Method for producing polyacetal copolymer

Abstract

To provide a method for producing a polyacetal copolymer capable of obtaining a polyacetal copolymer having excellent hue and thermal stability, even when a polyacetal copolymer is produced using a protic acid as a polymerization catalyst.SOLUTION: There is provided a method for producing a polyacetal copolymer which comprises: a step of obtaining a crude polyacetal copolymer by copolymerization of trioxane as a main monomer (a) and a compound copolymerizable with trioxane as a comonomer (b), using a protic acid as a polymerization catalyst (c); a step of obtaining a mixture by mixing the crude polyacetal copolymer and a cyclic compound (d) containing an oxygen atom in the ring; and a step of feeding the mixture into an extruder to melt-knead while adding a predetermined basic compound (e) to the mixture.SELECTED DRAWING: None

Description

Technical Field

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

Background Art

[0002] Polyacetal copolymers are excellent in the balance of mechanical properties, chemical resistance, slidability, etc., and are widely used as engineering plastics mainly for electrical and electronic parts, automotive parts and other various mechanical parts because they are easy to process.

[0003] A polyacetal copolymer is a copolymer (copolymer) in which trioxane is a main monomer and a compound copolymerizable with the trioxane is a comonomer. And, as a method for producing a polyacetal copolymer (copolymer), cationic copolymerization using trioxane as a main monomer and a cyclic ether and / or cyclic formal having at least one carbon-carbon bond as a comonomer is known. Among the cationic active catalysts used for copolymerization, boron trifluoride or a coordination compound of boron trifluoride and an organic compound such as ethers is the most common polymerization catalyst using trioxane as a main monomer and is also widely used industrially.

[0004] However, generally used polymerization catalysts such as boron trifluoride-based compounds require a relatively large amount (for example, 40 ppm or more based on all monomers) of the catalyst for polymerization. Therefore, it is difficult to sufficiently perform the catalyst deactivation treatment after polymerization, and even if it is deactivated, substances derived from the catalyst remain in the copolymer, which may cause problems such as acceleration of the decomposition of the copolymer. In addition, the polymerization yield is low and several percent to several tens of percent of unreacted monomers remain. Therefore, the deactivation of the catalyst is generally carried out in a large amount of high-temperature aqueous solution containing a basic compound such as triethylamine, and at that time, the unreacted monomer elutes into the treatment solution. A complicated process such as a process of separating, washing and drying the copolymer from the treatment solution in which the unreacted monomer is dissolved after the catalyst is deactivated is required, and there are also economic problems.

[0005] On the other hand, the polymerized product after deactivation as described above has thermally unstable terminals. Therefore, a purification and stabilization treatment by hydrolyzing the unstable part of the terminal using an aqueous solution of triethylamine or the like is necessary, which increases the man-hours and causes an increase in cost.

[0006] Therefore, in order to solve the above problems, it has been proposed to use a heteropolyacid or its acidic salt as a polymerization catalyst (see Patent Document 1).

Prior Art Documents

Patent Documents

[0007]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0008] By producing a polyacetal copolymer using a protonic acid such as a heteropolyacid or its acidic salt as a polymerization catalyst as in Patent Document 1, the above various problems can be solved and certain results have been obtained. However, in the production of such a polyacetal copolymer, there are problems such as a decrease in fluidity during molding and resulting poor appearance of the molded product, and there is still room for improvement.

[0009] The present invention has been made in view of the above conventional problems, and the problem is to provide a method for producing a polyacetal copolymer that is excellent in fluidity during molding and surface properties of the molded product even when a protonic acid is used as a polymerization catalyst.

Means for Solving the Problems

[0010] The inventors have found that by mixing a solution of a cyclic compound containing an oxygen atom in the ring with the crude polyacetal copolymer after copolymerization, it is possible to maintain the good polymerization yield, which is an advantage when using a protonic acid as a polymerization catalyst, while improving the decrease in fluidity during molding and the poor appearance of the molded product, and thus have completed the present invention. One aspect of the present invention for solving the above problems is as follows.

[0011] (1) A step of copolymerizing trioxane as the main monomer (a) and a compound copolymerizable with the trioxane as the comonomer (b) using a protonic acid as the polymerization catalyst (c) to obtain a crude polyacetal copolymer, A step of mixing the crude polyacetal copolymer and a cyclic compound (d) containing an oxygen atom in the ring to obtain a mixture, and A step of adding, as the basic compound (e), a carbonate, bicarbonate or carboxylate of an alkali metal element or a Group 2 element (excluding Be) or a nitrogen-containing organic compound having a pH of 10 or more in a 10 g / L aqueous solution to the mixture and charging it into an extruder to perform melt kneading, which is a method for producing a polyacetal copolymer.

[0012] (2) The method for producing a polyacetal copolymer according to (1) above, wherein the cyclic compound (d) is a cyclic ether or a cyclic formal.

[0013] (3) The method for producing a polyacetal copolymer according to (1) or (2) above, wherein the cyclic compound (d) is 1,3-dioxolane or tetrahydrofuran.

[0014] (4) The method for producing a polyacetal copolymer according to any one of (1) to (3) above, wherein a heteropolyacid represented by the following general formula (1) is used as the polymerization catalyst (c). H m [M 1 x ·M 2 y O Z ·nH2O ··· General formula (1) 〔In the general formula (1), M 1represents a central element composed of elements selected from P, Si, B, and Ge. M 2 represents one or more coordination elements selected from W, Mo, and V. x represents an integer of 1 or more and 10 or less, y represents an integer of 6 or more and 40 or less, z represents an integer of 10 or more and 100 or less, m represents an integer of 1 or more, and n represents an integer of 0 or more and 50 or less. ]]

[0015] (5) The method for producing a polyacetal copolymer according to (4) above, wherein the heteropolyacid 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] (6) The method for producing a polyacetal copolymer according to any one of (1) to (5) above, wherein the carbonate, bicarbonate, carboxylate, or hydrate thereof of the alkali metal element or Group 2 element (excluding Be) is a carbonate, bicarbonate, carboxylate, or hydrate thereof of an alkali metal element.

[0017] (7) The method for producing a polyacetal copolymer according to any one of (1) to (6) above, wherein the comonomer (b) 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.

Advantages of the Invention

[0018] According to the present invention, even when a polyacetal copolymer is produced using a protonic acid as a polymerization catalyst, a method for producing a polyacetal copolymer excellent in fluidity during molding and surface properties of the molded article can be provided.

Embodiments for Carrying Out the Invention

[0019] The method for producing a polyacetal copolymer according to this embodiment includes a step of copolymerizing trioxane as the main monomer (a) and a compound copolymerizable with trioxane as the comonomer (b) using a protonic acid as the polymerization catalyst (c) to obtain a crude polyacetal copolymer (hereinafter, also referred to as "step A"), a step of mixing the crude polyacetal copolymer and a cyclic compound (d) containing an oxygen atom in the ring to obtain a mixture (hereinafter, also referred to as "step B"), and a step of adding the mixture to an extruder while adding a basic compound (e) which is a carbonate, bicarbonate or carboxylate of an alkali metal element or a Group 2 element (excluding Be) or a nitrogen-containing organic compound having a pH of 10 or more in a 10 g / L aqueous solution and performing melt-kneading (hereinafter, also referred to as "step C").

[0020] In the production method of this embodiment, in the step of copolymerizing trioxane as the main monomer (a) and a compound copolymerizable with trioxane as the comonomer (b), a copolymerization reaction is carried out using a protonic acid as the polymerization catalyst (c). Then, the crude polyacetal copolymer obtained by copolymerization and a cyclic compound (d) containing an oxygen atom in the ring are mixed to obtain a mixture. Next, while adding a predetermined basic compound (e) to the mixture, it is charged into an extruder and melt-kneading is performed. By doing so, the steps of catalyst deactivation and removal of unstable ends occurring in the extruder proceed stably, and the obtained copolymer is excellent in fluidity during molding and surface properties when formed into a molded article. The principle of this is unclear, but it is clear from experimental facts. Hereinafter, each step will be described.

[0021] [Step A] In step A, trioxane as the main monomer (a) and a compound copolymerizable with trioxane as the comonomer (b) are copolymerized using a protonic acid as the polymerization catalyst (c) to obtain a crude polyacetal copolymer.

[0022] Trioxane as the main monomer (a) is a cyclic trimer of formaldehyde and is generally obtained by reacting an aqueous formaldehyde solution in the presence of an acidic catalyst, which is then purified by methods such as distillation and used. The trioxane used for polymerization preferably has impurities such as water and methanol reduced as much as possible.

[0023] As the comonomer (b), a compound capable of copolymerizing with trioxane is used. Examples of the comonomer (b) include cyclic ethers and / or cyclic formals having at least one carbon-carbon bond. Representative examples of the compound used as the comonomer (b) include, for example, 1,3-dioxolane, diethylene glycol formal, 1,4-butanediol formal, 1,3-dioxane, ethylene oxide, propylene oxide, epichlorohydrin, and the like. Among them, 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 is preferable in consideration of the stability of polymerization. Furthermore, as long as it is within a range that does not significantly reduce the performance of the obtained polyacetal copolymer, in addition to the main monomer (a) and the comonomer (b), a known modifier comonomer such as a branching agent can be added in combination as a third comonomer component.

[0024] In the present embodiment, the amount of the compound selected from cyclic ethers and / or cyclic formals used as the comonomer (b) is preferably 0.1 to 20 mol% and more preferably 0.2 to 10 mol% as a proportion in all monomers (the total amount of the main monomer (a) and the comonomer (b)). If the amount of the comonomer (b) is less than 0.1 mol%, the unstable end portions of the polyacetal copolymer produced by polymerization may increase and the stability may deteriorate. If the amount of the comonomer (b) exceeds 20 mol%, the produced copolymer may become soft and the melting point may decrease.

[0025] In the production method of the present embodiment, a protonic acid is used as the polymerization catalyst (c). Examples of the protonic acid include heteropolyacids, isopolyacids, perfluoroalkanoic acids, and the like. Among them, as the protonic acid, it is preferable to use a heteropolyacid represented by the following general formula (1).

[0026] H m [M 1 x ·M 2 y O Z ·nH2O ··· General formula (1) 〔In the general formula (1), M 1 represents a central element composed of an element selected from P, Si, B, and Ge. M 2 represents one or more coordination elements selected from W, Mo, and V. x represents an integer of 1 or more and 10 or less, y represents an integer of 6 or more and 40 or less, z represents an integer of 10 or more and 100 or less, m represents an integer of 1 or more, and n represents an integer of 0 or more and 50 or less.〕 Note that y represents the number of M 2 , when M 2 is single, it represents the number, and when M 2 consists of multiple types, it represents the total of these multiple types of elements.

[0027] M 1 represents a central element composed of an element selected from P, Si, B, and Ge, and P or Si is preferable.

[0028] As the heteropolyacid represented by the general formula (1) as the polymerization catalyst (c), it is preferably 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.

[0029] In the present embodiment, as the polymerization catalyst (c), in addition to the heteropolyacid represented by the general formula (1), the H mAn acidic salt having a structure in which part or all of it is replaced with various metals may be used in combination.

[0030] When the polymerization catalyst (c) is in the form of a solution, solvents include esters obtained by condensing low molecular weight carboxylic acids having 1 to 10 carbon atoms such as formic acid, acetic acid, propionic acid, and butyric acid with low molecular weight alcohols having 1 to 10 carbon atoms such as methanol, ethanol, 1-propanol, 2-propanol, 1-butanol, 2-butanol, 2-methyl-1-propanol, 2-methyl-2-propanol, 1-pentanol, 3-methyl-1-butanol, and 1-hexanol; low molecular weight ketones having 1 to 10 carbon atoms such as acetone, 2-butanone, 2-pentanone, 3-pentanone, 2-hexanone, 3-hexanone, methyl isobutyl ketone, and methyl-t-butyl ketone are preferably mentioned, but are not limited thereto. Considering industrial availability and the like, methyl formate, ethyl formate, methyl acetate, ethyl acetate, butyl acetate, acetone, 2-butanone, methyl isobutyl ketone, etc. are most suitable. The polymerization catalyst (c) is preferably dissolved in the above inert solvent at a concentration of 0.1 to 30 mass / mass%, but is not limited thereto.

[0031] In the production method of this embodiment, even if the amount of the polymerization catalyst (c) used is reduced, a copolymer can be obtained in a high yield. Specifically, the amount of the polymerization catalyst (c) used relative to the total amount of the main monomer (a) and the comonomer (b) can be 1.0 to 20.0 mass ppm, and preferably 1.5 to 10.0 mass ppm. And the fact that copolymerization is possible even with such a small amount of the polymerization catalyst (c) is effective in minimizing undesirable reactions such as main chain decomposition and depolymerization of the polymer by the polymerization catalyst, and suppressing the formation of unstable formate end groups (-O-CH=O), hemiacetal end groups (-O-CH2-OH), etc., and is also economically advantageous.

[0032] In Project A, the main monomer (a), the comonomer (b), and the polymerization catalyst (c) are introduced into a polymerization reactor to carry out a copolymerization reaction. At this time, among the main monomer (a), the comonomer (b), and the polymerization catalyst (c), after mixing the main monomer (a) and the comonomer (b), the polymerization catalyst (c) is added, or after mixing the polymerization catalyst (c) with the main monomer (a) or the comonomer (b), it is mixed with the comonomer (b) or the main monomer (a). Further, the polymerization reaction is preferably carried out by bulk polymerization with the main monomer (a) in a molten state, and usually starts at 65°C or higher and 114°C or lower. Since the polyacetal copolymer is insoluble in the main monomer (a), it precipitates, but strong stirring is carried out at high speed so as not to form lumps, and the reaction product is pulverized. In order to obtain a continuous reaction, it is necessary to keep the temperature at 65°C or higher, but it is preferably kept at 130°C or lower so that the depolymerization reaction does not occur. More preferably, it is 70 to 125°C.

[0033] By carrying out the copolymerization reaction as described above, a crude polyacetal copolymer can be obtained in a high yield. In this crude polyacetal copolymer, almost no unreacted monomer remains, and a removal step of washing with hot water becomes unnecessary.

[0034] In the method for producing a polyacetal copolymer of the present embodiment, in Step A, a molecular weight regulator may be used as necessary. As the molecular weight regulator, a linear formal compound can be used. Examples of the linear formal compound include methylal, ethylal, dibutoxymethane, bis(methoxymethyl) ether, bis(ethoxymethyl) ether, bis(butoxymethyl) ether, and the like. Among them, it is preferably at least one selected from the group consisting of methylal, ethylal, and dibutoxymethane.

[0035] Furthermore, in the method for producing a polyacetal copolymer of the present embodiment, in Step A, an antioxidant may be added as necessary.

[0036] [Step B] In Step B, a crude polyacetal copolymer and a cyclic compound (d) having an oxygen atom in the ring are mixed to obtain a mixture.

[0037] In Step B, the crude polyacetal copolymer obtained in Step A and a cyclic compound (d) (hereinafter also simply referred to as "cyclic compound (d)") having an oxygen atom in the ring are mixed to obtain a mixture. The cyclic compound (d) can lose the activity of the polymerization catalyst (c) to some extent. Here, to obtain a mixture of the crude polyacetal copolymer and the cyclic compound (d), a commonly used mixer can be used. On the other hand, to sufficiently disperse the cyclic compound (d), it is preferable to use a continuous mixing apparatus for powder and liquid configured to disperse and contact the powder with the continuously supplied liquid and obtain a uniform mixed fluid of the powder and the liquid through a rotating mixing disk. By using such a continuous mixing apparatus, the powder of the crude polyacetal copolymer and the liquid of the cyclic compound (d) become a uniform mixed fluid, and the cyclic compound (d) is uniformly dispersed in the crude polyacetal copolymer. Details of such a continuous mixing apparatus are described, for example, in JP-A-2002-248330 and JP-A-2004-168055.

[0038] In the present embodiment, as the cyclic compound (d), it is preferable that the ring has one or two oxygen atoms, that is, a cyclic ether or a cyclic formal. More specifically, as the cyclic compound (d), 1,3-dioxolane or tetrahydrofuran is preferable.

[0039] In the present embodiment, the above cyclic compound (d) may be of one type or two or more types may be used in combination.

[0040] [Step C] In Step C, while adding a carbonate, bicarbonate, or carboxylate of an alkali metal element or a Group 2 element (excluding Be), or a nitrogen-containing organic compound with a pH of 10 or more in a 10 g / L aqueous solution to the mixture obtained in Step B, it is charged into an extruder and melt-kneaded. The polymerization catalyst (c) has its activity somewhat lost by the cyclic compound (d) in Step B, but its activity is further lost by the basic compound (e) in Step C. That is, by Steps B and C, the polymerization catalyst (c) is sufficiently deactivated. As a result, discoloration prevention and improvement of the thermal stability of the obtained polyacetal copolymer can be achieved.

[0041] In Step C, as the basic compound (e), a carbonate, bicarbonate, or carboxylate of an alkali metal or a Group 2 element or its hydrate, or a nitrogen-containing organic compound with a pH of 10 or more in a 10 g / L aqueous solution is used. Examples of the carbonate, bicarbonate, or carboxylate of an alkali metal or a Group 2 element or its hydrate include sodium carbonate, sodium bicarbonate, potassium carbonate, calcium carbonate, calcium bicarbonate, sodium formate, sodium acetate, disodium succinate, sodium laurate, sodium palmitate, sodium stearate, calcium stearate, sodium hydroxide, potassium hydroxide, etc. Examples of the nitrogen-containing organic compound with a pH of 10 or more in a 10 g / L aqueous solution include amine compounds such as triethylamine, choline hydroxide, trimethylamine, ethanolamine, etc. Among them, it is preferably a carbonate, bicarbonate, or carboxylate of an alkali metal element or its hydrate. The pH in the nitrogen-containing organic compound with a pH of 10 or more in a 10 g / L aqueous solution is the pH at 25°C. The basic compound (e) may be added as a solid (powder) or as an aqueous solution.

[0042] Since deactivation is carried out in a homogeneous molten resin, the polymerization catalyst (c) can be deactivated without immersing the powder obtained by pulverizing the crude polyacetal copolymer in an aqueous solution of a deactivating agent and treating it for a long time in a solid-liquid heterogeneous state as in the prior art. Therefore, the steps from immersion in the aqueous solution of the deactivating agent to drying can be omitted. Furthermore, since the generation of thermally unstable terminals generated by long-term immersion in an aqueous solution of the basic compound (e) can be suppressed, stabilization treatment is not required. Examples of the thermally unstable terminal include -CH2CH2O-(CH2O) n -CH2OH and -CH2CH2O-(CH2O) n -CH2O-CHO. In the group representing the above unstable terminal, n represents zero or any positive integer. Furthermore, in the prior art, when deactivating the catalyst in the crude copolymer by immersion in a basic solution, unreacted monomers extracted into the aqueous solution can also be recovered, and monomer loss can be suppressed.

[0043] For Step C, for example, (1) a method of directly melt-kneading the mixture obtained in Step B to perform deactivation and stabilization to obtain a polyacetal copolymer, (2) a method of adding other additives to the mixture obtained in Step B, melt-kneading, and performing deactivation and stabilization to obtain a resin composition, etc. can be adopted. In the case of (2) above, examples of the addition method of the additive include adding it together with the mixture to the main feed section of the extruder and adding it alone from the side feed section of the extruder. Also, in both of the above (1) and (2), the polyacetal copolymer or resin composition discharged from the discharge port of the extruder can be pelletized by a known method, such as cutting the cooled resin discharged from the discharge port of the extruder with a strand cutter.

Examples

[0044] Hereinafter, the present embodiment will be described in more detail by way of examples, but the present embodiment is not limited to the following examples.

[0045] [Examples 1 to 12, Comparative Examples 1 to 3] (Step A) A continuous twin-screw polymerization machine was used as the polymerization reactor. This polymerization machine is equipped with a jacket for passing a heating or cooling medium on the outside, and inside it, two rotating shafts with a number of paddles for stirring, propulsion, and pulverization are provided in the longitudinal direction. Then, while rotating the two rotating shafts of the polymerization machine at a constant speed so that the circumferential speed of the paddle tip becomes 0.5 m / s, the main monomer (a) (trioxane) and the comonomer (b) shown in Table 1 were added and mixed at the ratios shown in Table 1. To the resulting mixture, a polymerization catalyst (c) (in a 2 g / L methyl formate solution, 5 ppm with respect to all monomers) shown in Table 1 was further added. Here, in Table 1, the addition amounts of the additives (cyclic compound (d) and basic compound (e)) are mass ratios with respect to the total amount of the main monomer (a) and the comonomer (b). Next, methylal was supplied as a molecular weight regulator so that the melt flow rate of the resulting copolymer became 9 g / 10 min. Bulk polymerization was carried out in the above state to obtain a powdery crude polyacetal copolymer that was pulverized and discharged from the polymerization machine. In Table 1, the comonomers are shown by abbreviations, but specifically they are as follows. DO: 1,3-dioxolane BDF: 1,4-butanediol formal Furthermore, in Table 1, the polymerization catalysts C1 and C2 are as follows. Polymerization catalyst C1: phosphotungstic acid (H3PW 12 O 40 ) Polymerization catalyst C2: phosphomolybdic acid (H3PMo 12 O 40 )

[0046] (Step B) The powdery crude polyacetal copolymer discharged continuously from the polymerization reactor and the cyclic compound (d) shown in Table 1 were introduced into a continuous mixing device (Flow Jet Mixer Continuous Injection Mixer Model 100, manufactured by Funken Poutecks Co., Ltd.) at a flow rate such that the addition amount of the cyclic compound (d) was the ratio shown in Table 1 to obtain a mixture of the cyclic compound (d) and the crude polyacetal copolymer. At this time, the Flow Jet Mixer system was mixed so that the circumferential speed of the outer periphery of the rotating mixing disk became 2.5 m / s. In Table 1, cyclic compounds D1 to D2 are as follows. Cyclic compound D1: 1,3-dioxolane Cyclic compound D2: tetrahydrofuran

[0047] (Step C) Subsequently, 15 ppm of the basic compound (e) shown in Table 1, 0.3% by mass of Irganox 1010, and 0.1% by mass of melamine were added to the mixture of the obtained crude polyacetal copolymer and the cyclic compound (d), and the mixture was charged into a twin-screw extruder and melt-kneaded (cylinder temperature: 200 °C) to deactivate the polymerization catalyst (c) and obtain pellets of the polyacetal copolymer. In Table 1, deactivators E1 to E4 are as follows. Deactivator E1: sodium carbonate Deactivator E2: potassium carbonate Deactivator E3: sodium hydrogen carbonate Deactivator E4: sodium stearate

[0048] [Molded product appearance evaluation] (Evaluation method) The obtained polyacetal copolymer pellets were injection-molded into a 50° angle 3t flat plate with a center one-point gate of φ1.5 mm under the following conditions using an injection molding machine (FANUC injection molding machine S100iA (φ36)). Subsequently, the size of the flow mark near the gate of the molded product was measured, and the appearance evaluation was visually evaluated in five grades. (Molding conditions) Cylinder temperature (Nozzle head) 200 °C - 200 °C - 180 °C - 170 °C (hopper side) Mold temperature: 90 °C Holding pressure: 75 MPa Injection time: 4.5 seconds Injection conditions: metering position 20 mm, cushion 5 mm, V-P switching position 8 mm (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

[0049] [Bar flow] The obtained copolymer pellets were each injected into a 2 mm thick evaluation mold using a molding machine (injection molding machine ES3000 manufactured by Nissei Plastic Industrial Co., Ltd.) to measure the flow length. The flow length (unit: mm) at an injection pressure of 100 MPa was evaluated in 5 grades. (Molding conditions) Cylinder temperature (Nozzle head) 195°C - 195°C - 195°C - 195°C - 175°C (hopper side) Mold temperature: 80°C Injection speed: 70 mm / s Injection pressure: 100 MPa (Evaluation) 5: The flow length is 450 mm or more 4: The flow length is 440 mm or more and less than 450 mm 3: The flow length is 430 mm or more and less than 440 mm 2: The flow length is 420 mm or more and less than 430 mm 1: The flow length is less than 420 mm

[0050] [Table 1]

[0051] From Table 1, it can be seen that all evaluations of Examples 1 to 12 obtained good results, and the molded product appearance and fluidity were excellent. On the other hand, in Comparative Examples 1 to 3 where the cyclic compound (d) was not used, good results were not obtained in both evaluations of the molded product appearance and fluidity. Also, from the comparison between Example 2 and Example 5 where all other components except the cyclic compound (d) had the same composition, it can be seen that better evaluation results were obtained when using the cyclic compound D2 (tetrahydrofuran).

Claims

1. A step of copolymerizing trioxane as the main monomer (a) and a compound copolymerizable with the trioxane as the comonomer (b) using a protonic acid as the polymerization catalyst (c) to obtain a crude polyacetal copolymer; A step of mixing the crude polyacetal copolymer and a cyclic compound (d) containing an oxygen atom in the ring to obtain a mixture; and A step of adding, as the basic compound (e), a carbonate, bicarbonate or carboxylate of an alkali metal element or a Group 2 element (excluding Be), or a nitrogen-containing organic compound having a pH of 10 or more in a 10 g / L aqueous solution to the mixture, and charging it into an extruder to perform melt-kneading, which is included in a method for producing a polyacetal copolymer.

2. The method for producing a polyacetal copolymer according to claim 1, wherein the cyclic compound (d) is a cyclic ether or a cyclic formal.

3. The method for producing a polyacetal copolymer according to claim 1 or 2, wherein the cyclic compound (d) is 1,3-dioxolane or tetrahydrofuran.

4. The method for producing a polyacetal copolymer according to claim 1 or 2, wherein a heteropolyacid represented by the following general formula (1) is used as the polymerization catalyst (c). H ｍ [M １ ｘ ·M ２ ｙ O Ｚ ]·nH ２ O ··· General formula (1) [In the general formula (1), M １ represents a central element composed of an element selected from P, Si, B and Ge. M ２ represents one or more coordination elements selected from W, Mo and V. x represents an integer of 1 or more and 10 or less, y represents an integer of 6 or more and 40 or less, z represents an integer of 10 or more and 100 or less, m represents an integer of 1 or more, and n represents an integer of 0 or more and 50 or less. ]

5. The method for producing a polyacetal copolymer according to claim 4, wherein the heteropolyacid 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.

6. The method for producing a polyacetal copolymer according to claim 1 or 2, wherein the carbonate, hydrogen carbonate, carboxylate or hydrate thereof of the alkali metal element or Group 2 element (excluding Be) is a carbonate, hydrogen carbonate, carboxylate or hydrate thereof of an alkali metal element.

7. The method for producing a polyacetal copolymer according to claim 1 or 2, wherein the comonomer (b) 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.

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