Metal ion reduction in novolak resin solution using an anion exchange resin

A method for producing water insoluble, alkali soluble novolak resins having a very low level of metal ions which process utilizes a basic anion exchange resin to purify the novolak resin solution, comprising:

• a) washing an anion exchange resin with water followed by washing with a mineral acid solution, washing again with water, followed by washing with an ammonium hydroxide solution, followed by washing with deionized water, and thereby providing a level of sodium and iron ions in the anion exchange resin of less than 200 ppb each;
• b) preparing a solution of a novolak resin in a suitable novolak resin solvent;
• c) washing the anion exchange resin with a solvent which is the same as, or at least compatible with, the novolak resin solvent, to remove substantially all of the water;
• and
• d) passing the solution of novolak resin through the washed anion exchange resin bed at a flow rate such that the residence time is greater than 60 minutes, and thereby providing a level of sodium and iron ions in the novolak resin solution of less than 100 ppb each.