Electricity: electrical systems and devices – Electrostatic capacitors – Fixed capacitor
Reexamination Certificate
2002-09-06
2003-08-12
Dinkins, Anthony (Department: 2831)
Electricity: electrical systems and devices
Electrostatic capacitors
Fixed capacitor
C361S508000
Reexamination Certificate
active
06606236
ABSTRACT:
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a capacitor having a large capacitance appearance ratio and a good moisture resistance value and also relates to a powder for the capacitor and a sintered body using the powder.
BACKGROUND ART
Earth-acid metals represented by tantalum and niobium are chemically stable and therefore, being used for various uses. For example, tantalum is widely used as a capacitor material for electronic instruments such as cellular phone and personal computers. Studies of niobium as a capacitor material are just starting; but its high dielectric performance is acknowledged as highly valuable.
The form of the earth-acid metal used as a capacitor material is usually powder and this powder is integrated through molding and sintering and becomes an electrode called a sintered body. Such a powder material from which a capacitor electrode is obtained is called a powder for capacitor.
The inside of the sintered body obtained as such has a three-dimensional complicated form where powders are electrically and mechanically connected with each other. On the inside and outside surfaces of this sintered body, a dielectric film layer is formed and thereinto, a material working out to another part electrode (also called “counter electrode”) is impregnated, whereby a capacitor is fabricated. As long as the dielectric film layer uniformly adheres to the inside and outside surfaces of the sintered body, the capacitance of the capacitor manufactured greatly depends on, microscopically, the contact state between the another part electrode material and the dielectric film layer.
Assuming that the contact state with a dielectric film layer is complete when:i an aqueous phosphoric acid solution is used as another part electrode material and that the capacitance appearance ratio at this time is 100%, a capacitance appearance ratio of 100% can be hardly attained by using an electrode material having high viscosity, particularly a solid electrode material. In particular, as the average particle size of the powder for capacitor is smaller, the difficulty more increases and in an extreme case, the capacitance appearance ratio may not reach even 50%. When the capacitance appearance ratio is low as such, the capacitor manufactured suffers from an insufficient moisture resistance value.
DISCLOSURE OF THE INVENTION
As a result of extensive investigations, the present inventors have found that when a powder for capacitor, comprising as the main component an earth-acid metal containing a very slight amount of phosphorus is used, surprisingly, a capacitance appearance ratio which cannot be heretofore reached can be achieved and also that a capacitor using the powder has a good moisture resistance value. The present invention has been accomplished based on these findings. The main component is a component contained in a largest mount and a component contained in a proportion of more than 50% is the main component.
It is conventionally known that the sintering property of a sintered body can be improved by mixing phosphorus to the powder for capacitor and thereby the specific surface area of the sintered body can be increased. For example, U.S. Pat. No. 4,084,965 discloses a technique where from 5 to 600 ppm of phosphorus is added and thereby the CV value (a product of the capacitance in an electrolytic solution and the electrochemical forming voltage at the formation of a dielectric film; a physical value proportional to the specific surface area) is elevated. However, in the present invention, by adding phosphorus in a concentration by far smaller than the concentration described in the above-described publication, the capacitance after the impregnation of another part electrode material can be greatly elevated while not increasing the specific surface area of the sintered body. If phosphorus is added in a high concentration as conventionally known, the CV value increases but the capacitance after the impregnation of another part electrode material cannot be elevated to the same degree as the increase ratio of CV value. In the present invention, only the capacitance appearance ratio is elevated but this duly implies that by the addition of a slight amount of phosphorus, the contact state between the another part electrode material and the pore inside the sintered body is improved. Addition of phosphorus in a large amount seems to rather disturb the impregnation of the another part electrode material. Furthermore, although the strength of the sintered body decreases as the specific surface area increases, such a thing cannot occur in the present invention.
That is, the present invention relates to a powder for capacitor, a sintered body using the powder and a capacitor using the sintered body, which are described below.
(1) A powder for capacitor, comprising as the main component an earth-acid metal containing from 3 mass ppb to 1 mass ppm of phosphorus.
(2) The powder for capacitor as described in (1) above, wherein the earth-acid metal is niobium.
(3) The powder for capacitor as described in (1) or (2) above, wherein the average particle size is from 0.2 to 5 &mgr;m.
(4) The powder for capacitor as described in any one of (1) to (3) above, wherein the specific surface area of the powder is from 0.5 to 15 m
2
/g.
(5) The powder for capacitor as described in any one of (1) to (4) above, wherein a part of the earth-acid metal is nitrided.
(6) A powder for capacitor, having an average particle size of 10 to 300&mgr;m, which is obtained by granulating the powder for capacitor described in any one of (1) to (5) above.
(7) A sintered body using the powder for capacitor described in any one of (1) to (6) above.
(8) The sintered body as described in (7) above, wherein the specific surface area is from 0.2 to 7 m
2
/g.
(9) A capacitor comprising the sintered body described in (7) or (8) above as one part electrode, a dielectric material formed thereon, and another part electrode.
(10) The capacitor as described in (9) above, wherein the dielectric material comprises niobium oxide or tantalum oxide as the main component.
(11) The capacitor as described in (10) above, wherein niobium oxide or tantalum oxide is formed by electrolytic oxidation.
(12) The capacitor as described in any one of (9) to (11) above, wherein the another part electrode is composed of an organic semiconductor and the organic semiconductor is at least one organic semiconductor selected from the group consisting of an organic semiconductor comprising a benzopyrroline tetramer and chloranile, an organic semiconductor mainly comprising tetrathiotetracene, an organic semiconductor mainly comprising tetracyanoquino-dimethane, and an organic semiconductor mainly comprising an electrically conducting polymer obtained by doping a dopant into a polymer containing two or more repeating units represented by the following formula (1) or (2):
(wherein R
1
to R
4
, which may be the same or different, each represents hydrogen, an alkyl group having from 1 to 6 carbon atoms or an alkoxy group having from 1 to 6 carbon atoms, X represents an oxygen atom, a sulfur atom or a nitrogen atom, R
5
is present only when X is a nitrogen atom, and represents hydrogen or an alkyl group having from 1 to 6 carbon atoms, and each of the pairs R
1
and R
2
, and R
3
and R
4
may combine with each other to form a ring).
(13) The capacitor as described in (12) above, wherein the organic semiconductor is at least one member selected from the group consisting of polypyrrole, polythiophene and substitution derivatives thereof.
(14) The capacitor as described in (12) above, wherein the electrically conducting polymer is an electrically conducting polymer containing a repeating unit represented by the following formula (3): (3)
(wherein R
6
and R
7
each independently represents a hydrogen atom, a linear or branched, saturated or unsaturated alkyl group having from 1 to 6 carbon atoms, or a substituent for forming at least one 5-, 6- or 7-membered saturated hydrocarbon ring structure containing two oxygen elements when the alkyl groups
Kozono Shuji
Naito Kazumi
Dinkins Anthony
Showa Denko Kabushiki Kaisha
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