JPH07100120A - Medical conductive medium - Google Patents

Abstract

(57) [Summary] [Purpose] Electrodes for living organisms that are used to transmit electrical signals from living organisms to medical diagnostic equipment and to introduce low frequencies into the living organisms for pain reduction and treatment, etc. A medium for contacting with a skin surface, particularly a medical conductive medium having low irritation to the skin is provided. [Structure] An acrylic polymer formed by polymerizing an alkyl (meth) acrylate having an alkyl group having 1 to 14 carbon atoms as a main component, and an inorganic salt composed of a carbonate and a monovalent or divalent metal ion. A gel-like conductive medium is obtained by containing it and crosslinking it.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a conductive medium used for medical purposes, and more specifically, it is a conductive medium used as a contact medium in an electrode for a living body for sticking to a living body surface for diagnosis and treatment. Regarding sex media.

[0002]

2. Description of the Related Art Conventionally, as a biomedical electrode formed by forming a conductive medium layer on an electrode plate, a weak current such as a low frequency is applied to a living body from an external device to promote blood flow and massage effect. Various electrodes such as expected therapeutic electrodes, diagnostic electrodes used in electrocardiographs for measuring and measuring weak currents in the body, earth electrodes used when using an electric scalpel, electrodes used for cosmetic purposes such as hair removal, etc. Things are being developed.

The conductive medium functions as a contact medium between the electrode plate and the surface of the living body in such various electrodes, and requires appropriate skin adhesion and conductivity. As a conductive medium used for medical purposes, a water-containing gel-like adhesive medium is known in which a water-soluble polymer such as sodium polyacrylate or polyvinyl alcohol is used as a base polymer, sodium chloride is used as an electrolyte, and water is further contained. ing.

However, such a water-containing pressure-sensitive adhesive medium is easily affected by atmospheric humidity during storage and use, and moisture in the atmosphere and perspiration from the surface of the adhered skin are adsorbed to the pressure-sensitive adhesive medium. However, water in the adhesive medium may be desorbed, resulting in fluctuations in adhesive properties and conductivity. Therefore, in reality, expensive packaging materials are usually used for hermetically sealing even during storage.

On the other hand, a so-called non-water type adhesive medium has been proposed in order to solve the drawbacks of the water-containing type electrically conductive adhesive medium (see Japanese Patent Laid-Open No. 267041/1993).
This adhesive medium contains an alkyl acrylate having a long chain of alkylene oxide and a side chain having a dissociative functional group as a base polymer, and contains a low-molecular dissociable salt as an electrolyte.
It is composed of a three-dimensional crosslinked structure.

However, since alkyl acrylate having a long chain of alkylene oxide as a side chain is not a general-purpose polymer, its preparation is complicated. Further, in order to exert practical conductivity, it is necessary to contain a relatively large amount of a low-molecular dissociative salt, for example, when using lithium perchlorate described in Examples of the same publication. However, an amount of 1 part by weight or more per 100 parts by weight of the base polymer is required. As described above, the adhesive medium containing a large amount of lithium perchlorate has excellent conductivity, but has a large irritation to the skin surface and is liable to cause rashes, etc., which is practically not preferable.

[0007]

DISCLOSURE OF THE INVENTION It is an object of the present invention to exert excellent conductivity in developing the above-mentioned non-aqueous type conductive medium and also to stimulate the skin surface to be adhered. The purpose of the present invention is to provide a medical conductive medium.

[0008]

Means for Solving the Problems As a result of extensive studies conducted by the present inventors to achieve the above object, an acrylic polymer containing a general-purpose polymer (meth) acrylic acid alkyl ester as a main monomer In addition, it was found that the content of the inorganic salt as the electrolyte can be reduced by adding the carbonate ester as the solvent, and the present invention has been completed.

That is, according to the present invention, an acrylic polymer obtained by polymerizing at least 50% by weight of a (meth) acrylic acid alkyl ester having an alkyl group having 1 to 14 carbon atoms in the ester side chain, a carbonic acid ester, and a monovalent ester. Alternatively, the present invention provides a medical conductive medium containing an inorganic salt composed of a divalent metal ion and subjected to a crosslinking treatment. In particular, when propylene carbonate is used as the carbonic acid ester and a lithium salt is used as the inorganic salt, the effect of the present invention is remarkably exhibited, which is a preferred embodiment.

The acrylic polymer as the base polymer of the medical conductive medium in the present invention is to be freely compatible with the carbonic acid ester which will be described later, and to impart appropriate skin adhesiveness as necessary. And a (meth) acrylic acid alkyl ester having an alkyl group having 1 to 14 carbon atoms in the ester side chain as a main component monomer is at least 50
It is obtained by polymerizing in the range of 60% by weight, preferably 60 to 99% by weight. Specifically, it is an esterified product of an alkyl alcohol having 1 to 14 carbon atoms and acrylic acid or methacrylic acid, and can be used alone or in combination of two or more. Needless to say, the alkyl group may be linear or branched. If the polymerization amount of the (meth) acrylic acid alkyl ester is less than 50% by weight, sufficient skin adhesion may not be exhibited when tackiness is imparted as an adhesive medium.

The acrylic polymer in the present invention can be copolymerized with the above-mentioned (meth) acrylic acid alkyl ester having an alkyl group having 1 to 14 carbon atoms in the ester side chain as a main component monomer. It is possible to use a monomer obtained by copolymerizing such a monomer in an amount of 50% by weight or less, preferably 1 to 40% by weight. By copolymerizing such a monomer, it is possible to impart cohesiveness to the resulting polymer and to impart a crosslinking point during the crosslinking treatment described below. Even when the acrylic polymer does not have a functional group which becomes a reaction point at the time of cross-linking, the functional group which becomes a cross-linking point can be provided by performing known chemical modification such as hydrolysis treatment. It may be a polymer using only the above-mentioned (meth) acrylic acid alkyl ester.

As such a copolymerizable monomer,
For example, carboxyl group-containing monomers such as (meth) acrylic acid, (anhydrous) maleic acid, itaconic acid, crotonic acid, fumaric acid, (meth) acrylic acid 2-hydroxyethyl ester, (meth) acrylic acid 2-hydroxy Examples thereof include hydroxyl group-containing monomers such as propyl ester, and functional monomers such as (meth) acrylamide and (meth) acrylic acid phosphoric acid alkyl ester. Further, an appropriate amount of (meth) acrylic acid alkyl ester having a side chain of an alkyl group having 15 or more carbon atoms may be polymerized as long as the compatibility with the carbonic acid ester is not impaired.

The carbonate ester to be contained in the conductive medium of the present invention together with the above-mentioned acrylic polymer is an organic solvent which is hydrophilic and has a relatively high dielectric constant, and has an extremely important function in the present invention. Is. That is,
This carbonic acid ester dissolves an inorganic salt contained as an electrolyte and exhibits good conductivity, and when it is compatible with the acrylic polymer, it has a viscoelastic property as a non-aqueous gel-like substance. It is given. In particular, the inclusion of carbonic acid ester makes it possible to reduce the amount of the inorganic salt added as an electrolyte, and thus plays an important role also in reducing skin irritation.

Examples of such carbonic acid esters include ethylene carbonate (ethylene carbonate), propylene carbonate (propylene carbonate), butylene carbonate (butylene carbonate), glycerin carbonate (glycerin carbonate), and the like. From the viewpoint of compatibility, it is preferable to use propylene carbonate. If the content of carbonic acid ester is small, practical conductivity cannot be expected, and if it is too large, the tackiness is lost and the cohesiveness is lowered. Therefore, in the range of 20 to 90% by weight, preferably 40 to 80% by weight. Include.

The inorganic salt to be contained as an electrolyte together with the carbonate ester is an inorganic salt having a cation component of a monovalent alkali metal ion such as lithium ion or sodium ion or a divalent alkaline earth metal ion such as calcium. Is. On the other hand, examples of the anion component include halogen ions such as chlorine ion, bromine ion, and iodine ion, perchlorate ion, and alkylsulfonate ion, which are combined with the above cation component. Of these, lithium salts are preferable from the viewpoint of conductivity, and lithium bromide, lithium iodide, lithium perchlorate, and lithium trifluorosulfonate are particularly preferable in view of the solubility with the carbonate ester. If such an inorganic salt is contained in a large amount, it may cause skin irritation when it comes into contact with the skin for a long time.
The content may be in the range of wt%, preferably 0.1 to 0.6 wt%.

As described above, the medical conductive medium of the present invention contains an acrylic polymer, a carbonic acid ester, and an inorganic salt as essential components. If necessary, a plasticizer or a softening agent may be added.
It can be blended in an amount of 0% by weight or less, preferably 5 to 30% by weight. Specifically, vegetable oils such as olive oil and castor oil, mineral oils such as process oil, dibutyl phthalate, dioctyl phthalate, diethyl adipate,
An ester oil such as isopropyl myristate can be used, and it is effective in improving the compatibility between the acrylic polymer and the carbonic acid ester and modifying the adhesive property.

The composition containing the respective components as described above is
By performing the cross-linking treatment, it is three-dimensionally cross-linked to be a gel-like material having conductivity. As a method of cross-linking treatment, a cross-linking agent is blended and heated to chemically cross-link the acrylic polymer in a state of containing a carbonic acid ester, or a radiation such as an ultraviolet ray, an electron beam or a γ-ray is used for physical treatment. Specifically, there is a method of crosslinking an acrylic polymer.

Examples of the cross-linking agent include phenylene diisocyanate, 2,4-toluylene diisocyanate, 4,
Diisocyanate compounds such as 4-diphenylmethane diisocyanate, hexamethylene diisocyanate, hydrogenated products of 4,4-diphenylmethane diisocyanate,
Compounds having at least two epoxy groups in the molecule such as polyethylene glycol diglycidyl ether and glycerin triglycidyl ether, and polyvalent metal organic compounds such as aluminum alcoholate and aluminum chelate can be used. Further, in the crosslinking reaction, an organic tin catalyst such as dioctyltin dilaurate or a neutralizing agent such as sodium hydroxide or triethanolamine can be used to control the crosslinking reaction.

The amount of such a cross-linking agent compounded greatly affects the cohesiveness and adhesive properties of the resulting cross-linked product.
0.01 to 10% by weight, preferably 0.05 to 5% by weight
Set to. If the blending amount is less than 0.01% by weight, the crosslinking is insufficient, resulting in insufficient cohesiveness, resulting in a gel-like material having no shape retention. Also, the compounding amount is 10% by weight
When it exceeds, the carbonic acid ester which is a liquid component is likely to bleed and the adhesive property is deteriorated.

On the other hand, in the case of crosslinking by irradiation with radiation such as electron beam or γ-ray, various peroxides such as benzoyl peroxide and lauroyl peroxide are added, if necessary, for the same reason as in the case of the above crosslinking agent. , The irradiation dose is 10 to 100 kGly, preferably 20 to 70
Adjust to the range of kGly. In the case of UV irradiation, UV irradiation can be carried out by coexisting with a UV radical initiator such as benzophenone and benzoylalkyl ether, and various sensitizers.

The medical conductive medium of the present invention obtained as described above is an acrylic polymer in a state where a specific inorganic salt is dissolved and dissociated as an electrolyte in carbonate ester which is a solvent having a relatively high dielectric constant. It is compatible with and contained in and retained, and exhibits excellent conductivity. Moreover, since this conductive medium is subjected to a cross-linking treatment, it not only has excellent cohesiveness, but also causes less irritation to the skin surface to which it is applied.

[0022]

EXAMPLES Examples of the medical conductive medium of the present invention will be shown below, which will be described more specifically. Needless to say, various applications can be made without departing from the technical idea of the present invention. In the following text, "parts" means "parts by weight".

Example 1 97 parts of acrylic acid n-butyl ester, methacrylic acid 3
Parts were copolymerized in toluene using azobisisobutyronitrile as the polymerization initiator. The weight average molecular weight (GLP method) of the obtained acrylic polymer was 570,000.

To 30 parts of the obtained acrylic polymer, 40 parts of propylene carbonate and 30 parts of diethyl phthalate were added and uniformly dissolved and stirred, and then 0.2 parts of lithium perchlorate was added and dissolved to obtain a uniform viscosity. A thick solution was prepared.

Next, 0.1 part of dioctyltin dilaurate and 0.5 part of carbodiimide-modified isocyanate were added to this viscous solution, and the mixture was stirred. .3
It was applied so as to have a thickness of mm and dried to obtain the medical conductive medium of the present invention.

Example 2 To 40 parts of the acrylic polymer used in Example 1, 40 parts of propylene carbonate and 20 parts of dibutyl phthalate were added and uniformly dissolved and stirred, and then 0.2 parts of lithium perchlorate was added. Added and dissolved to give a uniform viscous solution.

Next, 0.1 part of dioctyltin dilaurate and 0.3 part of aluminum chelate were added to this viscous solution and stirred, and then the solution was dried on a surface-treated silicone separator to a thickness of 0. It was applied so as to have a thickness of 3 mm and dried to obtain the medical conductive medium of the present invention.

Example 3 70 parts of acrylic acid ethyl ester, 29 parts of acrylic acid 2-ethylhexyl ester and 1 part of acrylic acid 2-hydroxymethyl ester were copolymerized in the same manner as in Example 1 to obtain an acrylic polymer. . The weight average molecular weight was 420,000.

To 35 parts of the obtained acrylic polymer, 45 parts of propylene carbonate and 20 parts of dibutyl phthalate were added and uniformly stirred, and then 0.4 parts of lithium iodide was added.
Dissolved into a uniform viscous solution.

Next, 0.1 part of dioctyltin dilaurate and 0.5 part of carbodiimide-modified isocyanate were added to this viscous solution and stirred, and then this solution was dried on a surface-treated silicone separator to a thickness of 0. .3
It was applied so as to have a thickness of mm and dried to obtain the medical conductive medium of the present invention.

Example 4 To 30 parts of the acrylic polymer used in Example 2, 40 parts of ethylene carbonate and 30 parts of dibutyl phthalate were added and uniformly stirred, and then 0.2 parts of lithium perchlorate was added. Addition,
Dissolved into a uniform viscous solution.

Next, 0.1 part of dioctyltin dilaurate and 0.2 part of carbodiimide-modified isocyanate were added to this viscous solution and stirred. .3
It was applied so as to have a thickness of mm and dried to obtain the medical conductive medium of the present invention.

Example 5 To 35 parts of the acrylic polymer used in Example 1, 45 parts of propylene carbonate and 20 parts of dibutyl phthalate were added and uniformly dissolved and stirred, and then 0.2 parts of lithium perchlorate, 0.1 part of benzoyl peroxide was added and dissolved to obtain a uniform viscous solution.

Next, this viscous solution was put into a petri dish to a depth of 0.3 mm, and after purging with nitrogen, 60 kGl.
The y-ray of y was irradiated to obtain a medical conductive medium of the present invention solidified in a gel form.

Comparative Example 1 Polyethylene glycol nonyl phenyl ether (EO = 2) was added to 30 parts of the acrylic polymer used in Example 1.
After 40 parts and 30 parts of dibutyl phthalate were added and uniformly stirred, 0.2 part of lithium perchlorate was added and dissolved to obtain a uniform viscous solution.

Next, 0.3 part of aluminum chelate was added to this viscous solution and stirred, and then this solution was applied onto a separator subjected to surface silicone treatment so that the thickness after drying would be 0.3 mm, and dried. Thus, a medical conductive medium was obtained.

Comparative Example 2 Polyethylene glycol nonyl phenyl ether (EO = 2) was added to 30 parts of the acrylic polymer used in Example 1.
After 40 parts and 30 parts of dibutyl phthalate were added and uniformly stirred, 1 part of lithium perchlorate was added and dissolved to obtain a uniform viscous solution.

Next, 0.3 part of aluminum chelate was added to this viscous solution and stirred, and then this solution was coated on a surface-silicone-treated separator so that the thickness after drying was 0.3 mm, and dried. Thus, a medical conductive medium was obtained.

Comparative Example 3 30 parts of the acrylic polymer used in Example 1, 40 parts of dibutyldiethylene glycol and 30 parts of dibutyl phthalate were used.
Parts and uniformly dissolved and stirred, then 0.2 parts of lithium perchlorate was added and dissolved to obtain a uniform viscous solution.

Next, 0.1 part of dioctyltin dilaurate and 0.6 part of carbodiimide-modified isocyanate were added to this viscous solution, and the mixture was stirred. .3
It was applied so as to have a thickness of mm and dried to obtain a medical conductive medium.

The electroconductivity, cohesiveness, tackiness, and skin irritation of the electroconductive mediums obtained in Examples 1 to 5 and Comparative Examples 1 to 3 were measured or judged according to the following criteria, and the results were obtained. Is shown in Table 1.

<Electrical Conductivity> An electrically conductive medium having a thickness of 0.3 mm obtained in each of the examples and the comparative examples was treated with an area of 10 mm × 10.
It was cut into mm, sandwiched by copper plates from both sides, and the impedance was measured using an LCR meter when an alternating voltage of 1 kHz and 1 mV was applied.

<Cohesiveness> The conductive medium having a thickness of 0.3 mm obtained in each of the examples and comparative examples was treated with an area of 20 mm × 20.
It was cut into mm, placed on a flat plate, and allowed to stand for 24 hours under the condition of 40 ° C., and its shape collapse (deformation) and outflow were observed. [○: good cohesiveness, x: poor cohesiveness]

<Adhesiveness> The conductive medium having a thickness of 0.3 mm obtained in each of the examples and comparative examples was treated with an area of 20 mm × 20.
It was cut into mm and the stickiness was judged by touching with a finger.
[○: Adhesiveness is sufficient, Δ: Slightly adhesiveness, X: No adhesiveness]

<Skin irritation> The conductive medium having a thickness of 0.3 mm obtained in each of Examples and Comparative Examples was treated with an area of 10 mm ×
It was cut into 10 mm and attached to the inside of the upper arm, and the skin irritation after 8 hours was evaluated. When pain or itch occurred during the test, the test was interrupted and the stimulation state was determined. [○: no irritation, △: weak irritation, x: obvious irritation]

[0046]

[Table 1]

As is clear from the results of Table 1, the medical conductive medium of the present invention has sufficient conductivity and cohesiveness, and has no skin irritation. Further, the tackiness can be appropriately imparted depending on the kind of the acrylic polymer which is a general-purpose polymer used.

The effect of the addition amount of lithium perchlorate as an electrolyte on the conductivity in the product of the present invention using a carbonic acid ester as an organic solvent and the conventional product using an ether type organic solvent was examined as follows. The results were examined in Examples and Comparative Examples.

Example 6 To 35 parts of the acrylic polymer used in Example 1, 40 parts of propylene carbonate and 25 parts of dibutyl phthalate were added and uniformly stirred. Lithium perchlorate was added as shown in Table 2 below. The indicated quantity was added and dissolved to give a uniform viscous solution.

Next, 0.3 part of aluminum chelate was added to this viscous solution and stirred, and then this solution was applied onto a separator subjected to surface silicone treatment so that the thickness after drying would be 0.3 mm, and dried. Then, the medical conductive medium of the present invention was obtained.

Comparative Examples 4 and 5 Polyethylene glycol nonyl phenyl ether (EO = 2) was added to 35 parts of the acrylic polymer used in Example 1.
40 parts (Comparative Example 4) or 40 parts of dibutyldiethylene glycol (Comparative Example 5) was added, 25 parts of dibutyl phthalate was further added, and the mixture was uniformly dissolved and stirred, and then lithium perchlorate was added in the number shown in Table 2 below. Dissolved into a uniform viscous solution.

Next, 0.3 part of aluminum chelate was added to this viscous solution and stirred, and then this solution was applied onto a separator subjected to surface silicone treatment so that the thickness after drying was 0.3 mm, and dried. Thus, a medical conductive medium was obtained.

[0053]

[Table 2]

As is clear from Table 2, the product of the present invention containing a carbonic acid ester shows a low resistance value even if the amount of lithium perchlorate is small, but the conventional product containing an ether type organic solvent contains a large amount. It can be seen that the resistance value cannot be lowered sufficiently if the condition is not met.

[0055]

INDUSTRIAL APPLICABILITY As described above, the medical conductive medium of the present invention contains an acrylic polymer as a general-purpose polymer, a carbonate ester as an organic solvent, and a specific inorganic salt as an electrolyte in a compatible state. Since the gel medium is crosslinked in this state, the impedance is low and excellent conductivity is exhibited. In addition, it has a good balance between cohesiveness and adhesiveness and has low skin irritation. Therefore, it is useful as a contact medium with various biological electrodes such as medical electrodes and therapeutic electrodes.

Claims (5)

[Claims] 1. An acrylic polymer obtained by polymerizing at least 50% by weight of a (meth) acrylic acid alkyl ester having an alkyl group having 1 to 14 carbon atoms in an ester side chain,
A medical conductive medium comprising a carbonic acid ester and an inorganic salt composed of a monovalent or divalent metal ion and having been subjected to a crosslinking treatment. 2. The medical conductive medium according to claim 1, wherein the carbonic acid ester is propylene carbonate. 3. The medical conductive medium according to claim 1, wherein the inorganic salt is a lithium salt. 4. The medical conductive medium according to claim 1, wherein the cross-linking treatment is carried out by blending a cross-linking agent or by irradiating with radiation. 5. The medical conductive medium according to claim 1, further comprising a plasticizer and / or a softening agent.