Pellet blend, masterbatch, and method for producing resin composition

Abstract

Provided are a pellet blend, and a method for producing a masterbatch and a resin composition comprising a pellet blend. This pellet blend comprises: a masterbatch (1) containing 0.5-3.0 parts by mass of a formaldehyde scavenger (B) relative to 100 parts by mass of a polyacetal resin (A) having a melt volume rate (MVR) of 5-50 cm3 / 10 min as measured under conditions of 190°C and a load of 2.16 kg in accordance with ISO1133; and a pellet (2) containing a polyacetal resin (C) having a melt volume rate (MVR) of 0.1-4 cm3 / 10 min or less as measured under conditions of 190°C and a load of 2.16 kg in accordance with ISO1133.

Description

Method for producing pellet blend, masterbatch, and resin composition

[0001] The present invention relates to a method for producing a pellet blend, a masterbatch, and a resin composition.

[0002] Polyacetal resins have high mechanical strength and rigidity, excellent oil resistance and organic solvent resistance, a well-balanced resin over a wide temperature range, and are easy to process. Therefore, polyacetal resins are widely used as a representative engineering plastic in office automation equipment, digital home appliances, automobile parts, and other industrial parts.

[0003] However, since polyacetal resins tend to generate formaldehyde, formaldehyde scavengers are blended into polyacetal resins (Patent Documents 1 and 2).

[0004] JP 2017-137386 A JP 2023-030823 A

[0005] As described above, polyacetal resins are typically blended with formaldehyde scavengers. However, when a formaldehyde scavenger is blended with a high-viscosity polyacetal resin and then melt-kneaded, significant shear heat generation occurs in the extruder. As a result, a large amount of the formaldehyde scavenger is consumed during melt-kneading. Molded articles formed from such resin compositions have the problem of insufficient formaldehyde scavenging. While increasing the blending amount of formaldehyde scavenger is an option, this approach results in mold contamination during molding. The present invention aims to solve this problem by providing a pellet blend containing a high-viscosity polyacetal resin and a formaldehyde scavenger, which has a high formaldehyde scavenging effect and is less likely to cause mold contamination, as well as a masterbatch and a method for producing a resin composition using the pellet blend.

[0006] The present inventors have conducted research to address the above-mentioned problems and have found that the problems can be solved by blending a formaldehyde scavenger with a relatively low-viscosity polyacetal resin, pelletizing the resulting mixture, and then blending the pellets with pellets containing a high-viscosity polyacetal resin. Specifically, the problems have been solved by the following means: <1> A pellet blend comprising: <1> a masterbatch (1) containing 0.5 to 3.0 parts by mass of a formaldehyde scavenger (B) per 100 parts by mass of a polyacetal resin (A) having a melt volume rate (MVR) of 5 to 50 cm3 / 10 min measured at 190°C under a load of 2.16 kg in accordance with ISO 1133; and <2> pellets (2) containing a polyacetal resin (C) having a melt volume rate (MVR) of 0.1 to 4 cm3 / 10 min measured at 190°C under a load of 2.16 kg in accordance with ISO 1133. <2> The pellet blend according to <1>, containing 3 to 25 parts by mass of the masterbatch (1) per 100 parts by mass of the pellets (2). <3> The pellet blend according to <1> or <2>, wherein the formaldehyde scavenger (B) contains at least one selected from the group consisting of hydrazide compounds, hydrazones of hydrazine compounds, guanamine compounds, and urea compounds. <4> A masterbatch containing 0.5 to 3.0 parts by mass of a formaldehyde scavenger (B) per 100 parts by mass of a polyacetal resin (A) having a melt volume rate (MVR) of 5 to 50 cm3 / 10 min measured in accordance with ISO 1133 under conditions of 190°C and a load of 2.16 kg. <5> The masterbatch according to <4>, wherein the formaldehyde scavenger (B) includes at least one selected from the group consisting of hydrazide compounds, hydrazones of hydrazine compounds, guanamine compounds, and urea compounds.<6> A method for producing a resin composition, comprising melt-kneading a polyacetal resin (C) having a melt volume rate (MVR) of 0.1 to 4 cm3 / 10 min or less, measured in accordance with ISO 1133 at 190°C under a load of 2.16 kg, with a masterbatch (1), wherein the masterbatch (1) contains 0.5 to 3.0 parts by mass of a formaldehyde scavenger (B) per 100 parts by mass of a polyacetal resin (A) having a melt volume rate (MVR) of 5 to 50 cm3 / 10 min, measured in accordance with ISO 1133 at 190°C under a load of 2.16 kg.

[0007] The present invention makes it possible to provide a pellet blend containing a high-viscosity polyacetal resin and a formaldehyde scavenger, which has a high formaldehyde scavenging effect and is less likely to cause mold contamination, a masterbatch, and a method for producing a resin composition.

[0008] 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 only this embodiment. Note that in this specification, the word "to" is used to mean that the numerical values ​​written before and after it are included as lower and upper limits. In this specification, various physical property values ​​and characteristic values ​​are those at 23°C unless otherwise specified. When the measurement methods etc. described in the standards shown in this specification vary depending on the fiscal year, they are based on the standards as of January 1, 2023, unless otherwise specified.

[0009] The pellet blend of this embodiment is characterized by comprising a masterbatch (1) containing 0.5 to 3.0 parts by mass of a formaldehyde scavenger (B) per 100 parts by mass of a polyacetal resin (A) having a melt volume rate (MVR) of 5 to 50 cm3 / 10 min measured at 190°C under a load of 2.16 kg in accordance with ISO 1133, and pellets (2) containing a polyacetal resin (C) having a melt volume rate (MVR) of 0.1 to 4 cm3 / 10 min or less measured at 190°C under a load of 2.16 kg in accordance with ISO 1133. This configuration makes it possible to obtain a pellet blend containing a high-viscosity polyacetal resin and a formaldehyde scavenger, which has a high formaldehyde scavenging effect and is less likely to cause mold contamination.

[0010] Conventionally, when a formaldehyde scavenger is blended with a polyacetal resin, the two are compounded directly in an extruder. During compounding, the extruder temperature for the polyacetal resin is typically set to around 200°C. However, it has been found that even when a high-viscosity polyacetal resin is melt-kneaded at around 200°C, significant shear heat generation occurs in the extruder, resulting in the resin temperature being significantly higher than the extruder temperature. This elevated resin temperature results in a large amount of formaldehyde scavenger being consumed in the extruder. Under these circumstances, in this embodiment, a formaldehyde scavenger (B) is blended in advance with a polyacetal resin (A) having an MVR of 5 to 50 cm³ / 10 min, and the resulting mixture is melt-kneaded to form a masterbatch, which is then blended with pellets of a polyacetal resin (C) having an MVR of 0.1 to 4 cm³ / 10 min or less. By adopting this method, the formaldehyde scavenger (B) can be blended into the polyacetal resin without excessive shear heat being generated during compounding (pellet production). As a result, it has been discovered that the heating step for the formaldehyde scavenger (B) can be limited to the molding step, thereby avoiding unnecessary consumption of the formaldehyde scavenger (B). As a result, despite the use of a high-viscosity polyacetal resin and the blending of a formaldehyde scavenger, a pellet blend was obtained in which the molded product had a sufficiently high formaldehyde scavenging effect and mold contamination was suppressed. The details of this embodiment are described below.

[0011] <Masterbatch (1)> The masterbatch (1) of this embodiment contains 0.5 to 3.0 parts by mass of a formaldehyde scavenger (B) based on 100 parts by mass of a polyacetal resin (A) having a melt volume rate (MVR) of 5 to 50 cm / 10 min measured at 190°C under a load of 2.16 kg in accordance with ISO 1133. In such a masterbatch (1), excessive shear heating does not occur during melt-kneading to form the masterbatch, and therefore consumption of the formaldehyde scavenger (B) during melt-kneading can be minimized.

[0012] <<Polyacetal Resin (A)>> The masterbatch (1) contains a polyacetal resin (A) having a melt volume rate (MVR) of 5 to 50 cm3 / 10 min measured in accordance with ISO 1133 at 190°C under a load of 2.16 kg.

[0013] The melt volume rate (MVR) of the polyacetal resin (A), measured in accordance with ISO 1133 at 190°C under a load of 2.16 kg, is preferably 7 cm / 10 min or more, more preferably 10 cm / 10 min or more, even more preferably 15 cm / 10 min or more, even more preferably 20 cm / 10 min or more, and even more preferably 25 cm / 10 min or more, and is preferably 45 cm / 10 min or less, more preferably 40 cm / 10 min or less, even more preferably 35 cm / 10 min or less, and even more preferably 30 cm / 10 min or less. By setting the MVR at or above the lower limit, shear heat generation during melt-kneading can be suppressed, and consumption of formaldehyde scavenger can be reduced, which tends to further improve the formaldehyde scavenging effect. Meanwhile, by setting the MVR at or below the upper limit, continuous productivity tends to be improved by preventing strand breakage during masterbatch production. The masterbatch (1) of the present embodiment may contain only one type of polyacetal resin (A) or may contain two or more types. When two or more types are contained, the MVR of the mixture is preferably in the above range.

[0014] The polyacetal resin (A) is not particularly limited in terms of type, etc., as long as it satisfies the above MVR, and 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.

[0015] In the polyacetal resin (A), the proportion of oxyalkylene groups having 2 or more carbon atoms in the total number of moles of oxymethylene groups and oxyalkylene groups having 2 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 2 or more, but is preferably 6 or less, and more preferably 4 or less.

[0016] To produce the polyacetal resin (A), trioxane is typically used as the main raw material. Furthermore, to introduce oxyalkylene groups having 2 to 6 carbon atoms into the polyacetal resin (A), 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. To introduce oxyethylene groups into the polyacetal resin (A), for example, 1,3-dioxolane can be used; to introduce oxypropylene groups, 1,3-dioxane can be used; and to introduce oxybutylene groups, 1,3-dioxepane can be used.

[0017] In addition, it is preferable that the polyacetal resin (A) has a small amount of hemiformal terminal groups, formyl terminal groups, and terminal groups unstable to heat, acid, or base. Here, the hemiformal terminal groups are represented by —OCHOH, and the formyl terminal groups are represented by —CHO.

[0018] The content of polyacetal resin (A) in masterbatch (1) of this embodiment is preferably 90% by mass or more, more preferably 95% by mass or more, even more preferably 97% by mass or more, and even more preferably 98% by mass or more. The upper limit of the content of polyacetal resin (A) is the amount at which all components other than formaldehyde scavenger (B) are polyacetal resin (A). Masterbatch (1) of this embodiment may contain only one type of polyacetal resin (A), or may contain two or more types. When two or more types are contained, the total amount is preferably within the above range.

[0019] <<Formaldehyde Scavenger (B)>> The masterbatch (1) of this embodiment contains 0.5 to 3.0 parts by mass of the formaldehyde scavenger (B) relative to 100 parts by mass of the polyacetal resin (A). The type and other characteristics of the formaldehyde scavenger (B) used in this embodiment are not particularly limited, and a wide variety of compounds used as formaldehyde scavengers for polyacetal resins can be used. The formaldehyde scavenger (B) is preferably a compound containing a nitrogen atom, more preferably at least one selected from the group consisting of hydrazide compounds, hydrazones of hydrazine compounds, guanamine compounds, and urea compounds, and even more preferably at least one selected from the group consisting of hydrazide compounds and urea compounds.

[0020] The hydrazide compound is preferably a hydrazide compound having two or more hydrazide groups. Examples of the dihydrazide compound include aliphatic dihydrazide compounds and aromatic dihydrazide compounds.

[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, maleic acid dihydrazide, fumaric acid dihydrazide, and 7,11-octadecadiene-1,18-dicarbohydrazide.

[0022] Examples of aromatic dihydrazide compounds include isophthalic acid dihydrazide, terephthalic acid dihydrazide, 1,5-naphthalenedicarbohydrazide, 1,8-naphthalenedicarbohydrazide, 2,6-naphthalenedicarbohydrazide, 4,4'-oxybisbenzenesulfonylhydrazide, and 1,5-diphenylcarbonohydrazide.

[0023] The hydrazide compound used in this embodiment is preferably represented by the following formula (1): (In formula (1), R11 represents an aliphatic hydrocarbon group having 2 to 18 carbon atoms, an alicyclic hydrocarbon group having 6 to 10 carbon atoms, or an aromatic hydrocarbon group having 6 to 10 carbon atoms; R12 to R15 each independently represent a hydrogen atom or an alkyl group having 1 to 6 carbon atoms; R12 and R13, and R14 and R15 may be bonded to each other to form a ring.)

[0024] In formula (1), R11 represents an aliphatic hydrocarbon group having 2 to 18 carbon atoms, an alicyclic hydrocarbon group having 6 to 10 carbon atoms, or an aromatic hydrocarbon group having 6 to 10 carbon atoms, 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 16 or fewer carbon atoms, more preferably 14 or fewer carbon atoms, and even more preferably 12 or fewer carbon atoms. 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.

[0025] 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.

[0026] Examples of aromatic hydrocarbon groups include arylene groups such as phenylene and naphthylene. Substituents may be bonded to at least some of the carbon atoms of the aromatic hydrocarbon group. Examples of such substituents include halogen groups, nitro groups, and alkyl groups having 1 to 20 carbon atoms.

[0027] In formula (1), R12 to R15 are each independently preferably a hydrogen atom, a methyl group or an ethyl group, more preferably a hydrogen atom.

[0028] Specific examples of the compound represented by formula (1) include adipic acid dihydrazide and 1,12-dodecanedioic acid dihydrazide.

[0029] The hydrazone compound of the hydrazine compound is preferably at least one hydrazine compound selected from the group consisting of compounds represented by the following formula (2) and compounds represented by the following formula (3): Formula (2): (In formula (2), R1 represents an aliphatic hydrocarbon group having 4 to 20 carbon atoms, an alicyclic hydrocarbon group having 6 to 10 carbon atoms, or an aromatic hydrocarbon group having 6 to 10 carbon atoms. R2 to R5 each independently represent a hydrogen atom or an alkyl group having 1 or 2 carbon atoms, at least one of R2 and R3 represents an alkyl group having 1 or 2 carbon atoms, and at least one of R4 and R5 represents an alkyl group having 1 or 2 carbon atoms.)

[0030] In formula (2), R1 represents an aliphatic hydrocarbon group having 4 to 20 carbon atoms, an alicyclic hydrocarbon group having 6 to 10 carbon atoms, or an aromatic hydrocarbon group having 6 to 10 carbon atoms. 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, 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, more effectively suppressing the generation of formaldehyde. Furthermore, mold contamination during molding can be more fully suppressed. The alicyclic hydrocarbon group may be saturated or unsaturated. Examples of the alicyclic hydrocarbon group include cycloalkylene groups having 6 to 10 carbon atoms. Examples of the cycloalkylene group include cyclohexylene groups. Examples of the aromatic hydrocarbon group include arylene groups such as phenylene and naphthylene groups. Substituents may be bonded to at least some of the carbon atoms of the aromatic hydrocarbon group. Examples of such substituents include halogen groups, nitro groups, and alkyl groups having 1 to 20 carbon atoms. In formula (2), R2 to R5 each independently represent a hydrogen atom or an alkyl group having 1 or 2 carbon atoms, at least one of R2 and R3 represents an alkyl group having 1 or 2 carbon atoms, and at least one of R4 and R5 represents an alkyl group having 1 or 2 carbon atoms. In formula (2), when R2 and R4 are ethyl groups, it is preferable that R3 and R5 are hydrogen atoms, and when R2 and R4 are methyl groups, it is preferable that R3 and R5 are hydrogen atoms or methyl groups. In this case, the reactivity of the hydrazone of the hydrazine compound with formaldehyde is increased, and the generation of formaldehyde is more effectively suppressed.

[0031] Specific examples of the compound represented by the formula (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( 1,6-bis[2-(1-methylpropylidene)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-methylpropylidene)hydrazino]-1,6-hexanedione, 1,6-bis[2-(1-ethylpropylidene)hydrazino]-1,6-hexanedione, and 1,6-bis[2-(1-ethylpropylidene)hydrazino]-1,6-hexanedione.

[0032] Formula (3) (In formula (3), R8 represents an aliphatic hydrocarbon group having 4 to 20 carbon atoms, an alicyclic hydrocarbon group having 6 to 10 carbon atoms, or an aromatic hydrocarbon group having 6 to 10 carbon atoms. R6 and R7 each independently represent an alicyclic hydrocarbon group having 3 to 12 carbon atoms.)

[0033] In formula (3), R8 is the same as R1, and the preferred range is also the same. R6 and R7 each independently represent 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 (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.

[0034] Examples of the guanamine compound include benzoguanamine and N-methylol benzoguanamine.

[0035] The urea compound refers to a compound having a -(HN)C(=O) structure, and the type thereof is not particularly limited. Examples of the urea compound include urea, ethylene urea, allantoin, biurea, dimethylethylene urea, propylene urea, and tetrabutyl urea, and preferably contains ethylene urea and / or allantoin, more preferably contains ethylene urea.

[0036] The molecular weight of the formaldehyde scavenger (B) used in this embodiment is preferably 60 or more, more preferably 86 or more. The upper limit is preferably 1,000 or less, more preferably 800 or less, and even more preferably 500 or less.

[0037] The content of the masterbatch (1) of this embodiment is 0.5 parts by mass or more, more preferably 1 part by mass or more, and preferably 3.0 parts by mass or less, and 2.5 parts by mass or less, relative to 100 parts by mass of the polyacetal resin (A). By making the content equal to or greater than the lower limit, the generation of formaldehyde, particularly the generation of formaldehyde when the residence time in the molding machine is long, tends to be more effectively suppressed. By making the content equal to or less than the upper limit, the effect of suppressing mold contamination is more effectively exhibited. The masterbatch (1) of this embodiment may contain only one type of formaldehyde scavenger (B), or may contain two or more types. When two or more types are contained, the total amount is preferably within the above range.

[0038] The masterbatch (1) of this embodiment may or may not contain components other than the polyacetal resin (A) and the formaldehyde scavenger (B). Examples of other components include functional group-containing compounds (e.g., melamine compounds), heat stabilizers, antioxidants, weathering stabilizers, light stabilizers, UV absorbers, release agents, lubricants, nucleating agents, antistatic agents, antibacterial agents, and colorants (pigments, dyes). These may be used alone or in combination of two or more. The content of these other components is preferably less than 5% by mass of the masterbatch (1), more preferably less than 3% by mass, even more preferably less than 1% by mass, even more preferably less than 0.5% by mass, and even more preferably less than 0.1% by mass. The lower limit is 0% by mass.

[0039] <Pellet (2)> Pellet (2) contains a polyacetal resin (C) having a melt volume rate (MVR) of 0.1 to 4 cm³ / 10 min or less, measured in accordance with ISO 1133 at 190°C under a load of 2.16 kg. In this embodiment, since the formaldehyde scavenger (B) can be pre-masterbatched using a low-viscosity polyacetal resin (A), a high-viscosity polyacetal resin (C) can be preferably used as a constituent component of the pellet blend. The MVR is preferably 3.5 cm³ / 10 min or less, and more preferably 0.5 cm³ / 10 min or more, more preferably 1 cm³ / 10 min or more, even more preferably 1.5 cm³ / 10 min or more, even more preferably 2 cm³ / 10 min or more, and even more preferably 2.5 cm³ / 10 min or more. By setting the polyacetal resin (C) at or below the upper limit, the formaldehyde capture effect generated during molding of high-viscosity polyacetal, which cannot be achieved with ordinary compounds, tends to be further improved. Furthermore, by setting the polyacetal resin (C) at or above the lower limit, the formaldehyde capture effect by this method tends to be further improved within the range that allows molding. The pellets (2) in this embodiment may contain only one type of polyacetal resin (C) or two or more types. When two or more types are contained, it is preferable that the MVR of the mixture be within the above range.

[0040] The polyacetal resin (C) is not particularly limited in type, etc., as long as it satisfies the above MVR, and 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.

[0041] In the polyacetal resin (C), the proportion of oxyalkylene groups having 2 or more carbon atoms in the total number of moles of oxymethylene groups and oxyalkylene groups having 2 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 2 or more, but is preferably 6 or less, and more preferably 4 or less.

[0042] To produce the polyacetal resin (C), trioxane is typically used as the main raw material. Furthermore, to introduce oxyalkylene groups having 2 to 6 carbon atoms into the polyacetal resin (C), 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. To introduce oxyethylene groups into the polyacetal resin (C), for example, 1,3-dioxolane can be used; to introduce oxypropylene groups, 1,3-dioxane can be used; and to introduce oxybutylene groups, 1,3-dioxepane can be used.

[0043] In addition, it is preferable that the polyacetal resin (C) has a small amount of hemiformal terminal groups, formyl terminal groups, and terminal groups unstable to heat, acid, or base. Here, the hemiformal terminal groups are represented by —OCHOH, and the formyl terminal groups are represented by —CHO.

[0044] The content of polyacetal resin (C) in pellet (2) in this embodiment is preferably 90% by mass or more, more preferably 95% by mass or more, even more preferably 97% by mass or more, and even more preferably 99% by mass or more, and may be 100% by mass or less. Pellets (2) in this embodiment may contain only one type of polyacetal resin (C) or may contain two or more types. When two or more types are contained, the total amount is preferably in the above range.

[0045] The pellets (2) in this embodiment may or may not contain components other than the polyacetal resin (C). Examples of other components include functional group-containing compounds (e.g., melamine compounds), heat stabilizers, antioxidants, weathering stabilizers, light resistance stabilizers, UV absorbers, release agents, lubricants, nucleating agents, antistatic agents, antibacterial agents, and colorants (pigments, dyes). These may be used alone or in combination of two or more. The content of these other components is preferably less than 5% by mass of the pellets (2), more preferably less than 3% by mass, even more preferably less than 1% by mass, even more preferably less than 0.5% by mass, and even more preferably less than 0.1% by mass. The lower limit is 0% by mass. The pellets (2) in this embodiment may contain, but preferably substantially do not contain, a formaldehyde scavenger (B). The term "substantially free" in this embodiment means that the content of the formaldehyde scavenger (B) in the pellets (2) is preferably less than 0.5% by mass, more preferably less than 0.3% by mass, even more preferably less than 0.1% by mass, still more preferably less than 0.05% by mass, even more preferably less than 0.01% by mass, and particularly preferably less than 0.001% by mass. The lower limit is 0% by mass.

[0046] <Blending of Pellet Blend> The pellet blend of this embodiment contains 3 to 25 parts by mass of masterbatch (1) per 100 parts by mass of the pellets (2). The content of masterbatch (1) in the pellet blend of this embodiment is preferably 4 parts by mass or more, more preferably 6 parts by mass or more, even more preferably 8 parts by mass or more, even more preferably 11 parts by mass or more, even more preferably 15 parts by mass or more, and preferably 22 parts by mass or less, per 100 parts by mass of the pellets (2). By setting the content at or above the lower limit, the formaldehyde scavenging effect of the masterbatch can be exerted. On the other hand, by setting the content at or below the upper limit, the formaldehyde scavenging effect tends to be further improved while suppressing mold contamination. The pellet blend of this embodiment may contain only one type of masterbatch (1) and / or pellets (2), or may contain two or more types. When the pellet blend of this embodiment contains two or more types of masterbatch (1) and / or pellets (2), the total amount is preferably within the above range. The pellet blend of this embodiment can usually be produced by dry blending the masterbatch (1) and the pellets (2).

[0047] The pellet blend of this embodiment may further contain a second masterbatch. Examples of the second masterbatch include a masterbatch of a resin additive other than the formaldehyde scavenger, such as a pigment or a flame retardant. The pellet blend of this embodiment may also consist essentially of only the masterbatch (1) and the pellets (2). "Substantially" means, for example, that the total amount of the masterbatch (1) and the pellets (2) in the pellet blend is 90% by mass or more of the total amount of the pellet blend, preferably 95% by mass or more, more preferably 97% by mass or more, and even more preferably 99% by mass or more. The upper limit is 100% by mass.

[0048] <Method for Producing Resin Composition> The method for producing a resin composition according to this embodiment includes melt-kneading a polyacetal resin (C) having a melt volume rate (MVR) of 0.1 to 4 cm3 / 10 min or less, measured in accordance with ISO 1133 at 190°C under a load of 2.16 kg, with a masterbatch (1), wherein the masterbatch (1) contains 0.5 to 3.0 parts by mass of a formaldehyde scavenger (B) per 100 parts by mass of a polyacetal resin (A) having a melt volume rate (MVR) of 5 to 50 cm3 / 10 min, measured in accordance with ISO 1133 at 190°C under a load of 2.16 kg. The masterbatch (1) is synonymous with the masterbatch (1) described above. The polyacetal resin (C) is exemplified by the pellets (2) described above, and the preferred ranges are also similar. More specifically, examples of the resin composition include a method in which the masterbatch (1) and the polyacetal resin (C) are fed into an extruder and melt-kneaded to obtain a pellet-shaped composition, and a method in which the masterbatch (1) and the polyacetal resin (C) are molded as they are. The resin composition of this embodiment includes pellets, molded articles molded by injection molding, etc.

[0049] <Molded Article> Next, a molded article formed from the pellet blend of this embodiment or the resin composition will be described. The molded article of this embodiment significantly reduces the generation of formaldehyde. 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.

[0050] The pellet blend, masterbatch, 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, on-board 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, and mechanical parts such as door lock actuator parts, mirror parts, wiper motor system parts, and fuel system parts.

[0051] 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.

[0052] 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.

[0053] 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.

[0054] 1. Raw Materials (A) Polyacetal Resin Polyacetal resin (MVR: 9 cm3 / 10 min): Iupital F20-05, manufactured by Global Polyacetal Corporation Polyacetal resin (MVR: 27 cm3 / 10 min): Iupital F30-05, manufactured by Global Polyacetal Corporation Polyacetal resin (MVR: 3 cm3 / 10 min): Iupital F10-EW, manufactured by Global Polyacetal Corporation The above MVR was measured in accordance with ISO 1133 under conditions of 190°C and a load of 2.16 kg. The unit is cm3 / 10 min.

[0055] (B) Formaldehyde Scavenger Adipic acid dihydrazide: manufactured by Nippon Finechem Co., Ltd., product number: ADH 1,12-dodecanedioic acid dihydrazide: manufactured by Nippon Finechem Co., Ltd., product number: N-12 Ethylene urea: manufactured by HUBEI KANG ZHUANG ENVIRONMENT TECHNOLOGY CO., LTD., 2-imidazolidinone

[0056] 2. Production of Masterbatches (MB-1 to MB-5) The polyacetal resin and formaldehyde scavenger were uniformly mixed using a Super Mixer manufactured by Kawada Manufacturing Co., Ltd. in the blending ratios shown in Table 1 (all values ​​in Table 1 are shown in parts by mass), and then the mixture was 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, and then extruded into strands and cut with a pelletizer to produce masterbatches MB-1 to MB-5.

[0057] Examples 1 to 8, Comparative Examples 1 to 5 Polyacetal resin (pellets) and the masterbatches (MB-1 to MB-5) obtained above, or formaldehyde scavengers that were not masterbatched, were uniformly mixed using a Super Mixer manufactured by Kawada Manufacturing Co., Ltd. in the blending ratios shown in Table 2 or Table 3 (Tables 2 and 3 are shown in parts by mass), 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 pellets (resin compositions).

[0058] <Measurement of Formaldehyde Generation Amount> The pellets obtained above were heated for 1 minute in a cylinder heated to 215°C using an SE-30 manufactured by Sumitomo Heavy Industries, Ltd., and then injection molded at a mold temperature of 80°C to prepare flat test pieces measuring 100 mm x 40 mm x 2 mm.

[0059] The flat test specimens were left to stand for 24 hours in an atmosphere of 23°C and 50% relative humidity. The amount of formaldehyde generated per 1 g of polyacetal resin (unit: μg / g-POM) was then measured using the following method, in accordance with the method described in German Automotive Industry Standard VDA275 (Automotive Interior Parts - Determination of Formaldehyde Emission by the Revised Flask Method). (i) 50 mL of distilled water was placed in a polyethylene container, and the flat test specimen was suspended in the air with the lid closed. The container was then heated in a sealed state at 60°C for 3 hours. (ii) After leaving the container at room temperature for 60 minutes, the flat test specimen was removed. (iii) The amount of formaldehyde absorbed in the distilled water in the polyethylene container was measured using a UV spectrometer by the acetylacetone colorimetric method. The amount of formaldehyde thus absorbed was divided by the mass of POM in the flat test specimen, and the resulting value was used as the amount of formaldehyde generated.

[0060] <Mold Contamination> Mold contamination was evaluated as follows. First, the pellets obtained above were continuously molded for 500 shots using a Minimat M8 / 7A molding machine manufactured by Sumitomo Heavy Industries, Ltd., using a teardrop-shaped mold at a molding temperature of 200°C and a mold temperature of 40°C. After molding was completed, the condition of the inner wall surface of the mold was observed with the naked eye. The criteria for the mold contamination suppression effect were as follows. Five experts also observed with the naked eye and judged by majority vote. A: No matter attached to the mold, good mold contamination suppression effect B: Other than the above A, for example, matter attached to the mold, poor mold contamination suppression effect

[0061]

[0062]

[0063] As is clear from the above results, the pellet blend of this embodiment had a high formaldehyde trapping effect and also caused little mold contamination (Examples 1 to 8). In contrast, when a masterbatch was made using a high-viscosity polyacetal resin (Comparative Example 1), the amount of formaldehyde generated was large, at a level comparable to that when no formaldehyde scavenger was blended (Comparative Example 2). Furthermore, when the formaldehyde scavenger was blended directly into the high-viscosity polyacetal resin without being made into a masterbatch (Comparative Examples 3 and 4), formaldehyde could not be trapped. On the other hand, when the content of the formaldehyde scavenger was increased in Comparative Examples 3 and 4 (Comparative Example 5), formaldehyde generation was suppressed, but mold contamination was significant.

Claims

1. A pellet blend comprising: a master batch (1) containing 100 parts by mass of a polyacetal resin (A) having a melt volume rate (MVR) of 5 to 50 cm3 / 10 min measured at 190°C under a load of 2.16 kg in accordance with ISO 1133, and 0.5 to 3.0 parts by mass of a formaldehyde scavenger (B); and pellets (2) containing a polyacetal resin (C) having a melt volume rate (MVR) of 0.1 to 4 cm3 / 10 min or less measured at 190°C under a load of 2.16 kg in accordance with ISO 1133.

2. The pellet blend according to claim 1, comprising 3 to 25 parts by mass of the master batch (1) per 100 parts by mass of the pellets (2).

3. The pellet blend according to claim 1 or 2, wherein the formaldehyde scavenger (B) comprises at least one member selected from the group consisting of hydrazide compounds, hydrazones of hydrazine compounds, guanamine compounds, and urea compounds.

4. A master batch comprising 100 parts by mass of a polyacetal resin (A) having a melt volume rate (MVR) of 5 to 50 cm3 / 10 min measured at 190°C under a load of 2.16 kg in accordance with ISO 1133, and 0.5 to 3.0 parts by mass of a formaldehyde scavenger (B).

5. The master batch according to claim 4, wherein the formaldehyde scavenger (B) comprises at least one member selected from the group consisting of hydrazide compounds, hydrazones of hydrazine compounds, guanamine compounds, and urea compounds.

6. A method for producing a resin composition, comprising melt-kneading a polyacetal resin (C) having a melt volume rate (MVR) of 0.1 to 4 cm3 / 10 min or less, measured in accordance with ISO 1133 at 190°C under a load of 2.16 kg, with a masterbatch (1), wherein the masterbatch (1) contains 0.5 to 3.0 parts by mass of a formaldehyde scavenger (B) per 100 parts by mass of a polyacetal resin (A) having a melt volume rate (MVR) of 5 to 50 cm3 / 10 min, measured in accordance with ISO 1133 at 190°C under a load of 2.16 kg.

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