Silver ink compositions containing a cationic styrene/acrylate copolymer additive for inkjet printing
The present invention provides an aqueous ink containing ≧3% silver particles having much improved adhesion. It has been found that the adhesion can be improved by adding an aqueous cationic dispersion of a styrene/acrylate copolymer, PEI (polyethyleneimine), or arabinogalactan as an additive to the ink. The advantage of using one of these materials to improve the adhesion of the silver ink is the stability of the ink is maintained and the resistivity goal is met when printed onto the specified media. In other words, this invention provides a silver ink with great adhesion properties while still able to meet the <0.1 Ω/square resistivity requirement and remain stable for up to 4 weeks at 60° C. at accelerated oven aging conditions.
1. An aqueous inkjet ink composition for ink jet printers comprising silver particles having diameter in the range of from about 15 nm to about 50 nm, a cationic dispersion of a styrene/acrylate copolymer as an additive for improving adhesion, a humectant mixture, a surfactant, an aqueous carrier, wherein said cationic dispersion of styrene/acrylate copolymer is present in an amount of from about 0.1 to about 3% by weight based on the weight percentage of the styrene/acrylate copolymer solids in the aqueous inkjet composition.
2. The aqueous inkjet ink of claim 1 wherein said aqueous inkjet comprises from about 0.2 to about 1.0% by weight of said additive, based on the weight percentage of the styrene/acrylate copolymer solids in the aqueous inkjet ink.
3. The aqueous inkjet ink of claim 1 wherein said aqueous inkjet ink comprises from ≧3% to about 30% of the silver particles.
4. The aqueous inkjet ink of claim 3 wherein said aqueous inkjet ink comprises from about 11% to about 27% of the silver particles.
5. The aqueous inkjet ink of claim 4 wherein said silver particles have a diameter in the range of from about 20 nm to about 42 nm.
6. The aqueous inkjet ink of claim 1 wherein said surfactant is ethoxylated 2,4,7,9-tetramethyl 5 decyn-4,7-diol.
7. The aqueous inkjet ink of claim 1 wherein said humectant comprises a mixture of 1,2-propanediol and a glycol ethers compound having the following structure: R—[OCH 2 CH 2 ] n —OH wherein R is a C1-C4 alkyl group and n=1 to 3.