| 摘要 |
PROBLEM TO BE SOLVED: To improve, quickly and in a simple manner, thermal stability and resistances to discoloration due to aging and coloration during the stay in a molding machine of a polyoxymethylene copolymer having thermally unstable terminals by thermally treating the copolymer with a specified amt. of a specific quaternary ammonium compd. SOLUTION: A polyoxymethylene copolymer in the molten state is thermally treated at a temp. not lower than its m.p. but not higher than 260 deg.C in the presence of a quaternary ammonium compd. of the formula: [R1R2R3R4N+]nXn- [wherein R1 to R4 are each independently a 1-30C (substd.) alkyl or the like; (n) is 1-3; and X is a hydroxyl group or an acid residue such as of a 1-20C carboxylic acid]. The ammonium compd. is used in such an amt. that, based on the sum of wts. of the copolymer and the compd., the amt. of nitrogen derived from the compd., i.e., represented by the formula: P×14/Q [wherein P is the content (wt.ppm) of the compd. based on the sum; and Q is the mol.wt. of the compd.], is 0.05-50 wt.ppm and that the amt. of a halogen introduced into the copolymer is 0.1 wt.ppm or lower based on the copolymer.
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