U.S. patent application number 11/398605 was filed with the patent office on 2006-08-17 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 Yuji Furuta, Ryuji Monden, Hideki Ohata, Atsushi Sakai, Toru Sawaguchi, Katsuhiko Yamazaki.
Application Number | 20060179627 11/398605 |
Document ID | / |
Family ID | 27554221 |
Filed Date | 2006-08-17 |
United States Patent
Application |
20060179627 |
Kind Code |
A1 |
Sakai; Atsushi ; et
al. |
August 17, 2006 |
Solid electrolytic capacitor and method for producing the same
Abstract
A method for producing a solid electrolytic capacitor,
comprising coating a solution containing a monomer of an
electroconducting polymer and a solution containing an oxidizing
agent in repeating sequence on a valve-acting metal anode having
formed on the surface thereof an oxide dielectric film, and then
polymerizing wherein the electroconducting polymer is formed by
setting the humidity in the atmosphere of polymerization process to
from 10% to less than 60%.
Inventors: |
Sakai; Atsushi; (Nagano,
JP) ; Monden; Ryuji; (Nagano, JP) ; Sawaguchi;
Toru; (Nagano, JP) ; Yamazaki; Katsuhiko;
(Nagano, JP) ; Furuta; Yuji; (Nagano, JP) ;
Ohata; Hideki; (Chiba, JP) |
Correspondence
Address: |
SUGHRUE MION, PLLC
2100 PENNSYLVANIA AVENUE, N.W.
SUITE 800
WASHINGTON
DC
20037
US
|
Assignee: |
SHOWA DENKO K.K.
|
Family ID: |
27554221 |
Appl. No.: |
11/398605 |
Filed: |
April 6, 2006 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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10743874 |
Dec 24, 2003 |
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11398605 |
Apr 6, 2006 |
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10303728 |
Nov 26, 2002 |
6696138 |
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10743874 |
Dec 24, 2003 |
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09576264 |
May 24, 2000 |
6517892 |
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10303728 |
Nov 26, 2002 |
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60135845 |
May 24, 1999 |
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60157074 |
Oct 1, 1999 |
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60182191 |
Feb 14, 2000 |
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Current U.S.
Class: |
29/25.03 ;
427/79 |
Current CPC
Class: |
Y10T 428/31692 20150401;
Y02E 60/13 20130101; H01G 11/48 20130101; H01G 9/028 20130101; H01G
9/0036 20130101; H01G 9/042 20130101; H01G 9/025 20130101; H01G
11/56 20130101; Y10T 428/24917 20150115 |
Class at
Publication: |
029/025.03 ;
427/079 |
International
Class: |
H01G 9/00 20060101
H01G009/00; B05D 5/12 20060101 B05D005/12 |
Foreign Application Data
Date |
Code |
Application Number |
Sep 7, 1999 |
JP |
11-252371 |
Dec 27, 1999 |
JP |
11-370296 |
Claims
1. A method for producing a solid electrolytic capacitor,
comprising coating a solution containing a monomer of an
electroconducting polymer and a solution containing an oxidizing
agent in repeating sequence on a valve-acting metal anode having
formed on the surface thereof an oxide dielectric film, and then
polymerizing wherein the electroconducting polymer is formed by
setting the humidity in the atmosphere of polymerization process to
from 10% to less than 60%.
2. The method for producing a solid electrolytic capacitor as
claimed in claim 1, wherein said monomer is a monomer for a polymer
having electric conductivity, and is selected from a pyrrole, a
thiophene, or an aniline.
3. The method for producing a solid electrolytic capacitor as
claimed in claim 2, wherein said monomer is
3,4-ethylenedioxythiophene.
4. The method for producing a solid electrolytic capacitor as
claimed in claim 1, wherein said oxidizing agent is a metal salt or
ammonium salt of an oxidative inorganic acid.
5. The method for producing a solid electrolytic capacitor as
claimed in claim 4, wherein said metal salt or ammonium salt of an
oxidative inorganic acid is persulfate.
Description
CROSS REFERENCE TO RELATED APPLICATIONS
[0001] This is a divisional of application Ser. No. 10/743,874,
filed Dec. 24, 2003, which is a divisional of application No.
10/303,728, filed Nov. 26, 2002 (now U.S. Pat. No. 6,696,138),
which is a divisional of U.S. application Ser. No. 09/576,264 filed
May 24, 2000 (now U.S. Pat. No. 6,517,892), the disclosures of
which are incorporated by reference herein, which claims benefit
pursuant to 35 U.S.C. .sctn.119(e)(i) of the filing dates of
Provisional Application 60/135,845 filed May 24, 1999, Provisional
Application 60/157,074 filed Oct. 1, 1999 and Provisional
Application 60/182,191, filed Feb. 14, 2000 pursuant to 35 U.S.C.
.sctn. 111(b).
TECHNICAL FIELD
[0002] The present invention relates to a solid electrolytic
capacitor and a production method thereof. More specifically, the
present invention relates to a solution of an oxidizing agent (an
oxidizing agent solution) and a solution of a monomer (a monomer
solution) necessary for forming a solid electrolyte of the solid
electrolytic capacitor. The present invention further relates to a
solid electrolytic capacitor or a production method thereof,
comprising preferably a solid electrolyte formed of an
(electrically conducting) polymer composition obtained by
specifying the viscosity of the oxidizing agent solution or the
monomer solution.
[0003] The present invention even further relates to a solid
electrolytic capacitor and a production method thereof, preferably
comprising a solid electrolyte formed of an electroconducting
(electrically conducting) polymer composition obtained by
specifying the humidity in the polymerization of an oxidizing agent
solution and a monomer solution in the solid electrolyte.
[0004] The present invention even further relates to a solid
electrolytic capacitor, more specifically, a solid electrolytic
capacitor in which the solid electrolyte formed on the outer
surface of an anode body is an electrically conducting polymer
containing a lamellar structure, wherein the solid electrolyte
provided on the dielectric film formed on a valve acting metal
occupies from 10 to 95% of the space within a pore of the
electrode, so that the adhesive property between the solid
electrolyte and the dielectric layer formed on a metal oxide film
can be improved, high capacitance and low impedance can be
realized, the leakage current can be improved, and good moisture
resistance load characteristics and excellent heat resistance can
be achieved.
[0005] The present invention also relates to a solid electrolytic
capacitor, more specifically, a solid electrolytic capacitor in
which the solid electrolyte formed on the outer surface of an anode
body is an electrically conducting polymer containing a lamellar
structure, wherein the solid electrolyte provided on the dielectric
film formed on a valve acting metal covers 60% or more of the
dielectric film, so that the adhesive property between the solid
electrolyte and the dielectric layer formed on a metal oxide film
can be improved, high capacitance and low impedance can be
realized, and good moisture resistance load characteristics and
excellent heat resistance can be achieved.
DESCRIPTION OF RELATED ART
[0006] A solid electrolytic capacitor is a device where an oxide
dielectric film is formed on the surface of an anode substrate
comprising a metal foil subjected to etching treatment or the like,
a solid semiconductor layer (hereinafter referred to as a "solid
electrolytes") is formed as a counter electrode outside the
dielectric layer, and an electrically conducting layer such as an
electrically conducting paste is further formed thereon. The device
is actually used as a product after completely sealing the entire
device with epoxy resin or the like and leading out terminals from
respective electrodes.
[0007] In recent years, with the progress toward digitized
electrical equipment or personal computers capable of high speed
processing, demands are increasing for a compact capacitor having a
large capacitance or a capacitor showing low impedance in the high
frequency region. As the compact capacitor having a large
capacitance, electrolytic capacitors such as aluminum electrolytic
capacitor and tantalum electrolytic capacitor are known. The
aluminum electrolytic capacitor can be advantageously produced to
have a large capacitance at a low cost but has a problem in that
when an ion conducting liquid electrolyte is used as the
electrolyte, high impedance results in the high frequency region
and the capacitance decreases accompanying the evaporation of
electrolytic solution with the elapse of time, and in addition, the
temperature characteristics are bad. The tantalum electrolytic
capacitor has a problem in that a manganese oxide is generally used
as the electrolyte and since this manganese oxide is mainly
produced by the thermal decomposition of manganese nitrate, the
possibility of damage of the dielectric film at the thermal
decomposition cannot be eliminated, and moreover, due to relatively
high specific resistance of manganese oxide, the impedance is high
in the high frequency region.
[0008] For the solid electrolyte, it is already known to use, for
example, an inorganic semiconductor material such as manganese
dioxide and lead dioxide, a TCNQ complex salt, an intrinsic
electrically conducting polymer having an electric conductivity of
from 10.sup.-3 to 5.times.10.sup.3 S/cm (JP-A-1-169914 (the term
"JP-A" as used herein means an "unexamined published Japanese
patent application", corresponding to U.S. Pat. No. 4,803,596)) or
an electrically conducting polymer such as .pi.-conjugated
polyaniline (see, JP-A-61-239617), polypyrrole (see,
JP-A-61-240625), polythiophene derivative (see, JP-A-2-15611) or
polyisothianaphthene (see, JP-A-62-118511). These electrically
conducting polymers comprising a .pi.-conjugated structure are
mostly used as a composition containing a dopant. In recent years,
not only the addition of a dopant but also a combination use with,
for example, manganese dioxide (see, JP-B-6-101418 (the term "JP-B"
as used herein means an "examined Japanese patent publication")
(corresponding to U.S. Pat. No. 4,959,753)) or filler (see,
JP-A-9-320901) is employed.
[0009] In the case of using lead dioxide, precautions as to the
environment are additionally required.
[0010] Capacitors using a TCNQ complex salt solid for the solid
electrolyte have good heat fusion workability and excellent
electric conductivity but are considered to show poor reliability
in heat resistance (soldering heat resistance) at the solder
joining because the TCNQ complex salt itself has a problem in heat
resistance.
[0011] Capacitors using an electrically conducting polymer for the
solid electrolyte do not have a dielectric film rupture problem and
favored with a high impedance property but disadvantageously are
deficient in heat resistance, thermal shock resistance and
vibration resistance.
[0012] The electrically conducting polymer layer as a solid
electrolyte has a high electric conductivity and is formed to cover
throughout the inner surfaces of pores inside the cathode. At this
time, for satisfying the fundamental characteristics of the
capacitor, such as leakage current and heat resistance, the
structure formed inside the foil pore and the coverage must be
considered.
[0013] An example of the electrically conducting polymer formed
article of which the structure is controlled is a sponge-like
electrically conducting polymer formed article having a continuous
phase of an electrically conducting polymer disclosed in
JP-A-8-53566. This formed article is produced by a method of
cooling a solvent-containing polyaniline or derivative thereof in
any molding container to freeze the solvent and then removing the
solvent, or a method of cooling a solution containing aniline or an
aniline derivative as a monomer and a protonic acid/oxidizing agent
to freeze the solvent and polymerizing the solution at a
temperature lower than the melting point of the solvent.
[0014] In particular, as regarding the solid electrolyte provided
on a dielectric film formed on a valve acting metal which is a
constituent element of a capacitor, JP-A-7-122464 refers to a
structure of an electrically conducting polymer formed within a
microfine pore and discloses a tantalum solid electrolytic
capacitor comprising a sintered body of tantalum powder, an oxide
dielectric film formed on the surface of the sintered body and as a
solid electrolyte, an electrically conducting polymer compound
covering the oxide dielectric film. The tantalum solid electrolytic
capacitor disclosed in this patent publication is constructed such
that the electrically conducting polymer compound covers the oxide
dielectric film while leaving a cavity in a pore constituting the
surface of a sintered body and the electrically conducting polymer
compound occupies, in terms of the volume ratio, 70% or less of the
volume of the pore.
[0015] However, JP-A-8-53566 does not disclose an application
example of the sponge-like electrically conducting polymer formed
article as to a solid electrolytic capacitor. According to the
production method disclosed in this patent publication, the
sponge-like electrically conducting polymer formed article is
produced by cooling an electrically conducting polymer solution to
freeze the solvent, polymerizing the solution and then removing the
solvent by freeze-drying or melting it. This method has a problem
as to operativity and moreover, the oxide dielectric film is
readily damaged on freezing or melting. Therefore, it is difficult
to apply this technique to a solid electrolytic capacitor.
[0016] In the method disclosed in JP-A-7-122464 of forming a
structure such that an electrically conducting polymer compound
covers an oxide dielectric film while leaving a cavity in the pore,
the ratio of the cavity occupying the pore is controlled by the
repetition of oxidation polymerization. Therefore, if an
electrically conducting polymer layer is formed to have a large
thickness on the outer surface of an anode body after forming the
electrically conducting polymer while leaving a cavity in the pore,
the cavity already present in the microfine pore is clogged. Thus,
an electrically conducting polymer layer cannot be formed to have a
predetermined thickness on the outer surface while maintaining the
cavity in a microfine pore. Furthermore, the surface of the polymer
layer is not uneven, therefore, the adhesion to the electrically
conducting paste layer is poor. Moreover, the ratio of the
electrically conducting polymer compound as a solid electrolyte is
specified only by volume. This patent publication does not refer at
all to the covering area which relates to adhesion (which is an
important factor governing capacitor properties) between the
dielectric film and the electrically conducting polymer as a solid
electrolyte.
[0017] As such, in regard of a solid electrolytic capacitor where
an electrolytic conducting polymer to work out to a solid
electrolyte is formed on a dielectric film of a solid electrolytic
capacitor electrode foil comprising a valve acting metal having
formed thereon an oxide film, no technique has been heretofore
known on the optimal ratio in covering the dielectric film with the
polymer.
[0018] As the oxidizing agent for use in conventional techniques,
for example, chemical polymerization of 5-membered heterocyclic
compounds such as thiophene, iron(III) chloride,
Fe(ClO.sub.4).sub.3, organic acid iron(III) salt, inorganic acid
iron(III) salt, alkyl persulfate, ammonium persulfate (hereinafter
simply referred to as "APS"), hydrogen peroxide,
K.sub.2Cr.sub.2O.sub.7, etc., (see, JP-A-2-15611), cupric
compounds, silver compounds, etc., (see, JP-A-10-32145) are
known.
[0019] With respect to the method for forming a solid electrolyte
using an electrically conducting polymer, for example, a method of
fusing the electrically conducting polymer (solid electrolyte)
described above on a dielectric film on the surface of a
valve-acting metal having fine void structures to form an
electrically conducting polymer layer, and a method of depositing
the above-described electrically conducting polymer on a dielectric
film are known.
[0020] More specifically, in the case of using, for example, a
polymer of a 5-membered heterocyclic compound such as pyrrole or
thiophene for the solid electrolyte, a method of dipping an anode
foil having formed thereon a dielectric film in a lower alcohol
and/or water-based solution of a 5-membered heterocyclic compound
monomer and after removing it, again dipping the foil in an aqueous
solution having dissolved therein an oxidizing agent and an
electrolyte to cause chemical polymerization of the monomer,
thereby forming an electrically conducting polymer layer (see,
JP-A-5-175082), a method of coating simultaneously or sequentially
a 3,4-ethylenedioxythiophene monomer and an oxidizing agent each
preferably in the form of a solution on the oxide film of a metal
foil to form an electrically conducting polymer layer (see,
JP-A-2-15611 and JP-A-10-32145), and the like are known.
[0021] In order to solve the above-described problems, the
electrically conducting polymer such as polypyrrole is formed by
electrolytic or chemical polymerization and used for the solid
electrolyte of a solid electrolytic capacitor. However, the
electrically conducting polymer film obtained fails to have
sufficiently high uniformity or when the electrolytic capacitor is
fabricated, the soldering heat resistance, the impedance property
and the like are not satisfactory.
[0022] In recent years, a method of forming an electrically
conducting polymer, particularly polypyrrole, is disclosed, where a
methanol solution of dodecylbenzenesulfonic acid iron salt used as
an oxidizing agent for causing chemical oxidation polymerization is
specified to have a viscosity of less than 100 cp by taking account
of production efficiency (see, JP-A-4-94110). However, in this
technique, thiophene, aniline and derivatives thereof are not
described and the oxidizing agent used is a metal salt of an
organic acid. Therefore, the viscosity inevitably increases in the
process for obtaining a concentration effective in the
polymerization.
[0023] Also, a method for forming an electrically conducting
polymer, particularly polypyrrole, is disclosed, where the
viscosity of the oxidizing agent using an aromatic sulfonic acid
metal salt is from 100 to 500 cp and thereby the repetition
frequency of dipping in an oxidizing agent solution and in a
monomer solution is decreased (see, JP-A-10-14954). When the
viscosity of the oxidizing agent is reduced to 100 cp or less, the
polymerization efficiency of the monomer in turn decreases, as a
result, the amount of the electrically conducting polymer formed is
disadvantageously small.
[0024] Recently, also a method of forming an electroconducting
polymer by chemical oxidative polymerization is known, where an
isopropyl alcohol mixed solution containing
3,4-ethylenedioxythiophene as a monomer and ferric
p-toluenesulfonate as an oxidizing agent is allowed to stand in an
air at a temperature of from about 30.degree. C. to about
50.degree. C. and a humidity of about 60% or more for about 30
minutes (see, JP-A-10-64761).
[0025] However, because of the formation into a mixed solution of
monomer, oxidizing agent and isopropyl alcohol, the monomer and the
oxidizing agent are difficult to recover and the yield of products
decreases. Furthermore, the mixed solution readily evaporates due
to the isopropyl alcohol used. As a result, the polymerization
reaction is accelerated and the polymer thus formed at a high rate
is duly considered to have very coarse form. For obtaining a
polymer form capable of exhibiting sufficiently high electric
conductivity, the humidity condition of about 60% or more seems to
be necessary as water content in the atmosphere.
DISCLOSURE OF THE INVENTION
[0026] An object of the present invention is to provide a solid
electrolytic capacitor having excellent properties satisfying the
requirements with respect to compact size, reduction in weight,
high capacitance, high frequency property, tan .delta. (tangent of
loss angle), leakage current, heat resistance (reflow soldering
property), durability and the like.
[0027] In particular, an object of the present invention is to
provide a heat resistant solid electrolytic capacitor having
excellent low impedance property and high durability in a sparking
voltage test using an electrically conducting polymer obtained by
specifying the viscosity of an oxidizing agent solution and/or a
monomer solution.
[0028] First, increase in viscosity of an oxidizing agent solution
and/or a monomer solution causes a reduction in capacitance.
[0029] More specifically, an aluminum foil having formed thereon a
dielectric material obtained by etching the surface is dipped with
an oxidizing agent solution or a monomer solution and then dried,
as a result, a highly viscous oxidizing agent or monomer film is
formed on the surface of a porous body, and microfine pore openings
present on the surface of the porous body are clogged. The polymer
is formed on the surface by contact with a monomer or an oxidizing
agent, therefore, the polymer is not formed inside the pores, which
causes a reduction in capacitance.
[0030] Second, a decrease in the viscosity of an oxidizing agent
solution and/or a monomer solution causes reduction in the amount
of polymer adhered in a single polymerization step. Therefore, a
satisfactory solid electrolyte may not be formed unless the number
of polymerization steps is increased. That is, the decrease in
viscosity of an oxidizing agent solution and/or a monomer solution
abates capability of oxidizing the monomer, lessens the amount of
monomer, and reduces the amount of polymer formed.
[0031] Under these circumstances, it is necessary to obtain
capacitor properties with a small number of polymerization steps to
allow an oxidizing agent solution and/or a monomer solution to have
a viscosity of a certain level and to increase the capacitance.
[0032] An object of the present invention is to provide a method
for producing a solid electrolyte capable of achieving appearance
of capacitor properties with a reduced dipping frequency in an
oxidizing agent solution and in a monomer solution, where the
viscosity of an oxidizing agent solution and/or a monomer solution
used for forming a solid electrolyte of a solid electrolytic
capacitor from an electrically conducting polymer is specified and
thereby the monomer oxidation efficiency is increased.
[0033] In particular, a further object of the present invention is
to provide a solid electrolytic capacitor having small leakage
current and excellent tan .delta. by using an electroconducting
polymer obtained by specifying the humidity in the polymerization
process.
[0034] The mixed solution of a monomer and an oxidizing agent has a
problem in the humidity control and yield during the polymerization
process.
[0035] This is ascribable to the fact that in the case of
impregnating a dielectric film obtained by etching the surface of a
valve-acting metal with a mixed solution of a monomer and an
oxidizing agent and polymerizing it at a low humidity, a highly
viscous film is formed on the surface of the porous body due to the
presence of a monomer and an oxidizing agent dispersed together. As
a result, microfine pore inlets present on the surface of porous
body are blocked and the polymer cannot be satisfactorily formed in
the inside of pores, which causes reduction in the capacitance.
Accordingly, in this embodiment the humidity must be controlled to
about 60%,or more as a polymerization condition.
[0036] Furthermore, the polymerization proceeds on aging due to the
presence of a monomer and an oxidizing agent together, as a result,
the oligomer ratio increases, the mixed solution itself
polymerizes, the monomer and the oxidizing agent cannot be
recovered, and the yield decreases.
[0037] Even in the case of forming an electroconducting polymer
composition film by repeatedly coating a solution containing a
monomer of the polymer and a solution containing an oxidizing agent
one after another, the humidity in the polymerization process must
also be controlled so as to ensure high electric conductivity and
high reliability.
[0038] This is because if the humidity is excessively high in the
polymerization process, the polymerization slowly proceeds and the
yield of polymer decreases, whereas if the humidity is excessively
low, the adhered water and the monomer evaporate and the yield of
polymer decreases.
[0039] Accordingly, also an object of the present invention is to
provide a method for producing a solid electrolyte capable of
achieving appearance of good capacitor properties by specifying the
humidity range in the polymerization process for forming a solid
electrolyte of a solid electrolytic capacitor using an
electroconducting polymer, and thereby increasing the oxidation
efficiency of monomer.
[0040] In order to attain the above-described objects, extensive
investigations have been made on the oxidizing agent solution
and/or the monomer solution necessary for the electrically
conducting polymer composition forming the solid electrolyte. As a
result, it has been found that a compact and high-performance solid
electrolytic capacitor having low impedance and high durability in
a sparking voltage test can be obtained by a solid electrolytic
capacitor comprising counter electrodes with one party electrode
being assigned a microfine structure dielectric film comprising a
metal oxide on the surface of a valve-acting metal foil, and a
solid electrolyte comprising an electrically conducting polymer
composition formed on the dielectric film, where the electrically
conducting polymer forming the solid electrolyte is formed from an
oxidizing agent solution and/or a monomer solution having a
viscosity of less than 100 cp. An embodiment of the present
invention has been accomplished based on this finding.
[0041] It has also been found that a compact and high-performance
solid electrolytic capacitor having small leakage current and
excellent tan .delta. can be obtained when in a solid electrolytic
capacitor comprising counter electrodes with one part electrode
being assigned to a microfine structure dielectric film comprising
a metal oxide on the surface of a valve-acting metal foil, and a
solid electrolyte comprising an electroconducting polymer
composition formed on the dielectric film, the solid electrolyte is
an electroconducting polymer produced by the polymerization in a
humidity atmosphere of from 10% to less than 60%. Another
embodiment of the present invention has been accomplished based on
this finding.
[0042] As a result of additional investigations to solve the
above-described problems, the present inventors have first found
that in a solid electrolytic capacitor, more specifically, in a
solid electrolytic capacitor where the solid electrolyte on the
outer surface of an anode body is an electrically conducting
polymer containing a lamellar structure, when the solid electrolyte
is provided on the dielectric film formed on a valve acting metal,
to occupy from 10 to 95% of the space within a pore of the
electrode, the solid electrolytic capacitor obtained has improved
adhesion between the solid electrolyte and the dielectric film
formed on the valve acting metal and favored with excellent
stability of various fundamental properties such as capacitance and
dielectric loss (tan .delta.), and stability of reflow soldering
heat resistance and moisture resistance load characteristics.
[0043] Furthermore, as a result of extensive investigations to
solve the above-described problems, the present inventors have also
found that in a solid capacitor, more specifically, in a solid
electrolytic capacitor where the solid electrolyte is an
electrically conducting polymer containing a lamellar structure,
when the solid electrolyte is provided on a dielectric film formed
on a valve acting metal, to cover 60% or more of the dielectric
film, the solid electrolytic capacitor obtained is favored with
excellent stability of various fundamental properties such as
capacitance and dielectric loss (tan .delta.), and stability of
reflow soldering heat resistance and moisture resistance load
characteristics. A further embodiment of the present invention has
been accomplished based on these findings.
[0044] More specifically, objects of the present invention has been
attained by the following embodiments:
[0045] (1) a method for producing a solid electrolytic capacitor,
comprising covering a valve-acting metal anode foil having formed
on the surface thereof an oxide dielectric film with a repeating
sequence of a solution containing a monomer of an electrically
conducting polymer and a solution containing an oxidizing agent to
form an electrically conducting polymer composition film on the
dielectric film, wherein the solution containing a monomer of an
electrically conducting polymer and/or the solution containing an
oxidizing agent has a viscosity of less than 100 cp;
[0046] (2) a solid electrolytic capacitor comprising an oxide
dielectric film having thereon an electrically conducting polymer
composition layer, which is produced by the method described in (1)
above, wherein the electrically conducting polymer in the
composition contains as a repeating chemical structure a structural
unit represented by the following formula (1a): ##STR1## wherein
the substituents R.sup.1 and R.sup.2 each independently represents
a monovalent group selected from the group consisting of a hydrogen
atom, a linear or branched, saturated or unsaturated hydrocarbon
group having from 1 to 6 carbon atoms, a linear or branched,
saturated or unsaturated alkoxy group having from 1 to 6 carbon
atoms, a hydroxyl group, a halogen atom, a nitro group, a cyano
group, a trifluoromethyl group, a phenyl group and a substituted
phenyl group; R.sup.1 and R.sup.2 may be combined with each other
at an arbitrary position to form at least one divalent chain for
forming at least one 5-, 6- or 7-membered saturated or unsaturated
ring structure; X.sub.a represents a hetero atom selected from the
group consisting of S, O, Se or Te; the alkyl group and the alkoxy
group represented by R.sup.1 or R.sup.2 each may optionally contain
in the chain thereof a carbonyl bond, an ether bond, an ester bond,
an amide bond or an imino bond; and .delta. represents a number of
from 0 to 1;
[0047] (3) the solid electrolytic capacitor as described in (2)
above, wherein the structural unit represented by formula (1a) is a
chemical structure represented by the following formula (2):
##STR2## wherein the substituents R.sup.4 and R.sup.5 each
independently represents a hydrogen atom, a linear or branched,
saturated or unsaturated hydrocarbon group having from 1 to 6
carbon atoms, or a substituent for forming at least one 5-, 6- or
7-membered saturated or unsaturated ring structure containing the
two oxygen elements shown in the formula by combining hydrocarbon
groups having from 1 to 6 carbon atoms with each other at an
arbitrary position; the ring structure formed as described above
includes a chemical structure such as a substituted vinylene group
and a substituted o-phenylene group; and .delta. represents a
number of from 0 to 1;
[0048] (4) the method for producing a solid electrolytic capacitor
as described in (1) above, comprising an oxide dielectric film
having provided thereon an electrically conducting polymer
composition layer, the method comprising polymerizing a monomer
compound on an oxide dielectric film by an oxidizing agent, wherein
the monomer compound is a compound represented by the following
formula (3a): ##STR3## wherein the substituents R.sup.1, R.sup.2
and X.sub.a are the same as defined in formula (1a) and the
polymerization is performed in the presence of a compound capable
of providing an anion of an organic sulfonic acid compound or
sulfonate anion having a doping ability;
[0049] (5) the method for producing a solid electrolytic capacitor
as described in (4) above, wherein the monomer compound represented
by formula (1a) is a compound represented by the following formula
(4): ##STR4## wherein the substituents R.sup.4 and R.sup.5 are the
same as defined in formula (2);
[0050] (6) the method for producing a solid electrolytic capacitor
as described in (1), (4) and (5) above, wherein the oxidizing agent
is a metal salt solution of an oxidative inorganic acid;
[0051] (7) the method for producing a solid electrolytic capacitor
as described in (1), (4), (5) and (6) above, wherein the metal salt
of an oxidative inorganic acid is a persulfate;
[0052] (8) the method for producing a solid electrolytic capacitor
as described in (1), (4), (5), (6) and (7) above, wherein the
monomer compound is a monomer compound of a polymer having electric
conductivity, and thiophene, aniline or derivatives thereof;
[0053] (9) the method for producing a solid electrolytic capacitor
as described in (1), (4), (5), (6), (7) and (8) above, wherein the
thiophene derivative is 3,4-ethylenedioxythiophene;
[0054] (10) a method for producing a solid electrolytic capacitor,
comprising a polymerization step of coating a solution containing a
monomer of an electroconducting polymer and a solution containing
an oxidizing agent in repeating sequence on a valve-acting metal
anode having formed on the surface thereof an oxide dielectric
film, wherein the electroconducting polymer is formed by setting
the humidity in the atmosphere of polymerization process to from
10% to less than 60%;
[0055] (11) a solid electrolytic capacitor comprising an
electroconducting polymer composition layer provided on the oxide
dielectric film according to the method of (10) above, wherein the
electroconducting polymer in the composition contains a structural
unit represented by the following formula (1b) as a repeating
chemical structure: ##STR5## wherein the substituents R.sup.1 and
R.sup.2 each independently represents a monovalent group selected
from the group consisting of a hydrogen atom, a linear or branched,
saturated or unsaturated hydrocarbon group having from 1 to 6
carbon atoms, a linear or branched, saturated or unsaturated alkoxy
group having from 1 to 6 carbon atoms, a hydroxyl group, a halogen
atom, a nitro group, a cyano group, a linear or branched
perfluoroalkyl group having from 1 to 6 carbon atoms, a phenyl
group and a substituted phenyl group; the substituents R.sup.1 and
R.sup.2 may be combined with each other at an arbitrary position to
form at least one divalent chain for forming at least one 5-, 6- or
7-membered saturated or unsaturated ring structure; X.sub.b
represents a hetero atom selected from S, O, Se, Te and NR.sup.3;
R.sup.3 represents a hydrogen atom, a linear or branched, saturated
or unsaturated hydrocarbon group having from 1 to 6 carbon atoms, a
phenyl group, or a linear or branched, saturated or unsaturated
alkoxy group having from 1 to 6 carbon atoms; and the alkyl group
and the alkoxy group represented by R.sup.1, R.sup.2 or R.sup.3
each may optionally contain in the chain thereof a carbonyl bond,
an ether bond, an ester bond, an amide bond or an imino bond;
provided that .delta. is a number of from 0 to 1;
[0056] (12) the solid electrolytic capacitor as described in (11)
above, wherein the structural unit represented by formula (1b) is a
chemical structure represented by the following formula (2):
##STR6## wherein the substituents R.sup.4 and R.sup.5 each
independently represents a hydrogen atom, a linear or branched,
saturated or unsaturated hydrocarbon group having from 1 to 6
carbon atoms or a substituent forming at least one 5-, 6- or
7-membered saturated or unsaturated ring structure containing the
two oxygen atoms shown in the formula when the hydrocarbon groups
having from 1 to 6 carbon atoms are combined with each other at an
arbitrary position, the ring structure formed including a chemical
structure such as a substituted vinylene group and a substituted
o-phenylene group, and .delta. represents a number of from 0 to
1;
[0057] (13) the method for producing a solid electrolytic capacitor
as described in (10) above, the solid electrolytic capacitor
comprising an electroconducting polymer composition layer provided
on the oxide dielectric film, wherein a monomer is polymerized on
the oxide dielectric film by an oxidizing agent, the monomer is a
compound represented by the following formula (3b): ##STR7##
wherein the substituents R.sup.1, R.sup.2 and X.sub.b are the same
as defined in formula (1b), and the polymerization is performed in
the presence of a compound capable of providing an anion of an
organic sulfonic acid or sulfonate anion having a doping
ability;
[0058] (14) the method for producing a solid electrolytic capacitor
as described in (13) above, wherein the monomer represented by
formula (1b) is a compound represented by the following formula
(4): ##STR8## wherein the substituents R.sup.4 and R.sup.5 are the
same as defined in formula (2);
[0059] (15) the method for producing a solid electrolytic capacitor
as described in (11) and (14) above, wherein the oxidizing agent is
a metal salt or ammonium salt solution of an oxidative inorganic
acid;
[0060] (16) the method for producing a solid electrolytic capacitor
as described in (11), (14) and (15) above, wherein the metal salt
or ammonium salt of an oxidative inorganic acid is persulfate;
[0061] (17) the method for producing a solid electrolytic capacitor
as described in (11), (14), (15) and (16) above, wherein the
monomer is a monomer for a polymer having electric conductivity,
and pyrrole, thiophene, aniline or a derivative thereof;
[0062] (18) the method for producing a solid electrolytic capacitor
as described in (11), (14), (15), (16) and (17) above, wherein the
thiophene derivative is 3,4-ethylenedioxythiophene;
[0063] (19) a solid electrolytic capacitor comprising a porous
valve acting metal having formed thereon a dielectric film and a
solid electrolyte formed on the dielectric film, wherein the solid
electrolyte occupies from 10 to 95% of the space within a pore of
the porous metal;
[0064] (20) the solid electrolytic capacitor as described in (19)
above, wherein the solid electrolyte is an electrically conducting
polymer containing a lamellar structure;
[0065] (21) a solid electrolytic capacitor comprising a porous
valve acting metal having formed thereon a dielectric film and a
solid electrolyte formed on the dielectric film, wherein the solid
electrolyte covers 60% or more of the dielectric film;
[0066] (22) the solid electrolytic capacitor as described in (21)
above, wherein the solid electrolyte is an electrically conducting
polymer containing a lamellar structure;
[0067] (23) the solid electrolytic capacitor as described in (20)
or (22) above, wherein at least a portion of an interlayer portion
in said lamellar structure comprises a space portion;
[0068] (24) the solid electrolytic capacitor as described in any
one of (19) to (23) above, wherein the space within a pore, partly
occupied by the solid electrolyte, is an independent or
communicated bubble void space;
[0069] (25) the solid electrolytic capacitor as described in any
one of (19) to (24) above, wherein the solid electrolyte is an
electrically conducting polymer containing as a repeating unit a
divalent group comprising a 5-membered heterocyclic ring-containing
compound or a derivative thereof;
[0070] (26) the solid electrolytic capacitor as described in (25)
above, wherein the electrically conducting polymer containing as a
repeating unit a divalent group comprising a 5-membered
heterocyclic ring-containing compound or a derivative thereof is an
electrically conducting polymer containing as a repeating unit a
structure represented by the following formula (5): ##STR9##
wherein the substituents R.sup.6 and R.sup.7 each independently
represents a monovalent group selected from the group consisting of
a hydrogen atom, a linear or branched, saturated or unsaturated
hydrocarbon group having from 1 to 10 carbon atoms, an alkoxy
group, an alkyl ester group, a halogen atom, a nitro group, a cyano
group, a primary, secondary or tertiary amino group, CF.sub.3, a
phenyl group and a substituted phenyl group, the hydrocarbon chains
of R.sup.6 and R.sup.7 may be combined with each other at an
arbitrary position to form at least one divalent chain for forming
at least one 3-, 4-, 5-, 6- or 7-membered saturated or unsaturated
hydrocarbon cyclic structure together with the carbon atoms
substituted by R.sup.6 and R.sup.7, the cyclic combined chain may
optionally contain a bond selected from the group consisting of
carbonyl, ether, ester, amide, sulfide, sulfinyl, sulfonyl and
imino, .delta. is in the range of 0 to 1, Z represents an anion,
and j represents the valency of Z and is 1 or 2;
[0071] (27) the solid electrolytic capacitor as described in (26)
above, wherein the electrically conducting polymer has an electric
conductivity of from 0.1 to 200 S/cm;
[0072] (28) the solid electrolytic capacitor as described in (19)
to (27) above, wherein the valve acting metal is any one of
aluminum, tantalum, niobium and titanium;
[0073] (29) a method for producing a solid electrolytic capacitor,
comprising forming a dielectric film on a porous valve acting metal
and forming a solid electrolyte on the dielectric film, wherein the
solid electrolyte is formed to occupy from 10 to 95% of the space
within a pore of the porous metal;
[0074] (30) a method for producing a solid electrolytic capacitor
comprising forming a dielectric film on a porous valve acting metal
and forming a solid electrolyte on the dielectric film, wherein the
solid electrolyte is formed to cover about 60% or more of the
dielectric film;
[0075] (31) a method for producing a solid electrolytic capacitor,
comprising covering a valve-acting metal anode foil having formed
on the surface thereof an oxide dielectric film with repeating
sequence of a solution containing a monomer of an electrically
conducting polymer and a solution containing an oxidizing agent and
then polymerizing to form an electrically conducting polymer
composition film on the dielectric film, wherein the solution
containing a monomer of the electrically conducting polymer and/or
the solution containing the oxidizing agent has a viscosity of less
than about 100 cp at 23.degree. C.; wherein the electrically
conducting polymer composition film is formed by setting the
humidity in the atmosphere of the polymerization process to from
about 10% to less than about 60%; and wherein the solid electrolyte
is formed on the dielectric film to occupy from about 10 to about
95% of the space within a pore of the valve metal;
[0076] (32) a method for producing a solid electrolytic capacitor,
comprising covering a valve-acting metal anode foil having formed
on the surface thereof an oxide dielectric film with repeating
sequence of a solution containing a monomer of an electrically
conducting polymer and a solution containing an oxidizing agent and
then polymerizing to form an electrically conducting polymer
composition film on the dielectric film, wherein the solution
containing a monomer of the electrically conducting polymer and/or
the solution containing the oxidizing agent has a viscosity of less
than about 100 cp at 23.degree. C.; wherein the electrically
conducting polymer composition film is formed by setting the
humidity in the atmosphere of the polymerization process to from
about 10% to less than about 60%; and wherein the solid electrolyte
is formed on the dielectric film to cover about 60% or more of said
dielectric film;
[0077] (33) a solid electrolytic capacitor produced by the process
of embodiment (31); and
[0078] (34) a solid electrolytic capacitor produced by the process
of embodiment (32).
BRIEF DESCRIPTION OF DRAWING
[0079] FIG. 1 is a cross-sectional view showing one example of the
solid electrolytic capacitor according to the present invention,
where
[0080] 1 is a valve-acting metal electrode,
[0081] 2 is a pore (microfine pore),
[0082] 3 is a dielectric film,
[0083] 4 is an electrically conducting polymer composition,
[0084] 5 is an electrically conducting layer,
[0085] 6 is a jacket, and
[0086] 7 is a connecting lead.
DETAILED DESCRIPTION OF THE INVENTION
[0087] The present invention is described in detail below.
[0088] In an embodiment of the present invention, as described in
the foregoing, the viscosity of the oxidizing agent solution and/or
the monomer solution in the electrically conducting polymer
composition is specified, so that an electrically conducting
polymer composition layer (charge-transfer complex) improved in the
capacitor property can be advantageously formed, as a result, a
high-performance solid electrolytic capacitor having excellent low
impedance property and high durability in a sparking voltage test
or the like can be provided and also a production method thereof
can be provided.
[0089] In another embodiment of the present invention, as described
in the foregoing, the humidity in the polymerization process of an
electroconducting polymer composition from a oxidizing agent
solution and a monomer solution is specified, so that an
electroconducting polymer composition layer (charge-transfer
complex) improved in the capacitor properties can be advantageously
formed, as a result, a compact and high-performance solid
electrolytic capacitor exhibiting low impedance and excellent tan
.delta. can be provided and also a production method thereof can be
provided.
[0090] The electrically conducting polymer in the electrically
conducting polymer composition suitable for the capacitor of the
present invention is a polymer having a .pi. electron-conjugated
structure in the polymer main chain. The polymer has a
polymerization degree of from 2 to about 1,000, preferably from
about 5 to about 500. Specific examples thereof include
polyaniline, poly-p-phenylene, poly-p-phenylenevinylene,
polythienylenevinylene, 5-membered polyheterocyclic polymers and
substituted derivatives thereof. A copolymer obtained by
copolymerizing at least two monomers capable of producing the
above-described polymers may also be used.
[0091] The polyheterocyclic polymers as specific examples are
preferably a .pi. electron-conjugated polymer containing a
structural unit represented by formula (1), more preferably a .pi.
electron-conjugated polymer containing a structural unit
represented by formula (2).
[0092] In formulae (1), (3) and (5) shown above, useful examples of
the linear or branched, saturated or unsaturated hydrocarbon group
having from 1 to 6 carbon atoms represented by the substituent
R.sup.1, R.sup.2, R.sup.3, R.sup.6 and R.sup.7 include a methyl
group, an ethyl group, a vinyl group, a propyl group, an allyl
group, an isopropyl group, a butyl group and a 1-butenyl group.
Useful examples of the linear or branched, saturated or unsaturated
alkoxy group having from 1 to 6 carbon atoms include a methoxy
group, an ethoxy group, a propoxy group, an isopropoxy group and a
butoxy group.
[0093] Useful examples of the substituent other than the
hydrocarbon group and the alkoxy group include a nitro group, a
cyano group, a phenyl group and a substituted phenyl group (e.g., a
phenyl group substituted by a halogen group such as Cl, Br, F,
etc.). The alkyl group or the alkoxy group represented by R.sup.1,
R.sup.2, R.sup.6 and R.sup.7 each may optionally contain in the
chain thereof a carbonyl bond, an ether bond, an ester bond, an
amide bond or an imino bond. Particularly useful examples thereof
include a methoxyethoxy group and a methoxyethoxyethoxy group.
[0094] The substituents R.sup.1 and R.sup.2 and R.sup.6 and R.sup.7
may be combined with each other at an arbitrary position to form at
least one divalent chain for forming at least one 5-, 6- or
7-membered saturated or unsaturated ring structure. Examples of the
substitution in formula (1b) or (3b) include
3,4-propylene-substituted structure (formula (a)),
3,4-butylene-substituted structure (formula (b)),
3,4-butenylene-substituted structure (formula (c)),
3,4-butadienylene-substituted structure (formula (d)) and
naphtho[2,3-c]-condensed structure (formula (e)): ##STR10##
[0095] In the formulae above, X.sub.b represents a hetero atom and
examples thereof include S, O, Se, Te and NR.sup.3. The
3,4-butadienylene-substituted structure (formula (d)) where X.sub.b
is S is denoted an isothianaphthenylene structure in the case of
the repeating structural unit of formula (1b) or denoted an
isothianaphthene in the case of the monomer compound structure of
formula (3b). Similarly, the naphtho[2,3-c]condensed structure
(formula (e)) is denoted a naphtho[2,3-c]thienylene structure in
the case of formula (1b) or denoted a naphtho[2,3-c]thiophene in
the case of the monomer compound structure of formula (3b). In the
formulae, .delta. represents a number of charges per the repeating
structural unit and is a value of from 0 to 1.
[0096] Useful examples of the substituents R.sup.4 and R.sup.5 in
formulae (2) and (4) include a methyl group, an ethyl group, a
propyl group, an isopropyl group, a vinyl group and an allyl group.
Also, the hydrocarbon groups having from 1 to 6 carbon atoms
represented by the substituents R.sup.4 and R.sup.5 may be combined
with each other at an arbitrary position to form at least one 5-,
6- or 7-membered heterocyclic ring structure containing the two
oxygen elements shown in formula (2) or (4). Preferred examples
thereof include 1,2-ethylene, 1,2-propylene and
1,2-dimethylethylene.
[0097] Furthermore, the hydrocarbon groups having from 1 to 6
carbon atoms represented by R.sup.4 and R.sup.5 may be combined
with each other at an arbitrary position to form an unsaturated
hydrocarbon ring structure such as a substituted vinylene group and
a substituted o-phenylene group. Examples thereof include
1,2-vinylene (formula (f)), 1,2-propenylene (formula (g)),
2,3-butylen-2-ene (formula (h)), 1,2-cyclohexylene (formula (i)),
methyl-o-phenylene (formula (j)), 1,2-dimethyl-o-phenylene (formula
(k)) and ethyl-o-phenylene (formula (1)): ##STR11##
[0098] Among the monomer compounds represented by formula (3b) for
use in the solid electrolytic capacitor of the present invention
and the production method thereof, monomer compounds such as
thiophene (R.sup.1.dbd.R.sup.2.dbd.H and X.sub.b.dbd.S) or pyrrole
(R.sup.1.dbd.R.sup.2.dbd.R.sup.3.dbd.H and X.sub.b.dbd.NR.sup.3) or
among the thiophenes represented by formula (4),
3,4-ethylenedioxy-thiophene, are suitable. Also, many of oxidizing
agents which can polymerize such a monomer compound are known.
[0099] In the electrically conducting polymer composition of the
present invention, the viscosity of the oxidizing agent solution
and/or the monomer solution is specified and thereby an
electrically conducting polymer capable of ensuring improved
capacitor properties can be advantageously formed therefrom. The
viscosity (all viscosities herein are at 23.degree. C.) of the
oxidizing agent solution and/or the monomer solution is preferably
less than 100 cp, preferably 20 cp or less, more preferably from 1
to 10 cp. The capacitor comprising a solid electrolyte formed from
the composition is free of the above-described problems and
additionally has excellent low impedance property. Such a capacitor
has not been heretofore known.
[0100] If the viscosity exceeds 100 cp, when an alumina foil having
thereon a dielectric material obtained by etching the surface is
dipped with an oxidizing agent solution or a monomer solution and
then dried, a highly viscous oxidizing agent or monomer film is
formed on the surface of a porous body, and the microfine pore
openings present on the surface of the porous body are clogged.
Furthermore, the polymer is formed on the surface by contact with a
monomer or an oxidizing agent, therefore, the polymer is not formed
inside the pores, which causes a decrease in capacitance.
[0101] When the solution(s) has a viscosity of less than 100 cp,
preferably 20 cp or less, more preferably from 1 to 10 cp, the
electrically conducting polymer can be filled into the inside of
pores present on the surface of the porous body, therefore, a
capacitor having high capacitance and excellent low impedance
property can be obtained.
[0102] In the present invention, a two-solution system using a
solution comprising a monomer and a solution comprising an
oxidizing agent is employed, so that as compared with the
one-solution system using a mixed solution of oxidizing agent and
monomer, the monomer and the oxidizing agent can be recovered and
the yield can be increased.
[0103] In the polymerization process, if the humidity is
excessively elevated, the solution state in a low concentration
continues long and the polymerization slowly proceeds, therefore,
the yield of polymer decreases.
[0104] On the other hand, if the humidity is excessively lowered in
the polymerization process, the adhered water on the dielectric
film evaporates within a short time. As a result, the oxidizing
agent is solidified and the monomer is evaporated, whereby the
yield of polymer decreases.
[0105] Therefore, in one embodiment of the present invention, the
humidity in the polymerization process of an electroconducting
polymer composition is specified, so that the reaction in the
solution state and the reaction in the solid-liquid state can be
balanced and an electroconducting polymer increased in the
capacitor properties can be advantageously obtained.
[0106] The humidity in the atmosphere of the polymerization process
is preferably from 10% to less than 60%, more preferably from 20%
to 50%. The temperature and the pressure in the atmosphere vary
depending on the kind of polymer composition and the polymerization
method, and thus cannot be particularly limited, however, a
temperature of from -70.degree. C. to 250.degree. C. and a pressure
below the atmospheric pressure are generally preferred.
[0107] The dopant may be any compound as long as it has a doping
ability. For example, an organic sulfonic acid, an inorganic
sulfonic acid, an organic carboxylic acid or salts thereof such as
a metal salt or an ammonium salt may be used. The method for adding
the dopant is not limited and the compound may be added to the
oxidizing agent solution and/or the monomer solution, may be
allowed to be present together at the time of polymerization or may
be added by other methods.
[0108] Usually, the method for producing (forming) the
above-described solid electrolyte plays an important role in the
production of a solid electrolytic capacitor for attaining high
capacitance and high frequency property and improving tan .delta.,
leakage current, heat resistance (reflow soldering property),
impedance property and durability. For this purpose, important are
the .pi. electron-conjugated structure forming the solid
electrolyte, the structure of the electrically conducting polymer
composition combined with a dopant, and dense filling and formation
of the electrically conducting polymer composition layer on a
dielectric film so as to increase or improve the homogeneity of the
electric conducting path. In particular, the structure of the
electrically conducting polymer composition has great effects on
the capacitor properties.
[0109] In the production method of the present invention, the
viscosity of an oxidizing agent solution or, a mixed solution of a
dopant and a monomer greatly contributes to formation of a polymer
having a .pi. electron-conjugated structure and imparting electric
conductivity.
[0110] In the production method used in the present invention, the
humidity in the polymerization process for forming a polymer having
the .pi. electron-conjugated system affects the capacitor
properties. Furthermore, the production method is characterized in
that the above-described organic sulfonate anion or a combination
of the organic sulfonate anion and anion other than that is used as
the dopant.
[0111] More specifically, in one embodiment a monomer compound
represented by formula (3b) or (4) is induced to undergo oxidative
polymerization on the dielectric film having pores of an anode
substrate by an oxidizing agent solution having a specified
viscosity and the polymer composition produced works out to the
solid electrolyte on the dielectric material surface. This
production process is performed at least once per anode substrate
and the process is preferably repeated from 3 to 30 times, whereby
a dense solid electrolyte layer can be easily formed.
[0112] Further, a monomer represented by formula (3b) or (4)
undergoes oxidative polymerization on the dielectric film having
microfine pores of an anode substrate by the action of an oxidizing
agent and moisture in air in the presence of a compound capable of
donating a dopant, and the polymer composition produced works out
to the solid electrolyte on the dielectric material surface. This
production process is repeated at least once, preferably from 3 to
30 times, per one anode substrate, whereby a highly dense and
uniform solid electrolyte layer having high coatability can be
easily formed.
[0113] In a further embodiment, the dielectric film for use in the
present invention is formed by subjecting a porous formed article
of a valve acting metal to electrochemical forming or the like. The
forming solution for use in the electrochemical forming and the
electrochemical forming conditions such as forming voltage cannot
be indiscriminately specified but must be experimentally verified
in particular by freely varying them according to the capacitance,
voltage resistance and the like of the solid electrolytic capacitor
produced using the electrode.
[0114] In this embodiment, the pore diameter of the electrode for
use in the present invention is a factor governing the homogeneous
formation of a solid electrolyte layer. The microfine structure,
the pore shape and the pore distribution of the porous formed
article having formed thereon a dielectric film may be any as long
as they can be used for ordinary capacitors. However, in order to
more successfully bring out the effects by the coverage of an
electrically conducting polymer or its occupancy in a pore
according to the present invention, the pores formed on the valve
acting metal are preferably specified in the distribution and the
specific surface area. For, example, the formed article which can
be used has a pore diameter of about 2.times.10.sup.-7 m or less
with the volumetric sum of pores per unit mass being about
5.times.10.sup.-3 cm.sup.3/g or more, preferably a pore size of
about 1.2.times.10.sup.-7 m or less with the volumetric sum of
pores per unit mass being about 5.times.10.sup.-3 cm.sup.3/g or
more.
[0115] In general, for forming an electrically conducting polymer
on a dielectric film, for example, on an oxide dielectric film,
means of solution chemical oxidation polymerization, vapor phase
chemical oxidation polymerization, electrolytic polymerization or
the like is used. However, depending on the intensity of surface
tension of the solution, the solid electrolyte layer may be
prevented from the formation in the inside of a pore due to the
effect of wettability to the oxide film or the like.
[0116] For example, in the solution chemical oxidation
polymerization, a monomer is polymerized oxidativelly on a
dielectric film having microfine pores of an anode substrate by the
action of an oxidizing agent in the presence of a compound which
can work out to a dopant of the electrically conducting polymer,
and the polymer composition produced on the dielectric surface
forms a solid electrolyte. By repeating this production step once
or more, preferably from 3 to 30 times, per anode substrate, the
occupancy (the ratio of the electrically conducting polymer volume
occupying the pore volume) may be controlled with good accuracy to
from 10 to 95% or the coverage to 60% or more, whereby a desired
solid electrolyte layer can be easily formed.
[0117] For example, in one preferred embodiment, the polymerization
reaction process includes a step of dipping a valve-acting metal
anode foil having formed thereon a dielectric film in a solution
having a specified viscosity and containing an oxidizing agent
(Solution 1), and a step of dipping the foil in a solution having a
specified viscosity and containing a monomer compound and a dopant
(Solution 2). The valve-acting metal anode foil may be dipped in
the order written above, namely, dipping in Solution 1 and then
dipping in Solution 2, or in the order reversed thereto, namely,
dipping in Solution 2 and then dipping in Solution 1.
[0118] In another specific embodiment, the process may include a
step of dipping the anode foil in a solution having a specified
viscosity and containing an oxidizing agent and a dopant (Solution
3), and a step of dipping the foil in a solution having a specified
viscosity and containing a monomer compound (Solution 4). Also in
this case, the anode foil may be dipped in the order written above,
namely, dipping in Solution 3 and then dipping in Solution 4, or in
the order reversed thereto, namely, dipping in Solution 4 and then
dipping in Solution 3. Solutions 1 to 4 each may be used in the
form of a suspension.
[0119] For example, in another preferred embodiment of the
production process, the polymerization process may include a step
of dipping a valve-acting metal anode foil having formed thereon a
dielectric film in a solution containing an oxidizing agent
(Solution 1), and a step of dipping the anode foil in a solution
containing a monomer and a dopant (Solution 2). The valve-acting
metal anode foil may be dipped in the order written above, namely,
may be dipped in Solution 1 and then in Solution 2, or in the
reverse order, namely, may be dipped in Solution 2 and then in
Solution 1.
[0120] The dipping process may be replaced by a covering process
such as coating, spraying or spreading, which enables the
polymerization reaction to proceed on the anode foil.
[0121] The solvents in Solutions 1 to 4 may be the same or
different. Depending on the kind of solvent, a drying step may be
interposed between covering with Solution 1 and covering with
Solution 2, or between covering with Solution 3 and covering with
Solution 4.
[0122] After the solid electrolyte is formed, a step of washing the
capacitor device with organic solvents or with water may be used.
In this case, it is simple and preferred to use the solvents used
in Solutions 1 to 4 as the organic solvents for washing, however,
any solvent may be used as long as it can merely dissolve the
monomer compounds or the compounds with anions having a doping
ability. By using the washing step with the solvent, the content of
the dopant in the electrically conducting polymer composition may
be reduced. However, in view of the properties of the solid
electrolytic capacitor of the present invention, it is necessary to
specify the viscosity of the oxidizing agent solution and/or the
monomer solution. The specified viscosity contributes to the
properties of the solid electrolytic capacitor.
[0123] When the thickness of the solid electrolyte layer is
increased by repeating the above-described oxidative polymerization
treatment, a solid electrolyte having excellent soldering heat
resistance (heat stability) may be easily produced. The solid
electrolytic capacitor using a solid electrolyte comprising an
electrically conducting polymer composition according to the
present invention has excellent heat stability and shows good
stability of the doped state.
[0124] In an embodiment of this invention, the viscosity of the
oxidizing agent solution and/or the monomer solution is specified
and thereby the oxidation efficiency is improved. As a result, the
electrically conducting polymer composition containing dopant anion
in combination can be stepwise deposited with good filling on the
dielectric material surface and even insides of the pores to form a
thin film of the polymer composition. In particular, when a
structure of thin film layers being stacked over and over again is
formed, the above-described properties can be brought out, so that
a capacitor having heat stability highly enough to prevent the
polymer from damaging the dielectric film can be provided.
[0125] In another embodiment of this invention, the humidity in the
polymerization step is specified and thereby the oxidation
efficiency of monomer is increased, as a result, the
electroconducting polymer composition containing dopant anion in
combination can be stepwise deposited with good filling on the
dielectric material surface and even insides of the pores to form a
thin film of the polymer composition. In particular, when a
structure of thin film layers being stacked over and over again is
formed, the above-described properties can be brought out and a
capacitor having heat stability highly enough to prevent the
polymer from damaging the dielectric film can be provided.
[0126] As the dopant for use in the present invention,
conventionally known dopants (e.g., ClO.sub.4.sup.-,
BF.sub.4.sup.-, Cl.sup.-, SO.sub.4.sup.2-, benzenesulfonate anion)
and almost all dopants having a high aromaticity in the
heterocyclic skeleton and a sulfonic acid group may be used.
[0127] As the compound which provides the above-described anion,
alkali metal salts such as the sodium salt and the potassium salt,
and quaternary nitrogen-based compound salts such as the ammonium
salt of the sulfonic acid compound may also be preferably used.
[0128] The oxidizing agent for use in the present invention may be
any oxidizing agent if it is suitable for the oxidation
polymerization of anilines or thiophenes. Examples of oxidizing
agents which can used include oxidizing agents over a wide range,
such as iron(III) chloride, Fe(ClO.sub.4).sub.3, organic acid
iron(III) salt, inorganic acid iron(III) salt, alkyl persulfate,
persulfate, hydrogen peroxide and K.sub.2Cr.sub.2O.sub.7 as
described in JP-A-2-15611.
[0129] Examples of the organic acid in the organic acid iron(III)
salt include an alkylsulfonic acid having from 1 to 20 carbon atoms
such as methanesulfonic acid and dodecylbenzenesulfonic acid, and
an aliphatic carboxylic acid having from 1 to 20 carbon atoms.
However, the strict use range of the oxidizing agent may be
sometimes limited by the chemical structure of the monomer compound
represented by formula (3b), the oxidizing agent, the reaction
conditions and the like.
[0130] For example, according to the Handbook of Conducting
Polymers, page 99, FIG. 5, Marcel Dekker, Inc. (1987), the species
of the substituent greatly affects the oxidation potential (one
index for showing whether the polymerization occurs readily or
difficultly) and in turn, governs the oxidation (polymerization) of
thiophenes (oxidation potential expands over a wide range of from
about 1.8 to about 2.7 V). Accordingly, it is known that the
combination of the monomer compound and the oxidizing agent used in
practice is important. In the present invention, a combination
capable of improving the capacitor properties in the production has
been found and thereby the problems have been overcome.
[0131] The anion as a dopant may be one which can be derived from a
reductant anion after the reaction of the oxidizing agent. Specific
examples thereof include chloride ion, ClO.sub.4.sup.-, aliphatic
organic carboxylate anion having from 1 to 12 carbon atoms, sulfate
ion, phosphate anion, aliphatic organophosphate anion having from 1
to 12 carbon atoms and borate anion. Furthermore, an electron
acceptor dopant such as NO.sup.+ and NO.sub.2.sup.+ salts (e.g.,
NOBF.sub.4, NOPF.sub.6, NOSbF.sub.6, NOAsF.sub.6,
NOCH.sub.3SO.sub.3, NO.sub.2BF.sub.4, NO.sub.2PF.sub.6,
NO.sub.2CF.sub.3SO.sub.3) may also be used.
[0132] In the present invention, an aromatic compound (e.g.,
sulfoquinone, anthracenemonosulfonic acid, substituted
naphthalenemonosulfonic acid) or a heterocyclic sulfonic acid may
be used, which differs from conventionally known molecular anions
(e.g., ClO.sub.4.sup.-, BF.sub.4.sup.-) in doping ability (e.g.,
the stability of charge transfer complex, electric conductivity)
and the chemical properties, and exhibits superior effects as
compared with the system of using a conventionally known molecular
anion (e.g., ClO.sub.4.sup.-, BF.sub.4.sup.-) alone, in other
words, which can bring about particularly excellent effects when a
plurality of capacitor devices are manufactured and compared on the
capacitor performance.
[0133] The sulfoquinone for use in the present invention is a
generic term for compounds having one or more sulfonic acid groups
and a quinone structure within the molecule. The chemical structure
may be any structure if the compound can effectively act as a
dopant in the form of sulfonate anion. Examples of sulfoquinone
basic skeletons include p-benzoquinone, o-benzoquinone,
1,2-naphthoquinone, 1,4-naphthoquinone, 2,6-naphthoquinone,
9,10-anthraquinone (hereinafter simply referred to as an
"anthraquinone"), 1,4-anthraquinone, 1,2-anthraquinone,
1,4-chrysenequinone, 5,6-chrysenequinone, 6,12-chrysenequinone,
acenaphthoquinone, acenaphthenequinone, camphorquinone,
2,3-bornanedione, 9,10-phenanthrenequinone and
2,7-pyrenequinone.
[0134] The sulfonic acid group in the sulfoquinone includes an
aromatic sulfonic acid structure resulting from displacing at least
one hydrogen of the quinone compound by a sulfonic acid group, and
an aliphatic sulfonic acid structure resulting from replacing at
least one hydrogen by a sulfoalkylene group through a divalent
saturated or unsaturated hydrocarbon group having from 1 to 12
carbon atoms. Furthermore, a chemical structure resulting from
displacing at least one hydrogen of the sulfoquinone by a saturated
or unsaturated alkyl group having from 1 to 12, preferably from 1
to 6, carbon atoms, by an alkoxy group having 1 to 12, preferably
from 1 to 6, carbon atoms, or by a substituent selected from F, Cl
and Br may also be used.
[0135] In particular, the sulfoquinone for use in the present
invention is preferably a sulfoquinone having an anthraquinone
skeleton, a 1,4-naphthoquinone skeleton or a 2,6-naphthoquinone
skeleton. Examples thereof include, in the case of anthraquinones,
anthraquinone-1-sulfonic acid, anthraquinone-2-sulfonic acid,
anthraquinone-1,5-disulfonic acid, anthraquinone-1,4-disulfonic
acid, anthraquinone-1,3-disulfonic acid,
anthraquinone-1,6-disulfonic acid, anthraquinone-1,7-disulfonic
acid, anthraquinone-1,8-disulfonic acid,
anthraquinone-2,6-disulfonic acid, anthraquinone-2,3-disulfonic
acid, anthraquinone-2,7-disulfonic acid,
anthraquinone-1,4,5-trisulfonic acid,
anthraquinone-2,3,6,7-tetrasulfonic acid, and the alkali metal
salts and ammonium salts thereof.
[0136] Examples thereof include, in the case of
1,4-naphthoquinones, 1,4-naphthoquinone-5-sulfonic acid,
1,4-naphthoquinone-6-sulfonic acid,
1,4-naphthoquinone-5,7-disulfonic acid,
1,4-naphthoquinone-5,8-disulfonic acid, the alkali metal salts and
ammonium salts thereof.
[0137] Examples thereof include, in the case of
2,6-naphthoquinones, 2,6-naphthoquinone-1-sulfonic acid,
2,6-naphthoquinone-3-sulfonic acid, 2,6-naphthoquinone-4-sulfonic
acid, 2,6-naphthoquinone-3,7-disulfonic acid,
2,6-naphthoquinone-4,8-disulfonic acid, and the alkali metal salts
and ammonium salts thereof.
[0138] The sulfoquinone may also be selected from industrial dyes
and examples thereof include Anthraquinone Iris R and Anthraquinone
Violet RN-3RN. These industrial dyes are a useful
sulfoquinone-based dopant and each may be used in the form of the
above-described salt.
[0139] Some sulfoquinone compounds for use in the present invention
participate in the polymerization reaction of the monomer compound
and act as an oxidative dehydrogenating agent. As a result, the
sulfoquinone is reduced and the resulting proton adduct of the
quinone structure, namely, the hydroquinone structure, or
quinhydron may be present as it is as a dopant in the solid
electrolyte.
[0140] The anthracenemonosulfonic acid for use in the present
invention is a generic term of anthracenemonosulfonic acid
compounds of which the anthracene skeleton is substituted by one
sulfonic acid group. Preferred examples of the compound include
substituted compounds such that at least one hydrogen of an
unsubstituted anthracenesulfonic acid or at least one hydrogen on
the anthracene ring of anthracenesulfonic acid is displaced by a
linear or branched, saturated or unsaturated hydrocarbon group
having from 1 to 12, preferably from 1 to 6, carbon atoms or by a
linear or branched, saturated or unsaturated alkoxy group having
from 1 to 12, preferably from 1 to 6, carbon atoms.
[0141] Specific examples of the compound which provides an
unsubstituted anthracenemonosulfonate anion include
anthracene-1-sulfonic acid, anthracene-2-sulfonic acid,
anthracene-9-sulfonic acid, and alkali metal salts and ammonium
salts thereof. Specific examples of the substituent of the
substituted anthracenemonosulfonic acid compound where a hydrogen
atom on the anthracene ring is further substituted, include an
alkyl group such as methyl, ethyl, propyl, isopropyl, butyl,
isobutyl, t-butyl, pentyl, hexyl, octyl, decyl and dodecyl; an
unsaturated group such as vinyl, allyl, 3-butenyl and 5-hexenyl;
and a alkoxy group such as methoxy, ethoxy, propyloxy, butoxy,
pentoxy, hexyloxy, octyloxy, decyloxy, dodecyloxy, etc.
[0142] Specific examples of compounds which provide the substituted
naphthlenemonosulfonate anion include compounds having a compound
skeleton such as naphthalene-1-sulfonic acid,
naphthalene-2-sulfonic acid, and an alkali metal salt, an ammonium
metal salt and an organic quaternary ammonium salt thereof, and
also having a chemical structure where at least one hydrogen atom
on the naphthalene ring may be displaced by an alkoxy group.
[0143] The substituted benzenesulfonic acid for use in the present
invention is a generic term for benzenesulfonic acid of which the
benzene skeleton is substituted by at least one sulfonic acid
group, and alkyl-substituted benzenesulfonic acid. Preferred are
the substituted compounds resulting from displacing at least one
hydrogen atom of unsubstituted benzenesulfonic acid or at least one
hydrogen on the benzene ring of benzenesulfonic acid by a linear or
branched, saturated or unsaturated hydrocarbon group having from 1
to 20, preferably from 1 to 12, carbon atoms.
[0144] The heterocyclic sulfonate anion which can be used in the
present invention is a generic term for heterocyclic sulfonic acid
compound anion having a chemical structure where the heterocyclic
ring is substituted by at least one sulfonic acid group directly or
indirectly through an alkylene group. Examples of preferred
skeletons for the heterocyclic compound include substituted
skeletons of morpholine, piperidine, piperazine, imidazole, furan,
1,4-dioxane, benzimidazole, benzothiazolylthio, benzoisoxazole,
benzotriazole and benzofuran.
[0145] Specific examples of compounds which provide the
heterocyclic sulfonate anion include 2-imidazolesulfonic acid,
4-morpholinopropanesulfonic acid, furan-3-sulfonic acid,
2-benzimidazolesulfonic acid, 2-benzimidazole-propanesulfonic acid,
4-methyl-1-piperazinomethanesulfonic acid,
2,3-benzofurane-3-sulfonic acid, and their alkali metal salts such
as the sodium salt, the ammonium salts and the quaternary ammonium
salts.
[0146] Although not necessarily limited, an aromatic sulfonic acid
compound (e.g., sodium dodecylbenenesulfonate, sodium
naphthalenesulfonate, sodium anthraquinone-2-sulfonate, ammonium
anthraquinone-2,6-disulfonate, sodium
1,4-naphthoquinone-2-sulfonate, sodium
3-methyl-2-anthraquinolylmethanesulfonate, sodium
anthracene-1-sulfonate, sodium anthracene-2-sulfonate,
tetrabutylammonium 9,10-dimethoxy-anthracene-2-sulfonate,
tetrabutyl-ammonium 9,10-dihexylanthracene-2-sulfonate, sodium
2-propyloxynaphthalene-6-sulfonate, tetrabutylammonium
2-propyloxynaphthalene-6-sulfonate, sodium
2-methoxynaphthalene-6-sulfonate, tetrabutylammonium
2,3-dimethoxynaphthalene-6-sulfonate) or a heterocyclic sulfonic
acids (e.g., sodium 4-morpholinopropanesulfonate, sodium
2-benzimidazolpropanesulfonate, sodium
4-methyl-1-piperazinomethanesulfonate, sodium
2,3-benzofurane-3-sulfonate) is preferably used.
[0147] In the method for producing a solid electrolytic capacitor
of the present invention, the oxidizing agent used to cause
chemical polymerization of the thiophene monomer compounds
represented by formula (4) is suitably persulfate. Examples of
persulfates which can be particularly suitably used for causing
chemical polymerization of thiophenes represented by formula (4)
include ammonium persulfate and potassium persulfate. Use of
iron(III) salt-based oxidizing agent is disadvantageous in view of
the capacitor properties because iron (element) inevitably remains
in the electrically conducting polymer composition.
[0148] Also, persulfates which are suitable for the monomer
compound represented by formula (4) is not suitable for thiophene
(R.sup.1.dbd.R.sup.2.dbd.H, X.sub.b.dbd.S) monomer represented by
formula (3b). Thus, the persulfate has a limit in that depending on
the kind of monomer, use thereof may not be appropriate.
[0149] Preferred conditions in the formation (polymerization
reaction) of the electrically conducting polymer composition layer
are described below.
[0150] In the production method of a capacitor according to the
present invention, the concentrations of the monomer compound
represented by formula (3b) or (4), the oxidizing agent and the
sulfonic acid used each varies depending on the kind of the
monomer, oxidizing agent or sulfonic acid compound (including the
kind of the substituent) or depending on the combination with a
solvent or the like. In general, the concentration is from
1.times.10.sup.-4 to 10 mol/l, preferably from 1.times.10.sup.-3 to
5 mol/l.
[0151] The reaction temperature varies depending on the kind of
each reaction composition, the reaction method or the like and
cannot be specifically limited, but in general, the reaction
temperature is from -70 to 250.degree. C., preferably from -20 to
150.degree. C., more preferably from 0 to 100.degree. C.
[0152] Examples of the solvent in the production method of the
present invention or for use in washing after the polymerization
include ethers such as tetrahydrofuran (THF), dioxane and diethyl
ether; ketones such as acetone and methyl ethyl ketone; aprotic
polar solvents such as dimethylformamide, acetonitrile,
benzonitrile, N-methylpyrrolidone (NMP) and dimethylsulfoxide
(DMSO); esters such as ethyl acetate and butyl acetate;
non-aromatic chlorine-type solvents such as chloroform and
methylene chloride; nitro compounds such as nitromethane,
nitroethane and nitrobenzene; alcohols such as methanol, ethanol
and propanol; organic acids such as formic acid, acetic acid and
propionic acid; acid anhydrides of the organic acid (e.g., acetic
anhydride); water and a mixed solvent thereof. Among these, water,
alcohols, ketones and/or mixed systems thereof are preferred.
[0153] The thus-produced solid electrolyte has an electric
conductivity of from 0.1 to 200 S/cm, preferably from 1 to 100
S/cm, more preferably from 10 to 100 S/cm.
[0154] For example, when an alcohol such as methanol, ethanol and
propanol is used as the solvent for the monomer or oxidizing agent,
the rate in taking up the oxidizing agent solution can be
controlled by adjusting the humidity in the polymerization
atmosphere. In turn, the amount of solid electrolyte formed per
once polymerization can be controlled. This reveals that in forming
a constant amount of solid electrolyte, the occurrence of
polymerization can be increased or reduced by specifying the
humidity. Accordingly, the polymer can be produced in the form and
amount particularly necessary for obtaining excellent capacitor
properties favored with high capacitance and reduced leakage
current, by specifying the humidity range in the polymerization
atmosphere.
[0155] In one embodiment of the invention, the adhesion between the
solid electrolyte layer and the dielectric film is a factor
governing the important capabilities of a capacitor, such as
capacitance, capacitance stability and moisture resistance load
characteristics. Along the progress in the formation of microfine
pores, bonding points between the electrically conducting polymer
and the dielectric film increase and this is a situation
advantageous for attaining the above-described capabilities. With
respect to the occupancy of the solid electrolyte in the space of a
microfine pore at the formation of the solid electrolyte on the
electrode surface, if the occupancy is 10% or less, the capacitance
stability is deficient and the non-occupied space causes adverse
effects on the moisture resistance load characteristics, such as
water invasion, or on the mechanical strength characteristics of
the capacitor. On the other hand, if the occupancy of the solid
electrolyte in the space of a microfine pore exceeds 95%, the
capacitance stability and the moisture resistance load
characteristics may be attained, however, the ratio of space
occupied by the solid electrolyte is too large and this adversely
affects the self recoverability using oxygen or the like present
within the space. The occupancy is preferably from 20 to 90%, more
preferably from 30 to 85%.
[0156] The continuous or independent space relatively generated by
having a lamellar structure in the solid electrolyte covering the
outer surface of an anode body can relieve the influence of thermal
stress, mechanical stress and the like imposed during the
production process of a capacitor, such as sealing. This structure
can cope with various stresses imposed not only during the
production process but also from an environment where the capacitor
is actually used.
[0157] The coverage in covering the dielectric film with the solid
electrolyte layer is a factor governing also important capabilities
of a capacitor, such as capacitance, capacitance stability and
moisture resistance load characteristics. In this embodiment of the
present invention, 60% or more of the dielectric film is covered
with the solid electrolyte because if the coverage is less than
this range, the moisture resistance property may change for the
worse due to deterioration of the dielectric film which is exposed
at the final stage. Furthermore, in order to obtain a predetermined
capacitance, the area must be increased but if the valve acting
metal is rendered porous by etching or the like, the metal
electrode itself is reduced in the strength, and if a larger
electrode is used for obtaining the capacitance, this contradicts
the current tendency toward downsizing.
[0158] The coverage is preferably 70% or more, more preferably 75%
or more.
[0159] With respect to the shape of the electrically conducting
polymer as a solid electrolyte directly covering the dielectric
film, a fibril structure and a lamella structure are preferred. The
fibril structure and the lamella structure are a folded structure
having overlapping of polymer chains in a broad range and this
gives a good effect on the factor of improving the electric
conductivity, therefore, the properties such as low impedance which
is a tendency nowadays can be improved.
[0160] The construction of the solid electrolytic capacitor of the
present invention is roughly described below by referring to FIG.
1.
[0161] For one part electrode (anode) 1 having on the entire
surface thereof pores 2 connected to a connecting lead 7, a known
material may be used, for example, a metal foil or bar having a
valve action such as aluminum, titanium, tantalum, niobium, or an
alloy using such a metal as a substrate, or a sintered slug mainly
comprising such a material. The surface of the metal electrode is
subjected to etching or electrochemical forming using a
conventional method so as to form a dielectric film and increase
the specific surface area. Thus, a metal foil having formed thereon
a metal oxide film (dielectric film) 3 is used.
[0162] The solid electrolyte (electrically conducting polymer
composition) 4 is preferably formed by a method of polymerizing a
monomer compound on the dielectric film, more preferably by a
method of chemically depositing an electrically conducting polymer
composition having excellent heat resistance of the present
invention on the dielectric layer comprising a dielectric film
having a porous or void structure.
[0163] On the thus-formed electrically conducting polymer
composition layer, another electrically conducting layer is
preferably further provided so as to achieve good electrical
contact. The electrically conducting layer 5 is formed, for
example, by applying electrically conducting paste, plating,
metallization or electrically conducting resin film.
[0164] The solid electrolytic capacitor thus manufactured by the
production method of the present invention is covered with a jacket
6 by resin molding on the electrically conducting layer, by housing
in a resin case or a metal-made jacket case or by resin dipping and
then, connecting leads 7 are provided thereto. Thereafter, the
capacitor can be used as a solid electrolytic capacitor product
suitable for various uses.
[0165] The viscosity herein was measured according to the method
described in JIS K7117-1987 and the viscometer was calibrated
according to JIS Z 8809. The use conditions were as follows.
TABLE-US-00001 Apparatus Model DB Viscometer, manufactured by Toki
Sangyo K.K. Container used: Method D Temperature: 23.degree. C.
Humidity: 40% The humidity is a relative humidity measured by a
digital thermo-hygrometer (SK-110 TRH TYPE 1, manufactured by Sato
K.K.)
BEST MODE FOR CARRYING OUT THE INVENTION
[0166] The present invention is described in greater detail below
by referring to Examples and Reference Examples. Unless otherwise
indicated, all parts, percents, ratios and the like are by
weight.
EXAMPLE 1
[0167] A formed aluminum foil processed to have a prescribed area
was subjected to electrochemical forming at 13V in a 10 wt %
aqueous ammonium adipate solution to form a dielectric film on the
foil surface. The formed aluminum foil (substrate) was dipped in an
aqueous solution (Solution 3, viscosity: 2.5 cp) adjusted to 2
mol/l of ammonium persulfate (hereinafter simply referred to as
"APS") and 0.7 wt % of sodium 2-anthraquinonesulfonate (produced by
Tokyo Kasei K.K.), and subsequently dipped in 1.2 mol/l of an
isopropyl alcohol (hereinafter simply referred to as "IPA")
solution (Solution 4, viscosity: 1.8 cp) having dissolved therein 5
g of 3,4-ethylenedioxythiophene.
[0168] The resulting substrate was removed and left standing in an
environment at 60.degree. C. for 10 minutes, thereby completing the
oxidative polymerization, and then the substrate was washed with
water. The polymerization reaction treatment and the washing
process each was repeated 10 times.
[0169] The substrate after the polymerization treatment was
compensated with hydrazine in a water/IPA and then carefully
extracted and the contents of sulfate ion and sodium
2-anthraquinonesulfonate ion in the electrically conducting polymer
composition were determined by an ion chromatography method. As a
result, the sulfate ion content was 1.5 mol % and the
2-anthraquinonesulfonate ion content was 14.0 mol %, per all
repeating structural units of the polymer in the electrically
conducting polymer composition. The increase in the weight of the
substrate due to attachment was 15% of the weight of the substrate
without any addition. The solid electrolyte layer had an electric
conductivity of 73 S/cm.
[0170] Thereafter, the aluminum foil substrate having deposited
thereon poly-3,4-ethylenedioxythiophene composition was treated in
an aqueous 10 wt % ammonium adipate solution and then examined on
the sparking voltage. The test was performed by increasing the
number of devices for the comparison purpose of the device
properties (the same in the following Examples). Namely, the test
was performed n=5 times in an environment of 50.degree. C. under
the condition of a current density being 10 mA/cm.sup.2. The
results obtained are shown in Table 1 below.
[0171] Subsequently, the aluminum core part of the substrate was
welded with a plus side lead for collecting the current from the
anode and also, connected to a minus side lead through carbon paste
and silver paste for collecting the current from the cathode. These
elements were finally sealed with epoxy resin to manufacture a
capacitor device. The thus-manufactured capacitor device was aged
at 125.degree. C. for 2 hours and then subjected to measurement of
initial properties. The results obtained are shown together in
Table 2 below.
[0172] In Table 1, C in the column of initial properties indicates
a capacitance and DF indicates a tangent of the loss angle (DF=tan
.delta..times.100%). These were each measured at 120 Hz. Z
(impedance) is shown by the value at a resonance frequency. LC
(leakage current) was measured one minute after application of a
rated voltage. The measured values each is an average of 30
samples. With respect to LC, those having an LC of 1 .mu.A or more
were determined as defective and those having an LC of 10 .mu.A or
more were determined as shorted products. The average LC is
calculated exclusive of the defective units.
EXAMPLE 2
[0173] A capacitor device was obtained through the same processing
as in Example 1 except that the dopant was changed to an aqueous
solution (viscosity: 2.7 cp) adjusted to 0.07 wt % of sodium
4-morpholinopropanesulfonate (produced by Tokyo Kasei K.K.) in
Example 1, and then evaluated in the same manner as in Example 1.
The results obtained are shown in Tables 1 and 2 below.
[0174] The contents of sulfate ion and 4-morpholinopropanesulfonate
ion in the polymer composition were determined by the method
described in Example 1. As a result, the sulfonate ion content was
1.2 mol % and the 4-morpholinopropanesulfonate ion content was 13.0
mol %. The solid electrolyte layer had an electric conductivity of
70 S/cm.
EXAMPLE 3
[0175] The surface of a dielectric material prepared by the method
described in Example 1 was dipped in an aqueous solution (Solution
1) adjusted to 20 wt % of APS, and then dipped in an IPA/water
mixed solution (Solution 2, viscosity: 1.9 cp) obtained by adding
tetrabutylammonium 4-morpholinopropanesulfonate (hereinafter simply
referred to as "MOPSTB") to 1.2 mol/l of IPA solution having
dissolved therein 5 g of 3,4-ethylenedioxythiophene and adjusted to
have a MOPSTB concentration of 0.1 wt %. At this time, the MOPSTB
salt used was obtained from sodium 4-morpholinopropanesulfonate
(produced by Tokyo Kasei K.K.) by mixing and reacting therewith
tetrabutylammonium bromide to recrystallize the salt. The resulting
substrate was removed and left standing in an environment at
60.degree. C. for 10 minutes, thereby completing the oxidative
polymerization, and then the substrate was washed with water. The
polymerization reaction treatment and the washing process were both
repeated 10 times. The capacitor device obtained was measured and
evaluated in the same manner as in Example 1. The results are shown
in Tables 1 and 2 below.
[0176] The contents of sulfate ion and 4-morpholinopropanesulfonate
ion in the polymer composition were determined by the same method
as in Example 1. As a result, the sulfonate ion content was 1.6 mol
% and the 4-morpholinopropanesulfonate ion content was 8.1 mol %.
The solid electrolyte layer had an electric conductivity of 56
S/cm.
EXAMPLE 4
[0177] An aluminum foil having formed thereon a dielectric material
prepared in the same manner as in Example 1 was dipped in 1.2 mol/l
of an IPA solution (Solution 4) having dissolved therein 5 g of
3,4-ethylenedioxythiophene, and then dipped in an IPA/water mixed
solution (Solution 3, viscosity: 2.1 cp) having an APS
concentration of 20 wt % and adjusted to have a sodium
2-anthraquinonesulfonate concentration of 0.06 mol/l. The resulting
substrate was removed and left standing in an environment at
60.degree. C. for 10 minutes, thereby completing the oxidative
polymerization, and then the substrate was washed with water.
[0178] The polymerization reaction treatment and the washing
process were both repeated 10 times. The capacitor device obtained
was evaluated in the same manner as in Example 1. The results are
shown in Tables 1 and 2 below.
[0179] The contents of sulfate ion and 2-anthraquinone-sulfonate
ion in the polymer composition were determined by the method
described in Example 1. As a result, the sulfonate ion content was
2.0 mol % and the 2-anthraquinonesulfonate ion content was 0.6 mol
%. The solid electrolyte layer had an electric conductivity of 80
S/cm.
COMPARATIVE EXAMPLE 1
[0180] A capacitor device was obtained in the same manner as in
Example 2 except that thiophene and a butanol solution of a
p-toluenesulfonate iron salt having a viscosity of 200 cp were used
in place of the 3,4-ethylenedioxythiophene and APS, respectively,
in Example 1, and then evaluated in the same manner as in Example
1. The results obtained are shown in Tables 1 and 2 below. The
solid electrolyte layer had an electric conductivity of 5 S/cm.
[0181] The content of p-toluenesulfonate ion in the polymer
composition was determined by the method described in Example 1 and
found to be 2.5 mol %. However, 8 mol % of iron ion was present and
the sulfate ion content was in excess of 10 mol %, therefore, the
percent defective of capacitors was high.
[0182] In the sparking voltage test of Examples 1 to 4, the voltage
was scarcely reduced and the sparking voltage at the completion of
reaction was 19V or more in any Example. However, in Comparative
Example 1 using p-toluenesulfonate iron salt, the sparking voltage
greatly decreased due to iron ion remaining in a large amount of 8
mol % and since decrease in the sparking voltage occurred before
the completion of prescribed reaction, insufficient filling of the
solid electrolyte disadvantageously resulted. TABLE-US-00002 TABLE
1 Sparking Voltage (unit: V, n = 5) Number of Reaction Times 1 2 3
4 5 6 8 10 Example 1 19 19 19 19 19 19 19 19 Example 2 19 19 19 19
19 19 19 19 Example 3 19 19 19 19 19 19 19 19 Example 4 19 19 19 19
19 19 19 19 Comparative 18 14 10 3 Example 1
[0183] TABLE-US-00003 TABLE 2 Initial Properties Number of
Defective/Number C DF Z LC of Sample, Short .mu.F % m.OMEGA. .mu.A
units/units Circuit Example 1 8.0 0.6 60 0.02 0/30 0 Example 2 8.2
0.7 60 0.02 0/30 0 Example 3 7.9 0.8 60 0.03 0/30 0 Example 4 7.8
0.8 60 0.03 0/30 0 Comparative 5.8 3.2 90 0.44 27/30 19 Example
1
EXAMPLE 5
[0184] A formed aluminum foil processed to have a prescribed area
was subjected to electrochemical formation at 13V in a 10 wt %
aqueous ammonium adipate solution to form a dielectric film on the
foil surface. The formed aluminum foil (substrate) was dipped in
1.2 mol/l of an isopropyl alcohol (hereinafter simply referred to
as "IPA") solution having dissolved therein 5 g of
3,4-ethylenedioxythiophene, and subsequently dipped in an aqueous
solution adjusted to contain 2 mol/l of ammonium persulfate
(hereinafter simply referred to as "APS") and 0.07 mol/l of sodium
2-anthraquinonesulfonate (produced by Tokyo Kasei K.K.).
[0185] This substrate was removed and left standing in an
environment at 40.degree. C. and a humidity of 40% for 10 minutes,
thereby completing the oxidative polymerization. This
polymerization reaction treatment process was repeated 25 times and
then the substrate was washed with water. The solid electrolyte
layer formed had an electric conductivity of 80 S/cm.
[0186] On the thus-obtained capacitor device having deposited
thereon poly-3,4-ethylenedioxythiophene composition, commonly known
carbon paste and silver paste were coated in this order. Four
sheets of the devices obtained were stacked, mounted on a lead
frame and welded to a cathode lead. Subsequently, the aluminum core
part of substrate was welded to an anode side lead for collecting
the current from the anode. These elements as a whole were finally
sealed with epoxy resin to produce a capacitor. The
thus-manufactured capacitor was aged at 125.degree. C. for 2 hours
while applying thereto a rated voltage and then the initial
properties were measured. The results obtained are shown together
in Table 3 below.
[0187] In Table 3, C in the column of initial properties indicates
capacitance and DF indicates tangent of loss angle (DF=tan
.delta..times.100%). These were each measured at 120 Hz. LC
(leakage current) and short circuit was tested by applying a rated
voltage (13 V) and measurement after one minute. The measured
values each is an average of 50 samples. With respect to LC, those
having an LC of 1 .mu.A or more were determined as defective and
those having an LC of 10 .mu.A or more were determined as short
circuit products. The average LC is calculated exclusive of the
short circuit products, if any.
EXAMPLE 6
[0188] A capacitor device was obtained through the same treatment
as in Example 5 except that the humidity in the polymerization
process in Example 5 was changed to 10%, and then evaluated in the
same manner as in Example 5. The solid electrolyte layer had an
electric conductivity of 70 S/cm. The results are shown in Table 3
below.
EXAMPLE 7
[0189] A capacitor device was obtained through the same treatment
as in Example 5 except that the humidity in the polymerization
process in Example 5 was changed to 60%, and then evaluated in the
same manner as in Example 5. The solid electrolyte layer had an
electric conductivity of 40 S/cm. The results are shown in Table 3
below.
EXAMPLE 8
[0190] A formed aluminum foil having formed thereon a dielectric
material was prepared in the same manner as in Example 5 and dipped
in an aqueous solution adjusted to contain 2 mol/l of ammonium
persulfate (hereinafter simply referred to as "APS") and 0.07 mol/l
of sodium 2-anthraquinonesulfonate (produced by Tokyo Kasei K.K.)
and then in 1.2 mol/l of an isopropyl alcohol (hereinafter simply
referred to as "IPA") solution having dissolved therein 5 g of
3,4-ethylenedioxythiophene.
[0191] The substrate was removed and left standing in an
environment at 40.degree. C. in an atmosphere at humidity of 40%
for 10 minutes, thereby completing the oxidative polymerization.
This polymerization treatment process was repeated 20 times, the
substrate obtained was washed with water and then dried. The
thus-obtained capacitor device was evaluated in the same manner as
in Example 5. The solid electrolyte layer had an electric
conductivity of 70 S/cm. The results are shown in Table 3
below.
EXAMPLE 9
[0192] A formed aluminum foil having formed thereon a dielectric
material was prepared in the same manner as in Example 5. The
surface of this dielectric material was dipped in 1.2 mol/l of an
IPA solution having dissolved therein 5 g of pyrrole and then in an
aqueous solution adjusted to contain 2 mol/l of APS and 0.07 mol/l
of sodium 2-anthraquinonesulfonate.
[0193] The substrate was removed and left standing in an
environment at 5.degree. C. in an atmosphere at humidity of 40% for
10 minutes, thereby completing the oxidative polymerization. After
repeating each dipping process 20 times, the substrate was washed
with water and dried. The thus-obtained capacitor device was
evaluated in the same manner as in Example 5. The solid electrolyte
layer had an electric conductivity of 65 S/cm. The results are
shown in Table 3 below.
COMPARATIVE EXAMPLE 2
[0194] A capacitor device was obtained in the same manner as in
Example 5 except that the polymerization humidity in Example 5 was
changed to 65%, and then evaluated in the same manner as in Example
5. The solid electrolyte layer had an electric conductivity of 18
S/cm. The results are shown in Table 3.
COMPARATIVE EXAMPLE 3
[0195] A capacitor device was obtained in the same manner as in
Example 5 except that the polymerization humidity in Example 5 was
changed to 5%, and then evaluated in the same manner as in Example
5. The solid electrolyte layer had an electric conductivity of 15
S/cm. The results are shown in Table 3 below. TABLE-US-00004 TABLE
3 Initial Properties Number Number of of C DF Defective/ Short
(.mu.F) (%) LC Number of Sample Circuit 120 Hz 120 Hz (.mu.A)
(units/units) (units) Example 5 50 0.6 0.2 0/50 0 Example 6 50 0.8
0.8 4/50 0 Example 7 50 0.7 0.4 1/50 0 Example 8 50 0.6 0.2 0/50 0
Example 9 50 0.6 0.2 0/50 0 Comparative 48 1.2 5.0 22/50 15 Example
2 Comparative 48 1.0 4.0 19/50 12 Example 3
EXAMPLE 10
[0196] An etched aluminum foil having a specified capacitance of
119 .mu.F/cm.sup.2 was cut into a size of 3 mm.times.10 mm and a
polyimide solution was coated in a width of 1 mm on both surfaces
to make a round and thereby divide the surface into a 4-mm portion
and a 5-mm portion in the long axis direction, and then dried to
form a masking. A 3 mm.times.4 mm portion of this formed aluminum
foil was electrochemically formed with an aqueous 10 wt % ammonium
adipate solution by applying a voltage of 13 V and thereby an oxide
dielectric film was formed on the cut end parts. The pore
distribution of this formed foil (preheated at 200.degree. C. for 2
hours) was measured using an automatic specific area measuring
apparatus (JEMINI 2375, manufactured by Shimadzu-Micromellitics)
and a sample degassing apparatus (Vacprep 061, manufactured by the
same company). As a result, the pore volume per unit mass was 1.83
cm.sup.3/g. Thereafter, this 3 mm.times.4 mm portion of the
aluminum foil was dipped in 1.2 mol/l of an isopropyl alcohol
(hereinafter simply referred to as "IPA") having dissolved therein
3,4-ethylenedioxy-thiophene (produced by Bayer AG) and then in 2
mol/l of an aqueous ammonium persulfate solution having suspended
therein sodium 2-anthraquinonesulfonate in a concentration of 0.07%
by weight. Subsequently, this aluminum foil was left standing in an
atmosphere at about 40.degree. C. for about 10 minutes to allow the
oxidation polymerization to proceed. After a desired electrically
conducting polymer is formed in the inside of micropores of the
etched aluminum foil, the pore volume per unit mass was again
measured in the same manner as above and found to be 1.04
cm.sup.3/g. From these values, the occupancy as a ratio of the
electrically conducting polymer occupying the space of a microfine
pore was calculated according to the following formula (II): Pore
.times. .times. .times. Occupancy = pore .times. .times. .times.
volume .times. .times. before .times. .times. formation .times.
.times. of .times. .times. electrically .times. .times. conducting
.times. .times. polymer - pore .times. .times. volume .times.
.times. after .times. .times. formation .times. .times. .times. of
.times. .times. electrically .times. .times. .times. conducting
.times. .times. .times. polymer .times. .times. pore .times.
.times. volume .times. .times. .times. before .times. .times.
formation .times. of .times. .times. electrically .times. .times.
conducting .times. .times. .times. polymer 100 .times. ( % ) ( II )
##EQU1## and found to be 43%. By repeating this sequence of dipping
and polymerization 25 times, a solid electrolyte layer comprising
the electrically conducting polymer was formed on the outer surface
of the etched aluminum foil. The finally produced
poly(3,4-ethylenedioxythiophene) was washed in warm water at
50.degree. C. and then dried at 100.degree. C. for 30 minutes to
form the solid electrolyte layer. At this time, the pore volume was
again measured and found to be 0.64 cm.sup.3/g and the occupancy in
pore was 65%. The error of the occupancy was found to be at most 5%
by separately observing the cross section.
[0197] Then, carbon paste and silver paste were applied to the
aluminum foil in the portion where the electrically conducting
polymer composition layer was formed. Four sheets of the
thus-prepared aluminum foils were stacked and a cathode lead was
connected thereto. To the portion where the electrically conducting
polymer was not formed, an anode lead was connected by welding. The
resulting device was sealed with an epoxy resin and aged at
125.degree. C. for 2 hours by applying thereto a rating voltage. In
this manner, 30 capacitors were completed.
[0198] The capacitance and the loss factor (DF=tan
.delta..times.100%) at 120 Hz as initial properties, the impedance
at a resonance frequency, and the leakage current of these
capacitors were measured. The leakage current was measured one
minute after the application of rated voltage. In Table 4 below,
respective averages of these measured values, the defective ratio
on the criterion that the device having a leakage current of 0.592
.mu.A (0.002 CV) or more is a defective unit, and the number of
short-circuited products are shown. The average of the leakage
current is the value calculated exclusive of the defective units.
The coverage was determined from the specified capacitance of the
etched aluminum foil and the capacitance after the formation of the
solid electrolyte according to the following formula (III):
Coverage = capacitance .times. .times. .times. after .times.
.times. .times. formation .times. .times. .times. of .times.
.times. solid .times. .times. .times. electrolyte specified .times.
.times. .times. capacitance .times. .times. .times. of .times.
etched .times. .times. aluminum .times. .times. foil .times.
.times. in .times. .times. the .times. .times. product 100 .times.
( % ) = 51.9 0.3 0.4 4 119 100 .times. ( % ) ( III ) ##EQU2## and
found to be 91%.
[0199] In Table 5, the results in the reflow soldering test and the
subsequent moisture resistance test are shown. In the moisture
resistance test, the device having a leakage current of 11.8 .mu.A
(0.04 CV) was evaluated as a defective unit. The reflow soldering
test was performed by passing the device through a temperature zone
of 230.degree. C. for 30 seconds and the moisture resistance test
was performed by allowing the device to stand under
high-temperature and high-humidity conditions of 85.degree. C. and
85% RH for 240 hours.
EXAMPLE 11
[0200] Thirty capacitors were fabricated in the same manner as in
Example 10 except for using ferric sulfate in place of ammonium
persulfate and using dihydroisothianaphthene in place of
3,4-ethylenedioxythiophene in Example 10. The properties of these
capacitor devices were evaluated in the same manner as in Example
10. The results obtained are shown in Tables 4 and 5 below.
EXAMPLE 12
[0201] Thirty capacitors were fabricated in the same manner as in
Example 10 except for using pyrrole in place of
3,4-ethylenedioxythiophene in Example 10. The properties of these
capacitor devices were evaluated in the same manner as in Example
10. The results obtained are shown in Tables 4 and 5 below.
EXAMPLE 13
[0202] Thirty capacitors were fabricated in the same manner as in
Example 10 except for using furan in place of
3,4-ethylenedioxythiophene in Example 10. The properties of these
capacitor devices were evaluated in the same manner as in Example
10. The results obtained are shown in Tables 4 and 5 below.
EXAMPLE 14
[0203] Thirty capacitors were fabricated in the same manner as in
Example 10 except for using aniline in place of
3,4-ethylenedioxythiophene in Example 10. The properties of
capacitor devices were evaluated in the same manner as in Example
10. The results obtained are shown in Tables 4 and 5 below.
COMPARATIVE EXAMPLE 4
[0204] Thirty capacitors were fabricated in the same manner as in
Example 10 except for forming the solid electrolyte such that the
electrically conducting polymer occupied 8% of the space in a
microfine pore in Example 10. The properties of these capacitor
devices were evaluated in the same manner as in Example 10. The
results obtained are shown in Tables 4 and 5 below.
COMPARATIVE EXAMPLE 5
[0205] Thirty capacitors were fabricated in the same manner as in
Example 10 except for forming the solid electrolyte such that the
electrically conducting polymer occupied 97% of the space in a
microfine pore in Example 10. The properties of these capacitor
devices were evaluated in the same manner as in Example 10. The
results obtained are shown in Tables 4 and 5 below.
COMPARATIVE EXAMPLE 6
[0206] Thirty capacitors were fabricated in the same manner as in
Example 10 except for forming the solid electrolyte by repeating
the polymerization 5 times to have a coverage of 55% on the
dielectric film in Example 10. The properties of these capacitor
devices were evaluated in the same manner as in Example 10. The
results obtained are shown in Tables 4 and 5 below. TABLE-US-00005
TABLE 4 Initial Properties Number of Capacitance Loss Factor
Impedance Leakage Defective Short-Circuited .mu.F % m.OMEGA.
Current .mu.A Ratio Products Example 10 51.9 6.03 0.008 0.03 0/30 0
Example 11 50.3 6.35 0.013 0.05 0/30 0 Example 12 50.9 6.24 0.012
0.06 0/30 0 Example 13 49.8 6.53 0.017 0.07 0/30 0 Example 14 49.6
6.78 0.019 0.09 0/30 0 Comparative 26.7 6.58 0.031 0.89 4/30 3
Example 4 Comparative 51.7 9.45 0.017 0.21 1/30 0 Example 5
Comparative 36.5 7.56 0.034 0.96 2/30 1 Example 6
[0207] TABLE-US-00006 TABLE 5 Reflow Soldering Test Moisture
Resistance Test Number of Number of Short- Short- Defective
circuited Leakage Defective Circuited Ratio Products Current Ratio
Products Example 10 0/30 0 0.49 0/30 0 Example 11 0/30 0 0.54 0/30
0 Example 12 0/30 0 0.59 0/30 0 Example 13 0/30 0 0.57 0/30 0
Example 14 0/30 0 0.61 0/30 0 Comparative 2/27 1 4.59 1/25 1
Example 4 Comparative 1/29 1 3.49 4/28 2 Example 5 Comparative 2/28
1 3.56 3/26 2 Example 6
INDUSTRIAL APPLICABILITY
[0208] As described in the foregoing, the solid electrolytic
capacitor of the present invention comprises a solid electrolyte
formed of an electrically conducting polymer polymerized from an
electrically conducting polymer composition improved in capacitor
property as a result of specifying the viscosity of an oxidizing
agent solution and/or a monomer solution, so that a compact,
low-impedance and high-performance solid electrolytic capacitor and
a production method thereof can be provided.
[0209] Furthermore, the solid electrolytic capacitor of the present
invention comprises a solid electrolyte formed using a specific
5-membered polyheterocyclic compound as a .pi. electron-conjugated
polymer in the above-described method, so that effects are provided
such that the voltage withstanding property (a sparking voltage
test), high frequency property, tan .delta., impedance property,
leakage current, heat resistance (reflow soldering property) and
the like are greatly improved.
[0210] In particular, in one embodiment by specifying the viscosity
of a solution containing a monomer of the above-described
electrically conducting polymer composition and/or an oxidizing
agent solution to less than 100 cp, a solid electrolytic capacitor
having capacitor properties of a higher degree can be provided.
[0211] In particular, in another embodiment the electroconducting
polymer layer comprising a monomer or a derivative thereof as a
repeating unit and also containing an anionic dopant is polymerized
employing a system using two solutions of a solution comprising an
oxidizing agent and a solution comprising a monomer by setting the
humidity in the atmosphere of polymerization process to from 10% to
less than 60%, whereby the monomer and the oxidizing agent can be
recovered and a solid electrolytic capacitor having capacitor
properties of higher degree can be provided in a high yield.
[0212] According to another embodiment, in a solid electrolytic
capacitor comprising an anode body having provided on the outer
surface thereof a solid electrolyte formed of an electrically
conducting polymer containing a lamellar structure, the solid
electrolyte is provided on a dielectric film formed on a valve
acting metal, to occupy from 10 to 95% of the space in pores of the
electrode, whereby the solid electrolytic capacitor obtained can
have improved adhesion of the solid electrolyte formed on the metal
oxide film and a capacitor favored with various basic properties
such as capacitance and dielectric loss (tan .delta.) and also with
excellent stability of reflow soldering heat resistance and
moisture resistance load characteristics can be provided.
[0213] Furthermore, according to the present invention, a valve
acting metal having formed thereon an oxide film is used as the
anode body for a solid electrolytic capacitor and a solid
electrolyte layer comprising an electrically conducting polymer is
formed thereon to cover the dielectric film in a predetermined
ratio (60%) or more, whereby a solid electrolytic capacitor device
favored with various basic properties such as capacitance and
dielectric loss (tan .delta.) and also with excellent stability of
reflow soldering heat resistance and moisture resistance load
characteristics can be provided.
[0214] While the invention has been described in detail and with
respect to specific embodiments, 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.
* * * * *