Method for producing polyacetal copolymer

Abstract

The method for producing a polyacetal copolymer according to the present invention is a method for producing a polyacetal copolymer by copolymerizing trioxane and a comonomer capable of copolymerizing with the trioxane in the presence of a polymerization catalyst. The polymerization catalyst is a heteropolyacid (A) and a heteropolyacid salt (B), and the heteropolyacid (A) and the heteropolyacid salt (B) are used in a mixed manner.

Description

Technical Field

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

[0002] As a method for producing a polyacetal copolymer, the following method is known: in the presence of a cationic polymerization catalyst, a cationic polymerization is carried out between a main monomer (trioxane) and a comonomer capable of copolymerizing with the main monomer. As the cationic polymerization catalyst, Lewis acids such as boron trifluoride, tin tetrachloride, titanium tetrachloride, phosphorus pentafluoride, phosphorus pentachloride, and antimony pentafluoride, and their complexes or their salts are generally widely used.

[0003] However, polymerization catalysts such as boron trifluoride need to be added in a relatively large amount (for example, 40 ppm or more relative to all monomers) during polymerization. Therefore, in the manufacturing process, there is a problem that it is difficult to sufficiently deactivate the catalyst remaining in the polyacetal copolymer after polymerization. In addition, even if the catalyst can be deactivated, sometimes adverse conditions such as the decomposition of the copolymer being promoted due to the residue of substances derived from the catalyst in the copolymer may occur. Furthermore, the catalyst deactivation process is carried out in a large amount of aqueous solution (treatment liquid) containing an alkaline compound such as triethylamine, so after this process, complex processes such as separating and drying the copolymer from the treatment liquid and recovering unreacted monomers dissolved in the treatment liquid are further required.

[0004] In recent years, there has been a demand for high-quality polyacetal copolymers having excellent thermal stability and extremely low formaldehyde generation. Therefore, research is being conducted on the efficient deactivation of catalysts and the stabilization of the unstable end portions of the crude polyacetal copolymer after catalyst deactivation by decomposition treatment.

[0005] For example, Patent Document 1 describes a method for producing a polyacetal copolymer, which includes the steps of: copolymerizing using a specified heteropolyacid as a polymerization catalyst; and adding a specified salt or its hydrate to the obtained reaction product and performing a melt-kneading treatment to deactivate the polymerization catalyst. In addition, Patent Document 2 describes that by using a polymerization catalyst mixed with a specified heteropolyacid and a specified heteropolyacid metal salt, the stability of polymerization can be obtained in industrial production.

[0006] Prior Art Documents

[0007] Patent Documents

[0008] Patent Document 1: Japanese Patent Application Laid-Open No. 2014-105278

[0009] Patent Document 2: Japanese Patent Application Laid-Open No. 2019-178187 Summary of the Invention

[0010] Problems to be Solved by the Invention

[0011] According to Patent Document 1, by using a specified highly active heteropolyacid as a polymerization catalyst and performing melt-kneading treatment together with an inactivator, polymerization can be carried out with a small amount of catalyst, complex processes can be reduced, the amount of formaldehyde generated is extremely small, and a high-quality polyacetal copolymer can be obtained. However, when increasing the production amount of the polyacetal resin with a small amount of polymerization catalyst, a decrease in the polymerization yield of the polyacetal copolymer and differences in the quality of the polyacetal resin occur.

[0012] In addition, according to Patent Document 2, by using a polymerization catalyst in which a specified heteropolyacid and a specified heteropolyacid metal salt are mixed, the polymerization reaction can be stabilized, and the resin quality is also good due to the reduction in the amount of formaldehyde generated. However, sometimes the appearance of the molded product formed from the obtained polyacetal resin is poor, and improvement is required.

[0013] The present invention has been completed in view of the above circumstances, and an object thereof is to provide a method for producing a polyacetal copolymer that can stably produce a polyacetal copolymer even in mass production, the polyacetal copolymer not only reduces the amount of formaldehyde generated, but also has excellent fluidity during molding and can produce a molded product having excellent appearance.

[0014] Solutions to the Problems

[0015] The present inventors conducted in-depth research and as a result completed the following inventions [1] to [6].

[0016] [1] A method for producing a polyacetal copolymer, which is a method for producing a polyacetal copolymer in which trioxane is copolymerized with a comonomer capable of copolymerizing with the aforementioned trioxane in the presence of a polymerization catalyst,

[0017] The aforementioned 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),

[0018] The aforementioned heteropolyacid (A) and the aforementioned heteropolyacid salt (B) are used in combination.

[0019] H h [M 1 p ·M 2 q M 3 r O s ·iH2O ……(1)

[0020] L j [N 1 v ·N 2 w N3 x O y ·kH2O ……(2)

[0021] (In 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 that are the same as or different from each other, and N 2 and N 3 are coordination elements of W, Mo or V that are the same as or different from each other. Among them, M 2 and M 3 , and N 2 and N 3 at least one pair of which is composed of different coordination elements. 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. Among them, when M 2 and M 3 are the same coordination elements, q + r is an integer of 6 or more and 40 or less, and when N 2 and N 3 are the same coordination elements, w + x is an integer of 6 or more and 40 or less.)

[0022] [2] The method for producing a polyoxymethylene copolymer according to [1] above, wherein the mass ratio (B / A) of the heteropolyacid salt (B) to the heteropolyacid (A) is 0.2 to 10.

[0023] [3] The method for producing a polyoxymethylene 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.

[0024] [4] The method for producing a polyoxymethylene 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.

[0025] [5]The method for producing a polyacetal copolymer according to any one of the foregoing [1] to [4], 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.

[0026] [6]A polyacetal copolymer produced by the production method according to any one of the foregoing [1] to [5].

[0027] Effects of the Invention

[0028] According to the present invention, there can be provided a method for producing a polyacetal copolymer which can stably produce the polyacetal copolymer even in mass production, and the polyacetal copolymer can not only reduce the amount of formaldehyde generated, but also has excellent fluidity during molding and can produce molded articles having excellent appearance. Detailed Description of Embodiments

[0029] Hereinafter, embodiments of the present invention will be described in detail, but the present invention is not limited to the following embodiments.

[0030] 1. Method for Producing Polyacetal Copolymer

[0031] The method for producing a polyacetal copolymer according to an embodiment of the present invention is a method for producing a polyacetal copolymer in which trioxane is copolymerized with a comonomer capable of copolymerizing with the trioxane in the presence of a polymerization catalyst. Hereinafter, each constituent will be described.

[0032] (Trioxane)

[0033] Trioxane is a cyclic trimer of formaldehyde. Trioxane according to an embodiment of the present invention is used as a main monomer. Here, the main monomer means the monomer that is contained alone in the largest amount among all monomers. It should be noted that trioxane is usually obtained by reacting an aqueous formaldehyde solution in the presence of an acidic catalyst and purified by a method such as distillation before use.

[0034] (Comonomer)

[0035] The comonomer according to an embodiment of the present invention is not particularly limited as long as it copolymerizes with trioxane. As the comonomer, those selected from the group consisting of cyclic ethers and cyclic formal acetals having at least one carbon-carbon bond are preferred.

[0036] 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.

[0037] In addition, as the comonomer, diglycidyl ethers of alkylene glycols such as butanediol diglycidyl ether, compounds having two polymerizable cyclic ether groups or cyclic formal groups such as diformal, and compounds having three or more polymerizable cyclic ether groups or cyclic formal groups such as glycerol triglycidyl ether, trimethylolpropane triglycidyl ether, and pentaerythritol tetraglycidyl ether can also be used. By using these comonomers, a polyacetal copolymer having a branched structure or a crosslinked structure can be obtained.

[0038] In one embodiment of the present invention, the content of the comonomer is preferably 0.01 to 20 parts by mass, 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 part by mass or more and 20 parts by mass or less relative to 100 parts by mass of trioxane, polymerization can be carried out stably, and a decrease in the crystallization rate and crystallinity of the polymer chain can be suppressed.

[0039] (Polymerization catalyst)

[0040] The polymerization catalyst in one embodiment 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 one embodiment of the present invention, the heteropolyacid (A) and the heteropolyacid salt (B) are used in combination.

[0041] H h [M 1 p ·M 2 q M 3 r O s ·iH2O ……(1)

[0042] L j [N 1 v ·N 2 w N 3 x O y ·kH2O ……(2)

[0043] In the formulas (1) and (2), L is an alkali metal element, and as the alkali metal element, any one of lithium, sodium, and potassium is preferred. M1 and N 1 Each independently is a central element of P or Si, M 2 and M 3 are coordination elements of W, Mo or V that are the same as or different from each other, N 2 and N 3 are coordination elements of W, Mo or V that are the same as or different from each other. Among them, M 2 and M 3 , and N 2 and N 3 at least one pair of which is composed of different coordination elements. 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, preferably an integer of 30 or more and 80 or less. h is an integer of 1 or more, preferably an integer of 1 or more and 10 or less. i is an integer of 0 or more and 50 or less, preferably an integer of 30 to 50 or less. In addition, 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, preferably an integer of 30 or more and 80 or less. j is an integer of 1 or more, preferably an integer of 1 or more and 10 or less. k is an integer of 0 or more and 50 or less, preferably an integer of 30 or more and 50 or less. Among them, when M 2 and M 3 are the same coordination element, q + r is an integer of 6 or more and 40 or less, preferably an integer of 10 or more and 20 or less. In addition, when N 2 and N 3 are the same coordination element, w + x is an integer of 6 or more and 40 or less, preferably an integer of 10 or more and 20 or less.

[0044] 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 polymerization stability and the stability of the heteropolyacid itself, phosphotungstic acid, phosphomolybdotungstovanadic acid, and phosphotungstovanadic acid are preferred, and phosphotungstovanadic acid is more preferred.

[0045] From the viewpoint of solubility in a solvent, the heteropolyacid salt (B) is preferably a salt of an alkali metal. Examples of such a heteropolyacid salt (B) include lithium phosphotungstate, sodium phosphotungstate, potassium phosphotungstate, sodium silicotungstate, sodium phosphomolybdate, sodium phosphomolybdotungstate, sodium silicomolybdotungstate, etc. Among these, sodium phosphotungstate, sodium silicotungstate, sodium phosphomolybdate, and sodium phosphomolybdotungstate are preferred.

[0046] In one embodiment of the present invention, a heteropolyacid (A) and a heteropolyacid salt (B) are used in combination. Examples of the combination of the heteropolyacid (A) and the heteropolyacid salt (B) include phosphotungstic vanadic acid and sodium phosphotungstate, phosphotungstic vanadic acid and lithium phosphotungstate, phosphotungstic vanadic acid and potassium phosphotungstate, phosphomolybdotungstic vanadic acid and sodium phosphotungstate, phosphotungstic vanadic acid and sodium silicotungstate, phosphotungstic vanadic acid and sodium phosphomolybdate, phosphotungstic acid and sodium phosphotungstovanadate, etc.

[0047] Among these, phosphotungstic vanadic acid and sodium phosphotungstate, phosphomolybdotungstic vanadic acid and sodium phosphotungstate, phosphotungstic vanadic acid and sodium silicotungstate, phosphotungstic vanadic acid and sodium phosphomolybdate, phosphotungstic acid and sodium phosphotungstovanadate are preferred.

[0048] By using the heteropolyacid (A) and the heteropolyacid salt (B) in combination, a polyoxymethylene copolymer can be obtained which not only reduces the amount of formaldehyde generated, but also has excellent fluidity during molding and can produce molded articles with excellent appearance.

[0049] In addition, the mass ratio (B / A) of the heteropolyacid salt (B) to the heteropolyacid (A) is preferably 0.2 to 10, more preferably 0.5 to 10. When the mass ratio (B / A) is 0.2 to 10, the fluidity during molding becomes good, and the appearance of the molded article also becomes good.

[0050] In one embodiment of the present invention, the content of the polymerization catalyst is preferably 0.05 to 100 ppm, more preferably 0.1 to 50 ppm, based on the total amount of the above monomers (trioxane and comonomer). In addition, the content of the polymerization catalyst can be appropriately changed according to its type. It should be noted that "ppm" represents "mass / mass ppm".

[0051] In addition, the polymerization catalyst is preferably diluted with a solvent that is inactive to the polymerization reaction (hereinafter also referred to as "solvent") before use. The concentration of the polymerization catalyst diluted with the solvent is preferably 0.05 to 30% by mass, more preferably 0.1 to 20% by mass, and further preferably 0.5 to 10% by mass. When the concentration of the diluted polymerization catalyst is 0.05 to 30% by mass, the polymerization catalyst can be sufficiently diffused into the monomers, so that the polymerization reaction can proceed uniformly.

[0052] Examples of the solvent include esters such as methyl formate, ethyl formate, methyl acetate, ethyl acetate, butyl acetate, and ketones such as acetone, 2-butanone, 2-pentanone, 3-pentanone, 2-hexanone, 3-hexanone, methyl isobutyl ketone, and methyl tert-butyl ketone. Among these, methyl formate, ethyl formate, methyl acetate, ethyl acetate, butyl acetate, acetone, 2-butanone, and methyl isobutyl ketone are preferred.

[0053] (Other additives)

[0054] In the method for producing a polyacetal copolymer according to an embodiment of the present invention, in addition to the above components, it is preferable to use known chain transfer agents such as methylal and butyral for adjusting the degree of polymerization (molecular weight), and hindered phenol antioxidants such as triethylene glycol bis[3-(3-tert-butyl-5-methyl-4-hydroxyphenyl)propionate] and pentaerythritol tetra[3-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate].

[0055] (Method for producing a polyacetal copolymer)

[0056] The method for producing a polyacetal copolymer according to an embodiment of the present invention is a method of copolymerizing trioxane with the above-mentioned comonomer in the presence of the above polymerization catalyst (heteropolyacid (A) and heteropolyacid salt (B)).

[0057] The production of the polyacetal copolymer according to an embodiment of the present invention can be carried out, for example, using known methods and polymerization apparatuses such as batchwise and continuous methods.

[0058] In a batchwise polymerization apparatus, a reaction tank with a stirrer commonly used can be used. In addition, in a continuous polymerization apparatus, a kneader, a twin-screw continuous extrusion mixer, a twin-shaft paddle screw extruder type, a twin-screw extruder with exhaust holes, etc. can be used. The industrially preferred production method is continuous.

[0059] The polyacetal copolymer according to an embodiment of the present invention can be obtained, for example, by continuously supplying a mixed solution containing trioxane, the above-mentioned comonomer, optional additives for polymerization reaction, and a polymerization catalyst (heteropolyacid (A) and heteropolyacid salt (B)) to a continuous twin-shaft paddle screw extruder type polymerization reaction apparatus having a jacket for passing a heating or cooling medium, and carrying out polymerization for a specified time.

[0060] In addition, by adding an alkaline compound such as an alkali metal compound, a quaternary amine compound, or a triazine compound having an amino group to the polyacetal copolymer obtained by the above method, and further carrying out melt-kneading to perform catalyst deactivation treatment, etc., a desired polyacetal copolymer can be produced.

[0061] In addition, when performing catalyst deactivation treatment, other components such as other polymers, other fillers, nitrogen compounds, ultraviolet absorbers and other stabilizers, metal salts and other acid scavengers, antistatic agents, flame retardants, dyes, pigments and other colorants, lubricants, mold release agents, crystallization promoters, crystal nucleating agents, etc. can be appropriately added according to the required properties. The other components can be used alone or in combination of two or more.

[0062] In the method for producing a polyacetal copolymer according to an embodiment of the present invention, a heteropolyacid (A) and a heteropolyacid salt (B) are mixed and used as a polymerization catalyst, so that a polyacetal copolymer can be stably produced even in mass production. The polyacetal copolymer can not only reduce the amount of formaldehyde generated, but also has excellent fluidity during molding and can produce molded articles with excellent appearance.

[0063] 2. Polyacetal copolymer

[0064] The polyacetal copolymer according to an embodiment of the present invention is a copolymer produced by the production method of the present invention. That is, it 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)).

[0065] The polyacetal copolymer obtained by the production method according to an embodiment of the present invention has excellent fluidity during molding. In addition, the molded article produced from the polyacetal copolymer can reduce the amount of formaldehyde generated and has excellent appearance.

[0066] Examples

[0067] Hereinafter, the present invention will be specifically described by way of examples, but the present invention is not limited to these.

[0068] 1. Production of polyacetal copolymers 1 to 22

[0069] [Polyacetal copolymer 1]

[0070] (Polymerization apparatus)

[0071] As the polymerization apparatus, a continuous twin-screw paddle extruder type (hereinafter also referred to as "polymerization apparatus") is used. The extruder type has a jacket for passing a heating or cooling medium on the outside of the main body. In addition, the main body is a vertically divided structure and is a structure that can be opened at the upper part. Inside the extruder type, two rotating shafts with a plurality of paddles for stirring and propulsion are provided along the length direction.

[0072] (Production method)

[0073] A mixed solution containing 100 parts by mass of trioxane (TOX), 4.0 parts by mass of 1,3-dioxolane (DO) and a specified amount of methylal is continuously supplied per unit time to a polymerization apparatus heated by passing a medium at 80 °C through the jacket. At the same time, a mixture of 2.5 ppm of phosphotungstic acid vanadium (A1) as the heteropolyacid (A) and 0.6 ppm of sodium phosphotungstate (B1) as the heteropolyacid salt (B) is added in the form of a methyl formate solution, and a polymerization reaction is carried out.

[0074] For the crude polymer obtained from the discharge port of the polymerization apparatus, 0.1% by mass of melamine and 0.3% by mass of IRGANOX 1010 (manufactured by BASF Japan Ltd., "IRGANOX" is a registered trademark of BASF Corporation) were added, and a twin-screw extruder with vent holes was continuously used. Melting and kneading were carried out under the conditions of a barrel temperature of 220°C of the extruder and a vacuum degree of 5 mmHg at the vent hole part, and then extrusion was performed to obtain pellets of polyacetal copolymer 1.

[0075] It should be noted that the addition amount of methylal was adjusted to an amount such that the melt flow rate (MFR) of the obtained copolymer became 9 g / 10 minutes. Here, "9 g" means the range of "9 g ± 0.3". For the above MFR, in accordance with ISO1133, using a Melt indexer L220 type (manufactured by TATEYAMA KAGAKU HIGH-TECHNOLOGIES CO., LTD.), the measurement was carried out under the conditions of a load of 2.16 kg, a temperature of 190°C, and a resin discharge acquisition time of 7 minutes.

[0076] [Polyacetal copolymer 2 - 8]

[0077] As shown in Table 1, the addition amounts of heteropolyacid (A) and / or heteropolyacid salt (B) were changed, and the addition amount of methylal was changed such that the MFR of the obtained copolymer became 9 g / 10 minutes. Except for this, pellets of polyacetal copolymers 2 - 8 were obtained using the same manufacturing method as that of polyacetal copolymer 1.

[0078] [Polyacetal copolymer 9]

[0079] As shown in Table 1, the type of comonomer, the addition amount of heteropolyacid salt (B), and the addition amount of methylal were changed such that the MFR of the obtained copolymer became 9 g / 10 minutes. Except for this, pellets of polyacetal copolymer 9 were obtained using the same manufacturing method as that of polyacetal copolymer 1.

[0080] [Polyacetal copolymers 10 - 14]

[0081] As shown in Table 1, the type of heteropolyacid salt (B) and the addition amount of methylal were changed such that the MFR of the obtained copolymer became 9 g / 10 minutes. Except for this, pellets of polyacetal copolymers 10 - 14 were obtained using the same manufacturing method as that of polyacetal copolymer 1.

[0082] [Polyacetal copolymers 15 - 17, 19, 20]

[0083] As shown in Table 1, the type of heteropolyacid salt (A), the addition amount of heteropolyacid salt (B), and the addition amount of methylal were changed in such a way that the MFR of the resulting copolymer became 9 g / 10 min. Otherwise, pellets of polyoxymethylene copolymers 15 to 17, 19, and 20 were obtained using the same production method as that of polyoxymethylene copolymer 1.

[0084] [Polyoxymethylene copolymer 18]

[0085] As shown in Table 1, the type of heteropolyacid salt (A), the type of heteropolyacid salt (B), and the addition amount of methylal were changed in such a way that the MFR of the resulting copolymer became 9 g / 10 min. Otherwise, pellets of polyoxymethylene copolymer 18 were obtained using the same production method as that of polyoxymethylene copolymer 1.

[0086] [Polyoxymethylene copolymer 21]

[0087] A mixed solution containing 100 parts by mass of trioxane (TOX), 4.0 parts by mass of 1,3-dioxolane (DO), and a specified amount of methylal was continuously supplied to the above polymerization apparatus per unit time. At the same time, 3.3 ppm of phosphotungstic acid (A5) as heteropolyacid (A) was added in the form of a methyl formate solution, and a polymerization reaction was carried out.

[0088] For the crude polymer obtained from the discharge port of the polymerization apparatus, 0.1% by mass of melamine and 0.3% by mass of IRGANOX 1010 were added, and a twin-screw extruder with vent holes was continuously used for melt-kneading and extrusion under the conditions of 220°C and a vacuum degree of 5 mmHg at the vent hole part to obtain pellets of polyoxymethylene copolymer 21.

[0089] It should be noted that the addition amount of methylal is the amount adjusted by the same method as that of polyoxymethylene copolymer 1.

[0090] [Polyoxymethylene copolymer 22]

[0091] A mixed solution containing 100 parts by mass of trioxane (TOX), 4.0 parts by mass of 1,3-dioxolane (DO), and a specified amount of methylal was continuously supplied to the above polymerization apparatus per unit time. At the same time, 30 ppm of boron trifluoride (C) was added to carry out a polymerization reaction. Then, the crude polymer obtained from the discharge port of the polymerization apparatus was added to an aqueous solution containing 0.1% of triethylamine to stop the polymerization reaction, and the copolymer was dried. It should be noted that boron trifluoride (C) was added in the form of a 0.3 wt% cyclohexane solution of dibutyl ether complex.

[0092] To the dried copolymer, 0.1% by mass of melamine and 0.3% by mass of IRGANOX 1010 were added, and continuous melt-kneading and extrusion were carried out using a twin-screw extruder with vent holes under the conditions of 220 °C and a vacuum degree of 5 mmHg at the vent hole part to obtain pellets of polyacetal copolymer 22.

[0093] It should be noted that the addition amount of methylal is the amount adjusted by the same method as that of polyacetal copolymer 1.

[0094] The heteropolyacid (A), heteropolyacid salt (B), and Lewis acid (C) described in the above manufacturing method are the compounds shown in Table 1.

[0095] 2. Evaluation

[0096] For the polyacetal copolymers 1 to 22 obtained by the above manufacturing method, the polymerization yield of the polyacetal copolymer, the appearance evaluation of the molded article using the polyacetal copolymer, the amount of formaldehyde generated, and the bar-flow (BF) evaluation were evaluated.

[0097] [Polymerization Yield of Polyacetal Copolymer]

[0098] (Evaluation Method)

[0099] The reaction products ejected from the ejection port of the polymerization apparatus were continuously collected for a certain period of time, and after being respectively added to an aqueous solution containing 0.1% of triethylamine, stirring was carried out for a specified time to deactivate the catalyst and wash the unreacted monomers. Then, the aqueous solution was filtered, and the obtained crude polymer was washed with acetone and dried. The proportion of the obtained copolymer relative to all monomers, that is, the polyacetal copolymer yield, was calculated from the weight of the dried polyacetal copolymer. A polymerization yield of the polyacetal copolymer of 70% or more is preferably practical.

[0100] [Amount of Formaldehyde Generated from Melt]

[0101] (Evaluation Method)

[0102] 5 g of each of the polyacetal copolymers 1 to 22 were respectively filled into a barrel maintained at 200 °C, and after melt retention for 5 minutes, the melt of the polyacetal copolymer was respectively extruded into a closed container. Nitrogen was introduced into the closed container, and the formaldehyde contained in the released nitrogen was dissolved in water and collected. The formaldehyde concentration in this water was measured according to JIS K0102 (2013), and from this, the mass of formaldehyde from the melt was obtained. The mass of this formaldehyde was divided by the mass of the polyacetal copolymer used as the formaldehyde generation amount (unit: ppm). A formaldehyde generation amount of 70 ppm or less is preferably practical.

[0103] [Appearance Evaluation of Molded Article]

[0104] (Evaluation method)

[0105] For polyoxymethylene copolymers 1 to 22, an injection molding machine (injection molding machine "S100iA" manufactured by FANUC ") was used to injection mold into a 50-square 3t flat plate with a center single-point pin gate under the following conditions. Then, the size of the flow mark near the gate of the molded product was measured, and the appearance was evaluated on a 5-grade scale.

[0106] (Molding conditions)(Molding conditions)

[0107] Barrel temperature (temperature of the nozzle tip: 200 °C)

[0108] Mold temperature: 90 °C

[0109] Holding pressure: 75 MPa

[0110] Injection time: 4.5 seconds

[0111] Injection conditions: Measurement position: 20 mm, Back suck: 5 mm, V-P switching position: 8 mm

[0112] (Evaluation)

[0113] 5: The size of the flow mark is less than 6 mm

[0114] 4: The size of the flow mark is 6 mm or more and less than 8 mm

[0115] 3: The size of the flow mark is 8 mm or more and less than 10 mm

[0116] 2: The size of the flow mark is 10 mm or more and less than 12 mm

[0117] 1: The size of the flow mark is 12 mm or more

[0118] [Bar flow evaluation]

[0119] (Evaluation method)

[0120] Using an injection molding machine (ES3000, manufactured by Nissei Plastic Industrial Co., Ltd.), polyoxymethylene copolymers 1 to 22 were injected into an evaluation mold with a thickness of 2 mm t, and the flow length was measured. The flow length (unit: mm) under each injection pressure was evaluated on a 5-grade scale.

[0121] (Molding conditions)

[0122] Barrel temperature (temperature of the nozzle tip: 195 °C)

[0123] Mold temperature: 80 °C

[0124] Injection speed: 70 mm / s

[0125] Injection pressure: 100 MPa

[0126] (Evaluation)

[0127] 5: The flow length at an injection pressure of 100 MPa is 450 mm or more

[0128] 4: The flow length at an injection pressure of 100 MPa is 440 mm or more and less than 450 mm

[0129] 3: The flow length at an injection pressure of 100 MPa is 430 mm or more and less than 440 mm

[0130] 2: The flow length at an injection pressure of 100 MPa is 420 mm or more and less than 430 mm

[0131] 1: The flow length at an injection pressure of 100 MPa is less than 420 mm

[0132] [Measurement of MFR]

[0133] In the production of polyacetal copolymers 1 to 22, the MFR, which is an index of the fluidity during melting of the obtained crude polymer, is determined as follows.

[0134] (Measurement method)

[0135] Measurement is carried out using a Melt indexer L220 type manufactured by TATEYAMA KAGAKU HIGH-TECHNOLOGIES CO., LTD. according to ISO1133 under the conditions of a load of 2.16 kg, a temperature of 190 °C, and a resin discharge acquisition time of 7 minutes.

[0136] Table 1 shows the main constituent components of polyacetal copolymers 1 to 22 and the evaluation results for each. In addition, in the abbreviations in Table 1, the names of heteropolyacid (A), heteropolyacid salt (B), and Lewis acid (C) are as described below.

[0137] (Main monomer)

[0138] TOX: Trioxane

[0139] (Comonomer)

[0140] DO: 1,3-Dioxolane

[0141] BDF: 1,4-Butanediol formal

[0142] [Polymerization catalyst]

[0143] (Heteropolyacid (A))

[0144] A1: H5PV2W 10 O40 (Phosphotungstic vanadic acid)

[0145] A2: H4PV1W 11 O 40 (Phosphotungstic vanadic acid)

[0146] A3: H6PV3W9O 40 (Phosphotungstic vanadic acid)

[0147] A4: H3PMo2W 10 O4 (Phosphomolybdic tungstic acid)

[0148] A5: H3PW 12 O 40 (Phosphotungstic acid)

[0149] (Heteropoly acid salt (B))

[0150] B1: Na3PW 12 O 40 (Sodium phosphotungstate)

[0151] B2: Li3PW 12 O 40 (Lithium phosphotungstate)

[0152] B3: K3PW 12 O 40 (Potassium phosphotungstate)

[0153] B4: NaSiW 12 O 40 (Sodium silicotungstate)

[0154] B5: Na3PMo 12 O 40 (Sodium phosphomolybdate)

[0155] B6: Na3PV2W 10 O 40 (Sodium phosphotungstic vanadate)

[0156] (Lewis acid (C))

[0157] C: BF3 (Boron trifluoride)

[0158] (Evaluation item)

[0159] HCHO: Formaldehyde

[0160] BF: Rod flow

[0161] [Table 1]

[0162]

[0163] As can be seen from Table 1, by using a mixture of a heteropolyacid (A) and a heteropolyacid salt (B) as a polymerization catalyst, it is possible to produce a polyacetal copolymer that can not only reduce the amount of formaldehyde generated but also obtain a stable polymerization yield and quality even in large-scale production. In particular, it is known that when using H5PV2W 10 O 40 (phosphotungstic vanadic acid) as the heteropolyacid (A) and Na3PW 12 O 40 (sodium phosphotungstate) as the heteropolyacid salt (B), the best results were obtained in all evaluation items.

[0164] Industrial applicability

[0165] By using the method of the present invention, it is possible to stably produce a polyacetal copolymer that can not only reduce the amount of formaldehyde generated but also has excellent fluidity during molding and excellent appearance of the molded product even in large-scale production. Therefore, it is expected to contribute to the technological development and popularization in the same field.

Claims

1. A method for producing a polyacetal copolymer, which is a method for producing a polyacetal copolymer by copolymerizing trioxane and a comonomer capable of copolymerizing with the trioxane in the presence of a polymerization catalyst. 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. H h [M 1 p ·M 2 q M 3 r O s ·iH2O·····(1) L j [N 1 v ·N 2 w N 3 x O y ·kH2O·····(2) In 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 that are the same as or different from each other, N 2 and N 3 are coordination elements of W, Mo, or V that are the same as or different from each other, where M 2 and M 3 as well as N 2 and N 3 At least one pair of which is composed of different coordination elements, where p is an integer greater than or equal to 1 and less than or equal to 10, q and r are positive integers, s is an integer greater than or equal to 10 and less than or equal to 100, h is an integer greater than or equal to 1, i is an integer greater than or equal to 0 and less than or equal to 50, v is an integer greater than or equal to 1 and less than or equal to 10, w and x are positive integers, y is an integer greater than or equal to 10 and less than or equal to 100, j is an integer greater than or equal to 1, k is an integer greater than or equal to 0 and less than or equal to 50, wherein, when M 2 and M 3 are the same coordination element, q + r is an integer greater than or equal to 6 and less than or equal to 40, when N 2 and N 3 are the same coordination element, w + x is an integer greater than or equal to 6 and less than or equal to 40.

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

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. 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. 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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