Method for producing polyacetal resin

Abstract

The invention relates to a method for producing polyacetal resin. Provided is a method for producing a polyacetal resin with which it is possible to stably and continuously produce a polyacetal resin over a long period of time while suppressing the generation of a tar-like precipitate caused by a polymerization catalyst. A method for producing a polyacetal resin, characterized by comprising a polymerization step in which a polymerization reaction is carried out using (a) a cyclic ether and / or a cyclic formal containing at least trioxymethylene, (b) boron trifluoride or a boron trifluoride complex, and (c) an organic solvent. And the organic solvent (c) is a compound represented by a predetermined formula (1).

Description

[0001] This application is a divisional application of the Chinese Patent Application No. 202211162407.5, filed on September 23, 2022, entitled "Manufacturing Method of Polyoxymethylene Resin", and priority to which is claimed. TECHNICAL FIELD

[0002] The present application relates to a manufacturing method of polyoxymethylene resin. BACKGROUND

[0003] Polyoxymethylene resin is a resin excellent in mechanical strength such as rigidity and toughness, slidability, and creep, and is widely used in a range centered on automobile parts, electrical / electronic equipment, and various mechanical parts.

[0004] The automobile parts, electrical / electronic equipment, and various mechanical parts using the polyoxymethylene resin are mostly important parts, and it is important to stabilize the quality, that is, to reduce the variation in the quality of the parts obtained by molding. Also, in order to achieve the quality stabilization, long-term stable operation at the time of manufacturing the polyoxymethylene resin is important.

[0005] Conventionally, at the time of polymerization of the polyoxymethylene resin, as a cause of hindering the long-term stable operation, the generation of tar-like precipitates caused by the polymerization catalyst can be exemplified, which leads to unstable polymerization operation.

[0006] As a prior art for suppressing the generation of tar-like precipitates caused by the polymerization catalyst, a technique is known in which the amount of catalyst with respect to the amount of organic compound not forming a complex is specified in a solution containing a complex as a polymerization catalyst (for example, see Patent Literature 1).

[0007] In addition, as another method, a technique is disclosed in Patent Literature 2 in which a pre-mixing step of preliminarily mixing a part of raw material with a polymerization catalyst is provided, and is supplied to a polymerization reactor while being kept in a state in a specific temperature range.

[0008] The above-described techniques are all techniques capable of achieving long-term stable operation of polymerization at the time of manufacturing the polyoxymethylene resin.

[0009] PRIOR ART DOCUMENTS

[0010] PATENT LITERATURE

[0011] Patent Literature 1: Japanese Patent Application Laid-Open No. 10-81722

[0012] Patent Literature 2: Japanese Patent No. 6034572 SUMMARY

[0013] PROBLEMS TO BE SOLVED BY THE INVENTION

[0014] However, even in the technologies disclosed in Patent Literatures 1 and 2, it cannot be said that the generation of tar-like deposits caused by the polymerization catalyst is sufficiently suppressed, and there is room for improvement from the viewpoint of achieving long-term and more stable continuous production of the polyoxymethylene resin.

[0015] Therefore, an object of the present application is to provide a method for producing a polyoxymethylene resin, which can suppress the generation of tar-like deposits caused by a polymerization catalyst and can continuously produce a polyoxymethylene resin stably for a long period of time.

[0016] Means for solving the problem

[0017] In order to solve the above problem, the present inventors conducted intensive studies, and as a result, found that, when a monomer component of a polyoxymethylene resin, a polymerization catalyst, and an organic solvent are supplied to a polymerization reactor and polymerization is performed, by using an organic compound having a specific chemical structure as the above organic solvent, the generation of tar-like deposits caused by the polymerization catalyst can be reduced, and a high-purity polyoxymethylene resin can be continuously produced stably for a long period of time, thereby completing the present application.

[0018] That is, the present application is as follows. [1]

[0020] A method for producing a polyoxymethylene resin, characterized by

[0021] The method for producing a polyoxymethylene resin includes a polymerization step of supplying (a) a cyclic ether and / or a cyclic formal, (b) boron trifluoride or a boron trifluoride complex, and (c) an organic solvent, and performing a polymerization reaction,

[0022] The (a) cyclic ether and / or cyclic formal contains at least trioxane, and

[0023] The (c) organic solvent is a compound represented by the following formula (1),

[0024]

[0025] (In formula (1), R 1 and R 2 each independently is a hydrocarbon group having 1 or 2 carbon atoms, R 3 is a hydrocarbon group having 2 to 5 carbon atoms, and n is 1). [2]

[0027] The method for producing a polyoxymethylene resin according to [1], wherein R 1 and R 2 in formula (1) each are a hydrocarbon group having 1 carbon atom. [3]

[0029] The method for producing a polyacetal resin according to any one of [1] to [3], wherein the (c) organic solvent is 1,2-dimethoxyethane.

[0030] Effects of the Invention

[0031] In the present application, when polymerization is performed using a monomer component, a polymerization catalyst, and an organic solvent of a polyacetal resin, by using a compound having a specific chemical structure as the above organic solvent, the generation of tar-like precipitates caused by the polymerization catalyst can be reduced, and a high-purity polyacetal resin can be continuously produced stably over a long period of time. DETAILED DESCRIPTION

[0032] Hereinafter, a mode for carrying out the present application (hereinafter referred to as "the present embodiment") will be described in detail. Note that the present application is not limited to the following description, and can be carried out with various modifications within the scope of the gist thereof.

[0033] [Method for producing polyacetal resin]

[0034] The method for producing a polyacetal resin of the present embodiment includes a polymerization reaction using (a) a cyclic ether and / or a cyclic formal, (b) boron trifluoride or a boron trifluoride complex, and (c) an organic solvent, and is characterized in that (a) the cyclic ether and / or the cyclic formal contains at least trioxane, and (c) the organic solvent is a prescribed compound. In addition, in the method for producing a polyacetal resin of the present embodiment, other components such as a low-molecular-weight acetal compound can be further used in addition to the above components.

[0035] (Materials)

[0036] The materials used in the method for producing a polyacetal resin of the present embodiment will be described.

[0037] (a) Cyclic ether and / or cyclic formal

[0038] In the present embodiment, (a) a cyclic ether and / or a cyclic acetal is used as the monomer component. The cyclic ether and / or the cyclic acetal refers to a cyclic compound having at least one carbon-oxygen bond or carbon-oxygen-carbon bond, and in addition, the cyclic ether and / or the cyclic acetal includes polymers (trimers, tetramers, etc.) of formaldehyde. As the cyclic ether and / or the cyclic acetal, for example, triformaldehyde, tetraformaldehyde, oxirane, oxetane, oxetane, epichlorohydrin, epibromohydrin, styrene oxide, oxetane, 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. can be exemplified. The (a) cyclic ether and / or the cyclic acetal can be used alone only one kind (i.e., only triformaldehyde), or two or more kinds can be used in combination.

[0039] As described above, the (a) cyclic ether and / or the cyclic acetal used in the present embodiment includes at least triformaldehyde. Note that triformaldehyde is a cyclic trimer of formaldehyde, and is generally obtained by reacting an aqueous formaldehyde solution in the presence of an acidic catalyst. This triformaldehyde sometimes contains water, methanol, formic acid, methyl formate, etc. as impurities that cause chain transfer, and thus it is preferable to purify it by, for example, distillation or the like in advance by removing these impurities.

[0040] In the case where the triformaldehyde is purified as described above, the total amount of the impurities that cause chain transfer is preferably adjusted to 1 x 10 -3 or less, and more preferably to 0.5 x 10 -3 or less, with respect to 1 mole of the triformaldehyde. By reducing the amount of the impurities to the above values, the polymerization reaction rate can be sufficiently improved in practice, and various properties of the polymer produced, such as thermal stability, can be improved.

[0041] As the cyclic ether and / or the cyclic acetal other than triformaldehyde, 1,3-dioxolane and 1,4-butanediol formal are particularly preferable.

[0042] In addition, in the case where triformaldehyde and the cyclic ether and / or the cyclic acetal other than triformaldehyde are used in combination as the (a) cyclic ether and / or the cyclic acetal, the amount of the cyclic ether and / or the cyclic acetal other than triformaldehyde added is preferably in the range of 1 mole% to 20 mole%, more preferably in the range of 1 mole% to 15 mole%, further preferably in the range of 1 mole% to 10 mole%, and further more preferably in the range of 1 mole% to 5 mole%, with respect to 1 mole of the triformaldehyde.

[0043] <(b) boron trifluoride or a boron trifluoride complex>

[0044] In the present embodiment, (b) boron trifluoride or a boron trifluoride complex (hereinafter sometimes referred to as (b) polymerization catalyst) is used. The polyacetal resin described above can be obtained by a cationic polymerization method, and as a cationic polymerization catalyst, a Lewis acid, a protonic acid, an ester or an anhydride thereof, and the like can be generally exemplified, but in the present embodiment, (b) boron trifluoride or a boron trifluoride complex is used as a polymerization catalyst. The (b) polymerization catalyst can be used alone with only one kind, or two or more kinds can be used in combination. Note that the boron trifluoride described above includes a boron trifluoride hydrate. In addition, as the complex described above, a coordination complex of an organic compound containing an oxygen atom or a sulfur atom and boron trifluoride can be exemplified.

[0045] For example, in the case where trioxane is used as the (a) component, the (b) polymerization catalyst is preferably added in an amount of 1 x 10 -9 to 1 x 10 -2 to 1 x 10 -9 to 1 x 10 -2 to 1 x 10 -9 to 1 x 10 -3 to 1 x 10

[0046] <Low molecular weight acetal compound>

[0047] In the present embodiment, a low molecular weight acetal compound can be further used. The low molecular weight acetal compound functions as a chain transfer agent in the polymerization process described later, and the low molecular weight acetal compound is an acetal compound having a molecular weight of 200 or less, preferably 60 to 170. As appropriate examples of the low molecular weight acetal compound, specifically, methy l acetal, methoxy methyl acetal, dimethoxy methyl acetal, and trimethoxy methyl acetal can be exemplified. The low molecular weight acetal compound can be used alone with only one kind, or two or more kinds can be used in combination.

[0048] In the case where trioxane is used as the monomer component and a low molecular weight acetal compound is used, from the viewpoint of controlling the molecular weight of the polyacetal resin to an appropriate range, the low molecular weight acetal compound is preferably added in an amount of 0.1 x 10 -4 to 0.6 x 10 -2 to 0.6 x 10

[0049] <(c) Organic solvent>

[0050] In the present embodiment, (c) an organic solvent is used. As the (c) organic solvent, it is important that it is an ether compound which does not participate in the polymerization reaction or does not produce an adverse effect, and which does not have a hydroxyl group, and specifically, a compound represented by the following formula (1) is used,

[0051]

[0052] (in formula (1), R 1 and R 2 each independently is a hydrocarbon group having 1 or 2 carbon atoms, R 3 is a hydrocarbon group having 2 to 5 carbon atoms, and n is 1). The (c) organic solvent can be used singly with only one kind, or two or more kinds can be used in combination.

[0053] In the present embodiment, by using the compound having the above chemical structure as the (c) organic solvent, the (b) polymerization catalyst (boron trifluoride or a boron trifluoride complex) forms a unique complex with the (c) organic solvent to thereby be stabilized for a long period of time, and the generation of a tar-like precipitate due to deterioration of the polymerization catalyst is suppressed. As a result, the flow rate of the solution containing the polymerization catalyst in the polymerization reaction (catalyst solution) is stabilized, and long-term continuous production can be performed.

[0054] In addition, a part of the organic solvent can be mixed into the polymer and remain. When the organic solvent remains in the polymer product, the organic solvent also remains in the final product, and becomes a cause of odor emission from the product. In this regard, in the present embodiment, by using the above compound as the (c) organic solvent, the amount of the organic solvent remaining in the polymerization reaction product is small, and a high-purity polymer (polyacetal resin) can be obtained.

[0055] n in formula (1) is 1. As the above compound, specifically, 1,2-dimethoxyethane, propylene glycol dimethyl ether, butylene glycol dimethyl ether, pentylene glycol dimethyl ether, ethylene glycol ethyl methyl ether, and ethylene glycol diethyl ether can be cited.

[0056] R 1 and R 2 in formula (1) are preferably saturated hydrocarbon groups, and in the present embodiment, methyl and ethyl can be cited. In addition, R 1 and R 2 in formula (1) are more preferably each a methyl group. That is, R 1 and R 2 in formula (1) are preferably each a methyl group.

[0057] R 3R in the formula (1) is preferably a saturated hydrocarbon group, and examples thereof include ethylene, 1,2-propylene, 1,3-propylene, various kinds of straight-chain or branched butylene, various kinds of straight-chain or branched pentylene, and the like. In addition, R in the formula (1) is more preferably a saturated hydrocarbon group having 2 to 3 carbon atoms. 3 R in the formula (1) is preferably a saturated hydrocarbon group, and examples thereof include ethylene, 1,2-propylene, 1,3-propylene, various kinds of straight-chain or branched butylene, various kinds of straight-chain or branched pentylene, and the like. In addition, R in the formula (1) is more preferably a saturated hydrocarbon group having 2 to 3 carbon atoms.

[0058] As the (c) organic solvent, 1,2-dimethoxyethane, propylene glycol dimethyl ether is more preferable. As the (c) organic solvent, 1,2-dimethoxyethane is most preferable.

[0059] For example, in the case where trioxane is used as the (a) component, the amount of the (c) organic solvent to be added is preferably in the range of 0.1 x 10 -3 mole to 0.2 mole, and more preferably in the range of 0.2 x 10 -3 mole to 0.1 mole, with respect to 1 mole of trioxane. When the amount of the (c) organic solvent to be added is in the above range, the amount of the scale formation in the supply part of the polymerization reactor can be more effectively reduced, and the polyacetal resin can be obtained at a high yield. Note that when the amount of the organic solvent to be added is too much, the overall monomer concentration is relatively reduced, and the reaction can be slow. In addition, when the amount of the organic solvent to be added is too little, the polymerization reaction can be sharply performed, and thus the scale can be generated.

[0060] With respect to the ratio of the (b) polymerization catalyst to the (c) organic solvent, the concentration of the (b) polymerization catalyst in the catalyst solution containing the (b) polymerization catalyst and the (c) organic solvent is preferably in the range of 0.01 mass% to 10.0 mass%. If the concentration of the (b) polymerization catalyst in the catalyst solution is 0.01 mass% or more, the polymerization reaction can be more reliably performed. If the concentration of the (b) polymerization catalyst in the catalyst solution is 10.0 mass% or less, the sharp reaction can be suppressed, and the stable long-time polymerization reaction can be more effectively performed.

[0061] (Procedure)

[0062] Each procedure included in the production method of the polyacetal resin of the present embodiment will be described.

[0063] The production method of the polyoxymethylene resin of the present embodiment includes a polymerization step of performing a polymerization reaction using (a) a cyclic ether and / or a cyclic formal (at least containing a trioxane), (b) a polymerization catalyst (boron trifluoride or a boron trifluoride complex), and (c) an organic solvent (a compound represented by formula (1)), and can optionally appropriately include a deactivation step of deactivating the polymerization catalyst, a drying step, and the like. As described above, in the production method of the present embodiment, the generation of tar-like precipitates caused by the polymerization catalyst can be reduced, and the polyoxymethylene resin can be continuously produced stably for a long period of time. In addition, in the production method of the present embodiment, a polymerization yield equivalent to or higher than that of the past can be achieved.

[0064] <the polymerization step>

[0065] As the polymerization method in the polymerization step, any one of a bulk method, a melt method, and the like can be employed. In addition, the polymerization step can be performed in a polymerization reactor, and the shape (structure) of the polymerization reactor used is not particularly limited. However, as the polymerization reactor, any one of a stirring and mixing type polymerization device of a double shaft paddle type or a screw type, which has a jacket through which a hot medium can pass, is appropriately used.

[0066] In the polymerization step, (b) the polymerization catalyst is preferably dissolved in (c) the organic solvent (diluted with (c) the organic solvent), and thereby a catalyst solution is prepared, and the catalyst solution is appropriately stabilized, and then (a) the cyclic ether and / or the cyclic formal is charged and a polymerization reaction is performed. In this case, the generation of tar-like precipitates caused by the polymerization catalyst can be further reduced, and further stabilization of continuous production can be achieved.

[0067] The temperature of the polymerization reactor (the holding temperature of the reaction system) when the polymerization step is performed is preferably in the range of 63°C to 155°C, more preferably in the range of 70°C to 145°C, and further preferably in the range of 70°C to 140°C. In addition, the residence (reaction) time in the polymerization reactor (in the reaction system) is preferably 0.1 minutes to 30 minutes, more preferably 0.1 minutes to 25 minutes, and further preferably 0.1 minutes to 20 minutes. If the temperature and the residence time are in the above ranges, respectively, there is a tendency that a stable polymerization reaction is continuously performed.

[0068] <the deactivation step>

[0069] The crude polyacetal resin obtained by the above polymerization step can then be subjected to a deactivation step. As a method of deactivating the polymerization catalyst, the following method can be cited: the crude polyacetal resin discharged from the polymerization reactor is put into an aqueous or organic solution of at least one neutralization deactivator selected from the group consisting of amines such as ammonia, triethylamine, tri-n-butylamine, hydroxides of alkali metals or alkaline earth metals, inorganic salts, organic acid salts, and the like, and is continuously stirred in a slurry state at a temperature in the range of room temperature to 100°C or lower for several minutes to several hours. At this time, in the case where the crude polyacetal resin is in the form of a large block, it is preferable to first perform treatment by pulverization after the polymerization step.

[0070] < Drying Step >

[0071] In addition, a drying step of drying the obtained crude polyacetal resin can be performed. Specifically, the crude polyacetal resin after the polymerization step or the deactivation step can be filtered using a centrifugal separator, and dried under nitrogen. Thereby, the target polyacetal resin (polymer) is obtained.

[0072] As a method of bringing the crude polyacetal resin into a dry state in the drying step, there is no particular limitation. For example, the crude polyacetal resin can be heated by using a hot-air type dryer, a vacuum dryer, or a dryer having a stirring function that enables a hot medium to pass therethrough, and the like, so as to be brought into a dry state.

[0073] As the drying temperature, it is sufficient to be at a temperature of 115°C or higher and 165°C or lower, and at a temperature at which the crude polyacetal resin does not melt. That is, it is preferable to be in the range of 115°C to 165°C. It is further preferable to be in the range of 120°C to 155°C.

[0074] Note that, in the method of producing a polyacetal resin according to the present embodiment, in addition to the above components, other copolymerizable monomer components capable of forming a block structure, a branched structure, a crosslinked structure can of course be used in combination.

[0075] Example

[0076] Hereinafter, specific examples and comparative examples are cited to explain the present application in detail, but the present application is not limited to the following examples.

[0077] Note that the various evaluation methods in the examples and comparative examples are as described below.

[0078] < Polymerization Yield >

[0079] The polymerization yield is calculated by dividing the discharge amount per unit time of the crude polyacetal resin discharged from the polymerization reactor by the feed amount per unit time of the entire monomers.

[0080] Note that the polymerization yield is calculated after 1 hour from the start of polymerization.

[0081] <Condition of precipitates in catalyst solution>

[0082] After the end of the continuous operation, the condition of precipitates in the catalyst solution containing the polymerization catalyst and the organic solvent was visually confirmed. Also, the following evaluation was made: if there was no two-layer separation of the solution and precipitates in the visual confirmation, it was indicated that the operation was stable.

[0083] <Condition of deposits on the wall surface of the catalyst solution supply piping>

[0084] After the end of the continuous operation, the polymerization reactor was opened, and the condition of deposits on the wall surface of the catalyst solution supply piping was visually confirmed. Also, the following evaluation was made: the less the deposits such as viscous tar-like substances were, the more stable the operation was indicated to be in the visual confirmation.

[0085] <Amount of residual solvent in polymer>

[0086] In a glass-made closed container, a dry polymer (polyacetal resin) obtained by polymerization was added, and then, 1.5 ml of distilled water (Fuji Photo Film and Optical Manufacturing) was added in an amount of 1 g of the polymer, and the container was closed. The closed container containing the polymer and the distilled water was heated at 90°C for 12 hours, thereby extracting the components of the (c) organic solvent remaining in the polymer. The extract was measured by gas chromatography, and the amount of the residual solvent in the polymer was quantified. Note that the measurement conditions of the gas chromatography were as described below.

[0087] Apparatus: GC-2014 manufactured by Shimadzu Corporation

[0088] Column: TC-1 manufactured by GL science (inner diameter 0.25 mm x film thickness 0.25 μm x length 30 m)

[0089] Carrier gas: nitrogen

[0090] Injection amount: 1 μl

[0091] Gas flow rate: 1.38 ml / min

[0092] Inlet temperature: 250°C

[0093] Column temperature: heated at 5°C / min from 50°C to 300°C

[0094] Detector: FID

[0095] [Example 1]

[0096] A double shaft paddle type continuous polymerization reactor (manufactured by Kibun Tekkojo, diameter 2B, L / D = 14.8) having a jacket through which a hot medium can pass was adjusted to 80°C.

[0097] A solution obtained by mixing a boron trifluoride-ether complex (boron trifluoride complex) as the (b) polymerization catalyst and 1,2-dimethoxyethane as the (c) organic solvent was used as a catalyst solution, and at this time, the concentration of the polymerization catalyst in the catalyst solution was adjusted to 3.0 mass%.

[0098] A mixed solution obtained by continuously mixing trioxane as the (a) component, 1,3-dioxolane (4.2 moles of 1,3-dioxolane per 1 mole of trioxane) as the (a) component, and methylal as the low molecular weight acetal compound in a pipe and the above catalyst solution were continuously supplied to the polymerization reactor using respective pipes and a polymerization reaction was performed, thereby obtaining a crude polyacetal resin. At this time, the flow rates were appropriately adjusted so that the amount of the polymerization catalyst was 2.0 x 10 -5 moles per 1 mole of trioxane.

[0099] The crude polyacetal resin discharged from the polymerization reactor was sampled into a 0.5 mass% aqueous triethylamine solution, then stirred for 1 hour at ordinary temperature, then filtered using a centrifugal separator, and dried under nitrogen at 140°C for 3 hours, thereby obtaining a polyacetal resin.

[0100] The polymerization yield and the amount of the residual solvent in the polymer were calculated for the obtained polyacetal resin using the above method. In addition, the state of the precipitates in the catalyst solution and the state of the deposits on the wall surface of the supply pipe of the catalyst solution were evaluated 240 hours after the start of the polymerization. The evaluation results are shown in Table 1.

[0101] [Example 2]

[0102] The (b) polymerization catalyst of Example 1 was changed to a boron trifluoride-di-n-butyl ether complex (boron trifluoride complex). The other conditions were the same as in Example 1, thereby obtaining a polyacetal resin, and the same evaluation was performed. The evaluation results are shown in Table 1.

[0103] [Examples 3, 5]

[0104] The (c) organic solvent of Example 1 was changed to the (c) organic solvents shown in Table 1. The other conditions were the same as in Example 1, thereby obtaining a polyacetal resin, and the same evaluation was performed. The evaluation results are shown in Table 1.

[0105] [Examples 4, 6]

[0106] The organic solvent in Example 2(c) was changed to the organic solvent in Table 1(c). Other conditions were the same as in Example 2, resulting in a polyacetal resin, which was then evaluated in the same manner. The evaluation results are shown in Table 1.

[0107] [Comparative Example 1]

[0108] The organic solvent in Example 1 was changed to benzene. Other conditions were the same as in Example 1, resulting in a polyacetal resin, which was then evaluated in the same manner. The evaluation results are shown in Table 1.

[0109] [Comparative Example 2]

[0110] The organic solvent in Example 2 was changed to cyclohexane. Other conditions were the same as in Example 2, resulting in a polyacetal resin, which was then evaluated in the same manner. The evaluation results are shown in Table 1.

[0111] [Comparative Example 3]

[0112] As shown in Table 1, the organic solvent in (c) of Example 1 was changed to diethylene glycol dimethyl ether (equivalent to the compound in formula (1) above where n is 2). Other conditions were the same as in Example 1, resulting in a polyacetal resin, which was then evaluated in the same manner. The evaluation results are shown in Table 1.

[0113] [Comparative Example 4]

[0114] As shown in Table 1, the organic solvent in (c) of Example 2 was changed to diethylene glycol dimethyl ether (equivalent to the compound in formula (1) above where n is 2). Other conditions were the same as in Example 2, resulting in a polyacetal resin, which was then evaluated in the same manner. The evaluation results are shown in Table 1.

[0115]

[0116] As shown in Table 1, in Examples 1-6, no precipitates were detected in the catalyst solution even after prolonged operation, and no deposits were found on the walls of the supply pipes, enabling the stable production of polyacetal resin over extended periods. Furthermore, the amount of residual solvent in the polymer was sufficiently low to achieve high purity of the polyacetal resin.

[0117] On the other hand, in Comparative Examples 1 and 2, the catalyst solution was homogeneous and transparent immediately after the polymerization catalyst and organic solvent were mixed. However, after operation, brown precipitates (tar-like substances) or transparent precipitates formed at the bottom of the catalyst solution. Furthermore, brown and viscous tar-like substances adhered to the entire wall of the catalyst solution supply pipe after operation. Therefore, under the conditions of these comparative examples, precipitates were generated after 240 hours of operation. In longer-term industrial-scale operation, the amount of precipitates generated also increased, increasing the likelihood of operation stoppage due to sudden pipe blockage.

[0118] In addition, in Comparative Examples 3 and 4, although no brown and viscous tar-like substance was precipitated, the amount of residual solvent in the polymer increased compared with Examples 1 to 6, resulting in a decrease in purity.

[0119] Industrial practicality

[0120] This invention provides a method for manufacturing polyacetal resin that can stably produce polyacetal resin over a long period of time, and has industrial applicability.

Claims

1. A method for manufacturing polyacetal resin, characterized in that, The method for manufacturing the polyacetal resin comprises the following polymerization steps: supplying (a) cyclic ethers and / or cyclic formaldehyde, (b) boron trifluoride or a boron trifluoride complex and (c) an organic solvent, and carrying out a polymerization reaction. The (a) cyclic ether and / or cyclic formaldehyde contains at least trioxymethylene, and The organic solvent (c) is a compound represented by the following formula (1). In equation (1), R 1 and R 2 Each is independently a hydrocarbon group having 1 or 2 carbon atoms, R 3 It is a hydrocarbon group with 2 to 5 carbon atoms, and n is 1.

2. The method for manufacturing polyacetal resin as described in claim 1, wherein, R in equation (1) 1 and R 2 The number of carbon atoms in each is 1.

3. The method for manufacturing polyacetal resin as described in claim 1, wherein, The organic solvent (c) is one or more selected from the group consisting of 1,2-dimethoxyethane, propylene glycol dimethyl ether, butanediol dimethyl ether, pentanediol dimethyl ether, ethylene glycol ethyl ether methyl ether, and ethylene glycol diethyl ether.

4. The method for manufacturing polyacetal resin according to any one of claims 1 to 3, wherein, The organic solvent in (c) is 1,2-dimethoxyethane.

5. The method for manufacturing polyacetal resin according to any one of claims 1 to 4, wherein, The amount of organic solvent (c) added relative to 1 mole of paraformaldehyde is 0.1 × 10⁻⁶. -3 Within the range of 0.2 moles to 0.2 moles.

6. The method for manufacturing polyacetal resin according to any one of claims 1 to 5, wherein, The amount of organic solvent (c) added relative to 1 mole of paraformaldehyde is 0.2 × 10⁻⁶. -3 The range is from 0.1 moles to 0.1 moles.

7. The method for manufacturing polyacetal resin according to any one of claims 1 to 6, wherein, The concentration of boron trifluoride or boron trifluoride complex in the solution containing (b) boron trifluoride or boron trifluoride complex and (c) organic solvent is 0.01% by mass to 10.0% by mass.

8. The method for manufacturing polyacetal resin according to any one of claims 1 to 7, wherein, The (a) cyclic ether and / or cyclic formaldehyde further comprises one or more of the following: tetraoxymethylene, ethylene oxide, propylene oxide, butane oxide, epichlorohydrin, bromopropylate, 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, and 1,6-hexanediol formaldehyde.

9. The method for manufacturing polyacetal resin as described in claim 8, wherein, The amount of cyclic ethers and / or cyclic formaldehydes other than trioxymethylene added relative to 1 mole of trioxymethylene is in the range of 1 mol% to 20 mol%.

10. The method for manufacturing polyacetal resin as described in claim 8 or 9, wherein, The amount of cyclic ethers and / or cyclic formaldehydes other than trioxymethylene added relative to 1 mole is in the range of 1 mol% to 15 mol%.

11. The method for manufacturing polyacetal resin according to any one of claims 8 to 10, wherein, The amount of cyclic ethers and / or cyclic formaldehydes other than trioxymethylene added relative to 1 mole of trioxymethylene is in the range of 1 mol% to 10 mol%.

12. The method for manufacturing polyacetal resin according to any one of claims 8 to 11, wherein, The amount of cyclic ethers and / or cyclic formaldehydes other than trioxymethylene added relative to 1 mole of trioxymethylene is in the range of 1 mol% to 5 mol%.

13. The method for manufacturing polyacetal resin according to any one of claims 1 to 12, wherein, The boron trifluoride or boron trifluoride complex is selected from one or more of the group consisting of boron trifluoride, boron trifluoride hydrate, boron trifluoride-diethyl ether complex, and boron trifluoride-di-n-butyl ether complex.

14. The method for manufacturing polyacetal resin according to any one of claims 1 to 13, wherein, The amount of (b) boron trifluoride or boron trifluoride complex added relative to 1 mole of paraformaldehyde is 1 × 10⁻⁶. -9 mole ~ 1×10 -2 Within the range of moles.

15. The method for manufacturing polyacetal resin according to any one of claims 1 to 14, wherein, The amount of (b) boron trifluoride or boron trifluoride complex added relative to 1 mole of paraformaldehyde is 2 × 10⁻⁶. -9 mole ~ 1×10 -2 Within the range of moles.

16. The method for manufacturing polyacetal resin according to any one of claims 1 to 15, wherein, The amount of (b) boron trifluoride or boron trifluoride complex added relative to 1 mole of paraformaldehyde is 5 × 10⁻⁶. -9 mole ~ 1×10 -3 Within the range of moles.

17. The method for manufacturing polyacetal resin according to any one of claims 1 to 16, wherein, In the polymerization process, a low molecular weight acetal compound with a molecular weight of less than 200 is further used.

18. The method for manufacturing polyacetal resin as described in claim 17, wherein, The low molecular weight acetal compound is one or more selected from the group consisting of methyl acetal, methoxymethyl acetal, dimethoxymethyl acetal, and trimethoxymethyl acetal.

19. The method for manufacturing polyacetal resin as described in claim 17 or 18, wherein, The amount of the low molecular weight acetal compound added relative to 1 mole of paraformaldehyde is 0.1 × 10⁻⁶. -4 moles ~ 0.6 × 10 -2 Within the range of moles.

20. The method for manufacturing polyacetal resin according to any one of claims 1 to 19, wherein, The polymerization reaction can be carried out using either the bulk polymerization method or the melt polymerization method.

21. The method for manufacturing polyacetal resin according to any one of claims 1 to 20, wherein, The temperature of the polymerization reactor during the polymerization process is in the range of 63°C to 155°C.

22. The method for manufacturing polyacetal resin according to any one of claims 1 to 21, wherein, The temperature of the polymerization reactor during the polymerization process is in the range of 70°C to 145°C.

23. The method for manufacturing polyacetal resin according to any one of claims 1 to 22, wherein, The temperature of the polymerization reactor during the polymerization process is in the range of 70°C to 140°C.

24. The method for manufacturing polyacetal resin according to any one of claims 1 to 23, wherein, The residence time in the polymerization reactor during the polymerization process is 0.1 minutes to 30 minutes.

25. The method for manufacturing polyacetal resin according to any one of claims 1 to 24, wherein, The residence time in the polymerization reactor during the polymerization process is 0.1 minutes to 25 minutes.

26. The method for manufacturing polyacetal resin according to any one of claims 1 to 25, wherein, The residence time in the polymerization reactor during the polymerization process is 0.1 minutes to 20 minutes.

27. The method for manufacturing polyacetal resin according to any one of claims 1 to 26, wherein, In the polymerization step, the boron trifluoride or boron trifluoride complex (b) is dissolved in the organic solvent (c) to prepare a catalyst solution. After the catalyst solution is stabilized, the cyclic ether (a) and / or cyclic formaldehyde are added and a polymerization reaction is carried out.

Images