Method for producing oxymethylene copolymer and method for producing molded article

Abstract

Provided is a method for producing an oxymethylene copolymer having good physical properties.　A method for producing an oxymethylene copolymer including the copolymerization of a trioxane and a monomer capable of copolymerizing with the trioxane in the presence of a cationic polymerization catalyst and a polymerization control agent, the polymerization control agent being a 4-membered or more cyclic ether that includes one oxygen atom.

Description

Method for producing oxymethylene copolymer and method for producing molded article

[0001] The present invention relates to a method for producing an oxymethylene copolymer and a method for producing a molded article.

[0002] Oxymethylene copolymers (polyacetal copolymers) have been widely used in electronic devices, vehicles, etc. as fibers, films, gears, bearings, etc. due to their excellent strength, elastic modulus, impact resistance, sliding properties, etc.

[0003] In recent years, the applications in which oxymethylene copolymers are used have seen progress in improving performance and functionality, and high physical properties are also being demanded of the oxymethylene copolymers that are used as raw materials.

[0004] For example, Patent Document 1 describes an invention relating to a method for producing a polyacetal copolymer by polymerizing trioxane with a cyclic ether and / or a cyclic formal in the presence of a polymerization catalyst, which is a metal halide containing a metal element belonging to Periods 3 to 6 and Groups 3 to 16 of the periodic table.

[0005] Patent Document 1 describes that when boron trifluoride or its coordination compound is used as a polymerization catalyst, tar-like precipitates derived from the polymerization catalyst are generated, which disrupts the feed rate of the polymerization catalyst and can lead to uneven polymer precipitation. It also describes that when perfluoromethanesulfonic acid or its derivatives, heteropolyacids, isopolyacids, or acid salts thereof are used as a polymerization catalyst, high catalytic activity and high polymerization rate cause rapid polymerization and polymer precipitation in a part of the apparatus, which places a load on the parts of the apparatus and causes the apparatus to vibrate, resulting in adverse effects on production.

[0006] In contrast, the invention described in Patent Document 1 discloses that by using a specific polymerization catalyst, it is possible to obtain a polyacetal copolymer with high thermal stability while stably operating or using a polymerization reaction apparatus.

[0007] Japanese Patent Application Laid-Open No. 2018-154797

[0008] According to the invention described in Patent Document 1, an oxymethylene copolymer having high thermal stability can be obtained. However, even with the production method described in Patent Document 1, the oxymethylene copolymer obtained may not satisfy the required physical properties.

[0009] Therefore, the present invention provides a method for producing an oxymethylene copolymer having high physical properties.

[0010] The present invention is, for example, as follows.

[0011] [1] A method for producing an oxymethylene copolymer, comprising copolymerizing trioxane and a comonomer copolymerizable with the trioxane in the presence of a cationic polymerization catalyst and a polymerization inhibitor, wherein the polymerization inhibitor is a cyclic ether having a four- or greater ring size and containing one oxygen atom. [2] The method according to [1] above, wherein the amount of the polymerization inhibitor added is 250 μg or less per gram of trioxane. [3] The method according to [1] or [2] above, wherein the amount of the polymerization inhibitor added is 7.1 μg or more per gram of trioxane. [4] The method according to any one of [1] to [3] above, wherein the cyclic ether contains at least one of a five-membered cyclic ether containing one oxygen atom and a six-membered cyclic ether containing one oxygen atom. [5] The method according to any one of [1] to [4] above, wherein the cyclic ether comprises at least one selected from the group consisting of tetrahydrofuran (THF), 4-methyltetrahydropyran (MTHP), and 2-methyltetrahydrofuran (MHF). [6] The method according to any one of [1] to [5] above, wherein a first solution containing a polymerization inhibitor and a cationic polymerization catalyst is added to a second solution containing trioxane and a comonomer copolymerizable with trioxane. [7] The method according to any one of [1] to [6] above, wherein the cationic polymerization catalyst is a Lewis acid and / or a protonic acid. [8] The method according to any one of [1] to [7] above, wherein the cationic polymerization catalyst comprises at least one selected from the group consisting of boron trifluoride and its coordination compounds, fluoroarylboron compounds and their coordination compounds, and perchloric acid and its derivatives. [9] The method according to any one of the above [1] to [8], wherein the amount of the comonomer added is 0.1 to 6.5 parts by mass per 100 parts by mass of trioxane.

[10] A method for producing a molded article, comprising molding the oxymethylene copolymer produced by the method according to any one of the above [1] to [9].

[0012] According to the present invention, a method for producing an oxymethylene copolymer having high physical properties is provided.

[0013] Hereinafter, embodiments of the present invention will be described in detail.

[0014] <Method for Producing Oxymethylene Copolymer> The method for producing an oxymethylene copolymer according to the present invention comprises copolymerizing trioxane with a comonomer copolymerizable with trioxane in the presence of a cationic polymerization catalyst and a polymerization inhibitor. The polymerization inhibitor is a four- or higher-membered cyclic ether containing one oxygen atom. The copolymerization may further include the presence of a chain transfer agent, a solvent, an antioxidant, and the like.

[0015] The above-described production method allows the production of an oxymethylene copolymer with excellent physical properties. While the reason for this is not entirely clear, it is believed to be due to the following reasons: In the production method of an oxymethylene copolymer, a monomer such as trioxane is first subjected to ring-opening or the like in the presence of a cationic polymerization catalyst to generate cationic active species. The cationic active species then undergo a continuous copolymerization reaction to obtain an agglomerated oxymethylene copolymer. Depending on the polymerization rate of the copolymerization reaction, agglomeration may not occur uniformly in the reaction system. For example, if the polymerization rate is high, agglomerated oxymethylene copolymer may be produced locally in the reaction system, which may result in variations in the rate at which the agglomerates are produced within the reaction system. As a result, at least a portion of the resulting oxymethylene copolymer may be insufficiently polymerized, failing to meet the required physical properties.

[0016] In conventional methods for producing an oxymethylene copolymer, the polymerization reaction occurs very quickly in at least a portion of the reaction system, resulting in the formation of locally agglomerated oxymethylene copolymers and variations in the polymerization rate within the reaction system, which can result in the resulting oxymethylene copolymers having insufficient physical properties such as crystallinity.

[0017] In contrast, the present invention allows for a uniform polymerization reaction by using a predetermined polymerization inhibitor in combination with a cationic polymerization catalyst. Specifically, the polymerization inhibitor acts on the cationic active species generated directly or indirectly by the cationic polymerization catalyst, thereby adjusting the reaction rate and achieving a uniform polymerization reaction. This makes it possible to prevent or suppress the formation of localized clumps of oxymethylene copolymer within the reaction system. Furthermore, the polymer production efficiency is improved, and the resulting oxymethylene copolymer can have a uniform molecular weight distribution. As a result, the resulting oxymethylene copolymer has high physical properties, such as crystallinity.

[0018] [Trioxane] Trioxane (1,3,5-trioxane) undergoes ring-opening polymerization during the polymerization reaction, and the oxymethylene unit ([-CH ２ O-] ｎ )

[0019] [Comonomer] The comonomer is a monomer other than trioxane that can be copolymerized with the trioxane. The comonomer improves the thermal stability of the oxymethylene copolymer. The comonomer exists as an amorphous component in the oxymethylene copolymer.

[0020] The comonomer is not particularly limited, but examples thereof include 1,3-dioxolane, 2-ethyl-1,3-dioxolane, 2-propyl-1,3-dioxolane, 2-butyl-1,3-dioxolane, 2,2-dimethyl-1,3-dioxolane, 2-phenyl-2-methyl-1,3-dioxolane, 4-methyl-1,3-dioxolane, 2,4-dimethyl-1,3-dioxolane, 2-ethyl-4-methyl-1,3-dioxolane, 4,4-dimethyl-1,3-dioxolane, 4,5-dimethyl-1,3-dioxolane, 2,2,4-trimethyl-1,3-dioxolane, 4- Examples of the comonomer include comonomers that derive oxyethylene units, such as hydroxymethyl-1,3-dioxolane, 4-butyloxymethyl-1,3-dioxolane, 4-phenoxymethyl-1,3-dioxolane, 4-chloromethyl-1,3-dioxolane, ethylene oxide, propylene oxide, butylene oxide, styrene oxide, epichlorohydrin, epibromohydrin, glycidyl methyl ether, ethyl glycidyl ether, butyl glycidyl ether, and phenyl glycidyl ether; and cyclic formals of the comonomers that derive oxyethylene units. These comonomers may be used alone or in combination of two or more.

[0021] Among these, from the viewpoint of excellent thermal stability and crystallinity, the comonomer preferably contains a comonomer that induces an oxyethylene unit, more preferably contains 1,3-dioxolane and / or ethylene oxide, and even more preferably contains 1,3-dioxolane.

[0022] The amount of the comonomer added is preferably 0.01 to 10 parts by mass, more preferably 0.1 to 6.5 parts by mass, and even more preferably 0.1 to 6.0 parts by mass, relative to 100 parts by mass of trioxane. From the viewpoint of increasing the melting point of the oxymethylene copolymer, it is particularly preferably 0.1 to 5.0 parts by mass, extremely preferably 0.1 to 3.0 parts by mass, and most preferably 0.3 to 1.0 part by mass.

[0023] In one embodiment, the amount of the comonomer added is preferably 0.001 to 1 mol, more preferably 0.001 to 0.1 mol, even more preferably 0.001 to 0.06 mol, particularly preferably 0.001 to 0.04 mol, and most preferably 0.003 to 0.01 mol, relative to 1 mol of trioxane.

[0024] The smaller the amount of comonomer added, the higher the crystallinity of the resulting oxymethylene copolymer tends to be, which makes it easier for agglomerated oxymethylene copolymers to be locally produced in the copolymerization reaction system, thereby enhancing the effect of improving physical properties according to the present invention.

[0025] [Cationic Polymerization Catalyst] The cationic polymerization catalyst has a function of acting on trioxane and / or a comonomer to generate cationic active species, thereby accelerating the copolymerization reaction.

[0026] The cationic polymerization catalyst is preferably a Lewis acid and / or a protonic acid.

[0027] The Lewis acid is not particularly limited, but examples thereof include inorganic Lewis acids, organic Lewis acids, and coordination compounds thereof.

[0028] Inorganic Lewis acids include boron trifluoride (BF ３ ), boron trichloride (BCl ３ ), aluminum chloride (AlCl ３ ), tin tetrachloride (SnCl ４ ), zinc chloride (ZnCl ２ ), iron chloride (FeCl ３ ), gallium chloride (GaCl ３ ), zirconium chloride (ZrCl ４ ), niobium pentachloride (NbCl ５ ) etc.

[0029] Examples of organic Lewis acids include triphenylborane (TPB), tris(pentafluorophenyl)borane, bis(pentafluorophenyl)fluoroborane, pentafluorophenyldifluoroborane, tris(2,3,4,5-tetrafluorophenyl)borane, tris(2,3,4,6-tetrafluorophenyl)borane, tris(2,3,5,6-tetrafluorophenyl)borane, tris(2,3,5-trifluorophenyl)borane, and tris(2,4 ,6-trifluorophenyl)boron, tris(1,3-difluorophenyl)boron, tris(2,3,5,6-tetrafluoro-4-methylphenyl)boron, tris(2,3,4,6-tetrafluoro-5-methylphenyl)boron, tris(2,4,5-trifluoro-6-methylphenyl)boron, tris(2,3,6-trifluoro-4-methylphenyl)boron, tris(2,4,6-trifluoro-3-methylphenyl)boron, tris(2 ,6-difluoro-3-methylphenyl)boron, tris(2,4-difluoro-5-methylphenyl)boron, tris(3,5-difluoro-2-methylphenyl)boron, tris(4-methoxy-2,3,5,6-tetrafluorophenyl)boron, tris(3-methoxy-2,4,5,6-tetrafluorophenyl)boron, tris(2-methoxy-3,5,6-trifluorophenyl)boron, tris(3-methoxy-2,5,6-trifluorophenyl)boron

[0033] Examples of fluoroarylboron compounds include fluoroarylboron compounds such as tris(3-methoxy-2,4,6-trifluorophenyl)boron, tris(2-methoxy-3,5-difluorophenyl)boron, tris(3-methoxy-2,6-difluorophenyl)boron, tris(3-methoxy-4,6-difluorophenyl)boron, tris(2-methoxy-4,6-difluorophenyl)boron, and tris(4-methoxy-2,6-difluorophenyl)boron.

[0030] The coordination compound is not particularly limited, but examples thereof include coordination compounds of an inorganic Lewis acid, an organic Lewis acid, or a fluoroarylboron compound with water (hydrate), ammonia, dimethyl ether, diethyl ether, dibutyl ether, phenol, ethylamine, or the like.

[0031] The protonic acid is not particularly limited, but may be perchloric acid (HClO ４ ), hydrogen chloride (HCl), sulfuric acid (H ２ SO ４ ), trifluoroacetic acid (CF ３ COOH), trichloroacetic acid (CCl ３ COOH), trifluoromethanesulfonic acid (CF ３ SO ３ H), p-toluenesulfonic acid, and derivatives thereof.

[0032] The derivative is not particularly limited, but examples thereof include perchloric anhydride and peroxyacetyl perchlorate.

[0033] The above-mentioned cationic polymerization catalysts may be used alone or in combination of two or more kinds.

[0034] Among the above, the cationic polymerization catalyst preferably contains at least one selected from the group consisting of boron trifluoride and its coordination compounds, fluoroarylboron compounds and its coordination compounds, and perchloric acid and its derivatives, more preferably contains at least one selected from the group consisting of boron trifluoride and its coordination compounds, perchloric acid and its derivatives, and even more preferably contains at least one selected from the group consisting of boron trifluoride coordination compounds and perchloric acid, and a coordination compound of boron trifluoride and diethyl ether (boron trifluoride diethyl ether complex: BF ３ ・Et ２ O) is particularly preferred.

[0035] The amount of the cationic polymerization catalyst added is preferably 0.00001 to 1 mmol, more preferably 0.0001 to 0.1 mmol, and even more preferably 0.0001 to 0.05 mmol, per 1 mol of trioxane.

[0036] [Polymerization Control Agent] The polymerization control agent is a cyclic ether having a four- or greater ring containing one oxygen atom. The polymerization control agent has polarity in the molecule, and acts on the cationic active species generated during the polymerization reaction. This stabilizes at least a portion of the cationic active species, and adjusts the rate of the polymerization reaction, thereby enabling a uniform polymerization reaction.

[0037] The polymerization inhibitor is not particularly limited, but examples thereof include four-membered cyclic ethers containing one oxygen atom such as oxetane, 2-methyloxetane, 3-methyloxetane, 2-ethyloxetane, 3-ethyloxetane, 2-propyloxetane, 2,2-dimethyloxetane, 3,3-dimethyloxetane, 2,3-dimethyloxetane, and 2-ethyl-3-methyloxetane; tetrahydrofuran (THF), 2-methyltetrahydrofuran (MHF), 3-methyltetrahydrofuran, 2-ethyltetrahydrofuran, 3-ethyltetrahydrofuran, 2-propyltetrahydrofuran, 2,2-dimethyltetrahydrofuran, 3,3-dimethyltetrahydrofuran, 2,3-dimethyltetrahydrofuran, and 2,4-dimethyltetrahydrofuran; and 6-membered cyclic ethers containing one oxygen atom, such as tetrahydropyran, 2-methyltetrahydropyran, 3-methyltetrahydropyran, 4-methyltetrahydropyran (MTHP), 2-ethyltetrahydropyran, 3-ethyltetrahydropyran, 4-ethyltetrahydropyran, 2-propyltetrahydropyran, 2,2-dimethyltetrahydropyran, 3,3-dimethyltetrahydropyran, 4,4-dimethyltetrahydropyran, 2,3-dimethyltetrahydropyran, 2,5-dimethyltetrahydropyran, and 2-ethyl-5-methyltetrahydropyran. These polymerization inhibitors may be used alone or in combination of two or more.

[0038] Of the above, the polymerization inhibitor preferably contains at least one of a 5-membered cyclic ether containing one oxygen atom and a 6-membered cyclic ether containing one oxygen atom, more preferably contains at least one selected from the group consisting of tetrahydrofuran (THF), 2-methyltetrahydrofuran (MHF), 3-methyltetrahydrofuran, 2-ethyltetrahydrofuran, 3-ethyltetrahydrofuran, tetrahydropyran, 4-methyltetrahydropyran (MTHP), and 4-ethyltetrahydropyran (MTHP), and even more preferably contains at least one selected from the group consisting of tetrahydrofuran (THF), 4-methyltetrahydropyran (MTHP), and 2-methyltetrahydrofuran (MHF).

[0039] The amount of polymerization inhibitor added is preferably 1000 μg or less, more preferably 500 μg or less, even more preferably 250 μg or less, particularly preferably 200 μg or less, and most preferably 90 μg or less, per gram of trioxane.

[0040] The amount of polymerization inhibitor added is preferably 1 μg or more, more preferably 7.1 μg or more, even more preferably 20 μg or more, particularly preferably 30 μg or more, and most preferably 40 μg or more, per 1 g of trioxane.

[0041] In a preferred embodiment, the amount of the polymerization inhibitor added is preferably 1 to 1000 μg, more preferably 1 to 500 μg, even more preferably 7.1 to 250 μg, particularly preferably 20 to 200 μg, and most preferably 30 to 90 μg, per 1 g of trioxane.

[0042] In another embodiment, the amount of the polymerization inhibitor added is preferably 0.0001 to 10 mmol, more preferably 0.005 to 1 mmol, further preferably 0.01 to 0.75 mmol, particularly preferably 0.05 to 0.25 mmol, and particularly preferably 0.05 to 0.1 mmol, relative to 1 mol of trioxane.

[0043] [Chain Transfer Agent] The chain transfer agent has the function of adjusting the molecular weight of the oxymethylene copolymer.

[0044] The chain transfer agent is not particularly limited, but examples thereof include protic compounds such as water, formic acid, methanol, formaldehyde, phenol, and 2,6-dimethylphenol; ether compounds such as methylal, methoxymethylal, and dibutoxymethane; etc. These chain transfer agents may be used alone or in combination of two or more.

[0045] Of these, the chain transfer agent preferably contains an ether compound, and the terminal of the resulting oxymethylene copolymer is preferably a stable methoxy group (—OCH ３ ), and therefore more preferably contains methylal.

[0046] The chain transfer agent may be derived from the trioxane production process or may be added separately, but is preferably added separately. Examples of chain transfer agents derived from the trioxane production process include water, formic acid, methanol, and formaldehyde. These chain transfer agents derived from the trioxane production process are preferably removed before the copolymerization reaction by purifying the trioxane by distillation or the like.

[0047] The amount of the chain transfer agent to be added may be appropriately determined depending on the desired melt flow rate (MFR) of the oxymethylene copolymer. Although not particularly limited, the amount is generally preferably 10 mmol or less, more preferably 5 mmol or less, per 1 mol of trioxane.

[0048] [Solvent] The solvent has the function of dispersing the substrates of the copolymerization reaction.

[0049] The solvent is not particularly limited as long as it is not a polymerization inhibitor, and examples thereof include aliphatic hydrocarbons such as hexane, heptane, cyclohexane, etc.; aromatic hydrocarbons such as benzene, toluene, xylene, etc.; ether solvents such as dimethyl ether, diethyl ether, dibutyl ether, 1,4-dioxane, etc. These solvents may be used alone or in combination of two or more.

[0050] The amount of solvent added is preferably 0.5 g or more, more preferably 1.0 g or more, per 1 mmol of cationic polymerization catalyst. There is no upper limit to the amount of solvent added, but it is usually 50 g or less, preferably 25 g or less.

[0051] [Copolymerization] Copolymerization is carried out by reacting trioxane with a comonomer copolymerizable with trioxane in the presence of a cationic polymerization catalyst and a polymerization inhibitor.

[0052] The order of addition of the raw materials used in the copolymerization is not particularly limited and can be changed as appropriate.

[0053] In one embodiment, a method for producing an oxymethylene copolymer includes adding a first solution containing a polymerization inhibitor and a cationic polymerization catalyst to a second solution containing trioxane and a comonomer copolymerizable with trioxane. That is, the polymerization inhibitor is added to the second solution together with the cationic polymerization catalyst. When a chain transfer agent is used, the chain transfer agent is typically added to the second solution. When a solvent is used, the solvent is added to the first solution and / or the second solution. According to this embodiment, since there is no need to separately add a polymerization inhibitor, production costs can be reduced.

[0054] In another embodiment, a method for producing an oxymethylene copolymer includes a first step of adding a polymerization inhibitor-containing solution containing a polymerization inhibitor to a second solution containing trioxane and a comonomer copolymerizable with trioxane, and a second step of adding a polymerization catalyst-containing solution containing a cationic polymerization catalyst to the mixed solution obtained in the first step. That is, the polymerization inhibitor is added to the second solution before the addition of the cationic polymerization catalyst. When a chain transfer agent is used, the chain transfer agent is usually added to the second solution. When a solvent is used, the solvent is added to at least one of the second solution, the polymerization inhibitor-containing solution, and the polymerization catalyst-containing solution. According to this embodiment, adding the polymerization inhibitor to the second solution in advance can prevent deterioration of the polymerization inhibitor due to contact with the cationic polymerization catalyst.

[0055] The reaction temperature for copolymerization is preferably 50 to 150°C, more preferably 60 to 120°C.

[0056] The reaction time for copolymerization is preferably 0.1 to 60 minutes, more preferably 1 to 30 minutes.

[0057] The clouding time after the start of the copolymerization reaction is preferably 1 to 30 seconds, more preferably 2 to 25 seconds, even more preferably 3 to 20 seconds, and particularly preferably 5 to 18 seconds. A clouding time of 1 second or more is preferred because the copolymerization reaction does not proceed rapidly upon addition of the cationic polymerization catalyst, thereby increasing the uniformity of the polymerization reaction. On the other hand, a clouding time of 30 seconds or less is preferred because it increases the production efficiency of the oxymethylene copolymer. In this specification, the "clouding time" is measured by the method described in the Examples.

[0058] After the copolymerization, it is preferable to add a polymerization terminator to deactivate the cationic polymerization catalyst and / or cationic active species, thereby terminating the copolymerization reaction.

[0059] The polymerization terminator is not particularly limited, but examples thereof include triphenylphosphine, ammonia, amines such as diethylamine, triethylamine, and tributylamine, and ethanolamines such as triethanolamine, N-methyldiethanolamine, N,N-diethylhydroxylamine, N-isopropylhydroxylamine, N,N-bisoctadecylhydroxylamine, and N,N-dibenzylhydroxylamine. These polymerization terminators may be used alone or in combination of two or more.

[0060] The amount of the polymerization terminator to be added is not particularly limited as long as it is an amount sufficient to deactivate the cationic polymerization catalyst. However, the molar ratio of the polymerization terminator to the amount of the cationic polymerization catalyst to be added (amount of polymerization terminator added / amount of cationic polymerization catalyst added) is preferably 1.0×10 －１ ~1.0 x 10 １ It is usually used in the range

[0061] The polymer content, which is related to the yield of the copolymerization reaction, is preferably 80% or more, more preferably 85% or more, even more preferably 90% or more, and particularly preferably 95% or more. The upper limit of the polymer content is 100%. In this specification, the "polymer content" is measured by the method described in the Examples.

[0062] [Terminal Stabilization] In one embodiment, after copolymerization, the oxymethylene copolymer may be subjected to terminal stabilization. The oxymethylene copolymer obtained by copolymerization has an unstable moiety (-(CH ２ O) ｎ By performing terminal stabilization, the unstable portion can be depolymerized to form a stable terminal (—CH ２ CH ２ OH).

[0063] The method for terminal stabilization is not particularly limited, but a method in which the oxymethylene copolymer is melted and heated is preferred. Terminal stabilization is usually carried out by melt-kneading in an extruder. In this case, terminal stabilization is preferably carried out in the presence of at least one selected from the group consisting of a terminal stabilizer, inorganic particles, an antioxidant, and a scavenger.

[0064] (Terminal Stabilizer) The terminal stabilizer has the function of improving the decomposition rate of the unstable moiety in the oxymethylene copolymer.

[0065] Examples of terminal stabilizers include, but are not limited to, ammonia; amines such as trimethylamine, triethylamine, and tributylamine; and hydroxide salts, hydrochlorides (hydrochlorides, hydrobromides, etc.), oxoacid salts (sulfates, nitrates, carbonates, etc.), and carboxylates (formates, acetates, propionates, benzoates, oxalic acid, etc.) of quaternary ammonium such as tetramethylammonium, tetraethylammonium, ethyltrimethylammonium, trimethyl(2-hydroxyethyl)ammonium, triethyl(2-hydroxyethyl)ammonium, tripropyl(2-hydroxyethyl)ammonium, benzyltrimethylammonium, benzyltriethylammonium, and benzyltripropylammonium. These terminal stabilizers may be used alone or in combination of two or more.

[0066] Of these, the terminal stabilizer preferably contains a hydroxide salt of a quaternary ammonium, and more preferably contains at least one of hydroxide salts of tetramethylammonium, tetraethylammonium, ethyltrimethylammonium, trimethyl(2-hydroxyethyl)ammonium, triethyl(2-hydroxyethyl)ammonium, tripropyl(2-hydroxyethyl)ammonium, benzyltrimethylammonium, benzyltriethylammonium, and benzyltripropylammonium.

[0067] The amount of the terminal stabilizer added is preferably 0.01 to 10 parts by mass, more preferably 0.05 to 5 parts by mass, based on 100 parts by mass of the oxymethylene copolymer.

[0068] (Inorganic Particles) The inorganic particles have the function of improving the thermal stability of the resulting oxymethylene copolymer.

[0069] The inorganic particles are not particularly limited, but examples thereof include talc, mica, wollastonite, silica, layered double hydroxide, calcium carbonate, magnesium hydroxide, calcium hydroxide, etc. These inorganic particles may be used alone or in combination of two or more kinds.

[0070] Of these, the inorganic particles preferably contain at least one selected from the group consisting of talc, mica, and layered double hydroxide, and more preferably contain layered double hydroxide.

[0071] The amount of inorganic particles added is preferably 0.0001 to 1 part by mass, more preferably 0.005 to 0.5 part by mass, and even more preferably 0.01 to 0.2 part by mass, relative to 100 parts by mass of the oxymethylene copolymer.

[0072] (Antioxidant) The antioxidant has the function of preventing oxidation of the resulting oxymethylene copolymer.

[0073] The antioxidant is not particularly limited, and examples thereof include hindered phenols, such as n-octadecyl-3-(3',5'-di-t-butyl-4'-hydroxyphenyl)propionate, n-octadecyl-3-(3'-methyl-5'-t-butyl-4'-hydroxyphenyl)propionate, n-tetradecyl-3-(3',5'-di-t-butyl-4'-hydroxyphenyl)propionate, and 1,6-hexanediol-bis[3-(3,5-di-t-butyl-4-hydroxyphenyl)propionate]. t-butyl-4-hydroxyphenyl)propionate], 1,4-butanediol-bis[3-(3,5-di-t-butyl-4-hydroxyphenyl)propionate], triethylene glycol-bis[3-(3-t-butyl-5-methyl-4-hydroxyphenyl)propionate], tetrakis[methylene-3-(3'-t-butyl-4-hydroxyphenyl)propionate]methane, N,N'-bis[3-(3,5-di-t-butyl-4-hydroxyphenyl)propionyl]hydrazine, etc. These antioxidants may be used alone or in combination of two or more.

[0074] Of these, the antioxidant preferably contains triethylene glycol-bis[3-(3-t-butyl-5-methyl-4-hydroxyphenyl)propionate].

[0075] The amount of antioxidant added is preferably 0.0001 to 1 part by mass, more preferably 0.001 to 5 parts by mass, and even more preferably 0.003 to 3 parts by mass, per 100 parts by mass of the oxymethylene copolymer.

[0076] (Scavenger) The scavenger has the function of capturing formic acid and / or formaldehyde generated by decomposition or the like of at least a part of the oxymethylene copolymer.

[0077] The scavenger is not particularly limited, and examples thereof include polyamide resins such as nylon 6, nylon 11, nylon 12, nylon 66, nylon 610, nylon 6T, and nylon 612; amide compounds such as stearyl stearamide, stearyl oleamide, stearyl erucamide, ethylenediamine-distearate amide, and ethylenediamine-dibehenic amide; urea compounds such as urea, N-phenylurea, N,N'-diphenylurea, N-phenylthiourea, and N,N'-diphenylthiourea; and triazine compounds such as melamine, benzoguanamine, N-phenylmelamine, melem, N,N'-diphenylmelamine, N-methylolmelamine, N,N'-trimethylolmelamine, and 2,4-diamino-6-cyclohexyltriazine. These scavengers may be used alone or in combination of two or more.

[0078] Of these, the scavenger preferably contains a urea compound and / or a triazine compound, more preferably contains a triazine compound, and further preferably contains melamine.

[0079] The amount of the scavenger added is preferably 0.0001 to 10 parts by mass, more preferably 0.001 to 5 parts by mass, and even more preferably 0.003 to 3 parts by mass, per 100 parts by mass of the oxymethylene copolymer.

[0080] (Terminal Stabilization Conditions) The temperature for terminal stabilization is not particularly limited, but is preferably 260°C or lower, and more preferably 240°C or lower. The lower limit of the temperature for terminal stabilization is not particularly limited as long as it is a temperature equal to or higher than the melting point of the oxymethylene copolymer, but is preferably 150°C or higher, more preferably 180°C or higher, and even more preferably 200°C or higher. In one embodiment, the temperature for terminal stabilization is preferably 150 to 260°C, more preferably 180 to 260°C, and even more preferably 200 to 240°C.

[0081] The time for terminal stabilization is not particularly limited, but is preferably 1 minute to 3 hours, more preferably 2 minutes to 1 hour, and even more preferably 3 minutes to 30 minutes.

[0082] The terminal stabilization may be carried out under reduced pressure. In this case, the pressure for terminal stabilization is not particularly limited, but is preferably 10 to 100 KPa, more preferably 10 to 80 KPa, and even more preferably 10 to 50 KPa.

[0083] [Oxymethylene Copolymer] The oxymethylene copolymer can be produced by a uniform polymerization reaction and has high physical properties such as crystallinity.

[0084] The melting point of the oxymethylene copolymer is preferably 155°C or higher, more preferably 165°C or higher, even more preferably 168°C or higher, particularly preferably 170°C or higher, and most preferably 171°C or higher. There is no particular upper limit to the melting point of the oxymethylene copolymer, but it is usually 250°C or lower, preferably 200°C or lower, and more preferably 180°C or lower. In this specification, the "melting point" is measured by the method in the Examples.

[0085] The oxymethylene copolymer may contain an additive. That is, the oxymethylene copolymer may be a composition. Thus, in one aspect of the present invention, a composition containing the oxymethylene copolymer and the additive is provided.

[0086] The additives are not particularly limited, but include stabilizers, inorganic particles, antioxidants, scavengers, colorants, plasticizers, release agents, fluorescent brighteners, antistatic agents, and the like.

[0087] The additives may be added during the production process (for example, the stabilization process) or may be added after the production of the oxymethylene copolymer.

[0088] <Method for Producing Molded Article> According to one aspect of the present invention, there is provided a method for producing a molded article, which comprises molding the oxymethylene copolymer produced by the method described above.

[0089] The oxymethylene copolymer produced by the above method has high physical properties such as thermal stability because amorphous and crystalline portions can be uniformly distributed. As a result, molded articles made using the oxymethylene copolymer also have high physical properties and can be suitably used for high-performance, high-function fibers, films, gears, and bearings.

[0090] The present invention will be specifically described below with reference to examples, but the present invention is not limited to these examples.

[0091] Example 1: Cationic polymerization catalyst boron trifluoride diethyl ether complex (BF ３ ・Et ２ A first solution was prepared containing tetrahydrofuran (THF), a polymerization inhibitor.

[0092] Next, 1000 g of trioxane (manufactured by Mitsubishi Gas Chemical Company, Inc., purity: 99.96%), 5 g (0.5 parts by mass relative to 100 parts by mass of trioxane) of 1,3-dioxolane (manufactured by Toho Chemical Industry Co., Ltd., purity: 99.99%) as a comonomer, and 0.35 g of methylal (manufactured by Kuraray Co., Ltd.) as a chain transfer agent were poured into a 5 L polymerization reactor equipped with a stirrer maintained at 65°C under a nitrogen atmosphere to prepare a second solution.

[0093] The first solution was added to the second solution, and the polymerization reaction was carried out at 65° C. for 15 minutes to produce an oxymethylene copolymer.

[0094] In addition, BF３ ・Et ２ The amount of O used was 0.045 mmol per 1 mol of trioxane, and the amount of THF used was 700 μg per 1 g of trioxane.

[0095] [Example 2] An oxymethylene copolymer was produced in the same manner as in Example 1, except that the amount of THF used was changed to 230 μg per 1 g of trioxane used. The amount of THF used was adjusted by reducing the amount of THF added to the first solution so as to achieve the above amount, and then adding benzene in an amount equivalent to the reduced amount.

[0096] [Example 3] An oxymethylene copolymer was produced in the same manner as in Example 1, except that the amount of THF used was changed to 70 μg per 1 g of trioxane used. The amount of THF used was adjusted by reducing the amount of THF added to the first solution so as to achieve the above amount, and then adding benzene in an amount equivalent to the reduced amount.

[0097] [Example 4] BF ３ ・Et ２ An oxymethylene copolymer was produced in the same manner as in Example 1, except that the amount of O used was changed to 0.03 mmol per 1 mol of trioxane and the amount of THF used was changed to 47 μg per 1 g of trioxane used. The amount of THF used was adjusted by reducing the amount of THF added to the first solution so as to achieve the above amounts, and then adding benzene in an amount equivalent to the reduced amount.

[0098] [Example 5] An oxymethylene copolymer was produced in the same manner as in Example 1, except that the amount of THF used was changed to 35 μg per 1 g of trioxane used. The amount of THF used was adjusted by reducing the amount of THF added to the first solution so as to achieve the above amount, and then adding benzene in an amount equivalent to the reduced amount.

[0099] [Example 6] BF ３ ・Et ２An oxymethylene copolymer was produced in the same manner as in Example 1, except that the amount of O used was changed to 0.03 mmol per 1 mol of trioxane and the amount of THF used was changed to 25 μg per 1 g of trioxane used. The amount of THF used was adjusted by reducing the amount of THF added to the first solution so as to achieve the above amounts, and then adding benzene in an amount equivalent to the reduced amount.

[0100] [Example 7] An oxymethylene copolymer was produced in the same manner as in Example 1, except that the amount of THF used was changed to 7 μg per 1 g of trioxane used. The amount of THF used was adjusted by reducing the amount of THF added to the first solution so as to achieve the above amount, and then adding benzene in an amount equivalent to the reduced amount.

[0101] Example 8 An oxymethylene copolymer was produced in the same manner as in Example 1, except that the amount of 1,3-dioxolane used was changed to 13 g (1.3 parts by mass per 100 parts by mass of trioxane) and the amount of THF used was changed to 70 μg per 1 g of trioxane used. The amount of THF used was adjusted by reducing the amount of THF added to the first solution so as to achieve the above amounts, and then adding benzene in an amount equivalent to the reduced amount.

[0102] [Example 9] BF ３ ・Et ２ An oxymethylene copolymer was produced in the same manner as in Example 8, except that the amount of O used was changed to 0.03 mmol per 1 mol of trioxane and the amount of THF used was changed to 25 μg per 1 g of trioxane used. The amount of THF used was adjusted by reducing the amount of THF added to the first solution so as to achieve the above amounts, and then adding benzene in an amount equivalent to the reduced amount.

[0103] [Example 10] An oxymethylene copolymer was produced in the same manner as in Example 8, except that the amount of THF used was changed to 7 μg per 1 g of trioxane used. The amount of THF used was adjusted by reducing the amount of THF added to the first solution so as to achieve the above amount, and then adding benzene in an amount equivalent to the reduced amount.

[0104] Example 11 An oxymethylene copolymer was produced in the same manner as in Example 1, except that the amount of 1,3-dioxolane used was changed to 40 g (4.0 parts by mass per 100 parts by mass of trioxane) and the amount of THF used was changed to 70 μg per 1 g of trioxane used. The amount of THF used was adjusted by reducing the amount of THF added to the first solution so as to achieve the above amounts, and then adding benzene in an amount equivalent to the reduced amount.

[0105] Example 12 An oxymethylene copolymer was produced in the same manner as in Example 1, except that the amount of 1,3-dioxolane used was changed to 60 g (6.0 parts by mass per 100 parts by mass of trioxane) and the amount of THF used was changed to 70 μg per 1 g of trioxane used. The amount of THF used was adjusted by reducing the amount of THF added to the first solution so as to achieve the above amounts, and then adding benzene in an amount equivalent to the reduced amount.

[0106] Example 13: Cationic polymerization catalyst boron trifluoride diethyl ether complex (BF ３ ・Et ２ A polymerization catalyst-containing solution containing benzene was prepared.

[0107] Also, a polymerization inhibitor-containing solution containing tetrahydrofuran (THF) and benzene as polymerization inhibitors was prepared.

[0108] Next, 1000 g of trioxane (manufactured by Mitsubishi Gas Chemical Company, Inc., purity: 99.96%), 5 g (0.5 parts by mass relative to 100 parts by mass of trioxane) of 1,3-dioxolane (manufactured by Toho Chemical Industry Co., Ltd., purity: 99.99%) as a comonomer, and 0.35 g of methylal (manufactured by Kuraray Co., Ltd.) as a chain transfer agent were poured into a 5 L polymerization reactor equipped with a stirrer maintained at 65°C under a nitrogen atmosphere to prepare a second solution.

[0109] The polymerization inhibitor solution was added to the second solution and stirred for 1 minute. Then, the polymerization catalyst solution was added to the resulting mixed solution, and the polymerization reaction was carried out at 65° C. for 15 minutes to produce an oxymethylene copolymer.

[0110] In addition, BF３ ・Et ２ The amount of O used was 0.045 mmol per 1 mol of trioxane, and the amount of THF used was 100 μg per 1 g of trioxane.

[0111] Example 14 An oxymethylene copolymer was produced in the same manner as in Example 3, except that 4-methyltetrahydropyran (MTHP) was used instead of THF.

[0112] Example 15 An oxymethylene copolymer was produced in the same manner as in Example 3, except that 2-methyltetrahydrofuran (MHF) was used instead of THF.

[0113] [Example 16] BF was used as a cationic polymerization catalyst. ３ ・Et ２ An oxymethylene copolymer was produced in the same manner as in Example 8, except that BF and triphenylborane (TPB) were used and the amount of THF used was changed to 65 μg per 1 g of trioxane. ３ ・Et ２ The amount of O used was 0.03 mmol relative to 1 mol of trioxane, and the amount of TPB used was 0.0003 mmol relative to 1 mol of trioxane. The amount of THF used was adjusted by reducing the amount of THF added to the first solution so as to achieve the above amounts, and then adding benzene in an amount equivalent to the amount of the reduction.

[0114] Example 17 BF ３ ・Et ２ Instead of O, perchloric acid (HClO ４ An oxymethylene copolymer was produced in the same manner as in Example 8, except that 0.0003 mmol of methyl methylpropional per 1 mol of trioxane was used, and the amount of THF used was changed to 65 μg per 1 g of trioxane. The amount of THF used was adjusted by reducing the amount of THF added to the first solution so as to achieve the above amount, and then adding benzene in an amount equivalent to the reduced amount.

[0115] Comparative Example 1 An oxymethylene copolymer was prepared in the same manner as in Example 1, except that THF was not added.

[0116] Comparative Example 2 An oxymethylene copolymer was prepared in the same manner as in Example 4, except that THF was not added.

[0117] Comparative Example 3 An oxymethylene copolymer was prepared in the same manner as in Example 8, except that THF was not added.

[0118] Comparative Example 4 An oxymethylene copolymer was produced in the same manner as in Example 4, except that 50 μg of 1,4-dioxane (DOX) was used per 1 g of trioxane instead of THF.

[0119] Comparative Example 5 An oxymethylene copolymer was prepared in the same manner as in Example 16, except that THF was not added.

[0120] Comparative Example 6 An oxymethylene copolymer was prepared in the same manner as in Example 17, except that THF was not added.

[0121] Examples 1 to 17 and Comparative Examples 1 to 6 are shown in Table 1 below.

[0122]

[0123] [Evaluation] Examples 1 to 17 and Comparative Examples 1 to 6 were evaluated for polymerization uniformity, polymer content, clouding time, and melting point.

[0124] [Polymerization Uniformity] The produced oxymethylene copolymer was visually inspected and evaluated according to the following criteria. The results are shown in Table 2 below.

[0125] ○: Agglomerates in the oxymethylene copolymer occurred all at once throughout the reaction solution. △: Agglomerates occurred locally in the oxymethylene copolymer, and the entire solution became agglomerated within 2 seconds. ×: Agglomerates occurred locally in the oxymethylene copolymer, and the entire solution became agglomerated after 2 seconds or more.

[0126] [Polymer Content] A composition containing an oxymethylene copolymer was obtained by separating the oxymethylene copolymer in bulk form from the reaction solution after the polymerization reaction.

[0127] Next, the composition containing the oxymethylene copolymer was washed twice with acetone and vacuum dried for 2 hours at 60° C. using a vacuum dryer, thereby removing acetone and remaining unreacted monomers.

[0128] The polymer content (%) was calculated from the mass of the composition before and after the removal of the unreacted monomer using the following formula: The results are shown in Table 2 below.

[0129]

[0130] [Clouding Time] The time from the addition of the cationic polymerization catalyst until the reaction solution became cloudy due to the polymerization reaction was measured. The results are shown in Table 2 below.

[0131] [Melting Point] The melting point of the produced oxymethylene copolymer was measured after the cationic polymerization catalyst was deactivated and the terminals were stabilized.

[0132] The cationic polymerization catalyst was deactivated and terminal stabilized as follows. A composition containing an oxymethylene copolymer was obtained by separating a bulk oxymethylene copolymer from the reaction solution after the polymerization reaction. The composition was wet-pulverized in a 2% triethylamine solution (water:methanol = 1:4 (mass ratio)), washed twice with acetone, and vacuum-dried at 60°C for 2 hours using a vacuum dryer. To 100 parts by mass of the dried composition, 0.3 parts by weight of triethylene glycol-bis[3-(3-t-butyl-5-methyl-4-hydroxyphenyl)propionate] (Irganox® 245, manufactured by BASF Japan Ltd.) and 0.05 parts by weight of melamine (manufactured by Mitsui Chemicals, Inc.) were added, and the mixture was melt-kneaded at 220°C for 20 minutes using a heated kneader (LaboPlastomill 4C150, manufactured by Toyo Seiki Seisaku-sho, Ltd.).

[0133] The terminal-stabilized oxymethylene copolymer was freeze-pulverized and its melting point was measured using a differential scanning calorimeter (DSC8500, manufactured by PerkinElmer). Specifically, the melting point was measured as follows: the oxymethylene copolymer was heated to 210°C to melt, then cooled to 30°C, and heated again at a rate of 20°C / min, and the peak top of the exothermic peak generated during this process was measured. The results are shown in Table 2 below.

[0134]

[0135] From the results in Table 2, it can be seen that Examples 1 to 17 have higher polymerization uniformity than Comparative Examples 1 to 6. As a result, it can be seen that the oxymethylene copolymer exhibits high physical properties.

[0136] Furthermore, it is clear that Examples 1 to 17 have a high polymer content and the polymerization reaction proceeds smoothly.

[0137] Furthermore, in Examples 1 to 17, the clouding time was long (1 second or more), and it is believed that agglomeration did not occur before the cationic polymerization catalyst was uniformly dispersed in the reaction solution. Note that the clouding time is preferably 25 seconds or less, more preferably 22 seconds or less, even more preferably 12 seconds or less, particularly preferably 9 seconds or less, and most preferably 5 seconds or less, because this increases productivity.

[0138] Furthermore, since Examples 1 to 17 have high melting points, it is clear that the oxymethylene copolymers have high crystallinity and high strength.

Claims

1. A method for producing an oxymethylene copolymer, comprising copolymerizing trioxane and a comonomer copolymerizable with the trioxane in the presence of a cationic polymerization catalyst and a polymerization controller, wherein the polymerization controller is a cyclic ether having a ring of 4 members or more containing one oxygen atom.

2. The production method according to claim 1, wherein the addition amount of the polymerization controller is 250 μg or less with respect to 1 g of trioxane.

3. The production method according to claim 1, wherein the addition amount of the polymerization controller is 7.1 μg or more with respect to 1 g of trioxane.

4. The production method according to claim 1, wherein the cyclic ether contains at least one of a 5-membered cyclic ether containing one oxygen atom and a 6-membered cyclic ether containing one oxygen atom.

5. The production method according to claim 1, wherein the cyclic ether contains at least one selected from the group consisting of tetrahydrofuran (THF), 4-methyltetrahydropyran (MTHP), and 2-methyltetrahydrofuran (MHF).

6. The production method according to claim 1, comprising adding a first solution containing a polymerization controller and a cationic polymerization catalyst to a second solution containing trioxane and a comonomer copolymerizable with the trioxane.

7. The production method according to claim 1, wherein the cationic polymerization catalyst is a Lewis acid and / or a protonic acid.

8. The production method according to claim 1, wherein the cationic polymerization catalyst contains at least one selected from the group consisting of boron trifluoride and its coordination compounds, aryl boron fluoride compounds and their coordination compounds, and perchloric acid and its derivatives.

9. The production method according to claim 1, wherein the addition amount of the comonomer is 0.1 to 6.5 parts by mass with respect to 100 parts by mass of trioxane.

10. A method for producing a molded article, comprising molding an oxymethylene copolymer produced by the method according to any one of claims 1 to 9.