JP2023047188A - Magnetic viscoelastic fluid and device - Google Patents

Abstract

To provide a magnetic viscoelastic fluid that is excellent in the long-term dispersion stability of magnetic particles and in the fluidity of magnetic particles.SOLUTION: The magnetic viscoelastic fluid includes magnetic particles and a dispersion medium. The dispersion medium includes an organic compound which has at least two amide groups in one molecule. The ratio of the volume of the organic compound to the total volume of the magnetic viscoelastic fluid is in the range of 48% to 85%.SELECTED DRAWING: None

Description

The present invention relates to magneto-rheological fluids and devices.

A magneto-rheological fluid (hereinafter also referred to as “MR fluid”) is a fluid in which magnetic particles such as iron are dispersed in a base oil such as silicone oil as a dispersion medium. In the MR fluid, when no magnetic field is applied to the MR fluid from the outside, the magnetic particles are randomly suspended in the dispersion medium. It has the property of forming a large number of clusters in which magnetic particles are linked in a chain. This allows the MR fluid to control the formation and release of clusters by applying and not applying a magnetic field, and when clusters are formed, the apparent viscosity of the MR fluid changes and the yield stress increases. MR fluids can transmit and attenuate forces and torques through the application of magnetic fields. Therefore, application of the MR fluid to dampers and the like is being studied (see, for example, Patent Document 1).

Since the MR fluid normally uses large magnetic particles with a diameter of several μm to several tens of μm in order to generate a certain amount of stress, if the MR fluid is left unattended, the magnetic particles will sediment out of the dispersion medium. I have a separation problem. Attempting to operate a device using an MR fluid while the magnetic particles have settled and solidified may result in the device not working or damaging the mechanism of the device.

In Patent Documents 1 and 2, the present inventors have proposed a magneto-rheological fluid that exhibits excellent long-term dispersion stability of magnetic particles and a large maximum change in yield stress under magnetic field application conditions.

Japanese Patent No. 6434672 Japanese Patent No. 6682608

In addition to excellent long-term dispersion stability of magnetic particles, MR fluids are also required to have excellent fluidity. The poor flowability of the MR fluid can make it difficult to fill a machine or device using the MR fluid with the MR fluid. Also, if the fluidity of the MR fluid is low, the superior feature of reverse mobility is lost due to excessively high de-excitation torque.

Fluidity generally means the property of flowing without being constant, but the fluidity in the present invention represents the property of flowing because the fixed shape causes a creep phenomenon and can no longer maintain the initial shape for a certain period of time. .

In addition, the magnetic particles are excellent in long-term dispersion stability, and even if the magnetic particles are not separated from the dispersion medium, the fluidity of the MR fluid is low. can no longer be used. In addition, it is necessary to agitate the solidified MR fluid with a strong force to restore the fluidity of the MR fluid.

SUMMARY OF THE INVENTION Accordingly, it is an object of the present invention to provide a magneto-rheological fluid that exhibits excellent long-term dispersion stability of magnetic particles and excellent fluidity.

Another object of the present invention is to provide a device that is excellent in long-term stable driving and mechanical reliability.

A magneto-rheological fluid according to the present invention is a magneto-rheological fluid containing magnetic particles and a dispersion medium,
The dispersion medium contains an organic compound having two or more amide groups in one molecule,
The magneto-rheological fluid, wherein the volume ratio of the organic compound to the total volume of the magneto-rheological fluid is 48 to 85%. As a result, the long-term dispersion stability of the magnetic particles is excellent, and the fluidity of the magneto-rheological fluid is also excellent.

を有し、
式中、Ｌは、価数ｙの連結基であり、
Ｒは、水素またはメチル基であり、
Ａは、アルキレン基であり、
ｘは、１～３０の数であり、
ｙは、２以上の数である。 In one embodiment of the magneto-rheological fluid according to the invention, the organic compound has the formula (1):

has
wherein L is a linking group with a valence of y;
R is hydrogen or a methyl group;
A is an alkylene group,
x is a number from 1 to 30,
y is a number of 2 or more.

In one embodiment of the magneto-rheological fluid according to the invention, said linking group is a hydrocarbon group.

In one embodiment of the magneto-rheological fluid according to the invention, said L is an alkylene group.

In one embodiment of the magneto-rheological fluid according to the present invention, said L is an alkylene group having 2 to 8 carbon atoms.

In one embodiment of the magneto-rheological fluid according to the invention, the magnetic particles have an average particle size of 1 to 50 μm.

In one embodiment of the magneto-rheological fluid according to the invention, said magneto-rheological fluid does not comprise resin particles.

The device according to the present invention is a device selected from the group consisting of robots, brakes, clutches, dampers, shock absorbers, vibration control devices, haptics, haptic presentation devices, medical equipment, welfare equipment and adsorption devices, and any of the above is a device using a magneto-rheological fluid. This ensures long-term stable driving and excellent mechanical reliability.

According to the present invention, it is possible to provide a magneto-rheological fluid that exhibits excellent long-term dispersion stability of magnetic particles and excellent fluidity. Moreover, according to the present invention, it is possible to provide a device that is stable for a long period of time and has excellent mechanical reliability.

Embodiments of the present invention will be described below. These descriptions are intended to be illustrative of the invention and are not intended to limit the invention in any way.

In the present invention, two or more embodiments can be arbitrarily combined.

In the present invention, the term "solid content" is a concept encompassing solid content, non-volatile matter and active ingredients.

Numerical ranges herein are intended to include the upper and lower limits of the range unless otherwise indicated. For example, 48-85% means a range of 48% or more and 85% or less.

In the present invention, the average particle size means the median value (median size) of the particle size distribution. The average particle size is measured using a laser diffraction particle size distribution analyzer, a scanning electron microscope (SEM), or the like.

(Magnetorheological fluid)
A magneto-rheological fluid according to the present invention is a magneto-rheological fluid containing magnetic particles and a dispersion medium,
The dispersion medium contains an organic compound having two or more amide groups in one molecule,
The magneto-rheological fluid, wherein the volume ratio of the organic compound to the total volume of the magneto-rheological fluid is 48 to 85%.

Each component contained in the magneto-rheological fluid of the present invention will be described below.

• Magnetic Particles As the magnetic particles, any magnetic particles whose yield stress changes under the condition of applying a magnetic field can be used, and known magnetic particles can be used. The magnetic particles may be used singly or in combination of two or more of different materials or different average particle sizes.

Materials for magnetic particles include, for example, iron, iron nitride, iron carbide, carbonyl iron, chromium dioxide, low carbon steel, nickel, cobalt; aluminum-containing iron alloys, silicon-containing iron alloys, cobalt-containing iron alloys, and nickel-containing iron alloys. , vanadium-containing iron alloys, molybdenum-containing iron alloys, chromium-containing iron alloys, tungsten-containing iron alloys, manganese-containing iron alloys, copper-containing iron alloys, and oxides of the above materials; gadolinium, paramagnetic consisting of gadolinium organic derivatives , superparamagnetic, and ferromagnetic compound particles.

Carbonyl iron is preferred as the magnetic particles.

The average particle size of the magnetic particles is, for example, 1 to 50 μm. In one embodiment, the average particle size of the magnetic particles is 1 μm or more, 2 μm or more, 3 μm or more, 4 μm or more, 5 μm or more, 6 μm or more, 7 μm or more, 8 μm or more, 9 μm or more, 10 μm or more, 15 μm or more, 20 μm or more, 25 μm. 30 μm or more, 35 μm or more, 40 μm or more, or 45 μm or more. In another embodiment, the average particle size of the magnetic particles is 50 μm or less, 45 μm or less, 40 μm or less, 35 μm or less, 30 μm or less, 25 μm or less, 20 μm or less, 15 μm or less, 10 μm or less, 9 μm or less, 8 μm or less, 7 μm or less, 6 μm or less, 5 μm or less, 4 μm or less, 3 μm or less, or 2 μm or less.

As the magnetic particles, in addition to the magnetic particles (large magnetic particles having an average particle size of 1 μm or more), small magnetic particles having a smaller average particle size may or may not be used.

Examples of materials for the small magnetic particles include iron, ferrite (ferrite (III) salts such as Mn(II), Co(II), Ni(II), Cu(II), and Zn(II)), magnetite ( iron (III) acid salt of Fe (II)) and the like. Examples of ferrites include Mn ferrite, Mn--Zn ferrite, Mn--Mg ferrite, Mn--Mg--Sr ferrite, Mg ferrite; and the above ferrites containing alkali metals, alkaline earth metals and light metals. In addition, the above-mentioned materials can also be used.

At least one selected from the group consisting of magnetite and ferrite is preferable as the small magnetic particles.

In one embodiment, the small magnetic particles are Mn--Mg--Sr ferrites.

The average particle size of the small magnetic particles is, for example, 20-300 nm. The average particle size of the small magnetic particles is preferably 40 to 200 nm from the viewpoint of yield stress and suppression of sedimentation.

If the magnetic particles comprise small magnetic particles, the proportion of small magnetic particles is for example less than 5% by weight relative to the total weight of the magnetic particles.

In one embodiment of the magneto-rheological fluid according to the invention, the magnetic particles have an average particle size of 1 to 50 μm. That is, in this embodiment the magnetic particles do not include small magnetic particles.

In the magneto-rheological fluid of the present invention, the magnetic particles may be surface-treated with a silane coupling agent or the like for enhancing dispersibility, or may not be surface-treated. In the magneto-rheological fluid of the present invention, excellent long-term dispersion stability of the magnetic particles can be obtained without surface treatment of the magnetic particles by using the resin particles described later.

In one embodiment, the magnetic particles are not surface treated, such as with a silane coupling agent, to enhance dispersibility.

The amount of magnetic particles in the magneto-rheological fluid of the present invention is such that the volume ratio of the organic compound having two or more amide groups in one molecule, which will be described later, is 48 to 85% of the total volume of the magneto-rheological fluid. is not particularly limited as long as the amount is The volume ratio of the magnetic particles in the magneto-rheological fluid of the present invention is, for example, 52% or less of the total volume of the magneto-rheological fluid. In one embodiment, the volume fraction of the magnetic particles in the magneto-rheological fluid of the present invention is 52% or less, 50% or less, 40% or less, 30% or less, 20% or less of the total volume of the magneto-rheological fluid. , 10% or less, or 5% or less. In another embodiment, the volume fraction of the magnetic particles in the magneto-rheological fluid of the present invention is 5% or more, 10% or more, 15% or more, 20% or more, 30% of the total volume of the magneto-rheological fluid. 40% or more, or 50% or more.

Dispersion medium The dispersion medium of the magneto-rheological fluid of the present invention is an organic compound having two or more amide groups (-CON(R)-) in one molecule (hereinafter sometimes simply referred to as "dispersion medium compound"). ), and the volume ratio of the dispersion medium compound to the total volume of the magneto-rheological fluid is 48-85%.

Without wishing to be bound by theory, the magneto-rheological fluid of the present invention exhibits excellent long-term dispersion stability of the magnetic particles and magneto-viscoelastic fluid by using a dispersion medium containing such a dispersion medium compound. The reason why the fluidity of the elastic fluid is also excellent is that, for example, when the number of amide groups in one molecule of the dispersion medium compound is two or more, the dispersion medium is more likely to adhere to the surface of the magnetic particles due to the amide group than in the case where there is only one amide group. It is presumed that this is because the compound is easily adsorbed and the dispersibility of the magnetic particles is enhanced.

The dispersion medium compound may be nonionic, cationic, or anionic. In one embodiment, the carrier compound is nonionic.

を有し、式（１）中、Ｌは、価数ｙの連結基であり；Ｒは、水素またはメチル基であり；Ａは、アルキレン基であり；ｘは、１～３０の数であり；ｙは、２以上の数である。 For example, the dispersion medium compound has the formula (1):

wherein L is a linking group of valence y; R is hydrogen or a methyl group; A is an alkylene group; x is a number from 1 to 30 ; y is a number of 2 or more;

Linking groups for L include, for example, linear, branched or cyclic organic groups. Organic groups include, for example, hydrocarbons such as aliphatic hydrocarbons and aromatic hydrocarbons. The aliphatic hydrocarbon may be a saturated aliphatic hydrocarbon or an unsaturated aliphatic hydrocarbon having one or more unsaturated bonds.

In one embodiment, the linking group is a hydrocarbon group.

In one embodiment, L is a saturated or unsaturated alkylene group. In another embodiment, L is a saturated or unsaturated alkylene group of 2, 3, 4, 5, 6, 7 or 8 carbon atoms. In yet another embodiment, L is a saturated or unsaturated 4-carbon alkylene group.

The valency y, ie the number of amide groups, is a number of 2 or more, eg 2, 3, 4 or 5.

R is hydrogen or a methyl group. When R is a methyl group (--CON(CH ₃ )--), the electron-withdrawing property of the amide group is higher when R is hydrogen (--CONH--) than when R is a methyl group (--CON(CH 3 )--). It is presumed that the adsorptivity of the compound increases.

A is a saturated or unsaturated alkylene group, such as an alkylene group having 2, 3, 4, 5 or 6 carbon atoms. Alkylene groups may be linear, branched or cyclic.

x is a number from 1 to 30; From the viewpoint of enhancing the hydrophobicity of the dispersion medium compound by increasing the repeating number of the AO group and further enhancing the dispersion stability of the magnetic particles, x is preferably 4 or more. In one embodiment, x is 1 or greater, 2 or greater, 3 or greater, 4 or greater, 6 or greater, 8 or greater, 10 or greater, 12 or greater, 14 or greater, 16 or greater, 18 or greater, or 20 or greater. In another embodiment, x is 30 or less, 20 or less, 18 or less, 16 or less, 14 or less, 12 or less, 10 or less, 8 or less, 6 or less, 4 or less, 3 or less, or 2 or less.

In one embodiment, the carrier compound of Formula (1) is represented by Formula (2): H—(OA)x—NRCO—L—CONR—(AO)x—H (ie, y=2 in Formula (1) ). In another embodiment, the carrier compound of Formula (1) is represented by Formula (2): H—(OA)x—NHCO—L—CONH—(AO)xH (ie, in Formula (1) y= 2).

A dispersion medium compound may be used individually by 1 type, and may be used in combination of 2 or more type.

The ratio of the dispersion medium compound to the total mass of the dispersion medium is, for example, 50% by mass or more. In one embodiment, the ratio of the dispersion medium compound to the total weight of the dispersion medium is 50% by weight or more, 60% by weight or more, 65% by weight or more, 70% by weight or more, 75% by weight or more, 80% by weight or more, 85% by weight % or more, 90 mass % or more, 95 mass % or more, or 100 mass %. In another embodiment, the proportion of the dispersion medium compound to the total weight of the dispersion medium is 100% by weight or less, 95% by weight or less, 90% by weight or less, 85% by weight or less, 80% by weight or less, 75% by weight or less, 70% by weight or less. % by mass or less, 65% by mass or less, or 60% by mass or less.

The dispersion medium of the magneto-rheological fluid of the present invention includes a dispersion medium other than the dispersion medium compound, for example, a dispersion medium such as those disclosed in Patent Documents 1 or 2, or a dispersion medium such as silicone oil, fluorine oil, or paraffin. may or may not be included.

The volume ratio of the carrier compound to the total volume of the magneto-rheological fluid of the present invention is 48-85%. When the volume ratio of the dispersion medium compound is 48% or more, the fluidity of the magneto-rheological fluid is enhanced. Further, when the volume ratio of the dispersion medium compound is 85% or less, the long-term dispersion stability of the magnetic particles is excellent. In one embodiment, the volume ratio of the carrier compound to the total volume of the magneto-rheological fluid is 48% or greater, 50% or greater, 55% or greater, 60% or greater, 65% or greater, 70% or greater, 75% or greater. Or 80% or more. In another embodiment, the volume percentage of the carrier compound relative to the total volume of the magneto-rheological fluid is 85% or less, 80% or less, 75% or less, 70% or less, 65% or less, 60% or less, 55%. or less or 50% or less.

・Other Additives In addition to the components described above, the magneto-rheological fluid according to the present invention contains a dispersing aid, resin particles, a rheology control agent, a metallic detergent-dispersant, an ashless detergent-dispersant, an oily agent, and an abrasion agent. Other additions such as inhibitors, extreme pressure agents, rust inhibitors, friction modifiers, solid lubricants, antioxidants, metal deactivators, defoamers, colorants, viscosity index improvers and pour point depressants It may or may not contain an agent. Each of these other additives may be used alone or in combination of two or more.

- Dispersing Aid As the dispersing aid, a generally used non-aqueous or aqueous wetting and dispersing agent can be used. The functional group of the dispersing aid that contributes to the adsorption of the magnetic material may be acidic, basic or salt, but basic or salt is preferred because it interacts less with magnetic particles of some materials. The molecular weight of the dispersing aid may be selected appropriately from low molecular weight to high molecular weight in combination with the dispersion medium. Dispersion aids may be used singly or in combination of two or more.

When using a dispersing aid, the amount thereof may be adjusted as appropriate. For example, the proportion of the dispersing aid is 0.5 to 10% by mass with respect to the total mass of the mass of the magnetic particles, the mass of the dispersion medium and the mass of the dispersing aid.

In one embodiment, the magneto-rheological fluid does not contain a dispersing aid. In another embodiment, the magneto-rheological fluid comprises a dispersing aid.

- Resin particles Resin particles are particles made of resin and contribute to the dispersion stability of the magnetic particles. The resin particles may be used singly or in combination of two or more.

The material of the resin particles is not particularly limited, and a known resin may be appropriately selected and used. Materials for resin particles include, for example, acrylic resin, styrene resin, polyolefin resin, polyester resin, melamine resin, benzoguanamine resin, polyacrylonitrile resin, polyamide resin, polycarbonate resin, phenol resin, urea resin, fluororesin, cellulose resin, and polyurethane. Examples include resins, vinyl chloride resins, polyether resins, silicone resins, alkyd resins, and the like.

Acrylic resins may be homopolymers or copolymers of monomers such as acrylic acid, methacrylic acid, acrylic acid esters, and methacrylic acid esters, or one or more of these monomers and monomers such as ethylene and styrene. It may be a copolymer with (e.g., ethylene-acrylic acid copolymer, styrene-acrylic acid copolymer, etc.), or a modified product of these polymers or copolymers (e.g., fluorine-substituted acrylic resin ).

The resin particles may be core-shell particles in which the core and shell are each composed of one or more of the materials described above.

The resin particles may be, for example, non-crosslinked resin particles in which the polymers in the resin are not crosslinked, or crosslinked resin particles in which the polymers in the resin are crosslinked. Crosslinked resin particles have better heat resistance and solvent resistance than non-crosslinked resin particles, so they are less likely to be melted by the heat generated by sliding devices to which magneto-rheological fluids are applied, or by the dispersion medium itself, resulting in more stable magnetic field generation. It is preferable because stress can be obtained.

The crosslinked resin particles are not particularly limited, and known crosslinked resin particles can be used. Examples of crosslinked resin particles include resin particles described in Patent Document 2; organic resin particles (A) described in International Publication No. 2015/152187; crosslinked resin particles described in JP-A-2010-024289; 2009-235351, resin particles made of a resin having a crosslinked structure obtained mainly from ethylenically unsaturated monomers, resin particles made of an internally crosslinked urethane resin, crosslinked resin particles made of an internally crosslinked melamine resin, etc. crosslinked resin particles; crosslinked resin particles that are a carboxyl group-containing acrylic resin described in JP-A-2009-114392; and acrylic resin fine particles having an internal crosslinked structure described in JP-A-6-025567. .

In one embodiment, the resin particles are crosslinked resin particles. In another embodiment, the resin particles are one or more selected from the group consisting of acrylic resins, polyurethane resins, melamine resins, and modified products thereof. In yet another embodiment, the resin particles are one or more crosslinked resin particles selected from the group consisting of acrylic resins, polyurethane resins, melamine resins, and modifications thereof.

In one embodiment, the acrylic resin is an acrylic acid ester polymer, a methacrylic acid ester polymer, a styrene-acrylic acid copolymer, a styrene-methacrylic acid copolymer, an ethylene-acrylic acid copolymer, an ethylene-methacrylic acid copolymer. It is one or more selected from the group consisting of polymers and modified products thereof.

The weight average molecular weight (Mw) of the resin particles is not particularly limited and can be adjusted as appropriate. In one embodiment, the Mw of the resin particles is 1,000 or greater, 5,000 or greater, 6,000 or greater, 10,000 or greater, 50,000 or greater, 100,000 or greater, 500,000 or greater, or 1,000, 000 or more. In another embodiment, Mw of the resin particles is 10,000,000 or less, 5,000,000 or less, 3,000,000 or less, 1,000,000 or less, 500,000 or less, 300,000 100,000 or less, or 50,000 or less.

The average particle size of the resin particles is, for example, 20-1500 nm. In one embodiment, the average particle diameter of the resin particles is 50 nm or more, 80 nm or more, 100 nm or more, 150 nm or more, 200 nm or more, 300 nm or more, 400 nm or more, 500 nm or more, 600 nm or more, 700 nm or more, 800 nm or more, 900 nm or more, 1000 nm. 1100 nm or more, 1200 nm or more, 1300 nm or more, or 1400 nm or more. In another embodiment, the average particle diameter of the resin particles is 1400 nm or less, 1300 nm or less, 1200 nm or less, 1100 nm or less, 1000 nm or less, 900 nm or less, 800 nm or less, 700 nm or less, 600 nm or less, 500 nm or less, 400 nm or less, and 300 nm. Below, it is 200 nm or less or 150 nm or less.

The average particle size of the resin particles may be in the range of 20 to 1500 nm, and two or more kinds of resin particles having different average particle sizes may be used in combination. For example, the first resin particles having an average particle size of 20 to 200 nm and the second resin particles having an average particle size of more than 200 nm and 1500 nm or less may be used in combination.

When resin particles are blended, the mass ratio of the resin particles is, for example, 0.3 to 20% by mass with respect to the total mass of the magneto-rheological fluid. In one embodiment, the percentage is 0.5 wt% or more, 1 wt% or more, 2 wt% or more, 3 wt% or more, 4 wt% or more, 5 wt% or more, 6 wt% or more, 7 wt% or more. , 8% by mass or more, 9% by mass or more, 10% by mass or more, or 15% by mass or more. In another embodiment, the proportion is 19% by mass or less, 15% by mass or less, 10% by mass or less, 9% by mass or less, 8% by mass or less, 7% by mass or less, 6% by mass or less, 5% by mass. 4% by mass or less, 3% by mass or less, 2% by mass or less, or 1% by mass or less.

In one embodiment of the magneto-rheological fluid according to the invention, said magneto-rheological fluid does not comprise resin particles.

・Method for preparing magneto-rheological fluid The method for preparing the magneto-rheological fluid is not particularly limited. can. For example, a method for preparing a magneto-rheological fluid includes preparing a dispersion medium and magnetic particles, adding the dispersion medium to the magnetic particles and stirring, and then optionally adding other additives such as dispersion aids. and stir.

Applications of the magneto-rheological fluid according to the present invention are not particularly limited, and can be used for known MR fluid applications. Applications of magneto-viscoelastic fluids include, for example, robots, brakes, clutches, dampers, shock absorbers, damping devices, haptics, haptic devices, medical devices, welfare devices, and adsorption devices.

(Device)
The device according to the present invention is a device selected from the group consisting of robots, brakes, clutches, dampers, shock absorbers, vibration control devices, haptics, haptic presentation devices, medical equipment, welfare equipment and adsorption devices, and any of the above is a device using a magneto-rheological fluid. This ensures long-term stable driving and excellent mechanical reliability.

EXAMPLES The present invention will be described in more detail below with reference to Examples, but these Examples are intended to illustrate the present invention and do not limit the present invention in any way.

Materials used in the examples are as follows.
・ Magnetic particles: carbonyl iron powder, trade name “CIP-SQ” manufactured by BASF, average particle size 4.5 μm, density 7.87 (g / cc)
- Dispersion medium adipic acid diamide: manufactured by Aoki Oil Industry Co., Ltd., trade name "AA PO-20", two amide groups, L in formula (2) is an alkylene group with 4 carbon atoms, A is an alkylene group with 3 carbon atoms, x is 20 and R is hydrogen. Density 0.92 (g/cc)
Succinic acid diamide: manufactured by Aoki Oil Industry Co., Ltd., trade name "SA PO-20", two amide groups, L in formula (2) is an alkylene group with 2 carbon atoms, A is an alkylene group with 3 carbon atoms, x is 20 , R is hydrogen. Density 0.92 (g/cc)
Succinic acid diamide: manufactured by Aoki Oil Industry Co., Ltd., trade name “SA PO-4”, two amide groups, L in formula (2) is an alkylene group with 2 carbon atoms, A is an alkylene group with 3 carbon atoms, x is 4 , R is hydrogen. Density 0.93 (g/cc)
Comparative dispersion medium polyoxyethylene oleylamide: manufactured by Aoki Yushi Kogyo Co., Ltd., trade name "Brownon O-15", 1 amide group, polyoxyethylene adduct of oleic acid amide, number of repetitions of polyoxyethylene 7, density 0 .92 (g/cc)
Succinic acid diester: trade name “SAES PO-4” manufactured by Aoki Yushi Kogyo Co., Ltd., formula: H(OC ₃ H ₆ ) ₄ OCOC ₂ H ₄ COO(C ₃ H ₆ O) ₄ H, density 0.91 (g/cc)
・ Resin particles: styrene-acrylic acid copolymer fine particles (crosslinked resin particles), trade name “MG-451” manufactured by Nippon Paint Industrial Coatings, average particle size 100 nm, density 1.01 (g / cc)

The devices used in the examples are as follows.
Three-roll disperser: trade name "50I" manufactured by EXAKT
Rheometer: Anton Paar's product name "MCR 302", equipped with a double gap structure MRD cell (magnetic field measurement unit)

(Examples 1-11 and Comparative Examples 1-4)
Magnetic particles, a dispersion medium, a comparative dispersion medium, and resin particles were prepared according to the formulations (% by mass) shown in Table 1. A vessel was filled with magnetic particles, then either or both of the dispersion medium and the comparative dispersion medium were added and stirred briefly until uniform. The mixture was then dispersed with a 3-roll disperser at the narrowest opening 5 times to prepare a magneto-rheological fluid or a comparative MR fluid.

Dispersion stability, flowability, and maximum change in yield stress were measured for each magneto-rheological or comparative MR fluid prepared as follows.

(dispersion stability)
Immediately after preparation of the magneto-rheological fluid or comparative MR fluid, a 30 mL sample tube was immediately filled up to the shoulder with the magneto-rheological fluid or comparative MR fluid and stored at 25°C. For the magneto-rheological fluid or the comparative MR fluid after storage for 90 days, the distance (separation width) from the shoulder of the sample tube to the interface where the dispersion medium and the magnetic particles were separated was measured, and the dispersion stability was evaluated according to the following criteria. evaluated. The smaller the separation width, the better the dispersion stability. Criteria A, B or C at 90 days after storage pass.
・ Criteria A: No separation is observed B: Separation width is 5 mm or less C: Separation width is over 5 mm and 10 mm or less D: Separation width is over 10 mm

(Liquidity)
2 cc of the immobilized magneto-rheological fluid or comparative MR fluid was removed from the container onto a plate and allowed to stand at 25° C. for 5 minutes. Then, the state of the magneto-rheological fluid or the comparative MR fluid was observed and evaluated according to the following criteria.
Pass: The magneto-rheological fluid or comparative MR fluid flowed and flattened. Fail: The magneto-rheological fluid or comparative MR fluid maintained its initial shape.

(maximum amount of change in yield stress)
A rheometer was filled with 0.6 mL of a magneto-rheological fluid or a comparative MR fluid, and 10% strain, 10 Hz frequency vibration analysis was performed under magnetic field application conditions with a magnetic flux density of 1 T (Tesla). The shear yield stress (Pa) generated under the magnetic field application conditions was measured and evaluated according to the following criteria. The results are also shown in Table 1.
A: Shear yield stress exceeds 20000 Pa B: Shear yield stress exceeds 7000 Pa to 20000 Pa or less C: Shear yield stress is 7000 Pa or less

As shown in Table 1, according to the present invention, it was possible to provide a magneto-rheological fluid that has excellent long-term dispersion stability of magnetic particles and excellent fluidity.

According to the present invention, it is possible to provide a magneto-rheological fluid that exhibits excellent long-term dispersion stability of magnetic particles and excellent fluidity. Moreover, according to the present invention, it is possible to provide a device that is stable for a long period of time and has excellent mechanical reliability.

Claims (8)

A magneto-rheological fluid comprising magnetic particles and a dispersion medium,
The dispersion medium contains an organic compound having two or more amide groups in one molecule,
A magneto-rheological fluid, wherein the volume ratio of the organic compound to the total volume of the magneto-rheological fluid is 48-85%. The organic compound has the formula (1):

has
wherein L is a linking group with a valence of y;
R is hydrogen or a methyl group;
A is an alkylene group,
x is a number from 1 to 30,
2. The magneto-rheological fluid of claim 1, wherein y is a number greater than or equal to 2. 3. The magneto-rheological fluid of claim 2, wherein said linking group is a hydrocarbon group. 3. The magneto-rheological fluid of claim 2, wherein L is an alkylene group. 5. The magneto-rheological fluid according to claim 4, wherein said L is an alkylene group having 2 to 8 carbon atoms. The magneto-rheological fluid according to any one of claims 1 to 4, wherein the magnetic particles have an average particle size of 1 to 50 µm. The magneto-rheological fluid according to any one of claims 1 to 6, wherein the magneto-rheological fluid does not contain resin particles. Any one of claims 1 to 7 for devices selected from the group consisting of robots, brakes, clutches, dampers, shock absorbers, vibration control devices, haptics, haptic presentation devices, medical equipment, welfare equipment and adsorption devices A device using the magneto-rheological fluid described in .