Compositions – Electrically conductive or emissive compositions
Patent
1993-06-02
1995-07-18
Lieberman, Paul
Compositions
Electrically conductive or emissive compositions
252518, 252 622, 128640, 523105, 523111, 4283202, 4284111, 428913, H01B 100, A61B 504
Patent
active
054338921
DESCRIPTION:
BRIEF SUMMARY
The invention concerns electrically conductive transparent pressure-sensitive adhesive films with an electric conductivity above 10.sup.-5 S, suitable for the production of biomedical electrodes.
The popular, conventional design of such biomedical electrodes comprises an electrically conductive gel in a hole punched out of foamed material, whose storage life is limited owing to the drying-out which increasingly occurs as the period of storage progresses. A further disadvantage of this drying-out is that the skin has to be cleansed from remainders of the gel after the electrodes have been used and that the patient's clothing may become soiled if the remainders of the gel are not removed carefully enough. Efforts were, therefore, made to eliminate or substantially reduce these disadvantages, by providing a pressure-sensitive adhesive coating, stable in storage and geared for electric conductivity.
Conventional methods for the realization of electric conductivity, such as, for example, the incorporation of graphite powder, are not practical, as the pressure-sensitive adhesive film has to remain transparent.
According to DE-OS 15 94 137, pressure-sensitive adhesive conductive strips are known which contain film-forming ionized organic polymer salts. The polymers themselves are only slightly soluble in water, but are rendered hydrophilic and ionogenic by the built-in functional groups, which are capable of forming salts. The sodium salts of sulphonated styrene and polybenzyl sulphonate can be cited as suitable examples. A further preferred group are the salts of quaternary polymers from dimethylaminoethyl methacrylate or its copolymers with butyl acrylate and 4-vinyl pyridine, that has been 95 to 100% quaternized with methyl bromide or allyl chloride.
According to EP-A 0 263 586, conductive pressure-sensitive adhesives from a hydrogen-donor monomer (e.g. acrylic acid) and a hydrogen-acceptor monomer (e.g. N-vinyl pyrrolidone) are used to produce electrically conductive pressure-sensitive adhesive films.
A mixture of water and glycerine is used as the polymerization medium. A water-soluble salt and--as a cross-linking agent--bifunctional (meth)acrylate are also added to the copolymer.
In EP-A 0 322 098 a production of electrically conductive pressure-sensitive adhesive films is described in which a hydrophilic pressure-sensitive adhesive based on N-vinyl lactam is used, mixed with a softening agent and cross-linked with multifunctional derivatives that have not been saturated with ethylene.
When used to produce biomedical electrodes, however, these known pressure-sensitive adhesive films exhibit a number of shortcomings, which restrict their practical application. Their power of cohesion is reduced, due to their sensitivity to the moisture of the skin. After they have been in contact with the skin for several hours, traces of adhesive remain on the skin when they are peeled off, making the reuse of such biomedical electrodes equipped with these electrically conductive pressure-sensitive adhesive films impossible.
The task forming the basis of the invention in question is thus that of producing electrically conductive pressure-sensitive adhesive films which manifest excellent resistance to moisture and stable inner strength and which are exceptionally suitable for the production of reusable biomedical electrodes.
The problem underlying the invention is solved suprisingly by electrically conductive transparent pressure-sensitive adhesive films with an electric conductivity above 10.sup.-5 S, consisting of 100 parts by weight of a copolymer containing a carboxyl group, on an acrylate basis; 50 to 150 parts by weight of a water-soluble amine; 50 to 250 parts by weight of polyoxyalkylene with a molecular mass of below 1000 and/or a polyalcohol and/or its derivatives; 50 to 200 parts by weight of a solution of electrolytes; and 0.1 to 6 parts by weight of a cross-linking agent.
The favoured carboxyl group-containing copolymers on an acrylate basis are synthesized, preferably by means of a radical solvent polymerizatio
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Kopec M.
Lieberman Paul
Lohmann GmbH & Co. KG
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