Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – Processes of preparing a desired or intentional composition...
Reexamination Certificate
1999-06-09
2001-05-15
Kopec, Mark (Department: 1751)
Synthetic resins or natural rubbers -- part of the class 520 ser
Synthetic resins
Processes of preparing a desired or intentional composition...
C252S500000, C156S327000, C600S391000, C424S448000, C428S041500
Reexamination Certificate
active
06232366
ABSTRACT:
FIELD OF THE INVENTION
The invention relates to a conductive pressure sensitive adhesive that has hot melt properties (or that can be hot-melt processed) suitable for as an ionically conductive pressure sensitive adhesive for a biomedical electrode.
BACKGROUND OF THE INVENTION
Biomedical electrodes are used for diagnostic and therapeutic purposes including electrocardiographic monitoring and diagnosis, electrosurgery, iontophoretic (electrically enhanced) transdermal delivery of drugs, and defibrillation. In their most basic form, these electrodes have a conductive medium contacting mammalian skin and a means for electrical communication interacting between the conductive medium and electrical diagnostic, therapeutic, or electrosurgical equipment.
The conductive medium used in these electrodes is generally an ionically conductive adhesive or gel. A conductive adhesive composition which both serves to adhere a biomedical electrode to skin and to establish an electrical connection between skin and an electrical medical apparatus should desirably have multiple characteristics which are difficult to achieve in one composition. At minimum, the composition should have the characteristics of a good medical adhesive and those of a good ionic conductor. A good medical pressure-sensitive adhesive needs to be dermally non-irritating, compliant and tacky enough so as to wet onto skin and adhere, and sufficiently cohesive both to resist shear and peel forces and to pull away from skin without leaving a residue. To optimize electrical performance, low impedance at the interface of the composition and the skin is desirable.
It is known that ionically conductive adhesives can be compounded from a polar polymeric network which is plasticized with a humectant material such as glycerin or poly(ethylene glycol). Water, a salt, or a pharmaceutical can also be included depending on the application. Generally a relatively thick layer of adhesive or gel is used (10 to 100 mil (0.25 to 2.5 mm) or greater).
Much work has been done in recent years to optimize conductive adhesives for biomedical applications, to achieve better properties in one area without having to compromise excessively in another. One area that has not had as much development is the preparation of conductive adhesives that are melt processable after the polymeric material has been formed for use in the manufacture of a biomedical electrode. The available materials are viscous, cohesive, and non-water soluble. Once placed by polymerization onto a backing material, they cannot be practically reprocessed or recycled. Any adhesive that is placed on material, i.e., the “weed” which is cut away during the automated die cutting of bioelectrodes, must now be discarded as waste.
In addition, known processing methods involve polymerization on the substrate or coating from a carrier solvent (organic or water). These processes are typically slow and can involve difficult drying steps because of the thickness of the electrode material.
SUMMARY OF THE INVENTION
What the art needs is a skin-compatible, non-water soluble, pressure sensitive adhesive, preferably ionically conductive, to be formulated in a manner which permits the recycling of such material after application to a substrate. The possibility to coat thick layers of conductive adhesive at high process speeds is also economically attractive. Any drying step otherwise needed in prior art processing is eliminated.
The present invention solves these current problems in the art by providing a conductive adhesive with all the desired properties discussed in the paragraph immediately above. Further, the conductive adhesive of the present invention is additionally melt-processible at a suitably low temperature to reduce manufacturing costs. As a result of the use of low temperatures, there is no need to rehydrate the adhesive after processing. The adhesive can be spread in a molten state onto a substrate, such as an electrode backing material. Thereafter, any waste material can be recovered and reprocessed by the application of mild heat. Because the adhesive is melt-processible before and after electrode formation, the adhesive can be used in manufacturing electrodes using a wider variety of methods so that initial waste is minimized.
The present invention concerns a formulation which is skin-compatible, non-water soluble, cohesive, and conductive, and yet is melt-processible because of a thermo-reversible crosslinking mechanism.
Compared to currently used application and curing methods, use of the present invention can also provide the benefits of lower residual monomers, or a higher coating speed. Compared to methods that require exposure of the adhesive to UV radiation, the adhesive is easier to coat in greater thickness because no light penetration is necessary such as required for UV radiation polymerized or crosslinked adhesives.
Formulations suitable for low temperature melt-processible ionically conductive pressure sensitive adhesives (PSAs) for skin application according to the present invention can be made from a copolymer of alkyl acrylate monomers and hydrophilic comonomers, polymerized either through thermal polymerization or UV polymerization. This can be performed even in the presence of humectants and/or hydrophilic plasticizers such as glycerin and/or polyethylene glycol (PEG). The plasticized polymer can thereafter be melt-processed with a mixture having surfactant, amine containing polymeric ionic crosslinker, a salt to improve ionic conductivity properties (usually KCl) and water. The temperature of melt processing ranges from about 50° C. to about 100° C. and more preferably from about 55° C. to about 85° C. to make thick layers useful in biomedical electrodes as the conductive medium. Alternatively, the material can be used in other ionically conductive and pressure-sensitive adhesive articles.
Briefly, one aspect of the present invention provides a skin-compatible, hot-melt processible, pressure sensitive adhesive, comprising:
between about 30 and about 45 parts by weight of a copolymer comprised of between about 30 to 45 parts by weight of an (meth)acrylate ester monomer having C
4
-C
20
alkyl chains, and between about 55 to 70 parts by weight of an acidic comonomer;
between about 0 and about 35 parts by weight of a hydrophilic plasticizer;
between about 20 and about 40 parts by weight of water,
between about 0 and about 3 parts by weight of a water soluble salt,
between about 10 and about 20 parts by weight of a surfactant, and
between about 0.5 and about 10 parts by weight of a polymer having amine functionality.
Another aspect of the present invention provides a method for preparing skin-compatible, hot-melt processible, pressure sensitive adhesive, comprising the steps of:
a) preparing a mixture of ethylenically unsaturated monomers comprising:
between about 30 and about 45 parts by weight of an (meth)acrylate ester monomer having C
4
-C
20
alkyl chains, and
between about 55 and about 70 parts by weight of an acidic comonomer;
b) mixing between about 30 and about 45 parts by weight of the mixture of the ethylenically unsaturated monomers with between about 0 and about 35 parts by weight of a hydrophilic plasticizer so as to form a hydrophilic plasticizer/monomer mixture;
c) polymerizing the monomers to form a polymer matrix containing the plasticizer;
d) blending an additive mixture into the polymer matrix, the additive mixture comprising
between about 20 and about 40 parts by weight of water,
between about 0 and about 3 parts by weight of a water soluble salt,
between about 10 and about 20 parts by weight of a surfactant, and
between about 0.5 and about 10 parts by weight of a polymer having amine functionality,
so as to form a skin-compatible hot-melt processible, ionically conductive, pressure sensitive adhesive.
Yet another aspect of the present invention provides a method for preparing skin-compatible, hot-melt processible, pressure sensitive adhesive, comprising the steps of:
a) preparing a mixture of ethylenically unsaturated monomers comprising:
between ab
Everaerts Albert I.
Stark Peter A.
Wang DanLi
3M Innovative Properties Company
Burtis John A.
Kopec Mark
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