The solvent used in such cases may be any common solvent used for conventional coating, etc., examples of which are aromatic hydrocarbons such as toluene and xylene, alcohols such as ethanol, 2-propanol and 1-butanol, ketones such as acetone, methyl ethyl ketone and methyl isobutyl ketone, ethers such as diethyleneglycol dimethyl ether and triethyleneglycol dimethyl ether, esters such as ethyl ace