Resin composition, pellets, and molded article

Abstract

Provided are a resin composition, pellets, and a molded article. The resin composition comprises (A) 100 parts by mass of a polyacetal resin, (B) 0.005-0.3 parts by mass of an aliphatic carboxylic acid hydrazide and / or an aliphatic hydrazone, and (C) 0.02-0.3 parts by mass of a urea compound represented by formula (N), wherein the urea compound (C) contains a silicon-containing compound in an amount exceeding 0 mass% but not exceeding 0.007 mass% in terms of silicon atom amount based on the urea compound (C).

Description

Resin composition, pellets, and molded products

[0001] The present invention relates to a resin composition, a pellet, and a molded article, and more particularly to a resin composition containing a polyacetal resin as a main component.

[0002] Polyacetal resin, an engineering plastic, has excellent mechanical properties, sliding properties, friction and wear properties, heat resistance, moldability, and the like. For this reason, resin compositions containing polyacetal resin as a primary component are widely used in various mechanical and electrical components, such as those for automobiles and office automation equipment. However, because polyacetal resin uses formaldehyde as its primary raw material, it undergoes slight thermal decomposition reactions due to thermal history during processing and molding, generating trace amounts of formaldehyde. Formaldehyde is believed to potentially cause sick building syndrome and other conditions, and therefore resin compositions in which formaldehyde generation is sufficiently suppressed are in demand. Patent Documents 1 to 4 are examples of studies that have investigated the suppression of formaldehyde generation.

[0003] International Publication No. 2015 / 115386 JP 2007-070574 A JP 2005-171158 A JP 2022-015084 A

[0004] As described above, the generation of formaldehyde due to the thermal history of polyacetal resins has been studied for some time, but it cannot be said that sufficient research has been conducted on the suppression of formaldehyde generation from polyacetal resins after retention. The present invention aims to solve this problem by providing an excellent resin composition, pellets, and molded articles in which formaldehyde generation is effectively suppressed.

[0005] In light of the above-mentioned problems, the present inventors have conducted research and found that the above-mentioned problems can be solved by using an aliphatic carboxylic acid hydrazide and / or aliphatic hydrazone in combination with a urea compound as a formaldehyde scavenger, and further adjusting the amount of a silicon-containing compound in the urea compound. Specifically, the above-mentioned problems have been solved by the following means: <1> A resin composition comprising, per 100 parts by mass of (A) a polyacetal resin, (B) 0.005 to 0.3 parts by mass of an aliphatic carboxylic acid hydrazide and / or aliphatic hydrazone, and (C) 0.02 to 0.3 parts by mass of a urea compound represented by formula (N), wherein the (C) urea compound contains the silicon-containing compound in such a proportion that the silicon atom content in the (C) urea compound is greater than 0% by mass and not more than 0.007% by mass. (In formula (N), R is a hydrocarbon group having 1 to 5 carbon atoms, and n is an integer of 0 to 4. When n is 2 or more, each R may be the same or different.) <2> The resin composition according to <1>, wherein the mass ratio (B) / (C) of the (B) aliphatic carboxylic acid hydrazide and / or aliphatic hydrazone to the (C) urea compound is 1.0 or less. <3> The resin composition according to <1> or <2>, wherein the (C) urea compound contains ethylene urea. <4> The resin composition according to any one of <1> to <3>, wherein the (C) urea compound contains a silicon-containing compound in such a ratio that the silicon atoms in the (C) urea compound are 0.002 to 0.007 mass%. <5> The resin composition according to any one of <1> to <4>, wherein the (B) aliphatic carboxylic acid hydrazide and / or aliphatic hydrazone contain an aliphatic carboxylic acid hydrazide. <6> The resin composition according to any one of <1> to <5>, wherein the (B) aliphatic carboxylic acid hydrazide and / or aliphatic hydrazone includes at least one selected from the group consisting of adipic acid dihydrazide, azelaic acid dihydrazide, sebacic acid dihydrazide, and dodecanedioic acid dihydrazide. <7> The resin composition according to any one of <1> to <6>, wherein the mass ratio (B) / (C) of the (B) aliphatic carboxylic acid hydrazide and / or aliphatic hydrazone to the (C) urea compound is 1.0 or less, the (C) urea compound includes ethylene urea, the (C) urea compound includes a silicon-containing compound in such a proportion that the silicon atom content in the (C) urea compound is 0.002 to 0.007 mass%, and the (B) aliphatic carboxylic acid hydrazide and / or aliphatic hydrazone includes at least one selected from the group consisting of adipic acid dihydrazide, azelaic acid dihydrazide, sebacic acid dihydrazide, and dodecanedioic acid dihydrazide. <8> The resin composition pellet according to any one of <1> to <7>. <9> A molded article formed from the resin composition according to any one of <1> to <7>. <10> A molded article formed from the pellets according to <8>.

[0006] According to the present invention, it is possible to provide a resin composition, pellets, and molded articles in which the generation of formaldehyde is effectively suppressed.

[0007] Hereinafter, a mode for carrying out the present invention (hereinafter simply referred to as "the present embodiment") will be described in detail. Note that the following present embodiment is an example for explaining the present invention, and the present invention is not limited to this embodiment. Note that in this specification, the use of "to" means that the numerical values ​​before and after it are included as the upper and lower limits. Furthermore, any combination of the upper and lower limit values ​​of numerical values ​​in this specification is cited as an example of this embodiment. In this specification, various physical property values ​​and characteristic values ​​are at 23°C unless otherwise specified. If the measurement methods, etc. described in the standards shown in this specification vary depending on the fiscal year, they shall be based on the standards as of January 1, 2023, unless otherwise specified. If the measurement methods, etc. described in the standards shown in this specification are discontinued as of January 1, 2023, they shall be based on the standards at the time of discontinuation.

[0008] The resin composition of the present embodiment is characterized in that it contains, relative to 100 parts by mass of (A) polyacetal resin, 0.005 to 0.3 parts by mass of (B) aliphatic carboxylic acid hydrazide and / or aliphatic hydrazone (sometimes referred to as "component (B)" in this specification), and 0.02 to 0.3 parts by mass of (C) a urea compound represented by formula (N), and the (C) urea compound contains a silicon-containing compound in such a proportion that silicon atoms in the (C) urea compound are more than 0% by mass and not more than 0.007% by mass. (In formula (N), R is a hydrocarbon group having 1 to 5 carbon atoms, and n is an integer from 0 to 4. When n is 2 or greater, the Rs may be the same or different.) This configuration effectively suppresses formaldehyde generation. In particular, it is possible to effectively suppress both the initial generation of formaldehyde and the generation of formaldehyde from the retained resin. Specifically, component (B) has a fast reaction rate and is therefore effective in suppressing the initial generation of formaldehyde. On the other hand, the urea compound (C) has a slow reaction rate and is therefore effective in suppressing formaldehyde from the retained polyacetal resin. However, a high content of the urea compound (C) can cause mold contamination. In this embodiment, this problem is solved by setting an upper limit for the content of the urea compound (C). Furthermore, in this embodiment, a urea compound containing a silicon-containing compound in a proportion of silicon atoms greater than 0 mass% and not greater than 0.007 mass% is used. This configuration effectively suppresses formaldehyde generation while maintaining industrial convenience. Specifically, a silicon-containing compound is used as a catalyst during the synthesis of urea compounds, and some final products contain trace amounts of the silicon-containing compound. Such urea compounds containing silicon-containing compounds are industrially advantageous. However, the present inventors have conducted research and found that the inclusion of a silicon-containing compound in a urea compound promotes the generation of formaldehyde from polyacetal resins. This is believed to be because the silicon-containing compound in the urea compound has active groups (reactive sites) that decompose from the terminals of the polyacetal resin to generate formaldehyde. In this embodiment, the inventors have found that by precisely adjusting the amount of silicon-containing compound in the (C) urea compound, the generation of formaldehyde can be sufficiently suppressed even when a urea compound containing a silicon-containing compound is used.

[0009] <(A) Polyacetal Resin> The resin composition of this embodiment contains (A) polyacetal resin. The type of (A) polyacetal resin is not particularly limited, and it may be a homopolymer containing only divalent oxymethylene groups as structural units, or a copolymer containing divalent oxymethylene groups and divalent oxyalkylene groups having two or more carbon atoms as structural units. Examples of oxyalkylene groups having two or more carbon atoms include oxyethylene groups, oxypropylene groups, and oxybutylene groups.

[0010] In the polyacetal resin (A), the proportion of oxyalkylene groups having two or more carbon atoms in the total number of moles of oxymethylene groups and oxyalkylene groups having two or more carbon atoms is not particularly limited, and may be, for example, 0.5 to 10 mol %. The number of carbon atoms in the oxyalkylene groups may be two or more, but is preferably six or less, and more preferably four or less.

[0011] (A) To produce polyacetal resin, trioxane is typically used as the main raw material. Furthermore, to introduce oxyalkylene groups having 2 to 6 carbon atoms into polyacetal resin, for example, cyclic formals or cyclic ethers can be used. Specific examples of cyclic formals include 1,3-dioxolane, 1,3-dioxane, 1,3-dioxepane, 1,3-dioxocane, 1,3,5-trioxepane, and 1,3,6-trioxocane. Specific examples of cyclic ethers include ethylene oxide, propylene oxide, and butylene oxide. For example, 1,3-dioxolane can be used to introduce oxyethylene groups into polyacetal resin, 1,3-dioxane can be used to introduce oxypropylene groups, and 1,3-dioxepane can be used to introduce oxybutylene groups.

[0012] In the polyacetal resin (A), it is preferable that the amount of hemiformal terminal groups, formyl terminal groups, and terminal groups unstable to heat, acid, or base is small. ２ A formyl terminal group is represented by —CHO.

[0013] The MI (melt index) value of the polyacetal resin (A) is not particularly limited, but is typically 0.01 to 150 g / 10 min, preferably 0.1 to 100 g / 10 min, and more preferably 1 to 70 g / 10 min. In this case, the moldability of the resin composition when molded in an injection molding machine is better than when the MI value of the polyacetal resin is outside the above range. The MI value of the polyacetal resin (A) is the MI value measured according to ASTM-D1238 under conditions of 190°C and a load of 2.16 kg.

[0014] The polyacetal resin (A) used in this embodiment may be a recycled polyacetal resin product (including recovered products, material recycled products, chemical recycled products, etc.), a rejected product, or scrap material generated when a molded product is formed from a resin composition.

[0015] The content of the (A) polyacetal resin in the resin composition of this embodiment is preferably 80% by mass or more, more preferably 85% by mass or more, even more preferably 90% by mass or more, even more preferably 95% by mass or more, and even more preferably 98% by mass or more. The upper limit of the content of the (A) polyacetal resin is the amount at which all components other than the (B) component and the (C) urea compound are the (A) polyacetal resin. The resin composition of this embodiment may contain only one type of (A) polyacetal resin, or two or more types. When two or more types are contained, the total amount is preferably within the above range.

[0016] <(B) Aliphatic Carboxylic Acid Hydrazide and / or Aliphatic Hydrazone> The resin composition of this embodiment contains (B) an aliphatic carboxylic acid hydrazide and / or an aliphatic hydrazone. By containing component (B), it is possible to effectively suppress the generation of formaldehyde. (B) An aliphatic carboxylic acid hydrazide and / or an aliphatic hydrazone preferably contains an aliphatic carboxylic acid hydrazide.

[0017] The fatty acid hydrazide is preferably represented by formula (B-1): (In formula (B-1), R １１ represents an aliphatic hydrocarbon group having 2 to 18 carbon atoms, an alicyclic hydrocarbon group having 6 to 10 carbon atoms, or a group consisting of a combination thereof; R １２ ~R １５ each independently represents a hydrogen atom or an alkyl group having 1 to 6 carbon atoms; R １２ and R １３ , and R １４ and R １５ may be bonded to each other to form a ring.

[0018] In formula (B-1), R １１ represents an aliphatic hydrocarbon group having 2 to 18 carbon atoms, an alicyclic hydrocarbon group having 6 to 10 carbon atoms, or a group consisting of a combination thereof, with an aliphatic hydrocarbon group having 2 to 18 carbon atoms being preferred. The aliphatic hydrocarbon group having 2 to 18 carbon atoms preferably has 4 or more carbon atoms, and preferably 16 or less, more preferably 14 or less, and even more preferably 12 or less. The aliphatic hydrocarbon group may be saturated or unsaturated, and may be linear or branched. Specific examples of the aliphatic hydrocarbon group include alkylene groups such as butylene, pentylene, hexylene, heptylene, octylene, nonylene, decylene, undecylene, dodecylene, tridecylene, tetradecylene, pentadecylene, hexadecylene, heptadecylene, octadecylene, and nonadecylene.

[0019] The alicyclic hydrocarbon group may be saturated or unsaturated. Examples of the alicyclic hydrocarbon group include a cycloalkylene group having 6 to 10 carbon atoms. Examples of the cycloalkylene group include a cyclohexylene group.

[0020] In formula (B-1), R １２ ~R １５ are each independently preferably a hydrogen atom, a methyl group or an ethyl group, more preferably a hydrogen atom.

[0021] Examples of the aliphatic dihydrazide compounds include carbodihydrazide, oxalic acid dihydrazide, malonic acid dihydrazide, succinic acid dihydrazide, glutaric acid dihydrazide, adipic acid dihydrazide, azelaic acid dihydrazide, sebacic acid dihydrazide, dodecanedioic acid dihydrazide (1,12-dodecanedicarbohydrazide), 1,18-octadecanedicarbohydrazide, stearic acid dihydrazide, Examples thereof include maleic acid dihydrazide, fumaric acid dihydrazide, and 7,11-octadecadiene-1,18-dicarbohydrazide. At least one selected from the group consisting of adipic acid dihydrazide, azelaic acid dihydrazide, sebacic acid dihydrazide, and dodecanedioic acid dihydrazide is preferred, and adipic acid dihydrazide and / or dodecanedioic acid dihydrazide is more preferred.

[0022] The aliphatic hydrazone is preferably at least one aliphatic hydrazone selected from the group consisting of compounds represented by formula (B-2) and compounds represented by formula (B-3): (In formula (B-2), R １ represents an aliphatic hydrocarbon group having 4 to 20 carbon atoms, an alicyclic hydrocarbon group having 6 to 10 carbon atoms, or a group consisting of a combination thereof. ２ ~R ５ each independently represents a hydrogen atom or an alkyl group having 1 or 2 carbon atoms; R ２ and R ３ At least one of R represents an alkyl group having 1 or 2 carbon atoms; ４ and R ５ At least one of these represents an alkyl group having 1 or 2 carbon atoms.

[0023] In formula (B-2), the aliphatic hydrocarbon group represents an aliphatic hydrocarbon group having 4 to 20 carbon atoms, an alicyclic hydrocarbon group having 6 to 10 carbon atoms, or a group consisting of a combination thereof. The aliphatic hydrocarbon group may be saturated or unsaturated, linear or branched. Specific examples of the aliphatic hydrocarbon group include alkylene groups such as butylene, pentylene, hexylene, heptylene, octylene, nonylene, decylene, undecylene, dodecylene, tridecylene, tetradecylene, pentadecylene, hexadecylene, heptadecylene, octadecylene, nonadecylene, and icosylene. The aliphatic hydrocarbon group is preferably an aliphatic hydrocarbon group having 6 to 12 carbon atoms. In this case, the reactivity of the hydrazone of the hydrazine compound with formaldehyde is enhanced, and formaldehyde generation is more effectively suppressed. Furthermore, contamination of the mold during molding can be more sufficiently suppressed. The alicyclic hydrocarbon group may be saturated or unsaturated. Examples of the alicyclic hydrocarbon group include a cycloalkylene group having 6 to 10 carbon atoms. Examples of the cycloalkylene group include a cyclohexylene group.

[0024] In formula (B-2), R ２ ~R ５ each independently represents a hydrogen atom or an alkyl group having 1 or 2 carbon atoms; R ２ and R ３ At least one of R represents an alkyl group having 1 or 2 carbon atoms; ４ and R ５ At least one of R represents an alkyl group having 1 or 2 carbon atoms. ２ and R ４ is an ethyl group, R ３ and R ５ is a hydrogen atom, and R ２ and R ４ When is a methyl group, R ３ and R ５ is preferably a hydrogen atom or a methyl group.

[0025] Specific examples of the compound represented by formula (B-2) include 1,12-bis[2-(1-methylethylidene)hydrazino]]-1,12-dodecanedione, 1,12-bis(2-ethylidenehydrazino)-1,12-dodecanedione, 1,12-bis(2-propylidenehydrazino)-1,12-dodecanedione, 1,12-bis[2-(1-methylpropylidene)hydrazino]-1,12-dodecanedione, 1,12-bis[2-(1-ethylpropylidene)hydrazino]-1,12-dodecanedione, 1,10-bis[2-(1-methylethylidene)hydrazino]]-1,10-decanedione, 1,10-bis(2-propylidenehydrazino)-1,10-decanedione, 1,10-bis (2-propylidenehydrazino)-1,10-decanedione, 1,10-bis[2-(1-methylpropylidene)hydrazino]-1,10-decanedione, 1,10-bis[2-(1-ethylpropylidene)hydrazino]-1,10-decanedione, 1,6-bis[2-(1-methylethylidene)hydrazino]-1,6-hexanedione, 1,6-bis(2-ethylidenehydrazino)-1,6-hexanedione, 1,6-bis(2-propylidenehydrazino)-1,6-hexanedione, 1,6-bis[2-(1-methylpropylidene)hydrazino]-1,6-hexanedione, 1,6-bis[2-(1-ethylpropylidene)hydrazino]-1,6-hexanedione, and the like.

[0026] Formula (B-3) (In formula (B-3), R ８ represents an aliphatic hydrocarbon group having 4 to 20 carbon atoms, an alicyclic hydrocarbon group having 6 to 10 carbon atoms, or a group consisting of a combination thereof. ６ and R ７ each independently represents an alicyclic hydrocarbon group having 3 to 12 carbon atoms.

[0027] In formula (B-3), R ８ is R in formula (B-2) １ The same applies to the preferred ranges. ６ and R ７each independently represents an alicyclic hydrocarbon group having 3 to 12 carbon atoms. Examples of the alicyclic hydrocarbon group having 3 to 12 carbon atoms include a cyclohexylene group. Specific examples of the compound represented by formula (B-3) above include 1,12-bis(2-cyclohexylidenehydrazino)-1,12-dodecanedione, 1,10-bis(2-cyclohexylidenehydrazino)-1,10-decanedione, and 1,6-bis(2-cyclohexylidenehydrazino)-1,6-hexanedione.

[0028] The content of component (B) in the resin composition of this embodiment is 0.005 parts by mass or more, preferably 0.01 parts by mass or more, more preferably 0.02 parts by mass or more, and 0.3 parts by mass or less, preferably 0.2 parts by mass or less, more preferably 0.15 parts by mass or less, per 100 parts by mass of the polyacetal resin (A). By ensuring that the content is equal to or greater than the lower limit, the generation of formaldehyde tends to be more effectively suppressed when the residence time is long. Furthermore, by ensuring that the content is equal to or less than the upper limit, mold contamination tends to be more effectively suppressed. The resin composition of this embodiment may contain only one type of component (B), or may contain two or more types. When two or more types are contained, the total amount preferably falls within the above range.

[0029] <(C) Urea Compound> The resin composition of the present embodiment contains a urea compound represented by formula (N), and the (C) urea compound contains a silicon-containing compound in such a proportion that the silicon atom content in the (C) urea compound is more than 0 mass % and not more than 0.007 mass %. (In formula (N), R is a hydrocarbon group having 1 to 5 carbon atoms, and n is an integer of 0 to 4. When n is 2 or more, each R may be the same or different.)

[0030] Silicon-containing compounds are sometimes used as catalysts when synthesizing urea compounds, but in this embodiment, even when such urea compounds are used, the amount of formaldehyde generated can be reduced by reducing the silicon atom content. In particular, by including a urea compound, the generation of formaldehyde can be effectively suppressed even when the polyacetal resin is retained in a molding machine for a long period of time. Furthermore, it is also possible to suppress mold contamination.

[0031] In this embodiment, the urea compound (C) contains the silicon-containing compound in a proportion such that the silicon atom content in the urea compound (C) is greater than 0% by mass and less than or equal to 0.007% by mass. The value is preferably 0.0065% by mass or less, more preferably 0.0060% by mass or less, even more preferably 0.0056% by mass or less, even more preferably 0.0050% by mass or less, and even more preferably 0.0045% by mass or less. Furthermore, the value is preferably 0.0001% by mass or more, more preferably 0.0005% by mass or more, even more preferably 0.001% by mass or more, and even more preferably 0.002% by mass or more. Setting the content below the upper limit tends to effectively suppress the amount of formaldehyde generated. Setting the content above the lower limit allows for more efficient production of the urea compound. The urea compound (C) of this embodiment may contain only one type of silicon-containing compound, or may contain two or more types. When two or more types are contained, the total amount is preferably within the above range. The content of silicon atoms in the silicon-containing compound is measured using a fluorescent X-ray analyzer manufactured by Rigaku Corp. An example of the silicon-containing compound is a catalyst used in synthesizing a urea compound.

[0032] In formula (N), R is a hydrocarbon group having 1 to 5 carbon atoms, preferably an alkyl group having 1 to 5 carbon atoms, and more preferably a methyl group or an ethyl group. In formula (N), n is an integer of 0 to 4, preferably an integer of 0 to 3, more preferably an integer of 0 to 2, even more preferably 0 or 1, and even more preferably 0.

[0033] The urea compound (C) used in this embodiment is more preferably ethylene urea.

[0034] The molecular weight of the urea compound (C) used in the present embodiment is preferably 60 or more, more preferably 86 or more, and the upper limit thereof is preferably 500 or less, more preferably 300 or less, and even more preferably 200 or less.

[0035] The resin composition of the present embodiment may or may not contain a urea compound other than the urea compound (C). Examples of the urea compound other than the urea compound (C) include urea, allantoin, and biurea.

[0036] The content of the (C) urea compound in the resin composition of this embodiment is, relative to 100 parts by mass of the polyacetal resin, 0.02 parts by mass or more, preferably 0.04 parts by mass or more, more preferably 0.05 parts by mass or more, even more preferably 0.08 parts by mass or more, even more preferably 0.10 parts by mass or more, even more preferably 0.11 parts by mass or more, and 0.3 parts by mass or less, preferably 0.18 parts by mass or less, more preferably 0.16 parts by mass or less, even more preferably 0.14 parts by mass or less, even more preferably 0.13 parts by mass or less. By setting the content at or above the lower limit, formaldehyde generation tends to be more effectively suppressed, particularly when the residence time in the molding machine is long. By setting the content at or below the upper limit, mold contamination is more effectively suppressed. Furthermore, by setting the content of the (C) urea compound to 0.18 parts by mass or less relative to 100 parts by mass of the polyacetal resin, mold deposits tend to be more effectively suppressed. The resin composition of the present embodiment may contain only one type of (C) urea compound, or may contain two or more types. When two or more types are contained, the total amount is preferably in the above range.

[0037] In the resin composition of this embodiment, the mass ratio (B) / (C) of the component (B) to the urea compound (C) is preferably 1.0 or less, more preferably 0.7 or less, even more preferably less than 0.5, still more preferably 0.45 or less, and preferably 0.1 or more, more preferably 0.3 or more, and even more preferably 0.4 or more. By setting it to the upper limit or less, the generation of formaldehyde when the residence time is long tends to be more effectively suppressed. Furthermore, by setting it to the lower limit or more, the amount of formaldehyde generated tends to be suppressed while mold contamination is also suppressed.

[0038] <Other Components> The resin composition of this embodiment may contain components other than the above components. Specific examples of other components include functional group-containing compounds (such as melamine compounds), inorganic fillers, heat stabilizers, antioxidants, weathering stabilizers, light resistance stabilizers, UV absorbers, release agents, lubricants, nucleating agents, antistatic agents, antibacterial agents, and colorants (pigments, dyes). These can be used alone or in combination of two or more. For details about UV absorbers and stabilizers, please refer to paragraphs 0038 to 0056 of JP 2020-132662 A and paragraphs 0047 to 0103 of WO 2021 / 241471 A, the contents of which are incorporated herein by reference. The resin composition of this embodiment may also be substantially free of inorganic fillers. "Substantially free" means that the content of inorganic fillers in the resin composition of this embodiment is less than 1% by mass. The resin composition of this embodiment is formulated so that the total of the polyacetal resin (A), component (B), urea compound (C), and other components blended as needed is 100% by mass. The total amount of the polyacetal resin (A), component (B), and urea compound (C) preferably accounts for 95 to 100% by mass, and more preferably 99 to 100% by mass, of the resin composition.

[0039] <Method for Producing Resin Composition> The method for producing the resin composition of this embodiment is not particularly limited, and the resin composition can be prepared by various methods conventionally known for preparing resin compositions. For example, (1) a method in which all components constituting the resin composition are mixed, fed into an extruder, and melt-kneaded to obtain a pellet-shaped composition, (2) a method in which some of the components constituting the resin composition are fed through a main feed port of an extruder and the remaining components are fed through a side feed port, and melt-kneaded to obtain a pellet-shaped composition, (3) a method in which pellets with different compositions are prepared by extrusion or the like, and the pellets are mixed to adjust to a predetermined composition, or (4) a method in which a predetermined amount of a compounding component is mixed with pellets or pulverized material of a polyacetal resin, or a predetermined amount of a compounding component is coated on the surface of pellets or pulverized material of a polyacetal resin, to obtain a predetermined resin composition, can be employed.

[0040] <Pellets and Molded Articles> This embodiment also includes pellets of the resin composition of this embodiment, and molded articles formed from the resin composition or pellets of this embodiment. The molded article of this embodiment significantly suppresses the generation of formaldehyde due to the incorporation of component (B) and urea compound (C). In particular, even when the resin has a long residence time in a molding machine, the generation of formaldehyde can be effectively suppressed. The resin composition of this embodiment can be molded by known molding methods such as injection molding, extrusion molding, compression molding, blow molding, and vacuum molding.

[0041] The resin composition and molded article of this embodiment can be suitably used in applications where a reduction in formaldehyde emissions is strongly required, such as automobile parts, electrical and electronic parts, precision machinery parts, building materials and piping parts, daily necessities, cosmetic parts, medical equipment parts, etc. More specific examples of automobile parts include interior parts such as inner handles, fuel trunk openers, seatbelt buckles, assist wraps, various switches, knobs, levers, and clips, electrical system parts such as meters and connectors, in-vehicle electrical and electronic parts such as audio equipment and car navigation equipment, parts that come into contact with metal such as window regulator carrier plates, door lock actuator parts, mirror parts, wiper motor system parts, and fuel system parts.

[0042] Examples of electrical and electronic components include components or members of devices with many metal contacts, such as audio equipment such as cassette tape recorders and CD / DVD players, video equipment such as VTRs, 8mm video cameras, and digital video cameras, and office automation equipment such as copiers, facsimiles, word processors, and computers. Specific examples of these components or members include chassis, gears, levers, cams, pulleys, and bearings. Furthermore, the present invention can also be applied to optical and magnetic media components, at least a portion of which is made of molded products, such as metal music tape cassettes, digital audio tape cassettes, 8mm video tape cassettes, digital video cassettes, floppy disk cartridges, minidisk cartridges, and DVD disk cartridges.

[0043] Furthermore, the molded article of this embodiment can be suitably used for a wide range of lifestyle-related, cosmetic-related, and medical-related parts, such as building materials and piping parts, including lighting fixtures, fittings, piping, cocks, faucets, and toilet peripheral equipment parts, fasteners, stationery, lip balm and lipstick containers, cleaning devices, water purifiers, spray nozzles, spray containers, aerosol containers, general containers, and syringe needle holders.

[0044] In particular, in the automotive field, the interior of a vehicle is often placed in a closed environment, and the interior of the vehicle may reach a considerably high temperature, so the resin composition of the present embodiment, which generates a small amount of formaldehyde, is particularly suitable for use in molded articles in such fields.

[0045] The present invention will be explained in more detail below with reference to examples. The materials, amounts used, ratios, treatment contents, treatment procedures, etc. shown in the following examples can be changed as appropriate without departing from the spirit of the present invention. Therefore, the scope of the present invention is not limited to the specific examples shown below. If the measuring instruments used in the examples are difficult to obtain due to discontinuation or the like, measurements can be made using other instruments with equivalent performance.

[0046] The raw materials shown in Table 1 were used.

[0047] Examples 1 to 10 and Comparative Examples 1 to 3 (A) Polyacetal resin, (B) component, and (C) urea compound were uniformly mixed in the proportions shown in Tables 2 to 4 (the proportions in Tables 2 to 4 are shown in parts by mass) using a Super Mixer manufactured by Kawada Manufacturing Co., Ltd., and then melt-kneaded using a twin-screw extruder (PCM-30 manufactured by Ikegai Iron Works Co., Ltd., screw diameter 30 mm) under conditions of a screw rotation speed of 120 rpm and a cylinder set temperature of 190°C. The mixture was then extruded into strands and cut with a pelletizer to produce resin compositions (pellets).

[0048] (1) Inhibitory Effect of Formaldehyde Generation The inhibitory effect of formaldehyde generation was evaluated based on the amount of formaldehyde generated, measured. The amount of formaldehyde generated was determined as follows. <Preparation of Flat Test Pieces> Using the pellets obtained in the Examples and Comparative Examples, an SE-30 manufactured by Sumitomo Heavy Industries, Ltd. was used, and the pellets were heated for 1 minute in a cylinder heated to 215°C, and then injection molded at a mold temperature of 80°C to prepare 100mm x 40mm x 2mm flat test pieces. Using the pellets obtained in the Examples and Comparative Examples, an SE-30 manufactured by Sumitomo Heavy Industries, Ltd. was used, and the pellets were heated for 20 minutes in a cylinder heated to 215°C, and then injection molded at a mold temperature of 80°C to prepare 100mm x 40mm x 2mm flat test pieces.

[0049] The pellets obtained in the examples and comparative examples were used in an SE-30 manufactured by Sumitomo Heavy Industries, Ltd., and heated for 1 minute in a cylinder heated to 230°C. Then, they were injection molded at a mold temperature of 80°C to prepare flat test pieces measuring 100 mm x 40 mm x 2 mm.

[0050] <Measurement of Formaldehyde Emission Amount> The three types of flat test specimens were left to stand for 24 hours in an atmosphere of 23°C and 50% relative humidity, and then the amount of formaldehyde emitted per 1 g of polyacetal resin (unit: μg / g-POM) was measured for the flat test specimens in accordance with the method described in the German Automotive Industry Association standard VDA275 (Automobile interior parts - Determination of formaldehyde emission amount by the revised flask method) by the following method: (i) 50 mL of distilled water was placed in a polyethylene container, and the flat test specimens were suspended in the air with the lid closed, and heated in a sealed state at 60°C for 3 hours. (ii) After leaving it at room temperature for 60 minutes, the flat test specimens were removed. (iii) The amount of formaldehyde absorbed in the distilled water in the polyethylene container was measured by the acetylacetone colorimetric method using a UV spectrometer, and the value obtained by dividing this amount of formaldehyde by the mass of POM in the flat test piece was taken as the amount of formaldehyde generated.

[0051] (2) Mold deposits The pellets obtained above were heated for 1 minute in a cylinder heated to 215°C using an SE7M manufactured by Sumitomo Heavy Industries, Ltd., and then 1000 teardrop-shaped test pieces were injection molded at a mold temperature of 40°C. After completion, the state of contamination due to white deposits that occurred on the metal mirror surface on the mold fixing side was visually evaluated. The evaluation was carried out by five experts and was determined by majority vote. A: Almost no adhesion B: Slight adhesion C: Adherence but easy to wipe off D: Large amount of adhesion but easy to wipe off E: Adherence and very difficult to remove, or difficult to remove

[0052]

[0053]

[0054]

[0055] As is clear from the above results, the generation of formaldehyde was effectively suppressed in molded articles formed from the resin composition of this embodiment, including during retention (Examples 1 to 10). Furthermore, mold deposits could be effectively suppressed by adjusting the content of the (C) urea compound. In contrast, when the content of the silicon-containing compound in the (C) urea compound was high (Comparative Example 1), when the (B) component was not included (Comparative Example 2), and when the (C) urea compound was not included (Comparative Example 3), the amount of formaldehyde generated was high after retention at 215°C or after molding at 230°C.

Claims

1. A resin composition comprising: (A) 100 parts by mass of a polyacetal resin, (B) 0.005 to 0.3 parts by mass of an aliphatic carboxylic acid hydrazide and / or an aliphatic hydrazone, and (C) 0.02 to 0.3 parts by mass of a urea compound represented by the formula (N), wherein the (C) urea compound contains a silicon-containing compound in the (C) urea compound in a proportion such that the silicon atom is more than 0% by mass and 0.007% by mass or less. (In the formula (N), R is a hydrocarbon group having 1 to 5 carbon atoms, and n is an integer of 0 to 4. When n is 2 or more, each R may be the same or different.) 2. The resin composition according to claim 1, wherein the mass ratio (B) / (C) of the (B) aliphatic carboxylic acid hydrazide and / or aliphatic hydrazone to the (C) urea compound is 1.0 or less.

3. The resin composition according to claim 1 or 2, wherein the (C) urea compound contains ethylene urea.

4. The resin composition according to claim 1 or 2, wherein the (C) urea compound contains a silicon-containing compound in a proportion such that the silicon atom is 0.002 to 0.007% by mass in the (C) urea compound.

5. The resin composition according to claim 1 or 2, wherein the (B) aliphatic carboxylic acid hydrazide and / or aliphatic hydrazone contains an aliphatic carboxylic acid hydrazide.

6. The resin composition according to claim 1 or 2, wherein the (B) aliphatic carboxylic acid hydrazide and / or aliphatic hydrazone contains at least one selected from the group consisting of adipic acid dihydrazide, azelaic acid dihydrazide, sebacic acid dihydrazide, and dodecane diacid dihydrazide.

7. The resin composition according to claim 1, wherein the mass ratio (B) / (C) of the (B) aliphatic carboxylic acid hydrazide and / or aliphatic hydrazone to the (C) urea compound is 1.0 or less, the (C) urea compound contains ethylene urea, the (C) urea compound contains a silicon-containing compound in a proportion such that the silicon atom is 0.002 to 0.007% by mass in the (C) urea compound, and the (B) aliphatic carboxylic acid hydrazide and / or aliphatic hydrazone contains at least one selected from the group consisting of adipic acid dihydrazide, azelaic acid dihydrazide, sebacic acid dihydrazide, and dodecane diacid dihydrazide.

8. Pellets of the resin composition according to claim 1, 2, or 7.

9. A molded article formed from the resin composition according to claim 1, 2, or 7.

10. A molded article formed from the pellets according to claim 8.

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