JP6943806B2 - Polyoxymethylene resin composition and molded article - Google Patents

Description

The present invention relates to a polyoxymethylene resin composition and a molded product.

The polyoxymethylene resin is a crystalline resin and is a resin material having excellent rigidity, strength, toughness, slidability, and creep property.
Polyoxymethylene resins have a wide range of uses as resin materials for various mechanical parts such as automobile parts, electrical / electronic parts, and industrial parts.
In particular, polyacetal homopolymers are known to be superior in rigidity and toughness and have a high thermal deformation temperature as compared with polyacetal copolymers.

So far, the addition of various crystal nucleating agents has been studied as a formulation for improving the physical properties of polyacetal homopolymers, and the effects obtained are the improvement of working durability and quietness, high dimensional accuracy and low warpage. Improvement of productivity, improvement of shear strength and impact resistance, improvement of hardness and productivity, improvement of shrinkage rate and productivity, etc. are mentioned (for example, Patent Documents 1, 2, 3, 4, 5).

Japanese Unexamined Patent Publication No. 2008-291573 Japanese Unexamined Patent Publication No. 51-97652 Japanese Unexamined Patent Publication No. 5-279551 Japanese Unexamined Patent Publication No. 57-94036 Special Table 2002-500256

However, the techniques disclosed in Patent Documents 1 to 5 are not involved in the high temperature and low stress creep characteristics, that is, the creep rupture characteristics for a low stress load in a high temperature environment.
Further, the present inventors have found that when the amount of the crystal nucleating agent added is large, the variation in Charpy impact strength becomes large, and there is room for improvement from the viewpoint of reliability as a resin material for various mechanical parts. I noticed that.

Therefore, an object of the present invention is to provide a polyoxymethylene resin composition and a molded product having little variation in Charpy impact strength and excellent in high-temperature and low-stress creep characteristics.

As a result of diligent studies to solve the above problems, the present inventors have found polyoxymethylene resin homopolymers, polyamide polymers having a melting point of 140 ° C. or higher and 200 ° C. or lower, and boron nitride as a crystal nucleating agent. The present invention has been completed by finding that a polyoxymethylene resin composition in which the above-mentioned is blended in a specific ratio can solve the above-mentioned conventional problems.
That is, the present invention is as follows.

[1]
Polyoxymethylene resin homopolymer (A) 100 parts by mass and
Polyamide polymer (B) having a melting point of 140 ° C. or higher and 200 ° C. or lower, 0.005 parts by mass or more and 0.05 parts by mass or less.
Boron nitride (C) containing 0.0005 parts by mass or more and 0.005 parts by mass or less.
The mass ratio of the (B) polyamide polymer to the (C) boron nitride is (B) polyamide copolymer / (C) boron nitride = 95/5 or more and 70/30 or less.
A polyoxymethylene resin composition.
[2]
Acrylamide copolymer (D) 0.05 parts by mass or more and 0.3 parts by mass or less,
Antioxidant (E) 0.1 parts by mass 0.3 parts by mass or less,
The polyoxymethylene resin composition according to the above [1], which further contains.
[3]
The polyoxymethylene according to the above [1] or [2], wherein the melt flow rate (according to ISO 1133D) of the polyoxymethylene resin homopolymer (A) is 0.5 g / 10 minutes or more and 10 g / 10 minutes or less. Resin composition.
[4]
A molded product containing the polyoxymethylene resin composition according to any one of the above [1] to [3].

According to the present invention, it is possible to provide a polyoxymethylene resin composition and a molded product having little variation in Charpy impact strength and excellent in high temperature and low stress creep characteristics.

Hereinafter, a mode for carrying out the present invention (hereinafter, referred to as “the present embodiment”) will be described in detail.
It should be noted that the following embodiments are examples for explaining the present invention, and the present invention is not intended to be limited to the following contents. The present invention can be implemented with various modifications within the scope of the gist thereof.

[Polyoxymethylene resin composition]
The polyoxymethylene resin composition of the present embodiment is
Polyoxymethylene resin homopolymer (A) 100 parts by mass and
Polyamide polymer (B) having a melting point of 140 ° C. or higher and 200 ° C. or lower, 0.005 parts by mass or more and 0.05 parts by mass or less.
Boron nitride (C) containing 0.0005 parts by mass or more and 0.005 parts by mass or less.
The mass ratio of the (B) polyamide polymer to the (C) boron nitride is (B) polyamide copolymer / (C) boron nitride = 95/5 or more and 70/30 or less.
It is characterized by that.
The polyoxymethylene resin composition of the present embodiment may further contain an acrylamide copolymer (D), an antioxidant (E), various other additives and the like.
Hereinafter, each component that can be contained in the polyoxymethylene resin composition of the present embodiment will be described.

(Polyoxymethylene resin homopolymer (A))
The polyoxymethylene resin composition of the present embodiment contains a polyoxymethylene resin homopolymer (A).
The polyoxymethylene resin homopolymer (A) refers to a polyoxymethylene polymer in which 99.8 mol% or more of the main chain excluding both ends is composed of oximethylene groups, and 99.8 mol% of the main chain excluding both ends. The above is preferably composed of a polyoxymethylene group, and more preferably a polyoxymethylene homopolymer in which the main chain excluding both ends is composed of only a polyoxymethylene group. In particular, a polyoxymethylene homopolymer in which both ends of the polymer chain are sealed with an ester group is preferable.
The polyoxymethylene resin homopolymer (A) may contain 5 parts by mass, preferably 3 parts by mass, and more preferably 1 part by mass of the polyoxymethylene copolymer in 100 parts by mass.
The melt flow rate (MFR) (based on ISO 1133 D) of the polyoxymethylene resin homopolymer (A) of the present embodiment is preferably 0.5 g / 10 minutes or more, and is high, from the viewpoint of molding processability. From the viewpoint of impact resistance and durability, it is preferably 10 g / 10 minutes or less, more preferably 1.0 g / 10 minutes or more and 5.0 g / 10 minutes or less, and further preferably 1.5 g / 10 minutes. More than 2.5 g / 10 minutes or less. A melt flow rate polyoxymethylene resin homopolymer (A) in this range is suitable for the polyoxymethylene resin composition of the present embodiment as a material for parts used for a long period of time with low stress (low load). Can be used for.

((Manufacture of polyoxymethylene resin homopolymer (A)))
The polyoxymethylene resin homopolymer (A) is not particularly limited, but can be produced, for example, by carrying out a polymerization step and a terminal stabilization step described later.

<(1) Polymerization step>
In the polymerization step, a known slurry polymerization method (for example, the method described in Japanese Patent Publication No. 47-6420 and Japanese Patent Publication No. 47-10059) is used to carry out a monomer in a reactor using a chain transfer agent or a polymerization catalyst. Is polymerized to obtain a crude polyoxymethylene resin homopolymer having unstabilized ends.
Although the crude polyoxymethylene resin homopolymer itself can be used as the material of the polyoxymethylene resin composition of the present embodiment, the terminal of the crude polyoxymethylene resin homopolymer is subjected to the terminal stabilization step described later. It is preferable to use a stabilized product.

[(1) Monomer]
Examples of the monomer used for producing the polyoxymethylene resin homopolymer include a formaldehyde monomer or a cyclic oligomer of formaldehyde such as a trimeric (trioxane) or a tetramer (tetraoxane) thereof.

In order to continuously obtain a polyoxymethylene resin homopolymer having a stable molecular weight in the polymerization step, it is preferable to use a purified formaldehyde gas having a low impurity concentration.
As a method for purifying formaldehyde, a known method (for example, the method described in JP-A-5-32374 and JP-A-2001-521916) can be applied.

When formaldehyde gas is used as the monomer in the polymerization step, it is preferable to use a monomer that does not contain impurities such as water, methanol, and formic acid that have a polymerization terminating action and a chain transfer action during the polymerization reaction as much as possible.
By using a formaldehyde gas having a small amount of these impurities, an unexpected chain transfer reaction can be avoided, and a polyoxymethylene resin homopolymer having a target molecular weight can be obtained. In particular, the content of the impurity that induces a hydroxyl group in the polymer terminal group is preferably 100 mass ppm or less, and more preferably 50 mass ppm or less, based on the total amount of the monomers.

[(2) Chain transfer agent]
The chain transfer agent used in the production of the polyoxymethylene resin homopolymer is not particularly limited, and examples thereof include alcohols and acid anhydrides.
As the chain transfer agent, it is preferable to use one containing as little as possible impurities having a polymerization termination action and a chain transfer action during the polymerization reaction, such as water, methanol, formic acid, and acetic acid. As a method for obtaining a chain transfer agent having a small amount of impurities, for example, a chain transfer agent having a widely available water content exceeding a specified amount is bubbled with dry nitrogen, and impurities are removed by an adsorbent such as activated carbon or zeolite. , A method of purification and the like.
Only one type of chain transfer agent may be used alone, or two or more types may be used in combination.

[(3) Polymerization catalyst]
The polymerization catalyst used for producing the polyoxymethylene resin homopolymer is not particularly limited, and examples thereof include an onium salt-based polymerization catalyst.
Examples of the onium salt-based polymerization catalyst include compounds represented by the following general formula (1).
_{[R 1 R 2 R 3 R} 4 M] + X - ··· (1)
(In the general formula (1), R ₁ , R ₂ , R ₃ and R ₄ each independently represent an alkyl group, M represents an element having a lone electron pair, and X represents a nucleophilic group. R ₁ , R ₂ , R ₃ and R ₄ may be the same or different.)

Examples of the onium salt-based polymerization catalyst include, but are not limited to, quaternary ammonium salt-based compounds and quaternary phosphonium salt-based compounds, and in particular, tetramethylammonium bromide and dimethyl distearyl. Ammonium acetate, tetraethylphosphonium iodide, and tributylethylphosphonium iodide are preferred.

[(4) Reactor]
The reactor used for producing the polyoxymethylene resin homopolymer is not particularly limited, but for example, a reaction tank with a batch type stirrer, a continuous type conider, a twin-screw screw type continuous extrusion kneader, and a twin-screw paddle type continuous reactor. Examples include a mixer.
The reactor preferably has a structure capable of heating or cooling a reaction mixture such as a jacket on the outer periphery of the body.

<(2) Terminal stabilization step>
In the terminal stabilization step, the terminal of the crude polyoxymethylene resin homopolymer obtained in the polymerization step is subjected to an ether group by an etherifying agent by a known method (for example, the method described in Japanese Patent Publication No. 63-452). And / or seal with an ester group with an esterifying agent to stabilize.

The etherifying agent for sealing with an ether group is not particularly limited, and examples thereof include ortho ester and the like.

Examples of the ortho ester include, but are not limited to, an ortho ester of an aliphatic acid or aromatic acid and an aliphatic alcohol, an alicyclic group alcohol or an aromatic alcohol, and specific examples thereof. Examples thereof include methyl or ethyl orthoformates, methyl or ethyl orthoacetates and methyl or ethyl orthobenzoates, and orthocarbonates such as ethyl orthocarbonates.
Only one type of etherifying agent may be used alone, or two or more types may be used in combination.

The reaction of blocking with an etherifying agent, that is, the etherification reaction, is a Lewis of medium-strength organic acids such as p-toluenesulfonic acid, acetic acid and hydrobromic acid, and medium-strength mineral acids such as dimethyl and diethylsulfate. The acid type catalyst may be introduced in an amount of 0.001 part by mass or more and 0.02 part by mass or less with respect to 1 part by mass of the etherifying agent.
In the etherification reaction, for example, low boiling point aliphatic compounds such as pentane, hexane, cyclohexane and benzene; alicyclic groups and aromatic hydrocarbons; halogenation of methylene chloride, chloroform and carbon tetrachloride and the like. An organic solvent such as a lower aliphatic compound can be used.

As a method for sealing the ends of the crude polyoxymethylene resin homopolymer with an ester group to stabilize the ends, for example, a large amount of acid anhydride described in US Pat. No. 3,459,709 is used in a slurry state. In the gas phase, the method using the acid anhydride gas described in US Pat. No. 3,172,736 can be mentioned.

The esterifying agent for sealing with an ester group is not particularly limited, and examples thereof include organic acid anhydrides and the like.

Examples of the organic acid anhydride include an organic acid anhydride represented by the following general formula (2).
R ₅ COOCOR ₆ ... (2)
(In the general formula (2), R ₅ and R ₆ each independently represent an alkyl group or a phenyl group. R ₅ and R ₆ may be the same or different.)

Examples of the organic acid anhydride include, but are not limited to, propionic anhydride, benzoic anhydride, acetic anhydride, succinic anhydride, maleic anhydride, glutaric anhydride, phthalic anhydride and the like. Acetic anhydride is preferred.
Only one type of esterifying agent may be used alone, or two or more types may be used in combination.

As a method for terminal-sealing with an ester group in the gas phase, for example, it is preferable to perform terminal-sealing after removing the onium salt-based polymerization catalyst by the method described in JP-A-11-92542. By removing the onium salt-based polymerization catalyst in the polyoxymethylene, it is possible to avoid the decomposition reaction of the polyoxymethylene resin homopolymer derived from the onium salt-based polymerization catalyst when the end is closed, and the end is stable. The polymer yield in the chemical conversion step can be improved, and the coloration of the polyoxymethylene resin homopolymer can be suppressed.

It is preferable that the terminal of the polyoxymethylene resin homopolymer is sealed with an ether group and / or an ester group ^{to reduce the concentration of the terminal hydroxyl group to 5 × 10 -7} mol / g or less. When the concentration of the terminal hydroxyl group is 5 × 10 ^-7 mol / g or less, the thermal stability is excellent and the quality of the original polyoxymethylene resin homopolymer can be maintained, which is preferable. From the same viewpoint, the concentration of the terminal hydroxyl group ^{is more preferably 0.5 × 10 -7} mol / g or less, and further preferably 0.3 × 10 ^-7 mol / g or less.

(Polyamide polymer (B) having a melting point of 140 ° C. or higher and 200 ° C. or lower)
The polyoxymethylene resin composition of the present embodiment contains a polyamide polymer (B) having a melting point of 140 ° C. or higher and 200 ° C. or lower as a heat stabilizer containing formaldehyde-reactive nitrogen, and a more preferable melting point is 150 ° C. or higher. It is 190 ° C. or lower, and a more preferable melting point is 155 ° C. or higher and 180 ° C. or lower.
Examples of the polyamide polymer (B) having a melting point of 140 ° C. or higher and 200 ° C. or lower include polyamide 12, polyamide 11, polyamide 6/66 copolymer, polyamide 6/66/12 ternary copolymer, and polyamide 6/66 /. 610 ternary copolymer and the like can be mentioned. A more preferable polyamide polymer (B) is a polyamide 6/66/610 ternary copolymer.
The content of the polyamide polymer (B) having a melting point of 140 ° C. or higher and 200 ° C. or lower is 0.005 parts by mass or more and 0.05 parts by mass or less with respect to 100 parts by mass of the polyoxymethylene resin homopolymer (A). The range is preferably 0.008 parts by mass or more and 0.04 parts by mass or less, and more preferably 0.01 parts by mass or more and 0.03 parts by mass or less.
When the content of the polyamide polymer (B) having a melting point of 140 ° C. or higher and 200 ° C. or lower is within the above range, a polyoxymethylene resin composition having a small variation in Charpy impact strength and excellent high-temperature and low-stress creep characteristics can be obtained. Can be provided.

(Boron Nitride (C))
The polyoxymethylene resin composition of the present embodiment contains boron nitride (C) as a crystal nucleating agent.
The content of boron nitride (C) is in the range of 0.0005 parts by mass or more and 0.005 parts by mass or less, preferably 0.001 parts by mass, with respect to 100 parts by mass of the polyoxymethylene resin homopolymer (A). The range is 0.004 parts by mass or less, and more preferably 0.0015 parts by mass or more and 0.003 parts by mass or less.
When the content of boron nitride (C) is within the above range, it is possible to provide a polyoxymethylene resin composition having a small variation in Charpy impact strength and excellent high temperature and low stress creep characteristics.

((B) Polyamide polymer having a melting point of 140 ° C. or higher and 200 ° C. or lower / (C) Mass ratio of boron nitride)
In the polyoxymethylene resin composition of the present embodiment, the mass ratio of the polyamide polymer (B) having a melting point of 140 ° C. or higher and 200 ° C. or lower with respect to boron nitride (C), that is, the melting point of 140 ° C. or higher and 200 ° C. or lower. The mass ratio of the polyamide polymer (B) / boron nitride (C) (hereinafter, also referred to as “B / C”) is 95/5 or more and 70/30 or less on a mass basis, and 93/7 or more and 77/23. The following is preferable, and more preferably 93/7 or more and 85/15 or less.
By setting the mass ratio (B / C) to the above range, it is possible to provide a polyoxymethylene resin composition having a small variation in Charpy impact strength and excellent high temperature and low stress creep characteristics. Although not limited by theory, the reason for this can be inferred as follows.
The polyamide polymer is generally easy to aggregate, and is also easy to aggregate when it is added to the polyoxymethylene resin homopolymer (A) and mixed to produce a polyoxymethylene resin composition. When the polyamide polymer agglomerates in the polyoxymethylene resin composition, due to the difference in physical, mechanical or thermal properties between the agglomerated portion and the non-aggregated portion, the sharpy rupture and creep rupture occur in the molded product. It is considered that defects on the surface of the molded body, which is the starting point of the above, and foreign matter are generated, which affects the variation in the impact strength of the charpee and the high temperature and low stress creep characteristics. On the other hand, by setting the ratio of the polyamide polymer to boron nitride in a specific range, the dispersibility of the polyamide polymer in the polyoxymethylene resin composition can be enhanced and aggregation can be suppressed. It is considered that defects on the surface of the molded body, which are the starting points of sharpy rupture and creep rupture, and the generation of foreign matter can be suppressed.
Further, the lower the MFR of the polyoxymethylene resin composition obtained by adding and mixing the polyamide polymer (B) and boron nitride (C) to the polyoxymethylene resin homopolymer (A), the more the melt-kneading occurs. It is necessary to raise the temperature of the extruded resin, and as a result, foreign substances such as carbides and modified products are likely to be generated. Therefore, the lower the MFR of the polyoxymethylene resin composition, the greater the contribution of the effect of the present invention.

(Acrylamide copolymer (D))
The polyoxymethylene resin composition of the present embodiment may contain an acrylamide copolymer (D) as an optional component in addition to the above-mentioned essential components.
The content of the acrylamide copolymer (D) is not particularly limited, but is preferably 0.05 parts by mass or more and 0.3 parts by mass or less with respect to 100 parts by mass of the polyoxymethylene resin homopolymer (A). , More preferably 0.07 parts by mass or more and 0.25 parts by mass or less, and further preferably 0.1 parts by mass or more and 0.2 parts by mass or less.
The acrylamide copolymer (D) may be produced, for example, by using an alkaline earth metal alcoholate as a catalyst and copolymerizing acrylamide with a monomer having a vinyl group other than acrylamide. By using a copolymer of acrylamide and a monomer having a vinyl group (for example, a copolymer having a crosslinked structure) as the acrylamide copolymer (D), the formaldehyde trapping ability can be enhanced.

Examples of the monomer having a vinyl group other than acrylamide include a monomer having one or two vinyl groups.
Examples of the monomer having one vinyl group include n-butyl methacrylate, isobutyl methacrylate, t-butyl methacrylate, ethyl methacrylate, cyclohexyl methacrylate, 2-ethylhexyl methacrylate, cecil methacrylate, pentadecyl methacrylate, and stearyl methacrylate. Examples thereof include behenyl methacrylate, hydroxypropyl methacrylate, polypropylene glycol methacrylate, polyethylene glycol methacrylate and the like.
Examples of the monomer having two vinyl groups include divinylbenzene, ethylene bisacrylamide, N, N'-methylene bisacrylamide and the like. Among these monomers having a vinyl group, N, N'-methylenebisacrylamide is preferable.
When producing the acrylamide polymer, the amount of the monomer having a vinyl group added is preferably 0.05 to 20% by mass with respect to the total amount of the acrylamide and the monomer having a vinyl group.

The acrylamide copolymer (D) is not particularly limited, but preferably has a primary amide group of 30 mol% or more and 70 mol% or less, and more preferably has a primary amide group of 40 mol% or more and 60 mol% or less. Is.
Among them, particularly preferable acrylamide copolymer (D) is crosslinked polyacrylamide having an average particle size of 1 μm or more and 10 μm, and more preferably polyacrylamide having an average particle size of 1 μm or more and 7 μm or less. More preferably, it is a crosslinked type polyacrylamide having an average particle size of 1 μm or more and 5 μm or less.
Here, the average particle size of the acrylamide copolymer (D) is obtained from a volume-based particle size distribution measured by a dry method according to a laser diffraction / scattering method.
The above-mentioned acrylamide copolymer may be used alone or in combination of two or more.

(Antioxidant (E))
The polyoxymethylene resin composition of the present embodiment may contain an antioxidant (E) as an optional component in addition to the above-mentioned essential components.
The content of the antioxidant (E) is not particularly limited, but is preferably 0.1 part by mass or more and 0.3 part by mass or less with respect to 100 parts by mass of the polyoxymethylene resin homopolymer (A). It is more preferably 0.13 parts by mass or more and 0.27 parts by mass or less, and further preferably 0.15 parts by mass or more and 0.25 parts by mass or less.
The antioxidant (E) is not limited to the following, but is a hindered phenolic antioxidant, for example, n-octadecyl-3- (3', 5'-di-t-butyl-4'-hydroxyphenyl). -Propionate, n-octadecyl-3- (3'-methyl-5-t-butyl-4'-hydroxyphenyl) -propionate, n-tetradecyl-3- (3', 5'-di-t-butyl-4) '-Hydroxyphenyl) -propionate, 1,6-hexanediol-bis- [3- (3,5-di-t-butyl-4-hydroxyphenyl) -propionate], 1,4-butanediol-bis- [3 -(3,5-di-t-butyl-4-hydroxyphenyl) -propionate], triethylene glycol-bis- [3- (3-t-butyl-5-methyl-4-hydroxyphenyl) -propionate], Tetraquis- [methylene-3- (3', 5'-di-t-butyl-4'-hydroxyphenyl) propionate] methane, 3,9-bis {2- [3- (3-t-butyl-4-4-) Hydroxy-5-methylphenyl) propionyloxy] -1,1-dimethylethyl} 2,4,8,10-tetraoxaspiro (5,5) undecane, N, N'-bis-3- (3', 5) '-Di-t-Butyl-4-hydroxyphenol) prepionyl hexamethylenediamine, N, N'-tetramethylenebis-3- (3'-methyl-5'-t-butyl-4-hydroxyphenol) propionyl Diamine, N, N'-bis- [3- (3,5-di-t-butyl-4-hydroxyphenol) propionyl] hydrazine, N-salicyloyl-N'-salicylidene hydrazine, 3- (N-salicyloyl) ) Amino-1,2,4-triazole, N, N'-bis {2- [3- (3,5-di-butyl-4-hydroxyphenyl) propionyloxy] ethyl} oxyamide and the like.
Among the antioxidants, triethylene glycol-bis- [3- (3-t-butyl-5-methyl-4-hydroxyphenyl) -propionate] and tetrakis- [methylene-3- (3', 5)- '-Di-t-butyl-4'-hydroxyphenyl) propionate] Methane is preferred.
These may be used alone or in combination of two or more.

(Other additive ingredients)
The polyoxymethylene resin composition of the present embodiment further contains pigments, dyes, various reinforcing materials, other antioxidants, heat stabilizers, and formaldehyde as long as the characteristics of the polyoxymethylene resin homopolymer (A) are not impaired. And / or various additives such as stabilizers such as formic acid trapping agents, weather-resistant stabilizers, mold release agents, lubricants, conductive agents, thermoplastic resins, thermoplastic elastomers, inorganic fillers or organic fillers may be added. can.
Only one type of these additives may be used alone, or two or more types may be used in combination.

(Manufacturing method of polyoxymethylene resin composition)
The polyoxymethylene resin composition of the present embodiment contains the above-mentioned essential components (A), (B) and (C), optional components (D), (E), and other additive components. For example, it is manufactured by mixing with a Henschel mixer, a tumbler, a V-shaped blender, or the like, and then melt-kneading with a single-screw extruder or a kneader such as a twin-screw extruder, a heating roll, a kneader, or a Banbury mixer. It can be obtained as a product in various forms such as a strand shape and a pellet shape.
Further, without mixing in advance, each component can be continuously fed to the extruder individually or in groups of several types by a quantitative feeder or the like. It is also possible to prepare a high-concentration masterbatch composed of each component in advance and dilute it with a polyacetal resin at the time of extrusion melt kneading.
The kneading temperature may be in accordance with the preferable processing temperature of the polyoxymethylene resin homopolymer (A) to be used, and is generally in the range of 180 ° C. or higher and 240 ° C. or lower, preferably 190 ° C. or higher and 230 ° C. or lower. ..

The pellets or the like of the polyoxymethylene resin composition obtained as described above may be dried in advance and then used for producing a molded product. The drying method is not particularly limited, but is, for example, a drying method using a box-type dryer (normal pressure, vacuum), a rotary and aeration rotary dryer, a groove-type stirring dryer, a fluidized bed dryer, and the like. Can be mentioned.
The drying temperature is preferably 80 ° C. or higher, more preferably 100 ° C. or higher as the temperature of the heat medium. The drying time is preferably 0 to 10 hours, more preferably 0 to 6 hours, and 1 to 1 when the starting time is when the product temperature of the polyoxymethylene resin composition pellets reaches 100 ° C. or higher. 6 hours is even more preferred.

[Molded product]
The molded product of the present embodiment contains the polyoxymethylene resin composition of the present embodiment described above, and the desired molded product can be molded by using the pellet-shaped product obtained as described above. can.
The method for producing the molded product is not particularly limited, and commonly used known molding methods such as injection molding method, extrusion molding method, vacuum molding, blow molding, injection compression molding, decorative molding, and molding of other materials are used. , Gas-assisted injection molding, foam injection molding, low-pressure molding, ultra-thin wall injection molding (ultra-high-speed injection molding), in-mold composite molding (insert molding, outsert molding) and the like can be applied.

Hereinafter, the present embodiment will be described with reference to specific examples and comparative examples, but the present embodiment is not limited to the examples described later.
The evaluation method will be described below.

〔Evaluation method〕
1) Charpy evaluation Using a 5-ounce molding machine (manufactured by Toshiba Machine Co., Ltd., trade name "IS-100GN") set to a cylinder temperature of 215 ° C. from the polyoxymethylene resin composition pellets of the example or comparative example. An ISO dumbbell test piece for Charpy evaluation was molded under the conditions of a mold temperature of 90 ° C., an injection time of 35 seconds, and a cooling time of 15 seconds. Six test pieces were prepared for each polyoxymethylene resin composition.
The following tests were performed on these 6 test pieces.
(I) Charpy impact strength; measured based on ISO179 / 1eA. The numerical values shown in Tables 1 and 2 are arithmetic mean values of n = 6.
(Ii) Charpy standard deviation; Shows the standard deviation when the Charpy impact strength is measured at n = 6.
The smaller the value of the Charpy standard deviation, the smaller the variation in Charpy impact strength and the better the impact resistance.

2) High temperature and low stress creep characteristics (rupture time)
From the polyoxymethylene resin composition pellets of Examples or Comparative Examples, using an IS-100GN injection molding machine manufactured by Toshiba Corporation, a cylinder temperature of 200 ° C., an injection pressure of 50 MPa, an injection speed of 30%, an injection time of 15 seconds, and a cooling time. A strip-shaped test piece having dimensions of 110 mm × 6.5 mm × 3 mm was formed at a mold temperature of 70 ° C. for 25 seconds, and left at an environmental temperature of 23 ± 2 ° C. and a humidity of 50 ± 10% for 24 hours or more. Using the test piece after leaving and a creep tester (creep tester manufactured by Toyo Seiki: C200-6), a load with a set temperature of 130 ± 2 ° C. and a tensile stress of 8 MPa is applied, and the time until the test piece is destroyed ( Breaking time (hr)) was measured. Three pieces of each test piece were prepared, and the fracture times in Tables 1 and 2 indicate the arithmetic mean time of n = 3.
The longer the time until rupture, the better the creep resistance against low stress load in a high temperature environment.

[Components used in Examples and Comparative Examples]
((A) Polyoxymethylene resin homopolymer)
(A-1)
A formaldehyde homopolymer having an MFR value of 2 g / 10 min and having the terminal groups stabilized by acetylation was used.
(A-2)
A formaldehyde homopolymer having an MFR value of 5 g / 10 min and having the terminal groups stabilized by acetylation was used.
(A-3)
A formaldehyde homopolymer having an MFR value of 10 g / 10 min and having the terminal groups stabilized by acetylation was used.

((B) Polyamide polymer having a melting point of 140 ° C. or higher and 200 ° C. or lower)
((B-1) Polyamide 6/66/610 copolymer)
0.45 kg of equimolar salt of adipic acid and hexamethylenediamine, 0.32 kg of equimolar salt of sebacic acid and hexamethylenediamine, 1.67 kg of ε-caprolactam, and 2.5 kg of pure water are charged in a 5 L autoclave. , Stirred well. _{After sufficiently N 2} substitution in the autoclave, the temperature was raised from room temperature to 220 ° C. over about 1 hour with stirring. At this time, the internal pressure becomes 18 kg / cm ^2- G due to the natural pressure of water vapor in the autoclave, but further heating is continued while removing water from the reaction system so that the pressure does not exceed 18 kg / cm ^2-G. When the temperature reached 230 ° C., overheating was stopped, the exhaust valve of the autoclave was closed, and the mixture was cooled to room temperature over about 8 hours. After cooling, the autoclave was opened, and about 2 kg of the obtained polymer was taken out and frozen and pulverized into a powder. The melting point measured by the DSC method was 155 ° C.
((B-2) Polyamide 12)
Made by Daicel Degussa Co., Ltd., Product name: Daicel L1700
Since there is a problem in dispersibility in the pellet form, it is frozen and pulverized to form a powder. The melting point measured by the DSC method was 178 ° C.
((B-3) Polyamide 610))
Made by Asahi Kasei Corporation, product name: Leona 610
Since there is a problem in dispersibility in the pellet form, it is frozen and pulverized to form a powder. The melting point measured by the DSC method was 215 ° C.

((C) Crystal nucleating agent)
((C-1) Boron Nitride)
Made by Denka Co., Ltd .: Product name: Denka Boron Night Ride ((C-2) Talc)
Made by Nippon Tarku Co., Ltd .: Product name: MS (untreated surface)

((D) Acrylamide copolymer)
To a batch type 5L reactor equipped with a stirrer, 2400 g of acrylamide, 267 g of methylenebisacrylamide, and 0.54 g of zirconium tetraisopropoxide as a catalyst (1/10000 mol with respect to acrylamide) were added, and the mixture was stirred in _{an N 2 air flow.} The reaction was carried out at 125 ° C. for 4 hours.
After completion of the reaction, the obtained solid matter was pulverized with a jet mill pulverizer and washed with acetone.
Then, the ground product was dried under reduced pressure at 120 ° C. for 20 hours at a reduced pressure of −700 mmHg. The content of the primary amide group was 44.7 mol%, and the average particle size was 5.0 μm.
The content of the first amide group was measured based on the Kjeldahl method. The average particle size of the acrylamide copolymer was measured by a dry method using a laser diffraction type particle size distribution measuring device (SALD-2300 manufactured by Shimadzu Corporation).

((E) Hindered phenolic antioxidant)
Made by BASF Corporation: Trade name Irganox (registered trademark) 245

[Example 1]
Polyoxymethylene resin homopolymer (A) 100 parts by mass, polyamide 6/66/610 copolymer (B-1) 0.005 parts by mass, boron nitride (C) 0.002 parts by mass, acrylamide copolymer ( D) 0.1 parts by mass, antioxidant (E) 0.2 parts by mass, (B-1) / (C) mass ratio = 71/29) are uniformly mixed using a Henschel mixer to prepare a mixture. Obtained.
The mixture was melt-kneaded with a 30φ uniaxial extruder, extruded into strands, cooled, and pelletized to obtain resin composition pellets composed of a polyoxymethylene resin composition.
The obtained resin composition pellets were dried at 80 ° C. for 4 hours.
Using the dried resin composition pellets, (1) Charpy impact characteristics (impact strength and standard deviation) and (2) high temperature and low stress creep characteristics (rupture time) were evaluated by the above-mentioned various evaluation methods.
The evaluation results are shown in Table 1.
The extrusion conditions were a cylinder set temperature of 200 ° C., a discharge rate of 5 kg / hr, a screw rotation speed of 50 rpm, and a vent decompression degree of −720 mmHg.

[Examples 2 to 18]
The component composition of the polyoxymethylene resin composition was changed as shown in Table 1. Other than that, the same operation as in Example 1 was carried out to obtain dried resin composition pellets, which were evaluated in the same manner. The evaluation results are shown in Table 1.

[Comparative Examples 1 to 15]
The component composition of the polyoxymethylene resin composition was changed as shown in Table 2. Other than that, the same operation as in Example 1 was carried out to obtain dried resin composition pellets, which were evaluated in the same manner. The evaluation results are shown in Table 2.

As is clear from the evaluation results in Table 1, the polyoxymethylene resin homopolymer (A), the polyamide polymer (B) having a melting point of 140 ° C. or higher and 200 ° C. or lower, and the boron nitride (C) are predetermined. In the examples in which the mass ratio of the polyamide polymer (B) / boron nitride (C) having a melting point of 140 ° C. or higher and 200 ° C. or lower is within the range of the present invention, there is a variation in the sharpy impact strength. A small polyoxymethylene resin composition having excellent high-temperature and low-stress creep characteristics was obtained.
On the other hand, as is clear from the evaluation results in Table 2, the polyoxymethylene resin composition of the comparative example had a large variation in Charpy impact strength and was inferior in high temperature and low stress creep characteristics.

The polyoxymethylene resin composition of the present invention has industrial applicability as a material for automobile parts, various electric / electronic equipment parts, and other various industrial parts. In particular, it can be suitably used as a material for parts that are used for a long period of time with low stress (low load) in a high temperature environment.
The molded product of the present invention has industrial applicability as automobile parts, various electric / electronic equipment parts, various other industrial parts, and the like. In particular, it can be suitably used as a component that is used for a long period of time with low stress (low load) in a high temperature environment.

Claims (4)

Polyoxymethylene resin homopolymer (A) 100 parts by mass and
Polyamide polymer (B) having a melting point of 140 ° C. or higher and 200 ° C. or lower, 0.005 parts by mass or more and 0.05 parts by mass or less.
Boron nitride (C) containing 0.0005 parts by mass or more and 0.005 parts by mass or less.
The mass ratio of the (B) polyamide polymer to the (C) boron nitride is (B) polyamide copolymer / (C) boron nitride = 95/5 or more and 70/30 or less. , Polyoxymethylene resin composition. Acrylamide copolymer (D) 0.05 parts by mass or more and 0.3 parts by mass or less,
Antioxidant (E) 0.1 parts by mass or more and 0.3 parts by mass or less,
The polyoxymethylene resin composition according to claim 1, further comprising. The polyoxymethylene resin composition according to claim 1 or 2, wherein the melt flow rate (according to ISO 1133D) of the polyoxymethylene resin homopolymer (A) is 0.5 g / 10 minutes or more and 10 g / 10 minutes or less. .. A molded product containing the polyoxymethylene resin composition according to any one of claims 1 to 3.