JPH0812848A - Polyacetal resin composition - Google Patents

Abstract

PURPOSE:To obtain the subject composition developing no debonding on the surface of the molded products therefrom even under high shear stress, also excellent in sliding characteristics, by incorporating a polyacetal resin with an acid anhydride-modified polyolefin resin, polyisocyanate compound and specific lubricant. CONSTITUTION:This composition is obtained by incorporating (A) 100 pts.wt. of a polyacetal resin with (B) 1-100 pts.wt. of an acid anhydride-modified polyolefin resin, (C) 0.01-20 pts.wt. of a polylsocyanate compound or modified form thereof (pref. isophorone diisocyanate), and (D) 0.1-20 pts.wt. of a lubricant selected from silicone oils, perfluoropolyethers, polyalkylene glycols, a olefin oligomers, paraffin oils, alkyl-substituted diphenyl ethers and aliphatic full esters. It is preferable that the component B be prepared by modifying polyethylene, polypropylene or copolymers composed of at least two kinds of polymers including them with maleic anhydride.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a polyacetal resin composition which has excellent friction and wear characteristics and does not cause peeling on the surface of a molded article even under molding conditions of high shear.

[0002]

BACKGROUND OF THE INVENTION Polyacetal resins have well-balanced mechanical properties.
It is widely used in the fields of automobiles, electric / electronic products, etc. due to its excellent friction / wear resistance, chemical resistance, heat resistance, and electrical characteristics. However, the required properties in such fields are becoming more sophisticated, and as one example, further improvement in general physical properties as well as sliding properties such as friction coefficient and specific wear amount is desired. For the purpose of improving sliding properties, fluororesins and polyolefin resins are added to polyacetal resins, and sliding modifiers such as fatty acids, aliphatic esters and various synthetic lubricating oils are added. However, the addition of fluororesins and polyolefin-based resins improves sliding properties to some extent, but these resins have poor compatibility with polyacetal resins, causing peeling on the surface of molded products and deposition on molding dies. Easy to generate things. Further, in order to sufficiently modify the surface of the polyacetal resin, it is necessary to add a large amount of such a resin, and in this case, the physical properties originally possessed by the polyacetal resin are significantly reduced. Further, addition of the lubricating oil alone has some effect in reducing the coefficient of friction and the amount of specific wear, but there are various difficulties such as difficulty during extrusion processing and exudation during use. For the purpose of improving such a problem, there has been proposed a method in which a polyolefin-based resin and a lubricant are added and used in combination with a polyacetal resin (JP-A-49-99740, etc.). The performance of a general sliding member is improved by this method. However, depending on the lubricant used in combination, peeling may occur on the surface of the molded product during the molding process, particularly during the molding under the condition of high shearing.

[0003]

Therefore, as a result of diligent studies on the above points, the present inventors have found that an acid anhydride-modified polyolefin resin, a polyisocyanate compound or a modified product thereof and a lubricating oil are added to a polyacetal resin in combination. Thus, the surface of the molded product is not peeled off even under the condition of high shearing, and a polyacetal resin composition having excellent sliding properties has been successfully developed, and the present invention has been completed. That is, the present invention relates to (A) polyacetal resin 1
(B) 1-100 parts by weight of acid anhydride-modified polyolefin resin and (C) 0.01-20 parts by weight of polyisocyanate compound or its modified product, and (D) silicone oil, perfluoropolyether, relative to 00 parts by weight. , Polyalkylene glycol, α-olefin oligomer, paraffin oil,
The present invention provides a polyacetal resin composition containing 0.1 to 20 parts by weight of one or more lubricating oils selected from the group consisting of alkyl-substituted diphenyl ethers and aliphatic full esters.

The constituent components of the present invention will be described below. The polyacetal resin in the present invention is a thermoplastic resin containing a polymer compound having an oxymethylene unit (-CH ₂ O-) as a main repeating constitutional unit as a main component, and formaldehyde, trioxane, tetraoxane or the like by a usual method. Homopolymerized products, copolymers composed of two or more of these, or monomers and cyclic ethers such as ethylene oxide, propylene oxide, oxacyclobutane, and 1,3-dioxolane, β-propiolactone, γ-
A cyclic ester such as butyrolactone or a copolymer with a certain vinyl compound is used as the component (A). Further, the polyacetal resin may have a part of its molecular terminal converted to an ether bond, an ester bond, or the like.

The component (B) of the present invention is an acid anhydride-modified polyolefin resin obtained by modifying a polyolefin resin with an acid anhydride. As the polyolefin resin used here, ethylene, propylene, butene, hexene, octene, nonene, decene, homopolymers of α-olefins such as dodecene, or a random, block or graft copolymerization consisting of two or more of these. Coalesced, or these 1,4
-Non-conjugated dienes such as hexadiene, dicyclopentadiene, 5-ethylidene-2-norbornene and 2,5-norbonadiene, conjugated diene components such as butadiene, isoprene and piperylene, α, β- such as acrylic acid and methacrylic acid
Unsaturated acids or their derivatives such as esters, aromatic vinyl compounds such as acrylonitrile, styrene and α-methylstyrene, vinyl esters such as vinyl acetate, vinyl ethers such as vinyl methyl ether and comonomers such as derivatives of these vinyl compounds. Random, block or graft copolymers containing one or more of the components may be mentioned, regardless of the degree of polymerization, presence or absence of side chains or branches, degree, copolymer composition ratio, etc. From the viewpoint of dynamic characteristics, polyethylene, polypropylene, or a copolymer composed of two or more of these is preferably used. Further, as the acid anhydride used for modification, unsaturated carboxylic acid anhydrides such as maleic anhydride, citraconic anhydride, itaconic anhydride, tetrahydrophthalic anhydride, nadic anhydride, methylnadic acid anhydride, and allyl succinic anhydride. , Or at least one selected from derivatives thereof, and maleic anhydride is particularly preferably used. Further, as the modification method, a method of further adding an unsaturated carboxylic acid anhydride such as maleic anhydride or a derivative thereof when copolymerizing a polyolefin resin and copolymerizing the same is generally used. It is not limited. Here, the blending amount of both components is appropriately 0.1 to 20 parts by weight, preferably 0.1 to 10 parts by weight, with respect to 100 parts by weight of the polyolefin resin. When the amount of the effective acid anhydride in the acid anhydride-modified polyolefin resin is too small, the affinity between the polyacetal resin and the polyolefin resin is not sufficiently improved, and thus the effect of the present invention cannot be obtained, which is too large. In this case, gelation may occur, which may cause poor dispersibility or defective molding. The amount of the component (B) compounded is 1 to 100 parts by weight, preferably 1 to 30 parts by weight, based on 100 parts by weight of the (A) polyacetal resin. If the compounding amount of the component (B) is too low, the effect of the present invention will not be sufficiently exhibited, and if it is too large, the properties of the polyacetal resin will be impaired.

The polyisocyanate compound or its modified product used as the component (C) in the present invention is a compound having an iso (thio) cyanate group in the molecule, and
It is a compound containing two or more iso (thio) cyanate groups in the molecule. Examples of component (C) include, for example, 4,4 ′
-Diphenylmethane diisocyanate, 2,4-tolylene diisocyanate, 2,6-tolylene diisocyanate,
Xylene diisocyanate, 1,6-hexamethylene diisocyanate, isophorone diisocyanate, 1,5-naphthalene diisocyanate, or diisothiocyanate corresponding to these, and their dimers, trimers, and isocyanate groups (-NCO) Can be any compound protected in any form, but in consideration of various properties such as degree of discoloration such as melt processing, or safety in handling, 4,4′-diphenylmethane diisocyanate,
Isophorone diisocyanate, 1,5-naphthalene diisocyanate, 1,6-hexamethylene diisocyanate,
Particularly preferred are 2,4-tolylene diisocyanate, 2,6-tolylene diisocyanate, and modified products (or derivatives) such as dimers and trimers thereof. The blending amount of component (C) is
0.01 to 20 parts by weight per 100 parts by weight of component (A), preferably
It should be in the range of 0.01 to 10 parts by weight. If the component (C) is too small, the compatibility between the maleic anhydride-modified polyolefin resin and the polyacetal resin is not sufficient, and if it is too large, gelation occurs, and the fluidity and deterioration of the resin properties deteriorate. It does not happen. Also, (C)
As a catalyst for accelerating the activity of the polyisocyanate compound or a modified product thereof, amines, or an organometallic compound containing a metal selected from Sn, Zn and Pb is blended in any amount within a range not impairing the physical properties of the present invention. By doing so, the sliding characteristics and the appearance of the surface of the molded product are further improved.

Next, the (D) lubricating oil used in the present invention is
Refers to lubricating oils that improve the friction and wear properties of polyacetal, and more specifically, from silicone oils, perfluoropolyethers, polyalkylene glycols, α-olefin oligomers, paraffin oils, alkyl-substituted diphenyl ethers and aliphatic full esters. A lubricating oil based on one or more selected from the group consisting of: Hereinafter, each oil will be described in detail. As the silicone-based oil, polydimethylsiloxane and polymethylphenylsiloxane represented by the structure (1) are preferably used as typical examples.

[0008]

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(Here, R is a methyl group, a part of which is an alkyl group, a phenyl group, a halogenated alkyl group,
It may be a halogenated phenyl group, polyalkylene glycol, etc.) In addition, a part of the methyl group of dimethylsiloxane is represented by a halogenated phenyl group represented by a chlorophenyl group, an alkyl group of C ₈ or more, and a polyethylene glycol. Modified polyorganosiloxane substituted with various substituents such as a polyalkylene glycol-containing group, a higher aliphatic ester group that is a derivative of an aliphatic carboxylic acid having ₈ or more carbon atoms, and a halogenated alkyl group represented by a trifluoromethyl group. Can also be used. In the present invention, the silicone oil having an average molecular weight in the range of 5000 to 70,000 is preferably used. The polyalkylene glycol defined in the present invention is a polyethylene glycol or polypropylene glycol unit having a structure of single or random, block or graft copolymerization, and ring-opening polymerization of alkylene oxide mainly composed of ethylene oxide and propylene oxide. The lubricating oil obtained by
As such polyalkylene glycol, a derivative in which a terminal hydroxy group is etherified or esterified can also be used. As a typical ester or ether derivative, a terminal hydroxy group of polyalkylene glycol, a C ₈ or more aliphatic carboxylic acid or aliphatic alcohol, a compound having a structure in which an ester or ether bond, respectively,
In addition, ethers of polyhydric alcohols such as glycerin, polyglycerin and sorbitan with polyalkylene glycols can be used. In the present invention, the average molecular weight is 400
~ 5000 polypropylene glycol, polyethylene glycol / polypropylene glycol copolymer, and esters of these alkylene glycols with C ₁₂ or more fatty acids represented by lauric acid and stearic acid, or C represented by stearyl alcohol, etc. Ethers with ₁₂ or more fatty alcohols are particularly preferably used. Perfluoropolyether is a compound represented by the following general formula, which has a structure in which a hydrogen atom of polyalkylene glycol is substituted with a fluorine atom. In the present invention, those having an average molecular weight of 1000 to 15000 are preferably used. Branch type

[0010]

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(Here, 50> m ≧ 1, 10 ≧ n ≧ 0) Linear type CF ₃ O- (CF ₂ CFO) _m- (CF ₂ O) _n -CF ₃ (3) (where, 150 ≧ m ≧ 10, 200 ≧ n ≧ 1) α-olefin oligomer is a fatty acid having a structure mainly composed of C ₆ -C ₂₀ α-olefin alone or copolymerized with ethylene and C ₃ -C ₂₀ α-olefin. It is a group hydrocarbon.
In the present invention, ethylene / α-olefin cooligomers having a number average molecular weight of 400 to 4000 are preferably used. Paraffin oil refers to so-called paraffinic mineral oil obtained by refining petroleum fractions. In the present invention,
Those having an average molecular weight of 300 to 800 are preferably used. The alkyl-substituted diphenyl ether is, as shown in (4) below, at least one or more kinds of phenyl of diphenyl ether in which C ₁₂ or more saturated aliphatic chain is in the form of a substituent selected from an alkyl group, an ester group and an ether group. The compound introduced is shown. There is no particular regulation of molecular weight,
Any alkyl diphenyl ether is preferably used. Such a substituent may be introduced at any position of the phenyl group, but is preferably synthetically 2, 4, 6,
It is an alkyl-substituted diphenyl ether having a substituent at any of the 2 ', 4', and 6'positions, and is particularly preferably a disubstituted product at the 4,4 'position.

[0012]

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(R is an alkyl group, ether group or ester group introduced at part or all of the 2 to 6-position and 2'to 6'-position) The substituent of the alkyl-substituted diphenyl ether is, for example, dodecyl group or tetradecyl group. Groups, straight chain alkyl groups such as hexadecyl group and octadecyl group, and branched alkyl groups shown in (5).

[0014]

[Chemical 4]

(N and m are integers of 0 or more, n + m ≧ 11) Further, the ester group is a dodecyloxycarbonyl group,
Examples thereof include a tetradecyloxycarbonyl group, a hexadecyloxycarbonyl group, an octadecyloxycarbonyl group, a lauroyloxy group, a myristoyloxy group, a palmitoyloxy group and a stearoyloxy group. Examples of the ether group include lauroyl group, myristoyl group, palmitoyl group and stearoyl group. Further, it may be a derivative of such an ester or ether group having an aliphatic hydrocarbon chain having a branched structure, for example, isostearyl alcohol or isostearic acid derivative. As the aliphatic full ester, a full ester composed of a monovalent fatty acid having 16 or more carbon atoms and a monohydric aliphatic alcohol having 16 or more carbon atoms, a monovalent fatty acid having 16 or more carbon atoms and a polyvalent one having 16 or more carbon atoms Is a full ester composed of an aliphatic alcohol, and a full ester composed of a polyvalent fatty acid having 16 or more carbon atoms and a monohydric aliphatic alcohol having 16 or more carbon atoms. As the monovalent fatty acid, palmitic acid, stearic acid, isostearic acid,
Examples thereof include straight chain and / or branched unsaturated fatty acids such as arachidic acid, behenic acid and montanic acid. As the monohydric aliphatic alcohol, cetyl alcohol, stearyl alcohol, isostearyl alcohol, behenyl alcohol, erucyl alcohol, hexyldecyl alcohol,
Octyldodecyl alcohol and the like can be mentioned. Examples of the polyvalent fatty acid include phthalic acid, adipic acid, sebacic acid, trimellitic acid and the like. Examples of the polyhydric alcohol include ethylene glycol, glycerin, pentaerythritol and the like. Of these aliphatic full esters, from the viewpoints of price, availability (synthesis, purification), friction and wear characteristics, and processability, stearyl stearate, behenyl behenate, glycerin tribehenate, particularly preferably,
Examples thereof include ethylene glycol distearate, ethylene glycol dibehenate, glycerin tristearate, and pentaerythritol tetrastearate. In the present invention, 1 selected from these aliphatic full esters
One species or two or more species are preferably used. Generally, such an aliphatic full ester is industrially obtained as a mixture with a partial ester such as a monoester, but in the present invention, such a mixture is also preferably used practically. or,
(D) The amount of lubricating oil added is 100% of the above (A) polyacetal resin.
It is 0.1 to 20 parts by weight with respect to parts by weight. If the amount is less than 0.1 parts by weight, the effect of improving slidability cannot be expected.If the amount is more than 20 parts by weight, peeling occurs on the surface of the molded product even if this method is used, and in some cases, molding cannot be performed, or the base polymer is used. The properties of the sail resin may be significantly impaired. Preferably 0.5 to 10 parts by weight is blended.

During the melt-kneading of the composition, if necessary, an antioxidant, an ultraviolet absorber, a photoprotective agent, a phosphite stabilizer, a peroxide decomposer, a basic auxiliary agent, a nucleating agent, a plasticizer. Additives such as agents, antistatic agents, flame retardants, colorants, release agents, etc. may be added in arbitrary amounts within a range that does not impair the physical properties of the present invention. Next, the preparation of the composition or molded article of the present invention,
It is easily prepared by a known method that is generally used as a conventional resin composition preparation method. For example, after mixing the respective components, pellets are prepared by kneading and extruding with a single-screw or twin-screw extruder, followed by a method of molding, pellets having different compositions (masterbatch), and then preparing the pellets. Any method can be used, such as a method of mixing (diluting) a predetermined amount and subjecting to molding, and obtaining a molded product of the target composition after molding. or,
In the preparation of such a composition, it is preferable to grind a part or all of the base polyacetal resin, mix this with other components, and then carry out extrusion or the like in order to improve the dispersibility of the additive. Is.

The composition obtained according to the present invention can be molded by a usual method.

[0018]

As described above, the features and effects of the present invention are as follows: a polyacetal resin, an acid anhydride-modified polyolefin resin and a polyisocyanate compound or a modified product thereof,
Furthermore, by adding and blending a lubricating oil, the compatibility of the acid anhydride-modified polyolefin resin that retains the lubricating oil and the polyacetal resin is dramatically improved, and as a result, the surface of the molded product can be treated even under conditions of high shear. That is, no peeling occurs and a polyacetal resin having excellent sliding properties can be obtained.

[0019]

The present invention will be described in more detail with reference to the following examples, but the present invention is not limited thereto. Example 1 (A) 5 parts by weight of a maleic anhydride-modified polyethylene obtained by modifying 100 parts by weight of a polyacetal resin (B) 100 parts by weight of a low-density polyethylene resin with 1 part by weight of maleic anhydride, and (C) 1 part of isophorone diisocyanate. Parts by weight, (D) Add 2 parts by weight of polydimethylsiloxane as a lubricating oil
A 30 mm twin-screw extruder melt-kneaded at a set temperature of 190 ° C. and a screw rotation speed of 100 rpm to pelletize. This was dried at 80 ° C. for 2 hours or more. The pellets were molded into test pieces by an injection molding machine, and the following evaluations were performed. Table 2 shows the results. -Molded product surface condition Test pieces for evaluation (50 mm x 50 mm x 1 mm: center pin gate method) were molded at different injection speeds, and the peeling condition of the surface was evaluated on a scale of five. (Gate diameter: 1t) 1 ... There are many peelings on the entire molded product 2 ... Peeling on the entire molded product 3 ... Peeling only on the gate part 4 ... Slight peeling only on the gate part 5 ... No peeling ・ Sliding characteristics Suzuki type Using a friction / abrasion tester (contact area 2.0 cm ² ), under pressure (0.6 kg / cm ² ), linear velocity 150 mm / sec, running condition for 24 hours, against polyacetal resin (manufactured by Polyplastics Co., Ltd.), Dynamic friction coefficient with the product name DURACON M90-44),
The specific wear amount was measured. Examples 2 to 5 (B) The addition amount of maleic anhydride-modified polyethylene, (D) the type and addition amount of lubricating oil were changed, and other sample preparation methods and the like were performed in the same manner as in Example 1 and evaluated. Table 2 shows the results. Examples 6 to 11 (B) The addition amount of maleic anhydride-modified polyethylene, (C) the addition amount of isophorone diisocyanate, (D) the type and addition amount of lubricating oil were changed, and other sample preparation methods and the like were performed in Example 1. The evaluation was performed in the same manner as in. Table 2 shows the results.

Examples 12 to 16 (B) The amount of maleic anhydride in the maleic anhydride-modified polyethylene and (D) the kind and amount of the lubricating oil added were changed, and other sample preparation methods were the same as in Example 1. Performed and evaluated. The results are shown in Table 3. Example 17 (B) The main chain of maleic anhydride-modified polyethylene was changed to polypropylene, and the other sample preparation method was performed in the same manner as in Example 1 and evaluated. The results are shown in Table 3. Examples 18 and 19 (C) Isophorone diisocyanate was changed to 4,4′-diphenylmethane diisocyanate, and other sample preparation methods and the like were performed in the same manner as in Example 1 and evaluated. The results are shown in Table 3.

Comparative Example 1 (D) A test piece was prepared and evaluated in the same manner as in Example 1 except that the lubricating oil was not added. The results are shown in Table 4. Comparative Examples 2 to 6 (C) Isophorone diisocyanate was not added, and a test piece was prepared and evaluated in the same manner as in Example 1 except that the type and addition amount of the (D) lubricating oil were changed. The results are shown in Table 4. Comparative Examples 7 to 10 (B) Test pieces were prepared in the same manner as in Example 1 except that polyethylene or polypropylene was added instead of the maleic anhydride-modified polyethylene, and the type and amount of (D) lubricating oil was changed. And evaluated in the same manner. The results are shown in Table 4. Comparative Example 11 A test piece was prepared and evaluated in the same manner as in Example 1 except that (B) maleic anhydride-modified polyethylene and (C) isophorone diisocyanate were not added. The results are shown in Table 4. The components (B), (C) and (D) used in the examples and comparative examples are as follows.

(B) Maleic anhydride-modified polyolefin resin and unmodified polyolefin

[0023]

[Table 1]

(C) Type of polyisocyanate C-1 Isophorone diisocyanate (IPDI) C-2 4,4'-diphenylmethane diisocyanate (MD
I) (D) Lubricating oil A commercially available lubricating oil that is generally used was used.・ Silicone oil (SH2 manufactured by Toray Dow Corning Silicone Co., Ltd.)
00, SH510) -Straight chain perfluoropolyether (Fomblin M60 manufactured by Montecatini) -Branched perfluoropolyether (Fomblin YR1800 manufactured by Montecatini) -Polypropylene glycol (PP1000, PP300 manufactured by Sanyo Kasei Co., Ltd.)
0) ・ Polyethylene glycol / polypropylene glycol copolymer (manufactured by Sanyo Kasei Co., Ltd. 50HB-5100) ・ α-olefin / ethylene cooligomer (manufactured by Mitsui Petrochemical Industry Co., Ltd., Lucant HC40, H)
C600) ・ Paraffin oil (Process oil manufactured by Idemitsu Co., Ltd.) ・ Alkyl-substituted diphenyl ether (Moresco high lube manufactured by Matsumura Petrochemical Research Institute, Inc.)

[0025]

[Table 2]

[0026]

[Table 3]

[0027]

[Table 4]

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Claims (10)

[Claims] Claims: 1. To 100 parts by weight of (A) polyacetal resin, 1 to 100 parts by weight of (B) acid anhydride-modified polyolefin resin and (C) 0.01 to polyisocyanate compound or its modified product.
20 parts by weight and (D) silicone oil, perfluoropolyether,
Polyacetal resin composition prepared by adding 0.1 to 20 parts by weight of one or more lubricating oils selected from the group consisting of polyalkylene glycol, α-olefin oligomer, paraffin oil, alkyl-substituted diphenyl ether and aliphatic full ester. . 2. The polyacetal resin composition according to claim 1, wherein the acid anhydride-modified polyolefin resin as the component (B) is obtained by modifying 100 parts by weight of the polyolefin resin with 0.1 to 20 parts by weight of maleic anhydride. 3. The (C) component polyisocyanate compound or its modified product is 4,4′-diphenylmethane diisocyanate, isophorone diisocyanate, 1,5-naphthalene diisocyanate, 1,6-hexamethylene diisocyanate, 2,4-triisocyanate. A diisocyanate, 2,6-tolylene diisocyanate, and one or more selected from the group consisting of dimers and trimers thereof.
Alternatively, the polyacetal resin composition according to item 2. 4. The polyacetal resin composition according to claim 1, wherein the silicone oil as the component (D) is polydimethylsiloxane or polymethylphenylsiloxane having an average molecular weight of 5000 to 70,000. 5. The perfluoropolyether of component (D) is
The average molecular weight is 1000 to 15,000, and the average molecular weight is 1000 to 15,000.
The polyacetal resin composition according to the item. 6. The (D) component polyalkylene glycol comprises:
Polypropylene glycol with an average molecular weight of 400-5000,
4. A polyethylene glycol / polypropylene glycol copolymer, an ester of these alkylene glycols and fatty acids having 12 or more carbon atoms, or an ether of these alkylene glycols and aliphatic alcohols having 12 or more carbon atoms. The polyacetal resin composition according to item 1. 7. The α-olefin oligomer of component (D) comprises
The polyacetal resin composition according to any one of claims 1 to 3, which is an ethylene / α-olefin oligomer having an average molecular weight of 400 to 4000. 8. The polyacetal resin composition according to claim 1, wherein the paraffin oil as the component (D) has an average molecular weight of 300 to 800. 9. The (D) component alkyl-substituted diphenyl ether has one or more saturated aliphatic substituents selected from an alkyl group having 12 or more carbon atoms, an ester group, and an ether group, introduced into phenyl. The polyacetal resin composition according to any one of claims 1 to 3, wherein the polyacetal resin composition is a compound. 10. An aliphatic full ester of component (D) is a full ester composed of a monovalent fatty acid having 16 or more carbon atoms and a monovalent aliphatic alcohol having 16 or more carbon atoms, and a monovalent aliphatic ester having 16 or more carbon atoms. A full ester comprising a fatty acid and a polyhydric aliphatic alcohol having 16 or more carbon atoms, or a full ester comprising a polyhydric fatty acid having 16 or more carbon atoms and a monohydric aliphatic alcohol having 16 or more carbon atoms. The polyacetal resin composition according to any one of 3 above.