Expandable thermoplastic microspheres and process for the production and use thereof
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United States of America Patent
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Oct 13, 1992
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app pub date -
Nov 8, 1991
filing date -
Nov 12, 1990
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Abstract
A method for producing expandable thermoplastic microspheres by polymerisation in a reaction vessel of an ethylenically unsaturated monomer or a mixture of monomers in an aqueous suspension in the presence of a condensed propellant. In the method, the monomer or monomer mixture is suspended in the aqueous medium in the presence of a powder stabilizer which consists of a salt or hydroxide of any of the metals Ca, Mg, Ba, Fe, Zn, Ni or Mn. The powder stabilizer is insoluble in the aqueous medium at the pH the aqueous medium has at the polymerisation. The aqueous medium has at the polymerization. The aqueous medium may also contain a co-stabilizer. The method further comprises the step of washing off the powder stabilizer from the microspheres after the polymerization by lowering the pH of the aqueous medium by the addition of acid. Alternatively, amphoteric hydroxides can also be dissolved by a pH increase. The invention also relates to microspheres produced according to the method of the invention, and to the use thereof.
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