Stabilization of silicate solutions

#The present invention is directed to improvements in aqueous cleaning compositions. In particular, the invention is concerned with aqueous cleaning compositions which contain alkaline salts and a silicate salt either to enhance cleaning or to provide corrosion protection and to improvements in maintaining the silicate in aqueous solution.

#Silicates such as alkali metal silicates are extremely effective in protecting metals and ceramics against the corrosive effects of alkaline solutions. Moreover, such silicates also provide useful detergent boosting effects when present in cleaning solutions. Accordingly, alkali metal silicates are widely used in a broad range of detergent products such as automatic dishwashing detergents, metal cleaners and laundry detergents.

#Another important usage of alkali metal silicates is as an additive in aqueous cleaning solutions used to remove solder flux and other residues from electronic circuit assemblies such as printed circuit boards or printed wiring boards. As described in commonly-assigned co-pending application, U.S. Ser. No. 731,512, now abandoned, filed Jul. 17, 1991, it has been found that solder fluxes contained on electronic circuit assemblies, such as printed circuit boards and printed wiring boards, can be effectively removed by contact with aqueous solutions of alkaline salts such as alkali metal carbonates and mixtures of alkali metal carbonates and bicarbonates. It has further been found that the addition of alkali metal silicates to such formulations greatly improves the corrosion protection of ceramic and metal components on such electronic assemblies.

#The efficacy of this invention will be better understood by reference to FIGS. 1-7 herein wherein the test results of certain embodiments of the cleaners of this invention are illustrated.

#FIGS. 1, 2, 4, and 6 represent typical curves showing the cleaning efficiencies of various concentrations of cleaning solutions resulting from visual testing as described herein.

#FIGS. 3, 5, and 7 represent typical curves showing the cleaning efficiencies of various concentrations of cleaning solutions resulting from equilibrium resistivity measurements as described herein.

#The objects and advantages mentioned above as well as other objects and advantages may be achieved by the compositions and methods hereinafter described.

#Essentially, the flux removing compositions of the invention comprise mixtures of alkali metal salts. Accordingly, the term "flux removing compositions" as used herein is intended to define the mixture of essentially active ingredients comprised of the alkali metal salts, and additional performance enhancers such as silicate corrosion inhibitors and any other adjuvants such as surfactants, antifoam agents, etc. as hereinafter described.

#As hereinlater set forth, the flux removing compositions may be formulated into concentrated solutions. The terms "flux removing concentrated solutions" or "concentrates" as used herein define aqueous mixtures containing from about 5 to 45 or more percent by weight of the flux removing compositions with the balance being essentially water.