Suitable examples of the hydrophilic organic solvent include alcohols such as methanol, ethanol, and propanol; ketones such as acetone and methyl ethyl ketone; esters such as methyl acetate and ethyl acetate; and compounds represented by the general formula (1) shown above such as N-methyl-2-pyrrolidone and N,N???-dimethyl-2-imidazolidone.