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EP-4013829-B1 - INK COMPOSITION, KIT, METHOD OF MANUFACTURING A DEFORMABLE CONDUCTOR UTILIZING THE INK COMPOSITION, DEFORMABLE CONDUCTOR, ELECTRONIC DEVICE COMPRISING THE DEFORMABLE CONDUCTOR, METHOD OF MANUFACTURING A CONDUCTOR, CONDUCTOR AND ELECTRONIC DEVICE COMPRISING THE CONDUCTOR

EP4013829B1EP 4013829 B1EP4013829 B1EP 4013829B1EP-4013829-B1

Inventors

  • GRIESSER, THOMAS
  • KRAWCZYK, Krzysztof Konrad

Dates

Publication Date
20260506
Application Date
20200810

Claims (13)

  1. A method of manufacturing a deformable conductor, the method comprising the steps of: (a) applying an ink composition on at least a part of a surface of a deformable substrate; (b) thermally treating and/or irradiating the ink composition, wherein the ink composition comprises: a source of transition metal ions; a complexing agent, wherein the complexing agent is selected from the group consisting of ammonia, an alkyl amine or a salt thereof; a reducing agent; a polymer precursor, the polymer precursor comprising a polymerizable terminal multiple bond; and a polymerization initiator, wherein the polymerization initiator comprises a thermal initiator.
  2. The method of manufacturing a deformable conductor according to claim 1, wherein at least one of the following features is fulfilled: the source of transition metal ions comprises a transition metal salt, a transition metal oxide and/or a transition metal complex; and/or the transition metal comprises at least one of silver and copper; and/or the ink composition comprises from 5 to 50 wt.-% of the source of transition metal ions; and/or the reducing agent is selected from the group consisting of formate, carbamate, carboxylate, ammonium carbonate, amine carbonate, ammonium bicarbonate, amine bicarbonate, hydrazinecarboxylate and combinations thereof; and/or the ink composition comprises from 1 to 10 wt.-% wt.-% of the reducing agent; and/or the polymer precursor comprises at least one of a monomer and an oligomer; and/or the polymer precursor is selected from the group consisting of (meth)acrylic acid, acrylamide or a salt thereof; and/or the polymerizable terminal multiple bond comprises at least one of a carbon-carbon double bond and a carbon-carbon triple bond, in particular a carbon-carbon double bond; and/or the ink composition comprises from 0.5 to 10 wt.-% of the polymer precursor; and/or the ink composition comprises from 0.1 to 0.5 wt.-% wt.-% of the polymerization initiator; and/or the source of transition metal ions and the polymer precursor are represented by one compound; and/or the ink composition comprises from 10 to 60 wt.-% of the complexing agent.
  3. The method of manufacturing a deformable conductor according to any one of the preceding claims, wherein the ink composition further comprises: a viscosity-modifying agent; and/or a carboxylic acid, in particular acetic acid and/or propionic acid, or a salt thereof; and/or a surfactant.
  4. The method of manufacturing a deformable conductor according to any one of the preceding claims, wherein the ink composition further comprises a solvent.
  5. The method of manufacturing a deformable conductor according to claim 4, wherein the solvent is selected from the group consisting of ammonia, an alkyl amine, water, an alcohol, and mixtures thereof; and/or wherein the solvent comprises a mixture of water and at least one of ammonia and an alkyl amine in a volume ratio of water to the at least one of ammonia and an alkyl amine of from 1:1.6 to 1:2.3.
  6. The method of manufacturing a deformable conductor according to any one of the preceding claims, wherein the reducing agent, the complexing agent and the optional solvent are volatile.
  7. The method of manufacturing a deformable conductor according to any one of the preceding claims, wherein at least one of the following features is fulfilled: the step (a) of applying an ink composition on at least a part of a surface of a deformable substrate comprises printing the ink composition on at least a part of a surface of a deformable substrate; and/or the step (a) of applying an ink composition comprises applying the ink composition on only a part of a surface of the deformable substrate; and/or a thickness of the applied ink composition is from 5 µm to 200 µm; and/or the deformable substrate comprises at least one polymer material; and/or the step (b) of thermally treating the ink composition comprises a treatment at a temperature of from 40 °C to 300 °C and for a period of time of from 5 min to 90 min; and/or the step (b) of thermally treating and/or irradiating the ink composition comprises a heat treatment by means of near infrared (NIR) irradiation and/or an irradiation with near infrared radiation, in particular under a normal gas atmosphere.
  8. The method of manufacturing a deformable conductor according to any one of the preceding claims, wherein the step (b) of thermally treating and/or irradiating the ink composition comprises a step (b1) of reducing transition metal ions by the reducing agent and a step (b2) of polymerizing the polymer precursor via the polymerizable terminal multiple bond.
  9. The method of manufacturing a deformable conductor according to claim 8, wherein the step (b2) of polymerizing the polymer precursor via the polymerizable terminal multiple bond is carried out once at least 50 % of the transition metal ions are reduced.
  10. The method of manufacturing a deformable conductor according to any one of the preceding claims, wherein at least one of the following features is fulfilled: the step (b) of thermally treating and/or irradiating the ink composition is carried out such that a percolated network of metal nano- or microstructure is formed; and/or the step (b) of thermally treating and/or irradiating the ink composition is carried out such that metal nanoparticles embedded in a polymer matrix are obtained; and/or a thickness of the thermally treated and/or irradiated ink after step (b) is from 100 nm to 10 µm; and/or further comprising, after a step (b) of thermally treating the ink composition, a step of irradiating at least part of the thermally treated ink with an energy-carrying activation beam; and/or in step (a) the ink composition is applied on at least a part of a surface of a stretched deformable substrate.
  11. A deformable conductor obtainable by the method according to any one of the preceding claims .
  12. The deformable conductor according to claim 11, comprising metal nanoparticles embedded in a polymer matrix, in particular wherein the metal nanoparticles have an average particle size of from 5 to 500 nm, in particular of from 10 to 250 nm.
  13. An electronic device, in particular a wearable and/or stretchable electronic device, comprising the deformable conductor according to claims 11 or 12.

Description

FIELD OF THE INVENTION The present invention relates to a method of manufacturing a deformable conductor utilizing an ink composition, a deformable conductor obtainable by the method and an electronic device, in particular a wearable and/or stretchable electronic device, comprising the deformable conductor. BACKGROUND The field of flexible or elastic electronics has rapidly grown over the past decade as a result of the increasing demand for real-time health monitoring, light weight mobile electronics, wearable displays etc. In the proximate future multifunctional electronic devices are going to be incorporated on the human body or clothing and a stable performance under conditions of high strain and extreme body motion such as folding, twisting and stretching will be required. The growing demand for such devices has triggered research in the design and manufacturing of stretchable elastomers and elastomer composites. Although good conductivity and high stretchability seem to be mutually exclusive features, a few approaches to combine stretchability and good electrical conductivity have been proposed to date. A common strategy is to obtain stretchable conductors from stiff, non-stretchable materials: (a) coiled metal wires, (b) meanders of metal foil, (c) thin layers of metal sputtered on prestretched or buckled/microporous substrates. These interconnects are stretchable within the boundaries imposed by geometrical features of the conductive film due to the microporosity of the surface, pattern design (e.g. meanders), pre-stretching and/or grain boundary lithography. Within these limits, excellent conductivity, speed and only little fatigue are observed. Nevertheless, above critical strain values (i.e. approx. 40% for meanders) irreversible destruction of the circuitry occurs. Additionally, the fabrication of conductive layers on prestretched substrates poses some technical challenges, which significantly increase the cost of manufacturing. Liquid metal conductors on elastomers show optimal R/R0 at almost any strain values but are difficult to manufacture industrially. In a recent publication (Hirsch, A., Michaud, H.O., Gerratt, A.P., Mulatier, S. de & Lacour, S.P. Intrinsically stretchable biphasic (solid-liquid) thin metal films. Advanced Materials 28, 4507-4512 (2016)), a thin layer of noble metal (i.e. Au) was evaporated onto an elastomer surface, followed by the evaporation of a layer of Ga. This resulted in a biphasic AuGa2/Ga layer, which showed excellent conductivity and was virtually fatigue free. The practical applicability for large-scale production is however limited by the thermal evaporation steps, which require high vacuum. High stretchability with low R/R0 was reported for stretchable inks based on PEDOT:PSS. The conductive polymer is typically used together with a fluorosurfactant and can be applied via screen printing. The advantage of the system lies inter alia in high optical transparency, which makes it a stretchable analogue to ITO films. However, for applications in stretchable interconnects, the limited conductivity of PEDOT:PSS is a disadvantage. Well resolved stretchable interconnects were manufactured by infiltration of an elastomeric substrate with Ag+ ions, followed by chemical reduction. In this approach, the high solubility of silver trifluoroacetate in organic solvents was exploited. The reduction is carried out by means of hydrazine or formaldehyde treatment. These substances are toxic or require a harsh environment, so the produced stretchable wiring boards need to be extensively rinsed. The preparation requires a multistep procedure and works well only on selected substrates, which limits its applicability in industrial processes. Despite the advantages of the systems described above, the vast majority of stretchable conductive systems are based on conductive composites, in which the polymeric part is responsible for the stretchability, while percolated conductive fillers allow efficient charge transfer. Conductive fillers may be carbon based (e.g. graphite, amorphous carbon, carbon nanotubes (CNTs), graphene, pyrolyzed bacterial cellulose) or metallic (e.g. metal nanowires, microflakes, micropowders, microflowers and nanoparticles). Combinations of different kinds of fillers were also reported. One method of fabricating conductive composites is the infiltration of a percolated filler-network with a liquid elastomer resin, which is subsequently cured. Thus obtained composites show excellent conductivity, since the filler network is per se highly percolated. The drawback is the relatively complex, multistep manufacturing process and the difficulty in the precise deposition of the filler. In another approach, an ink contains both the elastomeric resin and the filler in a single component, which can be structured for instance by means of screen printing. The latter is the preferred deposition method for industrial applications because of the simplicity of the printing process,