Aqueous coating liquid for forming a magnesium oxide film

The present invention provides an aqueous coating liquid for forming a magnesium oxide film that comprises: (a) a magnesium carboxylate derived from a carboxylic acid having 1 to 6 carbon atoms, (b) a surfactant, (c) a polyhydric alcohol compound, and (d) a solvent made substantially of water; wherein the magnesium carboxylate is contained in a ratio of 5 wt% or more and 50 wt% or less, the surfactant is contained in a ratio of 0.01 wt% or more and 2.5 wt% or less, and the polyhydric alcohol compound is contained in a ratio of 0.05 wt% or more and 40 wt% or less, based on a weight of the entire coating liquid; wherein a content of the magnesium carboxylate is the same with or larger than that of the polyhydric alcohol compound, and a total weight of the magnesium carboxylate and the polyhydric alcohol compound is 80 wt% or less of the weight of the entire coating liquid; and wherein the magnesium carboxylate, the surfactant, and the polyhydric alcohol compound are dissolved in the solvent.