JP2000063464A - Stabilization of polyoxymethylene copolymer - Google Patents

Abstract

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.

Description

Detailed Description of the Invention

[0001]

TECHNICAL FIELD The present invention relates to a method for stabilizing a polyoxymethylene copolymer. More specifically, when a polyoxymethylene copolymer having a thermally unstable terminal portion is heat-treated and stabilized, a specific quaternary ammonium compound whose halogen content is restricted by the heat treatment is
The present invention relates to a method for stabilizing a polyoxymethylene copolymer performed in the presence of a specific amount. According to the stabilization method of the present invention, by adding a very small amount of a specific quaternary ammonium compound having a limited halogen content, the decomposition rate of the unstable terminal portion is dramatically improved and polyoxymethylene copolymerization Since it can accelerate the stabilization of the coalescence, a polyoxymethylene copolymer excellent in all of thermal stability, aging discoloration property, and retention coloring property, in which an unstable terminal portion hardly remains, can be obtained in a short time. And it becomes possible to manufacture easily.

[0002]

2. Description of the Related Art Polyoxymethylene copolymers are excellent in balanced mechanical properties, fatigue resistance, abrasion / wear resistance, chemical resistance, and moldability, and are suitable for automobiles, electric / electronic devices, and other precision products. It is used for machinery, building material piping, etc. A polyoxymethylene copolymer is produced by copolymerizing formaldehyde or a cyclic acetal such as trioxane, which is a cyclic trimer thereof, with either or both of a cyclic ether and a cyclic formal. However, the polyoxymethylene copolymer obtained by such copolymerization has-(OCH ₂ ) _n -OH at a part of the molecular end of the molecule.
Since it has a group, and this terminal group is thermally unstable, it is easily decomposed by heating during molding and the like to generate a large amount of formaldehyde, so that it cannot be put to practical use as it is.

That is, when a large amount of formaldehyde is generated, the resin foams during molding or the resin is colored in the molding machine. In addition, formaldehyde odor is easily generated, which deteriorates the working environment. In addition, when molding is performed for a long time, fine powdery substances / tar-like substances (mold deposits) adhere to the surface of the mold, which deteriorates the appearance of the molded product and causes inconveniences such as reduced dimensional accuracy. Further, the generated formaldehyde is oxidized by oxygen in the molding machine to form formic acid, which accelerates the main chain decomposition of the polyoxymethylene copolymer. Therefore, in practical use of the polyoxymethylene copolymer having an unstable terminal portion, the unstable terminal portion is decomposed and removed before use.

As a method for decomposing and removing the unstable terminal portion, for example, a single-screw extruder with a vent, a twin-screw extruder with a vent, or the like is used, and ammonia or an aliphatic amine such as triethylamine or tributylamine is used. ,
In the presence of a basic substance capable of decomposing unstable terminal parts such as hydroxide, inorganic weak acid salt, organic weak acid salt of alkali metal or alkaline earth metal typified by calcium hydroxide, It is industrially widely practiced to melt a polymer and decompose and remove an unstable terminal portion. However, the polyoxymethylene copolymer that has been subjected to such a treatment still has thermally unstable terminal portions, which cause mold deposits during molding, coloring of the polymer retained in the molding machine, and aging. Since it causes undesired phenomena such as discoloration of the polymer at times, there is a strong demand for a thermally stable polyoxymethylene copolymer with less unstable terminal portions.

Further, in the above method, in order to accelerate the decomposition of the unstable terminal portion, it was necessary to increase the amount of the basic substance added. However, if the amount of the aliphatic amine or the like is increased too much, it will remain in the polymer, causing a problem that the polymer retained in the molding machine is colored or the polymer is discolored during aging. Furthermore, in order to reduce the unstable terminal portion, it is necessary to perform treatment for a long time or a plurality of times. Therefore, not only the polyoxymethylene copolymer after decomposition and removal of the unstable terminal portion is colored and deteriorated. However, there is also a problem that the device becomes large and complicated. Therefore, there is a need for a stabilizing method that can easily and economically obtain a polyoxymethylene copolymer that has very few unstable terminal portions and is thermally stable, and that is excellent in aging discoloration and retention coloring. It was

[0006]

SUMMARY OF THE INVENTION An object of the present invention is to provide a polyoxymethylene copolymer which has very few unstable terminals and is excellent in heat stability and has improved aging discoloration property and retention coloration property. Another object of the present invention is to provide a method for stabilizing a polyoxymethylene copolymer, which can be manufactured easily in a short time.

[0007]

SUMMARY OF THE INVENTION In view of the above problems, the present inventors have found that polyoxymethylene having very few unstable terminal portions and excellent thermal stability, and improved aging discoloration property and retention coloring property. An intensive study was conducted to obtain a copolymer. As a result, the heat treatment is carried out in the presence of a very small amount of a specific quaternary ammonium compound having a limited halogen content, whereby the thermally unstable terminal portion of the polyoxymethylene copolymer is dramatically removed. And the thermal stability of the polyoxymethylene copolymer is significantly improved.
The present inventors have completed the present invention by finding that a polyoxymethylene copolymer having improved aging discoloration properties and retention coloring properties can be obtained.

That is, according to the present invention, a polyoxymethylene copolymer having a thermally unstable terminal is represented by the following general formula (1)
Above the melting point of the polyoxymethylene copolymer in the presence of at least one quaternary ammonium compound represented by
A method for stabilizing a polyoxymethylene copolymer having a thermally unstable terminal portion by heat-treating the polyoxymethylene copolymer in a molten state at a temperature of 60 ° C. or lower, wherein [R ¹ R ² R ³ R ⁴ N ⁺ ] _n X ^-n (1) (In the formula, R ¹ , R ² , R ³ , and R ⁴ are each independently an unsubstituted alkyl group having 1 to 30 carbon atoms or a substituted group. An alkyl group; an aryl group having 6 to 20 carbon atoms; an aralkyl group in which an unsubstituted alkyl group having 1 to 30 carbon atoms or a substituted alkyl group is substituted with at least one aryl group having 6 to 20 carbon atoms; or 6 carbon atoms Represents an alkylaryl group in which an aryl group of -20 is substituted with at least one unsubstituted alkyl group having 1 to 30 carbon atoms or a substituted alkyl group, and the unsubstituted alkyl group or the substituted alkyl group is linear, branched, Or circular The substituent of the substituted alkyl group is halogen, a hydroxyl group, an aldehyde group, a carboxyl group, an amino group, or an amide group, and the unsubstituted alkyl group, aryl group, aralkyl group, and alkylaryl group have a hydrogen atom as a halogen atom. May be substituted, n is 1 to
Represents an integer of 3. X is a hydroxyl group, a carboxylic acid having 1 to 20 carbon atoms, a hydrogen acid other than hydrogen halide, an oxo acid,
It represents an acid residue of an inorganic thioacid or an organic thioacid having 1 to 20 carbon atoms. ) Is converted into the amount of nitrogen derived from the quaternary ammonium compound represented by the following formula (2) with respect to the total weight of the polyooxymethylene copolymer and the quaternary ammonium compound. ,
0.05 to 50 ppm by weight, P × 14 / Q (2) [wherein P represents an amount (ppm) based on the total weight of the oxymethylene copolymer of the quaternary ammonium compound and the quaternary ammonium compound. , 14 is the atomic weight of nitrogen, and Q is the molecular weight of the quaternary ammonium compound. ] Further, the quaternary ammonium compound is used so that the amount of halogen introduced from the quaternary ammonium compound into the polyoxymethylene copolymer is 0.1 ppm by weight or less based on the polyoxymethylene copolymer. A method for stabilizing a polyoxymethylene copolymer, which comprises:

The above as well as additional objects, features, and advantages of the present invention will become apparent in the following detailed written description. First, the polyoxymethylene copolymer used in the stabilizing method of the present invention will be described. The polyoxymethylene copolymer used in the present invention is not particularly limited and may be any polyoxymethylene copolymer obtained by polymerization by a known method. For example, formaldehyde, or a cyclic acetal such as trioxane, which is a cyclic trimer thereof, and a known comonomer copolymerizable therewith, for example, a cyclic ether or a cyclic formal, are obtained by copolymerizing using a polymerization catalyst, Examples thereof include copolymers having two or more connecting carbon atoms in the main chain. Further, a multi-component copolymer obtained by copolymerizing a multi-component monomer containing a mono- or di-glycidyl compound or the like, or a copolymer having a branched or cross-linked structure in the molecule is also used in the method of the present invention. Included in the copolymer. Further, the stabilizing method of the present invention can be applied to a copolymer obtained by introducing a comonomer into a polyoxymethylene homopolymer. The polymerization method is not particularly limited, but examples thereof include bulk polymerization, and the bulk polymerization may be either batch type or continuous type. This bulk polymerization generally uses a monomer in a molten state and obtains a solid bulk polymer as the polymerization proceeds. As one example of preferred comonomers, the following formula (a)

[0010]

[Chemical 1] [In the formula, R ⁵ to R ⁸ each independently represent a hydrogen atom, a C _{1 to} C ₅ alkyl group which is unsubstituted or substituted with 1 to 3 halogen atoms, and each R ⁹ is Independently, an unsubstituted methylene group, 1 to 2 C _{1 to} C ₅ alkyl groups, or 1 to 2 halogen atom substituted methylene groups or oxymethylene groups (wherein p is 0 to 3) or a divalent group represented by the following formula (b) or the following formula (c) (in this case, p in the formula (a) represents 1, and the formulas (b) and (c) Q in) represents an integer of 1 to 4). — (CH ₂ ) q—O—CH ₂ — (b) — (OCH ₂ CH ₂ ) q—O—CH ₂ — (c)].

Examples of such comonomers include ethylene oxide, propylene oxide, 1,3-dioxolane, 1,3,5-trioxepane, diethylene glycol formal, 1,4-butanediol formal and 1,3-dioxane. Among them, preferred comonomers are cyclic formal such as 1,3-dioxolane, 1,3,5-trioxepane, and 1,4-butanediol formal, and particularly preferably 1,3-dioxolane. The amount of these comonomers used is preferably 0.02 to 15 mol% and more preferably 0.1 to 10 mol% based on trioxane. Further, in the polymerization method of the present invention, in order to control the molecular weight of the polyoxymethylene copolymer, an appropriate molecular weight modifier such as methylal may be used if necessary.

As the polymerization catalyst in the above-mentioned polymerization method, cationic active catalysts such as Lewis acid, protic acid and its ester or anhydride are preferable. As a Lewis acid,
Examples thereof include halides of boric acid, tin, titanium, phosphorus, arsenic and antimony, and specifically, boron trifluoride, tin tetrachloride, titanium tetrachloride, phosphorus pentafluoride, phosphorus pentachloride, pentafluoride. Antimony and its complex compounds or salts are mentioned. Further, specific examples of the protonic acid, its ester or anhydride include perchloric acid, trifluoromethanesulfonic acid, perchloric acid-tertiary butyl ester,
Acetyl perchlorate, trimethyloxonium hexafluorophosphate, etc. may be mentioned. Among them, boron trifluoride; boron trifluoride hydrate; and a coordination complex compound of an organic compound containing an oxygen atom or a sulfur atom and boron trifluoride are preferable, and specifically, boron trifluoride diethyl ether. Preferred examples include boron trifluoride di-n-butyl ether. The amount of these polymerization catalysts used is 1 × 10 ⁻⁶ mol to 1 × 10 3 with ^respect to 1 mol of the total amount of trioxane, cyclic ether and / or cyclic formal.
^-3 mol is preferable, and 5x10 ^-6 mol to 1x10 ^-4 mol is more preferable.

The method for stabilizing a polyoxymethylene copolymer of the present invention is a polymerization catalyst such as boron trifluoride or its complex compound remaining in the polyoxymethylene copolymer obtained by the above-mentioned polymerization reaction. May be carried out after deactivating, or may be carried out without deactivating the polymerization catalyst. Further, it is naturally applicable to a polyoxymethylene copolymer which has undergone a known treatment for decomposing and removing an unstable terminal portion, but still has an unstable terminal portion. The deactivation of the polymerization catalyst is carried out by using a polyoxymethylene copolymer obtained by the polymerization reaction, amines such as ammonia, triethylamine and tri-n-butylamine, or a hydroxide of an alkali metal or an alkaline earth metal, an inorganic acid. It is carried out by adding it to an aqueous solution or an organic solvent solution containing at least one catalyst neutralizing deactivator such as a salt or an organic acid salt, and generally stirring in a slurry state for several minutes to several hours. After the catalyst neutralization and deactivation, the slurry is filtered and washed to remove unreacted monomers, catalyst neutralization and deactivator,
After the catalyst neutralized deactivated salt is removed, it is dried.

Further, a method of deactivating the polymerization catalyst by contacting vapor of ammonia, triethylamine or the like with the polyoxymethylene copolymer, or a method of deactivating the polymerization catalyst, at least one of hindered amines, triphenylphosphine, calcium hydroxide and the like A method of deactivating the catalyst by bringing the oxymethylene copolymer into contact with a mixer can also be used. Further, without deactivating the polymerization catalyst, by heating at a temperature not higher than the melting point of the polyoxymethylene copolymer in an inert gas atmosphere, a polyoxymethylene copolymer in which the polymerization catalyst is volatilized and reduced can be obtained. The stabilizing method of the present invention may be carried out by using it. The deactivating operation of the polymerization catalyst and the volatilization reducing operation of the polymerization catalyst may be performed after pulverizing the polyoxymethylene copolymer obtained by the polymerization reaction, if necessary. The polyoxymethylene copolymer thus obtained or the known polyoxymethylene copolymer which has been subjected to a known decomposition and removal treatment of the unstable terminal portion is still present in the present invention. By applying the stabilization method described above, a polyoxymethylene copolymer having very few unstable terminals and excellent heat stability, and improved aging discoloration property and retention colorability can be obtained in a short time and It can be easily obtained.

First, the quaternary ammonium compound used in the stabilizing method of the present invention will be described. The quaternary ammonium compound used in the present invention is not particularly limited as long as it is represented by the general formula (1), but R ¹ , R ² , R ³ and R ⁴ in the general formula (1) are It is preferable that each independently is an alkyl group having 1 to 5 carbon atoms or a hydroxyalkyl group having 2 to 4 carbon atoms.
Further, it is particularly preferable that at least one of R ¹ , R ² , R ³ and R ⁴ is a hydroxyethyl group.

Specifically, tetramethylammonium,
Tetraethylammonium, tetrapropylammonium, tetra-n-butylammonium, cetyltrimethylammonium, tetradecyltrimethylammonium, 1,6-hexamethylenebis (trimethylammonium), decamethylene-bis- (trimethylammonium), trimethyl-3-chloro- 2-hydroxypropyl ammonium, trimethyl (2-hydroxyethyl)
Ammonium, triethyl (2-hydroxyethyl) ammonium, tripropyl (2-hydroxyethyl) ammonium, tri-n-butyl (2-hydroxyethyl) ammonium, trimethylbenzylammonium,
Triethylbenzylammonium, tripropylbenzylammonium, tri-n-butylbenzylammonium, trimethylphenylammonium, triethylphenylammonium, trimethyl-2-oxyethylammonium, monomethyltrihydroxyethylammonium, monoethyltrihydroxyethylammonium, octadecyltri ( Hydroxides such as 2-hydroxyethyl) ammonium and tetrakis (hydroxyethyl) ammonium; hydrohalides other than halogenated such as hydrogen azide; sulfuric acid, nitric acid, phosphoric acid, carbonic acid, boric acid, chloric acid, iodine acid Oxo acid salts such as silicic acid, perchloric acid, chlorous acid, hypochlorous acid, chlorosulfuric acid, chlorosulfuric acid, amidosulfuric acid, disulfuric acid and tripolyphosphoric acid; thiosulfuric acid salts such as thiosulfuric acid; formic acid, acetic acid, propionic acid, butanoic acid , Iso Acid, pentanoic acid, caproic acid,
Examples thereof include carboxylic acid salts such as caprylic acid, capric acid, benzoic acid and oxalic acid.

[0017] Among them, the hydroxide (OH ^-), sulfate (HS
_{^{O 4 -, SO 4 2-)}} , carbonate _{^{(HCO 3 -, CO 3 2-}} ),
Boric acid ^{_{(B (OH) 4 -)}} , a salt of a carboxylic acid. Of the carboxylic acids, formic acid, acetic acid, and propionic acid are particularly preferable. These quaternary ammonium compounds may be used alone or in combination of two or more. The amount of the quaternary ammonium compound added is 0.05 to 50 ppm by weight in terms of the amount of nitrogen derived from the quaternary ammonium compound represented by the following formula (2) with respect to the polyoxymethylene copolymer. Is. P × 14 / Q (2) [wherein P represents the concentration (weight ppm) of the quaternary ammonium compound relative to the polyoxymethylene copolymer,
14 is the atomic weight of nitrogen, and Q is the molecular weight of the quaternary ammonium compound. ] The amount of the quaternary ammonium compound added is 0.05 weight pp
If it is less than m, the rate of decomposing and removing the unstable end portion decreases,
Thermal stability deteriorates. On the other hand, when it exceeds 50 ppm by weight, the color tone of the polyoxymethylene copolymer after decomposing and removing the unstable terminal portion is deteriorated.

The quaternary ammonium compound used in the present invention is such that the amount of halogen introduced into the polyooxymethylene copolymer from the quaternary ammonium compound is 0.1 ppm by weight or less based on the polyoxymethylene copolymer. It is necessary to use Here, halogen means fluorine, chlorine, bromine, iodine of Group 7A of the periodic table,
It is a generic term for the five elements of astatine. The smaller the amount of halogen brought into the polyoxymethylene copolymer from the quaternary ammonium compound at the time of stabilization is, the more preferable it is, but the thermal stability and aging discoloration of the polyoxymethylene copolymer are bordered by 0.1 ppm by weight. However, the retention colorability changes greatly. That is, the amount of halogen coexisting during stabilization is 0.
When it exceeds 1 ppm by weight, the thermal stability, aging discoloration property, and retention coloring property of the polyoxymethylene copolymer are rapidly deteriorated.

The quaternary ammonium compound is commercially available in various forms such as a solid one, an aqueous solution containing a predetermined amount of the quaternary ammonium compound, an organic solvent (eg methanol) solution, etc., depending on the intended use. Can be selected in a timely manner. Also in the present invention, there is no problem in using the above-mentioned commercially available quaternary ammonium compound-containing reagents, but in that case, these reagents used are brought into the polyoxymethylene copolymer. In order to reduce the amount of halogen to 0.1 wt ppm or less, which is the object of the present invention, it is necessary to use a reagent that satisfies the following conditions. That is, a reagent containing a quaternary ammonium compound in which the amount of halogen contained as an impurity in the reagent containing the quaternary ammonium compound used is equal to or less than the amount of halogen (wt ppm) represented by the following formula (3) is used. It is necessary to use. 1000 × A / P (3) [wherein P represents the amount (ppm) of the quaternary ammonium compound based on the total weight of the oxymethylene copolymer and the quaternary ammonium compound, and A is the quaternary ammonium compound used. It represents the content (% by weight) of the quaternary ammonium compound in the reagent containing. ]

By using a reagent satisfying these conditions, the amount of halogen brought into the polyoxymethylene copolymer from the quaternary ammonium compound, which is the object of the present invention, is 0.1 wt ppm or less, which is a critical amount. It can be Here, as an example, consider a case where the stabilizing method of the present invention is carried out using an aqueous solution containing 15% by weight of tetramethylammonium hydroxide (molecular weight 91). 20 converted from tetramethylammonium hydroxide to the amount of nitrogen derived from tetramethylammonium hydroxide
Suppose stabilization is carried out using ppm by weight. At this time, P
Is 20 × 91/4 = 130 ppm, and from the formula (3), the halogen content in the tetramethylammonium hydroxide aqueous solution is 1000 × 15/130 = 115.4 weight p.
pm. Therefore, in order to carry out the stabilization of the present invention using an aqueous solution containing 15% by weight of tetramethylammonium hydroxide, the halogen content of the aqueous solution of tetramethylammonium hydroxide is the critical amount calculated above. It is necessary to use the one having a content of 0.4 ppm or less, which makes the amount of halogen introduced into the polyoxymethylene copolymer from the tetramethylammonium hydroxide aqueous solution 0.1%, which is the object of the present invention.
It can be ppm by weight.

Quaternary ammonium compounds are generally prepared by reacting a tertiary amine with an alkyl halide. Therefore, the quaternary ammonium compound generally contains a considerable amount of halogen. As a method of removing these halogens, for example, a method of treating with silver oxide in an aqueous solution to generate quaternary ammonium hydroxide and silver halide, and separating and removing silver halide can be implemented. The required quaternary ammonium salt can be produced by reacting the produced quaternary ammonium hydroxide with carboxylic acid or sulfuric acid. Further, when the halogen removal is insufficient by the silver oxide treatment, the halogen can be removed by electrolysis or the like.

In the present invention, by using these treatments, a quaternary ammonium compound having a halogen content of not more than the amount represented by the above formula (3) is used. 0.1 weight ppm of halogen introduced into the copolymer
You can: The amount of halogen introduced into the polyoxymethylene copolymer from the quaternary ammonium compound at the time of stabilization is 0.1 ppm by weight or less, and it is possible to sufficiently satisfy the intended effect of the present invention.
The content is more preferably 0.03 ppm by weight or less, and for that purpose, the quaternary ammonium compound used must satisfy the following formula (4). 300 × A / P (4) [wherein P represents the amount (ppm) of the quaternary ammonium compound based on the total weight of the oxymethylene copolymer and the quaternary ammonium compound, and A is the quaternary ammonium compound used. It represents the content (% by weight) of the quaternary ammonium compound in the reagent containing. In the present invention, in addition to the quaternary ammonium compound, known amines such as ammonia and triethylamine that are decomposition accelerators for unstable terminal parts are used within a range that does not affect the effects of the present invention. There is no problem.

[0023]

BEST MODE FOR CARRYING OUT THE INVENTION The stabilizing method of the present invention will be described below with reference to specific examples. In the present invention, it is necessary to melt and stabilize the polyoxymethylene copolymer by decomposing and removing unstable terminal portions. The melting is carried out, for example, by a vented single-screw extruder, a vented twin-screw extruder, etc., although the apparatus used is not particularly limited. The temperature is not lower than the melting point of the polyoxymethylene copolymer and not higher than 260 ° C., preferably not lower than 180 ° C. 2
It is 30 ° C or lower. If it exceeds 260 ° C, problems of polymer coloring and polymer main chain decomposition may occur. The quaternary ammonium compound may be added in advance before melting the polyoxymethylene copolymer, or
It may be added to the melted polyoxymethylene copolymer.

The method for adding the quaternary ammonium compound to the polyoxymethylene copolymer before melting is, for example, at least one solvent selected from the group consisting of water and an organic solvent capable of dissolving the quaternary ammonium compound. Specifically, a solution prepared by dissolving a quaternary ammonium compound in water, a lower aliphatic alcohol or the like (eg methanol, ethanol) was added in an amount of 0.1 to 5% by weight based on the polyoxymethylene copolymer. It is possible to mix them later. Mixing is horizontal cylinder type, V type, ribbon type, paddle type,
It may be carried out by using a general solid mixer such as a high-speed flow type, or the solution containing the quaternary ammonium compound is directly added to the chute portion which supplies the polyoxymethylene copolymer to the extruder. Alternatively, the polyoxymethylene copolymer may be directly added to the extruder body from the supply port of the extruder until the polyoxymethylene copolymer is melted. The above-mentioned addition of the quaternary ammonium compound can of course be performed directly without adding the quaternary ammonium compound as a solution.

As another method of previously adding the quaternary ammonium compound to the polyoxymethylene copolymer before melting, for example, the quaternary ammonium compound, water and the organic solvent (for example, a lower solvent such as methanol) are used. Polyoxymethylene copolymer is added to a solution with at least one solvent selected from the group consisting of (aliphatic alcohols) to form a slurry, and the quaternary ammonium compound is melted by filtering and drying the slurry. The method of leaving it in the polyoxymethylene copolymer before is mentioned. In this case, the solvent used for the solution is preferably one that does not dissolve the polyoxymethylene copolymer. By using such a solvent, post-treatments such as filtration and drying can be easily performed. The amount of the quaternary ammonium compound added is controlled to a specific amount by controlling the concentration of the quaternary ammonium compound in the solution and the liquid content of the polyoxymethylene copolymer after filtration.

By the above-mentioned method, the polyoxymethylene copolymer to which a predetermined amount of the quaternary ammonium compound has been added is melted in an extruder or the like as it is or after being dried if necessary, and heat treated. Be used for. At the time of melting, it may be stabilized by adding at least one of water, methanol, etc., which are conventionally known decomposition accelerators for unstable terminal parts, etc., and nothing else is added. Alternatively, it may be subjected to heat treatment. The addition amount of conventionally used decomposition accelerators such as amines, water and methanol is preferably 0.1 to 5 parts by weight with respect to 100 parts by weight of the polyoxymethylene copolymer. Moreover, you may further add a quaternary ammonium compound as needed. These amines, water, methanol, and quaternary ammonium compounds may be used alone or in combination of two or more.

On the other hand, as a method of adding the quaternary ammonium compound to the molten polyoxymethylene copolymer after melting the polyoxymethylene copolymer, water and water capable of dissolving the quaternary ammonium compound are used. Adding a solution of a quaternary ammonium compound dissolved in at least one solvent selected from the group consisting of organic solvents, specifically water, lower aliphatic alcohols (eg methanol, ethanol), or It can be mentioned that the quaternary ammonium compound and at least one solvent selected from the group consisting of water and an organic solvent capable of dissolving the quaternary ammonium compound are separately added. The addition amount of an organic solvent such as water or methanol is preferably 0.1 to 5 parts by weight with respect to 100 parts by weight of the polyoxymethylene copolymer. Further, conventionally known amines may be added in addition to the quaternary ammonium compound.

In the method for stabilizing a polyoxymethylene copolymer according to the present invention, the rate of decomposing and removing the unstable terminal portion is very fast, and the unstable terminal portion hardly remains after a short treatment only once. A polyooxymethylene copolymer having excellent thermal stability and excellent aging discoloration property and retention coloring property can be obtained. As described above, the quaternary ammonium compound was added to the polyoxymethylene copolymer in a molten state, and the unstable terminal portion in the polyoxymethylene copolymer was decomposed. Unreacted monomers remaining in the polyoxymethylene copolymer are removed from the vent under reduced pressure and pelletized to obtain a stable polyoxymethylene copolymer. If necessary, the polyoxymethylene copolymer may be added with stabilizers against decomposition caused by heat, light, oxidation, etc., and other additives such as formaldehyde scavenger, formic acid neutralizer, release agent and reinforcing agent. Then, the final product of the stable polyoxymethylene copolymer is obtained by melt-kneading with an extruder or the like.

In the stabilizing method of the present invention, when a single-screw or twin-screw extruder with a vent is used, the melt stabilization treatment of the present invention is followed by the latter half of the same apparatus, preferably the latter. Stabilizers and reinforcing agents can be added after the vent to produce the product in a single step, or, for example,
It is also possible to add a stabilizer or a reinforcing agent in advance before melting the polyoxymethylene copolymer, and carry out the melt-kneading treatment of the stabilizer or the reinforcing agent at the same time as the stabilizing method of the present invention. In the present invention is not necessarily an essential component,
Adding an antioxidant together with a quaternary ammonium compound and a boric acid compound is a preferable method for suppressing the oxidative decomposition of the polyoxymethylene copolymer during the decomposition and removal treatment of the unstable terminal portion. As the antioxidant, a sterically hindered phenol compound, a sterically hindered amine compound, a phosphorus compound, a sulfur compound and the like can be used, and there is no particular limitation, but the sterically hindered phenol compound is more effective.

Examples of such compounds include sterically hindered phenol compounds such as triethylene glycol-bis [3- (3-t-butyl-5-methyl-4-hydroxyphenyl) propionate] and pentaerythrium. Lytyl-tetrakis [3- (3,5-di-t-butyl-4]
-Hydroxyphenyl) propionate], 2,2'-
Methylene-bis- (4-methyl-6-t-butyl-phenol) and the like are sterically hindered amine compounds as 4-
Acetoxy-2,2,6,6-tetramethylpiperidine, 4-stearoyloxy-2,2,4,6-tramethylpiperidine and the like are tetrakis (2,4-di-t-butyl) as phosphorus compounds. Phenyl) -4,4-bisphenylene phosphonite, distearyl pentaerythritol diphosphite and the like, and sulfur compounds include dilauryl thiodipropionate and the like. When an antioxidant is used in combination, the amount added is polyoxymethylene copolymer 1
It is preferably 0.01 to 3 parts by weight, particularly preferably 0.03 to 1 part by weight, relative to 00 parts by weight. If the amount is less than 0.01 part by weight, the effect of suppressing the oxidative decomposition of the polyoxymethylene copolymer is small, and even if added more than 3 parts by weight, the effect of increasing the amount is not seen and it is economical. Will also be at a disadvantage.

[0031]

The present invention will be described in more detail with reference to the following examples and comparative examples, but the present invention is not limited thereto. The terms and measuring methods used in Examples and Comparative Examples are as follows. <Measurement of Halogen Content (ppm)> The halogen content was measured using an ion chromatograph (Yokogawa, IC-7000S type, column: ICS-A23). <Formaldehyde gas generation rate (ppm / min)>
Under a nitrogen stream, formaldehyde gas generated from the polyoxymethylene copolymer is absorbed in water at 230 ° C. for 90 minutes and then titrated and measured. The measured total formaldehyde amount was divided by 90 minutes to calculate the average formaldehyde gas generation rate per minute (ppm / min). The smaller the formaldehyde gas generation rate, the better the thermal stability. <Thermal stability (min)> A polyoxymethylene copolymer is retained in an injection molding machine (Arborg Allrounder 100, manufactured by Western Trading Co., Ltd.) having a cylinder temperature of 250 ° C. to prepare molded pieces of 12 × 120 × 3 mm. Then
Time (minutes) that a thrust leak occurs on the surface of the molded piece
I asked. The longer the time, the better the thermal stability of the polyoxymethylene copolymer. <Aging discoloration> A test piece molded under the following molding conditions was placed in a gear oven under an environment of 140 ° C.
BL value of the test piece after aging for 0 hr (JIS Z-87
30) is a handy color tester (manufactured by Suga Test Instruments Co.,
HC-T type). The smaller the bL value, the better the aging discoloration.

(Molding conditions) Molding machine: Toshiba Corp. IS-80A Cylinder temperature: 200 ° C. Injection pressure: 60 kgf / cm 2 Injection time: 15 seconds Cooling time: 25 seconds Mold temperature: 70 ° C. <Residual colorability> Color difference meter (Handy Color CR-200 manufactured by Minolta Co., Ltd.)
It was measured at. The smaller the b value, the better the retention coloring property.

(Molding condition) Molding machine: Sumitomo Heavy Industries, Ltd. Nestal injection molding machine 75 ton Mold size: Flow direction * Right angle direction * Thickness = 74 * 52 *
3 mm flat plate cylinder temperature: 200 ° C., mold temperature: 70 ° C., molding machine residence time: 3 hours <%, ppm> Unless otherwise specified, all are on a weight basis.

[0034]

[Examples 1 to 10 and Comparative Examples 1 to 3] A twin-screw paddle type continuous polymerization machine with a jacket through which a heat medium can pass is set to 80 ° C.
Adjusted to 12 kg / Hr of trioxane, 1,3-dioxolane 444 g / Hr as a comonomer (0.045 mol to 1 mol of trioxane), and methylal 7.1 g / Hr (to 1 mol of trioxane as a molecular weight regulator). 0.7 × 10 −3 mol) was continuously added. Further, as a polymerization catalyst, boron trifluoride di-n-
39.6 g / Hr of a cyclohexane solution containing 1% by weight of boron trifluoride di-n-butyl etherate was continuously added so that the amount of butyl etherate was 1.5 × 10 −5 mol per mol of trioxane. Polymerization was carried out by adding. The polyoxymethylene copolymer discharged from the mixer was put into a 0.1% triethylamine aqueous solution to deactivate the polymerization catalyst. The deactivated polyoxymethylene copolymer was filtered with a centrifuge, and then 1 part by weight of an aqueous solution containing a quaternary ammonium compound was added to 100 parts by weight of the filtered polyoxymethylene copolymer. And uniformly mixed and dried at 120 ° C. The addition amount of the quaternary ammonium compound was converted into the amount of nitrogen, and all were set to 20 ppm. The amount of the quaternary ammonium compound added was adjusted by adjusting the concentration of the quaternary ammonium compound in the aqueous solution containing the quaternary ammonium compound to be added.

With respect to 100 parts by weight of the dried polyoxymethylene copolymer, 2,2'-as an antioxidant was added.
Methylenebis- (4-methyl-t-butylphenol)
Was added to a twin screw type extruder with a vent. In Examples 1 to 9 and Comparative Examples 1 to 3, 0.5 parts by weight of water was used with respect to 100 parts by weight of the molten oxymethylene copolymer in the extruder. Add parts by weight and set extruder temperature 2
The unstable terminal part was decomposed at 00 ° C. for a residence time of 5 minutes in the extruder. The decomposed oxymethylene copolymer at the unstable terminal portion was devolatilized under the conditions of a vent vacuum degree of 20 Torr and extruded as a strand from the die portion of the extruder and pelletized. The final polyoxymethylene copolymer pellets were obtained by further mixing 0.15 parts by weight of calcium stearate and 0.05 parts by weight of nylon 66 with the pellets and melt-kneading the mixture with a vented single-screw extruder. It was Type of quaternary ammonium compound used, type and concentration of halogen contained in quaternary ammonium compound, critical amount of halogen contained in quaternary ammonium compound calculated from formula (3), fourth used Table 1 summarizes the amount of halogen brought into the polyoxymethylene copolymer from the quaternary ammonium compound, the formaldehyde gas generation rate of the final polyoxymethylene copolymer pellets obtained, thermal stability, aging discoloration, and retention coloring. Indicate.

[0036]

[Table 1]

Examples 11 to 13 and Comparative Examples 4 to 6 The same operations as in Examples 1 to 10 were performed until the deactivation of the polymerization catalyst. The deactivated polyoxymethylene copolymer was filtered with a centrifuge and then dried at 120 ° C. As an antioxidant with respect to 100 parts by weight of the dried polyoxymethylene copolymer,
0.3 parts by weight of 2'-methylenebis- (4-methyl-t-butylphenol) was added, and the mixture was fed to a vented twin-screw extruder. The quaternary ammonium compound is added as an aqueous solution containing the quaternary ammonium compound at a ratio of 1 part by weight of the aqueous solution to 100 parts by weight of the melted polyoxymethylene copolymer in the extruder, and the temperature is set at the extruder. The unstable terminal part was decomposed at 200 ° C. for a residence time of 5 minutes in the extruder.

The quaternary ammonium compound was added in an amount of 20 ppm in terms of nitrogen. The amount of the quaternary ammonium compound added was adjusted by adjusting the concentration of the quaternary ammonium compound in the aqueous solution containing the quaternary ammonium compound to be added. The oxymethylene copolymer decomposed at the unstable terminal part had a vent vacuum degree of 20To.
It was devolatilized under the condition of rr, extruded as a strand from the die part of the extruder and pelletized. The final polyoxymethylene copolymer pellets were obtained by further mixing 0.15 parts by weight of calcium stearate and 0.05 parts by weight of nylon 66 with the pellets and melt-kneading the mixture with a vented single-screw extruder. It was Type of quaternary ammonium compound used, type and concentration of halogen contained in quaternary ammonium compound, fourth calculated from formula (3)
Amount of critical halogen that can be contained in the quaternary ammonium compound, the amount of halogen introduced into the polyoxymethylene copolymer from the quaternary ammonium compound used, the formaldehyde gas generation rate of the final polyoxymethylene copolymer pellets obtained, the heat Table 2 shows the stability, aging discoloration property, and retention coloring property.

[0038]

[Table 2]

[0039]

Examples 14 to 15 and Comparative Examples 7 to 8 Ethylene oxide 264 g / Hr (0.045 mol per 1 mol of trioxane) as a comonomer, and boron trifluoride di-n-butyl etherate as a polymerization catalyst, Polymerization was carried out by continuously adding 118.8 g / Hr of a cyclohexane solution containing 1% by weight of boron trifluoride di-n-butyl etherate to 4.5 × 10 −5 mol with respect to 1 mol of trioxane. Except for the above, Examples 1 to 10 and Comparative Examples 1 to 3
The exact same operation was performed. Type of quaternary ammonium compound used, type and concentration of halogen contained in quaternary ammonium compound, critical amount of halogen contained in quaternary ammonium compound calculated from formula (3), fourth used Table 3 summarizes the amount of halogen introduced from the primary ammonium compound into the polyoxymethylene copolymer, the formaldehyde gas generation rate of the final polyoxymethylene copolymer pellets obtained, thermal stability, aging discoloration, and retention coloring. Indicate.

[0040]

[Table 3]

[0041]

Comparative Examples 9 to 10 Example 1 was repeated, except that powdery calcium hydroxide was inactivated instead of the quaternary ammonium compound and added to the dried polyoxymethylene copolymer.
-10, the same operation as in Comparative Examples 1 to 3 was performed, the amount of calcium hydroxide used, the type and concentration of halogen contained in calcium hydroxide, and the amount of calcium hydroxide introduced into the polyoxymethylene copolymer. Amount of halogen,
Table 4 shows the formaldehyde gas generation rate, thermal stability, aging discoloration property, and retention coloring property of the final polyoxymethylene copolymer pellets obtained.

[0042]

Comparative Examples 11 to 12 Example 11 was repeated except that triethylamine was used instead of the quaternary ammonium compound.
.About.13, the same operation as in Comparative Examples 4 to 6 was performed, the amount of triethylamine used, the type and concentration of halogen contained in triethylamine, the amount of halogen brought into the polyoxymethylene copolymer from triethylamine,
Table 4 shows the formaldehyde gas generation rate, thermal stability, aging discoloration property, and retention coloring property of the final polyoxymethylene copolymer pellets obtained.

[0043]

[Table 4]

[0044]

As is clear from the examples and comparative examples, according to the stabilization method of the present invention, as compared with the conventional method, the unstable terminal portion is very few in a very short time. It is possible to economically produce a polyoxymethylene copolymer that is excellent in heat stability and is also excellent in aging discoloration property and retention coloring property.

Claims (12)

[Claims] 1. A polyoxymethylene copolymer having a thermally unstable terminal portion is prepared by reacting a polyoxymethylene copolymer in the presence of at least one quaternary ammonium compound represented by the following general formula (1). In a method for stabilizing a polyoxymethylene copolymer having a thermally unstable terminal portion by heat-treating the polyoxymethylene copolymer in a molten state at a temperature of the melting point or higher and 260 ° C. or lower, [R ¹ R ² R ³ R ⁴ N ⁺ ] _n X ^-n (1) (In the formula, R ¹ , R ² , R ³ , and R ⁴ are each independently an unsubstituted alkyl group having 1 to 30 carbon atoms. Or a substituted alkyl group; an aryl group having 6 to 20 carbon atoms; an aralkyl group in which an unsubstituted alkyl group having 1 to 30 carbon atoms or a substituted alkyl group is substituted with at least one aryl group having 6 to 20 carbon atoms; or Ants with 6 to 20 carbon atoms Represents an alkylaryl group in which at least one unsubstituted alkyl group having 1 to 30 carbon atoms or a substituted alkyl group is substituted, and the unsubstituted alkyl group or the substituted alkyl group is linear, branched, or cyclic. The substituent of the substituted alkyl group is halogen, a hydroxyl group, an aldehyde group, a carboxyl group, an amino group, or an amide group, and the unsubstituted alkyl group, aryl group, aralkyl group, and alkylaryl group have a hydrogen atom. It may be substituted with halogen, n is 1 to
Represents an integer of 3. X is a hydroxyl group, a carboxylic acid having 1 to 20 carbon atoms, a hydrogen acid other than hydrogen halide, an oxo acid,
It represents an acid residue of an inorganic thioacid or an organic thioacid having 1 to 20 carbon atoms. ) Is converted into the amount of nitrogen derived from the quaternary ammonium compound represented by the following formula (2) with respect to the total weight of the polyooxymethylene copolymer and the quaternary ammonium compound. 0.05 to 50 ppm by weight, P × 14 / Q (2) [wherein P is an amount (ppm) relative to the total weight of the oxymethylene copolymer of the quaternary ammonium compound and the quaternary ammonium compound] Where 14 is the atomic weight of nitrogen and Q is the molecular weight of the quaternary ammonium compound. ] Further, the quaternary ammonium compound is used so that the amount of halogen introduced from the quaternary ammonium compound into the polyoxymethylene copolymer is 0.1 ppm by weight or less based on the polyoxymethylene copolymer. A method for stabilizing a polyoxymethylene copolymer, which comprises: 2. The quaternary ammonium compound is used in the form of a solution dissolved in at least one solvent selected from the group consisting of water and an organic solvent capable of dissolving the quaternary ammonium compound. The method for stabilizing a polyoxymethylene copolymer according to claim 1. 3. The heat treatment temperature is 180 ° C. or higher and 230 ° C.
It is the following, The stabilization method of the polyoxymethylene copolymer in any one of Claims 1-2. 4. A polyoxymethylene copolymer is copolymerized with trioxane as a main monomer and at least one selected from the group consisting of cyclic ethers and cyclic formal as a comonomer using at least one cationically active catalyst. The method for stabilizing a polyoxymethylene copolymer according to any one of claims 1 to 3, which is obtained by the above method. 5. The method for stabilizing a polyoxymethylene copolymer according to claim 4, wherein the cyclic formal is 1,3-dioxolane. 6. The polyoxymethylene according to any one of claims 1 to 5, wherein X in the general formula (1) is a hydroxyl group or an acid residue of carbonic acid, boric acid, sulfuric acid or carboxylic acid. A method for stabilizing a copolymer. 7. The method for stabilizing a polyoxymethylene copolymer according to claim 6, wherein the carboxylic acid is at least one selected from the group consisting of formic acid, acetic acid and propionic acid. 8. R ¹ , R ² in the general formula (1),
R ^3, and R ⁴ are each independently poly according to claim 1, characterized in that it is a hydroxyalkyl group having 2 to 4 alkyl or C1-5 atoms Method for stabilizing oxymethylene copolymer. 9. R ¹ , R ² in the general formula (1),
9. The method for stabilizing a polyoxymethylene copolymer according to claim 8, wherein at least one of R ³ and R ⁴ is a hydroxyethyl group. 10. In addition to a quaternary ammonium compound,
Stabilization of the polyoxymethylene copolymer according to any one of claims 1 to 9, characterized in that 0.01 to 3 parts by weight of an antioxidant is added to 100 parts by weight of the polyoxymethylene copolymer. Method. 11. The method for stabilizing a polyoxymethylene copolymer according to claim 10, wherein the antioxidant is a sterically hindered phenol compound. 12. The amount of halogen introduced into the polyoxymethylene copolymer from the quaternary ammonium compound is 0.1% by weight based on the polyoxymethylene copolymer.
The method for stabilizing a polyoxymethylene copolymer according to claim 1, wherein the quaternary ammonium compound is used so as to have a pm or less.