U.S. patent application number 09/863413 was filed with the patent office on 2002-01-10 for solid electrolytic capacitor and method for producing the same.
This patent application is currently assigned to SHOWA DENKO K.K.. Invention is credited to Furuta, Yuji, Sakai, Atsushi, Yamazaki, Katsuhiko.
Application Number | 20020003689 09/863413 |
Document ID | / |
Family ID | 26592509 |
Filed Date | 2002-01-10 |
United States Patent
Application |
20020003689 |
Kind Code |
A1 |
Sakai, Atsushi ; et
al. |
January 10, 2002 |
Solid electrolytic capacitor and method for producing the same
Abstract
An object of the present invention is to provide a solid
electrolytic capacitor with excellent electrostatic capacitance and
reduced dispersion of capabilities by treating the surface of a
chemically formed aluminum film to form a dielectric film which is
in contact an electrically conducting substance provided thereon
with sufficiently high adhesion. Another object of the present
invention is to provide a method for producing the solid
electrolytic capacitor, which includes providing an organic
electrically conducting polymer as a solid electrolyte on a
chemically formed aluminum substrate having thereon an aluminum
oxide dielectric film, where a chemically formed aluminum
substrate, which was cut into a predetermined shape, is treated
with an aqueous acid solution to dissolve a part of the dielectric
film on the substrate surface. The present invention also provides
an aluminum solid electrolytic capacitor obtained by the method,
and a chemically formed aluminum substrate for aluminum solid
electrolytic capacitors.
Inventors: |
Sakai, Atsushi; (Nagano,
JP) ; Furuta, Yuji; (Nagano, JP) ; Yamazaki,
Katsuhiko; (Nagano, JP) |
Correspondence
Address: |
SUGHRUE, MION, ZINN, MACPEAK & SEAS, PLLC
2100 Pennsylvania Avenue, N.W.
Washington
DC
20037-3213
US
|
Assignee: |
SHOWA DENKO K.K.
|
Family ID: |
26592509 |
Appl. No.: |
09/863413 |
Filed: |
May 24, 2001 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
09863413 |
May 24, 2001 |
|
|
|
60244878 |
Nov 2, 2000 |
|
|
|
Current U.S.
Class: |
361/525 ; 216/6;
428/472.2 |
Current CPC
Class: |
H01G 11/48 20130101;
Y02E 60/13 20130101; H01G 9/15 20130101; H01G 9/0029 20130101; H01G
11/56 20130101 |
Class at
Publication: |
361/525 ; 216/6;
428/472.2 |
International
Class: |
H01G 009/15; H01G
004/08; H01G 004/10 |
Foreign Application Data
Date |
Code |
Application Number |
May 24, 2000 |
JP |
P2000-153559 |
Claims
What is claimed is:
1. A method for producing an aluminum solid electrolytic capacitor,
comprising cutting a chemically formed aluminum substrate having
thereon an aluminum oxide dielectric film into a predetermined
shape, treating the chemically formed aluminum substrate with an
aqueous acid solution to dissolve a part of the dielectric film on
the substrate surface, and providing an organic electrically
conducting polymer as a solid electrolyte on the chemically formed
aluminum substrate.
2. A method for producing an aluminum solid electrolytic capacitor,
comprising cutting a chemically formed aluminum substrate having
thereon an aluminum oxide dielectric film into a predetermined
shape, treating the chemically formed aluminum substrate with an
aqueous acid solution to dissolve a part of the dielectric film on
the substrate surface and burrs generated during cutting, and
providing an organic electrically conducting polymer as a solid
electrolyte on a chemically formed aluminum substrate.
3. The method for producing an aluminum solid electrolytic
capacitor as claimed in claim 1 or 2, wherein the aqueous acid
solution comprises an acid selected from the group consisting of
sulfuric acid, oxalic acid, chromic acid and phosphoric acid.
4. The method for producing an aluminum solid electrolytic
capacitor as claimed in claim 3, wherein the aqueous acid solution
is an aqueous oxalic acid solution.
5. The method for producing an aluminum solid electrolytic
capacitor as claimed in claim 4, wherein a concentration of the
aqueous oxalic acid solution is from about 0.1 to about 15% by
mass.
6. The method for producing an aluminum solid electrolytic
capacitor as claimed in claim 1 or 2, wherein the treatment with an
aqueous acid solution is a dipping treatment of the chemically
formed aluminum substrate.
7. The method for producing an aluminum solid electrolytic
capacitor as claimed in claim 6, wherein the aqueous acid solution
is an aqueous oxalic acid solution having a concentration of about
0.1 to about 15% by mass, a dipping time is from about 20 seconds
to about 10 minutes, and a treatment temperature is from about 15
to about 40.degree. C.
8. The method for producing an aluminum solid electrolytic
capacitor as claimed in claim 1 or 2, further comprising chemically
re-forming the aluminum cut surface after the treatment with an
aqueous acid solution.
9. An aluminum solid electrolytic capacitor produced by the method
as claimed in claim 1 or 2.
10. A chemically formed aluminum substrate for an aluminum solid
electrolytic capacitor, comprising a chemically formed aluminum
substrate having thereon a dielectric film formed by a treatment
with an aqueous acid solution, wherein the dielectric film having
an average pore radius of 1,000 .ANG. or more and a pore volume of
1.4 cm.sup.3/g or less.
11. The chemically formed aluminum substrate for an aluminum solid
electrolytic capacitor as claimed in claim 10, wherein the aqueous
acid solution comprises an acid selected from the group consisting
of sulfuric acid, oxalic acid, chromic acid and phosphoric
acid.
12. The chemically formed aluminum substrate for an aluminum solid
electrolytic capacitor as claimed in claim 10, wherein the aqueous
acid solution is an aqueous oxalic acid solution.
13. The chemically formed aluminum substrate for an aluminum solid
electrolytic capacitor as claimed in claim 10, wherein the
concentration of the aqueous oxalic acid solution is from about 0.1
to about 15% by mass.
14. The chemically formed aluminum substrate for an aluminum solid
electrolytic capacitor as claimed in claim 10, wherein the
treatment with an aqueous acid solution is a dipping treatment of
the chemically formed aluminum substrate.
15. The chemically formed aluminum substrate for an aluminum solid
electrolytic capacitor as claimed in claim 10, wherein the aqueous
acid solution is an aqueous oxalic acid solution having a
concentration of about 0.1 to about 15% by mass, a dipping time is
from about 20 seconds to about 10 minutes, and a treatment
temperature is from about 15 to about 40.degree. C.
16. An aluminum solid electrolytic capacitor using the chemically
formed aluminum substrate as claimed in any one of claims 10 to
15.
17. The aluminum solid electrolytic capacitor as claimed in claim
16, wherein a solid electrolyte comprises an organic electrically
conducting polymer, wherein a monomer for forming said electrically
conducting polymer is a compound containing a 5-membered
heterocyclic ring.
18. The aluminum solid electrolytic capacitor as claimed in claim
17, wherein the monomer is a compound having a thiophene
skeleton.
19. The aluminum solid electrolytic capacitor as claimed in claim
17, wherein the monomer is a compound selected from the group
consisting of 3-ethylthiophene, 3-hexylthiophene,
3,4-dimethylthiophene, 3,4-diethylthiophene,
3,4-methylenedioxythiophene, 3,4-ethylenedioxythiophene,
1,3-dihydroisothianaphthene and 3,4-ethylenedioxyfuran.
Description
CROSS REFERENCE TO RELATED APPLICATIONS
[0001] This application is an application filed under 35 U.S.C.
.sctn.111(a) claiming benefit pursuant to 35 U.S.C. .sctn.119(e)(1)
of the filing date of Provisional Application 60/244,878 filed Nov.
2, 2000 pursuant to 35 U.S.C. .sctn.111(b).
FIELD OF THE INVENTION
[0002] The present invention relates to an aluminum solid
electrolytic capacitor using an organic electrically conducting
polymer as the solid electrolyte, and a method for producing the
capacitor. More specifically, the present invention relates to an
aluminum solid electrolytic capacitor, in which the pore
distribution (e.g., pore volume, average pore size) of the
dielectric film is adjusted by removing burrs of the chemically
formed aluminum substrate cut into a predetermined shape and
dissolving a part of the aluminum oxide dielectric film on the
substrate surface. As a result, the organic electrically conducting
polymer provided thereon is improved in adhesive property. The
present invention also relates to a method for producing the
capacitor and a chemically formed aluminum substrate for aluminum
solid electrolytic capacitors.
BACKGROUND OF THE INVENTION
[0003] A solid electrolytic capacitor using an electrically
conducting polymer has a fundamental structure so that a
high-density and uniform oxide dielectric film is formed on the
surface of a valve-acting metal, such as aluminum, tantalum or
titanium, previously subjected to an etching treatment to roughen
the surface, an electrically conducting polymer as a solid
electrolyte is formed on the oxide dielectric film, an anode lead
wire is connected to the anode terminal (metal surface area having
no solid electrolyte) of the valve-acting metal, and a cathode lead
wire is connected to the electrically conducting layer containing
an electrically conducting polymer, and the entire structure is
molded with an insulting resin such as epoxy resin.
[0004] Among the valve-acting metals, aluminum is advantageous
because the surface area can be easily expanded by an etching
treatment, and the oxide film formed on the surface by an
anodization treatment (chemical forming treatment) using the
aluminum as the anode can be used as a dielectric film. Therefore,
a capacitor having a smaller size and a larger capacitance can be
produced at a lower cost compared with other capacitors. Because of
these reasons, the aluminum solid electrolytic capacitor is being
widely used.
[0005] The etching treatment of aluminum is generally performed by
an alternating current etching in an electrolytic solution
containing chloride ion or the like. By this etching treatment, a
large number of pores are formed on the surface and the surface
area is expanded. The radius of a pore formed varies depending on
the current applied and the treatment time, but is approximately
from 0.05 to 1 .mu.m.
[0006] Subsequently, the surface with pores is subjected to an
anodization treatment (chemical forming treatment). By this
chemical forming treatment, a high-density and uniform anodic oxide
film (dielectric film) having a thickness of approximately from
0.005 to 0.1 .mu.m is formed.
[0007] The thus-obtained chemically formed aluminum substrate is
cut into a predetermined size for a solid electrolytic capacitor.
At this time, a protruding portion (burr) remains on the edge of
the cut surface but the exposed aluminum (ground metal) portion is
subjected to chemical re-forming to form an anodic oxide film
(dielectric film) on the cut surface part.
[0008] An electrostatic capacitance of a capacitor device is
determined by the thickness of the dielectric film, the dielectric
constant of the dielectric film, and the area of the dielectric
film covered by a solid electrolyte (electrically conducting
substance). However, the electrostatic capacitance of conventional
aluminum solid electrolytic capacitors is as small as about 80% of
the theoretical value of an electrostatic capacitance (C) of a
chemically formed aluminum foil (C=.epsilon.A/t, wherein .epsilon.
is a dielectric constant of the dielectric aluminum oxide, A is a
surface area of the dielectric layer, and t is a thickness of the
dielectric layer). Moreover, the dispersion in the electrostatic
capacitance of individual products is very large. These are
considered to be attributable to insufficient results in the
thickness and dielectric constant of the dielectric film and in the
covering area and adhesion of the solid electrolyte (electrically
conducting substance) to the dielectric film when a conventional
chemical forming method is used.
[0009] There is another problem in that the dielectric film in the
burr portion generated during cutting or in the peak portion of the
cut surface generates heat due to the current concentrated during
loading of a voltage and ruptures. As a result, the solid
electrolyte deteriorates in capability (e.g., voltage resistance,
heat resistance).
[0010] Accordingly, an object of the present invention is to
provide a solid electrolytic capacitor improved in electrostatic
capacitance and reduced in dispersion of capability by treating the
surface of a chemically formed aluminum film so that a dielectric
film with which the electrically conducting substance provided
thereon can be contacted with good adhesion over a sufficiently
large contact area. Another object of the present invention
includes providing a method for producing this solid electrolytic
capacitor.
[0011] Another object of the present invention is to provide a
solid electrolytic capacitor which is free from reduction in the
properties attributable to heat generation resulting from the
concentration of current by removing burrs or peak portions on the
cut surface (cut end) of the aluminum substrate. Another object of
the present invention includes providing a method for producing
this solid electrolytic capacitor.
[0012] As a result of extensive investigations to solve the
above-described problems, the present inventors discovered that
when a chemically formed aluminum substrate having an aluminum
oxide dielectric film is treated with an aqueous acid solution to
dissolve a part of the dielectric film, surprisingly, the adhesion
between the solid electrolyte (electrically conducting polymer) and
the substrate is enhanced. As a result, a capacitor produced has
increased electrostatic capacitance and reduced dispersion in the
electrostatic capacitance of individual capacitors. Furthermore, it
has been verified that the burrs on the cut surface and the peak
portions of the cut end are dissolved and the deterioration of
properties due to heat generation resulting from the concentration
of current is mitigated when the above-described treatment with an
aqueous acid solution is used. Based on this knowledge, the present
invention has been accomplished.
SUMMARY OF THE INVENTION
[0013] The present invention provides an aluminum solid
electrolytic capacitor, a method for producing the capacitor and a
chemically formed aluminum foil for aluminum solid electrolytic
capacitors, described below.
[0014] (1) A method for producing an aluminum solid electrolytic
capacitor, comprising cutting a chemically formed aluminum
substrate having thereon an aluminum oxide dielectric film into a
predetermined shape, treating the chemically formed aluminum
substrate with an aqueous acid solution to dissolve a part of the
dielectric film on the substrate surface, and providing an organic
electrically conducting polymer as a solid electrolyte on a
chemically formed aluminum substrate.
[0015] (2) A method for producing an aluminum solid electrolytic
capacitor, cutting a chemically formed aluminum substrate having
thereon an aluminum oxide dielectric film into a predetermined
shape, treating the chemically formed aluminum substrate with an
aqueous acid solution to dissolve a part of the dielectric film on
the substrate surface and burrs generated during cutting, and
providing an organic electrically conducting polymer as a solid
electrolyte on a chemically formed aluminum substrate.
[0016] (3) The method for producing an aluminum solid electrolytic
capacitor as described in 1 or 2 above, wherein the aqueous acid
solution comprises an acid selected from sulfuric acid, oxalic
acid, chromic acid and phosphoric acid.
[0017] (4) The method for producing an aluminum solid electrolytic
capacitor as described in 3 above, wherein the aqueous acid
solution is an aqueous oxalic acid solution.
[0018] (5) The method for producing an aluminum solid electrolytic
capacitor as described in 4 above, wherein a concentration of the
aqueous oxalic acid solution is from about 0.1 to 15% by mass.
[0019] (6) The method for producing an aluminum solid electrolytic
capacitor as described in any one of 1 to 5 above, wherein the
treatment with an aqueous acid solution is a dipping treatment of
the chemically formed aluminum substrate.
[0020] (7) The method for producing an aluminum solid electrolytic
capacitor as described in 6 above, wherein the aqueous acid
solution is an aqueous oxalic acid solution having a concentration
of about 0.1 to 15% by mass, a dipping time is from 20 seconds to
10 minutes, and a treatment temperature is from about 15 to
40.degree. C.
[0021] (8) The method for producing an aluminum solid electrolytic
capacitor as described in any one of 1 to 7 above, further
comprising chemically re-forming the aluminum cut surface after the
treatment with an aqueous acid solution.
[0022] (9) An aluminum solid electrolytic capacitor produced by the
method described in any one of 1 to 8 above.
[0023] (10) A chemically formed aluminum substrate for an aluminum
solid electrolytic capacitor, comprising a chemically formed
aluminum substrate having thereon a dielectric film formed by a
treatment with an aqueous acid solution, and the dielectric film
having an average pore radius of 1,000 .ANG. or more and a pore
volume of 1.4 cm.sup.3/g or less.
[0024] (11) An aluminum solid electrolytic capacitor using the
chemically formed aluminum substrate described in 10 above.
BRIEF DESCRIPTION OF THE DRAWINGS
[0025] FIG. 1 is a scanning electron microscope picture
(.times.30,000) showing a cross section of a dielectric film after
an acid treatment.
[0026] FIG. 2 is a scanning electron microscope picture
(.times.30,000) showing a cross section of a dielectric film before
an acid treatment.
[0027] FIG. 3A is a pore distribution curve showing the pore
distribution on the dielectric film surface before an acid
treatment, and FIG. 3B is a pore distribution curve showing the
pore distribution on the dielectric film surface after an acid
treatment.
DESCRIPTION OF THE PRESENT INVENTION
[0028] The present invention is described in detail below.
[0029] In manufacturing an aluminum solid electrolytic capacitor, a
chemically formed aluminum foil, which is available on the market,
is cut into a desired predetermined shape for the solid
electrolytic capacitor after the formation of an aluminum oxide
dielectric film. The ground aluminum portion on the cut surface is
subjected to chemical re-forming and then, an electrically
conducting polymer layer is formed. However, the solid electrolytic
capacitors manufactured by such method have a dispersion in
electrostatic capacitance as described above.
[0030] The present inventors believed that the dispersion in the
capability of solid electrolytic capacitors is probably
attributable to the surface properties of the chemically formed
aluminum substrate. Therefore, the average pore size and the pore
volume (cm.sup.3/g) on the surface of a chemically formed aluminum
substrate (dielectric film) available on the market and on the
surface of a chemically formed aluminum foil where a cut end
portion is subjected to a chemical re-forming treatment in a
conventional manner were measured by mercury intrusion porosimetry
using a porosimeter 2000WS manufactured by Fisons. As a result
thereof, the dielectric film of the chemically formed aluminum foil
available on the market had an average pore radius of approximately
540.+-.50 .ANG. and a pore volume of 1.49.+-.0.05 cm.sup.3/g. The
chemically formed aluminum substrate which was subjected to
chemical re-forming in a conventional manner, had an average pore
radius of 650 to 750 .ANG. and a pore volume of 0.4 to 0.6
cm.sup.3/g.
[0031] The present inventors also discovered that, when a
chemically formed aluminum substrate available on the market is cut
into a predetermined shape and then treated with an aqueous acid
solution to dissolve a part of the dielectric film, surprisingly,
the electrostatic capacity of the capacitor increases and the
dispersion in the electrostatic capacitance of individual
capacitors decreases.
[0032] At present, as a result of this acid dissolving treatment,
the pore volume of the dielectric film on the chemically formed
aluminum substrate decreases and the average pore radius increases.
More specifically, it is confirmed that with a pore volume of 1.4
cm.sup.3/g (percentage decrease in the pore volume: 94%) or less,
preferably 0.4 cm.sup.3/g or less, and an average pore radius of
600 .ANG. or more, preferably 1,000 .ANG. or more, excellent
properties can be obtained.
[0033] It is not clearly known why the properties of a solid
electrolytic capacitor are improved (namely, the electrostatic
capacitance increases and the dispersion decreases) by the change
in the surface properties, but the reason therefor is considered to
be because the contact area of the dielectric film with the
electrically conducting polymer is rendered uniform, thereby
substantially increasing the effective contact area with the
electrically conducting polymer.
[0034] Also, it is confirmed that burrs on the cut end generated
during cutting are dissolved by treatment with an acid solution,
and the peak portions of the cut end are changed into a rounded
shape. As a result, the deterioration in the properties due to
generation of heat caused by the concentration of current is
mitigated.
[0035] According to the method of the present invention, a part of
the (aluminum oxide) dielectric film on a chemically formed
aluminum substrate available on the market is dissolved with an
acid solution, thereby reducing the dispersion in the electrostatic
capacitance.
[0036] In the present invention, the acid used for dissolving a
part of the dielectric layer and burrs generated during cutting is
not limited, provided it has properties of dissolving aluminum and
aluminum oxide. Either an inorganic acid, such as sulfuric acid,
chromic acid or phosphoric acid, or an organic acid, such as oxalic
acid may be used. Among those acids, in view of workability, oxalic
acid and sulfuric acid are preferred, and oxalic acid is more
preferred. The concentration of the acid is selected from a range
that gives an appropriate dissolution rate of the dielectric
material in view of workability. The concentration varies depending
on the kind of acid, but when oxalic acid is used, the
concentration is preferably from about 0.1 to 15% by mass, more
preferably from about 1 to 10% by mass, and when sulfuric acid is
used, the concentration is preferably from about 5 to 25% by mass,
more preferably from about 10 to 15% by mass.
[0037] The method of contacting a chemically formed aluminum
substrate with an aqueous acid solution is not particularly limited
and examples thereof include a dipping method, a coating method and
an atomization method. Among these, a dipping method is
preferred.
[0038] In the dipping method, the dipping (contact) time varies
depending on the kind and concentration of acid and is not
specified. However, when oxalic acid, which is a preferred acid, is
used, the dipping time is approximately from 20 seconds to 10
minutes with an oxalic acid concentration of about 1 to 10% by
mass.
[0039] As the temperature of the aqueous acid solution during
contacting is higher, the dissolution rate of the film increases,
and therefore, a temperature near room temperature (15 to
40.degree. C.) is usually selected.
[0040] By treating the chemically formed aluminum foil with an acid
under the above-described conditions, a part of the dielectric
layer on the surface thereof dissolves, the pore volume decreases
and the average pore size increases. Also, when photographed
through an electron microscope that the peak portions of a burr on
the cut end are dissolved.
[0041] FIG. 1 is a scanning electron microscope picture
(.times.30,000) showing the surface of a chemically formed aluminum
foil after the treatment according to the present invention. FIG. 2
is a scanning electron microscope picture (.times.30,000) showing
the surface of an untreated chemically formed aluminum foil
surface.
[0042] As shown in FIGS. 1 and 2, the shape of the surface of a
chemically formed aluminum foil is not greatly changed by the acid
treatment.
[0043] The pore distribution on the surface of a chemically formed
film of an untreated chemically formed aluminum foil, the average
pore size is from 490 to 590 .ANG. and the pore volume is from 1.44
to 1.54 cm.sup.3/g, whereas after the acid treatment, the average
pore size is from 600 to 2,000 .ANG. and the pore volume is from
0.1 to 1.4 cm.sup.3/g.
[0044] FIGS. 3A and 3B are pore distribution curves showing a
dispersion in pore distribution before and after the acid treatment
(Comparative Example 1 and Example 3 described later). FIGS. 3A and
3B are graphs showing the change in the pore volume (V) with
respect to the change in the pore radius (R), where the ordinate in
the right shows the variation (dV/dLogR) and the ordinate in the
left side shows the cumulative pore volume (V). After the
treatment, the dispersion in the pore distribution is small and the
average pore radius is large (Example 3, FIG. 3B) compared with
those before the treatment (Comparative Example 1, FIG. 3A).
[0045] In the chemical re-forming treatment, conditions may be
selected so that only the exposed ground metal portion can be
selectively formed without damaging the dielectric film formed on
the effective surface of the chemically formed foil. Specifically,
using an electrolytic solution containing an acid, such as adipic
acid, boric acid or phosphoric acid, a constant-current chemical
forming is performed using the core part of the chemically formed
foil as the anode, under conditions so that the concentration of
electrolytic solution is from 0.95 to 20% by mass, the temperature
is from 0 to 90.degree. C., the current density is from 0.1 to
2,000 mA/cm.sup.3 and the current passing time is within 60
minutes.
[0046] The thickness of the valve acting metal foil varies
depending on the use end. However, for example, a foil having a
thickness of about 40 to 150 .mu.m is generally used. Furthermore,
the size and the shape of the valve acting metal foil vary
depending on the use. However, as a plate-like device unit, the
metal foil preferably has a rectangular form with a width of about
1 to 50 mm and a length of about 1 to 50 mm, more preferably a
width of about 2 to 15 mm and a length of about 2 to 25 mm.
[0047] The electrically conducting polymer for forming the solid
electrolyte used in the production method of a solid electrolytic
capacitor of the present invention is a polymer having a .pi.
electron-conjugate structure and the polymerization degree thereof
is preferably from 2 to 2,000, more preferably from 5 to 1,000.
Specific examples of the polymer include electrically conducting
polymers containing, as a repeating unit, a structure shown by a
compound having a thiophene skeleton, a compound having a
polycyclic sulfide skeleton, a compound having a pyrrole skeleton,
a compound having a furan skeleton or a compound having an aniline
skeleton.
[0048] Among the compounds (monomers) used as a starting material
of the electrically conducting polymer, specific examples of the
compound having a thiophene skeleton include 3-methylthiophene,
3-ethylthiophene, 3-propylthiophene, 3-butylthiophene,
3-pentylthiophene, 3-hexylthiophene, 3-heptylthiophene,
3-octylthiophene, 3-nonylthiophene, 3-decylthiophene,
3-fluorothiophene, 3-chlorothiophene, 3-bromothiophene,
3-cyanothiophene, 3,4-dimethylthiophene, 3,4-diethylthiophene,
3,4-butylenethiophene, 3,4-methylenedioxythiophene and
3,4-ethylenedioxythiophene. These compounds may be a compound
generally available on the market or may be prepared by a known
method (a method described, for example, in Synthetic Metals, Vol.
15, page 169 (1986)), however, the present invention is by no means
limited thereto. Specific examples of the compound having a
polycyclic sulfide skeleton include compounds having a
1,3-dihydro-polycyclic sulfide (also called
1,3-dihydrobenzo-[c]thiophene- ) skeleton and compounds having a
1,3-dihydronaphtho[2,3-c]thiophene skeleton. Furthermore, compounds
having a 1,3-dihydroanthra[2,3-c]thiophe- ne skeleton and compounds
having a 1,3-dihydronaphthaceno[2,3-c]thiophene skeleton may be
used. These compounds may be prepared by a known method, for
example, the method described in JP-A-8-3156. In addition,
1,3-dihydrophenanthra[2,3-c]thiophene derivatives as a compound
having a 1,3-dihydronaphtho[1,2-c]thiophene skeleton, and
1,3-dihydrobenzo[a]-anth- raceno[7,8-c]thiophene derivatives as a
compound having a 1,3-dihydrotriphenylo[2,3-c]thiophene skeleton
may also be used.
[0049] A compound in which the condensed ring arbitrarily contains
nitrogen or N-oxide may also be used. Examples thereof include
1,3-dihydrothieno[3,4-b]quinoxaline,
1,3-dihydrothieno[3,4-b]quinoxaline-- 4-oxide and
1,3-dihydrothieno[3 ,4-b]quinoxaline-4,9-dioxide.
[0050] Examples of the compound having a furan skeleton include
derivatives such as 3-methylfuran, 3-ethylfuran, 3-propylfuran,
3-butylfuran, 3-pentylfuran, 3-hexylfuran, 3-heptylfuran,
3-octylfuran, 3-nonylfuran, 3-decylfuran, 3-fluorofuran,
3-chlorofuran, 3-bromofuran, 3-cyanofuran, 3,4-dimethylfuran,
3,4-diethylfuran, 3,4-butylenefuran, 3,4-methylenedioxyfuran and
3,4-ethylenedioxyfuran. These compounds may be a compound available
on the market or may be prepared by a known method. Examples of the
compound having an aniline skeleton include derivatives such as
2-methylaniline, 2-ethylaniline, 2-propylaniline, 2-butylaniline,
2-pentylaniline, 2-hexyl-aniline, 2-heptylaniline, 2-octylaniline,
2-nonylaniline, 2-decylaniline, 2-fluoroaniline, 2-chloroaniline,
2-bromoaniline, 2-cyanoaniline, 2,5-dimethylaniline,
2,5-diethylaniline, 2,3-butyleneaniline, 2,3-methylene-dioxyaniline
and 2,3-ethylenedioxyaniline. These compounds may be a commercially
available compound or may be prepared by a known method.
[0051] The solid electrolyte produced by the method of the present
invention has an electric conductivity of about 0.1 to 200 S/cm,
preferably from about 1 to 150 S/cm, more preferably from about 10
to 100 S/cm.
[0052] The conditions for polymerization of the compound selected
from the group consisting of the above-described compounds are not
particularly limited and polymerization is performed after
confirming the conditions by preliminarily performing a simple
test.
[0053] For example, a method of coating a
3,4-ethylenedioxythiophene monomer and an oxidizing agent, each
preferably in the solution form, separately one after the other or
simultaneously on the dielectric film to form a solid electrolyte
layer may be used (JP-A-2-15611 and JP-A-10-32145). A method of
alternately dipping the chemically formed substrate in a monomer
solution and in an oxidizing agent solution is particularly
preferred.
[0054] In general, a compound (dopant) having a doping ability is
used for the electrically conducting polymer. The dopant can be add
to either the monomer solution or the oxidizing agent solution. The
dopant is preferably an aryl sulfonate-based dopant and, for
example, a salt of benzenesulfonic acid, toluenesulfonic acid,
naphthalene-sulfonic acid or anthraquinonesulfonic acid may be
used.
[0055] On the solid electrolyte layer, an electrically conducting
layer is provided using electrically conducting paste or plating to
attain good electrical contact with the cathode lead terminal.
Thereafter, a cathode lead terminal is connected and then, the
capacitor is applied with a jacket using resin mold, resin case,
metal-made outer-jacket case, resin dipping or the like, thereby
manufacturing a solid electrolytic capacitor for various uses.
EXAMPLES
[0056] The present invention is described below by referring to the
Examples and Comparative Examples, however, the present invention
is not limited to the following Examples. Unless indicated
otherwise herein, all parts, percents, ratios and the like are by
weight.
Example 1
[0057] A chemically formed aluminum foil (100LJA19B13VF, trade
name, produced by JCC (NIPPON CHIKUDENKI KOGYO)) (withstand rated
voltage: 13 VF) having formed on the surface thereof a chemically
formed film having an average pore radius of 540 .ANG. and a pore
volume of 1.49 cm.sup.3/g, was cut into a width of 3 mm and a
length of 13 mm and divided into a cathode part and an anode part
by a masking member. The side undertaking the cathode part was
dipped in an aqueous 5 mass% oxalic acid solution for 30 seconds,
washed with water and dried. Thereafter, the pore distribution
(pore volume and average pore radius) of the chemically formed
aluminum substrate was measured by mercury intrusion porosimetry
using porosimeter 2000WS manufactured by Fisons. The results are
shown in Table 1.
[0058] Subsequently, using an aqueous 10 mass % ammonium adipate as
an electrolytic solution, the foil was chemically re-formed under
conditions so that the temperature was 55.degree. C., the voltage
was 13 V, the electric current density was 5 mA/cm.sup.2 and the
current passing time was 10 minutes to form a dielectric film on
the cut end part. As a result of observation through an electron
microscope, it was confirmed that burrs on the cut surface and peak
portions of the cut end were dissolved and removed to give a
rounded shape.
[0059] Thereafter, the cathode part was dipped in 1 mol/l of an
isopropyl alcohol solution of 3,4-ethylenedioxythiophene, left
standing for 2 minutes, dipped in a mixed aqueous solution of an
oxidizing agent (ammonium persulfate: 1.8 mol/l) and a dopant
(sodium anthraquinone-2-sulfonate: 0.06 mol/l), and left standing
at 45.degree. C. for 5 minutes. This operation was repeated 25
times, followed by washing with water, to form an electrically
conducting layer. Carbon paste and silver paste were stacked in
this order to form an electrically conducting layer on the
electrically conducting layer. Four sheets of the thus-obtained
devices were disposed on a lead frame, one on another through
silver paste in the cathode side, and by welding in the anode side.
Subsequently, the entire structure was molded with a molding resin
to fabricate a capacitor device. 2000 Units of the devices in total
were manufactured. Each device was aged at 8 V and 105.degree. C.
for 1 hour and then the electrostatic capacitance and the leakage
current characteristics were measured. The results are shown in
FIG. 2.
[0060] The leakage current characteristics were evaluated by the
leakage current (LC) calculated while setting the threshold value
to 0.03 CV by applying a rated voltage (6.3 V) to the capacitor
device and measuring the leakage current after 1 minute.
Example 2
[0061] A capacitor device was manufactured in the same manner as in
Example 1, except for changing the dipping time in oxalic acid to
60 seconds, and then measuring the electrostatic capacitance and
the leakage current characteristics. The measurement results of the
average pore radius and the pore volume of the chemically formed
film are shown in Table 1 and the measurement results of the
electrostatic capacitance and the leakage current characteristics
are shown in Table 2.
Example 3
[0062] A capacitor device was manufactured in the same manner as in
Example 1, except for changing the dipping time in oxalic acid to
120 seconds, and then measuring the electrostatic capacitance and
the leakage current characteristics. The relationship between the
variation (dV/dLogR) of the pore volume (V) and the cumulative pore
volume with respect to the change in the pore radius (R) of the
chemically formed film is shown in FIG. 3B, the measurement results
of the average pore radius and the pore volume of the chemically
formed film are shown in Table 1, and the measurement results of
the electrostatic capacitance and the leakage current
characteristics are shown in Table 2.
Example 4
[0063] A capacitor device was manufactured in the same manner as in
Example 1, except for changing the dipping time in oxalic acid to
180 seconds, and then measuring the electrostatic capacitance and
the leakage current characteristics. The measurement results of the
average pore radius and the pore volume of the chemically formed
film are shown in Table 1 and the measurement results of the
electrostatic capacitance and the leakage current characteristics
are shown in Table 2.
Example 5
[0064] A capacitor device was manufactured in the same manner as in
Example 1, except for changing the dipping time in oxalic acid to
300 seconds, and then measuring the electrostatic capacitance and
the leakage current characteristics. The measurement results of the
average pore radius and the pore volume of the chemically formed
film are shown in Table 1 and the measurement results of the
electrostatic capacitance and the leakage current characteristics
are shown in Table 2.
Example 6
[0065] A capacitor device was manufactured in the same manner as in
Example 1, except for changing the dipping time in oxalic acid to
10 seconds, and then measuring the electrostatic capacitance and
the leakage current characteristics. The measurement results of the
average pore radius and the pore volume of the chemically formed
film are shown in Table 1 and the measurement results of the
electrostatic capacitance and the leakage current characteristics
are shown in Table 2.
Comparative Example 1
[0066] A capacitor device was manufactured in the same manner as in
Example 1, except for not performing the dipping in oxalic acid,
and then measuring the electrostatic capacitance and the leakage
current characteristics. The relationship between the variation
(dV/dLogR) of the pore volume (V) and the cumulative pore volume
with respect to the change in the pore radius (R) of the chemically
formed film is shown in FIG. 3A, the measurement results of the
average pore radius and the pore volume of the chemically formed
film are shown in Table 1, and the measurement results of the
electrostatic capacitance and the leakage current characteristics
are shown in Table 2.
1 TABLE 1 Dipping Time in Pore Volume Average Pore Oxalic Acid
(cm.sup.3/g) Radius (.ANG.) Example 1 30 sec. 0.18 1840 Example 2
60 sec. 0.17 1800 Example 3 120 sec. 0.16 1520 Example 4 180 sec.
0.17 1640 Example 5 300 sec. 0.18 1810 Example 6 10 sec. 1.45 510
Comparative not dipped 1.49 540 Example 1
[0067]
2 TABLE 2 Electrostatic Deviation of Dipping Time Capacitance
Electrostatic LC* Yield in Oxalic Acid (.mu.F) Capacitance (%)
Example 1 30 sec. 51.3 0.9 94 Example 2 60 sec. 52.2 0.8 97 Example
3 120 sec. 51.3 0.8 96 Example 4 180 sec. 51.6 0.8 97 Example 5 300
sec. 51.8 0.9 94 Example 6 10 sec. 50.1 1.4 90 Comparative not
dipped 50.0 1.5 90 Example 1 *LC: leakage current
[0068] As seen from Tables 1 and 2, the chemically formed film
passed through dipping treatment in an oxalic acid for 30 seconds
or more exhibited increased electrostatic capacitance of the
capacitor despite the reduction in the pore volume and increase in
the average pore radius compared with those obtained through no
dipping treatment (Comparative Example 1) or a dipping treatment in
oxalic acid only for 10 seconds (Example 6). Also, the
electrostatic capacitance deviation (dispersion) and LC yield were
improved.
[0069] The chemically formed aluminum substrate of the present
invention, where the dielectric layer surface is treated with a
specific aqueous acid solution, is made uniform on the surface of
the chemically formed film and exhibits good adhesion to the
electrically conducting polymer (solid electrolyte), and the solid
aluminum electrolytic capacitor using the substrate is favored with
a large electrostatic capacitance and a small dispersion in the
electrostatic capacitance compared with those that were not
subjected to the acid treatment. Furthermore, burrs generated
during cutting and peak portions of the cut end are dissolved and
removed to give a rounded shape. As a result, the electric
characteristics such as leakage current characteristics are
improved.
[0070] While the invention has been described in detail and with
reference to specific embodiments thereof, it will be apparent to
one skilled in the art that various changes and modifications can
be made therein without departing from the spirit and scope
thereof.
* * * * *