DE102024137141A1 - POLYACETAL RESIN COMPOSITION - Google Patents

Abstract

[Problems][Solution to the Problem]The object of the present invention is to provide a polyacetal resin composition which can suppress the amount of formaldehyde released from a molded article and can sufficiently suppress physical deterioration when the molded article is used for a long time under high temperature and dry conditions or under high temperature and humid conditions, in addition to having excellent dimensional stability after injection molding, and the solution to the object is the polyacetal resin composition comprising: based on 100 parts by mass of (A) polyacetal resin, 0.03 to 0.60 parts by mass of (B) ethylene urea, 0.05 to 0.50 parts by mass of (C) acrylamide polymer, and 0.0005 to 0.05 parts by mass of (D) ethylene bisstearamide.

Description

[Technical field]

The present invention relates to a polyacetal resin composition.

[Background]

Polyacetal resin is a material that exhibits excellent rigidity, strength, toughness, sliding properties, and creep properties. Polyacetal resin is widely used as a resin material for various mechanical parts, such as automotive parts, electrical and electronic parts, and industrial parts.

Polyacetal resin produces formaldehyde when decomposed by exposure to heat, light, oxygen, acid, alkali, etc. Especially during manufacturing and molding, formaldehyde gas generated by thermal decomposition remains in the resin molding. There are concerns that formaldehyde will gradually be released from the resin product, thereby deteriorating the interior environment. Especially in automotive interior parts, it is necessary to significantly reduce the amount of formaldehyde released from a molding.

Various techniques have been proposed as methods for suppressing the release of formaldehyde from polyacetal resin moldings. For example, techniques for adding hydrazide compounds, urea compounds, guanamine compounds, etc. as formaldehyde scavengers and techniques for adding polyamide resin as a heat stabilizer have been proposed ( WO 2016/126514 and JP 2005-263921 A ).

[List of citations]

[Patent literature]

• [Patent Literature 1] WO 2016/126514
• [Patent Literature 2] JP 2005-263921 A

[Overview of the invention]

[Problems of the invention]

In recent years, the application range of polyacetal resin has expanded, and there is a need to maintain mechanical strength when used for long periods in various transportation and usage environments, for example, to suppress physical deterioration when used for long periods in high temperatures and dry conditions or in high temperatures and humid conditions. Furthermore, due to the miniaturization and precision of polyacetal resin mechanical parts, there is a demand not only for improved impact resistance of these mechanical parts but also for dimensional stability after molding.

However, the molded articles of the polyacetal resin compositions proposed in the above-mentioned documents were not necessarily satisfactory in terms of suppressing the release of formaldehyde from the molded articles and suppressing physical deterioration when used for a long time under high temperature and dry conditions or under high temperature and humid conditions.

Therefore, the present invention aims to provide a polyacetal resin composition which can suppress the amount of formaldehyde released from a molded article and can sufficiently suppress the physical deterioration when the molded article is used for a long period of time under high temperature and dry conditions or under high temperature and humid conditions, in addition to having the excellent dimensional stability after injection molding.

[Solution to the problem]

We have found that by adding ethylene urea and acrylamide polymer as formaldehyde scavengers to polyacetal resin and adding ethylene bisstearamide in a predetermined ratio to the acrylamide polymer, the amount of formaldehyde released from a molded article can be suppressed and physical deterioration can be suppressed when the molded article is used for a long time under high temperature and dry conditions or under high temperature and humid conditions, in addition, polyacetal with excellent dimensional shrinkage stability in injection molding can be obtained, and then we have completed the present invention.

1. [1] Polyacetalharzzusammensetzung, umfassend:
   • bezogen auf 100 Massenteile (A) Polyacetalharz,
   • 0,03 bis 0,60 Massenteile (B) Ethylenharnstoff,
   • 0,05 bis 0,50 Massenteile (C) Acrylamidpolymer, und
   • 0,0005 bis 0,05 Massenteile (D) Ethylenbisstearamid.
2. [2] Polyacetalharzzusammensetzung nach Abschnitt [1], wobei das (A) Polyacetalharz ein Polyacetal-Homopolymer ist.
3. [3] Polyacetalharzzusammensetzung nach Abschnitt [1] oder [2], wobei das (A) Polyacetalharz bei einer Messung gemäß ISO 1133 eine Schmelzflussrate von 1,0 bis 10,0 g/10 min aufweist.
4. [4] Polyacetalharzzusammensetzung nach Abschnitt [3], wobei eine Schmelzflussrate des Polyacetalharzes (A) 1,0 bis 3,0 g/10 min beträgt.
5. [5] Polyacetalharzzusammensetzung nach einem der Abschnitte [1] bis [3], wobei eine Spitze der Molekulargewichtsverteilung des (A) Polyacetalharzes unimodal ist.
6. [6] Polyacetalharzzusammensetzung nach einem der Abschnitte [1] bis [5], die 0,05 bis 0,20 Massenteile des (C) Acrylamidpolymers enthält.
7. [7] Polyacetalharzzusammensetzung nach einem der Abschnitte [1] bis [6], wobei ein Massenverhältnis (D)/(C) von (D) Ethylenbisstearamid zu (C) Acrylamidpolymer 0,01 bis 0,5 beträgt.

That is, the present invention is as follows:

1. [1] A polyacetal resin composition comprising:
   • based on 100 parts by mass (A) polyacetal resin,
   • 0.03 to 0.60 parts by mass (B) ethylene urea,
   • 0.05 to 0.50 parts by mass (C) acrylamide polymer, and
   • 0.0005 to 0.05 parts by mass (D) ethylenebisstearamide.
2. [2] The polyacetal resin composition according to paragraph [1], wherein the (A) polyacetal resin is a polyacetal homopolymer.
3. [3] The polyacetal resin composition according to clause [1] or [2], wherein the (A) polyacetal resin has a melt flow rate of 1.0 to 10.0 g/10 min when measured according to ISO 1133.
4. [4] The polyacetal resin composition according to paragraph [3], wherein a melt flow rate of the polyacetal resin (A) is 1.0 to 3.0 g/10 min.
5. [5] The polyacetal resin composition according to any one of [1] to [3], wherein a peak of the molecular weight distribution of the (A) polyacetal resin is unimodal.
6. [6] The polyacetal resin composition according to any one of [1] to [5], which contains 0.05 to 0.20 parts by mass of the (C) acrylamide polymer.
7. [7] The polyacetal resin composition according to any one of [1] to [6], wherein a mass ratio (D)/(C) of (D) ethylenebisstearamide to (C) acrylamide polymer is 0.01 to 0.5.

[Advantageous effects of the invention]

According to the present invention, it is possible to provide a polyacetal resin composition which can suppress the amount of formaldehyde released from a molded article and can sufficiently suppress physical deterioration when the molded article is used for a long period of time under high temperature and dry conditions or under high temperature and humid conditions, in addition to having excellent dimensional stability after injection molding.

[Embodiments of the invention]

The following describes in detail the mode for carrying out the present invention (hereinafter referred to simply as "the present embodiment"). The present invention is not limited to the following description and can be embodied in various forms within the spirit of the invention.

<Polyacetal resin composition>

• bezogen auf 100 Massenteile (A) Polyacetalharz,
• 0,03 bis 0,60 Massenteile (B) Ethylenharnstoff,
• 0,05 bis 0,50 Massenteile (C) Acrylamidpolymer, und
• 0,0005 bis 0,05 Massenteile (D) Ethylenbisstearamid.

The polyacetal resin composition of the present embodiment comprises:

• based on 100 parts by mass (A) polyacetal resin,
• 0.03 to 0.60 parts by mass (B) ethylene urea,
• 0.05 to 0.50 parts by mass (C) acrylamide polymer, and
• 0.0005 to 0.05 parts by mass (D) ethylenebisstearamide.

The above-mentioned polyacetal resin composition can suppress the amount of formaldehyde released from a molded article made from the polyacetal resin composition and sufficiently suppress the physical deterioration when the molded article is used for a long time under high temperature and dry conditions or under high temperature and humid conditions, in addition to having excellent dimensional stability after injection molding.

<<(A) Polyacetal resin>>

The (A) polyacetal resin included in the polyacetal resin composition of the present embodiment refers to a polymer having an oxymethylene group in the main chain. (A) Polyacetal resin includes, for example: a polyacetal homopolymer obtained by homopolymerizing a formaldehyde monomer or the cyclic oligomers of formaldehyde such as its trimer (trioxane) or tetramer (tetraoxane) and consisting essentially of oxymethylene units; a polyacetal copolymer obtained by copolymerizing a formaldehyde monomer or the cyclic oligomers of formaldehyde such as its trimer (trioxane) or tetramer (tetraoxane), and the cyclic ethers or cyclic formals such as cyclic formals of glycol or diglycol such as ethylene oxide, propylene oxide, epichlorohydrin, 1,3-dioxolane, 1,4-butanediol formal, etc., a polyacetal copolymer having branches obtained by copolymerizing monofunctional glycidyl ether, and a polyacetal copolymer having a crosslinked structure obtained by copolymerizing multifunctional glycidyl ether.

In addition, as (A) polyacetal resin, there can be used: compounds having functional groups such as hydroxyl groups at both ends or at one end, for example, a polyacetal homopolymer having block components obtained in the presence of polyalkylene glycol by polymerizing a formaldehyde monomer or the cyclic oligomers of formaldehyde such as its trimer (trioxane) or tetramer (tetraoxane); or also compounds having functional groups such as hydroxyl groups at both ends or at one end, for example, a polyacetal copolymer obtained in the presence of hydrogenated polybutadiene glycol by copolymerizing a formaldehyde monomer or the cyclic oligomers of formaldehyde such as its trimer (trioxane) or tetramer (tetraoxane), and the cyclic ethers or cyclic formals.

The above-mentioned polyacetal resins can be used alone or in combination of two or more types.

Among these, the (A) polyacetal resin is preferably a polyacetal homopolymer from the viewpoint of improving mechanical strength, and is more preferably a polyacetal homopolymer obtained by homopolymerizing formaldehyde monomer alone.

In addition, the polymerization degree and comonomer content of (A) polyacetal resin are not particularly limited in the present embodiment.

In order to emphasize the excellent properties of engineering resins, the content of polyacetal resin is preferably 50 mass% or more based on 100 mass% of polyacetal resin composition, more preferably 60 mass% or more, and even more preferably 70 mass% or more.

The polyacetal resin preferably has a melt flow rate (MFR) of 1.0 to 10.0 g/10 min when measured according to ISO 1133. It is more preferable that the melt flow rate of the polyacetal resin be in the range of 1.0 g/10 min to 3.0 g/10 min. By setting the MFR of the polyacetal resin to the above range, a polyacetal composition can be obtained that has excellent mechanical strength, can suppress physical deterioration, and can suppress the amount of formaldehyde released.

The number average molecular weight (Mn) of the polyacetal resin is preferably 10,000 or more, more preferably 25,000 or more, and most preferably 30,000 to 150,000 from the viewpoint of mechanical strength.

In addition, the weight average molecular weight (Mw) of the polyacetal resin is preferably 30,000 or more, more preferably 100,000 or more, and most preferably 100,000 to 400,000.

The shape of the molecular weight distribution curve of the polyacetal resin in the present embodiment is not particularly limited, but it is preferable that the peak of the molecular weight distribution be unimodal. From the viewpoint of improving mechanical strength, it is more preferable to have a unimodal shape with a peak having a peak height in the range of logM = 4.5 to 8.0 (M is the molecular weight), even more preferable to have a unimodal shape with a peak having a peak height in the range of logM = 4.5 to 7.0, and particularly preferable to have a unimodal shape with a peak having a peak height in the range of logM = 4.5 to 6.0.

The term “unimodal” refers to a shape with only one mountain-like peak.

When components have low molecular weight, the molecular weight distribution curve in the region below 10,000 molecular weight does not form part of the mountain-like peak, but forms a shoulder or tapers off after the peak height.

The number average molecular weight (Mn), the weight average molecular weight (Mw) and the molecular weight distribution in the present embodiment can be measured by gel permeation chromatography (GPC) with PMMA as a standard material.

(polyacetal homopolymer)

The above-mentioned polyacetal resin is preferably a polyacetal homopolymer.

The above-mentioned polyacetal homopolymer can be produced by feeding formaldehyde as a monomer, a chain transfer agent (molecular weight regulator) and a polymerization catalyst into a polymerization reactor into which a hydrocarbon polymerization solvent is introduced, and polymerizing the mixture by a slurry polymerization method.

Here, the raw material monomers, chain transfer agents, and polymerization catalysts may include chain-transferable components (components that generate unstable terminal groups) such as water, methanol, and formic acid, so it is preferable to first adjust the content of these chain-transferable components. The content of these chain-transferable components is preferably 1 to 1000 ppm by mass based on the total mass of formaldehyde as a monomer, more preferably 1 to 500 ppm by mass, and even more preferably 1 to 300 ppm by mass. By adjusting the content of the chain-transferable components to the above range, a polyacetal homopolymer with excellent thermal stability can be obtained.

The molecular weight of the polyacetal homopolymer can be adjusted by chain transfer using a molecular weight regulator such as carboxylic anhydrides or carboxylic acids. Propionic anhydride and acetic anhydride are particularly preferred as molecular weight regulators, and acetic anhydride is even more preferred.

The amount of the molecular weight regulator to be introduced is controlled and determined according to the properties (particularly the melt flow rate) of the polyacetal homopolymer to be obtained. For example, it is preferable that the melt flow rate (measured according to ISO 1133) of the polyacetal homopolymer be in the range of 0.1 to 100 g/10 min, more preferable that the melt flow rate be in the range of 1.0 g/10 min to 10 g/10 min, and even more preferable that the melt flow rate be in the range of 1.0 g/10 min to 3.0 g/10 min. By making the MFR value of the polyacetal homopolymer fall within the above range, a polyacetal homopolymer with excellent mechanical strength can be obtained.

As the polymerization catalyst, an anionic polymerization catalyst is preferable, and an onium salt polymerization catalyst represented by the following general formula (I) is more preferable. [R ₁ R ₂ R ₃ R ₄ M] ⁺ X ^- (I) (In formula (I), R ₁ , R ₂ , R ₃ and R ₄ each independently represent an alkyl group, M represents an element having a free electron pair and X represents a nucleophilic group.)

The polymerization catalyst can be used alone or in a combination of two or more types.

Among the onium salt polymerization catalysts, quaternary phosphonium salt compounds such as tetraethylphosphonium iodide and tributylethylphosphonium iodide and quaternary ammonium salt compounds such as tetramethylammonium bromide and dimethyl distearylammonium acetate are preferred.

The amount of addition of the onium salt polymerization catalysts of these quaternary phosphonium salt compounds and quaternary ammonium salt compounds is preferably 0.0003 to 0.01 mol, more preferably 0.0008 to 0.005 mol, and even more preferably 0.001 to 0.003 mol.

Any solvent that does not react with formaldehyde is suitable as a hydrocarbon polymerization solvent, and there are no particular restrictions. However, solvents such as pentane, isopentane, hexane, cyclohexane, heptane, octane, nonane, decane, and benzene are mentioned, with hexane being particularly preferred. These hydrocarbon solvents can be used alone or in combination with two or more types.

In the preparation of polyacetal homopolymers, it is first desirable to obtain crude polyacetal homopolymers by polymerization and then to subject the unstable end groups to a stabilization treatment as described later.

The polymerization reactor used to produce crude polyacetal homopolymer is not particularly limited, as long as it is a device that can simultaneously feed formaldehyde as a monomer, a chain transfer agent (molecular weight regulator), a polymerization catalyst, and a hydrocarbon polymerization solvent. However, from the perspective of productivity, it is preferable to use a continuous polymerization reactor.

The crude polyacetal homopolymer obtained by polymerization has thermally unstable end groups. Therefore, it is preferable to subject these unstable end groups to a stabilization treatment by sealing them with an esterifying agent or etherifying agent, etc.

The end group stabilization treatment of crude polyacetal homopolymers by esterification can be carried out, for example, by introducing crude polyacetal homopolymers, esterification agents, and esterification catalysts into an end-stabilization reaction machine into which a hydrocarbon solvent is introduced, and reacting. In this case, the reaction temperature and reaction time are, for example, 130 to 155°C for 1 to 100 minutes, more preferably 135 to 155°C for 5 to 100 minutes, and even more preferably 140 to 155°C for 10 to 100 minutes.

As an esterification agent that seals and stabilizes the end groups of the above crude polyacetal homopolymer, an acid anhydride of the following general formula (II) can be used: R ₅ COOCR ₆ (II) (In formula (II), R ₅ and R ₆ each independently represent an alkyl group. R ₅ and R ₆ may be the same or different.)

Esterifying agents include, for example, but are not limited to, benzoic anhydride, succinic anhydride, maleic anhydride, glutaric anhydride, phthalic anhydride, propionic anhydride, and acetic anhydride, preferably acetic anhydride. These esterifying agents can be used alone or in a combination of two or more types.

As the above-mentioned esterification catalyst, an alkali metal salt of a carboxylic acid having 1 to 18 carbon atoms is preferred, and the amount of addition can be selected within a range of 1 to 1000 ppm by mass based on the mass of the polyacetal homopolymer. Examples of alkali metal salts of the carboxylic acid having 1 to 18 carbon atoms include, but are not limited to, alkali metal salts of formic acid, acetic acid, propionic acid, butyric acid, valeric acid, caproic acid, enanthic acid, caprylic acid, pelargonic acid, capric acid, lauric acid, myristic acid, palmitic acid, margaric acid, stearic acid, etc., and the alkali metals in question include lithium, sodium, potassium, rubidium, and cesium. Among these alkali metal salts of carboxylic acids, lithium acetate, sodium acetate, and potassium acetate are preferred.

As an etherifying agent that seals and stabilizes the end groups of the above crude polyacetal homopolymer, an orthoester of an aliphatic or aromatic acid and an aliphatic, alicyclic or aromatic alcohol, for example methyl orthoformate or ethyl orthoformate, methyl orthoacetate or ethyl orthoacetate, methyl orthobenzoate or ethyl orthobenzoate and orthocarbonate, specifically ethyl orthocarbonate, and stabilization can be achieved with medium-strength organic acids such as p-toluenesulfonic acid, acetic acid and oxalic acid.

When the end groups of crude polyacetal homopolymers are sealed and stabilized by etherification, the solvents used in the etherification reaction include, for example, but are not limited to: organic solvents such as low boiling point aliphatic hydrocarbon solvents such as pentane, hexane, etc., aliphatic and aromatic hydrocarbon solvents such as cyclohexane, benzene, etc., and halogenated lower aliphatic solvents such as dichloromethane, chloroform, carbon tetrachloride, etc.

The polyacetal homopolymer whose terminal groups are stabilized by the above method is dried by removing moisture by enclosing air or nitrogen gas adjusted to 100 to 150°C using a hot air dryer or vacuum dryer, etc., to obtain polyacetal homopolymer as (A) polyacetal resin.

(polyacetal copolymer)

Next, the materials used in the preparation of polyacetal copolymers are described, specifically trioxane, cyclic ether and/or cyclic formal, polymerization catalyst, low molecular weight acetal compound, and organic solvent.

- Trioxane -

Trioxane is a cyclic trimer of formaldehyde and is generally obtained by the reaction of an aqueous formalin solution in the presence of an acid catalyst.

Trioxane may contain impurities that cause chain transfer from water, methanol, formic acid, methyl formate, etc., so it is preferable to remove and refine these impurities by methods such as distillation. In this case, it is preferable to reduce the total amount of chain-transferring impurities to 1 × 10 ^-3 mol or less per 1 mol of trioxane, and it is more preferable to reduce it to 0.5 × 10 ^-3 mol or less. By reducing the total amount of impurities to the above-mentioned upper limit or less, the polymerization reaction rate can be sufficiently increased for practical use, and excellent thermal stability of the produced polymer can be obtained.

- Cyclic ethers and/or cyclic formals -

Cyclic ethers and/or cyclic formals are components that can be copolymerized with the above-mentioned trioxane, and include, for example, ethylene oxide, propylene oxide, butylene oxide, epichlorohydrin, epibromohydrin, styrene oxide, oxathane, 1,3-dioxolane, ethylene glycol formal, propylene glycol formal, diethylene glycol formal, triethylene glycol formal, 1,4-butanediol formal, 1,5-pentanediol formal, 1,6-hexanediol formal, etc. Among these, 1,3-dioxolane and 1,4-butanediol formal are preferred as cyclic ethers and/or cyclic formals. These can be used alone or in combination with two or more types.

The amount of cyclic ether and/or cyclic formal added is preferably in the range of 1 to 20 mol% based on 1 mol of the above trioxane, more preferably in the range of 1 to 15 mol%, even more preferably in the range of 1 to 10 mol%, and even more preferably in the range of 1 to 5 mol%.

- Polymerization catalyst -

Polymerization catalysts include, for example, Lewis acids such as metal halides and Brønsted acids such as heteropolyacids. Lewis acids include, for example, halides of boric acids, tin, titanium, phosphorus, arsenic, and antimony, and particularly preferred are boron trifluoride, boron trifluoride-based hydrates, and coordination complex compounds of organic compounds containing oxygen atoms or sulfur atoms, and boron trifluoride. For example, polymerization catalysts include boron trifluoride, boron trifluoride diethyl etherate, and boron trifluoride di-n-butyl etherate as suitable examples. Heteropolyacids include, for example, molybdophosphoric acid, tungstophosphoric acid, phosphomolybdotungstic acid, phosphomolybdotovanadic acid, phosphomolybdotungstivandavanadic acid, phosphotungstivandvanadic acid, silicotungstic acid, silicomolybdic acid, silicomolybdostungstic acid, and boromolybdostungsticvanadic acid. These can be used alone or in a combination of two or more types.

The amount of the polymerization catalyst added is preferably in the range of 0.1 × 10 ^-5 to 0.1 × 10 ^-3 mol relative to 1 mol of the above trioxane, and more preferably in the range of 0.3 × 10 ^-5 to 0.3 × 10 ^-4 mol, and even more preferably in the range of 0.5 × 10 ^-5 to 0.15 × 10 ^-4 mol. When the amount of the polymerization catalyst added is within the above range, a stable polymerization reaction can be carried out for a long period of time.

- Low molecular weight acetal compounds -

Low-molecular-weight acetal compounds act as chain transfer agents in polymerization reactions and are acetal compounds with a molecular weight of 200 or less, preferably 60 to 170. Specifically, methylal, methoxymethylal, dimethoxymethylal, and trimethoxymethylal are suitable examples. These can be used alone or in combination with two or more types.

The amount of the low molecular weight acetal compound added is preferably in the range of 0.1 × 10 ^-4 to 0.6 × 10 ^-2 mol based on 1 mol of the above trioxane from the viewpoint that the molecular weight of the polymer is kept in a suitable range.

- Organic solvent -

There are no specific restrictions on the organic solvents used, as long as they do not participate in or adversely affect the polymerization reaction, and include, for example: aromatic hydrocarbons such as benzene (boiling point 80°C), toluene (boiling point 110.63°C), and xylene (boiling point 144°C); aliphatic hydrocarbons such as n-hexane (boiling point 69°C), n-heptane (boiling point 98°C), and cyclohexane (boiling point 80.74°C); Halogenated hydrocarbons such as chloroform (boiling point 61.2°C), dichloromethane (boiling point 40°C), and carbon tetrachloride (boiling point 76.8°C), as well as ethers such as diethyl ether (boiling point 35°C), diethylene glycol dimethyl ether (boiling point 162°C), 1,4-dioxane (boiling point 101.1°C), etc., in particular, aliphatic hydrocarbons such as n-hexane, n-heptane, and cyclohexane can be cited as suitable examples from the viewpoint of suppressing tarry deposits. These organic solvents can be used alone or in a combination of two or more types.

The amount of organic solvent added is preferably in the range of 0.1 × 10 ^-3 to 0.2 mol based on 1 mol of trioxane, more preferably in the range of 0.2 × 10 ^-3 to 0.5 × 10 ^-1 mol, and even more preferably in the range of 0.5 × 10 ^-7 to 0.3 × 10 ^-1 mol. When the amount of organic solvent added is within the above range, a polyacetal copolymer having excellent productivity can be obtained.

- Polymerization of polyacetal copolymer -

There are no specific restrictions on the polymerization process for polyacetal copolymers, but in addition to the above-mentioned slurry polymerization process for producing polyacetal homopolymers, methods such as bulk polymerization and melt polymerization can also be used. Both batch and continuous polymerization processes can be used for the polymerization of polyacetal copolymers.

There are no particular restrictions on the polymerization reactor used, but self-cleaning extrusion mixers such as co-kneader, continuous twin-screw extrusion mixer, and continuous double-paddle mixer can be used. It is preferred that these devices have a jacket through which a heating medium can be passed.

After feeding each material to the polymerization reactor, it is preferable to maintain the temperature of the polymerization reactor during the polymerization reaction at 63 to 135°C, more preferably the temperature is in the range of 70 to 120°C, and even more preferably in the range of 70 to 100°C. In addition, the residence time (reaction time) in the polymerization reactor is preferably 0.1 to 30 minutes, more preferably 0.1 to 25 minutes, and even more preferably 0.1 to 20 minutes. When the temperature of the polymerization tion reactor and the residence time are within the above-mentioned ranges, there is a tendency for a stable polymerization reaction to continue.

The polymerization reaction yields a crude polyacetal copolymer. Here, the method for deactivating the polymerization catalyst is to add the crude polyacetal copolymer from the polymerization reactor to an aqueous or organic solution containing at least one of the following neutralizing deactivators: amines such as ammonia, triethylamine, tri-n-butylamine, etc., hydroxides, inorganic salts, organic acid salts of alkali or alkaline earth metals, etc., and continuously stir the slurry for several minutes to several hours at room temperature to 100°C or below. In this case, it is preferable to first crush the crude polyacetal copolymer after polymerization and then process it if it is in large pieces. The polyacetal copolymer is then obtained by filtering with a centrifugal separator and drying under nitrogen.

The resulting polyacetal copolymer may contain thermally unstable end portions [-(OC ₂ )n-OH groups] (hereinafter, such polyacetal copolymers may be referred to as "polyacetal copolymers before terminal stabilization"). Therefore, it is preferable to perform a treatment to decompose and remove these thermally unstable end portions (terminal stabilization) using a terminal stabilizer. There are no particular restrictions on the terminal stabilizer, and it includes: an aliphatic amine compound such as ammonia, triethylamine, or tributylamine; Basic substances such as hydroxides of alkali or alkaline earth metals such as sodium, potassium, magnesium, calcium or barium, etc., inorganic weak acid salts of alkali or alkaline earth metals such as carbonates, phosphates, silicates and borates, etc., and organic acid salts of alkali or alkaline earth metals such as formates, acetates, stearates, palmitates, propionates and oxalates, and among these, aliphatic amine compounds are preferred, and triethylamine is even more preferred.

There are no particular restrictions on the method for decomposing and removing the unstable end parts. For example, a method of thermally treating the polyacetal copolymer in a molten state at a temperature above the melting point of the polyacetal copolymer and below 260°C in the presence of an end stabilizer such as triethylamine is cited. A single-screw or twin-screw extruder with a venting and decompression device can be used as the thermal treatment device, for example, and a twin-screw extruder is preferred.

The polyacetal copolymer whose end parts have been stabilized by the above method is dried by removing moisture by enclosing air or nitrogen gas adjusted to 100 to 150°C using a hot air dryer, vacuum dryer or other dryer to obtain polyacetal copolymer as (A) polyacetal resin.

<<(B) Ethylene urea>>

The (B) ethylene urea comprised in the polyacetal resin composition of the present embodiment acts as a formaldehyde scavenger.

The method for producing (B) ethyleneurea included in the polyacetal resin composition of the present embodiment is not specifically defined, and any publicly known method can be used. For example, it can be obtained by reacting ethylenediamine with carbon dioxide, reacting ethylenediamine with urea, reacting ethylenediamine with phosgene, reacting ethylenediamine with dialkyl carbonate, or oxidizing ethylenethiourea.

The ethyleneurea of the present embodiment may comprise impurities such as raw materials, intermediates, and solvents. For example, it may comprise ethylenediamine, urea, dialkyl carbonate, 2-aminoethylcarbamic acid, 2-aminoethylcarbamide ester, and 2-aminoethylurea. The amount of impurities is preferably less than 10 wt% based on the weight of the ethyleneurea, more preferably less than 5 wt%, and even more preferably less than 1 wt%.

The content of ethylene urea in the present embodiment is 0.03 to 0.60 parts by mass based on 100 parts by mass of polyacetal resin. This makes it possible to suppress the amount of formaldehyde released from the molded articles obtained from the polyacetal resin composition of the present embodiment, and also makes it possible to suppress the decrease in mechanical strength during long-term use under high temperatures and humid conditions, and also makes it possible to suppress the formation of mold deposits during molding. At the same time, From this point of view, the content of (B) ethylene urea is preferably 0.03 to 0.40 parts by mass, and more preferably 0.05 to 0.20 parts by mass.

<<(C) Acrylamide polymer>>

(C) Acrylamide polymer comprised in the polyacetal resin composition of the present embodiment functions as a formaldehyde scavenger.

The (C) acrylamide polymer can be prepared, for example, by using an alkaline earth metal alkoxide as a catalyst and carrying out either the polymerization of acrylamide alone or the copolymerization of acrylamide and a monomer having a vinyl group other than acrylamide.

The moldability of polyacetal resin composition can be improved by using a copolymer of acrylamide and a monomer having a vinyl group (e.g., a copolymer having a crosslinking structure) as (C) acrylamide polymer.

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

Monomers with vinyl groups other than the above-mentioned acrylamide include monomers with one or two vinyl groups.

Monomers with a vinyl group include, for example: n-butyl methacrylate, isobutyl methacrylate, t-butyl methacrylate, ethyl methacrylate, cyclohexyl methacrylate, 2-ethylhexyl methacrylate, cetyl methacrylate, pentadecyl methacrylate, stearyl methacrylate, behenyl methacrylate, hydroxypropyl methacrylate, polypropylene glycol methacrylate, polyethylene glycol methacrylate, etc.

Monomers with two vinyl groups include, for example: divinylbenzene, ethylenebisacrylamide and N,N'-methylenebisacrylamide.

Among these monomers with vinyl groups, N,N'-methylenebisacrylamide is preferred.

In the preparation of the above-mentioned acrylamide polymer, the amount of the above-mentioned monomer having a vinyl group added to the total amount of the above-mentioned acrylamide and the above-mentioned monomer having a vinyl group is preferably 0.05 to 20 mass%.

(C) The polymer of acrylamide may be a copolymer having a primary amide group and a secondary amide group.

The molar content of the primary amide group in the acrylamide polymer is preferably 30 to 80 mol%, more preferably 30 to 70 mol%, and even more preferably 40 to 70 mol%. When the primary amide group is within the above range, it is possible to provide a polyacetal resin composition with excellent crushability and, furthermore, excellent moldability.

There are no specific restrictions on the method for measuring primary amide groups, but the following method is an example: Next, the sample polymer and a 40 mass percent potassium hydroxide solution are placed in a flask equipped with a stirrer, and then heated at 105 to 110°C with stirring for 20 minutes to hydrolyze the primary amide groups into ammonia. The contents of the flask are then cooled to below 50°C, methanol is added, and the ammonia is extracted with the methanol. This extraction solution is absorbed into a 0.1% aqueous sulfuric acid solution, and the amount of primary amide groups is then determined by neutralization titration with a 0.1% aqueous sodium hydroxide solution using methyl red as an indicator.

The average particle diameter of the (C) acrylamide polymer is preferably 0.1 to 20 µm, more preferably 0.1 to 15 µm, and even more preferably 0.1 to 10 µm. When the average particle diameter of the acrylamide polymer is within the above range, it is possible to provide a polyacetal resin composition with excellent moldability.

The above average particle diameter refers to a value measured by a laser diffraction particle size distribution meter.

The content of (C) acrylamide polymer in the present embodiment is 0.05 to 0.50 parts by mass based on 100 parts by mass of (A) polyacetal resin. This makes it possible to obtain a polyacetal resin composition with excellent moldability and thermal stability. From the same point of view, the content of the above-mentioned (C) acrylamide polymer is preferably 0.05 to 0.40 parts by mass based on 100 parts by mass of (A) polyacetal resin, and more preferably 0.05 to 0.20 parts by mass.

<<(D) Ethylene bisstearamide>>

The method for producing (D) ethylenebisstearamide included in the polyacetal resin composition of the present embodiment is not specifically defined, and a publicly known method can be used. For example, it can be obtained by reacting stearic acid with ethylenediamine.

The content of (D) ethylenebisstearamide in the present embodiment is 0.0005 to 0.05 parts by mass based on 100 parts by mass of polyacetal resin. This enables the production of a polyacetal resin composition with excellent moldability, and it is possible to suppress the decrease in mechanical strength during long-term use under high temperatures and humid conditions. From the same point of view, the content of the above-mentioned (D) ethylenebisstearamide is preferably 0.00051 to 0.03 parts by mass based on 100 parts by mass of the polyacetal resin, more preferably 0.001 to 0.03 parts by mass, and particularly preferably 0.003 to 0.02 parts by mass. In addition, from the viewpoint of suppressing the decrease in mechanical strength of molded articles obtained from the polyacetal resin composition of the present embodiment during long-term use under high temperatures and humid conditions, the content of (D) ethylenebisstearamide is also preferably 0.00051 to 0.009 parts by mass based on 100 parts by mass of the polyacetal resin, also preferably 0.001 to 0.009 parts by mass, and also preferably 0.001 to 0.007 parts by mass.

Furthermore, the mass ratio (D)/(C) of the above-mentioned (D) ethylenebisstearamide to the above-mentioned (C) acrylamide polymer is preferably in the range of 0.01 to 0.5, more preferably in the range of 0.01 to 0.3, and particularly preferably in the range of 0.03 to 0.1. The mass ratio (D)/(C) within the above-mentioned range is preferable because it can more effectively suppress the decrease in mechanical strength of molded articles of polyacetal resin composition during long-term use under high temperature and dry conditions or under high temperature and humid conditions.

<<(E) Other additives>>

In addition to the above-mentioned components (A) to (D), the polyacetal resin composition of the present disclosure may also comprise generally known additives ((E) Other Additives). (E) Other additives include, for example, antioxidants, heat stabilizers, formic acid scavengers, weather stabilizers, mold release agents, lubricants, conductive agents, thermoplastic resins, thermoplastic elastomers, inorganic fillers, organic fillers, pigments, and dyes, etc. These additives may be used alone or in a combination of two or more types.

As the above-mentioned antioxidants, hindered phenol antioxidants are preferred.

Preferred hindered phenol antioxidants include, for example: 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, 1,6-hexanediol-bis-[3-(3,5-di-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] and Pentaerythritol tetrakis[3-(3',5'-di-t-butyl-4'-hydroxyphenyl)propionate], etc. Among these, triethylene glycol bis[3-(3-t-butyl-5-methyl-4-hydroxyphenyl)propionate] and pentaerythritol tetrakis[3-(3',5'-di-t-butyl-4'-hydroxyphenyl)propionate] are preferred.

These antioxidants can be used alone or in a combination of two or more types.

The above-mentioned heat stabilizers include, for example: amino-substituted triazine compounds, adducts of amino-substituted triazine compounds and formaldehyde, condensates of amino-substituted triazine compounds and formaldehyde, urea, urea derivatives, hydrazine derivatives, amide compounds, polyamides, etc.

The above-mentioned amino-substituted triazine compounds include, for example, but are not limited to: 2,4-diamino-sym-triazine, 2,4,6-triamino-sym-triazine, N-butylmelamine, N-phenylmelamine, N,N-diphenylmelamine, N,N-diarylmelamine, benzoguanamine (2,4-diamino-6-phenyl-sym-triazine), acetoguanamine (2,4-diamino-6-methyl-sym-triazine), 2,4-diamino-6-butyl-sym-triazine, etc.

The above-mentioned urea derivatives include, for example, but are not limited to, N-substituted ureas, urea condensates, hydantoin compounds, and ureido compounds. In the present disclosure, the above-mentioned urea derivatives do not include ethyleneurea.

The above-mentioned N-substituted ureas include, but are not limited to, methylurea, alkylenebisurea, and aryl-substituted urea, which have substituents such as alkyl groups. The above-mentioned urea condensates include, but are not limited to, urea-formaldehyde condensates. The above-mentioned hydantoin compounds include, but are not limited to, hydantoin, 5,5-dimethylhydantoin, 5,5-diphenylhydantoin, etc. The above-mentioned ureido compounds include, but are not limited to, allantoin, etc.

The above-mentioned hydrazine derivatives include, but are not limited to, hydrazide compounds.

Hydrazide compounds include, for example, carboxylic acid monohydrazide compounds, carboxylic acid dihydrazide compounds, alkyl group-substituted monohydrazide compounds, and alkyl group-substituted dihydrazide compounds, which are synthesized by the reaction of carboxylic acids (including aromatic and alicyclic carboxylic acids) and hydrazine. The above-mentioned carboxylic acids can be monocarboxylic acids, dicarboxylic acids, or compounds (polyvalent carboxylic acids) comprising three or more carboxylic acids. Examples of monocarboxylic acids include formic acid, acetic acid, propionic acid, butyric acid, valeric acid, caproic acid, enanthic acid, caprylic acid, lauric acid, myristic acid, palmitic acid, margaric acid, stearic acid, behenic acid, benzoic acid, salicylic acid, gallic acid, cinnamic acid, pyruvic acid, lactic acid, and amino acids. Examples of dicarboxylic acids include: oxalic acid, malonic acid, succinic acid, glutaric acid, adipic acid, pimelic acid, suberic acid, azelaic acid, sebacic acid, phthalic acid, isophthalic acid, terephthalic acid, naphthalic acid, malic acid, fumaric acid, maleic acid, tartaric acid, and nitrocarboxylic acid. Examples of polyvalent carboxylic acids include: melitic acid, citric acid, and aconitic acid. Examples of unsaturated carboxylic acids include: oleic acid, linoleic acid, linolenic acid, arachidonic acid, docosahexaenoic acid, and eicosapentaenoic acid. Carboxylic acid mono(di)hydrazide compounds synthesized using these carboxylic acids include, for example: carbodihydrazide, oxalic acid mono(di)hydrazide, malonic acid mono(di)hydrazide, succinic acid mono(di)hydrazide, glutaric acid mono(di)hydrazide, adipic acid mono(di)hydrazide, pimelic acid mono(di)hydrazide, suberic acid mono(di)hydrazide, azelaic acid mono(di)hydrazide, sebacic acid mono(di)hydrazide, phthalic acid mono(di)hydrazide, isophthalic acid mono(di)hydrazide, terephthalic acid mono(di)hydrazide, 2,6-naphthalic acid mono(di)hydrazide, malic acid mono(di)hydrazide, fumaric acid mono(di)hydrazide, maleic acid mono(di)hydrazide, Tartaric acid mono(di)hydrazide, propionic acid mono(di)hydrazide, lauric acid mono(di)hydrazide, stearic acid mono(di)hydrazide, p-hydroxybenzhydrazide, 1,4-cyclohexanedicarboxylic acid dihydrazide, acetohydrazide, acrylohydrazide, benzohydrazide, nicotinohydrazide, isonicotinohydrazide, isobutylhydrazide, oleic acid hydrazide, etc. Among these, adipic acid mono(di)hydrazide, sebacic acid mono(di)hydrazide and lauric acid monohydrazide are preferred as hydrazide compounds.

The term “mono(di)hydrazide” indicates that one or both of the two carboxylic acids are hydrazidated.

The above-mentioned amide compounds include, but are not limited to, polyvalent carboxylic acid amides such as isophthalic acid diamide and anthranilamide. The above-mentioned amide compounds do not include acrylamide polymers and ethylene bisstearamide.

The above-mentioned polyamides include, for example: polyamide resins such as Nylon® (Nylon is a registered trademark in Japan, other countries, or both) 4-6, Nylon 6, Nylon 6-6 (Polyamide 66), Nylon 6-10, Nylon 6-12 and Nylon 12 and their polymers such as Nylon 6/6-6/6-10 and Nylon 6/6-12.

The formic acid scavengers mentioned above include, but are not limited to, alkali metal or alkaline earth metal hydroxides, salts of inorganic acids, carboxylates, or alkoxides. Examples include sodium, potassium, magnesium, calcium, or barium hydroxides, carbonates, phosphates, silicates, borates, carboxylates of the above-mentioned metals, and layered double hydroxides.

The formic acid scavenger can be used alone or in a combination of two or more types.

As the above-mentioned carboxylic acid of the above-mentioned carboxylate, a saturated or unsaturated aliphatic carboxylic acid having 10 to 36 carbon atoms is preferred, and these carboxylic acids may be substituted with a hydroxyl group. The saturated or unsaturated aliphatic carboxylates include, for example, but are not limited to, calcium dimyristate, calcium dipalmitate, calcium distearate, calcium (myristate palmitate), calcium (myristate stearate), calcium (palmitate stearate), calcium 12-hydroxystearate, and 12-hydroxystearic acid calcium, among which calcium dipalmitate, calcium distearate, and calcium 12-hydroxystearate are preferred.

The above-mentioned weathering stabilizers preferably include, for example, although not limited thereto: at least one compound selected from the group consisting of benzotriazole compounds, oxalic acid anilide compounds and hindered amine light stabilizers.

The above-mentioned benzotriazole compounds include, for example, but are not limited to: 2-(2'-hydroxy-5'-methylphenyl)benzotriazole, 2-(2'-hydroxy-3,5-di-t-butylphenyl)benzotriazole, 2-[2'-hydroxy-3,5-bis(α,α-dimethylbenzyl)phenyl]benzotriazole, 2-(2'-hydroxy-3,5-di-t-amylphenyl]benzotriazole, 2-(2'-hydroxy-3,5-di-isoamylphenyl)benzotriazole, 2-[2'-hydroxy-3,5-bis-(α,α-dimethylbenzyl)phenyl]-2H-benzotriazole, 2-(2'-hydroxy-4'-octoxyphenyl)benzotriazole, etc. These compounds can be used alone or in a combination of two or more kinds.

The above-mentioned oxalic acid bisanilide compounds include, for example, but are not limited to: 2-ethoxy-2'-ethyl-oxalic acid bisanilide, 2-ethoxy-5-t-butyl-2'-ethyl-oxalic acid bisanilide, 2-ethoxy-3'-dodecyl-oxalic acid bisanilide, etc. These compounds can be used alone or in a combination of two or more kinds.

The above-mentioned hindered amine light stabilizers include, for example, but are not limited to: 4-acetoxy-2,2,6,6-tetramethylpiperidine, 4-stearoyloxy-2,2,6,6-tetramethylpiperidine, 4-acryloyloxy-2,2,6,6-tetramethylpiperidine, 4-(phenylacetoxy)-2,2,6,6-tetramethylpiperidine, 4-benzoyloxy-2,2,6,6-tetramethylpiperidine, 4-methoxy-2,2,6,6-tetramethylpiperidine, 4-stearyloxy-2,2,6,6-tetramethylpiperidine, 4-cyclohexyloxy-2,2,6,6-tetramethylpiperidine, 4-benzyloxy-2,2,6,6-tetramethylpiperidine, 4-Phenoxy-2,2,6,6-tetramethylpiperidine, 4-(Ethylcarbamoyloxy)-2,2,6,6-tetramethylpiperidine, 4-(Cyclohexylcarbamoyloxy)-2,2,6,6-tetramethylpiperidine, 4-(Phenylcarbamoyloxy)-2,2,6,6-tetramethylpiperidine, Bis(2,2,6,6-tetramethyl-4-piperidyl) carbonate, Bis(2,2,6,6-tetramethyl-4-piperidyl) oxalate, Bis(2,2,6,6-tetramethyl-4-piperidyl) malonate, Bis(1,2,2,6,6-pentamethyl-4-piperidinyl) sebacate, Bis-(N-methyl-2,2,6,6-tetramethyl-4-piperidinyl) sebacate, Bis(2,2,6,6-tetramethyl-4-piperidyl) sebacate, bis(2,2,6,6-tetramethyl-4-piperidyl) adipate, bis(2,2,6,6-tetramethyl-4-piperidyl) terephthalate, 1,2-bis(2,2,6,6-tetramethyl-4-piperidyloxy) ethane, α,α'-Bis(2,2,6,6-tetramethyl-4-piperidyloxy)-p-xylene, Bis(2,2,6,6-tetramethyl-4-piperidyltrilene-2,4-dicarbamate, Bis(2,2,6,6-tetramethyl-4-piperidyl)-hexamethylene-1,6-dicarbamate, Tris(2,2,6,6-tetramethyl-4-piperidyl)benzene-1,3,5-tricarboxylate, Tris(2,2,6,6-tetramethyl-4-piperidyl)benzene-1,3,4-tricarboxylate, 1-[2-{3-(3,5-di-t-butyl-4-hydroxyphenyl)propionyloxy}butyl]-4-[3-(3,5-di-t-butyl)-4-hydroxyphenyl)propionyloxy]2,2,6,6-tetramethylpiperidine, condensate of 1,2,3,4-butanetetracarboxylic acid and 1,2,2,6,6-pentamethyl-4-piperidinol and β,β,β',β',-tetramethyl-3,9-[2,4,8,10-tetraoxaspiro(5,5)undecane]diethanol, etc. The above-mentioned hindered amine light stabilizers can be used each alone or in a combination of two or more kinds.

The preferred weather stabilizer among those mentioned above is: 2-[2'-Hydroxy-3,5-bis(α,α-dimethylbenzyl)phenyl]benzotriazole, 2-(2'-Hydroxy-3,5-di-t-butylphenyl)benzotriazole, 2-(2'-Hydroxy-3,5-di-t-amylphenyl]benzotriazole, Bis(1,2,2,6,6-pentamethyl-4-piperidinyl)sebacate, Bis-(N-methyl-2,2,6,6-tetramethyl-4-piperidinyl)sebacate, Bis(2,2,6,6-tetramethyl-4-piperidinyl)sebacate, Condensate of 1,2,3,4-butanetetracarbon acid and 1,2,2,6,6-pentamethyl-4-piperidinol and β,β,β',β',-tetramethyl-3,9-[2,4,8,10-tetraoxaspiro(5,5)undecane]diethanol.

The above-mentioned mold release agents and lubricants include, for example, but are not limited to, alcohols, fatty acids and fatty acid esters thereof, olefin compounds with an average polymerization degree of 10 to 500, and silicones. The above-mentioned mold release agents and lubricants can be used alone or in combination with two or more types.

The conductive materials mentioned above include, but are not limited to, conductive carbon black, metal powder, or fibers. The conductive materials can be used alone or in combination with two or more types.

The above-mentioned thermoplastic resins include, but are not limited to, polyolefin resins, acrylic resins, styrene resins, polycarbonate resins, and uncured epoxy resins. Thermoplastic resins can be used alone or in combination with two or more types.

The above-mentioned thermoplastic elastomers include, but are not limited to, polyurethane elastomers, polyester elastomers, polystyrene elastomers, and polyamide elastomers. Thermoplastic elastomers can be used alone or in combination with two or more types.

The above-mentioned color pigments include, but are not limited to, inorganic pigments, organic pigments, metallic pigments, and fluorescent pigments.

The above-mentioned inorganic pigments are those generally used for coloring resins and include, but are not limited to: zinc sulfide, titanium oxide, barium sulfate, titanium yellow, cobalt blue, calcined pigments, carbonates, phosphates, acetates, carbon black, acetylene black, etc.

The above-mentioned organic pigments include, for example, but are not limited to: condensed azo, quinone, monoazo, diazo, polyazo, anthraquinone, heterocyclic, penone, quinacridone, thioindigo, berylene, dioxazine, phthalocyanine pigments, etc.

The above-mentioned color pigments can be used alone or in combination with two or more types. The addition ratio of the above-mentioned color pigments varies greatly depending on the color tone, so it is difficult to specify exactly. However, they are generally used in the range of 0.05 to 5 parts by mass per 100 parts by mass of the polyacetal resin.

Other resins besides the thermoplastic resins mentioned above include, but are not limited to, polyolefin resins, acrylic resins, styrene resins, polycarbonate resins, and uncured epoxy resins.

The resins other than the above-mentioned thermoplastic resins can be used alone or in combination of two or more kinds.

As the above-mentioned inorganic fillers, fibrous, powdery, plate-like and hollow fillers are used, although they are not limited to these.

The above-mentioned fibrous fillers include, for example, but are not limited to, inorganic fibers such as glass fibers, carbon fibers, silicone fibers, silica-alumina fibers, zirconia fibers, boron nitride fibers, silicon nitride fibers, boron fibers, potassium titanate fibers, and metal fibers such as stainless steel, aluminum, titanium, copper, and brass. Whiskers such as potassium titanate whiskers and zinc oxide whiskers, which have short fiber lengths, are also included.

The above-mentioned powdered filler includes, for example, but is not limited to: talc, carbon black, silicon dioxide, quartz powder, glass beads, glass powder, calcium silicate, magnesium silicate, aluminum silicate, kaolin, clay, diatomaceous earth, silicate such as wollastonite, etc.; metal oxides such as iron oxide, titanium oxide, and aluminum oxide; metal sulfates such as calcium sulfate and barium sulfate; carbonates such as magnesium carbonate and dolomite; and other materials such as silicon carbide, silicon nitride, boron nitride, and various metal powders, etc.

The above-mentioned sheet-like filler includes, for example, but is not limited to, mica, glass flakes, and various metal foils.

The above-mentioned hollow filler includes, for example, but is not limited to: glass balloons, silica balloons, Shirasu balloons and metal balloons.

The above-mentioned organic fillers include, but are not limited to, high melting point organic fibrous fillers such as aromatic polyamide resin, fluororesin and acrylic resin, etc.

These fillers can be used alone or in combination with two or more types. It is possible to use either surface-treated or non-surface-treated fillers, but in some cases, it may be preferable to use fillers surface-treated with a surface treatment agent from the perspective of molded surface smoothness and mechanical properties.

The above-mentioned surface treatment agent is not particularly limited, and any conventionally well-known surface treatment agent can be used.

As the surface treatment agent, for example, although not limited to, various coupling agents such as silane, titanate, aluminum and zirconium coupling agents, resin acids, organic carboxylic acids, salts of organic carboxylic acids, surfactants, etc. can be used. Specifically, the surface treatment agent includes, for example, although not limited to, N-(2-aminoethyl)-3-aminopropyltriethoxysilane, 3-glycidoxypropyltrimethoxysilane, isopropyl tristearoyl titanate, diisopropoxyaluminum ethyl acetate, n-butyl zirconate, etc.

When including conventionally well-known additives, the content of (A) polyacetal resin in 100 mass% of the polyacetal resin composition is 75 mass% or more, more preferably 90 mass% or more, and even more preferably 95 mass% or more.

The molding method of the polyacetal resin composition of the present embodiment is not particularly limited, and generally known molding methods such as extrusion molding, injection molding, vacuum molding, blow molding, injection compression molding, decorative molding, other material molding, gas-assisted injection molding, foam injection molding, low-pressure molding, ultra-thin-wall injection molding (ultra-high-speed injection molding), in-mold composite molding (insert molding, outsert molding), melt-blow molding, etc. are cited.

The shape of the molded part is not particularly limited, and examples include injection-molded products (including insert molding and outsert molding), textiles and nonwovens, sheets and films, and extruded products, etc.

The application of the molded part is not particularly limited, and the molded part can be appropriately used for mechanical parts such as gears, cams, sliders, levers, shafts, bearings, and guides, as well as, in particular, door-related parts, belt-related parts, combination switch parts, and switches.

(Process for producing a

polyacetal resin composition)

This is not limited to the method for producing polyacetal resin composition of the present embodiment.

For example, (A) polyacetal resin, (B) ethylene urea, (C) acrylamide polymer, (D) ethylene bisstearamide, and, if necessary, the above-mentioned predetermined components ((E) other additives) are mixed in, for example, a Henschel mixer, tumbler, V-shaped mixer, etc., and then mixed and kneaded using a single- or multi-screw extruder, a heating roll, a kneader, a Banbury mixer, etc., to obtain the polyacetal resin composition. It is also preferable to add (D) ethylene bisstearamide during the polymerization of (C) acrylamide polymer. As the mixing and kneading method, mixing and kneading using an extruder equipped with a venting-decompression device is preferred from the viewpoint of thermal stability and productivity. For the stable production of large quantities of polyacetal resin composition, single-screw or twin-screw extruders are appropriately used, and in this case, it is possible to obtain pelletized polyacetal resin composition (hereinafter referred to as “polyacetal resin pellets”).

In addition, it is also possible to feed the individual components or multiple types of components continuously into the extruder without premixing using quantitative feeding, etc.

It is also possible to prepare a highly concentrated masterbatch from each component in advance and dilute it with polyacetal resin during extrusion melting, mixing and kneading.

The mixing and kneading temperature may correspond to the preferred processing temperature of the polyacetal resin used and is generally in the range of 140 to 260°C, preferably in the range of 180 to 230°C.

The drying method for the polyacetal resin pellets obtained above is not particularly limited, but includes, for example: drying methods using box dryers (normal pressure, vacuum), tunnel and belt dryers, rotary dryers and aeration rotary dryers, channel-type agitator dryers, fluidized bed dryers, multi-stage disc dryers, spray dryers, air jet dryers, infrared dryers, high frequency dryers, etc.

Among them, box dryers, rotary dryers and aeration rotary dryers, channel type agitator dryers, fluidized bed dryers, multi-stage disc dryers and air flow dryers are preferred, and from the point of view of productivity, fluidized bed dryers are more preferred.

Regarding the drying temperature, a temperature of 80°C or more for the heating medium is preferred, and 100°C or more is more preferred. Also, regarding the drying time, when the temperature of the polyacetal resin pellets reaches 100°C or more, a drying time of 0 to 10 hours is preferred, more preferably 0 to 6 hours, and even more preferably 1 to 6 hours.

[Forming of polyacetal resin composition]

The polyacetal resin composition of the present embodiment can be molded and used as a molded article. There are no particular restrictions on the molding method, and it can be molded by any of the well-known molding methods, such as extrusion molding, injection molding, vacuum molding, blow molding, injection-compression molding, decorative molding, molding with other materials, gas-assisted injection molding, foamed injection molding, low-pressure molding, ultra-thin-wall injection molding (ultra-high-speed injection molding), and in-mold composite molding (insert molding, outsert molding). Among them, the injection molding method is preferred from the viewpoint of stable productivity.

Furthermore, even in a continuous molding process using the polyacetal resin composition of the present embodiment, in a molding process in which the material is exposed to high temperatures for a long time, such as molding using a hot runner mold, there is little mold contamination.

[Applications of molded parts made of polyacetal resin composition]

The molded articles made from the polyacetal resin composition of the present embodiment exhibit excellent quality stability and can therefore be used as molded articles for a wide variety of applications. The molded articles are used, for example, for mechanical parts such as gears, cams, sliders, levers, shafts, bearings, and guides; resin parts for outsert molding or insert molding (chassis, trays, side panel parts); parts for printers or copiers; parts for digital cameras or digital video equipment; parts for music, video, or information equipment; parts for telecommunications equipment; parts for electrical equipment; and parts for electronic equipment.

Furthermore, the molded articles of the polyacetal resin composition of the present embodiment are appropriately used for use as automobile parts such as fuel-related parts including gasoline tanks, fuel pump modules, valves and gasoline tank flanges, door-related parts, belt-related parts, combination switch parts, and switches.

Furthermore, the molded articles of the polyacetal resin composition of the present embodiment can also be appropriately used as industrial components such as those used in housing technology.

The above describes the mode for carrying out the present disclosure, but the present disclosure is not limited to the present embodiment. The present disclosure may be varied in various ways without departing from the gist of the disclosure.

[Examples]

In the following, concrete examples and comparative examples of the present embodiment will be explained, but the present embodiment is not limited to the following examples.

The measurement and evaluation methods used in the examples and comparative examples are shown below.

<Measurement of the amount of formaldehyde released from molded parts>

1. (a) Formungsbedingungen
   • - Spritzgießmaschine: SHIBAURA MACHINE CO., LTD. IS-100GN
   • - Zylindereinstelltemperatur: 220°C
   • - Formeinstellungtemperatur: 80°C
   • - Formtyp: Kaltkanal-Typ
   • - Größe des Prüfstücks: 100 × 40 × 3 mm
   • - Formzyklus: Einspritzzeit/Abkühlzeit = 30 Sekunden/15 Sekunden
   • - Die Formaldehydmenge, die aus den Formteilen freigesetzt wurde, wurde mit der unten dargestellten Methode (VDA 275-Methode) gemessen.
2. (b) VDA275-Methode:
   • Ein Prüfstück einer bestimmten Größe (100 mm × 40 mm × 3 mm) wurde in einen Polyethylenbehälter mit 50 mL destilliertem Wasser gegeben und versiegelt, Formaldehyd wurde im destillierten Wasser extrahiert, während es 3 Stunden lang auf 60°C erhitzt wurde, und der Extrakt wurde danach auf Raumtemperatur abgekühlt.

The polyacetal resin pellets were molded according to the following (a) molding conditions. The amount of formaldehyde released from the molded parts was then measured using the VDA 275 method in (b) below.

1. (a) Forming conditions
   • - Injection molding machine: SHIBAURA MACHINE CO., LTD. IS-100GN
   • - Cylinder setting temperature: 220°C
   • - Mold setting temperature: 80°C
   • - Mold type: cold runner type
   • - Size of the test piece: 100 × 40 × 3 mm
   • - Molding cycle: injection time/cooling time = 30 seconds/15 seconds
   • - The amount of formaldehyde released from the molded parts was measured using the method shown below (VDA 275 method).
2. (b) VDA275 method:
   • A test piece of a certain size (100 mm × 40 mm × 3 mm) was placed in a polyethylene container with 50 mL of distilled water and sealed, formaldehyde was extracted in the distilled water while heating it to 60°C for 3 hours, and the extract was then cooled to room temperature.

After cooling, 5 mL of distilled water that had absorbed formaldehyde was mixed with 5 mL of a 0.4% aqueous solution of acetylacetone and 5 mL of a 20% aqueous solution of ammonium acetate to obtain a mixed solution, which was then heated to 40°C for 15 minutes to allow the reaction between formaldehyde and acetylacetone.

Furthermore, after cooling the mixture to room temperature, the amount of formaldehyde absorbed in the distilled water was determined using a UV spectrophotometer based on the absorption peak at 412 nm.

The amount of formaldehyde released from the molded part (mg/kg) was determined using the following formula: $$\begin{array}{l}\text{ Menge des aus dem Formteil freigesetzten}\\ \text{Formaldehyds}\left(\text{mg/kg}\right)=\text{Menge des im destillierten Wasser}\\ \text{absorbierten Formaldehyds}\left(\text{mg}\right)/\text{Masse des f}\ddot{\text{u}}\text{r die Messung}\\ \text{verwendeten Polyacetalharz}-\text{Formteils }\left(\text{kg}\right)\end{array}$$

<Notched impact strength>

The notched impact strength was measured as an indicator of mechanical strength.

Test pieces were molded using an EC100SX from SHIBAURA MACHINE CO., LTD. at a cylinder temperature of 205°C, an injection time of 35 seconds, a cooling time of 15 seconds, and a mold temperature of 90°C to form ISO dumbbell test pieces for physical property evaluation. The following tests were performed on these test pieces. Notched impact strength: Measured the day after molding, based on ISO 179/1eA.

<Tensile strain retention rate in a high temperature and high humidity environment>

Test pieces were molded using the EC100SX from SHIBAURA MACHINE CO., LTD. at a cylinder temperature of 205°C, an injection time of 35 seconds, a cooling time of 15 seconds, and a mold temperature of 90°C to form ISO dumbbell test pieces for physical property evaluation. After the resulting molded part was left to stand for 500 hours in an environment of 90°C and 80% humidity, the tensile elongation was measured with autographs, and the elongation retention rate was calculated using the sample left standing at a room temperature of 23°C as a standard.

<Tensile strength retention rate in a dry, high-temperature environment>

Test pieces were molded using the EC100SX from SHIBAURA MACHINE CO., LTD. at a cylinder temperature of 205°C, an injection time of 35 seconds, a cooling time of 15 seconds, and a mold temperature of 90°C to form ISO dumbbell test pieces for physical property evaluation. After the resulting molded part was left to stand for 1500 hours in an environment of 95°C and 20% humidity, the tensile strength was measured with autographs, and the strength retention rate was calculated using the sample left standing at a room temperature of 23°C as a standard.

<Mold deposition properties>

1. (a) Formungsbedingungen
   • - Spritzgießmaschine: TOYO MACHINERY & METAL CO., LTD. Si-30V
   • - Zylindereinstelltemperatur: 200°C
   • - Formeinstellungtemperatur: 43°C
   • - Formzyklus: Einspritzzeit/Abkühlzeit = 20 Sekunden/20 Sekunden
2. (b) Bewertungskriterien Die folgenden Bewertungskriterien wurden verwendet, um den Zustand der Formablagerungshaftung in der Formkavität nach den ersten 1000 Spritzvorgängen zu beobachten.
   1. A: Keine Formablagerungshaftung in der Formkavität
   2. B: Geringe Menge an Formablagerung in der Formkavität zu sehen
   3. C: Eine große Menge von filmartiger Formablagerung ist in der Formkavität zu sehen

The polyacetal resin pellets were molded according to the following (a) molding conditions. The mold deposition properties of the pellets were then evaluated using the following (b) evaluation criteria:

1. (a) Forming conditions
   • - Injection molding machine: TOYO MACHINERY & METAL CO., LTD. Si-30V
   • - Cylinder setting temperature: 200°C
   • - Mold setting temperature: 43°C
   • - Molding cycle: injection time/cooling time = 20 seconds/20 seconds
2. (b) Evaluation criteria The following evaluation criteria were used to observe the state of mold deposit adhesion in the mold cavity after the first 1000 injections.
   1. A: No mold deposit adhesion in the mold cavity
   2. B: Small amount of mold deposit seen in the mold cavity
   3. C: A large amount of film-like mold deposit is seen in the mold cavity

<Mold shrinkage rate>

The mold shrinkage rate was measured as an indicator of dimensional stability after injection molding.

1. (a) Formungsbedingungen
   • - Spritzgießmaschine: SHIBAURA MACHINE CO., LTD. IS-100GN
   • - Zylindereinstelltemperatur: 220°C
   • - Formeinstellungtemperatur: 80°C
   • - Formtyp: Kaltkanal-Typ
   • - Größe des Forms des Prüfstücks: Höhe 100 × Breite 40 mm × Dicke 3mm
   • - Formzyklus: Einspritzzeit/Abkühlzeit = 30 Sekunden/15 Sekunden
2. (b) Bewertungsverfahren Die Länge und Breite der 10 Formteile wurden gemessen und die Formschrumpfungsrate wurde mit dem folgenden Verfahren ermittelt: $$\begin{array}{l}\text{ Formschrumpfungsrate}\left(\%\right)=((1-(\text{durchschnittliche}\\ \text{L}\ddot{\text{a}}\text{nge der 10 Formteile/L}\ddot{\text{a}}\text{nge des Forms des Pr}\ddot{\text{u}}\text{fst}\ddot{\text{u}}\text{cks }100\\ \text{mm}))+((1-\text{durchschnittliche Breite der 10}\\ \text{Formteile/Breite des Forms des Pr}\ddot{\text{u}}\text{fst}\ddot{\text{u}}\text{cks }40\text{ mm})))/2\times \\ 100\\ \end{array}$$

The polyacetal resin pellets were molded according to the following (a) molding conditions. The mold shrinkage rate was evaluated using the method in (b) below.

1. (a) Forming conditions
   • - Injection molding machine: SHIBAURA MACHINE CO., LTD. IS-100GN
   • - Cylinder setting temperature: 220°C
   • - Mold setting temperature: 80°C
   • - Mold type: cold runner type
   • - Size of the test piece shape: height 100 × width 40 mm × thickness 3 mm
   • - Molding cycle: injection time/cooling time = 30 seconds/15 seconds
2. (b) Evaluation method The length and width of the 10 molded parts were measured and the mold shrinkage rate was determined using the following method: $$\begin{array}{l}\text{ Formschrumpfungsrate}\left(\%\right)=((1-(\text{durchschnittliche}\\ \text{L}\ddot{\text{a}}\text{nge der 10 Formteile/L}\ddot{\text{a}}\text{nge des Forms des Pr}\ddot{\text{u}}\text{fst}\ddot{\text{u}}\text{cks }100\\ \text{mm}))+((1-\text{durchschnittliche Breite der 10}\\ \text{Formteile/Breite des Forms des Pr}\ddot{\text{u}}\text{fst}\ddot{\text{u}}\text{cks }40\text{ mm})))/2\times \\ 100\\ \end{array}$$

(raw material components)

The raw material components used in the examples and comparative examples are listed below.

<(A) Polyacetal resin>

1. A-1: Polyacetal homopolymer (MFR: 2.0 g/10 min)
2. A-2: Polyacetal homopolymer (MFR: 10.0 g/10 min)

The process for producing A-1 and A-2 is explained below.

(A-1: Preparation of polyacetal homopolymer)

A polymerization reactor equipped with a stirred blade was filled with n-hexane, and purified formaldehyde gas (moisture content: 110 ppm), a polymerization catalyst (dimethyl distearylammonium acetate), and a molecular weight regulator (acetic anhydride) were continuously fed to conduct a polymerization reaction. The polymerization reaction temperature was set at 58°C.

The obtained crude polyacetal homopolymer was then added to a reaction vessel filled with a 1:1 mixture of n-hexane and acetic anhydride and stirred at 150°C for 2 hours to esterify the unstable ends of the crude polyacetal homopolymer. The mass ratio (slurry concentration) of the polymer and the 1:1 mixture of n-hexane and acetic anhydride was 20:100, with 20% of polymer being 100% relative to the 1:1 mixture of n-hexane and acetic anhydride.

After the end-stabilization treatment of the polyacetal homopolymer was completed, the "1:1 mixture of n-hexane and acetic anhydride" and the polyacetal homopolymer were removed from the reaction vessel, and the polyacetal homopolymer was repeatedly washed with n-hexane solvent to remove the acetic anhydride. The number of washings was repeated until the concentration of acetic anhydride in the polyacetal homopolymer was reduced to 10 ppm by mass or less.

Thereafter, the polyacetal homopolymer was dried for 3 hours at 120°C and -700 mmHg under reduced pressure to remove the n-hexane solvent used for washing, and then dried for 5 hours in a heated dryer set at 120°C to remove the moisture included in the polyacetal homopolymer, and (A-1) polyacetal homopolymer in powder form (average particle diameter of 200 μm) with an MFR of 2.0 g/10 min was obtained.

The average particle diameter of the polyacetal was measured using a laser diffraction particle size distribution meter.

(A-2: Preparation of polyacetal homopolymer)

The same preparation method as for polyacetal homopolymer (A-1) was used except that the amount of the added molecular weight regulator (acetic anhydride) was adjusted to change the molecular weight, and (A-2) polyacetal homopolymer in powder form (average particle diameter: 200 µm) with an MFR of 10.0 g/10 min was obtained.

<(B) Ethylene urea>

B-1: Ethylene urea (manufactured by Tokyo Chemical Industry Co., Ltd.)

<(C) Acrylamide polymer>

C-1: Acrylamide polymer (primary amide group content: 50.4 mol%, average particle diameter: 5.1 µm) (C-1) The acrylamide polymer was prepared as follows:

In a 5-liter batch reactor equipped with a stirrer, 2400 g of acrylamide, 267 g of N,N'-methylenebisacrylamide and 0.54 g of zirconium triisopropoxide (1/10000 mol based on acrylamide) as a catalyst were added and the mixture was stirred for 4 hours in a nitrogen gas stream at 125°C.

After the reaction, the solid material was ground in a jet mill and washed with acetone.

Then, it was decompressed and dried at 120°C for 20 hours at a reduced pressure of -700 mmHg to obtain (C-1) acrylamide polymer.

The obtained (C-1) acrylamide polymer had a primary amide group content of 50.4 mol% and an average particle diameter of 5.1 µm. The average particle diameter was measured using a laser diffraction particle size distribution meter.

<(D) Ethylene bisstearamide>

D-1: Ethylene bisstearamide (manufactured by Tokyo Chemical Industry Co., Ltd.)

<(E) Other additives>

1. E-1: Sebacic acid dihydrazide (heat stabilizer, manufactured by Tokyo Chemical Industry Co., Ltd.)
2. E-2: Allantoin (heat stabilizer, manufactured by Tokyo Chemical Industry Co., Ltd.)
3. E-3: Hydantoin (heat stabilizer, manufactured by Tokyo Chemical Industry Co., Ltd.)
4. E-4: Polyamide 66 (heat stabilizer, manufactured by Asahi Kasei Corporation)
5. E-5: Triethylene glycol bis[3-(3-t-butyl-5-methyl-4-hydroxyphenyl)propionate] (hindered phenol antioxidant, manufactured by Songwon International-Japan K.K.)

[Example 1, Examples 3 to 13]

The (A-1) polyacetal homopolymer powder as the polyacetal resin prepared above, (B-1) ethylene urea, (C-1) acrylamide polymer, and (E) other additives, triethylene glycol bis[3-(3-t-butyl-5-methyl-4-hydroxyphenyl)propionate] as a hindered phenol antioxidant, were uniformly mixed in the amounts shown in Table 1 below using a Henschel mixer to obtain a mixture. (D) Ethylene bisstearamide was added during the polymerization of (C) acrylamide polymer.

This mixture was fed into the top feed port of a 40 mm twin-screw extruder with L (screw length)/D (screw inner diameter) = 48, which is fixed at 200°C, and melted, mixed and kneaded at a screw speed of 200 rpm, a vent decompression of -0.08 MPa and a feed rate of 50 kg/hr, and after pelletizing by the hot cutting method At the extruder die exit, the pellets were placed in warm water (40°C) and stirred for a period of time, the water was then removed with a centrifugal separator, and the pellets were placed in a fluidized-bed hot-air dryer and dried at a hot air temperature of 100°C for 3 hours to obtain polyacetal resin pellets.

Based on the obtained polyacetal resin pellets, the amount of formaldehyde released from the molded parts, the mechanical properties after testing in a high-temperature and high-humidity environment and in a dry high-temperature environment, the mold deposition properties, and the mold shrinkage rate were evaluated and measured by the above-mentioned methods.

The evaluation results are shown in Table 1 below.

[Example 2]

The same procedures as in Example 1 were carried out except that (D) ethylene bisstearamide was added by mixing with (A-1) polyacetal homopolymer in powder to obtain polyacetal resin pellets.

Based on the obtained polyacetal resin pellets, the amount of formaldehyde released from the molded parts, the mechanical properties after testing in a high-temperature and high-humidity environment and in a dry high-temperature environment, the mold deposition properties, and the mold shrinkage rate were evaluated and measured by the above-mentioned methods.

The evaluation results are shown in Table 1 below.

(Comparative Examples 1 to 2, Comparative Examples 5 to 11, 13)

The same procedures as in Example 2 were carried out except that the composition was as shown in Table 2 to obtain polyacetal resin pellets.

Based on the obtained polyacetal resin pellets, the amount of formaldehyde released from the molded parts, the mechanical properties after testing in a high-temperature and high-humidity environment and in a dry high-temperature environment, the mold deposition properties, and the mold shrinkage rate were evaluated and measured by the above-mentioned methods.

The evaluation results are shown in Table 2 below.

(Comparative examples 3 to 4, Comparative example 12

The same procedures as in Example 1 were carried out except that the composition was as shown in Table 2 to obtain polyacetal resin pellets.

Based on the obtained polyacetal resin pellets, the amount of formaldehyde released from the molded parts, the mechanical properties after testing in a high-temperature and high-humidity environment and in a dry high-temperature environment, the mold deposition properties, and the mold shrinkage rate were evaluated and measured by the above-mentioned methods.

The evaluation results are shown in Table 2 below.

[Table 1] Table 1 Example 1 Example 2 Example 3 Example 4 Example 5 Example6 Example7 Example8 Example9 Example10 Example 11 Example12 Example13 (A) Polyacetal resin (mass part) A-1 100 100 100 100 100 100 - 100 100 100 100 100 100 A-2 - - - - - - 100 - - - - - - (B) Ethylene urea (mass fraction) B-1 0.05 0.05 0.1 0.2 0.05 0.05 0.1 0.5 0.1 0.1 0.1 0.1 0.1 (C) Acrylamide polymer (mass fraction) C-1 0.1 0.1 0.1 0.1 0.1 0.1 0.1 0.1 0.1 0.1 0.05 0.2 0.5 (D) Ethylene bisstearamide (mass part) D-1 0.005 0.005 0.005 0.005 0.01 0.05 0.005 0.005 0.001 0.03 0.005 0.005 0.005 (E) Other additives (mass fraction) E-1 - - - - - - - - - - - - - E-2 - - - - - - - - - - - - - E-3 - - - - - - - - - - - - - E-4 - - - - - - - - - - - - - E-5 0.15 0.15 0.15 0.15 0.15 0.15 0.15 0.15 0.15 0.15 0.15 0.15 0.15 (D)/(C) ratio 0.05 0.05 0.05 0.05 0.1 0.5 0.05 0.05 0.01 0.3 0.1 0.025 0.01 Amount of formaldehyde released from the molded part (mg/kg) 1.2 1.2 1.1 1.0 1.3 1.2 1.3 0.5 1.1 1.0 1.4 1.0 1.2 Notched impact strength (KJ/m ² ) 14.8 13.8 15.0 15.5 15.5 16.0 9.8 16.0 14.5 14.5 15.0 14.0 13.0 Tensile strain retention rate in a high-temperature and high-humidity environment (%) 88 86 85 78 80 80 75 82 80 80 80 79 75 Tensile strength retention rate in a dry, high-temperature environment (%) 70 69 80 80 75 78 70 70 68 69 70 70 72 Mold deposition properties A A A B A A A B A A A A A Mold shrinkage rate (%) 1.8 2.0 1.5 1.4 1.6 1.5 1.8 1.4 1.9 1.3 1.6 1.7 1.8
[Table 2] Table 2 Comparison example 1 Comparison example 2 Comparison example 3 Comparison example 4 Comparison example 5 Comparison example 6 Comparison example 7 Comparison example 8 Comparison example 9 Comparison example 10 Comparison example 11 Comparison example 12 Comparison example 13 (A) Polyacetal resin (mass part) A-1 100 100 100 100 100 100 100 100 100 100 100 100 100 A-2 - - - - - - - - - - - - - (B) Ethylene urea (mass fraction) B-1 - 0.05 0.02 1 0.05 0.05 - - - - - 0.1 - (C) Acrylamide polymer (mass fraction) C-1 0.1 - 0.1 0.1 - - 0.1 0.1 - 0.1 0.1 0.1 0.1 (D) Ethylene bisstearamide (mass part) D-1 - - 0.005 0.005 0.005 - - - - - - 0.25 0.01 (E) Other additives (by mass) E-1 - - - - - - 0.05 0.15 0.05 - - - 0.05 E-2 - - - - - - - - - 0.1 - - - E-3 - - - - - - - - - - 0.1 - - E-4 - - - - - 0.1 - - 0.1 - - - - E-5 0.15 0.15 0.15 0.15 0.15 0.15 0.15 0.15 0.15 0.15 0.15 0.15 0.15 (D)/(C) ratio - - 0.05 0.05 - - - - - - - 2.50 0.10 Amount of formaldehyde released from the molded part (mg/kg) 5.7 2.2 4.0 0.8 2.0 1.5 6.1 4.0 6.2 1.5 1.4 3.0 5.4 Notched impact strength (KJ/m ² ) 12.0 12.5 13.0 13.5 13.0 12.8 12.8 15.0 12.5 11.0 12.1 12.5 12.8 Tensile strain retention rate in a high temperature and high humidity environment (%) 75 55 76 62 60 50 55 50 50 45 55 55 58 Tensile strength retention rate in a dry, high-temperature environment (%) 65 50 65 61 55 30 65 50 45 35 60 63 66 Mold deposition properties A B A C B A C C C C C B C Mold shrinkage rate (%) 2.0 2.0 2.0 2.1 2.2 2.2 2.2 2.2 2.2 2.2 2.2 1.8 2.2

As shown in Table 1, it can be seen that the molded articles produced from the polyacetal resin compositions obtained in Examples 1 to 13 exhibit excellent properties in suppressing the amount of formaldehyde released from the molded articles, mechanical property retention in a high-temperature and high-humidity environment and in a dry, high-temperature environment, and dimensional stability after molding. Furthermore, it can also be seen that they exhibit excellent mold deposition properties.

In contrast, it is clear from Table 2 that in the molded articles made of the polyacetal resin compositions obtained in Comparative Examples 1 to 13, the amount of formaldehyde released from the molded articles is not suppressed, a decrease in the retention rate of mechanical properties occurs in a high-temperature and high-humidity environment and in a dry, high-temperature environment, and the molded articles have inferior mold deposition properties and dimensional stability after molding, so that the performance balance is reduced.

[Industrial applicability]

The polyacetal resin composition of the present disclosure can be suitably used in extensive fields such as automobile, electrical and electronic industries and other industrial fields.

QUOTES CONTAINED IN THE DESCRIPTION

This list of documents submitted by the applicant was generated automatically and is included solely for the convenience of the reader. This list is not part of the German patent or utility model application. The DPMA assumes no liability for any errors or omissions.

Cited patent literature

• WO 2016/126514 [0004]
• JP 2005-263921 A [0004]

Claims (7)

A polyacetal resin composition comprising: based on 100 parts by mass of (A) polyacetal resin, 0.03 to 0.60 parts by mass of (B) ethylene urea, 0.05 to 0.50 parts by mass of (C) acrylamide polymer, and 0.0005 to 0.05 parts by mass of (D) ethylene bisstearamide. Polyacetal resin composition according to Claim 1 , wherein the (A) polyacetal resin is a polyacetal homopolymer. Polyacetal resin composition according to Claim 1 or 2 , wherein the (A) polyacetal resin has a melt flow rate of 1.0 to 10.0 g/10 min when measured according to ISO 1133. Polyacetal resin composition according to Claim 3 wherein a melt flow rate of the polyacetal resin (A) is 1.0 to 3.0 g/10 min. Polyacetal resin composition according to Claim 1 or 2 , where a peak of the molecular weight distribution of the (A) polyacetal resin is unimodal. Polyacetal resin composition according to Claim 1 or 2 containing 0.05 to 0.20 parts by mass of the (C) acrylamide polymer. Polyacetal resin composition according to Claim 1 or 2 , wherein a mass ratio (D)/(C) of (D) ethylenebisstearamide to (C) acrylamide polymer is 0.01 to 0.5.