Method for producing polyacetal

Abstract

The invention relates to a method for producing polyacetal. In a method for producing polyacetal using a cationic active catalyst, the cationic active catalyst is efficiently deactivated and washed, thereby producing polyacetal having excellent thermal stability. A method for producing a polyacetal, characterized by comprising: a polymerization step for polymerizing at least one cyclic ether and / or cyclic formal containing trioxymethylene in the presence of at least one cationic active catalyst; and a deactivating and washing step in which the crude polyacetal obtained in the polymerization step is brought into contact with a deactivating and washing solution obtained by dissolving or suspending a basic compound in an aliphatic hydrocarbon solvent, thereby deactivating and washing the cationic active catalyst in the same step.

Description

Technical Field

[0001] This invention relates to a method for manufacturing polyacetal. Background Technology

[0002] Polyacetal resin is a resin material with excellent rigidity, strength, toughness, lubrication, and creep resistance, and is widely used primarily in automotive parts, electrical / electronic equipment, and various mechanical components. However, in recent years, the required properties of these components have become increasingly demanding and diverse. There is a growing demand for formaldehyde suppression, particularly addressing the unique problems associated with polyacetal resin, such as formaldehyde produced by thermal decomposition, ultraviolet decomposition, and natural degradation. Improvements using additives are ongoing. On the other hand, given the usage of polyacetal resin, there are also numerous problems caused by additives; therefore, there is a need for formaldehyde suppression that does not rely on additives.

[0003] Regarding polyacetals, it is known to obtain polyacetal polymers or copolymers by polymerizing at least one cyclic ether comprising trioxymethylene and / or cyclic formaldehyde in the presence of at least one cationic active catalyst, and various methods have been proposed. Among these, bulk polymerization that substantially does not use solvents, or quasi-bulk polymerization that uses less than 20% solvent relative to the monomers, is the industrially preferred method. Furthermore, the crude polymer of the polyacetal polymer or copolymer obtained by polymerization requires catalyst deactivation to prevent depolymerization.

[0004] Various methods have been proposed for deactivating catalysts. For example, a method using a metal sulfite salt as a solid deactivating agent has been proposed (see Patent Document 1). On the other hand, a method of adding an aqueous solution of an alkali metal compound or an alcoholic compound solution has been proposed (see Patent Document 2), and a method of adding a tertiary phosphine compound dissolved in an organic solvent with a specific SP value (solubility parameter) has also been proposed (see Patent Document 3).

[0005] In addition, a method for deactivation in an aqueous solution or organic solvent containing alkaline neutralizing agents such as triethylamine, tributylamine, and calcium hydroxide has been proposed (see Patent Document 4).

[0006] Existing technical documents

[0007] Patent documents

[0008] Patent Document 1: Japanese Patent Application Publication No. 63-27519

[0009] Patent Document 2: Japanese Patent Application Publication No. 2000-327732

[0010] Patent Document 3: Japanese Patent No. 4247586

[0011] Patent Document 4: Japanese Patent Application Publication No. 58-34819 Summary of the Invention

[0012] The problem that the invention aims to solve

[0013] However, in the technologies disclosed in the aforementioned patent documents 1, 2 and 3, due to poor dispersion of the deactivating agent, the deactivation of the cationic active catalyst becomes insufficient, and the thermal decomposition of polyacetal caused by the residual active cationic active catalyst cannot be suppressed.

[0014] Furthermore, Patent Document 4 only mentions solvents from the perspective of dissolving alkaline deactivating agents, without mentioning washing away substances from cationic active catalysts. In particular, even if deactivation treatment of non-volatile cationic active catalysts is performed, the residual substances from the catalyst will still promote the thermal decomposition of polyacetal.

[0015] The present invention was made in view of the above circumstances, and its objective is to provide a method for manufacturing polyacetal in which the thermal stability of polyacetal is improved by effective deactivation and washing of a cationic active catalyst.

[0016] means for solving problems

[0017] In order to solve the above problems, the inventors conducted repeated research and found that in the method of manufacturing polyacetal, the above problems can be solved by using a deactivating and washing liquid obtained by dissolving or suspending an alkaline compound in an aliphatic hydrocarbon solvent, thus completing the present invention.

[0018] That is, the present invention is as follows.

[0019] [1] A method for manufacturing polyacetal, characterized in that the method for manufacturing polyacetal comprises the following steps:

[0020] A polymerization step, wherein at least one cyclic ether comprising trioxymethylene and / or cyclic formaldehyde is polymerized in the presence of at least one cationic active catalyst; and

[0021] The deactivation and washing process involves contacting the crude polyacetal obtained through the polymerization process with a deactivation and washing solution, thereby deactivating and washing the cationic active catalyst in the same process. The deactivation and washing solution is obtained by dissolving or suspending an alkaline compound in an aliphatic hydrocarbon solvent.

[0022] [2] According to the method for manufacturing polyacetal as described in [1], in the deactivation and washing process, the crude polyacetal is brought into contact with the deactivation and washing liquid in a slurry state.

[0023] [3] The method for manufacturing polyacetal according to [1] or [2], wherein the aliphatic hydrocarbon solvent is at least one selected from n-hexane, cyclohexane and n-decane.

[0024] [4] The method for manufacturing polyacetal according to any one of [1] to [3], wherein the basic compound is at least one selected from amine compounds and phosphine compounds.

[0025] Invention Effects

[0026] According to the present invention, in the method for manufacturing polyacetal, by using a specific deactivation and washing solution, the deactivation and washing of the cationic active catalyst can be carried out in the same step, thereby producing polyacetal with excellent thermal stability. Furthermore, by performing deactivation and washing in the same step, the manufacturing process can be simplified, and manufacturing costs can be reduced. In addition, by using an aliphatic hydrocarbon solvent with low heat of vaporization, the drying of the deactivated and washed polyacetal becomes easier, thereby reducing greenhouse gas (GHG) emissions by shortening the drying process time. Detailed Implementation

[0027] Hereinafter, a detailed description will be given of the method for carrying out the present invention (hereinafter referred to as "this embodiment").

[0028] <Method for manufacturing polyacetal>

[0029] The method for manufacturing polyacetal in this embodiment includes the following steps:

[0030] A polymerization step, wherein at least one cyclic ether comprising trioxymethylene and / or cyclic formaldehyde is polymerized in the presence of at least one cationic active catalyst; and

[0031] The deactivation and washing process involves contacting the crude polyacetal obtained through the polymerization process with a deactivation and washing solution, thereby deactivating and washing the cationic active catalyst in the same process. The deactivation and washing solution is obtained by dissolving or suspending an alkaline compound in an aliphatic hydrocarbon solvent.

[0032] <At least one cyclic ether and / or cyclic formaldehyde>

[0033] In this embodiment, at least one cyclic ether and / or cyclic formaldehyde is used as a monomer component. Cyclic ethers and / or cyclic formaldehydes refer to cyclic compounds having at least one carbon-oxygen bond or carbon-oxygen-carbon bond; additionally, formaldehyde-containing polymers (trimers, tetramers, etc.) are also included. Examples of cyclic ethers and / or cyclic formaldehydes include: trioxymethylene, tetraoxymethylene, ethylene oxide, propylene oxide, butane oxide, epichlorohydrin, epibromohydrin, styrene oxide, oxetane, 1,3-dioxacyclopentane, ethylene glycol formaldehyde, propylene glycol formaldehyde, diethylene glycol formaldehyde, triethylene glycol formaldehyde, 1,4-butanediol formaldehyde, 1,5-pentanediol formaldehyde, 1,6-hexanediol formaldehyde, etc. A single cyclic ether and / or cyclic formaldehyde may be used alone, or two or more may be used in combination.

[0034] In this embodiment, at least one cyclic ether and / or cyclic formaldehyde used must contain trioxymethylene. It should be noted that trioxymethylene is a cyclic trimer of formaldehyde, typically obtained by reacting an aqueous formaldehyde solution in the presence of an acidic catalyst. This trioxymethylene sometimes contains impurities such as water, methanol, formic acid, and methyl formate, which can cause chain transfer; therefore, it is preferable to pre-purify it by methods such as distillation to remove these impurities.

[0035] When purifying paraformaldehyde as described above, it is preferable to adjust the total amount of impurities that cause chain transfer to 1 × 10⁻⁶ relative to 1 mole of paraformaldehyde. -3 Below 10 moles, a more preferable setting is 0.5 × 10⁻⁶. -3 Below the molar level. By reducing the amount of impurities as described above, it is practically possible to significantly increase the polymerization rate and improve various properties of the resulting polymer, such as thermal stability.

[0036] As cyclic ethers and / or cyclic formaldehydes other than trioxymethylene, 1,3-dioxane and 1,4-butanediol formaldehyde are particularly preferred.

[0037] Furthermore, when using trioxymethylene and cyclic ethers and / or cyclic formaldehyde other than trioxymethylene as at least one cyclic ether and / or cyclic formaldehyde, the amount of cyclic ethers and / or cyclic formaldehyde other than trioxymethylene added relative to 1 mole of trioxymethylene is preferably in the range of 0.1 mol% to 20 mol%, more preferably 0.1 mol% to 15 mol%, further preferably 0.1 mol% to 10 mol%, and even more preferably 0.1 mol% to 5 mol%.

[0038] <Catonic Active Catalysts>

[0039] There are no particular limitations on the cationic active catalyst used in the manufacturing method of this embodiment, as long as it is a catalyst capable of stably producing polyacetal. Examples of cationic active catalysts include Lewis acids, protic acids and their esters or anhydrides. Examples of Lewis acids include: boric acid, boron hydride (e.g., borane, diborane), boron halides (e.g., boron trifluoride, boron trichloride, boron tribromide, boron triiodide), trialkylboranes (e.g., trimethylborane, triethylborane), tin compounds (e.g., stannous fluoride (II), stannous chloride (II), stannous bromide (II), stannous iodide (II), etc. tin halides (IV); tin fluoride (IV), stannous chloride (IV), stannous bromide (IV), stannous iodide (IV), etc. tin halides (IV), etc.), titanium compounds (e.g., titanium difluoride (II), titanium dichloride (II), titanium dibromide (II), titanium diiodide (II), etc. titanium dihalides (II); titanium trifluoride (III), titanium trichloride (III), titanium tribromide (III), titanium triiodide (III), etc. titanium trihalides (III); titanium tetrafluoride (IV), titanium tetrachloride (IV) Titanium tetrabromide (IV), titanium tetraiodide (IV), and other titanium tetrahalides (IV), phosphorus compounds (phosphorus trifluoride, phosphorus trichloride, phosphorus tribromide, phosphorus triiodide, phosphorus pentafluoride, phosphorus pentachloride, phosphorus pentabromide, phosphorus pentaiodide, etc.), arsenic compounds (arsenic trifluoride, arsenic trichloride, arsenic tribromide, arsenic triiodide, arsenic pentafluoride, arsenic pentachloride, arsenic pentabromide, arsenic pentaiodide, etc.), and antimony compounds (antimony trifluoride, antimony trichloride, antimony tribromide, etc.). Antimony, antimony triiodide, antimony pentafluoride, antimony pentachloride, antimony pentabromide, antimony pentaiodide and other antimony halides, and their hydrates or coordination complexes are preferred. Boron trifluoride, boron trifluoride hydrates, and coordination complexes of organic compounds containing oxygen or sulfur atoms (e.g., ether compounds such as diethyl ether and tetrahydrofuran, alcohols such as methanol, compounds containing phenolic hydroxyl groups such as phenol, carboxylic acids such as acetic acid, sulfide compounds such as dimethyl sulfide, etc.) with boron trifluoride are particularly preferred. Examples of protic acids and their esters or anhydrides include: silimolybdic acid, silicotungstic acid, phosphomolybdic acid, phosphotungstic acid, perchloric acid, trifluoromethanesulfonic acid, tert-butyl perchlorate, acetyl perchlorate, trimethyloxymethanesulfonic acid, etc. Hexafluorophosphates, heteropoly acids, isopoly acids, and their acid salts are preferred, with particular preference given to silimolybdic acid, silicotungstic acid, phosphomolybdic acid or phosphotungstic acid and their acid salts.

[0040] From the viewpoint of stable continuous polymerization, the preferred addition amount of cationic active catalyst relative to 1 mole of paraformaldehyde is 1 × 10⁻⁶. -9 mole ~ 1×10 -2 Within the range of moles, more preferably within 2 × 10 -9 mole ~ 1×10 -2 Within the range of moles, a further preferred value is 5 × 10⁻⁶. -9 mole ~ 1×10 -3Within the range of moles.

[0041] <Catalyst dilution solvent>

[0042] The aforementioned cationic active catalyst can be used after being diluted to the desired concentration using an inert solvent. This is because when the cationic active catalyst is used directly without dilution, polymerization only begins in the portion in contact with the paraformaldehyde, resulting in increased polymer precipitation. Therefore, by diluting the cationic active catalyst with the aforementioned inert solvent, the polymerization reaction can proceed uniformly, resulting in a higher yield. It should be noted that the "inertness" of the solvent refers to its non-reaction with the paraformaldehyde and comonomers used in the polymerization, and its non-deactivation of the cationic active catalyst.

[0043] As such solvents, compounds without hydroxyl groups are preferred, including: aromatic hydrocarbons such as benzene, toluene, and xylene; aliphatic hydrocarbons such as n-hexane, n-heptane, and cyclohexane; ethers such as diethyl ether, dibutyl ether, ethylene glycol dimethyl ether, diethylene glycol dimethyl ether, triethylene glycol diethyl ether, and 1,4-dioxane; and esters such as methyl acetate, ethyl acetate, isopropyl acetate, and n-butyl acetate. The appropriate choice can be made based on factors such as the solubility of the cationic active catalyst used. These compounds can be used individually or in combination of two or more.

[0044] The preferred amount of diluent added during polymerization is 0.1 × 10⁻⁶ relative to 1 mole of raw material. -3 The range is from 0.2 moles to 0.2 moles, more preferably 0.2 × 10⁻⁶ moles. -3 Within the range of 0.1 moles, further preferably within 0.5 × 10⁻⁶ moles. -3 The amount of diluent added is in the range of 0.05 mol to 0.05 mol. It is preferable to add diluent within this range, considering that it does not hinder the polymerization reaction and can yield polyacetal in a higher yield.

[0045] <Chain transfer agent>

[0046] In the polymerization process of this embodiment, a chain transfer agent may be used, depending on the circumstances, for the purpose of controlling molecular weight.

[0047] For example, the formula RO-(CH2-O) can be used. n-R represents a low molecular weight acetal. (In the formula, R represents any one selected from the group consisting of hydrogen, or branched or straight-chain alkyl groups, and n represents an integer of 1 to 20.) In particular, by using an acetal with a molecular weight of 200 or less, preferably 60 to 170, the molecular weight of the final polyacetal can be well controlled. Examples of low molecular weight acetals represented by the above general formula include, but are not limited to, methyl acetal, methoxymethyl acetal, dimethoxymethyl acetal, trimethoxymethyl acetal, etc. These compounds can be used alone or in combination of two or more.

[0048] From the viewpoint of controlling the molecular weight of the target polyacetal within an appropriate range, the amount of low molecular weight acetal expressed by the above general formula added is preferably 0.1 × 10⁻⁶, relative to the total molar amounts of trioxymethylene, cyclic ether, and cyclic formaldehyde. -5 moles ~ 0.2 × 10 -2 Within the range of moles, more preferably within 0.1 × 10⁻⁶. -5 moles ~ 0.2 × 10 -3 Within the range of moles, a further preferred value is 0.1 × 10⁻⁶. -5 moles ~ 0.1 × 10 -3 Within the range of moles.

[0049] <Deactivation and washing solvent>

[0050] In the manufacturing method of this embodiment, the solvent used in the deactivation and washing liquid is an aliphatic hydrocarbon compound.

[0051] As aliphatic hydrocarbon compounds, including saturated and unsaturated aliphatic hydrocarbon compounds, saturated aliphatic hydrocarbon compounds are preferred from the viewpoint of chemical stability. Examples include: chain-like saturated aliphatic hydrocarbon compounds such as n-pentane, n-hexane, n-heptane, n-decane, and isooctane; and cyclic saturated aliphatic hydrocarbon compounds such as cyclohexane. These compounds can be used individually or in combination of two or more.

[0052] <Alkaline compounds>

[0053] The basic compound used in the manufacturing method of this embodiment is not particularly limited as long as it can deactivate the above-mentioned cationic active catalyst. Examples of basic compounds include: amines such as n-butylamine, diethylamine, triethylamine, and tri-n-butylamine; phosphines such as triphenylphosphine and trioctylphosphine; hydroxides of alkali metals or alkaline earth metals, inorganic salts, and organic acid salts, etc., which can be appropriately selected according to their reactivity with the above-mentioned cationic active catalyst. One of these compounds may be used alone, or two or more may be used in combination.

[0054] The amount of alkaline deactivating agent added is not particularly limited as long as it can fully deactivate the above-mentioned cationic active catalyst. It is preferably a very small amount, which is more preferably in the range of 0.001 mEq to 1.0 mEq relative to 1 kg of crude polyacetal obtained by polymerization reaction, more preferably in the range of 0.005 mEq to 0.75 mEq, and even more preferably in the range of 0.01 mEq to 0.5 mEq.

[0055] When the amount of alkaline deactivator added is excessive, the resulting polyacetal may produce an off-odor or discoloration. When the amount of alkaline deactivator added is insufficient, the deactivation of the above-mentioned cationic active catalyst becomes incomplete, which may cause poor thermal stability. From this perspective, it is not preferred.

[0056] <Deactivation and Washing Solution>

[0057] The deactivation and washing solution used in the manufacturing method of this embodiment is a liquid obtained by dissolving or suspending the above-mentioned alkaline compound in the above-mentioned deactivation and washing solvent. From the viewpoint of deactivation efficiency, the above-mentioned deactivation and washing solution is preferably a solution in which the above-mentioned alkaline compound is dissolved.

[0058] The concentration of the alkaline compound in the above-mentioned deactivation and washing liquid is preferably in the range of 0.005% by weight to 5.0% by weight, and more preferably in the range of 0.01% by weight to 1.0% by weight.

[0059] <Polymerization Process>

[0060] The polymerization step (polymerization) in this embodiment can be carried out by known methods, such as by adding a catalyst solution to the monomer. There are no particular limitations on the shape (structure) of the polymerization reactor used; for example, a polymerization reactor capable of allowing a heat medium to pass through a jacket is preferred, and more specifically, a biaxial paddle or screw-type stirred mixing polymerization reactor is preferred. Furthermore, in this embodiment, polyacetal is obtained through the polymerization step.

[0061] Examples of polymerization methods include supplying monomers, a catalyst solution, and optionally a chain transfer agent to a polymerization reactor and allowing them to polymerize. When supplying the monomers and catalyst solution to the polymerization reactor, it is preferable to use separate pipelines. In particular, paraformaldehyde often polymerizes readily due to cationic active catalysts, so it is preferable not to use the same pipeline as the catalyst solution for supply.

[0062] The polymerization reaction temperature can be any temperature higher than the melting point of the monomer used and lower than the boiling point of the monomer used. For example, when using paraformaldehyde, it is preferably maintained in the range of 63°C to 135°C, more preferably in the range of 70°C to 120°C, and even more preferably in the range of 70°C to 100°C. The residence (reaction) time in the polymerization reactor is preferably 0.1 minutes to 30 minutes, more preferably 0.1 minutes to 25 minutes, and even more preferably 0.1 minutes to 20 minutes. In addition, the residence (reaction) time is preferably set in a way that allows for appropriate sampling of the polymer to achieve the desired yield.

[0063] <Deactivation and Washing Process>

[0064] In the polyacetal manufacturing method of this embodiment, the deactivation and washing step is to contact the crude polyacetal obtained by the polymerization step with the above-mentioned deactivation and washing liquid, thereby performing the deactivation and washing of the cationic active catalyst in the same step.

[0065] There are no particular limitations on the contact method; specifically, it is preferable to contact the crude polyacetal with the deactivation and washing liquid in a slurry state. To form a slurry state, the crude polyacetal discharged from the polymerization reactor can be added to the deactivation and washing liquid, or the deactivation and washing liquid can be added to the crude polyacetal discharged from the polymerization reactor.

[0066] From the viewpoint of ensuring sufficient contact between the crude polyacetal and the deactivating and washing liquid, the slurry concentration (the amount of crude polyacetal in the slurry) is preferably in the range of 5% to 50% by weight, more preferably in the range of 10% to 40% by weight, and even more preferably in the range of 15% to 30% by weight.

[0067] From the viewpoint of ensuring sufficient contact between the crude polyacetal and the deactivating and washing liquid, the contact time is preferably 0.1 minutes or more, more preferably 5 minutes or more, further preferably 10 minutes or more, and even more preferably 20 minutes or more. Furthermore, from the viewpoint of efficiently manufacturing polyacetal, the contact time is preferably 10 hours or less, more preferably 5 hours or less, further preferably 3 hours or less, and even more preferably 2 hours or less.

[0068] Regarding the processing temperature, the operation is carried out at a temperature where deactivation and washing liquid are mainly in liquid form. That is, it is preferable to use a method of continuous stirring at 1 atmosphere within a range of 0°C to 100°C. From the perspective of ease of temperature control, the upper limit of the temperature is preferably 95°C or lower, more preferably 90°C or lower. From the viewpoint of suppressing the crystallization of unreacted paraformaldehyde, preventing its inclusion in the polymer during filtration, and preventing unexpected adverse conditions during the drying process, the lower limit of the temperature is preferably 20°C or higher, more preferably 30°C or higher, further preferably 40°C or higher, and even more preferably 50°C or higher. It should be noted that when the crude polyacetal is in large lumps, it is preferable to crush it after polymerization before processing.

[0069] There are no particular limitations on the method for obtaining polyacetal after deactivation and washing operations, as long as it is a commonly used method. Specifically, the target polyacetal is obtained by filtration using a centrifuge and drying under nitrogen.

[0070] Unreacted cyclic ethers and / or cyclic formaldehydes dissolved in the filtrate after centrifugation can be recovered and reused. Reuse can be achieved by cooling the filtrate, allowing the cyclic ethers and / or cyclic formaldehydes to crystallize and then separating them, or by distilling the cyclic ethers and / or cyclic formaldehydes using a distillation column or similar method.

[0071] In addition, in the polyacetal manufacturing method of this embodiment, in addition to the above-mentioned components, other copolymer components capable of forming block, branched, or cross-linked structures may also be used.

[0072] <End-of-line stabilization treatment>

[0073] The polyacetals obtained in the above polymerization process often have thermally unstable terminal groups. Therefore, it is preferable to perform a stabilization treatment on these unstable terminal groups after the deactivation process. Specifically, stabilization treatments include: end-capping treatment by reacting the unstable terminal groups with an esterifying agent or etherifying agent in the liquid or gas phase, or treatment to remove the unstable terminal portion. These treatments are preferred in terms of suppressing the decomposition of the polyacetal during melt processing.

[0074] The following describes the stabilization process by reacting an organic acid anhydride with the hydroxyl terminus. There are no particular limitations on the organic acid anhydride as long as it reacts with the unstable hydroxyl terminus of the polyacetal. Examples include propionic anhydride, benzoic anhydride, acetic anhydride, succinic anhydride, maleic anhydride, glutaric anhydride, and phthalic anhydride. Among these, propionic anhydride and acetic anhydride, which readily remove the organic acid anhydride after the reaction by high-temperature drying of the polyacetal, are preferred as they are gases that are below the melting point of the polyacetal.

[0075] The reaction between organic acid anhydrides and hydroxyl terminals can be in the liquid or gas phase. For example, the polyacetal obtained in the polymerization process can be dispersed or dissolved in an organic solvent that is inert to both the hydroxyl terminals of the polyacetal and the organic acid anhydride, and then reacted with the organic acid anhydride. Alternatively, for example, the vaporized organic acid anhydride can be brought into contact with the polyacetal obtained in the polymerization process to react with it.

[0076] In the reaction of organic acid anhydrides with hydroxyl terminals, the reaction temperature, reaction time (which can be the contact time), and amount of organic acid anhydride used can be determined arbitrarily.

[0077] There are no particular limitations on the apparatus used in the above reaction; known reactors and dryers can be used, such as stirred tanks, autoclaves, conical belt dryers, rotary dryers, and paddle dryers. Furthermore, the above apparatus can also include any equipment required to carry out the reaction.

[0078] Furthermore, in cases where stabilization is achieved by decomposing and removing the unstable end portions, it is preferable to use a decomposition treatment agent to treat the thermally unstable end portions [-(OCH2)] contained in the obtained polyacetal. n [-OH group] implementation.

[0079] There are no particular limitations on the decomposition agents mentioned above, and examples include: aliphatic amine compounds such as ammonia, triethylamine, and tributylamine; hydroxides of alkali metals or alkaline earth metals such as sodium, potassium, magnesium, calcium, or barium; inorganic weak acid salts of alkali metals or alkaline earth metals such as carbonates, phosphates, silicates, and borates; and organic acid salts of alkali metals or alkaline earth metals such as formates, acetates, stearates, palmitates, propions, and oxalates. Among these, aliphatic amine compounds are preferred as decomposition agents, and triethylamine is even more preferred.

[0080] There are no particular limitations on the method for decomposing and removing the unstable end portion. Examples include heat treatment in the presence of a decomposition agent such as triethylamine, at a temperature above the melting point of the polyacetal (e.g., above 170°C) and below 260°C, while the polyacetal is in a molten state. Examples of apparatus used in the heat treatment include, for example, a single-screw or twin-screw extruder equipped with a venting and pressure-reducing device, preferably a twin-screw extruder.

[0081] In the polyacetal obtained by the manufacturing method of this embodiment, antioxidants, formic acid scavengers, weather (light) stabilizers, release (lubricants), reinforcing agents, conductive agents, thermoplastic resins, thermoplastic elastomers, pigments, plasticizers, peroxide decomposers, alkaline additives, antistatic agents, flame retardants, dyes, fillers, etc., which are commonly used and known additives, may also be added as needed. Furthermore, in the polyacetal obtained in this embodiment, other polymers may also be added within a range that does not impair its physical properties. The proportions of these compounding agents and polymers can be appropriately selected.

[0082] The polyacetal obtained by the manufacturing method of this embodiment, and the composition containing the compounding agent described above as appropriate, can be molded into molded articles or parts for various applications. There are no particular limitations on these applications; it can be used for known applications of polyacetal, such as: gears, cams, sliders, rods, arms, clutches, pulleys, rollers, drums, key rods, keycaps, shafts, bearings, guides, and other components as electrical / electronic or industrial parts. Furthermore, it can be used for automotive parts, and specific examples include: fuel system peripheral parts such as fuel tanks, fuel pump modules, valves, and fuel tank flanges; door peripheral parts such as door locks, door handles, window regulators, and speaker grilles; seat belt peripheral parts such as seat belt slip rings and push-buttons; combination switch components, and switches.

[0083] The methods for implementing the present invention have been described above, but the present invention is not limited to the above-described embodiments. Various modifications can be made to the present invention without departing from its spirit.

[0084] The following examples are for illustrative purposes only and do not limit the scope of this implementation.

[0085] Example

[0086] (Thermogravimetric analysis)

[0087] For the polyacetals obtained in the examples and comparative examples, the weight loss (mass%) was measured using a TG apparatus (TG-DTA2500) manufactured by NETZSCH Co., Ltd. in Japan under a nitrogen atmosphere using the following procedure, and the weight loss from the start to the end of the measurement (from 30°C to 200°C) was calculated.

[0088] Sample amount: approximately 10 mg

[0089] Measurement atmosphere: Nitrogen (500 mL / min)

[0090] Measurement conditions: (1) Increase the temperature from 30℃ to 200℃ at 30℃ / min, (2) Hold at 200℃ for 90 minutes, (3) Calculate the weight loss rate (mass%) from 30℃ to 200℃.

[0091] The crude polyacetal is obtained as follows.

[0092] A catalyst solution was prepared by adding isopropyl acetate to 0.10 g of phosphotungstic acid triaqueous hydrate and adjusting the solution volume to 400 mL.

[0093] A co-rotating twin-shaft paddle-type continuous polymerization reactor (manufactured by Kurimoto Iron Works Co., Ltd., diameter 2B, L / D=14.8) set to 70°C was used as the polymerization reactor. It should be noted that to prevent oxygen contamination, 60L of nitrogen gas was introduced per hour near the feed inlet of the polymerization reactor. Trioxymethylene (moisture concentration: 10ppm), 1,3-dioxane, and methylal were supplied to the polymerization reactor at a rate of 3500g / hour, 42.9g / hour, and 0.60g / hour, respectively. The ratio of phosphotungstic acid to 1 mole of trioxymethylene was 1.0 × 10⁻⁶. -7 The catalyst solution is supplied in a molar manner. Paraformaldehyde and the catalyst solution are supplied via separate pipelines in a manner that prevents them from coming into contact with each other until they reach the impeller section located in the polymerization reactor.

[0094] Thirty minutes after the catalyst solution is started to be supplied, the polymer discharged from the polymerization reactor is put into a plastic tank that has been purged with nitrogen.

[0095] Next, the sample was dried at 30°C and 1.0 kPa for 6 hours using a vacuum sample dryer (manufactured by Ishii Rika Instruments Co., Ltd., VSD-95) to remove unreacted trioxymethylene, and then crude polyacetal was obtained.

[0096] [Example 1]

[0097] 0.5 g of the above-mentioned crude polyacetal with a particle size of 425 μm to 800 μm and 1.5 g of the deactivation and washing solution obtained by dissolving triethylamine in hexane at 0.1% by weight were added to a 6 mL spiral-tube bottle (manufactured by AS ONE) to form a slurry. The spiral-tube bottle was shaken and stirred at 25°C for 2 hours using a shaker (VORTEX3 manufactured by IKA). The solid components were then recovered by filtration and vacuum dried to obtain polyacetal. The evaluation results are shown in Table 1 below.

[0098] [Examples 2 to 7]

[0099] Except for changing the type of alkaline compound, the type of deactivation and washing solvent to the combinations shown in Table 1 below, the experiment was carried out under the same conditions as in Example 1. The evaluation results are shown in Table 1 below.

[0100] [Examples 8 to 10]

[0101] Except for changing the deactivation and washing temperatures to the combinations shown in Table 1 below, the procedure was carried out under the same conditions as in Example 1. The evaluation results are shown in Table 1 below.

[0102] [Comparative Examples 1 to 11]

[0103] Except for changing the type of alkaline compound, the type of deactivation and washing solvent to the combinations shown in Table 2 below, the experiment was carried out under the same conditions as in Example 1. The evaluation results are shown in Table 2 below.

[0104] [Table 1]

[0105]

[0106] [Table 2]

[0107]

[0108] (Table notes)

[0109] *1: Tetrahydrofuran

[0110] *2: N-methyl-2-pyrrolidone

[0111] As shown in Tables 1 and 2, compared to Examples 1-7, Comparative Examples 1-11 exhibited higher thermal weight loss rates and insufficient thermal stability. This result suggests that using polar compounds containing oxygen atoms or aromatic rings as deactivation solvents and washing liquids leads to poor thermal stability.

[0112] The following reasoning is merely speculation: using polar compounds containing oxygen atoms or aromatic rings as deactivation and washing solvents increases the affinity of the deactivation and washing solution for polyacetal, making it easier for the deactivation and washing solution to remain on and inside the polyacetal. It is speculated that as a result, substances from the cationic active catalyst contained in the deactivation and washing solution remain on and inside the polyacetal, promoting its thermal decomposition upon heating.

[0113] It is evident that, in the manufacture of polyacetal, by using a deactivation and washing solution obtained by dissolving or suspending an alkaline compound in an aliphatic hydrocarbon solvent, the deactivation and washing of the cationic active catalyst can be carried out in the same process, thereby improving the thermal stability of polyacetal.

Claims

1. A method for manufacturing polyacetal, characterized in that, The method for manufacturing the polyacetal includes the following steps: A polymerization step, wherein at least one cyclic ether comprising trioxymethylene and / or cyclic formaldehyde is polymerized in the presence of at least one cationic active catalyst; and The deactivation and washing process involves contacting the crude polyacetal obtained from the polymerization process with a deactivation and washing solution, thereby deactivating and washing the cationic active catalyst in the same process. The deactivation and washing solution is obtained by dissolving or suspending an alkaline compound in an aliphatic hydrocarbon solvent.

2. The method for manufacturing polyacetal according to claim 1, wherein, In the deactivation and washing process, the crude polyacetal is brought into contact with the deactivation and washing liquid in a slurry state.

3. The method for manufacturing polyacetal according to claim 1 or 2, wherein, The aliphatic hydrocarbon solvent is at least one selected from n-hexane, cyclohexane, and n-decane.

4. The method for manufacturing polyacetal according to claim 1 or 2, wherein, The basic compound is at least one selected from amine compounds and phosphine compounds.

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