Coating apparatus – Gas or vapor deposition – Means to coat or impregnate particulate matter
Reexamination Certificate
1998-11-20
2002-10-22
Mills, Gregory (Department: 1763)
Coating apparatus
Gas or vapor deposition
Means to coat or impregnate particulate matter
C118S719000, C118S715000
Reexamination Certificate
active
06468352
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to method and apparatus for modifying particles by forming a film of a modifying agent on the surface of particles, and more particularly, to method and apparatus for modifying particles by coating the particles with the modifying agent by letting the modifying agent condense on the surface of the particles under modifying agent's vaporous atmosphere.
BACKGROUND OF THE INVENTION
Besides a dry method, a method for modifying the surface of fine particles in a liquid phase has been known as a particle surface modifying method. Also, a kneading method, a stirring method using a medium, a spray dry method, etc. are widely adopted.
The above methods are well-known and described in detail in the references, such as:
1. “Fine Particle Engineering: Fundamentals and Applications of Distribution”, First Edition, edited by Japan Fine Particle Engineering Technology Association, and published by Asakura Shoten, 1994, pp
123-36; and
2. “Today's Chemical Engineering 45 Fine Particle Engineering”, edited by Chemical Engineering Association, and published by Chemical Industry Association on Nov. 25, 1993, pp16-23.
Also, Japanese Laid-open Patent Application No. 204545/1995 (Tokukaihei No. 7-204545) discloses a method of forming a film on the surface of a subject. To be more specific, aerosol containing a solvent is sprayed in a chamber to let the aerosol particles collide with the surface of the subject while vaporizing the solvent from the surface of the subject, whereby a film made of solute of the particles is formed on the surface of the subject.
However, according to the above conventional particle modifying method, the particles are electrically charged and become hard to handle thereafter. Moreover, not only the modifying treatment takes too long, but also it demands a complex and expensive apparatus. Further, the above conventional modifying method can hardly modify fine particles, particularly, those in the order of nanometer.
Another method of modifying the particle surface is a method of exposing the particles to a liquid element's saturated or supersaturated atmosphere at room temperature under atmospheric pressure. For example, Japanese Laid-open Patent Application No. 2865/1977 (Tokukaisho No. 52-2865) discloses, as a technique for capturing aerosol particles, a method for growing aerosol particles up to a predetermined particle size by mixing high-temperature saturated air with low-temperature saturated air, each being a gas containing the aerosol particles, and then letting a water vapor condense on the surface of the aerosol particles. Likewise, an European Patent No. EP 0 794 017 A2 discloses a method for forming a film of a surface modifying agent on the surface of the particles by exposing the particles to a supersaturated atmosphere of the surface modifying agent, and then letting the surface modifying agent condense on the surface of the particles, thereby modifying the surface properties of the particles.
However, the above two methods are silent about an idea of letting a solid surface modifying agent condense on the surface of the particles at room temperature under atmospheric pressure, and the surface modifying agent must be vaporized in each method. Thus, materials which do not vaporize, such as resin (polymer), can not be used as the element for a vapor, and there arises a problem that available materials are limited.
SUMMARY OF THE INVENTION
The present invention is devised to solve the above problem, and therefore, has an object to provide method and apparatus for modifying particles which can produce modified particles coated with a thick uniform film of the modifying agent by a very simple manipulation in a short time.
The inventors of the present invention conducted a study to solve the above problem, and has already discovered a particle modifying method as described below, which is totally different from any of the conventional methods.
That is, the inventors of the present invention discovered a particle modifying method for forming a film of the modifying agent on the surface of the particles by the following steps of:
(1) producing a saturated vapor of the modifying agent in a treatment space in a condensing chamber;
(2) exposing the particles to the saturated vapor of the modifying agent by letting the same flow across the treatment space in the condensing chamber; and
(3) turning the saturated vapor of the modifying agent into a supersaturated state by cooling the same in a delivery path connected to the treatment space in the condensing chamber to let the modifying agent condense and form a film on the surface of the particles.
The above method excels the conventional methods because it can modify the surface of the particles by a simple manipulation in a short time without electrically charging the particles. However, the above method needs improvement to form a satisfactory thick uniform film of the modifying agent on the surface of the particles.
Thus, the inventors of the present invention continued an assiduous study to improve the above method and apparatus for modifying the particles, and in due course, discovered following method and apparatus for modifying the particles.
To solve the above problem, a particle modifying method of the present invention has the steps of:
cooling particles to be surface-modified;
forming a vapor of a modifying agent for modifying the particles;
forming a film of the modifying agent on a surface of the particles by (1) producing a supersaturated vapor of the modifying agent around the particles by exposing the particles cooled in the cooling step to the vapor of the modifying agent to be mixed with each other, and (2) letting the modifying agent condense on the surface of the particles.
According to the above method, since the particles cooled in advance are exposed to the vapor of the modifying agent, a large temperature difference is made between the particles and vapor. Thus, a larger amount of the vapor of the modifying agent vapor-deposits on each particle, thereby making it possible to obtain the particles of a relatively large particle size.
Also, since all the particles are cooled to substantially the same temperature before they are introduced into a mixing section, the temperature does not vary much among the particles and is substantially the same. Thus, a substantially equal amount of the vapor of the modifying agent vapor-deposits on each particle, thereby making it possible to obtain the particles of a substantially uniform particle size.
Further, in case that the modifying agent is turned into a supersaturated state by cooling the walls of the mixing section, much of the modifying agent is lost as it deposits onto the wall surface. By contrast, in the present method, the loss of the modifying agent is very small because the supersaturated state is obtained by cooling the particles per se, thereby making it possible to let the modifying agent vapor-deposit on the surface of the particles efficiently. Moreover, in case that particles of a liquid are used, the evaporation of the particles per se when introduced into the saturated vapor of the modifying agent can be suppressed.
Further, since the above method employs a simple technique of cooling the vapor of the modifying agent to obtain the supersaturated atmosphere, it can offer another effect that both the modifying treatment manipulation and apparatus can be simpler.
Furthermore, the above method can form a film of the modifying agent on the surface of the particles without any step such that electrically charges the particles, for example, the stirring of the particles. Thus, the particles after the modifying treatment, namely, the modified particles, are not electrically charged by the modifying treatment, and therefore, easy-to-handle modified particles can be obtained. Also, compared with the stirring of the particles in the conventional particle modifying treatment, the cooling of the particles and the subsequent mixing with the vapor of the modifying agent takes a very short
Horiuchi Takahiro
Morimoto Kiyofumi
Conlin David G.
Dike Bronstein, Roberts & Cushman IP Group of Edwards & Angell,
Mills Gregory
Sharp Kabushiki Kaisha
Zervigon Rudy
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