Stock material or miscellaneous articles – Coated or structually defined flake – particle – cell – strand,... – Particulate matter
Reexamination Certificate
1999-09-22
2001-05-15
Le, Hoa T. (Department: 1773)
Stock material or miscellaneous articles
Coated or structually defined flake, particle, cell, strand,...
Particulate matter
C423S081000, C423S351000, C423S364000, C423S44500R, C423S598000, C423S610000, C428S404000, C428S698000, C428S702000
Reexamination Certificate
active
06231981
ABSTRACT:
TECHNICAL FIELD
The present invention relates to a carbon-coated titania powder containing titanium nitride which is suitably used as resin reinforcing material, conductive filler or the like, and a method of preparing the same.
BACKGROUND ART
Heretofore, as a conductive filler incorporated into resin or the like, there has been known a potassium titanate fiber and titania fiber to which conductivity is afforded by coating the fiber surface with a conductive substance, or by producing oxygen deficiency by means of reductive calcination. Since these fibers are excellent in reinforcing property, dispersibility and conductivity, they are put into practice for uses, such as the prevention of electrification, electromagnetic wave shield, and electrode material.
Meanwhile, in the recent years, fillers having more superior conductivity have been developed which can render the desired conductivity in a smaller amount. One superior method is to subject a titanate fiber to nitriding such that part of or the overall fiber is converted to titanium nitride. This method enables to render high conductivity without impairing the strength of the fiber.
For instance, there are known a method in which a fibrous titania or titania hydrate is heated and reduced at a temperature of 500 to 1000° C. in a reducing atmosphere containing ammonia gas, to obtain a conductive acid titanium nitride fiber (JP-A-215718/1989), and a method in which a potassium titanate fiber is calcinated with heating in an atmosphere of ammonia gas, to obtain a potassium titanate fiber, part of which has been converted to titanium nitride (JP-A-27573/1993).
Unfortunately, both methods have the following drawbacks. That is, since they require heat treatment in an atmosphere of ammonia gas, meticulous care should be taken in avoiding leakage to the surroundings, and it is difficult to adjust the partial pressure of ammonia gas in the atmosphere. Further, in order to obtain a high degree of nitriding, it is necessary to continue the reaction for a long period of time because the reduction reaction proceeds predominantly than the nitriding reaction. This can cause deformation of the starting fiber shape.
Furthermore, the fibers obtained by the above methods have high hardness because part of the fiber surface is directly exposed as titanium nitride. Therefore, when the fiber is used as a filler for resin, it is liable to wear a molding die. Additionally, a resin composition incorporating this fiber is poor in slidability and wear resistance.
An object of the present invention is to provide a conductive powder which is excellent in reinforcing property and conductivity, as well as slidability and wear resistance, and can prevent wear of dies.
Another object of the present invention is to provide a conductive powder having good conductivity which can be prepared at a relatively low temperature and in a short period of time.
DISCLOSURE OF THE INVENTION
The present invention relates to a carbon-coated titania powder containing titanium nitride in which at least part of the surface of the titania powder containing titanium nitride is coated with carbon, and a method of preparing the same. Hereinafter, the carbon-coated titania powder containing titanium nitride is referred to merely as “composite powder” in some cases. The term “powder” as used in this specification includes ones in a variety of shapes, such as granular powder, fibrous powder and scalelike powder.
As representative titania or titanate compound (hereinafter referred to as “titanium source compound” in some cases) to be used as the raw material in the present invention, there can be exemplified potassium 4-titanate, potassium 6-titanate, potassium 8-titanate, sodium titanate, barium titanate, calcium titanate, titania hydrate, monoclinic titania, anatase and rutile. The titanium source compound is not specifically limited to the above. Especially preferred is a titania fiber of potassium 4-titanate, potassium 6-titanate, potassium 8-titanate or monoclinic titania, having a fiber shape with a fiber length of about 1 to 20 &mgr;m and a fiber diameter of about 0.1 to 1 &mgr;m. With this fiber, it is possible to obtain a filler with high reinforcing property.
As a nitrogenous organic compound suitable for use as the starting material in preparing a composite powder of the invention, there can be exemplified melamine, (meth)acrylamide and dicyandiamide, without limitation, of these, melamine is preferred because of high efficiency of nitriding.
The ratio of nitrogenous organic compound to titanium source compound is not limited specifically, but it is usually in the range: Ti/N (mole ratio)=1/1 to 1/10. When the ratio of N is too small, nitriding might not proceed sufficiently to provide insufficient conductivity. Even with an excessive ratio of N, since the amount of N correlated to nitriding under this conditions is limited, an excess is a waste and hence less economical.
In one preferred method of preparing a composite powder of the invention, preferably a titanium source compound in a fibrous powder and preferably a nitrogenous organic compound in a powdery solid are mixed in powdery state, followed by heat treatment in a non-oxidizing atmosphere. Thereby, the nitrogenous organic compound is decomposed, and all of the reactions of partial nitriding, reduction and carbon coating by carbonization take place at the same time, to the titanium source compound. Also, when the titanium source compound is titanate, part of or the overall alkali metal and the like are removed, thereby obtaining a composite powder of the invention.
Examples of non-oxidizing atmosphere are nitrogen gas, argon gas and ammonia gas atmospheres. Of these, nitrogen gas is preferred because it is safe and inexpensive. As means of calcination with heating, a variety of means such as electric furnace, gas furnace, rotary kiln and continuous furnace can be employed insofaras the above-mentioned atmosphere is ensured.
Suitable heating temperature is above the temperature at which a nitrogenous organic compound decomposes, that is, it is usually about 400 to 1200° C., preferably about 700 to 1100° C. In accordance with a method of the invention, however, even at relatively low temperatures, that is, substantially under 1000° C., for example, 700 to 900° C., the nitriding of the starting titanium source compound proceeds and titanium nitride is formed. This enables to obtain the desired substance having a sufficient conductivity. Suitable heating time is usually about 0.5 to 24 hours, preferably about 1 to 5 hours.
The obtained conductive composite powder may be, as required, subjected to washing with water, washing with acid, grinding, fine pulverization, and classification or surface treatment using a coupling agent, etc., in order to remove impurities, obtain a uniform shape, and improve kneading property to resin.
A composite powder of the invention preferably comprises 1 to 70% by weight of titanium nitride, more preferably 5 to 25% by weight of titanium nitride. Less titanium nitride content is undesirable because it causes a decrease in conductivity. For a fibrous substance, an excess titanium nitride content is undesirable because the fiber loses its shape.
Titania part is reduced such as to be TiO
2−X
(0.1≦×≦1.5), thereby increasing conductivity. A carbon-coated layer on the powder surface is preferably about 1 to 30% by weight. The carbon-coated layer does not necessarily coat the entire surface of a composite powder, and at least part of the surface may be coated. The carbon-coated part lowers the hardness of the powder surface to improve slidability, and also contributes to the manifestation of conductivity. In a composite powder of the invention, impurity such as alkali metal derived from the starting material or the like may be contained somewhat, for example, from 0 to 10% by weight.
A composite powder of the invention can be suitably used as the material of additives to a matrix such as plastics, ceramics, coating composition and metal, which are aimed at rendering an
Kubovcik & Kubovcik
Le Hoa T.
Otsuka Kagaku Kabushiki Kaisha
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