U.S. patent number 3,834,373 [Application Number 05/228,827] was granted by the patent office on 1974-09-10 for silver, silver chloride electrodes.
Invention is credited to Takuya R. Sato.
United States Patent |
3,834,373 |
Sato |
September 10, 1974 |
**Please see images for:
( Certificate of Correction ) ** |
SILVER, SILVER CHLORIDE ELECTRODES
Abstract
Silver, silver chloride electrodes comprise a plurality of
silver particles and silver chloride particles and an electrically
insulating, water impermeable, inert organic matrix therefor. The
silver particles and silver chloride particles are interspersed
with each other in and throughout the matrix.
Inventors: |
Sato; Takuya R. (Culver City,
CA) |
Family
ID: |
22858704 |
Appl.
No.: |
05/228,827 |
Filed: |
February 24, 1972 |
Current U.S.
Class: |
600/396; 600/394;
252/514 |
Current CPC
Class: |
A61B
5/25 (20210101); A61B 2562/0215 (20170801); A61B
2562/0217 (20170801) |
Current International
Class: |
A61B
5/0408 (20060101); A61b 005/04 () |
Field of
Search: |
;128/2.6E,417,418,404,405,DIG.4,2.1E ;252/514 |
References Cited
[Referenced By]
U.S. Patent Documents
Primary Examiner: Gaudet; Richard A.
Assistant Examiner: Cohen; Lee S.
Attorney, Agent or Firm: Benoit Law Corporation
Claims
I claim:
1. A bioelectrode comprising in combination:
a silver, silver chloride electrode comprising a plurality of
silver particles, a plurality of silver chloride particles, and an
electrically insulating, water impermeable, inert organic matrix
for said silver particles and said silver chloride particles, said
silver particles and said silver chloride particles being
interspersed with each other in and throughout said matrix, and
said interspersed silver particles and silver chloride particles
being in electrical contact with each other;
said silver particles being present in said organic matrix in an
amount of from 15% to 70% by volume of said organic matrix with
said interspersed silver particles and silver chloride
particles;
said silver chloride particles being present in said organic matrix
in an amount of from 0.2 to 15 percent by volume of said organic
matrix with said interspersed silver particles and silver chloride
particles;
an electrical conductor connected to said silver, silver chloride
electrode;
means for retaining an electrolyte at said silver, silver chloride
electrode; and
container means for said silver, silver chloride electrode and for
at least part of said conductor and said electrolyte-retaining
means.
2. A bioelectrode as claimed in claim 1, wherein:
said matrix covers said electrical conductor within said container
means and has an exposed surface adjacent said
electrolyte-retaining means; and
said interspersed silver particles and silver chloride particles
are in electrical contact with said conductor and extend throughout
said matrix from said electrical conductor to said exposed surface
of said matrix.
3. A bioelectrode as claimed in claim 2, wherein:
said electrical conductor comprises a support for said matrix with
said interspersed silver particles and silver chloride
particles.
4. A bioelectrode as claimed in claim 1, wherein:
said silver, silver chloride electrode is bonded by said matrix to
said electrical conductor.
5. A bioelectrode as claimed in claim 4, wherein:
said electrolyte-retaining means are bonded by said matrix to said
silver, silver chloride electrode.
6. A bioelectrode as claimed in claim 1, wherein: said
electrolyte-retaining means include a sponge bonded by said matrix
to said silver, silver chloride electrode.
7. A bioelectrode as claimed in claim 1, wherein:
said electrolyte-retaining means include a flexible sponge spaced
from said electrode, and an open-cell rigid member located between
said flexible sponge and said electrode.
8. A bioelectrode as claimed in claim 1, including:
an adhesive pad connected to said container means to facilitate
attachment of the bioelectrode to body parts.
9. A bioelectrode as claimed in claim 1, wherein:
said silver particles consist essentially of silver.
10. A bioelectrode as claimed in claim 1, wherein:
essentially each of said silver particles comprises a particle core
and a coating of silver on said core.
11. A bioelectrode as claimed in claim 1, wherein:
essentially each of said silver particles comprises an inorganic
core and a coating of silver on said core.
12. A bioelectrode as claimed in claim 1, wherein:
said organic matrix is a resin matrix.
13. A bioelectrode as claimed in claim 1, wherein:
said organic matrix is an epoxy resin matrix.
14. A bioelectrode as claimed in claim 1, wherein:
said organic matrix is elastomeric.
15. A bioelectrode comprising in combination:
a silver, silver chloride electrode comprising a plurality of
silver particles, a plurality of silver chloride particles, and an
electrically insulating, water impermeable, inert organic matrix
for said silver particles and said silver chloride particles, said
silver particles and said silver chloride particles being
interspersed with each other in and throughout said matrix, and
said interpersed silver particles and silver chloride particles
being in electrical contact with each other;
said silver particles being present in said organic matrix in an
amount of from 70 to 90 percent by weight of said organic matrix
with said interspersed silver particles and silver chloride
particles;
said silver chloride particles being present in said organic matrix
in an amount of from 0.5 to 15 percent by weight of said organic
matrix with said interspersed silver particles and silver chloride
particles;
an electrical conductor connected to said silver, silver chloride
elecrode;
means for retaining an electrolyte at said silver, silver chloride
electrode; and
container means for said silver, silver chloride electrode and for
at least part of said conductor and said electrolyte-retaining
means.
16. A bioelectrode as claimed in claim 15, wherein:
said matrix covers said electrical conductor within said container
means and has an exposed surface adjacent said
electrolyte-retaining means; and
said interspersed silver particles and silver chloride particles
are in electrical contact with said conductor and extend throughout
said matrix from said electrical conductor to said exposed surface
of said matrix.
17. A bioelectrode as claimed in claim 16, wherein:
said electrical conductor comprises a support for said matrix with
said interspersed silver particles and silver chloride
particles.
18. A bioelectrode as claimed in claim 15, wherein:
said silver, silver chloride electrode is bonded by said matrix to
said electrical conductor.
19. A bioelectrode as claimed in claim 18, wherein:
said electrolyte-retaining means are bonded by said matrix to said
silver, silver chloride electrode.
20. A bioelectrode as claimed in claim 15, wherein:
said electrolyte-retaining means include a sponge bonded by said
matrix to said silver, silver chloride electrode.
21. A bioelectrode as claimed in claim 15, wherein:
said electrolyte-retaining means include a flexible sponge spaced
from said electrode, and an open-cell rigid member located between
said flexible sponge and said electrode.
22. A bioelectrode as claimed in claim 15, including:
an adhesive pad connected to said container means to facilitate
attachment of the bioelectrode to body parts.
23. A bioelectrode as claimed in claim 15, wherein:
said silver particles consist essentially of silver.
24. A bioelectrode as claimed in claim 23, wherein:
said organic matrix is an epoxy resin matrix.
25. A bioelectrode as claimed in claim 23, wherein:
said organic matrix is elastomeric.
Description
BACKGROUND OF THE INVENTION
1. Field of the Invention
The subject invention relates to silver, silver chloride electrodes
and to methods of making same.
2. Description of the Prior Art
Silver, silver chloride electrodes are useful and well known in the
fields of electrochemistry, biochemistry and medicine. For
instance, biopotential electrodes are widely used in medical work
for making electrical contact with a patient's skin in order to
detect and evaluate low-level electrical signals originating within
the body. A common use for biopotential electrodes is in the field
of cardiology for measurement of the electrocardiogram.
Silver, silver chloride biopotential electrodes are based in their
function on the classical silver, silver chloride half-cell of
electrochemistry in which the silver chloride stabilizes and
controls the electric potential on the surface of the electrode and
lowers the work function between the electrode and the electrolytic
solution with which it is in contact, thereby making the electrical
contact more stable. The performance of silver, silver chloride
electrodes is thus greatly superior to the performance of their
forerunners which includes silver electrodes and electrodes of a
copper-nickel-zinc alloy known as "German silver". The latter
electrodes made an extremely variable and easily disturbed
electrical contact with the skin which introduced a great deal of
electrical noise into the bioelectrical signal, leading to
erroneous diagnoses.
However, existing silver, silver chloride electrodes still suffer
from serious drawbacks. They are typically expensive to produce and
complex to utilize and maintain. Prior-art attempts to remedy these
drawbacks have resulted in electrodes that are easily damaged
and/or inferior in performance.
Prior-art tendencies and prejudices have seriously impeded the
development of a low-cost and preferably disposable silver, silver
chloride electrode that would take adequate advantage of the
superior features of that electrode type.
For instance, researchers in the field of silver, silver chloride
electrodes have found that organic compounds seem to contribute to
electrode poisoning. Researchers have also identified the apparent
dependence of the standard potential for a mixture of given
dielectric constant on the nature of the organic component as an
unexpected and particularly important stumbling block. This may,
for example, be seen from Janz and Ives, Silver, Silver Chloride
Electrodes, ANNALS OF THE NEW YORK ACADEMY OF SCIENCES, Volume 148,
Art. 1, BIOELECTRODES, Feb. 1, 1968, pp. 210-221, at p. 220, and
Feakins and French, Standard Potentials in Aqueous Organic Media: a
General Discussion of the Cell H.sub.2 (Pt)/HCl/AgCl-Ag, J. Chem.
Soc. (London), 1957, pp. 2581-2589, at pp. 2585 and 86. Findings of
this type have discouraged the use of organic compounds in the
electrode structure of silver, silver chloride electrodes.
It has also been assumed in the past that the silver chloride
component should occur at the surface of silver, silver choride
electrodes and that the silver component should be covered by the
silver chloride component except for possible pores. These assumed
restrictions have impeded the development of low-cost techniques of
high efficiency for manufacturing silver, silver chloride
electrodes. As Janz and Ives point out in their above mentioned
article, which is herewith incorporated by reference herein, the
best methods of preparation of silver, silver chloride electrodes
to attain maximum stability and reproducibility have been a matter
for controversy over the years, and conflicting opinions have
remained unresolved (see page 215).
Silver, silver chloride electrodes are also used in other fields of
electrochemistry, such as in the production and operation of
electric current generating cells and batteries. This may, for
instance, be seen in Vinal, PRIMARY BATTERIES (John Wiley &
Sons, 1950) pp. 17, and 274-281.
As early as 1882, Warren de la Rue built a 15,000 volt battery of
14,400 silver chloride cells. The individual cells consisted of a
silver chloride casting around a flattened silver wire and a
slender rod of zinc. More modern methods of manufacture of silver,
silver chloride electrodes for electric cells have continued to
take care that the silver chloride component occurs only on the
surface of the electrode and substantially covered the silver
component, except for possible pores.
SUMMARY OF THE INVENTION
The subject invention owes its existence to a radical departure
from prior-art thinking and prejudice. According to combined main
features of the subject invention the silver component and the
silver chloride component are located in and at the surface of an
electrically insulating, water impermeable, inert organic matrix,
and the silver component and silver chloride component are
interspersed with each other in and throughout the organic
matrix.
From one aspect thereof, the subject invention resides in a silver,
silver chloride electrode; and resides more specifically in the
improvement comprising, in combination, a plurality of silver
particles, a plurality of silver chloride particles, and an
electrically insulating, water impermeable, inert organic matrix
for the silver particles and silver chloride particles. In
accordance with the subject invention, the matrix is not only
organic as stated, but the silver particles and silver chloride
particles are interspersed with each other in and throughout the
matrix, and the interspersed silver particles and silver chloride
particles are in electrical contact with each other.
From another aspect thereof, the subject invention resides in a
bioelectrode comprising, in combination, a silver, silver chloride
electrode, an electrical conductor connected to the silver, silver
chloride electrode, means for retaining an electrolyte at the
silver, silver chloride electrode, and container means for the
silver, silver chloride electrode and for at least part of the
conductor and the electrolyte-retaining means. Further according to
the invention, the silver, silver chloride electrode in the latter
combination comprises a plurality of silver particles, a plurality
of silver chloride particles and an electrically insulating, water
impermeable, inert organic matrix for the silver particles and
silver chloride particles; with the silver particles and silver
chloride particles being interspersed with each other in and
throughout the matrix, and with the interspersed silver particles
and silver chloride particles being in electrical contact with each
other.
From yet another aspect thereof, the subject invention resides in a
method of making a silver, silver chloride electrode; and resides
more specifically in the improvement comprising in combination the
steps of providing a plurality of silver particles, providing a
plurality of silver chloride particles, providing a curable
material for forming an electrically insulating, water impermeable,
inert organic matrix for the silver particles and silver chloride
particles, intermixing the curable matrix material, silver
particles and silver chloride particles intimately with each other,
and curing the intermixed material to form a silver, silver
chloride electrode having the silver particles and silver chloride
particles interspersed with each other, and in electrical contact
with each other, in and throughout a cured electrically insulating,
water impermeable, inert organic matrix.
BRIEF DESCRIPTION OF THE DRAWINGS
The invention and its objects will become more readily apparent
from the following detailed description of preferred embodiments
thereof, illustrated by way of example in the following drawings,
in which:
FIG. 1 is a section through a silver, silver chloride electrode in
accordance with a preferred embodiment of the subject
invention;
FIG. 2 is a section through a bioelectrode in accordance with
another preferred embodiment of the subject invention;
FIG. 3 is a section through a bioelectrode in accordance with yet
another preferred embodiment of the subject invention; and
FIG. 4 is a section, on an enlarged scale, through silver particles
useful in the practice of the subject invention.
DESCRIPTION OF PREFERRED EMBODIMENTS
By way of example, electrodes according to the subject invention
have utility as reference electrodes, bioelectrodes and electric
cell electrodes. By way of further example, and not by way of
limitation, the illustrated preferred embodiments will be chiefly
described in terms of bioelectrodes that may be applied to the skin
of animals and humans for receiving and measuring electrical body
signals.
The silver, silver chloride electrode 10 of FIG. 1 consists
essentially of a plurality of silver particles 12, a plurality of
silver chloride particles 13, and an organic matrix 14 for the
silver particles 12 and the silver chloride particles 13. In
accordance with the subject invention, the silver particles 12 and
the silver chloride particles 13 are interspersed with each other
in and throughout the matrix 14. Also, the interspersed silver
particles 12 and silver chloride particles 13 are in electrical
contact with each other.
In FIG. 1, the silver particles are shown as spheres of a given
diameter and the silver chloride particles are shown as spheres of
a smaller diameter. This neither implies a limitation to particles
of spherical shape, nor is intended as any representation about the
relative sizes of the silver and silver chloride particles. Rather,
the graphical illustration of FIG. 1 is intended to convey the fact
that both the silver particles 12 and the silver chloride particles
13 are interspersed with each other in and throughout the organic
matrix 14, and that both silver particles 12 and silver chloride
particles 13 are present on the surface of the silver, silver
chloride electrode, as well as throughout the electrode body
including the organic matrix 14.
FIG. 1 also shows an electric conductor 16 extending into the
matrix 14 and being in electrical contact with the silver particles
12 and silver chloride particles 13. The conductor 16 is not an
electrode in the sense in which that term is used for the silver,
silver chloride electrode 10 located on the conductor 16. The
conductor 16 is also to be distinguished from the silver core of
prior-art silver, silver chloride electrodes. In those prior-art
electrodes, a silver conductor or silver-coated conductor formed
the silver component of the silver, silver chloride electrode and
had a thin coating of silver chloride provided thereon. Pursuant to
the teachings of the subject invention, there is no electrolytic or
ionic contact between the conductor 16 and the electrolyte to which
the silver, silver chloride electrode 10 is exposed in practice.
Rather, the conductor 16 makes electrical contact with the silver
particles 12 and silver chloride particles 13, and any electrical
conduction between the electrolyte and the conductor 16 proceeds
only by way of the silver particles 12 and silver chloride
particles 13.
In the preferred embodiment of FIG. 1, the silver component of the
electrode is interspersed in particulate form in the organic matrix
14 with the silver chloride component which is also in particulate
form. To be sure, the conductor 16 may be of silver or may have a
silver coating. Alternatively, the conductor 16, may, however, be
of another conducting metal, such as copper, nickel or stainless
steel. Use of silver or of a silver coating for the conductor 16 is
preferred to optimize the electrical contact between the conductor
16 and the particles 12 and 13.
The conductor 16 may serve to connect the electrode 10 to an
electric circuit or instrument and may, if desired, also serve as a
support for the electrode. In the following preferred ranges, the
presence and the weight of the conductor 16 are disregarded both
with respect to the weight of the electrode and with respect to the
weight of any electrode component.
The amounts of silver particles 12, silver chloride particles 13,
and organic matrix material 14 in the electrode 10 can vary in wide
ranges. In practice, sufficient silver and silver chloride should
be present to make sure that the silver and chloride components of
the electrode are in electrical contact within the organic matrix
14. This is similar to the provision of electrical contact between
silver particles in an electrically conductive varnish, paint or
resin of the silver type. Moreover, the silver chloride content
should be sufficient relative to the silver content or to the
weight of the electrode to provide for the desired contribution of
the silver chloride component in the silver, silver chloride
electrode. High silver chloride contents, on the other hand, tend
to impair the quality and stability of the electrode, including its
mechanical quality and stability.
Through various calculations and tests, I have determined preferred
broad ranges of weight percentages relative to the weight of the
organic matrix 14 and the silver particles 12 and silver chloride
particles 13 interspersed in the organic matrix. According to these
preferred ranges, the silver particles constitute substantially
from 70 to 90 percent by weight, the silver chloride particles
constitute substantially from 0.5 to 15 percent by weight, and the
organic matrix constitutes essentially the balance of the weight of
the organic matrix with the silver particles and silver chloride
particles dispersed therein.
Generally, if the silver particles are shape anisotropic (e.g.
needle-shaped silver particles or silver flakes), the content of
the silver particles can be lowered relative to the preferred
higher content for spherical silver particles.
Preferably, the silver particles and the silver chloride particles
are of a purity of about 99.9 percent or higher to avoid generation
of spurious potentials from electrode contaminants. Spherical,
needle-shaped and flaked silver particles of the desired purity are
readily available commercially. Silver chloride particles of the
desired purity are also commercially available from such suppliers
as J. T. Baker Chemical Company, Phillipsburg, New Jersey, and
Mallinckrodt Chemical Works, Saint Louis, Missouri.
Typically, the silver chloride particles are precipitated from an
aqueous solution of a soluble silver salt and filtered and washed
for providing the desired purity.
According to the subject invention, the matrix is of an
electrically insulating material to avoid the occurrence of
current-conducting paths within the matrix in parallel to the
silver and silver choride particles. The insulating material of the
organic matrix is also water impermeable to prevent electrolyte
contacting the electrode from providing ionic conduction within the
matrix in parallel to the silver and silver chloride particles. The
organic matrix is also of a material which is chemically inert to
the electrolyte encountered by the electrode.
A large number of organic materials qualify for the electrode
matrix, since there are many organic materials which are
electrically insulating, water impermeable and chemically inert to
the types of electrolyte encountered by silver, silver chloride
electrodes. Those skilled in the art of organic chemistry or in the
technology of electrical insulating materials will readily be able
to identify a large number of suitable organic materials.
By way of example and not by way of limitation, it is well known
that most resins are electrically insulating, water impermeable and
chemically inert to the types of electrolyte (e.g. aqueous sodium
chloride solutions in the case of bioelectrodes) encountered by
silver, silver chloride electrodes. By way of further example, it
is well known that most thermoplastic resins, thermosetting resins
and elastomers or rubbers are electrically insulating, water
impermeable and chemically inert in the above mentioned sense.
These properties are also possessed by many high molecular weight
waxes.
Typically, the silver particles consist essentially of solid or
pure silver as mentioned above and as shown at 12 in FIGS. 1 to 4.
However, the silver particles may alternatively be made of, or
comprise, silver-coated particles of a material other than silver.
In the context of the subject electrodes which function on the
basis of surface phenomena, the expression silver particles as
herein employed is intended to be broad enough to cover powders of
silver, including particles of solid silver, and silver-coated
particles of an inert material other than silver.
Suitable low-cost, low-density substitutes for powders of solid
silver particles include a product sold by Sigmatronics, of
Moorestown, New Jersey, under the designation "Siliclad G-100" and
consisting of a powder of finely divided ceramic particles
essentially each of which has a uniform coating of essentially pure
silver. Other substitutes include hollow silica microspheres
designated Eccospheres SI (thin-walled bubbles made from silica)
and hollow glass microspheres designated Eccospheres/Glass
Microballoons, sold by Emerson & Cuming, Inc., of Canton,
Massachussetts, and provided with essentially pure silver
coatings.
The silver coating shown in FIG. 4 at 12', may be applied to the
solid core particles shown in FIG. 4 at 51 or to the hollow core
particles shown in FIG. 4 at 52 by such well-known techniques as
vacuum deposition, sputtering, precipitation or electroless
plating, for instance. Inorganic materials other than ceramics and
glass, or organic materials such as plastics resins, may be
employed for the core particles on which the silver coating is
deposited or plated, since silver coatings have in the past been
successfully provided on a large variety of materials.
The above mentioned proportions, expressed in percent by weight,
are subject to wide variation if silver substitute powders of
silver layers coated on core particles having a density less than
the density of silver are employed in lieu of or in combination
with solid silver particles. For instance, the manufacturers of the
above mentioned silver-coated ceramic particles indicate for their
product a density of about one-third the density of silver. The
manufacturers of the above mentioned hollow silica microspheres
indicate for these microspheres a particle density of 0.26 g/cc and
a bulk density of 0.18g/cc.
This makes it impractical to provide constituent ranges in percent
by weight which would be generally applicable to solid silver
particles and to silver-clad silver particles. Since the function
of the silver and silver chloride constituents of the electrode
proceeds chiefly on the basis of surface phenomena, it is
appropriate under the circumstances to provide generally applicable
ranges for silver particles, silver-clad silver particles, and
silver chloride particles in terms of percent by volume.
I have in this respect determined through calculation and
experiment preferred broad ranges of volume percentages relative to
the volume of the organic matrix 14 and the silver particles 12 and
silver chloride particles 13 interspersed in the organic matrix.
According to these preferred ranges, the silver particles
constitute substantially from 15 to 70 percent by volume, the
silver chloride particles constitute substantially from 0.2 to 15
percent by volume, and the organic matrix constitutes essentially
the balance of the volume of the organic matrix with the silver
particles and silver chloride particles dispersed therein.
In similarity to the silver particles, the silver chloride
particles could either be made of pure silver chloride or of silver
chloride coated on an inert particle core. For economical and
practical reasons, it is, however, presently believed that pure
silver chloride particles (i.e. silver chloride particles that do
not have a core other than silver chloride) are preferable.
The following working examples are supplied by way of illustration,
rather than by way of example.
EXAMPLE I
Silver, silver chloride electrodes in accordance with preferred
embodiments of the subject invention were manufactured with the aid
of an electrically conductive silver epoxy resin commercially
available in liquid form from Emerson & Cuming, Inc., under the
trade name "Eccobond Solder 57C". This commercially available
product has a resin component which contains about 80 percent by
weight of silver powder and about 20 percent by weight of an epoxy
resin, relative to the weight of the resin component. This
commercial product further has a catalyst component comprising
about 80 percent by weight of silver powder and 20 percent by
weight of a catalyst, relative to the weight of the catalyst
component. The epoxy resin is bis-phenol A. The catalyst is a
polyamide. The resin component and the catalyst component were
intimately mixed in accordance with the manufacturer's
specifications. In accordance with a preferred embodiment, the
resin component and the catalyst component were mixed in a ratio of
one-to-one, and an amount of 10 milligrams silver chloride
particles were added to and intimately intermixed with the mixed
resin and catalyst components per each gram of the mixed resin and
catalyst components. The silver chloride particles were of a
precipitated grade sold by J. T. Baker Company.
If desired, the silver chloride particles may be added to the resin
component and/or catalyst component prior to intermixture of the
resin and catalyst components.
The silver chloride-doped resin and catalyst mixture was thereafter
cured in accordance with manufacturer's specifications by heat
exposure. In some runs the silver chloride-doped resin and catalyst
mixture was applied to electric conductors, including silver-plated
wires and flat metal pieces and blank copper wires, and was
thereafter cured on the conductors.
In this manner, low-cost and high-quality silver, silver chloride
electrodes were produced.
EXAMPLE II
Example I was repeated with the exception that silver chloride
particles were added to the resin component prior to the
intermixture of the resin and catalyst components in an amount of
100 milligrams of silver chloride particles per gram of the resin
component.
The silver chloride-doped resin component and the catalyst
component were intimately intermixed to disperse the silver
chloride component throughout the mixture.
This Example yielded low-cost, high-quality silver, silver chloride
electrodes upon curring by heat exposure.
EXAMPLE III
Example I was repeated except that silver chloride particles were
added to the resin component prior to intermixture of the resin and
catalyst component in an amount of 25 milligrams of silver chloride
particles per gram of the resin component.
EXAMPLE IV
An electrically conductive resin commercially available in liquid
form from Emerson & Cuming, of Canton, Massachusetts, under the
trade name "Eccobond Solder 57C" was used to make silver, silver
chloride electrodes in accordance with further preferred
embodiments of the subject invention. That commercially available
product has a resin component containing about 80 percent by weight
of silver powder and 20 percent by weight of an epoxy resin,
relative to the weight of the resin component; and a catalyst
component consisting of a liquid catalyst having no silver therein.
The epoxy resin in this product is bisphenol A. The liquid catalyst
in this product is a polyamide. Only a relatively small amount of
liquid catalyst is needed for catalyzation.
In accordance with a further preferred embodiment of the subject
invention, 6.25 milligrams of silver chloride particles were added
to and intimately admixed with the resin component per each gram of
the resin component. The silver chloride-doped resin component and
the catalyst were thereafter mixed and cured in accordance with
manufacturer's specifications to obtain excellent silver, silver
chloride electrodes upon curing by heat exposure.
In some runs the silver chloride-doped resin and catalyst mixture
was applied to electric conductors, including silver-plated wires
and flat metal pieces and blank copper wires, and was thereafter
cured on the conductors.
EXAMPLE V
Example IV was repeated except that silver chloride particles were
added to the resin component in an amount of 125 milligrams of
silver chloride particles per gram of the resin component.
EXAMPLE VI
Further silver, silver chloride electrodes in accordance with
preferred embodiments of the subject invention were manufactured
with the aid of an electrically conductive, silver-filled
styrene-butadiene elastomer commercially available in uncured form
from Emerson & Cuming, Inc., of Canton, Massachusetts, under
the trade name Eccocoat CC-4, and containing about 70 to 80 percent
by weight of silver particles.
In accordance with a preferred embodiment of the subject invention,
50 milligrams of silver chloride particles were added to and
intimately admixed with the uncured silver-filled styrene-butadiene
elastomer per gram of this elastomer.
The silver chloride-doped elastomer was thereafter cured by air
drying for 3 to 4 hours in some runs, and by forced drying for 30
minutes at 80.degree.C in others.
In some runs the silver chloride-doped elastomer was cured after
having been applied to electrical conductors, including
silver-plated wires and flat metal pieces and blank copper
wires.
In this manner, several low-cost and high-quality silver, silver
chloride electrodes were produced.
EXAMPLE VII
Example VI was repeated except that silver chloride particles were
added to the uncured silver-filled elastomer in an amount of 5
milligrams of silver chloride particles per gram of elastomer.
EXAMPLE VIII
Example VI was repeated except that silver chloride particles were
added to the uncured silver-filled elastomer in an amount of 100
milligrams of silver chloride particles per gram of elastomer.
RESULTS
All the electrodes made according to Examples I through VIII
performed well in practice and in clinical testing as
bioelectrodes. The off-set potentials (i.e. the potentials observed
when two silver, silver chloride electrodes were measured
face-to-face) typically were less than 0.5 millivolts. Such a high
half-cell stability usually is only found in expensive pressed
pellet type electrodes.
The electrode voltage was very stable. Essentially no long term
drift of the electrode voltage was observed. This renders the
electrodes made according to Examples I through VIII suitable for
long term monitoring applications.
Good low-impedance skin contact was established very rapidly after
application of these electrodes to human skin. The skin contact was
generally less than 1 kilohm assuring the production of sharp and
essentially noise-free ECG (electrocardiogram) records, and
permitting even the use of older ECG machines.
By way of general comment, silver, silver chloride electrodes
according to the subject invention provide performance equivalent
to that of the best available research grade electrodes at cost
savings of about 80 to 90 percent and more.
In general, the electrodes of the subject invention are, for
instance, suitable as electrodes in electric reference or
low-current cells, in reference electrodes, and as
bioelectrodes.
A disposable bioelectrode in accordance with a preferred embodiment
of the subject invention is shown in FIG. 2.
According to FIG. 2, a silver, silver chloride electrode 10 of the
above mentioned type is deposited on the inner part 19 of a snap
fastener 20. The parts of the snap fastener may be silver plated.
The electrode 10 comprises silver particles 12 and silver chloride
particles 13 interspersed in an organic matrix 14 as described
above. The electrode 10 is located in a plastic cup 21, and a
portion of the snap fastener part 19 extends through an aperture in
the cup 21. The cup 21 may be of a molded plastics resin, such as
polyethylene, polyvinyl chloride, or
acrylonitrile-butadiene-styrene.
The inner fastener part 19 is pressed into an outer fastener part
22 to form a swaged unit. A flexible opencell member or sponge is
located on top of the electrode 10 in the cup 21. The function of
the sponge 23 is to absorb and retain an electrolyte, such as a
saline solution, for the operation of the bioelectrode. The sponge
23 also functions as a shock absorber which isolates the electrode
10 from mechanical disturbances emanating from body parts.
The sponge 23 may be a sponge of cellulose or another hydrophilic
material, a rubber sponge, or a flexible polyurethane sponge.
In accordance with a preferred embodiment of the subject invention,
a supply of a silver chloride-doped, silver-filled resin and
catalyst mixture in accordance with one of the above mentioned
examples, or a supply of a silver chloride-doped, silver-filled
elastomer in accordance with another example, is deposited in its
uncured state on the upper fastener part 19 which has previously
been swaged with the outer fastener part 22. The sponge 23 is then
inserted into the cup 21 and is pressed against the uncured
electrode 10. The electrode 10 may then be cured (such as by heat
and pressure) and serve as an adhesive for the sponge 23 at the
same time. The sponge or electrolyteretaining means 23 is thus
bonded by the matrix 14 to the silver, silver chloride electrode
10, and the silver, silver chloride electrode 10 is bonded by the
matrix 14 to the electrical conductor or upper fastener part 19.
This greatly simplifies the design of the cup 21 and the
manufacture of the bioelectrode device.
To make the bioelectrode easily attachable to parts of the body, a
pad 25 of a soft material, such as rubber, closed-cell polyurethane
foam, or closed-cell polyethylene foam is provided with an adhesive
coating 26. The adhesive 26 may be a commercially available,
medical-grade pressure sensitive adhesive of the type marketed, for
instance, by Minnesota Mining and Manufacturing Company. The pad 25
has an aperture for receiving the cup 21 and an outer flange of the
cup 21 is attached by the adhesive 26 to the pad 25. The adhesive
layer 26 is covered with a conventional protective paper layer 28
which is peeled off the adhesive prior to the use of the
bioelectrode device. A protective cup 29, shown in dotted outline,
may be attached to the bioelectrode device as shown in FIG. 2 to
protect the device during storage and shipment. The protective cup
29, if used, is releasably attached to the bioelectrode device by
means of an adhesive, and may be manufactured of polyvinyl chloride
or polyethylene.
The swaged snap fastener unit 20 may be inserted into a
corresponding snap fastener receptacle 31 which is connected to an
electrocardiograph (ECG) or other bioelectric instrument 18 by an
electrically insulated wire 32. In practice, the protective cup 29,
if used, and the protective paper layer 28 are peeled off, a
suitable chloride electrolyte, such as a saline solution, is
applied to the sponge 23, and the bioelectrode device is applied to
the patient's skin and is fastened thereto by the adhesive 26.
Comparing FIGS. 1 and 2, it will be noted that the fastener part 19
performs in the device of FIG. 2 the function of the conductor 16
shown in FIG. 1.
A disposable bioelectrode in accordance with a further preferred
embodiment of the invention is shown in FIG. 3. Like reference
numerals among FIGS. 2 and 3 designate like or functionally
equivalent parts.
According to FIG. 3, the insulated electrical wire 32 has a
non-insulated end portion 34 which corresponds to the conductor 16
shown in FIG. 1. The wire may be of silver or at least the end
portion 34 may be silver plated. The electrically conductive wire
end portion 34 is embedded in a silver, silver chloride electrode
10 according to the subject invention. As mentioned above, the
electrode 10 has silver particles 12 and silver chloride particles
13 interspersed in an organic matrix 14. The electrode 10 may be
manufactured in accordance with one of the above mentioned
examples.
The electrode 10 has an open-cell rigid member 36 located thereon.
The member 36 may be of open-cell urethane or other open-cell rigid
plastic. Another suitable material for the member 36 is foam glass.
The rigid open-cell member retains electrolyte without undue
mobility thereof. A flexible sponge 38, which may be of the same
material as the sponge 23 in FIG. 2, is located on top of the rigid
member 36. In practice, electrolyte is applied to the sponge 38
until the pores of the rigid member 36 have been filled. In this
manner, the flexible sponge 38, which serves as a shock absorber
isolating the electrode 10 from mechanical disturbances emanating
from body parts, and as a retainer of electrolyte, is spaced from
the electrode 10, and the open-cell rigid member 36 is located
between the flexible sponge 38 and the electrode 10.
The electrode 10, member 36 and sponge 38 are packaged in a
laminate which is composed of heat-sealed plastics sheets 41 and 42
of such materials as polyvinyl chloride, polyethylene, ionomer
resin, or other material used for blister or vacuum packs. The top
sheet 42 has an opening through which the sponge 38 is exposed.
In accordance with a preferred manufacture of the bioelectrode
device of FIG. 3, the silver chloride-doped resin and catalyst
mixture is applied to the end portion 34 of the wire 32 in an
uncured state. The uncured electrode mass with the embedded wire
portion 34 is then placed onto the lower sheet 41 of the laminate.
The rigid porous member 36 is then placed on top of the uncured
electrode mass. The sponge member 38 is placed on top of the rigid
porous member 36, and the top sheet 42 is placed on top of the
whole assembly so that the central portion of the sponge 38 is
exposed. The laminate may then be heat sealed and the electrode
mass 10 cured in one operation.
The heat-sealed assembly 45 is then attached to the pad 25 by means
of the adhesive layer 26. A peelable protective paper layer 28 is
provided as before. A protective cup of the type indicated at 29 in
FIG. 2 may also be provided for the bioelectrode device of FIG.
3.
The wire 32 may be attached to the apparatus 18 in any conventional
manner. Both the bioelectrode device of FIG. 2 and the bioelectrode
device of FIG. 3 may be sealed in a moisture and airtight package
of a metal or plastics foil.
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