JP2013166868A - Pad for electrode - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a pad for an electrode composed of a polyurethane hydrous gel, having a sufficient threshold strength, preferably excellent in elastic force, durable to continuous usage and having little strength deterioration over time, and having reasonable elongation rate.SOLUTION: A polyurethane hydrous gel (1) is prepared by gelating a composition for forming a gel containing a polyisocyanate component and a polyol component, and has a methylenediphenyl structure in the main chain, wherein the polyisocyanate component before the urethanization reaction contains preferably 20 to 50 wt.% of a polymeric MDI (Cr-MDI).

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 elasticity and limit strength.
This electrode pad transmits electrical signals from the human body surface to recording devices such as electrocardiographs, electroencephalographs, electromyographs, etc. In addition, it is used between the metal electrode surface of the device and the human skin surface to maintain a good mechanical and electrical connection between them, and is particularly suitable for a suction electrode.

So far, when measuring an electrocardiogram or the like, a paste-like conductive cream has been applied to the metal electrode surface. However, since this conductive cream remains on the skin when the electrode is removed after the measurement, it has to be wiped off with paper or the like, and there are problems in terms of workability and usability.
In recent years, electrode pads using conductive gel molded products such as polyurethane polymers instead of this conductive cream have gradually increased, but sufficient elasticity, limit strength, and stability over time while maintaining conductivity ( Durability), there was no conductive gel molded product having elongation, and there were problems such as the need for replacement during use.
As a prior patent document, it is described in Unexamined-Japanese-Patent No. 2004-43577 (patent document 1) that the electrode pad of the outstanding performance is obtained by using a specific plasticizer. In addition, a method for producing a polyurethane hydrous gel having sufficient strength is described in Japanese Patent Application Laid-Open No. 2004-292718 (Patent Document 2) although the fields are different.

JP 2004-43577 A JP 2004-292718 A

However, in the electrode pad described in Japanese Patent Application Laid-Open No. 2004-43577 (Patent Document 1), strength deterioration with time is severe, and repeated loading and unloading to the electrode may tear along the electrode metal frame. In particular, a small size (small area) used for pediatric use is unsuitable because the thickness must be reduced.
In addition, in the invention described in Japanese Patent Application Laid-Open No. 2004-292718 (Patent Document 2), the reactivity is poor, it is difficult to gel, and a metal oxide or the like is used for imparting conductivity. It is unsuitable.
In the presence of such prior art, the present invention is an electrode comprising a polyurethane hydrogel having a sufficient limit strength, preferably excellent elastic force, little deterioration in strength over time, capable of withstanding continuous use, and having an appropriate elongation rate. The purpose is to provide a pad for use.

  In order to achieve the above object, a gel-forming composition comprising a polyisocyanate component and a polyol component is gelled to form an electrode pad comprising a polyurethane hydrous gel having a methylenediphenyl structure in the main chain, and before the urethanization reaction. An electrode pad comprising polymeric MDI (also referred to as “Cr-MDI”) in a polyisocyanate component is provided.

Since the gel-forming composition containing the polyisocyanate component and the polyol component is gelled to form a polyurethane hydrogel having a methylenediphenyl structure in the main chain, it is easy to form a thick gel and the water content can be set high. it can. Therefore, conductivity is required as compared with acrylic water-containing gel, which is preferable as an electrode pad formed so as to cover the electrode of the device.
Since polymeric MDI is contained in the polyisocyanate component before the urethanization reaction, a gel having excellent strength can be formed. The strength includes both a limit strength until it is pulled to break and a predetermined long strength that is a strength when pulled by a predetermined amount. Both strengths are excellent gels. Since it is excellent in the limit strength, it is an electrode pad that is difficult to tear even if it is a gel and has excellent practicality. In addition, in the case of conventional electrode pads, especially in the case of electrode pads with a thin film portion, such as children's electrode pads, the thin film portion is easily cut off by loading / unloading work, but it is superior in strength to a predetermined length. The thin film portion is also difficult to break, and is particularly suitable as an electrode pad having a thin film portion.

  In addition, since the content of polymeric MDI (Cr-MDI) in the polyisocyanate component before the urethanization reaction is 20 to 50% by weight, it is possible to obtain an electrode pad that is excellent in strength and good in terms of elongation. .

It can be set as the electrode pad which contains 10 to 50weight% of 2,4'-MDI in the polyisocyanate component before a urethanation reaction. Since 2,4′-MDI is contained in the polyisocyanate component before the urethanization reaction in an amount of 10 to 50% by weight, it is a highly stable electrode pad with little deterioration in strength over time.
An electrode pad having a limit strength of 11 N or more is not easily broken and excellent in practicality, and can be suitably used as an electrode pad used for an electrocardiogram measurement electrode or the like.
The critical strength here is measured by the following method. That is, it has a frustoconical outer shape with an upper base (diameter 18 mm) having an opening (diameter 7 mm) in the center, a lower base (diameter 25 mm) having an opening (diameter 4 mm), and a side wall. A hollow test sample (height between the upper and lower bases: 12 mm in height, 3 mm in thickness of each of the upper, lower and side walls) is hooked onto the upper opening of the test sample and a temperature of 2 mm is hooked. This is the maximum load applied when the test sample is pulled under the conditions of 23 ° C., humidity 54%, and tensile speed 300 mm / min.
Further, if the deterioration rate within one year of the limit strength is 35% or less, it is not necessary to replace frequently, and mixing of measurement noise due to product deterioration can be prevented.

The polyol component may have one or more polyoxyalkylene chains containing at least one of an oxypropylene group and an oxyethylene group.
Since a polyol component having at least one polyoxyalkylene chain containing at least one of an oxypropylene group and an oxyethylene group is used, a polyurethane water content having a high moisture retention and softness by urethanization with the isocyanate component A gel can be formed.

  It can be set as the electrode pad which contains 20-95 weight part of water in 100 weight part of the composition for gel formation. Since 20 to 95 parts by weight of water is contained in 100 parts by weight of the gel-forming composition, the gel can be made to have a good touch when it comes into contact with human skin. More preferably, the amount of water is 40 to 85 parts by weight.

It can be set as the electrode pad containing the plasticizer which is the polyalkylene glycol type | mold oil agent which has the polyoxyalkylene chain which consists of at least any one of oxyethylene or oxypropylene in a main skeleton.
Since it contains a plasticizer which is a polyalkylene glycol type oil having a polyoxyalkylene chain consisting of at least one of oxyethylene or oxypropylene in the main skeleton, a water-containing polyurethane water-containing gel having high moisture retention and excellent flexibility Can be obtained.

  It can be set as the pad for electrodes containing a polyoxyethylene polyoxypropylene block polymer as surfactant. Since the electrode pad includes a polyoxyethylene polyoxypropylene block polymer as a surfactant, a polyurethane hydrogel having higher moisture retention, excellent flexibility, and improved appearance can be obtained.

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

  The electrode pad of the present invention is an electrode pad obtained by gelling a gel-forming composition containing a polyisocyanate component and a polyol component to produce a polyurethane hydrogel having a methylenediphenyl structure in the main chain.

(1) Gel-forming composition The gel-forming composition is a raw material mixture for obtaining a polyurethane water-containing gel, and includes a polyisocyanate component and a polyol component, water, and other various additives as raw material components to be urethanated. Is included.
As the polyisocyanate component, a component derived from a known polyisocyanate can be used. Examples of polyisocyanates include methylene diphenyl diisocyanate abbreviated to MDI, toluene diisocyanate, hexamethylene diisocyanate, isophorone diisocyanate, cyclohexane diisocyanate and the like, triisocyanate, polymeric MDI (Cr-MDI, crude MDI, and polymethylene polyphenyl polyisocyanate). And the like). These polyisocyanates may be used alone or in combination of two or more.

  It is preferable that these polyisocyanate components contain polymeric MDI, and the content of polymeric MDI is preferably 20% to 50% by weight in the polyisocyanate component. If it is less than 20%, the polymer skeleton is reduced, so that the flexibility is high but the strength is inferior. When it is contained in excess of 50%, the reactivity with water is lowered and it does not gel, or it may be easily gelled with little elongation even when gelled.

  Some diisocyanates have isomers in the 2,2′-position, 2,4′-position, and 4,4′-position, and the polyisocyanate component contains 10 to 50 weight percent of 2,4′-MDI. % Is preferable. When the content of 2,4'-MDI in the polyisocyanate component is less than 10% by weight, main chain scission tends to proceed due to hydrolysis or the like, and deterioration with time tends to occur. Moreover, when it exceeds 50 weight%, reactivity may fall and it may be difficult to obtain a desired gel.

  The polyol component preferably has at least one polyoxyalkylene chain. The polyoxyalkylene chain includes an oxypropylene group, an oxyethylene group, an oxybutylene group, and the like. 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.

  The polyol component is preferably contained 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 shape retention of the gel may deteriorate, and the strength may decrease.

  Other components: In addition to the polyisocyanate component and the polyol component, the gel-forming composition contains various additives such as a plasticizer, a surfactant, an electrolyte, and a reaction accelerator as necessary. Also good. An example of components that can be mixed will be described below.

(I) Plasticizer The plasticizer plays a role of maintaining good affinity between the urethane skeleton component and water. Therefore, by including a plasticizer, moisture is not separated from the polyurethane hydrogel, and a desired shape can be maintained. And since the moisture retention property increases, the flexibility of the gel can be ensured.
As the plasticizer, a polyalkylene glycol type oil agent having a polyoxyalkylene chain in the main skeleton and containing at least one of oxyethylene or oxypropylene is preferable.
As such a plasticizer, polyoxypropylated glycerin (average molecular weight is preferably 200 to 5000), polyoxypropylated sorbitol (average molecular weight is preferably 300 to 5000), plastic containing two or more polyoxyalkylene chains. Agents, glycol diethers and the like.

Here, examples containing two or more polyoxyalkylene chains include a plasticizer (a): a polyalkylene containing an oxyethylene group and an oxypropylene group, of which the oxypropylene group accounts for 60 to 90% by weight of the total molecular weight. Glycol (average molecular weight is preferably 200 to 6000) and plasticizer (b): polyoxyethylene group and oxypropylene group, of which the oxypropylene group accounts for 30 to 90% by weight of the total molecular weight of the polyoxyalkylene chain Examples include monoethers of alkylene glycol (average molecular weight is preferably 200 to 4000). One hydroxyl group of the polyalkylene glycol monoether contained in the plasticizer (b) may be ether-bonded to the alkyl group.
Further, the plasticizer containing two or more kinds of polyoxyalkylene chains may be a random copolymer or a block copolymer.

  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 gel-forming composition 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 electrode may not be sufficiently adhered to the electrode. Moreover, when it exceeds 30 weight%, a polyurethane water-containing gel may become too soft and a shape may not be hold | maintained. A more preferable content is 10 to 20% by weight.

(Ii) Surfactant The surfactant has an action to increase the compatibility of the urethane skeleton component and water, prevents water separation after gelation, stabilizes the electrolyte solution, and prevents self-adhesion of the generated polyurethane water-containing gel. Etc. are effective.
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) Electrolyte As the electrolyte, commonly used sodium chloride, potassium chloride and the like are suitable. The content of the electrolyte is preferably 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.

(Iv) Chain extender Examples of the chain extender include diols such as ethylene glycol, propylene glycol and butanediol, diamines such as ethylenediamine, toluenediamine and isophoronediamine, and other known chain extenders.
(V) Others In addition to the above components, amines such as triethanolamine, reaction accelerators for polymerization such as sodium carbonate and sodium silicate, reaction inhibitors for acidic substances such as p-toluenesulfonic acid, Examples thereof include a gel reinforcing filler such as Aerosil, an antifungal agent such as Amical, and a coloring agent.

  In addition, it contains water other than the said component, and it is preferable that content of water is 20 to 95 weight% in the composition for gel formation. When the water content is less than 20% by weight, the produced gel may become too hard to attach to the electrode. Moreover, when it exceeds 95 weight%, the gel which has sufficient intensity | strength may not produce | generate. A more preferable content is 50 to 80% by weight.

(2) Gelation The gel-forming composition becomes a polyurethane hydrogel by gelation.
Gelation is performed by stirring the components of the gel-forming composition so that they are uniformly mixed, and then injecting them into a mold, etc., and maintaining (reacting, crosslinking) and aging them in an appropriate temperature and humidity environment. Do.
The reaction temperature is preferably 20 to 50 ° C. If the reaction between the polyisocyanate component and the polyol component is less than 20 ° C., the skeleton formation rate decreases and the dimensional stability of the gel decreases, and if the reaction exceeds 50 ° C., the foaming rate increases. This is because the appearance may be rough. The reaction humidity is preferably 40 to 70% RH (relative humidity). It is because the case where the moisture content in a gel does not become a desired moisture content may arise when it is outside the range of 40-70% RH. Although reaction time is suitably adjusted according to a molded article, it can be made into 3 to 60 minutes. If it is less than 3 minutes, the skeleton formation is insufficient and the dimensional stability of the gel is lowered, and if it exceeds 60 minutes, foaming increases and the appearance may be roughened. In the gelation step, the reaction rate may be adjusted by adding treatments such as heating, cooling, and pH adjustment as necessary.

(3) Electrode Pad The electrode pad can be produced by forming the polyurethane hydrogel in a mold or container for forming an electrode pad.
Examples of the shape of the electrode pad include an ellipse, a circle, a heart shape, a semicircle, a semi-elliptical shape, a square, a rectangle, a trapezoid, a truncated cone, a triangle, or a combination thereof. It is preferable to have a shape along the application site. A frustoconical (donut-shaped) electrode pad having one hole communicating from the viewpoint of improving adhesion to a subject such as skin and connectivity with the electrode is an example of a suitable shape.

(4) Applications of electrode pads Electrode pads are used to transmit electrical signals from the surface of the human body to devices such as electrocardiographs, electroencephalographs, and electromyographs, and from the devices such as low-frequency treatment devices to the surface of the human body. It can be used for purposes such as communicating. In other words, it can be suitably used for applications in which the mechanical and electrical connection between the electrodes and the human body is kept good by being interposed between the electrodes and the human body constituting these devices.

(5) Evaluation of electrode pads Test samples of electrode pads were prepared, and various tests were performed to evaluate the performance.
Test sample :
The molded product of the electrode pad shown in FIGS. 1 and 2 was produced as a test sample. FIG. 1 is a schematic perspective view of the electrode pad 1 as viewed obliquely from above, and FIG. 2 is a schematic cross-sectional view of the electrode pad 1.

  The electrode pad 1 is made of a polyurethane hydrogel, has a frustoconical outer shape having an upper bottom portion 2, a lower bottom portion 3, and a side wall portion 4. Further, the upper bottom 2 and the lower bottom 3 are respectively formed with openings 8 and 9 at the centers thereof. The electrode pad 1 has a diameter of 18 mm for the upper base 2, a diameter of 25 mm for the lower base 3, a height of 12 mm between the upper base 2 and the lower base 3, and each thickness of the upper base 2, the lower base 3 and the side wall 4. The diameter of the opening (upper opening) 8 of the upper bottom 5 is 7 mm, and the diameter of the opening (lower opening) 9 of the lower bottom 6 is 4 mm. Therefore, the upper opening 8 is larger than the lower opening 9.

Test method :
FIG. 3 shows a schematic view when a tensile test is performed using the electrode pad 1. As shown in FIG. 2 and FIG. 3, a hook 10 formed in a bowl shape was hooked on the upper opening 8 of the test sample, and a tensile test was conducted using a Tensilon universal testing machine (Orientec Co., Ltd., RTE-1210). The hook 10 formed in a bowl shape is a stainless wire having a diameter of 2 mm, and the hook 10 is formed so as to enter the upper opening 8.

(I) Limit strength The test sample was pulled under conditions of a temperature of 23 ° C., a humidity of 54%, and a test speed of 300 mm / min, and the maximum load applied when the test sample was torn was measured as the limit strength.
The limit strength is a measure representing the strength of the electrode pad, and if the strength is large, it becomes difficult to tear or chip during use. This limit strength is preferably 10 to 25 N, and more preferably 12 to 21 N, from the viewpoint of preventing breakage and workability (easy to attach and detach) when mounting to or removing from the electrode.

(Ii) Elastic force (predetermined long strength)
The load when a predetermined stress was applied to the test sample was measured. In actual measurement, a load (stress) when the distance of the hook 10 moved by 30 mm was measured, and this load value was defined as “predetermined length strength”, and this predetermined length strength was used as a measure of elastic force. The lower the predetermined length strength, the lower is the resistance of the thinly formed portion, and the more easily the portion is thinly formed. Therefore, the predetermined long strength is preferably 3N or more, and more preferably 4N or more. On the other hand, if the predetermined long strength is too high, the predetermined long strength is preferably 7N or less, more preferably 6N or less, because it is difficult to deform and the workability is deteriorated. Therefore, this elastic force is preferably 3 to 7N, more preferably 4 to 6N from the comprehensive viewpoint of prevention of breakage and workability at the time of attachment to or removal from the electrode.

(Iii) Elongation rate The elongation rate was obtained by dividing the sample length of the test sample when the maximum load (limit strength) was detected by the sample length before the test (22 mm in the above case) by 100.
Elongation rate (%) = (Test sample length when detecting limit strength) / (Initial test sample length) × 100
When the elongation rate is high, it can be greatly deformed. However, 400 to 600% is preferable, and 500 to 600% is preferable from the viewpoint of prevention of breakage and workability (easy to attach / detach) when attaching to / detaching from the electrode. More preferred.

(Iv) Deterioration with time (deterioration rate)
Empirically, it is known that the deterioration with time at 50 ° C. for 10 days is equivalent to the deterioration with time at room temperature for one year. Therefore, after performing an accelerated test in which the test sample was stored at 50 ° C. for 10 days, the tensile test was performed. The degree of deterioration with time was determined by multiplying 100 by the value obtained by dividing the limit strength before the acceleration test by the limit strength after the acceleration test.
Degradation rate (%) = (limit strength before acceleration test) / (limit strength after acceleration test) × 100

  The deterioration rate indicates the stability of the electrode pad over time, and a lower deterioration rate is preferable. Therefore, considering practical stability and replacement frequency, 35% or less is preferable, and 25% or less is more preferable.

Example 1 :
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 Warmed and then cooled. At this point, the ratio of urethane-modified (prepolymer or polymer having a urethane bond of one or more monomers) is 71.8% by weight, 2,4′-MDI is 15.6% by weight, 4,4 ′ -MDI was 12.6 wt%. Further, 8.42 g of liquid MDI similar to the above and 14.04 g of Cr-MDI (polymeric MDI, Lupranate M-20S BASF INOAC Polyurethane Co., Ltd.) were added and diluted to adjust the viscosity. When the obtained mixture was measured by GPC, the proportion of 2,4′-MDI was 17% by weight, the proportion of 4,4′-MDI was 27% by weight, and the proportion of Cr-MDI was 25.1% by weight. Met. When the content of each MDI is shown as a ratio in the polyisocyanate component before the urethanization reaction, 2,4′-MDI is 24.6% by weight, 4,4′-MDI is 39.1% by weight, Cr— MDI was 36.3% by weight.

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) 0.75 g, Yottle DP-95 (antibacterial agent manufactured by Mitsui Chemicals) 0.037 g, sodium chloride 0.63 g, sodium silicate solution (water glass manufactured by Junsei Chemical Co., Ltd.) 0.64 g 24.4 g of the eye mixture was stirred rapidly and poured into the mold after 20 seconds. The mold was held at a temperature of 25 ° C. and a humidity of 65% for 3 minutes to react and solidify, and then the gel was removed from the mold and further held at a temperature of 30 ° C. and a humidity of 45% for 6 minutes to react and age.
As a result, the frustoconical polyurethane hydrogel shown in FIGS. 1 and 2 was obtained. The obtained polyurethane hydrogel was sealed in an aluminum laminate film bag.

Example 2 :
In the same manner as in Example 1, while stirring under a nitrogen atmosphere, the temperature was raised and then cooled, and the ratio of those urethaned (prepolymer or polymer having a urethane bond of a monomer or higher) was 71.8% by weight. , 2,4′-MDI was 15.6 wt%, and 4,4′-MDI was 12.6 wt%. Next, 5.62 g and 16.85 g of the same liquid MDI and Cr-MDI as in Example 1 were added and diluted to adjust the viscosity. Then, when the obtained mixture was measured by GPC, the proportion of 2,4′-MDI was 15% by weight, the proportion of 4,4′-MDI was 29% by weight, and the proportion of Cr-MDI was 30.0% by weight. Met. When the content of each MDI is expressed as a ratio in the polyisocyanate component before the urethanization reaction, 2,4′-MDI is 20.3% by weight, 4,4′-MDI is 39.2% by weight, Cr— The MDI was 40.5% by weight.
Then, the same process as Example 1 was performed and gelatinized and the polyurethane hydrogel of the same shape as Example 1 was obtained. The obtained polyurethane hydrogel was sealed in an aluminum laminate film bag.

Example 3 :
In the same manner as in Example 1, while stirring under a nitrogen atmosphere, the temperature was raised and then cooled, and the ratio of those urethaned (prepolymer or polymer having a urethane bond of a monomer or higher) was 71.8% by weight. , 2,4′-MDI was 15.6 wt%, and 4,4′-MDI was 12.6 wt%. Next, 25.27 g of the same Cr-MDI as in Example 1 was added and diluted to adjust the viscosity. When the obtained mixture was measured by GPC, the proportion of 2,4′-MDI was 15.6 wt%, the proportion of 4,4′-MDI was 12.6 wt%, and the proportion of Cr-MDI was 42 0.9% by weight. When the content of each MDI is expressed as a ratio in the polyisocyanate component before the urethanization reaction, 2,4′-MDI is 21.9 wt%, 4,4′-MDI is 17.7 wt%, Cr— The MDI was 60.3% by weight.
Then, the same process as Example 1 was performed and gelatinized and the polyurethane hydrogel of the same shape as Example 1 was obtained. The obtained polyurethane hydrogel was sealed in an aluminum laminate film bag.

Example 4 :
Example 1 was performed in the same manner as in Example 1 except that the type of liquid MDI was changed to liquid MDI (manufactured by Lupranate MS BASF INOAC Polyurethane Co., Ltd.). At this time, the ratio of the urethane-modified product was 70.4% by weight, 2,4′-MDI was 0% by weight, and 4,4′-MDI was 29.6% by weight. To this mixture, 5.6 g of the same liquid MDI (manufactured by Lupranate MS BASF INOAC Polyurethane Co., Ltd.) and 16.8 g of the same Cr-MDI as in Example 1 were added and diluted to adjust the viscosity. And when the obtained mixture was measured by GPC, the proportion of 2,4′-MDI in this mixture was 0% by weight, the proportion of 4,4′-MDI was 44% by weight, and the proportion of Cr-MDI was 30%. .2% by weight. When the content of each MDI is expressed as a ratio in the polyisocyanate component before the urethanization reaction, 2,4′-MDI is 0% by weight, 4,4′-MDI is 59.3% by weight, and Cr-MDI is It was 40.7% by weight.
Then, the same process as Example 1 was performed and gelatinized and the polyurethane hydrogel of the same shape as Example 1 was obtained. The obtained polyurethane hydrogel was sealed in an aluminum laminate film bag.

Example 5 :
In the same manner as in Example 1, a first-stage mixture was obtained. Next, 2.81 g of the same liquid MDI (lupranate MI) as in Example 1 was added, 2.81 g of the same liquid MDI (lupranate MS) as in Example 4, and 16.8 g of the same Cr-MDI as in Example 1 were added and diluted. The viscosity was adjusted. The obtained second-stage mixture was measured by GPC. The proportion of 2,4′-MDI in this mixture was 6% by weight, the proportion of 4,4′-MDI was 38% by weight, and Cr-MDI. The ratio was 30.1% by weight. When the content of each MDI is expressed as a ratio in the polyisocyanate component before the urethanization reaction, 2,4′-MDI is 8.1 wt%, 4,4′-MDI is 51.3 wt%, Cr— The MDI was 40.6% by weight.
Then, the same process as Example 1 was performed and gelatinized and the polyurethane hydrogel of the same shape as Example 1 was obtained. The obtained polyurethane hydrogel was sealed in an aluminum laminate film bag.

Example 6 :
In the same manner as in Example 1, a first-stage mixture was obtained. Next, 33.7 g of the same liquid MDI (lupranate MI) as in Example 1 was added and diluted to adjust the viscosity. And when the obtained 2nd stage mixture was measured by GPC, the ratio of 2,4'-MDI in this mixture was 33.6 weight%, and the ratio of 4,4'-MDI was 30.5 weight%. The proportion of Cr-MDI was 0% by weight. When the content of each MDI is expressed as a ratio in the polyisocyanate component before the urethanization reaction, 2,4′-MDI is 52.4% by weight, 4,4′-MDI is 47.6% by weight, Cr— MDI was 0% by weight.
Then, the same process as Example 1 was performed and gelatinized and the polyurethane hydrogel of the same shape as Example 1 was obtained. The obtained polyurethane hydrogel was sealed in an aluminum laminate film bag.

The above-mentioned tensile test was performed on the obtained polyurethane hydrogel of each example, and the limit strength, elastic force (predetermined length strength), elongation rate, and deterioration with time (deterioration rate) were measured. The results are shown in Table 1.
Table 1 also shows 2,4′-MDI in the polyisocyanate component before the urethanization reaction,
The respective ratios of 4,4′-MDI and polymeric MDI (Cr-MDI) are shown.

The limiting strengths of Examples 1 to 5 containing polymeric MDI are all within the range of 17 to 21 N, and are practically excellent electrode pads. However, the limit strength of Example 6 that does not include polymeric MDI is 10.3 N, which is weak in strength and may be broken during loading and unloading. And Example 1, Example 2, Example 4, Example 5 which contains the content of polymeric MDI in 20-50 weight% in the isocyanate component before a urethanation reaction is 400% or more, and is to an electrode. Even if it is greatly deformed at the time of loading and unloading, it is hard to tear and excellent in handling.
The deterioration rate of Examples 1 to 3 containing 2,4′-MDI in the isocyanate component before the urethanization reaction is 10% by weight or less is 35% or less, and the limit strength after the acceleration test is 11N or more. It is stable over time that can be used as an electrode pad even after one year.

  Furthermore, Examples 1 and 2 containing 20 to 50% by weight of polymeric MDI in the isocyanate component before the urethanization reaction and 20% by weight or more of 2,4′-MDI have a predetermined long strength of 4 to 6N. In the case of a small and thin electrode pad such as a child electrode pad, it is particularly excellent in preventing damage and workability when attaching to and detaching from the electrode, and the deterioration rate is also high. It is 25% or less and is excellent from the viewpoint of long-term stability.

  The electrode pad comprising the polyurethane hydrogel of the present invention can be used for medical purposes, but can also be applied to the field of cushioning materials as other uses.

DESCRIPTION OF SYMBOLS 1 Electrode pad 2 Upper bottom part 3 Lower bottom part 4 Side wall part 7 Cavity 8 Opening (upper opening)
9 Opening (lower opening)
10 hook

Claims (8)

An electrode pad comprising a polyurethane hydrogel having a methylene diphenyl structure in the main chain by gelling a gel-forming composition containing a polyisocyanate component and a polyol component,
An electrode pad comprising polymeric MDI (Cr-MDI) in a polyisocyanate component before urethanization reaction.   The electrode pad according to claim 1, wherein the content of polymeric MDI in the polyisocyanate component before the urethanization reaction is 20 to 50% by weight.   The electrode pad according to claim 1 or 2, wherein 10 to 50% by weight of 2,4'-MDI is contained in the polyisocyanate component before the urethanization reaction.   It has a frustoconical outer shape with an upper bottom (diameter 18 mm) having an opening (diameter 7 mm) in the center, a lower bottom (diameter 25 mm) having an opening (diameter 4 mm) in the center, and a side wall. A hook with a diameter of 2 mm is hooked on the upper opening of the test sample (the height between the upper and lower bottoms is 12 mm, the thickness of each of the upper, lower and side walls is 3 mm), the temperature is 23 ° C., the humidity is 54%, and the tensile speed is The electrode pad according to any one of claims 1 to 3, wherein the test sample is pulled under a condition of 300 mm / min and a maximum load applied when the test sample is torn is defined as a limit strength, and the limit strength is 11 N or more. .   The electrode pad according to any one of claims 1 to 4, wherein the polyol component has at least one polyoxyalkylene chain containing at least one of an oxypropylene group and an oxyethylene group.   The electrode pad according to any one of claims 1 to 5, comprising 20 to 95 parts by weight of water in 100 parts by weight of the gel-forming composition.   The electrode pad according to any one of claims 1 to 6, comprising a plasticizer which is a polyalkylene glycol type oil having a polyoxyalkylene chain composed of at least one of oxyethylene or oxypropylene in the main skeleton. The electrode pad according to any one of claims 1 to 7, comprising a polyoxyethylene polyoxypropylene block polymer as a surfactant.

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