Compositions – Fluent dielectric – Metal- or insoluble component-containing; e.g. – slurry,...
Reexamination Certificate
1999-02-22
2001-08-28
Gupta, Yogendra N. (Department: 1751)
Compositions
Fluent dielectric
Metal- or insoluble component-containing; e.g., slurry,...
C252S074000, C252S075000, C252S062520
Reexamination Certificate
active
06280658
ABSTRACT:
DESCRIPTION
1. Technical Field
The present invention relates to an electrorheological fluid (ERF), a magnetorheological fluid (MRF), and an electromagnetorheological fluid (EMRF). More particularly, the present invention relates to a rheological fluid which contains particles capable of being quickly and reversibly actuated by the application of an electric field or a magnetic field thereto, and which, by means of an applied electric field or magnetic field, can be quickly and reversibly changed in flowability, viscosity, and the like, and changed into even a gel state showing no flowability. When the powder dispersed in the fluid has optical properties, the rheological fluid is expected to be used in various applications. By utilizing a multilayer-coated powder of a bright color, the rheological fluid can be used as a color ink especially for ink-jet printers, a liquid color toner, or a color display medium.
2. Background Art
A rheological fluid is a functional fluid which usually is in a liquid state and flowable but which, upon application of an electric field or magnetic field or both, undergoes a marked increase in viscosity and changes into even a gel state showing no flowability.
Proposed so far as electrorheological fluids are a certain kind of polymer solution and suspensions of various particles. However, the former fluid does not sufficiently perform functions of an electrorheological fluid because the viscosity increase thereof with increasing applied voltage is small. Investigations have hence been made mainly on the latter fluids of the particle dispersion type. This is because ERFs of the particles dispersion type show a relatively satisfactory viscosity increase with increasing applied voltage (Winslow effect) as compared with the polymer solution type.
Incidentally, the particulate materials which have been known as particles to be dispersed into oily media to prepare electrorheological fluids include various substances such as silica, ion-exchange resins, barium titanate, hydrous phenolic resins, and crystalline zeolites. Among such particulate materials, inorganic substances have a high ERF effect, while polymer particles have satisfactory dispersibility. Because of this, it has been proposed to deposit fine particles of an inorganic substance on the surface of polymer particles to form an inorganic/organic composite two-layer structure to thereby give a powder for use in an electrorheological fluid (Gekkan Tribology, p. 24 (August 1994)).
Among fluids which actuate in response to a magnetic field are magnetic fluids. Ultrafine particles of a magnetic material which have particle diameters of 0.006 to 0.015 &mgr;m are used in magnetic fluids so as to keep the dispersed particles in a colloidal state. However, the concentration of magnetic-material particles in a magnetic fluid is about 35% at the most because a layer of a surfactant is formed on the surface of the ultrafine particles. In addition, since these magnetic-material particles are small, the intensity of magnetic properties (magnetization) thereof is as low as from 70 to 80% of that of large particles. Consequently, when such ultrafine particles are used to prepare a rheological fluid, the actuating force exerted by this fluid is so weak that a desired actuating force is not obtained or an exceedingly intense magnetic field is necessary.
On the other hand, a solvent colored with a dye has conventionally been used as a color ink for ink-jet printers. However, when an ink prepared by coloring a solvent with a dye is used as a color ink for ink-jet printers, the prints obtained have a drawback that they cannot be preserved over long due to the poor light resistance and poor weather resistance of the ink.
Consequently, an object of the present invention is to eliminate such drawbacks and provide a rheological fluid which mightily and precisely actuates in response to an electric field or a magnetic field or both, and to provide a rheological fluid of a bright color which actuates in response to an electric field or a magnetic field or both.
Another object of the present invention is to provide a rheological fluid whose actuation in an electric field can be easily confirmed.
Still another object of the present invention is to provide a rheological fluid which, when used in ink-jet color recording, can give recorded images having excellent storage ability.
DISCLOSURE OF THE INVENTION
The present invention made intensive studies. As a result, it has been found that the above objects can be accomplished by forming one or more coating layers on the surface of base particles made of an insulating material, dielectric, or conductive material to produce a film-coated powder or multilayer-coated powder and dispersing the coated powder into a medium to obtain a rheological fluid. The present invention has thus been completed.
Specifically, the present invention can accomplish the above objects by the following means.
(1) A rheological fluid comprising a medium in which a film-coated powder comprising a base particle having thereon a coating layer(s) is dispersed.
(2) The rheological fluid according to (1), wherein the powder is a multilayer-coated powder having thereon coating layers which differ from each other in refractive index.
(3) The rheological fluid according to (1), which has an average particle diameter of 0.015 to 100 &mgr;m.
(4) The rheological fluid according to (1), wherein the base particles of the powder is selected from a conductive material, a dielectric material, an insulating material, and a magnetic material.
(5) The rheological fluid according to (2), wherein the multilayer-coated powder has a color attributable to interference.
(6) The rheological fluid according to (1), wherein at least one of the coating layers is an inorganic metal compound layer.
(7) The rheological fluid according to (1), wherein at least one of the coating layers is a metal layer or an alloy layer.
(8) The rheological fluid according to (1), wherein at least one of the coating layers is an organic layer.
(9) The rheological fluid according to (1), wherein the surface of the multilayer-coated powder has been treated beforehand so as to have an affinity for solvents.
(10) The rheological fluid according to (1), wherein the medium has been color with a colorant.
The film-coated powder (which means a powder having at least one coating layer) or multilayer-coated powder for use in the present invention is a powder which is produced by forming plural films having different refractive indexes on the surface of a base particles made of an insulating material, dielectric material, or conductive material so that the coated powder has a color due to multiple interference between the films.
The material of the particle constituting the core (base particle) may be any of an insulating material, a dielectric material, and a conductive material. In the case of an insulating material, it is preferred to use a resin powder especially because it is less apt to sediment due to its small specific gravity. Examples of the resin powder include powders consisting of spherical or crushed particles of an acrylic polymer, a styrene polymer, a copolymer, a vinyl polymer, and the like. An especially preferred resin powder is an acrylic resin powder consisting of spherical particles obtained by the polymerization of an acrylic or methacrylic ester.
In the case of a dielectric material, examples thereof include those having a high permittivity, such as oxides of titanium, barium, lead, lithium, chromium, aluminum, silicon, and magnesium and composite oxides of these metals, such as barium titanate, lead titanate, and the like, and further include clays and glasses.
Preferred examples of the base particles made of a conductive material include metals such as iron, nickel, chromium, titanium, aluminum, cobalt, and the like; metal alloys, such as iron-cobalt, iron nickel, and the like; metal nitrides, such as iron-nickel-cobalt nitride and the like; and metal carbides, such as iron carbide and the like.
In the case of a magnetic material, preferre
Atarashi Takafumi
Nakatsuka Katsuto
Gupta Yogendra N.
Hamlin Derrick G.
Nittesu Mining Co., Ltd.
Sughrue Mion Zinn Macpeak & Seas, PLLC
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