JPH07268180A - Polyoxymethylene composition - Google Patents

Abstract

PURPOSE:To obtain the subject composition significantly improved in thermal stability, suppressed to a minimum in mold deposit development even subjected to continuous molding for a long time, useful for impact-resistant engineering resins, by incorporating a polyoxymethylene composition with a specific melamine-formaldehyde polycondensate. CONSTITUTION:This composition is obtained by incorporating (A) poloxymethylene with (B) 1-40wt.% of a core-shell polymer made up of rubbery polymer core and glassy polymer shell, (C) 0.01-5wt.% of an antioxidant, and (D) 0.01-10wt.% of a melamine-formaldehyde polycondensate insoluble in warm water but soluble in dimethyl sulfoxide, produced by reaction, mainly, between (1) melamine and (2) formaldehyde. It is preferable that anions be unable to be detected in the component B and this component B be produced by emulsion polymerization using a nonionic surfactant and a polymerization initiator with neutral radicals generated.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a polyoxymethylene composition having excellent impact resistance and improved generation of mold deposits.

[0002]

2. Description of the Related Art As is well known, polyoxymethylene has excellent physical properties such as mechanical properties and electrical properties, or chemical properties such as chemical resistance and heat resistance. In recent years, it has been used as a typical engineering resin in an extremely wide range of fields. But,
Along with the expansion of fields in which polyoxymethylene is used, further improvement is required in the properties of the material. As an example of such a demand, it is desired to impart a high degree of impact resistance in a wide temperature range to a molded product used for automobile parts and the like. As a means for improving the impact resistance of polyoxymethylene, it has been conventionally proposed to add and blend thermoplastic polyurethane (for example, JP-A Nos. 59-145243 and 61-19652).
However, this method can provide a polyoxymethylene composition having desirable properties in terms of impact resistance, but the adhesion between the polyoxymethylene and the thermoplastic polyurethane is insufficient. Of the polyoxymethylene and polyurethane on the surface of the molded product is deteriorated, and the appearance of the molded product is impaired. Due to the accumulation of substances, there are drawbacks such as dimensional defects and deterioration of molding efficiency. On the other hand, as a means for improving the impact resistance of polyoxymethylene, the addition and blending of a so-called core-shell polymer in which a glass-like shell (shell) is formed in a rubber-like core (core) is also conventionally known. (For example, JP-A-60-219253). In this method, since the core-shell polymer is finely dispersed in the polyoxymethylene in the form of particles, the peeling phenomenon of the elastomer does not occur, therefore, there is no adhesion of the elastomer to the mold,
Further, the strength and elongation of the welded part of the molded product has been greatly improved as compared with the addition of polyurethane, and the field of application is expanding greatly. However, when the core-shell polymer is blended, the polyoxymethylene is decomposed more often than when the thermoplastic polyurethane is added, and the formaldehyde gas generated by this polyoxymethylene decomposition adheres to the mold during the molding process Accumulated as mold deposits on the mold, the appearance of the molded product is impaired, and dimensional accuracy cannot be maintained. In order to avoid this problem, a core-shell polymer which is difficult to decompose polyoxymethylene is disclosed in Japanese Patent Laid-Open No.
No. 14856, the decomposition of polyoxymethylene is greatly reduced and a remarkable effect is obtained, but it cannot be said to be sufficient for the recent requirements mentioned above. On the other hand, as a means for improving the thermal stability of polyoxymethylene during molding, there is known a method in which a sterically hindered phenol compound and a polyamide, an amidine compound, a hydroxide of an alkali or alkaline earth metal, or the like is used in combination. However, it is still insufficient for polyoxymethylene containing a core-shell polymer, and its improvement is required.

[0003]

[Means for Solving the Problems] The inventors of the present invention have conducted a detailed study on various stabilizers in order to solve the above-mentioned problems in polyoxymethylene resins containing a core-shell polymer, and as a result, specific melamine The present inventors have found that adding a formaldehyde polycondensate to a polyoxymethylene composition is effective in achieving the intended purpose, and have completed the present invention. That is, the present invention relates to (A) polyoxymethylene, (B) 1 to 40% by weight of a core-shell polymer having a rubbery polymer core and a glassy polymer shell, (C) 0.01 to 5% by weight of an antioxidant, and ( D) Melamine-which is mainly formed by reacting melamine and formaldehyde and is insoluble in warm water and soluble in dimethyl sulfoxide.
The present invention relates to a polyoxymethylene composition containing 0.01 to 10% by weight of a formaldehyde polycondensate.

The constituent components of the composition of the present invention will be described in detail below. A feature of the composition of the present invention is that (D) a melamine-formaldehyde polycondensate that is insoluble in warm water and soluble in dimethylsulfoxide is added. The melamine-formaldehyde polycondensate itself used in the present invention is a known method, preferably the melamine: formaldehyde molar ratio is 1: 0.8 to 1: 5, particularly preferably 1: 1.
It can be produced by reacting in an aqueous solution or an aqueous dispersion at 0 to 1: 2.0. For example, melamine is added to a formaldehyde aqueous solution adjusted to pH 8 to 9 and the temperature is adjusted to 60 to 90.
Hold at ℃, dissolve and react with stirring. Since the solution becomes cloudy as the reaction proceeds, the condensation reaction is stopped by cooling for an appropriate time. This is dried by a method such as spray drying to obtain a crude melamine-formaldehyde polycondensate powder. The crude melamine-formaldehyde polycondensate is washed with warm water (50 to 70 ° C.) for 30 minutes to 1 hour, filtered, and the residue is dissolved in dimethyl sulfoxide. After filtering and removing the insoluble solid matter remaining at this time, a white powder of a purified melamine-formaldehyde polycondensate can be obtained by adding a large excess of acetone to cause precipitation and filtering and drying. Melamine-formaldehyde polycondensate subjected to such treatment and (B) core-shell polymer described later
(C) By blending with polyoxymethylene in combination with an antioxidant, the object of the present invention is excellent in impact resistance, less decomposition gas is generated during molding, and the generated decomposition gas It is also possible to obtain a polyoxymethylene composition that does not form a deposit on the mold because it is prevented from adhering to the mold and has almost no sublimation or decomposability by itself. Here, if the melamine-formaldehyde polycondensate produced by the conventional method is used as it is, it contains a sublimable monomer component, or the condensation that promotes the generation of decomposition gas at the time of molding is excessively advanced. Because it contains ingredients,
It is difficult to obtain a thermally stable polyoxymethylene composition. The specific melamine-formaldehyde polycondensate defined in the present invention is further an alkanol having 1 to 4 carbon atoms, and the molar ratio of melamine: ether group is 1: 2.0 or less,
It may be partially etherified so that it is preferably 1: 1.0 or less. Furthermore, up to 50 mol% of melamine can be replaced with other condensable substances. Other condensable substances used in the melamine-formaldehyde polycondensate defined in the present invention include guanamine compounds represented by acetoguanamine, adipoguanamine, benzoguanamine, etc., dicyandiamide, and 2,5-diamino.
-1,3,4-triazole represented by amidine compounds,
Urea derivatives such as urea and ethylene urea, amides such as malonamide and isophthalic acid diamide, aliphatic amines such as monoethanolamine and diethanolamine, o-toluidine, p-toluidine, p-phenylenediamine Etc., aromatic amines such as p-aminobenzamide, sterically hindered phenols such as 2,4-t-butylphenol, hydrazine and N, N-bis- (3 ', 5) '-The-t
-Butyl-4'-hydroxyphenyl) -propionylhydrazine and other hydrazines. Further, the amount of the (D) melamine-formaldehyde polycondensate added and blended in the present invention is 0.01 to 10% by weight, preferably 0.02 to 3% by weight, particularly 0.05, based on (A) polyoxymethylene. ~ 1 wt% is preferred. This blend amount is 0.
If it is less than 01% by weight, it is not sufficient to improve the thermal stability of the polyoxymethylene composition, and if it exceeds 10% by weight, the mechanical properties of the material are significantly impaired and the composition becomes brittle.

The (B) core-shell polymer used in the present invention can be prepared by a known method, or a commercially available product can be used. A typical example is the Acryloid KM330 from Rohm and Haas and
KM653, Kureha Chemical's Paraloid KCA-102 and KCA-
301, Takeda Pharmaceutical Co., Ltd. Staphyroid PO-0270, P
O-0135, Kane Ace FM of Kanegafuchi Chemical Co., Ltd., Metabrene C-102, E-901, W-800, S- of Mitsubishi Rayon Co., Ltd.
2001 etc. are mentioned. Among such core-shell polymers,
Preferred is a core-shell polymer having a rubber-like polymer core and a glass-like polymer shell containing methyl methacrylate as a main component, and particularly a core-shell polymer in which substantially no anion is detected. In a polyacetal resin composition mixed with a core-shell polymer in which an anion is detected, the polyacetal may decompose and deteriorate during melting. Here, the core-shell polymer in which an anion is not substantially detected means a core-shell polymer in which an anion is not detected by a usual qualitative test of anion. For example, as a measuring method,
5 g of the sample (core shell polymer) was weighed in a 50 ml Erlenmeyer flask, 20 ml of ion-exchanged water was added, the mixture was stirred with a magnetic stirrer for 3 hours, and then the filtrate filtered through No. 5 C filter paper was divided into two, and 1% barium chloride was added to one. A method of comparing the occurrence of turbidity by adding 0.5 ml of an aqueous solution (a qualitative test of sulfate ion), and the same treatment, but adding a 0.1 N silver nitrate aqueous solution instead of a 1% barium chloride aqueous solution, and comparing the occurrence of turbidity The presence of anions can be confirmed by an observation method (a qualitative test for halogen ions). Preferably core-shell polymers are used in which these anions are completely absent.

The core-shell polymer preferably used in the present invention is one obtained by emulsion polymerization using a nonionic surfactant and a polymerization initiator in which the radicals generated are neutral. The emulsion polymerization can be carried out, for example, using the following surfactants and polymerization initiators. As the nonionic surfactant, polyoxyethylene nonylphenyl ether, polyoxyethylene stearyl ether, ether type such as polyoxyethylene lauryl ether, ester type such as polyoxyethylene monostearate,
Most widely used nonionic surfactants such as sorbitan ester type such as polyoxyethylene sorbitan monolaurate and block polymer type such as polyoxyethylene polyoxypropylene block copolymer can be used. The amount of addition is appropriately selected according to the particle stabilizing ability of the surfactant. Examples of the polymerization initiator include azobisisobutyronitrile, dimethyl 2,2′-azobisisobutyrate, 2,2′-azobis (2-aminopropane) dihydrochloride, and other azo polymerization initiators, cumene hydroperoxide, Peroxide-based polymerization initiators such as diisopropylbenzene hydroperoxide and hydrogen peroxide may be used alone or in combination of two or more. When emulsion polymerization is carried out in such a reaction system using a surfactant containing no anion and a polymerization initiator other than persulfate, the obtained core-shell polymer becomes substantially free of anion. A polyoxymethylene composition using such a core-shell polymer that does not substantially contain anions has excellent impact resistance.

The core-shell polymer in the present invention is
It is obtained by a continuous multi-step emulsion polymerization method in which the polymer of the previous step is sequentially coated with the polymer of the latter step, that is, a so-called seed emulsion polymerization method. At the time of particle generation polymerization, it is preferable to start the emulsion polymerization reaction by adding a monomer, a surfactant and water to a reactor, and then adding a polymerization initiator. The first stage polymerization is a reaction that forms a rubbery polymer. Examples of the monomer that constitutes the rubber-like polymer include conjugated dienes, alkyl acrylates having an alkyl group with 2 to 8 carbon atoms, and mixtures thereof. These monomers are polymerized to form a rubber-like polymer having a glass transition temperature of -30 ° C or lower. As such a conjugated diene, for example, butadiene,
Although there can be mentioned isoprene, chloroprene and the like,
In particular, butadiene is preferably used. Further, as an alkyl acrylate having an alkyl group having 2 to 8 carbon atoms,
For example, ethyl acrylate, propyl acrylate, butyl acrylate, cyclohexyl acrylate, 2-
Examples thereof include ethylhexyl acrylate, but butyl acrylate is particularly preferably used. In the first-stage polymerization, monomers copolymerizable with conjugated dienes and alkyl acrylates, for example, styrene, vinyltoluene, aromatic vinyl such as α-methylstyrene, aromatic vinylidene, acrylonitrile, methacrylonitrile, and cyanation It is also possible to copolymerize vinyl, vinylidene cyanide, alkyl methacrylate such as methyl methacrylate and butyl methacrylate. If the first stage polymerization does not contain conjugated dienes, or if it contains conjugated dienes and is 20% by weight or less of the total amount of monomers in the first stage, use a small amount of crosslinkable monomer and grafting monomer. It is possible to obtain a polymer having higher impact resistance. As the crosslinkable monomer, for example, an aromatic divinyl monomer such as divinylbenzene, ethylene glycol diacrylate, ethylene glycol dimethacrylate, butylene glycol diacrylate, hexanediol diacrylate, hexanediol dimethacrylate, oligoethylene glycol diacrylate,
Examples include alkane polyol polyacrylates such as oligoethylene glycol dimethacrylate, trimethylolpropane diacrylate, trimethylolpropane dimethacrylate, trimethylolpropane triacrylate, and trimethylolpropane trimethacrylate, and alkanepolyol polymethacrylates, but especially butylene. Glycol diacrylate and hexanediol diacrylate are preferably used. Examples of the grafting monomer include unsaturated carboxylic acid allyl esters such as allyl acrylate, allyl methacrylate, diallyl maleate, diallyl fumarate and diallyl itaconate, and allyl methacrylate is particularly preferably used. Such a crosslinkable monomer and a grafting monomer are used in an amount of 0 to 5% by weight, preferably 0.1 to 2% by weight, based on the total amount of the first stage monomers. The rubbery polymer core preferably ranges from 50 to 90% by weight of the total core-shell polymer. When the core is less than this weight range or more than this weight range, the effect of improving impact resistance of the resin composition obtained by melt-mixing the produced core-shell polymer may not be sufficient. When the glass transition temperature of the core is higher than -30 ° C, the effect of improving low temperature impact resistance may not be sufficient. A glassy polymer is formed in the outermost shell phase (shell phase). Examples of the monomer constituting the glassy polymer include methyl methacrylate and a monomer copolymerizable with methyl methacrylate. These monomers are methyl methacrylate alone or a mixture of monomers copolymerizable with methyl methacrylate, and form a glassy polymer having a glass transition temperature of 60 ° C. or higher. Examples of the monomer copolymerizable with methyl methacrylate include alkyl acrylates such as ethyl acrylate and butyl acrylate, alkyl methacrylates such as ethyl methacrylate and butyl methacrylate, aromatic vinyl such as styrene, vinyltoluene and α-methylstyrene, and aromatic vinylidene. , Vinyl cyanide such as acrylonitrile and methacrylonitrile, vinyl polymerizable monomer such as vinylidene cyanide, and the like, and particularly preferably ethyl acrylate, styrene, acrylonitrile and the like are used. The outermost shell phase is preferably in the range of 10 to 50% by weight based on the whole core-shell polymer. When the outermost shell phase is less than or more than this weight range, the effect of improving the impact resistance of the resin composition obtained by melt mixing the resulting core-shell polymer may not be sufficient.

Further, an intermediate phase may be present between the first stage and the final polymerized phase. For example, polymerized monomers having functional groups such as glycidyl methacrylate, methacrylic acid, hydroxyethyl methacrylate, etc., polymerized monomers that form glassy polymers such as methyl methacrylate, polymerized monomers that form rubbery polymers such as butyl acrylate, etc. The intermediate phase is formed by seed emulsion polymerizing. Such an intermediate phase can be variously selected depending on the desired properties of the core-shell polymer. Further, the polymerization ratio may be appropriately selected depending on the monomer used. For example, when the glassy polymer is used as the intermediate phase, its polymerization rate may be calculated as a part of the shell, and in the case of a rubbery polymer, it may be calculated as a part of the core. The structure of the core-shell polymer having such an intermediate phase is, for example, one having a multilayer system structure in which another layer is present between the core and the shell,
One having a salami structure in which the intermediate layer is finely dispersed in the core is listed. In a more extreme case of a core-shell polymer having a salami structure, the mesophase to be dispersed may form a new core at the center of the core. The core-shell polymer having such a structure may occur when a monomer represented by styrene is used as a mesophase structure monomer. When a core-shell polymer having an intermediate phase is used, in addition to impact resistance improvement, bending elastic modulus improvement, heat deformation temperature increase,
The appearance (surface peeling and suppression of pearl luster, change in color tone due to change in refractive index) is also improved. In the present invention, the amount of the (B) core-shell polymer added is 1 to 40% by weight, preferably 5 to 40% by weight, based on (A) polyoxymethylene.
Is. If the addition amount of the core-shell polymer is less than 1% by weight, the effect of improving the impact resistance of the obtained resin composition may not be recognized, and if it is more than 40% by weight, the obtained resin composition has rigidity and heat resistance. The sex is significantly impaired.

Next, as the (C) antioxidant used in the present invention, 2,2'-methylenebis (4methyl-6-t) is used.
-Butylphenol), 1,6-hexanediol-bis [3- (3,5-di-t-butyl-4-hydroxyphenyl) propionate], pentaerythritol tetrakis [3- (3,5-di-t-butyl) -4-Hydroxy-phenyl) propionate], triethylene glycol-bis- [3- (3-t-butyl-5-methyl-4-hydroxyphenyl) propionate], 1,3,5-trimethyl-2,4, 6-tris (3,5-di-t-butyl-4-hydroxy-benzyl) benzene, n-octadecyl-3-
(4'-Hydroxy-3 ', 5'-di-t-butylphenol) propionate, 4,4'-methylenebis (2,6-di-
t-butylphenol), 4,4'-butylidene-bis-
(6-t-butyl-3-methyl-phenol), di-stearyl-3,5-di-t-butyl-4-hydroxybenzylphosphonate, 2-t-butyl-6- (3-t-butyl-5) -Methyl-2-hydroxybenzyl) -4-methylphenyl acrylate, N, N'-hexamethylenebis (3,5-di-t-butyl-4-hydroxy-hydrocinnamamide) are hindered phenolic antioxidants Examples of the agent include triphenylphosphite, trisnonylphenylphosphite, tris (2,4-di-t-butylphenyl) phosphite, tris (2-t-butyl-4-).
Methylphenyl) phosphite, tris (2,4-di-t-
Amylphenyl) phosphite, tris (2-t-butylphenyl) phosphite, tris (2-t-phenylphenyl) phosphite, tris (2- (1,1-dimethylpropyl) -phenyl) phosphite, tris ( 2,4- (1,1-dimethylpropyl) -phenyl) phosphite, tris (2
-Cyclohexylphenyl) phosphite, tris (2-
Examples of the phosphorus-based antioxidant include t-butyl-4-phenylphenyl) phosphite. In addition, any antioxidant such as hindered amine type and sulfur type can be used, and at least one kind or two or more kinds thereof can be used. Among these, 1,6-hexanediol-bis [3- (3,5-di-t-butyl-4-hydroxyphenyl) propionate], pentaerythritol tetrakis [3- (3,5-di-t-butyl- 4-hydroxyphenyl) propionate], triethylene glycol-bis [3- (3-t-butyl-5-methyl-4-]
Hydroxyphenyl) propionate], N, N′-hexamethylenebis (3,5-di-t-butyl-4-hydroxy-hydrocinnamamide) are particularly preferred substances. The amount of the (C) antioxidant added and blended in the present invention is
(A) 0.01 to 5% by weight, preferably 0.05 to 2% by weight, especially 0.10 to 1% by weight, based on polyoxymethylene
Is preferred. If the amount is less than 0.01% by weight, it is not sufficient to improve the thermal stability of the polyoxymethylene composition, and if it exceeds 5% by weight, the effect of thermal stability reaches saturation and rather a discoloration tendency occurs. Absent.

(A) Polyoxymethylene, to which the above-mentioned additives are added, is a polymer compound having an oxymethylene group (--CH ₂ O--) as a main constituent unit, such as polyoxymethylene homopolymer and oxymethylene. It may be any of copolymers, terpolymers and block copolymers containing a small amount of other constitutional units in addition to the groups, and the molecule may have not only a linear structure but also a branched or crosslinked structure. Further, there is no particular limitation on the degree of polymerization or the like.

The composition of the present invention is not essential, but depending on the purpose thereof, a nitrogen-containing compound other than the melamine-formaldehyde polycondensate of the present application, a hydroxide of an alkali or alkaline earth metal, an inorganic acid salt, It is also possible to use one or more metal-containing compounds such as carboxylates or alkoxides in combination. In addition, in order to impart desired properties to the composition of the present invention depending on its purpose, conventionally known additives such as a lubricant, a nucleating agent, a weathering (light) stabilizer, an optical brightener, a release agent and the like are added. It is also possible to add one or more kinds of surfactants, organic polymer materials, inorganic or organic fibrous, powdery or plate-like fillers.

The method for preparing the composition of the present invention is not particularly limited, and can be easily prepared by the known equipment and method generally used as a conventional method for preparing a resin composition. For example,
i) After mixing each component, kneading and extruding with an extruder to prepare pellets, and then molding, ii) Once preparing pellets with different compositions, mixing the pellets in a prescribed amount and molding A method of later obtaining a molded article of the target composition,
iii) Any method such as directly charging one or more of each component into a molding machine can be used. In addition, mixing a part of the resin component in the form of fine powder with the other components and adding the powder is a preferable method for uniformly blending these components.
Further, the resin composition according to the present invention can be molded by any of extrusion molding, injection molding, compression molding, vacuum molding, blow molding, and foam molding.

[0013]

EXAMPLES The present invention will be described below with reference to examples, but the present invention is not limited to these examples. still,
The evaluation method shown in the following examples is as follows. 1) Izod impact test Using a test piece with a thickness of 6.4 mm, Izod impact strength (kg · cm / cm) was measured according to ASTM D256. 2) Amount of die deposit A molded product having a specific shape was continuously molded (about 24 hours) using an injection molding machine under the following conditions, and the amount of the die deposit was evaluated by visual observation on the following five grades. (Molding conditions) Injection molding machine: Toshiba IS30EPN (manufactured by Toshiba Machine Co., Ltd.) Cylinder temperature: 210 ° C Injection pressure: 750kg / cm ² Injection time: 4sec Cooling time: 3sec Mold temperature: 30 ° C Examples 1 to 7 (A) Polyoxymethylene copolymer (manufactured by Polyplastics Co., Ltd., DURACON), (B) core-shell polymer,
(C) Triethylene glycol-bis [3- (3-t-butyl-5-methyl-4-hydroxyphenyl) propionate]) as an antioxidant and (D) certain purified melamine-formaldehyde polycondensates are reported in Table 1. The mixture was added and mixed in the proportions shown in (1) to obtain a pelletized composition with a twin-screw extruder, and the above evaluation was performed. The results are shown in Table 1.

Comparative Examples 1 to 6 As shown in Table 1, in the case where crude melamine-formaldehyde polycondensation was blended in place of the melamine-formaldehyde polycondensation of Example, or when melamine was blended, the same as in Examples. The pellet composition was obtained and the above evaluation was performed. The results are shown in Table 1.

[0015]

[Table 1]

Note 1) Core-shell polymer (b-1) Takeda Pharmaceutical Co., Ltd., Staphyloid PO-
0135 (b-2) Kureha Chemical Industry Co., Ltd., Paraloid KCA-1
02 (b-3) Mitsubishi Rayon Co., Ltd., METABLEN S-200
1 Note 2) Melamine-formaldehyde polycondensate (d-1) Formaldehyde / melamine molar ratio is 1.0 / 1
After being prepared with the composition as described above, filtered with warm water at 60 ° C for 30 minutes, washed with acetone, dried at room temperature and dissolved in dimethylsulfoxide at a concentration of 0.5% by weight for 2 hours to remove impurities by filtration. A melamine-formaldehyde polycondensate purified by putting it in acetone for precipitation, filtering it, and then drying it at room temperature. (d-2) Formaldehyde / melamine molar ratio of 1.5 / 1
A melamine-formaldehyde polycondensate purified by the same treatment as in (d-1) after being prepared with the charged composition of. (d'-1) Formaldehyde / melamine molar ratio 1.0 / 1
A crude melamine-formaldehyde polycondensate prepared by the above composition (pretreatment polycondensate for obtaining a purified melamine-formaldehyde polycondensation of (d-1)).

[0017]

As is apparent from the above description and Examples, the present invention significantly improved the thermal stability of polyoxymethylene and suppressed the formation of mold deposits even during continuous molding for a long time. It is possible to obtain an impact resistant polyoxymethylene composition.

Claims (5)

[Claims] 1. A core-shell polymer having (A) polyoxymethylene and (B) a core of a rubbery polymer and a shell of a glassy polymer in an amount of 1 to 40% by weight, and (C) an antioxidant of 0.01 to
5% by weight and (D) Melamine-formaldehyde polycondensate, which is mainly formed by reacting melamine and formaldehyde and is insoluble in warm water and soluble in dimethyl sulfoxide.
A polyoxymethylene composition containing 0.01 to 10% by weight. 2. The polyoxymethylene composition according to claim 1, wherein the (B) core-shell polymer is a core-shell polymer in which substantially no anion is detected. 3. The polyoxy according to claim 1 or 2, wherein the core-shell polymer (B) is obtained by emulsion polymerization using a nonionic surfactant and a polymerization initiator in which radicals generated are neutral. Methylene composition. 4. The polyoxymethylene composition according to claim 1, wherein the shell of the core-shell polymer (B) is a polymer containing methyl methacrylate as a main component. 5. The melamine: formaldehyde molar ratio of the (D) melamine-formaldehyde polycondensate is 1: 0.8 to.
The polyoxymethylene composition according to any one of claims 1 to 4, which is 1: 5.