JP2718519B2 - Medical conductive adhesive - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Application Field] The present invention relates to a potential pickup electrode provided for medical use (for example, an electromyogram electrode, an electroencephalogram measurement electrode, an electrocardiogram electrode, an electro-oculography measurement electrode). The present invention relates to a conductive adhesive for medical use that electrically and physically connects an electrode for current passive use and an electrode for current passive use (for example, an electrode for an electrosurgical knife, an electrode for a low frequency treatment device, an electrode for iontophoresis, etc.) and a living body. It is.

[Prior art] In order to electrically and physically connect a potential pickup electrode and a current passive electrode to a living body,
Many conductive adhesives or conductive adhesive gels have been devised. A feature that is common to many of these already proposed technologies is that a polymer electrolyte is used as a means for expressing conductivity. One example is a carboxylate (for example, JP-A-56-36939, JP-B-57-28505),
Grade ammonium salts (for example, JP-A-62-95895, JP-A-6-95895)
2-133935, JP-A-62-3596391, JP-A-62-270135, JP-A-62-292140, JP-A-63-43646), sulfonic acid salt (for example, JP-A-55-81635, JP-A-58-1983) -135506, JP-A-59-125545), phosphates (for example, JP-A-61-8592)
5). Since these polymer electrolytes are very hard and brittle in a dry state, and have very low conductivity, a large amount of water or a large amount of water is required for the polymer to exhibit tackiness and conductivity. A plasticizer such as a polyhydric alcohol was required, and a long-term decrease in physical properties of the pressure-sensitive adhesive was inevitable. Furthermore, a fatal drawback when these polymer electrolytes are used for such a purpose is that the adhesive absorbs moisture when used under high humidity and absorbs sweat secreted from the skin, resulting in swelling of the adhesive. Is significantly reduced and the electrodes fall off the skin. This disadvantage is an unavoidable problem when the polymer electrolyte is used for such a purpose. JP-A-56-36
Since the polymer disclosed in 940 is composed of an anionic polymer, the drawback that the pressure-sensitive adhesive swells remarkably will be solved. The conductivity of the pressure-sensitive adhesive according to this technique is extremely low, and particularly when the potential pickup electrode and the living body are connected with this pressure-sensitive adhesive, it is highly expected that the power supply will suffer from hum noise.

Recently, the inventors have been interested in Japanese Patent Application Laid-Open No. Sho 62-1396.
28. An ion conductive adhesive gel disclosed in 28. This gel is a hydrophilic polyether urethane containing an alkali ion compound, and as an anionic hydrophilic gel having relatively good conductivity, is configured under an unconventional design concept. Attention is paid to the point. However, the gel resulting from this technique has two major drawbacks derived from the nature of the polymer making up the gel.

The first disadvantage is that the presence of water is not allowed during the gel formation reaction. Since the conductivity of the gel according to this technique is inferior to that of the gel according to the prior art using a polymer electrolyte, when the gel is used as an adhesive for a potential pickup electrode, it is necessary to further improve the conductivity. There is. As the simplest method, it is conceivable to mix a solvent having a high dielectric constant, for example, water, a low molecular weight (polyhydric) alcohol, etc. in the gel, but using the former involves the generation of carbon dioxide gas, It is expected that air bubbles will be present in the gel, and the use of the latter will make the physical properties of the gel close to that of the resin, making it unusable as an adhesive. Therefore, it is presumed that it is difficult to perform a gel forming reaction in these solvents. For this reason, in order to improve the conductivity, it is necessary to perform the above-mentioned addition of the solvent as a post-process after the completion of the gel-forming reaction, and as a result, mass production efficiency is significantly reduced. Would. Another drawback of this technique is that strict control of water is required in the gel formation reaction step and the raw material preservation step.

A second drawback is that when the gel according to this technique is applied to living skin, the adhesive strength is reduced in a relatively short time. It is difficult to identify the cause due to various factors, but one cause is the primary structure of the polymer. That is, since polyurethane has a highly polar urethane bond in the polymer main chain,
Although it is a suitable material for imparting rubbery elasticity to the polymer, the polymer matrix forms a hydrogen bond with the urethane bond and inhibits the fluidity of the polymer, so that it cannot follow the movement of the living body. It seems to fall off the skin easily. It has been pointed out that the inhibition of the motility of the polymer segment due to this hydrogen bond also has an adverse effect on conductivity (H. Tada and H. Kawahara;
DENKI KAGAKU: 55 (11), 834-840 (1987)) It is expected that overcoming this drawback will be extremely difficult because it is derived from the essence of the material.

[Object of the Invention] The object of the present invention is to solve the problems that could not be solved by the techniques proposed so far, namely, to maintain a sufficient adhesive force to the skin for a long time and to have good conductivity. It is still another object of the present invention to provide a medical conductive pressure-sensitive adhesive which has a very small decrease in adhesive force even when used under high humidity.

[Means for Achieving the Object] As a means for achieving the object, the medical conductive pressure-sensitive adhesive of the present invention is characterized in that an ionic compound is blended with a polymer having an alkylene oxide chain in a side chain. Is what you do. More preferably, the polymer has an alkyl group having 1 to 18 carbon atoms and an alkylene oxide chain in the side chain of the polymer, and the ionic compound is one that dissolves and coordinates to the polymer without requiring the addition of a plasticizer. It is a feature.

Means for rationally obtaining a polymer having an alkylene oxide chain in the side chain include a homopolymerization of an α / β-unsaturated carboxylic acid derivative having an alkylene oxide chain or an allyl alcohol derivative having an alkylene oxide chain. Alternatively, it can be obtained by copolymerization. Non-limiting examples of α / β-unsaturated carboxylic acids that can be used in the present invention include acrylic acid, methacrylic acid,
Examples thereof include fumaric acid, itaconic acid, and maleic acid. In order to more clearly explain the structures of these derivatives having an alkylene oxide chain, the general structure of these derivatives is shown in structural formula (I) using acrylic acid as an example.

In the structural formula (I), R is a lower alkyl group having 1 to 4 carbon atoms or a hydrogen atom. (AO) represents an alkylene oxide chain, and a structure of an alkylene oxide chain suitable for the present invention includes, but is not limited to, those represented by structural formula (II).

Here, n is the number of repeating alkylene oxide units, and is an integer of 2 or more. Represented by the structural formula (I) (A
O) may be a single compound of the structural formula (II) or a random compound or a block compound of plural kinds of alkylene oxide units, but from the viewpoint of hydrophilicity and conductivity,
It is preferable to have an ethylene oxide unit as a part of (AO) represented by the structural formula (I).

Homopolymers or copolymers composed of only the derivatives of α · β-unsaturated carboxylic acids having an alkylene oxide chain represented by the structural formula (I) or the derivatives of allyl alcohol have high hydrophilicity and therefore have long-lasting skin. When it is necessary to attach the adhesive to the skin, it absorbs sweat secreted from the skin of the living body, the adhesive slightly swells, and the adhesive strength tends to decrease due to its low water resistance. In order to improve the water resistance and make the polymer more suitable for long-term use, it is desirable to further introduce an alkyl group having 1 to 18 carbon atoms, preferably 4 to 12 carbon atoms into the polymer side chain. Such a rational means for introducing an alkyl group can be achieved by copolymerizing an alkyl ester of an α-β-unsaturated carboxylic acid with a monomer having an alkylene oxide chain represented by the structural formula (I). Non-limiting examples of suitable alkyl esters of α-β-unsaturated carboxylic acids suitable for the present invention include butyl acrylate, t-butyl acrylate, 2-ethylhexyl acrylate, butyl methacrylate, and methacrylic acid. Examples thereof include n-lauryl acid, tridecyl methacrylate, dibutyl fumarate, di-2-ethylhexyl fumarate, and dibutyl itaconate. If the general structure is alkyl acrylate, the structural formula (III) Indicated by

Here, R ₂ is an alkyl group having 1 to 18 carbon atoms, preferably 4 to 12 carbon atoms.

As described above, the copolymer having an alkylene oxide chain in the side chain and an alkyl group having 1 to 18 carbon atoms is obtained by changing the charge ratio with the species of the structural formulas (I), (II), and (III). It has very excellent characteristics in that the hydrophilicity and tackiness can be changed over a very wide range.
In fact, some of these copolymers exhibit strong cohesion and can be obtained more completely water-soluble, so that a small amount of water and / or (poly) alcohol is used as a low molecular weight electrolyte represented by NaCl. By dissolving and adding to the polymer, conductivity can be easily imparted.

However, in order to make the most of the characteristics of the polymer having an alkylene oxide chain in these side chains, a low molecular electrolyte capable of dissolving and coordinating the polymer having the alkylene oxide chain without containing any plasticizer is used. It is desirable. As the constitution of such an electrolyte, an alkali metal ion represented by Li ⁺ , Na ⁺ , K ⁺ as a cation component, or a quaternary ammonium represented by R ₄ N ⁺ , H ₄ N ⁺ (R is a lower alkyl group) Ions,
Examples of the anion component include halogen ions represented by Cl ⁻ , Br ⁻ , and I ⁻ , and further include sulfate ions, perchlorate ions, and various sulfonate ions. An electrolyte composed of a combination of these elements is dissolved in a polymer by previously dissolving it in a polymerization solvent and desolvating after polymer polymerization, or dissolving in a polymer polymer or polymerization solvent and then desolvating. It can be coordinated. From the viewpoint of exhibiting conductivity by such a mechanism, as the alkylene oxide chain of the structural formula (II), an ethylene oxide chain is most advantageous, and an alkylene oxide chain having a longer chain length is more advantageous. However, since the water resistance of such a polymer deteriorates, it is necessary to copolymerize an alkyl ester of an α-β-unsaturated carboxylic acid represented by the structural formula (III). As a result, improvement in the water resistance of the polymer was achieved, and the Tg of the polymer was lowered, which proved to be advantageous from the viewpoint of conductivity. Thus, it is a great feature of this technology that a polymer having excellent water resistance and excellent conductivity can be obtained.

The conductive pressure-sensitive adhesive having the above-described configuration has characteristics that cannot be obtained by the conventional technology, but a further advantage is that the monomer configuration having both the adhesiveness and the conductivity as described above is used. Once established, the technology that has been cultivated in the field of acrylic pressure-sensitive adhesives can be used as it is. Monomers, such as vinyl acetate, acrylonitrile, acrylamide, t-butylacrylamide, diacetone acrylamide, styrene, and methyl methacrylate, which are conventionally introduced for the purpose of modifying an acrylic pressure-sensitive adhesive, have an internal cohesive force of the polymer. Methacrylic acid, acrylic acid, itaconic acid, hydroxymethacrylate, hydroxypropyl methacrylate, dimethylaminoethyl methacrylate, acrylamide, methylolacrylamide, glycidyl methacrylate, maleic anhydride, etc. can be used to improve the polymer. Can be introduced to crosslink.

In some cases, when higher conductivity is required,
It is also possible to add water, a (polyhydric) alcohol, a lactam, or a solvent having an alkylene oxide chain and a relatively large dielectric constant.

[Function and Effect] According to the configuration of the conductive pressure-sensitive adhesive according to the present invention, a pressure-sensitive adhesive excellent in both water resistance, tackiness and conductivity can be obtained. It is possible to obtain an ideal adhesive to electrically and physically connect the skin.

[Examples] Next, the present invention will be described in more detail with reference to Examples.

Example 1: Polymerization of polymer 1-1. 11 parts of butyl acrylate and 11 parts of methoxypolyethylene glycol methacrylate (ethylene oxide repeating number n = 23) were dissolved in 34 parts of benzene, and the system was replaced with nitrogen. Further, 0.03 part of azobisisobutyrone tolyl was added as an initiator, and copolymerized at 80 ° C. for 5 hours under nitrogen.

After 11 parts of 1-2.2-ethylhexyl acrylate and 9 parts of polyethylene glycol methacrylate (the number of repeating ethylene oxide n = 8) were dissolved in 80 parts of ethanol, the system was replaced with nitrogen. Further, 0.09 parts of azobisisobutyronitrile was added as an initiator, and copolymerized under reflux for about 6 hours.

1-3. Methacrylate having polyethylene oxide and polypropylene oxide (ethylene oxide repeating number n = 7, propylene oxide repeating number m
= 3) 10 parts were dissolved in 90 parts of ethanol, and the atmosphere in the system was replaced with nitrogen. Asobisisobutyronitrile as initiator
0.005 parts were added, and homopolymerization was performed under a dry distillation temperature under nitrogen for about 6 hours.

Example 2: Hydrophilicity test To 1 part of the polymer obtained in Example 1, 10 parts of water was added, the mixture was allowed to stand at room temperature for 24 hours, and the solubility of the polymer in water was confirmed.

Example 3: Measurement of volume resistance After desolvation of the polymer obtained in Example 1, each polymer was dissolved in acetone, and about 3 wt.
% Of lithium perchlorate was mixed and dissolved. This homogeneous viscous liquid was cast on an aluminum foil and dried at 80 ° C. for about 2 days to completely evaporate acetone.
The upper and lower surfaces of the obtained conductive adhesive sheet are sandwiched between aluminum foils, punched out to a diameter of 20 mm, formed as one end of a bridge circuit, and the impedance when a 1 kHz sine wave is applied is measured by the Lissajous method. The volume resistance was calculated from the area and the thickness. Table 2 shows the results.

Example 4: Adhesive strength test The polymer solution obtained in Example 1 was cast on a polyester film having a thickness of 20 µm to obtain an adhesive sheet having a thickness of about 1 mm. This adhesive sheet was punched out to a size of 20 mmφ, attached to the human chest, and the adhesive strength was confirmed. The period was two days, and the skin condition was sometimes accompanied by sweating. Table 3 shows the results
Shown in

Claims (3)

(57) [Claims] 1. A medical conductive pressure-sensitive adhesive comprising an ionic compound blended with a polymer formed from an α, β-unsaturated carboxylic acid or allyl alcohol having an alkylene oxide chain in a side chain. 2. The medical conductive pressure-sensitive adhesive according to claim 1, wherein the ionic compound is dissolved and coordinated with the polymer. 3. The medical conductive pressure-sensitive adhesive according to claim 1, wherein the polymer side chain further has an alkyl group having 1 to 18 carbon atoms.