JP2011084702A - Polyacetal copolymer - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a polyacetal copolymer excellent in toughness and suitable for non-injection molded article. <P>SOLUTION: The polyacetal copolymer is produced by copolymerizing (A) 100 pts.wt. of a trioxane, (B) 0.1-30 pts.wt. of a cyclic ether compound copolymerizable with the trioxane and (C) 0.005-50 pts.wt. of at least one compound selected from monofunctional and/or polyfunctional cyclic siloxane compounds represented by general formula -[-SiO(R<SP>1</SP>)(R<SP>2</SP>)-]-<SB>n</SB>, (wherein, R<SP>1</SP>and R<SP>2</SP>are the same or different and are each a 1-20C hydrocarbon group; and n is an integer of 3-20). <P>COPYRIGHT: (C)2011,JPO&amp;INPIT

Description

  The present invention relates to a technique for improving physical properties of a polyacetal resin important as an engineering resin.

  Polyacetal resin has excellent balance of mechanical properties, chemical resistance, slidability, etc. and is easy to process. As a typical engineering plastic, it can be used for electrical / electronic parts, automobile parts and other various mechanical parts. Widely used as a center.

  However, with the expansion of fields where polyacetal resins are used, the required characteristics tend to become increasingly sophisticated, complex and specialized. As one of such required characteristics, there are cases where polyacetal resin has inherent solvent resistance, high toughness while maintaining rigidity, or application to non-injection molded products such as fibers and films. In this case, sufficient characteristics may not be obtained simply by increasing or decreasing the amount of comonomer or stabilizer.

  For example, a method of increasing the amount of comonomer for increasing toughness is known, but there is an upper limit for the amount added, and sufficient toughness cannot be obtained. Further, a method for improving flexibility, toughness, impact resistance and moldability by blending a specific multiphase interpolymer, an ester compound, and a polyalkylene glycol with a polyacetal resin is disclosed. And is not necessarily suitable for application to non-injection molded products (Patent Document 1).

  As a method for achieving both rigidity and toughness, a method in which a polyfunctional glycidyl ether compound is reacted to form a branched or cross-linked polyacetal polymer at the time of polymerization is disclosed, but sufficient improvement in toughness is not observed, and polyfunctional The inventors of the present application have found that, depending on the amount of glycidyl ether compound added, a decrease in toughness occurs (Patent Document 2). Furthermore, a method for providing a stretched product having a high strength and a high elastic modulus by including a specific oxyalkylene unit having a specific alkyl group or phenyl group is also disclosed, but further expansion to a highly toughened stretched product is also possible. (Patent Document 3).

  As a polyacetal copolymer having a siloxane skeleton, for example, a method of providing a polyacetal copolymer having a siloxane structure in a side chain by reacting a polysiloxane compound having a cyclohexene oxide group at the time of polymerization is disclosed. Although this method is said to be effective in sliding properties, the inventors have not obtained a clear effect in terms of improving toughness, and are particularly excellent in applications to non-injection molding such as films and fibers. The effect was not found (Patent Document 4).

Japanese Patent Laid-Open No. 7-109402 Japanese Patent Laid-Open No. 2001-234637 JP 2005-264355 A JP 2002-234924 A

  An object of the present invention is to provide a polyacetal copolymer which is excellent in toughness and suitable for non-injection-molded articles in view of the current situation.

As a result of intensive studies to solve the above-mentioned problems, the present inventors have found that a polyacetal copolymer in which a siloxane skeleton is introduced into the main chain by copolymerizing certain types of specific cyclic siloxane compounds, can be used together with other resins. It has been found that high toughness can be expressed without performing compounding, and an extruded product having a good appearance can be obtained as a day injection molded product. That is, the present invention includes (A) 100 parts by weight of trioxane and (B) 0.1-30 parts by weight of a cyclic ether compound copolymerizable with trioxane, (C) monofunctional and / or polyfunctional represented by the following general formula The present invention relates to a polyacetal copolymer obtained by copolymerizing 0.005 to 50 parts by weight of at least one compound selected from cyclic siloxane compounds.

（式中、R¹及びR^２は同一又は異なり、何れもC₁〜C₂₀の炭化水素基であり、nは3〜20の整数である）

(In the formula, R ¹ and R ² are the same or different, both are C _{1 to} C ₂₀ hydrocarbon groups, and n is an integer of 3 to 20)

    The present invention can provide a polyacetal copolymer having high toughness and suitable for non-injection molded products.

  As the polymerization method of the acetal copolymer in the present invention, a bulk polymerization method using substantially no solvent is suitable. This is a polymerization method using a monomer in a molten state. As the polymerization proceeds, the polymer is crystallized in the monomer mixture, and eventually the whole system is agglomerated and powdered to obtain a solid polymer. Is. The polymerization is carried out in the absence of oxygen, preferably in a nitrogen atmosphere.

Polymerization catalysts that can be used in the present invention include boron trifluoride, tin tetrachloride, titanium tetrachloride, phosphorus pentachloride, phosphorus pentafluoride, arsenic pentafluoride, antimony pentafluoride and their coordination compounds, heteropoly Cationic active catalysts such as acids, isopolyacids, perfluoroalkyl sulfonic acids or their derivatives are known. It is also known to use two or more of these catalysts in combination.
Among them, a compound containing boron trifluoride, or boron trifluoride hydrate and a coordination complex compound are particularly preferable. Boron trifluoride diethyl etherate and boron trifluoride dibutyl etherate, which are coordination complexes with ethers, are particularly preferred. The addition amount is generally 3.0 × 10 ^{−6 to} 2.0 × 10 ⁻⁴ wt%, preferably 8.0 ×, in terms of boron trifluoride with respect to trioxane as the main monomer. It is used in the range of 10 ^{−6 to} 8.0 × 10 ⁻⁵ wt%. In order to disperse these catalysts uniformly in the reaction system, it is preferable to dilute them with an organic solvent that does not adversely affect the polymerization reaction. Examples of the organic solvent include ethers such as ethylene glycol dimethyl ether, diethylene glycol dimethyl ether, and n-butyl ether, aromatic hydrocarbons such as benzene and toluene, aliphatic hydrocarbons such as n-hexane and cyclohexane, methylene dichloride, and ethylene dichloride. And halogenated hydrocarbons.

  The raw material monomer in the present invention is trioxane which is a cyclic trimer of formaldehyde as the component (A), and cyclic ether and / or cyclic formal having at least one carbon-carbon bond which is a comonomer is used as the component (B). . Specific examples of the comonomer include, for example, 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-hydroxymethyl-1 , 3-dioxolane, 4-butyloxymethyl-1,3-dioxolane, 4-phenoxymethyl-1,3-dioxolane, 4-chloromethyl-1,3-dioxolane 1,3-dioxabicyclo [3,4,0] nonane, ethylene oxide, propylene oxide, butylene oxide, epichlorohydrin, styrene oxide, oxytane, 3,3-bis (chloromethyl) oxetane, tetrahydrofuran, and 1,3-dioxepane Examples include oxepanes, oxocanes such as 1,3,6-trioxocane, and oxetanes. Of these, 1,3-dioxolane is particularly preferred.

The amount of the comonomer added is preferably 0.1 to 30 parts by weight, more preferably 0.5 to 25 parts by weight with respect to 100 parts by weight of trioxane. When the amount of comonomer used is larger than this, the polymerization yield decreases, and when it is small, the thermal stability decreases.

The cyclic siloxane compound as component (C) is represented by the following general formula.

（式中、R¹及びR^２は同一又は異なり、何れもC₁〜C₂₀の炭化水素基であり、nは3〜20の整数である）

(In the formula, R ¹ and R ² are the same or different, both are C _{1 to} C ₂₀ hydrocarbon groups, and n is an integer of 3 to 20)

Specifically, hexamethylcyclotrisiloxane, 1,3,5-trimethyl-1,3,5-trivinylcyclotrisiloxane, hexaethylcyclotrisiloxane, 1,3,5-tris (3,3,3 -Trifluoropropyl) -1,3,5-trimethylcyclotrisiloxane, 1,3,5,7-tetramethylcyclotetrasiloxane, octamethylcyclotetrasiloxane, 1,3,5,7-tetramethyl-1, 3,5,7-tetravinylcyclotetrasiloxane, 1,3,5,7-tetrakis (3,3,3-trifluoropropyl) -1,3,5,7-tetramethylcyclotetrasiloxane, decamethylcyclo Pentasiloxane, dodecamethylcyclohexasiloxane and the like are used.

  These cyclic siloxane compounds are added in the range of 0.005 to 50 parts by weight per 100 parts by weight of trioxane. When the amount is less than 0.005 parts by weight, the effect of improving toughness is thin. When the amount is more than 50 parts by weight, the polymerization activity is significantly lowered. Moreover, the preferable addition amount is 0.01-40 weight part, More preferably, it is 0.05-30 weight part.

  There is no particular restriction on the position where the cyclic siloxane compound is introduced. A method in which all of trioxane, a comonomer, a chain transfer agent, and a catalyst are combined together at the inlet of the polymerization machine and quickly introduced into the polymerization machine, or after mixing with one or more of trioxane, a comonomer, and a chain transfer agent in advance. It is possible to carry out a polymerization reaction by combining them with each other or by mixing them in advance with any one or more of a comonomer and a chain transfer agent and further including a catalyst and then combining them with trioxane.

Also in the polymerization method of the present invention, a chain transfer agent can be added to adjust the degree of polymerization of the acetal copolymer. Examples of chain transfer agents include carboxylic acids, carboxylic anhydrides, esters, amides, imides, phenols, acetal compounds, and the like, and phenol, 2,6-dimethylphenol, methylal, and polyacetal dimethoxide are particularly suitable. Used. Of these, methylal is most preferred, and it can be used alone or in the form of a solution. As the addition amount, it is usually used in the range of less than 2 × 10 ⁻¹ wt% as methylal with respect to the main monomer trioxane. When used in the form of a solution, examples of the solvent include aliphatic hydrocarbons such as hexane, heptane, and cyclohexane, aromatic hydrocarbons such as benzene, toluene, and xylene, and halogenated hydrocarbons such as methylene dichloride and ethylene dichloride. Can be mentioned.

For the deactivation after the polymerization reaction, a catalyst deactivator such as a trivalent organic phosphorus compound, an amine compound, an alkali metal or an alkaline earth metal hydroxide can be used. As the amine compound, primary, secondary, and tertiary aliphatic amines, aromatic amines, heterocyclic amines, hindered amines, and other known catalyst deactivators can be used. For example, ethylamine, diethylamine, triethylamine, mono-n-butylamine, di-n-butylamine, tri-n-butylamine, aniline, diphenylamine, pyridine, piperidine, morpholine and the like can be used. Of these, trivalent organophosphorus compounds and tertiary amines are particularly preferred, and triphenylphosphine is most preferred. As the addition amount is not particularly limited as long as it is an amount sufficient to deactivate the catalyst, the molar ratio to the catalyst, usually used in an amount of ^1.0 × 10 -1 ~1.0 × 10 ¹ Is done. When these catalyst deactivators are used in the form of a solution or suspension, the solvent used is not particularly limited, but water, alcohols, acetone, methyl ethyl ketone, hexane, cyclohexane, heptane, Various aliphatic and aromatic organic solvents such as benzene, toluene, xylene, methylene dichloride and ethylene dichloride can be used.

  After the polymerization and deactivation operations (the acetal copolymer before stabilization is referred to as “crude copolymer”), if necessary, washing the crude copolymer, separating and recovering unreacted monomers, drying, etc. In the present invention, a crude copolymer having a high yield and excellent thermal stability can be obtained, and therefore this step can be omitted.

  Examples of the stabilization treatment include a method of removing the unstable portion by heating and melting the acetal copolymer obtained above. At this time, in addition to the hindered phenol compound and the amine-substituted triazine compound, any one or more of alkali or alkaline earth metal hydroxide, inorganic salt, carboxylate, etc. may be added. . Further, if necessary, general additives for thermoplastic resins, such as colorants such as dyes and pigments, lubricants, mold release agents, antistatic agents, ultraviolet absorbers, light stabilizers, surfactants, or One or more organic polymer materials, inorganic or organic fibrous, powdery, and plate-like fillers can be added.

  Examples of the antioxidant include 1,6-hexanediol-bis [3- (3,5-di-t-butyl-4-hydroxyphenyl) propionate], triethylene glycol-bis-3- (3-t- Butyl-4-hydroxy-5-methylphenyl) propionate, pentaerythrityl-tetrakis-3- (3,5-di-t-butyl-4-hydroxyphenyl) propionate, 2,2′-methylenebis (6-t- Butyl-4-methylphenol), 3,9-bis {2- [3- (3-t-butyl-4-hydroxy-5-methylphenyl] propionyloxy) -1,1-dimethylethyl} -2,4 , 8,10-tetraoxaspiro [5,5] undecane, N, N′-hexane-1,6-diylbis [3- (3,5-di-tert-butyl-4-hydroxy Phenyl) propionamide], 3,5-bis (1,1-dimethylethyl) -4-hindered phenols such as hydroxy benzenepropanoic acid 1,6-hexanediyl ester. These may be used alone or in combination of two or more.

The amount of these hindered phenol compounds added is preferably 0.01 to 0.4 parts by weight, more preferably 0.005 to 0.3 parts by weight, based on 100 parts by weight of the polyacetal copolymer.
In particular, the allyl ether used in the present invention reduces the thermal stability to some extent, and if it is less than this, the thermal stability is significantly reduced. Moreover, when there is more addition amount than this, the fall of a mechanical physical property will arise.

  Examples of the heat stabilizer include melamine, methylol melamine, guanamine, benzoguanamine, cyanoguanidine, N, N-diarylmelamine, melamine-formaldehyde condensate, urea, urea heat condensate synthesized by heating from urea, polyacryl Examples thereof include nitrogen-containing compounds such as amines, polyethyleneimines, polyacrylamides, polyamides, urethane compounds, and pyridine compounds. Among these, melamine, methylol melamine, and melamine-formaldehyde condensates that are amine-substituted triazine compounds are more preferable. These may be used alone or in combination of two or more.

  The addition amount of these amine-substituted triazines is preferably 0.0001 to 0.15 parts by weight and more preferably 0.005 to 0.10 parts by weight with respect to 100 parts by weight of the polyacetal copolymer. If it is less than this, the viscosity drop during production will be remarkably increased, leading to a reduction in production, and the thermal stability will be significantly impaired when the colorant is compounded. When it is larger than this, the toughness is significantly reduced.

  In addition, it is preferable to mix a metal-containing compound represented by a group consisting of an alkali metal or alkaline earth metal hydroxide, an inorganic acid salt, or an alkoxide as a heat stabilizer, such as sodium, potassium, calcium, magnesium, barium. And hydroxides, inorganic acid salts, alkoxides, and the like. Among these, calcium hydroxide, magnesium hydroxide, potassium hydroxide, calcium carbonate, and magnesium carbonate are most preferable. These may be used alone or in combination of two or more.

  The amount of the metal-containing compound represented by the group consisting of the alkali metal or alkaline earth metal hydroxide, inorganic acid salt, or alkoxide is 0.001 to 5 with respect to 100 parts by weight of the polyacetal polymer. 0.0 part by weight is preferable, and 0.001 to 1.0 part by weight is more preferable.

  In the present invention, hindered amine compounds, benzophenone compounds, benzotriazole compounds, aromatic benzoate compounds, cyanoacrylate compounds, oxalic acid anilide compounds, and the like may be added as weathering (light stabilizer) agents. The addition amount of these weathering agents is preferably 0.01 to 5 parts by weight and more preferably 0.01 to 3 parts by weight with respect to 100 parts by weight of the polyacetal copolymer.

A metal salt of a higher fatty acid may be added as a lubricant and a heat stabilizer to the polyacetal copolymer of the present invention. Although the metal salt of a higher fatty acid is not particularly limited, magnesium salts, calcium salts, barium salts, and the like of higher fatty acids such as lauric acid, palmitic acid, stearic acid, behenic acid, and 12-hydroxystearic acid are preferable.
Moreover, the addition amount of the metal salt of these higher fatty acids is preferably 0.0001 to 5 parts by weight, more preferably 0.0001 to 3 parts by weight with respect to 100 parts by weight of the polyacetal copolymer.

  Moreover, it is preferable to mix | blend the higher fatty acid amide which has a C10 or more long chain, the fatty acid ester of a polyhydric alcohol, and paraffin wax as a mold release agent. The higher fatty acid amide having a long chain having 10 or more carbon atoms is not particularly limited, but examples thereof include stearic acid amide, ethylene bisstearamide, methylene bisstearamide, methylene bislauramide, palmitic acid amide, and oleic acid amide. be able to. Among these, ethylene bisstearamide, methylene bisstearamide, and methylene bislauramide are more preferable. Specific examples of fatty acid esters of polyhydric alcohols include polyhydric alcohols such as glycerin, diglycerin, pentaerythritol, sorbitan, ethylene glycol, diethylene glycol, trimethylolmethane, trimethylolethane, behenic acid, serotic acid, and montanic acid. And fatty acid esters such as laccellic acid and the like, and paraffin wax having a molecular weight of 1,000 to 2,000,000 is preferable. These may be used alone or in combination of two or more.

  The addition amount of these paraffin wax, higher fatty acid amide having a long chain having 10 or more carbon atoms and fatty acid ester of polyhydric alcohol is preferably 0.01 to 5 parts by weight with respect to 100 parts by weight of the polyacetal copolymer. More preferred is 01 to 3 parts by weight.

  A nucleating agent may be added to the polyacetal resin composition of the present invention for the purpose of improving moldability and shortening the molding cycle. The nucleating agent is not particularly limited, but boron nitride, hydrous magnesium silicate, three-dimensional crosslinked polyacetal and the like are more preferable.

  The amount of the nucleating agent added and blended in the present invention is preferably 0.0001 to 10.0 parts by weight and more preferably 0.001 to 5.0 parts by weight with respect to 100 parts by weight of the polyacetal copolymer.

  You may add a coumarin type | system | group fluorescent whitening agent and a benzoxazole type | system | group fluorescent whitening agent as a fluorescent whitening agent with respect to the polyacetal copolymer of this invention. The coumarin fluorescent whitening agent and the benzoxazole fluorescent whitening agent are not particularly limited, but 3- (4′-acetylaminophenyl) -7-acetylaminocoumarin, 3- (4′-carboxyphenyl) -4-methyl. -7-diethylaminocoumarin, 2,5-bis (5′-t-butylbenzoxazol-2′-yl) thiophene, 2,5-bis [5′-t-butylbenzoxazolyl (2)] Thiophene is preferred. The addition amount of these coumarin fluorescent brighteners and benzoxazole fluorescent brighteners is preferably 0.001 to 500 ppm, more preferably 0.01 to 100 ppm, based on the polyacetal polymer.

  Glass beads, mica, kaolin, silicon dioxide, clay, asbestos, silica, diatomaceous earth, graphite, molybdenum disulfide, carbon black, titanium oxide, glass fiber, milled fiber, potassium titanate fiber, boron fiber as fillers Carbon fiber, aramid fiber or the like may be added. The amount of these fillers is preferably 0.01 to 200 parts by weight and more preferably 0.1 to 100 parts by weight with respect to 100 parts by weight of the polyacetal polymer.

  The melt flow index (MI) value (190 ° C., load 2,160 g) of the polyacetal copolymer according to the present invention is usually 0.5 to 100 g / 10 min, preferably 1.0 to 70 g / 10 min.

  The polyacetal copolymer which has deactivated the polymerization catalyst can be sent to the subsequent stabilization step as it is, but if further purification is required, washing, separation and recovery of unreacted monomers, drying, etc. Can pass.

  In the present invention, these various stabilizers and additives are mixed with the polyacetal polymer in which the polymerization catalyst has been deactivated, and heated and melt-kneaded by a single-screw or twin-screw extruder, a twin-screw paddle type continuous mixer, or the like. Heat-stabilized. At this time, some of these various stabilizers or additives may be added separately after the thermal stabilization treatment, and water, alcohol, amine, etc. may be added during the thermal stabilization. .

    The method of blending and mixing these various stabilizers and additives with the polyacetal polymer that has deactivated the polymerization catalyst is not particularly limited, and any method that can be used industrially may be used. For example, after mixing each component with a blender such as a turnbull mixer or a Henschel mixer, a method of kneading with a single screw or twin screw extruder, a twin screw paddle type continuous mixer, a bumper mixer, a roll or the like is appropriately selected. . Each component is preferably dried before kneading.

    Examples and Comparative Examples of the present invention are shown below, but it goes without saying that the present invention is not limited to these. In addition, the term and measurement method in an Example and a comparative example are shown below.

Continuous reactor : It has an inner section with two overlapping circles, the inner section has a major axis of 20 cm, L / D of 7.2, and a pair of shafts in a long case with a jacket around it. , A continuous mixer in which each shaft is fitted with a large number of pseudo-triangular plates that mesh with each other, and the tip of the pseudo-triangular plate can clean the inner surface of the case and the surface of the counterpart pseudo-triangular plate.
Stopper mixer : An inner section with two overlapping circles, the inner section has a major axis of 12 cm, L / D of 7.2, and a pair of shafts in a long case with a jacket around it Equipped with a structure in which a number of screw-like blades are fitted in each shaft, and a stopper solution is injected from the supply port portion and continuously mixed with the polymerization product.
MI value (melting index) : Triethylene glycol-bis [3- (3-tert-butyl-5-methyl-4-hydroxyphenyl) propionate] (trade name: IRGA, manufactured by Ciba Geigy Co., Ltd.) with 100 parts by weight of the crude copolymer Knox 245) Add 0.3 parts by weight, 0.1 parts by weight of melamine, 0.05 parts by weight of magnesium hydroxide, mix, and then melt and knead in a lab plast mill at 220 ° C under a nitrogen stream for 20 minutes. After the treatment, the measurement was performed according to ASTM-D1238 (190 ° C., under a load of 2.16 kg). This MI value indicates that the lower the value, the higher the degree of polymerization of the crude copolymer.
Tensile test : A test piece was molded using an injection molding machine and measured according to the ISO 527-1,2 method.
Film appearance : A 30 μm film was extruded using a 25 mm extruder having a T-die connected to the tip, and the surface appearance was evaluated. The fisheye and smoothness were comprehensively evaluated and classified according to the following ranks.
◎: Good, ○: Somewhat good, △: Somewhat bad, ×: Bad

<Examples 1-4, Comparative Examples 1-5>
As the continuous reaction apparatus, an acetal copolymer was produced using the above-mentioned two continuous reactors and a stopper mixer connected in series. From the inlet of the first reactor, a mixture of 90.0 kg / hr of trioxane and 3.6 kg / hr of 1,3-dioxolane was mixed with a cyclic siloxane compound and a benzene solution of methylal (25 wt. %), And further a benzene solution of boron trifluoride diethyl etherate (preparation concentration: 0.6 mol / kg) was added as a catalyst and immediately introduced into the reactor to carry out the reaction continuously. The first unit jacket temperature (polymerization temperature) was set to 85 ° C., and the second stage and terminator mixer jacket temperatures were set to 60 and 40 ° C., respectively. Also, from the inlet of the terminator mixer, triphenylphosphine twice the amount of the catalyst used was continuously supplied as a benzene solution (preparation concentration: 0.6 mol / kg) to stop the polymerization and pulverize. As a result, a crude copolymer was obtained. The polymerization yield of the crude copolymer obtained at this time was 98%. Next, to 100 parts by weight of the obtained crude copolymer, glycol-bis-3- (3-tert-butyl-4-hydroxy-5-methylphenyl) propionate (manufactured by Ciba Specialty Chemicals, trade name; Irganox 245) ) 0.3 parts by weight and 0.05 parts by weight of melamine were added and premixed using a Henschel mixer. Thereafter, it was supplied to a vented twin-screw extruder, and melt-kneaded at 200 ° C. under reduced pressure of 21.3 kPa to be pelletized. Using the obtained pellets, they were molded and subjected to a tensile test. The results are shown in Table 1.

Claims (3)

(A) 100 parts by weight of trioxane, (B) 0.1-30 parts by weight of a cyclic ether compound copolymerizable with trioxane, and (C) a polyacetal copolymer obtained by copolymerizing 0.005-50 parts by weight of a cyclic siloxane compound. Polymer. (C) The polyacetal copolymer according to claim 1, wherein the cyclic siloxane compound is at least one selected from cyclic siloxane compounds represented by the following formula (1).

(In the formula, R ¹ and R ² are the same or different, both are C _{1 to} C ₂₀ hydrocarbon groups, and n is an integer of 3 to 20) The polyacetal copolymer according to claim ² , wherein R ¹ and R ² in the formula (1) are methyl groups.