Method for producing polyacetal

Abstract

To provide a production method of polyacetal capable of producing polyacetal which is controlled to have a high molecular weight and a small polydispersity without deteriorating polymerization activity even when using by diluting boron trifluoride or its ether complex as a polymerization catalyst.SOLUTION: A production method of polyacetal includes a polymerization step of supplying to a polymerization reactor, a catalyst solution containing a polymerization catalyst containing boron trifluoride or the ether complex of the boron trifluoride, and an organic solvent, and at least one kind of cyclic ether or cyclic formal containing trioxane, and mixing them followed by polymerizing. The organic solvent contains aliphatic hydrocarbon and a linear aliphatic ether compound, and an amount of the linear aliphatic ether compound in the catalyst solution is 0.0015 to 0.80 in volume ratio.SELECTED DRAWING: None

Description

[Technical Field]

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

[0002] Polyacetal is a representative engineering plastic widely used in electrical components, electronic components, automotive parts, and various other mechanical parts due to its excellent balance of mechanical properties, chemical resistance, and sliding properties, as well as its ease of processing. In recent years, as the range of applications for polyacetal has expanded, there has been a growing demand for increasingly advanced mechanical properties.

[0003] Cationic polymerization of cyclic ethers such as 1,3,5-trioxane (hereinafter sometimes simply referred to as trioxane) is widely used as a method for producing polyacetals.

[0004] Generally, boron trifluoride ether complexes (e.g., boron trifluoride diethyl ether complex, boron trifluoride dibutyl ether complex) are often used as polymerization catalysts for trioxane, and in such cases, the polymerization catalyst is often used after being diluted with a solvent. For example, Patent Document 1 discloses a method for producing polyacetal using a cyclohexane solution of boron trifluoride diethyl ether complex.

[0005] Furthermore, Patent Document 2 discloses a method for producing polyacetal using a dibutyl ether solution of a boron trifluoride dibutyl ether complex.

[0006] Furthermore, Patent Document 3 discloses a method for producing polyacetal using a boron trifluoride di-n-butyl ether complex in a mixture of cyclohexane and n-hexane, as an example of a method that suppresses scale formation inside a polymerization reactor and enables long-term stable operation. [Prior art documents] [Patent Documents]

[0007] [Patent Document 1] International Patent Publication No. 2022 / 085280 [Patent Document 2] International Patent Publication No. 2020 / 137414 [Patent Document 3] Japanese Patent Publication No. 2017-82099 [Overview of the Initiative] [Problems that the invention aims to solve]

[0008] For example, in order to obtain a high molecular weight polymer with controlled polydispersity in a twin-screw paddle type continuous polymerizer, it is essential to disperse the polymerization catalyst in a highly active state on the monomer (e.g., trioxane) and carry out polymerization as uniformly as possible in the polymerizer.

[0009] To achieve this, it is crucial to design the process so that the polymerization catalyst is diluted in a solvent and dispersed in the monomer, and then polymerization begins upon contact between the polymerization catalyst and the monomer after the catalyst has dispersed within the monomer.

[0010] However, when using highly reactive compounds such as boron trifluoride or its ether complexes as polymerization catalysts, the solvent used for dilution may react with the polymerization catalyst, reducing its activity.

[0011] The present invention has been made in view of the above circumstances, and aims to provide a method for producing polyacetals that, when using boron trifluoride or its ether complex as a polymerization catalyst, does not reduce polymerization activity even when diluted, thereby enabling the production of polyacetals with high molecular weight and controlled polydispersity. [Means for solving the problem]

[0012] The present inventors have conducted extensive studies to solve the above problems. As a result, when using a polymerization catalyst containing boron trifluoride or an ether complex of boron trifluoride and feeding a monomer such as trioxane into a polymerization reactor for polymerization, by using an organic solvent containing an aliphatic hydrocarbon and a linear aliphatic ether compound and containing a specific amount of the aliphatic ether compound as a diluent solvent, it has been found that the above problems can be solved, and the present invention has been completed.

[0013] That is, the present invention is as follows.

[0014] [1] A method for producing polyacetal, comprising: feeding a catalyst solution containing a polymerization catalyst containing boron trifluoride or an ether complex of boron trifluoride and an organic solvent, and at least one cyclic ether / or cyclic formal containing trioxane into a polymerization reactor, mixing them, and performing a polymerization step; wherein the organic solvent contains an aliphatic hydrocarbon and a linear aliphatic ether compound; a method for producing polyacetal, wherein the amount of the linear aliphatic ether compound in the catalyst solution is 0.0015 to 0.80 in terms of volume ratio.

[0015] [2] The method for producing polyacetal according to [1], wherein the standard boiling points of the aliphatic hydrocarbon and the linear aliphatic ether compound are 150 °C or lower.

[0016] [3] The method for producing polyacetal according to [1] or [2], wherein the standard boiling points of the aliphatic hydrocarbon and the linear aliphatic ether compound are 50 °C or higher.

[0017] [4] The method for producing polyacetal according to any one of [1] to [3], wherein the polymerization catalyst contains boron trifluoride diethyl ether complex or boron trifluoride di-n-butyl ether complex as the ether complex of boron trifluoride.

[0018] [5] The method for producing a polyacetal according to any one of [1] to [4], wherein the linear aliphatic ether compound is di-n-propyl ether, di-n-butyl ether or 1,2-dimethoxyethane.

[0019] [6] The method for producing a polyacetal according to any one of [1] to [5], further comprising a mixing step of mixing a polymerization catalyst containing boron trifluoride or a boron trifluoride ether complex and an organic solvent before the polymerization step. [Advantages of the Invention]

[0020] According to the present invention, when boron trifluoride or its ether complex is used as a polymerization catalyst, even if it is used after dilution, a polyacetal having a high molecular weight and a small polydispersity can be produced without reducing the polymerization activity. [Embodiments for Carrying Out the Invention]

[0021] Hereinafter, embodiments for carrying out the present invention (hereinafter simply referred to as "the present embodiment") will be described in detail.

[0022] The method for producing a polyacetal of the present embodiment has a polymerization step of supplying a catalyst solution containing a polymerization catalyst containing boron trifluoride or a boron trifluoride ether complex and an organic solvent and at least one cyclic ether / or cyclic formal containing trioxane to a polymerization reactor, mixing them and performing polymerization. The organic solvent contains an aliphatic hydrocarbon and a linear aliphatic ether compound, and the amount of the linear aliphatic ether compound in the catalyst solution is 0.0015 to 0.80 in terms of volume ratio.

[0023] <At least one cyclic ether and / or cyclic formal> In this embodiment, at least one cyclic ether and / or cyclic formal is used as the monomer component. A 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, oxatan, 1,3-dioxolane, ethylene glycol formal, propylene glycol formal, diethylene glycol formal, triethylene glycol formal, 1,4-butanediol formal, 1,5-pentanediol formal, 1,6-hexanediol formal, etc. A single cyclic ether and / or cyclic formal may be used alone, or two or more may be used in combination.

[0024] The cyclic ether / or cyclic formal used in this embodiment must contain trioxane. Trioxane is a cyclic trimer of formaldehyde and is generally obtained by reacting it with an aqueous solution of formalin in the presence of an acidic catalyst. Since this trioxane may contain chain-transfer impurities such as water, methanol, formic acid, and methyl formate, it is preferable to purify it beforehand to remove these impurities by methods such as distillation.

[0025] When purifying trioxane as described above, the total amount of impurities to be transferred via chain transfer should be 1 × 10⁻⁶ per mole of trioxane. -3 It is preferable to have a value of 0.5 × 10⁻¹⁰ or less, and more preferably 0.5 × 10⁻¹⁰. -3 The amount should be less than or equal to 100 moles. By reducing the amount of impurities to the above values, the polymerization reaction rate can be increased to a practically sufficient level, and various properties such as thermal stability of the resulting polymer can be improved.

[0026] As cyclic ethers and / or cyclic formals other than trioxane, 1,3-dioxolane and 1,4-butanediol formal are particularly preferred.

[0027] Furthermore, when trioxane and a cyclic ether and / or cyclic formal other than trioxane are used in combination as at least one cyclic ether and / or cyclic formal, the amount of the cyclic ether and / or cyclic formal other than trioxane added is preferably in the range of 1 to 20 mol%, more preferably 1 to 15 mol%, even more preferably 1 to 10 mol%, and even more preferably 1 to 5 mol% per mol of trioxane.

[0028] <Catalyst solution> In this embodiment, a catalyst solution containing a polymerization catalyst and an organic solvent is supplied to a polymerization reactor to carry out polymerization.

[0029] (Polymerization catalyst) The polymerization catalyst used in this embodiment includes boron trifluoride or a boron trifluoride ether complex. Among these, boron trifluoride dialkyl ether complex is more preferred, and boron trifluoride diethyl ether complex or boron trifluoride di-n-butyl ether complex is even more preferred. Furthermore, boron trifluoride diethyl ether complex is particularly preferred because it has a large number of moles per unit volume.

[0030] (organic solvent) The organic solvent used in this embodiment contains aliphatic hydrocarbons and linear aliphatic ether compounds. In this embodiment, the amount of linear aliphatic ether compound in the catalyst solution must be 0.0015 to 0.80 by volume.

[0031] In other words, in this embodiment, when the volume of the catalyst solution, which is a mixture of all the necessary compounds such as polymerization catalyst, aliphatic hydrocarbon, and linear aliphatic ether compound, is taken as 1, the amount of linear aliphatic ether compound used must be within the range of 0.0015 to 0.80. In practice, when preparing the catalyst solution as described above, the amount of linear aliphatic ether compound used can be adjusted to fall within the above range. Alternatively, the prepared catalyst solution can be analyzed, for example, by gas chromatography or 1H NMR, and a solution in which the amount of linear aliphatic ether in the catalyst solution falls within the above range can be selected and used.

[0032] Generally, boron trifluoride ether complexes are said to generate protons by reacting with water in the system, and these protons initiate the polymerization of monomers such as trioxane. The reason for keeping the amount of linear aliphatic ether compound within the above range is to maintain high activity of the polymerization catalyst. The reason for this effect is not clear, but it is speculated that if the amount is less than the above range, the equilibrium reaction in which the ether compound dissociates from the boron trifluoride ether complex is too biased towards dissociation, and the activity decreases as boron trifluoride reacts with impurities in the catalyst solution. Conversely, if the amount is more than the above range, it is speculated that the equilibrium reaction is too biased towards the original form, resulting in insufficient proton generation through reaction with water, and thus a decrease in polymerization activity. The same speculation applies to boron trifluoride as well.

[0033] From this viewpoint, the amount of linear aliphatic ether compound is undesirable if it is too much or too little, and is set in the range of 0.0015 to 0.80. From the same viewpoint, it is more preferably 0.003 or more, even more preferably 0.004 or more, even more preferably 0.75 or less, and even more preferably 0.50 or less.

[0034] The aliphatic hydrocarbon used in this embodiment is not particularly limited, but one that is liquid at room temperature and has low viscosity can be selected for ease of handling. Preferably, it is an aliphatic hydrocarbon having 5 to 12 carbon atoms. Such aliphatic hydrocarbon may be a linear aliphatic hydrocarbon, or an aliphatic hydrocarbon having a branched or cyclic structure. Examples of aliphatic hydrocarbons include linear or branched aliphatic hydrocarbons such as pentane, hexane, heptane, octane, nonane, decane, undecane, and dodecane (including structural isomers if they exist); cyclic aliphatic hydrocarbons such as cyclopentane, cyclohexane, cycloheptane, and cyclooctane; and aliphatic hydrocarbons containing both a cyclic structure and a linear or branched structure such as methylcyclopentane, methylcyclohexane, methylcyclooctane, ethylcyclohexane, dimethylcyclohexane, and trimethylcyclohexane (including structural isomers if they exist).

[0035] From the viewpoint of preventing the aliphatic hydrocarbon from remaining in the resulting polyacetal (and removing it if necessary), it is preferable that the aliphatic hydrocarbon has a standard boiling point of 150°C or lower.

[0036] Furthermore, from the viewpoint of handling the catalyst solution, the aliphatic hydrocarbon is preferably one with a standard boiling point of 50°C or higher.

[0037] In this embodiment, preferred aliphatic hydrocarbons include n-hexane, n-heptane, n-octane, isooctane, cyclopentane, cyclohexane, cyclooctane, methylcyclopentane, and methylcyclohexane.

[0038] The linear aliphatic ether compound used in this embodiment is not particularly limited, but it can be selected to be liquid at room temperature and have low viscosity. Preferably, examples include linear aliphatic ether compounds having 4 to 12 carbon atoms and one ether bond (carbon atom-oxygen atom-carbon atom) in the molecule, linear aliphatic ether compounds having 4 to 10 carbon atoms and two ether bonds in the molecule, and linear aliphatic ether compounds having 6 to 10 carbon atoms and three ether bonds in the molecule. When the aliphatic ether compound has two or more ether bonds in the molecule, it is preferable that the number of carbon atoms between the oxygen atoms constituting the ether bond is two or more.

[0039] Examples of such linear aliphatic ether compounds include compounds having one ether linkage in the molecule, such as diethyl ether, di-n-propyl ether, di-n-butyl ether, di-n-pentyl ether, and di-n-hexyl ether; compounds having two ether links in the molecule, such as 1,2-dimethoxyethane, 1,3-dimethoxypropane, 1,4-dimethoxybutane, 1,2-diethoxyethane, and 1,2-dibutoxyethane; and compounds having three ether links in the molecule, such as diethylene glycol dimethyl ether, diethylene glycol diethyl ether, dipropylene glycol dimethyl ether, and dipropylene glycol dimethyl ether. Among these, di-n-propyl ether, di-n-butyl ether, or 1,2-dimethoxyethane are preferred.

[0040] From the viewpoint of preventing the linear aliphatic ether compound from remaining in the resulting polyacetal (and removing it if necessary), it is preferable that the standard boiling point of the linear aliphatic ether compound be 150°C or lower.

[0041] Furthermore, the linear aliphatic ether compound is preferably one with a standard boiling point of 50°C or higher, from the viewpoint of ease of handling the catalyst solution.

[0042] In addition, preferred linear aliphatic ether compounds in such an embodiment include di-n-propyl ether, di-n-butyl ether, 1,2-dimethoxyethane, and the like.

[0043] These organic solvents can be appropriately selected according to the solubility of the polymerization catalyst used and the like.

[0044] <Chain transfer agent> In the polymerization step of this embodiment, a chain transfer agent can be used as needed for the purpose of controlling the molecular weight.

[0045] For example, the following general formula: RO-(CH2-O) n -R (In the formula, R represents any one selected from the group consisting of hydrogen or a branched or linear alkyl group, and n represents an integer of 1 or more and 20 or less.) A low molecular weight acetal represented by the formula 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 finally obtained polyacetal can be favorably adjusted. Examples of the low molecular weight acetal represented by the above general formula include, but are not limited to, methylal, methoxymethylal, dimethoxymethylal, trimethoxymethylal, and the like. These may be used alone or in combination of two or more.

[0046] The addition amount of the low molecular weight acetal represented by the above general formula is 0.1×10 with respect to the total amount in mol of trioxane, cyclic ether, and cyclic formaldehyde from the viewpoint of controlling the molecular weight of the target polyacetal within a suitable range. -5 ~0.2×10 -2 mol, preferably in the range of 0.1×10 -5 ~0.2×10 -3 mol, more preferably in the range of 0.1×10 -5 ~0.1×10 -3 mol is even more preferable.

[0047] <Polymerization process> The polymerization step (polymerization) in this embodiment can be carried out by known methods, for example, by adding a catalyst solution to the monomer. The shape (structure) of the polymerization reactor used is not particularly limited, but for example, a polymerization reactor that can pass a heat transfer medium through the jacket, more specifically a twin-screw paddle type or screw type stirred mixing polymerization reactor can be suitably used. In this embodiment, polyacetal is obtained by the polymerization step.

[0048] Polymerization methods include, for example, supplying monomers, a catalyst solution, and an optional chain transfer agent to a polymerization reactor and carrying out the polymerization. When supplying monomers and catalyst solutions to the polymerization reactor, it is preferable to supply them on separate lines. In particular, since trioxane often polymerizes easily with polymerization catalysts, it is preferable not to supply it on the same line as the catalyst solution.

[0049] The amount of polymerization catalyst added is not particularly limited as long as it is enough to polymerize most of the monomer to produce polyacetal, but preferably the amount of polymerization catalyst per mole of monomer is 1.0 × 10⁻⁶. -5 ~1.0×10 -3 It is preferable to keep the amount within the range of moles. Furthermore, when polyacetal is produced continuously using, for example, a flow reactor, it is preferable to adjust the molar ratio of monomer to polymerization catalyst supplied per unit time to fall within the above range.

[0050] A more preferable upper limit for the amount of polymerization catalyst is 2.0 × 10⁻⁶ per 1 mol of monomer. -4 It is less than or equal to 10⁻⁴ moles, while the lower limit of the more preferable range is 2.0 × 10⁻⁴. -5 The amount must be 100% or more (moles).

[0051] The polymerization reaction temperature should be higher than the melting point of the monomer used and lower than the boiling point. For example, when using trioxane, it is preferable to maintain the temperature 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 by appropriately sampling the polymer to obtain the desired yield.

[0052] <Other processes> In this embodiment, the polymerization catalyst is subjected to polymerization as a catalyst solution containing an organic solvent, as described above. Therefore, in this embodiment, it is preferable to further include a mixing step before the polymerization step in which the polymerization catalyst containing boron trifluoride or a boron trifluoride ether complex is mixed with an organic solvent.

[0053] Furthermore, in this embodiment, after the polymerization step, residual monomers and / or catalyst removal and deactivation (removal and deactivation step) can be performed from the polyacetal obtained in the polymerization step. Conventional methods can be used for removal and deactivation. Specifically, for example, the polyacetal discharged from the polymerization reactor can be added to an aqueous solution containing only water, or at least one deactivator such as ammonia, triethylamine, tri-n-butylamine, alkali metal or alkaline earth metal hydroxides, inorganic salts, or organic acid salts, in order to efficiently deactivate the catalyst, and the monomers and catalyst remaining in the polyacetal can be removed and deactivated while continuously stirring for several minutes to several hours in the range of room temperature to 100°C or below. In addition, from the viewpoint of improving the efficiency of catalyst washing and removal, it is also preferable to pulverize and finely refin the polyacetal, especially if it is in the form of large lumps.

[0054] Polyacetals obtained in the polymerization process described above often have hydroxyl group ends that are prone to thermal decomposition. In such cases, the polyacetals can be stabilized by reacting them with, for example, an organic acid anhydride. Alternatively, in such cases, the polyacetals can be heated before use as a product to pre-decompose easily decomposed components or parts.

[0055] The following describes the process of stabilizing the polyacetal by reacting it with an organic acid anhydride. The organic acid anhydride is not particularly limited as long as it reacts with the unstable hydroxyl group end of the polyacetal. For example, 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 because they become gaseous below the melting point of the polyacetal, from the viewpoint that they can be easily removed by high-temperature drying of the polyacetal after the reaction.

[0056] The reaction between the organic acid anhydride and the hydroxyl terminus may occur in either the liquid or gas phase. For example, the polyacetal obtained in the polymerization step may be dispersed or dissolved in an organic solvent inert to the hydroxyl terminus 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 reacted by contacting it with a gaseous organic acid anhydride.

[0057] In the reaction between organic acid anhydrides and hydroxyl termini, the reaction temperature, reaction time (which may be contact time), and the amount of organic acid anhydride used can all be determined arbitrarily. The apparatus used in the above reaction is not particularly limited, and known reactors and dryers can be used, such as stirred tanks, autoclaves, conical ribbon dryers, rotary dryers, and paddle dryers. Furthermore, the above apparatus may be equipped with any other equipment necessary to carry out the reaction.

[0058] Furthermore, the polyacetals obtained in the polymerization process described above often have thermally unstable end groups. Therefore, it is preferable to stabilize these unstable end groups after, for example, the removal and deactivation process. Specific stabilization treatments include sealing these unstable end groups by reacting them with an esterifying agent or etherifying agent in the liquid or gas phase, or decomposing and removing these unstable end groups. These treatments are preferable in terms of suppressing the decomposition of polyacetals during melt processing.

[0059] When unstable end portions are decomposed and removed to stabilize the polyacetal, thermally unstable end portions [-(OCH2)] may be present in the resulting polyacetal. n It is preferable to decompose and remove the -OH group using a decomposition agent. The decomposition agent is not particularly limited and can be an aliphatic amine compound such as ammonia, triethylamine, or tributylamine; an inorganic weak acid 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, or barium; or an organic acid of alkali metals or alkaline earth metals such as formate, acetate, stearate, palmitate, propionate, and oxalate. Among these, aliphatic amine compounds are preferred as decomposition agents, and triethylamine is more preferred.

[0060] There are no particular limitations on the method for decomposing and removing the unstable end portion. For example, one method is to heat-treat the polyacetal in a molten state at a temperature above the melting point of the polyacetal (e.g., 170°C or higher) and 260°C or lower, in the presence of a decomposition agent such as triethylamine. Examples of equipment used for the heat treatment include a single-screw or twin-screw extruder equipped with a vent vacuum device, with a twin-screw extruder being preferred.

[0061] The polyacetal obtained by the manufacturing method of this embodiment may be blended with commonly used known additives such as antioxidants, formic acid scavengers, weather (light) stabilizers, mold release (lubricant) agents, reinforcing agents, conductive agents, thermoplastic resins, thermoplastic elastomers, pigments, plasticizers, peroxide decomposing agents, basicity auxiliary agents, antistatic agents, flame retardants, dyes, fillers, etc., as desired. Furthermore, other polymers may be blended with the polyacetal obtained in this embodiment, as long as their physical properties are not impaired. The blending ratios of these additives and polymers can be selected as appropriate.

[0062] The polyacetal obtained by the manufacturing method of this embodiment, and optionally the compositions containing the above-mentioned compounding agents, can be used for various purposes as molded products or parts after undergoing various molding processes. Such uses are not particularly limited, but can be used for known uses of polyacetal, and examples include parts such as gears, cams, sliders, levers, arms, clutches, pulleys, rollers, rollers, key stems, key tops, shafts, bearings, and guides as electrical and electronic components and industrial parts. It can also be used as automotive parts, and specific examples include 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 grilles; seat belt-related parts such as seat belt slip rings and press buttons; combination switch parts and switches.

[0063] Although embodiments for carrying out the present invention have been described above, the present invention is not limited to the above embodiments. The present invention can be modified in various ways without departing from its essence. [Examples]

[0064] The following examples illustrate this embodiment without limiting it.

[0065] The analytical and evaluation methods used in the examples and comparative examples are as follows.

[0066] <Evaluation of polymerization activity> In the examples and comparative examples (Examples 1-7, Comparative Examples 1-4), the time it took for the entire solution to become cloudy after adding the catalyst solution to trioxane as a monomer was measured. The phenomenon of the entire solution becoming cloudy is caused by the formation of polyacetals in the system and the precipitation of insoluble polyacetals. A shorter time indicates higher polymerization activity.

[0067] <Measurement of peak top molecular weight and polydispersity (Mw / Mn)> For the polyacetals (dried polyacetal powder) obtained in the examples and comparative examples (Examples 8, 9, Comparative Example 5), the peak top molecular weight and polydispersity (Mw / Mn) were measured using a GPC instrument (HPLC8320) manufactured by Tosoh Corporation. 1,1,1,3,3,3-hexafluoropropanol (HFIP), prepared by dissolving 0.4% by weight of sodium trifluoroacetate in the eluent, was used. Polyacetal was dissolved in the above eluent to prepare a sample solution with a concentration of 0.5 mg / mL. One Shodex K-G4A column and one Shodex KF-606M column were connected in series and used with solvent replacement via HFIP. A differential refractive index (RI) detector was used, with an eluent flow rate of 0.3 mL / min, a column temperature of 40°C, and a sample solution injection volume of 60 μL.

[0068] Furthermore, the conversion from elution time obtained by GPC measurement to molecular weight was performed using a calibration curve prepared in advance using standard polymethyl methacrylate. The standard polymethyl methacrylate used was the following product number from Agilent. Part numbers: PL2022-3001, PL2022-6001, PL2023-1001, PL2023-4001, PL2023-8001, PL2024-1001. 60 μL of solutions, each containing 0.5 mg / mL of the above-mentioned eluent, were injected, and a calibration curve was created. The calibration curve was approximated using a cubic equation obtained by the least squares method. Furthermore, the baseline was defined as a straight line connecting the points with elution times of 10 minutes and 18 minutes. However, if the difference between the two points was 3% or more of the height of the maximum peak on the GPC curve, the measurement was repeated until it was less than 3%. The molecular weight corresponding to the peak of the largest peak mentioned above was defined as the peak-top molecular weight.

[0069] [Example 1] A catalyst solution was prepared by mixing 0.05 mL of boron trifluoride diethyl ether complex with 0.05 mL of di-n-butyl ether (hereinafter simply referred to as dibutyl ether), and then adding n-hexane to make a total solution volume of 25 mL. The amount of linear aliphatic ether compound (in this case, dibutyl ether) in the catalyst solution was calculated to be 0.002 by volume.

[0070] 10.8 g of trioxane containing 11 ppm of water was placed in a test tube and heated to 70°C, and the amount of boron trifluoride diethyl ether complex was 2.0 × 10⁶ per mole of trioxane. -5 The catalyst solution was added to a total volume of moles, and the trioxane was polymerized. Ten minutes after adding the catalyst solution, a 10-fold weight-ratio aqueous triethylamine solution (concentration 0.1% by weight) was added to the trioxane, the solid was filtered and recovered, and the mixture was vacuum-dried to obtain polyacetal.

[0071] [Examples 2-4, Comparative Examples 3,4] Polyacetal was obtained using the same method as in Example 1, except that the amount of dibutyl ether added (charging amount) was changed as shown in Table 1.

[0072] [Examples 5, 6] Polyacetal was obtained by following the same procedure as in Example 1, except that the amount of dibutyl ether added was changed as shown in Table 1, and cyclohexane was used instead of n-hexane.

[0073] [Example 7] Polyacetal was obtained by the same procedure as in Example 5, except that 1,2-dimethoxyethane was used in the amount shown in Table 1 instead of dibutyl ether.

[0074] [Comparative Example 1] The same procedure as in Example 1 was followed, except that dibutyl ether was not used.

[0075] [Comparative Example 2] The same procedure as in Example 1 was followed, except that n-hexane was not used, and dibutyl ether was used in the amounts shown in Table 1.

[0076] Table 1 shows the time it takes for the entire solution to become cloudy after adding the catalyst solution to the trioxane in the above example.

[0077] [Table 1]

[0078] As can be seen from Table 1, although the concentration of polymerization catalyst (boron trifluoride diethyl ether complex) in the catalyst solution was the same in Examples 1-7 and Comparative Examples 1-4, the time it took for the entire solution to become cloudy after adding the catalyst solution to trioxane tended to be longer in Comparative Examples 1-4 compared to Examples 1-7. Therefore, it can be said that Examples 1-7 have higher polymerization activity than Comparative Examples 1-4.

[0079] [Example 8] A catalyst solution was prepared by mixing 0.50 mL of boron trifluoride diethyl ether complex with 2.00 mL of dibutyl ether, and then adding cyclohexane to make a total solution volume of 250 mL.

[0080] A twin-screw paddle-type continuous polymerization reactor (manufactured by Kurimoto Iron Works Co., Ltd., diameter 2B, L / D = 14.8) rotating in the same direction was used as the polymerization reactor, set to 80°C. To prevent oxygen contamination, 60 L of nitrogen per hour was flowed from near the feed port of the polymerization reactor. Trioxane (water concentration: 10 ppm) was fed into this polymerization reactor at a rate of 3500 g / hr, 1,3-dioxolane at 120 g / h, and methylal at 0.60 g / h. The amount of boron trifluoride diethyl ether complex was 2.0 × 10⁶ per mole of trioxane. -5 The catalyst solution was fed in a quantity of moles. The trioxane and the catalyst solution were supplied via separate lines so that they could not come into contact with each other until they reached the paddle section installed in the polymerization reactor.

[0081] Subsequently, the polyacetal discharged from the polymerization reactor was added to water and stirred at room temperature for 1 hour to wash away the polymerization catalyst. Next, the polyacetal from which the polymerization catalyst had been washed away was filtered using a centrifuge, and then 1 part by mass of an aqueous solution containing triethylamine was added to 100 parts by mass of polyacetal (polyacetal copolymer), mixed uniformly, and dried at 120°C for 3 hours to obtain dried polyacetal powder.

[0082] [Example 9] A polyacetal dry powder was obtained by the same procedure as in Example 8, except that 1,2-dimethoxyethane was used instead of dibutyl ether.

[0083] [Comparative Example 5] Polyacetal dry powder was obtained by following the same procedure as in Example 8, except that cyclohexane was not used.

[0084] Table 2 shows the results of GPC measurements performed on the above example.

[0085] [Table 2]

[0086] As can be seen from Table 2, the molecular weight of Comparative Example 5 was slightly lower than that of Examples 8 and 9. Furthermore, it was found that Comparative Example 5 was undesirable because the polydispersity (Mw / Mn) was high and the amount of low molecular weight components increased. Considering that Comparative Example 5 used the same catalyst setup as Comparative Example 2, the above results are thought to be due to uneven polymerization initiation caused by a decrease in polymerization activity. Therefore, it is important to prepare a catalyst solution that does not reduce polymerization activity.

Claims

1. A method for producing polyacetal, The polymerization process involves supplying a catalyst solution containing a polymerization catalyst including boron trifluoride or a boron trifluoride ether complex and an organic solvent, along with at least one cyclic ether containing trioxane / or a cyclic formal, to a polymerization reactor, mixing them, and carrying out polymerization. The organic solvent comprises an aliphatic hydrocarbon and a linear aliphatic ether compound. A method for producing polyacetal, wherein the amount of the linear aliphatic ether compound in the catalyst solution is 0.0015 to 0.80 by volume.

2. A method for producing polyacetal according to claim 1, wherein the standard boiling points of the aliphatic hydrocarbon and the linear aliphatic ether compound are 150°C or lower.

3. A method for producing polyacetal according to claim 1 or claim 2, wherein the standard boiling points of the aliphatic hydrocarbon and the linear aliphatic ether compound are 50°C or higher.

4. A method for producing a polyacetal according to claim 1 or claim 2, wherein the polymerization catalyst comprises, as the ether complex of boron trifluoride, a boron trifluoride diethyl ether complex or a boron trifluoride di-n-butyl ether complex.

5. The method for producing a polyacetal according to claim 1 or claim 2, wherein the linear aliphatic ether compound is di-n-propyl ether, di-n-butyl ether, or 1,2-dimethoxyethane.

6. The method for producing a polyacetal according to claim 1 or claim 2, wherein the aliphatic hydrocarbon is n-hexane, n-heptane, n-octane, isooctane, cyclopentane, cyclohexane, cyclooctane, methylcyclopentane, or methylcyclohexane.

7. A method for producing a polyacetal according to claim 1 or 2, further comprising a mixing step of mixing a polymerization catalyst containing boron trifluoride or a boron trifluoride ether complex with an organic solvent before the polymerization step.

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