Method for producing an oxymethylene copolymer

Patent metadata

Field	Value
Publication number	US-2016102190-A1
Application number	US-201414892319-A
Country	US
Kind code	A1
Filing date	May 23, 2014
Priority date	May 24, 2013
Publication date	Apr 14, 2016
Grant date	—

Abstract

Provided is a method for producing an oxymethylene copolymer having excellent extrusion moldability and reduced voids in a molded article without lowering the inherent performance of an oxymethylene copolymer. Provided is a method for producing an oxymethylene copolymer, including: a step for copolymerizing a monomer raw material containing trioxane and 5-7 mass % of 1,3-dioxolane relative to the trioxane, in the presence of 0.025-0.07 mmol of boron trifluoride per mol of trioxane and 0.006-2.0 mass % of sterically hindered phenol relative to the trioxane; a step for adding a polymerization terminator to the reaction system when the polymerization yield of this copolymer has reached 92% or higher, and terminating polymerization; and a thermal stabilization step for heating and melting the crude oxymethylene copolymer in the presence of 0.05-5 mass % of an antioxidant and 0.005-5 mass % of a nitrogen-containing compound relative to the crude oxymethylene copolymer.

First claim

1 . A method for producing an oxymethylene copolymer, comprising the steps of:
subjecting a monomer raw material comprising trioxane and 1,3-dioxolane in an amount of 5 to 7% by mass based on the mass of the trioxane, to a copolymerization reaction, in the presence of boron trifluoride in a proportion of 0.025 to 0.07 mmol per 1 mol of the trioxane and a sterically hindered phenol in an amount of 0.006 to 2.0% by mass based on the mass of the trioxane; at a point in time when the copolymerization reaction gives a polymerization yield of 92% or more, adding a polymerization terminator to the reaction system to terminate the copolymerization reaction, to obtain a crude oxymethylene copolymer; and thermally stabilizing the crude oxymethylene copolymer by heat-melting the crude oxymethylene copolymer in the presence of an antioxidant in an amount of 0.05 to 5% by mass and a nitrogen-containing compound in an amount of 0.005 to 5% by mass, each based on the mass of the crude oxymethylene copolymer.

2 . The method according to claim 1 , wherein an amine is contained in the trioxane in a proportion of 0.00001 to 0.003 mmol per 1 mol of the trioxane.

3 . The method according to claim 1 , wherein the antioxidant is a sterically hindered phenol.

4 . The method according to claim 1 , wherein the nitrogen-containing compound is at least one member selected from the group consisting of melamine, methylolmelamine, benzoguanamine, cyanoguanidine, an amine-substituted triazine, a polyamide, an urea derivative, and an urethane.

5 . The method according to claim 1 , wherein the polymerization terminator is at least one member selected from the group consisting of triphenylphosphine, a hindered amine compound, and an alkylated melamine.

6 . The method according to claim 1 , wherein, at a point in time when the copolymerization reaction gives a polymerization yield in 97% or more, the polymerization terminator is added to the reaction system to terminate the copolymerization reaction.

7 . The method according to claim 1 , which is performed using a continuous polymerization apparatus comprising a continuous polymerizer and a polymerization terminator mixing machine which are connected in series.

8 . The method according to claim 7 , wherein a part of or all of the sterically hindered phenol is added through an inlet of the continuous polymerizer.

9 . The method according to claim 1 , wherein the thermal stabilization step is performed by melt-kneading the crude oxymethylene copolymer at a temperature in the range of from the melting temperature of the crude oxymethylene copolymer to a temperature 100° C. higher than the melting temperature under a pressure of 760 to 0.1 mmHg.

10 . The method according to claim 1 , wherein the thermal stabilization step is performed by means of an apparatus comprising a combination of a single-, twin- or multi-screw vented extruder and a surface renewal-type mixer.

11 . The method according to claim 1 , wherein the crude oxymethylene copolymer as such is subjected to the thermal stabilization step.

Assignees

• Mitsubishi Gas Chemical Co

Inventors

• Ito Akira
• Mikami Sunao

Classifications

• C08K5/17 Primary

  Amines; Quaternary ammonium compounds · CPC title

• C08K5/134

  Phenols containing ester groups · CPC title

• C08G4/00

  Condensation polymers of aldehydes or ketones with polyalcohols; Addition polymers of heterocyclic oxygen compounds containing in the ring at least once the grouping —O—C—O— (of cyclic oligomers of aldehydes C08G2/00) · CPC title

• C08G2/04

  Polymerisation by using compounds which act upon the molecular weight, e.g. chain-transferring agents · CPC title

• C08G2/10

  Polymerisation of cyclic oligomers of formaldehyde · CPC title