JP7793377B2 - Polyacetal resin composition - Google Patents

Description

The present invention relates to a polyacetal resin composition.

Polyacetal resin is a crystalline resin that has excellent rigidity, strength, toughness, sliding properties, and creep resistance, and has therefore traditionally been used in a wide range of applications, including as a material for mechanical components such as automotive parts, electrical and electronic parts, and industrial parts.

In recent years, there has been an increasing demand for smaller, thinner, and more precise polyacetal resin molded products. To meet these demands, molding methods and molding conditions that subject the products to more heat than before are becoming more common.
Examples of such molding methods include molding using a pin gate mold and high-cycle molding. In these molding methods, the shear rate is increased, and the screw rotation and molding temperature are increased in order to shorten the plasticization time, so that the polyacetal resin is subjected to a higher thermal history than in ordinary molding methods.

Furthermore, even in general molding methods, when molding defects such as flow marks, weld lines, and jetting occur, they are often addressed by raising the resin temperature, which also results in high thermal history. Furthermore, if a hot runner is used in the mold, partial retention of the resin occurs, further increasing the resin temperature and potentially causing decomposition of the resin.
When a polyacetal resin is molded using a molding method and molding conditions that involve various thermal histories as described above, adding a weather stabilizer to the resin to improve its weather resistance has the problem of making it difficult to achieve a good balance of properties in relation to thermal stability. That is, when a large amount of weather stabilizer is added with an emphasis on weather resistance stability, the thermal stability deteriorates, and the resin is more likely to release volatile organic compounds (VOCs) including formaldehyde.

To solve these problems that occur when molding polyacetal resins, for example, Patent Document 1 discloses that by adding specific amounts of an aliphatic carboxylic acid hydrazide, a hydantoin compound having two hydrazinocarbonylalkyl groups, and an alkaline earth metal salt of an aliphatic carboxylic acid to a polyacetal polymer, the generation of formaldehyde from molded articles can be suppressed to extremely low levels, and a polyacetal resin composition can be obtained that stably suppresses mold deposits during molding.

Furthermore, Patent Document 2 discloses that by adjusting the total amount of an aliphatic carboxylic acid hydrazide and a hydantoin compound having two hydrazinocarbonyl alkyl groups to a specific amount relative to a polyacetal polymer, it is possible to suppress the generation of formaldehyde from molded articles to an extremely low level and to stably suppress mold deposits during molding.

International Publication No. 2020/129663 Japanese Patent Application Laid-Open No. 2020-100713

However, both of the technologies described in Patent Documents 1 and 2 leave room for improvement in terms of discoloration caused by retention when the polyacetal resin composition is retained in the cylinder of a molding machine during molding. There is also room for improvement in extrusion characteristics and weather resistance stability during molding.

In light of the above circumstances, the present invention aims to provide a polyacetal resin composition that has excellent extrusion properties and weather resistance stability, and that exhibits good retention discoloration during molding processing.

As a result of extensive research into resolving the above-mentioned problems, the inventors discovered that a polyacetal resin composition containing a polyacetal resin and at least two or more fatty acid metal salts can solve the above-mentioned problems, leading to the completion of the present invention.

That is, the present invention is as follows.
[1]
(A) a polyacetal resin; and (B) a fatty acid metal salt having an alkyl group having 5 to 30 carbon atoms,
The (B) fatty acid metal salt having an alkyl group having 5 to 30 carbon atoms includes (B1) a fatty acid metal salt represented by (RCOO) ₂ M (wherein M is a metal salt and R is composed only of carbon and hydrogen), and (B2) a fatty acid metal salt represented by (R'COO) ₂ M (wherein M is a metal salt and R' is composed of carbon, hydrogen and other elements) which is different from the (B1),
the (B2) fatty acid metal salt is a fatty acid metal salt having a hydroxyl group,
further containing (C) a light stabilizer,
the mass ratio of the fatty acid metal salt having a hydroxyl group to the light stabilizer (C) is 1:1 to 1:75 ;
A polyacetal resin composition comprising:
[2]
The polyacetal resin composition according to [1], wherein the alkyl group has 8 or more carbon atoms.
[3]
The polyacetal resin composition according to [1] or [2], wherein the total amount of the fatty acid metal salt (B) is 0.01 parts by mass or more and 0.35 parts by mass or less per 100 parts by mass of the polyacetal resin (A).
[4]
The polyacetal resin composition according to any one of [1] to [3] , comprising 0.005 parts by mass or more and 0.50 parts by mass or less of the (B2) fatty acid metal salt having a hydroxyl group per 100 parts by mass of the (A) polyacetal resin.
[5]
The polyacetal resin composition according to any one of [1] to [4] , comprising 0.05 parts by mass or more and 1.50 parts by mass or less of a light stabilizer (C) relative to 100 parts by mass of the polyacetal resin (A).
[6]
The polyacetal resin composition according to any one of [1] to [5] , wherein the (C) light stabilizer is a hindered amine-based light stabilizer having a weight-average molecular weight of 1,000 or more.
[7]
The polyacetal resin composition according to any one of [1] to [6] , comprising 0.01 parts by mass or more and 1.00 parts by mass or less of a formaldehyde scavenger (D) relative to 100 parts by mass of the polyacetal resin (A).

The present invention makes it possible to provide a polyacetal resin composition that has excellent extrusion properties and weather resistance stability, and that exhibits good discoloration resistance during molding retention.

The following describes in detail the mode for carrying out the present invention (hereinafter referred to as the "present embodiment"). Note that the present invention is not limited to the following embodiment, and can be implemented in various modifications within the scope of its gist.

(Polyacetal resin composition)
The polyacetal resin composition of this embodiment includes (A) a polyacetal resin and (B) a fatty acid metal salt having an alkyl group of 5 to 30 carbon atoms, wherein the (B) fatty acid metal salt having an alkyl group of 5 to 30 carbon atoms includes (B1) a fatty acid metal salt represented by (RCOO) ₂ M (wherein M is a metal salt and R is composed only of carbon and hydrogen), and (B2) a fatty acid metal salt represented by (R'COO) ₂ M (wherein M is a metal salt and R' is composed of carbon, hydrogen, and other elements) that is different from the (B1) fatty acid metal salt.

This embodiment will be described in detail below. First, the components that make up the polyacetal resin composition of this embodiment will be described.

-(A) Polyacetal resin-
The polyacetal resin (A) used in the present invention is not particularly limited, but examples thereof include polyacetal homopolymers and polyacetal copolymers.

The polyacetal homopolymer is not particularly limited, but a typical example is one consisting essentially of oxymethylene units, obtained by homopolymerizing formaldehyde monomer or a cyclic oligomer of formaldehyde, such as its trimer (trioxane) or tetramer (tetraoxane). Additionally, polyacetal homopolymers can also be used that contain block components obtained by polymerizing formaldehyde monomer or a cyclic oligomer of formaldehyde in the presence of a compound having functional groups such as hydroxyl groups at both or one end, such as polyalkylene glycol.

The polyacetal copolymer is not particularly limited, but a representative example is one obtained by copolymerizing formaldehyde monomer or a cyclic oligomer of formaldehyde, such as its trimer (trioxane) or tetramer (tetraoxane), with a cyclic ether and/or cyclic formal, such as ethylene oxide, propylene oxide, epichlorohydrin, glycols such as 1,3-dioxolane and 1,4-butanediol formal, or a cyclic formal of diglycol. Additionally, polyacetal copolymers containing block components obtained by copolymerizing formaldehyde monomer or a cyclic oligomer of formaldehyde with a cyclic ether and/or cyclic formal in the presence of a compound having functional groups such as hydroxyl groups at both or one end, such as hydrogenated polybutadiene glycol, can also be used. Furthermore, polyacetal copolymers that can be used include, for example, branched polyacetal copolymers obtained by copolymerizing monofunctional glycidyl ethers, and those with crosslinked structures obtained by copolymerizing polyfunctional glycidyl ethers.

In this embodiment, the polyacetal resin (A) may be either a polyacetal homopolymer or a polyacetal copolymer, and may be used alone or in combination of two or more types; there is no particular limitation. The polyacetal resin (A) is preferably a polyacetal copolymer.

When the (A) polyacetal resin contains the above-mentioned polyacetal copolymer, it is preferable, although not particularly limited, to use trioxane, a formaldehyde trimer, in the copolymerization of the polyacetal copolymer. Furthermore, in such cases, the comonomer (e.g., 1,3-dioxolane) used in the polyacetal copolymer is generally used in an amount of 0.1 to 60 mol %, preferably 0.1 to 20 mol %, and more preferably 0.13 to 10 mol %, per 1 mol of trioxane.

The melting point of the polyacetal copolymer is preferably 162°C to 173°C, more preferably 167°C to 173°C, and even more preferably 167°C to 171°C. Polyacetal copolymers with a melting point of 167°C to 171°C can be obtained by using approximately 1.3 to 3.5 mol% of comonomer per 1 mol of trioxane.

As a polymerization catalyst for the polymerization of polyacetal copolymers, it is preferable to use cationic active catalysts such as Lewis acids, protonic acids, and their esters or anhydrides. Examples of Lewis acids include boric acid, tin, titanium, phosphorus, arsenic, and antimony halides, such as boron trifluoride, tin tetrachloride, titanium tetrachloride, phosphorus pentafluoride, phosphorus pentachloride, antimony pentafluoride, and complex compounds or salts thereof. Specific examples of protonic acids, their esters, and anhydrides include perchloric acid, trifluoromethanesulfonic acid, perchloric acid tertiary butyl ester, acetyl perchlorate, and trimethyloxonium hexafluorophosphate. Among these, boron trifluoride; boron trifluoride hydrate; and coordination complex compounds of boron trifluoride with organic compounds containing oxygen atoms or sulfur atoms are more preferred, with specific examples including boron trifluoride diethyl ether and boron trifluoride di-n-butyl ether.

There are no particular limitations on the polymerization method for polyacetal copolymers, but they are generally bulk polymerization, and either batch or continuous polymerization is possible. Polymerization equipment used includes self-cleaning extrusion kneaders such as co-kneaders, twin-screw continuous extrusion kneaders, and twin-screw paddle continuous mixers. Molten monomers are fed into the polymerization machine, and as the polymerization progresses, solid bulk polyacetal copolymer is obtained.

The polyacetal copolymer obtained by the above polymerization contains thermally unstable terminal groups [-(OCH ₂ ) _n -OH groups] and cannot be used in practical applications as is. Therefore, it is necessary to carry out a treatment to decompose and remove the unstable terminal groups. To achieve this, it is preferable to carry out the treatment to decompose and remove the specific unstable terminal groups described below. An example of a treatment to decompose and remove the specific unstable terminal groups is to heat treat the polyacetal copolymer in a molten state at a temperature of not less than the melting point of the polyacetal copolymer but not more than 260°C in the presence of at least one quaternary ammonium compound represented by the following general formula (1):
[R ¹ R ² R ³ R ⁴ N ⁺ ] _n X ^n- Formula (1)
(Wherein R ¹ , R ² , R ³ and R Each ⁴ independently represents an unsubstituted or substituted alkyl group having 1 to 30 carbon atoms; an aryl group having 6 to 20 carbon atoms; an aralkyl group in which an unsubstituted or substituted alkyl group having 1 to 30 carbon atoms is substituted with at least one aryl group having 6 to 20 carbon atoms; or an alkylaryl group in which an aryl group having 6 to 20 carbon atoms is substituted with at least one unsubstituted or substituted alkyl group having 1 to 30 carbon atoms, wherein the unsubstituted or substituted alkyl group is linear, branched, or cyclic. The substituent of the substituted alkyl group is a halogen, a hydroxyl group, an aldehyde group, a carboxyl group, an amino group, or an amide group. The hydrogen atoms of the unsubstituted alkyl group, aryl group, aralkyl group, and alkylaryl group may be substituted with halogen. n represents an integer from 1 to 3. X represents a hydroxyl group, or an acid residue of a carboxylic acid having 1 to 20 carbon atoms, a hydrogen acid other than a hydrogen halide, an oxo acid, an inorganic thioacid, or an organic thioacid having 1 to 20 carbon atoms.

The quaternary ammonium compound is not particularly limited as long as it is represented by the general formula (1). However, it is preferred that R ¹ , R ² , R ³ and R ⁴ in the general formula (1) are each independently an alkyl group having 1 to 5 carbon atoms or a hydroxyalkyl group having 2 to 4 carbon atoms, and it is particularly preferred that at least one of R ¹ , R ² , R ³ and R ⁴ is a hydroxyethyl group. Specifically, tetramethylammonium, tetraethylammonium, tetrapropylammonium, tetra-n-butylammonium, cetyltrimethylammonium, tetradecyltrimethylammonium, 1,6-hexamethylenebis(trimethylammonium), decamethylene-bis-(trimethylammonium), trimethyl-3-chloro-2-hydroxypropylammonium, trimethyl(2-hydroxyethyl)ammonium, triethyl(2-hydroxyethyl)ammonium, tripropyl(2-hydroxyethyl)ammonium, tri-n-butyl(2-hydroxyethyl)ammonium, trimethylbenzylammonium, triethylbenzylammonium, tripropylbenzylammonium, tri-n-butylbenzyl and hydroxides such as trimethylammonium, trimethylphenylammonium, triethylphenylammonium, trimethyl-2-oxyethylammonium, monomethyltrihydroxyethylammonium, monoethyltrihydroxyethylammonium, octadecyltri(2-hydroxyethyl)ammonium, and tetrakis(hydroxyethyl)ammonium; hydrochloric acid salts such as hydrochloric acid, hydrobromic acid, and hydrofluoric acid; oxoacid salts such as sulfuric acid, nitric acid, phosphoric acid, carbonic acid, boric acid, chloric acid, iodic acid, silicic acid, perchloric acid, chlorous acid, hypochlorous acid, chlorosulfuric acid, amidosulfuric acid, disulfuric acid, and tripolyphosphoric acid; thioacid salts such as thiosulfuric acid; and carboxylates such as formic acid, acetic acid, propionic acid, butanoic acid, isobutyric acid, pentanoic acid, caproic acid, caprylic acid, capric acid, benzoic acid, and oxalic acid. Among these, hydroxides (OH ⁻ ), sulfuric acid (HSO ₄ ⁻ , SO ₄ ²⁻ ), carbonic acid (HCO ₃ ⁻ , CO ₃ ²⁻ ), boric acid (B(OH) ₄ ⁻ ), and carboxylic acid salts are preferred. Of the carboxylic acids, formic acid, acetic acid, and propionic acid are particularly preferred. These quaternary ammonium compounds may be used alone or in combination of two or more. Furthermore, in this embodiment, there is no problem in using in combination with the above-mentioned quaternary ammonium compounds ammonia, amines such as triethylamine, and the like, which are known agents for promoting the decomposition of unstable terminal groups.

The decomposition and removal of unstable terminal groups from the polyacetal resin used in this embodiment is achieved by heat-treating the polyacetal copolymer in a molten state at a temperature above the melting point and below 260°C. There are no particular restrictions on the equipment used, but heat treatment using an extruder, kneader, or the like is preferred. Furthermore, formaldehyde generated by decomposition is removed under reduced pressure. There are no particular restrictions on the method of adding the quaternary ammonium compound, and examples include adding it as an aqueous solution during the polymerization catalyst deactivation process, or spraying it onto the polyacetal copolymer powder produced by polymerization. Regardless of the addition method used, it is sufficient that the compound is added during the heat treatment process of the polyacetal copolymer. For products in which fillers or pigments are blended using an extruder, or the like, the compound can be injected into an extruder, or impregnated into resin pellets, and the unstable terminal removal operation can be performed during the subsequent blending process.

The unstable terminal removal operation can be carried out after deactivating the polymerization catalyst in the polyacetal copolymer obtained by polymerization, or it can be carried out without deactivating the polymerization catalyst. A typical example of a polymerization catalyst deactivation operation is a method in which the polymerization catalyst is neutralized and deactivated in a basic aqueous solution of an amine or the like. Another effective method is to heat the polymerization catalyst at a temperature below its melting point in an inert gas atmosphere to volatilize and reduce the polymerization catalyst without deactivating it, and then carry out the unstable terminal removal operation.
By the above-mentioned specific treatment for decomposing and removing unstable terminals, it is possible to obtain a polyacetal copolymer that is almost free of unstable terminals and has very excellent thermal stability.

In this embodiment, the mass proportion of the polyacetal resin (A) in 100% by mass of the polyacetal resin composition is preferably 80 to 99.9% by mass, more preferably 90 to 99.8% by mass, and even more preferably 95 to 99.6% by mass.

-(B) Fatty acid metal salt-
The (B) fatty acid metal salt is preferably a fatty acid metal salt having an alkyl group with 5 to 30 carbon atoms, more preferably a fatty acid metal salt having an alkyl group with 10 to 30 carbon atoms. The alkyl group may have some (preferably one) hydrogen atoms substituted with a hydroxyl group.
Examples of the alkyl group include pentane, hexane, heptane, octane, nonane, decane, undecane, dodecane, tridecane, tetradecane, pentadecane, hexadecane, heptadecane, octadecane, nonadecane, icosane, henicosane, tetracosane, and triacontane, and alkyl groups having 8 or more carbon atoms are preferred.

Preferred metal salts include alkali metal salts such as sodium and lithium; and alkaline earth metal salts such as magnesium, calcium, and barium; with alkaline earth metal salts being more preferred.

The above-mentioned fatty acid metal salts include alkali metal salts or alkaline earth metal salts of fatty acids having an alkyl group containing 5 to 30 carbon atoms. Specific examples include, but are not limited to, calcium dimyristate, calcium dipalmitate, calcium distearate, calcium (myristate-palmitate), calcium (myristate-stearate), calcium (palmitate-stearate), calcium dilaurate, calcium 12-hydroxystearate, magnesium 12-hydroxystearate, barium 12-hydroxystearate, lithium 12-hydroxystearate, and sodium 12-hydroxystearate, with calcium 12-hydroxystearate and magnesium 12-hydroxystearate being particularly preferred.

The fatty acid metal salt contains two or more kinds of fatty acid metal salts, and preferably contains only two kinds of fatty acid metal salts.
From the viewpoint of excellent extrusion properties and weather resistance stability, the fatty acid metal salt includes at least a (B1) fatty acid metal salt represented by (RCOO) ₂ M (wherein M is a metal salt and R is composed only of carbon and hydrogen), and a (B2) fatty acid metal salt represented by (R'COO) ₂ M (wherein M is a metal salt and R' is composed of carbon, hydrogen and other elements) which is different from (B1), and preferably consists of only the (B1) fatty acid metal salt and the (B2) fatty acid metal salt.
M in the (B1) fatty acid metal salt and (B2) fatty acid metal salt is a divalent metal, and is preferably an alkaline earth metal from the viewpoint of achieving even better extrusion properties and weather resistance stability. M in (B1) and (B2) may be the same or different, and is preferably the same.
The (B1) contained in the (B) may be one type or multiple types. The (B2) contained in the (B) may be one type or multiple types. In particular, it is preferable that the (B) consists of only one type of (B1) and one type of (B2).

R in the fatty acid metal salt (B1) above is a group composed only of carbon and hydrogen, and from the viewpoint of achieving even better extrusion properties and weather resistance stability, is preferably an alkyl group having 5 to 30 carbon atoms, more preferably an alkyl group having 8 to 30 carbon atoms, and even more preferably an alkyl group having 10 to 25 carbon atoms.
R' in the fatty acid metal salt (B2) above is a group composed of carbon, hydrogen, and other elements, and from the viewpoint of achieving even better extrusion properties and weather resistance stability, it is preferably a group composed of carbon, hydrogen, and oxygen, and more preferably a group in which at least a portion (preferably one) of the hydrogen atoms of an alkyl group having 5 to 30 carbon atoms (preferably 8 to 30, more preferably 10 to 25) has been substituted with a hydroxyl group. The two R' in (B2) above may be the same or different in terms of the positions of the carbon atoms to which the substituted hydroxyl groups are bonded (for example, the number of atoms from the metal element to the carbon atom), and are preferably the same.
The two Rs in (B1) above may be alkyl groups having the same number of carbon atoms or alkyl groups having different numbers of carbon atoms, but preferably have the same number of carbon atoms.
The two R's in (B2) above may have the same number of carbon atoms or different numbers of carbon atoms, but preferably have the same number of carbon atoms.
The number of carbon atoms in the above R and R' may be the same or different.

From the viewpoint of achieving even better extrusion properties and weather resistance stability, the (B1) fatty acid metal salt is preferably an alkaline earth metal salt of a fatty acid having an alkyl group having 5 to 30 carbon atoms, more preferably calcium dimyristate, calcium dipalmitate, calcium distearate, calcium (myristate-palmitate), calcium (myristate-stearate), calcium (palmitate-stearate), or calcium dilaurate, and even more preferably calcium distearate or calcium dilaurate.

From the viewpoint of achieving even better extrusion properties and weather resistance stability, the (B2) fatty acid metal salt is preferably an alkaline earth metal salt of a fatty acid having a group in which at least a portion (preferably one) of the hydrogen atoms of an alkyl group having 5 to 30 carbon atoms is substituted with a hydroxyl group, more preferably calcium bis(12-hydroxystearate), magnesium bis(12-hydroxystearate), or barium bis(12-hydroxystearate), and even more preferably calcium bis(12-hydroxystearate) or magnesium bis(12-hydroxystearate).

Fatty acid metal salts improve the color tone of pellets after granulation, and fatty acid metal salts with hydroxyl groups improve extrusion processability. Furthermore, combining two or more types of straight-chain fatty acid metal salts and fatty acid metal salts with hydroxyl groups improves the bite during extrusion process, improving pellet color tone and weather resistance.

From the viewpoint of improving thermal stability, the total mass of the (B) fatty acid metal salt in the polyacetal resin composition of this embodiment is preferably 0.005 parts by mass or more, more preferably 0.01 parts by mass or more, and even more preferably 0.05 parts by mass or more, per 100 parts by mass of the (A) polyacetal resin.
Furthermore, from the viewpoint of preventing discoloration during molding, the blending amount is preferably 0.75 parts by mass or less, more preferably 0.50 parts by mass or less, and even more preferably 0.35 parts by mass or less, per 100 parts by mass of the polyacetal resin (A).
The mass ratio of the (B1) fatty acid metal salt relative to 100 parts by mass of the polyacetal resin is preferably 0.005 parts by mass or more and 0.5 parts by mass or less, more preferably 0.008 parts by mass or more and 0.4 parts by mass or less, and even more preferably 0.01 parts by mass or more and 0.3 parts by mass or less, from the viewpoint of achieving even better extrusion properties and weather resistance stability.
The mass proportion of the (B2) fatty acid metal salt relative to 100 parts by mass of the polyacetal resin is preferably 0.005 parts by mass or more and 0.50 parts by mass or less, more preferably 0.008 parts by mass or more and 0.4 parts by mass or less, and even more preferably 0.01 parts by mass or more and 0.3 parts by mass or less, from the viewpoint of achieving even better extrusion properties and weather resistance stability.
The mass ratio of the (B2) fatty acid metal salt to 100 parts by mass of the (B1) fatty acid metal salt is preferably 50 to 150 parts by mass, more preferably 75 to 125 parts by mass, and even more preferably 90 to 110 parts by mass, from the viewpoint of achieving even better extrusion properties and weather resistance stability. The mass ratio of the (B1) fatty acid metal salt and the mass ratio of the (B2) fatty acid metal salt to 100 parts by mass of the polyacetal resin composition of this embodiment may be the same.

-(C) Light stabilizer-
From the viewpoint of weather resistance stability, the polyacetal resin composition of the present embodiment preferably further contains (C) a light stabilizer.
The (C) light stabilizer is preferably one or more selected from the group consisting of benzotriazole-based ultraviolet absorbers, anilide oxalate-based ultraviolet absorbers, and hindered amine-based light stabilizers.

Examples of benzotriazole-based UV absorbers include, but are not limited to, 2-(2'-hydroxy-5'-methyl-phenyl)benzotriazole, 2-(2'-hydroxy-3',5'-di-t-butyl-phenyl)benzotriazole, 2-[2'-hydroxy-3',5'-bis(α,α-dimethylbenzyl)phenyl]-2H-benzotriazole, and 2-(2'-hydroxy-4'-octoxyphenyl)benzotriazole.

Examples of oxalic acid anilide-based UV absorbers include, but are not limited to, 2-ethoxy-2'-ethyl oxalic acid bisanilide, 2-ethoxy-5-t-butyl-2'-ethyl oxalic acid bisanilide, and 2-ethoxy-3'-dodecyl oxalic acid bisanilide.

Examples of hindered amine light stabilizers include, but are not limited to, N,N',N'',N'''-tetrakis-(4,6-bis-(butyl-(N-methyl-2,2,6,6-tetramethylpiperidin-4-yl)amino)-triazin-2-yl)-4,7-diazadecane-1,10-diamine, polycondensate of dibutylamine, 1,3,5-triazine, N,N'-bis(2,2,6,6-tetramethyl-4-piperidyl-1,6-hexamethylenediamine, and N-(2,2,6,6-tetramethyl-4-piperidyl)butylamine, poly[{6-(1,1,3,3-tetramethylbutyl )amino-1,3,5-triazine-2,4-diyl}{(2,2,6,6-tetramethyl-4-piperidyl)imino}hexamethylene{(2,2,6,6-tetramethyl-4-piperidyl)imino}], condensation products of dimethyl succinate and 4-hydroxy-2,2,6,6-tetramethyl-1-piperidineethanol, reaction products of decanoic acid bis(2,2,6,6-tetramethyl-1(octyloxy)-4-piperidinyl) ester with 1,1-dimethylethyl hydroperoxide and octane, bis(1,2,2,6,6-pentamethyl-4-piperidyl)[[3,5-bis(1,1-dimethyl ethyl)-4-hydroxyphenyl]methyl]butyl malonate, methyl 1,2,2,6,6-pentamethyl-4-piperidyl sebacate, bis(2,2,6,6-tetramethyl-4-piperidyl)-sebacate, bis-(N-methyl-2,2,6,6-tetramethyl-4-piperidinyl)sebacate, condensation product of 1,2,3,4-butanetetracarboxylic acid, 1,2,2,6,6-pentamethyl-4-piperidinol, and β,β,β',β'-tetramethyl-3,9-[2,4,8,10-tetraoxaspiro(5,5)undecane]diethanol, decanedioic acid 1,10-bis(2,2,6,6 -tetramethyl-4-piperidinyl), 1,2,3,4-butanetetracarboxylic acid/2,2-bis(hydroxymethyl)-1,3-propanediol/3-hydroxy-2,2-dimethylpropanal polycondensate and 1,2,2,6,6-pentamethyl-4-piperidinyl ester, 1,6-hexanediamine, reaction products of N,N'-bis(2,2,6,6-tetramethyl-4-piperidinyl)-polymer with 2,4,6-trichloro-1,3,5-triazine, N-butyl-1-butanamine, and N-butyl-2,2,6,6-tetramethyl-4-piperidinamine.

From the viewpoint of weathering (light) stability, the (C) light stabilizer is preferably a benzotriazole-based ultraviolet absorber such as 2-[2'-hydroxy-3',5'-bis-(α,α-dimethylbenzyl)phenyl]-2H-benzotriazole or 2-(2'-hydroxy-3',5'-di-t-butyl-phenyl)benzotriazole, or a hindered amine-based light stabilizer such as bis(2,2,6,6-tetramethyl-4-piperidyl)sebacate, bis-(N-methyl-2,2,6,6-tetramethyl-4-piperidinyl)sebacate, or a condensate of 1,2,3,4-butanetetracarboxylic acid, 1,2,2,6,6-pentamethyl-4-piperidinol, and β,β,β',β'-tetramethyl-3,9-[2,4,8,10-tetraoxaspiro(5,5)undecane]diethanol.
These light stabilizers may be used alone or in combination of two or more.

From the viewpoint of weather resistance stability, the mass proportion of the (C) light stabilizer in the polyacetal resin composition of this embodiment is preferably 0.05 parts by mass or more, more preferably 0.10 parts by mass or more, and even more preferably 0.30 parts by mass or more, per 100 parts by mass of the (A) polyacetal resin. Furthermore, from the viewpoint of processability during extrusion, the mass proportion is preferably 1.50 parts by mass or less, more preferably 1.00 parts by mass or less, and even more preferably 0.75 parts by mass or less, per 100 parts by mass of the (A) polyacetal resin.

The weight average molecular weight of the (C) light stabilizer is preferably 1,000 or more, more preferably 1,500 to 5,000, and even more preferably 2,000 to 4,000, from the viewpoint of pellet color tone.
The (C) light stabilizer is preferably a hindered amine-based light stabilizer having a weight-average molecular weight of 1,000 or more.

When the (B2) fatty acid metal salt is a fatty acid metal salt having a hydroxyl group, from the viewpoint of suppressing a decrease in processability during extrusion due to the light stabilizer, the mass ratio of the fatty acid metal salt having a hydroxyl group to the (C) light stabilizer (fatty acid metal salt having a hydroxyl group:(C) light stabilizer) is preferably in the range of 1:1 to 1:75. If there is an excess of fatty acid metal salt having a hydroxyl group, the color tone of the pellets will deteriorate, and if there is an excess of light stabilizer, it will be impossible to suppress a decrease in processability.

-(D) Formaldehyde Scavenger-
The polyacetal resin composition of the present embodiment preferably further contains (D) a formaldehyde scavenger.
The formaldehyde scavenger (D) is not particularly limited, but examples thereof include compounds containing formaldehyde-reactive nitrogen, such as melamine and polyamide resins, polymers thereof, hydrazide compounds, etc. More specifically, the compounds containing formaldehyde-reactive nitrogen and polymers thereof are polymers or compounds (monomers) having a nitrogen atom capable of reacting with formaldehyde in the molecule.
Examples include polyamide resins such as nylon 4-6, nylon 6, nylon 6-6, nylon 6-10, nylon 6-12, and nylon 12, and polymers thereof such as nylon 6/6-6/6-10 and nylon 6/6-12.
Examples of compounds containing formaldehyde-reactive nitrogen and polymers thereof include acrylamide and its derivatives, and copolymers of acrylamide and its derivatives with other vinyl monomers, such as poly-β-alanine copolymers obtained by polymerizing acrylamide and its derivatives with other vinyl monomers in the presence of a metal alcoholate.
Further, examples of polymers or compounds having formaldehyde-reactive nitrogen include amide compounds, amino-substituted triazine compounds, adducts of amino-substituted triazine compounds and formaldehyde, condensates of amino-substituted triazine compounds and formaldehyde, urea, urea derivatives, imidazole compounds, and imide compounds.
The hydrazide compound is not particularly limited as long as it has a hydrazine structure (N—N) with a single bond between nitrogen atoms, and known compounds can be used.
For example, hydrazine; hydrazine hydrate; carboxylic acid monohydrazides such as succinic acid monohydrazide, glutaric acid monohydrazide, adipic acid monohydrazide, pimelic acid monohydrazide, suberic acid monohydrazide, azelaic acid monohydrazide, and sebacic acid monohydrazide; saturated aliphatic carboxylic acid dihydrazides such as oxalic acid dihydrazide, malonic acid dihydrazide, succinic acid dihydrazide, glutaric acid dihydrazide, adipic acid dihydrazide, pimelic acid dihydrazide, suberic acid dihydrazide, azelaic acid dihydrazide, sebacic acid dihydrazide, and dodecanedioic acid dihydrazide; maleic acid dihydrazide, fumaric acid dihydrazide, and itaconic acid dihydrazide; aromatic carboxylic acid dihydrazides such as isophthalic acid dihydrazide, phthalic acid dihydrazide, 2,6-naphthalenedicarbodihydrazide, etc.; dihydrazide of pyromellitic acid; trihydrazides such as trimer acid trihydrazide, cyclohexanetricarboxylic acid trihydrazide, benzenetricarboxylic acid trihydrazide, nitrilotriacetic acid trihydrazide, citric acid trihydrazide, etc.; tetrahydrazides such as pyromellitic acid tetrahydrazide, naphthoic acid tetrahydrazide, ethylenediaminetetraacetic acid tetrahydrazide, 1,4,5,8-naphthoic acid tetrahydrazide, etc.
These formaldehyde scavengers may be used alone or in combination of two or more.

From the viewpoint of low VOCs, the amount of formaldehyde scavenger (D) in the polyacetal resin composition of this embodiment is preferably 0.01 parts by mass or more, more preferably 0.03 parts by mass or more, and even more preferably 0.05 parts by mass or more, per 100 parts by mass of polyacetal resin (A). Furthermore, from the viewpoint of reducing the amount of mold deposits generated during molding, the amount is preferably 1.50 parts by mass or less, more preferably 1.00 parts by mass or less, and even more preferably 0.75 parts by mass or less, per 100 parts by mass of polyacetal resin (A).

-others-
The polyacetal resin composition of the present embodiment may contain known additives other than the above components, provided that the effects of the present invention are not impaired. Examples of polyacetal resin compositions containing such additives include polyacetal resin compositions containing a release (lubricant), a reinforcing agent, a conductive material, a thermoplastic resin, a thermoplastic elastomer, and a pigment.

In this embodiment, the total mass proportion of (A) the polyacetal resin and (B) the fatty acid metal salt having an alkyl group having 5 to 30 carbon atoms in 100% by mass of the polyacetal resin composition is preferably 80 to 100% by mass, more preferably 90 to 99.9% by mass, and even more preferably 95 to 99.8% by mass.

(Method for producing polyacetal resin composition)
The method for producing the polyacetal resin composition of this embodiment is not particularly limited. Generally, the polyacetal resin composition of this embodiment can be produced by mixing (A) polyacetal resin, (B) saturated fatty acid metal salt, and, if necessary, (C) light stabilizer, (D) component, and additives using a Henschel mixer, tumbler, V-shaped blender, or the like, followed by melting and kneading using a single-screw or twin-screw extruder. Alternatively, the polyacetal resin composition of this embodiment can be produced by continuously feeding each component, either individually or in batches, into the extruder using a metering feeder or the like, without premixing. Alternatively, the polyacetal resin composition of this embodiment can be produced by preparing a high-concentration masterbatch consisting of component (A), component (B), and, if necessary, component (C), component (D), and additives, in advance, and diluting it with polyacetal resin during extrusion melt-kneading or injection molding.

The polyacetal resin composition of this embodiment can be used, for example, as a molding material for mechanical parts such as automobile parts, electrical and electronic parts, and industrial parts.

The present embodiment will be explained in more detail below using examples and comparative examples, but the present invention is not limited to these in any way.

The physical property measurement methods and raw materials used in the examples and comparative examples are shown below.

<Extrusion discharge amount>
Using a twin-screw extruder (PCM30 manufactured by Ikegai Corporation), extrusion was carried out under the following conditions: cylinder temperature 210°C, die temperature 190°C, screw rotation speed: 50 rpm, and nozzle shape: 3 mm diameter, circular. Materials that could be easily stranded and pelletized at a discharge rate of 5.0 kg/h or more without problems such as poor penetration into the extruder were rated as ○ (good), while materials that had problems such as poor penetration into the extruder at a discharge rate of 4.0 kg/h or less and required a reduced discharge rate for stranding and pelletization were rated × (bad). A higher discharge rate indicates a shorter residence time in the extruder.

<Pellet color>
The yellowness (b value) of the pellets was measured using a spectrophotometer SE7700 manufactured by Nippon Denshoku Kogyo Co., Ltd. The smaller the b value, the better the pellet color tone.

<Weather stability>
Using an injection molding machine (IS-100GN manufactured by Toshiba Machine Co., Ltd.), molded pieces (JIS No. 1A dumbbell pieces) were obtained from the polyacetal resin compositions obtained in the examples and comparative examples described below under the following conditions: cylinder temperature: 205°C, injection pressure: 72 MPa, injection time: 15 seconds, cooling time: 20 seconds, and mold temperature: 90°C.
The obtained molded specimens were used to evaluate weather resistance stability.
A weather resistance tester (Sunshine Weather Meter S80 manufactured by Suga Test Instruments Co., Ltd.) was used to conduct the weather resistance stability test under the conditions of a black panel temperature of 83° C., no rain, and an exposure time of 1500 hours.
The color difference ΔE was measured on the light-irradiated surface of the molded piece before the weather resistance stability test and after 1500 hours of exposure using a colorimeter (manufactured by Konica Minolta, Inc., product name "CR-200") in the Lab color system. The color difference ΔE was calculated using the following formula, where the measured values of the colorimeter before the weather resistance stability test were L, a, and b, and the measured values after 1500 hours of exposure were L ^* , a ^* , and b ^* . A lower ΔE value indicates better weather resistance stability.

<VOC>
Using an injection molding machine (IS-100GN manufactured by Toshiba Machine Co., Ltd.), test pieces having specified dimensions (length 100 mm × width 40 mm × thickness 3 mm) were molded from the polyacetal resin compositions obtained in the examples and comparative examples described below under the following conditions: cylinder temperature: 220°C, injection pressure: 70 MPa, injection time: 15 seconds, cooling time: 20 seconds, and mold temperature: 80°C.
The amount of formaldehyde released from the obtained test piece was measured in accordance with the VDA275 method described below, and the amount of formaldehyde released from the molded article was determined.
In the VDA275 method, 50 mL of distilled water and the test piece were placed in a sealed polyethylene container. The container was then heated at 60°C for 3 hours, after which the formaldehyde in the distilled water was reacted with acetylacetone in the presence of ammonium ions. The absorption peak of the reaction product at a wavelength of 412 nm was measured using a UV spectrometer to determine the amount of formaldehyde (mg/kg) released from the molded article.
In the "VOC property" row of Table 1, "-" indicates that the measurement was not performed.

[Raw materials]
The following components were used in the examples and comparative examples.

<(A) Polyacetal Resin>
A twin-screw self-cleaning type polymerization reactor equipped with a jacket and capable of passing a heat transfer medium (L/D=8 (L: distance (m) from the raw material inlet to the discharge outlet of the polymerization reactor; D: inner diameter (m) of the polymerization reactor; the same applies hereinafter)) was adjusted to 80°C, and trioxane was continuously added at 4 kg/hr, 1,3-dioxolane as a comonomer at 128.3 g/h (3.9 mol % relative to 1 mol of trioxane), and methylal as a chain transfer agent (1.50 × 10 ^-3 mol relative to 1 mol of trioxane). Furthermore, boron trifluoride di-n-butyl etherate (1.5 × 10 ^-5 mol relative to 1 mol of trioxane) was continuously added as a polymerization catalyst to carry out polymerization. The polyacetal copolymer discharged from the polymerization reactor was introduced into a 0.1% aqueous triethylamine solution to deactivate the polymerization catalyst. The deactivated polyacetal copolymer was filtered using a centrifuge, and the dried polyacetal copolymer was fed to a vented twin-screw extruder, and 0.5 parts by mass of water was added to 100 parts by mass of the molten polyacetal copolymer in the extruder, and the unstable terminal moieties were decomposed and removed at an extruder set temperature of 200° C. for a residence time of 7 minutes. The polyacetal copolymer from which the unstable terminal moieties had been decomposed was devolatilized under a vent vacuum of 20 Torr, extruded as strands from the extruder die, and pelletized.

<(B) Saturated Fatty Acid Metal Salt>
B-1: Calcium stearate (C18) manufactured by Nitto Kasei Kogyo Co., Ltd.
B-2: 12-hydroxystearate calcium (C18) manufactured by Nitto Kasei Kogyo Co., Ltd.
B-3: Calcium laurate (C12) manufactured by Nitto Kasei Kogyo Co., Ltd.

<(C) Light Stabilizer>
C-1: Hindered amine light stabilizer, 1,10-bis(2,2,6,6-tetramethyl-4-piperidinyl) decanedioate [bis(2,2,6,6-tetramethyl-4-piperidyl) sebacate]
C-2: Hindered amine light stabilizer, ester of 1,2,3,4-butanetetracarboxylic acid/2,2-bis(hydroxymethyl)-1,3-propanediol/3-hydroxy-2,2-dimethylpropanal polycondensate and 1,2,2,6,6-pentamethyl-4-piperidinyl C-3: Hindered amine light stabilizer, 1,6-hexanediamine, reaction products of N,N'-bis(2,2,6,6-tetramethyl-4-piperidinyl)-polymer with 2,4,6-trichloro-1,3,5-triazine, N-butyl-1-butanamine and N-butyl-2,2,6,6-tetramethyl-4-piperidinamine

<(D) Formaldehyde Scavenger>
D-1: Adipic acid dihydrazide D-2: Sebacic acid dihydrazide

Example 1
A mixture was obtained by uniformly mixing 0.01 parts by mass of (B-1) calcium stearate, 0.01 parts by mass of (B-2) calcium 12-hydroxystearate, and 0.30 parts by mass of (C-2) a polycondensate of 1,2,3,4-butanetetracarboxylic acid/2,2-bis(hydroxymethyl)-1,3-propanediol/3-hydroxy-2,2-dimethylpropanal and 1,2,2,6,6-pentamethyl-4-piperidinyl ester per 100 parts by mass of polyacetal resin (A) using a Henschel mixer. The mixture was fed through the main feed port of a 30 mm vented twin-screw extruder with an L/D ratio of 30 set at 200°C, melt-kneaded at a screw rotation speed of 100 rpm, extruded into strands, cooled, and pelletized to obtain resin pellets consisting of a polyacetal resin composition. The obtained resin pellets were dried at 80° C. for 4 hours, and the <pellet color> and <weather resistance stability> were evaluated by the various evaluation methods described above.
The extrusion rate was measured using the above-mentioned evaluation method. The results are shown in Table 1.

Examples 2 to 11
Resin pellets were obtained in the same manner as in Example 1, except that the components (A) to (C) were used in the prescribed blending ratios shown in Table 1. The pellets were evaluated using the various evaluation methods described above. The results are shown in Table 1.

Examples 12 and 13
Resin pellets were obtained in the same manner as in Example 1, except that the components (A) to (D) were changed to the prescribed blending ratios shown in Table 1. The pellets were evaluated by the various evaluation methods described above.

Comparative Examples 1 to 5
Resin pellets were obtained in the same manner as in Example 1, except that the components (A) to (D) were changed to the prescribed blending ratios shown in Table 1. The pellets were evaluated by the various evaluation methods described above.

As is clear from the evaluation results in Table 1, in Examples 1 to 13 and Comparative Examples 1 to 5, by mixing (B1) a fatty acid metal salt, a fatty acid metal salt having a hydroxyl group, and (C) a light stabilizer, a polyacetal resin composition was obtained that had excellent extrusion processability, pellet color tone, and weather resistance stability.

The polyacetal resin composition of the present invention has the effects of being excellent in extrusion processability, and having good pellet color tone and weather resistance stability.
Molded articles made from the polyacetal resin composition of the present invention can be suitably used as automobile parts, various electric and electronic equipment parts, and various other industrial parts.

Claims (7)

(A) a polyacetal resin; and (B) a fatty acid metal salt having an alkyl group having 5 to 30 carbon atoms,
The (B) fatty acid metal salt having an alkyl group having 5 to 30 carbon atoms includes (B1) a fatty acid metal salt represented by (RCOO) ₂ M (wherein M is a metal salt and R is composed only of carbon and hydrogen), and (B2) a fatty acid metal salt represented by (R'COO) ₂ M (wherein M is a metal salt and R' is composed of carbon, hydrogen and other elements) which is different from the (B1),
the (B2) fatty acid metal salt is a fatty acid metal salt having a hydroxyl group,
further containing (C) a light stabilizer,
the mass ratio of the fatty acid metal salt having a hydroxyl group to the light stabilizer (C) is 1:1 to 1:75 ;
A polyacetal resin composition comprising: The polyacetal resin composition according to claim 1, wherein the alkyl group has 8 or more carbon atoms. The polyacetal resin composition according to claim 1 or 2, wherein the total amount of the (B) fatty acid metal salt is 0.01 parts by mass or more and 0.35 parts by mass or less per 100 parts by mass of the (A) polyacetal resin. The polyacetal resin composition according to any one of claims 1 to 3 , comprising 0.005 parts by mass or more and 0.50 parts by mass or less of the (B2) fatty acid metal salt having a hydroxyl group per 100 parts by mass of the (A) polyacetal resin. The polyacetal resin composition according to any one of claims 1 to 4 , comprising 0.05 parts by mass or more and 1.50 parts by mass or less of a light stabilizer (C) relative to 100 parts by mass of the polyacetal resin (A). The polyacetal resin composition according to any one of claims 1 to 5 , wherein the (C) light stabilizer is a hindered amine-based light stabilizer having a weight-average molecular weight of 1,000 or more. The polyacetal resin composition according to any one of claims 1 to 6 , further comprising 0.01 parts by mass or more and 1.00 parts by mass or less of a formaldehyde scavenger (D) relative to 100 parts by mass of the polyacetal resin (A).