JP2001011144A - Polyoxymethylene copolymer and its production - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain the subject copolymer with high thermal stability, extremely slight in formaldehyde gas emission when subjected to molding operation by copolymerization between a monomer having a specific oxymethylene unit and another monomer having a specific copolymerization component unit in specified proportions. SOLUTION: This copolymer is such one as to be composed of the total of 100 mol% of (A) 99.9-80 mol% of oxymethylene unit of formula I and (B) 0.1-20 mol% of a copolymerization component unit of formula II [Rij ((i) is 1-6; (j) is 1 or 2) is H, a 1-8C alkyl, or the like; (a) to (f) are each 0 or 1, at least two of them being each 1; (m) is 1-3, and when (m) is >=2, from the 2nd member among (a) to (f), at least one of them being 1], has 5,000-400,000 weight- average molecular weight and <=1,000 ppm content of a polyoxymethylene copolymer with a molecular weight of <=3,000 having terminal group of formula III.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a polyoxymethylene copolymer having excellent thermal stability and a method for producing the polyoxymethylene copolymer. More specifically, the present invention relates to a polyoxymethylene copolymer in which the content of a thermally unstable low molecular weight polyoxymethylene copolymer having a hemiformal terminal group is 1,000 ppm or less, and an economical production method thereof. Such a polyoxymethylene copolymer generates a very small amount of formaldehyde gas during molding.

[0002]

2. Description of the Related Art Polyoxymethylene copolymers (hereinafter abbreviated as copolymers) are excellent in mechanical properties, heat resistance, chemical resistance, electrical properties, slidability, etc., and are also excellent in moldability. Therefore, they are used as engineering plastics in a wide range of applications such as mechanical parts, automobile parts, and electric / electronic device parts. However, with the expansion and diversification of applications, the demand for the quality has been increasing. One of the important characteristics among the required characteristics is that the polyoxymethylene copolymer is decomposed by heat or oxygen in the cylinder of the molding machine at the time of molding, and formaldehyde gas is generated. If a large amount of formaldehyde gas is generated, not only does the environment deteriorate, but also a fine powder or tar-like substance (also referred to as a mold deposit or MD) adheres to the mold surface over a long period of time to form a molded product. This causes the appearance to deteriorate. As a means for suppressing the decomposition of such a copolymer and improving its thermal stability, a method of stabilizing the molecular terminal or preventing the decomposition by adding an antioxidant or a heat stabilizer has been attempted. I have. Regarding the method of preventing the decomposition of polyoxymethylene by the additive, a sterically hindered phenol compound or a sterically hindered amine compound as an antioxidant, and polyamides, urea derivatives, amidine compounds, alkali or A method of adding a hydroxide of an alkaline earth metal has been proposed, but if the base polymer itself has poor thermal decomposability, satisfactory results are not necessarily obtained, and addition of a large amount is disadvantageous in terms of cost. Become. WO96 / 1
No. 3548 discloses that the polyacetal oligomer content is 50 to 5,000 ppm and the fluorine content is 3 to 13 ppm.
Polyacetal resin composition has been proposed,
This publication aims at improving the melt fluidity and does not describe the amount of oligomer having an unstable terminal.

[0003]

SUMMARY OF THE INVENTION An object of the present invention is to provide a polyoxymethylene copolymer in which the generation of formaldehyde gas during molding is suppressed and a method for efficiently producing the same.

[0004]

Means for Solving the Problems The present inventors have conducted intensive studies to obtain a polyoxymethylene copolymer which generates less formaldehyde gas during molding, and as a result, have found that the low molecular weight polyolefin contained in the polyoxymethylene copolymer is low. By reducing the amount of the oxymethylene copolymer having a hemiformal terminal group to a specific ratio or less, it has been found that a polyoxymethylene copolymer having extremely excellent thermal stability can be obtained. It was completed.

That is, a first aspect of the present invention is that the following formula (A)
99.9 to 80 mol% of oxymethylene units represented by
And a copolymer component unit 0.1 to 20 m represented by the formula (B)
ol% (the total of both is 100 mol%), and is a polyoxymethylene copolymer having a weight-average molecular weight of 5,000 to 400,000 and a molecular weight of 3,000 or less. Among the oxymethylene copolymers, a low molecular weight polyoxymethylene copolymer having a hemiformal terminal group represented by the following formula (C) has a content of 1,000 p with respect to the polyoxymethylene copolymer.
pm or less.

[0006]

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A second aspect of the present invention provides the polyoxymethylene copolymer according to the first aspect, wherein the copolymer component unit is oxyethylene, oxybutylene, oxydiethylene, or a combination thereof. A third aspect of the present invention is that the monomer (A ′) having the oxymethylene unit represented by the formula (A) shown in the first aspect of the present invention is 99.9 to 80 mol% in terms of oxymethylene unit, and the formula (A) A monomer (B ′) having a copolymer component unit represented by B) is copolymerized with 0.1 to 20 mol% in terms of a copolymer component unit to obtain a polyoxy resin having a weight average molecular weight of 5,000 to 400,000. When producing a methylene copolymer, a low molecular weight polyoxymethylene copolymer having a hemiformal terminal group represented by the following formula (C) among low molecular weight polyoxymethylene copolymers having a molecular weight of 3,000 or less. The copolymerization step, the catalyst deactivation step after the copolymerization step, the drying step after the catalyst deactivation step, and the drying step, so that the union becomes a content of 1,000 ppm or less with respect to the polyoxymethylene copolymer. Instability after process End processing step, provides a process for the production of an unstable terminal treatment process after the stabilizer compounding step, or polyoxymethylene copolymer which is characterized in that a combination of these steps. According to a fourth aspect of the present invention, there is provided a polyoxymethylene copolymer according to the third aspect, wherein the reaction product from the copolymerization step is brought into contact with an aqueous solution of a basic compound to perform a catalyst deactivation step. Provided is a method for producing a united product. A fifth aspect of the present invention is
A method for producing a polyoxymethylene copolymer according to the third aspect of the present invention, wherein the drying step is performed at 80 ° C. or higher. A sixth aspect of the present invention provides the method for producing a polyoxymethylene copolymer according to the third aspect of the present invention, wherein the unstable terminal treatment is thermal decomposition or hydrolysis.
A seventh aspect of the present invention is characterized in that the stabilizer is a hindered phenol compound, a sterically hindered amine compound, a polyamide, a urea derivative, an amidine compound, an alkali or alkaline earth metal hydroxide, or a mixture thereof. And a method for producing the polyoxymethylene copolymer according to the third aspect of the present invention. An eighth aspect of the present invention is that the copolymerization component is ethylene oxide, 1,3-dioxolan, 1,4
The third to seventh aspects of the present invention which are butanediol formal, diethylene glycol formal, or a mixture thereof;
And a method for producing the polyoxymethylene copolymer according to any one of the above.

[0008]

BEST MODE FOR CARRYING OUT THE INVENTION In the present invention, a polyoxymethylene copolymer comprises 99.9 to 80 mol% of an oxymethylene unit represented by the formula (A) and a copolymer component represented by the formula (B). Unit: 0.1 to 20 mol% (the total of both is 1
00 mol%. ) And having a weight average molecular weight of 5,000 to 400,000. The polyoxymethylene copolymer includes a low-molecular-weight polyoxymethylene copolymer having a molecular weight of 3,000 or less. And, in the low molecular weight polyoxymethylene copolymer, the low molecular weight polyoxymethylene copolymer having a hemiformal terminal group is included in the polyoxymethylene copolymer.
It is contained at a content of 1,000 ppm or less. The copolymer may be any of a copolymer and a terpolymer containing a small amount of an oxymethylene group unit and a copolymer component unit.Also, the molecule may have not only a linear but also a branched, crosslinked, or cyclic structure. Good. As the polyoxymethylene copolymer in the present invention, it is needless to say that those having a chemically active terminal stabilized are preferably used.

First, the polyoxymethylene copolymer will be described. The polyoxymethylene copolymer can be produced as follows. For example, a cyclic acetal such as trioxane or formaldehyde as a main monomer, a cyclic acetal or a cyclic ether giving a copolymer component unit represented by the formula (B) as a comonomer, and a chain for adjusting the degree of polymerization according to the purpose. It is obtained by adding a transfer agent and copolymerizing using a cationically active catalyst. The cyclic acetal or cyclic ether (also referred to as a comonomer) is a cyclic compound having at least one pair of a linking carbon atom and an oxygen atom as shown in the formula (B). To further explain equation (B),
R _ij in the formula (i = 1 to 6, j = 1 to 2 each an integer)
Is hydrogen, an alkyl group or an alkoxy group having 1 to 8 carbon atoms, or a phenyl-substituted alkyl group having 7 to 20 carbon atoms, which may be the same or different. a,
b, c, d, e and f are 0 or 1, and at least two of them are 1. m is an integer of 1 to 3, and when m is 2 or more, the groups a, b, c, d, e, and f may be different from each other for each group. At least one of them is one. Taking 1,3-dioxolan as an example, m is 2 and the first group is a =
b = 1, c = d = e = f = 0 and R _ij are all H, and the second group is a = 1, b = c = d = e = f = 0
And R _ij are all H. Such cyclic acetals include 1,3-dioxolan, 1,3-dioxane,
1,4-butanediol formal, diethylene glycol formal and the like can be mentioned. Examples of the cyclic ether include ethylene oxide, propylene oxide, and styrene oxide. Among these, preferred comonomers are 1,3-dioxolan, 1,3-dioxane,
Cyclic formals such as 4-butanediol formal and diethylene glycol formal; and cyclic ethers such as ethylene oxide. At least one of these comonomers may be used, or two or more of them may be used in combination depending on the purpose. The composition of the copolymer is such that the monomer (A ′) having an oxymethylene unit represented by the formula (A) is 99.9 to 80 mol% in terms of the oxymethylene unit, and the copolymer component represented by the formula (B) The monomer (B ′) having a unit is 0.1 to 20 mol% in terms of a copolymerization component unit. Therefore,
When the main monomer is, for example, trioxane, the amount of the comonomer used is 0.3 to 60 mol%, preferably 0.6 to 45 mol%, and more preferably 1.
5 to 30 mol%. The larger the amount of the comonomer, the more advantageous the thermal stability of the produced copolymer. However, if the amount is more than the above range, the produced copolymer becomes soft and the melting point is lowered, which is not preferable.

In producing the polyoxymethylene copolymer, a general cationic polymerization catalyst is used. Such cationic polymerization catalysts include Lewis acids,
Specifically, halides such as boron, tin, titanium, phosphorus, arsenic, and antimony, such as boron trifluoride, tin tetrachloride, titanium tetrachloride, phosphorus pentachloride, phosphorus pentafluoride, arsenic pentafluoride, and pentafluoride Antimony bromide and its complex compounds or salts; and cationic polymerization initiators include protic acids such as trifluoromethanesulfonic acid, perchloric acid, and esters thereof, particularly esters of perchloric acid with lower aliphatic alcohols ( For example, t-butyl perchlorate), anhydrides, particularly mixed anhydrides of perchloric acid and lower aliphatic carboxylic acids (eg, acetyl perchlorate) and the like;
Examples include isopolyacid, heteropolyacid (for example, phosphomolybdic acid), triethyloxonium hexafluorophosphate, triphenylmethylhexafluoroarsenate, and acetylhexafluoroborate.
These can be used in combination of two or more.
Among them, boron trifluoride or a coordination compound of boron trifluoride and an organic compound (for example, ethers) is most commonly used. The amount of the catalyst used is 7 × 10 ^{−5 to} 1.5 × 10 ⁻³ mol / kg, preferably 7 × 10 ^{−5 to} 7 × 10 ⁻⁴ mol / kg, more preferably, based on the total amount of the raw material monomers. Is 1.5 × 10 ^{−4 to} 4.5 × 10 ⁻⁴ mol /
kg. If the amount of the catalyst used is too large, the excess heat generated during the polymerization will lower the molecular weight of the copolymer, and it will be difficult to deactivate the catalyst following the polymerization step. If the amount of the catalyst is too small, the progress of the polymerization reaction becomes difficult, and the conversion of the monomer becomes insufficient. Further, polymerization initiators such as heteropolyacids and isopolyacids have high activity and can be used in a small amount, so that they can be easily deactivated. The amount of these used is 2 × 10
⁻⁷ to 4 × 10 ⁻⁶ mol / kg, preferably 4 × 10 ⁻⁷ to
It is 2.4 × 10 ⁻⁶ mol / kg. Furthermore, polymerization initiators such as trifluoromethanesulfonic acid and perchloric acid, which are protonic acids, are also highly active polymerization initiators, and the amount of these used is 3 × 10 ^{-7 to} 7
× 10 ⁻⁵ mol / kg, preferably 7 × 10 ⁻⁷ to
It is 4 × 10 ⁻⁵ mol / kg. However, when a Lewis acid catalyst such as boron trifluoride is used, water acts as a co-catalyst.
A cyclic acetal containing about 300 ppm to about 300 ppm is brought into contact with a catalyst (which is also an initiator), continuously mixed for 0.5 to 300 seconds in the absence of trioxane, which is a main monomer, and the mixture is added to trioxane; It is also possible to carry out cationic polymerization via improving the dispersibility of the catalyst and the initiator and generating active species.

Since raw materials such as monomers and comonomers have high water absorption, they usually contain trace amounts of water as impurities. Water acts as a chain transfer agent during polymerization and causes the formation of hemiformal end groups. Therefore, in order to obtain a high-quality crude polyoxymethylene copolymer (referred to as a product obtained in the polymerization step), the smaller the amount of water in the mixture of the monomer, the comonomer and the molecular weight regulator, the better,
m, preferably 10 ppm or less. However, when a Lewis acid catalyst such as boron trifluoride is used, it is also preferable that 1 ppm or more of water remains in the mixture. Also, in the actual production process, formic acid by-produced in the monomer production step, the recovery step, etc. may be mixed into the monomer in a trace amount, but this also acts as a chain transfer agent,
Hemiformal group formation factor. Therefore, it is preferable that this amount is also small, and 50 ppm or less in the raw material mixture,
It is more preferably at most 30 ppm.

In the copolymerization step, if necessary, an appropriate amount of a chain transfer agent, for example, an oxymethylene compound such as methylal, butyral, or dioxymethylene dimethyl ether, is added to adjust the molecular weight of the crude polyoxymethylene copolymer. Can also be polymerized. In order to have mechanical properties, the polyoxymethylene copolymer has a weight average molecular weight of 5,000 to 400,000, preferably 10,000 to 200,000.

The copolymerization reaction can be carried out in the presence of an antioxidant such as a hindered phenol compound. As a result, the oxidative decomposition of the resulting polyoxymethylene copolymer in the copolymerization step or the oxidative decomposition of the polyoxymethylene copolymer at a high temperature in the subsequent catalyst deactivation step was suppressed, and high quality was maintained. The polyoxymethylene copolymer can be subjected to an unstable terminal treatment step to be treated effectively.

The production of the crude polyoxymethylene copolymer is as follows:
Conventionally known equipment and methods can be used. That is, any of a batch system, a semi-batch system, and a continuous system is possible, and any of solid phase bulk polymerization, solution polymerization, and melt bulk polymerization may be used. Preferably, a continuous bulk method using a liquid monomer to obtain a polymer in the form of a solid powder with the progress of polymerization is industrially common, and an inert liquid medium may be used if necessary. As a polymerization apparatus, a co-kneader, a twin-screw continuous extrusion mixer, a twin-screw paddle type continuous mixer, or the like can be used.

In general, in the crude polyoxymethylene copolymer after the completion of the copolymerization step (abbreviated as a crude copolymer), a polymerization catalyst is present in an active state, so that the copolymer can be easily depolymerized. Or an increase in the unstable terminal portion. Therefore, after completion of the copolymerization step, the crude copolymer is converted into an organic or inorganic basic compound such as an alkylamine, an alkoxyamine, a hindered amine, a hydroxide of an alkali metal or an alkaline earth metal or the like in a catalyst. Deactivation processing by sum or the like is performed. At this time, since the crude copolymer is an insoluble porous material, deactivation of the catalyst proceeds in a non-uniform state. Therefore, from the viewpoint of increasing the efficiency of the catalyst treatment, it is preferable that the coarse copolymer is finely pulverized and deactivated, and it is particularly preferable that the component having a particle size exceeding 1.0 mm is 50% by weight or less. Further, in performing the pulverizing treatment, the pulverizer to be used is not particularly limited, but it is more preferable to almost eliminate the abrasion and blockage of the surface pores by selecting a pulverizing apparatus and adjusting the operation conditions thereof, for example, a screen mesh is provided. It is also a good method to use a pin mill or the like.

The polyoxymethylene copolymer after the catalyst deactivation treatment is supplied to an unstable terminal treatment step, if necessary, after washing, drying, etc., to decompose and remove hemiformal terminals and the like. For example, by heating in the presence of a basic compound as described above and optionally water, alcohol or the like, decomposition and removal of the unstable terminal portion are performed. Usually, the melt is homogenized at the melting point of the polymer to 250 ° C., preferably 190 to 230 ° C. using a single-screw or twin-screw melt-kneading extruder equipped with a degassing facility, and the unstable terminal is treated.

Various stabilizers such as an antioxidant and a formic acid scavenger are then added to the polyoxymethylene copolymer whose unstable terminal portion has been treated in order to impart heat resistance, long-term stability and the like. It is blended, and if necessary, various additives, reinforcing agents and the like are blended for imparting properties according to the purpose, and the mixture is melt-kneaded to obtain a stabilized polyoxymethylene copolymer which can be put to practical use. Examples of the stabilizer to be blended include a hindered phenol compound, a nitrogen-containing compound, an alkali metal or alkaline earth metal hydroxide, an inorganic salt, a carboxylate and the like, or a mixture thereof. Further, as long as the present invention is not impaired, if necessary, general additives for thermoplastic resins, for example, coloring agents such as dyes and pigments, lubricants, nucleating agents, release agents, antistatic agents, and slidability improvements Agents, weathering (light) stabilizers, other surfactants, or one or more of organic polymer materials, inorganic or organic fibrous, powdery, or plate-like fillers. it can. Fillers include glass fiber, aramid fiber, potassium titanate fiber, glass beads, crosslinked polystyrene beads, crosslinked melamine resin, talc, mica, white mica,
Wollastonite and the like. However, the amount of the low molecular weight copolymer having a hemiformal terminal contained in the polyoxymethylene resin composition obtained by blending these additives with the polyoxymethylene copolymer must be kept at 1,000 ppm or less.

Next, the low molecular weight polyoxymethylene copolymer will be described. The polyoxymethylene copolymer obtained as described above contains a low molecular weight polyoxymethylene copolymer (hereinafter, also referred to as a low molecular weight copolymer). In the present invention, the low molecular weight polyoxymethylene copolymer can be obtained by dissolving the polyoxymethylene copolymer in hexafluoroisopropanol (HFIP), adding a small amount of distilled water dropwise thereto, separating the solvent, and filtering. Almost concentrated in the melting part. For more details, see the item 3) of the embodiment. The molecular weight of the low molecular weight copolymer is measured by matrix-assisted laser desorption / ionization-mass spectrometry (MALDI-TOF-MS) by reacting the soluble portion with a trimethylsilylating agent to trimethylsilylate unstable terminals. The molecular weight was 3,000 or less.

Such a low-molecular weight copolymer is inevitably produced during the production of a polyoxymethylene copolymer, but has a low molecular weight, so that it has higher mobility than a high-molecular-weight component. The thermal stability of the low molecular weight polyoxymethylene copolymer greatly affects the thermal stability of the entire polyoxymethylene resin. The low molecular weight copolymer has a thermally and chemically unstable hemiformal terminal (C) in the molecule; a compound having only a thermally and chemically stable alkoxy (eg, methoxy) terminal; It can be broadly divided into those having a thermally and chemically stable cyclic structure without having. The terminal of the polyoxymethylene copolymer of the present invention is substantially a hemi-formal group (C) as described below.
Hydroxyalkoxy group (D), alkoxy group (E),
And a formate group (F),
It is believed that low molecular weight copolymers having terminal groups also include the same.

[0020]

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[0021] Among these low molecular weight copolymers, the presence of a low molecular weight copolymer having a hemiformal terminal (C) which is thermally and chemically unstable has an excessive adverse effect on the thermal stability of the polyoxymethylene resin. If the content of the low-molecular-weight copolymer is large, the low-molecular-weight copolymer is easily decomposed at the time of molding the polyoxymethylene resin, and a large amount of formaldehyde gas is generated. It was found that it was important to suppress the generation of formaldehyde gas, and various investigations were made on how, at what stage, and how much the production process was reduced.
As described above, in WO 96/13548, attention is paid only to the content of a stable low molecular weight polyoxymethylene copolymer, and nothing is said about the amount of an unstable low molecular weight polyoxymethylene copolymer. Absent. The present inventors have found that the amount of stable low molecular weight copolymer is not important with respect to the thermal stability of polyoxymethylene copolymer, and the amount of unstable low molecular weight copolymer having a hemiformal terminal is I found an important relationship.

It is important that the amount of the low molecular weight copolymer having a hemiformal terminal group contained in the polyoxymethylene copolymer is 1,000 ppm or less, preferably 200 ppm or less, particularly preferably 50 pp.
m or less. When the content of the low molecular weight copolymer is 1,000,
If the content exceeds 0 ppm, not only is the amount of formaldehyde gas generated by decomposition from the low molecular weight copolymer large, but also the generated formaldehyde gas is further oxidized to generate formic acid, which is probably caused by polyoxymethylene. As the thermal stability of the copolymer worsens and the amount of hemiformal terminal low molecular weight copolymer increases,
Thermal stability deteriorates remarkably.

The content of the low molecular weight copolymer having a hemiformal terminal group is determined by dissolving the polyoxymethylene resin in hexafluoroisopropyl alcohol, adding distilled water dropwise, and separating the solvent as described above. The low molecular weight copolymer contained therein was heated to a predetermined temperature and quantified by measuring the amount of formaldehyde generated. According to this analysis method, the hemiformal-terminated low-molecular-weight copolymer dissolved in the soluble part is decomposed into a monomer during the analytical treatment, and can be detected as the amount of formaldehyde. No formaldehyde is detected by this method from a low molecular weight polyoxymethylene copolymer having the following formula:

In the present invention, the polyoxymethylene copolymer may be prepared by any method as long as the content of the low molecular weight copolymer having a hemiformal terminal is not more than a predetermined value. It is important to pay attention to the reduction of water, formic acid), the efficiency of deactivation of the catalyst after polymerization, and the efficiency of drying the crude polymer. For example, one of the preferable methods is to increase the drying time by setting the deactivation time or the drying temperature of the crude polyoxymethylene copolymer to a predetermined temperature or higher.

[0025]

EXAMPLES The present invention will now be described specifically with reference to examples, but the present invention is not limited to these examples. The terms and measurement methods in the examples and comparative examples are as follows. 1) All percentages or ppm are expressed by weight. 2) Amount of formaldehyde gas generated: A sample of polyoxymethylene copolymer or polyoxymethylene copolymer
rganox1010 ^™ (Ciba-Geigy) 0.3%
About 5 g of a sample (pellet or the like) of the polyoxymethylene resin composition to which melamine and 0.2% of melamine are added is accurately weighed (X g), and placed in a metal container equipped with a heater.
C. Hold for 5 minutes. Thereafter, a gas generated through nitrogen is blown into water in the container for 5 minutes, the amount of formaldehyde collected in the water is quantified (Y μg), and the amount of formaldehyde gas generated per gram of sample (Zppm)
(See JIS K0102, 2L formaldehyde analysis). Y μg / Xg = Zppm 3) Content of low molecular weight copolymer having a hemiformal terminal: 0.5 g of a sample of the polyoxymethylene copolymer or the polyoxymethylene resin composition is accurately weighed into 20 ml of HFIP which has been purified by distillation at 25 ° C. And dissolved. Thereafter, the mixture is cooled to 0 ° C., and distilled water 6
ml was added dropwise and stirred for 10 minutes to perform reprecipitation. Next, the soluble part obtained by filtering off the precipitate was heat-decomposed according to the method 2), the amount of formaldehyde generated (yμg) was determined, and the amount of the low-molecular-weight copolymer having a hemiformal terminal was determined as a sample. It was calculated as the amount of formaldehyde (zppm) contained per gram. In the above method, the low molecular weight copolymer having a hemiformal terminal dissolved in the soluble part is all one-component during the analysis treatment.
It can be decomposed into monomers, detected as formaldehyde and quantified. However, in the above method, formaldehyde is not generated from other stable low molecular weight copolymers. Therefore, this method is a method for selectively quantifying a low molecular weight copolymer having a hemiformal terminal.

[Examples 1 to 5, (Example 6), Comparative Example 1]
-3] Two rotating shafts having a cross section in which two circles are partially overlapped and having a jacketed barrel through which a heat medium passes on the outside and a number of paddles for agitation and propulsion inside the barrel are arranged in the longitudinal direction. Using the provided continuous mixing reactor, warm water of 80 ° C. was passed through the jacket, and the two rotating shafts were rotated at a constant speed, and 3.3 wt% of 1,3-wt. A dioxane-containing trioxane is continuously supplied, and simultaneously, a solution in which boron trifluoride butyl etherate is dissolved in cyclohexane at a concentration of 0.7% to the same raw material supply port is mixed with all monomers (trioxane + 1,3-dioxolane). At a concentration of 5.9 × 10 ⁻⁴ mol / kg (as BF ₃ ). Next, the reaction product discharged from the polymerization machine discharge port is pulverized (the particle size of the obtained pulverized product is 95% or more and 2 mm or less), and triethylamine is added at 1,000 p.
pm-containing aqueous solution is added to the copolymer in an amount of about 5 to 10 times by weight, mixed and pulverized, deactivated at 50 to 120 ° C for 30 to 120 minutes, and then centrifuged and dried (140 ° C,
After 30 minutes to 300 minutes), a polyoxymethylene copolymer in which the amount of the unstable low molecular weight copolymer was changed was obtained. About the obtained polyoxymethylene copolymer, by the method described above,
The amount of formaldehyde generated and the amount of low molecular weight copolymer having a hemiformal terminal were measured. The results are shown in Table 1 together with the treatment conditions with the aqueous triethylamine solution after the copolymerization.

[0027]

[Table 1]

In Example 6, the amount of the low-molecular-weight copolymer having a hemiformal terminal was 1,200 ppm. In Example 12 in which this was used as an extruded raw material and a stabilizer was added, a low-molecular-weight copolymer having a hemiformal terminal was used. Since the molecular weight copolymer amount was 1,000 ppm, it was expressed as (Example 6) for convenience.

Examples 7 to 12, Comparative Examples 3 to 4 The polyoxymethylene copolymers used in Examples 1 to 5, (Example 6), and Comparative Examples 1 to 3 were stable as shown in Table 2. Polyoxymethylene resin compositions having various unstable low-molecular-weight polyoxymethylene copolymer contents were obtained by compounding the components and melt-extruding using an extruder equipped with a vent. For the polyoxymethylene resin composition, the amount of formaldehyde generated and the amount of low molecular weight copolymer having a hemiformal terminal were measured in the same manner. The results are summarized in Table 2.

[0030]

[Table 2]

The molecular weight of each molecule in the polyoxymethylene copolymer obtained by the above method and the low molecular weight polyoxymethylene copolymer contained in the polyoxymethylene resin composition is determined by the above-described MALDI-TOF. Measurement by a method using -MS confirmed that all samples had a molecular weight of 3,000 or less.

[0032]

According to the present invention, the obtained polyoxymethylene copolymer has a small amount of formaldehyde gas generated during molding, reduces environmental deterioration, and has a fine powdery material in the mold surface. In addition, tar-like substances are less likely to adhere to the molded product and to deteriorate the appearance of the molded product.

Claims (8)

[Claims] 1. An oxymethylene unit represented by the following formula (A): 99.9 to 80 mol%, and a copolymer component unit represented by the formula (B): 0.1 to 20 mol% (the total of both is 1
00 mol%. And a low molecular weight polyoxymethylene copolymer having a weight average molecular weight of 5,000 to 400,000 and a molecular weight of 3,000 or less, A polyoxymethylene copolymer, wherein the low molecular weight polyoxymethylene copolymer having a hemiformal terminal group represented by C) is contained at a content of 1,000 ppm or less based on the polyoxymethylene copolymer. Embedded image 2. The polyoxymethylene copolymer according to claim 1, wherein the copolymer component unit is oxyethylene, oxybutylene, oxydiethylene, or a combination thereof. 3. The monomer (A ′) having an oxymethylene unit represented by the formula (A) shown in claim 1 is 99.9 to 80 mol% in terms of the oxymethylene unit, and is represented by the formula (B). The monomer (B ′) having the copolymer component unit to be used is 0.1 to 20 mol% in terms of the copolymer component unit.
Is copolymerized to have a weight average molecular weight of 5,000 to 40.
When producing a polyoxymethylene copolymer having a molecular weight of 3,000 or less, a low molecular weight polyoxymethylene copolymer having a hemiformal terminal group represented by the following formula (C) in a low molecular weight polyoxymethylene copolymer having a molecular weight of 3,000 or less is used. A copolymerization step, a catalyst deactivation step after the copolymerization step, and a catalyst deactivation step such that the molecular weight polyoxymethylene copolymer has a content of 1,000 ppm or less based on the polyoxymethylene copolymer. A method for producing a polyoxymethylene copolymer, comprising performing a subsequent drying step, an unstable terminal treatment step after the drying step, a stabilizer compounding step after the unstable terminal treatment step, or a combination of these steps. 4. The method for producing a polyoxymethylene copolymer according to claim 3, wherein the catalyst deactivation step is carried out by bringing a reaction product from the copolymerization step into contact with an aqueous solution of a basic compound. . 5. The method for producing a polyoxymethylene copolymer according to claim 3, wherein the drying step is performed at 80 ° C. or higher. 6. The method for producing a polyoxymethylene copolymer according to claim 3, wherein the unstable terminal treatment is thermal decomposition or hydrolysis. 7. The hindered phenol compound as a stabilizer,
The polyoxymethylene copolymer according to claim 3, which is a sterically hindered amine compound, a polyamide, a urea derivative, an amidine compound, an alkali or alkaline earth metal hydroxide, or a mixture thereof. Method. 8. The copolymer component comprising ethylene oxide, 1,1,
The method for producing a polyoxymethylene copolymer according to any one of claims 3 to 7, which is 3-dioxolan, 1,4-butanediol formal, diethylene glycol formal, or a mixture thereof.