FORMATION OF ELECTRICALLY CONDUCTIVE LAYERS AT NEAR AMBIENT TEMPERATURE USING SILVER NANOPARTICULATE PROCESSING AND INKS FOR FORMING THE LAYERS
Near ambient temperature processing has successfully resulted in highly conductive coatings formed from silver nanowires. The electrically conductive materials can have a high loading of silver and low resistivities. The highly conductive materials can be formed using aqueous inks with high loadings of silver nanowires with greater than 3 wt % metal that is primarily silver nanowires. Methods of preparing the high loading inks can comprise forming a good dispersion of the silver nanowires and removing solvent to concentrate the dispersions. A range of binders can be used including, for example, UV crosslinkable binders. Generally, the organic concentration of the highly conductive materials is no more than 25 wt %, although this can correspond to higher volume fractions of organics while still achieving good electrical conduction.
1 . An electrically conductive composite material comprising from about 75 wt % to about 98 wt % silver particulates and least about 2 wt % polymer binder, wherein the silver particulates comprise at least about 67 wt % silver nanowires having an aspect ratio of at least about 75.
2 . The electrically conductive composite material of claim 1 having a resistivity of no more than about 5×10 −3 Ohm-cm.
3 . The electrically conductive composite material of claim 1 having a resistivity of no more than about 5×10 −4 Ohm-cm.
4 . The electrically conductive composite material of claim 1 wherein the composite material has at least about 25 vol % silver.
5 . The electrically conductive composite material of claim 1 wherein the polymer binder comprises a polysaccharide.
6 . The electrically conductive composite material of claim 1 wherein the polymer binder comprises a polyethylene terephthalate (PET), polyethylene naphthalate (PEN), polyacrylate, poly(methyl methacrylate), polyamide, polyimide, polysulfone, polysiloxane, polyester, epoxy, polyurethane, polyvinyl alcohol, polyvinyl acetate, copolymers thereof, or blends of polymers.
7 . The electrically conductive composite material of claim 1 wherein the composite material consists essentially of the discrete silver particulates, the polymer binder and no more than about 2 wt % crosslinking agents and/or viscosity modifiers.
8 . The electrically conductive composite material of claim 1 wherein the silver nanowires have an average diameter from about 15 nm to about 80 nm and an aspect ratio from about 100 to about 1500.
9 . The electrically conductive composite material of claim 1 wherein the silver particulates comprise at least about 90 wt % nanowires.
10 . The electrically conductive composite material of claim 1 comprising at least about 90 wt % silver particulates.
11 . An electrically conductive structure comprising the electrically conductive composite material of claim 1 and having a transmittance of visible light of no more than about 70%.
12 . The electrically conductive structure of claim 11 wherein the electrically conductive structure comprises a layer having an average thickness of from about 0.2 microns to about 2 millimeters.
13 . The electrically conductive structure of claim 11 wherein the electrically conductive structure comprises a layer having an average thickness of no more than about 5 microns and a sheet resistance of no more than about 5 Ohms/sq.
14 . The electrically conductive structure of claim 11 wherein the electrically conductive structure comprises an opaque layer having an average thickness of no more than about microns and a sheet resistance of no more than about 1 Ohms/sq.
15 . The electrically conductive structure of claim 11 wherein the electrically conductive structure comprises a layer comprising at least about 90 wt % silver particulates and wherein the silver particulates comprise at least about 90 wt % silver nanowires.
16 . The electrically conductive structure of claim 11 wherein the electrically conductive composite material has a resistivity of no more than about 5×10 −4 Ohm-cm.
17 . The electrically conductive structure of claim 11 wherein the composite does not have deposits of in situ reduced metal.
18 . The electrically conductive structure of claim 11 wherein the electrically conductive structure comprises the electrically conductive composite material disposed on a heat sensitive substrate unstable over about 100° C.
19 . The electrically conductive structure of claim 11 wherein the electrically conductive composite material is in the form of an electrical interconnect.
20 . The electrically conductive structure of claim 11 wherein the electrically conductive structure (composite material) is processed at temperatures below about 100 C.
21 . The electrically conductive structure of claim 11 wherein the electrically conductive composite material is disposed on a substrate in roll form.