Stock material or miscellaneous articles – All metal or with adjacent metals – Foil or filament smaller than 6 mils
Reexamination Certificate
1998-08-31
2001-11-13
Koehler, Robert R. (Department: 1775)
Stock material or miscellaneous articles
All metal or with adjacent metals
Foil or filament smaller than 6 mils
C029S527100, C072S274000, C228S126000, C148S516000, C148S530000, C148S534000, C148S670000, C148S421000, C428S607000, C428S612000, C428S660000, C428S683000, C428S687000, C428S903000, C428S926000
Reexamination Certificate
active
06316122
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates to a titanium fiber or a titanium alloy fiber having an equivalent area diameter of 5-30 &mgr;m and a method of producing the same, and more particularly to a titanium fiber or titanium alloy fiber having a large specific surface area and a method of producing the same.
Throughout the specification, the titanium and titanium alloy are generically called as “titanium”.
2. Description of Related Art
Extrafine metal fibers having a diameter of about 5-30 &mgr;m are used in various fields such as a material for a filter or a catalyst carrier, or as a filler for giving an electric conductivity or a strength to plastics, cloth and the like. As the extrafine metal fiber, there are widely used stainless fibers produced by a bundle-drawing method. On the other hand, it is demanded to develop a material for the filter or catalyst carrier having a corrosion resistance higher than that of the stainless fiber, or a filler having a light weight and a high strength as compared with those of the stainless fiber, and hence titanium fibers are recently noticed. Particularly, the titanium fibers having a larger specific surface area are demanded in the catalyst field requiring a surface area participant in the reaction as an important factor.
In the production of the extrafine metal fiber having a diameter of about 5-30 &mgr;m, there is known a bundle-drawing method as follows.
For example, JP-A-2-52117 discloses a method wherein a bundle-drawn composite body (composite filament) having an outer housing of steel and containing metal fibers embedded in copper matrix is prepared, and then the outer housing of steel and the copper matrix (covering layer) are removed by substitution reaction and electrolysis to obtain a bundle of metal fibers. However, this method is not suitable for the production of titanium fibers having a large specific surface area because the titanium fiber obtained by this method is small in the surface unevenness, so that in order to obtain titanium fibers having a large specific surface area, the fiber size should be made finer and hence labor and cost required for the working undesirably increase.
And also, JP-A-5-177244 discloses a method wherein a covered wire consisting of a core wire of high corrosion-resistant alloy with a covering layer of steel having a carbon content of not more than 0.12% by weight is subjected to cold drawing to form a covered filament, and a plurality of the covered filaments are bundled and inserted into an inside of a steel tube to form a composite wire, and the composite wire is subjected to cold drawing to form a composite filament, and then the steel tube and portion corresponding to the coated layer are dissolved out by electrolysis to obtain a bundle of metal fibers. However, when this method is applied to the production of titanium fibers, it implies a problem of insufficient dissolution in the final step causing low yield of titanium fibers though the surface unevenness becomes can be made large as compared with the case of JP-A-2-52117.
SUMMARY OF THE INVENTION
It is, therefore, an object of the invention to solve the afore-mentioned problems of the conventional techniques and to provide a titanium fiber having a specific surface area larger than that of the conventional titanium fiber having the same fiber size and a method of surely producing the same in a high efficiency.
According to a first aspect of the invention, there is the provision of a metal fiber made of titanium or titanium alloy by a bundle drawing method and having an equivalent area diameter d of 5-30 &mgr;m and a specific surface area A (m
2
/g) satisfying A≧25/d, preferably 30/d≦A≦50/d.
According to a second aspect of the invention, there is the provision of a method of producing a bundle of metal fibers made of titanium or titanium alloy, which comprises the steps of:
covering a bundle of covered filaments, each consisting of a core wire made of titanium or titanium alloy and a covering layer formed around the core wire with an outer housing to form a composite wire;
subjecting the composite wire to repetition of cold drawing and heat treatment to form a composite filament containing fibers of a given size; and
removing portions of the composite filament corresponding to the covering layer and the outer housing to obtain a bundle of metal fibers made of titanium or titanium alloy, wherein material of each of the covering layer and the outer housing is a mild steel containing not more than 0.25% by weight of carbon, and maximum temperature of the composite wire reached in the heat treatment is within a range of 580-650° C.
In a preferable embodiment of the second aspect of the invention, the production of the covered filaments comprises a step of forming a covering layer around a core wire to form a covered wire and a step of subjecting the covered wire to heat treatment and cold drawing at least one time to form a covered filament having a given diameter, in which maximum temperature of the covered wire reached in the heat treatment is within a range of 580-650° C. In another embodiment of the invention, a thickness of the covering layer in the covered filament is 5-20% of a diameter of the covered filament. In the other embodiment of the invention, total amount of the cold drawing applied to the composite wire defined by &egr;
T
=2×ln(D
S
/D
F
) is within a range of 5.5-7.5 (wherein D
S
is a diameter of the composite wire before the cold drawing and D
F
is a diameter of the composite filament).
REFERENCES:
patent: WO 97/04152 (1997-02-01), None
patent: 2-187212-A (1990-07-01), None
patent: 5-177244-A (1993-07-01), None
Patent Abstracts of Japan, vol. 017, No. 592 (JP 05-177244), Oct. 28, 1993.
Patent Abstracts of Japan, vol. 014, No. 231 (JP 02-059109), Feb. 28, 1990.
DataBase WPI, Section Ch, Week 9035, Derwent Publications Ltd., XP002104395 (JP 02-187212A), Jul. 23, 1990.
DataBase WPI, Section Ch, Week 9040, Derwent Publications Ltd., XP002104396 (JP 02-211901A), Aug. 23, 1990.
Bridgestone Metalpha Corporation
Koehler Robert R.
Sughrue Mion Zinn Macpeak & Seas, PLLC
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