JP2024055767A - Polyoxymethylene resin composition - Google Patents

Abstract

To provide a polyoxymethylene resin composition that balances thermal stability during molding with thermal decomposition after molding.SOLUTION: A polyoxymethylene resin composition comprises (a) a polyoxymethylene polymer and a (b) fluorinated aryl boron compound (derivative). The methoxy terminal content of the (a) polyoxymethylene polymer is 0.5×10-6 mol or more per 1 g of the polyoxymethylene polymer. The content of the (b) fluorinated aryl boron compound (derivative) is 10 ppm or more and 1000 ppm or less based on the total mass of the polyoxymethylene resin composition.SELECTED DRAWING: None

Description

The present invention relates to a polyoxymethylene resin composition.

Polyoxymethylene resin compositions are engineering plastics that have excellent mechanical properties, moldability, and sliding properties and are therefore used in a wide range of fields, such as the fields of electric and electronic materials, automobiles, and various industrial materials.
It is known that polyoxymethylene resin compositions undergo decomposition and foaming during thermal processing such as injection molding, which can have a negative effect on odor and appearance. To solve this problem, stable structures are introduced by copolymerization or terminal stabilization is performed after polymerization.

On the other hand, in recent years, polyoxymethylene resins are also used as binders for powder injection molding.
In such applications, a process is included in which the polyoxymethylene resin composition is removed by thermal decomposition after molding and, as described above, the decomposition of the terminal-stabilized polyoxymethylene resin composition requires heating to a high temperature.

Special table 2013-501148

As described above, the polyoxymethylene resin composition is used as a binder in powder injection molding and then removed by thermal decomposition, which requires heating to a high temperature.
In conventional thermal decomposition processes, it takes time for the polyoxymethylene resin composition to be completely removed, and therefore, from the viewpoint of productivity, there has been a demand for decomposition at lower temperatures or for an improved decomposition rate.
Furthermore, such a thermal decomposition process requires a large amount of energy, and from the standpoint of the recent need to reduce greenhouse gas emissions, it has been desirable to be able to perform decomposition at lower temperatures.

Therefore, the present invention aims to provide a polyoxymethylene resin composition that has a good balance between thermal stability during molding and thermal decomposition after molding.

As a result of extensive research into solving the above problems, the present inventors discovered that in a resin composition comprising a polyoxymethylene polymer containing a fluoroaryl boron compound and/or a derivative thereof and having a certain amount or more of a methoxy terminal structure, by setting the mass ratio of the fluoroaryl boron compound and/or a derivative thereof within a specific range, it is possible to achieve a high level of balance between thermal stability during molding and thermal decomposition after molding, and thus completed the present invention.

That is, the present invention is as follows.
[1] A composition comprising: (a) a polyoxymethylene polymer; and (b) a fluoroaryl boron compound (derivative),
(a) the amount of methoxy terminals in the polyoxymethylene polymer is 0.5×10 ⁻⁶ mol or more per 1 g of the polyoxymethylene polymer;
A polyoxymethylene resin composition, characterized in that the content of the (b) fluoroaryl boron compound (derivative) is 10 ppm or more and 1000 ppm or less based on the total mass of the polyoxymethylene resin composition.
[2] The polyoxymethylene resin composition according to [1], wherein the amount of methoxy terminals in the polyoxymethylene polymer (a) is 0.75×10 ⁻⁶ mol or more and 10×10 ⁻⁶ mol or less per 1 g of the polyoxymethylene polymer.
[3] The polyoxymethylene resin composition according to [1] or [2], characterized in that the content of the (b) fluoroaryl boron compound is 100 ppm or more and 1000 ppm or less based on the total mass of the polyoxymethylene resin composition.
[4] The polyoxymethylene resin composition according to any one of [1] to [3], characterized in that the fluoroaryl boron compound is at least one compound selected from the group consisting of compounds represented by formula (1), formula (2), or formula (3).
(In formulas (1) to (3), Ar ¹ to Ar ³ are each independently a substituent consisting of an aryl group in which at least one hydrogen atom is replaced with a fluorine atom (a fluoroaryl group).)
[5] The polyoxymethylene resin composition according to any one of [1] to [3], characterized in that the fluoroaryl boron compound is at least one selected from the group consisting of tris(pentafluorophenyl)borane, bis(pentafluorophenyl)fluoroborane, and pentafluorophenyl difluoroborane.
and [6] the polyoxymethylene resin composition according to any one of [1] to [3], characterized in that the fluoroaryl boron compound contains at least tris(pentafluorophenyl)borane.

The polyoxymethylene resin composition of the present invention has an excellent balance between thermal stability during molding and thermal decomposition after molding.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment for carrying out the present invention (hereinafter, referred to as the present embodiment) will be described in detail below.
It should be noted that the present invention is not limited to the following embodiment, and can be practiced in various modified forms within the scope of the invention.

<Polyoxymethylene resin composition>
The polyoxymethylene resin composition of the present embodiment contains (a) a polyoxymethylene polymer and (b) a fluoroaryl boron compound (derivative).
and (a) the amount of methoxy terminals in the polyoxymethylene polymer is 0.5×10 ⁻⁶ mol or more per 1 g of the polyoxymethylene polymer;
The content of the (b) fluoroaryl boron compound (derivative) is 10 ppm or more and 1000 ppm or less based on the total mass of the polyoxymethylene resin composition.

The polyoxymethylene resin composition of this embodiment may consist of only (a) a polyoxymethylene polymer and (b) a fluoroaryl boron compound (derivative), or may contain other components (e.g., additives described below) in addition to (a) a polyoxymethylene polymer and (b) a fluoroaryl boron compound (derivative).

In this specification, (a) polyoxymethylene polymer may be simply referred to as "(a)." Also, (b) fluoroaryl boron compound may be simply referred to as "(b)."

((a) Polyoxymethylene Polymer)
The polyoxymethylene polymer (a) in the polyoxymethylene resin composition of the present embodiment has repeating oxymethylene units (acetal structure) represented by ( _{--CH.sub.2O--} ) as its main constituent units, and any known polyoxymethylene polymer may be used.
The (a) polyoxymethylene polymer in this embodiment may be a polyoxymethylene homopolymer (hereinafter may be simply referred to as a "homopolymer") consisting of only oxymethylene units, or may be a polyoxymethylene copolymer, terpolymer, or multicomponent copolymer (hereinafter may be simply referred to as a "copolymer") containing structural units other than oxymethylene units.

Furthermore, in the copolymer, the monomer sequence is not limited, and it may have any sequence such as random, block, gradient, etc.
The polyoxymethylene polymer (a) in this embodiment may have not only a linear structure but also a cyclic, branched or crosslinked structure.

The amount of methoxy terminals in the (a) polyoxymethylene polymer in this embodiment is 0.5×10 ⁻⁶ mol or more, preferably 0.75×10 ⁻⁶ mol or more, and more preferably 1×10 ⁻⁶ mol or more, per 1 g of polyoxymethylene polymer.
Within the above range, the dispersibility of (b) is improved, and the thermal decomposition rate of a molded article using the polyoxymethylene resin composition is improved.

The amount of the methoxy terminal can be controlled by a method of introducing a methoxy ether such as methylal as a chain transfer agent during the polymerization process, or by a method of introducing the methoxy terminal in a polymer reaction after polymerization by the Williamson ether synthesis method, or the like.
Alternatively, the above amount may be achieved by mixing a polymer having a large amount of methoxy terminal groups with a polymer having a small amount of methoxy terminal groups.

The polyoxymethylene polymer (a) may be used alone or in combination of two or more.

(b) Fluoroarylboron compounds (derivatives)
The (b) fluoroaryl boron compound (derivative) in the polyoxymethylene resin composition of the present embodiment may be a fluoroaryl boron compound, a fluoroaryl boron compound derivative, or a mixture of both.

In the polyoxymethylene resin composition of this embodiment, the content of the (b) fluoroaryl boron compound (derivative) is 10 ppm or more, preferably 25 ppm or more, and more preferably 50 ppm or more, based on the total mass of the polyoxymethylene resin composition.
When the content is within the above range, the thermal decomposition rate of the polyoxymethylene resin composition is improved.

The (b) fluoroaryl boron compound (derivative) in the polyoxymethylene resin composition of this embodiment is 1000 ppm or less, preferably 500 ppm or less, and more preferably 250 ppm or less, based on the total mass of the polyoxymethylene resin composition. By being in the above range, the thermal stability during molding processing is improved.

The (b) fluoroaryl boron compound (derivative) in the polyoxymethylene resin composition of the present embodiment may be contained as a residue of a polymerization catalyst, or may be added in the terminal stabilization step or pelletization step of a polyoxymethylene polymer.
Alternatively, the content may be adjusted to the above range by washing the polyoxymethylene polymer with, for example, acetic anhydride.

The type of fluoroaryl boron compound in the polyoxymethylene resin composition of the present embodiment is not particularly limited.
For example, tris(pentafluorophenyl)borane, bis(pentafluorophenyl)fluoroborane, pentafluorophenyl difluoroborane, tris(2,3,5,6-tetrafluorophenyl)borane, bis(2,3,5,6-tetrafluorophenyl)fluoroborane, 2,3,5,6-tetrafluorophenyl difluoroborane, tris(2,3,5-trifluorophenyl)borane, bis(2,3,5-trifluorophenyl)fluoroborane, 2,3,5-trifluorophenyl difluoroborane, tris(2,4,6-trifluorophenyl)borane, bis(2,4,6-trifluorophenyl)fluoroborane, 2,4,6-trifluorophenyl difluoroborane, tris(3,5-difluorophenyl)borane, bis(3,5-difluorophenyl)fluoroborane, 3,5-difluorophenyl difluoroborane, tris(2,3,5,6-tetrafluoro-4-methylphenyl)borane, Bis(2,3,5,6-tetrafluoro-4-methylphenyl)fluoroborane, 2,3,5,6-tetrafluoro-4-methylphenyldifluoroborane, tris(2,3,5,6-tetrafluoro-4-trifluoromethylphenyl)borane, bis(2,3,5,6-tetrafluoro-4-trifluoromethylphenyl)fluoroborane, 2,3,5,6-tetrafluoro-4-trifluoromethylphenyldifluoroborane, tris(2,6-difluoro-4-triphenylmethylphenyl)borane, bis(2,6-difluoro-4-triphenylmethylphenyl)fluoroborane, 2,6-difluoro-4-triphenylmethylphenyldifluoroborane, tris(4-methoxy-2,3,5,6-tetrafluorophenyl)borane, bis(4-methoxy-2,3,5,6-tetrafluorophenyl)fluoroborane, 4-methoxy-2,3,5,6-tetrafluorophenyldifluoroborane, and the like.

Among the above, the fluoroarylborane compound is preferably at least one compound selected from the group consisting of compounds represented by formula (1), formula (2), or formula (3).
(In formulas (1) to (3), Ar ¹ to Ar ³ each represent a substituent independently selected from the group of substituents consisting of aryl groups in which at least one hydrogen atom is replaced with a fluorine atom (fluoroaryl groups).)
By using such a compound, the efficiency of thermal decomposition of the polyoxymethylene resin composition is further improved.

From the same viewpoint, the fluoroarylboron compound is more preferably at least one selected from the group consisting of tris(pentafluorophenyl)borane, bis(pentafluorophenyl)fluoroborane, and pentafluorophenyldifluoroborane, and further preferably contains at least tris(pentafluorophenyl)borane.

The fluoroaryl boron compound derivative in this embodiment is not particularly limited, but examples include hydrogen adducts of fluoroaryl boron compounds, complexes of fluoroaryl boron compounds with water, alcohols, ethers, esters, and amines, etc.

(Additive)
The polyoxymethylene resin composition of the present embodiment may contain conventionally known additives as necessary, such as aging improvers such as fatty acid metal salts, sliding agents, weather resistance agents, light resistance agents, release agents, nucleating agents, colorants, organic and inorganic reinforcing agents, and various thermoplastic elastomers.
The content of the additive is not particularly limited, but is preferably 40% by mass or less with respect to 100% by mass of the polyoxymethylene resin composition.

<Method for preparing polyoxymethylene resin composition>
The method for preparing the polyoxymethylene resin composition of the present embodiment is not particularly limited, and the composition can be produced by a known melt-kneading method.
For example, (a) a polyoxymethylene polymer, (b) a fluoroaryl boron compound (derivative), and other additives as required may be mixed in a stirrer such as a Henschel mixer, and then fed to a single-screw or twin-screw melt kneading device (extruder) for melt kneading. Alternatively, (a) a polyoxymethylene polymer may be fed from the upstream of a single-screw or twin-screw extruder to be in a molten state, and then (b) a fluoroaryl boron compound (derivative), and other additives as required may be fed downstream and melt kneaded.

The method for preparing the polyoxymethylene polymer (a) of this embodiment is not particularly limited, and the polymer can be produced by a known method. For example, the polyoxymethylene polymer (a) can be prepared by preparing a crude polyoxymethylene polymer in a polymerization step, washing the crude polyoxymethylene polymer, and stabilizing the terminals.

The polymerization process is not particularly limited, and any known method can be used. For example, anionic polymerization or cationic polymerization can be used.

Here, an example of a method for obtaining the crude polyoxymethylene polymer by anionic polymerization will be described below.
For example, the polymerization can be carried out by a slurry method using formaldehyde gas, in which formaldehyde as a monomer, a chain transfer agent (molecular weight regulator), and a polymerization catalyst are fed into a polymerization reactor to which a polymerization solvent has been added, and polymerization can be carried out.
Formaldehyde gas usually contains chain-transferable components (impurities) such as water, methanol, and formic acid. If these chain-transferable components are contained, a polyoxymethylene polymer having a desired molecular weight may not be obtained. Therefore, it is preferable to purify and remove these chain-transferable components (impurities) to a certain concentration before the start of polymerization. In particular, the water content is preferably 100 mass ppm or less, more preferably 50 mass ppm or less, relative to 100 mass% of formaldehyde gas.

In the preparation of the crude polyoxymethylene polymer by the anionic polymerization, a chain transfer agent may be used, if necessary, for the purpose of controlling the molecular weight.
The chain transfer agent is not particularly limited, and examples thereof include carboxylic acid anhydrides, carboxylic acids, alcohols, etc. Among these, propionic acid anhydride, acetic acid anhydride, and methanol are preferred.
These chain transfer agents may be used alone or in combination of two or more.

The polymerization catalyst is not particularly limited as long as it is a compound that causes anionic polymerization, but for example, an onium salt-based polymerization catalyst such as an oxonium salt or an ammonium salt can be used. The counter anion structure of the onium salt-based polymerization catalyst is not particularly limited, but examples thereof include acetate and halide.
These polymerization catalysts may be used alone or in combination of two or more.

The onium salt polymerization catalyst is preferably a quaternary phosphonium salt compound such as tetraethylphosphonium iodide or tributylethylphosphonium iodide, or a quaternary ammonium salt compound such as tetramethylammonium bromide or dimethyldistearylammonium acetate.

The amount of the onium salt polymerization catalyst added is preferably 0.00001 to 0.01 mol per 1 mol of formaldehyde, more preferably 0.00003 to 0.005 mol, and even more preferably 0.00005 to 0.003 mol.

The polymerization solvent is not particularly limited as long as it does not inhibit the polymerization reaction. Examples of the polymerization solvent include pentane, isopentane, hexane, cyclohexane, heptane, octane, nonane, decane, and benzene, and hexane is particularly preferred.
These polymerization solvents may be used alone or in combination of two or more.

An example of the method for obtaining the crude polyoxymethylene polymer by cationic polymerization will be described below.
For example, polymerization can be performed by a bulk method using trioxane, which is a cyclic trimer of formaldehyde. Polymerization can be performed by continuously feeding trioxane, a comonomer, a chain transfer agent, and a polymerization catalyst into a polymerization reactor. The shape (structure) of the polymerization reactor used is not particularly limited, but generally, a two-shaft paddle-type or screw-type stirring and mixing type polymerization reactor capable of passing a heat medium through the jacket can be used.

The trioxane usually contains chain-transferable components (impurities) such as water and formic acid. If these chain-transferable components are present, a polyoxymethylene polymer of the desired molecular weight may not be obtained. Therefore, it is preferable to purify and remove these chain-transferable components (impurities) to a certain concentration before the start of polymerization.

In the preparation of the crude polyoxymethylene polymer by the cationic polymerization, a comonomer may be used, if necessary.
The comonomer is not particularly limited, but for example, a cyclic ether or a cyclic formal can be used.

Examples of the cyclic ether include oxirane, oxetane, oxane, 1,4-dioxane, tetrahydrofuran, and glycidyl ether.
Examples of the cyclic formals include 1,3-dioxolane, 1,3-dioxane, 1,3-dioxepane, 1,3-dioxocane, 1,3-dioxonane, and 1,3,6-trioxocane.
These comonomers may be used alone or in combination of two or more kinds. Any amount of these comonomers may be used, for example, in the range of 0.001 to 0.1 mol per 1 mol of trioxane.

In the preparation of the crude polyoxymethylene polymer by the cationic polymerization, a chain transfer agent can be used, if necessary, for the purpose of controlling the molecular weight and the terminal structure.
The chain transfer agent is not particularly limited, but for example, low molecular weight acetals and alcohols can be used.

As the low molecular weight acetal, those represented by the following general formula can also be used.
RO-(CH ₂ -O) _n -R
(In the formula, R represents any one selected from the group consisting of hydrogen and branched or linear alkyl groups, and n represents an integer of 1 to 20.) In particular, by using an acetal in which R in the above formula is a methyl group, the amount of methoxy terminals in the finally obtained polyoxymethylene polymer can be adjusted to a suitable range. These may be used alone or in combination of two or more.

Examples of the alcohol include low molecular weight alcohols such as methanol, ethanol, and propanol.

From the viewpoint of controlling the molecular weight of the target polyoxymethylene within a suitable range, the amount of the chain transfer agent added is preferably in the range of 0.1×10 ⁻⁵ to 0.2×10 ⁻² mol, more preferably in the range of 0.1×10 −5 to 0.2×10 −3 mol, and even more preferably in the range of 0.1×10 ⁻⁵ to 0.1× ^{10 −3} mol, based on the total amount of trioxane ^{, cyclic ether} , and cyclic formal, each expressed in moles.

The polymerization catalyst is not particularly limited as long as it is a compound capable of polymerizing trioxane. For example, a fluoroarylboron compound, a metal halide having a metal element in Periods 3 to 6 and Groups 3 to 16 of the periodic table, a Lewis acid such as boron trifluoride (which may be a dialkyl ether complex), a heteropoly acid such as phosphotungstic acid, or a protonic acid such as sulfuric acid or trifluoromethanesulfonic acid can be used.
Among these, boron trifluoride dialkyl ether complexes are more preferable, and boron trifluoride diethyl ether complexes and boron trifluoride di-n-butyl ether complexes are particularly preferable.

These polymerization catalysts can be used by diluting them with an inert solvent to a desired concentration.
If the polymerization catalyst is used as is, polymerization often begins only in the area where it comes into contact with trioxane, resulting in the precipitation of the polymer. In such cases, diluting the catalyst with an inert solvent allows the polymerization reaction to proceed uniformly, making it possible to achieve a high polymerization yield. In addition, vigorously stirring the mixture when combining the monomer and catalyst can also prevent localized precipitation of the polymer.
The term "inactive" used herein means that it does not react with trioxane or comonomers used in the polymerization and does not deactivate the polymerization catalyst.

Such a solvent is preferably a compound that does not have a hydroxyl group, and examples of the solvent include aromatic hydrocarbon compounds such as benzene, toluene, and xylene, aliphatic hydrocarbon compounds such as n-hexane, n-heptane, and cyclohexane, and ether compounds such as diethyl ether, dibutyl ether, ethylene glycol dimethyl ether, diethylene glycol dimethyl ether, triethylene glycol diethyl ether, and 1,4-dioxane. The solvent can be appropriately selected depending on the solubility of the polymerization catalyst used, etc.

After the polymerization step, the crude polyoxymethylene polymer obtained can be washed to remove residual monomers and to remove and deactivate the catalyst. Conventionally proposed methods can be used for removal and deactivation. For example, the crude polyoxymethylene polymer discharged from the polymerization reactor can be added to an aqueous solution containing only water or at least one deactivator such as amines such as ammonia, triethylamine, and tri-n-butylamine, hydroxides of alkali metals or alkaline earth metals, inorganic salts, and organic acid salts for the purpose of efficiently deactivating the catalyst, and the monomers and catalyst remaining in the crude polyoxymethylene polymer can be removed and deactivated while continuously stirring at room temperature to 100°C or less for several minutes to several hours. From the viewpoint of increasing the efficiency of washing and removing the catalyst, if the crude polyoxymethylene polymer is in the form of large chunks, it is also preferable to pulverize the crude polyoxymethylene polymer to make it finer. In addition, when a fluoroaryl boron compound is used as the polymerization catalyst, the above washing conditions can be selected for the purpose of adjusting the amount of (b) fluoroaryl boron compound (derivative) contained in the final polyoxymethylene resin composition.

In addition, the crude polyoxymethylene polymer obtained by the polymerization method described above often has hydroxyl terminals that are prone to become the starting point of thermal decomposition. In such cases, for example, the hydroxyl terminals can be reacted with an organic acid anhydride or alcohol to stabilize the polymer, or the crude polyoxymethylene polymer can be heated to decompose the easily decomposed components and sites in advance.

For example, the case where stabilization is achieved by reacting an organic acid anhydride or an alcohol with the hydroxyl end is shown below.
The organic acid anhydride or alcohol is not particularly limited as long as it reacts with the unstable hydroxyl group terminal of the polyoxymethylene polymer.Specific examples include propionic anhydride, benzoic anhydride, acetic anhydride, succinic anhydride, maleic anhydride, glutaric anhydride, phthalic anhydride, and methanol.Of these, by using methanol, the amount of methoxy terminal of the finally obtained polyoxymethylene polymer (a) can also be adjusted.
The polyoxymethylene resin composition of this embodiment can be used by mixing it with a metal powder or a ceramic powder, molding it, and then removing it by pyrolysis.

The present invention will be specifically described below with reference to examples and comparative examples. The present invention is not limited in any way by these examples.

<Examples 1 to 3, Comparative Examples 1 to 3>
To a unidirectional rotating twin-shaft paddle-type continuous polymerization reactor (manufactured by Kurimoto, Ltd., diameter 2B, L/D=14.8) set at 80° C., 3.5 kg/h of trioxane, 120 g/h of 1,3-dioxolane as a comonomer, methylal and/or methanol as a chain transfer agent, and tris(pentafluorophenyl)borane dissolved in advance in toluene as a polymerization catalyst were fed in the amounts shown in Table 1, and polymerization was carried out.
The crude polyoxymethylene polymer discharged from the polymerization reactor was put into water and stirred at room temperature for 1 hour to remove unreacted trioxane and the like. The resulting mixture was then filtered using a centrifuge and dried at 100°C for 10 hours to obtain a polyoxymethylene polymer.
To the polyoxymethylene polymer obtained as above, 0.35 phr of Irganox 245 was added, mixed in a Henschel mixer, and extruded to obtain a polyoxymethylene resin composition.

Example 4
To the polyoxymethylene resin composition obtained in Example 3, 0.4 phr of trispentafluorophenylborane and 0.35 phr of Irganox 245 were added, mixed in a Henschel mixer, and extruded to obtain a polyoxymethylene resin composition.

<Comparative Example 4>
A polyoxymethylene resin composition was obtained under the same conditions as in Example 1, except that a trifluoroboron-dibutyl ether complex was used as the polymerization catalyst.

<Evaluation>
The polyoxymethylene resin compositions obtained in the respective Examples and Comparative Examples were evaluated as follows. The evaluation results are shown in Table 1.

(1) Content of fluoroaryl boron compound (derivative) The content of fluoroaryl boron (derivative) in the final resin composition was quantified by liquid chromatography/electrospray ionization mass spectrometry (LC/MS (ESI-)). The specific method is as follows.
About 3 g of the polyoxymethylene resin composition was pressed at 5 MPa for 5 seconds using a heat press machine heated to 205°C to form a sheet. 1 g of the sheet-shaped polyoxymethylene resin composition was dissolved in about 20 mL of 1,1,1,2,2,2-hexafluoro-2-isopropanol (HFIP). If any residue remained, it was heated at 50°C for 1 hour. If any residue remained, it was filtered off, and the filtrate was used for the following operation. The HFIP solution thus prepared was dropped into about 90 mL of methanol while vigorously stirring, and the resulting insoluble and soluble components were separated by suction filtration. The solvent was removed from the filtrate using an evaporator, and the filtrate was air-dried and then diluted again with 2 mL of methanol. This was further diluted 10 times with methanol twice to prepare a measurement sample.
The measurement sample obtained by the above operation was subjected to liquid chromatography/electrospray ionization mass spectrometry (LC/MS (ESI-)) to quantify the fluoroaryl boron compound (derivative) in the final sample. The liquid chromatography device used was a Waters UPLC. The column used was an Imtakt Cadenza CX-C18HT (2 mm ID x 50 mm, 3 μm) at 40° C. The mobile phase used was a mixture of 10 mmol/L ammonium acetate aqueous solution and acetonitrile in a ratio of 9:1. The flow rate was 0.3 mL/min. The sample injection volume was 1 μL. The mass spectrometer used was a Waters Synapt G2.
As a result, a water adduct (m/z 529), a fluorine adduct (m/z 531), a methanol adduct (m/z 543), and an HFIP adduct (m/z 679) of tris(pentafluorophenyl)borane were detected in Example 1. Assuming that the sensitivity of each adduct was equivalent, calculations were performed using a calibration curve prepared using tris(pentafluorophenyl)borane trihydrate as the standard sample.
The results of the quantification are shown in Table 1 as the amount of fluoroarylborane compound residue.

(2) Amount of Methoxy Terminal Groups The amount of methoxy terminal groups in the final polyoxymethylene resin composition was determined by proton nuclear magnetic resonance ( ¹ H NMR).
About 3 g of the polyoxymethylene resin composition was pressed at 5 MPa for 5 seconds using a heat press machine heated to 205° C. to form a sheet. About 2 mg of the sheet-like polyoxymethylene resin composition was dissolved in 1 mL of HFIP-d2, and the obtained solution was subjected to ¹ H NMR measurement.
The measurement device used was AVANCE III 500HD Prodigy manufactured by Bruker Biospin. The amount of the substance was quantified by assuming the peak at 2.5 ppm to be the peak derived from the methoxy terminal, and the amount of the methoxy terminal per gram was quantified by dividing the amount by the sample weight. The quantitative results are shown in Table 1 as the amount of the methoxy terminal.

(3) Evaluation of Thermal Decomposition Property The thermal decomposition property of the finally obtained polyoxymethylene resin composition was evaluated by thermogravimetric analysis (TGA).
10 mg of the polyoxymethylene resin composition was directly subjected to evaluation analysis.
The measurement equipment used was Thermo plus EVO2 manufactured by Rigaku.
The measurement was carried out in a nitrogen atmosphere. The initial amount of decomposition was evaluated based on the amount of decomposition when heated at 200° C. for 30 minutes.
The evaluation was shown in Table 1 as "good" when the initial decomposition amount was less than 20 wt %, and as "poor" when it was 20 wt % or more.
In addition, when the temperature was raised at a rate of 5° C./min, the temperature at which the amount of thermal decomposition reached 50 wt % was taken as "Td50" and is shown in Table 1. In addition, in Comparative Example 2, the entire amount was decomposed at the beginning of the measurement, so "Td50" was not defined.

From Table 1, it can be seen that Comparative Example 1 has a lower Td50 than Example 3. This is presumably because the amount of methoxy terminals is not appropriate, so the dispersion of the fluoroaryl boron compound is poor, resulting in a decrease in the thermal decomposition efficiency.
In addition, in Comparative Example 2, the initial decomposition amount was large, and it was difficult to perform stable molding processing.
Furthermore, in Comparative Examples 3 and 4, since no fluoroaryl boron compound was contained or the amount was small, the decomposition rate was slow.

The present invention provides a polyoxymethylene resin composition that has a good balance between thermal stability during molding and thermal decomposition after molding.

Claims (6)

(a) a polyoxymethylene polymer; and (b) a fluoroaryl boron compound (derivative),
(a) the amount of methoxy terminals in the polyoxymethylene polymer is 0.5×10 ⁻⁶ mol or more per 1 g of the polyoxymethylene polymer;
A polyoxymethylene resin composition, characterized in that the content of the (b) fluoroaryl boron compound (derivative) is 10 ppm or more and 1000 ppm or less based on the total mass of the polyoxymethylene resin composition. 2. The polyoxymethylene resin composition according to claim 1, wherein the amount of methoxy terminals in the polyoxymethylene polymer (a) is 0.75×10 ⁻⁶ mol or more and 10×10 ⁻⁶ mol or less per 1 g of the polyoxymethylene polymer. The polyoxymethylene resin composition according to claim 1 or 2, characterized in that the content of the (b) fluoroaryl boron compound is 100 ppm or more and 1000 ppm or less with respect to the total mass of the polyoxymethylene resin composition. The polyoxymethylene resin composition according to claim 1 or 2, characterized in that the fluoroaryl boron compound is at least one compound selected from the group consisting of compounds represented by formula (1), formula (2), or formula (3).
(In formulas (1) to (3), Ar ¹ to Ar ³ are each independently a substituent consisting of an aryl group in which at least one hydrogen atom is replaced with a fluorine atom (a fluoroaryl group).) The polyoxymethylene resin composition according to claim 1 or 2, characterized in that the fluoroaryl boron compound is at least one selected from the group consisting of tris(pentafluorophenyl)borane, bis(pentafluorophenyl)fluoroborane, and pentafluorophenyldifluoroborane. The polyoxymethylene resin composition according to claim 1 or 2, characterized in that the fluoroaryl boron compound contains at least tris(pentafluorophenyl)borane.