Among these, a linear or branched alkyl group having 1 to 18 carbon atoms and a cycloalkyl group having 3 to 7 carbon atoms are preferable, a linear alkyl group having 1 to 6 carbon atoms such as methyl group, ethyl group, n-propyl group, n-butyl group, n-pentyl group, and n-hexyl group, a branched alkyl group having 3 to 6 carbon atoms such as isopropyl group and t-butyl group, and a cycloalkyl g