Patent ID: 8361361

Claim:
A method of preparing a foaming agent masterbatch for a thermoplastic resin, comprising: (a) melt-mixing a selected amount of an ultra-fine sodium bicarbonate powder with a thermoplastic resin and selected amounts of suitable functional additives and minerals; and (b) cold-pressing the melt into a solidified foaming agent masterbatch composition, wherein said sodium bicarbonate powder is prepared by providing an aqueous solution of sodium chloride and an aqueous solution of ammonium bicarbonate; mixing the two aqueous solutions in a stirring vessel and stirring at high speed for a period from 20 to 60 seconds at a reaction temperature below 30° C.; separating precipitated sodium bicarbonate from the stirred mixture; and drying the sodium bicarbonate to produce an ultra-fine powder having a particle size of less than 5 microns and a standard deviation in particle size less than the mean particle size.