Self-adhesive electrode patch

Abstract

Disclosed is a layered body comprising a polymer comprising repeating units having the general structure CH.sub.2CHR.sup.1COOR.sup.2 as defined herein, to a process for producing such a layered body, to a layered body produced by that process and to the use of a layered body for electrophysical measurements.

Claims

1. A dispersion comprising i) particles A) of polymer comprising repeating units having the general structure CH.sub.2CR.sup.1COOR.sup.2 wherein R.sup.1 represent H or an alkyl group, and R.sup.2 represents an optionally substituted C.sub.1-C.sub.10-alkyl group, wherein particles A) have a mass average particle diameter (d.sub.50) of at least 800 nm; ii) particles B) of a conductive polymer, wherein the particles B) have a mass average particle diameter of less than 150 nm; iii) at least one dispersant; wherein the weight ratio of the polymer in particles A) to the conductive polymer in particles B) is at least 15:1.

2. The dispersion according to claim 1, wherein the polymer of particles A) has a glass transition temperature of less than 35? C.

3. The dispersion according to claim 1, wherein R.sup.1 is H and R.sup.2 is selected from the group consisting of CH.sub.3, CH.sub.2CH.sub.3, C.sub.4H.sub.9, CH.sub.2CH(C.sub.2H.sub.5)(C.sub.4H.sub.9) and C.sub.8H.sub.17.

4. The dispersion according to claim 1, wherein at least 25% of the repeating units in the polymer of particles A) are monomers in which R.sup.1 is H and R.sup.2 is selected from the group consisting of CH.sub.3, CH.sub.2CH.sub.3, C.sub.4H.sub.9, CH.sub.2CH(C.sub.2H.sub.5)(C.sub.4H.sub.9) and C.sub.8H.sub.17, based on the total number of repeating units in the polymer of particles A).

5. The dispersion according to claim 1, wherein the polymer of particles A) is a copolymer of acrylic acid or a salt of acrylic acid or both and an acrylic acid ester selected from the group consisting of methyl acrylate, ethyl acrylate, n-butyl acrylate, 2-ethylhexylacrylate and n-octyl acrylate.

6. The dispersion according to claim 1, wherein the conductive polymer of particles B) comprises a PEDOT/PSS-complex.

7. The dispersion according to claim 1, wherein the dispersion further comprises, as component iv), a polar high boiling compound having a boiling point (at 1013 mbar) of at least 120? C.

8. A process for producing a layered body, the process comprising ?1) providing a dispersion as defined in claim 2; ?2) applying the dispersion onto at least a part of at least one surface of a substrate; ?3) at least partial removal of the dispersant iii) for the formation of a conductive adhesive layer that is superimposed on at least a part of at least one surface of the substrate, wherein the at least partial removal of the dispersant is accomplished by heating the dispersion that has been applied onto the substrate to a temperature above the glass transition temperature of the polymer of particles A).

9. The dispersion according to claim 1, wherein the dispersant is water.

10. The dispersion according to claim 1, wherein particles B) of a conductive polymer are particles B) of a complex of a cationic polythiophene and a polymeric anion.

11. The dispersion according to claim 10, wherein the weight ratio of the polymer in particles A) to the total weight of the cationic polythiophene and the polymeric anion in the complex of particles B) is at least 15:1.

12. The dispersion according to claim 7, wherein the dispersion further comprises, as component iv), ethylene glycol.

Description

(1) The invention is now explained in more detail with the aid of test methods and non-limiting figures and examples.

(2) FIG. 1 shows a cross section of a preferred layered body according to the present invention.

(3) FIG. 2 shows a substrate that can be used for the formation of a layered body according to the present invention from the top.

(4) As can be seen in FIGS. 1 and 2, the layered body 1 according to the present invention comprises a substrate 2 onto which the conductive adhesive layer 3 according to the present invention is superimposed. Substrate 2 preferably comprises a non-conductive polymer layer 2a, which in the examples of the present application is a thin polyimide-film, onto which a further conductive layer 2b is superimposed. In the examples of the present application the further conductive layer 2b is a silver grid that has been applied onto the polyimide-film by means of a silver paste.

EXAMPLES

(5) Test Methods:

(6) Determination of the d.sub.50-Value of Particles A) and Particles B)

(7) The d.sub.50-value for particles A) and particles B) is determined via ultracentrifugation. The details of the method are described under Schlotan et al. (Kolloid-Z und Z Polymer; 250 (1972) page 782, Bestimmung der Teilchengr??enverteilung von Latices mit der Ultrazentrifuge) and M?ller (Colloid & Polymer Science: 267 (1989) page 1113). If required, particles A) and/or particles B) can be separated from other particles that may interfere with the determination of the d.sub.50-value by techniques known to the person skilled in the art, such a density gradient centrifugation, gel permeation chromatographie or gel electrophoresis.

(8) Determination of the Glass Transition Temperature

(9) The glass transition temperature is measured by means of differential calorimetry (DSC) (ISO 11357-2). This is, strictly speaking, a glass transition region, which extends over a temperature range. The glass transition temperatures referred to in the present invention represents average values.

(10) Determination of Moisture Absorption

(11) Between 8 and 9 g of the dispersion according to the present invention were given in an aluminium tray and the tray is dried at a temperature of 120? C. for 135 minutes in an oven with recirculating air. A dried films remains in the tray the weight of which is determined by weighing (tray.sub.before storage).

(12) Subsequently, the aluminium tray is stored in a closed desiccator at a temperature of 25? C. at 80% rel. humidity that is created with the aid of a saturated salt solution. After 22 hours the aluminium tray is weight again (tray.sub.after storage) and the moisture absorption (in wt. %) is calculated as follows:
Moisture absorption=100%?(tray.sub.after storage?tray.sub.before storage)/tray.sub.before storage
Determination of the Lateral and Transversal Resistance

(13) The specific resistance of the conductive adhesive layer in the lateral direction (R.sub.lateral) is determined by measuring the surface resistance (in ?/sq.) by means of an ACL 800 Digital Megohmmeter (ACL Staticide, Chicago, IL, USA). The specific resistance is calculated by multiplying the surface resistance with the thickness of the conductive adhesive layer (in m). The thickness of the conductive adhesive layer is calculated on the basis of the solid content of the dispersion used to prepare the conductive adhesive layer and the wet film thickness in which the dispersion is applied onto the substrate.

(14) The specific resistance of the conductive adhesive layer in the transversal direction (R.sub.transversal) is determined by impedance spectrometry using a SP-300 potentiostat/galvanostat (Bio-Logic SAS, Claix, France). A platinum electrode that was attached onto the surface of the conductive adhesive layer served as the counter electrode for a silver grid electrode that was located beneath the conductive adhesive layer. The specific resistance of the conductive adhesive layer in the transversal direction was determined at a frequency of 1 kHz.

Example 1: Preparation of Conductive Adhesive Compositions

(15) Mixtures of conductive polymer, anionic acrylic ester copolymer dispersion and optionally ethylene glycol were prepared. For that purpose a highly conductive aqueous PEDOT/PSS-dispersion (Clevios? P HC V6 Screen:solids content 1 wt. %) was introduced into a in a beaker.

(16) Subsequently, aqueous acrylate dispersions Rucocoat AC 1010 (solids content 65 wt. %), AQP 275 (solids content 60 wt. %) and Acronal S728 (solids content 50 wt. %) were added dropwise, followed by the addition of ethylene glycol. The mixtures were subsequently stirred for 30 minutes.

(17) TABLE-US-00001 solids Rucocoat ethyl- content PEDOT:PSS- AC AQP Acronal ene (calcu- Sam- dispersion 1010 275 S728 glykol lated) ple [g/g] [g/g] [g/g] [g/g] [g/g] [wt. %] A 10 20 1 42 B 4 20 0.4 53 C 10 10 1 31 D 10 10 0 33 E 20 10 2 21 F 10 10 1 29 G 10 10 1 24

(18) For the characterization, the samples were coated onto a Melinex PET film substrate by means of a manual squeegee with a wet film thickness of 40 ?m and dried for 5 minutes at 120? C. in a forced-air drying cabinet. The electrical surface resistance (Ohm/sq; ACL 800, Staticide) was measured and the adhesive force was determined qualitatively with the fingers (finger pressure/number of fingers need to lift the film having a size of about 20 cm?30 cm). Furthermore, adhesive layers prepared by means of these samples were analyzed with respect to the moisture absorption of dried films that have been prepared with these samples.

(19) TABLE-US-00002 amount of conductive relative polymer in moisture surface thickness the film absorp- resistance adhesive of the film (calculated) tion Sample [Ohm/sq] force (calculated) [wt. %] [wt. %] A 6 ? 10.sup.5 strong 1.4 0.8 B 2 ? 10.sup.8 very strong 1.75 0.3 1.6 C 2 ? 10.sup.5 medium 1 1.5 D 3 ? 10.sup.7 medium 1 1.5 2.1 E 2 ? 10.sup.3 weak 0.7 3.0 3.2 F 5 ? 10.sup.3 medium 1 1.6 G n. d. not 0.8 2.0 adhesive

Example 2: Preparation of Electrode

(20) A glass support substrate was coated with PAA (polyamidocarboxylic acid) which was subsequently thermally polycondensed to give PI (polyimide). The resulting polymer film has a thickness of 10 ?m. A silver paste on a PI-basis for potential homogenization was then screen printed by means of screen printing as shown in FIG. 2.

(21) This system was subsequently coated with the samples A to G obtained in Example 1. For this purpose, the samples were coated on the polyimide electrode substrate with a 90 ?m wet film thickness by lacquer coating and were subsequently dried for 5 minutes at 120? C. in a circulating air drying cabinet. This operation was performed a second time to obtain a thick conductive adhesive layer. The samples thus obtained were provided with a non-polarized electrode made of Pt-foil in order to test the impedance behavior in the range of 5 MHz to 100 mHz. All samples showed a purely ohmic behavior with a slightly inductive component which, however, is caused by the leads.

(22) As a comparison reference, the real part of the resistance was used at 1 kHz, which represents a suitable guide number for physiological systems. The determined values were additionally surface-normalized by the electrode surfaces of 44?51 mm. The following values have been measured:

(23) TABLE-US-00003 Sample used for Re at 1 kHz rho at 1 kHz layer preparation [Ohm] [Ohm/cm.sup.2] A 1.27 28.38704 B 1.44 32.18688 C 1.43 31.96336 D 3.27 73.09104 E 0.73 16.31696 F 0.36 8.04672 G 0.62 13.85824

(24) In the following table the specific resistance in both, the lateral and the transversal direction, for the conductive adhesive layers that have been made with Samples A, B, C, D and E are listed:

(25) TABLE-US-00004 Sample used for layer R.sub.transversal R.sub.lateral preparation [Ohm ? m] [Ohm ? m] A 45.8 10.08 B 82.0 4240 C 31.7 2.48 D 14.7 396 E 27.8 0.024

(26) As can be seen, the addition of ethylene glycol has an influence on the orientation of the PEDOTIPSS from anisotropic orthogonal to lateral conductivity. By adding ethylene glycol the proportion of the required metal grid on the flexible substrate can thus be reduced.

(27) Compared to the electrodes of the prior art the electrodes according to the present invention show purely ohmic behavior and the relevant resistances are also lower than for the known electrolyte-based electrode systems.