Abstract: A flame-retardant polyacetal resin composition comprising 60 to 90% by weight of a polyacetal resin, 1 to 30% by weight of red phosphorus, 1 to 40% by weight of at least one resin selected from phenol resins and polycarbonate resins, and 0.1 to 5% by weight of a metal salt of a fatty acid. The polyacetal resin composition of the present invention is provided with flame retardancy while maintaining the excellent innate properties of polyacetal resins, so that it can be applied to the fields where the use of polyacetal resins has been restricted.

Abstract: A polyacetal resin composition which comprises about 100 parts by weight of a polyacetal having a residual fluorine concentration of not more than about 13 ppm and a concentration of formaldehyde generated when the polyacetal is heated at about 230° C. for about 30 minutes in nitrogen of not more than about 500 ppm; from about 0.01 to about 3 parts by weight of an antioxidant; and from about 0.001 to about 5 parts by weight of a basic substance. The above polyacetal resin composition is excellent in long-term thermal aging resistance under high-temperature circumstances.

Abstract: A process for producing methylal that involves feeding a liquid containing methanol, formaldehyde and water to an uppermost reactor of at least four solid acid catalyst-filled reactors which are each externally connected to an intermediate portion of a distillation column; and forcibly circulating a liquid containing methanol, formaldehyde, water and produced methylal in a temperature range of 80° C. to 100° C.

Abstract: A flame-retardant polyacetal resin composition comprising 60 to 90% by weight of a polyacetal resin, 1 to 30% by weight of red phosphorus, 1 to 40% by weight of at least one resin selected from phenol resins and polycarbonate resins, and 0.1 to 5% by weight of a metal salt of a fatty acid. The polyacetal resin composition of the present invention is provided with flame retardancy while maintaining the excellent innate properties of polyacetal resins, so that it can be applied to the fields where the use of polyacetal resins has been restricted.

Abstract: A process for producing a polyoxymethylene using a reactor having a discharging port having a weir, which process comprises introducing trioxane or a mixture of trioxane and a compound reactive therewith into the reactor from its feeding port and continuously recovering the powdery polyoxymethylene formed, from said discharging port having a weir. Owing to the presence of the weir, the residence time of reaction mixture in reactor is long, making high the conversion of the monomer.

Abstract: A polyoxymethylene copolymer prepared by copolymerizing a mixture comprising trioxane and 1,3-dioxolane in the presence of at least one polymerization catalyst selected from the group consisting of boron trifluoride, a boron trifluoride hydrate and a coordination complex compound of an organic compound containing an oxygen atom or a sulfur atom with boron trifluoride, wherein the 1,3-dioxolane has a 2-methyl-1,3-dioxolane content of not more than 500 ppm by weight and a 1,3-dioxolane peroxide content of not more than 15 ppm by weight in terms of hydrogen peroxide, and contains at least one hindered phenol in an amount of from 10 to 500 ppm by weight, each based on the weight of the 1,3-dioxolane.

Abstract: Disclosed is a method for stabilizing unstable terminals of a crude oxymethylene copolymer, wherein use is made of an extruder comprising a casing having a supply inlet and an extrusion outlet which casing has at least two rotation shafts extending longitudinally through the extruder in which a melting zone, a terminal stabilization reaction zone and a volatile matter exhaustion zone are consecutively arranged from the supply inlet toward the extrusion outlet, wherein the terminal stabilization zone has a plurality of kneading elements having a thickness of from 0.1D to 0.

Abstract: The present invention provides a method for producing an oxymethylene copolymer, which comprises:copolymerizing trioxane and a cyclic ether and/or a cyclic formal in the presence of at least one selected from the group consisting of boron trifluoride, boron trifluoride hydrate, and a coordination compound of an organic compound having an oxygen or a sulphur atom with boron trifluoride,volatilizing the residual polymerization catalyst to decrease its amount, by heating the obtained oxymethylene copolymer in an atmosphere of inert gas at or below its melting point, and/or reducing the pressure, without conducting any operation of deactivating the residual polymerization catalyst before volatilizing the residual polymerization catalyst, andstabilizing terminal moities of the oxymethylene copolymer after deactivating residual catalyst or stabilizing terminal moieties of the oxymethylene copolymer directly.