Processes for producing coated particles

Details Processes for producing coated particles Processes for producing coated particles

1995-04-11

1998-12-08

Beck, Shrive

Coating processes

Particles, flakes, or granules coated or encapsulated

Solid encapsulation process utilizing an emulsion or...

427215, 118716, B05D 700, C23C 1600

Patent

active

058466002

DESCRIPTION:

BRIEF SUMMARY
TECHNICAL FIELD

This invention relates to a process for producing coated particles and an apparatus therefor. More specifically, the invention relates to a production process of the coated particles for coating coat forming substances on particles in a powder of fine core particles or core particles comprising mainly fine particles and an apparatus therefor.


BACKGROUND ART

Vapor-phase process in which inorganic materials, metallic materials and other coat forming substances are applied to provide coatings on the surfaces of the particles in the powder as films and various other forms theoretically have major features that are unattainable by other coating techniques, such as: (1) easy control of the atmosphere; (2) the selection of coat forming substances is basically unlimited and various kinds of substances including elemental metallic substances (e.g. active metals), alloys, nitrides, carbides, borides and oxides can be coated on the surfaces of the particles of the powder; (3) the highly pure substance can be coated; and (4) the coating weight of the coat forming substance can be controlled freely.
However, for the reasons to be set forth below, none of the vapor-phase process have been capable of forming substantially the coatings with the coat forming substances on each surface of the particles not larger than 10 .mu.m in the powder of the fine core particles or the core particles comprising mainly fine particles.
That is, the particles in the powder of the fine core particles or the core particles comprising mainly the fine particles are cohesive enough to have a great tendency to agglomerate together, whereby almost all single particles form agglomerates. Since these agglomerates cannot be disintegrated unless they are subjected to a special action greater than their cohesive force, even if they are simply coated with the coat forming substances, eventually coated agglomerates in which the surfaces of the agglomerates are covered with the coating of the coat forming substances are yielded. This has caused a problem with the individual particles forming the agglomerates which suffer from uneven coating in that the surfaces of the particles located on the surfaces of the agglomerates have large coating weights whereas the particles located within the agglomerates are not covered at all.
With a view to solving above-described problems, attempts have already been made to coat the particles in a dispersed state in order to assure the coating of the individual particles in the powder of the fine core particles or the core particles comprising the fine particles.
For instance, Unexamined Published Japanese Patent Application (kokai) Sho 58-31076 teaches an apparatus and method, according to which a vessel placed in PVD equipment is charged with the particles in a powder of core particles and vibrated by an electromagnetic means so that the core particles in the vessel are rolled as they are coated by a PVD process. Unexamined Published Japanese Patent Application (kokai) Sho 61-30663 teaches an apparatus, according to which a vessel placed in PVD equipment is charged with the particles in a powder of core particles and vibrated by a mechanical means so that the core particles in the vessel are rolled as they are coated by a PVD process. However, in the actual practice with those apparatus or methods in which the vessel was vibrated so that the particles in the powder of core particles were rolled as they were provided with coatings, the necessary action for disintegrating the agglomerates of the particles in the powder of the fine core particles or the core particles comprising mainly the fine particles by applying a force exceeding their cohesive force could not be produced and, hence, the agglomerates could not be disintegrated; to the contrary, a granulating action developed to form agglomerates that were greater in number or size than before the powder of core particles was supplied into the vessel.
Unexamined Published Japanese Patent Application (kokai) Hei 3-153864 teaches an apparatus and meth

REFERENCES:
patent: 4314525 (1982-02-01), Hsu et al.
patent: 4328042 (1982-05-01), Ostertag et al.
patent: 4940523 (1990-07-01), Takeshima

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