JPH0242858B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to stabilized oxymethylene copolymer compositions. Oxymethylene copolymers obtained by copolymerizing formaldehyde or its cyclic oligomers such as trioxane or tetraoxane with monomers that can be copolymerized with these copolymers are treated with various terminals to prevent depolymerization from the terminals of the polymer. Various oxymethylene copolymer compositions are known, which are subjected to base treatment and then mixed with additives such as antioxidants, heat stabilizers, light stabilizers, and lubricants. In particular, blending a thermal oxidative stabilizer with terminal group treatment is necessary and essential for maintaining and improving the quality of oxymethylene copolymers, and various stabilizers and combinations thereof have been proposed. It has been. For example, Japanese Patent Publication No. 40-21148 discloses a combination of an amidine compound and a sterically hindered phenol, and specifically proposes cyanoguanidine and N,N'-diarylmelamine as the amidine compound. There is. Also, Tokko Akira
55-50502 proposes a combination of an insoluble reticulated melamine-formaldehyde polycondensate and an antioxidant. Furthermore, West German Patent Application No. 1694097 describes water-soluble melamine-formaldehyde polycondensates or melamine-formaldehyde polycondensates.
A combination of a cyanoguanidine-formaldehyde copolycondensate and an antioxidant has been proposed. However, when considering the balance of performance of the oxymethylene copolymer composition, such a combination of binary systems has drawbacks that should be further improved, particularly in various thermal stability properties. That is, conventional oxymethylene copolymer composition molding materials are usually molded at a temperature in the range of 185 to 220°C, and must be molded in an extremely narrow temperature range of up to 225°C at most. For oxymethylene copolymer composition molding materials, which are often molded into small items such as mechanical parts such as gears and bearings, even within the above molding temperature range, depending on the capacity of the molding machine, The current situation is that the residence time often exceeds the time limit for the material to start decomposing, and as a result, undesirable phenomena such as material decomposition and foaming occur within the cylinder, resulting in the production of defective molded products. be. Under these circumstances, there is a strong need in the market for an oxymethylene copolymer composition molding material that maintains the original physical property balance of the oxymethylene copolymer composition and has extremely excellent thermal stability during molding. It has been. By the way, regarding oxymethylene copolymer molding materials that are currently on the market, retention tests at material temperatures of 235°C and 250°C (molding materials at 235°C or
This is a test to evaluate the appearance and other physical properties of the molded product by keeping it at a temperature of 250℃ for 60 minutes and then injection molding.It is a test to evaluate the appearance and other physical properties of the molded product. It can be evaluated as a thermal stability test during molding, which shows results that correspond extremely well to deterioration tests, etc. ), it was found that in most of the materials, severe yellowing was already observed at a material temperature of 235°C, indicating that the material itself had deteriorated significantly, and silver streaks on the surface of the molded product. ) was also observed to occur quite frequently.Furthermore, at a material temperature of 250℃, the material decomposes violently within the cylinder, resulting in a foaming state, which prevents the material from flowing sufficiently within the mold, making injection molding virtually impossible. It turned out that the situation would become impossible. Furthermore, regarding the above molded materials, the material temperature
Continuous injection molding test at 220℃ and 230℃ (1
When continuous molding was carried out, silver streaks, flashes, flow marks, etc. appeared on the surface of the molded product, resulting in a poor appearance.In addition, mold deposits were often observed, resulting in poor molding. It was found that the appearance of the product deteriorated further. The present inventors aimed to improve the drawbacks of the conventionally known oxymethylene copolymer composition molding materials, and to provide an oxymethylene copolymer composition having extremely high thermal stability. As a result of extensive research, it was discovered that the desired objective could be achieved by incorporating the following ternary stabilizer, and the present invention was completed. That is, the present invention provides an oxymethylene copolymer with (1) general formula (A) [In the formula, R ₁ and R ₂ each represent an amino group or a substituted amino group, and R ₃ represents a hydrogen atom, a hydroxyl group, an alkyl group, an alkoxy group, an aryl group, a hydrogenated aryl group, an amino group or a substituted amino group. . ] Amino resin initial polycondensates of amine-substituted triazines (hereinafter abbreviated as "compound A") and formaldehyde (hereinafter "stabilizer A")
(2) General formula (B) [In the formula, R ₄ and R ₅ are each an alkyl group,
Represents a substituted alkyl group or a substituted triazole group, R ₆ is an alkyl group, a substituted alkyl group,
Represents an alkoxy group or a substituted amino group. ] At least one sterically hindered phenol (hereinafter abbreviated as "stabilizer B") shown in (3) hydration of an alkali metal such as sodium or potassium or an alkaline earth metal such as magnesium, calcium or barium. thing,
A stabilized oxymethylene copolymer composition containing at least one metal-containing compound (hereinafter abbreviated as "stabilizer C") represented by the group consisting of inorganic acid salts, carboxylic acid salts, or alkoxides. be. The oxymethylene copolymer composition of the present invention obtained by blending the ternary stabilizer as described above differs from the above-mentioned conventional molding materials of the same type of composition obtained on the market, in that it has a 60°C temperature at 250°C. Not only can molding be performed suitably even after holding for 1 minute, but the resulting molded product has substantially improved appearance in terms of color, gloss, etc. compared to the initial molded product with a cycle time of 1 minute at a material temperature of 250°C. It can be obtained as being comparable. This fact means that the oxymethylene copolymer composition of the present invention can have a material temperature of 250°C or higher as an upper limit temperature range for molding, and this temperature range is higher than that of the conventional oxymethylene copolymer compositions described above. This far exceeds the upper limit temperature of 220°C or 225°C which is commonly applied to polymer composition molding materials. It can be put to practical use in copolymer-based molding materials. In the oxymethylene copolymer composition of the present invention,
In addition, in both cases of continuous molding at material temperatures of 220°C and 230°C, the appearance defect rate is significantly reduced to 1/3 to 1/4 compared to conventional products. No mold deposits, which are one of the problems, were observed, and these facts also indicate that the present invention provides a molded material with excellent thermal stability. Furthermore, regarding the various physical properties of the obtained molded product,
Compared to conventional oxymethylene copolymer compositions, it is equivalent or superior in terms of tensile strength, bending strength, tensile impact strength, Izot impact value, heat distortion temperature, dielectric constant, etc., and is also resistant to 120℃ hot air environment. In the long-term hot air environment test described below, in terms of retention of tensile strength and tensile impact strength, while the conventional product virtually deteriorated after 500 hours, the molded product obtained from the composition of the present invention showed ,
Even after 500 hours, virtually no deterioration tendency is observed. As is clear from the above description, the oxymethylene copolymer composition of the present invention provides an extremely high-performance molding material that eliminates all the defects found in conventional compositions of the same type. was achieved only through the synergistic action of the above-mentioned ternary stabilizers. Among the three stabilizers used in the present invention, the amino resin initial polycondensate ("stabilizer A") is produced by a method known per se. That is, amine-substituted triazines represented by general formula (A) ("compound A")
It is a water-soluble and/or alcohol-soluble substance that can be easily obtained by polycondensation reaction by heating formaldehyde in an aqueous solution or dispersion under a weak alkali in an amount of at most 10 moles per mole. , mere methylolated products of Compound A are not included. Furthermore, as described in the above-mentioned Japanese Patent Publication No. 55-50502, the reaction has progressed further from the water-soluble and/or alcohol-soluble stage, that is, virtually all of the N atoms of the amino group have been substituted. However, even if this compound is used, it cannot exhibit the amazing thermal stability effect achieved in the present invention, even if it is used as an insoluble amino resin in the form of a network. and is not included in "stabilizer A". “Compound A” is the starting compound of “Stabilizer A”
as guanamine (2,4-diamino-sym
-triazine), melamine (2,4,6-triamino-sym-triazine), N-butylmelamine,
N-phenylmelamine, N,N'-diphenylmelamine, N,N'-diallylmelamine, N,N',
N'-triphenylmelamine, N-monomethylolmelamine, N,N'-dimethylolmelamine,
N,N′,N″-trimethylolmelamine, begzoguanamine (2,4-diamino-6-phenyl-
sym-triazine), N-monomethylolbenzoguanamine, N,N'-dimethylolbenzoguanamine, 2,4-diamino-6-methyl-sym-
Triazine, 2,4-diamino-6-butyl-
sym-triazine, 2,4-diamino-6-benzyloxy-sym-triazine, 2,4-diamino-6-butoxy-sym-triazine, 2,4-
Illustrative examples include diamino-6-cyclohexyl-sym-triazine and 2-oxy-4,6-diamino-sym-triazine (Ameline). Among them, melamine, guanamine, benzoguanamine, N-methylolated melamine, and N-methylolated benzoguanamine can be particularly preferably used. As "stabilizer B", compounds known as antioxidants can be used, and specifically, the following can be mentioned. That is, 2,2'-
Methylene-bis(4-methyl-6-t-butylphenol), 1,6-hexanediol-bis[3-(3,5-di-t-butyl-4-hydroxyphenyl)propionate], Pentaerythrityl -Tetrakis [3-(3,5-di-t-butyl-4-hydroxyphenyl)propionate],
Distearyl-3,5-di-t-butyl-4-hydroxybenzylphosphonate, 2,6,7-trioxa-1-phosphor-bi-cyclo[2,2,
2]-oct-4-yl-methyl-3,5-di-
t-Butyl-4-hydroxyhydrocinnamate, 3,5-di-t-butyl-4-hydroxyphenyl-3,5-distearyl-thiotriazylamine, 2(2'-hydroxy-3',5 '-di-t-butylphenyl)-5-chlorobenzotriazole, 2,6-di-t-butyl-4-hydroxymethylphenol, 1,3,5-trimethyl-2,
4,6-tris(3,5-di-t-butyl-4-
hydroxybenzyl)benzene, 4,4'-methylene-bis(2,6-di-t-butylphenol),
Examples include 3,5-di-t-butyl-4-hydroxybenzylmethylamine and N,N'-hexamethylenebis(3,5-di-t-butyl-4-hydroxy-hydrocinnamide), Among them, 2,2'-methylene-bis(4-methyl-
6-t-butylphenol), 1,6-hexanediol-bis[3-(3,5-di-t-butyl-4-hydroxyphenyl)propionate] and pentalisrityl-tetrakis[3-(3,
5-di-t-butyl-4-hydroxyphenyl)
propionate] is particularly effective and preferred. "Stabilizer C" is a metal-containing compound as described above, and examples of inorganic acid salts include carbonate, phosphate, silicate, and borate, and examples of carboxylate include acetic acid and butyric acid. Examples thereof include salts of monovalent carboxylic acids such as oxalic acid, malonic acid, succinic acid, and adipic acid. Examples of alkoxides include methoxide and ethoxide. Among these metal-containing compounds, calcium hydroxide, magnesium hydroxide, potassium hydroxide, and magnesium carbonate are effective and preferred. "Stabilizer A", "Stabilizer B" and "Stabilizer C"
Even if used alone in each category, 2
A mixture of two or more types of stabilizers may be used, and one or more of the stabilizers may be blended into the oxymethylene copolymer as a ternary stabilizer. The amount of each stabilizer varies depending on the type, and usually
"Stabilizer A" is 0.01 to 7 parts by weight, preferably 0.01 to 5 parts by weight, relative to 100 parts by weight of the oxymethylene copolymer.
In the range of parts by weight, "stabilizer B" is 0.05 to 5 parts by weight,
Preferably in the range of 0.05 to 3 parts by weight, and "Stabilizer C" in the range of 0.004 to 5 parts by weight, preferably 0.005 to 5 parts by weight.
It is appropriately selected within the range of 5 parts by weight. If outside these limited ranges, the appearance of the molded product may deteriorate (for example, poor color tone, generation of silver streaks) in a thermal stability test during molding using an injection molding machine, and/or the appearance of the molded product may deteriorate during a continuous molding test using the same injection molding machine. This is undesirable as it leads to an increase in the number of defective products. The order of addition of each stabilizer is not limited, and the form when added may be a powder, a solution, an emulsion, or a suspension. In the present invention, the oxymethylene copolymer refers to a copolymer containing 0.4 to 40 mol%, preferably 0.4 to 10 mol%, of oxyalkylene units in the oxymethylene main chain. Such copolymers include formaldehyde and/or cyclic oligomers thereof,
For example, it can be obtained by reacting trioxane or tetraoxane with a cyclic ether and/or a cyclic acetal in the presence of a polymerization catalyst. As the polymerization catalyst, general cationic polymerization catalysts are used, but compounds containing boron fluoride are particularly suitable, and hydrates and coordination complex compounds are used. Boron fluoride diethyl etherate may be mentioned as a particularly preferred catalyst. The cyclic ether or cyclic acetal used as a comonomer refers to a compound represented by the following general formula. Here, in the formula, R ₁₀ , R ₁₁ , R ₁₂ and R ₁₃ are the same or different and represent a hydrogen atom, an alkyl group or an alkyl group substituted with a halogen. R ₁₄ means a methylene group or an oxymethylene group, or a methylene group or an oxymethylene group each substituted with an alkyl group or a halogenated alkyl group [n is an integer from 0 to 3], or furthermore, (-CH ₂ )― _n OCH ₂ ―(―O―CH ₂ -CH ₂ )― _n O―CH ₂
- In this case, n is equal to 1 and m is an integer from 1 to 4]. The alkyl group mentioned above has 1 to 5 carbon atoms, and 1 to 3 of its hydrogen atoms may be replaced by halogen atoms, especially chlorine atoms. Specific cyclic acetals or ethers include, in particular, ethylene oxide, glycol formals or diglycol formals. For example, propylene oxide or epirohydrin can also be used. Furthermore, cyclic formals of long-chain α,ω diols, such as butanediol formals, ie 1,3-dioxepane, or hexanediol formals are also suitable. The oxymethylene copolymer obtained by the polymerization reaction may be subjected to a catalyst removal treatment by a known method, or after the polymerization reaction, the oxymethylene copolymer obtained by the general formula (D) may be used as a reaction terminator. [In the formula, R ₇ , R ₈ and R ₉ are each an alkyl group,
means a cycloalkyl group, halogenated alkyl group, aryl group, substituted aryl group, aralkyl group, alkoxy group, substituted alkoxy group, mercapto group, aryloxy group or substituted aryloxy group,
These may be the same or different, and R ₈ and R ₉ may be linked to form one alkylene group. ] The catalyst may be deactivated using a trivalent organic phosphorus compound represented by the following. Examples of the trivalent organic phosphorus compound represented by the general formula (D) include ethyltetramethylenephosphine, n-butyldimethylphosphine, triethylphosphine, ethylpentamethylenephosphine, dimethylphenylphosphine, methyl Ethyl-n-pentylphosphine, diethylbutylphosphine, tri-n-
Butylphosphine, methyldiphenylphosphine, ethyl-n-pentylphenylphosphine,
Methylbenzylphenylphosphine, ethyldiphenylphosphine, ethyl-n-hexylphenylphosphine, benzyl-n-butyl-n-propylphosphine, ethyldicyclohexylphosphine, isopropyldiphenylphosphine, ethylbenzylphenyl phosphine, dibenzylethylphosphine, n-butyldiphenylphosphine, n-propylbenzylphenylphosphine,
n-Butylbenzylphenylphosphine, triphenylphosphine, cyclohexyldiphenylphosphine, dibenzyl n-butylphosphine, dicyclohexylphenylphosphine, tricyclohexylphosphine, diphenylbenzylphosphine, dibenzylphenylphosphine Tribenzylphosphine, Ethyl dipropylphosphinate, Ethyl butylphosphinate, Ethyl methylphenylphosphinate, Ethyl ethyl phenyl phosphinate, Ethyl dibutyl phosphinate, Methyl diphenyl phosphinate, Ethyl diphenyl phosphinate, Diphenyl Phenyl phosphinate, phenyl dibenzyl phosphonite, dimethyl ethyl phosphonite, diethyl ethyl phosphonite, diphenyl ethyl phosphonite, diethyl propyl phosphonite, diethyl butyl phosphonite, diethyl phenyl phosphonite, phenyl phosphonite Dimethyl acid, diethyl benzylphosphonate, trimethyl phosphite, triethyl phosphite, tri-n-propyl phosphite,
Tri-isopropyl phosphite, tri-n phosphite
-Butyl, triphenyl phosphite, tricyclohexyl phosphite, tribenzyl phosphite, tritolyl phosphite, β-naphthyl phosphite, tridecyl phosphite, trinonylphenyl phosphite, tristearyl trithiophosphite Among these, triphenylphosphine, triphenyl phosphite, tritolyl phosphite, and the like are particularly preferred. When the above-mentioned reaction terminator is used, the polymerization catalyst is not only deactivated and the polymerization reaction is stopped, but even if the deactivated catalyst remains in the copolymer, it will cause heat loss in the copolymer. This method is preferable because it provides a simplified method for producing an oxymethylene copolymer since it does not have any adverse effect on stability and does not require a subsequent washing operation. Additionally, the ternary stabilizer used in the present invention acts particularly effectively on the oxymethylene copolymer obtained by treatment with the above-mentioned organophosphorus compound, and is therefore less expensive. Provided is an oxymethylene copolymer composition which is more stable and has better stability. EXAMPLES Below, the present invention will be explained in more detail with reference to Examples and Comparative Examples. In addition, in the following description, the intrinsic viscosity is p with 2% by weight of α-binene added.
-Values measured in chlorophenol at 60°C. In addition, "phr", which is a unit for the amount of stabilizers added, means parts by weight per 100 parts by weight of the oxymethylene copolymer. Example 1 100 parts by weight of trioxane and 2.5 parts by weight of ethylene oxide were polymerized using boron fluoride diethyl etherate as a catalyst to obtain a crude oxymethylene copolymer. The obtained copolymer was divided into two parts, and one part was suspended in an aqueous solution containing tri-n-butylamine, heated to remove the catalyst, washed and dried, and had an intrinsic viscosity of 1.45.
A purified oxymethylene copolymer of dl/g was obtained. This refined oxymethylene copolymer is added to a benzoguanamine-formaldehyde initial polycondensate (softening point 55).
~59℃, Nippon Shokubai Kagaku Kogyo Co., Ltd. (trade name: "Dehydrated benzoguanamine resin") 0.3phr, 1,6-hexanediol-bis-3 (3,5-di-t-butyl-)
4-Hydroxyphenyl) propionate (manufactured by Ciba Geigy, trade name: Irganox)
259'') and 0.1 phr of magnesium hydroxide were added, mixed homogeneously using a Henschel mixer, and the mixture was heated for about 15 minutes using a vented twin screw extruder with L/D = 27 and a diameter of 32 mm. It was heated in residence to melt, stabilize and extrude the white resin as a strand from the die head. The strands were immediately commercialized into pellets. The test results of the stabilized oxymethylene copolymer compositions obtained are shown in Tables 3 (1) to (3). Example 2 To the other side of the crude oxymethylene copolymer of Example 1, triphenylphosphine was added in an amount equivalent to twice the amount of the catalyst by mole to deactivate the catalyst. To this, the same stabilizer as in Example 1 was added in the same proportion, and Example 1
Product pellets were obtained by processing in the same manner as above. The test results of the obtained compositions are shown in Tables 3 (1) to (3). Examples 3 to 13 The oxymethylene copolymer obtained in Example 2, in which the catalyst was deactivated by the addition of triphenylphosphine, was treated with "stabilizer A" as shown in Table 1.
"Stabilizer B" and "Stabilizer C" were mixed with "other" additives as desired, and product pellets were obtained in the same manner as in Example 1. The test results of the obtained composition are shown in Table 3 (1) and (2).
Shown below.

【table】

[Table] Example 14 A crude oxymethylene copolymer was obtained in exactly the same manner as in Example 1 except that 3.5 parts by weight of 1,3-dioxepane was used instead of 2.5 parts by weight of ethylene oxide, and this was used. Add triphenylphosphine equivalent to twice the mole of the catalyst amount,
A purified oxymethylene copolymer having an intrinsic viscosity of 1.43 dl/g was obtained. The same stabilizer as in Example 1 was added thereto in the same proportion and treated in the same manner as in Example 1 to obtain product pellets. The test results are shown in Table 3 (1) and (2). Comparative Example 1 In Example 1, magnesium hydroxide was not used, and the benzoguanamine-formaldehyde initial polycondensate was added so that the total amount added was the same.
0.35 phr and 0.55 phr of Irganox 259 were blended into the oxymethylene copolymer. The test results of the obtained composition are shown in Table 4 (1) and (2).
Shown below. Comparative Examples 2 to 4 In Example 2, one of the three types of additives was not used, the total amount added was the same, and the second
Stabilizers were blended as shown in the table. The test results of the obtained composition are shown in Table 4 (1) and (2).
Shown below. Comparative Example 5 The same procedure as in Example 10 was carried out except that instead of the melamine-formaldehyde initial polycondensate, a reticulated melamine-formaldehyde polycondensate, which is insoluble in water and alcohol and does not melt and flow when heated, was used. , product pellets were obtained. The test results are shown in Table 4 (1) and (2). Comparative Example 6 In Example 14, magnesium hydroxide was not used, and the benzoguanamine-formaldehyde initial polycondensate was added so that the total amount added was the same.
0.35 phr and 0.55 phr of Irganox 259 were blended into the oxymethylene copolymer. The test results of the obtained composition are shown in Table 4 (1) and (2).
Shown below.

【table】

【table】

【table】

【table】

[Table] * Polyplastics product
Product name 〓Jyuracon M〓9002〓
Intrinsic viscosity 1.44dl/g

【table】

[Table] Note 1 to Tables 3 and 4) Thermal stability test during molding Injection molding machine used: Famous machine SJ-35B Test method: Normal molding (cycle time 50 seconds) at a material temperature of 235°C or 250°C ) (this is the initial molded product), and then injection molding is performed after a residence time of 60 minutes in the cylinder (this is the post-retention molded product). Tests the degree of change in the appearance of the product using color tone, amount of silver streaks, etc. 2) Retention test in the molding machine ◎: Indicates that a molded product with a good appearance was obtained after residence at the material temperature for 60 minutes and could be molded. △: Indicates that the appearance of the molded product obtained after staying at the material temperature for 60 minutes has deteriorated due to the occurrence of silver streaks, etc. × mark: After staying at the material temperature for 60 minutes, due to decomposition and foaming of the material in the injection machine cylinder,
This indicates that even if the injection operation is performed, the material does not flow into the mold, making molding impossible. 3 Change in color tone Equipment used: Hunter color difference meter (manufactured by Nippon Denshoku Kogyo) Change in b value: Difference between the b value of the molded product after 60 minutes of residence and the b value of the initial molded product <Change in b value>: <Observation with the naked eye> 0-2: No change in color tone was observed with the naked eye. 3-5: Some change in yellowness is observed with the naked eye. 6-7: Somewhat strong change in yellowness is observed with the naked eye. 8-9: Strong yellowing is clearly observed with the naked eye. 10 or more: There is a brownish color change. Change in w value: Difference between the w value of the molded product after staying for 60 minutes and the w value of the initial molded product <Change in w value>: <Observation with the naked eye> 0 to 2: No change in color tone is observed with the naked eye. 3-5: A change in color tone is strongly observed with the naked eye. 6 or more: The color tone changes greatly depending on the naked eye. 4) Amount of silver streaks generated <Numerical value>: <Degree of silver streaks generated> 0: No silver streaks are observed on the surface of the molded product. 1: Very slight silver streaks are observed on the surface of the molded product. 2-3: Silver streaks are partially observed on the surface of the molded product. 4-5: Silver streaks are considerably observed on the surface of the molded product. 6 to 7: Silver stripes are observed on almost the entire surface of the molded product. 8 or more: The surface of the molded product is extremely poor due to resin decomposition. 5) Regarding the XX marks in the section on changes in molded product appearance: XX: Molding is not possible at that material temperature.
This indicates a case in which it was not possible to sample the molded product, and therefore it was not possible to measure the color tone or observe the extent of silver streaks. 6) Continuous molding test Injection molding machine used: famous machine SJ-35B Test method: Continuous molding was performed for about 1 hour using a disk with a test piece shape of 3.2 mm thickness x 100 mm diameter at a material temperature of 220°C or 230°C. After the molding is completed, the appearance of the molded product is observed, and the appearance of silver streaks, flashes, flow marks, etc. is visually determined between good and defective products, and the percentage of non-defective products is calculated as a percentage. 7) Amount of mold deposit Based on the results of observing the mold surface with the naked eye after approximately 1 hour of continuous molding. <Number>: <Extent of occurrence of mold deposits> 0: No mold deposits attached at all. 1: Very slight mold deposit is observed. 2 to 3: Mold deposits are observed evenly on the surface. 4-5: Mold deposit adhered somewhat thickly. 6-7: Mold deposit is thickly attached to the entire surface of the mold.

Claims (1)

[Claims] 1 The oxymethylene copolymer (1) general formula (A) [In the formula, R ₁ and R ₂ each represent an amino group or a substituted amino group, and R ₃ represents a hydrogen atom, a hydroxyl group, an alkyl group, an alkoxy group, an aryl group, a hydrogenated aryl group, an amino group or a substituted amino group. ] At least one of the amino resin initial polycondensates of amine-substituted triazines and formaldehyde represented by (2) General formula (B) [In the formula, R ₄ and R ₅ are each an alkyl group,
Represents a substituted alkyl group or a substituted triazole group, R ₆ is an alkyl group, a substituted alkyl group,
Represents an alkoxy group or a substituted amino group. ] at least one sterically hindered phenol represented by (3) a hydroxide of an alkali metal such as sodium or potassium or an alkaline earth metal such as magnesium, calcium or barium;
A stabilized oxymethylene copolymer composition comprising at least one metal-containing compound represented by the group consisting of an inorganic acid salt, a carboxylic acid salt, or an alkoxide. 2. For 100 parts by weight of the oxymethylene copolymer, (1) 0.01 to 7 parts by weight of the amino resin initial polycondensate, (2) 0.05 to 5 parts by weight of the sterically hindered phenols, (3) The composition according to claim 1, which contains 0.004 to 5 parts by weight of the metal-containing compound. 3. The composition of claim 1, wherein the amine-substituted triazine compound is melamine, benzoguanamine, N-methylolated melamine or N-methylolated benzoguanamine. 4 The sterically hindered phenols are 2,2'-methylene-bis(4-methyl-6-t-butylphenol), 1,6-hexanediol-bis-3
(3,5-di-t-butyl-4-hydroxyphenyl)propionate or pentaerythrityl-tetrakis [3-(3,5-di-t-butyl-
4-Hydroxyphenyl) propionate]. 5. The composition according to claim 1, wherein the metal-containing compound is potassium, calcium or magnesium hydroxide or magnesium carbonate. 6 The oxymethylene copolymer is a polymer obtained by copolymerizing formaldehyde and/or its cyclic oligomer with other cyclic ether and/or cyclic acetal in the presence of a polymerization catalyst, and if desired, the polymer The composition according to claim 1, which is a polymer that has been subjected to terminal stabilization treatment. 7 The oxymethylene copolymer is obtained by copolymerizing formaldehyde and/or a cyclic oligomer thereof with another cyclic ether and/or a cyclic acetal in the presence of a polymerization catalyst, and then using the general formula (D) as a reaction terminator. [In the formula, R ₇ , R ₈ and R ₉ are each an alkyl group,
Represents a cycloalkyl group, halogenated alkyl group, aryl group, substituted aryl group, aralkyl group, alkoxy group, substituted alkoxy group, mercapto group, aryloxy group or substituted aryloxy group,
These may be the same or different, and R ₈ and R ₉ may be linked to form one alkylene group. ] The composition according to claim 1, which is a polymer obtained by adding a trivalent organic phosphorus compound represented by the following to stop the polymerization reaction.