U.S. patent application number 12/933817 was filed with the patent office on 2011-01-27 for electrically conductive polymer suspension, electrically conductive polymer composition, solid electrolytic capacitor, and method for producing the same.
This patent application is currently assigned to NEC TOKIN CORPORATION. Invention is credited to Ryuta Kobayakawa, Tomoki Nobuta, Yasuhisa Sugawara, Satoshi Suzuki, Naoki Takahashi.
Application Number | 20110019340 12/933817 |
Document ID | / |
Family ID | 41199094 |
Filed Date | 2011-01-27 |
United States Patent
Application |
20110019340 |
Kind Code |
A1 |
Nobuta; Tomoki ; et
al. |
January 27, 2011 |
ELECTRICALLY CONDUCTIVE POLYMER SUSPENSION, ELECTRICALLY CONDUCTIVE
POLYMER COMPOSITION, SOLID ELECTROLYTIC CAPACITOR, AND METHOD FOR
PRODUCING THE SAME
Abstract
An electrically conductive polymer composition has high
electrical conductivity, excellent water resistance, high density,
and excellent smoothness. Also disclosed is a solid electrolyte
capacitor which is prevented from the reduction in electrical
conductivity, has low ESR, and also has excellent reliability.
Further disclosed is a method for producing the solid electrolyte
capacitor. The electrically conductive polymer composition is
produced by removing a dispersion medium from an electrically
conductive polymer suspension, wherein the electrically conductive
polymer suspension includes: an electrically conductive polymer
material including a dopant composed of a polyacid or a salt
thereof and an electrically conductive polymer; at least one
compound (A) selected from erythritol, xylitol and pentaerythritol;
and the dispersion medium.
Inventors: |
Nobuta; Tomoki; (Miyagi,
JP) ; Kobayakawa; Ryuta; (Miyagi, JP) ;
Takahashi; Naoki; (Miyagi, JP) ; Sugawara;
Yasuhisa; (Miyagi, JP) ; Suzuki; Satoshi;
(Miyagi, JP) |
Correspondence
Address: |
YOUNG & THOMPSON
209 Madison Street, Suite 500
Alexandria
VA
22314
US
|
Assignee: |
NEC TOKIN CORPORATION
Sendai-shi, Miyagi
JP
|
Family ID: |
41199094 |
Appl. No.: |
12/933817 |
Filed: |
April 10, 2009 |
PCT Filed: |
April 10, 2009 |
PCT NO: |
PCT/JP2009/057348 |
371 Date: |
September 21, 2010 |
Current U.S.
Class: |
361/525 ;
205/188; 252/500; 427/79 |
Current CPC
Class: |
C08K 2201/001 20130101;
H01B 1/127 20130101; C08G 2261/3223 20130101; C08K 5/06 20130101;
H01B 1/128 20130101; C08L 101/12 20130101; C08K 5/053 20130101;
H01G 9/15 20130101; H01G 9/0036 20130101; C08K 5/053 20130101; H01G
9/042 20130101; H01G 9/025 20130101; H01G 9/028 20130101; C08L
65/00 20130101; C08L 25/18 20130101 |
Class at
Publication: |
361/525 ;
252/500; 427/79; 205/188 |
International
Class: |
H01G 9/02 20060101
H01G009/02; H01B 1/12 20060101 H01B001/12; B05D 5/12 20060101
B05D005/12; C23C 28/00 20060101 C23C028/00 |
Foreign Application Data
Date |
Code |
Application Number |
Apr 16, 2008 |
JP |
2008-106369 |
Claims
1. An electrically conductive polymer suspension comprising: an
electrically conductive polymer material comprising a dopant
composed of a polyacid or a salt thereof and an electrically
conductive polymer; at least one compound (A) selected from
erythritol, xylitol and pentaerythritol; and a dispersion
medium.
2. The electrically conductive polymer suspension according to
claim 1, wherein the electrically conductive polymer material
comprises, as the dopant, a polysulfonic acid or a polycarboxylic
acid.
3. The electrically conductive polymer suspension according to
claim 2, wherein the electrically conductive polymer material
comprises, as the dopant, a polystyrene sulfonic acid or a
polyester sulfonic acid.
4. The electrically conductive polymer suspension according to
claim 1, wherein the electrically conductive polymer material
comprises, as the electrically conductive polymer, a polymer
obtained by polymerizing at least one monomer selected from a group
consisted of pyrrole, thiophene, aniline and derivatives
thereof.
5. An electrically conductive polymer composition obtained by
removing the dispersion medium from the electrically conductive
polymer suspension according to claim 1.
6. The electrically conductive polymer composition according to
claim 5, wherein removing the dispersion medium is carried out at
the melting temperature of the compound (A) or higher.
7. A solid electrolytic capacitor comprising a solid electrolyte
layer comprising the electrically conductive polymer composition
according to claim 5.
8. The solid electrolytic capacitor according to claim 7, further
comprising an anode body made of a valve action metal, and a
dielectric layer formed on the surface of the anode body, wherein
the solid electrolyte layer is formed on the dielectric layer.
9. The solid electrolytic capacitor according to claim 7, wherein
the valve action metal is at least one selected from aluminum,
tantalum or niobium.
10. A method for producing a solid electrolytic capacitor,
comprising: forming a dielectric layer on a surface of an anode
body made of a valve action metal; and forming a first electrically
conductive polymer layer by application or impregnation of the
electrically conductive polymer suspension according to claim 1
onto the dielectric layer, and by removing the dispersion medium
from the electrically conductive polymer suspension.
11. The method for producing a solid electrolytic capacitor
according to claim 10, further comprising, before forming the first
electrically conductive polymer layer, forming a second
electrically conductive polymer layer on the dielectric layer by a
chemical oxidation polymerization or an electrolysis
polymerization.
12. The method for producing a solid electrolytic capacitor
according to claim 10, wherein in forming the first electrically
conductive polymer layer, removing the dispersion medium is carried
out at the melting temperature of the compound (A) or higher.
13. The method for producing a solid electrolytic capacitor
according to claim 12, wherein the temperature at which the
dispersion medium is removed is 150.degree. C. or higher and lower
than 270.degree. C.
14. The method for producing a solid electrolytic capacitor
according to claim 10, wherein an oxidation film covering the valve
action metal is formed as the dielectric layer.
15. The method for producing a solid electrolytic capacitor
according to claim 10, wherein the valve action metal is at least
one selected from aluminum, tantalum or niobium.
16. The electrically conductive polymer suspension according to
claim 2, wherein the electrically conductive polymer material
comprises, as the electrically conductive polymer, a polymer
obtained by polymerizing at least one monomer selected from a group
consisted of pyrrole, thiophene, aniline and derivatives
thereof.
17. The electrically conductive polymer suspension according to
claim 3, wherein the electrically conductive polymer material
comprises, as the electrically conductive polymer, a polymer
obtained by polymerizing at least one monomer selected from a group
consisted of pyrrole, thiophene, aniline and derivatives
thereof.
18. An electrically conductive polymer composition obtained by
removing the dispersion medium from the electrically conductive
polymer suspension according to claim 2.
19. An electrically conductive polymer composition obtained by
removing the dispersion medium from the electrically conductive
polymer suspension according to claim 3.
20. An electrically conductive polymer composition obtained by
removing the dispersion medium from the electrically conductive
polymer suspension according to claim 4.
Description
TECHNICAL FIELD
[0001] The present invention relates to an electrically conductive
polymer suspension, an electrically conductive polymer composition,
a solid electrolytic capacitor, and a method for producing the
same, more particularly, to an electrically conductive polymer
suspension having excellent dispersibility, an electrically
conductive polymer composition having high electrical conductivity
and excellent water-resistance, a solid electrolytic capacitor
having low equivalent series resistance and excellent reliability,
and a method for producing the same.
BACKGROUND ART
[0002] A solid electrolytic capacitor has been developed in which a
porous body made of valve-action metal such as tantalum or aluminum
is subjected to anodizing process so that a dielectric oxidation
film is formed on the porous body and, then, a electrically
conductive polymer layer is formed on the dielectric oxidation
film, and the electrically conductive polymer layer is employed as
the solid electrolyte of the capacitor.
[0003] A method of forming the electrically conductive polymer
layer which serves as the solid electrolyte of the capacitor is
mainly classified into chemical oxidation polymerization or
electrolysis polymerization. The monomers of which the electrically
conductive polymer material is composed are known to include
pyrrole, thiophene, 3,4-ethylenedioxythiophene, and aniline.
[0004] Such solid electrolytic capacitors have lower ESR
(Equivalent Series Resistance) than a conventional capacitor
employing manganese dioxide as the solid electrolyte and, thus,
begins to be utilized in various purposes. Recently, as integrated
circuits tend to operate at high frequency and large current, a
solid electrolytic capacitor has been in demand which has lower ESR
and large capacitance and small loss.
[0005] As the technique related to such solid electrolytic
capacitors, Patent document 1 discloses the improved process for
producing the solid electrolytic capacitor with low ESR in which a
high-density polymer outer layer with good covering of the edges
can be simply achieved and reliably reproduced, comprising the
steps of: applying a dispersion a) comprising particles b) of an
electrically conductive polymer which comprises polyaniline and/or
polythiophene onto a capacitor body which comprises a porous
electrode body made of electrode material, a dielectric covering
the surface of the electrode material, and a solid electrolyte
comprising a electrically conductive material on the dielectric
surface; and at least partly removing a dispersing agent d) and/or
curing a binder c) in order to form an electrically conductive
polymeric outer layer; wherein the particles b) of the electrically
conductive polymer in the dispersion a) have an average diameter of
70 to 500 nm.
[0006] It is preferable that the dispersion a) further comprises a
compound including an ether, lactone, amide or lactam group; a
sulfone; a sulfoxide; a sugar; a sugar derivative; a sugar alcohol;
a furan derivative; and/or a di- or poly-alcohol in order to
increase the conductivity.
DOCUMENT(S) OF PRIOR ART
Patent Document
[0007] Patent Document 1: Japanese Patent Application Laid-Open No.
2006-295184.
SUMMARY OF THE INVENTION
Problem to be Solved by the Invention
[0008] However, in case that a sugar alcohol in which the number of
OH group of sorbitol and mannitol are relatively rich are contained
as the additive in the polymer solution, there occur their
precipitations in the drying of a film-formation process. The
resultant electrically conductive polymer film has low density, low
conductivity, and bad state of surface smoothness (whether or not
there are residual bubbles, whether or not there are
precipitations). In the capacitor with the film in this state,
there is large resistance at the interface between the film and a
graphite layer or an inner polymeric layer, and there is a problem
that ESR becomes higher. Further, because of the bad state of the
surface smoothness, sealing performance is bad and, hence, ESR
deterioration comes into being accelerated in long-term stability
tests such as a moisture-resistance or a heat-resistance.
[0009] As mentioned above, although the solid electrolytic
capacitor employing the electrically conductive polymer as the
solid electrolyte has been studied in various aspects, current
situation has still been that both of the low ESR and the good
long-term stability are not yet sufficiently accomplished at the
same time.
[0010] Purposes for the present invention is to provide an
electrically conductive polymer composition having high electrical
conductivity, excellent water-resistance, high density and
excellent smoothness; to provide a solid electrolytic capacitor
avoiding reduction of the conductivity and having low ESR and
excellent reliability, and a method for producing the same, and
further to provide a method of conveniently producing a solid
electrolytic capacitor using substituted compound being easy to
handle and being safe additive.
Means for Solving the Problem
[0011] An electrically conductive polymer suspension according to
the present invention is characterized in that the suspension
comprises an electrically conductive polymer material comprising
dopant composed of a polyacid or a salt thereof and an electrically
conductive polymer; at least one compound (A) selected from
erythritol, xylitol and pentaerythritol; and a dispersion
medium.
[0012] It is preferable that the electrically conductive polymer
material comprises, as the dopant, a polysulfonic acid or a
polycarboxylic acid. It is more preferable that the electrically
conductive polymer material comprises, as the dopant, a polystyrene
sulfonic acid or a polyester sulfonic acid. It is preferable that
the electrically conductive polymer material comprises, as the
electrically conductive polymer, a polymer obtained by polymerizing
at least one monomer selected from a group consisted of pyrrole,
thiophene, aniline and derivatives thereof.
[0013] An electrically conductive polymer composition according to
the present invention is characterized in that the composition is
obtained by removing the dispersion medium from the electrically
conductive polymer suspension. It is preferable that removing the
dispersion medium is carried out at the melting temperature of the
compound (A) or higher.
[0014] A solid electrolytic capacitor according to the present
invention is characterized in that the capacitor comprises a solid
electrolyte layer comprising the electrically conductive polymer
composition. It is preferable that the solid electrolytic capacitor
further comprises an anode body made of a valve action metal; and a
dielectric layer formed on the surface of the anode body, wherein
the solid electrolyte layer is formed on the dielectric layer. It
is preferable that the valve action metal is at least one selected
from aluminum, tantalum or niobium.
[0015] A method for producing a solid electrolytic capacitor
according to the present invention is characterized in that the
method comprises forming a dielectric layer on a surface of an
anode body made of a valve action metal; and forming a first
electrically conductive polymer layer by application or
impregnation of the electrically conductive polymer suspension onto
the dielectric layer, and by removing the dispersion medium from
the electrically conductive polymer suspension. It is preferable
that the method further comprises, before forming the first
electrically conductive polymer layer, forming a second
electrically conductive polymer layer on the dielectric layer by a
chemical oxidation polymerization or an electrolysis
polymerization. It is preferable that in forming the first
electrically conductive polymer layer, removing the dispersion
medium is carried out at the melting temperature of the compound
(A) or higher. It is preferable that temperature at which the
dispersion medium is removed is equal to 150.degree. C. or higher
and lower than 270.degree. C. It is preferable that an oxidation
film covering the valve action metal is formed as the dielectric
layer. It is preferable that the valve action metal is at least one
selected from aluminum, tantalum or niobium.
EFFECT OF THE INVENTION
[0016] According to the present invention, in that at least one
compound (A) selected from erythritol, xylitol and pentaerythritol
is contained in the electrically conductive polymer layer, the
electrically conductive polymer composition having high density,
high electrical conductivity and good moisture-resistance can be
obtained. Moreover, the solid electrolytic capacitor having low ESR
and excellent reliability and the method for producing the same can
be provided. Further, a method of conveniently producing the solid
electrolytic capacitor using a material to be easy to handle can be
provided.
BRIEF DESCRIPTION OF THE DRAWINGS
[0017] FIG. 1 shows a schematic view illustrating an inner
structure of a solid electrolytic capacitor according to the
present invention.
MODE(S) FOR CARRYING OUT THE INVENTION
[0018] An electrically conductive polymer suspension according to
the present invention is characterized in that the suspension
comprises an electrically conductive polymer material comprising
dopant composed of a polyacid or a salt thereof and an electrically
conductive polymer; at least one compound (A) selected from
erythritol, xylitol and pentaerythritol; and a dispersion
medium.
[0019] A polyacid or salt thereof can be used as the dopant.
Specific examples of polyacid may include, but is not limited to,
polysulfonic acids such as polyvinyl sulfonic acids, polystyrene
sulfonic acids and poly(2-acrylicamide-2-methylpropane sulfonic
acid), and polycarboxylic acids such as polyacrylic acids,
polymethacrylic acids and polymaleic acids. Among them, polystyrene
sulfonic acids and polyester sulfonic acids are more preferable.
The polyacid or salt thereof may be used alone or in combinations
of two or more thereof. Weight-average molecular weight of the
polyacid or salt thereof is not limited.
[0020] As an electrically conductive polymer, a polymer obtained by
polymerizing at least one monomer selected from a group consisted
of pyrrole, thiophene, aniline and derivatives thereof can be used.
Derivatives of thiophene may include 3,4-ethylenedioxythiophene. As
an electrically conductive polymer, 3,4-ethylenedioxythiophene is
preferably used. The electrically conductive polymer may be used
alone or in combinations of two or more thereof.
[0021] As a dispersion medium, it is preferable to choose a
dispersion medium which has good compatibility with a monomer of
which the electrically conductive polymer is composed, and any one
of water, organic solvent and water-miscible organic solvent may be
used. Specific examples of the organic solvent may include, but is
not limited to, alcohol-based solvents such as methanol, ethanol
and propanol; aromatic hydrocarbon-based solvents such as benzene,
toluene and xylene; and aliphatic hydrocarbon-based solvents such
as hexane. The organic solvent may be used alone or in combinations
of two or more thereof. Among them, water is preferable.
[0022] The density of the electrically conductive polymer in the
electrically conductive polymer suspension may preferably be in a
range of 0.1 to 20 weight % and, more preferably be in a range of
0.5 to 10 weight %. In order to obtain the electrically conductive
polymer with high conductivity, it is preferable to use 20 to 3000
weight of the dopant, more preferable to use 30 to 1000 weight of
the dopant, in relation to 100 weight of the electrically
conductive polymer.
[0023] The electrically conductive polymer suspension according to
the present invention comprises at least one compound (A) selected
from erythritol, xylitol and pentaerythritol. The compound (A)
provides good dispersion ability for the electrically conductive
polymer suspension and, hence, provides high density, high
conductivity and good moisture-resistance for the electrically
conductive polymer composition. In particular, pentaerythritol can
exhibit the above-mentioned function even when the suspension
contains small amount of pentaerythritol, and, hence,
pentaerythritol is suitably used.
[0024] The dispersion ability in the electrically conductive
polymer suspension before/after adding the compound (A) may be
evaluated by a particle size distribution measurement method and,
also, may be evaluated by a centrifugal sedimentation method, a
light transmission method, a laser diffraction method, a dynamic
light scattering method, or supersonic wave method as well.
[0025] It is preferable that the compound which is added into the
electrically conductive polymer suspension is in form of solid
powder. In addition, it is preferable that the compound can be
dissolved into the dispersion medium of the electrically conductive
polymer suspension and the melting temperature of the compound is
equal to or higher than the boiling point of the dispersion medium.
For example, in case that the suspension contains water as the
dispersion medium, it is preferable that the compound to be added
has a melting temperature equal to or higher than 100.degree. C.
Here, the melting temperature of the compound may be measured by
TG/DTA (differential thermal analysis) or DSC (differential
scanning calorimetric analysis).
[0026] The content of the compound (A) is not limited and only
mixing the compound (A) may be effective. Mixing the compound (A)
with molar amount equal to or more than that of polyacid component
is preferable because particle dispersion ability in the
electrically conductive polymer suspension becomes excellent and,
hence, the electrically conductive polymer composition with high
density or high conductivity may be obtained. An upper limit of the
content of the compound (A) is not limited as long as the compound
(A) is able to be dissolved into the electrically conductive
polymer suspension.
[0027] Erythritol is preferable in that crystallinity of erythritol
is higher than, for example, that of polyhydric alcohol such as
sorbitol and maltose and, hence, erythritol has good
moisture-resistance and is easy to handle.
[0028] Erythritol and xylitol are also preferable in that they are
known to be additives for food, e.g. a sweetener, and, hence, they
have excellent safety and stability and impose low load onto the
environment. Moreover, they are desirable in that their solubility
levels into water are several times larger than those of
non-aqueous solvents such as ethylene glycol and glycerin and,
hence, freedom degrees to design added amounts thereof are higher
than those of the non-aqueous solvents.
[0029] Pentaerythritol is characterized in that when it is heated,
it sublimates slowly, and in that by heating it at a temperature
equal to or higher than the melting point, it comes into be
dehydrated and polymerized. By this, quality of the polymer film
changes and film density and strength may improve, thereby the
polymer film with excellent reliability may be obtained. Such
reaction characteristics result from its chemical structure, and it
is hard for such reaction characteristics to occur, for example,
with chemical structures of erythritol and sorbitol.
[0030] The electrically conductive polymer composition according to
the present invention is characterized in that it is obtained by
removing the dispersion medium from the above-mentioned
electrically conductive polymer suspension. The temperature, at
which the dispersion medium is removed, is not limited as long as
the temperature is equal to or more than a boiling point thereof,
but it is preferable that the temperature is equal to or more than
a melting temperature of the compound (A) because the resultant
electrically conductive polymer composition has high density and
high moisture-resistance. It is understood that this effect results
from generation of ester as mentioned above.
[0031] To be specific, the temperature, at which the dispersion
medium is removed, is preferably equal to or higher than
150.degree. C. and more preferably equal to 180.degree. C. or
higher than 180.degree. C. and less than 270.degree. C. The drying
time needs to be appropriately optimized according to drying
temperature but, is not limited as long as deterioration of the
electrically conductive polymer due to heating for the duration
does not occur.
[0032] The present invention is directed to a solid electrolytic
capacitor comprising a solid electrolyte layer comprising the
above-mentioned electrically conductive polymer composition.
Specifically, the solid electrolytic capacitor further comprises an
anode body made of a valve action metal, and a dielectric layer
formed on the surface of the anode body, wherein the solid
electrolyte layer is formed on the dielectric layer.
[0033] The solid electrolytic capacitor according to the present
invention can be produced by forming a dielectric layer on a
surface of an anode body made of the valve action metal; and
forming a first electrically conductive polymer layer by
application or impregnation of the above-mentioned electrically
conductive polymer suspension onto the dielectric layer, and by
removing the dispersion medium from the electrically conductive
polymer suspension.
[0034] In the following, configuration of the solid electrolytic
capacitor according to the present invention and method for
producing the same will be explained. FIG. 1 shows a schematic view
illustrating an inner structure of a solid electrolytic capacitor
according to the present invention.
[0035] In the solid electrolytic capacitor (also called as
capacitor element) of FIG. 1, dielectric layer 2, solid electrolyte
layer 3 and cathode layer 4 in this order are formed on anode body
1.
[0036] Anode body 1 is made of a plate, a foil or a line of the
valve action metal; a sintered body made of valve-action metal
particles; or a porous body of metal which has been subjected to a
surface-enlargement treatment by etching. Specific examples of the
valve action metal may include, but is not limited to, tantalum,
aluminum, titanium, niobium, zirconium or alloys thereof, and it is
preferable that the valve action metal is at least one selected
from tantalum, aluminum or niobium.
[0037] Dielectric layer 2 is, for example, an oxidation film
obtained by electrolysis oxidizing of the surface of anode body 1,
and is also formed in porous portions of the sintered body or the
porous body. The thickness of the oxidation film can be
appropriately adjusted based on the voltage in the electrolysis
oxidizing.
[0038] Solid electrolyte layer 3 may include at least an
electrically conductive polymer layer but, in the present
invention, may include at least first electrically conductive
polymer layer 3B containing the above-mentioned electrically
conductive polymer composition. The electrically conductive polymer
layer may include the polymer obtained by polymerizing at least one
monomer selected from a group consisted of pyrrole, thiophene,
aniline and derivatives thereof. In particular, pyrrole, thiophene,
or derivatives thereof is preferably used, and pyrrole, thiophene
or 3,4-ethylenedioxythiophene is more preferably used.
[0039] Solid electrolyte layer 3 may include an oxide derivative
such as manganese dioxide or ruthenium oxide; or an organic
semiconductor such as TCNQ (7,7,8,8-tetracyanoquionodimethane
complex salt).
[0040] The first electrically conductive polymer layer 3B is formed
by, after forming dielectric layer 2 on the surface of anode body 1
made of the valve action metal, application or impregnation of the
above-mentioned electrically conductive polymer suspension onto the
dielectric layer, and by removing the dispersion medium from the
electrically conductive polymer suspension. Moreover, before
forming the first electrically conductive polymer layer 3B, second
electrically conductive polymer layer 3A may be formed on
dielectric layer 2 by a chemical oxidation polymerization or an
electrolysis polymerization. The monomer which is used in forming
the second electrically conductive polymer layer 3A may be the same
as that used in forming the above-mentioned electrically conductive
polymer suspension. A metal salt or a sulfate may be used as an
oxidizing agent.
[0041] As the method for applying the electrically conductive
polymer suspension onto the dielectric layer, it is preferable that
the applied suspension is left for several minutes to several of
ten minutes after the application so that the suspension can be
sufficiently filled into the porous portions of the porous body. As
the method for impregnating the dielectric layer with the
suspension, it is preferable that immersing the dielectric layer
into the suspension is repeated. A pressurizing method or a
depressurizing method is also preferable.
[0042] The temperature at which the dispersion medium is removed is
not limited as long as the dispersion medium can be removed at the
temperature, but the removal is preferably carried out at the
temperature equal to or more than the melting temperature of the
compound (A), more preferably carried out at the temperature lower
than 270.degree. C. in order to avoid the deterioration of the
element due to the heat.
[0043] It is preferable that the first electrically conductive
polymer layer 3B and the second electrically conductive polymer
layer 3A closely formed on the surface of dielectric layer 2 have
the same back-bone structure as that of the electrically conductive
polymer.
[0044] The dopant used in forming the second electrically
conductive polymer layer 3A may preferably be a sulfonic acid
based-compound such as naphthalene sulfonic acid, benzene sulfonic
acid, phenol sulfonic acid, styrene sulfonic acid, camphor sulfonic
acid or a derivative thereof. Further, with regard to the molecular
weight of the dopant, the dopant is appropriately selected from low
molecular weight compounds to high molecular weight compounds.
[0045] Cathode layer 4 is not limited as long as it is electrically
conductive, and may have two layered structure including graphite
layer 5 made of graphite and silver/electrically conductive resin
layer 6.
[0046] (Operation)
[0047] By mixing at least one compound (A) selected from
erythritol, xylitol and pentaerythritol into the electrically
conductive polymer suspension comprising the dopant composed of
polyacid or salt thereof, excessive dopants (resistance
components), which exist on outer surfaces of the electrically
conductive polymer particles dispersed in the suspension and which
do not function as the dopant, are isolated, and thereby the
resistances between the electrically conductive polymer particles
may decrease and density of the electrically conductive polymer may
increase. Therefore, the polymer film with high density can be
obtained and, as a result, high conductivity is accomplished.
Further, there are not bubbles in the electrically conductive
polymer film and, therefore, the film has a smooth surface.
Additionally, the electrically conductive polymer film with good
moisture-resistance can be produced.
[0048] Specifically, since the compound (A) has a hydroxyl group at
the terminal end, the compound functions so as to dissociate, for
example, a sulfonic acid compound as the above-mentioned dopant
into ion pairs, and, consequently, the conductivity of the
electrically conductive polymer film may increase, and the
dispersion ability of the particles in the suspension may improve
with the electric charge repulsions between the particle surfaces
by the ion pairs.
[0049] In addition, it is thought that by removing the dispersion
medium, there occurs dehydration condensation between sulfonic acid
group or carboxylic acid group derived from polyacid and the
hydroxyl group and, hence, the ester is generated, so that the
sulfonic acid or the carboxylic acid reduces, thereby changing
hydrophilic property to hydrophobic property.
[0050] By these operations, in the solid electrolytic capacitor
according to the present invention, the first electrically
conductive polymer layer with high density is formed and, at the
same time, it penetrates into more internal regions of the porous
body being the anode body, so that the contact region between the
dielectric layer or the second electrically conductive polymer
layer and the first electrically conductive polymer layer in the
external region (surface region) may increase, and adhesion ability
of the first electrically conductive polymer layer in the inner
porous portion/the external portion may improve due to anchoring
effect, whereby realizing an electrically conductive path
sufficiently.
[0051] Additionally, since it has the electrically conductive
polymer film with high density and low moisture adsorption,
interfacial peeling due to thermal stress or moisture adsorption is
prevented.
[0052] Accordingly, since interfacial peeling due to thermal stress
or moisture adsorption is prevented without decreasing the
conductivity of the electrically conductive polymer layer, the
capacitor with low ESR and improved reliability is realized.
[0053] (Comparison with Prior Art)
[0054] When comparing the present invention with the technology
disclosed in Patent document 1, configurations of the electrically
conductive polymer layers are different between them. Specifically,
Patent document 1 exemplifies many kinds of materials as one for
increasing the conductivity and uses among them only dimethyl
sulfoxide in Examples. However, dimethyl sulfoxide is completely
different from erythritol, xylitol or pentaerythritol used in the
present invention in a back-bone structure and material
characteristics. Moreover, Patent document 1 never explicitly
discloses the operation that these compounds increase the
conductivity.
[0055] Any one of erythritol, xylitol and pentaerythritol used in
the present invention is not disclosed in Patent document 1. Among
them, pentaerythritol is the material which is realized by focusing
the reactivity of polycondensation from the characteristic of the
chemical structure.
[0056] That is, it is apparent that Patent document 1 adds the
material into the suspension with the focus and intended operation
which are different from those in the present invention in which
the material containing the hydroxyl group is used. Therefore, it
is obvious that Patent document 1 never teaches the present
invention and that the present invention can not be easily
realized.
EXAMPLES
[0057] Now, the present invention will be described in details with
reference to Examples, but the present invention is not limited to
the Examples.
[0058] In addition, erythritol, xylitol and pentaerythritol used in
the examples are commercially available.
Example 1
[0059] Example 1 will be explained referring to FIG. 1. A porous
body aluminum foil which has 3.times.4 mm size and which has been
subjected to a surface enlargement treatment by etching was used as
anode body 1, and, then, an oxidation film as dielectric layer 2
was formed on the surface of the foil using an electrolysis
oxidizing method. After that, the resultant structure was
repeatedly immersed into a bath containing a monomer solution and a
bath containing a dopant and an oxidizing agent solution.
Subsequently, second electrically conductive polymer layer 3A made
of poly(3,4-ethylenedioxythiophene) was formed in internal porous
portions of the porous body by a chemical polymerization
method.
[0060] Thereafter, 1 g of 3,4-ethylenedioxythiophene was poured
into a mixture solution of 100 g of pure water and 2 g of
polystyrene sulfonic acid (M.w.: 50,000) and the resultant mixture
was stirred at normal temperature for five minutes. Next, 40 wt %
persulfuric acid ammonium water solution was poured by 1 ml/min so
that the total poured amount thereof comes to 5 g, and, then, the
resultant mixture was stirred (with 1,000 rpm) for 50 hours at
normal temperature so that oxidation polymerization thereof
occurred. In this way, obtained was a polymer suspension containing
approximately 3 wt % of the electrically conductive polymer
material component composed of poly(3,4-ethylenedioxythiophene) and
polystyrene sulfonic acid. At this time, the color of the
suspension changed as follows: light yellow.fwdarw.light
gray.fwdarw.gray.fwdarw.dark green.fwdarw.light deep
blue.fwdarw.dark deep blue. After collecting 10 g of the suspension
with dark deep blue, 0.5 g of erythritol was mixed thereto, and,
then, the mixture was stirred for 30 minutes to be dissolved, and,
as a result, the electrically conductive polymer suspension was
obtained.
[0061] The particle size distribution of the electrically
conductive polymer suspension was measured using a laser
diffraction method. As the result of the measurement, D50 value was
0.92 Here, D50 was a particle diameter when the accumulation mass
became 50% in an accumulation particle size curve.
[0062] 5 .mu.l of this electrically conductive polymer suspension
was dropped onto second electrically conductive polymer layer 3A
and was left for 10 minutes at normal temperature. Next,
preliminary drying was performed for 10 minutes at 120.degree. C.
and, subsequently, main drying was performed for 30 minutes at
180.degree. C., thereby forming first electrically conductive
polymer layer 3B.
[0063] Visual appearance of the first electrically conductive
polymer layer 3B was checked by human eyes and film density thereof
also was measured. In checking the visual appearance of the first
electrically conductive polymer layer 3B, precipitations were not
visible after the preliminary drying, and the film was smooth after
the main drying. The film density of the first electrically
conductive polymer layer 3B was 0.5 .mu.m/mlcm.sup.2.
[0064] Regarding calculating the film density, a thickness of the
film obtained after dropping 5 .mu.l of the suspension onto the
aluminum porous body foil which has 3.times.4 mm size and after
performing the main drying was measured, and the measured film
thickness was converted into the film thickness per 1 ml and 1
cm.sup.2.
[0065] Further, graphite layer 5 was formed on first electrically
conductive polymer layer 3B and silver/electrically conductive
resin layer 6 was formed on layer 5, so that the capacitor device
was fabricated. After measuring initial ESR of the capacitor device
at 100 kHz, ESR change ratio (times) (=(ESR after test, 100
kHz)/(initial ESR, 100 kHz)) was calculated as a heat-resistance
property and a moisture-resistance property. Here, the condition
for the heat-resistance test was that the device was left with no
load under the atmosphere at 125.degree. C. for 500 hours, while
the condition for the moisture-resistance test was that the device
was left with no load under 95% R.H. atmosphere at 65.degree. C.
for 500 hours.
[0066] The number of the capacitors to be tested is 10 in each case
and the average values of measurement results are shown in Table
1.
[0067] As shown in Table 1, the initial ESR of the capacitor device
at 100 kHz was 5.2 m.OMEGA. while the ESR change ratio after the
heat-resistance test was 1.5 times and the ESR change ratio after
the moisture-resistance test was 1.4 times.
Example 2
[0068] Example 2 was carried out in the same way as in Example 1
except that the electrically conductive polymer suspension was made
with mixing 0.03 g of erythritol. The results thereof are shown in
Table 1.
[0069] As shown in Table 1, the D50 value in the particle size
distribution of the electrically conductive polymer suspension was
1.31 .mu.m. In checking the visual appearance of the first
electrically conductive polymer layer 3B, precipitations were not
visible after the preliminary drying, and the film was smooth after
the main drying. The film density of the first electrically
conductive polymer layer 3B was 0.53 .mu.m/mlcm.sup.2. The initial
ESR of the capacitor device at 100 kHz was 5.6 m.OMEGA. while the
ESR change ratio after the heat-resistance test was 1.6 times and
the ESR change ratio after the moisture-resistance test was 1.5
times.
Example 3
[0070] Example 3 was carried out in the same way as in Example 1
except that the electrically conductive polymer suspension was made
with mixing 2 g of erythritol. The results thereof are shown in
Table 1.
[0071] As shown in Table 1, the D50 value in the particle size
distribution of the electrically conductive polymer suspension was
1.89 .mu.m. In checking the visual appearance of the first
electrically conductive polymer layer 3B, precipitations were not
visible after the preliminary drying, and the film was smooth after
the main drying. The film density of the first electrically
conductive polymer layer 3B was 0.51 .mu.m/mlcm.sup.2. The initial
ESR of the capacitor device at 100 kHz was 5.5 m.OMEGA. while the
ESR change ratio after the heat-resistance test was 1.5 times and
the ESR change ratio after the moisture-resistance test was 1.4
times.
Example 4
[0072] Example 4 was carried out in the same way as in Example 1
except that the electrically conductive polymer suspension was made
with mixing 0.5 g of xylitol instead of 0.5 g of erythritol. The
results thereof are shown in Table 1.
[0073] As shown in Table 1, the D50 value in the particle size
distribution of the electrically conductive polymer suspension was
0.79 .mu.m. In checking the visual appearance of the first
electrically conductive polymer layer 3B, precipitations were not
visible after the preliminary drying, and the film was smooth after
the main drying. The film density of the first electrically
conductive polymer layer 3B was 0.51 .mu.m/mlcm.sup.2. The initial
ESR of the capacitor device at 100 kHz was 4.8 m.OMEGA. while the
ESR change ratio after the heat-resistance test was 1.4 times and
the ESR change ratio after the moisture-resistance test was 1.4
times.
Example 5
[0074] Example 5 was carried out in the same way as in Example 1
except that the electrically conductive polymer suspension was made
with mixing 0.03 g of xylitol instead of 0.5 g of erythritol. The
results thereof are shown in Table 1.
[0075] As shown in Table 1, the D50 value in the particle size
distribution of the electrically conductive polymer suspension was
0.89 .mu.m. In checking the visual appearance of the first
electrically conductive polymer layer 3B, precipitations were not
visible after the preliminary drying, and the film was smooth after
the main drying. The film density of the first electrically
conductive polymer layer 3B was 0.56 .mu.m/mlcm.sup.2. The initial
ESR of the capacitor device at 100 kHz was 5.2 m.OMEGA. while the
ESR change ratio after the heat-resistance test was 1.5 times and
the ESR change ratio after the moisture-resistance test was 1.5
times.
Example 6
[0076] Example 6 was carried out in the same way as in Example 1
except that the electrically conductive polymer suspension was made
with mixing 0.5 g of pentaerythritol instead of 0.5 g of
erythritol. The results thereof are shown in Table 1.
[0077] As shown in Table 1, the D50 value in the particle size
distribution of the electrically conductive polymer suspension was
0.90 .mu.m. In checking the visual appearance of the first
electrically conductive polymer layer 3B, the film was smooth after
the main drying. The film density of the first electrically
conductive polymer layer 3B was 0.48 .mu.m/mlcm.sup.2.
[0078] In forming first electrically conductive polymer layer 3B,
the appearance of first electrically conductive polymer layer 3B
was checked by the human eyes when drying temperature changes. To
be specific, after dropping 0.5 .mu.l of the prepared electrically
conductive polymer suspension onto second electrically conductive
polymer layer 3A, 1) it had been left at normal temperature for 10
minutes; 2) it had been dried at 120.degree. C. for 10 minutes; 3)
it had been dried at 150.degree. C. for 30 minutes; and 4) it had
been dried at 180.degree. C. for 30 minutes, and, then, the
checkings were respectively carried out. As the results, at the
conditions 1) and 2), white precipitations remained on the surface
of first electrically conductive polymer layer 3B. At the condition
3), approximately 90% of the precipitations disappeared. At the
condition 4), all of the precipitations disappeared. From this, it
was appreciated that precipitations of pentaerythritol appeared in
first electrically conductive polymer layer 3B at the preliminary
drying condition 2) but all of the precipitations of
pentaerythritol disappeared in view of the human eyes after the
main drying at 180.degree. C. Further, it was confirmed that as the
drying temperature increased, dehydration polymerization reaction
was ongoing.
[0079] The initial ESR of the capacitor device at 100 kHz was 5.1
m.OMEGA. while the ESR change ratio after the heat-resistance test
was 1.3 times and the ESR change ratio after the
moisture-resistance test was 1.3 times.
Example 7
[0080] Example 7 was carried out in the same way as in Example 16
except that the main drying was performed at 225.degree. C. for 5
minutes. The results thereof are shown in Table 1.
[0081] As shown in Table 1, in checking the visual appearance of
the first electrically conductive polymer layer 3B, precipitations
were not visible after the main drying, and the film was smooth.
The film density of the first electrically conductive polymer layer
3B was 0.45 .mu.m/mlcm.sup.2. The initial ESR of the capacitor
device at 100 kHz was 4.7 m.OMEGA. while the ESR change ratio after
the heat-resistance test was 1.3 times and the ESR change ratio
after the moisture-resistance test was 1.2 times.
Example 8
[0082] Example 8 was carried out in the same way as in Example 6
except that the main drying was performed at 265.degree. C. for 1
minute. The results thereof are shown in Table 1.
[0083] As shown in Table 1, in checking the visual appearance of
the first electrically conductive polymer layer 3B, precipitations
were not visible after the main drying, and the film was smooth.
The film density of the first electrically conductive polymer layer
3B was 0.44 .mu.m/mlcm.sup.2. The initial ESR of the capacitor
device at 100 kHz was 4.8 m.OMEGA. while the ESR change ratio after
the heat-resistance test was 1.2 times and the ESR change ratio
after the moisture-resistance test was 1.2 times.
Example 9
[0084] Example 9 was carried out in the same way as in Example 1
except that a tantalum porous body was employed as the anode body
1. The results thereof are shown in Table 1.
[0085] As shown in Table 1, in checking the visual appearance of
the first electrically conductive polymer layer 3B, precipitations
were not visible after the preliminary drying, and the film was
smooth after the main drying. The film density of the first
electrically conductive polymer layer 3B was 0.51 .mu.m/mlcm.sup.2.
The initial ESR of the capacitor device at 100 kHz was 6.7 m.OMEGA.
while the ESR change ratio after the heat-resistance test was 1.6
times and the ESR change ratio after the moisture-resistance test
was 1.4 times.
Comparative Example 1
[0086] An porous body aluminum foil which has 3.times.4 mm size and
which has been subjected to a surface enlargement treatment by
etching was used as anode body 1, and, then, an oxidation film as
dielectric layer 2 was formed on the surface of the foil using an
electrolysis oxidizing method. After that, the resultant structure
was repeatedly immersed into a bath containing a monomer solution
and a bath containing a dopant and oxidizing agent solution.
Subsequently, second electrically conductive polymer layer 3A made
of poly(3,4-ethylenedioxythiophene) was formed in internal porous
portions of the porous body by a chemical polymerization
method.
[0087] Thereafter, 1 g of 3,4-ethylenedioxythiophene was poured
into a mixture solution of 100 g of pure water and 2 g of
polystyrene sulfonic acid (M.w.: 50,000) and the resultant mixture
was stirred at normal temperature for five minutes. Next, 40 wt %
persulfuric acid ammonium water solution was poured by 1 ml/min so
that total poured amount thereof comes to 5 g, and, then, the
resultant mixture was stirred (with 1,000 rpm) for 50 hours at
normal temperature so that oxidation polymerization thereof
occurred. In this way, obtained was a polymer suspension containing
approximately 3 wt % of the electrically conductive polymer
material component composed of poly(3,4-ethylenedioxythiophene) and
polystyrene sulfonic acid.
[0088] 5 .mu.l of this electrically conductive polymer suspension
was dropped onto second electrically conductive polymer layer 3A
and was left for 10 minutes at normal temperature. Next,
preliminary drying was performed for 10 minutes at 120.degree. C.
and, subsequently, main drying was performed for 30 minutes at
180.degree. C., thereby forming first electrically conductive
polymer layer 3B. Further, graphite layer 5 was formed on first
electrically conductive polymer layer 3B and silver/electrically
conductive resin layer 6 was formed on layer 5, so that the
capacitor device was fabricated. The results thereof are shown in
Table 1.
[0089] As shown in Table 1, the D50 value in the particle size
distribution of the electrically conductive polymer suspension was
2.3 .mu.m. In checking the visual appearance of the first
electrically conductive polymer layer 3B, relatively many bubbles
appeared after the main drying and the film was smooth. The film
density of the first electrically conductive polymer layer 3B was
0.76 .mu.m/mlcm.sup.2. The initial ESR of the capacitor device at
100 kHz was 10.1 m.OMEGA. while the ESR change ratio after the
heat-resistance test was 3.1 times and the ESR change ratio after
the moisture-resistance test was 3.4 times.
Comparative Example 2
[0090] After collecting 10 g of the suspension obtained in
Comparative Example 1, thereto was mixed 0.5 g of ethylene glycol,
and, then, the resultant mixture was stirred for 30 minutes to be
dissolved, and, as a result, the electrically conductive polymer
suspension was obtained.
[0091] 5 .mu.l of this electrically conductive polymer suspension
was dropped onto second electrically conductive polymer layer 3A
and was left for 10 minutes at normal temperature. Next,
preliminary drying was performed for 10 minutes at 120.degree. C.
and, subsequently, main drying was performed for 30 minutes at
180.degree. C., thereby forming first electrically conductive
polymer layer 3B. Further, graphite layer 5 was formed on first
electrically conductive polymer layer 3B and silver/electrically
conductive resin layer 6 was formed on layer 5, so that the
capacitor device was fabricated. The results thereof are shown in
Table 1.
[0092] As shown in Table 1, the D50 value in the particle size
distribution of the electrically conductive polymer suspension was
2.15 .mu.m. In checking the visual appearance of the first
electrically conductive polymer layer 3B, the film was smooth after
the main drying. The film density of the first electrically
conductive polymer layer 3B was 0.61 .mu.m/mlcm.sup.2. The initial
ESR of the capacitor device at 100 kHz was 8.1 m.OMEGA. while the
ESR change ratio after the heat-resistance test was 1.7 times and
the ESR change ratio after the moisture-resistance test was 1.8
times.
Comparative Example 3
[0093] Comparative Example 3 was carried out in the same way as in
Comparative Example 2 except that the electrically conductive
polymer suspension was made with mixing 0.5 g of glycerin instead
of 0.5 g of ethylene glycol. The results thereof are shown in Table
1.
[0094] As shown in Table 1, the D50 value in the particle size
distribution of the electrically conductive polymer suspension was
0.99 .mu.m. In checking the visual appearance of the first
electrically conductive polymer layer 3B, the film was smooth after
the main drying. The film density of the first electrically
conductive polymer layer 3B was 0.59 .mu.m/mlcm.sup.2. The initial
ESR of the capacitor device at 100 kHz was 7.1 m.OMEGA. while the
ESR change ratio after the heat-resistance test was 1.8 times and
the ESR change ratio after the moisture-resistance test was 1.7
times.
Comparative Example 4
[0095] Comparative Example 4 was carried out in the same way as in
the second example except that in this example, the electrically
conductive polymer suspension was made with mixing 0.5 g of
sorbitol instead of 0.5 g of ethylene glycol. The results thereof
are shown in Table 1.
[0096] As shown in Table 1, the D50 value in the particle size
distribution of the electrically conductive polymer suspension was
1.73 .mu.m. In checking the visual appearance of the first
electrically conductive polymer layer 3B, precipitations were not
visible after the main drying, but a few bubbles were visible, and
the film was lack in the smoothness. The film density of the first
electrically conductive polymer layer 3B was 0.67 .mu.m/mlcm.sup.2.
The initial ESR of the capacitor device at 100 kHz was 6.9 m.OMEGA.
while the ESR change ratio after the heat-resistance test was 2.1
times and the ESR change ratio after the moisture-resistance test
was 2.7 times.
Comparative Example 5
[0097] Comparative Example 5 was carried out in the same way as in
the second example except that the electrically conductive polymer
suspension was made with mixing 0.5 g of mannitol instead of 0.5 g
of ethylene glycol and that particle size distribution measurement
was performed and the visual appearance of first electrically
conductive polymer layer 3B was checked by the human eyes. The
results thereof are shown in Table 1.
[0098] As shown in Table 1, the D50 value in the particle size
distribution of the electrically conductive polymer suspension was
1.91 .mu.m. In checking the visual appearance of the first
electrically conductive polymer layer 3B, a lot of precipitations
were visible after the main drying, and the film was lack in the
smoothness. Further, it was impossible to measure the film density
of the first electrically conductive polymer and fabrication of the
capacitor device was given up.
TABLE-US-00001 TABLE 1 mixture particle ESR change ESR change mixed
size main after after amount distribution drying film film density
initial ESR heat-resistance water-resistance kind (g) (.mu.m, D50)
temp. (.degree. C.) appearance (.mu.m/ml cm.sup.2) (m.OMEGA., 100
kHz) test (times) test (times) Ex. 1 erythritol 0.5 0.92 180 good
0.50 5.2 1.5 1.4 Ex. 2 0.03 1.31 180 good 0.53 5.6 1.6 1.5 Ex. 3
2.0 1.89 180 good 0.51 5.5 1.5 1.4 Ex. 4 xylitol 0.5 0.79 180 good
0.51 4.8 1.4 1.4 Ex. 5 0.03 0.89 180 good 0.56 5.2 1.5 1.5 Ex. 6
penta- 0.5 0.90 180 good 0.48 5.1 1.3 1.3 erythritol Ex. 7 225 good
0.45 4.7 1.3 1.2 Ex. 8 265 good 0.44 4.8 1.2 1.2 Ex. 9 erythritol
0.5 0.92 180 good 0.51 6.7 1.6 1.4 Comp. 2.30 180 bubbles 0.76 10.1
3.1 3.4 Ex. 1 appeared Comp. ethylene- 0.5 2.15 180 good 0.61 8.1
1.7 1.8 Ex. 2 glycol Comp. glycerin 0.5 1.99 180 good 0.59 7.1 1.8
1.7 Ex. 3 Comp. sorbitol 0.5 1.73 180 a few bubbles 0.67 6.9 2.1
2.7 Ex. 4 appeared Comp. mannitol 0.5 1.91 180 a lot of cannot --
-- -- Ex. 5 precipitations measured
[0099] From Examples 1 to 9 that by mixing at least one compound
(A) selected from erythritol, xylitol and pentaerythritol into the
electrically conductive polymer suspension, the particles in the
electrically conductive polymer suspension become finer and, hence,
the dispersion ability of the suspension improves. It was found
from the results that the first electrically conductive polymer
layer 3B formed by the method had high density, that the capacitor
device had reduction of the initial ESR, and that ESR risings were
drastically suppressed at the heat-resistance test and
moisture-resistance test.
[0100] On the other hand, such effects were not accomplished in
Comparative Example 1 in which none was added into the suspension.
Further, the drastic suppression of the ESR risings as in the
present invention did not appear in Comparative Examples 2 to 5. In
particular, in Comparative Example 4 in which sorbitol was added,
the ESR risings were not considerably suppressed, and in
Comparative Example 5 in which mannitol was added, it was hard to
form the electrically conductive polymer layer.
[0101] It was found from the results of Examples 1 to 3 that even
if the amount of the compound (A) mixed into the suspension was
small, mixing the compound (A) was sufficiently effective. This
implies that the amount of the compound (A) may further reduce. It
is found from the result of Example 6 that when pentaerythritol is
added, the film with high density is obtained, so that the initial
the ESR of the capacitor device is low and, the ESR risings at the
heat-resistance test and moisture-resistance test are considerably
suppressed.
[0102] It was found from the results of Examples 6 to 8 that by
increasing the temperature in the main drying, the film has further
high density, and, hence, the initial ESR of the capacitor device
was low and, the ESR risings at the heat-resistance test and
moisture-resistance test were considerably suppressed. Such effects
may mainly result from the dehydration polymerization reaction in
the polymer film.
[0103] It was found from the above results that by mixing at least
one compound (A) selected from erythritol, xylitol and
pentaerythritol into the electrically conductive polymer
suspension, the electrically conductive polymer suspension with
good dispersion ability can be provided. Further, It was found that
the electrically conductive polymer film with high density and
excellent smoothness can be formed using the electrically
conductive polymer suspension and that the constituents of the
present inventions are suitable to produce the solid electrolytic
capacitor with low ESR and with good heat-resistance and
water-resistance properties
Example 10
[0104] The electrically conductive polymer films were respectively
formed on a glass substrate using the electrically conductive
polymer suspensions made in Examples 1, 4, 6 and 8 and in
Comparative Example 1. The temperatures at which the dispersion
mediums were removed were respectively set to the same conditions
(formation of first electrically conductive polymer layer 3B) as
those in the corresponding Examples.
[0105] Visual appearances (colors and transparencies) of the
obtained electrically conductive polymer films were checked.
Subsequently, the electrically conductive polymer films were
immersed into pure water for 1 hour, and, then, the
water-resistance properties (swelling of the electrically
conductive polymer film and peeling-off of the film from the glass
substrate) thereof were evaluated. The results are shown in Table
2.
TABLE-US-00002 TABLE 2 electrically conductive polymer film Visual
appearance water-resistance property Ex. 1 Dark deep blue no
swelling transparent no peeling-off Ex. 4 black no swelling
transparent no peeling-off Ex. 6 dark blue no swelling (water
repellency) non-transparent no peeling-off Ex. 8 Dark deep blue no
swelling (water repellency) non-transparent no peeling-off Comp.
dark blue swelling, Ex. 1 transparent peeling-off
[0106] Subsequently, FTIR (Fourier transform infrared spectroscopy)
was executed onto the electrically conductive polymer film (Table
2, Example 1). From the result, it was found that a peak of
hydroxyl group derived from erythritol disappears and a new
spectrum which looks like that of ester appears. Thus, it was known
that the organic structure changed.
Example 11
[0107] Polystyrene sulfonic acid aqueous solution (20 wt %, M.w.:
50,000) which was commercially available was diluted into 1 wt %
thereof by pure water. Thereafter, 10 g of the 1 wt % polystyrene
sulfonic acid aqueous solution was collected, and 1 g of erythritol
was mixed thereto, and, then, the mixture was stirred at normal
temperature for 30 minutes to be dissolved. The solution was
dropped onto the glass substrate and was left at normal
temperature.
[0108] Thereafter, TG/DTA (differential thermal analysis) was
executed onto erythritol. Condition for this analysis was that the
temperature was incremented by 10.degree. C./min under air. As the
result, a melting peak appeared at near 120.degree. C. Next, the
temperature of the composition on the glass substrate was
incremented step-by-step within a constant-temperature tank, and,
the visual appearance thereof was checked. As the result, the
visual appearance of the composition became transparent at near
125.degree. C., and the color turned into light brown near
150.degree. C., and turned into dark brown at near 180.degree.
C.
[0109] At the same time, the visual appearance of the composition
which did not contain erythritol but which contained only
polystyrene sulfonic acid was checked. As the result, the visual
appearance of the composition does not substantially change though
the temperature increases to 180.degree. C. and the color was light
yellow.
Example 12
[0110] Example 12 was carried out in the same way as in Example 11
except that 0.3 g of pentaerythritol was mixed instead of 1 g of
erythritol.
[0111] Thereafter, TG/DTA (differential thermal analysis) was
executed onto pentaerythritol. As the result, a melting peak
appeared at near 193.degree. C. Next, temperature of the
composition on the glass substrate was incremented step-by-step
within a constant-temperature tank, and, the visual appearance
thereof was checked. As the result, the visual appearance of the
composition did not change near at 150.degree. C., and the color
turned into light brown at near 180.degree. C., turned into dark
brown at near 225.degree. C., and turned into slightly blackish
dark brown at near 265.degree. C.
Example 13
[0112] Example 13 was carried out in the same way as in Example 11
except that a water-soluble polyester sulfonic acid resin (25 wt %,
M.w.: 28,000) which was commercially available was used instead of
the polystyrene sulfonic acid aqueous solution (20 wt %, M.w.:
50,000). As the result, the visual appearance of the composition
has, at near the same temperature, similar changed state.
Example 14
[0113] Example 14 was carried out in the same way as in Example 11
except that a polyacrylic acid (45 wt %, M.w.: 10,000) which was
commercially available was used instead of the polystyrene sulfonic
acid aqueous solution (20 wt %, M.w.: 50,000). As the results, the
visual appearance of the composition has, at near the same
temperature, similar changed state.
Example 15
[0114] 10 g of the electrically conductive polymer solution (amount
of solid component: approximately 3.5 wt %) composed of
poly(3,4-ethylenedioxythiophene) and polystyrene sulfonic acid
which are commercially available was collected, and 1 g of
erythritol was mixed thereto, and, then, the mixture was stirred
for 30 minutes to be dissolved.
[0115] Thereafter, the dissolved solution was dropped onto a glass
substrate and was dried for 30 minutes at 180.degree. C. to form a
electrically conductive polymer film. The visual appearance thereof
changes from dart blue to dark deep blue. Subsequently,
water-resistance properties were evaluated in the same way as in
Example 10. As the results, there was small swelling of the
electrically conductive polymer film, but peeling off from the
glass substrate thereof does not occur. Subsequently, FTIR (Fourier
transform infrared spectroscopy) was executed onto the electrically
conductive polymer film. From the result, it was found that a peak
of hydroxyl group derived from erythritol disappeared and a new
spectrum which looks like that of ester appeared. Thus, it was
known that the organic structure changed.
Example 16
[0116] Example 16 was carried out in the same way as in Example 15
except that 1 g of xylitol was mixed instead of 1 g of erythritol,
and the water-resistance properties were evaluated. As the results,
swelling and peeling-off did not appear.
Example 17
[0117] Example 17 was carried out in the same way as in Example 15
except that 0.3 g of pentaerythritol was mixed instead of 1 g of
erythritol, and the water-resistance properties were evaluated. As
the results, swelling and peeling-off did not appear. Further, the
surface of the electrically conductive polymer film changed to
hydrophobic surface which had water repellency.
Example 18
[0118] Example 18 was carried out in the same way as in Example 15
except that 0.3 g of pentaerythritol as well as 1 g of erythritol
was mixed and the water-resistance properties were evaluated. As
the results, swelling and peeling-off did not appear. Further, the
surface of the electrically conductive polymer film changed to
hydrophobic surface which has water repellency.
[0119] It was found from the results of Example 10 that as for the
electrically conductive polymer composition obtained by removing
the dispersion medium from the electrically conductive polymer
suspension containing at least one compound (A) selected from
erythritol, xylitol and pentaerythritol, the appearance (color and
transparency) changed and the water-resistance properties (swelling
and peeling off from the glass substrate) drastically improved. In
particular, as for the electrically conductive polymer film
containing pentaerythritol, the surface has changed to the
hydrophobic surface and, hence, such specific change was confirmed.
It is understood from this specific change that pentaerythritol has
different back-bone structure from that of erythritol having equal
hydroxyl groups and, in turn, the difference causes the specific
change.
[0120] Additionally, from the FTIR analysis results, a peak of
hydroxyl group disappeared and, thereafter, the similar new
spectrum appeared. Accordingly, it is understood that an organic
structure changes by interaction with polyacid.
[0121] In Examples 11 to 13 in which the polyacid component was
used, the polysulfonic acids having different main chains from each
other exhibited the same appearance change. Accordingly, it is
implied that there are interactions with the sulfonic acid group
and it is understood that the main chains are not particularly
limited. Similarly, in Example 14 in which the polyacrylic acid was
used, the same appearance change was exhibited. Accordingly, it is
implied that there are interactions with the carboxylic acid group,
as in the sulfonic acid group, and it is understood that the
carboxylic acid may be used.
[0122] In Examples 11 and 12, from the results of the visual
appearance changes of the composition at near the melting
temperatures of erythritol and pentaerythritol, it was found that
the visual appearance changed in temperature range above the
melting temperature. Further, it was confirmed that this appearance
change corresponded to those of the electrically conductive polymer
films (in Examples 6 and 8) which are written in Table 2 of Example
10.
[0123] In Examples 15 to 17, the water-resistance improved, and, in
particular, the surface of the electrically conductive polymer film
containing pentaerythritol especially changed to the hydrophobic
surface.
[0124] In Example 18 in which both of erythritol and
pentaerythritol were added, the surface of the electrically
conductive polymer film changed to the hydrophobic surface which
had water repellency, as in the case that only pentaerythritol was
added.
[0125] In those ways, it was apparent that by adding at least one
compound (A) selected from erythritol, xylitol and pentaerythritol,
the electrically conductive polymer composition in which the
appearance (color and transparency) change characteristics and
water-resistance properties drastically improves can be
provided.
LIST OF COMPONENTS
[0126] 1: anode body [0127] 2: dielectric layer [0128] 3: solid
electrolyte layer [0129] 3A: second electrically conductive polymer
layer [0130] 3B: first electrically conductive polymer layer [0131]
4: cathode layer [0132] 5: graphite layer [0133] 6:
silver/electrically conductive resin layer
* * * * *