JPH0280030A - Medical conducting adhesive - Google Patents

Abstract

PURPOSE:To maintain a sufficient adhesive force to a skin over a long period, obtain good conductivity, and prevent the reduction of adhesion at the time of usage under high humidity by arranging an ion compound in a polymer having an alkylene oxide chain for the side chain. CONSTITUTION:A homopolymer or a copolymer made of only a derivative of alpha.beta-unsaturated carboxylic acid having an alkylene oxide chain expressed by the formula I, where R is a low-grade alkyl group with the carbon number of 1-4 or hydrogen atom and AO indicates an alkylene oxide chain, or a derivative of allyl alcohol has a high hydrophilic property, thus its adhesion is liable to be reduced due to low water resistance when it is fitted to a skin for a long period. When alkyl ester of alpha.beta-unsaturated carboxylic acid is copolymerized with a monomer having an alkylene oxide chain expressed by the formula I, this water resistance is improved, and it can be used for a long period.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention relates to a potential pickup electrode (
For example, electromyogram electrodes, electroencephalogram measurement electrodes, electrocardiogram electrodes, electrooculogram measurement electrodes, etc.) and current passive electrodes (p
For example, it relates to a medical conductive adhesive that electrically and physically connects a living body (return electrode plate for an electric scalpel, electrode for a low-frequency treatment device, electrode for iontophoresis, etc.) and a living body.

[Prior Art] Many conductive adhesives or conductive adhesive gels have been devised to electrically and physically connect potential pickup electrodes and current passive electrodes to living bodies. A common feature of many of these proposed techniques is the use of a polymer electrolyte as a means for developing electrical conductivity. - Examples include carboxylic acid salts (e.g., JP-A-56-36939, JP-A-57285)
05), quaternary ammonium salts (for example, JP-A-52-9
5895, JP-A-62-133935, JP-A-62-3
5963911 JP-A-62-270135, JP-A-62
-2921401 JP-A-63-43646), sulfonates (e.g. JP-A-55-81635, JP-A-58-
135506, JP-A-59-125545), and phosphates (eg, JP-A-61-85925). These polymer electrolytes are very hard and brittle in a dry state, and have very low electrical conductivity. Therefore, in order for these polymers to exhibit adhesiveness and electrical conductivity, large amounts of water or , a plasticizer such as polyhydric alcohol is required, and the long-term physical properties of the adhesive inevitably deteriorate. Furthermore, the fatal disadvantage of using these polymer electrolytes for such purposes is that they absorb moisture when used under high humidity and sweat secreted from the skin.
The adhesive swells, resulting in a significant loss of tack and the electrode falling off the skin. This drawback is an unavoidable problem when using polyelectrolytes for such purposes.

Since the polymer disclosed in JP-A No. 56-36940 is composed of an anionic polymer, it seems that the drawback of significant swelling of the adhesive can be overcome, but this can be predicted by those involved in this field. However, the conductivity of the adhesive used in this technology is extremely low, and especially when the potential pickup electrode and the living body are connected using this adhesive, it is highly likely that interference from commercial power supply hum noise will occur. It is something.

Recently, the patent application published in 1986-13 has attracted the attention of inventors.
This is an ion conductive adhesive gel disclosed in US Pat. No. 9,628. This gel is made of hydrophilic polyether urethane containing an alkali ionic compound, and is said to be constructed based on an unprecedented design concept for an anionic hydrophilic gel with relatively good conductivity. It is notable for this point. However, the gel produced by this technology has two major drawbacks that originate from the nature of the polymer that constitutes it.

The first drawback is that the presence of water is not allowed during the gel-forming reaction. The conductivity of the gel used in this technology is
Since it is inferior to gels made of conventional technology using polymer electrolytes, it is necessary to further improve the conductivity when used as an adhesive for potential pickup electrodes. The simplest method would be to incorporate a solvent with a high dielectric constant, such as water or a low-molecular (polyhydric) alcohol, into the gel, but using the former would involve the generation of carbon dioxide gas. Since air bubbles will be present in the gel, and the use of the latter will make the physical properties of the gel close to those of resin, it is expected that it will become unusable as an adhesive. Therefore, it is presumed that it is difficult to carry out the gel-forming reaction in these solvents. Therefore, in order to improve conductivity, it is necessary to add the solvent as a post-process after the gel formation reaction is completed.
This will result in a significant reduction in mass production efficiency. In addition, the step of gel formation reaction and
Another disadvantage of this technology is that it requires strict moisture control during the raw material preservation process.

The second drawback is that when a gel based on this technology is applied to the skin of a living body, the adhesive strength decreases in a relatively short period of time. Various factors can be considered to cause this, and it is difficult to specify, but one cause is the primary structure of the polymer. In other words, since polyurethane has highly polar urethane bonds in its main chain, it is a suitable material for imparting rubber-like elasticity to polymers. It is thought that as a result of hydrogen bonding and inhibiting the fluidity of the polymer, it becomes unable to follow the movements of living organisms and easily falls off from the skin. It has been pointed out that inhibition of polymer segment mobility due to hydrogen bonding also has a negative effect on electrical conductivity (Il, Tada and
H, Kavahara; DENKI KAGAKU
: 55(11).

834-840 (1987)), it is expected that it will be extremely difficult to overcome this drawback because it originates from the nature of the material.

[Objective 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 sufficient adhesion to the skin for a long time and have good conductivity. Furthermore, it is an object of the present invention to provide a medical conductive adhesive that exhibits extremely little decrease in adhesive strength even when used under high humidity conditions.

[Means for achieving the object] As a means for achieving the above object, the medical conductive adhesive of the present invention is characterized in that an ionic compound is blended into a polymer having an alkylene oxide chain in a side chain. It is something to do. More preferably, the polymer side chain has an alkyl group having from I to 18 carbon atoms and an alkylene oxide chain, and the ionic compound dissolves and coordinates with the polymer without the need for adding a plasticizer. This is a characteristic feature.

As a means to rationally obtain a polymer having an alkylene oxide chain in the side chain, homopolymerization and/or 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, fumaric acid, itaconic acid, and maleic acid. In order to more clearly explain the structure of these derivatives having an alkylene oxide chain, the general structure of these derivatives is shown in Structural Formula (1) using acrylic acid as an example.

CHt=CHO=c-(Ao)-R, (1) In the structural formula (r), R is a lower alkyl group having 1 to 4 carbon atoms or a hydrogen atom. Further, (AO) represents an alkylene oxide chain, and non-limiting examples of the structure of the alkylene oxide chain suitable for the present invention include structural formula (II).

(CHto )II, (CH2CHtO)n(CH
tCHO)n, (c HzCHICHtCH!0)nH
3 (It) Here, n is the number of repeating alkylene oxide units and is an integer of 2 or more. (AO
) may be a single unit of the structural formula ( ) or a random or block unit of multiple types of alkylene oxide units, but from the viewpoint of hydrophilicity and conductivity, the structural formula ( It is desirable to have an ethylene oxide unit as a part of (AO) shown in 1).

A homopolymer or copolymer consisting only of an α/β-unsaturated carboxylic acid derivative having an alkylene oxide chain represented by the structural formula (1) or an allyl alcohol derivative has high hydrophilicity, so it remains on the skin for a long time. When it is necessary to attach the adhesive to a body, it absorbs sweat secreted from the skin of a living body, causing the adhesive to swell slightly, and its adhesive strength tends to decrease due to its low water resistance. Improve this water resistance,
In order to make the polymer 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. A means for rationally introducing such an alkyl group is 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 (1). Non-limiting examples of preferred 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 methacrylate. Examples include n-lauryl acid, tridecyl methacrylate, dibutyl fumarate, di-2-ethylhexyl fumarate, dibutyl itaconate, etc.
Taking an alkyl acrylate as an example, the intrashell structure is represented by the structural formula (III).

CH,=Cl-1 0=CRz (III) Here, R2 is an alkyl group having 1 to 18 carbon atoms, preferably 4 to 12 carbon atoms.

As mentioned above, a copolymer having an alkylene oxide chain and an alkyl group having 1 to 18 carbon atoms in the side chain has the structural formula (
1) It has an extremely excellent feature in that the hydrophilicity and adhesiveness can be varied over a very wide range by changing the species and charging ratio of (n)U). In fact, some of these copolymers exhibit strong adhesion and can also yield more completely water-soluble polymers, so that small amounts of water and/or
Alternatively, conductivity can be easily imparted by dissolving a low molecular electrolyte represented by NaCl2 in a (polyhydric) alcohol and adding it to the polymer.

However, in order to take full advantage of the characteristics of polymers that have alkylene oxide chains in their side chains, it is necessary to use a low molecular electrolyte that can be dissolved and coordinated without containing any plasticizer in the polymer that has alkylene oxide chains. It is desirable to do so. The composition of such an electrolyte includes, as a cationic component, an alkali metal ion represented by Li'', Na'', and +, or 1. N”, H.

Examples include quaternary ammonium ions represented by N'' (R is a lower alkyl group), and examples of anionic components include C(
Examples include halogen ions represented by 1-, Br-, and I-, as well as sulfate ions, perchlorate ions, various sulfonate ions, and the like. An electrolyte made of a combination of these elements can be dissolved in a polymer by dissolving it in advance in a polymerization solvent and adding it to the solvent after polymerization, or by dissolving it in a polymerization solvent and removing the solvent after polymerization. It can be coordinated. From the viewpoint of developing conductivity through such a mechanism, an ethylene oxide chain is most advantageous as the alkylene oxide chain of structural formula (n), and a longer chain length is more advantageous. However, since the water resistance of such polymers deteriorates, it is necessary to copolymerize an alkyl ester of an α/β-unsaturated carboxylic acid represented by the structural formula (III).

It has been found that this improves the water resistance of the polymer and further reduces the Tg of the polymer, which is also advantageous in terms of electrical conductivity. In this way, it has excellent water resistance,
Polymers with excellent conductivity can be obtained by:
This is a major feature of this technology.

The conductive adhesive with the above-mentioned structure has features that could not be obtained with conventional technology, but an even more advantageous point is that it has a monomer structure that has both adhesiveness and conductivity. Once it is determined, the technology that has been cultivated in the field of acrylic adhesives can be used as is. Monomers conventionally introduced for the purpose of modifying acrylic pressure-sensitive adhesives, such as vinyl acetate, acrylonitrile, acrylamide, t-butylacrylamide, diacetone acrylamide, styrene, and methyl methacrylate, are known to improve the internal cohesive strength of Moeki polymers. In addition, methacrylic acid, acrylic acid, itaconic acid, hydroxymethacrylate, hydroxydipropyl methacrylate, dimelaminoethyl methacrylate, acrylamide, methylolacrylamide, glycidyl methacrylate, maleic anhydride, etc. can be used to improve the above-mentioned Can be introduced to crosslink the polymer.

If even higher conductivity is required than in □, it is also possible to add water, (polyhydric) alcohol, lactams, or a solvent having a relatively high dielectric constant having an alkylene oxide chain.

[Functions and Effects] According to the structure of the conductive adhesive of the present invention, water resistance,
Since it is possible to obtain an adhesive with excellent adhesiveness and conductivity, it is possible to obtain an adhesive that is ideal for electrically and physically connecting potential pickup electrodes and current passive electrodes to biological skin. is possible.

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

Example 1: Polymerization of polymers 1-1. After dissolving 11 parts of butyl acrylate and 11 parts of methoxypolyethylene glycol methacrylate (number of repetitions of ethylene oxide, n=23) in 34 parts of benzene, the inside of the system was purged with nitrogen. Furthermore, 0.03 part of azobisisobutyronetolyl was added as an initiator, and the mixture was heated under nitrogen for 8 hours.
Copolymerization was carried out at 0°C for 5 hours.

After dissolving 11 parts of 1-2.2-ethylhexyl acrylate and 9 parts of polyethylene glycol methacrylate (number of repetitions of ethylene oxide, n=8) in 80 parts of ethanol, the inside of the system was purged with nitrogen. Further, 0.09 parts of azobisisobutyronitrile was added as an initiator, and the mixture was refluxed for about 6 hours.
Copolymerized.

1 to 3, 10 parts of methacrylate having polyethylene oxide and polypropylene oxide (number of repetitions of ethylene oxide n = 7, number of repetitions of propylene oxide m 3) is dissolved in 90 parts of ethanol, and the system is purged with nitrogen. 0.005 part of azobisisobutyronitrile was added as an initiator, and homopolymerization was carried out for about 6 hours under carbonization temperature conditions over nitrogen.

Example 2: Hydrophilicity test example! 10 parts of water was added to 1 part of the polymer obtained in step 1, and the mixture was left at room temperature overnight. The solubility of the polymer in water was confirmed. Table 1 shows the results.

Table 1.111 Aqueous test (O: completely dissolved, △ partially dissolved) Example 3: Measurement of volume resistivity After removing the solvent from the polymer obtained in Example 1, each polymer was dissolved in acetone, and the polymer Approximately 3% of weight
of lithium chlorate was mixed and dissolved. This homogeneous viscous liquid was cast on aluminum foil and heated at 80°C.
Drying was carried out for about 2 days to completely evaporate the acetone. The upper and lower surfaces of the obtained conductive adhesive sheet were sandwiched between aluminum foils, punched into a 20 mm diameter piece, formed as one end of a bridge circuit, and the impedance was measured using the Lissajous method when a sine wave of I kHz was applied. The bond resistance was calculated from the cross-sectional area and thickness. The results are shown in Table 2.

Table 23 Measurement of volume resistance was sometimes accompanied by sweating. The results are shown in Table 3.

Table 3. Adhesion test

Claims (3)

[Claims] (1) A medical conductive adhesive characterized in that an ionic compound is blended into a polymer having an alkylene oxide chain in its side chain. (2) The medical conductive adhesive according to claim (1), wherein the ionic compound is dissolved and coordinated with the polymer. (3) The scope of patent claims in which the polymer side chain further has an alkyl group having 1 to 18 carbon atoms (1)
) to (2).