JPH08325432A - Polyacetal resin composition - Google Patents

Abstract

PURPOSE: To obtain a polyacetal resin composition which has improved flowability and excellent hinge properties while retaining the mechanical properties, frictional and wear properties, moldability, toughness, etc., inherent in polyacetals. CONSTITUTION: This resin composition comprises (A) 100 pts.wt. polyacetal resin, (B) l-50 pts.wt. core-shell polymer comprising cores made of a rubbery polymer and shells made of a vitreous polymer, and (C) 0.1-20 pts.wt. oxyalkylene polymer having a primary or secondary amine and containing two to eight adjacent carbon chains.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION The present invention comprises a core-shell polymer and an oxyalkylene polymer having a primary or secondary amine, and has excellent hinge properties, impact resistance and weld properties. The present invention relates to an excellent polyacetal resin composition, and a polyacetal resin hinge component formed by molding the composition. The hinge component referred to herein is, for example, one as shown in FIG. 1, and refers to a thin wall portion to which a bending or bending load is applied one or more times in a certain portion of the component. The hinge (indicated by 1 in the figure) Call. The shape of the hinge is not particularly limited, and may be a sheet shape, a band shape, a string shape, or the like. The thickness and the length of the hinge are not specified, and those having a function substantially as a hinge are included in the elbow part according to the present invention. In addition, in the present specification, the hinge characteristic is defined as durability against one or more bending or bending loads of the hinge as described above.

[0002]

2. Description of the Related Art As is well known, polyacetal resin is an engineering material having excellent physical properties such as mechanical properties and electrical properties, or chemical properties such as chemical resistance and heat resistance. Recently, it has been used as a resin in a very wide range of fields. However, with the expansion of fields in which polyacetal resins are used, the properties of the materials may be required to be more specific. As one of such properties, there is a demand for development of a material having excellent flexibility, that is, a material having excellent hinge characteristics. In recent years, in particular, due to the need to reduce costs by reducing the number of parts, it is becoming more and more desirable to integrate several parts with a hinge to assemble them easily and inexpensively. There are many factors that deteriorate the hinge characteristics, such as those used below, or those in which the preferable hinge shape cannot be obtained due to the structure, and the requirement for the essentially excellent hinge characteristics has become more severe. Further, in the fields of general electric equipment, building materials, etc., there are increasing opportunities to use various materials in combination depending on the purpose, but further improvement in impact resistance of polyacetal resin is required. As a method for satisfying the requirement for hinge characteristics, there is known a method for improving the hinge characteristics by adding a rubber-like substance such as thermoplastic polyurethane to a polyacetal resin. Even with this method, it is possible to show an improvement in the hinge characteristics, but by incorporating a rubber-like substance, a peeling phenomenon easily occurs on the surface of the molded product, and there is a problem that the appearance of the molded product is significantly impaired. There have been various problems such as a decrease in stability and a further decrease in the degree of freedom in hinge design due to a marked decrease in the weld strength and elongation of the molded product, and improvements have been demanded. An object of the present invention is to provide a polyacetal resin composition having a hinge property which is more excellent than conventional ones without impairing other physical properties, and a polyacetal resin hinge component.

[0003]

The present inventors have solved the above problems and have excellent hinge characteristics without sacrificing the original characteristics of the polyacetal resin as much as possible.
As a result of intensive studies to develop a polyacetal resin material having excellent impact resistance, it has been found that a core-shell polymer and an oxyalkylene polymer having a primary or secondary amine are added to the polyacetal resin in combination. They have found that they are effective and have completed the present invention. That is, the present invention is (A) 100 parts by weight of a polyacetal resin (B) a core-shell polymer having a core of a rubber-like polymer and a shell of a glass-like polymer 1 to 50 parts by weight and (C)
A polyacetal resin composition containing 0.1 to 20 parts by weight of an oxyalkylene polymer having a primary or secondary amine and having 2 to 8 adjacent carbon chains, and a polyacetal resin hinge component formed by molding the same Is. The resin composition of the present invention has excellent hinge characteristics, impact resistance, and weld characteristics, which have been difficult to obtain by the conventional techniques, and is therefore a very suitable material for hinges.

The constituent components of the present invention will be described in detail below. First, the (A) polyacetal resin used in the present invention is a polymer compound having an oxymethylene group (-CH ₂ O-) as a main constituent unit, and a polyoxymethylene homopolymer and other constituent units other than the oxymethylene group. It may be a copolymer, a terpolymer or a block copolymer having a small amount of, and the molecule may have not only a linear structure but also a branched or crosslinked structure. The degree of polymerization and the like are not particularly limited as long as they have melt moldability.

The core-shell polymer (B) used in the present invention is an organic compound having a rubber-like polymer core and a glass-like polymer shell, and can be prepared by a known method, or a commercially available product can be used. It can also be used. Typical examples are Acryloid KM330 and KM653 manufactured by Rohm and Haas, Paraloid KCA-102 and KCA-301 manufactured by Kureha Chemical Industry Co., Ltd., and Takeda Pharmaceutical Co., Ltd.
STAPHYLOID PO-0143 and 0148, Kane Ace FM of Kanegafuchi Chemical Industry Co., Ltd., and METABLEN C-102, E-901, W-800 and S-2001 of Mitsubishi Rayon Co., Ltd. Among such core-shell polymers, preferred are core-shell polymers having a rubbery polymer core and a glassy polymer shell containing methyl methacrylate as a main component, and particularly a core-shell polymer in which anions are not substantially detected. When a core-shell polymer in which anions are detected is used, decomposition of polyacetal may be promoted during melt-kneading or injection molding, and desired clip properties may not be obtained. In some cases, too much decomposition may make melting and kneading impossible. Here, the core-shell polymer in which an anion is not substantially detected means a core-shell polymer in which an anion is not detected by a usual qualitative test of anion. For example, as a measuring method, 5 g of the sample (core shell polymer) is weighed in a 50 ml Erlenmeyer flask, 20 ml of ion-exchanged water is added, the mixture is stirred with a magnetic stirrer for 3 hours, and then the filtrate obtained by filtering with No. 5 C filter paper is divided into two parts. 1% barium chloride solution in one side
Add 0.5 ml and compare and observe the occurrence of turbidity (sulfate ion qualitative test). Also, perform the same treatment and add 0.1 N silver nitrate aqueous solution instead of 1% barium chloride aqueous solution.
The presence of anions can be confirmed by a method for comparatively observing the occurrence of turbidity (a qualitative test for halogen ions). A core-shell polymer in which these anions are not present is preferably used.

The core-shell polymer preferably used in the present invention is one obtained by emulsion polymerization using a nonionic surfactant and a polymerization initiator in which the radicals generated are neutral. Such a core-shell polymer can be produced, for example, by using the emulsion polymerization technique described in JP-A-3-14856. The emulsion polymerization can be carried out, for example, using the following surfactants and polymerization initiators. Nonionic surfactants include ether type such as polyoxyethylene nonylphenyl ether, polyoxyethylene stearyl ether, polyoxyethylene lauryl ether, ester type such as polyoxyethylene monostearate, polyoxyethylene sorbitan monolaurate and the like. Most of the widely used nonionic surfactants such as sorbitan ester type and block polymer type such as polyoxyethylene polyoxypropylene block copolymer can be used. The amount of addition is appropriately selected according to the particle stabilizing ability of the surfactant. As the polymerization initiator, azobisisobutyronitrile, 2,2 '
-Azo-based polymerization initiators such as dimethyl azobisisobutyrate and 2,2'-azobis (2-aminopropane) dihydrochloride, and peroxide-based polymerization initiation such as cumene hydroperoxide, diisopropylbenzene hydroperoxide and hydrogen peroxide The agents are used alone or in combination of two or more kinds. If emulsion polymerization is carried out in such a reaction system using a surfactant containing no anion and a polymerization initiator other than persulfate, the obtained core-shell polymer contains substantially no anion, or contains anion. Even if it is, a very small amount of core-shell polymer can be obtained. The polyacetal resin composition using such a core-shell polymer that does not substantially contain anions has excellent hinge properties.

The (B) core-shell polymer in the present invention has a rubber-like polymer core and a glass-like polymer shell, and in the seed emulsion polymerization method, the polymer of the previous stage is usually added to the polymer of the latter stage. It is obtained by a continuous multi-stage emulsion polymerization method in which the coalescence is sequentially coated. When the core-shell polymer has an intermediate phase to be described later, the intermediate phase may be formed by a multi-step emulsion polymerization method in which the polymer of the later step penetrates into the polymer of the earlier step.
At the time of particle generation polymerization, it is preferable to start the emulsion polymerization reaction by adding a monomer, a surfactant and water to a reactor, and then adding a polymerization initiator. The first stage of polymerization is a reaction that forms a rubbery polymer. Examples of the monomer that constitutes the rubber-like polymer include conjugated dienes, alkyl acrylates having an alkyl group with 2 to 8 carbon atoms, and mixtures thereof. By polymerizing these monomers, the glass transition temperature of −30
It forms a rubbery polymer below ° C. Examples of such conjugated dienes include butadiene, isoprene, chloroprene, and the like, but butadiene is particularly preferably used. Examples of the alkyl acrylate having an alkyl group having 2 to 8 carbon atoms include ethyl acrylate, propyl acrylate, butyl acrylate, cyclohexyl acrylate, 2-ethylhexyl acrylate, etc., but butyl acrylate is particularly preferably used. In the first-stage polymerization, a copolymerizable monomer such as a conjugated diene and an alkyl acrylate, for example, styrene, vinyltoluene, aromatic vinyl such as α-methylstyrene, aromatic vinylidene, acrylonitrile, methacrylonitrile, and other cyanide vinyl are used. It is also possible to copolymerize vinylidene cyanide, alkyl methacrylate such as methyl methacrylate and butyl methacrylate. If the first stage polymerization does not contain conjugated dienes, or if it contains conjugated dienes and is 20% by weight or less of the total amount of monomers in the first stage, use a small amount of crosslinkable monomer and grafting monomer. It is possible to obtain a polymer having higher impact resistance. As the crosslinkable monomer, for example, an aromatic divinyl monomer such as divinylbenzene, ethylene glycol diacrylate,
Ethylene glycol dimethacrylate, butylene glycol diacrylate, hexanediol diacrylate, hexanediol dimethacrylate, oligoethylene glycol diacrylate, oligoethylene glycol dimethacrylate, trimethylolpropane diacrylate, trimethylolpropane dimethacrylate, trimethylolpropane triacrylate, Examples thereof include alkane polyol polyacrylates such as trimethylolpropane trimethacrylate, alkane polyol polymethacrylates, and the like, but butylene glycol diacrylate and hexanediol diacrylate are particularly preferably used. As a grafting monomer,
Examples thereof include allyl acrylate, allyl methacrylate, diallyl maleate, diallyl fumarate, unsaturated carboxylic acid allyl esters such as diallyl itaconate, and the like, and allyl methacrylate is particularly preferably used. Such a crosslinkable monomer and a grafting monomer are each contained in an amount of 0 to 5 of the total amount of the first stage monomer.
It is used in an amount of 0.1% by weight, preferably 0.1 to 2% by weight.

The core of the rubber-like polymer is preferably in the range of 50 to 90% by weight based on the whole core-shell polymer. When the core is less than this weight range or more than this weight range, the effect of improving impact resistance of the resin composition obtained by melt-mixing the produced core-shell polymer may not be sufficient. When the glass transition temperature of the core is higher than −30 ° C., the effect of improving the low-temperature impact resistance may not be sufficient. A glassy polymer is formed in the outermost shell phase (shell phase). Examples of the monomer constituting the glassy polymer include methyl methacrylate and a monomer copolymerizable with methyl methacrylate. These monomers are methyl methacrylate alone or a mixture of monomers copolymerizable with methyl methacrylate, and form a glassy polymer having a glass transition temperature of 60 ° C. or higher. As the monomer copolymerizable with methyl methacrylate,
For example, alkyl acrylate such as ethyl acrylate and butyl acrylate, alkyl methacrylate such as ethyl methacrylate and butyl methacrylate, styrene,
Vinyltoluene, aromatic vinyl such as α-methylstyrene, aromatic vinylidene, acrylonitrile, vinyl cyanide such as methacrylonitrile, vinyl polymerizable monomers such as vinylidene cyanide, but particularly preferably ethyl acrylate, Styrene, acrylonitrile, etc. are used. The outermost shell phase (shell phase) is preferably in the range of 10 to 50% by weight based on the whole core-shell polymer.
When the outermost shell phase is less than or more than this weight range, the effect of improving the impact resistance of the resin composition obtained by melt mixing the resulting core-shell polymer may not be sufficient. Further, an intermediate phase may be present between the first stage and the final polymerization phase. For example, polymerizable monomers having functional groups such as glycidyl methacrylate, methacrylic acid, hydroxyethyl methacrylate, etc.,
The intermediate phase is formed by seed emulsion polymerization of a polymerizing monomer that forms a glassy polymer such as methyl methacrylate, a polymerizing monomer that forms a rubbery polymer such as butyl acrylate, and the like. Such an intermediate phase can be variously selected depending on the desired properties of the core-shell polymer. Further, the polymerization ratio may be appropriately selected depending on the monomer used. For example, when the glassy polymer is used as the intermediate phase, its polymerization rate may be calculated as a part of the shell, and in the case of a rubbery polymer, it may be calculated as a part of the core.

The structure of the core-shell polymer having such an intermediate phase has, for example, a multi-layered structure in which another layer is present between the core and the shell, or the intermediate phase has a fine granular structure in the core. One that has a salami structure that is dispersed. In a more extreme case of a core-shell polymer having a salami structure, the mesophase to be dispersed may form a new core at the center of the core. The core-shell polymer having such a structure may occur when a monomer represented by styrene is used as a monomer constituting the mesophase. In addition, when a core-shell polymer having an intermediate phase is used, in addition to improving impact resistance, the flexural modulus is improved, the heat deformation temperature is increased, the appearance (surface peeling and pearl luster is suppressed, and the change in color tone due to the change in the refractive index). ) Is also improved. Core-shell polymer (B) of the present invention
1 to 100 parts by weight of polyacetal resin
It is 50 parts by weight, preferably 5 to 40 parts by weight. If the addition amount of the core-shell polymer is too small, impact resistance is not sufficiently exerted, and even if it is added excessively, a mechanical property, particularly rigidity, is significantly reduced, and the heat stability is not adversely affected. Occurs.

By adding and blending the core-shell polymer (B) into the polyacetal resin, the impact resistance is improved without deteriorating the excellent mechanical properties of the polyacetal resin, but the hinge property is inferior, and it is used for hinge parts. Could not be used for. The reason is that in the molded product obtained by adding and blending the core-shell polymer into the polyacetal resin, the core-shell polymer is present on the surface.
The particles are dispersed in the form of particles of about 0.5 to 2 μm, and when the molded part is bent, the core-shell polymer becomes the starting point and breaks or breaks. Therefore, (A) polyacetal resin
(B) The one in which the core-shell polymer is blended is significantly inferior in hinge characteristics. Therefore, the present invention is characterized by further blending (C) an oxyalkylene polymer having a primary or secondary amine in the above components (A) and (B). By blending the three components (B) and (C), the hinge characteristics can be improved without impairing the well-balanced characteristics inherent in the polyacetal resin.

In the present invention, it is used for such a purpose.
(C) An oxyalkylene polymer having a primary or secondary amine means a glycol having two to eight carbon chains adjacent to each other, specifically ethylene glycol, propylene glycol, tetramethylene glycol homopolymer and copolymer terminals. Alternatively, it may be a polymer having a primary or secondary amine in the molecular chain, and may be a slightly modified polymer such as an ester with a fatty acid or an ether with an aliphatic alcohol, for example, polyethylene glycol, polypropylene glycol, Examples include polytetramethylene glycol or copolymers thereof such as dipropylamine and dioctylamine. In particular, a poly (ethylene oxide) -based polymer is most preferable. Further, the number average molecular weight of the oxyalkylene polymer having a primary or secondary amine as the component (C) can be appropriately selected and used within the range of improving the hinge property, but is preferably 400 to 300,000, particularly Preferably
It is between 1000 and 100,000. The amount of the oxyalkylene polymer having a primary or secondary amine as the component (C) is (A)
0.1 to 20 parts by weight is suitable for 100 parts by weight of the polyacetal resin, and 0.5 to 10 parts by weight is particularly preferable. When the amount is less than 0.1 parts by weight, the effect of improving the hinge characteristic is small,
If the amount is more than 20 parts by weight, the improvement effect reaches saturation, and the original properties of the polyacetal resin are adversely affected. Level 1 or 2
Even if the oxyalkylene polymer (C) having a primary amine is added to the polyacetal resin alone, a slight effect can be obtained in improving the hinge characteristics, but it is not effective in improving the impact resistance. Therefore, 3 components with (B) core-shell polymer
The combined use of (A + B + C) has the effect that it has excellent impact resistance and also has extremely excellent hinge characteristics. The action and effect are such that the oxyalkylene polymer portion of the oxyalkylene polymer having a primary or secondary amine as the component (C) has a compatibilizing effect with the polyacetal resin (A). Reduces the high crystallinity of ordinary polyacetal resin and reduces the elastic modulus, and the primary or secondary amine part of the oxyalkylene polymer has the chemical / physical adsorption effect of the core-shell polymer (B). It is speculated that The action and effect are not always clear, and the present invention is not limited by this.

It is desirable that the composition of the present invention further comprises various known stabilizers to reinforce the thermal stability. For this purpose, known antioxidants, nitrogen-containing compounds, alkali or alkaline earth metal compounds are known. It is desirable to use one kind or a combination of two or more kinds. In order to further impart desired properties to the composition of the present invention depending on its purpose, conventionally known additives such as lubricants, nucleating agents, release agents, antistatic agents and other surfactants, or other than the component (C) Organic polymer materials,
It is possible to add one or more kinds of inorganic or organic fibrous, powdery or plate-like fillers. The composition of the present invention can be prepared by the equipment and method generally known as a method for preparing a synthetic resin composition. That is, the necessary components can be mixed, kneaded using a uniaxial or biaxial extruder, extruded into pellets for molding, and then molded, and the composition can be molded by a molding machine. It is also possible to do it at the same time. Further, in order to improve the dispersion and mixing of the respective components, a method of pulverizing a part or all of the resin components, mixing and molding the pellets melt-extruded, or the like is possible. Further, the above-mentioned stabilizers, additives and the like may be added at any arbitrary stage, and it is of course possible to add and mix them just before obtaining the final molded product. The resin composition according to the present invention can be molded by any of extrusion molding, injection molding, compression molding, vacuum molding, blow molding, and foam molding.

[0013]

The present invention will be described in more detail below with reference to examples, but the present invention is not limited thereto.
The characteristic evaluations in Examples and Comparative Examples were performed according to the following methods. (1) Evaluation of Hinge Property A test piece having the shape shown in FIG. 1 was molded and evaluated based on the following criteria. Number of samples: n = 10 Test method: Samples at -10 ° C and 50% RH for 24 hours
After leaving it for more than an hour, the hinge part was repeatedly bent 100 times at an angle of 180 degrees under the same conditions.

Evaluation A: The number of broken hinge parts during 100 bendings (the smaller the number, the better).

Evaluation B: The state of the hinge portion after bending 100 times was evaluated by the following criteria and expressed as an average point (the larger the value, the better).

5: Almost no abnormality was observed 4: Microcracks were generated on the surface of the hinge part 3: Cracks on the surface of the hinge part grew and became large 2: Cracks on the hinge part were further centered That grows toward the edge and the hinge becomes extremely thin 1: The thinned hinge has a cut and is about to cut 0: Broken (2) Surface layer peeling test 1/32 inch test piece surface After the cellophane tape was attached to and peeled off, the peeling condition was visually observed to evaluate the presence or absence of the peeled surface layer. (3) Impact characteristics (Izod impact strength) The resin pellets prepared in Examples and Comparative Examples were subjected to in-line injection molding with a mold clamping force of 75 tons (J75SA, manufactured by Japan Steel Works) at a cylinder temperature of 190 ° C. A test sample (a rectangular parallelepiped having a width of 12.7 mm, a thickness of 6.4 mm, and a length of 64 mm) was molded, a notch was formed according to the method of ASTM D 256, and the Izod impact value was measured. A higher Izod impact value is judged to be better. (4) Weld Strength and Elongation A test piece was molded using a 1 / 32-inch thick mold for molding a welded test piece having gates at both ends, and measured according to ASTM-D638. The tensile strength and tensile elongation at this time were made into weld strength and weld elongation, and these were combined and made into weld characteristics. Generally, it is important that the weld elongation is particularly large. Practically, the weld elongation is required to be at least 10%, and 20% or more is considered to be good. Note that the embodiment,
All "parts" in Comparative Examples represent parts by weight. The methods used in the evaluation of the characteristic values such as mechanical properties in the examples are as follows.・ Molding machine: J75SA, manufactured by Japan Steel Works ・ Molding conditions Nozzle C1 C2 C3 Cylinder temperature (℃) 200 190 180 160 Injection pressure 650 (kg / cm ² ) Injection speed 1.0 (m / min) Mold temperature 80 (℃) Examples 1 to 9 Various polyacetal resins (manufactured by Polyplastics Co., Ltd., DURACON (trade name)), various core-shell polymers shown below, and oxyalkylene resins having various primary or secondary amines shown below. The polymer was blended in the composition shown in Table 1 and mixed with a Henschel mixer, then 30 mm
Melt kneading was performed using a twin-screw extruder to prepare a pelletized composition. Then, a test piece was molded from the pellets using an injection molding machine under the molding conditions described above, and gloss and other characteristics were measured and evaluated. Table 1 shows the results. Comparative Examples 1 to 12 As shown in Table 2, a polyacetal composition was obtained in the same manner as in the above Examples, except that one or both of the core-shell polymer and the oxyalkylene polymer were not blended. Similarly, each test piece was prepared from this composition and evaluated. Table 2 shows the results.

The abbreviations of the components shown in the table are as follows. <Polyacetal> A-1 Melt Index (190 ℃) 9.0 (g / 10min) A-2 Melt Index (190 ℃) 2.5 (g / 10min) A-3 Melt Index (190 ℃) 27.0 (g / 10min) <Core Shell Polymer> B-1 Takeda Yakuhin Kogyo Co., Ltd. Staphyloid (trade name) PO-01143 B-2 Takeda Yakuhin Kogyo Co., Ltd. Staphyloid (trade name) PO-0148 <Oxy having primary or secondary amine Alkylene-based polymer> C-1 poly (oxyethylene) dipropylamine number average molecular weight 100
0 C-2 poly (oxyethylene) dipropylamine number average molecular weight 4000 C-3 poly (oxyethylene) dipropylamine number average molecular weight 10000 C'-1 polyoxyethylene number average molecular weight 4000 <thermoplastic polyurethane> Takeda Bardish Urethane Industry Co., Ltd., trade name [Elastollan-S80A]

[0018]

[Table 1]

[0019]

[Table 2]

[0020]

EFFECTS OF THE INVENTION As is clear from the above description and Examples, the present invention is a polyacetal resin in which a specific core-shell polymer and an oxyalkylene polymer having a primary or secondary amine are used in combination. The composition of (1) showed a remarkable effect of maintaining the balanced mechanical properties of polyacetal while having excellent hinge properties and maintaining toughness and weld properties. Further, a very preferable resin composition having improved fluidity can be obtained. Examples of such a polyacetal resin composition and an application example of a hinge part formed by molding the composition include various hinge parts in the fields of automobiles, electric / electronics, building materials, sundries, etc., but more specifically Examples thereof include connectors for automobiles and connectors for electric devices, which are preferably used for these applications.

[Brief description of drawings]

FIG. 1 is a schematic view of a test piece used for measuring hinge characteristics, and (a), (b), and (c) are a plan view, a side view, and an enlarged view of a hinge portion, respectively. The unit of other numerical values is mm.

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Claims (6)

[Claims] Claims: (A) 100 parts by weight of polyacetal resin (B)
Core-shell polymer having a rubbery polymer core and a glassy polymer shell 1 to 50 parts by weight and (C) a primary or secondary amine having 2 to 8 carbon chains adjacent to each other, an oxyalkylene polymer 0.1 to 20 A polyacetal resin composition containing parts by weight. 2. The core-shell polymer (B) is a core-shell polymer in which substantially no anion is detected.
The polyacetal resin composition described. 3. The core-shell polymer (B) is obtained by emulsion polymerization using a nonionic surfactant and a polymerization initiator in which radicals generated are neutral.
The polyacetal resin composition described. 4. The polyacetal resin composition according to claim 1, wherein the shell of the core-shell polymer (B) is a polymer containing methyl methacrylate as a main component. 5. An oxyalkylene polymer (C) having an average molecular weight in the range of 400 to 300,000.
The polyacetal resin composition according to the item. 6. A hinge component made of a polyacetal resin obtained by molding the polyacetal resin composition according to any one of claims 1 to 5.