Pretreat compositions
A method for forming parts with electrically conductive features includes applying a layer of thermoplastic polymer powder particles in a powder bed and selectively applying an aqueous pretreat composition including a metal chloride salt on a portion of the layer. A conductive fusing ink including transition metal particles and a dispersing agent is selectively applied onto the applied aqueous pretreat composition on the portion of the layer, wherein the dispersing agent binds to, and passivates surfaces of the transition metal particles. The layer is exposed to electromagnetic radiation to fuse the thermoplastic polymer powder particles in the portion of the layer and sinter the transition metal particles, thereby forming a conductive feature.
1 . A method for forming parts with electrically conductive features, the method comprising:
a) applying a layer of thermoplastic polymer powder particles in a powder bed;
b) selectively applying an aqueous pretreat composition including a metal chloride salt on a portion of the layer of thermoplastic polymer powder particles;
c) selectively applying a conductive fusing ink including transition metal particles and a dispersing agent onto the applied aqueous pretreat composition on the portion of the layer, wherein the dispersing agent binds to, and passivates surfaces of the transition metal particles; and
d) exposing the layer to electromagnetic radiation to fuse the thermoplastic polymer powder particles in the portion of the layer and sinter the transition metal particles, thereby forming a conductive composite including interlocked matrices of fused thermoplastic polymer powder particles and sintered transition metal particles.
2 . The method as defined in claim 1 , further comprising repeating b), c) and d) for one or more additional passes to obtain a predetermined conductivity of the conductive composite.
3 . The method as defined in claim 1 wherein b), c) and d) occur prior to an application of an additional layer of thermoplastic polymer powder particles.
4 . The method as defined in claim 3 , further comprising applying an additional layer of thermoplastic polymer powder particles on the exposed layer, and then repeating b), c) and d) one or more times.
5 . The method as defined in claim 1 wherein each of the selectively applying of the aqueous pretreat composition and the selectively applying of the conductive fusing ink is accomplished by thermal inkjet printing, or piezoelectric inkjet printing.
6 . The method as defined in claim 1 wherein each of the selectively applying of the aqueous pretreat composition and the selectively applying of the conductive fusing ink is accomplished by thermal inkjet printing.
7 . The method as defined in claim 1 wherein the transition metal particles:
are in the form of elemental transition metal particles that are selected from the group consisting of silver particles, copper particles, gold particles, platinum particles, palladium particles, chromium particles, nickel particles, zinc particles, and a combination thereof;
are present in the conductive fusing ink in an amount ranging from about 5 wt % to about 50 wt %, based on a total weight of the conductive fusing ink; and
have an average particle size from 10 nm to 200 nm.
8 . The method as defined in claim 1 wherein the metal chloride salt:
is selected from the group consisting of sodium chloride, potassium chloride, lithium chloride, calcium chloride, magnesium chloride, manganese chloride, zinc chloride, nickel chloride, cobalt chloride, and iron chloride; and
is present in the aqueous pretreat composition in an amount ranging from 0.1 wt % to 15 wt %, based on a total weight of the pretreat composition.
9 . The method as defined in claim 8 wherein the aqueous pretreat composition consists of water and the metal chloride salt.
10 . The method as defined in claim 8 wherein the metal chloride salt is selected from the group consisting of sodium chloride, potassium chloride, and a combination thereof.
11 . The method as defined in claim 1 , further comprising selectively applying a reducing agent to the portion of the layer before or after selectively applying the aqueous pretreat composition thereon, but before selectively applying the conductive fusing ink onto the applied aqueous pretreat composition on the portion of the layer;
wherein the reducing agent is selected from the group consisting of glucose, fructose, maltose, maltodextrin, trisodium citrate, ascorbic acid, sodium borohydride, ethylene glycol, 1,5-pentanediol, and 1,2-propylene glycol.
12 . The method as defined in claim 1 wherein the dispersing agent:
is capable of being removed from the surfaces of the transition metal particles by a reaction with the metal chloride salt; and
is selected from the group consisting of sulfonic acid, phosphonic acid, carboxylic acid, dithiocarboxylic acid, phosphonate, sulfonate, thiol, carboxylate, dithiocarboxylate, an amine, an alkylamine, and an alkylthiol.
13 . The method as defined in claim 1 wherein the exposing the layer to electromagnetic radiation is accomplished with a fusing lamp, and wherein the method further comprises selecting the fusing lamp that emits a range of wavelengths of light that matches a peak absorption range of wavelengths of light of the conductive fusing ink.