JP2005255701A - Electric rheology gel and its sheet - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an ER gel, in which electric rheology particles (ER particles) are not precipitated/flocculated even when allowed to stand for a long period and stable ER effect is exhibited, returning to original state when application of voltage is stopped, having good controlling property of shear stress by electric field, free from leaching of a liquid electric insulation medium and keeping good storage stability. <P>SOLUTION: Precipitation/aggregation of ER particles are prevented and leaching of the liquid electric insulation medium is prevented and the controlling property of shear stress by electric field is improved by keeping the content of electric rheology particles (ER particles) in the electric rheology gel to 5-90 wt.%. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to an electrorheological fluid that can be used in power transmission devices such as clutches, dampers, shock absorbers, braking devices, and the like. The present invention relates to an electrorheological gel that prevents sedimentation.

  An electrorheological fluid (ER fluid) is a fluid in which special particles are dispersed in an electrically insulating medium, and the viscosity of the fluid increases significantly when an electric field is applied. Such a property is called an electrorheological effect (ER effect) or a Winslow effect. Polarization occurs in the dispersed particles due to an electric field applied between the electrodes, and the interparticle force based on the polarization causes the particles between the electrodes. Are combined in the direction of charge to form a chain structure called a cluster, which is considered to flow resistance and change viscosity. ER fluids with such properties have good response to electric fields, a wide range of viscosity changes, and apparent viscosity can be controlled by the electric field strength, so application to power transmission elements and braking elements is expected. Yes.

  As described above, a typical ER fluid is obtained by dispersing special particles having a particle size of several tens of microns in an electrically insulating medium such as silicone oil. Has settled and aggregated, and the reproducibility of the ER effect is reduced. In addition, since it is a fluid, a seal structure is required for use, which has been an obstacle to practical use.

In order to solve such a problem, as described in JP-A No. 2002-80881, the present inventors dispersed and dispersed the liquid electrical insulating medium and the dispersed phase particles in the gel, thereby causing the sedimentation / aggregation of the dispersed phase particles. An electrorheological gel (ER gel) was proposed. However, in this ER gel, it takes a long time to return to the state before the voltage application even after the voltage application is stopped (the shear stress controllability is poor), and the liquid electrically insulating medium oozes on the gel surface. However, it has a problem that it is difficult to handle and it is difficult to uniformly form an ER gel on the electrode surface.
JP 2002-80881 A

  In the present invention, electrorheological particles (ER particles) do not settle and agglomerate even after standing for a long period of time, exhibit a stable ER effect, return to the original state in a short time when voltage application is stopped, and liquid electrical insulating properties An object of the present invention is to provide an ER gel that is free from leaching of the medium and maintains good storage stability.

  The inventors of the present invention have made extensive studies to solve the above-described problems. As a result, the content of the electrorheological particles (ER particles) in the electrorheological gel is set to 35 to 90 wt%. The inventors have found that it is possible to prevent agglomeration and to prevent the liquid electrically insulating medium from exuding and to improve the controllability of the shear stress due to the electric field, thereby completing the present invention. Furthermore, the handleability can be improved by using a sheet shape, and the ER gel can be uniformly formed on the electrode surface.

  The ER gel in the present invention exhibits stable ER effect because no sedimentation or aggregation of ER particles occurs even after standing for a long period of time, and exhibits good storage stability because there is no leaching of the liquid electrically insulating medium. In addition, the ER gel in the present invention is excellent in handleability because there is no exudation of the liquid electrically insulating medium, and can be easily applied to devices. For example, a variable damper system can be configured. Furthermore, the ER gel of the present invention is excellent in controllability of the shear stress due to the electric field because the responsiveness at the time of removing the electric field is particularly good. In addition, current consumption is very small and a large shear stress can be generated.

  The present invention will be described in detail below.

  The ER gel in the present invention has a structure in which a liquid electrical insulating medium in which ER particles are dispersed in a gel skeleton is enclosed.

  The ER particles in the present invention are dispersed in a liquid electrically insulating medium and exhibit an ER effect. For example, silica gel, cellulose, starch, soybean casein, polystyrene ion exchange resin, etc. Examples include solid particles and carbon particles that absorb and store water. Also, composite-type particles comprising a core material of an organic polymer compound and a surface layer of electrosemiconductor inorganic particles can be used. If desired, such a composite-type particle can further surface-treat the surface layer and adjust the affinity with the liquid electrically insulating medium. As the ER particles in the present invention, it is preferable to use composite particles because a stable ER effect and good storage stability can be obtained. These composite particles are described in, for example, JP-A No. 2001-026793, JP-A No. 10-121084, JP-A No. 09-079404 and the like.

  The content of ER particles in the ER gel of the present invention is essential to be 35 to 90 wt%, and from the viewpoint of controllability of shear stress due to an electric field, the content of ER particles in the ER gel is 50 to 90 wt%. More preferably, it is 60-90 wt%, More preferably, it is 45-65 wt%. When the content of ER particles is less than 35 wt%, the content of the gel skeleton or the liquid electrically insulating medium is relatively increased, so that a sufficient ER effect may not be obtained or storage stability may be deteriorated. It is not preferable. Moreover, when content of ER particle | grains exceeds 90 wt%, an ER gel sheet will become hard too much and it is unpreferable.

Examples of the liquid electrically insulating medium in the present invention include silicone oil, diphenyl chloride, and trans oil. Of these, silicone oil is preferably used because it has excellent electrical insulation, is physically and chemically stable, and has high flame retardancy. The viscosity of the liquid electrically insulating medium is not limited in the present invention, preferably from 1 to 100,000 ^mm 2 / s at 25 ° C., in particular 5~1000mm ² / s are preferred. When the viscosity of the liquid electrically insulating medium is less than 1 mm ² / s, the storage stability of the ER gel is lowered, which is not preferable. On the other hand, when the viscosity of the liquid electrically insulating medium exceeds 100,000 mm ² / s, it is not preferable because bubbles entrained during the preparation of the ER gel are difficult to escape.

Examples of the silicone oil used in the present invention include one or more of dimethyl silicone oil, fluorine-modified silicone oil, and phenyl-modified silicone oil. Examples of the fluorine-modified silicone oil include polysiloxane having a trifluoropropyl group (CF ₃ C ₂ H ₄ —), polysiloxane having a nonafluorohexyl group (C ₄ F ₉ C ₂ H ₄ —), and cyclic poly Examples include siloxane compounds.

  The content of the liquid electrically insulating medium in the ER gel of the present invention is preferably 1 to 55 wt%. If the content of the liquid electrically insulating medium is less than 1 wt%, the ER gel may become too hard, which is not preferable. If the content of the electrically insulating medium exceeds 55 wt%, the liquid electrically insulating medium may ooze out, which is not preferable.

  The gel skeleton in the present invention is not limited, but an electrically insulating one is preferable. In particular, a crosslinked polysiloxane obtained by a hydrosilylation reaction of hydrogen silicone and an unsaturated group-containing compound is preferred. This polysiloxane crosslinked body is easy to manufacture and can hold a large amount of a liquid electrical insulating medium in which ER particles are dispersed in the skeleton.

Examples of the hydrogen silicone used in the present invention include an alkylsiloxane when it has a hydrogen atom bonded to a silicon atom of a siloxane chain as shown in the following formula (A).

(Wherein R ¹ independently represents a substituted or unsubstituted alkyl group having 1 to 18 carbon atoms, an aralkyl group having 7 to 21 carbon atoms, or a substituted or unsubstituted aryl group having 6 to 20 carbon atoms; n represents an integer of 0 to 500.) Examples of the alkyl group represented by R ¹ include a methyl group, an ethyl group, a propyl group, a butyl group, an octyl group, a dodecyl group, and the like. Examples include a benzyl group and a phenethyl group. Examples of the aryl group include a phenyl group, a toluyl group, and a naphthyl group. Examples of the substituted alkyl group represented by R ¹ include halogenated alkyl groups such as trifluoropropyl group and chloropropyl group, and cyanoalkyl groups such as 2-cyanoethyl group. Among these, R ¹ is preferably a methyl group, n is an integer of 10 to 200, and specific examples include those represented by the following formulas (A-1) to (A-3). .

Moreover, as an unsaturated group containing compound used by this invention, what is shown by a following formula (B) is mentioned, for example.

(In the formula, R ² independently represents a hydrogen atom, a substituted or unsubstituted alkyl group having 1 to 18 carbon atoms, or a substituted or unsubstituted aryl group having 6 to 20 carbon atoms, and R ³ represents 1 carbon atom. Represents an alkylene group having ˜18, an arylalkylene group having 7 to 21 carbon atoms, a hetero atom-containing alkylene group having 1 to 6 heteroatoms and 1 to 12 carbon atoms, or a direct bond, m is an integer of 3 or more Z is a linking group having the same valence as m, and is a carbon atom, silicon atom, monosubstituted trivalent silicon atom, aliphatic group having 1 to 30 carbon atoms, 1 to 6 heteroatoms and 1 carbon atom. Any one of ˜30 heteroatom-containing organic groups or linear, branched or cyclic alkylsiloxane groups having 2 to 50 silicon atoms.)
Examples of the alkyl group represented by R ² include a methyl group, an ethyl group, a propyl group, a butyl group, an octyl group, and a dodecyl group. Examples of the aryl group include a phenyl group, a toluyl group, and a naphthyl group. Is mentioned. Examples of the alkylene group represented by R ³ include a methylene group, an ethylene group, a propylene group, a butylene group, an octylene group, a dodecylene group, and the like, and examples of the arylalkylene group include a phenylmethylene group, a phenylethylene group, And phenylethylidene group. Here, the “hetero atom-containing alkylene group” used for R ³ is a group containing an oxygen, sulfur or nitrogen atom as a hetero atom, and the hetero atom is regarded as a carbon atom. It means a group that can be an alkylene group. Such heteroatom-containing alkylene groups include methyleneoxymethylene, methyleneoxyethylene, methyleneoxypropylene, ethyleneoxypropylene, methyleneoxyethyleneoxymethylene, ethyleneoxyethyleneoxyethylene, propyleneoxyethyleneoxypropylene Groups, or those in which these oxygen atoms are replaced with sulfur or nitrogen atoms, and those in which some of these oxygen atoms are replaced with sulfur and / or nitrogen atoms. Examples of the aliphatic group represented by Z include a trivalent or higher linear or branched alkyl group, and examples thereof include a methynyl group, an ethynyl group, a propynyl group, a butynyl group, an octynyl group, and a dodecynyl group. It is done. Here, the “hetero atom-containing organic group” used for Z means an aliphatic or aromatic functional group containing an oxygen, sulfur, or nitrogen atom as a hetero atom. Such heteroatom-containing organic groups include methyleneoxymethynyl, methyleneoxyethynyl, methyleneoxypropynyl, ethyleneoxypropynyl, methyleneoxyethyleneoxymethynyl, ethyleneoxyethyleneoxyethynyl, propyleneoxyethylene An oxypropynyl group, a phenylenebis (methyloxyethynyl) group, or a group in which these oxygen atoms are replaced with sulfur or nitrogen atoms, or a group in which some of these oxygen atoms are replaced with sulfur and / or nitrogen atoms Can be mentioned. Examples of the monosubstituted trivalent silicon atom of Z include an alkyl group —Si≡, and specific examples include CH ₃ —Si≡.

Among these, R ² is preferably a hydrogen atom or a methyl group, and R ³ is —CH ₂ OCH ₂ —, —CH ₂ OCH ₂ CH ₂ —, or —CH ₂ OCH ₂ CH ₂ OCH ₂ —. Specific examples of these unsaturated group-containing compounds include those represented by the following formulas (B-1) to (B-7).

  The hydrosilylation reaction between the hydrogen silicone and the unsaturated group-containing compound described above is a highly temperature-dependent reaction and can be accelerated by heating. This is a great advantage of the hydrosilylation reaction. The raw materials can be mixed in a state having an appropriate viscosity, and after forming and then heated, a polymer having a desired shape can be obtained at once. In this case, the heating temperature is preferably 50 to 150 ° C, more preferably 60 to 120 ° C.

  A catalyst is preferably used for the hydrosilylation reaction. As catalysts usable for the hydrosilylation reaction, compounds such as platinum, ruthenium, rhodium, palladium, osmium, iridium and the like are known, and platinum compounds are particularly useful. Examples of the platinum compound include chloroplatinic acid, platinum alone, alumina, silica, carbon black and the like supported on solid platinum, platinum-vinylsiloxane complex, platinum-phosphine complex, platinum-phosphite complex, A platinum-alcolate catalyst or the like can be used. In the case of a platinum catalyst, about 0.0001 wt% can be added to the ER gel.

The ER gel in the present invention preferably has a gel skeleton crosslinking density satisfying the following formula, and particularly preferably has a lower limit of 0.8 and an upper limit of 1.2.

  The content of the gel skeleton in the ER gel of the present invention is preferably 3 to 64 wt%. When the content of the gel skeleton is less than 3 wt%, the fluidity of the ER gel is high, and a seal structure is required when used for a braking element or the like. On the other hand, when the content of the gel skeleton exceeds 64 wt%, the content of the ER particles relatively decreases, and a sufficient ER effect cannot be obtained.

  In order to retain the liquid electrical insulating medium in which the ER particles are dispersed in the gel skeleton, the liquid electrical insulating medium in which the ER particles are dispersed before the hydrosilylation may be impregnated. It is preferable to mix with hydrogen silicone and an unsaturated group-containing compound and then react by heating.

  Further, the liquid electrical insulating medium in the ER gel sheet is preferably obtained by holding the liquid electrical insulating medium in which ER particles are dispersed in the gel skeleton by the above-described method, and then extracting the liquid electrical insulating medium by squeezing or suctioning under reduced pressure or pressure. The amount may be adjusted. This method is particularly effective when it is desired to reduce the content of the liquid electrically insulating medium in the ER gel sheet. At the time of ER particle dispersion, a sufficient amount of the liquid electric insulating medium for dispersion is used, and the ER particles can be uniformly arranged by extracting the liquid electric insulating medium after being held in the gel skeleton.

  In order for the ER gel sheet of the present invention to generate a sufficient ER effect, it is necessary to apply an electric field strength of 250 V / mm or more. Therefore, the thickness of the ER gel sheet in the present invention is not limited as long as a power source capable of generating an electric field strength of 250 V / mm or more is used. Judging from the practical level, the thickness of the ER gel sheet is preferably about 0.05 to 10 mm.

  As described above, in the ER gel of the present invention, since the liquid insulating medium in which ER particles are dispersed is held in the gel skeleton, the ER particles do not settle and aggregate even if left for a long time. . Further, it is considered that the ER effect is obtained by arranging the ER particles in the gel skeleton when an electric field is applied. Furthermore, the ER gel of the present invention does not require a sealing mechanism when incorporated in a device such as a braking element.

  In addition, the ER gel of the present invention can reduce power consumption because the content of the liquid electrically insulating medium, which is a medium for carrying charges, is smaller than that of the conventional example.

  Hereinafter, specific examples of the present invention will be shown based on examples, but the present invention is not limited thereto.

(Production of ER particles)
Antimony-doped tin oxide (Ishihara Sangyo Co., Ltd., SN-100P, electrical conductivity: 1.0 × 10 ⁰ Ω ^-1 / cm) 30 g, Titanium hydroxide (Ishihara Sangyo Co., Ltd., C-11, electrical conductivity) : 9.1 × 10 ⁻⁶ Ω ⁻¹ / cm) 10 g, butyl acrylate 300 g, 1,3-butylene glycol dimethacrylate 100 g, and azobisisovaleronitrile (polymerization initiator) 2 g are dispersed. The dispersion was dispersed in 1800 ml of distilled water containing 25 g of tricalcium phosphate as a stabilizer, and suspension polymerization was performed at 60 ° C. for 1 hour with stirring. The obtained product was filtered, and after acid treatment, washed with water and dehydrated and dried to obtain inorganic / organic composite particles. 2 g of iron phthalocyanine (P-26, manufactured by Sanyo Dyeing Co., Ltd.) was added to 200 g of the particles, and the composite treatment was performed with a ball mill for 75 hours, and then a jet air flow stirrer (produced by Nara Machinery Co., Ltd., Hybridizer) Was used for 210 seconds at a wind speed of 75 m / sec to obtain ER particles.

(Example 1)
50.0 parts by weight of the ER particles, 36.0 parts by weight of dimethyl silicone oil (manufactured by Nippon Unicar Co., Ltd., L-45 (100)), 13.15 parts by weight of hydrogen silicone represented by the formula (A-1) Then, 0.85 part by weight of the unsaturated group-containing compound represented by the formula (B-1) and 0.0001 part by weight of a zero-valent platinum catalyst were uniformly mixed at room temperature. This mixture was poured between two aluminum plates maintained at a distance of 1 mm, heat-treated at 100 ° C. for 1 hour, and then allowed to stand at room temperature for 1 day to prepare an ER gel sheet. The obtained ER gel sheet was 75 mm long, 50 mm wide, and 1 mm thick.

(Example 2)
An ER gel sheet was prepared in the same manner as in Example 1 except that the sheet size was 75 mm in length, 50 mm in width, and 0.5 mm in thickness.

(Example 3)
50.4 parts by weight of the ER particles, 33.6 parts by weight of dimethyl silicone oil (Nihon Unicar Co., Ltd., L-45 (100)), 15.03 parts by weight of hydrogen silicone represented by the formula (A-1) Then, 0.97 part by weight of the unsaturated group-containing compound represented by the formula (B-1) and 0.0001 part by weight of a zero-valent platinum catalyst were uniformly mixed at room temperature. The mixture was poured between two aluminum plates maintained at a distance of 0.5 mm, heat-treated at 100 ° C. for 1 hour, and then allowed to stand at room temperature for 1 day to prepare an ER gel sheet. The obtained ER gel sheet was 75 mm long, 50 mm wide, and 0.5 mm thick.

Example 4
The mixture obtained in Example 3 was poured between two aluminum plates and heated at 100 ° C. for 1 hour. Thereafter, at room temperature, the two aluminum plates were slowly pressurized from both sides until the distance became 0.5 mm, and left as it was for 1 day to extract the dimethyl silicone oil in the ER gel sheet. From the weight of the obtained dimethyl silicone oil, the composition of this ER gel sheet was calculated to have an ER particle content of 60.58 wt%, a gel skeleton content of 19.23 wt%, and a dimethyl silicone oil content of 20.19 wt%. . The ER gel sheet was cut into a length of 75 mm and a width of 50 mm.

(Comparative Example 1)
26.8 parts by weight of the ER particles, 59.2 parts by weight of dimethyl silicone oil (manufactured by Nippon Unicar Co., Ltd., L-45 (100)), and 13.2 of hydrogen silicone represented by the formula (A-1). ER gel sheet having a length of 75 mm, a width of 50 mm, and a thickness of 1 mm in the same manner as in Example 1 except that 15 parts by weight and the unsaturated group-containing compound represented by the formula (B-1) were changed to 0.85 parts by weight. Was made.

Oil Bleeding When the surface of the produced ER gel sheet was observed, the surface of the ER gel sheet produced in Examples 1 to 3 was dry and no oil bleeding was observed. On the other hand, the ER gel sheet of Comparative Example 1 was thinly oily on the surface.

ER characteristic evaluation 1
The apparatus shown in FIG. 1 was used for ER characteristic evaluation. The ER gel sheet produced in Example 1 or Comparative Example 1 was sandwiched between two parallel plate electrodes so that the lower electrode was fixed and the upper electrode could be slid. The upper electrode was slid by 20 μm while an electric field of 1 kV / mm was applied to the ER gel sheet, and the amount of displacement of the upper electrode at this time was measured by an eddy current displacement meter and the shear stress was measured by a load cell. (FIG. 2) As a result, in both the example and the comparative example, the generation of shear stress was recognized as the displacement amount of the upper electrode increased. In the case of the example, however, a significantly greater shear stress was generated than in the comparative example.

ER characteristic evaluation 2
Using the apparatus described above, the shear stress when the upper electrode was displaced to 600 μm with the electric field strength of 0 to 1500 V / mm was measured for the ER gel sheets of Examples 1 and 2. (FIG. 3) As a result, compared with Example 1, the ER gel sheet of Example 2 having a thickness as thin as 0.5 mm was able to generate a wide range of shear stress depending on the electric field strength.

ER characteristic evaluation 3
The ER gel sheet of Example 2 was set in the apparatus described above, and the upper electrode was vibrated at a swing width of 100 μm and a vibration frequency of 10 Hz. When an electric field strength of 1500 V / mm was applied between the electrodes, the vibration stopped after about 10 to 30 ms. Further, when the electric field was removed, vibration started again after about 100 to 300 ms (FIG. 4).

ER characteristic evaluation 4
Using the apparatus described above, the shear stress when the upper electrode was displaced to 600 μm was measured once a day for 7 days for the ER gel sheet of Example 2 at an electric field strength of 1500 V / mm. As a result, almost the same shear stress was observed each time, and it was confirmed that the storage stability and reproducibility were high (FIG. 5).

ER characteristic evaluation 5
The ER gel sheet of Example 3 was set in the apparatus described above, and the upper electrode was vibrated at a vibration width of 300 μm and a vibration frequency of 10 Hz. When an electric field strength of 1500 V / mm was applied between the electrodes, the vibration stopped after about 10 to 30 ms. When the electric field was removed, vibration started again after about 700 to 900 ms (FIG. 6). Moreover, the ER gel sheet of Example 4 was set in the apparatus mentioned above, and the upper electrode was vibrated with a swinging width of 100 μm and a vibration frequency of 10 Hz. When an electric field strength of 1500 V / mm was applied between the electrodes, the vibration stopped after about 10 to 30 ms. Next, when the electric field was removed, vibration started again after about 200 to 300 ms (FIG. 6). When Example 3 and Example 4 were compared, Example 4 resumed vibration in a short period of time after removing the electric field, even though the swing width was reduced to 100 μm.

It is the schematic of an ER effect characteristic evaluation apparatus. It is a graph which shows the evaluation result of the ER effect in Example 1 and Comparative Example 2. It is a graph which shows the relationship between the thickness of ER gel sheet, and the generated shear stress. It is a graph which shows the result of a vibration experiment. It is a graph which shows the result of a storage stability confirmation experiment. It is a graph which shows the response experiment result at the time of electric field removal.

Claims (4)

  An electrorheological gel containing at least 35 to 90 wt% of an electrorheological particle in an electrorheological gel including at least an electrorheological particle, a liquid electric insulating medium, and a gel skeleton.   The electrorheological gel according to claim 1, wherein the content of the liquid electrically insulating medium is 1 to 55 wt%.   The electrorheological gel according to claim 2, wherein the content of the gel skeleton is 3 to 64 wt%.   An electrorheological gel sheet comprising the electrorheological gel according to any one of claims 1 to 3.

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