JP2013032489A - Pad for electrode - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a pad for an electrode having sufficient strength and flexibility, excellent in electroconductivity, exhibiting little deterioration of strength over time, and composed of a polyurethane hydrous gel.SOLUTION: The pad for an electrode is manufactured by a step of gelatinizing a mixture of a hydrophilic polyurethane prepolymer containing a polyisocyanate component and a polyol component, and water, wherein an isomer having isocyanate groups on the 2- and 4-positions is contained in 10 to 50 wt% with respect to the prepolymer in the prepolymer; the tensile strength is ≥10 (N); and the deterioration rate of the tensile strength is ≤35%.

Description

  The present invention relates to an electrode pad comprising a polyurethane hydrogel used in the medical and industrial fields, and more particularly to an electrode pad comprising a polyurethane hydrogel having improved strength. The electrode pad of the present invention transmits an electrical signal from the human body surface to a recording device such as an electrocardiograph, an electroencephalograph, an electromyograph, or transmits an electrical signal from the device to the human body surface like a low frequency electrode. Electrode pads for maintaining good mechanical and electrical connection between the metal electrode surface of the device and the human skin surface and maintaining good mechanical and electrical connection between them, especially for electrodes of suction type It can be suitably used for a pad.

Conventionally, when measuring an electrocardiogram or the like, a paste-like conductive cream is often used instead of an electrode pad. However, since this conductive cream remains on the skin when the electrode is removed after use, it has to be wiped off with paper or the like, and there are problems in terms of workability and usability.
In recent years, there has been a gradual increase in the use of conductive gel molded products using polyurethane polymers in place of this cream, but it has sufficient strength, durability, and conductivity, and sufficient flexibility. There was no gel molded product, and there was a problem that it had to be replaced during use.
Patent Document 1 reports an electrode pad that can solve the above-mentioned problems. Patent Document 1 describes that an electrode pad with excellent performance can be obtained by using a specific plasticizer for the electrode pad. Moreover, although the field is different, Patent Document 2 describes a method for producing a polyurethane gel having sufficient strength.

JP 2004-43577 A JP 2004-292718 A

However, the conventional polyurethane gel has the following problems. In Patent Document 1, it is possible to prepare a polyurethane hydrogel having both moisture retention and flexibility, but strength deterioration occurs with time (probably due to hydrolysis). In Patent Document 2, 2,2MDI is used, the reactivity is poor, it is difficult to gel, and a metal oxide or the like is used for imparting conductivity, so that it is not suitable as an electrode pad.
Accordingly, an object of the present invention is to provide an electrode pad comprising a polyurethane hydrogel having sufficient strength and flexibility, excellent conductivity, and little deterioration in strength over time.

  As a result of intensive studies, the present inventor has found that the tensile strength is high due to the ratio of the isomer of MDI in the prepolymer constituting the main chain of the polyurethane water-containing gel, especially 2,4 MDI, and further, there is little strength deterioration with time, flexibility. It has been found that a polyurethane hydrogel having (stretchability) can be obtained, and the present invention has been completed.

  That is, the present invention is produced by a step of gelling a mixture containing a hydrophilic polyurethane prepolymer containing a polyisocyanate component and a polyol component and water, and in the hydrophilic polyurethane prepolymer, an isocyanate is placed at positions 2 and 4. It is an electrode pad containing 10 to 50% by weight of an isomer having a group. According to the present invention, there is also provided an electrode pad comprising a polyurethane hydrogel having a tensile strength of 10 (N) or more and a deterioration rate with time of 35% or less. In particular, according to the present invention, it is produced by a step of gelling a mixture comprising a hydrophilic polyurethane prepolymer containing a polyisocyanate component and a polyol component and water, and has a tensile strength of 10 (N) or more, An electrode pad made of a water-containing polyurethane gel having a deterioration rate of 35% or less is provided.

  According to the present invention, the hydrophilic polyurethane prepolymer contains 10 to 50% by weight of an isomer (compound) having an isocyanate group at positions 2 and 4 so that the tensile strength is high, the deterioration rate is small, and flexibility is obtained. A polyurethane gel and an electrode pad excellent in properties can be provided.

The mixture further includes a plasticizer, the plasticizer has a polyoxyalkylene chain in the main skeleton, and the polyoxyalkylene chain is composed of at least one of an oxyethylene group and an oxypropylene group. When it is a mold oil, it is possible to provide a polyurethane gel having high moisture retention and excellent flexibility.
Furthermore, when the mixture contains a surfactant and contains a polyoxyethylene polyoxypropylene block polymer as the surfactant, the polyurethane has higher moisture retention, excellent flexibility, and improved appearance. A gel can be provided.
According to the present invention, there is also provided an electrode pad comprising a polyurethane hydrogel having a tensile strength of 10 (N) or more and a deterioration rate with time of 35% or less.

It is the schematic perspective view seen from the slanting upper side which shows one Embodiment of the pad for this electrode suitable for a suction type electrode. It is a schematic sectional drawing of the pad for the electrodes. It is the schematic which shows the tensile strength test of the pad for the electrodes.

  The electrode pad of the present invention can be obtained by gelling a mixture containing a hydrophilic polyurethane prepolymer and water. Here, the hydrophilic polyurethane prepolymer contains a polyisocyanate component and a polyol component.

(Hydrophilic polyurethane prepolymer)
(1)
Polyisocyanate Component As the polyisocyanate component, components derived from known polyisocyanates can be used. Examples of the polyisocyanate include methylene diphenyl diisocyanate, toluene diisocyanate, hexamethylene diisocyanate, isophorone diisocyanate, and cyclohexane diisocyanate. These polyisocyanates may be used alone or in combination of two or more. Some of the above polyisocyanates have isomers at the 2-, 2-, 4-, 4-, and 4-positions. In the present invention, the 2,4-isomer is 10 to 50 weights in the prepolymer. %contains. When the 2,4 isomer is less than 10% by weight, since it is a hydrogel, main chain scission tends to proceed due to hydrolysis or the like, and deterioration with time tends to occur. In the case of 50% by weight or more, the reactivity may be lowered and it may be difficult to obtain a desired gel.

(2)
Polyol component
The polyol component has at least one polyoxyalkylene chain containing an oxypropylene group. The polyoxyalkylene chain includes an oxyethylene group, an oxybutylene group and the like in addition to the oxypropylene group. A polyoxyalkylene chain having a molecular weight of 500 to 3000 is preferably used. The polyoxyalkylene chain can be obtained, for example, by polymerizing at least one monomer such as ethylene oxide, propylene oxide, butylene oxide. Further, the polyoxyalkylene chain may partially contain units derived from other polyols such as heptanediol, hexanediol, and cyclohexanediol. Moreover, when using a copolymer as a polyoxyalkylene chain, the constitution of the copolymer may be a random copolymer or a block copolymer.

(3) Ratio of polyol component in prepolymer The polyol component is preferably contained in the hydrophilic polyurethane prepolymer in an amount of 20 to 60% by weight based on the total amount of the polyisocyanate component and the polyol component.
When the content of the polyol component is less than 20% by weight, the molecular weight between the crosslinking points of the polyisocyanate component and the polyol component is decreased, and as a result, the strength may be decreased. When it exceeds 60% by weight, gelation becomes insufficient, and the strength may be lowered due to poor shape retention of the gel.

(water)
The urethane prepolymer and water are contained in the mixture at a ratio of 300 to 600 parts by weight with respect to 100 parts by weight of the urethane prepolymer. By containing water in this proportion, a polyurethane gel having an improved appearance can be obtained. When the proportion of water is less than 300 parts by weight, not only the strength is lowered, but the gel may not be sufficiently hardened and molding may be difficult. When it exceeds 600 parts by weight, foaming during gelation is severe, and the appearance of the gel may be deteriorated. A preferred ratio is 330 to 550 parts by weight.
The water content is preferably 20 to 95% by weight in the polyurethane gel. When the water content is less than 20% by weight, the produced gel may become too hard to be adapted to the adherend. If it exceeds 95% by weight, a gel having sufficient strength may not be formed. A more preferable content is 50 to 80% by weight.

(Other ingredients)
(I) The mixture may further contain a plasticizer.
The plasticizer has a role of maintaining a good affinity between the hydrophilic polyurethane prepolymer and water. By including a plasticizer, moisture is not separated during gel formation, the desired shape is maintained, moisture retention during use is good, and flexibility of the gel can be ensured even when dried.
Although it does not specifically limit as a plasticizer, The polyoxyalkylene chain | strand which has a polyoxyalkylene chain in a main skeleton, and the polyoxyalkylene chain consists of at least 1 sort (s) in oxyethylene and oxypropylene is preferable.

For example, there are the following representative plasticizers.
-Polyoxypropylated glycerin (average molecular weight is preferably 200-5000),
-Polyoxypropylated sorbitol (average molecular weight is preferably 300 to 5000),
-Plasticizers containing two or more oxyalkylene chains,
-Glycol diethers are mentioned.

Here, containing two or more oxyalkylene chains means, for example,
Plasticizers (a) There are polyalkylene glycols (containing an average molecular weight of 200 to 6000), which contain oxyethylene groups and oxypropylene groups, of which the oxypropylene groups account for 60 to 90% by weight of the total molecular weight.
Plasticizer (b) Polyether glycol monoether containing an oxyethylene group and an oxypropylene group, wherein the oxypropylene group accounts for 30 to 90% by weight of the total molecular weight of the polyoxyalkylene chain (average molecular weight is preferably 200 to 4000) )
The plasticizer containing two or more oxyalkylene chains may be a random copolymer or a block copolymer. One hydroxyl group of the monoether of polyalkylene glycol contained in the plasticizer (b) is, for example, ether-bonded to an alkyl group.

  Specific examples of glycol diethers include ethylene glycol dimethyl ether, diethylene glycol dimethyl ether, triethylene glycol dimethyl ether, tetraethylene glycol dimethyl ether, polyethylene glycol dimethyl ether, diethylene glycol diethyl ether, diethylene glycol ethyl methyl ether, ethylene glycol dibutyl ether, diethylene glycol dibutyl ether, diethylene glycol Examples include propylene glycol dimethyl ether and tripropylene glycol dimethyl ether.

  The content of the plasticizer in the mixture is preferably 5 to 30% by weight. When the content of the plasticizer is less than 5% by weight, the flexibility during drying is small and the polyurethane gel adherence may be insufficient. Moreover, when it exceeds 30 weight%, a polyurethane gel may become too soft and a shape may not be hold | maintained. A more preferable content is 10 to 20% by weight.

(Ii) The mixture may further contain a surfactant. The surfactant has an action of increasing the compatibility between the polyurethane prepolymer and water, and is effective in preventing water separation after gelation, stabilizing the electrolyte solution, and preventing self-adhesion of the generated gel.
Specific examples of the surfactant include oxyethylene alkyl ether, polyoxyethylene alkyl phenyl ether, polyoxyethylene polyoxypropylene glycol, polyoxyethylene hydrogenated castor oil, and the like. Examples thereof include oxypropylene block polymers (average molecular weight is preferably about 1000 to 8000).

(Iii) The mixture may further contain a chain extender. A known material can be used as the chain extender. Examples thereof include diols such as ethylene glycol, propylene glycol, and butanediol, and diamines such as ethylenediamine, toluenediamine, and isophoronediamine.
(Iv) In the mixture, reaction suppression of acidic substances such as p-toluenesulfonic acid such as amines such as triethanolamine as a reaction accelerator for urethane prepolymer, sodium carbonate, sodium silicate and the like as other additives An agent, a gel reinforcing filler such as Aerosil, an antifungal agent such as Amical, and a coloring agent can be added.

(4) Gelation The mixture containing the hydrophilic polyurethane prepolymer becomes a polyurethane gel by gelation.
The content of the hydrophilic polyurethane prepolymer in the mixture is preferably 5 to 30% by weight. When the content of the hydrophilic polyurethane prepolymer is less than 5% by weight, a gel having sufficient strength may not be generated. On the other hand, if it exceeds 30% by weight, the gel may become too hard to fit the adherend. A more preferable content is 10 to 20% by weight.
Gelation is performed by stirring a mixed liquid containing a hydrophilic polyurethane prepolymer and water, a plasticizer, a surfactant, an electrolyte, a reaction accelerator, and the like so that each compound is uniformly mixed, and then, in a mold container or the like. It is made to gel by injecting, reacting (crosslinking) and aging while maintaining an appropriate temperature and humidity environment.
The reaction temperature is preferably 20 to 50 ° C. The reaction humidity is preferably 40 to 70% RH (relative humidity). Although reaction time is suitably adjusted according to a molding, it can be set as about 3 to 60 minutes. In the gelation, the reaction rate may be adjusted by adding treatments such as heating, cooling, and pH adjustment as necessary.

(Electrode pad)
The electrode pad preferably contains an electrolyte.
(1) Electrolyte As the electrolyte, normally used sodium chloride, potassium chloride and the like are suitable. The content of the electrolyte is preferably in the range of 0.1 to 2.0 parts by weight with respect to 100 parts by weight of water from the viewpoint of conductivity and solubility in water. If it is less than 0.1 part by weight, the conductivity may be insufficient. If it exceeds 2.0 parts by weight, a large amount of the electrolyte component may be deposited on the gel surface.

(2) Formation method of electrode pad The formation method of the electrode pad is preferably the same method as the formation method of the polyurethane gel. In this method, the moisture retention of the electrode pad can be further improved.
The shape of the electrode pad is not particularly limited, and examples include an elliptical shape, a circular shape, a heart shape, a semicircular shape, a semielliptical shape, a square shape, a rectangular shape, a trapezoidal shape, a truncated cone shape, a triangular shape, a shape according to the application site, or a combination thereof. However, the one having a truncated cone shape (donut shape) having one hole communicating from the viewpoint of improvement in adhesion to the subject and connectivity with the electrode is preferable.

(3) Use of electrode pads Electrode pads can be used to transmit electrical signals from the human body surface to devices such as electrocardiographs, electroencephalographs, and electromyographs, or from devices such as low-frequency treatment devices. When detecting the weak current generated by electronic devices, etc., between the electrodes constituting these devices and the human body or electronic device surface, the electrodes and the human body or electronic device surface It can be suitably used for applications in which the mechanical and electrical connection states of the above are kept good.

(Quantitative method of hydrophilic urethane prepolymer and MDI)
In order to inactivate the isocyanate group of the hydrophilic urethane prepolymer, an inactivated MeOH aqueous solution was used for the measurement. The measurement used "HPLCLC-6A system" by Shimadzu Corporation by GPC method. The column used is Shodex KF-801, 802, 804, the detector is “RID-10A” manufactured by Shimadzu Corporation, the flow rate is 1.0 ml / min, the solvent is THF, the temperature is 50 ° C., and the method of conversion by the universal calibration method is used. It was.

(Testing and testing methods for electrode pads)
(Tensile strength)
For example, the molded product of the electrode pad shown in FIGS. 1 and 2 was tested and inspected as a test sample. FIG. 1 is a schematic perspective view of the main electrode pad as viewed obliquely from above. FIG. 2 is a schematic sectional view of the electrode pad. FIG. 3 is a schematic view showing a tensile strength test of the electrode pad.
As shown in FIGS. 1 and 2, the electrode pad 1 has an upper base 2 having a diameter of 18 mm, a lower base 3 having a diameter of 25 mm, a height between the upper base 2 and the lower base 3 of 12 mm, an upper base 2 and a lower base. 3 and a side wall portion 4 each having a thickness of 3 mm and a truncated cone shape (donut shape). The electrode pad 1 of this molded product is made of the polyurethane hydrogel of the present invention, and has a diameter of 7 mm at the upper bottom portion 5, a diameter of 4 mm at the lower bottom portion 6, and an inner space portion 7 between the upper bottom portion 5 and the lower bottom portion 6. Is provided. The electrode pad 1 has an upper hole 8 that opens from the upper bottom 5 of the inner space 7 to the outside of the upper bottom 2 at the upper bottom 5 of the inner space 7. On the other hand, reference numeral 9 is a pilot hole that opens from the lower bottom 6 of the inner space 7 to the outside of the lower bottom 3 in the lower bottom 6 of the inner space 7. The diameter of the upper hole 8 is 7 mm and the diameter of the lower hole 9 is 4 mm, and the diameter of the upper hole 8 is larger than the diameter of the lower hole 9.
As shown in FIGS. 3 and 2, the test sample was hooked with a hook formed in a U-shape in the upper hole 8 of the test sample, and a temperature of 23 ° C. was measured with a Tensilon universal tester (Orientec, RTE-1210). The sample was pulled under conditions of humidity 54% and test speed 300 mm / min, and the maximum load point of the load applied until the gel was torn was measured as the tensile strength. The hook formed in a U-shape is a stainless steel wire having a diameter of 2 mm, and the U-shaped portion 10 of the hook is formed so as to enter the upper hole 8 as shown in FIG.
The tensile strength is preferably 10N or more and 25N or less, and more preferably in the range of 12 to 20N, from the viewpoint of preventing damage to the electrode pad when mounting the electrode on the electrode pad and ease of attachment / detachment.

(Deterioration test method)
There is aging (time) deterioration as a method of confirming deterioration. Actually stored for one year is desirable, but it is difficult to wait for one year for sample evaluation. As a simple evaluation, it was stored for 10 days at 50 ° C. I found out. Therefore, the sample was stored at 50 ° C. for 10 days (aging), and the change in physical properties was confirmed by the tensile strength test. The deterioration rate is calculated by the following formula.
Degradation rate (%) = (Tensile strength immediately after gelation−Tensile strength after storage at 50 ° C. for 10 days (time)) / (Tensile strength immediately after gelation) × 100

  The deterioration rate is preferably 35% or less from the viewpoint of preventing damage to the electrode pad when mounting the electrode on the electrode pad and ease of attachment / detachment, and more preferably 25% or less.

(Evaluation of elongation rate)
The elongation obtained by dividing the elongation (length) of the sample at the maximum load in the tensile strength measurement by the sample length before the test (22 mm in the above case) by 100 is taken as the elongation rate.
The elongation rate is preferably 400% to 600%, more preferably 500% to 600%, from the viewpoint of preventing damage to the electrode pad when mounting the electrode on the electrode pad and ease of attachment / detachment.

Example 1
(Method for producing hydrophilic urethane prepolymer)
7.7 g of liquid MDI (manufactured by Lupranate MI BASF INOAC Polyurethane Co., Ltd.) was added to 26 g of polyoxypropylated glycerin (Sanix GP-1000, Sanyo Chemical Industries, Ltd., average molecular weight 1000) while stirring under a nitrogen atmosphere The mixture was heated and then cooled to obtain a first stage prepolymer. When a calibration curve was prepared in advance and measured by GPC, the ratio of those prepolymerized (monomer or higher) was 71.8%, 2,4-MDI 15.6%, and 4,4-MDI. It was 12.6%. To this first-stage prepolymer, 8.42 g of the above liquid MDI and 14.04 g of Cr-MDI (polymeric MDI, Lupranate M-20S BASF INOAC Polyurethane Co., Ltd.) were added to obtain a hydrophilic polyurethane prepolymer. When this was measured by GPC, the ratio of 2,4MDI was 17%, and the ratio of 4,4MDI was 27%.

(Method for producing urethane hydrogel)
84.5 g of water, polyoxypropylated glycerin (Sanyo Chemical Industries, Ltd. Sannix GP-400, average molecular weight 400) 23.1 g, polyoxyethylene polyoxypropylene block polymer (Daiichi Kogyo Seiyaku Epan 450, average molecular weight) 2400) 0.75g, Yotor DP-95 (Mitsui Chemicals antibacterial agent) 0.037g, Sodium chloride 0.63g, Sodium silicate solution (Pure Chemical Co., Ltd. water glass) 0.64g mixed liquid and prepared first. 24.4 g of the urethane prepolymer was rapidly stirred and poured into a predetermined mold after 20 seconds. The mold was held at 25 ° C. and a humidity of 65% for 3 minutes, reacted and solidified, and then the gel was taken out of the mold, and further held at a temperature of 30 ° C. and a humidity of 45% for 6 minutes, reacted and aged.
As a result, the frustoconical (donut-shaped) urethane hydrogel shown in FIGS. 1 and 2 was obtained. The obtained polyurethane gel was sealed in an aluminum laminated film bag.
Table 1 shows the result of measuring the tensile strength of the obtained polyurethane gel and the result of measuring the tensile strength of a sample stored at 50 ° C. for 10 days as a deterioration acceleration test.

Example 2
(Method for producing hydrophilic urethane prepolymer)
7.7 g of liquid MDI (manufactured by Lupranate MI BASF INOAC Polyurethane Co., Ltd.) was added to 26 g of polyoxypropylated glycerin (Sanix GP-1000, Sanyo Chemical Industries, Ltd., average molecular weight 1000) while stirring under a nitrogen atmosphere The mixture was heated and then cooled to obtain a first stage prepolymer. When a calibration curve was prepared in advance and measured by GPC, the ratio of those prepolymerized (monomer or higher) was 71.8%, 2,4-MDI 15.6%, and 4,4-MDI. It was 12.6%. To this prepolymer, 5.62 g of the above liquid MDI and 16.85 g of Cr-MDI (polymeric MDI, Lupranate M-20S BASF INOAC Polyurethane Co., Ltd.) were added to obtain a hydrophilic polyurethane prepolymer. When this was measured by GPC, the ratio of 2,4MDI was 15%, and the ratio of 4,4MDI was 29%.
The same operation as in Example 1 was performed except that the hydrophilic polyurethane prepolymer was used.

Comparative Example 1
(Method for producing hydrophilic urethane prepolymer)
7.7 g of liquid MDI (manufactured by Lupranate MS BASF INOAC Polyurethane Co., Ltd.) is added to 26 g of polyoxypropylated glycerin (Sanix GP-1000, Sanyo Chemical Industries, Ltd., average molecular weight 1000) while stirring under a nitrogen atmosphere The mixture was heated and then cooled to obtain a first stage prepolymer. At this time, the ratio of those prepolymerized (monomer or higher) was 70.4%, 2,4MDI 0%, and 4,4MDI 29.6%. To this prepolymer, 5.6 g of the above liquid MDI and 16.8 g of Cr-MDI (polymeric MDI, Lupranate M-20S BASF INOAC Polyurethane Co., Ltd.) were added to obtain a hydrophilic urethane prepolymer. When this was measured by GPC, the ratio of 2,4MDI was 0%, and the ratio of 4,4MDI was 44%.
The same operation as in Example 1 was performed except that the above hydrophilic polyurethane prepolymer was used.

Comparative Example 2
(Method for producing hydrophilic urethane prepolymer)
7.7 g of liquid MDI (manufactured by Lupranate MI BASF INOAC Polyurethane Co., Ltd.) was added to 26 g of polyoxypropylated glycerin (Sanix GP-1000, Sanyo Chemical Industries, Ltd., average molecular weight 1000) while stirring under a nitrogen atmosphere. The mixture was heated and then cooled to obtain a first stage prepolymer. At this time, the ratio of those prepolymerized (monomer or higher) was 71.8%, 2,4MDI 15.6%, and 4,4MDI 12.6%. To this prepolymer, 2.81 g of liquid MDI (manufactured by Lupranate MI BASF INOAC Polyurethane Co., Ltd.) and 2.81 g of another liquid MDI (manufactured by Lupranate MS BASF INOAC Polyurethane Co., Ltd.), Cr-MDI (Polymeric MDI, Lupranate M-) 16.85 g of 20S BASF INOAC Polyurethane Co., Ltd.) was added to obtain a hydrophilic urethane prepolymer. When this was measured by GPC, the ratio of 2,4MDI was 6%, and the ratio of 4,4MDI was 38%.
The same operation as in Example 1 was performed except that the urethane prepolymer was used.

  The electrode pads obtained in Examples 1 and 2 have higher tensile strength and lower deterioration rate than Comparative Examples 1 and 2, and have a quality that can be used as an electrode pad even after 1 year. It was.

  The electrode pad made of the water-containing polyurethane gel of the present invention is used in the fields of medical and cushioning materials.

Claims (6)

Produced by a step of gelling a mixture comprising a hydrophilic polyurethane prepolymer comprising a polyisocyanate component and a polyol component and water;
An electrode pad comprising 10 to 50% by weight of an isomer having an isocyanate group at positions 2 and 4 in the hydrophilic polyurethane prepolymer.   The electrode pad according to claim 1, wherein the isomer is 2,4 methylenediphenyl diisocyanate.   The polyol component has at least one polyoxyalkylene chain selected from an oxyethylene group or an oxypropylene group, and is contained in an amount of 300 to 600 parts by weight of water with respect to 100 parts by weight of the hydrophilic polyurethane prepolymer. 3. The electrode pad according to 1 or 2.   A polyalkylene glycol type oil agent further comprising a plasticizer, wherein the plasticizer has a polyoxyalkylene chain in a main skeleton, and the polyoxyalkylene chain is composed of at least one of oxyethylene and oxypropylene. The electrode pad according to any one of items 1 to 3   The electrode pad according to any one of claims 1 to 4, further comprising a surfactant, and comprising a polyoxyethylene polyoxypropylene block polymer as the surfactant. Produced by a step of gelling a mixture comprising a hydrophilic polyurethane prepolymer comprising a polyisocyanate component and a polyol component and water;
An electrode pad comprising a polyurethane hydrogel having a tensile strength of 10 (N) or more and a deterioration rate of the tensile strength of 35% or less.

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