KR100884305B1 - A magneto rheological fluid and a process for preparing the same - Google Patents

Abstract

The present invention relates to a magnetorheological fluid comprising a magnetic particle, a dispersion medium, a dispersant and a sedimentation inhibitor and a method of manufacturing the same. The magnetorheological fluid has a low viscosity change due to temperature change, low sedimentation degree, and good viscoelasticity and redispersibility, and thus, the magnetorheological fluid of the present invention has various equipment using magnetorheological fluids such as clutches, dampers, and brakes. It can be widely used in the development of.

Description

Magnetorheological fluid and preparation method thereof {A magneto rheological fluid and a process for preparing the same}

1 is a graph showing the change in viscosity with the temperature of the magnetorheological fluid.

The present invention relates to a magneto rheological fluid and a method of manufacturing the same. More specifically, the present invention relates to a magnetorheological fluid having improved dispersion stability and improved heat resistance and a method of manufacturing the same.

Magnetorheological fluid is a material that reversibly changes the viscosity characteristic of a fluid according to the strength of an externally added magnetic field, and is one of intelligent materials. It refers to a non-colloidal suspension in which iron or nickel cobalt and its magnetic alloy magnetic solids of fine particles of several to several tens of microns in diameter are dispersed in a dispersion medium such as mineral oil, synthetic hydrocarbon, water, silicone oil and esterified fatty acid.

The magnetorheological fluid has a large variation in the flow characteristics such as the viscosity characteristics of the fluid upon application of the magnetic field, is not only excellent in durability, but also relatively less sensitive to contaminants, and has a response speed of 10 ^-3 seconds. It is fast and reversible, so it is highly applicable to various industries such as vibration control device such as automobile clutch, engine mount, damper, high-rise seismic device, and driving device of robotic system. It has significant advantages over other controllable fluids.

The magnetorheological fluid exhibits the properties of Newtonian fluids when no magnetic field is applied, but when the magnetic field is applied, the dispersed particles form a dipole, forming a fiber structure in a direction parallel to the applied magnetic field, which increases the viscosity. It has a shear force or a resistance to flow that hinders the flow of the fluid, thereby greatly increasing the dynamic yield stress. Yield stress at this time increases with the strength of the magnetic field.

In order to use this magnetorheological fluid effectively, the magnetorheological fluid should have high yield stress, the magnetic particles should be distributed uniformly in the dispersion medium, and the fluid will return to its original state if the magnetic field is not applied again after applying the magnetic field. The viscosity of the fluid must be low enough to allow it to return. In addition, there is little change in viscosity due to the change of temperature, so it should always show a constant flow characteristic.

However, magnetorheological fluids are severely hampered by rheological behavior due to gravitational precipitation problems. The main reason for this precipitation is that the density of the dispersion medium is approximately 0.5-3 g / cm 3, whereas the density of the magnetic particles is about 7.86 g / cm 3 and the density of the magnetic particles is much larger than that of the dispersion medium. This is because they tend to precipitate in the dispersion medium. Due to the precipitation of the magnetic particles as described above it is technically very difficult to secure a good dispersion stability of the magnetorheological fluid.

Many methods have been tried to date to prevent the sedimentation of magnetic particles in the magnetorheological fluid to improve dispersion stability of the magnetorheological fluid.

Although a method of securing dispersion stability by using a polymer thickener such as a high molecular weight hydrocarbon or a polyurea has been proposed, it is possible to obtain sufficient stability against precipitation without using a thickener such as grease in the composition of the magnetorheological fluid. Is difficult. In addition, even if sedimentation is minimized, the magnetorheological fluid will exhibit an unacceptably high viscosity that will no longer flow freely.

As another conventional method proposed to increase the dispersion stability of the magnetorheological fluid, a method using fumed silica is proposed. Fumed silica can get excellent sedimentation prevention effect, but if a certain amount or more is used, coagulation occurs during long-term storage, making it difficult to redisperse and the variation of viscosity with temperature is relatively large.

In addition, a method of improving the dispersion stability of the magnetorheological fluid using organic clay has been proposed. However, if a small amount of organic clay is added, the desired sedimentation prevention effect cannot be obtained, and a relatively large amount of fumed silica can be added to obtain a desired dispersion stability. This results in a decrease in the yield stress when applying the magnetic field, that is, the intrinsic property of the magnetorheological fluid.

In US Pat. No. 5,645,752, a thixotropic network was formed using colloidal silica and a silicone oligomer to pursue dispersion stability. However, as described above, the dispersion was not easy to redisperse due to aggregation during long-term storage.

In US Pat. No. 6,203,717, redispersibility was improved using only organic clay, but the addition of excess (3-6 wt% of total magnetorheological fluid) did not overcome the deterioration of magnetorheological properties. In addition, the process of using a polar activator (activator) to activate the organic clay has been added is economically unsuitable.

Therefore, the necessity of developing a magnetorheological fluid with improved dispersion stability has been constantly emerging.

Therefore, the present inventors have made intensive efforts to solve the above problems, and when the fumed silica and the organic clay, which have been used as sedimentation inhibitors in the manufacture of the conventional magnetorheological fluid, are added together, the magnetic particles are uniformly distributed in the dispersion medium. The present invention was completed by discovering that a magnetorheological fluid having low viscosity change due to temperature change and easy redispersibility can be manufactured.

Accordingly, an object of the present invention is to provide a magnetorheological fluid having a uniform distribution of magnetic particles in a dispersion medium, easy redispersibility, and a low viscosity change due to temperature change, and a method of manufacturing the same.

The present invention provides a magnetorheological fluid containing magnetic particles, a dispersion medium, a dispersant and an antisettling agent, wherein the antisettling agent comprises fumed silica and an organic clay.

In addition, the present invention comprises the first step of preparing a dispersion medium to which the anti-settling agent is added by adding and stirring the fumed silica and the organic clay as a sedimentation inhibitor; And a second step of further adding magnetic particles and a dispersant to the dispersion medium to which the anti-settling agent obtained in the first step is added, stirring and pulverizing to produce a magnetorheological fluid. It provides a manufacturing method.

Hereinafter, the present invention will be described in detail.

The present invention provides a magnetorheological fluid containing magnetic particles, a dispersion medium, a dispersant and an antisettling agent, wherein the antisettling agent comprises fumed silica and an organic clay. The magnetorheological fluid is characterized in that the magnetic particles are uniformly distributed in the dispersion medium, the redispersibility is easy, and the viscosity change due to the temperature change is small.

Since the magnetorheological fluid of the present invention contains magnetic particles, upon application of a magnetic field, dipoles are formed to arrange the particles in a row, thereby increasing the viscosity of the fluid to change into a solid form. Here, when the magnetic field is removed, the dipole force is lost, causing the particles to scatter irregularly and return the fluid to its original state. Magnetic particles that can be used in the magnetorheological fluid of the present invention may be particles having a particle diameter of 1 to 100 µm and at least one particle selected from the group consisting of iron, nickel, cobalt, carbonyl iron, soft ferrite, and alloys thereof. And preferably, particles of soft ferrite or carbonyl iron having a particle diameter of 1 to 20 μm. Specific products that can be purchased and used include Carbonyl Iron Powder CD (CM, HS) of BASF Corporation.

The magnetorheological fluid of the present invention is characterized in that it comprises magnetic particles in an amount of 30 to 90% by weight, preferably 55 to 85% by weight relative to the total weight of the magnetorheological fluid. If the content of the magnetic particles is less than 30% by weight, there is a problem that the desired yield stress cannot be obtained.In the case of more than 90% by weight, the yield stress increases when the magnetic field is applied to the magnetorheological fluid, but the dispersion stability is lowered. In use, there is a problem in that the viscosity of the fluid rapidly decreases during use, thereby deteriorating the rheological properties of the fluid, thereby making it impossible to operate devices such as dampers.

As the dispersion medium in the magnetorheological fluid of the present invention, one or more selected from the group consisting of natural fatty oil, mineral oil, paraffin oil, synthetic hydrocarbon oil, fatty acid ester and silicone oil can be used. Preferably, synthetic hydrocarbon oil prepared by adding hydrogen to mineral oil and purifying only pure hydrocarbons is used. Synthetic hydrocarbon oil prepared by the hydrogenation method is used as a high lubricating base oil with a high viscosity index. Specific products that can be purchased and used include YUBASE YU-L3, YUBASE YU-3, YUBASE YU-4 from SK Corp. and NEXBASE 3020, NEXBASE 3030 and NEXBASE from Neste Oil, Finland. 3043 etc. are mentioned. The magnetorheological fluid of the present invention contains the dispersion medium in an amount of 8 to 50% by weight, preferably 8 to 30% by weight, based on the total weight of the magnetorheological fluid. When the amount of the dispersion medium is less than 8% by weight, there is a problem in that the rheological properties of the fluid are lowered due to a sharp increase in viscosity, and when the amount of the dispersion medium exceeds 30% by weight, the yield stress is lowered.

In the manufacture of general magnetorheological fluids, sedimentation inhibitors are used to prevent sedimentation of magnetic particles. In the present invention, anti-settling agents including fumed silica and organoclay are used. Fumed silica is widely used as a sedimentation inhibitor for paints, and has excellent sedimentation prevention effect, but sediment occurs during long-term storage, and has a disadvantage that it hardens and is not restored to its original state. The change is greater than that of organic clay. Organoclay is used in the manufacture of grease and has excellent thermal stability and redispersibility, but its ability to prevent sedimentation is inferior to fumed silica. To obtain the desired anti-sedimentation effect, an excess of organic clay should be used, which leads to a decrease in the magnetic properties resulting in a decrease in the yield stress of the magnetorheological fluid.

The magnetorheological fluid of the present invention contains a sedimentation inhibitor comprising fumed silica and an organic clay, in an amount of 0.1 to 10% by weight, preferably 0.5 to 7% by weight, based on the total weight of the magnetorheological fluid. If the amount of the anti-settling agent is less than 0.1 parts by weight, there is a problem that the dispersion stability is lowered, if it exceeds 10 parts by weight, dispersion stability is improved but yield stress is lowered.

In addition, the anti-settling agent is preferably used by mixing the fumed silica and the organic clay in a weight ratio of 1: 3 to 1: 1.

The fumed silica used in the present invention, preferably the lipophilic fumed silica, can be purchased and used. Specific products that can be purchased include CAB-O-SIL TS-530, TS-610, TS-720, etc. of CABOT having a specific surface area of 100 m² / g or more and a particle diameter of 0.2 to 0.3 μm, and also the specific surface area. DEGUSSA's AEROSIL R711, R7200, R812 etc. which are 100 m <2> / g or more and particle diameter of 20-30 nm are mentioned.

The organoclay used in the present invention is quaternary ammonium bentonite, and the general organoclay should be activated using a polar solvent which is a polar activator, but the quaternary ammonium bentonite used in the present invention does not require an activator to eliminate unnecessary processes. Can be. The organic clay is available from SOUTHERN CLAY PRODUCTS and SUDO CHEMIE, and specific product names include TIXOGEL EZ100, TIXOGEL MP, TIXOGEL MPG, TIXOGEL MP100, TIXOGEL MP100-V, and TIXOGEL MP250.

According to the present invention, by adding the fumed silica and the organic clay as a sedimentation inhibitor in a desirable mixing ratio, the magnetic particles are uniformly distributed in the dispersion medium, easily redispersible, and have a low viscosity change due to temperature change. Can be obtained.

The dispersant in the magnetorheological fluid of the present invention is used to prevent reaggregation of magnetic particles. The dispersant should contain at least one polar group such as amino group (-NH ₂ ), hydroxyl group (-OH), carboxyl group (-COOH) and the like. Water molecules adsorb on the surface of the magnetic particles and contain hydroxyl groups on the surface, thereby forming hydrogen bonds with the polar groups of the dispersant. As a dispersant, fatty acid metal soaps, polyalcohols, ammonium salts, fatty acids, polyethylene oxides, phosphates, phosphonates, and the like may be used. In the present invention, nonylphenol ethylene oxide was used. The magnetorheological fluid of the present invention contains the dispersant in an amount of 0.1 to 10% by weight, preferably 0.5 to 7% by weight based on the total weight of the magnetorheological fluid. When the amount of the dispersant is less than 0.1% by weight, there is a problem in that the dispersion stability is lowered. When the amount of the dispersant is more than 10% by weight, the dispersion stability is improved but the yield stress is lowered.

The magnetorheological fluid of the present invention may further contain additives including antioxidants, rust inhibitors, clean dispersants, viscosity index improvers, antifoaming agents and solid lubricants which are commonly used in the art, as long as they do not adversely affect the effects of the present invention. Can be.

In addition, the present invention comprises the first step of preparing a dispersion medium to which the anti-settling agent is added by adding and stirring the fumed silica and the organic clay as a sedimentation inhibitor; And a second step of adding magnetic particles and a dispersant to the dispersion medium to which the anti-settling agent obtained in the first step is added, stirring and pulverizing to prepare a magnetorheological fluid. It provides a manufacturing method.

The magnetorheological fluid of the present invention has a low viscosity change with time, has a low sedimentation degree, and has good viscoelasticity and redispersibility, so that the magnetorheological fluid can be applied to an apparatus and a system using a magnetorheological fluid.

Hereinafter, the present invention will be described in more detail with reference to Examples. However, the following examples are merely to illustrate the invention, the present invention is not limited by the following examples.

Sedimentation inhibitor  Preparation of Added Dispersion Medium

Reference Example  One

In a 200 ml beaker, 100 g of YUBASE YU-L3 as a dispersion medium, 2 g of fumed silica TS-720 as a sedimentation inhibitor and 6 g of TIXOGEL MP100, an organic clay, were added and stirred at 1,000 rpm for 30 minutes or more.

Reference Example  2 ~ 3

Prepared in the same manner as in Reference Example 1, but prepared by changing the composition ratio to the composition shown in Table 1 below.

Comparative example  1 ~ 2

It was prepared in the same manner as in Reference Example 1, but prepared by changing its composition ratio to the composition as shown in Table 1 below. In detail, organic clay was not added in Comparative Example 1, and fumed silica was not added in Comparative Example 2.

The viscosity of the dispersion medium to which the anti-settling agent of Reference Examples 1 to 3 and Comparative Examples 1 and 2 added according to the present invention was added was 25, which is a driving temperature of a clutch, damper, brake, etc., a device in which a magnetorheological fluid is generally used. It is shown in Table 2 by measuring the viscosity (η) from to 80 ℃. Viscosity measurement was performed using a Brookfield RV type viscometer and measured using spindle # 4,100 rpm.

As shown in Table 2, in the case of Reference Examples 1 to 3 in which fume silica and organic clay, which are anti-settling agents, were added together, compared with Comparative Examples 1 and 2 in which fumed silica or organic clay was added, respectively, There was little change in viscosity. A dispersion medium exhibiting the above viscosity stability was used in the following examples.

Magnetorheological  Produce

Example  One

To a 1000 ml stainless steel beaker, 100 g of YUBASE YU-L3 as a dispersion medium, 2 g of fumed silica TS-720 as a sedimentation inhibitor, and 6 g of TIXOGEL MP100, an organic clay, were added and stirred at 1,000 rpm for at least 30 minutes. 500 g of carbonyl iron powder (BASF Co., Ltd.) having an average diameter of 5 μm and 6 g of nonylphenol ethylene oxide as a dispersant were added, stirred at 1500 rpm for 30 minutes, and then put in a ball mill to mill for 24 hours to prepare a magnetorheological fluid. .

Example  2

Prepared in the same manner as in Example 1, but prepared by changing the composition ratio to the composition shown in Table 3 below.

Comparative example  3 ~ 4

Prepared in the same manner as in Example 1, but prepared by changing the composition ratio to the composition shown in Table 3 below. Specifically, in Comparative Example 3, no organic clay was added, and in Comparative Example 4, fumed silica was not added.

Test Example

The viscosity of the magnetorheological fluid to which the additives of Examples 1 and 2 and Comparative Examples 3 and 4 added according to the present invention are added is 25, which is a driving temperature of a clutch, damper, brake, etc., a device in which magnetorheological fluid is generally used. It was shown in Table 4 and Figure 1 by measuring the viscosity (η) from to 80 ℃. Viscosity measurement was performed using a Brookfield RV type viscometer, and was measured using a spindle # 5,100 rpm.

In addition, the viscoelasticity of the magnetorheological fluid was quantified using Equation 1 below, and is shown in Table 5.

In addition, the sedimentation degree of the magnetorheological fluid was carried out based on ASTM D869-85, and the volume of the supernatant after two weeks of manufacture was expressed as a percentage, which was quantified using Equation 2 below. Table 5 shows.

In addition, the redispersibility of the magnetorheological fluid of the present invention was measured by the following method. 100 ml of Examples 1 and 2 and Comparative Examples 1 and 2 were placed in a 100 ml transparent plastic bottle and left for 2 weeks. After two weeks, shake the plastic bottle up and down vigorously for about one minute, then pour the fluid in the bottle into a new beaker, and after five minutes, determine the degree of redispersion by measuring the volume of fluid remaining in the plastic bottle. The degree of redispersion was determined as high when the volume of the remaining fluid was less than 1%, medium when 1 to 5%, and low when 5% or more.

As shown in Table 5, in Examples 1 and 2, in which fume silica and organic clay, which are antisettling agents, were added together as an additive, compared to Comparative Examples 1 and 2, respectively, in which fumed silica or organic clay was added, It was found that the viscosity change due to temperature change was small, the sedimentation degree was low, and the viscoelasticity and redispersibility were excellent.

As described above, the magnetorheological fluid of the present invention has a low viscosity change, low sedimentation, viscoelasticity and redispersibility compared to magnetorheological fluids containing fumed silica or organic clay, respectively. As a result, it can be usefully used in equipment and systems using magnetorheological fluids.

Claims (9)

A magnetorheological fluid containing magnetic particles, a dispersion medium, a dispersant and a sedimentation inhibitor, It contains 30 to 90% by weight of magnetic particles, 8 to 50% by weight of dispersion medium, 0.1 to 10% by weight of antisettling agent and 0.1 to 10% by weight of dispersant, based on the total weight of the magnetorheological fluid, The sedimentation inhibitor is a magnetorheological fluid, characterized in that the mixture of fumed silica and organic clay in a weight ratio of 1: 3 ~ 1: 1. delete The magnetorheological fluid of claim 1, wherein the magnetic particles have a particle diameter of 1 to 100 μm and are selected from iron, nickel, cobalt, carbonyl iron, soft ferrite, and alloys thereof. . The magnetorheological fluid according to claim 1, wherein the dispersion medium is selected from the group consisting of natural fatty oil, mineral oil, paraffin oil, synthetic hydrocarbon oil, fatty acid ester and silicone oil. delete The magnetorheological fluid of claim 1, wherein the fumed silica is a lipophilic fumed silica. The magnetorheological fluid according to claim 1, wherein the organoclay is quaternary ammonium bentonite. The magnetorheological fluid according to claim 1, wherein the dispersant is selected from the group consisting of fatty acid metal soaps, polyalcohols, ammonium salts, fatty acids, polyethylene oxides, phosphates and phosphonates. delete

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