Method for recovering unreacted alpha, beta-ethylenically unsaturated nitrile monomer contained in latex of carboxyl group-containing nitrile rubber

A method for recovering an unreacted α,β-ethylenically unsaturated nitrile monomer contained in a latex of a carboxyl group-containing nitrile rubber obtained by emulsion polymerizing a monomer mixture comprising an α,β-ethylenically unsaturated nitrile monomer, a carboxyl group-containing monomer, and a diene monomer, comprising the steps of:

• adjusting a pH of the latex of the carboxyl group-containing nitrile rubber to 6.5 or more;
• performing a treatment for removing the unreacted diene monomer before or after the step of adjusting the pH of the latex of the carboxyl group-containing nitrile rubber to 6.5 or more,
• decompressing the latex of the carboxyl group-containing nitrile rubber having the pH adjusted to 6.5 or more that is obtained by removing the unreacted diene monomer under a heating condition;
• and
• recovering a component evaporated by the decompression under the heating condition;
• wherein
• a pressure reduction condition is −100 to −85 kPa in a gauge pressure when decompressing the latex of the carboxyl group-containing nitrile rubber under the heating condition, and
• a pressure reduction condition in a treatment for removing the unreacted diene monomer is −70 to −50 kPa in a gauge pressure.