WO2005026259A1

WO2005026259A1 - Polyoxymethylene resin composition with excellent heat stability

Info

Publication number: WO2005026259A1
Application number: PCT/KR2003/001890
Authority: WO
Inventors: Chong-Won Chin; Young-Heup Kim; Kyung-Seob Byun
Original assignee: Korea Engineering Plastics Co., Ltd.
Priority date: 2003-09-16
Filing date: 2003-09-16
Publication date: 2005-03-24
Also published as: AU2003261010A1

Abstract

This invention is to provide a polyoxymethylene resin composition with excellent heat stability. The polyoxymethylene resin composition includes 0.01 to 2 parts by weight of an amine-substituted triazine compound, and 0.01 to 5 parts by weight of a compound of an ethylene-propylene copolymer and an ethylene-propylene trimer grafted by 0.05 to 5 wt.% maleic anhydride based on 100 parts by weight of a polyoxymethylene copolymer. Furthermore, the polyoxymethylene resin composition exhausts a relatively small amount of formaldehyde gas while molding the polyoxymethylene resin composition or from molded products thereof.

Description

POLYOXYMETHYLENE RESIN COMPOSITION WITH EXCELLENT HEAT STABILITY

Technical Field

The present invention pertains, in general, to a polyoxymethylene resin composition with excellent heat stability and, in particular, to a polyoxymethylene resin composition with excellent heat stability, which exhausts a small amount of formaldehyde gas while molding the polyoxymethylene resin composition or from molded products thereof.

Background Art As well known to those skilled in the art, a polyoxymethylene polymer has been widely used in various electric and electronic parts and mechanical devices requiring complex physical properties because of its excellent mechanical properties, creep resistance, fatigue resistance, and abrasion resistance. However, the polyoxymethylene polymer is easily degraded by a thermal or mechanical impact, or additives during forming it because of its poor heat stability which generates formaldehyde, a gas harmful to workers. Additionally, the formaldehyde gas, harmful to humans, remains on molded products made of the polyoxymethylene polymer. Much effort has been made to improve the heat stability of the polyoxymethylene polymer. For example, some methods were suggested, in which additives such as amines, amides, and hydrazines are added to the polyoxymethylene polymer so as to react the additives with gases, including formaldehyde generated from the thermally degraded polyoxymethylene polymer. In detail, the addition of acrylamides and borate compounds to a polyoxymethylene resin has been developed in the art, as indicated by Japanese Patent Laid-open No. Hei. 10-1592. Furthermore, Japanese Patent Laid-open No. Sho. 59-213752 discloses a process of adding alanine compounds to a polyoxymethylene resin. However, these patents have some problems in improving the heat stability of the polyoxymethylene resin because the thermally unstable additives bring about a yellowing phenomenon and are bled out of the polyoxymethylene resin to cause an undesirable mold deposit phenomenon. Other processes were suggested to improve the heat stability of polyoxymethylene, in which formaldehyde and trioxane are polymerized in the presence of an anion catalyst to produce a polyoxymethylene homopolymer and unstable terminal ends of polyoxymethylene are capped with a predetermined material so as to stabilize the unstable terminal ends. For example, Japanese Patent Publication No. Sho. 33-6099, US Pat. No. 2,964,500, and Japanese Patent Publication No. Sho. 42-8706 disclose a process of improving the heat stability of a polyoxymethylene polymer, in which carbonic anhydride, alkaline metal salts, and pyridine are heated at 50 to 200 °C to lead an esterification of terminal ends of the polyoxymethylene polymer. Additionally, iso-cyanate groups react with terminal hydroxyl groups of a polyoxymethylene polymer to lead an urethanation of terminal ends of the polyoxymethylene polymer in Japanese Patent Publication No. Sho. 35- 6233 and Japanese Patent Publication No. Sho. 36-3492. However, the above patents are disadvantageous in that a main chain of the polyoxymethylene polymer is easily broken by a solvolisys mechanism, and the polyoxymethylene polymer becomes thermally unstable because an unreacted capping material remains at the terminal ends of the polyoxymethylene polymer. To avoid the above disadvantages, a process was developed to improve the heat stability of the polyoxymethylene homopolymer, in which co-monomers, for example, cyclic ether, such as ethylene oxide, or cyclic formal, such as dioxolane, are co-polymerized with formaldehyde and trioxane in the presence of a catalyst to produce a copolymer, and the copolymer thus produced is randomly dispersed in a homopolymer. However, the production of the copolymer must be accompanied by a stabilizing process because the terminal ends of the copolymer are very unstable. Various researches about the stabilizing process have been conducted, in which the unstable terminal ends are forcibly decomposed into co-monomers. For example, Japanese Patent Publication No. Sho. 60-63216 and Japanese Patent Publication No. Sho. 60-60121 disclose a process of improving the heat stability of a polyoxymethylene polymer, in which terminal ends of the polyoxymethylene polymer are decomposed using an alkaline solution of pH7 or higher in a heterogeneous medium, thereby stabilizing the terminal ends. Additionally, US. Pat. No. 1,407,145 proposes a process of improving the heat stability of a polyoxymethylene polymer, in which the terminal ends of the polyoxymethylene polymer are hydrolyzed using alkaline alcohols, an antacid and an anti-oxidant in a heterogeneous medium to stabilize the terminal ends. However, the above patents are not useful in producing the polyoxymethylene polymer with excellent heat stability. Meanwhile, Japanese Patent Publication No. Sho. 43-18714 discloses a process of improving the heat stability of a polyoxymethylene resin composition, in which a polyoxymethylene copolymer is liquefied in a homogeneous medium to remove the unstable terminal ends of the polyoxymethylene resin composition. However, in this case, it is cumbersome to remove polymers precipitated in a polymerization bath and to remove a solvent. Accordingly, a purification process using a homogeneous medium was suggested so as to avoid the reduction of a purification efficiency of polyoxymethylene in the homogeneous medium. For example, the removal of volatile materials in the polyoxymethylene resin composition using three-step rotating disk-type kneader is disclosed in Japanese Patent Publication No. Sho. 62-119219. This patent has disadvantages in that it takes a long time to completely remove the terminal ends of the polyoxymethylene polymer, and the terminal ends are not completely stabilized. Disclosure of the Invention

Accordingly, the present invention has been made keeping in mind the above problems occurring in the prior art, and an object of the present invention is to provide a polyoxymethylene resin composition with excellent heat stability, which is produced by providing substances useful to stabilize terminal ends and compounds containing nitrogen to a polyoxymethylene polymer having unstable terminal ends in a stabilizing process of polyoxymethylene, thereby exhausting a small amount of formaldehyde gas while molding the polyoxymethylene resin composition or from molded products thereof. In order to accomplish the above object, the present invention provides a polyoxymethylene resin composition, including 0.01 to 2 parts by weight of an amine- substituted triazine compound (B), and 0.01 to 5 parts by weight of a compound (C) of an ethylene-propylene copolymer and an ethylene-propylene trimer grafted by 0.05 to 5 wt% maleic anhydride based on 100 parts by weight of a polyoxymethylene copolymer (A).

Best Mode for Carrying Out the Invention

According to the present invention, a polyoxymethylene copolymer (A) may be a homopolymer containing an oxymethylene unit expressed by the following Formula 1, or may be a copolymer in which a unit expressed by the following Formula 2 is randomly combined with another unit expressed by the following Formula 3. In this regard, a molecular weight of the polyoxymethylene copolymer is preferably 10,000 to 200,000 g/mol.

Formula 1 -(-CH₂0-)- Formula 2 -KCX^O-]- In the Formula 2, Xi and X₂ may or may not be the same, and are selected from the group consisting of hydrogen, an alkyl group, and an aryl group, provided that both Xi and X₂ are not hydrogen at the same time. Additionally, x is an integer ranging from two to six. The oxymethylene homopolymer is produced by polymerizing formaldehyde or its cyclic oligomer, i.e. trioxane. Furthermore, formaldehyde or its cyclic oligomer is random-copolymerized with cyclic ether expressed by the following Formula 3 or cyclic formal expressed by the following Formula 4 to produce the oxymethylene copolymer, including units of the Formulae 1 and 2. Formula 3

Formula 4

XB I . (C)rr I Xε O CH;

In the Formulae 3 and 4, X₃, X₄, X₅ and X₆ may or may not be the same, are selected from the group consisting of hydrogen and an alkyl group, and are all bonded to one carbon atom or are bonded to the different carbon atoms. Additionally, n and m are both integers ranging from two to six. As described above, cyclic ether and cyclic formal are used as a monomer to produce the oxymethylene copolymer. In this regard, cyclic ether is selected from the group consisting of ethylene oxide, propylene oxide, butylene oxide, and phenylene oxide, and cyclic formal is selected from the group consisting of 1,3-dioxolane, diethyleneglycolformal, 1,3-propandiolformal, 1,4-butandiolformal, 1,3- dioxepanformal, and 1,3,6-trioxocan. Preferably, the monomer is selected from the group consisting of ethylene oxide, 1,3-dioxolane, 1,4-butandiolformal, and a mixture thereof, and is added to trioxane or formaldehyde acting as a main monomer. The resulting mixture is then random-copolymerized in the presence of a Lewis acid catalyst to produce the oxymethylene copolymer with a melting point of 150°C or higher including two or more carbon atoms bonded to a main chain thereof. In the oxymethylene copolymer, a molar ratio of a combination structure of oxymethylene to an oxymethylene repeating unit is 0.05 to 50, and preferably 0.1 to 20. Additionally, a catalyst used to produce the oxymethylene polymer is selected from the group consisting of BF₃ OH₂, BF₃ OEt₂, BF₃-OBu₂, BF₃-CH₃CO₂H, BF₃-PF₅ΗF, and BF₃-10-hydroxyacetphenol. At this time, Et denotes an ethyl group, and Bu denotes a butyl group. It is preferable that the catalyst is selected from the group consisting of BF₃-OEt₂ and BF₃OBu₂. The amount of the catalyst used to produce the oxymethylene polymer is preferably 2 x 10^"6 to 2 x 10^"2 mole based on 1 mole trioxane. The oxymethylene polymer may be produced according to a bulk polymerization, an emulsion polymerization, or a solution polymerization process. Furthermore, a polymerization temperature of the oxymethylene polymer is 0 to 100 °C , and preferably 20 to 80 °C . Meanwhile, a deactivating agent for deactivating the catalyst remaining on the polymer after the completion of polymerization is selected from the group consisting of tertiary amines such as triethylamine, cyclic sulphur compounds such as thiophene, and phosphorus-based compounds such as triphenylphosphine. At this time, these compounds are all Lewis base materials having unshared electron pairs, and form complexes in conjunction with the catalyst. Additionally, alkyl-substituted phenols or ethers, preferably alkylether such as dimethoxymethane may be used as a chain transferring agent while producing polyoxymethylene.

Meanwhile, an amine-substituted triazine compound (B) is added to polyoxymethylene to improve the heat stability of the polyoxymethylene resin composition according to the present invention, and is selected from the group consisting of guanamin, melamine, N-butylmelamine, N-phenylmelamine, N,N- diphenylmelamine, N,N-diallylmelamine, N,N',N"-triphenylmelamine, N,N',N"- trimethylolmelamine, benzoguanamin, 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-diamino-6-cyclohexyl-sym-triazine, 2,4-diamino-6-chloro- sym-triazine, 2,4-diamino-6-mercapto-sym-triazine, 2-oxy-4,6-diamino-sym-triazine (ameline), and N,N,N',N'-tetracyanoethyl benzoguanamin. In this regard, it is most preferable to add melamine expressed by the following Formula 5 to polyoxymethylene.

Formula 5

An amount of amine-substituted triazine compound (B) added to the polyoxymethylene resin composition according to the present invention is 0.01 to 2 parts by weight, and preferably 0.01 to 1 parts by weight based on 100 parts by weight of the polyoxymethylene polymer (A). For example, when the amount of the amine- substituted triazine compound (B) is less than 0.01 parts by weight, the heat stability of the polyoxymethylene resin composition is not sufficiently improved. On the other hand, when the amount is more than 2 parts by weight, the physical properties of molded products including the polyoxymethylene resin composition are poor. Further, a component (C) used in the present invention functions to stabilize unstable terminal ends of polyoxymethylene, and is a compound of an ethylene- propylene copolymer and an ethylene-propylene trimer grafted by 0.05 to 5.0 wt% maleic anhydride. At this time, the ethylene-propylene copolymer contains 10 to 90 wt% ethylene, and the ethylene-propylene trimer contains 10 to 90 wt% ethylene and 0.1 to 20 wt% diene. Additionally, a weight ratio of the ethylene-propylene copolymer to the ethylene-propylene trimer is 0 - 90 : 100 - 10. Examples of the component (C) include HIGHLER P-0424K (Doo Hyun Co., LTD) and VA1803 (EXXON Chemical Co., Ltd). As well, the component (C) may be added to polyoxymethylene in a form of pellet or powder manufactured by pulverizing lumps of component (C) (frozen). The amount of the component (C) added to the polyoxymethylene resin composition according to the present invention is 0.01 to 5 parts by weight, and preferably 0.01 to 2 parts by weight based on 100 parts by weight of the polyoxymethylene polymer (A). For example, when the amount of the component (C) is less than 0.01 parts by weight, the heat stability of the polyoxymethylene resin composition is not sufficiently improved. On the other hand, when the amount is more than 5 parts by weight, the physical properties of the molded products including the polyoxymethylene resin composition are poor. Additionally, it is preferable that phenol (D) with steric hindrance is added to polyoxymethylene to improve the heat stability of the polyoxymethylene resin composition. In this regard, phenol (D) with steric hindrance is selected from the group consisting of 2,2'-methylene-bis(4-methyl-6-t-butylphenol), 4,4'-methylene- bis(2,6-di-t-butylρhenol), l,3,5-trimethyl-2,4,6-tris(3,5-di-t-butyl-4- hydroxybenzyl)benzene, 2,5-di-t-butyl-4-hydroxybenzyl dimethylamine, stearyl-3,5- di-t-butyl-4-hydroxybenzyl phosphonate, diethyl-3 ,5-di-t-butyl-4-hydroxybenzyl phosphonate, 2,6,7-trioxa-l-phospho-bicyclo[2,2,2]-octo-4-yl-methyl-3,5-di-t-butyl-4- hydroxyhydrocinnamate, 3,5-di-t-butyl-4-hydroxyphenyl-3,5-distearyl-tiotriazylamine, 2(2'-hydroxy-3',5'-di-t-butylphenyl)-5-chlorobenzotriazole, 2,6-di-t-butyl-4- hydroxymethylphenol, 2,4-bis-(n-octylthio)-6-(4-hydroxy-3,5-di-t-butylallyllino)-

1,3,5-triazine, N,N'-hexamethylenebis(3,5-di-t-butyl-4-hydroxy-hydrocinnamamide), octadecyl-3-(3,5-di-butyl-4-hydroxyphenyl)propionate, l,6-hexandiol-bis[3-(3,5-di-t- butyl-4-hydroxyphenyl)propionate], pentaerythrityl-tetrakis[3-(3,5-di-t-butyl-4- hydroxyphenyl)propionate], triethyleneglycol-bis[3-(3,5-dimethyl-4- hydroxyphenyl)propionate], triethyleneglycol-bis-3-(3-t-butyl-4-hydroxy-5- methylphenyl)propionate, triethyleneglycol-bis[3-(3,5-di-t-butyl-4- hydroxyphenyl)propionate], and 2,2'-thiodiethyl-bis[3-(3,5-di-t-butyl-4- hydroxyphenyl)propionate]. Of them, triethyleneglycol-bis-3-(3-t-butyl-4-hydroxy-5- methylphenyl)propionate is most preferable to use as phenol (D) with steric hindrance. At this time, an amount of phenol (D) added to the polyoxymethylene resin composition according to the present invention is 0.01 to 3 parts by weight, and preferably 0.01 to 1 parts by weight based on 100 parts by weight of the polyoxymethylene polymer (A). For example, when the amount is less than 0.01 parts by weight, the heat stability of the polyoxymethylene resin composition is not sufficiently improved. On the other hand, when the amount is more than 3 parts by weight, the physical properties of the molded products including the polyoxymethylene resin composition are poor and the surfaces of the molded products are not smooth. Moreover, it is preferable to add one or more metal compounds to the polyoxymethylene resin composition to improve the heat stability of the polyoxymethylene resin composition according to the present invention. At this time, the metal compounds are selected from the group consisting of alkaline metal hydroxides or alkaline earth metal hydroxides, salts of inorganic acids, salts of organic acids, and alkoxides. Examples of salts of the inorganic acids include carbonate, phosphate, silicate, and borate, and salts of the organic acids are selected from the group consisting of laurylate, stearylate, oleylate, and behenylate. Additionally, examples of alkoxides include Cl-5 alkoxides such as methoxide and ethoxide. Of them, magnesium hydroxide (E), that is, alkaline earth metal, is preferably added to polyoxymethylene. An amount of magnesium hydroxide (E) added to the polyoxymethylene resin composition according to the present invention is 0.01 to 1 parts by weight, and preferably 0.01 to 0.5 parts by weight based on 100 parts by weight of the polyoxymethylene polymer (A). For example, when the amount is less than 0.01 parts by weight, the heat stability of the polyoxymethylene resin composition is not sufficiently improved. On the other hand, when the amount is more than 1 part by weight, physical properties of the molded products comprising the polyoxymethylene resin composition are poor and a great quantity of harmful gas is generated from the polyoxymethylene resin composition. A better understanding of the present invention may be obtained through the following example which is set forth to illustrate, but is not to be construed as the limit of the present invention. Hereinafter, test methods will be described of a polyoxymethylene resin composition. 1 ) The measurement of high temperature CH₂O 2 g of the polyoxymethylene resin composition was heated to 222 ^°C while nitrogen was blown on the polyoxymethylene resin composition, and a CH₂O gas generated while molding the polyoxymethylene resin composition was collected using ice water. A content of the CH₂O gas in water was then measured in such a way that the color of the water was analyzed using a UV spectrophotometer, thereby measuring the amount of CH₂O generated while heating the polyoxymethylene resin composition. The smaller the amount of CH₂O becomes, the more stable the heat stability of the polyoxymethylene resin composition becomes. 2) The measurement of CH₂O generated from molded products The polyoxymethylene resin composition was cut to form a sample with a size of 100 mm x 40 mm x 2 mm, placed in a bottle with a volume of 1 L containing 50 mL water in such a way that the polyoxymethylene resin composition did not come into contact with water. The bottle was then sealed. After the resulting bottle was left at 60 °C for three hours, the content of the CH₂O gas in water was then measured in such a way that the color of the water was analyzed using the UV spectrophotometer, thereby measuring the amount of CH₂O generated from the molded products being composed of the polyoxymethylene resin composition. The smaller the amount of CH₂O becomes, the more stable the heat stability of the polyoxymethylene resin composition becomes.

3) Color The sample was observed by naked eyes in terms of color. 'White' denotes no yellowing phenomenon in the sample, but 'yellow' denotes the intense yellowing phenomenon in the sample.

PREPARATION EXAMPLE 1

Production of a polyoxymethylene copolymer 100 parts by weight of trioxane and 4.5 parts by weight of 1,3-dioxolane acting as a co-monomer were polymerized in the presence of BF₃O(Et)₂ acting as a catalyst to produce the polyoxymethylene copolymer. At this time, metiral was used as a chain transferring agent, and the catalyst was deactivated using triphenylphosphine.

EXAMPLE 1

0.01 parts by weight of HIGHLER P-0424K(D. H. Co., hereinafter, referred to as "PK") (components C), 0.05 parts by weight of melamine as amine-substituted triazine compound, 0.3 parts by weight of triethyleneglycol-bis-3-(3-tert-butyl-4- hydroxy-5-methylphenyl)propionate (Irganox 245 manufactured by Ciba-Geigy Co.), and 0.05 parts by weight of magnesium hydroxide (Mg(OH)₂) were added to 100 parts by weight of a polyoxymethylene copolymer produced according to preparation example 1, and were left in 500 cc of a kneader having two pairs of ∑ -type blades at 230 °C under a nitrogen atmosphere for 40 min. The resulting product was evaluated by the above test methods, and the results are described in Table 1.

EXAMPLES 2 TO 8

The procedures of example 1 were repeated except that PK (component C) was added to 100 parts by weight of polyoxymethylene copolymer produced according to preparation example 1 in the amounts of 0.05 parts by weight, 0.10 parts by weight,

0.20 parts by weight, 0.30 parts by weight, 0.50 parts by weight, 1.00 parts by weight, and 2.00 parts by weight (examples 2 to 8). The results are described in Table 1.

EXAMPLE 9 The procedure of example 1 was repeated except that 0.05 parts by weight of

PK (component C) and 0.10 parts by weight of melamine were added to 100 parts by weight of polyoxymethylene copolymer produced according to preparation example 1. The results are described in Table 1.

EXAMPLE 10

The procedure of example 1 was repeated except that 0.20 parts by weight of PK (component C) and 0.10 parts by weight of melamine were added to 100 parts by weight of polyoxymethylene copolymer produced according to preparation example 1. The results are described in Table 1.

EXAMPLE 11

The procedure of example 1 was repeated except that 0.01 parts by weight of VA 1803 (EXXON Chemical Co., Ltd, Hereinafter, referred to as "VA") (component C) was added to 100 parts by weight of polyoxymethylene copolymer produced according to preparation example 1. The results are described in Table 1.

EXAMPLES 12 TO 18

The procedures of example 1 were repeated except that VA (component C) was added to 100 parts by weight of polyoxymethylene copolymer produced according to preparation example 1 in the amounts of 0.05 parts by weight, 0.10 parts by weight,

0.20 parts by weight, 0.30 parts by weight, 0.50 parts by weight, 1.00 parts by weight, and 2.00 parts by weight. The results are described in Table 1.

EXAMPLE 19

The procedure of example 1 was repeated except that 0.05 parts by weight of VA (component C) and 0.10 parts by weight of melamine were added to 100 parts by weight of polyoxymethylene copolymer produced according to preparation example 1. The results are described in Table 1.

EXAMPLE 20

The procedure of example 1 was repeated except that 0.20 parts by weight of VA (component C) and 0.10 parts by weight of melamine were added to 100 parts by weight of polyoxymethylene copolymer produced according to preparation example 1. The results are described in Table 1.

COMPARATIVE EXAMPLE 1

The procedure of example 1 was repeated except that neither PK nor VA were used. The results are described in Table 1.

COMPARATIVE EXAMPLE 2 The procedure of example 1 was repeated except that neither PK nor V A were used and 0.10 parts by weight of melamine was added to 100 parts by weight of polyoxymethylene copolymer produced according to preparation example 1. The results are described in Table 1.

COMPARATIVE EXAMPLE 3

The procedure of example 1 was repeated except that 0.10 parts by weight of isophthalic hydrazid (Japan Hydrazine, K-IDH) was added instead of PK or VA to 100 parts by weight of polyoxymethylene copolymer produced according to preparation example 1. The results are described in Table 1. COMPARATIVE EXAMPLE 4

The procedure of comparative example 3 was repeated except that 0.10 parts by weight of melamine was added to 100 parts by weight of polyoxymethylene copolymer produced according to preparation example 1. The results are described in Table 1.

COMPARATIVE EXAMPLE 5

The procedure of example 1 was repeated except that 0.10 parts by weight of urea (DUKSAN Pure Chemicals) was added instead of PK or VA to 100 parts by weight of polyoxymethylene copolymer produced according to preparation example 1. The results are described in Table 1.

COMPARATIVE EXAMPLE 6

The procedure of comparative example 5 was repeated except that 0.10 parts by weight of melamine was added to 100 parts by weight of polyoxymethylene copolymer produced according to preparation example 1. The results are described in Table 1.

TABLE 1

'An amount of high temperature CH₂0 (ppm): An amount of high temperature CH₂0 generated while molding the polyoxymethylene resin composition From Table 1, it can be seen that in examples 1 to 20 of the present invention, the polyoxymethylene resin compositions have no yellowing phenomenon, the amount of CH₂O generated while heating the polyoxymethylene resin composition at a high temperature of 222 ^°C ranges from 200 to 470 ppm, and the amount of CH₂O generated from the molded products is 3.05 to 5.85 mg/kg. On the other hand, in the case of comparative examples 1 to 6, the amount of CH₂O generated while heatig the polyoxymethylene resin composition at a high temperature is 540 to 1205 ppm, and the amount of CH₂O generated from the molded products is 8.70 to 12.83 mg/kg. Accordingly, the polyoxymethylene resin compositions according to examples 1 to 20 of the present invention have better heat stability than comparative examples, and generate a relatively small amount of CH₂O in comparison with comparative examples.

Industrial Applicability

As described above, the present invention provides a polyoxymethylene resin composition with excellent heat stability, which exhausts a small amount of formaldehyde gas while molding the polyoxymethylene resin composition or from molded products thereof. The present invention has been described in an illustrative manner, and it is to be understood that the terminology used is intended to be in the nature of description rather than of limitation. Many modifications and variations of the present invention are possible in light of the above teachings. Therefore, it is to be understood that within the scope of the appended claims, the invention may be practiced otherwise than as specifically described.

Claims

1. A polyoxymethylene resin composition, comprising 0.01 to 2 parts by weight of an amine-substituted triazine compound, and 0.01 to 5 parts by weight of a compound of an ethylene-propylene copolymer and an ethylene-propylene trimer grafted by 0.05 to 5 wt% maleic anhydride based on 100 parts by weight of a polyoxymethylene copolymer.

2. The polyoxymethylene resin composition as set forth in claim 1, wherein the amine-substituted triazine compound is melamine.

3. The polyoxymethylene resin composition as set forth in claim 1, wherein a weight ratio of the ethylene-propylene copolymer to the ethylene-propylene trimer is 0

- 90 : 100 - 10.

4. The polyoxymethylene resin composition as set forth in any one of claims 1 to 3, further comprising 0.01 to 3 parts by weight of triethyleneglycol-bis-3-(3-tert- butyl-4-hydroxy-5-methylphenyl)propionate based on 100 parts by weight of the polyoxymethylene copolymer.

5. The polyoxymethylene resin composition as set forth in any one of claims 1 to 3, further comprising 0.01 to 1 parts by weight of magnesium hydroxide based on 100 parts by weight of the polyoxymethylene copolymer.

6. The polyoxymethylene resin composition as set forth in claim 4, further comprising 0.01 to 1 parts by weight of magnesium hydroxide based on 100 parts by weight of the polyoxymethylene copolymer.