KR101588051B1 - Preparing method of magnetic composite particles using polyvinyl butyral and carbonyl iron and magnetorheological fluid comprising the same - Google Patents

Abstract

The present invention relates to a method for synthesizing magnetic particles as a main raw material to be dispersed in a fluid in the preparation of a magnetorheic fluid whose rheological properties vary according to a magnetic field. More particularly, the present invention relates to a method for synthesizing magnetic particles by dispersing polyvinyl butyral, (Carbonyl iron) to synthesize magnetic composite particles. Industrial Applicability According to the present invention, an organic / inorganic hybrid of polyvinyl butyral, which is a synthetic resin having high magnetic properties and low density and high impact resistance, is easy to manufacture, and has a low carbonyl And has excellent properties of dispersibility and surface properties in a fluid than an iron.

Organic / inorganic composites, carbonyl irons, magnetorheological fluids, polyvinyl butyral

Description

FIELD OF THE INVENTION [0001] The present invention relates to a magnetic composite particle and a magnetorheological fluid using polyvinyl butyral and a carbonyl iron, and a method for producing the magnetic composite particle and a magnetorheological fluid using the same. BACKGROUND ART < RTI ID = 0.0 >

TECHNICAL FIELD The present invention relates to a method of synthesizing magnetic particles as a main raw material to be dispersed in a fluid in the preparation of a magnetorheic fluid in which the rheological properties are changed according to a magnetic field. More particularly, the present invention relates to a method for synthesizing magnetic particles comprising polyvinyl butyral (Polyvinyl butyral) on a carbonyl iron having excellent magnetic properties to synthesize magnetic composite particles and a magnetorheological fluid containing the same.

Magnetorheological Fluid is a material in which the rheological properties change rapidly as the magnetic field is given. When a magnetic field is given, it changes from a freely flowing fluid to a solid property with a high yield strength. Such a magnetorheological fluid is a suspension in which magnetic particles are dispersed in a nonmagnetic solvent. The rheological behavior of the magnetorheological fluid varies depending on the magnitude of the magnetic field provided from the outside, and the electrical, thermal, and mechanical physical properties (Hereinafter referred to as " MR ").

This fluid can control the mechanical force, such as having a high yield stress of 10-100 kPa or more by simply applying an external magnetic field, and the mechanical force can be controlled without the need for an additional exercise device by applying only a magnetic field. Can be simplified. Also, since the fluid characteristics are changed according to the magnitude of the applied magnetic field from the outside, the rheological properties can be changed by the control of the magnetic field, and precise flow characteristic control is possible.

The magnetic rheological phenomenon is a phenomenon in which the magnetic particles dispersed in the solvent are polarized in accordance with the magnetic field applied to the suspension, and gravitation acts between the magnetic dipoles to form a chain-like structure in the direction of the applied magnetic field, It increases the viscosity and yield stress, which is a rheological phenomenon, by showing resistance to fluid flow and shear force externally applied. As long as the magnetic field is maintained, the inter-particle chain structure is reversibly formed. As the flow velocity is lower, more particles form a chain shape. In the stationary state without external force, the chains are not destroyed and are well developed. More shear stress is required, i.e., yield stress is required as the minimum stress to cause flow in the material. The chain-like bundle created by the interaction of particles is destroyed by external force, and the particles forming the chain are ruptured by repetition of the force to restore the original structure against the magnitude of the shear rate in order to maintain the chain structure. A change in physical properties occurs. That is, in the region where the shear rate is low, the interactions between the particles that can maintain the chain become dominant due to the interaction of the particles due to the magnetic field, and due to the hydrodynamic force inducing the flow in the high shear rate region, The rheological behavior can be explained by the difference in the magnitude of these two forces as the structure of the chain is destroyed. That is, the phenomenon that the particles in the magnetorheological fluid are aligned in the direction of the magnetic field and the shear resistance is increased is due to mutual magnetic forces appearing when the particles are polarized. The yield stress along with the improvement of viscosity is important for the material's yield stress and related rheological properties, since the rheological behavior of materials with magnetic rheological properties plays an essential role in evaluating the performance of actual processes and products. In addition, since the magnetorheological fluid must have stable dispersion fluid characteristics when the magnetic field is not applied, stable dispersion of the particles is important.

The shear stress of a magnetorheological fluid in a steady-state shear flow field is measured according to the shear rate and is generally taken as the yield stress value when the shear rate is extrapolated to zero from this stress behavior. In the experiment of measuring the stress by adjusting the shear rate, the value is defined as the dynamic yield stress because it is possible to measure only in the finite shear rate region that does not include the zero shear rate strictly. In order to form the chain structure of the particles under a magnetic field and to increase the viscosity and yield stress, the particles or the medium itself can act interdependently by their magnetic polarization. This property has many advantages in the device design because it has the advantages of fluid permanence and solid torque transmission to the fatigue limit which is pointed out as a disadvantage in the conventional solid. In addition, this reaction is very rapid, with a level of 10 ^-3 seconds, and appears as a reversible reaction, enabling continuous variable real-time operation. These advantages can overcome the degradation of accuracy due to the nonlinear friction problems caused by various factors such as wear, temperature, and humidity occurring in conventional mechanical systems, and the corresponding reaction can be controlled by electrical control Since it can be controlled by magnetic field, it is getting a spotlight as a new concept of intelligent system.

Magneto-rheological fluid is an important element in applications, and it can be applied in various applications with its low initial viscosity and dispersion stability, high shear stress of external load and low power consumption. In addition, the system can be miniaturized, lightweight, or simplified in its overall structure, as well as being able to simplify its structure, and utilize the reversibility of the fluid response and the rheological effect on the magnetic field, shock absorbers, engine mounts, valve systems for flow control and positioning, robots, actuators, and the like.

In general, the magnetorheological fluid shows the yield stress as a basis for determining the degree of stress-induced stress transfer with the Bingham model. That is, when a magnetorheological fluid receives a strong magnetic field, it means that the shear stress has a constant value at a small shear rate range. As the electric field increases, the chain is hardly formed, Can be maintained. Since most magnetorheological fluids are suspensions with high volume fraction of particles, they do not necessarily exhibit Newtonian fluids behavior even in the absence of a magnetic field, but they have low viscosity at relatively large shear rates. At this time, when a magnetic field is applied from the outside, the phenomenon of viscosity and stress is remarkably improved at a very high speed.

According to a common particle magnetic dipole mechanism, soft magnetic materials such as carbonyl irons with a high polarizing tendency and high magnetic properties should be used. However, most of these materials have disadvantages of high density and unstable surface properties. Particularly, a high density is a major obstacle to the fact that the magnetorheological fluid exists as a normally stable fluid, and also causes a difficulty in re-dispersion when the magnetic field is lowered or removed. Many studies have been conducted to solve these problems. Particularly, there was a problem of solving the problem by increasing the density of the fluid and adding various dispersants. In order to increase the dispersing force, polymer gel was formed by dissolving the polymer in the fluid in order to generate steric hindrance between particles and particles. [&Quot; Development and characterization of hydrocarbon polyol polyurethane and silicone magnetorheological polymeric gels ", Journal of Applied Polymer Science 2003, Vol. 92 (2), p. 1176]. However, it is difficult to control the range because it shows a very high viscosity even in the absence of a magnetic field. As a method of improving the dispersion stability, water was added to the oil droplets and a stable layer was formed to collect the magnetic particles. That is, the attraction between magnetic particles surface-treated with hydrophilicity and water acts to allow magnetic particles to exist in the emulsion phase of water, thereby improving dispersibility. [&Quot; Rheological properties and stabilization of magnetorheological fluids in a water-in-oil emulsion ", Journal of Colloid and Interface Science 2001, Vol. 241 (1) p. 349]. However, this method has a problem that it is difficult to maintain stability for a long time and it can not perform a reversible action according to a magnetic field when applied to a device.

The particle size also has a large effect on the rheology of the fluid, which has a higher yield stress than the smaller particles (nm) for larger particles (μm), and if the particle size is larger than 10 μm Precipitation will occur due to the weight of the particles, which will interfere with maintaining the stability of the MR fluid. However, in order to solve the dispersion problem due to the difference in the specific gravity between the magnetic particles and the non-magnetic solvent, when the magnetic particles having a small size are added, there is a problem that the yield stress is remarkably reduced. To solve this problem, The mixing of nanosized particles in the amount of about 20% increases magnetorheological properties and helps to maintain the stability of the MR fluid. However, these studies have limitations because they are more concerned with the external influences rather than solving the density of the particles themselves.

Accordingly, the present inventors have developed a magnetic particle having MR effect by a system of a magnetorheological fluid composed of a complex of a carbonyl iron coated with a polymer as a magnetic particle and an organic solvent, The present inventors have accomplished the present invention while improving the dispersion stability while maintaining the MR effect.

Accordingly, it is an object of the present invention to provide a method for producing an organic solvent which is easy to be dispersed in a solvent by increasing the affinity with an organic solvent, a mineral oil hydrocarbon base oil, a synthetic base oil, And a method for producing magnetic composite particles by coating a polybutyral having excellent surface properties on a carbonyl iron which is a magnetic particle by a simple method.

Another object of the present invention is to provide a magnetorheological fluid comprising the magnetic composite particles produced by the above method.

According to another aspect of the present invention, there is provided a method for producing magnetic composite particles,

(a) dissolving polyvinyl butyral in a first solvent, and dispersing a carbonyl iron in the first solvent to prepare a dispersion solution; And

(b) adding the dispersion solution to a second solvent in which the polyvinyl butyral is not dissolved, and then volatilizing the first solvent under stirring,

According to another aspect of the present invention, there is provided a magnetic rheology fluid comprising 70 to 85% by weight of magnetic composite particles prepared according to the above method, wherein the magnetic composite particles are dispersed in a non-magnetic dispersion medium .

According to the present invention, by coating polyvinyl butyral on a carbonyl iron which is a magnetic particle, it provides a magnetorheological fluid which can exhibit the effect of lowering the density of particles and improving the dispersion characteristics while maintaining the magnetic property similar to that of conventional magnetic particles.

These characteristics can be applied to mechanical devices such as clutches, brakes, valves and the like by adjusting the magnetic field, and magnetorheological fluids can be applied to the connecting parts of real-time mechanical devices, as well as to potential applications for vibration control, Can be used.

Hereinafter, the present invention will be described in more detail.

The present invention relates to a method for forming magnetic composite particles by coating a polyvinyl butyral on a carbonyl iron in a magnetorheological fluid in which magnetic particles are dispersed in a non-magnetic solvent, Lt; RTI ID = 0.0 > volumetric < / RTI > particles.

Polyvinylbutyral is a polymeric material widely used for building exterior walls, ceilings, floors, inner windows, show window windows, and shelves due to its excellent rubber properties and polymer properties. In addition, carbonyl iron is the most widely used magnetic material for magnetorheological fluids because it has a particle size of 4-10 microns and suitable particle size for magnetorheological fluid and mostly spherical shape. If the average particle size is smaller than 4 탆, the yield stress is significantly reduced. If the average particle size is larger than 10 탆, precipitation may occur due to the weight of the particles themselves.

Coating these carbonyl irons with polyvinyl butyral promotes the result of lowering the density of the particles while maintaining the properties as magnetic particles and making the surface properties of the carbonyl irons excellent.

The present invention is to add low density and surface properties of polyvinyl butyral as magnetic particles to the magnetic properties of carbonyl irons to maintain inherent magnetic properties and to lower the density to promote dispersion stability.

A magnetic fluid is prepared by coating a polyvinyl butyral with a magnetic particle carbonyl iron to form a composite. The method of coating polyvinyl butyral uses a phase separation technique.

The phase separation technique dissolves a polymer coated on a first solvent capable of dissolving a polymer using two solvents having different solubilities, and disperses particles to be coated to prepare a dispersion solution. The polymer solution is added to the second solvent which does not dissolve the polymer, and the polymer solution is coated by stirring until the first solvent is volatilized. In the above process, the second solution contains a first surfactant for increasing the wettability between the particles and the polymer, and a second surfactant and dispersant for stabilizing the particles coated in the water.

Depending on the ratio of the carbonyl iron to the polyvinyl butyral, the coated thickness, or density, is different from the coating efficiency. When the density of the coated final particles is limited to 6.5 to 7.5 g / cm ³ , the yield stress values are similar but the dispersibility is increased. Therefore, the weight ratio of carbonyl iron to polyvinyl butyral is adjusted to 2 to 4 (carbonyl iron): 1 (polyvinyl butyral) for coating at a density of 6.5 to 7.5 g / cm ³ .

In the phase separation technique, the viscosity, solubility constant, and volatility of the first solvent affect the particle coating. Organic solvents such as acetone, chloroform, THF, and ethyl acetate may be used. Among them, acetone is the most suitable solvent. Acetone is low in viscosity (0.306 cP, 25 ° C) and has good affinity with water. It is light and volatile and is suitable for coating polymer with thin thickness (final particle density 6.5 ~ 7.5).

When the density of the coated final particles is limited to 6.5 to 7.5 g / cm ³ as described above, the yield stress value is similar to that of pure carbonyl irons (density 7.8 to 8.1 g / cm ³ ) (FIG. 3 b) One of the most important consideration in the application of the mechanical device is the dispersibility, which can be confirmed by the attached FIGS. 4A and 4B.

As the second solvent, a solvent in which the polymer used does not dissolve is suitable, and water is most suitable.

The first surfactant is an amphoteric substance which is compatible with carbonyl iron and capable of collecting the polymer and is also compatible with water. Examples thereof include PEGn-PPGm-PEGn, polyoxyethylene octyl phenyl ether such as polyoxyethylene sorbitan monolaurate (trade name " Tween 20-80 "), such as phenyl ether, C ₁₄ H ₂₂ O (C ₂ H ₄ O) n, trade name Triton X- surfactant series are suitable, and PEGn-PPGm-PEGn triblock copolymer and polyoxyethylene octylphenyl ether are most suitable when acetone and water are used. Among them, polyoxyethylene octylphenyl ether is excellent in affinity with acetone for its molecular size.

As the second surfactant, general low molecular weight surfactant may be used, and as the dispersing agent, PVA (polyvinyl alcohol), which is a water-soluble polymer, is suitable.

The magnetorheological fluid may be prepared by dispersing the magnetic composite particles coated with polyvinylbutyral in the non-magnetic solvent, wherein 70 to 85% by weight of the magnetic composite particles of the entire magnetorheological fluid And it is preferably dispersed in a non-magnetic solvent. If the amount of the magnetic composite particles is less than 70% by weight, the flow property is too strong to be used as a suitable magnetorheological fluid. On the other hand, if the magnetic composite particles are more than 85% by weight, too much particles may cause problems such as high initial viscosity and poor dispersibility have.

In the present invention, the dispersion medium for the magnetic particles may be variously used, but must be stable to magnetic particles. Therefore, oils with low oxidation characteristics should be used. Effective dispersion media generally exhibit good dispersibility and should have low initial viscosity and high density, low boiling point with low volatility and evaporability, chemically stable and suitable stability within normal operating temperature ranges Do. Therefore, the present invention mainly uses mineral oil base oils and synthetic base oils such as YUBASE Oil and Polyalphaolefin (PAO), but also transformer oil, halocarbon oil, paraffin oil, mineral oil mineral oil, olive oil, corn oil, and soybean oil, or a mixture thereof. Among them, mineral base hydrocarbon base oils and synthetic base oils are excellent in oxidation stability, chemical stability and low temperature performance with lubricant and can be used in a wide temperature range and can be suitably used because they are highly compatible with rubber parts and components of machinery . Also, it is easy to control viscosity and density and can be used for various application fields.

In addition, a dispersant is used for better dispersion of particles, and polyalkenyl succinic amide having a weight average molecular weight of 2,000 to 3,000 is used in the present invention. It has good affinity with carbonyl iodine particles and has a suitable molecular weight and can be suitably used for improving dispersion of particles. The dispersant may include 0.05 to 3% by weight based on the total weight of the fluid.

Hereinafter, the present invention will be described in more detail with reference to the following examples. However, the scope of the present invention is not limited to the following examples.

≪ Example 1 >

The magnetic particles, carbonyl iron, were coated with polyvinyl butyral coating

15 g of polyvinyl butyral polymer (MW = 220,000) was dissolved in 80 ml of acetone, and then 50 g of carbonyl iron was mixed with 400 ml of distilled water, 25 g of polyvinyl alcohol stabilizer, 10 g of emulsifier and PEG ₁₅ PPG ₅₃ PEG ₁₅ 30 ml (instead of 1% by weight of polyoxyethylene sorbitan monolaurate (Tween 20 ~ 80 ™, Figure 1c) or polyoxyethylene octyl phenyl ether (Triton X-100 ™ (Figure 1d) can be used) Stir barley irons. The thus dispersed material is stirred using a mechanical overhead stirrer. If most of the acetone evaporates after stirring for 24 hours, the polyvinyl butyral remains adsorbed on the carbonyl irons. The carbonyl iron particles coated with polyvinyl butyral are washed with distilled water.

≪ Example 2 >

Manufacture of Magneto-Rheological Fluid using Polyvinyl Butyral / Carbonyl Iron Complex

The magnetic particles produced by the above method are spherical and have a size of about 4-10 microns, similar to those of conventional particles. The density of these composite particles are made when a 6.5 ~ 7.5g / cm ³ as a range of pure carbonyl iron (density: 7.8 ~ 8.1g / cm ³⁾ compared to the density decrease. 70 to 85% by weight of the coated composite particles were dispersed in a mineral oil base oil (YUBASE Oil) and a synthetic base oil (PAO) to prepare a magnetorheological fluid. The yield stress of the magnetorheological fluid produced is similar to that of pure carbonyl irons (Fig. 3b). The dispersibility, which is one of the most important consideration in the application of the mechanical device, shows a great improvement over the pure carbonyl irons. (Figures 4a and 4b)

The magnetic composite particles prepared above were observed and the MR effect of the magnetorheological fluid was measured as follows.

<Experimental Example 1>

Observation of polyvinyl butyral / carbonyl iron complex type

In order to observe the surface of the polyvinyl butyral-coated carbonyl iron of the present invention, it was observed by using an SEM (S-4300, Hitachi, Japan).

Figure 1A shows SEM photographs of particles of pure carbonyl irons. 1B is a result of observation and magnification of the surface of the composite particles of polyvinyl butyral / carbonyl iron. From the above results, it can be seen that the shape of the surface of the pure carbonyl iron and the coated one was changed, and thus it can be seen that the polyvinyl butyral adhered well to the carbonyl iron.

<Experimental Example 2>

Observation of chemical structure of polyvinylbutyral / carbonyl iron composite particles

The composite particles of polyvinyl butyral / carbonyl iron prepared in Example 1 were observed through FT-IR. Fig. 2 shows the FT-IR results of the polyvinyl butyral / carbonyl iron composite prepared from Example 1. Fig. CI, PVB and CI-PVB, respectively, represent carbonyl iron, polyvinyl butyral, and composite particles. Molecular motion characteristic peaks of the composite particles show that carbonyl iron and polyvinyl butyral are mixed.

<Experimental Example 3>

Magnetorheological fluid based on polyvinylbutyral / carbonyl iron complex particles

FIG. 3A is a graph showing the shear viscosity of a magnetorheic fluid using a polyvinyl butyral / carbonyl iron complex prepared in Example 1 at a particle weight ratio of 70 to 85 wt% Respectively. The results show that the shear viscosity increases with increasing intensity of given magnetic field. In addition, shear viscosity decreased with increasing shear rate.

FIG. 3B shows a change in shear stress according to the magnetic field of the magnetorheological fluid. As a result of the measurement, it was found that the shear stress was increased with the magnetic field and the shear stress was not affected by the increase of the shear rate.

<Experimental Example 4>

Observation of dispersion stability of magnetorheological fluid based on polyvinylbutyral / carbonyl iron complex particles

4A is a photograph of a reagent bottle prepared to observe the dispersion stability of a magnetorheological fluid prepared using carbonyl iron coated with polyvinyl butyral. FIG. 4B is a photograph of the magnetorheological fluid observed after about 2 days, that is, 48 hours, after being prepared for the reagent bottle. As shown in the figure, the fluid made from only pure carbonyl iron decreased most after 48 hours, but the particles coated with polyvinyl butyral were found to be slightly precipitated and only the upper part appeared to be transparent. Thus, it can be seen that the dispersion stability of the particles is improved after coating with polyvinyl butyral.

In the present invention, a magnetorheological fluid based on the carbonyl iron, which is a conventional magnetic particle, is coated with polyvinyl butyral, and the magnetorheological fluid thus prepared is used as a high magnetic dipole of the carbonyl iron It is possible to show high dispersion stability and particle stability with polyvinyl butyral having high surface stability and impact stability with low density and high speed and effective MR effect.

FIG. 1A is an SEM photograph of carbonyl iron which is a raw material of Example 1 of the present invention, and is magnified 30000 times. FIG.

1B is an SEM photograph of the composite material of Example 1 of the present invention, which is magnified 30000 times.

1C is an SEM photograph of a composite material using Polyoxyethylene (20) sorbitan monolaurate (Tween 20) instead of the triblock copolymer of Example 1 of the present invention.

FIG. 1D is an SEM photograph of a composite material using polyethylene glycol octylphenyl ether (Triton X-100) instead of the triblock copolymer of Example 1, which is magnified 30000 times.

2 shows the chemical structure of the polyvinyl butyral / carbonyl iron composite particle prepared in Example 1 of the present invention through FT-IR.

FIG. 3A shows the relationship between the shear viscosity of the magnetorheological fluid based on the magnetic field of the polyvinyl butyral / carbonyl iron complex prepared in Example 2 of the present invention. FIG.

FIG. 3B shows the relationship between the shear stress due to the magnetic field of the magnetorheological fluid and the pure carbonyl iron based on the polyvinyl butyral / carbonyl iron complex prepared in Example 2 of the present invention.

4A is a photograph immediately after immersing in a reagent bottle to observe the dispersion stability of the magnetorheological fluid based on the polyvinyl butyral / carbonyl iron complex prepared in Example 2 of the present invention.

4B is a photograph of the dispersion stability of the magnetorheological fluid based on the polyvinyl butyral / carbonyl iron complex prepared in Example 2 of the present invention after 2 days (48 hours) after storage in a reagent bottle .

Claims (10)

(a) dissolving polyvinyl butyral in a first solvent, and dispersing a carbonyl iron in the first solvent to prepare a dispersion solution; And (b) adding the dispersion solution to a second solvent in which the polyvinyl butyral is not dissolved, and then volatilizing the first solvent under stirring, to prepare magnetic composite particles for a magnetic reluctive fluid, Here, the weight ratio of the carbonyl iron to the polyvinyl butyral is 2 to 4: 1, the magnetic composite particles have a size of 4 to 10 μm, and the composite has a density of 6.5 to 7.5 g / cm ³ Wherein the magnetic composite particles are dispersed in water. The method for producing magnetic composite particles for a magnetic reluctive fluid according to claim 1, wherein a nonionic surfactant and a low molecular weight surfactant are further added in the step (b). delete The method of claim 1, wherein the first solvent is selected from the group consisting of acetone, chloroform, THF, and ethyl acetate. The method of producing magnetic composite particles for a magnetic reluctive fluid according to claim 1, wherein the second solvent is water. The magnetic composite according to claim 2, wherein the nonionic surfactant is selected from the group consisting of PEGn-PPGm-PEGn, polyoxyethylene octyl phenyl ether, and polyoxyethylene sorbitan monolaurate. / RTI &gt; delete A magnetorheic fluid comprising 70 to 85% by weight of magnetic composite particles prepared by the method of claim 1, wherein said magnetic composite particles are dispersed in a non-magnetic dispersion medium. 9. The method of claim 8, wherein the dispersing medium is selected from the group consisting of YUBASE Oil, Polyalphaolefin (PAO), silicone oil, transformer oil, transformer sealing solution, halocarbon oil, paraffin oil, wherein the oil is a single or mixed oil selected from the group consisting of mineral oil, olive oil, corn oil, and soybean oil. The magnetorheic fluid according to claim 8 or 9, wherein the magnetorheological fluid further comprises a polyalkenyl succinic acid amide dispersant having a weight average molecular weight of 2,000 to 3,000.

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