JP7240272B2 - Polyacetal resin composition and method for producing the same - Google Patents

Description

The present invention provides a polyacetal resin composition in which the molded article has excellent friction and wear properties, the amount of formaldehyde generated from the molded article is remarkably suppressed, and mold deposits during molding are stably suppressed, and It relates to the manufacturing method thereof.

Polyacetal resins have well-balanced mechanical properties and are excellent in friction/wear properties, chemical resistance, heat resistance, electrical properties, and the like. For this reason, polyacetal resins are widely used in the fields of automobiles, electrical and electronic parts, and the like, and the forms of use and processing techniques of polyacetal resins continue to advance. Under these circumstances, the properties required of polyacetal resins tend to be sophisticated and specialized. As one example, polyacetal resins are required to improve sliding properties under sliding conditions of high surface pressure and high load.

To address this problem, a resin composition containing a specific graft copolymer in a polyacetal resin and a resin composition containing a specific graft copolymer and a lubricant have been disclosed (Patent Document 1).

Further, a resin composition obtained by adding and blending a specific graft copolymer, a lubricant and an inorganic powder having a specific particle size to a polyacetal resin is disclosed (Patent Document 2).
Furthermore, studies have been made on how molded articles have excellent abrasion resistance and wear resistance, and the generation of formaldehyde from the molded articles can be suppressed, and this technology has also been disclosed (Patent Document 3).

The amount of formaldehyde generated from polyacetal resin molded products under normal usage conditions is extremely small, but the generated formaldehyde is chemically active, and when oxidized, it becomes formic acid, which adversely affects the heat resistance of polyacetal resin.・When used in electronic equipment parts, metal contact parts may be corroded by formaldehyde or its oxide, formic acid, or organic compounds may adhere to cause discoloration or contact failure.

Therefore, in order to stabilize the polyacetal resin, antioxidants and other stabilizers are blended. Antioxidants added to polyacetal resins include sterically hindered phenol compounds (hindered phenols) and sterically hindered amine compounds (hindered amines). Alkali metal hydroxides, alkaline earth metal hydroxides and the like are used. Antioxidants are also commonly used in combination with other stabilizers.

However, it is difficult to greatly reduce formaldehyde generated, especially formaldehyde generated from molded products, simply by blending such a general-purpose stabilizer with a polyacetal resin having normal formaldehyde quality. Furthermore, polyacetal resin compositions containing various compounds have been disclosed in order to solve the above problems and reduce the amount of formaldehyde generated.

For example, a technique is disclosed in which a polyacetal resin having a specific terminal group, a hindered phenol-based antioxidant, a hydrazide compound and an isocyanate compound are used in combination (Patent Document 4). Further, a technique of coexisting a hindered phenol-based antioxidant, a hydrazide compound and an alkaline earth metal salt of a specific carboxylic acid has also been disclosed (Patent Document 5).

JP-A-2-138357 JP-A-3-111446 JP 2013-112727 A JP 2009-286874 A JP-A-2006-45489

According to the techniques disclosed in these Patent Documents 1 and 2, although improvement in sliding properties can be seen, generation of formaldehyde cannot be sufficiently suppressed.
According to the technology disclosed in Patent Document 3, under conditions where constant friction and wear characteristics are maintained and the effect of suppressing formaldehyde generation is greatly exhibited, the effect of suppressing mold deposits is insufficient, and stable molding technology It wasn't.

According to the technique disclosed in Patent Document 4, it is possible to reduce mold deposits during molding of polyacetal resin to a considerable level. However, although this is an effective technique for reducing mold deposits, the reality is that the generation of formaldehyde cannot be sufficiently suppressed, and the friction and wear properties need to be improved.

Moreover, according to the technique disclosed in Patent Document 5, an effect of suppressing the generation of formaldehyde was exhibited. However, the effect of suppressing mold deposits was insufficient, and it was not a stable molding technology. In addition, it was necessary to improve friction and wear characteristics.

An object of the present invention is to provide a polyacetal resin composition that has excellent friction and wear properties, can suppress the generation of formaldehyde from molded articles to an extremely low level, and stably suppresses mold deposits during molding, and a method for producing the same. is to provide

The objects of the invention have been achieved by:

1. At least (A) 100 parts by mass of polyacetal polymer,
(B) 0.01 to 1 part by mass of a hindered phenol antioxidant;
(C) 0.01 to 0.50 parts by mass of an aliphatic carboxylic acid hydrazide;
(D) 0.001 to 0.50 parts by mass of a hydantoin compound having two hydrazinocarbonylalkyl groups;
(E) 0.001 to 0.30 parts by mass of an alkaline earth metal salt of an aliphatic carboxylic acid;
(F) 2 to 10 parts by mass of a graft copolymer,
(G) blended with 0.5 to 5 parts by mass of fatty acid ester,
The total amount of (C) and (D) is 0.03 to 0.55 parts by mass with respect to 100 parts by mass of the polyacetal polymer (A),
The (F) graft copolymer has a polyethylene main chain and an acrylonitrile-styrene copolymer as a side chain,
The (G) fatty acid ester is a polyacetal resin composition comprising a fatty acid having 12 to 32 carbon atoms and a monohydric or polyhydric alcohol having 2 to 30 carbon atoms.
2. 1. The polyacetal resin composition according to 1 above, further comprising (H) 2 to 18 parts by mass of spindle-shaped calcium carbonate.
3. 3. The polyacetal resin composition as described in 1 or 2 above, wherein (C) the aliphatic carboxylic acid hydrazide is dihydrazide sebacate.
4. 4. The polyacetal resin composition according to any one of 1 to 3 above, wherein (E) the alkaline earth metal salt of an aliphatic carboxylic acid is at least one selected from calcium stearate and calcium 12-hydroxystearate.
5. 5. The polyacetal resin composition according to any one of 1 to 4 above, wherein (D) the hydantoin compound having two hydrazinocarbonylalkyl groups is 1,3-bis(hydrazinocarbonoethyl)-5-isopropylhydantoin.
6. 6. The method for producing a polyacetal resin composition according to any one of 1 to 5 above, wherein the polyacetal polymer (A) contains trioxane as the main monomer (a) and has at least one carbon-carbon bond. Comonomer (b) is one or more selected from cyclic ethers and cyclic formals having a comonomer (b), copolymerization is performed using a heteropolyacid as a polymerization catalyst (c), and then an alkali metal element or alkaline earth metal element carbonate, carbonate A method for producing a polyacetal resin composition, which is a polyacetal copolymer obtained by melt-kneading a hydrogen salt, a carboxylate or a hydrate thereof (d) to deactivate a polymerization catalyst (c).

According to the present invention, there are provided a polyacetal resin composition and a molded article which are excellent in friction and wear properties, significantly reduce the amount of formaldehyde generated, and stably suppress mold deposits during molding.

The present invention will be described in detail below.
<(A) Polyacetal polymer>
The (A) polyacetal polymer used in the present invention may be a homopolymer having an oxymethylene group (--OCH ₂ --) as a constituent unit, or a copolymer having other comonomer units in addition to the oxymethylene unit. It is preferably a copolymer.

In general, it is produced by copolymerizing formaldehyde or a cyclic compound of formaldehyde as a main monomer and a compound selected from cyclic ethers and cyclic formals as a comonomer. It is stabilized by removing unstable parts.

In particular, trioxane, which is a cyclic trimer of formaldehyde, is generally used as the main monomer. Trioxane is generally obtained by reacting an aqueous formaldehyde solution in the presence of an acidic catalyst, and is used after being purified by a method such as distillation. The trioxane used for polymerization preferably contains as little impurities as possible such as water, methanol and formic acid.
As comonomers, general cyclic ethers and cyclic formals, glycidyl ether compounds capable of forming a branched structure or a crosslinked structure, and the like can be used alone or in combination of two or more.

Polyacetal polymers such as those described above can generally be obtained by adding an appropriate amount of a molecular weight modifier and carrying out cationic polymerization using a cationic polymerization catalyst. Molecular weight modifiers to be used, cationic polymerization catalysts, polymerization methods, polymerization equipment, catalyst deactivation treatment after polymerization, terminal stabilization treatment methods for crude polyacetal polymers obtained by polymerization, etc. are known from many documents. Yes, you can basically use any of them.

Particularly preferred methods for producing the polyacetal polymer include the following. That is, trioxane is used as the main monomer (a), at least one carbon-carbon bond-containing cyclic ether and cyclic formal are used as comonomers (b), and a heteropolyacid is used as the polymerization catalyst (c). After copolymerization, carbonates, hydrogen carbonates, carboxylates or hydrates thereof (d) of alkali metal elements or alkaline earth metal elements are added and melt-kneaded to eliminate the polymerization catalyst (c). It is something that makes you live. By using the polyacetal polymer obtained by this method, the amount of formaldehyde generated from the molded article and the generation of mold deposits during molding can be further reduced.

The heteropolyacid used as the polymerization catalyst (c) is a general term for polyacids produced by dehydration condensation of different oxygen acids, and a specific heteroatom is present in the center, and oxygen atoms are shared to form a condensed acid. It has a mononuclear or polynuclear complex ion formed by condensation of groups.

Specific examples of the above heteropolyacid include phosphomolybdic acid, phosphotungstic acid, phosphomolybdotungstic acid, phosphomolybdovanadate, phosphomolybdotungstovanadate, phosphotungstovanadate, silicotungstic acid, silicomolybdic acid, silico Molybdotungstic acid, silicomolybdotungstic tovanadic acid, and the like. Above all, considering the stability of polymerization and the stability of the heteropolyacid itself, the heteropolyacid is preferably one or more of silicomolybdic acid, silicotungstic acid, phosphomolybdic acid and phosphotungstic acid.

The amount of the heteropolyacid to be used varies depending on the type of the heteropolyacid, and can be changed appropriately to control the polymerization reaction. mass/mass ppm), preferably 0.1 to 50 ppm.

As a polymerization apparatus, a reaction tank with a stirrer that is generally used in a batch system can be used, and as a continuous system, a co-kneader, a twin-screw continuous extrusion mixer, a twin-screw paddle type continuous mixer, etc. A continuous polymerization apparatus such as trioxane that has been proposed so far can be used, and a combination of two or more types of polymerization apparatuses can also be used.

The polymerization method is not particularly limited, but as previously proposed, trioxane, a comonomer, and a heteropolyacid as a polymerization catalyst are sufficiently mixed in advance while maintaining a liquid phase state, and the obtained reaction raw material is If the mixed solution is supplied to the polymerization apparatus and the copolymerization reaction is carried out, the required amount of catalyst can be reduced, and as a result, it is advantageous to obtain a polyacetal copolymer that emits less formaldehyde, and is a more suitable polymerization method. is. The polymerization temperature is in the temperature range of 60-120°C.

In the present invention, when the main monomer (a) and comonomer (b) are polymerized to prepare a polyacetal copolymer, a known chain transfer agent such as a low molecular weight wire such as methylal is used to adjust the degree of polymerization. It is also possible to add acetal and the like.

In addition, the polymerization reaction is desirably carried out in a state in which impurities having active hydrogen, such as water, methanol, formic acid, etc., are substantially absent, for example, in a state in which each of these is 10 ppm or less. It is desirable to use trioxane, cyclic ether and/or cyclic formal prepared to contain as little as possible as the main monomer or comonomer.

A carbonate of an alkali metal element or an alkaline earth metal element is added to the polyacetal polymer (crude polyacetal polymer) containing the polymerization catalyst and having unstable moieties at the ends thereof, obtained by polymerization as described above. , Hydrogen carbonate, carboxylate or hydrate thereof (d) are melt-kneaded to deactivate the polymerization catalyst and reduce the unstable terminal groups of the polyacetal polymer (crude polyacetal polymer) to stabilize it. become

The molecular weight of the polyacetal polymer used in the present invention is not particularly limited. things are preferred. In addition, the melt index (measured at 190° C. and a load of 2.16 kg according to ASTM-D1238), which is an index of resin fluidity, is preferably 0.1 to 100 g/10 minutes, more preferably 0.5. ~80 g/10 min.

It is particularly preferred that the (A) polyacetal polymer used in the present invention has specific terminal characteristics. Specifically, the amount of hemiformal terminal groups is 1.0 mmol/kg or less, the amount of formyl terminal groups is 0.5 mmol/kg or less, and the amount of unstable terminals is 0.5% by mass or less. Here, the hemiformal terminal group is represented by —OCH ₂ OH, and is also called a hydroxymethoxy group or a hemiacetal terminal group. A formyl end group is also indicated by -OCHO. The amounts of such hemiformal terminal groups and formyl terminal groups can be determined by ¹ H-NMR measurement, and the specific measuring method can be referred to the method described in JP-A-2001-11143.

The term "unstable terminal amount" refers to the amount of the terminal portion of the polyacetal polymer, which is unstable to heat and base and easily decomposed. Such an unstable terminal amount was obtained by placing 1 g of polyacetal polymer in a pressure-tight sealed container together with 100 ml of a 50% (volume %) methanol aqueous solution containing 0.5% (volume %) of ammonium hydroxide and heat-treating at 180° C. for 45 minutes. After cooling, the amount of formaldehyde decomposed and eluted in the solution obtained by opening the package was quantified and expressed in % by mass relative to the polyacetal polymer.

The (A) polyacetal polymer used in the present invention preferably has a hemiformal terminal group content of 1.0 mmol/kg or less, more preferably 0.6 mmol/kg or less. The amount of formyl terminal groups is preferably 0.5 mmol/kg or less, more preferably 0.1 mmol/kg or less. The amount of unstable ends is preferably 0.5% by mass or less, more preferably 0.3% by mass or less. The lower limits of the amount of hemi-formal terminal groups, the amount of formyl terminal groups, and the amount of unstable terminals are not particularly limited.

The (A) polyacetal polymer having specific terminal properties as described above can be produced by reducing impurities contained in monomers and comonomers, selecting a production process and optimizing the production conditions.

As a method for producing the (A) polyacetal polymer having specific terminal properties that satisfy the requirements of the present invention, the method described in JP-A-2009-286874, for example, can be used. However, it is not limited to this method.

In the present invention, a polyacetal polymer having a branched or crosslinked structure may be added to the polyacetal polymer (A), and in that case, the blending amount is 0.01 per 100 parts by mass of the polyacetal polymer (A). 20 parts by mass, particularly preferably 0.03 to 5 parts by mass.

<(B) Hindered Phenolic Antioxidant>
The (B) hindered phenol-based antioxidant that can be used in the present invention is not particularly limited. cresol, etc.), polycyclic hindered phenol compounds linked by a group containing a hydrocarbon group or a sulfur atom (e.g., 2,2′-methylenebis(4-methyl-6-t-butylphenol), 4,4′- methylenebis(2,6-di-t-butylphenol), 1,1,3-tris(2-methyl-4-hydroxy-5-t-butylphenyl)butane, 4,4'-butylidenebis(3-methyl-6 -t-butylphenol), 1,3,5-trimethyl-2,4,6-tris(3,5-di-t-butyl-4-hydroxybenzyl)benzene, 4,4′-thiobis(3-methyl- 6-t-butylphenol), etc.), hindered phenol compounds having an ester group or an amide group (e.g., n-octadecyl-3-(4′-hydroxy-3′,5′-di-t-butylphenyl) propionate, n-octadecyl-2-(4'-hydroxy-3',5'-di-t-butylphenyl)propionate, 1,6-hexanediol bis[3-(3,5-di-t-butyl-4- hydroxyphenyl)propionate], triethylene glycol bis[3-(3-t-butyl-5-methyl-4-hydroxyphenyl)propionate] (also known as ethylenebis(oxyethylene)bis[3-(3-(5- t-butyl-4-hydroxy-m-tolyl)propionate]), pentaerythritol tetrakis [3-(3,5-di-t-butyl-4-hydroxyphenyl)propionate], 3,9-bis{2-[ 3-(3-t-butyl-4-hydroxy-5-methylphenyl)propionyloxy]-1,1-dimethylethyl}-2,4,8,10-tetraoxaspiro[5.5]undecane, 2- t-butyl-6-(3′-t-butyl-5′-methyl-2′-hydroxybenzyl)-4-methylphenyl acrylate, 2-[1-(2-hydroxy-3,5-di-t- pentylphenyl)ethyl]-4,6-di-t-pentylphenyl acrylate, di-n-octadecyl-3,5-di-t-butyl-4-hydroxybenzylphosphonate, N,N'-hexamethylenebis(3 ,5-di-t-butyl-4-hydroxy-dihydrocinnamamide), N,N'-ethylenebis [3-(3,5-di-t-butyl-4-hydroxyphenyl)propionamide], N,N'-tetramethylenebis[3-(3,5-di-t-butyl-4-hydroxyphenyl) propionamide], N,N'-hexamethylenebis[3-(3,5-di-t-butyl-4-hydroxyphenyl)propionamide], N,N'-ethylenebis[3-(3-t- butyl-5-methyl-4-hydroxyphenyl)propionamide], N,N'-hexamethylenebis[3-(3-t-butyl-5-methyl-4-hydroxyphenyl)propionamide], N,N' -bis[3-(3,5-di-t-butyl-4-hydroxyphenyl)propionyl]hydrazine, N,N'-bis[3-(3-t-butyl-5-methyl-4-hydroxyphenyl) propionyl]hydrazine, 1,3,5-tris(3,5-di-t-butyl-4-hydroxybenzyl)isocyanurate, 1,3,5-tris(4-t-butyl-3-hydroxy-2, 6-dimethylbenzyl)isocyanurate and the like are exemplified.

In the present invention, at least one or two or more selected from these antioxidants can be used.

The content of (B) the hindered phenol-based antioxidant in the present invention is 0.01 parts by mass or more and 1 part by mass or less with respect to 100 parts by mass of the (A) polyacetal polymer.
<(C) Aliphatic carboxylic acid hydrazide>
(C) The aliphatic carboxylic acid hydrazide used in the present invention includes adipic acid dihydrazide, sebacic acid dihydrazide, dodecanedioic acid dihydrazide, stearic acid hydrazide and the like. Sebacic acid dihydrazide is preferred, and when used in combination with a hydantoin compound that scavenges formaldehyde and has a hydrazide group, mold deposits that originally occur can be remarkably suppressed.

In the present invention, the amount of (C) added is 0.01 to 0.50 parts by mass, preferably 0.02 to 0.30 parts by mass, per 100 parts by mass of the polyacetal polymer (A).

<(D) Hydantoin compound having two hydrazinocarbonylalkyl groups>
The (D) hydantoin compound having two hydrazinocarbonylalkyl groups (hereinafter sometimes abbreviated as hydantoin compound) of the present invention includes 1,3-bis(hydrazinocarbonoethyl)hydantoin, 1,3-bis (Hydrazinocarbonoethyl)-5-methylhydantoin, 1,3-bis(hydrazinocarbonoethyl)-5,5-dimethylhydantoin, 1,3-bis(hydrazinocarbonoethyl)-5-isopropylhydantoin and the like, and the 5-position of the hydantoin has one or two substituents (a linear or branched alkyl group having 1 to 6 carbon atoms such as a methyl group, an aryl group having 6 to 10 carbon atoms such as a phenyl group, etc. ), and the two substituents at the 5-position may form a ring together with the carbon atom at the 5-position. Preferably, 1,3-bis(hydrazinocarbonoethyl)-5-isopropylhydantoin is used.

The (D) hydantoin compound of the present invention suppresses mold deposit when used in combination with (C) the aliphatic carboxylic acid hydrazide of the present invention. In particular, the combined use with sebacic acid dihydrazide is highly effective.

In the present invention, the amount of the hydantoin compound (D) added is 0.001 to 0.50 parts by mass, preferably 0.01 to 0.30 parts by mass, per 100 parts by mass of the polyacetal polymer (A). .

In the present invention, if both (C) an aliphatic carboxylic acid hydrazide and (D) a hydantoin compound are contained, the effect of the present invention can be obtained. is preferably 0.03 to 0.55 parts by mass. The content ratio of (C) and (D) is preferably (C):(D)=10:90 to 99:1.

<(E) Alkaline earth metal salt of aliphatic carboxylic acid>
The aliphatic carboxylic acid constituting (E) the alkaline earth metal salt of an aliphatic carboxylic acid of the present invention may be either a saturated aliphatic carboxylic acid or an unsaturated aliphatic carboxylic acid. Examples of such aliphatic carboxylic acids include monovalent or divalent aliphatic carboxylic acids having 10 or more carbon atoms, such as monovalent saturated aliphatic carboxylic acids having 10 or more carbon atoms [capric acid, lauric acid, myristic acid, , saturated aliphatic carboxylic acids with 10 to 34 carbon atoms (preferably saturated aliphatic carboxylic acids with 10 to 30 carbon atoms) such as pentadecylic acid, palmitic acid, stearic acid, arachidic acid, behenic acid, montanic acid, etc.], 10 carbon atoms The above monovalent unsaturated aliphatic carboxylic acids [oleic acid, linoleic acid, linolenic acid, arachidonic acid, erucic acid and other unsaturated aliphatic carboxylic acids with 10 to 34 carbon atoms (preferably unsaturated fatty acids with 10 to 30 carbon atoms group carboxylic acid), etc.], divalent aliphatic carboxylic acids having 10 or more carbon atoms (dibasic aliphatic carboxylic acids) [sebacic acid, dodecanedioic acid, tetradecanedioic acid, thapsiic acid, etc. -30 saturated aliphatic carboxylic acid (preferably divalent saturated aliphatic carboxylic acid with 10 to 20 carbon atoms), etc.], divalent unsaturated aliphatic carboxylic acid with 10 or more carbon atoms [decenedioic acid, dodecenedioic acid, etc. divalent C10-30 unsaturated aliphatic carboxylic acid (preferably divalent C10-20 unsaturated aliphatic carboxylic acid)] can be exemplified.

In the above aliphatic carboxylic acid, some of the hydrogen atoms are substituted with a substituent such as a hydroxyl group, and an aliphatic carboxylic acid having one or more hydroxyl groups in the molecule (e.g., 12-hydroxy Hydroxy-saturated aliphatic carboxylic acids with 10 to 26 carbon atoms such as stearic acid) are also included, and aliphatic carboxylic acids with slightly different carbon atoms depending on the precision of purification are also included.

In the present invention, the alkaline earth metal is preferably calcium or magnesium, and particularly preferably calcium.
In the present invention, particularly preferred alkaline earth metal salts of aliphatic carboxylic acids are calcium stearate and calcium 12-hydroxystearate.

The amount of the alkaline earth metal salt of an aliphatic carboxylic acid added in the polyacetal resin composition is 0.001 to 0.30 parts by mass, preferably 0.001 to 0.30 parts by mass, per 100 parts by mass of the polyacetal polymer (A). 01 to 0.25 parts by mass.

<(F) Graft copolymer>
The (F) graft copolymer in the present invention has a polyethylene main chain and an acrylonitrile-styrene copolymer as a side chain.

(F) The ratio of polyethylene (d1) and acrylonitrile-styrene copolymer (d2) constituting the graft copolymer is preferably d1:d2 = 80:20 to 20:80 (mass ratio), particularly preferably d1 :d2=60:40 to 40:60.

In the present invention, the blending amount of the graft copolymer (F) is 2 to 10 parts by mass per 100 parts by mass of the polyacetal polymer (A). If the amount of component (F) is less than 2 parts by mass, the intended effect of the present invention for improving friction and wear characteristics will be insufficient. On the other hand, if the amount of component (F) added exceeds 10 parts by mass, mechanical properties such as rigidity are impaired, and friction and wear characteristics are deteriorated, which is not preferable.

<(G) fatty acid ester>
The (G) fatty acid ester used in the present invention is a fatty acid ester of a fatty acid having 12 to 32 carbon atoms and a monohydric or polyhydric alcohol having 2 to 30 carbon atoms.

(G) Fatty acids constituting fatty acid esters include saturated fatty acids such as lauric acid, myristic acid, palmic acid, stearic acid, behenic acid, lignoceric acid, cerotic acid, montanic acid and melissic acid, oleic acid, elaidic acid, Examples include unsaturated fatty acids such as linoleic acid, linolenic acid, arachidonic acid, erucic acid and ricinoleic acid.

In addition, alcohols constituting (G) fatty acid esters include monohydric alcohols such as propyl, isopropyl, butyl, octyl, capryl, lauryl, myristyl, stearyl, and behenyl, and ethylene glycol, propylene glycol, butanediol, glycerin, and pentaerythritol. , sorbitan and other polyhydric alcohols.

(G) Fatty acid esters preferably include fatty acids selected from lauric acid, palmitic acid, stearic acid and behenic acid, monohydric alcohols selected from stearyl alcohol and behenyl alcohol, ethylene glycol, propylene glycol, glycerin, pentaerythritol, Esters with polyhydric alcohols selected from sorbitan, specific examples include stearyl stearate, behenyl behenate, ethylene glycol monostearate, ethylene glycol distearate, glycerin monostearate, glycerin distearate, glycerin tristearate, glycerin monobehenate, sorbitan monostearate, sorbitan distearate, sorbitan monobehenate and the like.

In the present invention, the amount of (G) fatty acid ester compounded is 0.5 to 5 parts by mass per 100 parts by mass of (A) polyacetal polymer. If the amount of component (G) blended is less than 0.5 parts by mass, a sufficient slidability improving effect cannot be expected. properties may be impaired.

<(H) Spindle-shaped calcium carbonate>
In the present invention, when it is desired to further improve the surface properties (surface hardness, smoothness, etc.) and mechanical properties of the molded article, (H) spindle-shaped calcium carbonate is blended to achieve this.
The (H) spindle-shaped calcium carbonate compounded in the (A) polyacetal polymer in the present invention is particles belonging to light calcium carbonate and having a spindle-like shape. The spindle shape refers to a shape similar to a spindle used in spinning yarn, that is, a cylindrical shape with a thick central portion and gradually tapering at both ends. Calcium carbonate may have a shape generally similar to this.

Preferably, the average particle diameter is 0.1-1 μm, the average particle length is 0.5-10 μm, and the average value of particle length/particle diameter is 2-10. Here, the particle diameter refers to the diameter of the spindle-shaped particle's maximum diameter (usually the central part in the length direction), the particle length refers to the length of the spindle-shaped particle, and the average particle diameter and average particle length are , refers to a value measured by photographing spindle-shaped calcium carbonate with an electron microscope, reading the particle diameter and particle length of 50 particles randomly selected from the photograph, and calculating the average value.

Examples of such specific (H) spindle-shaped calcium carbonate include Silver W, PC, PCX and Callite SA manufactured by Shiraishi Kogyo Co., Ltd. The spindle-shaped calcium carbonate (H) used in the present invention is preferably surface-treated with a surface treating agent, and more preferably surface-treated with aminosilane. SL-101 manufactured by Shiraishi Kogyo Co., Ltd. is exemplified as such surface-treated (H) spindle-shaped calcium carbonate. By performing surface treatment, the adhesion between the resin and calcium carbonate is improved, and the dynamic frictional resistance is improved.

In the present invention, the amount of (H) spindle-shaped calcium carbonate compounded is 2 to 18 parts by mass, preferably 3 to 15 parts by mass, per 100 parts by mass of the polyacetal polymer (A). If the blending amount of component (H) is less than 2 parts by mass, excellent friction and wear properties cannot be achieved under a wide range of sliding conditions including severe sliding conditions, and mechanical properties (especially Rigidity, surface hardness, etc.) cannot be expected to improve either. If the blending amount of the component (H) exceeds 18 parts by mass, the smoothness of the surface of the molded product will be insufficient, and the amount of wear and increase (deterioration) of the coefficient of friction will tend to occur.

<Other additives>
The polyacetal resin composition of the present invention may optionally further contain a weather resistance improver, an impact resistance improver, a glossiness control agent, a filler, a coloring agent, a nucleating agent, and an electrifying agent, as long as they do not interfere with the present invention. One or two or more of inhibitors, surfactants, antibacterial agents, antifungal agents, fragrances, foaming agents, compatibilizers, physical property modifiers (boric acid or its derivatives, etc.), perfumes, etc. can be blended.
<Method for producing polyacetal resin composition>

The method for producing the polyacetal resin composition of the present invention is not particularly limited, and it can be prepared by various conventionally known methods for preparing resin compositions. For example, (1) a method of mixing all the components that make up the composition, feeding this to an extruder and melt-kneading to obtain a pellet-like composition, (2) a method of obtaining a pellet-like composition, A method of obtaining a composition in the form of pellets by supplying the remaining components from the main feed port of the extruder and melt-kneading them from the side feed port. A method of adjusting the composition to a predetermined composition can be adopted.

In the preparation of the composition using an extruder, it is preferable to use an extruder having one or more devolatilization vent ports, and water or a low-boiling point About 0.1 to 10 parts by mass of alcohol is supplied to 100 parts by mass of the polyacetal polymer, and formaldehyde and the like generated in the extrusion process are preferably devolatilized and removed from the devolatilization vent port together with water and low boiling point alcohols. . Thereby, the amount of formaldehyde generated from the polyacetal resin composition and its molded article can be further reduced.

The polyacetal resin composition of the present invention thus prepared can be molded by various conventionally known molding methods such as injection molding, extrusion molding, compression molding, vacuum molding, blow molding and foam molding. .

The present invention also includes the recycling of molded articles comprising the polyacetal resin composition and the colored polyacetal resin composition described above. Specifically, a recycled resin composition obtained by melt-kneading and extruding molded articles made of these resin compositions or pulverized products thereof alone or together with resin materials or molded articles having the same or different compositions, and these A recycled molded product obtained by melting and kneading a molded product made of the resin composition of (1) or a pulverized product thereof alone or together with a resin material or molded product having the same or a different composition.

In this way, the recycled resin composition and recycled molded article prepared by repeated melting heat history are also kept at an extremely low level of formaldehyde generation, similar to the polyacetal resin composition on which they are based. is.

EXAMPLES The present invention will be specifically described below by way of examples, but the present invention is not limited to these. In addition, all "parts" in the examples and comparative examples represent parts by mass. Various properties evaluated in Examples and Comparative Examples and evaluation methods thereof are as follows. The unit of numerical values shown in Tables 1 and 2 is parts by mass.

Various components shown in Tables 1 and 2 were added and mixed in the proportions shown in Tables 1 and 2, and the mixture was melt-kneaded with a vented twin-screw extruder to prepare a pellet-like composition.
Each component described in Tables 1 and 2 used in the examples is as follows.

(A) Polyacetal polymer A-1: 3.3% by mass of 1,3-dioxolane based on total monomers (trioxane and 1,3-dioxolane) using a twin-screw paddle type continuous polymerization machine , Trioxane added with 1000 ppm of methylal was continuously supplied, and at the same time boron trifluoride dibutyl etherate (catalyst concentration: cyclohexane solution of 20 ppm (as boron trifluoride) relative to all monomers) was supplied to the same place. and polymerized.
An aqueous solution containing 1000 ppm of triethylamine was added to the polymer discharged from the outlet of the polymerizer immediately after the discharge, and mixed and pulverized, and stirred. After that, centrifugal separation and drying were carried out to obtain a catalyst-inactivated polymer. This polymer is supplied to a twin-screw extruder having a vent port, melted and kneaded at a resin temperature of about 220 ° C., and while devolatilizing under reduced pressure at the vent port, unstable ends are removed to obtain a pellet-shaped polymer. got After that, drying was carried out to obtain the desired polymer. (Melt index (measured at 190°C and a load of 2.16 kg): 9 g/10 minutes)

A-2: Using a twin-screw paddle type continuous polymerization machine, trioxane added with 3.3% by mass of 1,3-dioxolane and 1000 ppm of methylal based on total monomers (trioxane and 1,3-dioxolane). It was continuously supplied, and at the same time, phosphotungstic acid (catalyst concentration: 3 ppm methyl formate solution with respect to all monomers) was supplied as a heteropolyacid catalyst and polymerized. 20 ppm of sodium stearate is added to the polymer discharged from the outlet of the polymerizer, supplied to a twin-screw extruder having a vent port, melt-kneaded at a resin temperature of about 220 ° C., and devolatilized under reduced pressure at the vent port. , the catalyst was deactivated and the unstable ends were removed to obtain a pellet-shaped polymer. After that, drying was carried out to obtain the desired polymer. (Melt index (measured at 190°C and a load of 2.16 kg): 9 g/10 minutes)

- (B) Hindered phenol antioxidant B-1: ethylene bis (oxyethylene) bis [3-(3-(5-t-butyl-4-hydroxy-m-tolyl) propionate] (manufactured by BASF, IRGANOX245)
B-2: Pentaerythritol tetrakis [3-(3,5-di-t-butyl-4-hydroxyphenyl) propionate] (manufactured by BASF, IRGANOX1010)
(C) Aliphatic carboxylic acid hydrazide C-1: Sebacic acid dihydrazide C-2: Adipic acid dihydrazide C-3: Dodecanedioic acid dihydrazide (D) Hydantoin compound D-1: 1,3-bis(hydrazinocarbohydrate noethyl)-5-isopropylhydantoin (manufactured by Ajinomoto Fine-Techno Co., Ltd., "Amicure" VDH)
(E) alkaline earth metal salt of aliphatic carboxylic acid E-1: calcium stearate E-2: calcium 12-hydroxystearate (F) graft copolymer
F-1: PE-g-AS (manufactured by NOF Corporation, Modiper A1401) graft copolymer composed of polyethylene and acrylonitrile-styrene copolymer)
- (G) fatty acid ester G-1: glycerin monobehenate (Rikemar B-100, manufactured by Riken Vitamin Co., Ltd.)
G-2: Glycerin monostearate (Rikemar S-100, manufactured by Riken Vitamin Co., Ltd.)
G-3: Stearyl stearate (manufactured by NOF Corporation, Unistar M-9676)
・ (H) Spindle-shaped calcium carbonate H-1: Spindle-shaped calcium carbonate (manufactured by Shiraishi Kogyo Co., Ltd., SL-101 (aminosilane surface-treated product)

<Evaluation>
The property evaluation items and evaluation methods in the examples are as follows. Tables 3 and 4 show the results.

<Evaluation of Formaldehyde Generation Amount (VOC) from Molded Products>
Using the polyacetal resin compositions prepared in Examples and Comparative Examples, flat test pieces (100 mm×40 mm×2 mmt) were molded under the following conditions. Two of these flat test pieces were enclosed in a 10 L polyvinyl fluoride sampling bag, degassed, 4 L of nitrogen was introduced, and heated at 65° C. for 2 hours. 3 L was withdrawn at min, and the generated formaldehyde was adsorbed on a DNPH (2,4-dinitrophenylhydrazine) collection tube (Sep-Pak DNPH-Silica, manufactured by Waters).

Thereafter, the reaction product of DNPH and formaldehyde was extracted with acetonitrile from the DNPH collection tube, and the amount of generated formaldehyde was determined by the calibration curve method using a standard substance of the reaction product of DNPH and formaldehyde on a high-performance liquid chromatograph. , the amount of formaldehyde generated per unit mass of test piece (μg/g) was calculated.

*Molding machine: FANUC ROBOSHOT α-S100ia (Fanuc Corporation)
*Molding conditions: Cylinder temperature (°C) Nozzle - C1 - C2 - C3
190 190 180 160°C
Injection pressure 60 (MPa)
Injection speed 1.0 (m/min)
Mold temperature 80 (°C)

<Evaluation of mold deposit (MD)>
Using the polyacetal resin compositions prepared in Examples and Comparative Examples, mold deposit test pieces (33 mm×23 mm×1 mmt) were molded under the following conditions.
[Evaluation method]
After 5,000 shots were continuously molded, the surface of the cavity portion in the mold was visually observed, and the amount of deposit was determined visually according to the following criteria.
⊚: No deposits observed ◯: Substantially no deposits observed △: Some deposits observed.
×: Deposits are observed throughout XX: A large amount of deposits are observed throughout

* Molding machine: FANUC ROBOSHOT S-2000i 50B (Fanuc Corporation)
*Molding conditions: Cylinder temperature (°C) Nozzle - C1 - C2 - C3
205 215 205 185°C
Injection pressure 40 (MPa)
Injection speed 1.5 (m/min)
Mold temperature 80 (°C)

<Evaluation of friction/wear characteristics>
Using the polyacetal resin compositions prepared in Examples and Comparative Examples, cylindrical test pieces (outer diameter: 25.6 mm, inner diameter: 20 mm) were molded under the following conditions. Then, according to the Suzuki friction and wear test, the dynamic friction coefficient and the specific wear amount (×10 ⁻³ mm ³ /(N·km)) were measured using two types of test pieces as mating materials. One of the two test pieces was a polyacetal resin molding (product name: Duracon (registered trademark) M90-44, manufactured by Polyplastics), and the other was carbon steel S45C.
The measurement conditions are, when the mating material is a polyacetal resin molded body (against POM), surface pressure: 0.06 MPa, speed: 15 cm / s, and when the mating material is carbon steel (against metal), the surface pressure : 0.98 MPa, speed: 30 cm/s. The measurement was performed in an atmosphere of 23°C and 55RH%.
*Molding machine: FANUC ROBOSHOT α-S50ia (Fanuc Corporation)
*Molding conditions: Cylinder temperature (°C) Nozzle - C1 - C2 - C3
200 200 180 170°C
Injection pressure 60 (MPa)
Injection speed 1.0 (m/min)
Mold temperature 80 (°C)

As described above, it is clear that within the composition range of the present invention, excellent friction and wear properties are obtained, and the amount of formaldehyde generated and the amount of mold deposits generated are stably suppressed.

Claims (6)

At least (A) 100 parts by mass of polyacetal polymer,
(B) 0.01 to 1 part by mass of a hindered phenol antioxidant;
(C) 0.01 to 0.50 parts by mass of an aliphatic carboxylic acid hydrazide;
(D) 0.001 to 0.50 parts by mass of a hydantoin compound having two hydrazinocarbonylalkyl groups;
(E) 0.001 to 0.30 parts by mass of an alkaline earth metal salt of an aliphatic carboxylic acid;
(F) 2 to 10 parts by mass of a graft copolymer,
(G) blended with 0.5 to 5 parts by mass of fatty acid ester,
The total amount of (C) and (D) is 0.03 to 0.55 parts by mass with respect to 100 parts by mass of the polyacetal polymer (A),
The (F) graft copolymer has a polyethylene main chain and an acrylonitrile-styrene copolymer as a side chain,
The (G) fatty acid ester is a polyacetal resin composition comprising a fatty acid having 12 to 32 carbon atoms and a monohydric or polyhydric alcohol having 2 to 30 carbon atoms. The polyacetal resin composition according to claim 1, further comprising (H) 2 to 18 parts by mass of spindle-shaped calcium carbonate. 3. The polyacetal resin composition according to claim 1, wherein the (C) aliphatic carboxylic acid hydrazide is sebacic acid dihydrazide. 4. The polyacetal resin composition according to any one of claims 1 to 3, wherein (E) the alkaline earth metal salt of an aliphatic carboxylic acid is at least one selected from calcium stearate and calcium 12-hydroxystearate. The polyacetal resin composition according to any one of claims 1 to 4, wherein (D) the hydantoin compound having two hydrazinocarbonylalkyl groups is 1,3-bis(hydrazinocarbonoethyl)-5-isopropylhydantoin. . 6. The method for producing a polyacetal resin composition according to any one of claims 1 to 5, wherein the (A) polyacetal polymer contains trioxane as the main monomer (a) and has at least one carbon-carbon bond. Comonomer (b) is one or more selected from cyclic ethers and cyclic formals having the A method for producing a polyacetal resin composition, which is a polyacetal copolymer obtained by melt-kneading a hydrogen carbonate, a carboxylate or a hydrate thereof (d) to deactivate a polymerization catalyst (c).