JP2517642B2 - Polyoxymethylene composition with excellent heat stability - Google Patents

Description

The present invention relates to a polyoxymethylene composition having excellent mechanical properties, heat resistance stability, and color tone.

More specifically, it relates to a composition obtained by adding and mixing a specific hindered phenol and an organic phosphite to polyoxymethylene.

[Conventional technology]

Polyoxymethylene obtained by homopolymerization of formaldehyde, trioxane or tetraoxane or copolymerization with a copolymerizable monomer tends to easily release formaldehyde molecules and decompose by a zipper type decomposition reaction from the end.

Therefore, usually, the polymer terminal is blocked by acylation or the like, and in the case of a copolymer, it is stabilized by decomposing and removing the unstable terminal, but the bond of the polymer main chain is still easily oxidized and in the air. Decomposes on heating. Therefore, it has been attempted to improve the heat resistance stability of the polymer by blending and kneading various heat resistance stabilizers.

For example, Japanese Patent Publication No. 34-5439 and Japanese Patent Publication No. 45-18790.
Japanese Patent Laid-Open No. 47-15448 discloses a polyoxymethylene composition containing a hindered phenol. Further, for example, Japanese Patent Publication No. 39-14519 discloses a polyoxymethylene composition containing an organic or inorganic phosphorus compound.

[Problems to be Solved by the Invention]

However, in order to increase the heat resistance stability of polyoxymethylene before it can withstand melt molding, the blending of one type of stabilizer is not sufficient, and it is necessary to blend two or more types of stabilizers. In fact, the above Japanese Patent Publication No. 34-5439,
45-18790, 39-14519, and JP-A-47-15448 also describe examples of combined use with other additives.
In recent years, small-sized molded products such as gears and tape reels are often manufactured by unmanned operation for a long time, and it is necessary to suppress the incidence of defective products to a low level. in this case,
Defective product refers to a product with a particularly poor surface condition, mainly silver streak or mold deposit based on formaldehyde gas generated by thermal decomposition.To suppress this, stabilize the polymer to a high degree. There is a need.

Therefore, as a result of intensive studies to solve the above problems, the present invention has been found.

[Means for solving the problem]

That is, the present invention is: 0.01 to 5 parts by weight of at least one hindered phenol represented by the general formula (A) and having a molecular weight of 300 or more, relative to 100 parts by weight of polyoxymethylene. (In the formula, R ¹ and R ² represent an alkyl, a substituted alkyl or a substituted triazole group, and R ³ represents an alkyl, a substituted alkyl, an alkoxy or a substituted amino group.) Tristearyl phosphite, 3,9-distearyloxy -2,4,8,10-Tetraoxa-3,9-diphosphaspiro [5.5] undecane, 3,9-bis (nonylphenyl)-
2,4,8,10-Tetraoxa-3,9-diphosphaaspiro [5.
5] Undecane and 3,9-bis (di-t-butylphenyl) -2,4,8,10-tetraoxa-3,9-diphospha [5.
5] A polyoxymethylene composition having excellent heat resistance stability, which is prepared by blending 0.01 to 5 parts by weight of at least one organic phosphite selected from undecane.

The hindered phenol used in the present invention is represented by the general formula (A) and has a molecular weight of 300 or more.

(In the formula, R ¹ and R ² represent an alkyl, a substituted alkyl, or a substituted triazole group, and R ³ represents an alkyl, a substituted alkyl, an alkoxy, or a substituted amino group.) When the molecular weight is less than 300, the bleeding phenomenon is remarkable, It is not preferable because the appearance of the molded article is significantly impaired and the heat resistance stability of the composition is reduced. Further, if the melt molding is continued for a long time, it is not preferable because it is deposited and deposited on the mold as a mold deposit.

Specific compounds include 2,2'-methylene-bis (4-methyl-6-t-butylphenol), triethylene glycol-bis [3- (3-t-butyl-5-methyl-4-hydroxyphenyl). ) Propionate], 1,
6-hexanediol-bis [3- (3,5-di-t-butyl-4-hydroxyphenyl) propionate], pentaerythrityl-tetrakis [3- (3,5-di-t-butyl-4-hydroxy) Phenyl) propionate], N,
N'-hexamethylenebis (3,5-di-t-butyl-4-
Hydroxy-hydrocinnamamide), 1,3,5-trimethyl-2,4,6-tris (3,5-di-t-butyl-4-hydroxybenzyl) benzene, 2,4-bis-n-octylthio -6- (4-Hydroxy-3,5-di-t-butylanilino) -1,3,5-triazine, 2,2-thio-diethylenebis [3- (3,5-di-t-butyl-4] -Hydroxyphenyl) propionate], octadecyl-3- (3,5-
Di-t-butyl-4-hydroxyphenyl) propionate, 2,2'-thiobis (4-methyl-6-t-butylphenol), 3,5-di-t-butyl-4-hydroxy-benzylphosphonate- Diethyl ester, N, N '
-Bis [3- (3,5-di-t-butyl-4-hydroxyphenyl) propionyl] hydrazine, 2- (3,5-di-t-butyl-2-hydroxyphenyl) benzotriazole, 2- (3 -T-butyl-5-methyl-2-hydroxyphenyl-5-chlorobenzotriazole, 2-
(3,5-di-t-butyl-2-hydroxyphenyl)-
5-chlorobenzotriazole, 1,3,5-tris (4-
t-Butyl-3-hydroxy-2,6-dimethylbenzyl) isocyanuric acid, 1,1,3-tris (2-methyl-4)
-Hydroxy-5-t-butylphenyl) butane, 1,1
-Bis (2-methyl-4-hydroxy-5-t-butylphenyl) butane, 3,9-bis [1,1-dimethyl-2-
[Β- (3-t-butyl-4-hydroxy-5-methylphenyl) propionyloxy] ethyl] -2,4,8,10-
Tetraoxaspiro [5.5] undecane and the like can be mentioned. Among them, 2,2'-methylene-bis (4-methyl-6-t-butylphenol), triethyleneglycol-bis [3- (3-t- Butyl-5-methyl-4
-Hydroxyphenyl) propionate], 1,6-hexanediol-bis [3- (3,5-di-t-butyl-4]
-Hydroxyphenyl) propionate], pentaerythrityl-tetrakis [3- (3,5-di-t-butyl-
4-Hydroxyphenyl) propionate], N, N'-
Hexamethylene bis (3,5-di-t-butyl-4-hydroxy-hydrocinnamamide), 1,3,5-trimethyl-
2,4,6-Tris (3,5-di-t-butyl-4-hydroxybenzyl) benzene is preferably used.

Addition amount is 0.01 per 100 parts by weight of polyoxymethylene
-5 parts by weight, preferably 0.1-3 parts by weight. If the amount is less than 0.01 parts by weight, the heat resistance stability of the polymer is remarkably low and it cannot be used at all. On the other hand, if the amount is more than 5 parts by weight, it may deposit on the surface of the molded product or cause mold deposit, which is not preferable.

Organic phosphites used in the present invention include tristearyl phosphite, 3,9-distearyloxy-2,4,
8,10-Tetraoxa-3,9-diphosphaspiro [5.5] undecane, 3,9-bis (nonylphenyl) -2,4,8,10-
Tetraoxa-3,9-diphosphaspiro [5.5] undecane and 3,9-bis (di-t-butylphenyl) -2,4,
It is at least one selected from 8,10-tetraoxa-3,9-diphosphaspiro [5.5] undecane.

The polyoxymethylene used in the present invention means an oxymethylene homopolymer and an oxymethylene copolymer mainly composed of oxymethylene units and containing oxyalkylene units having 2 to 8 carbon atoms in the polymer main chain. .

Oxymethylene homopolymer, for example, by introducing substantially anhydrous formaldehyde into an organic solvent containing an organic amine, an organic or inorganic tin compound, a basic polymerization catalyst such as a metal hydroxide, and polymerizing, After separating the polymer, it is produced by acetylating the terminal by heating in acetic anhydride in the presence of sodium acetate.

The oxymethylene copolymer is obtained by dissolving or suspending a cyclic oligomer of formaldehyde such as substantially anhydrous trioxane or tetraoxane and a cyclic ether as a copolymerization component in an organic solvent such as cyclohexane or benzene. Then, a Lewis acid catalyst such as boron trifluoride / diethyl etherate is added and polymerized. If desired, the polymer is produced by removing the catalyst from the polymer by washing and decomposing and removing the unstable terminal. Alternatively, the polymerization component, the copolymerization component, and the polymerization catalyst are charged into a self-cleaning type mixing reactor in a substantially solvent-free state, and bulk polymerization is performed. If desired, the polymer is produced by removing the catalyst from the polymer by washing and decomposing and removing the unstable terminal.

The cyclic ether as a copolymerization component is a compound represented by the following general formula (D).

(However, Y _{1 to} Y _{4 in the} formula represent a hydrogen atom, an alkyl group having 1 to 6 carbon atoms, or a halogen-substituted alkyl group having 1 to 6 carbon atoms, and they may be the same or different. ,
Z represents a methylene or oxymethylene group, which may be substituted with an alkyl group or a halogen-substituted alkyl group,
m represents an integer of 0 to 3. Alternatively, Z is - (CH ₂₎ p
It may be —O—CH ₂ — or —O—CH ₂ — (CH ₂ ) p—O—CH ₂ —, in which case m = 1 and p is an integer from 1 to 3. ) Among the cyclic ethers represented by the general formula (D), preferred compounds include ethylene oxide, propylene oxide, 1,3-dioxolane, 1,3-dioxane, 1,3-
Examples thereof include dioxepane, 1,3,5-trioxepane, 1,3,6-trioxocane, epichlorohydrin and the like, with ethylene oxide, 1,3-dioxolane and 1,3-dioxepane being particularly preferable. The copolymerization amount is 0.1 to 10 mol%, particularly preferably 0.2 to 6 mol% based on the oxymethylene unit.
It is necessary to be in the range of 0.1 mol% or less, the thermal stability of the obtained composition is low, and if it is 10 mol% or more, the melting point and crystallinity of the obtained composition are lowered, and the mechanical strength is lowered. Also, it is not preferable because the moldability is deteriorated.

Particularly preferred as the polyoxymethylene used in the present invention, trioxane and a cyclic ether, boron trifluoride, boron trifluoride hydrate and boron trifluoride and an organic compound containing an oxygen atom or a sulfur atom. Polymer obtained by bulk polymerization in the presence of at least one polymerization catalyst selected from the group consisting of the coordination compounds, and then adding the hindered amine compound represented by the general formula (C) to terminate the polymerization reaction. Is.

(In the formula, R ⁷ represents a hydrogen atom or a monovalent organic residue having 1 to 30 carbon atoms, and R ^{8 to} R ¹¹ represent an alkyl group having 1 to 5 carbon atoms, which may be the same or different. Good.
n represents an integer of 1 or more, and R ¹² represents an n-valent organic residue. ) Specifically, the following compounds may be mentioned.

Among them, bis (2,2,6,6-tetramethyl-4-piperidinyl) sebacate (C-13) and bis (1,2,2,6,6-pentamethyl-4-piperidinyl) sebacate (C-1)
4), 1,2,3,4-butanetetracarboxylic acid tetrakis (2,
2,6,6-Tetramethyl-4-piperidinyl) ester (C-37), poly [[6- (1,1,3,3-tetramethylbutyl) amino-1,3,5-triazine-2, 4-diyl] [2,
2,6,6-Tetramethyl-4-piperidinyl] imino] hexamethylene [(2,2,6,6-tetramethyl-4-pyridinyl) imino]] (C-39) is preferred.

The addition amount of the hindered amine compound is preferably such that the mol number of the hindered amine structure is equivalent to or more than the polymerization catalyst used. Even if the number of moles of the hindered amine structure is less than the number of moles of the polymerization catalyst used, the catalyst deactivating effect can be seen, but the heat stability of the obtained polymer is slightly lowered, so that the target heat stability cannot be achieved. It is necessary to adjust the addition amount according to the situation.

When the polymerization reaction is stopped by using the hindered amine compound, the catalyst is completely deactivated, and the catalyst can be proceeded to the next step without being washed and removed, which is very advantageous in terms of process.

As a device for producing the above-mentioned preferred polymer, a kneader having a sigma type stirring blade, a cylindrical barrel as a reaction zone, and a screw having coaxial and many interrupted peaks in the barrel are provided. A mixer that operates so that teeth protruding from the inner surface of the barrel engage, a conventional screw extruder with a pair of parallel screws that mesh with each other in a long case having a heating or cooling jacket, and two horizontal stirring shafts. A self-cleaning mixer having a large number of paddles and rotating with a slight clearance between the paddle surface and the inner surface of the case, when the shafts are simultaneously rotated in the same direction, may be mentioned. .

Also, in bulk polymerization, a strong stirring ability is required because it solidifies rapidly in the initial stage of the polymerization reaction, but once it is pulverized, a large stirring ability is not required thereafter, so the bulk polymerization step is performed twice. It may be divided into stages.

Further, in order to allow the reaction between the terminating agent and the polymerization catalyst to proceed sufficiently, it is preferable that the polymer is in the form of powder as fine as possible. Therefore, if desired, the polymer may be pulverized by a pulverizer before the addition of the terminating agent. Alternatively, it may be crushed after adding the terminating agent.

Further, in the composition of the present invention, calcium carbonate, barium sulfate, clay, titanium oxide, silicon oxide, fillers such as mica powder, carbon fiber, glass fiber, ceramic fiber, aramid within a range that does not impair the effects of the present invention. Reinforcing agents such as fibers, colorants (pigments, dyes), nucleating agents, plasticizers, release agents such as ethylene bisstearamide, flame retardants, antistatic agents, conductive agents such as carbon black, adhesives Additives such as a lubricant, a hydrolysis resistance improver, and an adhesion aid can be optionally contained.

In particular, it is preferable to use an alkali metal hydroxide or an alkaline earth metal hydroxide and / or a formaldehyde scavenger in combination as a stabilizing aid, because it shows more excellent properties in terms of heat resistance stability.

Specific examples of the alkali metal and alkaline earth metal hydroxides include lithium hydroxide, sodium hydroxide, potassium hydroxide, magnesium hydroxide, calcium hydroxide, barium hydroxide, and strontium hydroxide. , Magnesium hydroxide, calcium hydroxide and strontium hydroxide are preferred.

The amount of the alkali metal or alkaline earth metal hydroxide added is 0.001 to 5 parts by weight, preferably 0.05 to 3 parts by weight, based on 100 parts by weight of polyoxymethylene. If it is less than 0.001 part by weight, the effect of the addition is not obtained, and if it is more than 5 parts by weight, mechanical properties and hydrolysis resistance are deteriorated, which is not preferable.

The formaldehyde scavenger is a compound capable of chemically trapping formaldehyde by reacting with formaldehyde, and includes amide compounds, urethane compounds, pyridine derivatives, pyrrolidone derivatives, urea derivatives, triazine derivatives, hydrazine derivatives, amidine compounds and the like. Can be mentioned.

Specifically, N, N-dimethylformamide, N, N-dimethylacetamide, N, N-diphenylformamide, N, N
-Diphenylacetamide, N, N-diphenylbenzamide, N, N, N ', N'-tetramethyladipamide, oxalic acid dianilide, adipic acid dianilide, N-phenylacetanilide, nylon 6, nylon 11, nylon 12, etc. Homopolymers or copolymers of lactams, derived from dicarboxylic acids such as adipic acid, sebacic acid, decanedicarboxylic acid, dimer acid and diamines such as ethylenediamine, tetramethylenediamine, hexamethylenediamine and metaxylylenediamine. Polyamide homopolymers or copolymers, lactams and polyamide copolymers derived from dicarboxylic acids and diamines, polyacrylamide, polymethacrylamide, N, N-bis (hydroxymethyl) sveramide, poly (γ-methylglutamate) ), Poly (γ-d Rugurutameto), poly (N- vinyl lactams), poly (N- vinylpyrrolidone) amide compounds such as, toluene diisocyanate,
Polyurethanes derived from diisocyanates such as diphenylmethane diisocyanate and glycols such as 1,4-butanediol and polymeric glycols such as poly (tetramethylene oxide) glycol, polybutylene adipate and polycaprolactone, melamine, benzoguanamine, acetoguanamine, N- Butyl melamine, N
-Phenylmelamine, N, N'-diphenylmelamine, N,
N ', N "-triphenylmelamine, N-methylolmelamine, N, N'-dimethylolmelamine, N, N', N" -trimethylolmelamine, 2,4-diamino-6-benzyloxytriazine, 2, Triazine derivatives such as 4-diamino-6-butoxytriazine, 2,4-diamino-6-cyclohexyltriazine, melem and melam, N-phenylurea, N, N'-diphenylurea, thiourea, N-phenylthiourea, N , N'-Diphenylthiourea, ethylene urea, urea derivatives such as nonamethylene polyurea, phenylhydrazine, diphenylhydrazine, benzaldehyde hydrazone, benzaldehyde semicarbazone, benzaldehyde 1-methyl-1-phenylhydrazone, benzaldehyde thiosemicarba Zon, 4-
(Dialkylamino) hydrazine derivatives such as hydrazone of benzaldehyde, dicyandiamide, guanzine, guanidine, aminoguanidine, guanine, guanacrine, guanoclor, guanoxane, guanosine,
Amidine, amidine compounds such as N-amidino-3-amino-6-chloropyrazinecarboxamide, poly (2-vinylpyridine), poly (2-methyl-5-vinylpyridine), poly (2-ethyl-5-vinyl) Pyridine), 2-vinylpyridine / 2-methyl-5-vinylpyridine copolymer, 2-vinylpyridine / styrene copolymer, and other pyridine derivatives.

Among them, dimer acid polyamide, nylon 6 / 6,6 / 6,10
Ternary copolymer, nylon 6 / 6,6 / 6,10 / 12 quaternary copolymer,
Melamine, guanamine, benzoguanamine, N-methylol melamine, N-methylol benzoguanamine,
Thermoplastic polyurethane resin, dicyandiamide, guanidine, poly (vinylpyrrolidone), poly (2-vinylpyridine), polyurea, melem, melam, N, N'-diphenylurea are the thermal stability of polyoxymethylene containing them. Is particularly preferable because it is excellent.

The amount of the formaldehyde scavenger added is 0.001 to 5 parts by weight, preferably 0.1 to 100 parts by weight of polyoxymethylene.
05 to 3 parts by weight. If it is less than 0.001 part by weight, the effect of addition is not obtained, and if it is more than 5 parts by weight, it is precipitated on the surface of the composition or the composition is colored, which is not preferable.

The polyoxymethylene composition produced by the present invention is excellent in moldability, color tone, mechanical properties, melt stability and heat aging resistance, so that it can be used in a wide range of applications such as machine mechanism parts, automobile parts, and electric / electronic parts. Can be used.

<Example> Next, the present invention will be described with reference to Examples and Comparative Examples. The evaluation items shown in Examples and Comparative Examples were measured as follows.

Mechanical Properties of Molded Products Using an injection molding machine with an injection capacity of 5 ounces, a tensile test piece of 1/8 inch thickness at a cylinder temperature of 200 ° C. and a mold temperature of 80 ° C., a 1/2 inch width × 1/2 inch thick Izod Impact test pieces were injection molded. Using these test pieces, tensile properties were measured according to ASTM D-638, and notched Izod impact values were measured according to ASTM D-256.

Melt index (abbreviated as MI) A sample dried in a hot air dryer at 80 ° C. for 3 hours was used and measured according to ASTM D-1238 at a temperature of 190 ° C. and a load of 2,160 g.

Yellow index (abbreviated as YI) Suga Tester Co., Ltd. S
Yellowness YI value was measured by M color computer SM-3.

Polymer melting point (Tm), crystallization temperature (Tc) Using a differential scanning calorimeter, increase the temperature at a heating rate of 10 ° C / min in a nitrogen atmosphere, measure the polymer melting point (Tm), and then measure 10 ° C.
The temperature was lowered at / min, and the crystallization temperature (Tc) was measured.

Reference Example Manufacture of Polyoxymethylene Manufacture of Oxymethylene Homopolymer POM-1 Formaldehyde obtained by pyrolyzing paraformaldehyde at 140 to 180 ° C was placed in a continuous two reaction vessel containing toluene at 0 ° C as a reaction medium. Introduced. As the polymerization initiator, an equimolar mixture of tetra (n-butyl) ammonium iodide and lauric acid dissolved in toluene was supplied. All reaction components were continuously pumped and the polymeric dispersion product was taken off at such a rate that the residence time was 10 minutes. Formaldehyde is passed through the reactor at a rate of about 8 g / min, and the polymerization initiator is such that the concentration of tetra (n-butyl) iodide is 1.87 mg per reaction medium and the concentration of lauric acid is 0.99 mg per reaction medium. Supplied in proportion. The reaction medium was kept at 65 ° C and well stirred. Reaction medium 1
A polymer was produced at a rate of 400 g / h. The obtained polymer was filtered out, washed with acetone and methanol, and dried. 500 g of this crude polymer, 4,000 acetic anhydride
A mixture of g and 1.6 g of sodium acetate was heated at 139 ° C. and refluxed for 1 hour. After cooling, the polymer was filtered, washed with acetone and water, and then dried. The melting point of this polymer is 179 ° C,
The crystallization temperature was 150 ° C., MI = 7.9.

Preparation of oxymethylene copolymer POM-2 900 g of trioxane and 8.8 g of ethylene oxide were dissolved in 450 g of cyclohexane, and 60 ml of benzene containing 0.3 g of boron trifluoride / diethyl etherate was added,
Stirred at ° C. About 1 minute after the addition of boron trifluoride / diethyl etherate, the reaction solution became cloudy and a polymer was precipitated. After 30 minutes, 10% benzene solution of triethylamine
After 10 ml was added to stop the polymerization reaction, the precipitated polymer was collected by filtration, washed with acetone and then washed with water. Methanol / water / ammonia = 59.5 / 40/0.
The mixture was put into a hydrolysis solution 10 having a weight ratio of 5 and heated and stirred in an autoclave at 160 ° C for 10 minutes. After cooling, the polymer was filtered, washed with water, washed with acetone and dried. The melting point of this polymer is 167 ℃, the crystallization temperature is 147 ℃, MI = 8.2
Met.

Production of Oxymethylene Copolymer POM-3 Benzene containing 3,000 g of trioxane, 50 ml of 1,3-dioxolane and 0.3 g of boron trifluoride / diethyl etherate in a kneader (volume 3) having two Σ type stirring blades.
30 ml was added, and the mixture was stirred at 65 ° C. and 40 rpm. The reaction started after about 1 minute and the internal temperature rose. Although the temperature rose to about 95 ° C, the mixture was stirred for 10 minutes as it was. The reaction mixture was ground to a white powder.

5.4 g of bis (1,2,2,6,6-pentamethyl-4-piperidinyl) sebacate ("Sanol": LS 765 from Chiba-Geigy) was added to the reaction mixture.
50 ml of benzene containing was added and stirred at 35 ° C. for 15 minutes. This polymer has a melting point of 167 ° C, crystallization temperature of 146 ° C, MI
= 8.5.

Examples 1 to 29 Polyoxymethylene POM-1 produced according to the reference example
Each compound was added to and mixed with 3 to 3 at the compounding ratio shown in Table 1.

The mixture was continuously fed to a vented twin-screw extruder with 45 mmφ and L / D = 31.5, and melt-kneaded at 230 ° C./100 rpm.

The composition was extruded as strands, pelletized and dried in a hot air circulating oven at 80 ° C for 5 hours.

Comparative Examples 1 to 18 Polyoxymethylene POM-1 produced according to Reference Example
Samples were prepared in the same manner as in Examples 1 to 29 except that each compound was added to and mixed with each other at the compounding ratios shown in Table 2 with respect to 3 to 3.

 The abbreviations in the table represent the following compounds.

Irganox 1010: pentaerythrityl-tetrakis [3- (3,5-di-t, manufactured by Ciba-Geigy, Inc.
-Butyl-4-hydroxyphenyl) propionate] Irganox 245: Ciba-Geigy triethylene glycol-bis [3- (3-t-butyl-5-methyl-4-hydroxyphenyl) propionate] Irganox 259: Ciba-Geigy 1,6-hexanediol-bis [3- (3,5-di-t-butyl-4-hydroxyphenyl) propionate] MARK PEP-4C: Adeka Argus 3,9-bis (nonylphenyl) -2,4,8,10-Tetraoxa-3,9-diphospher spiro [5.5] undecane MARK PEP-8: ADEKA ARGUS 3,9-Distearyloxy-2,4,8,10-tetraoxa −
3,9-Diphospher spiro [5.5] undecane MARK PEP-24G: 3,9-bis (di-t-butylphenyl) -2,4,8,10-tetraoxa-3,9- manufactured by ADEKA ARGUS CORPORATION Diphosphorspiro [5.5] undecane Nylon 6 / 6,6 / 6,10: Nylon 6, Nylon 6,6, Nylon 6,10 terpolymer.

The initial physical properties and color tone of Examples and Comparative Examples and the physical properties and color tone after repeated extrusion at high temperature were measured, and the results are shown in Table 3.
Summarized in 4.

From Examples 1-2, 6-8, 21-23 and Comparative Examples 1-18,
It can be seen that while hindered phenol and organic phosphite alone significantly deteriorate the physical properties due to heat history, the combined use of both suppresses the physical property deterioration.

Further, from Examples 3 to 5, 9 to 14 and 24 to 26, when a hydroxide of an alkaline earth metal is used in combination with the hindered phenol and the organic phosphite, the deterioration of physical properties due to heat history is further suppressed. I understand.

From Examples 15-20, 21-29, hindered phenol,
It can be seen that when a formaldehyde scavenger is used in addition to the organic phosphite, the alkali metal or alkaline earth metal hydroxide, the deterioration of the physical properties due to thermal history is further suppressed.

Further, from Examples 21 to 29, it is found that the use of the polymer in which the catalyst is deactivated by the hindered amine compound makes it possible to obtain a composition having particularly good thermal stability.

[Effects of the Invention] The polyoxymethylene composition of the present invention is particularly excellent in heat resistance stability and mechanical properties, and therefore, mechanical mechanism parts, electric
It can be used in a wide range of applications such as electronic parts.

Claims (5)

(57) [Claims] 1. To 100 parts by weight of polyoxymethylene,
0.01 to 5 parts by weight of at least one hindered phenol represented by the general formula (A) and having a molecular weight of 300 or more; (In the formula, R ¹ and R ² represent an alkyl, a substituted alkyl or a substituted triazole group, and R ³ represents an alkyl, a substituted alkyl, an alkoxy or a substituted amino group.) Tristearyl phosphite, 3,9-distearyloxy -2,4,8,10-tetraoxa-3,9-diphosphaaspiro [5.5] undecane, 3,9-bis (nonylphenyl) -2,
4,8,10-Tetraoxa-3,9-diphosphaaspiro [5.5]
Undecane and 3,9-bis (di-t-butylphenyl) -2,4,8,10-tetraoxa-3,9-diphospha [5.
5] A polyoxymethylene composition having excellent heat resistance stability, which is prepared by blending 0.01 to 5 parts by weight of at least one organic phosphite selected from undecane. 2. The hindered phenol is 2,2'-methylene-bis (4-methyl-6-t-butylphenol), triethylene glycol-bis [3- (3-t-phenol).
Butyl-5-methyl-4-hydroxyphenyl) propionate], 1,6-hexanediol-bis [3- (3,5
-Di-t-butyl-4-hydroxyphenyl) propionate], pentaerythrityl-tetrakis [3- (3,3,
5-di-t-butyl-4-hydroxyphenyl) propionate], N, N'-hexamethylenebis (3,5-di-t
-Butyl-4-hydroxy-hydrocinnamamide), and 1,3,5-trimethyl 2,4,6-tris (3,5-di-t-
The composition according to claim 1, which is one or more compounds selected from butyl-4-hydroxybenzyl) benzene. 3. The composition according to claim 1, wherein the polyoxymethylene is a polymer obtained by copolymerizing formaldehyde and / or trioxane with another cyclic ether in the presence of a polymerization catalyst. 4. The polyoxymethylene is obtained by copolymerizing formaldehyde and / or trioxane with another cyclic ether in the presence of a polymerization catalyst, and then formula (C)
The composition according to claim 1, which is a polymer obtained by stopping the polymerization reaction by adding a hindered amine compound represented by (In the formula, R ⁷ represents a hydrogen atom or a monovalent organic residue having 1 to 30 carbon atoms. R ^{8 to} R ¹¹ each represent an alkyl group having 1 to 5 carbon atoms, which may be the same or different. Good n
Represents an integer of 1 or more, and R ¹² represents an n-valent organic residue. ) 5. The hindered amine compound is bis (2,2,
6,6-tetramethyl-4-piperidinyl) sebacate,
Bis (1,2,2,6,6-pentamethyl-4-piperidinyl)
Sepamate, 1,2,3,4-butanetetracarboxylic acid tetrakis (2,2,6,6-tetramethyl-4-piperidinyl) ester, and poly [[6- (1,1,3,3-tetramethyl Butyl) amino-1,3,5-triazine-2,4-diyl]
[2,2,6,6-Tetramethyl-4-piperidinyl) imino] hexamethylene [(2,2,6,6-tetramethyl-4-
The composition according to claim 4, which is one or more compounds selected from piperidinyl) imino]).