Magnetoviscous fluid

Abstract

To obtain a magnetic viscous fluid that utilizes the properties of a thixotropic agent and has balanced sedimentation properties.SOLUTION: A magnetic viscous fluid includes a magnetic agent and a medium capable of dispersing the magnetic agent, and contains at least one dispersant selected from sepiolite and smectite, or a dispersant consisting of sepiolite and bentonite.SELECTED DRAWING: None

Description

Technical Field

[0001] The present invention relates to a magnetorheological fluid.

Background Art

[0002] A magnetorheological (MR) fluid is a fluid in which magnetic substances such as iron and magnetite are dispersed in a predetermined dispersion medium (see, for example, Patent Document 1).

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] When a magnetorheological fluid is left standing, there is a problem that the magnetic substance settles. Therefore, as a countermeasure against the settlement of the magnetic substance, for example, a thickener or a high-viscosity medium is used, or a thixotropic agent addition technique for suppressing the precipitation rate of the magnetic substance is adopted. However, in the above thixotropic agent addition technique, even if the magnetorheological fluid has a high viscosity in a static state, it has a problem that the hydrogen bonds between the thixotropic agents are broken in a dynamic state, resulting in a decrease in viscosity and causing the settlement of the magnetic substance. An object of the present invention is to obtain a magnetorheological fluid that utilizes the characteristics of a thixotropic agent and has a balanced sedimentation property.

Means for Solving the Problems

[0005] According to the present invention, there is provided a magnetorheological fluid comprising a magnetic substance, a medium in which the magnetic substance can be dispersed, and at least one dispersant selected from sepiolite and smectite.

[0006] Furthermore, the present invention provides a magnetorheological fluid characterized by comprising a magnetic material, a medium capable of dispersing the magnetic material, and a dispersant comprising sepiolite and bentonite.

[0007] In this case, it is preferable that the concentration of the magnetic material in the magnetorheological fluid is 25% to 75% by weight, the concentration of the medium is 25% to 75% by weight, and the concentration of the dispersant is 0.5% to 6% by weight. Furthermore, it is preferable to include a reinforcing agent. The reinforcing agent is preferably selected from polyhydroxycarboxylic acid derivatives, including polyhydroxycarboxylic acid amides or polyhydroxycarboxylic acid esters. In the magnetorheological fluid, the concentration of the reinforcing agent is preferably 0.025% to 18% by weight. [Effects of the Invention]

[0008] According to the present invention, a magnetorheological fluid with a balanced settling property can be obtained by utilizing the properties of the thixotropic agent. [Modes for carrying out the invention]

[0009] The following describes embodiments for carrying out the present invention (hereinafter referred to as embodiments). However, the present invention is not limited to the following embodiments and can be implemented in various ways within the scope of its gist.

[0010] (medium) In this embodiment, mineral oil, vegetable oil, glycol-based liquid, silicone oil, water, etc., can be used as the medium for the magnetorheological fluid. Specifically, examples include poly-α-olefin, rapeseed ester oil, hydrocarbon oil, ethylene glycol, propylene glycol, isoparaffin, alkylnaphthalene, fluorine oil, perfluoroether, etc. These mediums can be used individually or in various mixtures. In this embodiment, a mixed medium of ethylene glycol, propylene glycol, and water is used as the medium.

[0011] In this embodiment, the concentration of the medium in the magnetorheological fluid is 25% to 75% by weight, preferably 30% to 50% by weight. If the amount of medium in the magnetorheological fluid is excessively low, the viscosity of the viscous fluid tends to increase significantly, and the fluidity of the magnetorheological fluid itself tends to decrease, which is undesirable. If the amount of medium in the composition is excessively high, the relative content of the magnetic material decreases, and sufficient viscosity change and shear stress tend not to be obtained when a magnetic field is applied, which is also undesirable.

[0012] (magnetic material) In this embodiment, paramagnetic compounds, superparamagnetic compounds, and ferromagnetic compounds are used as magnetic materials. Specifically, examples include iron, iron alloys, iron oxide, iron nitride, iron carbide, chromium dioxide, low-carbon steel, silicon steel, nickel, cobalt, and mixtures thereof. Iron oxide includes pure iron oxide and those containing small amounts of manganese, zinc, barium, etc. Other examples include magnetic materials with hydrophilic surface treatment, carbonyl iron powder, iron with an oxide film formed on the surface (hard grade), iron with the oxide film removed from the surface (soft grade), magnetite, manganese zinc ferrite, etc. Furthermore, alloys containing aluminum, silicon, cobalt, nickel, vanadium, molybdenum, chromium, tungsten, manganese, copper, etc. can also be used. Depending on the solvent used, these surfaces may also be subjected to hydrophobic treatment.

[0013] The particle size of the magnetic material is typically 0.5 μm to 50 μm, preferably 1 μm to 20 μm. If the particle size of the magnetic material is excessively small, it tends not to provide sufficient shear stress when an external magnetic field is applied, which is undesirable. If the particle size of the magnetic material is excessively large, it tends to cause the magnetic material to settle easily and increases friction during sliding, which is also undesirable.

[0014] In this embodiment, the concentration of magnetic material in the magnetorheological fluid is 25% to 75% by weight, preferably 50% to 70% by weight. If the amount of magnetic material in the magnetorheological fluid is excessively low, the kinematic viscosity under the applied magnetic field conditions will not increase, and the performance as a magnetorheological fluid will be significantly inferior, which is undesirable. If the amount of magnetic material in the magnetorheological fluid is excessively high, the fluid will become clay-like, and the fluidity, which is a characteristic of magnetorheological fluids, will be extremely reduced, which is also undesirable.

[0015] (Dispersant) The dispersant used in this embodiment is considered to be a substance that disperses magnetic materials in a medium while enclosing them in a network structure, and also forms a network within the medium. Examples of substances that can be used as a dispersant include sepiolite, smectite, and bentonite.

[0016] (Sepiolite) Sepiolite is a naturally occurring clay mineral that is a hydrated magnesium silicate with a chain-like structure, unlike common layered clay minerals such as kaolin and talc. A typical chemical structure of sepiolite is shown in equation (1) below. Mg8(OH)4Si 12 O 30 (H2O) 12 (1) The chemical composition is determined by the X-ray fluorescence fundamental parameter method. Furthermore, the chemical composition of sepiolite can vary depending on its origin and refining method, and the molar ratio of Si to Mg is not limited to that shown in equation (1). Additionally, it may contain impurities such as Ca, Al, and Fe. Sepiolite exists in two forms: the long-fiber α-type and the clay-like β-type. Sepiolite from China is mainly α-type, while sepiolite from Spain, Turkey, and the United States is mainly β-type. The inclusion of sepiolite as a dispersant is preferable because it tends to suppress rusting of magnetic materials. This means that, for example, when used primarily as a linear motion device such as mounting devices and damper devices for automobiles and seat dampers for construction machinery, wear prevention during operation can be expected.

[0017] (Smectite) Smectite is a silicate mineral having a tetrahedral layered structure of Si-O, and various natural or synthetic clay minerals can be used. For example, dioctahedral smectites such as montmorillonite (acidic clay, bentonite, etc.), beidellite, nontronite; trioctahedral smectites such as saponite, hectorite, sauconite, frypontite; and stevensite, etc. can be exemplified, and these may be used alone or in combination of two or more. Among these, at least one structure selected from the group consisting of montmorillonite and stevensite is preferable. These structures have isomorphous substitution, defects, etc. with low-valent metal elements in a part of the metal elements of the octahedral sheet.

[0018] (Bentonite) Bentonite is a clay mainly composed of montmorillonite and has a structure in which several three-layer structures composed of SiO4 tetrahedral layer - AlO6 octahedral layer - SiO4 tetrahedral layer are stacked. Between the layers of this three-layer structure, there are cations of alkali metals such as K and Na, alkaline earth metals such as Ca; hydrogen ions; water molecules coordinated to the hydrogen ions. Examples of bentonite include natural bentonite, calcium-type bentonite, and activated bentonite such as sodium-type bentonite produced by alkali treatment of natural bentonite or acid clay.

[0019] In the present embodiment, at least one dispersant selected from sepiolite and smectite is used. Also, in the present embodiment, a dispersant composed of sepiolite and bentonite is used.

[0020] In this embodiment, the concentration of the dispersant in the magnetorheological fluid is 0.5% to 6% by weight, preferably 2% to 6% by weight. If the amount of dispersant in the magnetorheological fluid is excessively low, a sufficient network structure to hold the magnetic material cannot be formed, and the settling resistance tends to decrease, which is undesirable. If the amount of dispersant in the magnetorheological fluid is excessively high, the viscosity of the magnetorheological fluid increases, and the degassing ability and handling workability of the fluid, which can cause cavitation, tend to decrease, which is also undesirable.

[0021] (Reinforcement agent) In this embodiment, the network is reinforced by incorporating a reinforcing agent. This suppresses aggregation between magnetic materials and reduces the settling properties of the magnetic materials. Examples of reinforcing agents include polyhydroxycarboxylic acid derivatives. Specific examples of polyhydroxycarboxylic acid derivatives include polyhydroxycarboxylic acid amides and polyhydroxycarboxylic acid esters.

[0022] In this embodiment, the concentration of the reinforcing agent in the magnetoviscous fluid is 0.025% to 18% by weight, preferably 0.05% to 12% by weight. If the amount of reinforcing agent in the magnetoviscous fluid is excessively low, the reinforcing effect of the structure formed by the dispersant will not be sufficiently obtained, and the sedimentation resistance of the magnetic material tends to decrease, which is undesirable. If the amount of reinforcing agent in the magnetoviscous fluid is excessively high, the reinforcing agents will self-associate with each other, so the reinforcing effect of the structure formed by the dispersant will not be sufficiently obtained, and the sedimentation resistance of the magnetic material tends to decrease, which is also undesirable.

[0023] Furthermore, the magnetorheological fluid according to this embodiment may contain, if necessary, other additives in addition to the components described above, such as anti-wear agents, extreme pressure agents, rust inhibitors, friction modifiers, solid lubricants, antioxidants, defoamers, colorants, viscosity modifiers, and so on. In this case, each of these additives may be used individually or in combination of two or more types. [Examples]

[0024] The present invention will be described in more detail below based on examples. However, the present invention is not limited to these examples. All percentages in the examples and comparative examples are based on weight unless otherwise specified.

[0025] (1) Preparation of magnetoviscous fluid Magnetorheological fluids with the compositions shown in Table 1 were prepared. First, a dispersant and a reinforcing agent are added to the medium and stirred. Next, a magnetic material is added and stirred. When stirring is stopped, a network structure is formed by the bonding of the dispersant and reinforcing agent, and the viscosity increases. At this time, the magnetic material is held in place by the magnetic material holding structure formed by the gaps in the network structure. Subsequently, when a shear force is applied to the solution again, the network structure collapses, and the viscosity decreases. The method for producing the magnetorheological fluid according to this embodiment is not particularly limited, and it can be prepared by mixing the medium, magnetic material, dispersant, reinforcing agent, and other additives as needed in any order.

[0026] (2) Testing of magnetoviscous fluids (a) Settling test A magnetorheological fluid was prepared in a sample bottle (container capacity 24 ml) and stored at 23°C. After 240 hours, the height from the fluid surface to the interface where the medium (supernatant) and the magnetic material mixture component (sedimented component) separated (separation amount [mm]) was measured relative to the total fluid height (total liquid volume [mm]) of the magnetorheological fluid. The dispersion stability was evaluated using the sedimentation rate [%] = (separation amount [mm] / total liquid volume [mm]) × 100. A smaller sedimentation rate [%] indicates better resistance to sedimentation.

[0027] (b) Kinematic viscosity measurement Using a Type B viscometer, the kinematic viscosity (cSt) of a magnetorheological fluid placed in a sample vial was measured under two conditions: with and without a magnetic field, using a Kanetec Corporation magnetic base (model MB-T3). A smaller measured value indicates lower viscosity.

[0028] (c) Magnetic field characteristics The ratio of the kinematic viscosity under magnetic field application conditions (ON) to the kinematic viscosity under unapplied magnetic field conditions (OFF) (kinematic viscosity ratio: ON / OFF ratio) was determined and used as an indicator of the magnetic field characteristics of the magnetorheological fluid. A larger kinematic viscosity ratio (ON / OFF ratio) indicates a more widely applicable and user-friendly magnetorheological fluid.

[0029] (Examples) 2、4、6、8、10、 12. Comparative Example 1) For the magnetorheological fluids shown in Tables 1 to 3, the sedimentation rate and kinematic viscosity were measured (Examples). 2、4、6、8、10、 12). In addition, as a comparative example, the compositions shown in Table 1 were prepared, Reference example The settling rate and kinematic viscosity were measured under the same conditions as in 1 (Comparative Example 1). The results are shown in Tables 1 to 3. The amounts of each component in Tables 1 to 3 are listed as the concentration (weight %) in the magnetorheological fluid. The components of the magnetorheological fluid used in the examples and comparative examples are listed in the lower column of Table 3.

[0030] [Table 1]

[0031] [Table 2]

[0032] [Table 3]

[0033] (medium) 1) Ethylene glycol-based solvent: Manufactured by CCI Corporation

[0034] (magnetic material) 2) Carbonyl iron powder: MRF-35, manufactured by Jiangsu Tianyi Ultra-Fine Metal Powder Co., Ltd., particle size 2.5 microns

[0035] (Reinforcement agent) 3) Polyhydroxycarboxylic acid amide derivative: RHEOBKY-7405 (Polyhydroxycarboxylic acid amide in polypropylene glycol 600, concentration 52%) manufactured by BYK-Chemie GmbH.

[0036] (Dispersant) 4) Sepiolite 1: TOLSA PANGEL B20 5) Sepiolite 2: TOLSA PANGEL B42 6) Hectorite: Smecton-SEN manufactured by Kunimine Industries Co., Ltd. 7) Montmorillonite: Kunimine Industries Co., Ltd. Kunipia-RC-G 8) GARA manufactured by BYK MI TE-7305 9) GARA manufactured by BYK MI TE-1958

[0037] The results shown in Tables 1 to 3 indicate that when sepiolite is used as a dispersant (Examples) 2、 Example 4) Smectite as a dispersant (Hectolite, Montmorillonite) When this is incorporated (Example) 6、 Example 8) shows that the sedimentation rate (%) of the magnetic material contained in the magnetorheological fluid is improved. Examples 2、4、6、 In step 8, by incorporating a reinforcing agent (polyhydroxycarboxylic acid amide derivative), the law of nature, A trend towards improvement in the sedimentation rate (%) of magnetic materials is observed.

[0038] Furthermore, when sepiolite and bentonite are incorporated as dispersants (Examples) 10、 Example 12) shows that the sedimentation rate (%) of magnetic material contained in the magnetorheological fluid is significantly improved. In this case as well, by incorporating a reinforcing agent (polyhydroxycarboxylic acid amide derivative) (Examples 10 and 12), there is a tendency for the sedimentation rate (%) of the magnetic material to improve. Thus, 2、4、6、8、10、From the results in 12, it can be seen that the magnetoviscous fluid according to this embodiment is a magnetoviscous fluid in which the settling and aggregation of magnetic materials are suppressed and the balance between viscosity and settling properties is good.

[0039] In contrast, when none of sepiolite, smectite, or bentonite are included as dispersants (Comparative Example 1), the sedimentation rate (%) of the magnetic material does not improve, indicating that a magnetoviscous fluid with a balanced viscosity as a magnetoviscous fluid and a good sedimentation rate for the magnetic material cannot be obtained.

Claims

1. Magnetic materials and, A medium capable of dispersing the magnetic material, At least one silicate compound selected from sepiolite and smectite, Polyhydroxycarboxylic acid amides, A magnetorheological fluid containing, A magnetorheological fluid characterized in that the concentration of the magnetic material in the magnetorheological fluid is 25% to 58.3% by weight, the concentration of the medium is 25% to 50% by weight, the concentration of the silicate compound is 0.5% to 6% by weight, and the concentration of the polyhydroxycarboxylic acid amide is 0.025% to 18% by weight (however, the sum of the concentrations of each component is adjusted to be 100% by weight).

2. The magnetorheological fluid according to claim 1, characterized in that the medium is at least one selected from ethylene glycol, propylene glycol, and water.

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