JPS6054985B2 - polyoxymethylene composition - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a polyoxymethylene composition having extremely small molding distortion and high cycle performance.

More specifically, in the presence of an addition compound having a structure in which linear polyoxymethylene and alkylene oxide are added to a polyhydric alcohol and having at least three or more alcoholic hydroxyl groups in one molecule, formaldehyde or trioxane is added. The present invention relates to a low-distortion, high-cycle polyoxymethylene composition comprising a branched polyoxymethylene obtained by homopolymerizing formaldehyde or trioxane with a cyclic ether. Polyoxymethylene is used in a wide range of fields as an engineering plastic with excellent mechanical properties.

When polyoxymethylene is used, it is usually shaped using an injection molding machine. Polyoxymethylene is prone to molding distortion during injection molding due to its fast crystallization rate, high crystallinity, and anisotropy during resin flow. In molded products, this distortion appears as warpage.

As a method to eliminate low form distortion,
No. 16 discloses polyoxymethylene glycol. Japanese Patent Publication No. 37-8815 proposes the addition of an aliphatic alcohol, and Japanese Patent Publication No. 37-16174 proposes the addition of glycerin.

These methods have the disadvantage of deteriorating the mechanical properties of the resin and impairing the inherent performance of polyoxymethylene. On the other hand, special public service 1977-
Publication No. 8254 describes adding an inorganic nucleating agent to make the crystal structure uniform, and JP-A-57-1924 also describes adding an inorganic compound.

Although inorganic nucleating agents function as excellent nucleating agents, they have deficiencies that greatly reduce the thermal stability of polyoxymethylene. Polyoxymethylene to which an inorganic nucleating agent is added tends to undergo thermal decomposition during molding. In the Tokuko Shotei-4262 Trowel Gazette and the Tokuko Shōtei-4262 Trowel Bulletin and the Tokuko Shōtei-1994 Sora Gazette, there are proposals to add branched/reticular polyoxymethylene.

These publications describe the synthesis of branched and network polyoxymethylene using a polyfunctional comonomer (termonomer) such as 1,4-butanediol diglycidyl ether as a crosslinking agent. These branched/reticular polyoxymethylenes have a function as a nucleating agent, and the size of the spherulites of the molded article is reduced by the addition of these branched/reticular polyoxymethylenes. By adding Rogakore's branched/reticular polyoxymethylene, the molded product becomes hard and brittle. That is, the addition improves strengths such as hardness, descending stress, tear strength, and torsional strength, but conversely decreases toughness such as elongation. The feature of polyoxymethylene is that it has well-balanced mechanical properties, and it is never desirable that toughness such as elongation decreases due to the addition of these branched/reticular polyoxymethylenes. The inventors of the present invention have extensively studied methods for reducing molding distortion of polyoxymethylene and improving high-cycle performance without impairing the well-balanced mechanical properties of polyoxymethylene.The results are detailed below. completed the invention described in .

The present invention relates to linear polyoxymethylene and an addition compound (hereinafter abbreviated as addition compound) having a structure in which an alkylene oxide is added to a polyhydric alcohol and having at least three or more alcoholic hydroxyl groups in one molecule. In the presence of
It is a composition consisting of branched polyoxymethylene (hereinafter abbreviated as branched polyoxymethylene) obtained by homopolymerizing formaldehyde or trioxane or copolymerizing formaldehyde or trioxane with a cyclic ether.

The composition of the present invention is characterized by maintaining the mechanical properties of linear polyoxymethylene without impairing it at all, and having low strain and high cycle performance.

The present invention will be explained in detail below.

The first linear polyoxymethylene used in the present invention is
It is a homopolymer of formaldehyde or trioxane and has a chain structure of oxymethylene groups.

It is a copolymer of linear polyoxymethylene, secondary formaldehyde or trioxane, and a cyclic ether compound, and has a structure in which oxyalkylene groups are randomly inserted between chains of oxymethylene groups.

The third linear polyoxymethylene is a copolymer obtained by the reaction of a polyoxymethylene homopolymer and a cyclic ether compound, and has a structure equivalent to the above-mentioned second linear polyoxymethylene. It is something.

Cyclic ether compounds that are components of linear polyoxymethylene include alkylene oxides such as ethylene oxide, propylene oxide, butylene oxide, styrene oxide, and cyclohexene oxide, ethylene glycol formal, diethylene glycol formal, triethylene glycol formal, and 1,4-butane. There are cyclic formals such as diol formals.

Among these cyclic ether compounds, ethylene oxide, ethylene glycol formal and 1,4-butanediol formal are particularly preferred from the viewpoint of improving the mechanical properties of linear polyoxymethylene.

When synthesizing these linear polyoxymethylenes, an anionic polymerization catalyst is used for formaldehyde homopolymerization, an anionic polymerization catalyst and a cationic polymerization catalyst are used for formaldehyde copolymerization, and a cationic polymerization catalyst is used for all other cases. be done.

The linear polyoxymethylene is stabilized using known terminal stabilization methods (eg, terminal esterification, terminal etherification, terminal hydrolysis) before addition. Linear polyoxymethylene at 190°C, 2.16k9 standard load (ASTM-
The melting index (MI) under Dl238-5'7T) is 0
．． It is in the range of 0.01 to 70 (Gr'/1 powder), and more preferably in the range of 0.1 to 30 from the viewpoint of satisfying practical mechanical properties.

The first type of branched polyoxymethylene that can be used in the present invention is a polymer obtained by homopolymerizing formaldehyde or trioxane in the presence of an addition compound.

The second branched polyoxymethylene is a polymer obtained by copolymerizing formaldehyde or trioxane with a cyclic ether in the presence of an addition compound.

Cyclic ethers that are components of branched polyoxymethylene include alkylene oxides such as ethylene oxide, propylene oxide, butylene oxide, styrene oxide, and cyclohexene oxide, ethylene glycol formal, diethylene glycol formal, triethylene glycol formal, and 1,4-butanediol formal. There are cyclic formals such as Among these cyclic ethers, ethylene oxide and ethylene glycol formal are particularly preferred from the viewpoint of chain branching efficiency.

The addition compound that can be used in the present invention is a compound having a structure in which an alkylene oxide is added to a polyhydric alcohol, and has at least three or more alcoholic hydroxyl groups in one molecule.

The addition compound is usually obtained by adding an alkylene oxide to a polyhydric alcohol such as triol, tetraol, pentaol, hexaol, etc. Examples of polyhydric alcohols include glycerin, trimethylolpropane,
Examples include triols such as sorbitan monoester and diglycene monoester, tetraols such as pentaerythritol, diglycerin, and sorbitan, pentaols such as fructose and glucose, and hexaols such as sorbitol.

Among these polyhydric alcohols, glycerin, trimethylolpropane, sorbitan monoester, pentaerythritol, and diglycerin are particularly preferred from the viewpoint of ease of availability and purification. The alkylene oxide to be added to the polyhydric alcohol in the present invention includes:
Ethylene oxide, propylene oxide, butylene oxide, isobutylene oxide, oxetane, 3,3-bis(chloromethyl)oxetane, tetrahydrofuran,
Examples include oxepane, styrene oxide, and cyclohexane 7 oxide.

Among these alkylene oxides, ethylene oxide, propylene oxide, butylene oxide, isobutylene oxide, styrene oxide and cyclohexene oxide are particularly preferred, and ethylene oxide is particularly preferred. The point to be noted here is the number of moles of alkylene oxide added to the polyhydric alcohol.

That is, only when branched polyoxymethylenes obtained using alkylene oxide adducts to polyhydric alcohols are used, the mechanical properties of the linear polyoxymethylenes to which these branched polyoxymethylenes are added are completely impaired. It becomes possible to impart low distortion and high cycle properties to the composition without any problems. When using a compound in which 1 mole of alkylene oxide is added per 1 mole of polyhydric alcohol, when using the polyhydric alcohol directly, or when using a polyfunctional crosslinking agent such as 1,4-butanedioldiglycidyl ether Compared to this, the decrease in mechanical properties, especially toughness, is halved. I have to say that this is a truly surprising effect. The average number of moles of alkylene oxide added per mole of polyhydric alcohol is required to be between 1 and 150.

The lower limit of the number of moles added is limited from the viewpoint of suppressing deterioration of mechanical properties, and the upper limit is limited mainly from the viewpoint of chain branching efficiency during polymerization in which the addition compound is used. That is, when the average number of added moles exceeds 150, the chain transfer efficiency (chain branching efficiency) of the addition compound during homopolymerization/copolymerization of formaldehyde or trioxane decreases. When the efficiency of chain branching decreases, the effect of adding the branched polyoxymethylene produced also decreases, and low strain and high cycle performance cannot be sufficiently achieved.

From this point of view, a more preferable range of the average number of added moles is 2 to 70.

Specific examples of the addition compounds are as follows.

Glycerin ethylene oxide adduct (average molecular weight 800
), glycerin propylene oxide adduct (average molecular weight 660), trimethylol propane ethynylene oxide. Propylene oxide mixed adduct (average molecular weight 1050
sEthylene oxide/propylene oxide 3/1 (weight ratio), sorbitan monolaurate ethylene oxide adduct (average molecular weight 2,000), sorbitan monostearate butylene 3 oxide adduct (average molecular weight 2,15)
0), diglycerin monoacetate isobutylene oxide adduct (average molecular weight 1,630), pentaerythritol ethylene oxide adduct (average molecular weight 1,500)
), pentaerythritol detrahydrofuran adduct 4
(average molecular weight 1,870), diglycerol ethylene oxide adduct (average molecular weight 810), sorbitan propylene oxide adduct (average molecular weight 5,800), fructose ethylene oxide adduct (average molecular weight 1,250)
, glycose styrene oxide adduct (average molecular weight 1,
780), polyhydroxypolyolein cyclohexene oxide adduct (average molecular weight 4,890. Polymer synthesized by epoxidizing and hydrogenating the double bonds of polybutane diene and containing an average of 3.FB alcoholic hydroxyl groups in one molecule). In the synthesis of these branched polyoxymethylenes, an anionic polymerization catalyst is used for formaldehyde homopolymerization, an anionic polymerization catalyst and a cationic polymerization catalyst are used for formaldehyde copolymerization, and in other cases In both cases, a cationic polymerization catalyst is used.

After the branched polyoxymethylene is polymerized, it can be stabilized using a known stabilization method and then used for addition, or it can also be used for addition without being stabilized.

The melting index of the branched polyoxymethylene at 190 DEG C. and under a standard load of 2.16k9 (ASTM-Dl238-57T') is required to be between 0.01 and 30.

That is, the branched polyoxymethylene that can be used in the present invention must be melted in the 19th generation. When a branched/reticular polymer that does not melt is used, a decrease in mechanical properties, especially toughness, is observed. Therefore, in the present invention, a branched/network polymer that does not melt cannot be used. When a polyfunctional monomer (comonomer, termonomer) such as 1,4-butanediol glycidyl ether is used, the resulting polymer is usually crosslinked and becomes network-like.

Polymers that have been networked by crosslinking no longer melt and cannot be used in the present invention. The branched polyoxymethylene used in the present invention only has branches and is never crosslinked or networked.

It is therefore essentially a molten polymer. Moreover, the more preferable range of MI of branched polyoxymethylene is 0.05 to 1.
The range is 0.5 (Gr/10 minutes).

The amount of branched polyoxymethylene added to 10 parts by weight of linear polyoxymethylene is in the range of 0.01 to 2 parts by weight. The lower limit of the amount added is limited from the viewpoint of molding distortion, and the upper limit of the amount added is limited from the viewpoint of ease of injection molding, and the more preferable range of the amount added is 0.05 to 5 parts by weight. The size of the spherulites of linear polyoxymethylene to which branched polyoxymethylene is added is smaller than that of the case without addition.

From this fact, it is thought that the branched polyoxymethylene functions as a nucleating agent when the molten resin containing the branched polyoxymethylene is cooled and solidified. Since this function has been discovered, it is presumed that the composition of the present invention provides a molded article with extremely small molding distortion during molding.

Further, even if the molding time of the composition of the present invention is shortened, especially the cooling time, the molded product will not be distorted, and the composition of the present invention will give a good molded product even if the molding time (molding cycle) is extremely short. That is, the composition of the present invention has low molding distortion and high cycle performance. It is also possible to further add and use a conventionally known compound as a stabilizer for polyoxymethylene to the composition of the present invention.

The first of the known stabilizers are thermal stabilizers, which include amide compounds,
Examples include polyamide, amidine compounds, melamine, polyvinylpyrrolidone, etc. The second known stabilizer is an antioxidant, such as a hindered phenol compound. The third known stabilizer is a light stabilizer, which includes benzotriazole compounds, hydroxybenzophenone compounds, and the like. These stabilizers are usually used in an amount of 0.05 to 10 parts by weight, more preferably 0.05 to 10 parts by weight per 10 parts by weight of linear polyoxymethylene.
．． It is added in an amount of 1 to 5 parts by weight.

In order to produce the polyoxymethylene composition of the present invention, it is necessary to mix each component with each other in powder or granular form, and then homogenize using a melting device such as an extruder.

The present invention will be specifically explained below using Examples.

The meanings of the terms used in the examples are as follows. M
I: Melting index at 190℃ and 2.16k9 standard load (
ASTM-Dl238-57r) Addition amount (Phr): Addition amount per 100 parts by weight of linear polyoxymethylene Antioxidant AO-A; 2,2-methylenebis(4-methyl-6
-t-butylphenol) antioxidant AO-B: Pentaerythritol-tetrakis [3-(3,5-di-t-
Butyl-4-hydroxyphenol) propionate]
Crystallization temperature: A sample weighing 3.0 gr was heated in a DSC (PerkinElmer DSC-2C) at a rate of 10 C/min.
Heat to 00C and hold at 20CfC for 5 minutes.

Then, the temperature showing the piece value when cooled at a rate of 1 C) C/min is defined as the crystallization temperature. The higher the crystallization temperature, the faster the crystallization rate during molding, and the higher the cycleability. The value was determined based on molding and measurement conditions with warp of 2 or less, and the smaller the warp value, the smaller the molding distortion. Molding conditions Molding machine Nikko 70A molded product shape 1W! lThickness, diameter 150rIn disk center mold temperature 70・C cylinder temperature 195℃ injection pressure
45kg/Cl. G injection time
128 cooling time
2 (8 measurement conditions molded product at 25℃, 50% R.H.
．． After leaving it for 48 hours under the dial gauge (1110-
The warpage value is the maximum deviation from the reference plane of the circumference in μ units, with the center of the disc as the reference plane.

A sample piece was cut out from the molded product using a spherulite size microtome and measured using a polarizing microscope.

Tensile strength. Tensile descent point elongation: Measured according to ASTM-G-638.

- Example 1 (1) Linear polyoxymethylene Anhydrous formaldehyde was blown into cyclohexane containing dibutyltin dilaurate as a polymerization catalyst, and 56
Polymerization was carried out at ℃.

After separating the polymer from cyclohexane, the terminals of the polymer were acetylated with acetic anhydride to stabilize the polymer. The MI of this polymer was 15.2 (Gr/1 powder). (2) Branched polyoxymethylene anhydrous formaldehyde, dibutyltin dilaurate as a polymerization catalyst, trimethylolpropane ethylene oxide adduct as a molecular weight regulator (combined chain branching agent) (average molecular weight 31, average number of moles of ethylene oxide added is 4) The mixture was blown into cyclohexane containing 56°C and polymerized at 56°C.

After separating the polymer from cyclohexane, the polymer terminals were acetylated with acetic anhydride to stabilize the polymer. This polymer had a value of 1.4 (Gr/1 powder).
(3) After adding the following compound to the linear polyoxymethylene of composition (1), 5D1! The mixture was melt-mixed using a GRφ extruder.

(2) branched polyoxymethylene 0.4P8 nylon 660.5P8A0-AO-3P8 The MI of this composition is 15.1 (Gr/10 min),
The crystallization temperature is 151. It was CfC.

The molded product of this composition had a warpage of 130μ and a spherulite size of 8μ. From these facts, it has become clear that this composition has both low molding distortion and high cycle performance. The tensile strength of this molded product is 760k9/C.
The ltl tensile elongation at the falling point is 50%, and the stiffness (strength)
The toughness did not decrease at all. Example 2 (4) After mixing 98% linear polyoxymethylene anhydrous trioxane and 2% ethylene oxide in a kneader with two Σ blades, boron trifluoride dibutyl etherate was added as a polymerization catalyst. was added to initiate polymerization.

After one powder, tributylamine was added to stop the polymerization.

This polymer was then added with a 5% triethylamine-water mixture and a vented 65T! r! 3 were fed to the nφ extruder. The MI of the polymer which had undergone melt hydrolysis in an extruder to remove unstable terminal portions was 9.0 (Gr'/1 powder). (5) 97.5% branched polyoxymethylene anhydrous trioxane, 20% ethylene oxide, 0.5% glycerin propylene oxide adduct as a molecular weight regulator (combined chain branching agent) (average molecular weight 27%)
After mixing 0s propylene oxide (average number of added moles of 3) in a seconder, 4 (4) boron trifluoride dibutyl etherate as a polymerization catalyst was added to initiate polymerization.

After the second powder, the polymerization was stopped and the polymer was then stabilized by subjecting it to melt hydrolysis in an extruder.

The MI of this polymer was 0.95 (Gr/1 powder).
(6) The following compounds were added to the linear polyoxymethylene of composition (4), and then melt-mixed in a 65] NEφ extruder.

(5) Branched polyoxymethylene 0.5PHR melamine 0.3PHRA0-BO・
4PHR The physical properties of this powder composition were as follows.

■ 9.0 (Gr'/1 powder) Crystallization temperature 146. (Main) Warp
140μ spherulite size
7μ tensile strength
650k9/C7ll tensile yield elongation
60% This composition has low molding distortion and high cycleability, while retaining excellent mechanical properties.

Example 3: 7) Linear Polyoxymethylene Polyoxymethylene was suspended in n-hexane at a concentration of 25%.

Ethylene oxide was blown into this suspension and the concentration of ethylene oxide was adjusted to 0.05n101e/l-hexane. Then, boron trifluoride dibutyl etherate was added to this suspension and reacted at 60°C for 105j. During this period, ethylene oxide was 0.05rn01e/
1-Hexane was continuously fed to maintain it. After termination of the reaction, the polymer was separated from the solvent and then stabilized by melt hydrolysis. The MI of this polymer is 8.8 (G
A random copolymer in which oxyethylene groups were randomly inserted into polyoxymethylene was obtained. 3) Branched polyoxymethylene copolymer 95% anhydrous trioxane, 3% ethylene glycol formal, pentaerythritol ethylene oxide adduct (average molecular weight 5) as a molecular weight regulator (combined chain branching agent)
Tin tetrachloride was added to a mixture of 80s ethylene oxide with an average added mole number of 10) 2%, and one-powder polymerization was continued.

After termination of polymerization, catalyst residues were removed by washing the polymer three times with warm water. The MI of this polymer is 5.4 (Gr/1
It was. () After adding the following compound to the linear polyoxymethylene of composition (7), 65TnI1. The mixture was melted and mixed using a φ extruder.

(8) Branched polyoxymethylene 1.0PHR dicyandiamide 0.4PHRA0-AO
．． 4P81PEG6OOOl. OPHR The physical properties of this composition are as follows.

■ &9 (Gr/1 powder) Crystallization temperature 147.7C Warpage
120μ, spherulite size
7μ tensile strength
650k9/Cll tensile descent point elongation
8% This composition also has low molding distortion and high cycle performance.

Comparative Example 1 The following compounds were added to the linear polyoxymethylene obtained in Example 1 (1), and then melt-mixed using a 5iφ extruder.

Nylon 660.5PHR= AO-AO. 3PHR This composition has the following physical properties.

MIl5.2 (Gr/1 powder) Crystallization temperature 146. (Main) Warp
360μ spherulite size 215μ tensile strength
750k9/al tensile descent point elongation
If the branched polyoxymethylene obtained in 50% Example 1 (2) is not added, molding distortion is large and high cycle performance is not sufficient.

Comparative Example 2 The following compounds were added to the linear polyoxymethylene obtained in Example 2 (4), and then melt-mixed using a 65 mφ extruder.

Melamine 0.3PHRA0-
A.O. 4PHR This composition has the following physical properties.

MI9. O (Gr/l powder) Crystallization temperature 144.5℃ Warpage
390μ spherulite size 250μ tensile strength
645k9/Ai tensile descent point elongation
60% When the branched polyoxymethylene obtained in (5) of Example 2 is not added, molding distortion is large and high cycle performance is also insufficient.

Examples 4 to 18 1I Linear polyoxymethylene Linear polyoxymethylene was synthesized from the starting cyclic ether compounds shown in Table 1.

11) Branched polyoxymethylene A branched polyoxymethylene was synthesized from the starting material cyclic ether and the addition compound shown in Table 2.

The amounts added are also shown in Table 2. 1Z Composition The branched polyoxymethylene shown in Table 2 and the stabilizer shown below were added to the linear polyoxymethylene shown in Table 1 and melt-mixed using a 5"φ extruder.

Nylon 6/6-10 binary copolymer 0.5phfA0
-A.O. Table 3 shows the physical properties of these compositions.

In all Examples, compositions with low distortion and high cycle performance were obtained. Moreover, from Examples 15 to 18,
It can be seen that as the amount of branched polyoxymethylene added increases, the strain becomes smaller and the high cycle performance also improves.

Furthermore, in each of the examples, a composition having both rigidity (strength) and toughness was obtained.

Comparative Examples 3 to 9 (13) Linear Polyoxymethylene Linear polyoxymethylene was synthesized from the compounds shown in Table 4.

(10 branches. Network polyoxymethylene) A branched/network polyoxymethylene was synthesized from the compounds shown in Table 5.

The amounts added are also shown in Table 5. (15) Composition The branched network polyoxymethylene shown in Table 5 and the stabilizer shown below were added to the linear polyoxymethylene shown in Table 4, and the mixture was melt-mixed using a 5"φ extruder. .

Nylon 6/6-10: Original copolymer 0.5 phrA
0-AO.4 phr The physical properties of these compositions are shown in Table 6.

By adding branched/reticular polyoxymethylene,
Although the strain is certainly reduced, the polymer becomes hard and brittle, and the elongation decreases significantly. Addition of immediately branched/reticular polyoxymethylene improves rigidity (strength), but on the contrary, toughness decreases. Comparative Example 10 The same reagents as in Example 1 were used except that trimethylolpropane was used in place of the trimethylolpropane ethylene oxide adduct used in Example 1, and the same procedures as in Example 1 were carried out.

The physical properties of the obtained composition were as follows.

MIl4.9 (Gr/1 powder) crystallization temperature
150. CfC″ warpage
196μ spherulite size
Feather μ tensile strength 7
90kg/Cll tensile descent point elongation
In the case of a composition in which a polymer obtained by directly using trimethylolnoropane to which 32% ethylene oxide is not added is added, the elongation decreases significantly6.

Claims (1)

[Scope of Claims] 1 In the presence of a linear polyoxymethylene and an addition compound having a structure in which an alkylene oxide is added to a polyhydric alcohol and having at least three or more alcoholic hydroxyl groups in one molecule , a branched polyoxymethylene obtained by homopolymerizing formaldehyde or trioxane, or copolymerizing formaldehyde or trioxane with a cyclic ether. 2. The polyoxymethylene composition according to claim 1, wherein the linear polyoxymethylene is a homopolymer of formaldehyde or trioxane. 3. The polyoxymethylene composition according to claim 1, wherein the linear polyoxymethylene is a copolymer of formaldehyde or trioxane and a cyclic ether compound. 4. The polyoxymethylene composition according to claim 1, wherein the linear polyoxymethylene is a copolymer obtained by reacting a polyoxymethylene homopolymer with a cyclic ether compound. 5. Claims 1 and 3, wherein the cyclic ether compound that is a component of the linear polyoxymethylene is a compound selected from the group consisting of ethylene oxide, ethylene glycol formal, and 1,4-butanediol formal. Or the polyoxymethylene composition according to item 4. 6 Linear polyoxymethylene at 190°C, 2.16 kg
The melting index (MI) under standard load (ASTM-D1238-57T) is in the range of 0.01 to 70 (gr/10 min). A composition according to any one of the above. 7 Branched polyoxymethylene at 190°C, 2.16 kg
The polyoxymethylene composition according to claim 1, which has a melting index (MI) under standard load (ASTM-D1238-57T) in the range of 0.01 to 30 (gr/10 min). 8. The polyoxymethylene composition according to claim 1, wherein the amount of branched polyoxymethylene added to 100 parts by weight of linear polyoxymethylene is in the range of 0.01 to 20 parts by weight. 9. The polyoxymethylene composition according to claim 1, wherein the cyclic ether that is a component of the branched polyoxymethylene is ethylene oxide or ethylene glycol former. 10. The polyoxymethylene composition according to claim 1, wherein the polyhydric alcohol is a compound selected from the group consisting of glycerin, trimethylolpropane, sorbitan monoester, pentaerythritol, and diglycerin. 11. The polyoxymethylene composition according to claim 1, wherein the alkylene oxide is ethylene oxide. 12. The polyoxymethylene composition according to claim 1, wherein the alkylene oxide is a compound selected from the group consisting of propylene oxide, butylene oxide, isobutylene oxide, styrene oxide and cyclohexene oxide. 13. The polyoxymethylene composition according to claim 1, wherein the average number of moles of alkylene oxide added per mole of polyhydric alcohol is in the range of 1 to 150.