Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – From aldehyde or derivative thereof as reactant
Patent
1996-08-07
1998-09-22
Truong, Duc
Synthetic resins or natural rubbers -- part of the class 520 ser
Synthetic resins
From aldehyde or derivative thereof as reactant
528270, 528480, 528502, 528503, 525398, 26421112, 26421118, 2642112, C08G 200
Patent
active
058115110
DESCRIPTION:
BRIEF SUMMARY
BACKGROUND OF THE INVENTION
1. Technical Field
The present invention relates to a method for stabilizing unstable terminals of an oxymethylene copolymer. More particularly, the present invention is concerned with 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 specific thickness arranged longitudinally on and securely attached to each rotation shaft in a region thereof having a specific length, and wherein the molten crude oxymethylene copolymer is kneaded and agitated, in the presence of a basic substance capable of decomposing unstable terminals of the crude oxymethylene copolymer, in the terminal stabilization reaction zone of the extruder, thereby decomposing the unstable terminals of the crude oxymethylene copolymer. By the method of the present invention, the terminal stabilization reaction of a crude oxymethylene copolymer can be efficiently performed to a substantially complete degree in a short period of time.
2. Background Art
A crude oxymethylene copolymer which is produced by copolymerizing trioxane with a cyclic ether has a group --(OCH.sub.2).sub.n --OH at its molecular chain terminals. This terminal group --(OCH.sub.2).sub.n --OH needs to be stabilized because it is thermally unstable. As methods for stabilizing this crude oxymethylene copolymer, there are known a method of acetylating, etherifying or urethanizing the terminals of the crude copolymer, and a method of decomposing the unstable terminals of the crude copolymer. Of these above-mentioned methods, the decomposition of the unstable terminals is advantageously used for stabilizing the crude oxymethylene copolymer. As methods for decomposing the unstable terminals to stabilize the crude oxymethylene copolymer, there are known a method of heating the crude oxymethylene copolymer in water or an organic solvent in the presence of a basic substance capable of decomposing the unstable terminals, and a method of stabilizing a crude oxymethylene copolymer in a molten form. The former requires various operations, such as operations for separation, recovery and washing of the treated copolymer. Whereas, the latter is commercially advantageous since a stabilized copolymer can be directly obtained.
With respect to the conventionally known methods of treating a crude oxymethylene copolymer in a molten form to decompose unstable terminals thereof, there can be mentioned Examined Japanese Patent Application Publication No. 58-11450 (corresponding to U.S. Pat. No. 4,366,305), which discloses a method for stabilizing the unstable terminals of a crude oxymethylene copolymer by use of a special, surface-renewing mixer, after a heat treatment of the crude copolymer. In this method, a degassing apparatus which comprises in combination an extruder and a surface-renewing mixer having a plurality of scraping blades is used. The method consists in heat-melting the crude oxymethylene copolymer and kneading the crude copolymer in a molten state under a reduced pressure for a residence time of from 5 to 60 minutes, while constantly renewing the surface of the crude copolymer and volatilizing the volatiles contained in the crude copolymer, to thereby decompose the unstable terminals of the crude copolymer.
Further, another method for stabilizing unstable terminals of a crude oxymethylene copolymer, and apparatus for practicing the method are disclosed in Unexamined Japanese Patent Application Laid-Open Specification No. 58-152012 (corresponding to European Patent 0 088 541). The method comprises melting the crude oxymethylene copolymer in a single screw extruder, decomposing unst
REFERENCES:
patent: 4366305 (1982-12-01), Amemiya et al.
Morishita Hirohisa
Tanigawa Yukio
Asahi Kasei Kogyo Kabushiki Kaisha
Truong Duc
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