| 摘要 |
PROBLEM TO BE SOLVED: To provide a method for removing, in high efficiency, metals from a phenolic compound by passing an organic solvent solution of the phenolic compound with a specific molecular weight through a filter medium affected by zeta potential. SOLUTION: This method comprises passing an organic solvent (e.g. ethyl acetate) solution of a phenolic compound with a molecular weight of 200-3,000 [e.g. a compound of the formula ((a) and b are each 0-3, but both of them cannot be simultaneously 0; x and y are each 0-3, a+x<=5 and b+y<=5)] through a filter medium affected by zeta potential, to remove metals from the phenolic compound. A low-molecular weight phenolic compound with a molecular weight of 200-3,000 has been, for example, added to a resist composition in order to promote the alkali solubility of a novolak-based resin used as a material for photoresists. Cotton, cellulose, polyester, activated carbon, zeolite or the like each of which a cation charge regulator is added to, can be used, as the filter medium affected by zeta potential.
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