THERMOFORMABLE POLYMER THICK FILM SILVER CONDUCTOR FOR CAPACITIVE SWITCHES
This invention is directed to a polymer thick film conductive composition. More specifically, the polymer thick film conductive composition may be used in applications where thermoforming of the base substrate occurs as in capacitive switches. Polycarbonate substrates are often used as the substrate and the silver conductor composition may be used without any barrier layer.
1 . A polymer thick film conductive composition comprising:
(a) 30-70 wt % silver;
(b) 10-40 wt % first organic medium comprising 10-50 wt % thermoplastic urethane resin dissolved in a first organic solvent, wherein the weight percent of the thermoplastic urethane resin is based on the total weight of the first organic medium; and
(c) 10-40 wt % second organic medium comprising 10-50 wt % thermoplastic polyhydroxyether resin dissolved in an organic solvent wherein the weight percent of the thermoplastic polyhydroxyether resin is based on the total weight of the second organic medium;
wherein the weight percent of said silver, said first organic medium and said second organic medium are based on the total weight of said polymer thick film conductive composition.
2 . The polymer thick film conductive composition of claim 1 , further comprising:
(d) 1-20 wt % of a third organic solvent, wherein the third organic solvent is diacetone alcohol and wherein the weight percent is based on the total weight of said polymer thick film conductive composition.
3 . The polymer thick film conductive composition of claim 1 or 2 , wherein said silver is in the form of silver flakes.
4 . The polymer thick film conductor composition of claim 3 , wherein said thermoplastic urethane resin is a urethane homopolymer or a polyester-based copolymer
5 . The polymer thick film conductive composition of claim 4 , wherein said thermoplastic urethane resin is a polyester-based copolymer.
6 . A capacitive switch circuit comprising a conductor formed from the polymer thick film conductive composition of any of claims 1 - 5 .
7 . The capacitive switch circuit of claim 6 , wherein said capacitive switch circuit is thermoformed.