The development of ink based on water-soluble complexes (WSC) is one of actual and worthwhile directions for development of ink-jet printing technology. Printing using the WSC-based ink implies local deposition of the complex compound in the form of a necessary pattern on the substrate and subsequent decomposition of the deposited complex ink to the final functional material (metal, oxide, etc.) by subsequent treatment (UV, IR, etc.). WSC-based inks, which are true solutions, would significantly solve the problem of aging inherent for inks based on colloidal solutions. Since the use of the WSC-based inks eliminates any possibility of aggregation of particles, which has a favorable effect on the uniformity and trouble-free operation of the print heads of printers. Moreover, the creation of WSC-based inks with a low decomposition temperature will allow using a wide range of organic flexible materials as substrates.
The report presents the results of our research, which was directed on the development Ag-based ink for creating conductive paths of electronic circuits. The [Ag (NH3)2]2CO3-based ink has been developed and the decomposition processes of the Ag-based complex to the metal under low-temperature treatment (T < 120°C) have been investigated.
The [Ag(NH3)2]2CO3 complex was produced by the interaction of Ag2CO3 (1 g) with a 25% aqueous solution of ammonia (3 ml). Further, ammonium formate (AF) was added to the prepared solution in various molar ratios of Ag2CO3/NH4HCO2 (from 1:1 to 1:1.6). The prepared solutions had a viscosity of 2.13 mPa.s and a Ag content of 27 wt%.
Then the solutions were layered to a glass substrate and heated to 100°C, resulting in a Ag recovery reaction according to the equation:
[Ag(NH3)2]2CO3+NH4HCO2 → 2Ag+5NH3+2CO2+H2O.
The XRD analysis revealed that as a result of thermal decomposition, a mixture of silver and silver oxide was formed on the substrate, where the proportion of silver oxide in the layers decreased with increasing content of AF in the solution. At a ratio Ag2CO3/NH4HCO2 = 1:1.6, silver oxide is not detected, which determines this molar ratio as the most optimal for the WSC-based silver ink.
Further to optimize the rheological properties of the ink, various polyols (ethylene glycol, diethylene glycol, glycerin) were used as an additive to the [Ag (NH3)2]2CO3 complex solution (of 10 vol.%). It has been found that the additives of the polyols increased the viscosity and wetting coefficient. According to the study of the shape of the formed microdroplets of ink on the surface of the PET substrate the best wetting takes place in the case of the addition of ethylene glycol.
Finally, it can be concluded that the ink with the addition of ethylene glycol are most appropriate to technological requirements for ink-jet printing. The developed ink provided the highest wetting ratio necessary for both free passage of ink through the channels of the print head and for uniformly forming layers on heat-sensitive substrates.