JPH10168144A - Production of stabilized oxymethylene copolymer - Google Patents

Abstract

PROBLEM TO BE SOLVED: To suppress the oxidative decomposition of a raw material and enable the economically advantageous and easy obtaining of the subject copolymer useful for mechanical parts, etc., by adding a stabilizer and water to a specific crude polyoxymethylene copolymer and degassing the resultant mixture in a molten state under a reduced pressure. SOLUTION: (A2 ) Sterically hindered phenols such as a compound represented by the formula (R1 and R2 are each a >=40C group) in an amount of 0.001-2.0wt.% based on the total amount of (A1 ) a monomer are added thereto before polymerization and the component A1 is copolymerized. The resultant copolymer is then pulverized into a granular or a powdery material, having 0.3-0.7mm average particle diameter and containing 3-20wt.% particles having >1.0mm particle diameter, 50-97wt.% particles having 0.18-1.0mm particle diameter and 0-30wt.% particles having <0.18mm particle diameter in 100wt.% total amount thereof. A polymerization catalyst is deactivated to afford (A) a crude polyoxymethylene copolymer, which is used as a raw material. (C) Water, together with (B) a stabilizer (e.g. an antioxidant and a heat stabilizer), are added to the component A and degassing of the prepared mixture is carried out in a molten state under a reduced pressure.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

TECHNICAL FIELD The present invention relates to an economical method for producing an oxymethylene copolymer having excellent heat stability.

[0002]

2. Description of the Related Art Polyoxymethylene copolymer (hereinafter referred to as "polyoxymethylene copolymer")
It is called "POM copolymer". ) Is excellent in mechanical properties, heat resistance, chemical resistance, electrical properties, slidability, etc., and excellent in moldability. It is used for a wide range of applications such as equipment parts. It is known that a practically used stabilized POM copolymer is generally produced by the following process. First, a cyclic acetal such as trioxane is used as a main monomer, a cyclic acetal or a cyclic ether having adjacent carbon atoms is used as a comonomer, and a chain transfer agent for adjusting the degree of polymerization is added according to the purpose. The resulting copolymer is used to obtain a crude POM copolymer. Generally, such crude POM copolymers have a significant amount of unstable terminal moieties. Further, the polymerization catalyst remains in an active state, and when heat is applied, it causes depolymerization of the copolymer or an increase in unstable terminal portions. Therefore, the crude POM copolymer as a polymerization product is then catalyzed by an organic or inorganic basic compound such as an alkylamine, an alkoxyamine, a hindered amine or a hydroxide of an alkali metal or an alkaline earth metal. And then subjected to a step of decomposing and removing the unstable terminal portion, and heating in the presence of a basic compound, for example, a compound as described above, and optionally water, alcohol, etc. By doing
Degradation and removal of the unstable terminal portion is performed. The POM copolymer from which the unstable terminal portion is decomposed and removed in this manner includes:
Next, various stabilizers are blended for imparting heat resistance stability, long-term stability, etc., and, if desired, various additives, reinforcing agents, etc. are blended for imparting properties according to the purpose, and are melt-kneaded. Thus, a stabilized POM copolymer that can be practically used is obtained. On the other hand, various studies have been made to produce a stabilized POM copolymer more economically, for example, improvement of a polymerization machine and a polymerization catalyst in a polymerization step, and a deactivator in a catalyst deactivation step. It is known to improve the deactivation method and the like, and to improve the decomposition accelerator and the decomposition removing device in the step of decomposing and removing unstable terminals. However, each of these methods focuses on a specific process, and there is a natural limit to the improvement, and a more economical process is considered from the polymerization process to the final POM copolymer stabilization process. There has been a need for a method for producing a stabilized POM copolymer. Especially,
Among the above-mentioned steps, the step of decomposing and removing the unstable terminal portion requires a complicated treatment operation, and requires a large amount of energy for the treatment.
If the OM copolymer can be subjected to the final stabilization step, a very economically advantageous production can be attained. For this purpose, a high-quality crude POM copolymer is required in the polymerization step and / or the catalyst deactivation step. It is necessary to obtain a polymer. For this reason, the applicant of the present application preliminarily added a sterically hindered phenol to a monomer in an amount of 0.001 to 2.0% by weight based on the total amount of the monomers prior to the polymerization in the polymerization step, and polymerized the POM.
Method for stabilizing the copolymer by heating and melting it (Japanese Patent Publication Sho 62
No. -13369) was previously proposed. In this method, the sterically hindered phenol is added at the time of polymerization. As a result, the dispersibility of the sterically hindered phenol is improved as compared with the case where the sterically hindered phenol is added during the melt stabilization treatment.
It has been found that although the oxidative decomposition of the M copolymer is suppressed to a certain extent, POM decomposition products generated in the melt stabilization step cannot be sufficiently removed.
As a method for improving the catalyst deactivation, the crude POM copolymer, which is a polymerization product, is pulverized from the viewpoint of improving the efficiency of catalyst deactivation and the subsequent efficiency of decomposing and removing unstable terminals. It is known that activation treatment is performed. From these viewpoints, it is considered that the smaller the particle size of the pulverized product is, the more preferable it is (JP-A-57-80414, JP-A-58-34819). However, the present inventor studied that, when the crude POM copolymer was finely pulverized and deactivated as described above, although the quality of the obtained POM copolymer was improved,
It has been found that when the stabilizer is blended with the stabilizer and subjected to a melt kneading step without undergoing the step of decomposing and removing the unstable terminal portion, the operability becomes extremely poor. Therefore, in order to improve the operability in the stabilization step, Japanese Patent Application No. 8-258983 has previously proposed a method of distributing a POM copolymer having an unstable terminal into a certain particle size. Although the operability was remarkably improved in this method, it was found that POM decomposition products generated in the melt stabilization step could not be sufficiently removed yet. Further, in JP-A-7-233230, a crude POM copolymer having unstable terminals within a certain amount is used as a raw material,
In an extruder having a melting zone, a terminal stabilization reaction zone, and a degassing zone, a method of adding a stabilizer and water in the terminal stabilization zone has been proposed. Although it does not hinder the production of POM, it has been found that an end stabilization reaction zone of a sufficient length is still required, and there is an economical problem due to an increase in the length of the apparatus.

[0003]

SUMMARY OF THE INVENTION In order to solve the above-mentioned problems, an object of the present invention is to provide a method for producing a practically usable stabilized POM copolymer by an economical, extremely advantageous and simple process. Aim. That is, an object of the present invention is to provide a method for producing a stabilized POM copolymer which can be practically used by omitting the step of decomposing and removing an unstable terminal portion conventionally performed. Further, when a POM polymer having an unstable terminal, which is a raw material of the stabilization step, requires time to move to the stabilization step due to transportation / storage for economic reasons or the like, the oxidation of the raw material is suppressed, and the raw material is put into practical use. It is an object of the present invention to provide a method for producing a stabilized POM copolymer that can be provided.

[0004]

Means for Solving the Problems In order to achieve the above object, the present inventors have comprehensively studied the processes from the polymerization step of the POM copolymer to the stabilization step. POM having unstable terminal as raw material
The copolymer contains hindered phenols at the time of polymerization, and the particle size distribution is appropriately controlled at the time of pulverization of the polymer, and a small amount of water is added to the raw material, When water is added after the raw material is melt-plasticized in the stabilization step, the oxidative decomposition of the POM copolymer as the raw material is suppressed, and the operability such as a biting neck is solved in the stabilization step. It has been found that a POM copolymer decomposed product generated by thermal decomposition of can be easily removed by degassing under reduced pressure, and the present invention has been accomplished. Further, when the POM copolymer having an unstable terminal, which is a raw material in the stabilization step, has a constant amount of unstable terminal and a particle size distribution is appropriately controlled, a small amount of water is added to the raw material. Or, when water is added after the raw material is melt-plasticized in the stabilization step, the oxidative decomposition of the POM copolymer as the raw material is suppressed, and the operability such as a digging neck is solved in the stabilization step. The present inventors have found that a POM copolymer decomposition product generated by thermal decomposition at the time of melting can be easily removed by degassing under reduced pressure.

That is, the present invention provides: In stabilizing a polyoxymethylene copolymer having an unstable terminal portion, (A) the polyoxymethylene copolymer having an unstable terminal portion is prepared by preliminarily polymerizing a sterically hindered phenol in a monomer before the polymerization. Of the crude polyoxymethylene polymer after polymerization into a powder having a particle size distribution defined by the following (1) to (4) and a polymerization catalyst (B) using the polyoxymethylene copolymer as a raw material, adding water together with a stabilizer, and deaeration under reduced pressure in a molten state; (1) Average particle size 0.3 to 0.7 mm (2) 3 to 20% by weight having a particle size exceeding 1.0 mm (3) 50 to 50% having a particle size of 0.18 mm to 1.0 mm ~ 97% by weight (4) Particle size less than 0.18mm Is 0 to 30% by weight (however, the total amount is 100% by weight) In the stabilization of a polyoxymethylene copolymer having an unstable terminal portion, (A) the polyoxymethylene copolymer having an unstable terminal portion has an unstable terminal portion in an amount of 0.3 to 0.8% by weight (in the copolymer) (B) using the polyoxymethylene copolymer as a raw material, adding water together with a stabilizer, and melting the powder. A method for producing a stabilized polyoxymethylene copolymer, wherein degassing is performed under reduced pressure in a state, (1) an average particle diameter of 0.3 to 0.7 mm, and (2) a powder having a particle diameter exceeding 1.0 mm is 3 to 20% by weight. (3) 50 to 97% by weight of particles having a particle size of 0.18 mm or more and 1.0 mm or less (4) 0 to 30% by weight of particles having a particle size of less than 0.18 mm (however, the total amount is 100% by weight). 3. The method for producing a stabilized polyoxymethylene copolymer according to the above 1 or 2, wherein water is previously mixed with a raw material of the polyoxymethylene copolymer having an unstable terminal. 4. The method for producing a stabilized polyoxymethylene copolymer according to 1 or 2, wherein water is added after the raw material of the polyoxymethylene copolymer having an unstable terminal is melt-plasticized. 5. The method for producing a stabilized polyoxymethylene copolymer according to any one of the above 1 to 3, wherein water and a stabilizer are previously mixed with a raw material of a polyoxymethylene copolymer having an unstable terminal. The method according to the above item 1 or 2 or 4, wherein the stabilizer is premixed with the raw material of the polyoxymethylene copolymer having an unstable terminal, and water is added after the raw material of the polyoxymethylene copolymer having the unstable terminal is melt-plasticized. 6. A method for producing a stabilized polyoxymethylene copolymer, The above 1 wherein water and a stabilizer are added after the raw material of the polyoxymethylene copolymer having an unstable terminal is melt-plasticized.
Or a method for producing a stabilized polyoxymethylene copolymer according to 2 or 4.

[0006]

BEST MODE FOR CARRYING OUT THE INVENTION Hereinafter, the present invention will be described in detail. First, the (crude) oxymethylene copolymer (POM copolymer) to which the present invention is applied is a copolymer containing a cyclic acetal such as trioxane as a main monomer and a cyclic ether or cyclic formal as a comonomer in the presence of a cationically active catalyst. It is obtained by polymerization. Here, the cyclic ether or cyclic formal used as a comonomer is a cyclic compound having at least one pair of a connecting carbon atom and an oxygen atom, for example, ethylene oxide, 1,3-dioxolan, 1,3,5-trioxepane, diethylene glycol formal, Examples include 1,4-butanediol formal, 1,3-dioxane, propylene oxide and the like. Among these, preferred comonomers are ethylene oxide, 1,3-dioxolan, diethylene glycol formal, and 1,4-butanediol formal.
The amount used is based on trioxane, the main monomer.
It is 0.1 to 20 mol%, preferably 0.2 to 10 mol%. The (coarse) PO
In producing the M copolymer, a general cationic catalyst is used as a polymerization catalyst. Such cationic catalysts include Lewis acids, especially 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 antimony pentafluoride, and compounds such as complex compounds or salts thereof, protonic acids such as trifluoromethanesulfonic acid, perchloric acid, esters of protic acids, especially esters of perchloric acid with lower aliphatic alcohols ( For example, perchloric acid tertiary butyl ester), an anhydride of a protic acid, particularly a mixed anhydride of perchloric acid and a lower aliphatic carboxylic acid (eg, acetyl perchlorate), or an isopoly acid or a heteropoly acid (eg, phosphorus) Molybdic acid) or triethyloxonium hexafluorophosphate, Le hexafluoro ARUZE diisocyanate, acetyl hexafluoro borate and the like. Among them, boron trifluoride or a coordination compound of boron trifluoride and an organic compound (for example, ethers) is the most common. Further, protonic acids such as heteropolyacids and isopolyacids have a high activity as a catalyst, and it is easy to obtain a high-quality crude POM copolymer with a small amount of a catalyst, and it is easy to deactivate the catalyst. The crude POM copolymer to which is applied is preferably one obtained by polymerizing one or a mixture of two or more selected from such compounds as a catalyst. When a Lewis acid such as boron trifluoride is used as a catalyst, the amount of addition is 15
~ 25 ppm is preferred. In order to obtain a high quality crude POM copolymer, it is preferable to use a monomer containing 10 ppm or less of water. In addition, crude P obtained by copolymerization
In order to control the molecular weight of the OM copolymer, if necessary, a suitable chain transfer agent, for example, an appropriate amount of an acetal compound such as methylal or dioxymethylene dimethyl ether may be added for polymerization. The production of the crude POM copolymer by copolymerization can be carried out by a conventionally known equipment and method. That is, either a batch type or a continuous type is possible,
Although any of melt polymerization, melt bulk polymerization, and the like may be used, a continuous bulk method in which a liquid monomer is used and a solid powder bulk polymer is obtained with the progress of polymerization is generally industrially preferable. In this case, an inert liquid medium can coexist as necessary. As a polymerization apparatus, a co-kneader, a twin-screw type continuous extrusion mixer, a twin-screw paddle type continuous mixer and the like can be used.

According to the present invention, a crude POM copolymer obtained by adding a sterically hindered phenol is pulverized into powder having a specific particle size distribution, and a polymerization catalyst contained therein is lost. Using the activated POM copolymer having an unstable terminal as a raw material, the POM copolymer raw material is mixed with a stabilizer together with a stabilizer without substantially undergoing a terminal stabilization treatment by decomposing and removing an unstable terminal portion. , And degassing under reduced pressure in a molten state. That is, the crude P obtained by such copolymerization
The production of the OM copolymer needs to be performed in the presence of a sterically hindered phenol (a hindered phenol compound) which is an antioxidant. P at high temperature in subsequent process
The OM copolymer is effective in suppressing the oxidative decomposition and the like of the OM copolymer and maintaining the high quality POM copolymer in the final stabilization step. Therefore, the POM copolymer is suitable as a crude POM copolymer to which the present invention is applied. The sterically hindered phenol used in the present invention has the general formula

[0008]

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(However, R ₁ and R ₂ are groups having 4 or more carbon atoms, and both may be the same or different.) Sterically hindered phenols having the structure: For example, the following substances may be mentioned. That is, 2,
2'-methylene bis (4-methyl-6-t-butylphenol), hexamethylene glycol-bis (3,5-di-t
-Butyl-4-hydroxyhydrocinnamate), tetrakis [methylene (3,5-di-t-butyl-4-hydroxyhydrocinnamate)] methane, triethylene glycol-bis-3- (3-t-butyl- 4-hydroxy-
5-methylphenyl) propionate, 1,3,5-trimethyl-2,4,6-tris (3,5-di-t-butyl-4-hydroxy-benzyl) benzene, n-octadecyl-3-
(4'-hydroxy-3 ', 5'-di-t-butylphenol) propionate, 4,4'-methylenebis (2,6-di-t
-Butylphenol), 4,4'-butylidene-bis- (6
-T-butyl-3-methyl-phenol), 2,2'-thiodiethyl-bis- [3- (3,5-di-t-butyl-4-hydroxyphenyl) propionate, di-stearyl-
3,5-di-tert-butyl-4-hydroxybenzylphosphonate, 2-tert-butyl-6- (3-tert-butyl-5-
Methyl-2-hydroxybenzyl) -4-methylphenyl acrylate can be used. However, the invention is not limited to these, and other sterically hindered phenols of the same kind are all effective. Among these, hexamethylene glycol-
Bis (3,5-di-t-butyl-4-hydroxyhydrocinnamate) such as Irganox 259 (trade name, manufactured by Ciba Geigy), tetrakis [methylene (3,5-di-t-butyl-4-hydroxyhydrocinnamate) )] Methane, for example, Irganox 1010 manufactured by Ciba-Geigy, triethylene glycol-bis-3- (3-t-butyl-4-
Hydroxy-5-methylphenyl) propionate, for example, Irganox 245 (trade name, manufactured by Ciba Geigy) is particularly effective. On the other hand, antioxidants other than sterically hindered phenols, such as amines, amidines, or other substances generally used as stabilizers for polyacetals, do not cause a polymerization reaction when added to monomers. The amount of sterically hindered phenols added to the monomers prior to polymerization is effective even in very small amounts,
It is used in the range of 0.001 to 2.0% by weight, but is particularly preferably 0.005 to 1.0% by weight. If the added amount is too small, the effect of preventing oxidative decomposition is naturally small. If the added amount is too large, the polymerization reaction tends to be slowed down, and it is uneconomical, which is not desirable. As a method of adding these sterically hindered phenols to the monomer, the sterically hindered phenol may be added to a liquid monomer as it is and dissolved, or a solution dissolved in a small amount of a solvent inert to polymerization may be added. When performing continuous polymerization, it is also possible to continuously supply a certain amount to the monomer line supplied to the polymerization machine, to mix and dissolve in the monomer to reach the polymerization machine, and to perform the polymerization in the monomer reservoir. It can be added and dissolved.

Further, the crude POM copolymer thus polymerized must be pulverized and satisfy the particle size distribution defined by the following (1) to (4). (1) Average particle size: 0.3 to 0.7 mm (2) 3 to 20% by weight with a particle size exceeding 1.0 mm (3) 50 to 97% by weight with a particle size of 0.18 mm to 1.0 mm 0-30% by weight (less than 0.18 mm) (however, the total amount is 100% by weight) This particle size distribution indicates the quality of the POM copolymer obtained by grinding and deactivating the catalyst, especially From the viewpoint of satisfying both the stable terminal amount and the operability of the stabilization step of degassing and stabilizing the pulverized POM copolymer in a molten state together with water and a stabilizer in a molten state, the present inventors have studied diligently. It was found. Among these, the upper limit (0.7 mm) of the average particle size of (1) and the upper limit of the ratio of those exceeding 1.0 mm in (2) are mainly important requirements that are key to the quality of the POM copolymer. (1) lower limit of average particle size (0.3mm),
The lower limit of the ratio of those having a particle size of more than 1.0 mm in (2) and the upper limit of the ratio of those having a particle size of less than 0.18 mm in (4) are important requirements that are key to the operability of the stabilization step mainly with a stabilizer. . If the particle size is larger than the particle size distribution shown here, for example, if the average particle size exceeds the upper limit or the particle size
When the ratio of those exceeding 1.0 mm exceeds the upper limit, the quality of the obtained pulverized POM copolymer, particularly the amount of unstable terminals becomes large, without undergoing terminal stabilization treatment by decomposition and removal of unstable terminal portions. When subjected to the stabilization step with a stabilizer, a stable POM copolymer that can be marketed cannot be obtained. On the other hand, when the particle size is biased toward the smaller one from the particle size distribution, for example, the average particle size is at the lower end, the ratio of those having a particle size exceeding 1.0 mm is the lower end or the ratio of those having a particle size of less than 0.18 mm is at the upper limit. If exceeded, P
Although the quality of the OM copolymer is satisfactory, the operability of the stabilization step by kneading with the stabilizer becomes extremely poor, and it becomes difficult to economically produce the stabilized POM copolymer. From such a viewpoint, a preferable particle size distribution for satisfying both the better quality of the POM copolymer and the operability of the stabilization step is as follows. (1) 'Average particle size 0.4 to 0.7 mm; (2)' 5 to 15% by weight having a particle size exceeding 1.0 mm. (3) '60 to 95% by weight having a particle size of 0.18 mm to 1.00 mm. 0) 25% by weight having a particle size of less than 0.18 mm (however, the total amount is 100% by weight) In performing the pulverization as described above, the pulverizer to be used is not particularly limited. For example, a rotary mill, a hammer mill , A jaw crusher, a feather mill, a rotary cutter mill, a turbo mill, a classifying impact crusher, or the like is used. The particle size distribution can be controlled by the rotation speed and clearance of the crusher, a screen mesh provided in the crusher, and / or a sieve provided separately as required.

In deactivating the catalyst contained in the crude POM copolymer, a known method can be used as the deactivation method. In the present invention, in performing such catalyst deactivation treatment, an aqueous solution of an organic or inorganic basic compound represented by triethylamine, triethanolamine, sodium carbonate, calcium hydroxide and the like is used as a deactivation treatment agent. While performing the deactivation treatment, it is preferable to obtain the particle size distribution as described above by pulverization by wet pulverization,
Among them, it is preferable to add such a deactivating agent between immediately before the polymer outlet of the polymerization machine and the inlet of the pulverizer,
Thereby, a high quality POM copolymer can be obtained. The POM copolymer pulverized by the catalyst deactivation treatment is
Washing, drying and the like are performed as necessary. The crude POM copolymer thus treated is used as a raw material for the stabilization step.

Another method of the present invention is a method for stabilizing a polyoxymethylene copolymer having an unstable terminal portion, wherein the polyoxymethylene copolymer having an unstable terminal portion has an unstable terminal portion of from 0.3 to 0.3. A POM copolymer having unstable terminals, which is 0.8% by weight (in the copolymer) and has a specific particle size distribution, is used as a raw material.
A method for producing a stabilized POM copolymer, comprising adding water together with a stabilizer to a raw material of an M copolymer and degassing under reduced pressure in a molten state. The amount of unstable terminal of the POM copolymer specified here is determined by adding 1 g of the POM copolymer to 100 ml of a 50% aqueous methanol solution containing 0.5% ammonium hydroxide.
Together with a heat-resistant container at 45 ° C. for 45 minutes, cooled, taken out, quantitatively analyzed for the amount of formaldehyde decomposed and eluted in the solution, and expressed in terms of% by weight based on the copolymer. In order to make the unstable terminal portion 0.3 to 0.8% by weight, the polymerization method in which a sterically hindered phenol is added as described above, or even if the sterically hindered phenol is not added, the polymerization is lost. In the active step, the polymer is dissolved once using a methanol solution of an organic or inorganic basic compound represented by triethylamine, triethanolamine, sodium carbonate, calcium hydroxide, etc., and then the POM copolymer is precipitated again. You can do it by letting The thus-polymerized crude POM copolymer is formed into a powder material satisfying a particle size distribution defined by the following (1) to (4), and this is used as a raw material. (1) Average particle size: 0.3 to 0.7 mm (2) 3 to 20% by weight with a particle size exceeding 1.0 mm (3) 50 to 97% by weight with a particle size of 0.18 mm to 1.0 mm 0 to 30% by weight (less than 0.18mm) (however, the total amount is 100% by weight) Using the crude POM copolymer prepared as above as a raw material, water is added together with a stabilizer, and the mixture is decompressed in a molten state under reduced pressure. Care is taken to obtain a stabilized POM copolymer.

A feature of the present invention is that the crude POM copolymer prepared as described above is used as a raw material, and water is added in a stabilizing step of the raw material to remain in the raw material or to be generated during the stabilizing step. It is an object of the present invention to obtain a stabilized POM copolymer by mixing a stabilizer and the like while removing volatile components such as a decomposed POM polymer (formaldehyde gas). The amount of water added is 0.05 to 5.0% by weight, preferably 0.5 to 3.0% by weight, based on the weight of the raw material. If the amount is small, there is no devolatilizing effect, and if the amount is large, moisture remains in the kneaded material, which is not preferable. Further, as a method of adding water, the water may be previously mixed or pre-blended with the raw material, or may be added after the raw material is melt-plasticized. This is because water can be dispersed in the preblend in advance, and the water can be sufficiently dispersed after melt plasticization. However, it is not preferable that the raw material is added during the melt plasticization, since a large amount of water is locally present, which hinders the plasticization of the raw material and unplasticized portions may be mixed.

The stabilizer used here is not particularly limited, and any known stabilizer can be used. Generally, an antioxidant and a heat stabilizer are used in combination. Examples of the antioxidant include 1,6-hexanediol-bis [3
-(3,5-di-t-butyl-4-hydroxyphenyl) propionate], pentaerythrityltetrakis [3-
(3,5-di-t-butyl-4-hydroxyphenyl) propionate], triethylene glycol-bis [3-
(3-t-butyl-5-methyl-4-hydroxyphenyl) propionate], N, N'-hexamethylenebis (3,5
-Di-t-butyl-4-hydroxy-cinnamamide) and the like. As the heat stabilizer, for example, melamine,
Triazine compounds such as melamine-formaldehyde condensate, polyamides such as nylon 12, nylon 6,10,
Alkali metal or alkaline earth metal hydroxides, carbonates, phosphates, acetates, oxalates, and the like, metal salts of higher fatty acids such as stearic acid or higher fatty acids having a substituent such as a hydroxyl group, and the like. .

[0015] In addition, the POM copolymer of the present invention can contain various additives depending on the purpose.
Weather (light) stabilizers, lubricants, lubricants, nucleating agents, mold release agents, antistatic agents, dyes, pigments, other organic polymer materials, inorganic and organic fibrous, plate-like, and granular fillers, etc. Can be blended. As a device used in the stabilization step of the present invention, a continuous extruder such as a twin-screw extruder with a vent or a single-screw extruder with a vent can be used. Vacuum devolatilization is performed at the vent.

[0016]

EXAMPLES Examples and comparative examples are shown below, but the present invention is not limited to these examples. (Evaluation method)-Extrudability (Raw material biting property) Stabilizer is mixed with granular POM copolymer, and when melt kneading with an extruder, raw material biting into extruder and stabilized POM from extruder Observe the discharge status, and
Was evaluated in three steps. A: Both biting and discharging strands are stable. B: Occasionally poor biting occurs and the strand thickness fluctuates. C: Biting fluctuation is slightly large, strand thickness fluctuation is large, and occasional strand breakage occurs. Unstable terminal amount of coalescence 1 g of the POM copolymer was put into a pressure-tight container together with 100 ml of a 50% aqueous methanol solution containing 0.5% ammonium hydroxide, heated at 180 ° C. for 45 minutes, cooled, taken out, and put into the liquid. The amount of formaldehyde decomposed and eluted is quantitatively analyzed, and the result is shown in terms of% by weight based on the copolymer. -Monomer (formaldehyde) content in the polymer (formaldehyde extraction amount) 2 g of the POM copolymer was placed in 40 ml of distilled water, refluxed for 1.5 hours, and quantitatively analyzed for the amount of formaldehyde extracted in the water. It is shown by weight ratio to the polymer.

Examples 1 to 5 and Comparative Examples 1 to 5 [Preparation of Raw Material of Crude POM Copolymer (POM Copolymer Having Unstable Terminal)] Using a biaxial paddle type continuous polymerization machine, -Trioxane to which 2.5% by weight of dioxolane (in all monomers) was added was continuously supplied, and polymerization was carried out using boron trifluoride or phosphomolybdic acid as a catalyst. In this case, tetrakis [methylene (3,5-di-tert-butyl-4-
Hydroxycinnamate)] Methane (trade name: Irganox 1010, manufactured by Ciba-Geigy Co., Ltd.) was added or dissolved in 0.05% (of all monomers), and was not added. Tables 1 and 2 show the results. The crude POM copolymer discharged from the discharge port at the end of the polymerization machine was subjected to wet pulverization and catalyst deactivation treatment, followed by dehydration and drying.
A powdery POM copolymer having a particle size distribution shown in 2 was obtained. The particle size was controlled by changing the number of revolutions of the crusher and the size and shape of the screen mesh. [Stabilization treatment] For the powdery POM copolymer obtained by the above method, tetrakis [methylene (3,5
-Di-t-butyl-4-hydroxynamate)] methane (trade name Irganox 1010 manufactured by Ciba-Geigy)
0.45% by weight and 0.1% by weight of calcium stearate were mixed and melt-kneaded with a vented single-screw or twin-screw extruder. At that time, the addition of water was performed for (1) a case where the raw material was previously mixed or pre-blended, (2) a case where the raw material was added after melt plasticization, and (3) a case where no addition was made. The results are shown in Tables 1 and 2. In the following tables, abbreviations have the following meanings. Particle size distribution: Within the range: Within the particle size distribution range defined in claim 1 Outside the range 1: outside the particle size distribution range defined by claim 1,
When the distribution of particles having a particle size of less than 0.18 mm is more than 30% by weight. Out of range 2: outside the range of particle size distribution defined in claim 1,
When the particle size of 1.00 mm or more has a distribution exceeding 20% by weight. Addition method: Injection: Water is added to the extruder after the raw material is melt-plasticized. Preblend: Water is premixed with the raw material and added. Catalyst Species: BF ₃ ... boron trifluoride, HPA ... phosphomolybdic acid

[0018]

[Table 1]

[0019]

[Table 2]

Examples 6 to 8 and Comparative Examples 6 to 9 [Preparation of Raw Materials of Crude POM Copolymer (POM Copolymer Having Unstable Terminal)] Using a biaxial paddle type continuous polymerization machine, -Trioxane added with 2.5% by weight of dioxolane (of all monomers) is continuously supplied and boron trifluoride is added.
Polymerization was carried out using 20 ppm as a catalyst. The crude POM copolymer discharged from the outlet at the end of the polymerization machine was dissolved and heated at 180 ° C. in a methanol solution containing 0.25% by weight of triethylamine, and then cooled to precipitate the POM copolymer. Thereafter, desolvation and drying were performed, and a powdery POM copolymer having a predetermined particle size distribution was obtained by dry pulverization. The amount of unstable terminal groups of the raw POM copolymer was adjusted by changing the residence time in a 180 ° C. methanol solution. [Stabilization treatment] For the powdery POM copolymer obtained by the above method, tetrakis [methylene (3,5
-Di-t-butyl-4-hydroxynamate)] methane (trade name Irganox 1010 manufactured by Ciba-Geigy)
0.5% by weight and 0.1% by weight of calcium stearate were mixed and melt-kneaded with a single-screw or twin-screw extruder having a vent. At that time, the addition of water was performed for (1) a case where the raw material was previously mixed or pre-blended, (2) a case where the raw material was added after melt plasticization, and (3) a case where no addition was made. The results are shown in Tables 3 and 4. In the following tables, abbreviations have the following meanings. Particle size distribution: Within the range: Within the particle size distribution range defined in claim 1 Outside the range 1: outside the particle size distribution range defined by claim 1,
When the distribution of particles having a particle size of less than 0.18 mm is more than 30% by weight. Out of range 2: outside the range of particle size distribution defined in claim 1,
When the particle size of 1.00 mm or more has a distribution exceeding 20% by weight. Addition method: Injection: Water is added into the extruder after the raw material is melt-plasticized. Preblend: Water is mixed with the raw material in advance and added.

[0021]

[Table 3]

[0022]

[Table 4]

[0023]

As is clear from the results of the examples, according to the present method, a stabilized POM copolymer can be produced economically.

Claims (7)

[Claims] 1. A method for stabilizing a polyoxymethylene copolymer having an unstable terminal, comprising the steps of: (A) preparing a polyoxymethylene copolymer having an unstable terminal in a monomer before the polymerization; Are added at 0.001 to 2.0% by weight based on the total amount of monomers to carry out polymerization, and the crude polyoxymethylene polymer after polymerization is converted into powders satisfying the particle size distribution specified in the following (1) to (4). (B) using the polyoxymethylene copolymer as a raw material, adding water together with a stabilizer, and degassing in a molten state under reduced pressure. A method for producing a stabilized polyoxymethylene copolymer. (1) Average particle size: 0.3 to 0.7 mm (2) 3 to 20% by weight with a particle size exceeding 1.0 mm (3) 50 to 97% by weight with a particle size of 0.18 mm to 1.0 mm 0 to 30% by weight less than 0.18mm (However, the total amount is 100% by weight) 2. A method for stabilizing a polyoxymethylene copolymer having an unstable terminal, wherein (A) the polyoxymethylene copolymer having an unstable terminal comprises 0.3 to 0.8% by weight of the unstable terminal. (B) using the polyoxymethylene copolymer as a raw material, and water together with a stabilizer; and (B) a powder having a particle size distribution defined by the following (1) to (4). A method for producing a stabilized polyoxymethylene copolymer, comprising deaeration under reduced pressure in a molten state. (1) Average particle size: 0.3 to 0.7 mm (2) 3 to 20% by weight with a particle size exceeding 1.0 mm (3) 50 to 97% by weight with a particle size of 0.18 mm to 1.0 mm 0 to 30% by weight less than 0.18mm (However, the total amount is 100% by weight) 3. The method according to claim 1, wherein water is previously mixed with the raw material of the polyoxymethylene copolymer having an unstable terminal.
A method for producing the stabilized polyoxymethylene copolymer described above. 4. The method according to claim 1, wherein water is added after the raw material of the polyoxymethylene copolymer having an unstable terminal is melt-plasticized.
Or a method for producing a stabilized polyoxymethylene copolymer according to item 2. 5. A method for producing a stabilized polyoxymethylene copolymer according to claim 1, wherein water and a stabilizer are previously mixed with a raw material of the polyoxymethylene copolymer having an unstable terminal. Method. 6. The method according to claim 1, wherein the stabilizer is mixed in advance with the raw material of the polyoxymethylene copolymer having an unstable terminal, and water is added after the raw material of the polyoxymethylene copolymer having the unstable terminal is melt-plasticized. Or a method for producing a stabilized polyoxymethylene copolymer according to 2 or 4. 7. The process for producing a stabilized polyoxymethylene copolymer according to claim 1, wherein water and a stabilizer are added after the raw material of the polyoxymethylene copolymer having an unstable terminal is melt-plasticized. .