl cellulose, ethyl cellulose, methyl hydroxypropyl cellulose, carboxymethyl cellulose, hydroxymethyl cellulose, hydroxypropyl cellulose, nitrocellulose, sodium cellulose sulfate, sodium carboxymethyl cellulose, crystalline cellulose, cationized cellulose, cellulose powder; alginic acid-based polymers such as sodium alginate, propylene glycol alginate; vinyl-based polymers such as polyvinyl methyl ether, carboxyvinyl polymer; polyoxyethylene-based polymers, polyoxyethylene polyoxypropylene copolymer-based polymers; acrylic-based polymers such as sodium polyacrylate, polyethyl acrylate, polyacrylamide, acryloyldimethyltaurine salt copolymer; synthetic water-soluble polymers such as polyethyleneimine, cationic polymer; and inorganic water-soluble polymers such as bentonite, magnesium aluminum silicate, montmorillonite, beidellite, nontronite, saponite, hectorite, and silicic anhydride, etc.

[0063] 3. Liquid component The magnetorheological elastomer composition 1 may contain a liquid component as required. The liquid component is not particularly limited as long as it is a component that is liquid at normal temperature, and examples thereof include oil agents, aqueous solvents, and the like.

[0064] Examples of the oil agent include non-aqueous oils such as olefin oil, paraffin oil, naphthene oil, mineral oil, edible oil, silicone oil, and fluorine oil. Examples of the aqueous solvent include water, aqueous solution, and the like.

[0065] Such a liquid is impregnated into the matrix resin 3 and swollen. Thereby, the elastic modulus of the magnetorheological elastomer composition 1 can be decreased. That is, the elastic modulus of the magnetorheological elastomer composition 1 can be adjusted.

[0066] Among the liquid components, silicone oil is particularly preferably used. Since silicone oil has a high affinity with the magnetic powder 2, even if the matrix resin 3 is impregnated with silicone oil, the dispersion state of the magnetic powder 2 is less likely to deteriorate.

[0067] Examples of the silicone oil include dimethyl silicone oil, methyl hydrogen silicone oil, methyl phenyl silicone oil, cyclic dimethyl silicone oil, dimethyl polysiloxane oil, and the like, and one or a mixture of two or more of these is used.

[0068] The content of the liquid component is not particularly limited, but when the content of the matrix resin 3 is 100 parts by mass, it is preferably 5 parts by mass or more and 700 parts by mass or less, more preferably 50 parts by mass or more and 500 parts by mass or less, and still more preferably 100 parts by mass or more and 400 parts by mass or less. Thereby, while suppressing the bleeding of the oil agent and the aqueous solvent, the elastic modulus of the magnetorheological elastomer composition 1 can be adjusted within an appropriate range.

[0069] 4. Additives The magnetorheological elastomer composition 1 may contain an arbitrary additive. Examples of the additive include slip agent, antiblocking agent, heat stabilizer, antioxidant, light stabilizer, ultraviolet absorber, crystal nucleating agent, blocking preventive agent, mold release agent, lubricant, colorant, pigment, inorganic filler, organic filler, foaming agent, flame retardant, anti-aging agent, antistatic agent, antibacterial agent, tackifier, and the like.

[0070] When the content of the matrix resin 3 is 100 parts by mass, the content of the additive is preferably 20 parts by mass or less, and more preferably 0.1 part by mass or more and 10 parts by mass or less.

[0071] 5. Effects Exhibited by the Embodiment As described above, the magnetorheological elastomer composition 1 according to the embodiment includes the magnetic powder 2, which is the metal powder for magnetorheological elastomers according to the embodiment, and the matrix resin 3.

[0072] According to such a configuration, due to the action brought about by the magnetic powder 2, specifically, the action of excellent dispersibility of the magnetic powder 2 in the matrix resin 3, it is possible to realize the magnetorheological elastomer composition 1 having a large change width in elastic modulus before and after applying a magnetic field.

[0073] Note that the elastic modulus of the magnetorheological elastomer composition 1 refers to the storage elastic modulus G', and is measured using, for example, a viscoelasticity measuring device MCR102 and a magnetic field applying device MRD70 manufactured by Anton Paar GmbH.

[0074] FIG. 4 is a partial cross-sectional view showing a viscoelasticity measuring device 9 for measuring the elastic modulus of the magnetorheological elastomer composition 1. The viscoelasticity measuring device 9 shown in FIG. 4 includes a non-magnetic rotor 91, a base 92, a non-magnetic plate 93, a Hall element 94, a yoke 95, and a coil 96. A sample 90 of the magnetorheological elastomer composition 1 is sandwiched between the non-magnetic rotor 91 and the non-magnetic plate 93, and while rotating the non-magnetic rotor 91, the shear force is measured. Thereby, the storage elastic modulus G' is measured. Further, by applying a magnetic field from the yoke 95 toward the base 92, the storage elastic modulus G' can be measured in a state where a magnetic field is applied to the sample 90.

[0075] Hereinafter, the measurement procedure will be described. First, a disk-shaped sample 90 having a diameter of 20 mm and a thickness of 1.5 mm is cut out from the magnetorheological elastomer composition 1. The cut-out sample 90 is sandwiched between the non-magnetic rotor 91 and the non-magnetic plate 93.

[0076] Next, push down the non-magnetic rotor 91 toward the sample 90 and apply a load of 1 N to the sample 90. Next, apply a sinusoidal shear strain to the sample 90 and vibrate and rotate the non-magnetic rotor 91. The maximum shear strain is 0.1%, the frequency is 1 Hz, and the temperature of the sample 90 is 25°C. Next, measure the sinusoidal shear stress corresponding to the sinusoidal shear strain.

[0077] FIG. 5 is a graph showing an example of the time change of the shear strain γ applied to the sample and the measured shear stress τ when measuring the storage elastic modulus of the sample. As shown in FIG. 5, the change curves of the shear strain γ and the shear stress τ are each a sinusoidal curve. Let the maximum shear strain be +γmax and the minimum shear strain be -γmax. Also, let the maximum shear stress be +τmax and the minimum shear stress be -τmax. Also, let the phase difference between the change curve of the shear strain γ and the change curve of the shear stress τ be δ.

[0078] Next, obtain the absolute value of the complex elastic modulus G from the maximum shear strain +γmax and the maximum shear stress +τmax * The absolute value |G * | of the complex elastic modulus is obtained by |G * | = +τmax / +γmax.

[0079] Next, obtain the storage elastic modulus G' from the phase difference δ and the complex elastic modulus G * The relationship between the complex elastic modulus G * and the storage elastic modulus G' is expressed as G * = G' + iG" (i is the imaginary unit) using the loss elastic modulus G". That is, the storage elastic modulus G', which is the real part of the complex elastic modulus G * is obtained by G' = |G * | cos δ.

[0080] Note that the storage elastic modulus G' in the state where a magnetic field is applied is the value measured in the state where a magnetic field is applied from the yoke 95 to the sample 90. The strength of the applied magnetic field is measured by the Hall element 94. As described above, the storage elastic modulus G' can be measured when no magnetic field is applied and when a magnetic field is applied.

[0081] When the storage elastic modulus when no magnetic field is applied to the magnetorheological elastomer composition 1 according to the embodiment is set to 1, the storage elastic modulus when a magnetic field is applied at a magnetic flux density of 0.2 T is preferably 30 or more, more preferably 40 or more and 500 or less. Such a magnetorheological elastomer composition 1 has a sufficiently large change width in the storage elastic modulus before and after applying a magnetic field. Therefore, such a magnetorheological elastomer composition 1 is applicable to various uses including a damping force variable damper.

[0082] Further, as described above, the magnetorheological elastomer composition 1 is excellent in the dispersibility of the magnetic powder 2 in the matrix resin 3. This dispersibility can be quantitatively measured by the following method.

[0083] First, the magnetorheological elastomer composition 1 is imaged with an optical microscope or a scanning electron microscope. Next, the obtained microscope image is subjected to binarization processing. In this binarization processing, the particle image corresponding to the magnetic powder 2 is made white, and the image corresponding to other parts is made black. FIG. 6 is an example of a microscope image measured for the magnetorheological elastomer composition 1. The microscope image shown in FIG. 6 is an image forming a square with a side of 180 μm. In FIG. 6, it can be seen that the white particle images are distributed in the black matrix.

[0084] Next, the microscope image subjected to binarization processing is divided into n×m cells. At this time, the number of divisions n, m, and the imaging magnification of the microscope image are adjusted so that each cell contains 20 or more particle images. In FIG. 6, as an example, it is divided into 4×4 cells.

[0085] Next, the area ratio Pnm, which is the ratio of the area of the particle image in each cell, is obtained. This area ratio Pnm is the ratio of the total area of the particle image to the area of each cell. Instead of the area ratio Pnm, the number Nnm of particle images in each cell may be obtained.

[0086] Next, for all cells, the average value Pave and the standard deviation σ of the area ratio Pnm P are obtained. Or, the average value Nave and the standard deviation σ of the number Nnm N are obtained. Subsequently, the relative standard deviation σ P / Pave or the relative standard deviation σ N / Nave is obtained.

[0087] FIG. 7 is a list of the numbers Nnm obtained for each of the 4×4 cells shown in FIG. 6. As shown in FIG. 7, by using the number Nnm, the dispersibility of the magnetic powder 2 in the matrix resin 3 can be quantitatively evaluated.

[0088] The magnetorheological elastomer composition 1 according to the present embodiment has the relative standard deviation σ obtained as described above P / Pave or the relative standard deviation σ N / Nave preferably being 0.50 or less, more preferably 0.40 or less, and even more preferably 0.30 or less. When the relative standard deviation is within the above range, the dispersibility of the magnetic powder 2 in the matrix resin 3 becomes particularly good. As a result, in the magnetorheological elastomer composition 1, the followability of the position of the magnetic powder 2 with respect to the change in the magnetic field is excellent. That is, when a magnetic field is applied, the uniformly dispersed magnetic powder 2 aligns quickly and well. As a result, the change width of the storage elastic modulus before and after applying the magnetic field can be made larger.

[0089] Examples of the uses of the magnetorheological elastomer composition 1 include a buffer part, a power transmission part, an attitude control part, a clutch, a damper, a shock absorber, a vibration control device, the muscle part of an assembly robot, a valve for controlling liquid flow rate, a tactile display device, an acoustic device, a medical / welfare robot hand, a care hand, and the like.

[0090] 6. Method for producing magnetorheological elastomer composition Next, an example of the method for producing a magnetorheological elastomer composition will be described.

[0091] FIG. 8 is a process diagram for explaining an example of the method for producing a magnetorheological elastomer composition. The production method shown in FIG. 8 includes a silane coupling agent treatment step S102, a liquid component addition step S104, a resin precursor addition step S106, a stirring step S108, and a curing step S110. Hereinafter, each step will be sequentially described.

[0092] 6.1. Silane coupling agent treatment step In the silane coupling agent treatment step S102, a silica film 22 is formed on the surface of the magnetic metal particles 21.

[0093] Next, the magnetic metal particles 21 having the silica film 22 formed thereon are subjected to a silane coupling agent treatment. A coating film 23 can be formed on the surface of the silica film 22 by a method of putting the magnetic metal particles 21 and the silane coupling agent into a reactor and heating them, a method of spraying the silane coupling agent onto the magnetic metal particles 21, a method of putting the magnetic metal particles 21 into a solution containing the silane coupling agent and drying them, or the like. Thereby, the magnetic powder 2 is obtained.

[0094] Note that after the formation of the coating film 23, if necessary, the obtained coating film 23 may be heat-treated. The conditions for the heat treatment are, for example, a temperature of 60°C or higher and 120°C or lower, and a time of 10 minutes or longer and 24 hours or shorter. Thereby, the hydrates remaining in the coating film 23 can be removed, the unreacted silane coupling agent can be removed, and the adhesion of the coating film 23 can be enhanced.

[0095] 6.2. Liquid component addition step In the liquid component addition step S104, the magnetic powder 2 and the liquid component are mixed. Thereby, a slurry is prepared. Note that the order of this step may be reversed with respect to the resin precursor addition step S106. Also, if the liquid component is not added, this step is omitted.

[0096] 6.3. Resin Precursor Addition Step In the resin precursor addition step S106, a resin precursor is added to the slurry. The resin precursor is a precursor of the matrix resin 3.

[0097] 6.4. Stirring Step In the stirring step S108, the mixture of the slurry and the resin precursor is stirred. Thereby, the mixture is homogenized. Examples of stirring include stirring using a medicine spoon or the like, and stirring using a stirrer such as a vortex mixer.

[0098] 6.5. Curing Step In the curing step S110, the stirred mixture is subjected to a curing treatment. Thereby, the resin precursor is cured, and the magnetorheological elastomer composition 1 is obtained. The curing treatment is selected according to the type of the resin precursor, and examples thereof include heat curing treatment and photo-curing treatment.

[0099] Note that the stirring step S108 and the curing step S110 may overlap with each other in time. For example, a curing treatment may be performed on the resin precursor by applying heat or light while stirring the mixture.

[0100] As described above, the metal powder for magnetorheological elastomer and the magnetorheological elastomer composition of the present invention have been described based on preferred embodiments, but the present invention is not limited thereto.

[0101] For example, the metal powder for magnetorheological elastomer and the magnetorheological elastomer composition of the present invention may be those obtained by adding an arbitrary component to the above-described embodiment.

Example

[0102] Next, specific examples of the present invention will be described. 7. Preparation of Magnetorheological Elastomer Composition 7.1. Example 1 First, as the magnetic powder, carbonyl iron powder with a coating film formed thereon was prepared. The coercive force, average particle diameter, and mass fraction of the magnetic powder were as shown in Table 1. As the silane coupling agent for forming the coating film, branched silicone (1) with a weight-average molecular weight of 868 was used.

[0103] Next, the magnetic powder and silicone oil, which is a liquid component, were mixed to prepare a slurry. Dimethylpolysiloxane oil was used as the silicone oil. Next, a resin precursor was added to the slurry. As the resin precursor, a precursor of an addition-curing type silicone rubber was used. The mixing ratios of the magnetic powder, resin precursor, and liquid component were 24% by mass, 19% by mass, and 57% by mass, respectively.

[0104] Next, the mixture of the slurry and the resin precursor was stirred for 10 minutes. Then, the stirred mixture was placed in an oven and heated at 90°C for 2 hours. As a result, a curing reaction occurred in the resin precursor, and a magnetorheological elastomer composition was obtained.

[0105] 7.2. Example 2 A magnetorheological elastomer composition was obtained in the same manner as in Example 1, except that a silica film was provided between the carbonyl iron powder and the coating film. The Stover method was used to form the silica film. The average thickness of the silica film was 30 nm.

[0106] 7.3. Example 3 A magnetorheological elastomer composition was obtained in the same manner as in Example 1, except that the addition of silicone oil, which is a liquid component, was omitted.

[0107] 7.4. Examples 4 and 5 First, a magnetorheological elastomer composition was obtained in the same manner as in Example 1, except that amorphous metal powder with a coating film and a silica film formed thereon was used as the magnetic powder. The coercive force, average particle diameter, and mass fraction of the magnetic powder were as shown in Table 2.

[0108] 7.5. Example 6 A magnetorheological elastomer composition was obtained in the same manner as in Example 4, except that the addition of silicone oil as a liquid component was omitted.

[0109] 7.6. Examples 7 to 9 A magnetorheological elastomer composition was obtained in the same manner as in Example 4, except that branched silicones (2) to (4) were used as the silane coupling agent. The coercive force, average particle diameter of the amorphous metal powder, and mass fraction of the magnetic powder are as shown in Table 2.

[0110] 7.7. Examples 10 and 11 A magnetorheological elastomer composition was obtained in the same manner as in Example 4, except that the mass fraction of the magnetic powder was changed as shown in Table 2.

[0111] 7.8. Comparative Example 1 A magnetorheological elastomer composition was obtained in the same manner as in Example 1, except that the formation of the coating film was omitted.

[0112] 7.9. Comparative Example 2 A magnetorheological elastomer composition was obtained in the same manner as in Example 2, except that the formation of the coating film was omitted.

[0113] 7.10. Comparative Example 3 A magnetorheological elastomer composition was obtained in the same manner as in Comparative Example 2, except that the addition of silicone oil as a liquid component was omitted.

[0114] 7.11. Comparative Example 4 A magnetorheological elastomer composition was obtained in the same manner as in Example 2, except that a linear silicone compound was used as the silane coupling agent.

[0115] 7.12. Comparative Example 5 A magnetorheological elastomer composition was obtained in the same manner as in Example 3, except that a linear silicone compound was used as the silane coupling agent.

[0116] In addition, the above-mentioned branched silicones (1) to (4) and linear silicones refer to the following compounds. · Branched silicone (1): Triethoxysilylethylpolydimethylsiloxyehtylhexyldimethylsilicone · Branched silicone (2): Triethoxysilylethylpolydimethylsiloxyehtyldimethylsilicone · Branched silicone (3): (Acrylates / tridecyl acrylate / triethoxysilylpropyl methacrylate / dimethylsilicone methacrylate) copolymer · Branched silicone (4): Triethoxycaprylylsilane · Linear silicone: Glycidoxy octyl trimethoxysilane

[0117] 8. Evaluation of the magnetorheological elastomer composition 8.1 Measurement of the storage modulus under an applied magnetic field The storage moduli of the magnetorheological elastomer compositions obtained in Examples 1 and 2 and Comparative Example 1 were measured. The measurement of the storage modulus was carried out while applying a magnetic field to the magnetorheological elastomer composition. The relationship between the strength (magnetic flux density) of the applied magnetic field and the measured storage modulus G’ is shown in Fig. 9. Fig. 9 is a graph plotting the measurement results of the magnetorheological elastomer compositions obtained in Examples 1 and 2 and Comparative Example 1, with the horizontal axis representing the strength of the applied magnetic field and the vertical axis representing the storage modulus G’ of the magnetorheological elastomer composition.

[0118] As shown in Fig. 9, it was confirmed that as the magnetic field applied to the magnetorheological elastomer composition was increased, the storage modulus G’ gradually increased. Therefore, it was found that in the magnetorheological elastomer composition, the storage modulus G’ can be adjusted by the strength of the applied magnetic field.

[0119] Also, in the magnetorheological elastomer compositions obtained in Examples 1 and 2, the slope of the increase in the storage modulus G’ was larger than that of the magnetorheological elastomer composition obtained in Comparative Example 1. Therefore, according to the present invention, it was found that a magnetorheological elastomer composition with a large change range in the storage modulus before and after applying a magnetic field can be realized.

[0120] 8.2. Calculation of the ratio of storage modulus at the time of magnetic field application to that without magnetic field application From the graph shown in Fig. 9, the storage moduli G’ without magnetic field application, with 0.1 T magnetic field application, with 0.2 T magnetic field application, and with 0.5 T magnetic field application were extracted. Here, the state without magnetic field application means a state where no magnetic field is applied to the magnetorheological elastomer composition. The state with 0.1 T magnetic field application means a state where a magnetic field is applied to the magnetorheological elastomer composition at a magnetic flux density of 0.1 T. The state with 0.2 T magnetic field application means a state where a magnetic field is applied to the magnetorheological elastomer composition at a magnetic flux density of 0.2 T. The state with 0.5 T magnetic field application means a state where a magnetic field is applied to the magnetorheological elastomer composition at a magnetic flux density of 0.5 T.

[0121] Next, when the storage modulus G’ without magnetic field application was set to 1, the ratio of the storage modulus G’ at the time of magnetic field application was calculated. The same calculation was also performed for Example 3. The calculated ratios are shown in Table 1 as the storage modulus ratios.

[0122] Also, for the magnetorheological elastomer composition obtained in Comparative Example 6, when the storage modulus G’ without magnetic field application was designated as “F”, for the magnetorheological elastomer compositions obtained in Examples 4 to 11, the storage modulus G’ at the time of magnetic field application was relatively evaluated in five levels of “A to E”. The evaluation results are shown in Table 2. Note that the classes of “A to E” have a magnitude relationship of F < E < D < C < B < A.

[0123] 8.3. Evaluation of dispersibility For the magnetorheological elastomer compositions obtained in each example and each comparative example, the dispersibility of the magnetic powder was quantified by the method described above. Note that for the quantification of dispersibility, the relative standard deviation σ N / Nave was used. Then, the calculated relative standard deviation σ N / Nave was used to evaluate the dispersibility in accordance with the following evaluation criteria.

[0124] A: Particularly good dispersibility (relative standard deviation is 0.30 or less) B: Good dispersibility (relative standard deviation exceeds 0.30 and is 0.40 or less) C: Slightly good dispersibility (relative standard deviation exceeds 0.40 and is 0.50 or less) D: Slightly poor dispersibility (relative standard deviation is more than 0.50 and less than or equal to 0.60) E: Poor dispersibility (relative standard deviation is more than 0.60 and less than or equal to 0.70) F: Particularly poor dispersibility (relative standard deviation is more than 0.70) The evaluation results are shown in Table 1 and Table 2.

[0125]

Table 1

[0126]

Table 2

[0127] As is clear from Table 1 and Table 2, the magnetorheological elastomer compositions obtained in each example had a higher storage elastic modulus ratio when a magnetic field was applied compared to when no magnetic field was applied, compared to the magnetorheological elastomer compositions obtained in each comparative example. Also, in the magnetorheological elastomer compositions obtained in each example, the dispersibility of the magnetic powder was also good. Therefore, it was confirmed that according to the present invention, it is possible to realize a magnetorheological elastomer composition excellent in the dispersibility of magnetic metal particles and having a large change width in elastic modulus before and after applying a magnetic field.

Explanation of Reference Numerals

[0128] 1... Magnetorheological elastomer composition, 2... Magnetic powder, 3... Matrix resin, 9... Viscoelasticity measuring device, 21... Magnetic metal particles, 22... Silica film, 23... Coating film, 24... Organic compound, 31... Polymer chain, 90... Sample, 91... Non-magnetic rotor, 92... Base, 93... Non-magnetic plate, 94... Hall element, 95... Yoke, 96... Coil, S102... Silane coupling agent treatment step, S104... Liquid component addition step, S106... Resin precursor addition step, S108... Stirring step, S110... Curing step

Claims

1. Magnetic metal particles with a coercive force of 11 [Oe] (875 [A / m]) or less, a coating film provided on the surface of the magnetic metal particles and containing a compound derived from a silane coupling agent composed of a branched silicone compound, A metal powder for a magnetorheological elastomer, characterized by comprising the above.

2. The metal powder for a magnetorheological elastomer according to claim 1, further comprising a silica film containing silicon oxide and located between the magnetic metal particles and the coating film.

3. The metal powder for a magnetorheological elastomer according to claim 2, wherein the average thickness of the silica film is 1 nm or more and 500 nm or less.

4. The metal powder for a magnetorheological elastomer according to any one of claims 1 to 3, wherein the average particle diameter of the magnetic metal particles is 0.5 μm or more and 100 μm or less.

5. The metal powder for a magnetorheological elastomer according to any one of claims 1 to 4, wherein the branched silicone compound is a compound represented by the following formula (1). 【Chemical 1】 [wherein, R １ and R ２ are each independently an alkyl group having 1 to 8 carbon atoms which may be the same or different, and R ３ is represented by the following general formula (2) [Chemical 2] (R ５ and R ６ are each independently an alkyl group having 1 to 8 carbon atoms which may be the same as or different from each other, and r and s are positive integers such that their sum is 1 or more and 1000 or less.) is a group represented by, R ４ is the following general formula (3) [Chemical Formula 3] (R ７ independently represents an alkyl group having 1 to 5 carbon atoms each.) is a group represented by, where n and m are integers such that their sum is 0 or more and 1000 or less, and p and q are integers of 1 or more and 1000 or less, respectively. ]

6. The metal powder for a magnetorheological elastomer according to any one of claims 1 to 4, wherein the weight average molecular weight of the branched silicone compound is 150 or more and 1800 or less.

7. A magnetorheological elastomer composition, characterized by comprising the metal powder for a magnetorheological elastomer according to any one of claims 1 to 6, and a matrix resin. ​

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