magnetorheological fluid

Abstract

To obtain a magnetic viscous fluid with a good balance between viscosity and sedimentation.SOLUTION: A magnetic viscous fluid includes a magnetic material, a medium that can disperse the magnetic material, a dispersant that disperses the magnetic material in the medium while forming a magnetic material holding structure that holds the magnetic material, and a reinforcing agent that reinforces the magnetic material holding structure, and the blending amount of the magnetic material is 25 weight% to 75 weight% with respect to the sum of the medium and the magnetic material, and the blending amount of the medium is 25 weight% to 75 weight% with respect to the sum of the medium and the magnetic material. The blending amount of the dispersant is 0.5 weight% to 6 weight% with respect to the sum of the medium and the magnetic material, and the blending amount of the reinforcing agent is 5 weight% to 300 weight% with respect to the weight of the dispersant.SELECTED DRAWING: None

Description

[Technical Field]

[0001] The present invention relates to magnetorheological fluids. [Background technology]

[0002] Magneto-rheological (MR) fluids are fluids in which magnetic particles such as iron or magnetite are dispersed in a predetermined dispersion medium (see, for example, Patent Document 1). Because magnetorheological fluids are materials whose rheological properties and mechanical properties can be controlled, they are primarily used in linear motion devices such as mounting devices and damper devices for automobiles and seat dampers for construction machinery. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Special Publication No. 2006-505937 Summary of the Invention [Problem to be solved by the invention]

[0004] However, magnetorheological fluids have the problem of causing aggregation due to settling of magnetic particles when left unattended. In such cases, a thixotropic agent is added to the medium, which increases the viscosity of the medium and suppresses the settling rate of the magnetic particles. By imparting thixotropy to the magnetorheological fluid, the settling of magnetic particles when left unattended is suppressed, while the dynamic viscosity is reduced, allowing the fluid to exhibit its properties as a magnetic fluid.

[0005] However, increasing the static viscosity of a magnetorheological fluid to sufficiently suppress the settling of magnetic particles leads to problems such as difficulty in handling, and the increased dynamic viscosity also makes it difficult to obtain the properties required for a magnetorheological fluid. An object of the present invention is to obtain a magnetorheological fluid having a good balance between viscosity and sedimentation properties. [Means for solving the problem]

[0006] According to the present invention, there is provided a magnetorheological fluid comprising a magnetic material, a medium capable of dispersing the magnetic material, a dispersant that disperses the magnetic material in the medium while forming a magnetic material holding structure that holds the magnetic material, and a reinforcing agent that reinforces the magnetic material holding structure, wherein the amount of the magnetic material is 25% to 75% by weight of the sum of the medium and the magnetic material, the amount of the medium is 25% to 75% by weight of the sum of the medium and the magnetic material, the amount of the dispersant is 0.5% to 6% by weight of the sum of the medium and the magnetic material, and the amount of the reinforcing agent is 5% to 300% by weight of the weight of the dispersant.

[0007] Here, the dispersant preferably contains a rheology control agent. Furthermore, it is preferable that the dispersant contains silica, and the magnetic material holding structure has a network structure. The silica preferably has a primary particle size of greater than 10 nm. The silica is preferably wet-process silica. The wet-process silica preferably has a secondary particle diameter of less than 2.5 μm. The reinforcing agent is preferably selected from polyhydroxycarboxylic acid derivatives. Furthermore, the polyhydroxycarboxylic acid derivative preferably includes a polyhydroxycarboxylic acid amide or a polyhydroxycarboxylic acid ester. [Effects of the Invention]

[0008] According to the present invention, a magnetorheological fluid having a good balance between viscosity and sedimentation properties can be obtained. DETAILED DESCRIPTION OF THE INVENTION

[0009] Hereinafter, modes for carrying out the present invention will be described (hereinafter, "embodiments"). Note that the present invention is not limited to the following embodiments, and various modifications can be made within the scope of the gist of the present invention.

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

[0011] In this embodiment, the blending amount of the medium in the magnetorheological fluid is typically 25% to 75% by weight, preferably 30% to 50% by weight, based on the sum of the medium and magnetic material. If the amount of medium in the magnetorheological fluid is too small, the viscosity increases significantly, and the fluidity of the magnetorheological fluid itself tends to decrease, which is undesirable. If the amount of medium in the composition is too large, 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 undesirable.

[0012] (magnetic material) In this embodiment, the magnetic material may be a paramagnetic compound, a superparamagnetic compound, or a ferromagnetic compound. Specific examples include iron, iron alloys, iron oxide, iron nitride, iron carbide, chromium dioxide, low-carbon steel, silicon steel, nickel, cobalt, and mixtures thereof. Iron oxides include pure iron oxide and those containing small amounts of manganese, zinc, barium, etc. Other examples include iron powders with hydrophilic surface treatments such as carbonyl iron powder, iron with an oxide film formed on the surface (hard grade), iron with the oxide film removed (soft grade), magnetite, manganese-zinc ferrite, etc. Furthermore, alloys containing aluminum, silicon, cobalt, nickel, vanadium, molybdenum, chromium, tungsten, manganese, copper, etc. may also be used. Depending on the solvent used, these surfaces may be hydrophobized.

[0013] The particle size of the magnetic material is usually 0.5 μm to 50 μm, preferably 1 μm to 20 μm. If the particle size of the magnetic material is too small, sufficient shear stress tends to be insufficient when an external magnetic field is applied, which is undesirable. If the particle size of the magnetic material is too large, the magnetic particles tend to settle easily and friction during sliding tends to increase, which is undesirable.

[0014] In this embodiment, the blending amount of the magnetic material in the magnetorheological fluid is typically 25% to 75% by weight, preferably 50% to 70% by weight, based on the total weight of the medium and magnetic material. If the amount of magnetic material in the magnetorheological fluid is too small, the dynamic viscosity does not increase under magnetic field application conditions, and the performance of the magnetorheological fluid tends to be significantly inferior, which is undesirable. If the amount of magnetic material in the magnetorheological fluid is too large, the fluid tends to become clay-like, and the flowability, which is a characteristic of magnetorheological fluids, tends to be significantly reduced, which is undesirable.

[0015] (dispersant) The dispersant used in this embodiment is a substance that disperses the magnetic particles in a medium while enveloping them in a mesh-like manner, and forms a mesh in the medium. That is, the dispersant disperses the magnetic material in the medium while forming a magnetic material holding structure that holds the magnetic material. Such a magnetic material holding structure has a mesh structure. Such substances include thickeners that increase the viscosity of the composition by adding rheology control agents, polymeric thickeners, polysaccharide thickeners, etc.; surfactants that adsorb to magnetic particles, such as nonionic surfactants, amphoteric surfactants, polymeric surfactants, pigment dispersants, fatty acids, amines, amides, imides, metal soaps, fatty acid oligomer compounds, silane coupling agents, titanate coupling agents, and aluminate coupling agents.

[0016] Among these, rheology control agents are preferred as additives that impart flow characteristics such as increasing the shear viscosity of the magnetorheological fluid in the low shear rate range while decreasing the shear viscosity in the high shear rate range. Examples of rheology control agents include inorganic compound-based rheology control agents such as silica (e.g., wet process silica, dry process silica, gel process silica) and clay; and organic compound-based rheology control agents such as urea-modified polymers, urethane-modified polymers, castor oil wax, polyethylene wax, polyamide wax, fatty acid amide wax, fibrous polymer compounds, and cellulose nanofibers (CNF). These rheology control agents may be used alone or in combination of two or more.

[0017] In the present embodiment, for example, when wet-process silica is used as the rheology control agent, the particle size of the wet-process silica is typically 3 nm or more in primary particle size and 20 μm or less in secondary particle size. Furthermore, when dry-process silica is used, the primary particle size is typically 7 nm or more. If the silica particle size is too small, the silica particles tend to aggregate and form agglomerates, which is undesirable. If the silica particle size is too large, the mesh size of the three-dimensional network structure formed by the silica tends to become large, which is undesirable, as it reduces the retention effect.

[0018] In this embodiment, the amount of dispersant in the magnetorheological fluid is typically 0.5 to 6% by weight, preferably 2 to 6% by weight, based on the total weight of the medium and magnetic material. If the amount of dispersant in the magnetorheological fluid is too small, a network structure sufficient to hold the magnetic material cannot be formed, which tends to reduce sedimentation resistance, and is therefore undesirable. If the amount of dispersant in the magnetorheological fluid is too large, the viscosity of the magnetorheological fluid increases, which tends to reduce degassing and handling of the fluid, and is therefore undesirable.

[0019] (reinforcing agent) In this embodiment, by blending a reinforcing agent, the magnetic material formed by the dispersant described above is enclosed and the magnetic material in the medium is Magnetic material holding structureThis reinforces the magnetic particles. This inhibits aggregation of the magnetic particles, reducing the sedimentation of the magnetic particles. Examples of the reinforcing agent include polyhydroxycarboxylic acid derivatives. Specific examples of polyhydroxycarboxylic acid derivatives include polyhydroxycarboxylic acid amides and polyhydroxycarboxylic acid esters.

[0020] In this embodiment, the content of the reinforcing agent in the magnetorheological fluid is typically 5% by weight to 300% by weight, and preferably 10% by weight to 200% by weight, relative to the weight of the dispersant. If the amount of reinforcing agent in the magnetorheological fluid is too small, the reinforcing effect of the structure formed by the dispersant is insufficient, and the sedimentation resistance of the magnetic material tends to decrease, which is undesirable. If the amount of reinforcing agent in the magnetorheological fluid is too large, the reinforcing agents self-associate with each other, and the reinforcing effect of the structure formed by the dispersant is insufficient, and the sedimentation resistance of the magnetic material tends to decrease, which is undesirable.

[0021] In addition to the components described above, the magnetorheological fluid according to this embodiment may contain other additives, such as anti-wear agents, extreme pressure agents, rust inhibitors, friction modifiers, solid lubricants, antioxidants, anti-foaming agents, colorants, viscosity modifiers, etc. In this case, these additives may be used alone or in combination of two or more. [Example]

[0022] The present invention will be described in more detail below based on examples. However, the present invention is not limited to these examples. In the examples and comparative examples, all parts and percentages are by weight unless otherwise specified.

[0023] (1) Preparation of magnetorheological fluid Magnetorheological fluids having 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 combination of the dispersant and the reinforcing agent, and the viscosity increases. At this time, the magnetic material is held in place by the magnetic material holding structure, which consists of gaps in the network structure. After that, when 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 the fluid can be prepared by mixing the medium, magnetic material, dispersant, reinforcing agent, and other additives as required in any order.

[0024] (2) Testing of magnetorheological fluids (a) Sedimentation test The magnetorheological fluid was prepared in a sample bottle (container volume 24 ml) and stored at 23°C. After 1000 hours, the height (amount of separation [mm]) from the fluid surface to the interface where the medium (supernatant) and the magnetic mixture component (settling component) separated was measured relative to the total fluid height of the magnetorheological fluid (total liquid volume [mm]), and the dispersion stability was evaluated using the sedimentation rate [%] = (amount of separation [mm] / total liquid volume [mm]) x 100. The smaller the sedimentation rate [%], the better the resistance to sedimentation.

[0025] (b) Kinematic viscosity measurement Using a Brookfield viscometer, the kinematic viscosity (cSt) of a magnetorheological fluid placed in a sample bottle was measured at 25°C with and without a magnetic field applied using a magnet base (model MB-T3) manufactured by Kanetec Corporation. The smaller the measured value, the lower the viscosity.

[0026] (c) Magnetic field characteristics The ratio of the dynamic viscosity with an applied magnetic field (ON) to the dynamic viscosity without an applied magnetic field (OFF) (dynamic viscosity ratio: ON / OFF ratio) was calculated and used as an index of the magnetic field properties of the magnetorheological fluid. The larger the dynamic viscosity ratio (ON / OFF ratio), the wider the range of applications and the easier it is to use the magnetorheological fluid.

[0027] (Examples 1 to 10, Comparative Examples 1 to 5) The sedimentation tendency, dynamic viscosity, and shear stress of the magnetorheological fluids shown in Tables 1 and 2 were measured (Examples 1 to 10). As comparative examples, the compositions shown in Table 3 were prepared, and the sedimentation tendency and dynamic viscosity were measured under the same conditions as in Example 1 (Comparative Examples 1 to 5). The results are shown in Tables 1 to 3. The amount of reinforcing agent in Tables 1 to 3 is shown as the concentration (wt%) relative to the dispersant added to the magnetorheological fluid. The origins of the components of the magnetorheological fluids used in the examples and comparative examples are shown in the lower columns of Table 2.

[0028] [Table 1]

[0029] [Table 2]

[0030] (medium) Ethylene glycol solvent: CCI Co., Ltd.

[0031] (magnetic material) Carbonyl iron powder 1: MRF-35 manufactured by Jiangsu Tianyi Ultra-Fine Metal Powder Co., Ltd., particle size 2.5 microns Carbonyl iron powder 2: YMIM-73 manufactured by Jiangsu Tianyi Ultra-Fine Metal Powder Co., Ltd., particle size 5.0 microns

[0032] (dispersant) Silica 1: Nipseal CX-200 manufactured by Tosoh Corporation, primary particle size = 4 nm, secondary particle size = 1.7 μm Silica 2: Nipseal E-200A manufactured by Tosoh Corporation, primary particle size = 20 nm, secondary particle size = 2.5 to 3.5 μm Silica 3: Nipseal SP-200 manufactured by Tosoh Corporation, primary particle size = 15 nm, secondary particle size = 1 to 2 μm Silica 4: Nipseal VN3 manufactured by Tosoh Corporation, primary particle size = 15 nm, secondary particle size = 18 μm or more

[0033] (reinforcing agent) Polyhydroxycarboxylic acid amide derivative: RHEOBKY-7405 (solution of polyhydroxycarboxylic acid amide in polypropylene glycol 600, concentration 52%) manufactured by BYK-Chemie GmbH Polyhydroxycarboxylic acid ester derivative: RHEOBKY-606 (polyhydroxycarboxylic acid ester alone) manufactured by BYK-Chemie GmbH

[0034] [Table 3]

[0035] From the results shown in Tables 1 and 2, it can be seen that the magnetorheological fluids according to the present embodiment (Examples 1 to 10) have suppressed sedimentation and aggregation of the magnetic material contained therein, and are magnetorheological fluids with a good balance between viscosity and sedimentation.

[0036] In contrast, when no reinforcing agent (polyhydroxycarboxylic acid derivative) was added (Comparative Examples 1 and 2), the sedimentation properties of the magnetic material were not improved. When the amount of dispersant (silica) added was excessively high (8 wt%) (Comparative Example 3), the fluid became clayey, making it difficult to measure the dynamic viscosity. When the amount of magnetic material (carbonyl iron powder) added was excessively low (20 wt%) (Comparative Example 4), the dynamic viscosity ratio (ON / OFF ratio) was 29, but the dynamic viscosity of the magnetorheological fluid was low, and even when a magnetic field was applied, the dynamic viscosity was low, indicating poor performance as a magnetorheological fluid. When the amount of magnetic material (carbonyl iron powder) added was excessively high (80 wt%) (Comparative Example 5), the fluid became clayey, making it difficult to measure the dynamic viscosity.

Claims

1. A magnetic material, a medium containing ethylene glycol or propylene glycol in which the magnetic material can be dispersed; wet-process silica as a dispersant that disperses the magnetic material in the medium while forming a magnetic material holding structure that holds the magnetic material; a reinforcing agent that reinforces the magnetic body holding structure, the blending amount of the magnetic material is 25% by weight to 70% by weight of the total of the medium and the magnetic material; The blending amount of the medium is 30% by weight to 75% by weight of the sum of the medium and the magnetic material (however, the sum of the magnetic material and the medium is 100% by weight), the blending amount of the dispersant is 0.5% by weight to 6% by weight based on the sum of the medium and the magnetic material; The amount of the reinforcing agent to be blended is 5% by weight to 300% by weight based on the weight of the dispersant. A magnetorheological fluid characterized by:

2. 2. The magnetorheological fluid according to claim 1, wherein the medium is a mixture of ethylene glycol, propylene glycol, and water.

3. 2. The magnetorheological fluid according to claim 1, wherein the magnetic material holding structure formed by the wet process silica as the dispersant has a network structure.

4. 2. The magnetorheological fluid according to claim 1, wherein the wet-process silica has a primary particle diameter of greater than 10 nm.

5. 2. The magnetorheological fluid according to claim 1, wherein the wet-process silica has a secondary particle diameter of less than 2.5 μm.

6. 2. The magnetorheological fluid according to claim 1, wherein the reinforcing agent is selected from polyhydroxycarboxylic acid derivatives.

7. 7. The magnetorheological fluid according to claim 6, wherein the polyhydroxycarboxylic acid derivative comprises a polyhydroxycarboxylic acid amide or a polyhydroxycarboxylic acid ester.

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