U.S. patent application number 16/978172 was filed with the patent office on 2021-02-11 for silver-silver chloride electrode and electrical circuit.
The applicant listed for this patent is NOK CORPORATION. Invention is credited to Ryo FUTASHIMA.
Application Number | 20210041389 16/978172 |
Document ID | / |
Family ID | 1000005208250 |
Filed Date | 2021-02-11 |
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United States Patent
Application |
20210041389 |
Kind Code |
A1 |
FUTASHIMA; Ryo |
February 11, 2021 |
SILVER-SILVER CHLORIDE ELECTRODE AND ELECTRICAL CIRCUIT
Abstract
A silver-silver chloride electrode contains silicone rubber as a
binder in which silver powder, silver chloride powder and silica
powder are dispersed. A current density of a current flowing
through an electric circuit is equal to or greater than 0.64
.mu.A/mm.sup.2 after 5 minutes from the beginning of voltage
application to the electric circuit when the electric circuit in
which two silver-silver chloride electrodes and a phosphate
buffered saline are connected in series is made up of the two
silver-silver chloride electrodes and the phosphate buffered saline
containing no calcium and no magnesium interposed between the two
silver-silver chloride electrodes.
Inventors: |
FUTASHIMA; Ryo; (Fujisawa,
JP) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
NOK CORPORATION |
Tokyo |
|
JP |
|
|
Family ID: |
1000005208250 |
Appl. No.: |
16/978172 |
Filed: |
June 12, 2019 |
PCT Filed: |
June 12, 2019 |
PCT NO: |
PCT/JP2019/023195 |
371 Date: |
September 3, 2020 |
Current U.S.
Class: |
1/1 |
Current CPC
Class: |
G01N 27/30 20130101 |
International
Class: |
G01N 27/30 20060101
G01N027/30 |
Foreign Application Data
Date |
Code |
Application Number |
Jun 14, 2018 |
JP |
2018-113792 |
Claims
1. A silver-silver chloride electrode comprising: silver powder;
silver chloride powder; silica powder; and silicone rubber as a
binder in which silver powder, silver chloride powder and silica
powder are dispersed, a current density of a current flowing
through an electric circuit being equal to or greater than 0.64
.mu.A/mm.sup.2 after 5 minutes from the beginning of voltage
application to the electric circuit when the electric circuit in
which two silver-silver chloride electrodes and a phosphate
buffered saline are connected in series is made up of the two
silver-silver chloride electrodes and the phosphate buffered saline
containing no calcium and no magnesium interposed between the two
silver-silver chloride electrodes.
2. The silver-silver chloride electrode according to claim 1,
wherein the current density of the current flowing through the
electric circuit is equal to or greater than 7.61 .mu.A/mm.sup.2
after 5 minutes from the beginning of voltage application to the
electric circuit.
3. An electric circuit comprising: two silver-silver chloride
electrodes; and a phosphate buffered saline not containing calcium
or magnesium interposed between the two silver-silver chloride
electrodes, the two silver-silver chloride electrodes and the
phosphate buffered saline being connected in series, each
silver-silver chloride electrode comprising: silver powder; silver
chloride powder; silica powder; and silicone rubber as a binder in
which silver powder, silver chloride powder and silica powder are
dispersed, a current density of a current flowing through the
electric circuit being equal to or greater than 0.64 .mu.A/mm.sup.2
after 5 minutes from the beginning of voltage application to the
electric circuit.
4. The electric circuit according to claim 3, wherein the current
density of the current flowing through the electric circuit is
equal to or greater than 7.61 .mu.A/mm.sup.2 after 5 minutes from
the beginning of voltage application to the electric circuit.
5. The electric circuit according to claim 3, wherein the two
silver-silver chloride electrodes are formed on a substrate made of
silicone rubber.
6. The electric circuit according to claim 4, wherein the two
silver-silver chloride electrodes are formed on a substrate made of
silicone rubber.
Description
CROSS REFERENCE TO RELATED APPLICATIONS
[0001] This application is a U.S. National Phase application under
35 U.S.C. 371 of International Application No. PCT/JP2019/023195
filed on Jun. 12, 2019, which claims the benefit of priority from
Japanese Patent Application No. 2018-113792 filed Jun. 14, 2018.
The entire disclosures of all of the above applications are
incorporated herein by reference.
BACKGROUND
Technical Field
[0002] The present invention relates to silver-silver chloride
electrodes and to electric circuits.
Related Art
[0003] Silver-silver chloride electrodes are widely used as
measurement electrodes and reference electrodes for measuring
minute currents in electrochemistry and electrophysiology because
they are nonpolarizable, have a stable potential, and have a high
charge transfer reaction rate.
[0004] As a method for producing a silver-silver chloride
electrode, a method is known in which silver chloride is formed by
electrolysis on a surface of a silver plate or silver wire immersed
in a chloride solution.
[0005] Furthermore, a method for producing a silver-silver chloride
electrode composed of silver, silver chloride, and a heat-resistant
resin are formed on a substrate is known in which a conductive
paste obtained by dispersing silver powder, silver chloride powder,
and polyimide (binder) in an organic solvent is applied on the
substrate and heated (JP-A-05-142189). Furthermore,
JP-A-2005-292022 discloses a method in which a paste in which
silver particles are dispersed in a resin material is applied to a
substrate to form an electrode, and then the electrode is treated
with hypochlorous acid to make a surface of the electrode silver
chloride.
[0006] In recent years, studies using microfluidic devices has
progressed in electrochemistry and electrophysiology. For example,
it is conceivable to use silver-silver chloride electrodes to
measure the microcurrent of fluid in a microfluidic device. In this
case, a silver-silver chloride electrode that has high adhesion to
silicone rubber, which is a material for a plate used in a
microfluidic device, and that can stably maintain high
conductivity, is desired.
[0007] Accordingly, the present invention provides a silver-silver
chloride electrode having high adhesion to silicone rubber and
capable of stably maintaining high conductivity, and provides an
electric circuit having two silver-silver chloride electrodes.
SUMMARY
[0008] A silver-silver chloride electrode according to an aspect of
the present invention is a silver-silver chloride electrode
including silver powder, silver chloride powder, silica powder, and
silicone rubber as a binder in which silver powder, silver chloride
powder and silica powder are dispersed. The current density of the
current flowing through an electric circuit is equal to or greater
than 0.64 .mu.A/mm.sup.2 after 5 minutes from the beginning of
voltage application to the electric circuit when the electric
circuit in which two silver-silver chloride electrodes and a
phosphate buffered saline are connected in series is made up of the
two silver-silver chloride electrodes and the phosphate buffered
saline containing no calcium and no magnesium interposed between
the two silver-silver chloride electrodes.
[0009] In this aspect, it is possible to provide a silver-silver
chloride electrode that has high adhesion to silicone rubber and
can stably maintain high conductivity.
[0010] An electric circuit according to an aspect of the present
invention is an electric circuit including two silver-silver
chloride electrodes and a phosphate buffered saline not containing
calcium or magnesium interposed between the two silver-silver
chloride electrodes, the two silver-silver chloride electrodes and
the phosphate buffered saline being connected in series. Each
silver-silver chloride electrode includes silver powder, silver
chloride powder, silica powder, and silicone rubber as a binder in
which silver powder, silver chloride powder and silica powder are
dispersed. The current density of the current flowing through the
electric circuit is equal to or greater than 0.64 .mu.A/mm.sup.2
after 5 minutes from the beginning of voltage application to the
electric circuit.
[0011] Preferably, the current density of the current flowing
through the electric circuit is equal to or greater than 7.61
.mu.A/mm.sup.2 after 5 minutes from the beginning of voltage
application to the electric circuit.
[0012] Preferably, the two silver-silver chloride electrodes are
formed on a substrate made of silicone rubber.
BRIEF DESCRIPTION OF THE DRAWINGS
[0013] FIG. 1 is a plan view showing silver-silver chloride
electrodes manufactured on a substrate;
[0014] FIG. 2 is a table showing materials of multiple samples of
silver-silver chloride electrodes;
[0015] FIG. 3 is a schematic diagram showing an experimental
apparatus for testing the conductivities of the samples;
[0016] FIG. 4 is a graph showing the test results of the
conductivities of the samples;
[0017] FIG. 5 is a graph showing the test results of the
conductivities of the samples; and
[0018] FIG. 6 is a table showing the test results of the
conductivities of the samples.
DETAILED DESCRIPTION
[0019] Hereinafter, an embodiment according to the present
invention will be described.
Outline of Embodiment
[0020] A silver-silver chloride electrode according to the
embodiment contains silver powder, silver chloride powder, silica
powder, and silicone rubber as a binder in which silver powder,
silver chloride powder and silica powder are dispersed. In the
embodiment, when an electric circuit in which two silver-silver
chloride electrodes and a phosphate buffered saline are connected
in series is made up of the two silver-silver chloride electrodes
and the phosphate buffered saline containing no calcium and no
magnesium interposed between the two silver-silver chloride
electrodes, the current density of the current flowing through the
electric circuit is equal to or greater than 0.64 .mu.A/mm.sup.2
after 5 minutes from the beginning of voltage application to the
electric circuit.
[0021] A method for manufacturing a silver-silver chloride
electrode according to the embodiment includes: a step of producing
a paste by mixing silver powder, silver chloride powder, a
dispersant, and fumed silica powder with a liquid silicone rubber
binder; a step of coating the paste on a substrate made of silicone
rubber; and a step of curing the paste on the substrate to form an
electrode in which silver, silver chloride, and silica powder are
dispersed.
[0022] Preferably, the manufacturing method includes a step of
immersing the formed electrode in a sodium chloride aqueous
solution.
[0023] The step of producing a paste includes a step of producing a
mixture of fumed silica powder and silver chloride powder by,
first, adding fumed silica to silver chloride, pulverizing and
mixing the silver chloride and the fumed silica, and a step of
adding the mixture, silver powder, and a dispersant to an RTV (Room
Temperature Vulcanizing) silicone rubber.
[0024] Fumed silica powder functions as an aggregation inhibitor
for silver chloride powder. When fumed silica is not used, silver
chloride powder agglomerates. Preferably, the fumed silica powder
is a hydrophilic fumed silica powder.
[0025] The dispersant disperses silver powder and silver chloride
powder as uniformly as possible in a liquid silicone rubber binder.
The dispersant is preferably a polyether-modified silicone
surfactant having a polyether chain and a silicone chain, and/or a
polyglycerin-modified silicone surfactant having a polyglycerin
chain and a silicone chain.
[0026] In the step of coating the substrate with the paste, as
shown in FIG. 1, a surface of the substrate 1 made of silicone
rubber is coated with the paste 2 by a technique such as screen
printing or ink jet printing. Curing of the paste 2 results in
silver-silver chloride electrodes 3 in which silver, silver
chloride, and silica powder are dispersed. In other words, a plate
4 having the silver-silver chloride electrodes 3 provided on a
surface is manufactured.
[0027] Preferably, the silver-silver chloride electrodes 3 are
produced by immersing the silver-silver chloride electrodes in a
sodium chloride aqueous solution and drying them.
[0028] In the illustrated embodiment, two silver-silver chloride
electrodes 3 are formed on one surface of the substrate 1. However,
one or three or more silver-silver chloride electrodes 3 may be
formed on the substrate 1, or one or more silver-silver chloride
electrodes 3 may be formed on both surfaces of the substrate 1.
[0029] In accordance with the silver-silver chloride electrode
produced by this production method, in a case in which hydrophilic
fumed silica powder is used, it is assumed that the affinity
between the surfaces of silver chloride particles and electrolytes
(for example, electrolytes in a solution to be measured) is
improved since the surface of each silver chloride particle is
coated with hydrophilic fumed silica. Although the conductivity of
silver chloride itself is low, it is considered that the
conductivity is improved by coating silver chloride particles with
hydrophilic fumed silica. In addition, it is assumed that since the
dispersant disperses silver powder and silver chloride powder,
which are conductors, in silicone rubber, which is the binder, the
conductor particles within the silver-silver chloride electrode are
electrically connected to one other well, so that conductivity is
also improved.
[0030] Furthermore, the silicone rubber contained in the
silver-silver chloride electrode contains chloride ions and sodium
ions derived from sodium chloride if the step of immersing in a
sodium chloride aqueous solution is conducted. Therefore, it is
assumed that the conductivity is improved by ions in addition to
the electrical connection of the conductor particles, so that a
higher conductivity can be stably maintained.
[0031] In addition, by using silicone rubber as a binder, the
produced silver-silver chloride electrode 3 has high adhesion to
the silicone rubber and does not easily peel off or drop off from
the substrate 1. Furthermore, since the silicone rubber contained
in the silver-silver chloride electrode contains chloride ions and
sodium ions derived from sodium chloride, it is expected to improve
durability against external forces caused by, e.g., bending of the
silver-silver chloride electrode.
[0032] Production Examples
[0033] The inventor manufactured multiple samples each having
silver-silver chloride electrodes by the manufacturing method
according to the embodiment, and tested the conductivities of these
samples. For comparison, a sample (Sample 10) having silver
electrodes was produced, and the conductivity of the sample was
also tested.
[0034] FIG. 2 shows the materials of these samples and details of
immersion in a sodium chloride aqueous solution (salt water
treatment). In FIG. 2, unless otherwise noted, the numerical values
represent parts by weight. The "%" in the last line (salt water
treatment) indicates the concentration of sodium chloride in the
sodium chloride aqueous solution as a percentage, whereas "None" in
the last line indicates that the electrodes were intentionally
manufactured without performing the salt water treatment. The "-"
in the last line indicates that the salt water treatment was
abandoned, and that the conductivity test was not performed.
[0035] For Samples 1-9, in the step of producing a mixture of fumed
silica powder and silver chloride powder, fumed silica was added to
silver chloride, and then, silver chloride and fumed silica were
pulverized and mixed by means of a centrifugal mill. For Samples 1
to 9, the weight parts of silver chloride and fumed silica in the
entire material are as shown in FIG. 2. The raw material silver
chloride was produced by Inuisho Precious Metals Co., Ltd., Osaka,
Japan. As the fumed silica, there were prepared "AEROSIL 200",
which is a hydrophilic fumed silica manufactured by Nippon Aerosil
Co., Ltd., Tokyo, Japan, and "AEROSIL R972" which is a hydrophobic
fumed silica manufactured by the same company. "AEROSIL R972" was
used for the manufacture of Samples 2 and 7, whereas "AEROSIL 200"
was used for the manufacture of Samples 1, 3-6, 8, and 9. "AEROSIL"
is a registered trademark. For pulverization and mixing, a
centrifugal mill (trade name "ZM 200") manufactured by Retsch Co.,
Ltd. (currently Verder Scientific Co., Ltd.), Tokyo, Japan was
used. Silver chloride and fumed silica were pulverized and mixed,
so that the resulting particles passed through a 0.20 mm-mesh
screen.
[0036] In samples 10 to 12, no fumed silica powder was used. The
reason for not using fumed silica powder in Samples 11 and 12 was
to confirm the effect of fumed silica powder as an aggregation
inhibitor for silver chloride powder. The reason for not using
fumed silica powder in Sample 10 was that no silver chloride powder
was used, and therefore, fumed silica powder as an aggregation
inhibitor was unnecessary.
[0037] For silicone rubber as the binder, a mixture of "KE-106", an
RTV silicone rubber manufactured by Shin-Etsu Chemical Co., Ltd.,
Tokyo, Japan and "CAT-RG", a curing catalyst manufactured by the
same company, was used.
[0038] As silver powder, there were prepared a flaky silver powder,
"FA-2-3", manufactured by Dowa Hitech Co., Ltd., Saitama, Japan,
and an irregular-shaped silver powder, "G-35" manufactured by the
same company. Equal amounts of these were used in each of the
samples.
[0039] As the dispersant, there were prepared polyether-modified
silicone surfactant, "KF-6015" manufactured by Shin-Etsu Chemical
Co., Ltd., and polyglycerin-modified silicone surfactant,
"KF-6106", manufactured by the same company. Equal amounts of these
were used in each of the samples.
[0040] For Samples 1 to 9, a paste was produced by adding silver
powder, the dispersant, and the mixture of fumed silica powder and
silver chloride powder to the binder and mixing them.
[0041] For Samples 11 and 12, silver powder, the dispersant, and
silver chloride powder were added to the binder, and they were
mixed, but since they did not contain fumed silica powder as an
aggregation inhibitor for silver chloride powder, silver chloride
powder agglomerated and a uniform paste could not be produced
(thus, Samples 11 and 12 were not subjected to subsequent steps and
to the test. In FIG. 2, the "-" in salt water treatment for Samples
11 and 12 means that neither the salt water treatment nor the
conductivity test was conducted due to the paste being inferior).
Samples 11 and 12 differed in the amount of silver chloride, but
none of them could result in production of a uniform paste. Thus,
the effect of fumed silica was confirmed.
[0042] For Sample 10, a paste was produced by adding silver powder
and the dispersant to the binder and mixing them.
[0043] Then, for Samples 1 to 10, as shown in FIG. 1, the paste 2
was coated by screen printing at two locations on a surface of a
substrate 1 made of silicone rubber containing PDMS
(polydimethylsiloxane). Furthermore, the paste 2 was cured by
heating at 150 degrees Celsius for 30 minutes.
[0044] For Samples 3 to 7, and 10, except for Samples 1, 2, 8, and
9, after curing the paste 2, the substrate 1 was immersed in a
sodium chloride aqueous solution at room temperature for an hour
together with the electrodes resulting from the paste 2, and they
were then dried.
[0045] In each of produced Samples 1 to 9, the silver-silver
chloride electrodes 3 had high adhesion to the silicone rubber and
did not easily peel off or drop off from the substrate 1.
Furthermore, in Sample 10 manufactured for comparison, the silver
electrodes 3 had high adhesion to the silicone rubber and did not
easily peel off or drop off from the substrate 1. In these samples,
the length L of the electrodes 3 was 30 mm, the width W thereof was
5 mm, and the interval IN therebetween was 10 mm.
[0046] Next, using each of produced Samples 1 to 10, an
experimental apparatus 5 shown in FIG. 3 was assembled. The
experimental apparatus 5 has plates 4, 6, and 7 that are stacked
and bonded to one another. Through-holes 6a and 6b are formed in
the plate 6 immediately above the plate 4, and are overlapped with
the electrodes 3, respectively. In the uppermost plate 7, a groove
7g that penetrates the plate 7 is formed. One end of the groove 7g
is overlapped with the through-hole 6a of the plate 6 directly
below, whereas the other end of the groove 7g is overlapped with
the through-hole 6b.
[0047] Thus, the experimental apparatus 5 is provided with a micro
flow channel having the through-holes 6a and 6b and the groove 7g.
Both ends of the micro flow channel are closed with the two
electrodes 3. Liquid can be stored in the micro flow channel, and
liquid can be introduced through the groove 7g. The width of the
groove 7g was 1 mm, whereas the diameters of the through-holes 6a
and 6b were 2 mm.
[0048] PBS (phosphate buffered saline) was supplied to the micro
flow channel from the groove 7g. The PBS used was PBS (-) without
calcium or magnesium.
[0049] A battery 8 (DC power supply) was connected to the
electrodes 3 on the surface of the plate 4 via lead wires L, and a
voltage of 0.3V was applied so that a DC current flowed through the
electrodes 3. Variation of the electric current value was measured
by an ammeter 9 for 400 seconds (6 minutes and 40 seconds)
immediately after the beginning of electric current supply (voltage
application).
[0050] Therefore, an electric circuit having two electrodes 3 and
PBS (-) therebetween was formed in which the electrodes 3 and PBS
(-) were connected in series.
[0051] FIGS. 4 and 5 show the measurement results. The measurement
results in FIGS. 4 and 5 are the first measurement results after
the plates 4 were manufactured.
[0052] As is clear from FIGS. 4 and 5, in Samples 4 and 5, the
current value was stabilized for 400 seconds after the beginning of
voltage application. Samples 4 and 5 contain hydrophilic fumed
silica, and the sodium chloride concentration of the solution used
in the salt water treatment is high. It is presumed that the
silicone rubber contained in the silver-silver chloride electrodes
in Samples 4 and 5 contain a large amount of chloride ions and
sodium ions derived from sodium chloride, so that the conductivity
is improved and the higher conductivity can be stably maintained by
the ions.
[0053] As is clear from comparison of Samples 4 and 5, even though
the silver chloride content was different, the current value was
stable for a long time if the sodium chloride concentration of the
solution used in the salt water treatment was higher.
[0054] In Samples 1 to 3 and 6 to 9, a large current flowed
immediately after the beginning of voltage application, but the
current value decreased with time.
[0055] Sample 1 used the same materials as Sample 4, but was not
subjected to the salt water treatment. In sample 1, the current
value gradually decreased with time.
[0056] Samples 3 and 6 used the same materials as Sample 5, but the
sodium chloride concentration of the solution used in the salt
water treatment was low for Sample 3, and Sample 6 was not
subjected to the salt water treatment. In Samples 3 and 6, the
current value gradually decreased and then stabilized.
[0057] Sample 7 used the same materials as sample 5, but used
hydrophobic fumed silica instead of hydrophilic fumed silica. In
Sample 7, a very large current flowed immediately after the
beginning of voltage application, but the current value gradually
decreased and then stabilized.
[0058] Sample 2 used the same materials as Sample 7, but was not
subjected to the salt water treatment. In sample 2, the current
value decreased rapidly in the initial stage and then stabilized.
In Sample 2, the current flowing was smaller than that of Sample
7.
[0059] Samples 8 and 9 used the same materials as Sample 5, but the
ratio of hydrophilic fumed silica was low and the salt water
treatment was not performed. In Samples 8 and 9, the current value
gradually decreased and then stabilized.
[0060] In Sample 10 having the silver electrodes 3 manufactured for
comparison, the current values were lower continuously after the
beginning of voltage application than those of Samples 1 to 9
having the silver-silver chloride electrodes 3.
[0061] From the above, it is understood that among the samples
having the silver-silver chloride electrodes 3, Samples 4 and 5 had
good performance.
[0062] In microfluidic devices, from the viewpoint of shortening
the measurement time, it is required that electrodes have high
conductivity immediately after the beginning of voltage
application. Even Samples 1 to 3 and 6 to 9 having a large decrease
in current can also be used utilizing the high conductivity, as
long as the measurement is for a short time. Accordingly, FIG. 6
shows the current value for each sample at 300 seconds (5 minutes)
after the beginning of voltage application obtained from the
measurement results. Moreover, FIG. 6 shows the current density for
each sample at 300 seconds (5 minutes) after the beginning of
voltage application from a measurement result for universalization.
The current density was obtained by dividing the current value by
the cross-sectional area of the lead wires L. Since the lead wires
L had a diameter of 2 mm, the cross-sectional area thereof was 3.14
mm.sup.2.
[0063] Since Samples 1 to 3 and 6 to 9 can be used in microfluidic
devices, it is preferable that the current density of the current
flowing through the electric circuit be equal to or greater than
0.64 .mu.A/mm.sup.2 after 5 minutes from the beginning of voltage
application to the electric circuit.
[0064] In consideration of the good performance of Samples 4 and 5,
it is more preferable that the current density of the current
flowing through the electric circuit be equal to or greater than
7.61 .mu.A/mm.sup.2 after 5 minutes from the beginning of voltage
application to the electric circuit.
[0065] Although the present invention has been described above, the
foregoing description is not intended to limit the present
invention. Various modifications including omission, addition, and
substitution of structural elements may be made within the scope of
the present invention.
* * * * *