JPH04239048A - Acetal polymer composition - Google Patents

Abstract

PURPOSE:To obtain the title compsn. which is excellent in thermal stability and resistance to thermal aging and releases a low HCHO odor during molding by compounding an acetal polymer with a specific phenolic antioxidant and a specific amine compd. to impart a specific thermal decomposability. CONSTITUTION:The title compsn. comprises an acetal polymer (e.g. one obtd. by polymerizing HCHO and acetylating the molecular terminals of the polymer), a hindered phenolic antioxidant having a mol.wt. of 400 or higher (e.g. Irganox 245, a product of Ciba Geigy), and a hindered amine antioxidant having a mol.wt. of 300 or higher (Sanol LS765, a product of Sankyo) and has such a thermal decomposability that the thermal decomposition at 240 deg.C in air reaches 25% after at least 40min.

Description

Detailed Description of the Invention [0001] [Industrial Application Field] The present invention provides an acetal polymer composition which has excellent heat aging resistance, has very little formaldehyde odor during molding, and has excellent thermal stability. It is related to. [0002] Polyacetal resin is known as an engineering plastic with a good balance of mechanical strength and impact resistance, and is used in a wide range of fields as electronic equipment supplies and automobile parts. However, polyacetal resin has poor thermal stability due to its structure, and formaldehyde gas is generated during molding, which worsens the working environment, and the formation of oligomers, which are generally called mold deposits, formed on the mold. There are several points that should be improved, such as detracting from the appearance of the product. [0004] In order to improve the above-mentioned drawbacks of acetal polymers, various stabilizer formulations have been devised in the past. Addition of an antioxidant is an essential condition in the stabilizer formulation for such acetal polymers. but,
Generally, it is impossible to obtain sufficient thermal stability using a hindered phenol compound alone, which is used as an antioxidant for polyacetal resin. Further, although polyamide compounds have conventionally been added as heat stabilizers, sufficient heat stability cannot be obtained with these compounds alone or in combination with hindered phenolic antioxidants. For example, Japanese Patent Publication No. 62-4422 describes a resin composition prepared by adding polyamide and a fatty acid metal salt having 12 to 35 carbon atoms together with a hindered phenolic antioxidant to an acetal polymer. ing. [0005] Recently, a method using a hydroxy group-containing polymer or oligomer such as poly(ethylene vinyl alcohol) as a heat stabilizer has been described in JP-A-62-288648 and JP-A-62-288649. There is. Problem to be Solved by the Invention However, the stabilizers for resin compositions proposed in the above-mentioned Japanese Patent Publication No. 4422-1982, Japanese Patent Application Laid-open No. 288648-1982, and Japanese Patent Application Laid-open No. 288649-1982 It is difficult to obtain an acetal polymer with sufficient thermal stability through formulation. [0007] Therefore, the object of the present invention is to obtain an acetal polymer composition having excellent thermal stability and heat aging resistance sufficient to withstand high temperatures and long-term melt retention. [Means for Solving the Problems] As a result of intensive studies to solve the above problems, the present inventors found that a hindered phenolic antioxidant having a specific molecular weight for an acetal polymer, and a specific By blending and adding a hindered amine compound with a molecular weight of 240
The acetal polymer composition, whose thermal decomposition rate at °C is kept below a certain value, has extremely high thermal stability over a wide temperature range, as well as excellent heat aging resistance and good molding workability. The present invention was achieved based on the discovery that That is, the present invention provides an acetal polymer containing (A) a hindered phenol antioxidant having a molecular weight of 400 or more and (B) a hindered amine compound having a molecular weight of 300 or more, and Among them, an acetal polymer composition whose thermal decomposition rate Kx at 240°C reaches 25% in 40 minutes or more (however, Kx means the decomposition rate when left at x°C for a certain period of time, and the following formula Obtained from: 0010 Kx=(W0-Wy)×100/W0
(%) Here, W0 means the sample weight before heating, and Wy means the sample weight after heating for y minutes). The acetal polymer used in the present invention refers to an acetal homopolymer and an oxyalkylene unit consisting mainly of oxymethylene units and having 2 to 8 adjacent carbon atoms in the main chain. It means an acetal copolymer containing 15% by weight or less. [0012] The acetal homopolymer refers to an oxymethylene homopolymer stabilized by substituting an unstable terminal hydroxyl group with an ester group or an ether group. For example, substantially anhydrous formaldehyde is polymerized by introducing it into an organic solvent containing an organic amine, an organic or inorganic tin compound, or a basic polymerization catalyst such as a metal hydroxide, and the polymer is filtered out. , is produced by heating in acetic anhydride in the presence of sodium acetate to acetylate the terminal. Acetal copolymers can also be produced by polymerizing, for example, by introducing substantially anhydrous trioxane and copolymer components such as ethylene oxide and 1,3-dioxolane into an organic solvent such as cyclohexane. After that, a Lewis acid catalyst such as boron trifluoride/diethyl etherate is added to polymerize, and unstable terminals are decomposed and removed. Alternatively, trioxane, a copolymerization component, and a catalyst are introduced into a self-cleaning stirrer without using any solvent, and after polymerization is carried out in bulk, unstable terminals are further decomposed and removed. The hindered phenolic antioxidant (A) used in the present invention has a molecular weight of 400 or more, and specifically, 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-hydroxyphenyl)propionate], N,N '-hexamethylenebis(3,5-di-t-butyl-4-hydroxyhydrocinnamamide), 2-t-butyl-6-(3'-t-butyl-5'-methyl-2'-hydroxy benzyl)-4-
Methylphenyl acrylate, 3,9-bis[2-{3
-(3-t-butyl-4-hydroxy-5-methylphenyl)propionyloxy}-1,1-dimethylethyl]-2,4,8,10-tetraoxaspiro[5,5]
Examples include undecan. Among these, 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-hydroxyphenyl)propionate] is particularly preferred. If the molecular weight is less than 400, the bleeding phenomenon will be significant, the appearance of the acetal homopolymer composition will be impaired, and the thermal stability will be reduced, making it unusable. The amount added is usually 0.001 to 5.0 parts by weight, preferably 0.01 to 3.0 parts by weight, per 100 parts by weight of the acetal polymer. If it is less than 0.001 parts by weight, the thermal stability of the acetal polymer composition will not be sufficient, and if it is more than 5.0 parts by weight, a bleeding phenomenon will occur, which is not preferable. The hindered amine compound (B) used in the present invention has a molecular weight of 300 or more, and specifically, bis(1,2,2,6,6-pentamethyl-4-piperidinyl) sebacate, succinic acid Dimethyl 1-(2-
hydroxyethyl)-4-hydroxy-2,2,6,6
-tetramethylpiperidine polycondensate, N,N'-bis(
3-aminopropyl)ethylenediamine/2,4-bis[N-butyl-N-(1,2,2,6,6-pentamethyl-4-piperidinyl)amino]-6-chloro-1,3
, 5-triazine condensate, 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-piperidyl)imino)], bis(2,2,6,6-tetramethyl-4-piperidyl)sebacate, and the like. Among them, bis(1,2,2,6,6-pentamethyl-4-piperidinyl) sebacate, dimethyl succinate 1-(2-hydroxyethyl)-4-hydroxy-2,2,6,6-tetramethyl Piperidine polycondensate, N,N'-bis(3-aminopropyl)ethylenediamine/2,4-bis[N-
Butyl-N-(1,2,2,6,6-pentamethyl-4
-piperidinyl)amino]-6-chloro-1,3,5-
Triazine condensate, 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-piperidyl)imino)]
is particularly preferred. If the molecular weight is less than 300, the bleeding phenomenon will be significant, the appearance of the acetal polymer will be impaired, and the thermal stability will be reduced, making it unusable. The amount added is usually 0.001 to 5.0 parts by weight, preferably 0.01 to 3.0 parts by weight, per 100 parts by weight of the acetal polymer. If it is less than 0.001 parts by weight, the thermal stability of the acetal polymer composition will not be sufficient, and if it is more than 5.0 parts by weight, it will be undesirably colored due to heat. In order for the acetal polymer composition of the present invention to have excellent heat aging resistance and good molding workability, it is necessary to
It is important that the time required for the thermal decomposition rate Kx at 0° C. to reach 25% is 40 minutes or more. However, Kx means the decomposition rate when left at x°C for a certain period of time. For example, using a thermobalance device, leave the sample at x°C in an air atmosphere, measure the weight, and calculate it by the following formula. Desired. [0019] Kx=(W0-Wy)×100/W0
(%) Here, W0 means the sample weight before heating, and Wy means the sample weight after heating for y minutes. Under this air atmosphere, 2
The time required for the thermal decomposition rate Kx to reach 25% at 40°C is 40
If it is less than 1 minute, it becomes difficult to obtain excellent thermal stability over a wide temperature range, heat aging resistance decreases, and formaldehyde odor during molding becomes intense, which is not preferable. Further, when a formaldehyde scavenger (C) is added to the resin composition of the present invention, the thermal stability may be further improved. Examples of formaldehyde scavengers include polyamide compounds, urethane compounds, pyridine derivatives, pyrrolidone derivatives, urea derivatives, triazine derivatives, hydrazine derivatives, and amidine compounds. Specifically, polyamide 6, polyamide 66, polyamide 6/66 binary Copolymer, polyamide 6/66/610/
Preferred are 12 quaternary copolymers, melamine, benzoguanamine, acetoguanamine, N-methylolmelamine, N,N'-dimethylolmelamine, N,N',N''-trimethylolmelamine, dicyandiamide, and the like. Among these, polyamide 6/66/610/12 quaternary copolymer and melamine are particularly preferred. The polyamide 6/66/610/12 quaternary copolymer used in the present invention is a copolymer obtained by copolymerizing a salt of a dicarboxylic acid and a diamine, an ω-aminocarboxylic acid, or a lactam. 6, polyamide 66, polyamide 610,
It means a copolyamide having a structural unit consisting of polyamide 12. The composition of this copolyamide can have various ratios, and any ratio may be used in the present invention, but from the viewpoint of compatibility with the acetal polymer and dispersibility, this copolyamide usually has a melting point. ,50~200℃,
Particularly preferred is a composition within the range of 80 to 170°C. The amount of these formaldehyde scavengers added is usually 0.001 to 5 parts by weight per 100 parts by weight of the acetal polymer.
．． 0 parts by weight, preferably 0.01 to 3.0 parts by weight. If the amount is less than 0.001 part by weight, the addition effect will not appear.
Further, if the amount is more than 5.0 parts by weight, a bleed phenomenon may occur, which is not preferable. [0021] As a method for producing the acetal polymer composition of the present invention, generally known methods can be employed. For example, a method in which the stabilizer used in the present invention is added during the polymerization or stabilization process of the acetal polymer, and a method in which the acetal polymer and the stabilizer used in the present invention are mixed in the form of pellets, powder, or granules and then melted as is. Although it may be processed, a method of melt-mixing using a Banbury mixer, roll, extruder, etc. can also be adopted. It is also possible to adopt a method in which the stabilizer used in the present invention is melt-kneaded into a generally commercially available polyacetal resin in the same manner as described above. Especially one axis or two
A method of melt-mixing using a shaft extruder at a temperature of 150 to 250°C is preferred. [0022] The composition of the present invention may also contain fillers such as calcium carbonate, barium sulfate, clay, titanium oxide, silicon oxide, mica powder, glass beads, carbon fiber, glass, etc., to the extent that the effects of the present invention are not impaired. reinforcing agents such as fibers, ceramic fibers, aramid fibers, potassium titanate fibers,
Colorants (pigments, dyes), nucleating agents, plasticizers, mold release agents such as ethylene bisstearamide, polyethylene wax,
Conductive agents such as carbon black, antioxidants such as thioether compounds and phosphite compounds, light stabilizers such as benzophenone compounds and benzotriazole compounds, adhesives, lubricants such as metal soaps, and water resistance. Additives such as decomposition improvers and adhesion aids can be optionally included. [0023] The present invention will be explained below with reference to Examples, but the present invention is not limited thereto. [Examples] The present invention will be explained below with reference to Examples. Note that all percentages and parts in the examples are based on weight. [0025] Also, the thermal decomposition rate K of the acetal polymer compositions and molded products thereof shown in Examples and Comparative Examples
The time for x to reach 25%, MI value, mechanical properties, formaldehyde odor generation during continuous molding, polymer melt retention stability, and heat aging resistance were measured or observed as follows. Molding: Using an injection molding machine with an injection capacity of 5 ounces, the cylinder temperature was 190°C and the mold temperature was 65°C.
ASTM No. 1 dumbbell test pieces were injection molded at 50° C. and a molding cycle of 50 seconds.・Time for thermal decomposition rate Kx to reach 25%:
Kx means the decomposition rate when left at x°C for a certain period of time. Using a thermobalance device, approximately 15 milligrams of a sample was left at x°C on an aluminum pan while supplying 50 mL/min of air. , was calculated using the following formula. [0028] Kx=(W0-Wy)×100/W0
(%) Here, W0 means the sample weight before heating, and Wy means the sample weight after heating for y hours. The thermobalance device used was Seiko Electronics' TG/DTA200, and the samples were 3
Raise the temperature from 0°C to 240°C at a rate of 20°C/min, x
= 240°C (constant), and the sample weight was measured over time during that time. From the chart obtained from the measurement, the time from the start of heating until Kx reached 25% was read. - MI value: Measured at a temperature of 190°C and a load of 2160 grams according to the ASTM D-1238 method using pellets dried for 3 hours in a hot air oven at 80°C. - Mechanical properties: AS obtained by the above injection molding
Using TM1 dumbbell test piece, ASTM D-63
Tensile strength was measured according to Method 8. - Generation of formaldehyde odor during continuous molding: Continuous molding was performed for 50,000 shots under the above-mentioned molding conditions, and the generation of formaldehyde odor at that time was evaluated as follows. There is almost no formaldehyde odor: ◎, There is a slight formaldehyde odor: ○, A lot of formaldehyde gas is generated and it hurts your eyes and throat if you stay in the area: △, Formaldehyde gas is generated intensely and remains in the area Cannot: ×. Polymer melt retention stability: The MI value was measured according to the ASTM D-1238 method at a temperature of 190°C.
After being allowed to stay for 2 hours, measurements were taken with a load of 2160 grams. - Heat aging resistance: The ASTM No. 1 dumbbell obtained by the above injection molding is placed in an oven set at 140°C, taken out after a predetermined period of time, and subjected to ASTM D-
Tensile strength was measured according to the 638 method. In the Examples and Comparative Examples, an acetal homopolymer (P-1) produced by the following method, an acetal copolymer (P-2) produced by the following method, a commercially available homopolymer (DuPont " Delrin” II500NC10) (P
-3) or a commercially available copolymer (Polyplastics "Duracon" M90-44) (P-4) was used. - Production of acetal homopolymer (P-1) In a polymerization reaction tank with a diameter of 30 cm and a depth of 3 meters equipped with a stirring blade and a formaldehyde supply nozzle at the bottom,
- Filled with hexane. In this solution, 0.5 parts by weight of di-n-butyltin dimerate was dissolved, and formaldehyde gas was introduced through a supply nozzle. Formaldehyde gas was purified after thermally decomposing paraformaldehyde at 140 to 180°C, and was introduced at a rate of 1.5 kg/hour. The temperature inside the polymerization tank was adjusted to 50° C. by flowing cold or hot water through the jacket. Although fine polymer particles were gradually produced in the polymerization tank, the polymer slurry was extracted and the catalyst solution (n-hexane) was supplied so as to maintain the polymer solid content at about 50% by weight. The extracted polymer was filtered, thoroughly washed with water, and then poured into acetic anhydride in an amount 10 times the amount of the polymer. Further, sodium acetate was added in an amount of 0.1% by weight based on acetic anhydride, and the mixture was heated and stirred at 140°C for 5 hours. After the reaction mixture cooled to room temperature, the polymer was filtered off, thoroughly washed with acetone and water, and then dried.
P-1 was obtained.・Production of acetal copolymer (P-2) 2
Axial extruder type polymerization machine (25mmφ, L/D=10.2)
Trioxane (450 g/h), 1,3-dioxolane (14 g/h), 100 ppm relative to trioxane
Boron trifluoride/diethyl etherate (2.5% benzene solution) and 500 ppm of ethylal were respectively supplied to carry out continuous polymerization. The polymerization temperature was controlled at about 75° C. by passing hot water through the outer jacket, and the rotation speed was set at 100 rpm. Ethyral as a molecular weight regulator was dissolved in trioxane. Also, 1,
A premixing zone was provided so that 3-dioxolane and the catalyst solution were premixed immediately before being supplied to the kneader. The polymer was obtained at 445 g/h. This polymer was poured into a 3% ammonia aqueous solution and stirred. After the polymer was filtered and washed with water and then acetone, it was poured into a 10% ammonia aqueous solution and incubated at 150°C in an autoclave for 3 hours.
The mixture was heated and stirred for hours. After cooling to room temperature, the polymer was filtered, washed with water, then acetone, and dried.
I got it. The hindered phenol antioxidant, hindered amine compound, and formaldehyde scavenger used in the Examples and Comparative Examples are as follows.・O-1: Triethylene glycol-bis[3-(3-t-butyl-5-methyl-4-hydroxyphenyl)propionate] (Ciba Geigy “Irganox” 245) ・O-2: 1,6 -Hexanediol-bis[3-(3,5-di-t-butyl-4-hydroxyphenyl)propionate] (Ciba Geigy "Irganox" 259) ・O-3: Pentaerythrityl-tetrakis [3-(3, 5-di-t-butyl-4-hydroxyphenyl) propionate] (Ciba Geigy "Irganox" 1010) ・O-4:2,2'-methylenebis(4-methyl-6-t-butylphenol) (Sumitomo Chemical "Sumilizer""MDP-S)・O-5:2,6-
Di-t-butyl-4-methylphenol (Sumitomo Chemical “Sumilyzer” BHT)・A-1: Bis(1,2,2,6
, 6-pentamethyl-4-piperidinyl) sebacate (
Sankyo “Sanol” LS765)・A-2: Dimethyl succinate・1-(2-hydroxyethyl)-4-hydroxy-2,2,6,6-tetramethylpiperidine polycondensate (
Ciba Geigy "Tinuvin" 622LD)・A-3:N,
N'-bis(3-aminopropyl)ethylenediamine
2,4-bis[N-butyl-N-(1,2,2,6,6
-pentamethyl-4-piperidinyl)amino]-6-chloro-1,3,5-triazine condensate (Ciba Geigy)
KimaSorb”119FL)・A-4: 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-piperidyl)imino)}] (Ciba Geigy "Kimasorb" 944
FL)・T-1: Polyamide 6/66/610/12 quaternary copolymer (copolymer composition 6/66/610/12=22
/12/16/50 (wt%))・T-2: Melamine. Examples 1 to 8/Comparative Examples 1 to 7 Stabilizers were added to the acetal polymers P-1 to 4 in the proportions shown in Tables 1 and 2, and extruded using a vented twin screw 45 mmφ extrusion manufactured by Ikegai Iron Works. The mixture was melt-extruded and kneaded using a machine at 220 to 230° C./10 mm torr. The resulting composition was extruded as a strand and pelletized with a cutter. After drying the pellets at 80° C. for 3 hours in a hot air circulation oven, the pellets were molded and subjected to measurement of mechanical properties and heat aging resistance test. In addition, the occurrence of formaldehyde odor during continuous molding was evaluated. Furthermore, the melt retention stability was evaluated using the dried pellets. These results are summarized in Tables 3-6. [Table 1] [0041]

Example
Acetal Hindered Phosphor Hindered Amide Formaldehy Polymer
Nol-based antioxidant compounds
scavenger (parts by weight)
Stopping agent (parts by weight) (parts by weight) (parts by weight) 1 P-1
O-1 A-1
- (100)
(0.5) (0.2)
(-) 2 P-1
O-2 A-2
− (
100) (0.2) (0.4
) (-) 3
P-1 O-3
A-3 T-1
(100) (0.5) (
0.1) (0.1) 4
P-2 O-1
A-1-
(100) (0.5)
(0.1) (-) 5
P-3 O-1
A-4-
(100) (0.5
) (0.1) (-)
6 P-3 O
-1 A-4
T-2 (100) (
0.5) (0.1) (0.1
) 7 P-3
O-1 A-2
- (100)
(0.1) (1.0) (
- ) 8 P-4
O-1 A-1
- (100)
(0.5) (0.1)
(-) 0042] [Table 2] 0043]

Comparative example
Acetal Hindered Phosphor Hindered Amide Formaldehy Polymer
Nol-based antioxidant compounds
scavenger (parts by weight)
Stopping agent (parts by weight) (parts by weight) (parts by weight) 1 P-1
O-1 A-1
- (100)
(0.5) (0.0005) (
- ) 2 P-2
O-1-
- (100)
(0.5) (-)
(-) 3 P-3
O-1
− −
(100) (1.0) (
− ) (−) 4
P-1-
A-1-
(100) (-
) (0.5) (-)
5 P-3 O
-4 A-1
T-1 (100) (
0.5) (0.1) (0.1
) 6 P-1
O-5 A-1
T-2 (100)
(0.5) (0.1) (0.
1) 7 P-4
− −
- (100)
(-) (-)
(−) 0044 [Table 3] 0045]

Real Kx is 2
Time to reach 5% MI value Tensile strength Hole application during continuous molding
(g/10 min) (MPa) Example of maldehyde odor (min)

Occurrence status 1 43
15.7 6
9 ○2 45
15.3 6
8 ○3 53
15.2 7
0 ◎4 82
9.0
62 ◎5 60
16.2
68 ○6 72
16.1
69 ◎7 47
16.2
68 ○8 86
9.7
61 ◎ 0046] [Table 4] 0047

Ratio Kx is 2
Time to reach 5% MI value Tensile strength Hole comparison during continuous molding
(g/10 min) (MPa) Example of maldehyde odor (min)

Occurrence status 1 17
15.9 6
8 △2 25
10.3 5
9 △3 23
16.3 6
7 △4 11
16.1 6
7 ×5 12
16.5 6
8 ×6 7
16.2
66 ×7 26
9.7
60 △ 0048 [Table 5] 0049

Examples Melt retention stability Heat aging resistance
After staying at 190℃ for 2 hours
140℃, 20 days later
MI value (g/10 min) Tensile strength (
MPa) 1 16.1
64
2 15.6
64 3
15.3
69 4
9.1
59 5 16.5
64 6
16.1
68 7
16.5
63 8 10
．． 0 5
6 [0050] [Table 6] 0051]

Comparative example Melt retention stability Heat aging resistance
1 after staying at 190℃ for 2 hours
MI value after 20 days at 40℃ (
g/10 minutes) Tensile strength (MPa)
1-*
10 2
−＊
-* 3
−＊
28 4
−＊
-* 5 -*
−＊
6-*
-*7
19.7
31
*: Unable to measure due to severe decomposition. Effects of the Invention The acetal polymer composition of the present invention has very little formaldehyde odor during molding, has excellent thermal stability, and also has excellent heat aging resistance. Therefore, since it has excellent thermal stability and an extremely favorable working environment, long-term continuous production of molded products is possible. In addition, since it has good heat aging resistance, it can be widely used as mechanical parts in the electrical/electronic field, automobile field, etc.

Claims (6)

[Claims] 1. For the acetal polymer, (A) a hindered phenol antioxidant having a molecular weight of 400 or more;
and (B) an acetal polymer composition containing a hindered amine compound with a molecular weight of 300 or more and which takes 40 minutes or more to reach a thermal decomposition rate Kx of 25% at 240°C in air (provided that , Kx means the decomposition rate when left at x°C for a certain period of time, and is calculated from the following formula: Kx = (W
0-Wy)×100/W0 (%) where W0 means the sample weight before heating, and Wy means the sample weight after heating for y minutes). 2. The compound (A) is 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] and pentaerythrityl-tetrakis [3-(3,5-di-t-
The acetal polymer composition according to claim 1, which is at least one compound selected from the group consisting of butyl-4-hydroxyphenyl) propionate. Claim 3: The compound (B) is bis(1,2,2,
6,6-pentamethyl-4-piperidinyl) sebacate, dimethyl succinate 1-(2-hydroxyethyl)-
4-hydroxy-2,2,6,6-tetramethylpiperidine polycondensate, N,N'-bis(3-aminopropyl)
Ethylenediamine・2,4-bis[N-butyl-N-(
1,2,2,6,6-pentamethyl-4-piperidinyl)amino]-6-chloro-1,3,5-triazine condensate and 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- 2. The acetal polymer composition according to claim 1, wherein the acetal polymer composition is at least one compound selected from 4-piperidyl)imino). 4. The acetal polymer composition according to claim 1, further comprising (C) a formaldehyde scavenger. 5. The acetal polymer composition according to claim 4, wherein the compound (C) is at least one compound selected from polyamide, melamine, and cyanoguanidine. Claim 6: The compound (C) is polyamide 6/66
The acetal polymer composition according to claim 4, which is a /610/12 quaternary copolymer and/or melamine.