Method for producing polyacetal

Abstract

To provide a method for producing polyacetal using a cationic active catalyst, the method capable of producing polyacetal having excellent thermal stability by effectively deactivating and washing a cationic active catalyst.SOLUTION: A method for producing polyacetal comprises a polymerization step of polymerizing at least one cyclic ether and / or cyclic formal containing trioxane in the presence of at least one cationic active catalyst, and a deactivation / washing step in which crude polyacetal obtained from the polymerization step is brought into contact with a deactivation / washing solution prepared by dissolving or suspending a basic compound in an aliphatic hydrocarbon solvent, thereby performing deactivation and washing of the cationic active catalyst within the same step.SELECTED DRAWING: None

Description

[Technical Field]

[0001] The present invention relates to a method for producing polyacetal. [Background technology]

[0002] Polyacetal resin is a resin material with excellent rigidity, strength, toughness, sliding properties, and creep resistance, and is used in a wide range of applications, primarily in automotive parts, electrical and electronic devices, and various mechanical components. However, the required properties of these parts have become more sophisticated and diverse in recent years, and there has been an increasing demand for the suppression of formaldehyde, a problem unique to polyacetal resin that is generated through thermal decomposition, UV decomposition, and natural degradation. Improvements using additives are therefore being continuously implemented. However, depending on the usage conditions of polyacetal resin, additive-related problems often arise, and there is a growing demand for formaldehyde suppression that does not rely on additives.

[0003] It is known that polyacetal polymers or copolymers are obtained by polymerizing at least one cyclic ether and / or cyclic formal, including trioxane, in the presence of at least one cationic active catalyst, and various methods have been proposed. Among these, bulk polymerization, which uses substantially no solvent, or quasi-bulk polymerization, which uses 20% or less of a solvent relative to the monomer, are industrially desirable methods. Furthermore, the crude polyacetal polymer or copolymer obtained by polymerization must be deactivated to prevent depolymerization.

[0004] Various methods have been proposed for deactivating catalysts. For example, a method using a metal sulfite salt as a solid deactivator 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] Also proposed is a method of deactivating the enzyme in an aqueous solution containing a basic neutralizing agent such as triethylamine, tributylamine, or calcium hydroxide, or in an organic solvent (see Patent Document 4). [Prior art documents] [Patent documents]

[0006] [Patent Document 1] Japanese Patent Application Publication No. 63-27519 [Patent Document 2] Japanese Patent Application Laid-Open No. 2000-327732 [Patent Document 3] Patent No. 4247586 [Patent Document 4] Japanese Patent Application Publication No. 58-34819 Summary of the Invention [Problem to be solved by the invention]

[0007] However, in the techniques disclosed in Patent Documents 1, 2, and 3, the cationic active catalyst is insufficiently deactivated due to poor dispersion of the deactivator, and the thermal decomposition of polyacetal caused by the residual active cationic active catalyst cannot be suppressed.

[0008] Furthermore, Patent Document 4 only mentions the solvent from the viewpoint of dissolving the basic deactivator, and does not mention washing away substances derived from the cationic active catalyst. In particular, even if a non-volatile cationic active catalyst is deactivated, residual substances derived from the catalyst will accelerate the thermal decomposition of the polyacetal.

[0009] The present invention has been made in view of the above circumstances, and an object of the present invention is to provide a method for producing polyacetal that improves the thermal stability of polyacetal by effectively deactivating and washing a cationic active catalyst. [Means for solving the problem]

[0010] The present inventors have conducted extensive research to solve the above problems, and as a result have found that the above problems can be solved by using a deactivation / washing solution in which a basic compound is dissolved or suspended in an aliphatic hydrocarbon solvent in a method for producing polyacetal, and have thus completed the present invention.

[0011] That is, the present invention is as follows.

[0012] [1] a polymerization step of polymerizing at least one cyclic ether and / or cyclic formal containing trioxane in the presence of at least one cationic active catalyst; a deactivation / washing step in which the crude polyacetal obtained by the polymerization step is brought into contact with a deactivation / washing solution in which a basic compound is dissolved or suspended in an aliphatic hydrocarbon solvent, thereby deactivating and washing the cationic active catalyst in the same step; A method for producing polyacetal, comprising:

[0013] [2] The method for producing a polyacetal according to [1], wherein in the deactivation and washing step, the crude polyacetal is brought into contact with the deactivation and washing liquid in a slurry state.

[0014] [3] The method for producing a polyacetal according to [1] or [2], wherein the aliphatic hydrocarbon solvent is at least one selected from n-hexane, cyclohexane, and n-decane.

[0015] [4] The method for producing a polyacetal according to any one of [1] to [3], wherein the basic compound is at least one selected from an amine compound and a phosphine compound. [Effects of the Invention]

[0016] According to the present invention, in the method for producing polyacetal, the use of a specific deactivation and washing solution enables the deactivation and washing of cationic active catalysts in the same process, making it possible to produce polyacetal with excellent thermal stability. Furthermore, by performing deactivation and washing in the same process, the production process is simplified and production costs can be reduced. Furthermore, the use of an aliphatic hydrocarbon solvent with a small heat of vaporization facilitates drying of the polyacetal after deactivation and washing, making it possible to reduce greenhouse gas (GHG) emissions by shortening the drying process time. DETAILED DESCRIPTION OF THE INVENTION

[0017] Hereinafter, an embodiment of the present invention (hereinafter simply referred to as "the present embodiment") will be described in detail.

[0018] <Polyacetal manufacturing method> The method for producing a polyacetal of the present embodiment includes a polymerization step of polymerizing at least one cyclic ether and / or cyclic formal containing trioxane in the presence of at least one cationic active catalyst; a deactivation / washing step in which the crude polyacetal obtained by the polymerization step is brought into contact with a deactivation / washing solution in which a basic compound is dissolved or suspended in an aliphatic hydrocarbon solvent, thereby deactivating and washing the cationic active catalyst in the same step; Includes.

[0019] <At least one cyclic ether and / or cyclic formal> In this embodiment, at least one cyclic ether and / or cyclic formal is used as a monomer component. The cyclic ether and / or cyclic formal refers to a cyclic compound having at least one carbon-oxygen bond or carbon-oxygen-carbon bond, and also includes formaldehyde polymers (trimers, tetramers, etc.). Examples of cyclic ethers and / or cyclic formals include trioxane, tetraoxane, ethylene oxide, propylene oxide, butylene oxide, epichlorohydrin, epibromohydrin, styrene oxide, oxatane, 1,3-dioxolane, ethylene glycol formal, propylene glycol formal, diethylene glycol formal, triethylene glycol formal, 1,4-butanediol formal, 1,5-pentanediol formal, and 1,6-hexanediol formal. The cyclic ethers and / or cyclic formals may be used alone or in combination of two or more.

[0020] The at least one cyclic ether and / or cyclic formal used in this embodiment must contain trioxane. Trioxane is a cyclic trimer of formaldehyde and is generally obtained by reacting an aqueous formaldehyde solution in the presence of an acidic catalyst. This trioxane may contain impurities that cause chain transfer, such as water, methanol, formic acid, and methyl formate. Therefore, it is preferable to purify the trioxane by distillation or other methods to remove these impurities in advance.

[0021] When purifying trioxane as described above, the total amount of impurities to be chain transferred is 1 × 10 per 1 mol of trioxane. -3 It is preferably 0.5×10 mol or less, and more preferably 0.5×10 -3 By reducing the amount of impurities to the above values, the polymerization reaction rate can be increased sufficiently for practical use, and various properties of the produced polymer, such as thermal stability, can be improved.

[0022] As the cyclic ether and / or cyclic formal other than trioxane, 1,3-dioxolane and 1,4-butanediol formal are particularly preferred.

[0023] When trioxane and a cyclic ether and / or a cyclic formal other than trioxane are used in combination as the at least one cyclic ether and / or cyclic formal, the amount of the cyclic ether and / or the cyclic formal other than trioxane added is preferably in the range of 0.1 to 20 mol%, more preferably 0.1 to 15 mol%, even more preferably 0.1 to 10 mol%, and still more preferably 0.1 to 5 mol%, relative to 1 mol of trioxane.

[0024] <Cation-active catalyst> The cationic active catalyst used in the production method of this embodiment is not particularly limited as long as it is a catalyst that can stably produce polyacetal. Examples of the cationic active catalyst include Lewis acids, protonic acids, and their esters or anhydrides. Examples of Lewis acids include boric acid, boron hydrides (e.g., monoborane, diborane, etc.), boron halides (e.g., boron trifluoride, boron trichloride, boron tribromide, boron triiodide, etc.), trialkylboranes (e.g., trimethylborane, triethylborane, etc.), tin compounds (e.g., tin(II) halides such as tin(II) fluoride, tin(II) chloride, tin(II) bromide, and tin(II) iodide), tin(IV) fluoride, tin(IV) chloride, tin(IV) bromide, and tin(IV) iodide. Tin(IV) halides such as titanium(II) fluoride, titanium(II) chloride, titanium(II) bromide, titanium(II) iodide, titanium(III) halides such as titanium(III) fluoride, titanium(III) chloride, titanium(III) bromide, titanium(III) iodide, titanium(III) halides such as titanium(IV) fluoride, titanium(IV) chloride, titanium(IV) bromide, titanium(IV) iodide, etc.), phosphorus compounds ( Phosphorus halides such as phosphorus trifluoride, phosphorus trichloride, phosphorus tribromide, phosphorus triiodide, phosphorus pentafluoride, phosphorus pentachloride, phosphorus pentabromide, and phosphorus pentaiodide), arsenic compounds (arsenic halides such as arsenic trifluoride, arsenic trichloride, arsenic tribromide, arsenic triiodide, arsenic pentafluoride, arsenic pentachloride, arsenic pentabromide, and arsenic pentaiodide), antimony compounds (antimony trifluoride, antimony trichloride, antimony tribromide, antimony triiodide, antimony pentafluoride, antimony pentachloride, antimony pentabromide, and Examples of suitable antimony halides include antimony trifluoride, boron trifluoride hydrates, and coordination complex compounds of boron trifluoride with organic compounds containing oxygen or sulfur atoms (e.g., ether compounds such as diethyl ether and tetrahydrofuran, alcohols such as methanol, phenolic hydroxyl group-containing compounds such as phenol, carboxylic acids such as acetic acid, sulfide compounds such as dimethyl sulfide, etc.).Examples of protonic acids and their esters or anhydrides include silicomolybdic acid, silicotungstic acid, phosphomolybdic acid, phosphotungstic acid, perchloric acid, trifluoromethanesulfonic acid, perchloric acid tert-butyl ester, acetyl perchlorate, trimethyloxonium hexafluorophosphate, heteropolyacids, isopolyacids, and acid salts thereof, and particularly preferred are silicomolybdic acid, silicotungstic acid, phosphomolybdic acid, and phosphotungstic acid, and acid salts thereof.

[0025] The amount of cationic active catalyst added is 1 × 10 per 1 mol of trioxane from the viewpoint of stable continuous polymerization. -9 ~1×10 -2 mol range is preferred, more preferably 2×10 -9 ~1×10 -2 mol, more preferably in the range of 5×10 -9 ~1×10 -3 The range is mol.

[0026] <Catalyst dilution solvent> The cationic active catalyst can be used by diluting it with an inert solvent to a desired concentration. If the cationic active catalyst is used as is without dilution, polymerization will initiate only in the area that comes into contact with the trioxane, resulting in the precipitation of a polymer. Therefore, by diluting the cationic active catalyst with the inert solvent, the polymerization reaction can be carried out uniformly, resulting in a higher yield. The "inert" solvent means that it does not react with the trioxane and comonomers used in the polymerization and does not deactivate the cationic active catalyst.

[0027] Such a solvent is preferably a compound having no hydroxyl group, and examples thereof include aromatic hydrocarbon compounds such as benzene, toluene, and xylene; aliphatic hydrocarbon compounds such as n-hexane, n-heptane, and cyclohexane; ether compounds such as diethyl ether, dibutyl ether, ethylene glycol dimethyl ether, diethylene glycol dimethyl ether, triethylene glycol diethyl ether, and 1,4-dioxane; and ester compounds such as methyl acetate, ethyl acetate, isopropyl acetate, and n-butyl acetate. These solvents can be appropriately selected depending on the solubility of the cationic active catalyst to be used, etc. These may be used alone or in combination of two or more.

[0028] The amount of diluent added during polymerization was 0.1 × 10 per 1 mol of raw material. -3 The range of 0.2 mol to 1.0 mol is preferred, and 0.2×10 -3 The range is preferably 0.5×10 -3 The amount of diluent solvent added within the above range is preferable in that the polymerization reaction is not inhibited and polyacetal can be obtained in a higher yield.

[0029] <Chain transfer agent> In the polymerization step of this embodiment, a chain transfer agent may be used in some cases for the purpose of controlling the molecular weight.

[0030] For example, the following general formula: RO-(CH2-O) n -R (wherein R represents hydrogen or any one selected from the group consisting of branched or linear alkyl groups, and n represents an integer of 1 or more and 20 or less) can also be used. In particular, by using an acetal having a molecular weight of 200 or less, preferably 60 to 170, the molecular weight of the final polyacetal can be well adjusted. Examples of low-molecular-weight acetals represented by the above general formula include, but are not limited to, methylal, methoxymethylal, dimethoxymethylal, trimethoxymethylal, etc. These may be used alone or in combination of two or more.

[0031] The amount of the low-molecular-weight acetal represented by the above general formula to be added is 0.1 × 10 relative to the total amount of trioxane, cyclic ether, and cyclic formal expressed in moles, from the viewpoint of controlling the molecular weight of the target polyacetal within a suitable range. -5 ~0.2×10 -2 The preferred range is 0.1 × 10 -5 ~0.2×10 -3 The mol range is more preferred, with 0.1 x 10 -5 ~0.1×10 -3 The molar range is more preferred.

[0032] <Deactivation and washing solvent> In the production method of this embodiment, the solvent used in the deactivation / washing solution is an aliphatic hydrocarbon compound.

[0033] Aliphatic hydrocarbon compounds include saturated aliphatic hydrocarbon compounds and unsaturated aliphatic hydrocarbon compounds, and from the viewpoint of chemical stability, saturated aliphatic hydrocarbon compounds are preferred, including chain saturated aliphatic hydrocarbon compounds such as n-pentane, n-hexane, n-heptane, n-decane, isooctane, etc., and cyclic saturated aliphatic hydrocarbon compounds such as cyclohexane, etc. These may be used alone or in combination of two or more.

[0034] <Basic compounds> The basic compound used in the production method of this embodiment is not particularly limited as long as it can deactivate the cationic active catalyst, and examples of the basic compound 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, and can be appropriately selected depending on the reactivity with the cationic active catalyst used, etc. These compounds may be used alone or in combination of two or more.

[0035] The amount of the basic deactivator added is not particularly limited as long as it can sufficiently deactivate the cationic active catalyst, but it is preferably a very small amount, preferably in the range of 0.001 to 1.0 milliequivalents, more preferably in the range of 0.005 to 0.75 milliequivalents, and even more preferably in the range of 0.01 to 0.5 milliequivalents, per kg of crude polyacetal obtained by the polymerization reaction.

[0036] If the amount of basic deactivator added is excessive, the polyacetal obtained at the end may have an unpleasant odor or be discolored, whereas if the amount is too small, the cationic active catalyst may not be sufficiently deactivated, which may cause poor thermal stability.

[0037] <Inactivation and cleaning solution> The deactivation / washing solution used in the production method of this embodiment is a liquid in which the basic compound is dissolved or suspended in the deactivation / washing solvent. From the viewpoint of deactivation efficiency, the deactivation / washing solution is preferably a solution in which the basic compound is dissolved.

[0038] The concentration of the basic compound in the deactivation / washing solution is preferably in the range of 0.005 to 5.0 wt %, more preferably in the range of 0.01 to 1.0 wt %.

[0039] <Polymerization process> The polymerization step (polymerization) in this embodiment can be carried out by a known method, for example, by adding a catalyst solution to a monomer. The shape (structure) of the polymerization reactor used is not particularly limited, but for example, a polymerization reactor that can pass a heat medium through the jacket, more specifically, a twin-screw paddle-type or screw-type stirring and mixing polymerization reactor, can be suitably used. Then, in this embodiment, polyacetal is obtained by the polymerization step.

[0040] The polymerization method may be, for example, a method in which a monomer, a catalyst solution, and an optional chain transfer agent are supplied to a polymerization reactor and polymerized. When supplying the monomer and the catalyst solution to the polymerization reactor, it is preferable to supply them through separate lines. In particular, trioxane is often easily polymerized by a cationic active catalyst, so it is preferable not to supply it through the same line as the catalyst solution.

[0041] The polymerization reaction temperature may be any temperature higher than the melting point and lower than the boiling point of the monomer used. For example, when trioxane is used, the temperature is preferably kept in the range of 63 to 135°C, more preferably in the range of 70 to 120°C, and even more preferably in the range of 70 to 100°C. The residence (reaction) time in the polymerization reactor is preferably 0.1 to 30 minutes, more preferably 0.1 to 25 minutes, and even more preferably 0.1 to 20 minutes. It is also preferable to set the residence (reaction) time so as to obtain the desired yield by appropriately sampling the polymer.

[0042] <Inactivation and cleaning process> In the polyacetal production method of this embodiment, the deactivation and washing step is a step in which the crude polyacetal obtained in the polymerization step is brought into contact with the above-mentioned deactivation and washing solution to deactivate and wash the cationic active catalyst in the same step.

[0043] Although the contact method is not particularly limited, specifically, it is preferable to contact the crude polyacetal in a slurry state with the deactivation / washing liquid. To obtain a slurry state, the crude polyacetal discharged from the polymerization reactor may be introduced into the deactivation / washing liquid, or the deactivation / washing liquid may be introduced into the crude polyacetal discharged from the polymerization reactor.

[0044] The slurry concentration (amount of crude polyacetal in the slurry) is preferably in the range of 5 to 50 wt%, more preferably in the range of 10 to 40 wt%, and even more preferably in the range of 15 to 30 wt%, from the viewpoint of sufficient contact between the crude polyacetal and the deactivation / washing liquid.

[0045] From the viewpoint of sufficient contact between the crude polyacetal and the deactivation / washing solution, the contact time is preferably 0.1 minute or longer, more preferably 5 minutes or longer, even more preferably 10 minutes or longer, and even more preferably 20 minutes or longer. From the viewpoint of efficient polyacetal production, the contact time is preferably 10 hours or shorter, more preferably 5 hours or shorter, even more preferably 3 hours or shorter, and even more preferably 2 hours or shorter.

[0046] The treatment temperature is set at a temperature at which the deactivation / washing solution is primarily present as a liquid. That is, it is preferable to use a method in which continuous stirring is performed in the range of 0 to 100°C under 1 atmosphere. The upper limit of the temperature is preferably 95°C or lower, more preferably 90°C or lower, for ease of temperature control. The lower limit of the temperature is preferably 20°C or higher, more preferably 30°C or higher, even more preferably 40°C or higher, and even more preferably 50°C or higher, from the viewpoint of preventing unreacted trioxane from crystallizing and being entrained in the polymer during the filtration process, resulting in unexpected problems in the drying step. If the crude polyacetal is in the form of large blocks, it is preferable to crush it once after polymerization and then treat it.

[0047] After the deactivation and washing procedures, the polyacetal can be obtained by any commonly used method without any particular limitation. Specifically, the polyacetal is obtained by filtering the mixture with a centrifuge and drying it under nitrogen.

[0048] The filtrate obtained by centrifugation contains dissolved unreacted cyclic ether and / or cyclic formal, which can be recovered and reused. For reuse, the filtrate can be cooled to crystallize the cyclic ether and / or cyclic formal, followed by isolation, or by distillation of the cyclic ether and / or cyclic formal in a distillation column or the like.

[0049] In the method for producing polyacetal according to the present embodiment, it is naturally possible to use, in addition to the above components, other copolymer components capable of forming a block, branched or crosslinked structure.

[0050] <End stabilization treatment> The polyacetal obtained in the above-mentioned polymerization step often has thermally unstable terminal groups. Therefore, it is preferable to subject these unstable terminal groups to a stabilization treatment after the deactivation step. Specific examples of the stabilization treatment include a treatment in which the unstable terminal groups are blocked by reacting them with an esterifying agent or an etherifying agent in a liquid or gas phase, or a treatment in which the unstable terminals are decomposed and removed. These treatments are preferable in terms of suppressing decomposition of the polyacetal during melt processing.

[0051] The step of stabilizing the hydroxyl terminals by reacting an organic acid anhydride with them will be described below. The organic acid anhydride is not particularly limited as long as it reacts with the unstable hydroxyl terminals of the polyacetal. Specific examples include propionic anhydride, benzoic anhydride, acetic anhydride, succinic anhydride, maleic anhydride, glutaric anhydride, and phthalic anhydride. Among these, propionic anhydride and acetic anhydride are preferred as organic acid anhydrides, which become gaseous at or below the melting point of the polyacetal, from the viewpoint of ease of removal by high-temperature drying of the polyacetal after the reaction.

[0052] The reaction between the organic acid anhydride and the hydroxyl terminal may be in a liquid phase or a gas phase. For example, the polyacetal obtained in the polymerization step may be dispersed or dissolved in an organic solvent inert to the hydroxyl terminals of the polyacetal and the organic acid anhydride, and then reacted with the organic acid anhydride. Alternatively, for example, the polyacetal obtained in the polymerization step may be brought into contact with a gasified organic acid anhydride and reacted with the polyacetal.

[0053] In the reaction between the organic acid anhydride and the hydroxyl terminal, the reaction temperature, reaction time (which may be contact time), and amount of the organic acid anhydride used can each be determined arbitrarily. The apparatus used in the reaction is not particularly limited, and known reactors and dryers can be used, such as a stirring tank, autoclave, conical ribbon dryer, rotary dryer, paddle dryer, etc. The apparatus may also be equipped with any device necessary for carrying out the reaction.

[0054] In addition, when stabilization is achieved by decomposition and removal of unstable terminal groups, the thermally unstable terminal groups [-(OCH2) n It is preferable to carry out the decomposition treatment using a decomposition treatment agent.

[0055] The decomposition treatment agent is not particularly limited and includes basic substances such as aliphatic amine compounds such as ammonia, triethylamine, and tributylamine, inorganic weak acid salts of alkali metals or alkaline earth metals such as hydroxides, carbonates, phosphates, silicates, and borates of alkali metals or alkaline earth metals such as sodium, potassium, magnesium, calcium, and barium, and organic acid salts of alkali metals or alkaline earth metals such as formates, acetates, stearates, palmitates, propionates, and oxalates. Among these, aliphatic amine compounds are preferred as the decomposition treatment agent, and triethylamine is more preferred.

[0056] The method for decomposing and removing the unstable terminals is not particularly limited, and examples thereof include a method in which polyacetal is heat-treated in a molten state in the presence of a decomposition agent such as triethylamine at a temperature equal to or higher than the melting point of polyacetal (e.g., 170° C. or higher) and equal to or lower than 260° C. The apparatus used for the heat treatment may be, for example, a single-screw or twin-screw extruder equipped with a vent pressure reduction device, and a twin-screw extruder is preferred.

[0057] The polyacetal obtained by the production method of this embodiment can also be blended with commonly used known additives such as antioxidants, formic acid scavengers, weather (light) stabilizers, mold release (lubricants), reinforcing agents, conductive agents, thermoplastic resins, thermoplastic elastomers, pigments, plasticizers, peroxide decomposers, basic aids, antistatic agents, flame retardants, dyes, and fillers, as desired. Furthermore, the polyacetal obtained by this embodiment can also be blended with other polymers to the extent that the physical properties of the polyacetal are not impaired. The blending ratios of these additives and polymers can be appropriately selected.

[0058] The polyacetal obtained by the production method of this embodiment, and optionally a composition containing the above-described compounding agents, can be molded into various forms and used in a variety of applications as molded articles or parts. Such applications are not particularly limited, but include known applications of polyacetal, such as electrical and electronic components and industrial parts, including gears, cams, sliders, levers, arms, clutches, pulleys, rollers, key stems, key tops, shafts, bearings, and guides. It can also be used as automotive parts, including fuel-related parts such as gasoline tanks, fuel pump modules, valves, and gasoline tank flanges; door-related parts such as door locks, door handles, window regulators, and speaker grills; seatbelt-related parts such as seatbelt slip rings and press buttons; combination switch parts; and switches.

[0059] Although the embodiments of the present invention have been described above, the present invention is not limited to the above-described embodiments and can be modified in various ways without departing from the spirit and scope of the present invention.

[0060] The following examples illustrate the present embodiments without limiting them. [Example]

[0061] (Thermogravimetric measurement) The polyacetals obtained in the examples and comparative examples were measured under a nitrogen atmosphere using a TG apparatus (TG-DTA2500) manufactured by Netsch Japan Co., Ltd., using the following program, and the weight loss rate (mass%) from the start to the end of the measurement (from 30°C to 200°C) was calculated.

[0062] Sample amount: approx. 10 mg Measurement atmosphere: Nitrogen (500 mL / min) Measurement conditions: (1) temperature increase from 30°C to 200°C at 30°C / min, (2) holding at 200°C for 90 minutes, (3) weight loss rate (mass%) from 30°C to 200°C was calculated.

[0063] The crude polyacetal was obtained as follows.

[0064] A catalyst solution was prepared by adding isopropyl acetate to 0.10 g of phosphotungstic acid 30 hydrate to make the solution volume 400 mL.

[0065] The polymerization reactor used was a co-rotating, twin-screw paddle-type continuous polymerization reactor (manufactured by Kurimoto Iron Works Co., Ltd., diameter 2B, L / D=14.8) set at 70°C. To prevent oxygen contamination, 60 L of nitrogen was flowed per hour from the feed port of the polymerization reactor. Trioxane (water concentration: 10 ppm) was fed at 3500 g / hr, 1,3-dioxolane at 42.9 g / hr, and methylal at 0.60 g / hr. Phosphotungstic acid was added at a rate of 1.0 x 10 per mol of trioxane. -7The catalyst solution was fed so that the total amount of trioxane and the catalyst solution was 100 mol. The trioxane and the catalyst solution were fed through separate lines so that they could not come into contact with each other until they reached the paddle section installed in the polymerization reactor.

[0066] Thirty minutes after the start of the catalyst solution feed, the polymer discharged from the polymerization reactor was charged into a polyethylene tank purged with nitrogen.

[0067] Next, the mixture was dried for 6 hours at 30° C. under 1.0 kPa using a vacuum sample dryer (Ishii Rika Kiki Seisakusho, VSD-95) to remove unreacted trioxane, yielding crude polyacetal.

[0068] [Example 1] 0.5 g of the crude polyacetal with particle sizes of 425 to 800 μm and 1.5 g of a deactivation / washing solution prepared by dissolving 0.1 wt% triethylamine in hexane were placed in a 6 mL screw cap vial (manufactured by AS ONE Corporation) to form a slurry, and the screw cap vial was shaken and stirred at 25°C for 2 hours in a shaker (VORTEX3 manufactured by IKA). The solid content was then filtered and collected, and vacuum dried to obtain polyacetal. The evaluation results are shown in Table 1 below.

[0069] [Examples 2 to 7] The experiment was carried out under the same conditions as in Example 1, except that the types of basic compounds and the types of deactivation and washing solvents were changed to the combinations shown in Table 1 below. The evaluation results are shown in Table 1 below.

[0070] [Examples 8 to 10] The conditions were the same as in Example 1, except that the temperature during inactivation and washing was changed to the combination shown in Table 1 below. The evaluation results are shown in Table 1 below.

[0071] [Comparative Examples 1 to 11] The experiment was carried out under the same conditions as in Example 1, except that the types of basic compounds and the types of deactivation and washing solvents were changed to the combinations shown in Table 2 below. The evaluation results are shown in Table 2 below.

[0072] [Table 1]

[0073] [Table 2]

[0074] (Table notes) *1:Tetrahydrofuran *2: N-methyl-2-pyrrolidone

[0075] As can be seen from Tables 1 and 2, the thermal weight loss rate is large and the thermal stability is insufficient in Comparative Examples 1 to 11 compared to Examples 1 to 7. This result suggests that poor thermal stability occurs when a deactivation / washing solution uses a polar compound, such as a structure containing an oxygen atom or an aromatic ring, as a deactivation / washing solvent.

[0076] Although it is only a guess, deactivation and cleaning solutions that use polar compounds, such as those with structures containing oxygen atoms or aromatic rings, as deactivation and cleaning solvents have a high affinity with polyacetal, making the deactivation and cleaning solution more likely to remain on the surface and inside of polyacetal. As a result, it is presumed that substances derived from the cationic active catalyst contained in the deactivation and cleaning solution remain on the surface and inside of polyacetal, accelerating the thermal decomposition of polyacetal when heated.

[0077] In this way, when producing polyacetal, by using a deactivation / washing solution in which a basic compound is dissolved or suspended in an aliphatic hydrocarbon solvent, it is possible to deactivate and wash the cationic active catalyst in the same process, thereby improving the thermal stability of the polyacetal.

Claims

1. a polymerization step of polymerizing at least one cyclic ether and / or cyclic formal, including trioxane, in the presence of at least one cationically active catalyst; a deactivation / washing step in which the crude polyacetal obtained by the polymerization step is brought into contact with a deactivation / washing solution in which a basic compound is dissolved or suspended in an aliphatic hydrocarbon solvent, thereby deactivating and washing the cationic active catalyst in the same step; A method for producing polyacetal, comprising:

2. 2. The method for producing a polyacetal according to claim 1, wherein in the deactivation and washing step, the crude polyacetal is contacted with the deactivation and washing liquid in a slurry state.

3. 3. The method for producing a polyacetal according to claim 1, wherein the aliphatic hydrocarbon solvent is at least one selected from the group consisting of n-hexane, cyclohexane, and n-decane.

4. 3. The method for producing a polyacetal according to claim 1, wherein the basic compound is at least one selected from the group consisting of an amine compound and a phosphine compound.

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