Method for producing polyacetal copolymer

Abstract

To provide a production method which not only can reduce the amount of generation of formaldehyde but also can stably produce a polyacetal copolymer capable of producing a molded product having excellent fluidity during molding and excellent appearance even in mass production.SOLUTION: There is provided a method for producing a polyacetal copolymer by copolymerizing trioxane and a comonomer copolymerizable with the trioxane in the presence of a polymerization catalyst. The polymerization catalyst is a heteropolyacid (A) and a heteropoly acid salt (B) and the heteropoly acid (A) and the heteropoly acid salt (B) are mixed and used.SELECTED DRAWING: None

Description

[Technical field]

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

[0002] A method for producing a polyacetal copolymer is known in which a main monomer (trioxane) and a comonomer copolymerizable with the main monomer are cationic polymerized in the presence of a cationic polymerization catalyst. Lewis acids such as boron trifluoride, tin tetrachloride, titanium tetrachloride, phosphorus pentafluoride, phosphorus pentachloride, and antimony pentafluoride, as well as complex compounds or salts thereof, are widely and generally used as the cationic polymerization catalyst.

[0003] However, a polymerization catalyst such as boron trifluoride needs to be added in a relatively large amount (for example, 40 ppm or more relative to the total monomers) during polymerization. Therefore, in the production process, there is a problem that it is difficult to sufficiently deactivate the catalyst remaining in the polyacetal copolymer after polymerization. Even if the catalyst can be deactivated, there are cases where problems such as accelerated decomposition of the copolymer occur due to the catalyst-derived substances remaining in the copolymer. Furthermore, since the catalyst deactivation step is performed in a large amount of aqueous solution (treatment liquid) containing a basic compound such as triethylamine, further complicated steps are required after the step, such as a step of separating the copolymer from the treatment liquid and drying it, and a step of recovering unreacted monomer dissolved in the treatment liquid.

[0004] In recent years, there has been a demand for high-quality polyacetal copolymers that have excellent thermal stability and emit very little formaldehyde. To this end, studies have been conducted on efficient catalyst deactivation and stabilization of the crude polyacetal copolymers by decomposition of unstable terminals after catalyst deactivation.

[0005] For example, Patent Document 1 describes a method for producing a polyacetal copolymer, which includes a step of copolymerizing using a specific heteropolyacid as a polymerization catalyst, and a step of adding a specific salt or a hydrate thereof to the obtained reaction product and melt-kneading the product to deactivate the polymerization catalyst. Patent Document 2 describes that the use of a polymerization catalyst in which a specific heteropolyacid and a specific heteropolyacid metal salt are mixed can provide stable polymerization in industrial production. [Prior art documents] [Patent documents]

[0006] [Patent Document 1] JP 2014-105278 A [Patent Document 2] JP 2019-178187 A Summary of the Invention [Problem to be solved by the invention]

[0007] According to Patent Document 1, by using a specific highly active heteropolyacid as a polymerization catalyst and melt-kneading it together with a deactivator, polymerization becomes possible with a small amount of catalyst, complicated processes can be eliminated, the amount of formaldehyde generated is extremely small, and a high-quality polyacetal copolymer can be obtained. However, when the production amount of polyacetal resin was increased with a small amount of polymerization catalyst, a decrease in the polymerization yield of the polyacetal copolymer and variations in the quality of the polyacetal resin were observed.

[0008] According to Patent Document 2, the use of a polymerization catalyst containing a mixture of a specific heteropolyacid and a specific metal salt of a heteropolyacid stabilizes the polymerization reaction and improves the resin quality by reducing the amount of formaldehyde generated. However, molded products made of the obtained polyacetal resin may have poor appearance, and an improvement in this regard has been desired.

[0009] The present invention has been made in consideration of the above-mentioned points, and has an object to provide a method for stably producing, even in mass production, a polyacetal copolymer that not only reduces the amount of formaldehyde generated but also has excellent flowability during molding and can be used to produce molded articles with excellent appearance. [Means for solving the problem]

[0010] As a result of extensive investigations, the present inventors have completed the inventions relating to the following items [1] to [6].

[0011] [1] A method for producing a polyacetal copolymer, comprising copolymerizing trioxane and a comonomer copolymerizable with said trioxane in the presence of a polymerization catalyst, comprising: The polymerization catalyst is a heteropolyacid (A) represented by the following general formula (1) and a heteropolyacid salt (B) represented by the following general formula (2), The heteropolyacid (A) and the heteropolyacid salt (B) are used in combination. A method for producing a polyacetal copolymer.

[0012]

number

[0013] (In formulas (1) and (2), L is an alkali metal element, and M 1 and N 1 are each independently a central element of P or Si, and M 2 and M. 3 are coordination elements of W, Mo or V which may be the same or different from each other, and N 2 and N 3 are coordination elements of W, Mo or V, which may be the same or different from each other, provided that M 2 and M. 3 , and N 2 and N 3At least one of the elements is a different coordination element. Here, p is an integer of 1 or more and 10 or less, q and r are positive integers, s is an integer of 10 or more and 100 or less, h is an integer of 1 or more, and i is an integer of 0 or more and 50 or less. v is an integer of 1 or more and 10 or less, w and x are positive integers, y is an integer of 10 or more and 100 or less, j is an integer of 1 or more, and k is an integer of 0 or more and 50 or less. However, M 2 and M. 3 When the coordinate elements are the same, q+r is an integer between 6 and 40, and N 2 and N 3 When the coordinate elements are the same, w+x is an integer between 6 and 40.)

[0014] [2] The method for producing a polyacetal copolymer according to the above [1], wherein a mass ratio (B / A) of the heteropolyacid salt (B) to the heteropolyacid (A) is 0.2 to 10.

[0015] [3] The method for producing a polyacetal copolymer according to [1] or [2] above, wherein the heteropolyacid (A) is at least one selected from the group consisting of phosphomolybdic acid, phosphotungstic acid, phosphomolybdotungstic acid, phosphomolybdovanadic acid, phosphomolybdotungstovanadic acid, phosphotungstovanadic acid, silicotungstic acid, silicomolybdic acid, silicomolybdotungstic acid, and silicomolybdotungstovanadic acid.

[0016] [4] The method for producing a polyacetal copolymer according to [1] or [2] above, wherein the heteropolyacid salt (B) is at least one selected from the group consisting of lithium phosphotungstate, sodium phosphotungstate, potassium phosphotungstate, sodium silicotungstate, sodium phosphomolybdate, and sodium phosphotungstovanadate.

[0017] [5] The method for producing a polyacetal copolymer according to any one of [1] to [4] above, wherein the comonomer is at least one selected from the group consisting of 1,3-dioxolane, diethylene glycol formal, 1,4-butanediol formal, 1,3-dioxane, and ethylene oxide.

[0018] [6] A polyacetal copolymer produced by the production method according to any one of [1] to [5] above. Effect of the Invention

[0019] According to the present invention, it is possible to provide a production method that can stably produce, even in mass production, a polyacetal copolymer that can not only reduce the amount of formaldehyde generated but also has excellent flowability during molding and can be used to produce molded articles with excellent appearance. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0020] Hereinafter, the embodiments of the present invention will be described in detail, but the present invention is not limited to the following embodiments.

[0021] 1. Manufacturing method of polyacetal copolymer The method for producing a polyacetal copolymer of the present invention is a method for producing a polyacetal copolymer by copolymerizing trioxane and a comonomer copolymerizable with the trioxane in the presence of a polymerization catalyst. Each of the constituent components will be described below.

[0022] (Trioxane) Trioxane is a cyclic trimer of formaldehyde. In the present invention, the trioxane is used as a main monomer. Here, the main monomer refers to the monomer that is contained in the largest amount among all monomers. Note that trioxane is generally obtained by reacting an aqueous formaldehyde solution in the presence of an acid catalyst, and is used after being purified by a method such as distillation.

[0023] (Comonomer) The comonomer in the present invention is not particularly limited as long as it is copolymerizable with the trioxane. The comonomer is preferably selected from the group consisting of cyclic ethers and cyclic formals having at least one carbon-carbon bond.

[0024] Examples of the comonomer include 1,3-dioxolane, diethylene glycol formal, 1,4-butanediol formal, 1,3-dioxane, ethylene oxide, propylene oxide, epichlorohydrin, etc. Among these, from the viewpoint of polymerization stability, 1,3-dioxolane, diethylene glycol formal, 1,4-butanediol formal, 1,3-dioxane, and ethylene oxide are preferred.

[0025] Also usable as the comonomer are compounds having two polymerizable cyclic ether groups or cyclic formal groups, such as diglycidyl ether of alkylene glycol, such as butanediol diglycidyl ether, and diformal, and compounds having three or more polymerizable cyclic ether groups or cyclic formal groups, such as glycerin triglycidyl ether, trimethylolpropane triglycidyl ether, pentaerythritol tetraglycidyl ether, etc. By using these comonomers, it is possible to obtain a polyacetal copolymer having a branched structure or a crosslinked structure.

[0026] In the present invention, the content of the comonomer is preferably 0.01 to 20 parts by mass, and more preferably 0.05 to 5 parts by mass, relative to 100 parts by mass of trioxane. When the content of the comonomer is 0.01 to 20 parts by mass relative to 100 parts by mass of trioxane, the polymerization can proceed stably, and a decrease in the crystallization rate and the crystallization degree of the polymer chain can be suppressed.

[0027] (Polymerization catalyst) The polymerization catalyst of the present invention is a heteropolyacid (A) represented by the following general formula (1) and a heteropolyacid salt (B) represented by the following general formula (2). In the present invention, the heteropolyacid (A) and the heteropolyacid salt (B) are used in combination.

[0028]

number

[0029] In the formulas (1) and (2), L is an alkali metal element, and the alkali metal element is preferably any one of lithium, sodium, and potassium. 1 and N 1 are each independently a central element of P or Si, and M 2 and M. 3 are coordination elements of W, Mo or V which may be the same or different from each other, and N 2 and N 3 are coordination elements of W, Mo or V, which may be the same or different from each other, provided that M 2 and M. 3 , and N 2 and N 3 At least one of the elements is a different coordination element. Here, p is an integer of 1 or more and 10 or less. q and r are positive integers. s is an integer of 10 or more and 100 or less, and preferably an integer of 30 or more and 80 or less. h is an integer of 1 or more and preferably an integer of 1 or more and 10 or less. i is an integer of 0 or more and 50 or less, and preferably an integer of 30 to 50 or less. Also, v is an integer of 1 or more and 10 or less. w and x are positive integers. y is an integer of 10 or more and 100 or less, and preferably an integer of 30 or more and 80 or less. j is an integer of 1 or more and preferably an integer of 1 or more and 10 or less. k is an integer of 0 or more and 50 or less, and preferably an integer of 30 or more and 50 or less. However, M 2 and M. 3 When N is the same coordination element, q+r is an integer of 6 or more and 40 or less, and preferably an integer of 10 or more and 20 or less. 2 and N 3When w+x are the same coordination element, w+x is an integer of 6 or more and 40 or less, and preferably an integer of 10 or more and 20 or less.

[0030] Examples of the heteropolyacid (A) include phosphomolybdic acid, phosphotungstic acid, phosphomolybdotungstic acid, phosphomolybdovanadic acid, phosphomolybdotungstovanadic acid, phosphotungstovanadic acid, silicotungstic acid, silicomolybdic acid, silicomolybdotungstic acid, silicomolybdotungstovanadic acid, etc. Among these, from the viewpoints of the stability of the polymerization and the stability of the heteropolyacid itself, phosphotungstic acid, phosphomolybdotungstovanadic acid, and phosphotungstovanadic acid are preferred, and phosphotungstovanadic acid is more preferred.

[0031] From the viewpoint of solubility in a solvent, the heteropolyacid salt (B) of the present invention is preferably an alkali metal salt. Examples of such heteropolyacid salt (B) include lithium phosphotungstate, sodium phosphotungstate, potassium phosphotungstate, sodium silicate, sodium phosphomolybdate, sodium phosphotungstovanadate, sodium silicate, etc. Among these, sodium phosphotungstate, sodium silicate, sodium phosphomolybdate, and sodium phosphotungstovanadate are preferred.

[0032] In the present invention, it is preferable to use a mixture of the heteropolyacid (A) and the heteropolyacid salt (B). Examples of combinations of the heteropolyacid (A) and the heteropolyacid salt (B) include phosphotungstovanadic acid and sodium phosphotungstate, phosphotungstovanadic acid and lithium phosphotungstate, phosphotungstovanadic acid and potassium phosphotungstate, phosphomolybdotungstovanadic acid and sodium phosphotungstate, phosphotungstovanadic acid and sodium silicotungstate, phosphotungstovanadic acid and sodium phosphomolybdate, and phosphotungstic acid and sodium phosphotungstovanadate.

[0033] Among these, phosphotungstovanadic acid and sodium phosphotungstate, phosphomolybdotungstovanadic acid and sodium phosphotungstate, phosphotungstovanadic acid and sodium silicotungstate, phosphotungstovanadic acid and sodium phosphomolybdate, and phosphotungstic acid and sodium phosphotungstovanadate are preferred.

[0034] By using a mixture of the heteropolyacid (A) and the heteropolyacid salt (B), it is possible to reduce the amount of formaldehyde generated and also to obtain a polyacetal copolymer that has excellent flowability during molding and can be used to produce molded articles having excellent appearance.

[0035] The mass ratio (B / A) of the heteropolyacid salt (B) to the heteropolyacid (A) is preferably 0.2 to 10, and more preferably 0.5 to 10. When the mass ratio (B / A) is 0.2 to 10, the flowability during molding is good, and the appearance of the molded product is also good.

[0036] The content of the polymerization catalyst in the present invention is preferably 0.05 to 100 ppm, more preferably 0.1 to 50 ppm, based on the total amount of the above-mentioned monomers (trioxane and comonomer). The content of the polymerization catalyst may be appropriately changed depending on the type of the catalyst. Here, "ppm" stands for "mass / mass ppm".

[0037] The polymerization catalyst is preferably used after diluting with a solvent inert to the polymerization reaction (hereinafter also referred to as "solvent"). In the present invention, the concentration of the polymerization catalyst diluted with the above-mentioned solvent is preferably 0.05 to 30 mass%, more preferably 0.1 to 20 mass%, and even more preferably 0.5 to 10 mass%. When the concentration of the diluted polymerization catalyst is 0.05 to 30 mass%, the polymerization catalyst can be sufficiently diffused in the monomer, so that the polymerization reaction can be carried out uniformly.

[0038] Examples of the solvent include esters such as methyl formate, ethyl formate, methyl acetate, ethyl acetate, and butyl acetate, and ketones such as acetone, 2-butanone, 2-pentanone, 3-pentanone, 2-hexanone, 3-hexanone, methyl isobutyl ketone, and methyl-t-butyl ketone. Among these, methyl formate, ethyl formate, methyl acetate, ethyl acetate, butyl acetate, acetone, 2-butanone, and methyl isobutyl ketone are preferred.

[0039] (Other additives) In the present invention, in addition to the above-mentioned components, it is preferable to use known chain transfer agents for adjusting the degree of polymerization (molecular weight) such as methylal and butyral, and hindered phenol-based antioxidants such as triethylene glycol-bis[3-(3-tert-butyl-5-methyl-4-hydroxyphenyl)propionate] and pentaerythritol tetrakis[3-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate].

[0040] (Method for producing polyacetal copolymer) The method for producing the polyacetal copolymer of the present invention is a method for copolymerizing trioxane with the above-mentioned comonomer in the presence of the above-mentioned polymerization catalyst (heteropolyacid (A) and heteropolyacid salt (B)).

[0041] The polyacetal copolymer of the present invention can be produced by using known methods and polymerization apparatuses, such as a batch type or continuous type.

[0042] In the above polymerization apparatus, a reaction tank equipped with a stirrer that is generally used can be used in the batch type. In addition, in the continuous type, a co-kneader, a twin-screw type continuous extrusion mixer, a twin-screw paddle screw extruder type, a vented twin-screw extruder, etc. can be used. The continuous type is an industrially preferred production method.

[0043] The polyacetal copolymer of the present invention can be obtained, for example, by continuously supplying a mixed liquid containing trioxane, the above-mentioned comonomer, any additive for polymerization reaction, and a polymerization catalyst (heteropolyacid (A) and heteropolyacid salt (B)) to a continuous twin-screw paddle screw extruder-type polymerization reactor having a jacket for passing a heating or cooling medium, and polymerizing the mixture for a predetermined period of time.

[0044] Furthermore, a basic compound such as an alkali metal compound, a quaternary amine compound, or a triazine compound having an amino group can be added to the polyacetal copolymer obtained by the above-mentioned method, and the mixture can be melt-kneaded and subjected to a catalyst deactivation treatment or the like to obtain a desired polyacetal copolymer.

[0045] In addition, during the deactivation treatment of the catalyst, other components such as other polymers, other fillers, nitrogen compounds, stabilizers such as ultraviolet absorbers, acid inhibitors such as metal salts, antistatic agents, flame retardants, colorants such as dyes and pigments, lubricants, release agents, crystallization accelerators, crystal nucleating agents, etc. may be added appropriately depending on the required performance. The other components may be used alone or in combination of two or more.

[0046] The method for producing a polyacetal copolymer according to the present invention uses a mixture of a heteropolyacid (A) and a heteropolyacid salt (B) as a polymerization catalyst, and therefore not only can it reduce the amount of formaldehyde generated but also can stably produce, even in mass production, a polyacetal copolymer that has excellent flowability during molding and can be used to produce molded articles with excellent appearance.

[0047] 2. Polyacetal copolymer The polyacetal copolymer of the present invention is a copolymer produced by the production method of the present invention, that is, a polyacetal copolymer obtained by copolymerizing trioxane and the above-mentioned comonomer in the presence of a polymerization catalyst (heteropolyacid (A) and heteropolyacid salt (B)).

[0048] The polyacetal copolymer obtained by the production method according to the present invention has excellent flowability during molding. Furthermore, molded articles produced from the polyacetal copolymer can reduce the amount of formaldehyde generated and have excellent appearance. EXAMPLES

[0049] The present invention will be specifically described below with reference to examples, but the present invention is not limited to these.

[0050] 1. Preparation of polyacetal copolymers 1-22 [Polyacetal copolymer 1] (Polymerization equipment) A continuous twin-shaft paddle screw extruder (hereinafter also referred to as "polymerization apparatus") was used as the polymerization apparatus. The extruder has a jacket on the outside of the body for passing a heating or cooling medium. The body is divided into an upper and lower part, and the upper part can be opened. Inside the extruder, two rotating shafts with many paddles for stirring and propulsion are provided in the longitudinal direction.

[0051] (Manufacturing method) A mixed liquid containing 100 parts by mass of trioxane (TOX), 4.0 parts by mass of 1,3-dioxolane (DO), and a predetermined amount of methylal was continuously supplied per unit time to a polymerization apparatus in which a medium of 80° C. was passed through the jacket, and a mixture of 2.5 ppm of tungstophosphovanadic acid (A1) as the heteropolyacid (A) and 0.6 ppm of sodium tungstophosphoric acid salt (B1) as the heteropolyacid salt (B) was added as a methyl formate solution to carry out a polymerization reaction.

[0052] To the crude polymer obtained from the discharge outlet of the polymerization apparatus, 0.1 mass % of melamine and 0.3 mass % of IRGANOX 1010 (manufactured by BASF Japan, "IRGANOX" is a registered trademark of BASF) were added, and the mixture was continuously melt-kneaded and extruded using a vented twin-screw extruder under conditions of a cylinder temperature of 220°C and a vacuum degree of 5 mmHg in the vent section, to obtain pellets of polyacetal copolymer 1.

[0053] The amount of methylal added is adjusted so that the melt flow rate (MFR) of the resulting copolymer is 9 g / 10 min. In the present invention, "9 g" refers to a range of "9 g ± 0.3". The MFR was measured in accordance with ISO1133 using a Melt Indexer L220 (manufactured by Tateyama Kagaku High-Technologies Corporation) under conditions of a load of 2.16 kg, a temperature of 190°C, and a discharged resin acquisition time of 7 minutes.

[0054] [Polyacetal copolymer 2-8] As shown in Table 1, pellets of polyacetal copolymers 2 to 8 were obtained by the same production method as for polyacetal copolymer 1, except that the amount of heteropolyacid (A) and / or heteropolyacid salt (B) added and the amount of methylal added were changed so that the MFR of the resulting copolymer would be 9 g / 10 min.

[0055] [Polyacetal copolymer 9] As shown in Table 1, pellets of polyacetal copolymer 9 were obtained by the same production method as for polyacetal copolymer 1, except that the type of comonomer, the amount of heteropolyacid salt (B) added, and the amount of methylal added were changed so that the MFR of the resulting copolymer would be 9 g / 10 min.

[0056] [Polyacetal copolymer 10-14] As shown in Table 1, pellets of polyacetal copolymers 10 to 14 were obtained by the same production method as for polyacetal copolymer 1, except that the type of heteropolyacid salt (B) and the amount of methylal added were changed so that the MFR of the resulting copolymer was 9 g / 10 min.

[0057] [Polyacetal copolymers 15-17, 19, 20] As shown in Table 1, pellets of polyacetal copolymers 15 to 17, 19, and 20 were obtained by the same production method as for polyacetal copolymer 1, except that the type of heteropolyacid salt (A), the amount of heteropolyacid salt (B) added, and the amount of methylal added were changed so that the MFR of the resulting copolymer would be 9 g / 10 min.

[0058] [Polyacetal copolymer 18] As shown in Table 1, pellets of polyacetal copolymer 18 were obtained by the same production method as for polyacetal copolymer 1, except that the type of heteropolyacid salt (A), the type of heteropolyacid salt (B), and the amount of methylal added were changed so that the MFR of the resulting copolymer would be 9 g / 10 min.

[0059] [Polyacetal copolymer 21] A mixed solution containing 100 parts by mass of trioxane (TOX), 4.0 parts by mass of 1,3-dioxolane (DO), and a predetermined amount of methylal was continuously supplied to the above-mentioned polymerization apparatus per unit time, and 3.3 ppm of phosphotungstic acid (A5) was added as a heteropolyacid (A) in the form of a methyl formate solution to carry out a polymerization reaction.

[0060] To the crude polymer obtained from the discharge outlet of the polymerization apparatus, 0.1% by mass of melamine and 0.3% by mass of IRGANOX 1010 were added, and the mixture was continuously melt-kneaded and extruded using a vented twin-screw extruder at 220°C and a vacuum degree of 5 mmHg at the vent to obtain pellets of polyacetal copolymer 21.

[0061] The amount of methylal added was adjusted in the same manner as in the polyacetal copolymer 1.

[0062] [Polyacetal copolymer 22] A mixture containing 100 parts by mass of trioxane (TOX), 4.0 parts by mass of 1,3-dioxolane (DO), and a predetermined amount of methylal was continuously fed to the above-mentioned polymerization apparatus per unit time, and 30 ppm of boron trifluoride (C) was added to carry out a polymerization reaction. Next, the crude polymer obtained from the discharge port of the polymerization apparatus was added to an aqueous solution containing 0.1% triethylamine to terminate the polymerization reaction, and then the copolymer was dried. In this production method, boron trifluoride (C) was added as a 0.3 wt% cyclohexane solution of a dibutyl ether complex.

[0063] To the dried copolymer, 0.1% by mass of melamine and 0.3% by mass of IRGANOX 1010 were added, and the mixture was continuously melt-kneaded and extruded using a vented twin-screw extruder at 220°C and a vacuum degree of 5 mmHg at the vent to obtain pellets of polyacetal copolymer 22.

[0064] The amount of methylal added was adjusted in the same manner as in the polyacetal copolymer 1.

[0065] The heteropolyacid (A), heteropolyacid salt (B) and Lewis acid (C) described in the above production method are compounds shown in Table 1.

[0066] 2. Evaluation The polyacetal copolymers 1 to 22 obtained by the above production method were evaluated for polymerization yield of the polyacetal copolymer, appearance of molded articles using the polyacetal copolymer, amount of formaldehyde generated, and bar flow (BF).

[0067] [Polymerization yield of polyacetal copolymer] (Evaluation method) The reaction products discharged from the discharge port of the polymerization apparatus were continuously collected for a certain period of time, and each was added to an aqueous solution containing 0.1% triethylamine, followed by stirring for a predetermined period of time to inactivate the catalyst and wash away unreacted monomers. The aqueous solution was then filtered, and the crude polymer obtained was washed with acetone and dried. The polyacetal copolymer yield, which is the ratio of the copolymer obtained to the total monomers, was calculated from the weight of the dried polyacetal copolymer. It is practically preferable that the polymerization yield of the polyacetal copolymer is 70% or more.

[0068] [Formaldehyde emission from melt] (Evaluation method) 5 g of each of the polyacetal copolymers 1 to 22 was filled into a cylinder kept at 200°C, and after being kept molten for 5 minutes, the melts of the polyacetal copolymers were extruded into a sealed container. Nitrogen gas was passed through the sealed container, and the formaldehyde contained in the nitrogen gas that came out was dissolved in water and collected. The formaldehyde concentration in the water was measured in accordance with JIS K0102 (2013) to determine the mass of formaldehyde from the melt. The mass of this formaldehyde was divided by the mass of the polyacetal copolymer used to obtain the amount of formaldehyde generated (unit: ppm). In the present invention, it is practically preferable that the amount of formaldehyde generated is 70 ppm or less.

[0069] [Appearance evaluation of molded products] (Evaluation method) Polyacetal copolymers 1 to 22 were each injection molded into a 50mm square 3t flat plate with a φ1.5mm center pin gate under the following conditions using a molding machine (FANUC injection molding machine "S100iA (φ36)"). After that, the size of the flow marks near the gate of the molded product was measured, and the appearance was evaluated on a 5-point scale.

[0070] (Molding conditions) Cylinder temperature (nozzle head temperature: 200℃) Mold temperature: 90℃ Holding pressure: 75MPa Firing time: 4.5 seconds Injection conditions: Metering position: 20mm, Suck back: 5mm, VP switching position: 8mm

[0071] (evaluation) 5: The size of the flow mark is less than 6 mm. 4: The size of the flow mark is 6 mm or more and less than 8 mm. 3: The size of the flow mark is 8 mm or more and less than 10 mm. 2: The size of the flow mark is 10 mm or more and less than 12 mm. 1: The size of the flow mark is 12 mm or more.

[0072] [Barflow evaluation] (Evaluation method) Using an injection molding machine (ES3000, manufactured by Nissei Plastic Industrial Co., Ltd.), polyacetal copolymers 1 to 22 were each injected into an evaluation mold with a thickness of 2 mmt, and the flow length was measured. The flow length (unit: mm) at each injection pressure was evaluated on a 5-point scale.

[0073] (Molding conditions) Cylinder temperature (nozzle head temperature: 195℃) Mold temperature: 80℃ Injection speed: 70mm / s Injection pressure: 100MPa

[0074] (evaluation) 5: The flow length is 450 mm or more when the injection pressure is 100 MPa. 4: The flow length at an injection pressure of 100 MPa is between 440 mm and 450 mm. 3: The flow length at an injection pressure of 100 MPa is between 430 mm and 440 mm. 2: The flow length at an injection pressure of 100 MPa is between 420 mm and 430 mm. 1: The flow length is less than 420 mm at an injection pressure of 100 MPa.

[0075] [MFR measurement] In the production of the polyacetal copolymers 1 to 22, the MFR value, which is an index of fluidity of the resulting crude polymer when melted, was determined as follows. (Measurement method) Using a Melt Indexer L220 manufactured by Tateyama Kagaku High-Technologies Corporation, measurements were performed under conditions conforming to ISO1133: a load of 2.16 kg, a temperature of 190°C, and a discharged resin acquisition time of 7 minutes.

[0076] The main components of the polyacetal copolymers 1 to 22 and the evaluation results are shown in Table 1. The abbreviations and the names of the heteropolyacid (A), heteropolyacid salt (B) and Lewis acid (C) in Table 1 are as follows.

[0077] (Main Monomer) TOX: Trioxane (Comonomer) DO: 1,3-dioxolane BDF: 1,4-butanediol formal

[0078] [Polymerization catalyst] (Heteropolyacid (A)) A1:H5PV2W 10 O 40 (Tungstovanadic Phosphoate) A2:H4PV1W 11 O 40 (Tungstovanadic Phosphoate) A3:H6PV3W9O 40 (Tungstovanadic Phosphoate) A4: H3PMo2W 10 O4 (phosphomolybdotungstic acid) A5:H3PW 12 O 40 (phosphotungstic acid)

[0079] (Heteropolyacid salt (B)) B1:Na3PW 12 O 40 (Sodium phosphotungstate) B2: Li3PW 12 O 40 (Lithium phosphotungstate) B3:K3PW 12 O 40 (Potassium phosphotungstate) B4: NaSiW 12 O 40 (Sodium silicotungstate) B5: Na3PMo 12 O 40 (Sodium phosphomolybdate) B6:Na3PV2W 10 O 40 (Sodium phosphotungstovanadate)

[0080] (Lewis Acid (C)) C: BF3 (boron trifluoride)

[0081] (Evaluation items) HCHO: Formaldehyde BF: Barflow

[0082] [Table 1]

[0083] From Table 1, it was found that by using a mixture of heteropolyacid (A) and heteropolyacid salt (B) as a polymerization catalyst, not only can the amount of formaldehyde generated be reduced, but also a polyacetal copolymer can be produced with stable polymerization yield and quality even in mass production. In particular, when H5PV2W is used as the heteropolyacid (A), 10 O 40 (phosphotungstovanadic acid), Na3PW as heteropolyacid salt (B) 12 O 40 It was found that the best results were obtained in all evaluation items when sodium phosphotungstate was used. [Industrial Applicability]

[0084] The method of the present invention not only reduces the amount of formaldehyde generated, but also enables stable mass production of polyacetal copolymers that have excellent flowability during molding and excellent appearance of molded products, and is expected to contribute to the advancement and spread of technology in this field.

Claims

1. A method for producing a polyacetal copolymer, comprising copolymerizing trioxane and a comonomer copolymerizable with said trioxane in the presence of a polymerization catalyst, the method comprising the steps of: The polymerization catalyst is a heteropolyacid (A) represented by the following general formula (1) and a heteropolyacid salt (B) represented by the following general formula (2), The heteropolyacid (A) and the heteropolyacid salt (B) are used in combination. A method for producing a polyacetal copolymer. [0010] (In the formulas (1) and (2), L is an alkali metal element, M １ and N １ are each independently a central element of P or Si, M ２ and M. ３ are coordination elements of W, Mo or V which may be the same or different from each other, and N ２ and N ３ are coordination elements of W, Mo or V, which may be the same or different from each other, provided that M ２ and M. ３ , and N ２ and N ３ At least one of the above is composed of a different coordination element. Here, p is an integer of 1 or more and 10 or less, q and r are positive integers, s is an integer of 10 or more and 100 or less, h is an integer of 1 or more, and i is an integer of 0 or more and 50 or less. v is an integer of 1 or more and 10 or less, w and x are positive integers, y is an integer of 10 or more and 100 or less, j is an integer of 1 or more, and k is an integer of 0 or more and 50 or less. However, M ２ and M. ３ are the same coordination elements, q+r is an integer of 6 to 40, ２ and N ３ When the coordinate elements are the same, w+x is an integer of 6 or more and 40 or less.)

2. 2. The method for producing a polyacetal copolymer according to claim 1, wherein a mass ratio (B / A) of the heteropolyacid salt (B) to the heteropolyacid (A) is 0.2 to 10.

3. 3. The method for producing a polyacetal copolymer according to claim 1 or 2, wherein the heteropolyacid (A) is at least one selected from the group consisting of phosphomolybdic acid, phosphotungstic acid, phosphomolybdotungstic acid, phosphomolybdovanadic acid, phosphomolybdotungstovanadic acid, phosphotungstovanadic acid, silicotungstic acid, silicomolybdic acid, silicomolybdotungstic acid, and silicomolybdotungstovanadic acid.

4. 3. The method for producing a polyacetal copolymer according to claim 1 or 2, wherein the heteropolyacid salt (B) is at least one selected from the group consisting of lithium phosphotungstate, sodium phosphotungstate, potassium phosphotungstate, sodium silicotungstate, sodium phosphomolybdate, and sodium phosphotungstovanadate.

5. 2. The method for producing a polyacetal copolymer according to claim 1, wherein the comonomer is at least one selected from the group consisting of 1,3-dioxolane, diethylene glycol formal, 1,4-butanediol formal, 1,3-dioxane, and ethylene oxide.

6. A polyacetal copolymer produced by the production method according to claim 1.

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