JPH07173481A - Electroviscous fluid - Google Patents

Abstract

PURPOSE:To provide a fluid which is of a nonaqueous type, contains a polyhydric alcohol as a polarization accelerator, is excellent in dispersion stability and storage stability, does not cause aggregation even at elevated temps., and has a high electroviscous effect. CONSTITUTION:This fluid comprises an electrical-insulating fluid containing a polyhydric alcohol and fine silica particles esterified at the surfaces with a monohydric alcohol having an 8C or higher alkyl group as the main chain.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an electrorheological fluid that can be used for electrical control of variable damping dampers, engine mounts, bearing dampers, clutches, valves, shock absorbers, display elements and the like.

[0002]

2. Description of the Related Art Electro-Rheological Fluid, Electro-Viscous Fluid whose viscosity changes with the application of voltage
scous Fluid,) has been known for a long time (Duff, AWP
hysical Review Vol, 4, No.1 (1896) 23). Initial research on electrorheological fluids focused on liquid-only systems, and the effect was inadequate, but after that, we moved to research on electrorheological fluids in solid dispersion systems, and obtained considerable electrorheological effects. Came to be.

As a mechanism for producing a thickening effect (ER effect) in an electrorheological fluid, for example, Klass shows that each particle, which is a dispersoid in the electrorheological fluid, has a two-layered dielectric polarization in the electric field. Double Laye
r), which is the main cause (Klass, D.
L., et al., J. of Applied Physics, Vol.38, No1 (196
7) 67). This is an electric double layer
The ion adsorbed around the dispersoid (silica gel, etc.) is evenly arranged on the outer surface of the dispersoid when E (electric field) = 0, but when E (electric field) = finite value Causes a bias in the ion distribution, and each particle exerts an electrostatic action on each other in the electric field. In this way, each particle forms a bridge (crosslink) between the electrodes, and shear resistance against stress, that is, an ER effect is developed.

Winslow also proposed an electrorheological fluid using paraffin and silica gel powder and water as a polarizing agent (Winslow, WM, J. of Applied Physics, Vol.
20 (1949) 1137). According to this Winslow study, the electrorheological effect of electrorheological fluid is called the Winslow effect.

Porous solid particles are used as a dispersoid in such an electrorheological fluid, but there is a problem in the dispersibility of the dispersoid, and a hard precipitate is formed when left for a long time, or at 100 ° C. Under a moderate temperature condition, there is a problem that a gel-like substance is generated after standing for a few minutes to a few hours, and it does not function as an electrorheological fluid. In order to improve the dispersion stability, solid particles dispersed in an electrorheological fluid are miniaturized to a critical particle size and a dispersant such as polybutenyl succinimide is added. . However, polybutenyl succinimide has a high molecular weight, and since the molecular length of the dispersant is too long with respect to the particle diameter, sufficient attractive force between particles cannot be obtained, and the desired electrorheological effect can be obtained. It turned out to be a problem. Also, in terms of thermosetting, it is considered that the particles of the conventional electrorheological fluid are likely to aggregate with each other under heating conditions.

Further, in Japanese Patent Publication No. 45-10048, the particle size is 0.04 μm to 10 μm and the particle surface is 1 nm.
About 0.5 to 1.5 silica-bonded OR groups per ² and 1
˜3 silica particles having free water, where R is a polyoxy-substituted ester or a polyoxyalcohol ester residue having a molecular weight of about 130-400, to produce esterified silica, which has a high base viscosity and is electrically insulating. Although an electrorheological fluid dispersed in a fluid is disclosed, silica particles esterified with a polyhydric alcohol still have a problem in that they are likely to aggregate and have a low esterification rate and poor stationary stability. . In addition, since water is used as a polarization accelerator, the electroviscous effect is unstable at high temperatures, and when the silica particles are large in size, precipitation occurs when dispersed in an electrically insulating fluid with low base viscosity. There is a problem that it is easy.

[0007]

DISCLOSURE OF THE INVENTION The present invention is a non-aqueous electrorheological fluid using a polyhydric alcohol as a polarization accelerator, which has excellent dispersion stability and storage stability, and is capable of forming particles even under heating conditions. An object is to provide an electrorheological fluid that exhibits a high electrorheological effect without causing aggregation.

[0008]

The electrorheological fluid of the present invention comprises an electrically insulating fluid containing silica fine particles esterified with a monohydric alcohol whose surface has an alkyl group having 8 or more carbon atoms as a main chain and a polyhydric alcohol. It is characterized by being blended in.

Further, the monohydric alcohol in the electrorheological fluid of the present invention is characterized by having an alkyl group having 8 to 48 carbon atoms as a main chain.

Further, the particle diameter of the silica fine particles in the electrorheological fluid of the present invention is 0.01 to 4.0 μm.

Further, the particle diameter of the silica fine particles in the electrorheological fluid of the present invention is 0.01 to 1.5 μm.

The particle size of the silica fine particles in the electrorheological fluid of the present invention is 0.01 to 0.5 μm.

The particle size of silica fine particles in the electrorheological fluid of the present invention is 0.5 to 4.0 μm, and the monohydric alcohol has a straight chain alkyl group having 12 to 48 carbon atoms as a main chain. Is characterized in that.

Further, the particle size of the silica fine particles in the electrorheological fluid of the present invention is 0.01 to 0.5 μm, and 1
The polyhydric alcohol is characterized by having a straight-chain alkyl group having 8 to 32 carbon atoms as a main chain.

In the electrorheological fluid of the present invention, the number of esterified silanol groups bonded to the surface of the silica fine particles is 1.8 to 6.0 / nm ² .

The number of esterified silanol groups on the surface of the silica fine particles in the electrorheological fluid of the present invention is 2.0 to 5.5 / nm ² .

First, the silica fine particles in the present invention have a particle size of 0.01 μm to 4 μm, preferably 0.01 μm.
m-1.5 μm, more preferably 0.01 μm-0.5
μm, most preferably 0.01 μm to 0.1 μm.

The silanol groups on the surface of the silica fine particles are esterified with a monohydric alcohol having an alkyl group having 8 or more carbon atoms as the main chain.

Examples of monohydric alcohols include aliphatic alcohols having an alkyl group having 8 to 48 carbon atoms as a main chain. The alkyl group is preferably a straight chain type,
Further, those having no functional group in the carbon chain are preferable.

Examples of the aliphatic alcohol include octanol, nonanol, decanol, undecanol, dodecanol, tridecanol, tetradecanol, pentadecanol, hexadecanol, heptadecanol, octadecanol, nonadecanol, eicosanol, tetracosanol, and hexa. Examples thereof include cosanol, triacontanol, dotriacontanol, hexatriacontanol and the like.

In addition to such monohydric aliphatic alcohols, aromatic alcohols having an aromatic ring in the main chain or side chain of an alkyl group having 1 to 40 carbon atoms may be used,
Examples thereof include benzyl alcohol, phenethyl alcohol, tolylmethanol, ethylbenzyl alcohol and the like.

Further, polyether alcohols having 5 to 26 carbon atoms may be used, and examples thereof include diethylene glycol monomethyl ether, diethylene glycol monoethyl ether, triethylene glycol monomethyl ether and triethylene glycol monoethyl ether.

The relationship between the particle diameter of the silica fine particles and the molecular chain length of the ester group may be adjusted according to the particle diameter of the silica fine particles. When the particle size is large, monohydric alcohols having a long molecular chain are preferable, and when the particle size of silica fine particles is small, monohydric alcohols having a short molecular chain are preferable. For example, the particle size of silica fine particles is 0.5 to 4.0 μ.
When it is m, it has 12 to 48 carbon atoms, preferably 12 carbon atoms.
Having an alkyl group of ˜36 as the main chain, and when the particle size of the silica fine particles is 0.01 to 0.5 μm, an alkyl group having 8 to 32 carbon atoms, preferably 8 to 26 carbon atoms is the main chain. Those having as are preferable.

A method for esterifying the surface of the silica fine particles will be described. The silica fine particles are required to have a particle size in the range of 0.01 μm to 4 μm in a primary particle size or in an agglomerated state. Originally, particles in this range do not require a refining treatment, If the particle size is large, disperse it in an organic solvent and subject it to a ball mill treatment to obtain a particle size of 0.01 μm to 4 μm.
It is good to adjust to the range of m.

The esterification is carried out by reacting the silica fine particles having such a particle size with an alcohol under the condition of heating under reflux, and it is preferable to remove the produced water azeotropically during the reaction.

The number of silanol groups bonded on the surface of the silica fine particles corresponds to the yield in a normal chemical reaction,
It can be changed by adjusting the reaction conditions (reaction temperature, reaction time, amount of alcohol added, etc.) in the esterification reaction. The number of bonding groups can be determined by elemental analysis and surface area measurement. The number of bond groups of the esterified silanol group on the surface of the silica fine particles is
1.8 to 6.0 pieces / nm ² , preferably 2.0 to 5.5
The number of particles / nm ² is preferable. The higher the number of bonding groups, the higher the dispersion stability, but the lower the electrorheological effect, and the lower the number, the lower the stationary stability becomes.

In the electrorheological fluid of the present invention, the fine silica particles may be contained in an amount of 0.1% by weight to 50% by weight, preferably 3% by weight to 30% by weight.
If it exceeds the range, the electrorheological effect decreases, which is not preferable.

A polyhydric alcohol or a partial derivative thereof is added as a polarization accelerator to the electrorheological fluid of the present invention. Examples of the polyhydric alcohol include dihydric alcohols and trihydric alcohols such as ethylene glycol, glycerin, propanediol, butanediol, pentanediol,
Hexanediol, ethylene oxide unit 1 to 14
Polyethylene glycol having the general formula R [(OC ₃ H
₆ ) _m OH] _n (wherein R represents hydrogen or a polyhydric alcohol residue, m represents an integer of 1 to 17 and n represents an integer of 1 to 6), and the general formula R-CH (OH) ( CH ₂ ) _n OH
(In the formula, R is hydrogen or CH ₃ (CH ₂ ) _m − group,
m + n represents an integer of 2 to 14) and the like. Among these, triethylene glycol, tetraethylene glycol and polyethylene glycol are particularly preferable.

The partial derivative of polyhydric alcohol is a partial derivative of polyhydric alcohol having at least one hydroxyl group, and some of the terminal hydroxyl groups of the above polyhydric alcohol are methyl group, ethyl group and propyl group. , Butyl groups, alkyl-substituted phenyl groups (alkyl groups substituted with phenyl groups have 1 to 25 carbon atoms), and other partial ethers, and some of the terminal hydroxyl groups are acetic acid, propionic acid, butyric acid Partial esters which have been esterified by the above are mentioned.

These polyhydric alcohols or their partial derivatives are usually used in a proportion of 1% by weight to 100% by weight, preferably 2% by weight to 80% by weight, based on the silica fine particles. If the addition amount is less than 1% by weight, the ER effect is small, and if it exceeds 100% by weight, an electric current easily flows, which is not preferable.

As the electrically insulating fluid in the present invention,
There are mineral oils and synthetic lubricating oils, specifically, paraffinic mineral oils, naphthenic mineral oils, poly-α-olefins, polyalkylene glycols, ester oils, diesters, polyol esters, phosphate esters, fluorine oils, alkylbenzenes, alkyldiphenyl ethers, Examples thereof include alkyl biphenyls, alkyl naphthalenes, polyphenyl ethers, synthetic hydrocarbon oils, preferably mineral oils, alkylbenzenes, ester oils such as diesters and polyol esters, and poly-α-olefins. The viscosity range of the electrically insulating fluid is 1 cSt to 3 at 40 ° C.
Although it can be set to 00 cSt, when the silica fine particles of the present invention are used, particularly excellent dispersibility is exhibited when the viscosity is as low as 1 cSt to 20 cSt.

Further, the electrorheological fluid of the present invention is required to
Depending on the acid, salt or base components may be added. this
Such acid components include sulfuric acid, hydrochloric acid, nitric acid, perchloric acid,
Inorganic acids such as romic acid, phosphoric acid, boric acid, or acetic acid, formic acid,
Propionic acid, butyric acid, isobutyric acid, valeric acid, oxalic acid, mac
Organic acids such as rhoic acid are used. As salt, metal or
Basic group (NH_Four ⁺, N₂H_Five ⁺Etc.) and an acid group
And they can be used in any
It Among them, polyhydric alcohols and polyhydric alcohol partial derivatives
What dissolves in the system and dissociates, for example, alkali metals,
Typical ionic formations such as halides of Lucari earth metals
Crystals, or alkali metal salts of organic acids.
Which is preferable. LiCl, NaC as this kind of salt
l, KCl, MgCl₂, CaCl₂, BaCl₂, L
iBr, NaBr, KBr, MgBr ₂, LiI, Na
I, KI, AgNO₃, Ca (NO₃)₂, NaNO₂,
NH_FourNO₃, K₂SO_Four, Na₂SO_Four, NaHSO
_Four, (NH_Four)₂SO_FourOr formic acid, acetic acid, shu
There are metal salts of alkali acids such as acid and succinic acid. As a base
Is an alkali metal or alkaline earth metal hydroxide,
Alkali metal carbonates, amines, etc.
Dissolves in Cole or polyhydric alcohol derivative
Those are preferable. As this kind of base, NaOH, KO
H, Ca (OH)₂, Na₂CO₃, NaHCO₃, K
₃PO_Four, Na₃PO_Four, Aniline, alkylamine,
For example, ethanolamine. In addition, the above-mentioned salt and base
It can also be used together.

Acids, salts and bases can increase the polarization effect, but by using in combination with polyhydric alcohol and / or polyhydric alcohol partial derivative, the polarization effect can be further enhanced. It is possible, and it is advisable to use the electrorheological fluid in a proportion of 0% to 5% by weight. If it exceeds 5% by weight, it becomes easier to energize,
This is not preferable because it increases power consumption.

If desired, an ashless dispersant may be added to the electrorheological fluid of the present invention. When the ashless dispersant is added, the base viscosity of the electrorheological fluid can be lowered, and the application range of the mechanical system using the electrorheological fluid can be expanded. As the ashless dispersant, for example, sulfonates, phenates, phosphonates, succinimides, amines, nonionic dispersants and the like are used, and specifically, magnesium sulfonate, calcium sulfonate, calcium phosphonate, polybutenyl. Examples thereof include succinimide, sorbitan monooleate and sorbitan sesquioleate. Among them, polybutenyl succinimide is preferable. These are usually used in a proportion of 0% by weight to 20% by weight in the entire electrorheological fluid.

If desired, a surfactant may be added to the electrorheological fluid of the present invention. As the surfactant, a nonionic surfactant, an anionic surfactant, a cationic surfactant and an amphoteric surfactant can be used.

Examples of the nonionic surfactant include polyoxyethylene alkyl ether, polyoxyethylene alkylphenyl ether, polyoxyethylene alkylamide, polyoxyethylene-polyoxypropylene glycol, polyoxyethylene-polyoxypropylene glycol ethylenediamine, and polyoxyethylene-polyoxypropylene glycol. Oxyethylene fatty acid ester, polyoxyethylene-polyoxypropylene glycol fatty acid ester, polyoxyethylene sorbitan fatty acid ester, ethylene glycol fatty acid ester, propylene glycol fatty acid ester, glycerin fatty acid ester, pentaerythritol fatty acid ester,
Examples thereof include sorbitan fatty acid ester, sucrose fatty acid ester, and fatty acid ethanolamide.

As the anionic surfactant, fatty acid alkali salt, alcohol sulfate ester salt, polyoxyethylene alkyl ether sulfate ester salt, polyoxyethylene alkylphenyl ether sulfate ester salt, fatty acid polyhydric alcohol sulfate ester salt, sulfated Examples thereof include oils, fatty acid anilide sulfate ester salts, petroleum sulfonates, alkylnaphthalene sulfonates, dinaphthylmethane sulfonates, alkyldiphenyl ether disulfonates, and polyoxyethylene alkyl ether phosphate ester salts.

Further, as the cationic surfactant, a weak cationic cationic surfactant, for example, alkylamine and its polyoxyalkylene adduct, for example, octylamine, dibutylamine, trimethylamine, oleylamine, stearylamine and its ethylene oxide are used. 5 to 15 mol adduct, propylene oxide 5
˜15 mol addition product and the like. Further, as a weakly cationic cationic surfactant, a polyoxyalkylene adduct of polyamines such as alkylenediamine and dialkylenetriamine which may be substituted with a higher alkyl group, for example, ethylenediamine, ethylene oxide such as diethylenetriamine 0 to 100 mol Additive or ethylene oxide 0 to 100 mol and propylene oxide 0-1
Block or random adducts with 00 moles, oleyl propylene diamine, and ethylene oxide 0-100 mole adducts of stearyl propylene diamine are mentioned. Further, as weakly cationic cationic surfactants, polyoxyalkylene adducts such as higher fatty acid amides, for example, oleic acid amide, stearic acid amide with ethylene oxide 5 to 15 mol adduct, propylene oxide 5 to
15 mol addition products and the like can be mentioned. Examples of the strong cationic cationic surfactant include decanoyl chloride, alkylammonium salt, alkylbenzylammonium salt, and alkylamine salt. Specifically, cetyltrimethylammonium chloride, stearyltrimethylammonium chloride, behenyltrimethylammonium chloride, Examples thereof include distearyldimethylammonium chloride, stearyldimerbenzylammonium chloride, stearic acid diethylaminoethylamide, coconut amine acetate, stearyl amine acetate, coconut amine hydrochloride and stearyl amine hydrochloride. In the case of a cationic surfactant having a strong cationic property, the conductivity increases when the use temperature of the electrorheological fluid reaches a high temperature of about 100 ° C. Therefore, among the above surfactants, a weak cationic surfactant is used. Is preferable, and low conductivity can be maintained during operation in a wide temperature range from a low temperature range to a high temperature range.

The content of the surfactant in the electrorheological fluid is
It is preferable to use it in a proportion of 0% by weight to 10% by weight, preferably 0.1% by weight to 5% by weight, and if it exceeds 10% by weight, the conductivity becomes high, which is not preferable.

Further, if necessary, an antioxidant, a corrosion inhibitor, an antiwear agent, an extreme pressure agent, an antifoaming agent, etc. are added to the electrorheological fluid of the present invention.

The antioxidant is intended to prevent the oxidation of the polyhydric alcohol and the partial derivative of the polyhydric alcohol, which are polarization promoting agents, as well as the oxidation of the electrically insulating liquid. As the antioxidant, it is preferable to use one that is inactive to the polarization promoter and the dispersoid, and a commonly used phenol-based or amine-based antioxidant can be used. -6-di-t-butylparacresol, 4,4'-methylenebis (2.6-di-
t-butylphenol), 2,6-di-t-butylphenol, etc., and dioctyldiphenylamine, phenyl-α-naphthylamine, alkyldiphenylamine, N-nitrosodiphenylamine, etc. can be used as the amine type, and the whole electrorheological fluid can be used. 0% by weight to
10% by weight, preferably 0.1% to 2.0% by weight can be used. If it exceeds 10% by weight, the hue deteriorates,
There are problems such as generation of turbidity, generation of sludge, and increase in viscosity.

Although a corrosion inhibitor may be added, it is preferable to use one which is inert to the polarization accelerator, dispersoid, etc.
Specifically, for nitrogen compounds, benzotriazole and its derivatives, imidazoline, pyrimidine derivatives, etc., for compounds containing sulfur and nitrogen, 1.3.4-thiadiazole polysulfide, 1.3.4-thiadiazolyl-2.5-bisdialkyldithiocarbamate, 2- ( Alkyldithio) benzimidazole, etc., and β- (o-carboxybenzylthio) propionnitrile, propionic acid, etc. can be used.
It is recommended to use 0% by weight, preferably 0.01% by weight to 1.0% by weight. If it exceeds 10% by weight, there are problems such as deterioration of hue, generation of turbidity, generation of sludge, and increase in viscosity.

[0043]

When a polyhydric alcohol is used as a polarization accelerator and a non-aqueous system is used, the electrorheological effect can be excellent in durability. By using silica fine particles esterified with a monohydric alcohol having an alkyl group of 8 or more carbon atoms as the main chain as a dispersoid, an electrorheological fluid having more excellent dispersibility and no thermosetting can be obtained. Is found.

Although the detailed reason for this is not clear, it is possible to make the silica particles excellent in dispersibility by refining the silica particles to a critical particle size, and to make the silanol groups on the surface thereof a hydrocarbon having an appropriate molecular length. Since it is esterified by a group, it is considered that a high electrorheological effect can be obtained by a sufficient attractive force between particles. In addition, it is considered that the bonds do not decompose even under heating conditions, and as a result, aggregation between particles can be prevented.

The present invention will be described below based on examples.

[0046]

Example 1 To 200 g of toluene, 60 g of silica particles (“Sycilia 310” manufactured by Fuji Silysia Chemical Ltd., average particle size 1.4 μm) was mixed, and this was mixed with a ball mill (using beads made of zirconia, 250 rpm) for 6 hours. Process and
The silica particles had an average particle size of 0.1 μm. To this, 200 g of oleyl alcohol (C ₁₈ H ₃₅ OH) was added, and 1
The reaction was carried out at 11 ° C for 6 hours while heating under reflux, water was azeotropically removed, and an esterification reaction was carried out.

The obtained reaction product was washed with carbon tetrachloride, and particles were separated using an ultracentrifuge (18,000 rpm × 60 min). This washing operation and separation operation were repeated until the unreacted alcohol was removed. Carbon tetrachloride was removed with a rotary evaporator to obtain 37 g of oleyl esterified silica particles.

The surface area of the particles obtained is 194 m ² / g.
(BET method) and elemental analysis value (carbon): 14%, so that it was found that the number of bonding groups of the esterified silanol groups on the silica surface was 3.0 / nm ² .

Using the silica particles thus obtained, an electrorheological fluid having the following composition was prepared.

(Composition of electrorheological fluid) ・ Esterified silica fine particles ・ ・ ・ 15% by weight ・ Triethylene glycol ・ ・ ・ 3% by weight ・ Alkylbenzene (40 ° C., 4.3 cSt) ・ ・ ・ 82 % By Weight About the obtained electrorheological fluid, room temperature (25 ° C) to 10
When a current value was measured in an applied electric field of AC 50 Hz and 2 KV / mm in a temperature range of 0 ° C., it was 0.1 mA to 0.3 mA.
mA, which was extremely low.

[0051]

Example 2 60 g of silica particles (“Sycilia 440” manufactured by Fuji Silysia Chemical Ltd., average particle size 3.5 μm) and oleyl alcohol (C ₁₈ H ₃₅ ) in 200 g of toluene.
200 g of OH) was mixed and reacted with heating under reflux at 111 ° C. for 6 hours to azeotropically remove water to carry out an esterification reaction.

The obtained reaction product was washed with carbon tetrachloride, and the particles were separated using an ultracentrifuge (18,000 rpm × 60 min). This washing operation and separation operation were repeated until the unreacted alcohol was removed. Carbon tetrachloride was removed by a rotary evaporator to obtain 48 g of oleyl esterified silica particles.

The surface area of the particles obtained is 216 m ² / g.
(BET method) and elemental analysis value (carbon): 16%, and thus it was found that the number of bond groups of the silanol groups esterified on the silica surface was 3.1 / nm ² .

Using the silica particles obtained, Example 1
Similarly, an electrorheological fluid was prepared.

[0055]

Comparative Example 1 In 200 g of toluene, 60 g of silica particles (“Cycilia 450” manufactured by Fuji Silysia Chemical Ltd., average particle size 5.2 μm) and oleyl alcohol (C ₁₈ H ₃₅
200 g of OH) was mixed and reacted with heating under reflux at 111 ° C. for 6 hours to azeotropically remove water to carry out an esterification reaction.

The obtained reaction product was washed with carbon tetrachloride, and particles were separated using an ultracentrifuge (18,000 rpm × 60 min). This washing operation and separation operation were repeated until the unreacted alcohol was removed. Carbon tetrachloride was removed by a rotary evaporator to obtain 48 g of oleyl esterified silica particles.

The surface area of the obtained particles is 203 m ² / g
(BET method) and elemental analysis value (carbon): 15%, it was found that the number of bonding groups of silanol groups esterified on the silica surface was 3.1 / nm ² .

Using the resulting silica particles, Example 1
Similarly, an electrorheological fluid was prepared.

For the electrorheological fluids prepared in Examples 1 and 2 and Comparative Example 1 above, the effect of the particle size of the silica particles on the dispersibility was measured by the following evaluation method. Shown in.

(1) Dispersibility: The electrorheological fluid was placed in a graduated cylinder, allowed to stand at room temperature, particles settled, and the ratio (%) of the oil-only layer formed in the upper part to the total amount of two-layer separation , And the relationship with the number of stationary days was calculated.

As can be seen from FIG. 1, when silica fine particles having a particle size of more than 4 μm are used, the two-layer separation speed is high,
It turns out that it is not suitable for use.

[0062]

Example 3 Instead of oleyl alcohol in Example 1, 1-octanol (C ₈ H ₁₇ OH), 1-tetracosanol (C ₂₄ H ₄₉ OH), 1-dotriacontanol (C ₃₂ H ₆₅ OH). ), 1-hexatriacontanol (C
₃₆ H ₇₃ OH) in the same amount, and the number of esterified silanol groups on the particle surface is 2.
Silica particles of 7 to 3.3 particles / nm ² were obtained, respectively.

Using the silica particles obtained, Example 1
Similarly, an electrorheological fluid was prepared.

Using each electrorheological fluid, the influence of the main chain length of the alkyl group in the alcohol on the dispersibility of the silica fine particles and the electrorheological effect (thickening ratio) was evaluated.

The evaluation method is as follows. (1) Dispersibility: When an electrorheological fluid is placed in a graduated cylinder and allowed to stand at room temperature for 30 days, particles may settle and an oil-only layer may be formed on the upper part. The ratio (%) of the upper oil-only layer formed when left to stand was defined as the amount of two-layer separation.

(2) Thickening factor: An electrorheological fluid was filled in a double cylinder type rotational viscometer, and an alternating electric field (50 Hz, 2 Kv / mm) was applied between the inner and outer cylinders at 40 ° C., and the same shear rate (600 sec). ^-1 ) was measured.

FIG. 2 shows the measurement results of the dispersibility, and FIG. 3 shows the measurement results of the thickening ratio.

As shown in FIG. 2, two layers were separated only when 1-octanol (having 8 carbon atoms) was used for esterification. However, the separated lower layer was easily redispersed by slight vibration.

Further, as shown in FIG. 3, it can be seen that a thickening effect can be obtained by using an alcohol having an alkyl group having 8 to 36 carbon atoms for esterification. That is, it can be seen from FIGS. 2 and 3 that as the carbon number increases, the dispersion stability is excellent as shown in FIG. 2, but the thickening effect is reduced as shown in FIG.

Further, when an alcohol having an alkyl group having less than 8 carbon atoms was used for esterification, the two-layer separation rate was high, and therefore the thickening effect was not stable and could not be evaluated.

[0071]

Example 4 In the production of the silica fine particles in Example 1, the reaction conditions were changed so that the number of esterified silanol groups bonded to the silica surface was 2.0 / nm ² .

Using the silica particles obtained, Example 1
Similarly, an electrorheological fluid was prepared.

[0073]

Example 5 In the production of the silica fine particles in Example 1, the reaction conditions were changed to obtain a silica surface having an esterified silanol group having a number of bonding groups of 5.5 / nm ² .

Using the resulting silica particles, Example 1
Similarly, an electrorheological fluid was prepared.

[0075]

Comparative Example 2 In the production of the silica fine particles in Example 1, the reaction conditions were changed to obtain the number of esterified silanol groups bonded on the silica surface being 1.5 / nm ² .

Using the silica particles obtained, Example 1
Similarly, an electrorheological fluid was prepared.

[0077]

[Comparative Example 3] In the production of the silica fine particles in Example 1, the reaction conditions were changed to obtain a silica surface having a number of esterified silanol groups bonded to 8.0 per nm ² .

Using the resulting silica particles, Example 1
Similarly, an electrorheological fluid was prepared.

With respect to the electrorheological fluids obtained in Examples 4 and 5 and Comparative Examples 2 and 3, the dispersibility was evaluated by the dispersibility evaluation method described in the section of Comparative Example 1, and the thickening ratio was determined in Examples. It was evaluated by the evaluation method of the thickening ratio described in 3. The results of measurement of dispersibility are shown in FIG. 4, and the results of measurement of thickening ratio are shown in Table 1 below.

As can be seen from FIG. 4, when the number of esterified silanol groups on the silica surface is small, the stationary stability is poor and two layers are separated.

[0081]

[Table 1]

As can be seen from Table 1, when the number of esterified silanol groups bonded to the surface of silica is large, the thickening factor is low and the electrorheological effect is not observed. The dispersibility of the electrorheological fluids of Example 5 and Comparative Example 3 were such that they did not separate into two layers.

[0083]

Comparative Example 4 In the preparation of silica fine particles in Example 1, oleyl alcohol (C ₁₈ H ₃₅ OH) was added to 1,2-
2 in place of octadecanediol (HOC ₁₈ H ₃₆ OH)
An esterification reaction was performed in the same manner as in Example 1 except that 13 g was used to obtain 42 g of esterified silica fine particles.

The surface area of the obtained particles was 186 m ² / g.
(BET method) and elemental analysis value (carbon): 11%, it was found that the number of bond groups of silanol groups esterified on the silica surface was 2.5 / nm ² .

Using the resulting silica particles, Example 1
Similarly, an electrorheological fluid was prepared, and its static stability was evaluated by the dispersibility evaluation method described in the section of Comparative Example 1.

The measurement results are shown in FIG.

From FIG. 5, it is understood that when polyhydric alcohol is used for esterification of silica fine particles, precipitation which is difficult to redisperse occurs.

[0088]

Comparative Example 5 Using the esterified silica fine particles in Example 1, an electrorheological fluid having the following composition was prepared.

(Composition of electrorheological fluid) ・ Esterified silica fine particles ・ ・ ・ 15% by weight ・ Water ・ ・ ・ 0.4% by weight ・ Alkylbenzene (40 ° C., 4.3 cSt) ・ ・ ・ 84 About 6 wt% of the prepared electrorheological fluid and the electrorheological fluid prepared in Example 1, the thickening ratio was measured under the following conditions, and
The change with time was measured. The measurement result is shown in FIG.

Thickening ratio: An electrorheological fluid was filled in a double cylinder type rotational viscometer, and an alternating electric field (5
0 Hz, 2 Kv / mm is applied, and the same shear rate (60
The thickening ratio at ⁰ sec ^-1 ) was measured.

From FIG. 6, it can be seen that when water is used as the polarization promoting agent, the thickening factor is large due to evaporation and is not suitable for use at high temperature.

[0092]

[Comparative Example 6] Electro-rheological fluid having the following composition: -Silica fine particles (average particle size 1.4 μm, unmodified)-15% by weight-Triethylene glycol--3% by weight-Polybutenyl Succinimide: 20% by weight Alkylbenzene (40 ° C., 4.3 cSt): 62% by weight was prepared, and two layers were separated by the evaluation method for dispersibility described in the section of Comparative Example 1. When the amount was measured, it was 5%. Further, the lower layer had no fluidity, and the particles were dense and did not easily redisperse.

When this electrorheological fluid was heated to 100 ° C., it was thermoset in 20 minutes, while the electrorheological fluid in Example 1 was not thermoset even after 180 minutes.

[0094]

[Example 6] The silica particles used in Example 2 were "Sicyria 310" manufactured by Fuji Silysia Chemical Ltd., and the average particle size was 1.4.
μm), and as the alcohol, 1-octanol (C ₈ H ₁₇ OH), lauryl alcohol (C ₁₂ H
₂₅ OH), oleyl alcohol (C ₁₈ H ₃₅ OH), 1-
Example 2 using the same amount of tetracosanol (C ₂₄ H ₄₉ OH), 1-dotriacontanol (C ₃₂ H ₆₅ OH), and 1-hexatriacontanol (C ₃₆ H ₇₃ OH), respectively.
In the same manner as described above, silica particles having the number of esterified silanol groups bonded on the particle surface of 2.7 to 3.3 / nm ² were respectively obtained.

Using the silica particles obtained, Example 1
Similarly, after preparing an electrorheological fluid, the influence of the main chain length of the alkyl group in the alcohol on the dispersibility of the silica fine particles and the electrorheological effect (thickening ratio) was evaluated in the same manner as in Example 3.

FIG. 7 shows the measurement results of dispersibility, and FIG. 8 shows the measurement results of thickening ratio.

As shown in FIG. 7, 1-octanol (having 8 carbon atoms) and lauryl alcohol (having 1 carbon atoms) were used for esterification.
Two layers were separated only when 2) was used. However,
The separated lower layer was easily redispersed by slight vibration.

Further, as shown in FIG. 8, it can be seen that a thickening effect can be obtained by using an alcohol having an alkyl group having 8 to 36 carbon atoms for esterification. That is, it can be seen from FIGS. 7 and 8 that as the carbon number increases, the dispersion stability is excellent as shown in FIG. 7, but the thickening effect is reduced as shown in FIG.

When an alcohol having an alkyl group having less than 8 carbon atoms was used for esterification, the two-layer separation speed was high, and therefore the thickening effect was not stable and could not be evaluated.

[Brief description of drawings]

FIG. 1 is a diagram for explaining a relationship between a particle diameter of esterified silica fine particles and dispersion stability in an electrorheological fluid.

FIG. 2 is a diagram showing the relationship between the main chain length of an alkyl group in an alcohol used for esterification of the surface of silica fine particles and the two-layer separation amount in the electrorheological fluid.

FIG. 3 is a diagram showing the relationship between the main chain length of an alkyl group in an alcohol used for esterification of the surface of silica fine particles and the thickening ratio in the electrorheological fluid.

FIG. 4 is a diagram for explaining the relationship between the number of ester bond groups in the esterified silica fine particles and the dispersion stability in an electrorheological fluid.

FIG. 5 is a diagram for explaining the relationship between the type of ester in esterified silica fine particles and the dispersion stability in an electrorheological fluid.

FIG. 6 is a diagram for explaining the relationship between the type of polarization promoting agent in the electrorheological fluid and the thickening ratio in the electrorheological fluid.

FIG. 7 is a diagram showing the relationship between the main chain length of an alkyl group in an alcohol used for esterification of the surface of silica fine particles and the amount of two-layer separation in the electrorheological fluid.

FIG. 8 is a diagram showing the relationship between the main chain length of an alkyl group in an alcohol used for esterification of the surface of silica fine particles and the thickening factor in the electrorheological fluid.

Continuation of the front page (51) Int.Cl. ⁶ Identification number Reference number within the agency FI Technical indication location C10M 105: 14 107: 50) C10N 40:14 (72) Inventor Hirotaka Tomizawa Nishitsurugaoka, Nishii, Irima-gun, Saitama Prefecture 3-3-1 Tonen Co., Ltd. Research Institute

Claims (1)

[Claims] 1. An electrorheological fluid comprising silica fine particles esterified with a monohydric alcohol whose surface has an alkyl group having 8 or more carbon atoms as a main chain and a polyhydric alcohol in an electrically insulating fluid.