Method for producing polyacetal resin, and method for stabilizing polyacetal resin

Abstract

To provide a method for producing a polyacetal resin having a small outgas discharge amount and heat stability.SOLUTION: A method for producing a polyacetal resin includes: a polymerization process of copolymerizing trioxane, a cyclic ether and / or a cyclic formal in the presence of a cationic active catalyst; a deactivation process of the cationic active catalyst; and a cleaning process of the polyacetal resin, wherein the pH of an aqueous solution used for the cleaning process is 2 to 5.SELECTED DRAWING: None

Description

[Technical Field]

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

[0002] Polyacetal resin is a resin material that has excellent rigidity, strength, toughness, sliding properties, and creep properties, and is used in a wide range of applications, primarily in automotive parts, electrical and electronic equipment, and various mechanical parts. However, in recent years, the required properties of parts using polyacetal resins have become more sophisticated and diverse, and there has been an increasing demand for suppression of outgassing from polyacetal resins.

[0003] Generally, polyacetal resin copolymers are known to be produced by the following process. First, a polyacetal resin is obtained by copolymerizing a cyclic acetal such as trioxane as the main monomer with a cyclic acetal or cyclic ether having adjacent carbon atoms as the comonomer, and further adding a chain transfer agent to adjust the degree of polymerization according to the purpose, using a cationic active catalyst. In this polymerization, if by-products or reaction products of an undeactivated catalyst remain, these may become outgassing components of the polyacetal resin.

[0004] As a method for removing outgassing components from polyacetal resins, for example, Patent Document 1 discloses a method in which a copolymer after copolymerization is melted and heated in a methanol / water / trioxane mixture at 180°C under pressure to remove initiator residues and unstable terminal units.

[0005] Furthermore, Patent Document 2 discloses a method of washing a copolymer after copolymerization with a solvent such as water or methanol to remove residual monomers, and Patent Document 3 discloses a method of deactivating the copolymer by contacting it with an aqueous solution of pH 5 to 7 in a deactivation step after polymerization.

[0006] Furthermore, Patent Document 4 discloses a method for reducing the amount of volatile organic compounds emitted by drying the copolymer after copolymerization and deactivation in an air atmosphere at 140°C for 3 hours using a blower dryer. [Prior art documents] [Patent documents]

[0007] [Patent Document 1] Japanese Patent Application Laid-Open No. 2009-167425 [Patent Document 2] Japanese Patent Application Publication No. 8-73549 [Patent Document 3] Japanese Patent Application Laid-Open No. 2013-224378 [Patent Document 4] International Publication No. 2005 / 044917 Summary of the Invention [Problem to be solved by the invention]

[0008] As described above, when copolymerization is performed using a cationic active catalyst, outgassing components may be generated by side reactions, and although methods for reducing outgassing components are known, such as those disclosed in Patent Documents 1 to 4, the outgassing reduction effect is not necessarily sufficient, and the development of a technology that can reduce outgassing is still desired. Furthermore, when the method is performed under harsh conditions in order to reduce outgassing, there is a risk that the polyacetal resin may be decomposed, and there is a concern that the thermal stability may be reduced.

[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 a polyacetal resin that emits little outgas and has good thermal stability. [Means for solving the problem]

[0010] That is, the present invention is as follows. (1) A method for producing a polyacetal resin, comprising: a polymerization step of copolymerizing trioxane with a cyclic ether and / or a cyclic formal in the presence of a cationic active catalyst; a deactivation step of the cationic active catalyst; and a washing step of the polyacetal resin, A method for producing a stabilized polyacetal resin, wherein the aqueous solution used in the washing step has a pH of 2 to 5. (2) The method for producing a polyacetal resin according to (1), wherein the cationic active catalyst is at least one selected from the group consisting of boron fluoride, boron trifluoride diethyl etherate, and boron trifluoride dibutyl etherate. (3) The method for producing a polyacetal resin according to (1) or (2), wherein the aqueous solution having a pH of 2 to 5 is a dilute acid. (4) A method for stabilizing a polyacetal resin, comprising the step of washing polyacetal resin pellets with an aqueous solution having a pH of 2 to 5. [Effects of the Invention]

[0011] According to the present invention, by using an aqueous solution having a pH of 2 to 5 in the method for producing a polyacetal resin, it is possible to suppress the outgassing components that may potentially be generated and to produce a polyacetal resin with excellent thermal stability. DETAILED DESCRIPTION OF THE INVENTION

[0012] Hereinafter, an embodiment of the present invention (hereinafter referred to as "the present embodiment") will be described in detail. Note that the present invention is not limited to the following description, and various modifications can be made within the scope of the gist of the present invention.

[0013] [Method for producing polyacetal resin] The method for producing a polyacetal resin of the present embodiment includes a polymerization step of copolymerizing trioxane with a cyclic ether and / or a cyclic formal in the presence of at least one cationic active catalyst, a deactivation step of the cationic active catalyst, and a washing step of the polyacetal resin with an aqueous solution having a pH of 2 to 5.

[0014] (material) Hereinafter, the materials used in the method for producing the polyacetal resin of this embodiment will be described.

[0015] (1) Trioxane Trioxane is a cyclic trimer of formaldehyde, with the chemical formula C3H6O3. It is generally obtained by reacting aqueous formalin in the presence of an acid catalyst. This trioxane may contain impurities such as water, methanol, formic acid, and methyl formate that cause chain transfer, so it is preferable to purify the trioxane by removing these impurities using a method such as distillation.

[0016] In this case, 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 numerical values, the polymerization reaction rate can be increased sufficiently for practical use, and a polyacetal resin having excellent thermal stability can be obtained.

[0017] (2) Cyclic ether and / or cyclic formal The cyclic ether and / or cyclic formal are components copolymerizable with trioxane. The cyclic ether and / or cyclic formal are not particularly limited, but specific examples include 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. Among these, 1,3-dioxolane and 1,4-butanediol formal are preferred. These may be used alone or in combination of two or more.

[0018] The amount of the cyclic ether and / or cyclic formal 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 still more preferably 1 to 5 mol %, relative to 1 mol of the trioxane.

[0019] (3) Polymerization catalyst The polymerization catalyst is not particularly limited as long as at least one cationic active catalyst is used, and specific examples include boric acid, tin, titanium, phosphorus, arsenic, and antimonides, which are typified by Lewis acids. Among these, boron trifluoride, boron trifluoride hydrates, or coordination complex compounds of boron trifluoride with an organic compound containing an oxygen atom or a sulfur atom are preferred. As such a cationic active catalyst, for example, at least one selected from the group consisting of boron trifluoride, boron trifluoride diethyl etherate, and boron trifluoride-di-n-butyl etherate is preferred.

[0020] The amount of polymerization catalyst added was 0.1 × 10 per 1 mol of trioxane. -5 ~0.1×10 -3 mol range is preferred, and more preferably 0.3 × 10 -5 ~0.5×10 -4 mol, more preferably in the range of 0.5 × 10 -5 ~0.4×10 -4 When the amount of the polymerization catalyst added is within the above range, the amount of scale generated in the feed section of the polymerization reactor can be reduced, and the polymerization reaction can be carried out stably for a long period of time.

[0021] (4) Organic solvents In the method for producing a polyacetal resin according to this embodiment, an organic solvent can be used in the pre-mixing step described below, in order to mix the cyclic ether and / or the cyclic formal with the cationic active catalyst in advance. Such organic solvents are not particularly limited, but specific examples include aromatic hydrocarbons such as benzene (boiling point 80°C), toluene (boiling point 110.63°C), and xylene (boiling point 144°C); aliphatic hydrocarbons such as n-hexane (boiling point 69°C), n-heptane (boiling point 98°C), and cyclohexane (boiling point 80.74°C); halogenated hydrocarbons such as chloroform (boiling point 61.2°C), dichloromethane (boiling point 40°C), and carbon tetrachloride (boiling point 76.8°C); and ethers such as diethyl ether (boiling point 35°C), diethylene glycol dimethyl ether (boiling point 162°C), and 1,4-dioxane (boiling point 101.1°C). Among these, at least one selected from the group consisting of n-hexane, n-heptane, and cyclohexane is preferred, particularly from the viewpoint of suppressing tar-like deposits in the polymerization reactor. These may be used alone or in combination of two or more.

[0022] The amount of the organic solvent added was 0.1 × 10 -3 The range of 0.2 mol to 1.0 mol is preferred, and 0.2×10 -3 ~0.5×10 -1 mol, more preferably in the range of 0.5 × 10 -3 ~0.3×10 -1 When the amount of the organic solvent added is within the above range, the amount of scale generated in the feed section of the polymerization reactor can be reduced, and the polyacetal resin can be obtained in high yield.

[0023] (Pre-mixing process) The method for producing a polyacetal resin according to the present embodiment may further include a pre-mixing step of pre-mixing the cyclic ether and / or the cyclic formal, the cationic active catalyst, and the organic solvent (hereinafter also referred to as "pre-mixing") to obtain a pre-mixture before the polymerization step described below. This pre-mixing step allows for long-term stable operation.

[0024] In this pre-mixing step, it is preferable to first mix the polymerization catalyst and the organic solvent, and then mix the cyclic ether and / or cyclic formal. In this case, the entire amount of the cyclic ether and / or cyclic formal may be pre-mixed, or a portion of the cyclic ether and / or cyclic formal may be pre-mixed and the remainder may be mixed into trioxane. Among these, from the viewpoint of ease of operation, it is preferable to pre-mix the entire amount.

[0025] By carrying out the pre-mixing in this order, it is possible to prevent a sudden increase in viscosity of the pre-mixture and ensure long-term stable operation. The reasons for this are considered to be as follows. First, the organic solvent does not react with the polymerization catalyst, so the viscosity does not increase. Second, the organic solvent has the effect of suppressing the reaction between the polymerization catalyst and the cyclic ether and / or cyclic formal. As a result, it is believed that a sudden increase in viscosity can be suppressed by first mixing the polymerization catalyst with the organic solvent and then finally mixing the cyclic ether and / or cyclic formal.

[0026] In the pre-mixing step, the temperature at which the cationic active catalyst and the organic solvent are mixed is preferably in the range of 15° C. or higher and lower than the boiling point of the organic solvent, more preferably in the range of 25° C. or higher and lower than the boiling point of the organic solvent, and even more preferably in the range of 35° C. or higher and lower than the boiling point of the organic solvent. Mixing at 15° C. or higher can suppress the generation of tar-like precipitates, and mixing at a temperature lower than the boiling point of the organic solvent can prevent the organic solvent from volatilizing.

[0027] Furthermore, in order to maintain homogeneity of the pre-mixture after the pre-mixing step and during the period from when the pre-mixture is supplied to a polymerization reactor in which a polymerization step described below is carried out, it is preferable to thoroughly mix the raw materials. Examples of the mixing method include a method in which the raw materials are continuously joined and mixed in a pipe, a method in which the raw materials are continuously joined in a pipe and then mixed in a static mixer, and a method in which the raw materials are mixed in a vessel equipped with a stirrer. Among these, the method in which the raw materials are continuously joined in a pipe and then mixed in a static mixer is preferred.

[0028] The temperature at which the pre-mixing step is carried out is preferably in the range of more than 0° C. and less than 50° C. By carrying out pre-mixing within this temperature range, it becomes possible to carry out the pre-mixing at low cost, and a sudden increase in viscosity can be suppressed, enabling long-term stable operation.

[0029] The time for carrying out the pre-mixing step is preferably in the range of 0.01 to 120 minutes, more preferably in the range of 0.01 to 60 minutes. By setting the pre-mixing time within the above range, the raw materials are thoroughly mixed, and a sudden increase in viscosity of the mixture is suppressed, enabling long-term stable operation.

[0030] (Polymerization process) In the method for producing a polyacetal resin according to the present embodiment, the polymerization step is a step of copolymerizing the trioxane with the cyclic ether and / or cyclic formal in the presence of at least one cationic active catalyst, thereby obtaining a crude polyacetal resin before the deactivation step.

[0031] In the polymerization step, the trioxane, the premixture, and the low-molecular-weight acetal compound may be fed into a polymerization reactor, and then the polymerization reaction may be carried out to obtain a polyacetal resin.

[0032] The polymerization method for the crude polyacetal resin can be any of a slurry method, a bulk method, and a melt method, with the bulk method being preferred from the viewpoint of productivity.

[0033] The shape (structure) of the polymerization reactor to be used is not particularly limited, and any of the twin-screw paddle type or screw type stirring and mixing type polymerization apparatuses capable of passing a heat medium through the jacket can be suitably used.

[0034] The temperature of the polymerization reactor in the polymerization step is preferably maintained at 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. If the temperature and residence time of the polymerization reactor are within the above ranges, the polymerization reaction tends to continue stably for a long period of time with a high polymerization yield.

[0035] (Deactivation process) In the polyacetal resin production method of this embodiment, the deactivation step is a step for efficiently deactivating the catalyst or the crude polyacetal resin obtained in the polymerization step, for example, with water alone. Specifically, this step involves adding the polyacetal discharged from a polymerization reactor to an aqueous solution containing at least one deactivator selected from ammonia, amines such as triethylamine and tri-n-butylamine, hydroxides of alkali metals and alkaline earth metals, inorganic salts, and organic acid salts, and deactivating the cationic active catalyst while continuously stirring the mixture at room temperature to 100°C for several minutes to several hours.

[0036] (Stabilization process) The polyacetal obtained in the above-described polymerization step often has thermally unstable terminal groups. Therefore, for example, after the removal / deactivation step, it is preferable to subject these unstable terminal groups to a stabilization treatment. 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.

[0037] When the unstable terminals are decomposed and removed to stabilize the resulting polyacetal, the thermally unstable terminals (-(OCH2) nIt is preferable to decompose and remove the —OH group using a decomposition treatment agent. The decomposition treatment agent is not particularly limited, and examples thereof include 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, the decomposition treatment agent is preferably an aliphatic amine compound, and more preferably triethylamine.

[0038] 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 includes, for example, a single-screw or twin-screw extruder equipped with a vent pressure reducing device, and a twin-screw extruder is preferred.

[0039] (granulation process) The production method of this embodiment may further include a granulation step in which commonly used known additives such as antioxidants, formic acid scavengers, weather (light) stabilizers, release (lubricant) agents, reinforcing agents, conductive agents, thermoplastic resins, thermoplastic elastomers, pigments, plasticizers, peroxide decomposers, basic adjuvants, antistatic agents, flame retardants, dyes, and fillers are blended with the resulting polyacetal as desired. Furthermore, the polyacetal obtained in this embodiment can be blended with other polymers as long as the physical properties are not impaired. The blending ratios of these blending agents and polymers can be appropriately selected. Examples of the apparatus used for granulation include a single-screw or twin-screw extruder equipped with a vent pressure reduction device.

[0040] (Cleaning process) The method for producing a polyacetal resin according to the present embodiment includes a washing step. The washing step can suppress outgassing components that may potentially be generated, and can produce a polyacetal resin with excellent thermal stability. The specific washing method used in the washing step is not particularly limited, but it is preferable to bring the polyacetal resin in a pellet state into contact with an aqueous solution. The washing step is a step in which the polyacetal resin obtained through the granulation step and the like is brought into contact with an aqueous solution of pH 2 to 5 to remove residual monomers that are outgassing components. The timing of the washing step may be immediately after the granulation step described above, after a drying step or the like has been performed after the granulation step, or before the molding step of the polyacetal resin, but the washing step may be performed at any time.

[0041] Here, the aqueous solution having a pH of 2 to 5 is not particularly limited. For example, a dilute acid having a pH of 2 to 5 can be used as the aqueous solution. Among the dilute acids, sulfuric acid, hydrochloric acid, nitric acid, acetic acid, or formic acid diluted with tap water or distilled water is preferably used. This is because the pH of the aqueous solution can be controlled more simply and reliably.

[0042] The contact time between the polyacetal resin and the aqueous solution having a pH of 2 to 5 is preferably 1 minute or longer, more preferably 10 minutes or longer, and even more preferably 30 minutes or longer, from the viewpoint of sufficient contact between the polyacetal resin and the aqueous solution, and is preferably 10 hours or shorter, more preferably 5 hours or shorter, and even more preferably 3 hours or shorter, from the viewpoint of efficient production of the polyacetal resin.

[0043] The treatment temperature during contact is a temperature at which water exists primarily 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. From the viewpoint of ease of temperature control, the upper limit of the temperature is preferably 95°C or lower, more preferably 90°C or lower. From the viewpoint of the efficiency of removing residual monomers, 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.

[0044] After the washing step, the polyacetal resin can be recovered by any commonly used method without any particular limitation. For example, the polyacetal resin can be recovered by filtering with a centrifuge and drying under nitrogen.

[0045] In addition to the above components, the method for producing a polyacetal resin of this embodiment can also use other resin components capable of forming a block, branched, or crosslinked structure.

[0046] [Method for stabilizing polyacetal resin] The method for stabilizing a polyacetal resin according to the present embodiment includes at least a step of washing polyacetal resin pellets with an aqueous solution having a pH of 2-5. As described in the above-mentioned cleaning process, it is possible to suppress potentially generated outgassing components and also to increase the thermal stability of the polyacetal resin.

[0047] The conditions for the step of washing the polyacetal resin pellets are the same as those for the washing step described in the method for producing a polyacetal resin according to the present embodiment.

[0048] Furthermore, in the method for stabilizing a polyacetal resin according to the present embodiment, in addition to the step of washing the polyacetal resin pellets, any other steps can be appropriately carried out depending on the required performance. [Example]

[0049] The present invention will be described in detail below with reference to specific examples and comparative examples, but the present invention is not limited to the following examples.

[0050] <Measurement method> The methods for measuring thermal stability and pH in the examples and comparative examples were as follows. (1) Thermal stability The polyacetal resin (3±0.01 g) obtained in the examples and comparative examples described below was heated and melted at 230°C under a nitrogen atmosphere (50 nl / hr). The form gas generated during a residence time of 2 to 30 minutes was absorbed in a 1 mol / L aqueous sodium sulfite solution, and the sodium hydroxide produced was titrated with 1 / 100 N sulfuric acid and converted into the amount of form gas.

[0051] <Amount of outgassing> Outgassing amount: GC-MS method. 1.5 g of sample was heated to 120°C, and the outgas was injected at 1.5 ml / min. The sample was set in a GC-MS (Agilent Technologies, Agilent 8890) and desorbed. The outgassing was measured using a non-polar column. 1) Total outgassing amount: The total outgassing amount was calculated from the components detected at retention times of 10 to 25 minutes (amount (μg) per 1.5 g of sample; μg / g).

[0052] (2)pH measurement method The pH of the aqueous solution used in the washing process was measured using pH test paper (manufactured by Toyo Roshi Co., Ltd.). Specifically, the prepared aqueous solution was sucked up with a dropper, and a drop was placed on the pH test paper. The pH was measured by checking the color.

[0053] Example 1 A jacketed, twin-shaft paddle-type continuous polymerization reactor (manufactured by Kurimoto, diameter 2B, L / D=14.8 (L: distance from the raw material supply port to the discharge port of the polymerization reactor (m), D: inner diameter of the polymerization reactor (m); the same applies hereinafter)) capable of passing a heat transfer medium was adjusted to 80°C. (Pre-mixing process) 0.11 g / hr of boron trifluoride-di-n-butyl etherate as a polymerization catalyst and 6.5 g / hr of cyclohexane (boiling point: 80.74°C) as an organic solvent were first continuously mixed at a temperature of 28°C, and then 120.9 g / hr of 1,3-dioxolane as a cyclic ether and / or cyclic formal was continuously premixed at a temperature of 25°C for a mixing time of 2 minutes to obtain a premixed liquid. A static mixer was used for this premixing. (Polymerization process) The premixed solution (127.58 g / hr) and a mixture of 3500 g / hr of trioxane and 2.4 g / hr of methylal as a low molecular weight acetal compound were continuously fed simultaneously through separate pipes to a polymerization reactor to polymerize and obtain a crude polyacetal resin. The operation was stable throughout, and no scale was observed in the feed section of the polymerization reactor after 10 hours of operation. The yield was 77%. The crude polyacetal resin produced by this method was designated POM-1. (Deactivation process) The crude polyacetal resin discharged from the polymerization reactor was put into a 0.1% aqueous solution of triethylamine to deactivate the polymerization catalyst, and the deactivated polyacetal copolymer was filtered using a centrifuge. (granulation process) To 100 parts by mass of the obtained polyacetal resin, a 1% by mass aqueous solution of a quaternary ammonium salt ((2-hydroxyethyl)trimethylammonium formate) was added, and the mixture was uniformly mixed and dried at 120°C. The amount of the quaternary ammonium salt added was 20 ppm, calculated as nitrogen atoms, relative to the polyacetal resin. 0.3 parts by mass of 2,2'-methylenebis-(4-methyl-t-butylphenol) as an antioxidant was added to 100 parts by mass of the dried polyacetal resin, and the mixture was fed into a vented twin-screw extruder. The extruder was set at a temperature of 200°C, with a residence time of 5 minutes and a vent vacuum of 20 Torr, after which the volatile components were removed and the extruded strands were extruded from the extruder die and pelletized to obtain polyacetal resin pellets. (Cleaning process) The polyacetal resin pellets obtained in the granulation process were introduced into a 15-liter washing tank equipped with stirring turbine blades, and an aqueous solution of diluted sulfuric acid adjusted to a pH of 2 was added, followed by washing for 1 hour at a controlled temperature of 90°C. After washing, the aqueous solution with a pH of 2 was discharged, and distilled water (pH 7) was added to the washing tank, followed by stirring for 10 minutes at a controlled temperature of 90°C. The water was then drained, and the polyacetal resin was removed, filtered using a centrifuge, and dried.

[0054] [Examples 2 to 4, Comparative Examples 1 to 3] The washing step was carried out in the same manner as in Example 1, except that the pH of the aqueous solution in the washing tank and the washing time were changed to the amounts shown in Table 1 below, to produce a polyacetal resin.

[0055] Comparative Example 4 A polyacetal resin was produced in the same manner as in Example 1, except that washing after the granulation step was not carried out. The evaluation results are shown in Table 1 below.

[0056] [Table 1]

[0057] As shown in Table 1, in Examples 1 to 4, polyacetal resins with low outgassing and excellent thermal stability could be produced. On the other hand, the polyacetal resins produced in Comparative Examples 1 to 4 exhibited high outgassing amounts and / or high thermal stability. [Industrial Applicability]

[0058] INDUSTRIAL APPLICABILITY The present invention has industrial applicability as a method for producing a polyacetal resin that can suppress outgassing components by bringing the polyacetal resin into contact with an aqueous solution having a pH of 2 to 5 and washing the resin.

Claims

1. The method includes a polymerization step of copolymerizing trioxane with a cyclic ether and / or a cyclic formal in the presence of a cationic active catalyst, a deactivation step of the cationic active catalyst, and a washing step of the polyacetal resin, A method for producing a stabilized polyacetal resin, wherein the aqueous solution used in the washing step has a pH of 2 to 5.

2. 2. The method for producing a polyacetal resin according to claim 1, wherein the cationic active catalyst is at least one selected from the group consisting of boron fluoride, boron trifluoride diethyl etherate, and boron trifluoride dibutyl etherate.

3. 3. The method for producing a polyacetal resin according to claim 1, wherein the aqueous solution having a pH of 2 to 5 is a dilute acid.

4. A method for stabilizing a polyacetal resin, comprising the step of washing polyacetal resin pellets with an aqueous solution having a pH of 2 to 5.

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