Method for producing polyacetal copolymer

Abstract

A method for producing a polyacetal copolymer, which comprises: a step for obtaining a crude polyacetal copolymer by copolymerizing trioxymethylene, which is a main monomer (a), and a compound that is copolymerizable with trioxymethylene, which is a co-monomer (b), using a protonic acid as a polymerization catalyst (c); a step in which a solution of the crude polyacetal copolymer and the basic compound (d) is introduced into a predetermined continuous mixing device and mixed to obtain a mixture; and a step in which the mixture is introduced into an extruder and melt-kneaded, the basic compound (d) being a carbonate, bicarbonate or the like of an alkali metal element or a group 2 element (excluding Be), and the solvent of the solution of the basic compound (d) being a solvent having active hydrogen.

Description

Technical Field

[0001] This invention relates to a method for manufacturing a polyacetal copolymer. Background Technology

[0002] Polyacetal copolymers are widely used as engineering plastics, primarily in electrical and electronic components, automotive parts, and various other mechanical components, due to their excellent balance of mechanical properties, chemical resistance, and sliding performance, as well as their ease of processing.

[0003] Polyacetal copolymers are copolymers that use trioxymethylene as the main monomer and compounds that can copolymerize with trioxymethylene as comonomers. Furthermore, as a method for manufacturing polyacetal copolymers, cationic copolymerization using trioxymethylene as the main monomer and cyclic ethers having at least one carbon-carbon bond and / or cyclic methyl acetals as comonomers is known. As cationic active catalysts for copolymerization, boron trifluoride, or coordination compounds of boron trifluoride with organic compounds such as ethers, is the most common polymerization catalyst for trioxymethylene as the main monomer and is widely used in industry.

[0004] However, commonly used polymerization catalysts such as boron trifluoride compounds require relatively large amounts (e.g., more than 40 ppm relative to total monomers) during polymerization. Therefore, post-polymerization catalyst deactivation is difficult to achieve adequately. Furthermore, even when deactivated, catalyst-derived substances may remain in the copolymer, promoting copolymer decomposition. Additionally, polymerization yields are low, and unreacted monomers remain at several percent to tens of percent. Therefore, catalyst deactivation is generally carried out in a large volume of high-temperature aqueous solution containing alkaline compounds such as triethylamine, where unreacted monomers dissolve in the treatment solution. After catalyst deactivation, the copolymer requires a complex process involving separation, washing, and drying of the treatment solution containing dissolved unreacted monomers, which also presents economic challenges.

[0005] On the other hand, the polymer products deactivated using the above method contain thermally unstable ends. Therefore, purification and stabilization treatment is required by hydrolyzing the unstable ends that have been treated with triethylamine aqueous solution, which increases the workload and thus the cost.

[0006] Therefore, in order to solve the problems mentioned above, a scheme using heteropolyacids or their acidic salts as polymerization catalysts has been proposed (see Patent Document 1).

[0007] Existing technical documents

[0008] Patent documents

[0009] Patent Document 1: Japanese Patent Application Publication No. 1-170610 Summary of the Invention

[0010] The problem that the invention aims to solve

[0011] As in Patent Document 1, using protic acids such as heteropoly acids or their acidic salts as polymerization catalysts to manufacture polyacetal copolymers can solve many of the aforementioned problems and has yielded certain results. However, when solid substances are added as deactivators to deactivate the aforementioned polymerization catalysts, the deactivators are not sufficiently dispersed relative to the polymerization catalysts. Increasing the amount of deactivator to ensure sufficient deactivation of the polymerization catalyst sometimes results in discoloration of the obtained polyacetal copolymers.

[0012] The present invention was made in view of the above-mentioned problems, and its object is to provide a method for manufacturing polyacetal copolymers, which can obtain polyacetal copolymers with excellent color even when using protic acid as a polymerization catalyst to manufacture polyacetal copolymers.

[0013] Solution for solving the problem

[0014] The inventors discovered that by using a solution of an alkaline compound and a prescribed continuous mixing device in the deactivation of protic acid polymerization catalysts, the amount of deactivating agent used can be reduced, thus solving the aforementioned problems, thereby completing the present invention.

[0015] One aspect of the present invention that solves the aforementioned problems is as follows.

[0016] (1) A method for manufacturing a polyacetal copolymer, comprising the following steps:

[0017] A process of copolymerizing trioxymethylene (a) as a main monomer (a) with a compound (b) that can copolymerize with said trioxymethylene as a comonomer (b) by using a protic acid as a polymerization catalyst (c) to obtain a crude polyacetal copolymer.

[0018] The process of obtaining a mixture by introducing a solution of the crude polyacetal copolymer and the basic compound (d) into a continuous mixing device for powder and liquid and mixing them, wherein the continuous mixing device is configured to disperse and mix the powder in a continuously supplied liquid, and to obtain a uniform mixture of powder and liquid fluid by means of a rotating mixing disc; and

[0019] The process of feeding the mixture into an extruder and performing melt mixing.

[0020] The basic compound (d) is a carbonate, bicarbonate, or carboxylate of an alkali metal or a Group 2 element (except Be), or a nitrogen-containing organic compound with a pH of 10 or higher in a 10 g / L aqueous solution.

[0021] The solvent for the solution of the alkaline compound (d) is a solvent with active hydrogen.

[0022] (2) The method for manufacturing polyacetal copolymer according to (1) above, wherein a heteropolyacid represented by the following general formula (1) is used as the polymerization catalyst (c).

[0023] H m [M 1 x·M 2 y O Z ]·nH2O···General Formula (1)

[0024] In general formula (1), M 1 This represents the central element, which is composed of elements selected from P, Si, B, and Ge. 2 This represents one or more coordination elements selected from W, Mo, and V. x represents an integer greater than or equal to 1 and less than 10, y represents an integer greater than or equal to 6 and less than 40, z represents an integer greater than or equal to 100, m represents an integer greater than or equal to 1, and n represents an integer greater than or equal to 0 and less than 50.

[0025] (3) The method for manufacturing polyacetal copolymer according to (2) above, wherein the heteropolyacid is at least one selected from the group consisting of phosphomolybdic acid, phosphotungstic acid, phosphomolybdic tungstic acid, phosphomolybdic vanadate, phosphomolybdic tungstic vanadate, phosphomolybdic vanadate, phosphomolybdic vanadate, silicotungstic acid, silicotungstic acid, silicotungstic acid, and silicotungstic vanadate.

[0026] (4) The method for manufacturing polyacetal copolymer according to any one of (1) to (3) above, wherein the carbonate, bicarbonate or carboxylate or hydrate of the alkali metal element or group II element (except Be) is the carbonate, bicarbonate or carboxylate or hydrate of the alkali metal element.

[0027] (5) The method for manufacturing the polyacetal copolymer according to any one of (1) to (4) above, wherein the comonomer (b) is at least one selected from the group consisting of 1,3-dioxolane, diethylene glycol methyl acetal, 1,4-butanediol methyl acetal, 1,3-dioxane, and ethylene oxide.

[0028] Invention Effects

[0029] According to the present invention, a method for manufacturing polyacetal copolymers is provided, which can still obtain polyacetal copolymers with excellent color even when using protic acid as a polymerization catalyst to manufacture polyacetal copolymers. Detailed Implementation

[0030] The method for manufacturing the polyacetal copolymer of this embodiment includes the following steps: a step (hereinafter also referred to as "Step A") of copolymerizing trioxymethylene (a) as the main monomer (a) with a compound that can copolymerize with trioxymethylene (b) as a comonomer by using a protic acid as a polymerization catalyst (c); a step (hereinafter also referred to as "Step B") of obtaining a mixture by introducing a solution of the crude polyacetal copolymer and an alkaline compound (d) into a continuous mixing device for powder and liquid and mixing it, wherein the continuous mixing device is configured to disperse and mix the powder in a continuously supplied liquid and obtain a uniform mixed fluid of powder and liquid by rotating a mixing disc; and a step (hereinafter also referred to as "Step C") of feeding the mixture into an extruder and performing melt mixing. Furthermore, the alkaline compound (d) is a carbonate, bicarbonate, or carboxylate of an alkali metal element or a Group II element (excluding Be), or a nitrogen-containing organic compound with a pH of 10 or higher in a 10 g / L aqueous solution. In addition, the solvent of the solution of the alkaline compound (d) is a solvent containing active hydrogen.

[0031] In the manufacturing method of this embodiment, in the step of copolymerizing trioxymethylene (a) as the main monomer (a) with a compound that can copolymerize with trioxymethylene (b) as the comonomer, a protic acid is used as the polymerization catalyst (c) for the copolymerization reaction. Furthermore, the polymerization catalyst (c) is deactivated by mixing a basic compound (d) in solution with the crude polyacetal copolymer obtained through copolymerization. At this time, by using a prescribed continuous mixing device, the basic compound (d) is fully dispersed in the crude polyacetal copolymer to fully utilize the deactivation performance. Moreover, by feeding the mixture into an extruder and performing melt mixing in this state, the polymerization catalyst (c) can be fully deactivated. Furthermore, since a prescribed continuous mixing device is used, the amount of deactivating agent used can be reduced, thus obtaining particles with excellent color.

[0032] The following describes each process.

[0033] [Process A]

[0034] In step A, a crude polyacetal copolymer is obtained by copolymerizing trioxymethylene (a) as the main monomer (a) with a compound that can copolymerize with trioxymethylene (b) as a comonomer (c) using a protic acid as a polymerization catalyst (c).

[0035] Trioxymethylene (a), the main monomer, is a cyclic trimer of formaldehyde. It is generally obtained by reacting an aqueous solution of formaldehyde in the presence of an acidic catalyst, and then purified by methods such as distillation before use. The trioxymethylene used for polymerization is preferably a substance with as little impurities as possible, such as water and methanol.

[0036] The comonomer (b) is a compound that can copolymerize with trioxymethylene. Examples of comonomers (b) include cyclic ethers and / or cyclic methyl acetals having at least one carbon-carbon bond. Representative examples of compounds used as comonomers (b) include 1,3-dioxolane, diethylene glycol methyl acetal, 1,4-butanediol methyl acetal, 1,3-dioxane, ethylene oxide, propylene oxide, epichlorohydrin, etc. Preferably, from the perspective of polymerization stability, at least one selected from the group consisting of 1,3-dioxolane, diethylene glycol methyl acetal, 1,4-butanediol methyl acetal, 1,3-dioxane, and ethylene oxide is preferred.

[0037] Furthermore, if the performance of the obtained polyacetal copolymer is not significantly reduced, in addition to the main monomer (a) and comonomer (b), a known modifier comonomer such as a branching agent can be used as a third comonomer component.

[0038] In this embodiment, the amount of the compound selected from cyclic ethers and / or cyclic methyl acetals used as comonomer (b) is preferably 0.1 to 20 mol% as a percentage of the total monomers (the sum of the main monomer (a) and comonomer (b)), more preferably 0.2 to 10 mol%. When the amount of comonomer (b) is less than 0.1 mol%, the unstable ends of the polyacetal copolymer formed by polymerization sometimes increase, resulting in poor stability. When the amount of comonomer (b) exceeds 20 mol%, the copolymer sometimes becomes soft and the melting point decreases.

[0039] In the manufacturing method of this embodiment, a protic acid is used as a polymerization catalyst (c). Examples of protic acids include heteropolyacids, isopolyacids, and perfluoroalkyl acids.

[0040] Among them, as a protonic acid, a heteropoly acid represented by the following general formula (1) is preferred.

[0041] H m [M 1 x·M 2 y O Z ]·nH2O···General Formula (1)

[0042] In general formula (1), M 1 This represents the central element, which is composed of elements selected from P, Si, B, and Ge. 2 This represents one or more coordination elements selected from W, Mo, and V. x represents an integer greater than or equal to 1 and less than 10, y represents an integer greater than or equal to 6 and less than 40, z represents an integer greater than or equal to 100, m represents an integer greater than or equal to 1, and n represents an integer greater than or equal to 0 and less than 50.

[0043] In addition, y represents M 2 The number of, but in M 2 In the case of a single instance, the number of instances is represented in M. 2 In the case of multiple components, it represents the sum of these multiple elements.

[0044] Although M 1 It represents a central element composed of elements selected from P, Si, B, and Ge, but preferably P or Si.

[0045] The heteropolyacid represented by general formula (1) as the polymerization catalyst (c) is preferably at least one selected from the group consisting of phosphomolybdic acid, phosphotungstic acid, phosphomolybdic tungstic acid, phosphomolybdic vanadate, phosphomolybdic tungstic vanadate, phosphomolybdic ...silicotungstic acid, silicotungstic acid, silicotungstic acid, and silicotungstic vanadate.

[0046] In this embodiment, in addition to the heteropolyacid represented by the general formula (1), acidic salts of the heteropolyacid whose Hm is partially or completely replaced by various metals can also be used as polymerization catalysts (c).

[0047] When the polymerization catalyst (c) is a solution, preferred solvents include low molecular weight carboxylic acids with 1 to 10 carbon atoms such as formic acid, acetic acid, propionic acid, and butyric acid; esters obtained by condensation with low molecular weight alcohols with 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; and ketones with 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, but these are not limited to these. When considering ease of industrial use, methyl formate, ethyl formate, methyl acetate, ethyl acetate, butyl acetate, acetone, 2-butanone, and methyl isobutyl ketone are preferred. The polymerization catalyst (c) can be suitably dissolved in the above-mentioned inert solvent at a concentration of 0.1 to 30 wt% but is not limited thereto.

[0048] In the manufacturing method of this embodiment, copolymers can still be obtained in high yield even with a reduced amount of polymerization catalyst (c). Specifically, the amount of polymerization catalyst (c) used relative to the total amount of the main monomer (a) and comonomer (b) can be 1.0 to 20.0 ppm by mass, preferably 1.5 to 10.0 ppm by mass. Moreover, even such a small amount of polymerization catalyst (c) can copolymerize, which minimizes undesirable reactions such as main chain decomposition and depolymerization of the polymer induced by the polymerization catalyst. This is effective in suppressing the formation of unstable formate terminal groups (-O-CH=O), hemiacetal terminal groups (-O-CH2-OH), etc., and is also economically advantageous.

[0049] In step A, the main monomer (a), comonomer (b), and polymerization catalyst (c) are fed into a polymerization reactor to carry out a copolymerization reaction. At this time, the polymerization catalyst (c) is added after the main monomer (a) and comonomer (b) are mixed, or the polymerization catalyst (c) is mixed with either the main monomer (a) or the comonomer (b) and then mixed with either the main monomer (a) or the main monomer (a). Furthermore, the polymerization reaction is preferably carried out by bulk polymerization, where the main monomer (a) is molten, typically starting at 65°C to 114°C. Since the polyacetal copolymer is insoluble in the main monomer (a), it will precipitate; however, to prevent it from becoming lumpy, it is subjected to vigorous stirring at high speed to pulverize the reaction products. To obtain a sustained reaction, the temperature needs to be maintained above 65°C, but to avoid depolymerization, it is preferably maintained below 130°C. More preferably, it is 70–125°C.

[0050] The polymerization time depends on the concentration of the polymerization catalyst, the concentration of the comonomer, and the reaction temperature. There is no particular limitation, but a polymerization time of 0.5 to 10 minutes is generally chosen.

[0051] By employing the copolymerization reaction as described above, crude polyacetal copolymers can be obtained in high yield. These crude polyacetal copolymers contain almost no residual unreacted monomers, eliminating the need for a hot water washing process.

[0052] Furthermore, in the next step, step B, the crude polyacetal copolymer is used in powder form, so it is preferable that the crude polyacetal copolymer obtained in step A is in powder form.

[0053] Therefore, in cases where there are large lumps, a pulverizer can be used to crush them as needed.

[0054] In the method for manufacturing the polyacetal copolymer of this embodiment, a molecular weight regulator may be used in step A as needed. Linear methylal compounds may be used as molecular weight regulators. Examples of linear methylal compounds include dimethoxymethane (methylal), diethoxymethane (ethylal), dibutoxymethane, bis(methoxymethyl) ether, bis(ethoxymethyl) ether, and bis(butoxymethyl) ether. Preferably, one or more compounds selected from the group consisting of dimethoxymethane, diethoxymethane, and dibutoxymethane are preferred.

[0055] Furthermore, in the method for manufacturing polyacetal copolymers according to this embodiment, antioxidants may be added as needed in step A.

[0056] [Process B]

[0057] In step B, a mixture is obtained by introducing a solution of crude polyacetal copolymer and alkaline compound (d) into a continuous mixing device for powder and liquid (hereinafter also referred to as "continuous mixing device") and mixing them. The continuous mixing device is configured to disperse the powder in a continuously supplied liquid and obtain a uniform mixed fluid of powder and liquid by rotating a mixing disc.

[0058] In step B, a mixture is obtained by mixing the crude polyacetal copolymer obtained in step A with a solution of alkaline compound (d). The alkaline compound (d) functions as an alkaline deactivator for the polymerization catalyst (c), thereby deactivating the catalyst. Here, to obtain the mixture of the crude polyacetal copolymer and the solution of alkaline compound (d), a continuous mixing apparatus for powder and liquid is used, configured to disperse and mix powder in a continuously supplied liquid and obtain a uniform mixture of powder and liquid via a rotating mixing disc. That is, the continuously supplied liquid is used as a solution of alkaline compound (d), and the powder is used as the crude polyacetal copolymer for mixing. Such a continuous mixing apparatus is described in detail in, for example, Japanese Patent Application Publication Nos. 2002-248330 and 2004-168055.

[0059] In this embodiment, by using a continuous mixing device, the powder of the crude polyacetal copolymer and the liquid solution of the alkaline compound (d) are made into a homogeneous mixed fluid, with the alkaline compound (d) solution uniformly dispersed in the crude polyacetal copolymer. As a result, even with a reduced amount of alkaline compound (d), the polymerization catalyst (c) is sufficiently deactivated in the subsequent step C. Furthermore, because the amount of alkaline compound (d) used is small, discoloration of the polyacetal copolymer after melt mixing can be prevented.

[0060] As described above, the advantage of using a continuous mixing device is that the solution of the basic compound (d) is uniformly dispersed in the crude polyacetal copolymer. Other advantages include, for example, that while it is preferable to use as little of the solution of the basic compound (d) as possible, the amount of solution used can be controlled to a very small quantity by using a continuous mixing device. Specifically, currently only a continuous mixing device can achieve a concentration of the solution of the basic compound (d) at approximately 0.1 to 0.2% by mass relative to the powder of the crude polyacetal copolymer. Furthermore, even when using a continuous mixing device to use a small amount of the solution of the basic compound (d), the deactivation of the polymerization catalyst (c) achieved by the solution of the basic compound (d) is not poor.

[0061] When mixing via a continuous mixing device, it is preferable to set the outer circumferential speed of the rotating mixing disc to 0.1 to 20.0 m / s.

[0062] In step B, the basic compound (d) is a nitrogen-containing organic compound with a pH of 10 or higher, consisting of an alkali metal or a Group II element carbonate, bicarbonate, or carboxylate, or a hydrate thereof, or an aqueous solution of 10 g / L. Examples of alkali metal or Group II element carbonates, bicarbonates, or carboxylatees, or their hydrates, 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, and potassium hydroxide. Examples of nitrogen-containing organic compounds with a pH of 10 or higher, consisting of amine compounds such as triethylamine, choline hydroxide, trimethylamine, and ethanolamine, are also included. Preferably, the alkali metal element carbonate, bicarbonate, or carboxylate, or its hydrate, is used. Furthermore, the pH of the nitrogen-containing organic compound with a pH of 10 or higher in an aqueous solution of 10 g / L refers to the pH at 25°C.

[0063] On the other hand, a solvent containing active hydrogen is used as the solvent for the solution of the basic compound (d). Examples of solvents containing active hydrogen include water, alcohols with 1 to 5 carbon atoms, and formic acid. Examples of alcohols with 1 to 5 carbon atoms include methanol, ethanol, n-propanol, isopropanol, and n-butanol. Water is preferred.

[0064] Furthermore, when using an alkaline compound (d), the formaldehyde production in the final composition becomes particularly low, which is more preferable.

[0065] In this embodiment, the alkaline compound (d) described above can be one, or two or more can be used in combination, and can also be in the form of their hydrates, mixtures, double salts, etc.

[0066] In this embodiment, as described above, the amount of polymerization catalyst (c) used is small, so the amount of basic compound (d) used as the deactivator of the polymerization catalyst (c) can also be small. Specifically, it is 1 to 100 ppm relative to the polymerization product.

[0067] Following the polymerization and deactivation processes involved, unreacted monomers may be further separated, recovered, and dried using existing known methods, as needed.

[0068] [Process C]

[0069] In step C, a mixture of crude polyacetal copolymer and a solution of basic compound (d) is fed into an extruder and melt-blended. In step B, the basic compound (d) is in a uniformly dispersed state. Since melt-blending is carried out in this state in step C, the polymerization catalyst (c) can be fully deactivated.

[0070] Step C can be performed by, for example, the following methods: (1) directly melt-blending and deactivating the mixture obtained in step B to obtain a polyacetal copolymer; (2) adding other additives to the mixture obtained in step B, melt-blending and deactivating the mixture to obtain a resin composition. In (2), examples include adding the additives together with the mixture into the main feed section of the extruder and adding them separately from the side feed section of the extruder. Furthermore, either (1) or (2) above can be granulated from the polyacetal copolymer or resin composition ejected from the extruder nozzle by known methods, such as cutting the cooled resin ejected from the extruder nozzle using a wire cutter.

[0071] In step C, deactivation is carried out in a homogeneous molten resin. Therefore, unlike in the past, the crude polyacetal copolymer powder is not immersed in an aqueous solution of the deactivating agent for a long time in a non-uniform solid-liquid state, thus deactivating the polymerization catalyst (c). Therefore, the step of immersion in the aqueous solution of the deactivating agent until drying, which is performed up to this point for catalyst deactivation, can be omitted. Furthermore, the formation of thermally unstable ends generated by prolonged immersion in the aqueous solution of the deactivating agent can be suppressed, thus eliminating the need for stabilization treatment. Examples of thermally unstable ends include -CH2CH2O-(CH2O)n-CH2OH and -CH2CH2O-(CH2O)n-CH2O-CHO. In the groups representing these unstable ends, n represents zero or any positive integer. Moreover, when the catalyst in the crude polyacetal copolymer is deactivated by immersion in an alkaline solution in the past, unreacted monomers extracted in the aqueous solution can be recovered, thereby suppressing monomer loss.

[0072] Example

[0073] The following examples will be used to illustrate this embodiment in more detail, but this embodiment is not limited to the following examples.

[0074] [Examples 1-11, Comparative Examples 1-2]

[0075] (Process A)

[0076] A continuous twin-screw polymerizer was used as the polymerization reactor. The polymerizer has an outer jacket for the passage of heating or cooling media, and two rotating shafts with multiple blades arranged along its length for stirring, propulsion, and crushing. The two shafts were rotated at a fixed speed of 0.5 m / s at the blade tips, while the main monomer (a) (trioxymethylene) and the comonomer (b) shown in Table 1 were added and mixed in the proportions shown in Table 1. The polymerization catalyst (c) shown in Table 1 (a 2 g / L methyl formate solution, 5 ppm relative to the total monomers) was further added to the resulting mixture. Here, in Table 1, the amounts of additives (polymerization catalyst (c) and basic compound (d)) are relative to the total amount of the main monomer (a) and comonomer (b). Next, dimethoxymethane, as a molecular weight regulator, was supplied at a melt flow rate of 9 g / 10 min for the obtained copolymer. Bulk polymerization is carried out under the above conditions to obtain a powdered crude polyacetal copolymer that is pulverized and discharged from the polymerizer.

[0077] In addition, in Table 1, co-units are represented by abbreviations, but the specifics are as follows.

[0078] DO: 1,3-dioxolane

[0079] BDF: 1,4-Butanediol Methylal

[0080] Furthermore, in Table 1, catalysts C1 and C2 are as follows.

[0081] Catalyst C1: Phosphotungstic acid (H3PW) 12 O 40 )

[0082] Catalyst C2: Phosphomolybdic acid (H3PMo) 12 O 40 )

[0083] (Process B)

[0084] Next, the powdered crude polyacetal copolymer powder continuously discharged from the polymerization reactor and a 1 g / L aqueous solution of the basic compound (d) listed in Table 1 are introduced into a continuous mixing unit (FLOW JET MIXER Continuous Jet Mixer Type 100, manufactured by POWTECHS Co., Ltd.) at a flow rate where the amount of basic compound (d) added is in the ratio specified in Table 1, thereby obtaining a mixture of basic compound (d) and crude polyacetal copolymer. At this time, the FLOW JET MIXER system mixes the mixture at a circumferential speed of 2.5 m / s on the outer periphery of the rotating mixing disc.

[0085] However, in Comparative Examples 1 and 2, the alkaline compounds were not prepared into aqueous solutions but used directly in their original solid state.

[0086] Furthermore, the basic compounds D1 to D8 are listed in Table 1 below.

[0087] Basic compound D1: Sodium carbonate

[0088] Basic compound D2: Potassium carbonate

[0089] Basic compound D3: Sodium bicarbonate

[0090] Basic compound D4: Sodium oleate

[0091] Basic compound D5: Sodium acetate

[0092] Basic compound D6: Sodium formate

[0093] Basic compound D7: Triethylamine

[0094] Basic compound D8: Sodium stearate

[0095] (Process C)

[0096] Then, 0.3% by mass of BASF Irganox 1010 (manufactured by Japan Co., Ltd.) as an antioxidant is added to the mixture of crude polyacetal copolymer obtained in step B and alkaline compound (d), and the mixture is fed into a twin-screw extruder for melt mixing (cylinder temperature: 200°C) to deactivate the polymerization catalyst (c) and obtain polyacetal copolymer particles.

[0097] [Comparative Example 3]

[0098] After obtaining the crude polyacetal copolymer by the same operation as in Example 2, the alkaline compound (d) listed in Table 1 was added to the obtained crude polyacetal copolymer and fed into a twin-screw extruder for melt mixing (cylinder temperature: 200°C) to obtain polyacetal copolymer particles.

[0099] <Evaluation>

[0100] [Evaluation of grainy tone]

[0101] Using a SE-2000 colorimeter (manufactured by Nippon Denshoku Kogyo Co., Ltd.), a specified amount of particles were placed in the particle measurement cell (circular cell) and placed on the sample stage. The cover was then closed, and the b-value displayed during the measurement was read. The results are shown in Table 1.

[0102]

[0103] According to Table 1, Examples 1 to 11 all have negative b values ​​in the hue evaluation, indicating that no yellowing has occurred.

[0104] In contrast, in Comparative Examples 1 and 2, where the alkaline compound (d) was used directly in its original solid state and mixed with the crude polyacetal copolymer, and in Comparative Example 3, where no continuous mixing device was used, the b value in the hue evaluation was positive, indicating that yellowing had occurred.

Claims

1. A method for manufacturing a polyacetal copolymer, characterized in that, The process includes the following steps: A process of copolymerizing trioxymethylene (a) as a main monomer (a) with a compound (b) that can copolymerize with said trioxymethylene as a comonomer (b) by using a protic acid as a polymerization catalyst (c) to obtain a crude polyacetal copolymer. A process of obtaining a mixture by introducing a solution of the crude polyacetal copolymer and the basic compound (d) into a continuous mixing apparatus for powder and liquid and mixing therein, wherein the continuous mixing apparatus is configured to disperse and mix the powder in a continuously supplied liquid, and a uniform mixture of powder and liquid is obtained by rotating a mixing disc; and The process of feeding the mixture into an extruder and performing melt mixing. The basic compound (d) is a carbonate, bicarbonate, or carboxylate of an alkali metal or a Group 2 element other than Be, or a nitrogen-containing organic compound with a pH of 10 or higher in a 10 g / L aqueous solution. Furthermore, the solvent for the solution of the alkaline compound (d) is a solvent containing active hydrogen.

2. The method for manufacturing the polyacetal copolymer according to claim 1, characterized in that, The polymerization catalyst (c) is a heteropolyacid represented by the following general formula (1). H m [M 1 x·M 2 y O Z ]·nH2O···General Formula (1) In general formula (1), M 1 M represents the central element composed of elements selected from P, Si, B, and Ge. 2 The coordinate element is selected from one or more of W, Mo, and V. x represents an integer greater than or equal to 1 and less than 10, y represents an integer greater than or equal to 6 and less than 40, z represents an integer greater than or equal to 10 and less than 100, m represents an integer greater than or equal to 1, and n represents an integer greater than or equal to 0 and less than 50.

3. The method for manufacturing the polyacetal copolymer according to claim 2, characterized in that, The heteropolyacid is at least one selected from the group consisting of phosphomolybdic acid, phosphotungstic acid, phosphomolybdic tungstic acid, phosphomolybdic vanadate, phosphomolybdic tungstic vanadate, phosphomolybdic ...silicotungstic acid, silicotungstic acid, silicotungstic acid, and silicotungstic vanadate.

4. The method for manufacturing the polyacetal copolymer according to claim 1 or 2, characterized in that, The carbonates, bicarbonates, or carboxylates of the alkali metal elements or Group II elements other than Be, or their hydrates, are carbonates, bicarbonates, or carboxylates of the alkali metal elements or their hydrates.

5. The method for manufacturing the polyacetal copolymer according to claim 1 or 2, characterized in that, The comonomer (b) is at least one selected from the group consisting of 1,3-dioxolane, diethylene glycol methyl acetal, 1,4-butanediol methyl acetal, 1,3-dioxane, and ethylene oxide.

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