Polyacetal resin composition

Abstract

To provide a polyacetal resin composition which generates little formaldehyde, suppresses generation of a mold deposit, and is excellent in stability during molding residence.SOLUTION: A polyacetal resin composition contains 100 pts.mass of (A) a polyacetal resin, 0.01 to 10 pts.mass of (B) aluminum particles, and 0.02 to 0.4 pts.mass of (C) ethylene urea.SELECTED DRAWING: Figure 1

Description

Technical Field

[0001] The present invention relates to a polyacetal resin composition.

Background Art

[0002] Polyacetal resins are resins with high mechanical strength and rigidity, excellent oil resistance, organic solvent resistance, and self-lubricity, and having a good balance of various properties in a wide temperature range. Also, since they are easy to process, polyacetal resins are widely used as typical engineering plastics, mainly for structural parts and sliding parts such as precision instruments, home appliances, OA equipment, automobiles, industrial materials, and sundries. In particular, polyacetal copolymers are known to be superior in heat aging resistance, hydrolysis resistance, and molding stability because the comonomer component is chemically stable and decomposition does not proceed continuously even if the molecular chain is cut in the middle.

[0003] In recent years, with the expansion of the application fields of polyacetal resins, the required performance has been further increased. Under the above-described circumstances, in addition to the above various physical properties, in order to enhance the designability of the molded article, attempts have been made to improve the appearance characteristics and impart metallic luster.

[0004] For example, attempts have been made to impart metallic luster and designability by molding a resin composition containing a glossy pigment (see Patent Documents 1 and 2). Also, methods of containing a predetermined amount of a metallic pigment capable of optically changing and a colorant in a thermoplastic resin, a method of containing a glossy pigment for resin addition composed of specific aluminum particles (see Patent Documents 3 and 4), and a method of adding a metallic pigment together with a weathering agent and a formaldehyde inhibitor to a polyacetal resin having a specific terminal structure (see Patent Document 5) have been proposed, and suppression of the amount of formaldehyde generation and improvement of weather resistance have been shown as effects.

Prior Art Documents

Patent Documents

[0005]

Patent Document 1

Patent Document 2

Patent Document 3

Patent Document 4

Patent Document 5

Summary of the Invention

Problems to be Solved by the Invention

[0006] However, according to the technologies described in the above Patent Documents 1 to 4, problems such as heat generation during melt mixing and an increase in the amount of formaldehyde generated from the active sites on the metal surface may occur. Further, in the above Patent Document 5, although a technology aimed at the heat stability of the molded body and the suppression of formaldehyde has been proposed by a specific combination of compounding components, there are problems in terms of mold deposit during continuous molding and the occurrence of silver streaks due to residence during molding.

[0007] Therefore, in the present invention, in view of the problems of the above-described conventional technologies, an object is to provide a polyacetal resin composition and a molded body that suppress mold deposit, have excellent stability during residence, and suppress the generation of formaldehyde.

[0008] That is, the present invention is as follows. 〔1〕 (A) 100 parts by mass of a polyacetal resin, (B) 0.01 to 10 parts by mass of aluminum particles, (C) 0.02 to 0.4 parts by mass of ethylene urea and a polyacetal resin composition containing the same. 〔2〕 The resin composition according to 〔1〕, wherein the (A) polyacetal resin is a copolymer. 〔3〕 The resin composition according to [1] or [2], wherein the MFR of the (A) polyacetal resin is 2.5 to 20 g / 10 min. [4] The resin composition according to any one of [1] to [3], wherein the content of the (C) ethylene urea is 0.02 to 0.3 parts by mass. [Advantages of the Invention]

[0009] According to the present invention, it is possible to provide a polyacetal resin composition that suppresses mold deposits during molding, further suppresses the generation of silver streaks due to residence during molding, has a metallic luster, and suppresses the generation of formaldehyde. [Brief Description of the Drawings]

[0010]

Figure 1

[0011] Hereinafter, modes for carrying out the present invention (hereinafter referred to as "the present embodiment") will be described in detail. The present invention is not limited to the following description, and can be variously modified and implemented within the scope of the gist thereof. The resin composition of the present embodiment is characterized by containing 100 parts by mass of (A) polyacetal resin, 0.01 to 10 parts by mass of (B) aluminum particles, and 0.02 to 0.4 parts by mass of (C) ethylene urea.

[0012] [((A) Polyacetal Resin)] The (A) polyacetal resin is not particularly limited, and conventionally known polyacetals can be used. The (A) polyacetal resin can be used alone or in combination of two or more.

[0013] As the (A) polyacetal resin, substantially oxymethylene units —(CH obtained by homopolymerization of cyclic oligomers such as formaldehyde, trioxane or tetraoxane2 A polyoxymethylene homopolymer composed of O)-, or a copolymer obtained by copolymerizing formaldehyde and / or trioxane with a cyclic ether and / or a cyclic formal, or a cyclic formal to which a hindered phenolic antioxidant is added in an amount of 1 mass ppm or more and 500 mass ppm or less, having a structure in which an oxyalkylene unit represented by the following general formula (1) is randomly inserted into a chain composed of oxy-methylene units -(CH 2 Examples thereof include polyoxymethylene copolymers having a structure in which an oxyalkylene unit represented by the following general formula (1) is randomly inserted into a chain.

[0014]

Chemical formula

[0015] (In the above formula (1), R 1 and R 2 are each independently a hydrogen atom, an alkyl group, or an aryl group, and they may be the same or different, and n is an integer of 2 to 6.)

[0016] The polyoxymethylene copolymer used in this embodiment includes a branched polyoxymethylene copolymer in which the molecular chain is branched, and a polyoxymethylene block copolymer having a heterocomponent block in which the repeating unit of oxy-methylene is 50% by mass or more.

[0017] Also, the insertion rate of the above oxyalkylene unit in the polyoxymethylene copolymer is preferably 0.01 mol or more and 50 mol or less, more preferably 0.03 mol or more and 20 mol or less, per 100 mol of oxy-methylene units. Examples of the oxyalkylene unit include an oxyethylene unit, an oxypropylene unit, an oxytetramethylene unit, an oxybutylene unit, an oxyphenylethylene unit, etc. Among these oxyalkylene units, from the viewpoint of improving the physical properties of the resin composition, the oxypropylene unit -〔(CH 2 ) 3 O〕-, and the oxytetramethylene unit -〔(CH 2 ) 4It is preferable that it is -O-).

[0018] It is desirable to perform a terminal stabilization treatment on the polyacetal resin obtained by the above homopolymerization or copolymerization. As a method for terminal stabilization treatment, for example, a method of esterifying, etherifying, urethanizing, etc. the terminal hydroxyl group, or a method of stabilizing the unstable part at the terminal by hydrolysis, etc. is used. The polyacetal resin subjected to terminal stabilization treatment is, for example, a polyoxymethylene copolymer obtained by copolymerizing formaldehyde and / or trioxane with a cyclic ether and / or a cyclic formal, a step of stabilizing the molecular terminal immediately after polymerization, and then injecting and kneading water or alcohol or a mixture thereof in a molten state, and a devolatilization step of releasing the vapor of the hydroxyl group-containing compound such as the above-mentioned water and free formaldehyde, and is obtained by continuously supplying and treating it to a twin-screw extruder with non-intermeshing and reverse rotation that can perform the above steps. Further, when injecting and kneading the above-mentioned water or alcohol, or a mixture thereof, it is preferable to add a basic substance such as triethylamine as a pH adjuster.

[0019] The MFR (melt flow rate; conforming to ASTM D57E, temperature condition: 190 °C) of the polyacetal resin is preferably 2.5 to 40 g / 10 minutes, more preferably 3 to 30 g / 10 minutes. By adjusting the MFR of the polyacetal resin within the above range, the balance of the mechanical properties of the resin composition, the thermal stability in retention molding, and the amount of formaldehyde generated becomes good.

[0020] ((B) Aluminum particles) The resin composition of this embodiment contains (B) aluminum particles. Further, the (B) aluminum particles have a flat shape such as coin shape or flake shape, so that it is possible to exhibit better metallic luster. The (B) aluminum particles can be used alone or in combination of a plurality of kinds.

[0021] In the resin composition of the present embodiment, the content of (B) aluminum particles is 0.01 to 10 parts by mass with respect to 100 parts by mass of (A) polyacetal resin. Further, from the viewpoint of suppressing the weight of the composition and the molded article using the same, the content of (B) metal particles in the resin composition of the present embodiment is preferably 1 to 10 parts by mass, more preferably 0.1 to 7 parts by mass, and still more preferably 0.5 to 4 parts by mass with respect to 100 parts by mass of (A) polyacetal resin. By adjusting the content of (B) aluminum particles within the above range, in the molded body produced from the resin composition of the present embodiment, the rigidity and impact resistance, which are the mechanical properties inherent to (A) polyacetal resin, are better retained, the generation of formaldehyde is effectively suppressed, and it becomes possible to exhibit metallic luster.

[0022] Also, from the viewpoint of further improving the metallic appearance, the content of (B) aluminum particles in the resin composition of the present embodiment is preferably 4 to 10 parts by mass, more preferably 5 to 10 parts by mass with respect to 100 parts by mass of (A) polyacetal resin. Generally, when (B) aluminum particles are contained in a large amount in this way, there is a tendency for a large amount of mold deposit to occur due to the adhesion of aluminum particles to the mold. However, in the present embodiment, by using this (B) aluminum particles in combination with (C) ethylene urea described later, mold deposit can be suppressed.

[0023] (B) Aluminum particles preferably have a volume average particle diameter (D 50 ) of 3 to 60 μm, more preferably 3 to 40 μm, and still more preferably 5 to 30 μm from the viewpoint of increasing the reflectance. The volume average particle diameter (D 50 ) can be measured by the method described in the examples below.

[0024] (B) Aluminum particles can be produced by known methods. For example, (B) aluminum particles can be obtained by subjecting atomized powder, cut powder, foil powder, vapor-deposited powder, or other metal powders obtained by other methods to preliminary screening by primary classification or the like, and then subjecting them to wet grinding treatment using a ball mill, attritor, planetary mill, vibration mill, etc. in the coexistence of a grinding medium containing a grinding aid and a solvent, etc. After sieving classification in a wet state, solid-liquid separation is carried out using a filter press or the like to obtain them. Thereby, (B) aluminum particles with few uneven fracture surfaces present at the ends of the flakes can be produced.

[0025] (B) The shape of the aluminum particles is preferably a flat shape such as coin-shaped or flake-shaped as described above. The flat shape referred to here means that the value of the average shape ratio [average particle thickness (t) / volume average particle diameter (D 50 )] is 0.2 or less, preferably 0.1 or less, and more preferably 0.05 or less. By setting the average shape ratio within this range, the surface area of the portion having a high reflectivity characteristic of the metal can be increased with the addition of a small amount of metal particles. Therefore, by setting the average shape ratio within this range, the brightness of the molded body can be efficiently increased with a small addition amount of (B) aluminum particles.

[0026] ((C) Ethylene urea) The resin composition of this embodiment contains (C) ethylene urea. The production method of (C) ethylene urea is not particularly defined and known methods can be used. For example, it can be obtained by a method of reacting ethylenediamine with carbon dioxide gas, a method of reacting ethylenediamine with urea, a method of reacting ethylenediamine with phosgene, a method of reacting ethylenediamine with dialkyl carbonate, a method of oxidizing ethylenethiourea, etc.

[0027] The ethylene urea of the present embodiment may contain raw materials, intermediates, and solvents as impurities. For example, it may contain ethylenediamine, urea, dialkyl carbonate, 2-aminoethylcarbamic acid, 2-aminoethylcarbamic ester, 2-aminoethylurea, etc. The amount of impurities is preferably less than 10% based on the weight of ethylene urea, more preferably less than 5%, and still more preferably less than 1%.

[0028] In the resin composition of the present embodiment, the content of (C) ethylene urea is 0.02 to 0.4 parts by mass, preferably 0.02 to 0.3 parts by mass, and still more preferably 0.03 to 0.3 parts by mass with respect to 100 parts by mass of (A) polyacetal resin. When the content of (C) ethylene urea is within the above range, a sufficient formaldehyde suppressing effect can be obtained, and it is possible to suppress mold deposits during molding and silver streaks due to residence.

[0029] (Other additives) The resin composition of the present embodiment can contain other commonly used additives. The additives are not particularly limited, but stabilizers and the like used in conventional (A) polyacetal resins are preferred. Examples of the above stabilizers include heat stabilizers, antioxidants, weather stabilizers, etc., and further, a scavenger for formic acid or formaldehyde. In addition, in order to enhance the designability, the resin composition of the present embodiment can contain various colorants as additives as needed. The above additives can be used alone or in combination of two or more.

[0030] -Heat stabilizer- As the above heat stabilizer, polyamide resin (D) is preferred. Examples of polyamide resins include crystalline polyamide resins such as polyamide 4-6, polyamide 6, polyamide 6-6, polyamide 6-10, polyamide 6-12, polyamide 12, polyamide 6 / 6-6, polyamide 6 / 6-6 / 6-10, polyamide 6 / 6-12, semi-crystalline polyamides such as polyamide 4I, polyamide 5I, polyamide 6I, polyamide 7I, polyamide 8I, polyamide 9I, polyamide 10I, polyamide 6I / 6T, poly-β-alanine, polyacrylamide, etc. Among them, polyamide 6-6 and polyamide 6I are preferred from the viewpoints of suppressing the amount of formaldehyde generated and stability during residence.

[0031] The content of the heat stabilizer in the resin composition of the present embodiment is preferably 0.01 to 1.0 parts by mass, more preferably 0.02 to 0.7 parts by mass, based on 100 parts by mass of the (A) polyacetal resin. When the content of the heat stabilizer is 0.03 to 0.5 parts by mass, the heat stability during the molding process of the resin composition of the present embodiment is achieved, and a formaldehyde suppression effect is obtained.

[0032] -Antioxidant- As the above antioxidant, a hindered phenol-based antioxidant is preferred. 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), etc. are included.

[0033] In the resin composition of the present embodiment, the content of the antioxidant is preferably 0.01 to 2 parts by mass, more preferably 0.02 to 1 part by mass, based on 100 parts by mass of the (A) polyacetal resin. When the content of the antioxidant is 0.01 to 2 parts by mass, the thermal stability during the molding process of the resin composition of the present embodiment can be improved and it becomes good.

[0034] -Weather stabilizer- Examples of the weather stabilizer include hindered amine stabilizers. Examples of the hindered amine stabilizers include piperidine derivatives having a steric hindrance group, such as ester group-containing piperidine derivatives, ether group-containing piperidine derivatives, amide group-containing piperidine derivatives, and high molecular weight polycondensates of piperidine derivatives.

[0035] In the resin composition of the present embodiment, the content of the hindered amine stabilizer is preferably 0.01 to 5 parts by mass, more preferably 0.1 to 2 parts by mass, and still more preferably 0.1 to 1.5 parts by mass, based on 100 parts by mass of the (A) polyacetal resin.

[0036] Further, the resin composition of the present embodiment preferably further contains an ultraviolet absorber as the weather stabilizer. Thereby, in the molded article obtained from the resin composition of the present embodiment, an effect of improving weather resistance (light stability) can be obtained. Examples of the ultraviolet absorber include benzotriazole-based compounds, benzophenone-based compounds, oxalic acid anilide-based compounds, and hydroxyphenyl-1,3,5-triazine-based compounds.

[0037] When the resin composition of the present embodiment contains an ultraviolet absorber and a hindered amine stabilizer, the mass ratio of the hindered amine stabilizer to the ultraviolet absorber is preferably such that ultraviolet absorber / hindered amine stabilizer (mass ratio) is 10 / 90 to 80 / 20, more preferably 10 / 90 to 70 / 30, and still more preferably 20 / 80 to 60 / 40.

[0038] -Formic acid scavenger- The resin composition of this embodiment preferably further contains the above formic acid scavenger. Examples of the scavenger for formic acid or formaldehyde include calcium fatty acid salts, hydroxides of alkali metals or alkaline earth metals, inorganic acid salts, carboxylates, alkoxides, and the like. The content of the above calcium fatty acid salt, hydroxide of alkali metal or alkaline earth metal, inorganic acid salt, carboxylate or alkoxide is preferably in the range of 0.01 to 1 part by mass, more preferably 0.02 to 0.5 part by mass, based on 100 parts by mass of the polyacetal resin. When each content is in the range of 0.01 to 1 part by mass, the thermal stability during the molding process of the resin composition of this embodiment can be improved, the amount of formaldehyde generated from the molded body can be reduced, and the heat aging resistance can be made better.

[0039] - Colorant - Examples of the colorant include organic pigments and inorganic pigments, but it is not particularly limited, and a combination of one or more colorants may also be used. Examples of the above organic pigments include phthalocyanine pigments, condensed azo pigments, azo lake pigments, quinacridone pigments, dioxazine pigments, isoindolinone pigments, condensed polycyclic pigments, and the like. Examples of the above inorganic pigments include simple oxides such as zinc white, titanium dioxide, red lead, chromium oxide, iron black, sulfides such as cadmium yellow, cadmium orange, cadmium red, chromates such as lead yellow, zinc yellow, chrome vermilion, ferrocyanides such as ultramarine blue, silicates such as ultramarine, and carbon black.

[0040] The content of the above colorant in the resin composition of this embodiment is preferably 0.0001 to 2 parts by mass, more preferably 0.0005 to 1 part by mass, based on 100 parts by mass of (A) the polyacetal resin. By setting the content of the colorant within the above range, an effect of improving the designability can be obtained without reducing the mechanical strength of the molded body or promoting the generation of formaldehyde from (A) the polyacetal resin in particular.

[0041] The resin composition of the present embodiment may further contain various conventionally used inorganic fillers, other thermoplastic resins, softeners, crystal nucleating agents, mold release agents, etc., as long as the object of the present invention is not impaired as desired.

[0042] (Method for manufacturing resin composition) The resin composition of the present embodiment can be obtained, for example, by mixing while melting a part of the above raw materials using a generally used melt kneader. Examples of the melt kneader include a kneader, a roll mill, a single-screw extruder, a twin-screw extruder, a multi-screw extruder, and the like.

[0043] The temperature of the melt kneading can be appropriately selected according to the melting point or softening point of the (A) polyacetal resin to be used. However, a temperature 1 to 100°C higher than the melting point or softening point of the (A) polyacetal resin is preferable, a temperature 10 to 60°C higher is more preferable, and a temperature 20 to 50°C higher is even more preferable. The melting point or softening point of the (A) polyacetal resin can be determined by differential scanning calorimetry (DSC) measurement according to JIS K7121. In addition, in order to maintain the quality and working environment, it is preferable to replace the inside of the system with an inert gas or to degas with a single-stage or multi-stage vent.

[0044] (Properties of resin composition) The resin composition of the present embodiment has good retention stability during molding and extrusion, few appearance defects, less volatilization of organic solvents from the resin composition, and has an excellent metallic appearance, achieving a high glossiness and a flop index (FI) value, and a molded product having an excellent metallic appearance with good aesthetics can be obtained.

[0045] The amount of formaldehyde generated in the resin composition of the present embodiment is preferably 3 mg / kg or less, more preferably 2 mg / kg or less. The amount of formaldehyde generated can be measured by the method described in the examples below.

[0046] The resin composition of this embodiment preferably has an FI value of 9 or more, more preferably 13 or more, and still more preferably 14 or more. The FI value is one of the indices of a metallic appearance and can be measured by the method described later. Here, the phenomenon in which the lightness changes with the change in the viewing angle is called the flip-flop (F / F) phenomenon, and the quantitative value representing this is called the FI (flop index) value. The FI value is obtained from the lightness (L* 15 °, L* 45 °, and L* 110 °) values at 15°, 45°, and 110° using the formula first proposed by DuPont (A.B.J. Rodriguez, JOCCA, (1992(4)), pp. 150 - 153). Specifically, the FI value is obtained by the following mathematical formula. The higher the FI value, that is, the greater the difference in lightness (L * ) between the highlight direction (the direction of regular reflection with respect to the incident angle of light) and the shade direction (the non-regular reflection direction), the higher the metallic feeling is generally felt.

[0047]

Equation

[0048] <Method for Measuring FI Value> The method for measuring the FI value will be described with reference to FIG. 1. FIG. 1 is a diagram showing the evaluation method of the FI value. As shown in FIG. 1, first, light is irradiated onto the surface of a test piece (a molded product of the resin composition) from a certain direction, and the L * values (L* 15 °, L* 45 °, and L* 110 °) (lightness) are measured when the light-receiving angle is shifted by 15°, 45°, and 110° with respect to the regular reflection light. Next, the measured L * values are substituted into the above mathematical formula to obtain the FI value. Generally, the higher the FI value, the higher the metallic texture.

[0049] The glossiness of the resin composition of this embodiment is preferably 45 or more, more preferably 60 or more, and still more preferably 70 or more immediately after injection molding. The glossiness can be measured by the method described below. Here, the glossiness is one of the indices of a metallic appearance. Further, the glossiness depends on the smoothness of the surface of the molded product, and in a metallic material in which a brightening material such as a metallic pigment is kneaded and molded, the glossiness generally tends to be low. When the glossiness decreases, the brightness decreases due to the influence of scattered reflected light on the surface of the molded body, and thus the quality of the metallic appearance tends to decrease.

[0050] <Method for Measuring Glossiness> The glossiness can be measured at an angle of 60° to the surface of the molded body in accordance with JIS Z8741 using the above test piece used for the measurement of the FI value and a gloss meter (manufactured by Horiba, Ltd., "IG-320"). Generally, it is assumed that the higher the glossiness, the smoother the surface of the molded body and the higher the degree of followability to the surface of the mold.

[0051] (Use of Molded Product Obtained from Resin Composition) The molded product obtained from the resin composition of this embodiment can be particularly used for interior and exterior parts provided with mechanical parts or sliding parts. For example, it is used as any part selected from the group consisting of parts provided in OA equipment, music / video or information equipment, or communication equipment, industrial parts provided in office furniture or housing equipment, and interior and exterior parts of automobiles. In particular, it is preferably used as any part selected from the group consisting of a handle, a switch, and a button that require an excellent appearance. Further, in order to use the molded product obtained from the resin composition of this embodiment as an exterior part, it is preferable to use a textured mold at the time of molding or to apply a textured process to the molded product to impart a designed surface, since an effect of improving the appearance is exhibited.

[0052] According to the resin composition of this embodiment, a molded product having a metallic luster can be obtained without performing processing such as plating or painting on the surface. It has excellent thermal stability and weather resistance, retains good mechanical properties (e.g., tensile properties, impact strength), and has a high gloss and good appearance characteristics. Furthermore, since the molded product obtained from the resin composition according to this embodiment has good appearance characteristics as described above, it has an excellent appearance that is practically good even without painting. Therefore, an appearance with excellent design can be efficiently obtained without using a solvent. In addition, the resin composition of this embodiment is excellent in production stability, can be manufactured in a good working environment, and is also excellent in terms of cost and the environment.

Examples

[0053] Hereinafter, the present invention will be specifically described by way of examples, but the present invention is not limited to the examples described below.

[0054] (1) Preparation of main raw materials <Polyacetal resin> Manufactured by Asahi Kasei Corporation, "Tenac C 4513" (polyacetal copolymer, melting point 164°C)

[0055] <Aluminum particles> Atomized aluminum powder (volume average particle diameter (D 50 ) 11 μm) The volume average particle diameter (D 50 ) of the aluminum particles can be determined by the catalog description value or by the 50% value of the particle size distribution of the aluminum particles measured by a laser diffraction particle size distribution measuring device (manufactured by Shimadzu Corporation, trade name "SALD-2300").

[0056] <Formaldehyde scavenger> Ethylene urea (manufactured by Tokyo Chemical Industry) Sebacic acid dihydrazide (manufactured by Tokyo Chemical Industry) Benzoguanamine (manufactured by Tokyo Chemical Industry)

[0057] (2) Evaluation method <Evaluation of Long-Term Continuous Molding Mold Depositability> The prepared polyacetal resin pellets were molded according to the following molding conditions (a). And the mold depositability at this time was evaluated according to the following evaluation criteria (b). (a) Molding Conditions · Injection molding machine: Toshiba Machine Co., Ltd. IS-100GN · Cylinder set temperature: 200 °C · Mold set temperature: 45 °C · Mold size: 130×110 mm×3 mm · Molding cycle: Injection time / Cooling time = 20 / 20 seconds (b) Evaluation Criteria Based on the following evaluation criteria, the mold deposit adhesion status in the mold cavity at the 1000th shot from the start of molding was observed. 1: No deposits were observed, or deposits were observed in an area less than 5% of the area in the mold cavity. 2: Deposits were observed in an area of 5% or more but less than 10% of the area in the mold cavity. 3: Deposits were observed in an area of 10% or more but less than 15% of the area in the mold cavity. 4: Deposits were observed in an area of 15% or more but less than 20% of the area in the mold cavity. 5: Deposits were observed in an area of 20% or more of the area in the mold cavity.

[0058] <Stability During Residence> Using an injection molding machine (Si-15V manufactured by Toyo Machine Metal Co., Ltd.), the polyacetal resin composition was retained in a molten state in a cylinder set at a temperature of 205 °C. After 60 minutes, it was injected into a mold set at 90 °C under injection conditions of an injection pressure of 72 MPa, an injection time of 35 seconds, and a cooling time of 15 seconds to obtain a molded piece of 10×80 mm×3 mm. The state of silver streaks on the obtained molded piece was evaluated. 1: Almost no silver streaks occurred. 2: Silver streaks occurred in the range of 20 mm from the gate part. 3: Silver streaks occurred in the range of 50 mm from the gate part.

[0059] <Formaldehyde generation amount> Pellets of the resin composition prepared as described below were molded using an injection molding machine (IS-100GN manufactured by Toshiba Machine Co., Ltd.) under the injection conditions of a cylinder temperature of 220 °C, a mold temperature of 77 °C, an injection time of 15 seconds, and a cooling time of 10 seconds to prepare test pieces. Next, these test pieces were left in a thermostatic chamber at room temperature of 23 °C and humidity of 50% for 24 hours. Next, the amount of formaldehyde released from the test pieces was determined by the following method (VDA275 method). First, 50 mL of distilled water and a test piece (100 mm in length × 40 mm in width × 3 mm in thickness) were placed in a 500 mL polyethylene container and sealed, and heated at 60 °C for 2 hours. Then, formaldehyde in the distilled water was reacted with acetylacetone in the presence of ammonium ions. For the reaction product, the absorption peak at a wavelength of 412 nm was measured with a UV spectrometer to determine the formaldehyde generation amount (mg / kg) per unit mass of the test piece.

[0060] (3) Preparation of pellets of the resin composition According to the formulation shown in Table 1, the raw materials were put into a polyethylene bag and manually and vigorously mixed continuously for about 10 minutes, and this was repeated 3 times to obtain a mixture. The obtained mixture was melt-kneaded (melt-mixed) while degassing from the vent using a twin-screw extruder with a 30 mm vent under the conditions of a set temperature of 200 °C, a rotation speed of 80 rpm, and a discharge rate of 12 kg / hour, and dried at 80 °C for 3 hours to prepare pellets of the resin composition. Using these pellets of the resin composition, the above various evaluations were carried out. The results are shown in Table 1.

[0061]

Table 1

[0062] From Table 1, in Examples 1 to 4 according to the present invention, no clear mold deposit was observed, and the amount of formaldehyde generated was small, and excellent results were obtained in terms of stability during residence. Also, from these examples, it can be seen that good results can be obtained by adding aluminum particles and ethylene urea to the polyacetal resin.

[0063] On the other hand, in Comparative Examples 1 to 7, the results were inferior in terms of the amount of formaldehyde generated, the amount of mold deposit generated, and the stability during residence.

[0064] As is clear from the evaluation results in Table 1, according to Examples 1 to 4, by adding aluminum particles and ethylene urea, a resin composition with less formaldehyde generation, less mold deposit generation, and excellent stability during molding residence was obtained.

Industrial Applicability

[0065] The resin composition of the present invention has industrial applicability as a material for members of design parts such as automotive interior parts, for example.

Claims

1. (A) 100 parts by mass of a polyacetal resin, (B) 0.01 to 10 parts by mass of aluminum particles, and (C) 0.02 to 0.4 parts by mass of ethylene urea A polyacetal resin composition containing the same.

2. The polyacetal resin composition according to claim 1, wherein the (A) polyacetal resin is a copolymer.

3. The polyacetal resin composition according to claim 1 or 2, wherein the MFR of the (A) polyacetal resin is 2.5 to 20 g / 10 min.

4. The polyacetal resin composition according to claim 1 or 2, wherein the content of the (C) ethylene urea is 0.02 to 0.3 parts by mass.

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