JP6956648B2 - Polyoxymethylene resin composition and polyoxymethylene resin molded article - Google Patents

Description

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

Polyoxymethylene resin is a resin that has high mechanical strength and rigidity, is excellent in oil resistance, organic solvent resistance, and self-lubricating property, is well-balanced in a wide temperature range, and is easy to process. As a typical engineering plastic, it is widely used mainly for mechanical parts and sliding parts such as precision equipment, home appliances / OA equipment, automobiles, industrial applications and miscellaneous goods. In recent years, with the expansion of the fields of use of polyoxymethylene resin, while having the characteristics of polyoxymethylene resin, improvement of appearance and texture, improvement of load deflection temperature, accuracy and vibration damping property, reduction of heat ray expansion, etc. At present, the required performance for polyoxymethylene resin is increasing.

Attempts have been made to use polyoxymethylene resin compositions having a high specific density in order to improve the properties of these polyoxymethylene resins and propose new uses. For example, a technique using a polyoxymethylene resin composition having a high ratio of filler particles to obtain a heat conductive composite material (see, for example, Patent Document 1), and containing inorganic fine particles to obtain a monofilament having a high specific gravity. A technique for using a polyoxymethylene resin composition (see, for example, Patent Document 2), and a polyoxymethylene resin composition containing a high specific gravity material such as bronze powder is used in order to obtain a guideline for a measuring instrument in which a balancer is integrally molded. Techniques (see, for example, Patent Document 3) and the like have been proposed.

On the other hand, the use of metal injection molding (MIM) to obtain metal parts and ceramic injection molding (CIM) to obtain ceramic parts is expanding, and polyoxy containing high-concentration metals and ceramics as a raw material. Attempts have been made to use methylene resin compositions. For example, a technique using an injection molding composition of a metal powder composed of a sinterable metal powder and an organic binder composed of polyoxymethylene, polylactic acid, etc. (see, for example, Patent Document 4), a colored ceramic molded product. A technique using a polyoxymethylene resin composition composed of ceramic powder, polyoxymethylene, and colored particles (see, for example, Patent Document 5) has been proposed.

Japanese Unexamined Patent Publication No. 2011-038078 Japanese Unexamined Patent Publication No. 11-293523 Japanese Unexamined Patent Publication No. 10-281825 Japanese Unexamined Patent Publication No. 2012-2172 Japanese Unexamined Patent Publication No. 08-090528

However, the polyoxymethylene resin compositions disclosed in Patent Documents 1 to 5 have a problem that it is difficult to improve dimensional accuracy and quality while maintaining practically sufficient productivity. ..
Therefore, in the present invention, a polyoxymethylene resin composition capable of improving the dimensional accuracy and quality of the molded product while maintaining practically sufficient productivity, and a polyoxymethylene resin molded product having improved dimensional accuracy and quality. The purpose is to provide.

As a result of intensive studies on the above-mentioned problems of the prior art, the present embodiments have found that a polyoxymethylene resin composition having specific thermal properties can solve the above-mentioned problems of the prior art, and the present embodiment Has been completed.

That is, this embodiment is as follows.
[1]
A polyoxymethylene resin composition for sintered products containing an inorganic substance and a polyoxymethylene resin.
The contained polyoxymethylene resin has a number average molecular weight of 30,000 to 65,000.
Weight loss was measured and held for 150 minutes at 2 30 ° C. in air thermogravimetric analysis is 5-30%,
Ri weight loss rate is 4.4% / min der less at weight loss reaching 50% when the weight loss corresponding to the weight reduction rate is 100%,
The inorganic substances include aluminum (excluding aluminum hydroxide), cobalt, zinc, copper, nickel, iron, silicon, titanium, tungsten, and metal compounds and alloys based on these, or zinc oxide. aluminum oxide, zirconia, hydroxyapatite, silicon carbide, silicon nitride, and wherein boron nitride, fluorite, steatite, barium titanate, lead zirconate titanate, at least one der Rukoto selected from the group consisting of ferrite Polyoxymethylene resin composition.
[2]
The polyoxymethylene resin composition according to [1], which has a crystallization starting temperature of 142 ° C. to 154 ° C.
[3]
The polyoxymethylene resin composition according to [1] or [2], which further comprises two or more kinds of formaldehyde scavengers.
[4]
The polyoxymethylene resin composition according to any one of [1] to [3], wherein the inorganic substance contains a metal.
[5]
The polyoxymethylene resin composition according to any one of [1] to [3], wherein the inorganic substance contains ceramics.
[6]
An injection-molded product as an intermediate product for a sintered product , which comprises the polyoxymethylene resin composition according to any one of [1] to [5].

According to the present embodiment, a polyoxymethylene resin composition capable of improving the dimensional accuracy and quality of a molded product while maintaining practically sufficient productivity, and a polyoxymethylene resin having improved dimensional accuracy and quality. A molded product can be obtained.

An embodiment of GPC number average molecular weight measurement by PMMA conversion of the polyoxymethylene resin contained in the polyoxymethylene resin composition of the present embodiment is shown. An embodiment of the weight loss rate measurement by thermogravimetric analysis of the polyoxymethylene resin composition of the present embodiment is shown. An embodiment of the weight loss rate measurement by thermogravimetric analysis of the polyoxymethylene resin composition of the present embodiment is shown.

Hereinafter, an embodiment for carrying out the present embodiment (hereinafter, referred to as “the present embodiment”) will be described in detail with reference to the drawings. The present embodiment is not limited to the following description, and can be variously modified and implemented within the scope of the gist thereof. Unless otherwise specified, the positional relationships such as up, down, left, and right in each drawing are based on the positional relationships shown in each drawing, and the dimensional ratios in the drawings are not limited to the ratios shown.

The polyoxymethylene resin composition of the present embodiment, the method for producing the polyoxymethylene resin molded product, and the polyoxymethylene resin molded product will be described in detail in order.

[Polyoxymethylene resin composition]
The polyoxymethylene resin composition of the present embodiment contains an inorganic substance and a polyoxymethylene resin. The polyoxymethylene resin contained in the polyoxymethylene resin composition of the present embodiment has a number average molecular weight of 30,000 to 65,000. Further, in the polyoxymethylene resin composition of the present embodiment, the weight loss rate measured by thermogravimetric analysis at 230 ° C. for 150 minutes is 5 to 30% of the total mass of the resin composition. Further, when the weight reduction amount corresponding to this weight reduction rate is 100%, the weight reduction rate at the time when the weight reduction amount reaches 50% is 4.4% / min or less.
In the present specification, "the number average molecular weight of the polyoxymethylene resin contained (in the polyoxymethylene resin composition)" is based on the polyoxymethylene resin composition or the polyoxymethylene resin molded product as a sample. It refers to the number average molecular weight of the polyoxymethylene resin measured by the gel permeation chromatography method as described later.

Hereinafter, the polyoxymethylene resin composition, the characteristics of the polyoxymethylene resin composition, and the method for producing the polyoxymethylene resin composition will be described in detail in order.

<Polyoxymethylene resin composition P>
The polyoxymethylene resin composition P of the present embodiment contains the following polyoxymethylene resin (A) and inorganic substance (B), and may contain an additive (C) if necessary.

(Polyoxymethylene resin (A))
Examples of the polyoxymethylene resin (A) that can be used in the polyoxymethylene resin composition of the present embodiment include a polyoxymethylene homopolymer (a1) and a polyoxymethylene copolymer (a2).
As the polyoxymethylene resin (A) of the present embodiment, the polyoxymethylene homopolymer (a1) can be used alone, but from the viewpoint of productivity, a poly containing at least one polyoxymethylene copolymer (a2). The oxymethylene resin (A) is preferable, and the polyoxymethylene copolymer (a2) is particularly preferable to be used alone.

The number average molecular weight Mn of the polyoxymethylene resin used in the polyoxymethylene resin composition of the present embodiment is not particularly limited, but is preferably 30,000 to 70,000, more preferably 30,000 to 65,000, and 31,000 to 63,000. Is even more preferable, and 32000 to 59000 is even more preferable.
In the present specification, the "number average molecular weight of the polyoxymethylene resin used" refers to the number average molecular weight of the polyoxymethylene resin as a raw material, and is also referred to as "raw material polyoxymethylene resin" below.
By producing using the above-mentioned polyoxymethylene resin having a preferable number average molecular weight Mn, the number average molecular weight of the polyoxymethylene resin contained in the polyoxymethylene resin composition of the present embodiment can be set to 30,000 to 65,000. It is possible to improve the appearance and texture of the molded product, maintain sufficient productivity for practical use, and improve the dimensional accuracy and quality of the molded product.

If it is predicted that the number average molecular weight of the polyoxymethylene resin will be significantly reduced due to the influence of thermal decomposition after undergoing melt-kneading in the manufacturing process of the polyoxymethylene resin composition, polyoxy A polyoxymethylene resin having a number average molecular weight larger than the desired number average molecular weight of the polyoxymethylene resin contained in the methylene resin composition may be used as a raw material.
The case where the number average molecular weight of the polyoxymethylene resin is predicted to be significantly reduced due to the influence of thermal decomposition is not particularly limited, but for example, when the thermal stability of the polyoxymethylene resin itself is low. Or, there is a case where a large amount of a reactive metal is blended as the inorganic substance (B) described later.

The number average molecular weight Mn of the raw material polyoxymethylene resin according to the present embodiment can be measured by a gel permeation chromatography (GPC) method.
As a specific procedure, the number average molecular weight of the polyoxymethylene resin contained in the polyoxymethylene resin composition will be described later, except that a sample solution is prepared using a weighed polyoxymethylene resin as a sample. It can be obtained in the same manner as the measuring method.
The number average molecular weight Mn of the raw material polyoxymethylene resins having melt flow rates (MFR) (ISO1133 condition D, 190 ° C.) of 30 and 70 was measured by this measuring method and found to be 56000 and 46000, respectively.

The blending amount of the polyoxymethylene resin (A) used in the polyoxymethylene resin composition of the present embodiment is not particularly limited, but is in the range of 5% by mass or more and 30% by mass or less as 100% by mass of the polyoxymethylene resin composition. It can be appropriately set in the above, and is preferably 6% by mass or more and 28% by mass or less, and more preferably 7% by mass or more and 26% by mass or less.
As described above, when it is predicted that the number average molecular weight of the polyoxymethylene resin will be significantly reduced due to the influence of thermal decomposition, the blending amount of the polyoxymethylene resin (A) is larger than the above range. It may be increased by about 3% by mass.

The above-mentioned polyoxymethylene resin (A) is produced by the following (1) polymerization step, (2) terminal stabilization step, and (3) granulation step using the following monomer, chain transfer agent, polymerization catalyst and the like. be able to.

(1) Polymerization Steps Hereinafter, each polymerization step will be described separately for the case of the polyoxymethylene homopolymer (a1) and the case of the polyoxymethylene copolymer (a2).

(1) -1: Polymerization step of polyoxymethylene homopolymer (a1) The polyoxymethylene homopolymer (a1) is a polymer having only an oximethylene unit in the main chain. Both ends or one end of the polyoxymethylene homopolymer (a1) may be sealed with an ester group or an ether group.
The polyoxymethylene homopolymer (a1) can be produced by a known slurry polymerization method (for example, the methods described in Japanese Patent Publication No. 47-6420 and Japanese Patent Publication No. 47-10059). In the polymerization step, it can be obtained as a crude polyoxymethylene homopolymer whose terminal is not stabilized.

1) Monomer Examples of the monomer used for producing the polyoxymethylene homopolymer (a1) include formaldehyde.
In order to continuously obtain a polyoxymethylene homopolymer (a1) having a stable molecular weight, it is preferable to use a purified formaldehyde gas having a low impurity concentration and a stable formaldehyde gas. Examples of the method for purifying formaldehyde include known methods (for example, the methods described in JP-A-5-32374 and JP-A-2001-521916).
When formaldehyde gas is used as the monomer, it is preferable that it 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. The smaller the amount of these impurities, the more unexpected chain transfer reactions can be avoided, and the polyoxymethylene homopolymer (a1) having the desired molecular weight can be obtained. Above all, 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 homopolymer (a1) is not limited to the following, but generally alcohols, acid anhydrides and the like can be used.
As the chain transfer agent, it is preferable to use one that does not contain impurities having a polymerization termination action or a chain transfer action during the polymerization reaction such as water, methanol, formic acid, and acetic acid as much as possible. The method for obtaining a chain transfer agent having a small amount of impurities is not limited to the following, but for example, a chain transfer agent having a water content exceeding a specified amount, which is widely used and available, is bubbled with dry nitrogen to obtain activated carbon or the like. Examples thereof include a method of removing impurities with an adsorbent such as zeolite and purifying the mixture.
The chain transfer agent may be used alone or in combination of two or more.

3) Polymerization catalyst The polymerization catalyst used for producing the polyoxymethylene homopolymer (a1) is not limited to the following, and examples thereof include an onium salt-based polymerization catalyst.
The onium salt-based polymerization catalyst is not limited to the following, and examples thereof include compounds represented by the following formula (1).
_{[R 1 R 2 R 3 R} 4 M] + X - ··· (1)
(In 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, among which tetramethylammonium bromide and dimethyl distearyl. Ammonium acetate, tetraethylphosphonium iodide, and tributylethylphosphonium iodide are preferred.

4) Reactor The reactor used in the production of the polyoxymethylene homopolymer (a1) is not limited to the following, but for example, a batch type reactor with a stirrer, a continuous type conider, and a twin-screw screw. Examples include a type continuous extrusion kneader and a twin-screw paddle type continuous mixer.
The outer circumference of the reactor body preferably has a structure capable of heating or cooling the reaction mixture.

(1) -2: Polymerization step of polyoxymethylene copolymer (a2) The polyoxymethylene copolymer (a2) is a copolymer polymer having an oximethylene unit in the main chain. The comonomer unit may be a unit that can be copolymerized with the oxymethylene unit, and is not limited to the following, but is preferably an oxyalkylene unit having 2 or more carbon atoms, for example. Both ends or one end of the polyoxymethylene copolymer (a2) may be sealed by an ester group or an ether group, or both ends may be closed.
The polyoxymethylene copolymer (a2) preferably contains 0.3 mol or more, more preferably 0.4 mol or more, and more preferably 0.5 mol or more of the comonomer unit with respect to 100 mol of the oximethylene unit. It is even more preferable to contain 0.6 mol or more, and even more preferably 1.2 mol or more. Further, the polyoxymethylene copolymer (a2) preferably contains 3.0 mol or less of the comonomer unit, more preferably 2.0 mol or less, and further preferably 1.5 mol or less.
By setting the content ratio of the comonomer unit to 100 mol of the oximethylene unit in a preferable range, the polyoxymethylene resin composition of the present embodiment maintains sufficient productivity for practical use while improving the appearance and texture of the molded product. , There is a tendency to improve the dimensional accuracy and quality of molded products.
The polyoxymethylene copolymer (a2) is not limited to the following, but is a known polymerization method (for example, US Pat. No. 3,027,352, US Pat. No. 3,803,094, German Patent Invention No. 1161421). , German Patented Invention No. 1495228, German Patented Invention No. 1720358, German Patented Invention No. 3018898, JP-A-58-98322 and JP-A-7-70267). Can be manufactured. In the polymerization step, it can be obtained as a crude polyoxymethylene copolymer having unstabilized ends.

1) Main Monomer Examples of the main monomer used in the production of the polyoxymethylene copolymer (a2) include cyclic oligomers such as formaldehyde, trioxane which is a trimer thereof, and tetraoxane which is a tetramer.
In the present embodiment, the "main monomer" means a monomer unit contained in an amount of 50% by mass or more based on the total amount of monomers.

2) Comonomer The comonomer used in the production of the polyoxymethylene copolymer (a2) is not limited to the following, and examples thereof include cyclic ether compounds having an oxyalkylene unit having 2 or more carbon atoms in the molecule. ..
The cyclic ether compound is not limited to the following, and includes, for example, ethylene oxide, propylene oxide, 1,3-dioxolane, 1,3-propanediol formal, 1,4-butanediol formal, and 1,5-pentane. Diolformal, 1,6-hexanediolformal, diethylene glycolformal, 1,3,5-trioxepan, 1,3,6-triochiocane, and mono- or di-glycidyl compounds that can form branched or crosslinked structures in the molecule. Can be mentioned.
The cyclic ether compound may be used alone or in combination of two or more.

When the polyoxymethylene copolymer (a2) is polymerized, it is preferable that the main monomer and comonomer contain as little impurities as possible that have a polymerization terminating action and a chain transfer action during the polymerization reaction such as water, methanol and formic acid. By using a main monomer and a comonomer containing as little impurities as possible, an unexpected chain transfer reaction can be avoided, and a polyoxymethylene copolymer (a2) having a target molecular weight can be obtained. Above all, the content of the impurity that induces a hydroxyl group in the polymer terminal group is preferably 30 mass ppm or less, more preferably 10 mass ppm or less, and 3 mass ppm or less, based on the total amount of the monomers. Is even more preferable.

As a method for obtaining a main monomer and a comonomer having a small amount of impurities, a known method (for example, the method described in JP-A-3-123777 and JP-A-7-33761 for the main monomer, and the method for comonomer is special. The methods described in Kaisho 49-62469 and JP-A-5-271217).

3) Chain transfer agent In the production of the polyoxymethylene copolymer (a2), it is preferable to use a chain transfer agent.
The chain transfer agent is not particularly limited, and examples thereof include dialkyl acetals of formaldehyde and oligomers thereof; lower fatty alcohols such as methanol, ethanol, propanol, isopropanol and butanol. The alkyl group of the dialkyl acetal of formaldehyde is preferably a lower aliphatic alkyl group such as methyl, ethyl, propyl, isopropyl and butyl.
In order to obtain the long-chain branched polyoxymethylene copolymer (a2), it is preferable to use a polyether polyol and an alkylene oxide adduct of the polyether polyol as the chain transfer agent.
As the chain transfer agent, a polymer having one or more groups selected from the group consisting of a hydroxyl group, a carboxyl group, an amino group, an ester group and an alkoxy group may be used.
As the chain transfer agent, it is preferable to use one that does not contain impurities having a polymerization termination action or a chain transfer action during the polymerization reaction such as water, methanol, formic acid, and acetic acid as much as possible. 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. , Purification method and the like.
The chain transfer agent may be used alone or in combination of two or more. In any case, the obtained polyoxymethylene copolymer (a2) preferably has a small number of unstable terminals.

4) Polymerization catalyst The polymerization catalyst used for producing the polyoxymethylene copolymer (a2) is not particularly limited, but a cationically active catalyst such as Lewis acid, protonic acid, and ester or anhydride of protonic acid is preferable.
The Lewis acid is not particularly limited, and examples thereof include halides of boric acid, tin, titanium, phosphorus, arsenic, and antimony. Specific examples thereof include boron trifluoride, tin tetrachloride, titanium tetrachloride, phosphorus pentafluoride, phosphorus pentachloride and antimony pentafluoride, and complex compounds or salts thereof.
The ester or anhydride of the protonic acid and the protonic acid is not particularly limited, and examples thereof include perchloric acid, trifluoromethanesulfonic acid, perchloric acid-quaternary butyl ester, acetylparklorate, and trimethyloxonium hexafluorophosphate. Can be mentioned.
As the polymerization catalyst, boron trifluoride, boron trifluoride hydrate, an organic compound containing an oxygen atom or a sulfur atom and a coordination complex compound of boron trifluoride are preferable, and boron trifluoride diethyl ether and trifluoride are preferable. Boron trifluoride di-n-butyl ether is more preferred.
As the polymerization catalyst, for example, a catalyst that reduces the formation of the terminal formating group described in JP-A-05-05017 may be used in combination, if necessary.

5) Reactor The reactor used in the production of the polyoxymethylene copolymer (a2) is not limited to the following, but for example, a batch type reactor with a stirrer, a continuous type conider, and a twin-screw type. Examples include a continuous extrusion kneader and a twin-screw paddle type continuous mixer.
The outer circumference of the reactor body preferably has a structure capable of heating or cooling the reaction mixture.

(2) End Stabilization Steps Hereinafter, each end stabilization step will be described separately for the case of the polyoxymethylene homopolymer (a1) and the case of the polyoxymethylene copolymer (a2).

(2) -1: End stabilization step of polyoxymethylene homopolymer (a1) After the above (1) polymerization step, the end of the crude polyoxymethylene homopolymer is sealed with an ether group to stabilize the end. Carry out the polymerization process.
Examples of the method of sealing the end of the crude polyoxymethylene homopolymer with an ether group to stabilize the end include a known method (for example, the method described in Japanese Patent Publication No. 63-452).

The etherifying agent for sealing with an ether group is not limited to the following, and examples thereof include ortho ester.
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. Specific examples thereof include methyl or ethyl orthoformate, methyl or ethyl orthoacetate and methyl or ethyl orthobenzoate, and orthocarbonates such as ethyl orthocarbonate.
The etherifying agent may be used alone or in combination of two or more.

The etherification reaction uses a Lewis acid-type catalyst such as p-toluenesulfonic acid, medium-strength organic acids such as acetic acid and hydrobromic acid, and medium-strength mineral acids such as dimethyl and diethylsulfate by 1 mass of etherifying agent. 0.001 to 0.02 parts by mass may be introduced with respect to the part.
The etherification reaction may be carried out in the presence of a predetermined solvent. The solvent is not limited to the following, but is, for example, low boiling point aliphatic compounds such as pentane, hexane, cyclohexane and benzene; alicyclic group and aromatic hydrocarbons; methylene chloride, chloroform, carbon tetrachloride and the like. Examples thereof include organic solvents such as the halogenated lower aliphatic compounds of.

The method for sealing the end of the crude polyoxymethylene homopolymer obtained in the polymerization step with an ester group to stabilize the end is not limited to the following, but for example, US Pat. No. 3,459,709. Examples thereof include a method in which a large amount of the acid anhydride described in the specification is used in a slurry state and a method in which the acid anhydride gas described in US Pat. No. 3,172,736 is used in a gas phase. ..

The esterifying agent for sealing with an ester group is not particularly limited, and examples thereof include organic acid anhydrides.
The organic acid anhydride is not limited to the following, and examples thereof include an organic acid anhydride represented by the following formula (2).
R ₅ COOCOR ₆ ... (2)
(In 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.
The esterifying agent may be used alone or in combination of two or more.

In the method for sealing the ester group in the gas phase, it is preferable to perform terminal sealing after removing the onium salt-based polymerization catalyst by the method described in JP-A-11-92542. When the onium salt-based polymerization catalyst in the polyoxymethylene is removed, the decomposition reaction of the polyoxymethylene homopolymer (a1) derived from the onium salt-based polymerization catalyst can be avoided at the time of terminal sealing, and the terminal stabilization reaction can be carried out. The polymer yield can be improved, and the coloring of the polyoxymethylene homopolymer (a1) can be suppressed.

It is preferable that the terminal of the polyoxymethylene homopolymer (a1) 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 homopolymer (a1) can be maintained, which is preferable. 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.

(2) -2: Terminal stabilization step of polyoxymethylene copolymer (a2) The polymer obtained in (1) above is put into an aqueous solution or an organic solvent solution containing a catalyst neutralizing inactivating agent to be in a slurry state. Generally, the catalyst can be deactivated by stirring for several minutes to several hours. This gives a crude polyoxymethylene copolymer.
The catalytic neutralizing inactivating agent is not particularly limited, but for example, amines such as ammonia, triethylamine and tri-n-butylamine; hydroxides of alkali metals and alkaline earth metals; inorganic acid salts; organic acid salts and the like. Can be mentioned.
The catalyst neutralization inactivating agent may be used alone or in combination of two or more.

In order to obtain a crude polyoxymethylene copolymer, in addition to the use of the above-mentioned catalyst neutralizing inactivating agent, a method of contacting a polymer with steam such as ammonia and triethylamine to inactivate the polymerization catalyst, hindered amines, triphenyl, etc. A method of inactivating the catalyst by contacting at least one of phosphine and calcium hydroxide with a mixer can also be used.

Further, terminal stabilization is carried out to decompose and remove the unstable terminal portion contained in the crude polyoxymethylene copolymer.
The method for decomposing and removing the unstable end portion contained in the crude polyoxymethylene copolymer is not limited to the following, and examples thereof include a single-screw extruder with a vent and a twin-screw extruder with a vent. A method of melting and kneading a crude polyoxymethylene copolymer in the presence of a known decomposition remover to decompose and remove an unstable terminal portion can be mentioned.
When melt-kneading for terminal stabilization, it is preferable to replace the atmosphere with an inert gas or degas by a one-stage or multi-stage vent in order to maintain the quality and working environment. The resin temperature during melt-kneading is preferably the melting point or higher and 230 ° C. or lower of the polyoxymethylene copolymer (a2), more preferably the melting point or higher and 210 ° C. or lower, and further preferably the melting point or higher and 190 ° C. or lower.

1) Decomposition and removal agent The decomposition and removal agent used for decomposition and removal of unstable terminal portions contained in the crude polyoxymethylene copolymer is not limited to the following, but for example, ammonia and ammonium compounds, triethylamine and tributylamine and the like. Alibo amines; hydroxides of alkali metals or alkaline earth metals such as calcium hydroxide; inorganic weak salts; and basic substances such as organic weak salts.
The decomposition remover may be used alone or in combination of two or more.
The decomposition remover may be added in advance before melting the crude polyoxymethylene copolymer, or may be added to the melted crude polyoxymethylene copolymer.
Moreover, the catalyst neutralization inactivating agent used for obtaining the crude polyoxymethylene copolymer may be used as it is as a decomposition removing agent.

(3) Granulation step The terminal-stabilized polyoxymethylene homopolymer (a1) and polyoxymethylene copolymer (a2) are dried and used in a single-screw extruder, twin-screw extruder or multi-screw extruder. Granulation is performed to obtain a polyoxymethylene resin.
At this time, it is preferable to add the following formaldehyde scavenger (C1) and the following antioxidant (C2) and melt-knead.
When granulating, it is preferable to replace the atmosphere with an inert gas or degas by a one-stage or multi-stage vent in order to maintain the quality and working environment.
The resin temperature during melt-kneading is preferably 230 ° C. or higher than the melting point of the polyoxymethylene polymer, more preferably 210 ° C. or higher than the melting point of the polyoxymethylene polymer, and further preferably 195 ° C. or higher than the melting point of the polyoxymethylene polymer. The following is more preferable. The resin temperature referred to here is preferably measured by directly measuring the molten resin discharged from the die in the granulation process with a thermometer. It may also be measured with a non-contact thermometer.

In the method for granulating a polyoxymethylene resin, for example, a powder obtained by crushing a part of a terminal-stabilized polyoxymethylene polymer is mixed with a formaldehyde trapping agent (C1) and an antioxidant (C2), and then granulated. Alternatively, it is preferable to optimize the drying time before granulation with respect to the timing of a part of the terminal stabilization step and the granulation step in consideration of the productivity of the polyoxymethylene resin molded product and the like.
Further, the pellets of the polyoxymethylene resin obtained in the granulation step are preferably dried at 100 ° C. or higher and lower than 150 ° C. Normally, polyoxymethylene resin absorbs almost no water, so drying may be done by removing the water adhering to the surface. In the case of the present embodiment, it is preferable to continue drying for several hours even after the product temperature of the pellets reaches 100 ° C. or higher in a balance with productivity.
By using the polyoxymethylene resin pellets granulated by the above granulation method for production, the polyoxymethylene resin composition of the present embodiment has sufficient productivity for practical use while improving the appearance and texture of the molded product. It tends to be possible to improve the dimensional accuracy and quality of the molded product.

(Inorganic substance (B))
The polyoxymethylene resin composition of the present embodiment contains an inorganic substance.
The inorganic substance is a compound other than an organic compound, and specifically, a simple partial carbon compound, a compound composed of an element other than carbon, and the like. The inorganic substance (B) is not particularly limited, but it is preferable to use an inorganic substance (B) having a specific gravity of 2.0 or more. By producing using an inorganic substance having a specific gravity of 2.0 or more, the polyoxymethylene resin composition of the present embodiment maintains sufficient productivity for practical use while improving the appearance and texture of the molded product, and is molded. There is a tendency to improve the dimensional accuracy and quality of products.

The carbon compound is not particularly limited, but is, for example, an allotrope of carbon such as graphite and diamond; a compound composed of a negative element and carbon such as carbon monoxide, carbon dioxide, and carbon disulfide; or a metal carbonate and metal acetic acid. Salts such as salts, metal blue salts, metal cyanates, metal thiocyanates, metal carbides; and the like.

The compound composed of an element other than carbon is not particularly limited, and examples thereof include a compound of a metal element and a compound of a non-metal element (boron, silicon, etc.). Specific examples of the compound include, but are not limited to, hydrogen compounds, oxides, oxo acids, hydroxides, halides, sulfates, nitrates, metal complexes (coordination compounds) and the like.

In particular, as the inorganic substance, metals and ceramics are preferable in order to impart functionality. Specific metals include aluminum, magnesium, barium, calcium, cobalt, zinc, copper, nickel, iron, silicon, titanium, tungsten, and metal compounds and alloys based on these. Here, not only the already completed alloys, but also mixtures of individual alloy components can be used.
Specific ceramics include oxides such as zinc oxide, aluminum oxide and zirconia; hydroxides such as hydroxyapatite; carbides such as silicon carbide; nitrides such as silicon nitride and boron nitride; halides such as fluorite; Examples thereof include silicates such as stearite; titanates such as barium titanate and lead zirconate titanate; carbonates; phosphates; ferrites; high-temperature superconducting substances; and the like.
These inorganic substances may be used alone or in combination of several inorganic substances such as various metals, metal alloys, and ceramics.

The shape of the inorganic substance includes a fibrous shape, a needle shape, a grain (sphere) shape, a plate shape, a layered shape, an amorphous shape, and the like. When anisotropy is a problem as dimensional accuracy, plate-like and grain (sphere) shapes are preferable, and grain (sphere) shape is particularly preferable.

The amount of the inorganic substance contained in the polyoxymethylene resin composition of the present embodiment is not particularly limited depending on the use of the resin composition or the resin molded product, the type of the inorganic substance, etc., but the polyoxymethylene resin composition It can be appropriately set in the range of more than 70% by mass and 95% by mass or less in 100% by mass, more preferably more than 72% by mass and 94% by mass or less, and more than 74% by mass and 93% by mass. More preferred.

The inorganic substance used in the polyoxymethylene resin composition of the present embodiment may contain a surface treatment agent. The surface treatment agent refers to an agent added for the purpose of improving the dispersion of particles and the stability of the composition in the manufacturing process of an inorganic substance, the product after production, and the manufacturing process of an oxymethylene resin composition. As the surface treatment agent, it is preferable to add at least one of a known surface treatment agent, a spreading agent or a complexing agent, and an anti-aggregation agent.
Here, examples of known surface treatment agents, adhesives or complexing agents, and anti-aggregation agents include anionic surfactants; cationic surfactants; amphoteric surfactants; nonionic surfactants; aminosilanes. , Epoxysilane and other silane-based coupling agents; titanate-based coupling agents; fatty acids (saturated fatty acids and unsaturated fatty acids) and aliphatic carboxylic acids; metal shavings; paraffin-based and olefin-based oils; aliphatic hydrocarbons Aromatic hydrocarbons and modified products thereof; and mixtures thereof; alcohols; polyols; and fatty acid esters of polyols; and the like.
The polyoxymethylene resin composition of the present embodiment is produced by using an inorganic substance containing a surface treatment agent, thereby improving the appearance and texture of the molded product while maintaining practically sufficient productivity and being a molded product. There is a tendency to improve the dimensional accuracy and quality of the product.

The inorganic substance used in the polyoxymethylene resin composition of the present embodiment (hereinafter, also referred to as a raw material inorganic substance) preferably has an average particle size of 0.01 to 100 μm, more preferably 0.05 to 80 μm. It is preferably 0.1 to 60 μm, and more preferably 0.1 to 60 μm. When the average particle size of the inorganic substance is within the above range, the polyoxymethylene resin composition of the present embodiment maintains sufficient productivity for practical use while improving the appearance and texture of the molded product, and is a molded product. There is a tendency to improve the dimensional accuracy and quality of the product.
When a large shearing force is applied due to melt-kneading or the like in the manufacturing process of the polyoxymethylene resin composition, the average particle size of the inorganic substances contained in the polyoxymethylene resin composition is crushed and used as a raw material. It can be smaller than that of an inorganic substance. In such a case, an inorganic substance having an average particle size of about 0 to 10 μm larger than the desired average particle size of the inorganic substance contained in the polyoxymethylene resin composition may be used as a raw material.

_{Here, the average particle size of the inorganic substance is an average diameter D 50} with a cumulative weight of 50% measured using a particle size distribution measuring device using a laser diffraction / scattering method. As a particle size distribution measuring device using a laser diffraction / scattering method, for example, a SALD-2000 type manufactured by Shimadzu Corporation is used.
The inorganic substance having the average particle size may be obtained by using a commercially available inorganic substance as it is, or by further pulverizing and / or classifying.

(Additive (C))
The polyoxymethylene resin composition of the present embodiment may further contain an additive (C), if necessary, in addition to the polyoxymethylene resin (A) and the inorganic substance (B) described above.
The additive (C) is not particularly limited, but is, for example, a formaldehyde scavenger, an antioxidant, a plasticizer, a lubricant, a slidability imparting agent, a mold release agent, an antistatic agent, an inorganic or organic additive. Examples thereof include fillers / crystal nucleating agents, weather resistant (light) agents, appearance improving agents such as pigments and dyes, conductive agents, and flame retardants.
These additives (C) may be used alone or in combination of two or more.

The polyoxymethylene resin composition of the present embodiment contains, in particular, a formaldehyde scavenger, an antioxidant, a plasticizer, a lubricant, a slidability imparting agent, a mold release agent, and an antistatic agent as the additive (C). Is preferable.
It is preferable to add a plasticizer, lubricant, etc. because they are expected to have the effect of increasing the dispersibility of the inorganic substance (B) and lowering the resin temperature during kneading when kneading with the inorganic substance (B). .. Such plasticizers, lubricants and the like are not particularly limited, but for example, aliphatic hydrocarbons and aromatic hydrocarbons and their modified products, alcohols, fatty acid esters of polyols and polyols, and mixtures thereof. And so on.

The content of the additive (C) in the polyoxymethylene resin composition is preferably 10 parts by mass or less, more preferably 8 parts by mass or less, based on 100 parts by mass of the polyoxymethylene resin (A). It is preferably 5 parts by mass or less, and more preferably 5 parts by mass or less. By containing the above-mentioned preferable range amount of the additive (C), the polyoxymethylene resin composition of the present embodiment maintains sufficient productivity for practical use while improving the appearance and texture of the molded product. There is a tendency to improve the dimensional accuracy and quality of molded products.
When two or more of the above are used in combination as the additive (C), the total content may be in the above range.

Among the additives (C), the formaldehyde scavenger (C1) and the antioxidant (C2), which are particularly preferable to be added, will be further described below.
As described above for the formaldehyde scavenger (C1) and the antioxidant (C2), the additive (C) is added to the polyoxymethylene polymer in advance prior to the granulation step of the polyoxymethylene resin (A). You may.

(C1) Formaldehyde scavenger As a formaldehyde scavenger, in producing a polyoxymethylene resin composition or a molded product using the same, residual formaldehyde and formic acid generated by modification of the polyoxymethylene resin composition adversely affect the productivity and appearance. It has the function of capturing the product that gives formaldehyde or suppressing its influence. By containing the formaldehyde scavenger, the polyoxymethylene resin composition of the present embodiment improves the appearance and texture of the molded product, maintains sufficient productivity for practical use, and enhances the dimensional accuracy and quality of the molded product. Tend to be able to.

Examples of the formaldehyde scavenger include reactive nitrogen-containing compounds, metal salts of inorganic acids, metal oxides and metal salts of organic acids. Among these, it is preferable that the formaldehyde scavenger is a compound that does not contain an acid as an impurity as much as possible and / or does not easily generate an acid.
Only one type of the formaldehyde scavenger may be used alone, but it is preferable to use two or more types in combination.

The content of the formaldehyde scavenger is preferably 0.005 parts by mass or more and less than 5 parts by mass, more preferably 0.01 parts by mass or more and less than 3 parts by mass, based on 100 parts by mass of the polyoxymethylene resin (A). More preferably, it is 02 parts by mass or more and less than 1 part by mass.
When two or more types of formaldehyde scavengers are used in combination, the total content may be within the above range.

Examples of the reactive nitrogen-containing compound include polyamide resins such as nylon 4-6, nylon 6, nylon 6-6, nylon 6-10, nylon 6-12, and nylon 12. The polyamide resin may be, for example, a copolymer of nylon 6 / 6-6 / 6-10, nylon 6 / 6-12, or the like. Further, examples thereof include acrylamide and its derivatives, copolymers of acrylamide and its derivatives with other vinyl monomers, and the like, for example, obtained by polymerizing acrylamide and its derivatives with other vinyl monomers in the presence of metal alcoholate. It may be a poly-β-alanine copolymer.
Examples of the reactive nitrogen-containing compound include amide compounds, amino-substituted triazine compounds, amino-substituted triazine compounds and formaldehyde additives, amino-substituted triazine compounds and formaldehyde condensates, urea, urea derivatives, hydrazine derivatives, and imidazole compounds. Examples include imide compounds.

Specific examples of the amide compound include polyvalent carboxylic acid amides such as isophthalic acid diamide and anthranilamide.
Specific examples of the amino-substituted triazine compound include 2,4-diamino-sim-triazine, 2,4,6-triamino-sim-triazine, N-butyl melamine, N-phenyl melamine, N, N-diphenyl melamine, and N. , N-diallyl melamine, benzoguanamine (2,4-diamino-6-phenyl-sim-triazine), acetoguanamine (2,4-diamino-6-methyl-sim-triazine), 2,4-diamino-6-butyl -Sym-triazine and the like can be mentioned.
Specific examples of the amino-substituted triazine compound and the adduct of formaldehyde include N-methylol melamine, N, N'-dimethylol melamine, N, N', N "-trimethylol melamine and the like.
Specific examples of the condensate of the amino-substituted triazine compound and formaldehyde include a melamine-formaldehyde condensate.

Examples of urea derivatives include N-substituted urea, urea condensate, ethylene urea, hydantoin compound, ureido compound and the like. Specific examples of the N-substituted urea include methyl urea, alkylene bisurea, and aryl-substituted urea substituted with a substituent such as an alkyl group. Specific examples of the urea condensate include a condensate of urea and formaldehyde. Specific examples of the hydantoin compound include hydantoin, 5,5-dimethylhydantoin, 5,5-diphenylhydantoin and the like. Specific examples of the ureido compound include allantoin.

Examples of hydrazine derivatives include hydrazide compounds. Specific examples of the hydrazide compound include dicarboxylic acid dihydrazide, and more specifically, malonic acid dihydrazide, succi acid dihydrazide, glutarate dihydrazide, adipic acid dihydrazide, adipic acid dihydrazide, sperate dihydrazide, azelaic acid dihydrazide, and so on. Examples thereof include sebatic acid dihydrazide, dodecanodiic acid dihydrazide, isophthalic acid dihydrazide, phthalic acid dihydrazide, and 2,6-naphthalenedicarbodihydrazide.
Specific examples of the imidazole compound include imidazole, 1-methylimidazole, 2-methylimidazole, 1,2-dimethylimidazole and the like.
Specific examples of the imide compound include succinimide, glutarimide, and phthalimide.

Examples of other formaldehyde scavengers include metal salts of inorganic acids, metal oxides and metal salts of organic acids. For example, hydroxides such as sodium, potassium, magnesium, calcium or barium, carbonates, phosphates, silicates, borates, carboxylates and layered double hydroxides of the above metals can be mentioned.

The carboxylic acid of the carboxylic acid salt is preferably a saturated or unsaturated aliphatic carboxylic acid having 10 to 36 carbon atoms, and these carboxylic acids may be substituted with a hydroxyl group. Specific examples of saturated or unsaturated aliphatic carboxylates include calcium dimyristate, calcium dipalmitate, calcium distearate, calcium (myristic acid-palmitate), calcium (myristic acid-stearate), and (palmitic acid). −Stearate) Calcium and the like are mentioned, and calcium dipalmitate and calcium distearate are preferable.

Examples of the layered double hydroxide include hydrotalcites represented by the following formula (4).
_{^{[(M 2+) 1-x}} (M 3+) x (OH) 2] x + [(A n-) x / n · mH 2 O] x- ··· (1)
(In the formula (1), M ²⁺ is a divalent metal, M ³⁺ is a trivalent metal, A ^n-n-valent (n represents an anion of an integer of 1 or more), x is, 0 <x ≦ 0 It is in the range of .33, and m indicates a positive number.)
In the formula (1), examples of ^{M 2+ include Mg 2+} , Mn ²⁺ , Fe ²⁺ , Co ²⁺ , Ni ²⁺ , Cu ²⁺ , Zn ^2+, and examples of M ³⁺ . ^{the, Al 3+, Fe 3+, Cr} 3+, Co 3+, etc. in ^3+, and examples of a ^{n- is, OH -, F -, Cl} -, Br -, NO 3- ^{_{, CO 3 2-, SO 4 2-}} , Fe (CN) 6 3-, CH 3 COO -, oxalic acid ion, and salicylate ion. Examples of A ^{n- is,} OH ^-, CO ₃ ^2- is preferred.
Specific examples of hydrotalcites include _{natural hydrotalcites represented by Mg 0.75} Al _0.25 (OH) ₂ (CO ₃ ) _0.125・ 0.5H ₂ O, Mg _4.5 Al ₂ (OH) ₁₃ CO ₃・ 3. Examples thereof include synthetic hydrotalcite represented by _{5H 2} O, Mg _4.3 Al ₂ (OH) _12.6 CO _{3 and the like.}

(C2) Antioxidants Examples of antioxidants include phenolic antioxidants having a radical trapping action, aromatic amine-based antioxidants, sulfur-based antioxidants having a peroxide decomposition action, and phosphorus-based antioxidants. can give. The antioxidant may be used alone or in combination of two or more.
By containing the antioxidant, the polyoxymethylene resin composition of the present embodiment improves the appearance and texture of the molded product, maintains sufficient productivity for practical use, and enhances the dimensional accuracy and quality of the molded product. Tend to be able to.

The content of the antioxidant is preferably 0.01 part by mass or more and less than 5 parts by mass, more preferably 0.05 part by mass or more and less than 3 parts by mass, based on 100 parts by mass of the polyoxymethylene resin (A). More preferably, it is 1 part by mass or more and less than 1 part by mass.
When two or more kinds of antioxidants are used in combination, the total content may be within the above range.

In the polyoxymethylene resin composition of the present embodiment, among the above-mentioned antioxidants, a phenolic antioxidant is preferably used.
Specific examples of the phenolic antioxidant are not limited to the following, but 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], Pentaerythritol tetrakis [methylene-3- (3', 5'-di-t-butyl-4'-hydroxyphenyl) propionate] methane and the like can be mentioned. Preferably, triethylene glycol-bis- [3- (3-t-butyl-5-methyl-4-hydroxyphenyl) -propionate] and pentaerythritol tetrakis [methylene-3- (3', 5'-di-t). -Butyl-4'-hydroxyphenyl) propionate] Methane.

<Manufacturing method of polyoxymethylene resin composition>
As described above, the polyoxymethylene resin composition contains the polyoxymethylene resin (A), the inorganic substance (B), and if necessary, the additive (C).
The following shows a method for producing a polyoxymethylene resin composition containing all of the polyoxymethylene resin (A), the inorganic substance (B) and the additive (C). Specifically, the polyoxymethylene resin composition can be produced by kneading each of the above components (A) to (C) under heating and then forming them into flakes (crushed) or pellets (granulated).

The method is a method in which all the components (A) to (C) are charged and kneaded at once; the components (B) and (C) are added at the time of granulation of the polyoxymethylene resin (A) and melt-kneaded. Method: A method in which the component (C) is mixed with the polyoxymethylene resin (A) in advance and then kneaded with the inorganic substance (B); the component (B) and the component (C) are kneaded in advance and then polyoxymethylene. A method of kneading with the resin (A); and the like.
Further, the kneading may be performed while adding the component (B) and the component (C) to the component (A) in several times.
Further, the component (C) may be kneaded with the polyoxymethylene resin (A) in advance, and then the component (C) may be added again when the component (B) is kneaded again.

Furthermore, in order to enhance the uniform dispersibility of the components (A), (B), and (C), pellets of the polyoxymethylene resin (A) to be kneaded and polyoxymethylene in which the component (C) is mixed in advance. A part or all of the resin (A) may be crushed and mixed, and then melt-mixed.
Further, in the polyoxymethylene resin composition of the present embodiment, the molded polyoxymethylene resin molded product is subjected to a treatment such as pulverization or drying, and if the following characteristics are satisfied, a part or the whole amount thereof is used. It doesn't matter.

As the device for kneading, a normal kneader such as a Banbury mixer, a plast mill, a kneader, a pressure kneader, a roll mill, a screw type single-screw extruder or a twin-screw extruder can be used.
The kneading temperature is 165 to 230 ° C, preferably 170 to 210 ° C, and more preferably 175 to 200 ° C.

For example, as a preferable manufacturing method, a component (B) is obtained by supplying components (A) and (C) uniformly mixed in advance with a Henschel mixer from the top and plasticizing using an extruder with a vent capable of multi-stage side feed. Is supplied from the side in multiple stages, and after uniform mixing, granulation is performed and pellets are collected; the components (B) and (C) are mixed with a pressure roll mill heated to a temperature equal to or higher than the melting point of the component (A), and here. A method in which the component (A) is added in a timely manner to obtain a composition in which the components are uniformly integrated, and then the mixture is pulverized to collect flakes; and the like.

<Characteristics of polyoxymethylene resin composition>
The number average molecular weight of the polyoxymethylene resin contained in the polyoxymethylene resin composition of the present embodiment is 30,000 to 65,000. Further, in the polyoxymethylene resin composition of the present embodiment, the amount of weight loss in thermogravimetric analysis in air at 230 ° C. is 5 to 30% by mass of the total resin composition. Further, when the weight loss is 100%, the weight loss rate of 50% of the weight loss by thermogravimetric analysis is 4.4% / min or less.
In addition, the crystallization start temperature of the polyoxymethylene resin composition of the present embodiment is preferably 142 to 154 ° C.
Further, the average particle size of the inorganic substance contained in the polyoxymethylene resin composition of the present embodiment is preferably 0.01 to 100 μm.

(Number average molecular weight of polyoxymethylene resin contained in the polyoxymethylene resin composition)
The polyoxymethylene resin contained in the polyoxymethylene resin composition of the present embodiment has a PMMA-equivalent number average molecular weight Mn of 30,000 to 65,000 obtained by a cubic approximation curve using a standard PMMA (manufactured by Polymer Laboratories). Yes, it is preferably 31000 to 63000, and more preferably 32000 to 59000. By setting the above-mentioned preferable number average molecular weight, the polyoxymethylene resin composition of the present embodiment maintains sufficient productivity for practical use while improving the appearance and texture of the molded product, and dimensional accuracy and quality of the molded product. Can be enhanced.
The number average molecular weight of the polyoxymethylene resin contained in the polyoxymethylene resin composition of the present embodiment can be measured by a gel permeation chromatography (GPC) method.
A polyoxymethylene resin composition is weighed as a sample, and an eluent containing HFIP (1,1,1,3,3,3-hexafluoro-2-propanol) and 10 mM-CF ₃ COONa is added to a concentration of 1 to 5 mg. / ML. This solution is allowed to dissolve overnight at room temperature, shaken gently, and then filtered through a 0.1 μm PTFE cartridge filter, which is used as a sample solution for GPC measurement.
GPC is a GPC device (HLC-8220GPC manufactured by Tosoh), a column (TSKgelSuper AWM-H (6 mm ID x 15 cm) x 2 manufactured by Tosoh), a detector (differential refractometer (RI detector)), Polarity = (+). )), Using the above eluent, the measurement is performed at a flow velocity of 0.3 mL / min, a column temperature of 40 ° C., and a sample solution injection amount of 20 μL.
In the present embodiment, from the measurement results obtained by the above measurement, the components having a PMMA-equivalent molecular weight Mi of 8000 or less, which are affected by the solvent and the oligomer component, are excluded, and the numbers are selected from the components having a PMMA-equivalent molecular weight Mi of more than 8000. Obtain the average molecular weight Mn.

FIG. 1 shows a measurement example of the PMMA-equivalent number average molecular weight Mn of the polyoxymethylene resin. The vertical axis in the figure shows the differential dispersion value measured by GPC, and the horizontal axis shows the PMMA-equivalent molecular weight Mi per molecule of the polyoxymethylene (co) polymer constituting the polyoxymethylene resin.
Specifically, among the areas shown by the broken line cubic approximation curve, the components with PMMA-equivalent molecular weight Mi of 8000 or less, which are represented by diagonal lines, are excluded, and the remaining PMMA-equivalent molecular weight Mi is a number based on the components of more than 8000. Obtain the average molecular weight Mn.

In order to keep the number average molecular weight of the polyoxymethylene resin contained in the polyoxymethylene resin composition within the above range, a chain transfer agent is added in the above (1) polymerization step for obtaining the raw material polyoxymethylene resin. Then, a raw material polyoxymethylene resin having a number average molecular weight in a suitable range is obtained.
Further, in the present embodiment, it is preferable to reduce the amount of the polymerization catalyst added at the time of the polymerization of the above (1) while maintaining the polymerization yield. This is because if the amount of the polymerization catalyst is increased, it may take time to deactivate the catalyst residue, and the remaining catalyst may impair the stability of the raw material polyoxymethylene resin. Further, if the amount of the polymerization catalyst is too small, not only the yield decreases and the production amount varies, but also the concentration of the chain transfer agent with respect to the polyoxymethylene resin to be polymerized changes, so that the raw material poly having a number average molecular weight in the above-mentioned suitable range is used. Oxymethylene resin cannot be obtained stably. As a result, the number average molecular weight of the polyoxymethylene resin contained in the polyoxymethylene resin composition produced by using the raw material polyoxymethylene resin is reduced from the above range.
On the other hand, during the production of a polyoxymethylene resin composition containing an inorganic substance, the thermal stability of the polyoxymethylene resin may decrease due to the high reactivity of the inorganic substance or the like. Therefore, the polyoxymethylene resin having the above number average molecular weight contained in the produced polyoxymethylene resin composition can be stably obtained by surface-treating the inorganic substance itself or adding a heat stabilizer or the like.
That is, in the present embodiment, the polyoxymethylene resin having the number average molecular weight contained in the polyoxymethylene resin composition balances the polymerization catalyst and the chain transfer agent during the production of the raw material polyoxymethylene resin, or the additive. It can be obtained by making adjustments to the above.
In the present embodiment, it is preferable to reduce the amount of the polymerization catalyst while maintaining the polymerization yield.

(Weight loss rate measured by thermogravimetric analysis of polyoxymethylene resin composition)
The polyoxymethylene resin composition of the present embodiment has a weight loss rate of 5 to 30% and 6 to 28% of the total mass of the polyoxymethylene resin composition by thermogravimetric analysis in air at 230 ° C. It is preferably 7 to 26%, more preferably 7 to 26%.
By setting the weight reduction rate within the above range, the polyoxymethylene resin composition of the present embodiment maintains sufficient productivity for practical use while improving the appearance and texture of the molded product, and the dimensional accuracy of the molded product and the dimensional accuracy of the molded product. The dignity can be improved.

For the thermogravimetric analysis in this embodiment, for example, a thermal analyzer manufactured by NETZSCH: TG-DTA2500 is used.
When the sample to be measured is a polyoxymethylene resin composition, the required amount may be weighed and measured as it is.
When the sample to be measured is a polyoxymethylene resin molded product, a part thereof is sampled from the polyoxymethylene resin molded product and used directly as a sample for thermogravimetric analysis.
Approximately 5 mg of the sample is weighed and used, and the temperature of the sample is raised from room temperature to 230 ° C. at 20 ° C./min in air. The weight loss rate is defined as the weight loss rate when the weight is reduced while being held at 230 ° C. for 150 minutes, then gradually stabilizes, and the weight loss rate becomes 0.005% / min or less. If the weight loss rate is not stable, the weight loss rate after holding for 150 minutes is defined as the weight loss rate.

FIG. 2 shows an example of measuring the weight loss rate by thermogravimetric analysis. In the figure, the right vertical axis shows the temperature, and the broken line is the curve showing the temperature change. The left vertical axis shows the weight change of the sample to be measured, and the solid line is the curve showing the weight change. The horizontal axis shows the elapsed time after the start of temperature rise.
When the weight loss rate becomes stable and becomes 0.005% / min or less, the solid line becomes substantially vertical in the horizontal direction. The point X at which the solid line substantially vertical in the horizontal direction intersects the left vertical axis indicating the weight change is the residual weight ratio of the sample, and the weight reduction rate can be calculated by the following formula.
Weight loss rate (%) = 100-X
When the weight loss rate is not stable to 0.005% / min or less, the weight loss rate can be calculated by the above formula, where X is the residual weight rate of the sample 150 minutes after the start of temperature rise.

The polyoxymethylene resin composition of the present embodiment retains sufficient stability during production, but by holding in air at 230 ° C. for 150 minutes, most of the polyoxymethylene resin contained is maintained. Is sublimated by thermal decomposition. That is, the polyoxymethylene resin composition of the present embodiment having the above weight loss rate measured by the above thermogravimetric analysis has the content of an inorganic substance and the content of an additive having a decomposition temperature of 230 ° C. or higher. It can be obtained by appropriately adjusting the total amount so as to be in the range of 70 to 95% by mass.
The content of the polyoxymethylene resin contained may be less than the blending amount of the raw material polyoxymethylene resin. This is because a part of the raw material polyoxymethylene resin may be thermally decomposed by melt-kneading or the like in the manufacturing process of the polyoxymethylene resin composition.

(Weight reduction rate of polyoxymethylene resin composition)
The polyoxymethylene resin composition of the present embodiment has a weight loss when the weight loss reaches 50% when the weight loss corresponding to the weight loss rate in the thermogravimetric analysis at 230 ° C. for 150 minutes in air is 100%. The speed is 4.4% / min or less.
For the thermogravimetric analysis in this embodiment, for example, a thermal analyzer manufactured by NETZSCH: TG-DTA2500 is used. In the same manner as described above, the constituent polyoxymethylene resin composition is collected from the obtained polyoxymethylene resin molded product, and thermogravimetric analysis is performed using this as a sample.
FIG. 3 shows a measurement example of the weight loss rate.
Approximately 5 mg of the sample is weighed and used, and the temperature of the sample is raised from room temperature to 20 ° C./min in the air to reach 230 ° C. While holding at 230 ° C. for 150 minutes, the amount of weight loss corresponding to the above-mentioned weight loss rate can be measured. Let this weight loss amount be 100%, and let the weight loss rate per hour (minutes) when the weight loss amount reaches 50% be the weight loss rate (% / minute).

The polyoxymethylene resin composition of the present embodiment is composed of a polyoxymethylene resin having high stability, selection of an inorganic substance capable of reducing the influence of the polyoxymethylene resin on thermal stability, and surface treatment. By setting the mixing conditions so that the influence of the polyoxymethylene resin on the thermal stability can be reduced during the production of the product, sufficient stability is maintained during the production of the composition and the molded product as described above. That is, the polyoxymethylene resin composition having the weight reduction rate can be obtained by adjusting the additives and inorganic substances, conditions in the terminal stabilization step and granulation step of the polyoxymethylene resin, and the polyoxymethylene resin composition. It can be obtained by adjusting the conditions in the manufacturing method.

In the present embodiment, the weight loss rate is preferably 4.1% / min or less, more preferably 4.0% / min or less, and further preferably 3.9% / min or less. preferable. By setting the weight reduction rate as described above, the polyoxymethylene resin composition of the present embodiment maintains sufficient productivity for practical use while improving the appearance and texture of the molded product, and improves the dimensional accuracy and quality of the molded product. It can be further enhanced.

(Crystallization start temperature Cp of polyoxymethylene resin composition)
The polyoxymethylene resin composition of the present embodiment preferably has a crystallization start temperature Cp of 142 to 154 ° C, more preferably 142 to 153 ° C, and even more preferably 142 to 150 ° C. It is even more preferably 142 to 148 ° C. By setting the crystallization start temperature, the polyoxymethylene resin composition of the present embodiment maintains sufficient productivity for practical use while improving the appearance and texture of the molded product, and dimensional accuracy and quality of the molded product. Tends to be able to increase.

The crystallization start temperature Cp of the polyoxymethylene resin composition of the present embodiment can be measured using a differential scanning calorimeter, for example, a differential scanning calorimeter manufactured by NETZSCH: DSC350 or the like.
As the measurement conditions, a sample (polyoxymethylene resin composition) is set at a display temperature of 50 ° C., the temperature is raised to 220 ° C. at 320 ° C./min, and the temperature is maintained at 220 ° C. for 1 minute. Then, the temperature is lowered to 140 ° C. at 80 ° C./min and held at 140 ° C. for 5 minutes. The temperature is then raised to 210 ° C. at 20 ° C./min and held at 210 ° C. for 5 minutes. After that, the temperature is lowered to 100 ° C. at 20 ° C./min, and the extrapolation start temperature (onset) at this time is defined as the crystallization start temperature.

In order to obtain the polyoxymethylene resin composition having the above-mentioned preferable crystallization start temperature, an additive having a low melting point or the like is used, or a polyoxymethylene copolymer (a2) is used as the polyoxymethylene resin.
In the present embodiment, it is preferable to reduce the amount of the polymerization catalyst added at the time of polymerization of the copolymer while maintaining the polymerization yield. This is because if the amount of the polymerization catalyst is increased, it may take time to deactivate the catalyst residue, and the remaining catalyst may impair the stability of the polyoxymethylene resin. Further, if the amount of the polymerization catalyst is too small, not only the yield decreases and the production amount varies, but also the concentration of the comonomer with respect to the polyoxymethylene resin to be polymerized changes, so that the polyoxymethylene resin composition having the above-mentioned preferable crystallization start temperature is used. Cannot be obtained stably.
That is, the polyoxymethylene resin composition having the crystallization start temperature can be obtained by using the additive having a low melting point, using a copolymer in the polyoxymethylene resin, and balancing the amount of the polymerization catalyst and the comonomer. can.

(Average particle size of inorganic substances contained in the polyoxymethylene resin composition)
The average particle size of the inorganic substance contained in the polyoxymethylene resin composition of the present embodiment is not particularly limited, but is preferably 0.01 to 100 μm, preferably 0.05 to 80 μm. It is preferably 0.1 to 60 μm.
When the average particle size of the inorganic substance contained in the polyoxymethylene resin composition of the present embodiment is within the above range, the polyoxymethylene resin composition of the present embodiment improves the appearance and texture of the molded product. At the same time, it tends to be possible to maintain sufficient productivity for practical use and improve the dimensional accuracy and quality of the molded product.
The average particle size of the inorganic substance contained in the polyoxymethylene resin composition of the present embodiment is an average particle size D ₅₀ with a cumulative weight of 50% measured using a particle size distribution measuring device using a laser diffraction / scattering method. do. As a particle size distribution measuring device using a laser diffraction / scattering method, for example, a SALD-2000 type manufactured by Shimadzu Corporation is used. A part of the polyoxymethylene resin composition or the molded product is weighed as a sample, and a solution dissolved in HFIP (1,1,1,3,3,3-hexafluoro-2-propanol) is used as the sample solution. More specifically, it can be measured by the method described in Examples described later.
The above-mentioned inorganic substance having an average particle size may be crushed and classified using a commercially available inorganic substance to use an inorganic substance having a desired average particle size as a raw material, or the kneading conditions at the time of producing an oxymethylene resin composition may be adjusted. It can be obtained by such means.

[Polyoxymethylene resin molded product]
The polyoxymethylene resin composition of the present embodiment can be obtained by a molding method generally used for a resin, that is, by applying heat to melt it, putting it in a mold, applying pressure, and cooling it. Moreover, it is preferable that the obtained molded product is used in an environment where a polyoxymethylene resin can be used.

<Manufacturing method of polyoxymethylene resin molded product>
Various molding methods can be used for the polyoxymethylene resin composition of the present embodiment, and among them, it is preferable to prepare a molded product by injection molding, extrusion molding, calendar molding, or compression molding, and more particularly. Injection molding and compression molding are preferred.

Injection molding machines include hydraulic molding machines, electric injection molding machines, hydraulic electric hybrid molding machines, etc. from drive devices, and plunger-type injection molding machines, pre-plastic injection molding machines, screw-type injection molding machines, etc. from injection structures. , Direct pressure type injection molding machine, toggle type injection molding machine, mechanical lock type injection molding machine, etc. from the mold clamping device, vertical injection molding machine, horizontal injection molding machine from the injection mold clamping position, vent as a special injection molding machine Examples include a type injection molding machine and an injection molding machine for multicolor molding.

Depending on the mechanism and structure, the compression molding machine may be a mechanical press such as a crank press, a knuckle press, or a screw press, a liquid press such as a single-acting hydraulic press or a double-acting hydraulic press, or a heated material using a plunger. A transfer molding machine or the like that press-fits into the machine can be mentioned.

As the molding conditions, it is preferable to mold the material at a temperature of 180 to 250 ° C. and a mold temperature of 30 to 150 ° C. The polyoxymethylene resin molded product of the present embodiment can be obtained by adjusting the injection and / or pressurizing speed and / or pressure while checking the generation of burrs, hot water wrinkles, and the like.

<Usage of polyoxymethylene resin molded product>
The polyoxymethylene resin molded product of the present embodiment is preferably used in an environment in which a polyoxymethylene resin can be usually used, and for example, the constant use temperature is −50 to 140 ° C.
In addition, mechanical parts that are usually loaded with polyoxymethylene resin during driving or fixing, sliding parts that rub against other materials or the same materials, containers that require chemical resistance, and the like can be mentioned.

<Use of polyoxymethylene resin molded product>
The polyoxymethylene resin molded product of the present embodiment is used for precision equipment, home appliances / OA equipment, automobiles, industrial applications, miscellaneous goods, and other mechanical or sliding applications in which polyoxymethylene resin is usually used.
Furthermore, in addition to the above, by selecting the amount and type of inorganic substances contained, a feeling of weight / luxury is given, quietness / low vibration is given, low dimensional change / low line expansion is given, electron beam and magnetic force line are given. It is effective for applications that require the provision of shielding properties, adjustment of thermal conductivity, adjustment of electrical conductivity, etc.
For example, design parts such as emblems and logo marks, specific gravity adjusting parts such as balancers and weights, covers and cases for drive equipment / audio equipment and their surroundings, precision parts such as OA equipment and optical equipment, X-rays and electromagnetic waves. Examples include control containers, heat dissipation plates and heat insulating plates, and alternatives to ceramic / ceramic parts and metal parts. Further, by using the polyoxymethylene resin molded product of the present embodiment, complicated parts can be obtained without post-processing, so that man-hours can be expected to be reduced as compared with materials such as ceramics / pottery and metal.

Further, the polyoxymethylene resin molded product of the present embodiment is not only used as a molded product as it is as described above, but also tends to maintain sufficient productivity for practical use and improve the dimensional accuracy and quality of the molded product. Therefore, it can be used as an injection-molded product (green part) as an intermediate product for sintered products by selecting the amount and type of inorganic substances contained in the product. A brown part is obtained by removing the resin portion from this injection-molded product in a degreasing step, and a sintered product is obtained by sintering this.
Originally, in order to shorten the heat degreasing and sintering time, the resin molded product is preferably a material having good thermal decomposition performance. On the other hand, the polyoxymethylene resin molded product obtained by the present embodiment can suppress a decrease in thermal decomposition during production and molding of the composition, so that a stable, uniform and highly dimensionally accurate molded product can be obtained. It is possible to obtain, and in addition, the thermal decomposition performance at the sintering temperature is not significantly different from the conventional one. Therefore, it is possible to obtain a sintered product with high productivity, less defects, and high accuracy.

Hereinafter, the present embodiment will be described with reference to Examples and Comparative Examples, but the present embodiment is not limited to the following Examples.
The evaluation of the polyoxymethylene resin composition (P), the method for producing the polyoxymethylene resin molded product, the polyoxymethylene resin composition, and the polyoxymethylene resin molded product in Examples and Comparative Examples will be sequentially described.

[Polyoxymethylene resin composition (P)]
Regarding the polyoxymethylene resin composition (P) used in Examples and Comparative Examples, the polyoxymethylene resin composition (P), the method for producing the polyoxymethylene resin composition, and the characteristics of the polyoxymethylene resin composition will be described. ..

<Polyoxymethylene resin composition (P)>
The following polyoxymethylene resin (A), inorganic substance (B) and additive (C) were used as raw materials for preparing the polyoxymethylene resin composition (P).
(1. Polyoxymethylene resin (A1))
(Polymerization process)
A self-cleaning type twin-screw paddle type continuous mixing reactor with a jacket through which a heat medium can pass (screw diameter 2B, ratio of length to diameter (L / D) = 15) was adjusted to 80 ° C. The main monomer was trioxane at 3000 g / hr, the comonomer was 1,3-dioxolane at 100-150 g / hr, and the chain transfer agent (methylal) was adjusted at 1-10 g / hr, and the mixture was continuously connected to the continuous mixing reactor. Feeded. As a polymerization catalyst, a 1 mass% cyclohexane solution of boron trifluoride di-n-butyl etherate was added to a continuous mixing reactor so ^{that the catalyst was 2.0 × 10 -5 mol with respect to 1 mol of trioxane.} Polymerization was carried out to obtain polymerized flakes. The amount of the chain transfer agent and the comonomer added was adjusted so that the resin composition having the molecular weight and the crystallization start temperature shown in Table 1 could be obtained.
(Terminal stabilization process)
After pulverizing the obtained polymerization flakes, the pulverized product was put into a 1% by mass aqueous solution of triethylamine and stirred for 1 hour to inactivate the polymerization catalyst. Then, the triethylamine aqueous solution containing the polymerized flakes was filtered through a centrifuge and dried under nitrogen at 120 ° C. for 3 hours to obtain a dried polymer.
Next, terminal stabilization was carried out using the obtained dried polymer as follows. The obtained dry polymer is added to the front part of a screw type twin-screw extruder with a vent (manufactured by Plastic Engineering Laboratory Co., Ltd., BT-30, L / D = 44, set temperature 200 ° C., rotation speed 80 rpm). Further, 0.5 parts by mass of water was added to 100 parts by mass of the dried polymer, and degassing under reduced pressure was performed while stabilizing the polymer ends to obtain a stabilized polyoxymethylene resin (A1).
(Granulation process)
The obtained stabilized polyoxymethylene resin (A1) was dried for 12 hours after confirming that the product temperature was 100 ° C. or higher in a gear oven (set at 105 ° C.) in a nitrogen atmosphere.
The following (C1), (C2) and (C3) were mixed as additives at a ratio of 5: 5: 2 for 1 minute with a Henschel mixer. BT, screw type twin-screw extruder with vacuum vent (manufactured by Plastic Engineering Laboratory Co., Ltd.) so that the obtained mixture is 0.5 parts by mass with respect to 100 parts by mass of the polyoxymethylene resin (A). -30, L / D = 44, L: Distance from raw material supply port to discharge port of twin-screw extruder, D: inner diameter of twin-screw extruder) Set the screw rotation speed to 100 rpm, and from the die at 22 amperes or less. The melted resin was melt-kneaded so as to have a temperature of 205 ± 2 ° C. to obtain pellets of a polyoxymethylene resin (A1) containing the additives (C1), (C2) and (C3).
From the input of raw materials to the collection of polyoxymethylene resin pellets, operations were performed so as to avoid mixing of oxygen.

(2. Inorganic substance (B))
The following (B1) to (B3) were used as the inorganic substance (B).
(B1): Carbonyl iron-OM (D ₅₀ = 6 μm / manufactured by BASF Limited)
(B2): Alumina-LA4000 (D ₅₀ = 3 μm / manufactured by Pacific Random Co., Ltd.)
(B3): SUS316L-PF20 (D ₅₀ = 10 μm / manufactured by Epson Atmix Co., Ltd.)
(3. Additive (C))
The following additives (C1) to (C5) were used as the additive (C).
(C1): Antioxidant / Irganox 245 (manufactured by Chivas Specialty Chemicals Co., Ltd.)
(C2): Formaldehyde scavenger / H-3 (manufactured by Asahi Kasei Finechem Co., Ltd.)
(C3): Formaldehyde scavenger / NA100 (manufactured by Asahi Kasei Corporation)
(C4): Formaldehyde scavenger / dihydrazide sebacate (manufactured by Japan Finechem Co., Ltd.)
(C5): Formaldehyde scavenger / benzoguanamine (manufactured by Nippon Shokubai Co., Ltd.)

<Manufacturing of polyoxymethylene resin composition (P)>
The manufacturing process of the polyoxymethylene resin composition (P) used in Examples and Comparative Examples will be described.

(Preparation of resin compositions (P1) to (P5))
The pellet of the polyoxymethylene resin (A1) containing the above additives (C1), (C2) and (C3) and the inorganic substance (B1) are placed in a gear oven (set at 105 ° C.) under a nitrogen atmosphere at a product temperature. After confirming that the temperature is 100 ° C or higher and drying for 4 hours, use a pressure kneader (manufactured by Toshin, TD0.3-3M type) to prepare at the prescribed ratio shown in Table 1, set the temperature to 190 ° C, and set the temperature for 40 minutes. Kneading was performed. Next, the obtained kneaded product was crushed while cooling to obtain flakes of a polyoxymethylene resin composition P1 to P4 for molding having a size of about 5 mm. The flakes obtained are shown in Table 1.
In the polyoxymethylene resin composition P5, the polyoxymethylene resin (A1) and the inorganic substance (B1) were mixed at a ratio of 2:98 in the same manner as described above, but since flakes that were uniformly integrated were not obtained, analysis and analysis were performed. No evaluation was performed.

(Preparation of resin compositions P6 to P9)
The polyoxymethylene resin compositions P6 to P9 were prepared in the same manner as the polyoxymethylene resin composition P3 except for the following, and the weight loss rate at the time when the weight loss amount reached 50% was controlled as shown in Table 1. ..
As the polyoxymethylene resin composition P6, (A2) was used instead of the polyoxymethylene resin (A1). In (A2), in the (granulation step) of the above (A1), the 12-hour drying before the addition of the additives (C1) to (C3) is set to 24-hour drying, and the resin temperature 205 of the molten resin discharged from the die. ± 2 ° C was defined as 190 ± 2 ° C.
As the polyoxymethylene resin composition P7, (A3) was used instead of the polyoxymethylene resin (A1). In (A3), 12-hour drying was defined as 24-hour drying in the (granulation step) of (A1).
As the polyoxymethylene resin composition P8, (A4) was used instead of the polyoxymethylene resin (A1). In (A4), the resin temperature of 205 ± 2 ° C. was changed to 215 ± 2 ° C. in the (granulation step) of (A1).
As the polyoxymethylene resin composition P9, (A5) was used instead of the polyoxymethylene resin (A1). In (A5), 12-hour drying was defined as 2-hour drying in the (granulation step) of (A1).

(Preparation of Resin Compositions P10 to P13)
The polyoxymethylene resin compositions P10 to P13 used polyoxymethylene resins (A6) to (A9) obtained by changing the amount of the chain transfer agent and the amount of the polymerization catalyst used in the (polymerization step), except that the polyoxymethylene resins (A6) to (A9) were used. It was prepared in the same manner as the polyoxymethylene resin composition P3, and the number average molecular weight of the contained polyoxymethylene resin was controlled as follows.
As the polyoxymethylene resin composition P10, (A6) was used instead of the polyoxymethylene resin (A1). The number average molecular weight of A6 in P10 was 28,000 with respect to the number average molecular weight of A1 in P3 of 50,000.
As the polyoxymethylene resin composition P11, (A7) was used instead of the polyoxymethylene resin (A1). The number average molecular weight of A7 in P11 was 35,000 with respect to the number average molecular weight of A1 in P3 of 50,000.
As the polyoxymethylene resin composition P12, (A8) was used instead of the polyoxymethylene resin (A1). The number average molecular weight of A8 in P12 was 60,000 with respect to the number average molecular weight of A1 in P3 of 50,000.
As the polyoxymethylene resin composition P13, (A9) was used instead of the polyoxymethylene resin (A1). The number average molecular weight of A9 in P13 was 75,000 with respect to the number average molecular weight of A1 in P3 of 50,000.

(Preparation of Resin Compositions P14 to P17)
The polyoxymethylene resin compositions P14 to P17 are polyoxymethylene except that the polyoxymethylene resins (A10) to (A13) obtained by changing the amount of comonomer used and the amount of polymerization catalyst used in the (polymerization step) are used. It was prepared in the same manner as the resin composition P3, and the crystallization start temperature of the polyoxymethylene resin composition was controlled as follows.
As the resin composition P14, (A10) was used instead of the polyoxymethylene resin (A1). The crystallization start temperature of P14 was 155 ° C. with respect to the crystallization start temperature of P3 of 146 ° C.
As the resin composition P15, (A11) was used instead of the polyoxymethylene resin (A1). The crystallization start temperature of P15 was 151 ° C. with respect to the crystallization start temperature of P3 of 146 ° C.
As the resin composition P16, (A12) was used instead of the polyoxymethylene resin (A1). The crystallization start temperature of P16 was 143 ° C. with respect to the crystallization start temperature of P3 of 146 ° C.
As the resin composition P17, (A13) was used instead of the polyoxymethylene resin (A1). The crystallization start temperature of P17 was 141 ° C. with respect to the crystallization start temperature of P3 of 146 ° C.

(Preparation of resin compositions P18 to P20)
The polyoxymethylene resin compositions P18 to P20 are the same as the polyoxymethylene resin compositions P3, except that the polyoxymethylene resins (A14) to (A16) in which the type and compounding ratio of the additive (C) are changed are used. After preparation, the weight loss rate at the time when the weight loss amount reached 50% was controlled as shown in Table 1.
The resin composition P18 uses (A14) instead of the polyoxymethylene resin (A1), and uses (C1), (C2), and (C3) as additives in the (granulation step) of P3 at 5: 5: 2. Additives (C1) and (C2) were used in a blending ratio of 5: 7 instead of the blending ratio of.
The resin composition P19 uses (A15) instead of the polyoxymethylene resin (A1), and uses (C1), (C2), and (C3) as additives in the (granulation step) of P3 at 5: 5: 2. Additives (C1), (C2) and (C4) were used in a blending ratio of 5: 5: 2 instead of the blending ratio of.
The resin composition P20 uses (A16) instead of the polyoxymethylene resin (A1), and uses (C1), (C2), and (C3) as additives in the (granulation step) of P3 at 5: 5: 2. Additives (C1), (C2) and (C5) were used in a blending ratio of 5: 5: 2 instead of the blending ratio of.

(Preparation of resin compositions P21 to P22)
The polyoxymethylene resin compositions P21 and P22 were prepared in the same manner as the polyoxymethylene resin composition P3 except that the type and blending amount of the inorganic substance (B) were changed, and the weights were measured by thermogravimetric analysis in air at 230 ° C. The rate of weight loss and the rate of weight loss when the amount of weight loss reached 50% were controlled as shown in Table 1.
In the resin composition P21, (B2) was used instead of the inorganic substance (B1).
In the resin composition P22, (B3) was used instead of the inorganic substance (B1).

[Manufacturing of polyoxymethylene resin molded article]
The manufacturing process of the polyoxymethylene resin molded article used in Examples and Comparative Examples will be described. The polyoxymethylene resin composition is filled by using an injection molding machine (manufactured by Nissei Resin Industry Co., Ltd., PS40E5ASE type) at a cylinder temperature of 200 ° C. and a mold temperature of 80 ° C. while adjusting the injection pressure so as not to cause burrs. This was carried out to obtain a flat plate-shaped molded product (length 50 mm, width 50 mm, thickness 3 mm).

[Characteristics and evaluation of polyoxymethylene resin composition and evaluation of polyoxymethylene resin molded product]
The characteristics and evaluation of the polyoxymethylene resin composition constituting the polyoxymethylene resin molded product used in Examples and Comparative Examples and the evaluation of the polyoxymethylene resin molded product will be described.

<Characteristics of polyoxymethylene resin composition>
Regarding the characteristics of the polyoxymethylene resin composition and the polyoxymethylene resin contained in the polyoxymethylene resin composition constituting the polyoxymethylene resin molded product used in Examples and Comparative Examples, the number average molecular weight, the weight loss rate, and the decrease. The minutes, the crystallization start temperature, and the particle size of the inorganic substance were analyzed. The measurement method for each is shown below, and the analysis results are shown in Table 1.

(1. Number average molecular weight of resin)
To measure the number average molecular weight of the polyoxymethylene resin contained in the polyoxymethylene resin composition, the constituent polyoxymethylene resin composition was collected from the obtained polyoxymethylene resin molded product, and the composition was used. It was used as a sample.
Weigh the sample and add an eluent containing HFIP (1,1,1,3,3,3-hexafluoro-2-propanol / manufactured by Central Glass) and 10 mM-CF ₃ COONa (manufactured by Wako Pure Chemical Industries, Ltd.). In addition, the concentration was 4 mg / mL. This solution was allowed to dissolve overnight at room temperature, shaken gently, and then filtered through a 0.1 μm PTFE cartridge filter, which was used as a sample solution.
The number average molecular weight is measured by gel permeation chromatography, GPC device (HLC-8220GPC manufactured by Tosoh), column (TSKgelSuper AWM-H (6 mm I.D x 15 cm) x 2 manufactured by Tosoh), detector (differential refractometer). Using (RI detector) and Polarity = (+)), the measurement was performed at a flow velocity of 0.3 mL / min, a column temperature of 40 ° C., and an injection volume of 20 μL of the sample solution.
The obtained results are PMMA-equivalent molecular weights obtained by a cubic approximation curve using a standard PMMA (manufactured by Polymer Laboratories), and the results are shown in Table 1. Further, from the obtained measurement results, the number average molecular weight was determined from the portion excluding the portion having a PMMA-equivalent molecular weight of 8000 or less, which was affected by the solvent and the oligomer component.

(2. Weight loss rate by thermogravimetric analysis)
For the measurement of the weight loss rate, the constituent polyoxymethylene resin composition was collected from the polyoxymethylene resin molded product obtained in the same manner as described above, and thermogravimetric analysis was performed using this as a sample.
For thermogravimetric analysis, a thermal analyzer TG-DTA2500 manufactured by NETZSCH was used, and about 5 mg was weighed and used as a sample. When the temperature of the sample is raised from room temperature to 20 ° C./min in air, held at 230 ° C., and left for 150 minutes after the temperature rise, the weight loss rate becomes 0.005% by weight / min or less and the weight stabilizes. The residual weight was measured. The value obtained by subtracting the residual weight from the weighed weight at the start of thermogravimetric analysis was taken as the total reduced weight. The ratio of the total weight loss to the weight at the start of thermogravimetric analysis was calculated and used as the weight loss rate. The results are shown in Table 1.

(3. Weight loss rate)
Above 2. The weight loss rate (%) per hour (minutes) at the time when the weight loss of 50% was reached was defined as the weight loss rate (% / min) when the total weight loss obtained in the process of measurement was 100%. The results are shown in Table 1.

(4. Crystallization start temperature / Cp)
For the measurement of the crystallization start temperature Cp of the polyoxymethylene resin composition, the constituent polyoxymethylene resin composition was collected from the polyoxymethylene resin molded product obtained in the same manner as described above, and this was used as a sample to indicate the difference manufactured by NETZSCH. Formula scanning calorimeter: Measured using a DSC350. The measurement conditions include a sample set at a display temperature of 50 ° C., a temperature rise to 210 ° C. at 20 ° C./min, holding at 210 ° C. for 5 minutes, and then lowering the temperature to 100 ° C. at 20 ° C./min. The start temperature (onset) was defined as the crystallization start temperature. The results are shown in Table 1.

(5. Average particle size of inorganic substances)
For the measurement of the average particle size of the inorganic substance, the constituent polyoxymethylene resin composition was collected from the polyoxymethylene resin molded product obtained in the same manner as described above, and this was used as a sample. HFIP (1,1,1,3,3,3-hexafluoro-2-propanol / manufactured by Central Glass Co., Ltd.) was added to this sample, allowed to dissolve overnight at room temperature, and gently shaken, and then 0.1 μm. Filtering was performed with the PTFE cartridge filter of. _{The separated inorganic substances were washed and separated on a filter, and an average diameter D 50} with a cumulative weight of 50% was measured using a Shimadzu SALD-2000 particle size distribution measuring device using a laser diffraction / scattering method. The results are shown in Table 1.

<Evaluation of polyoxymethylene resin composition>
Regarding the polyoxymethylene resin composition constituting the polyoxymethylene resin molded product used in Examples and Comparative Examples, the productivity of the polyoxymethylene resin contained in the polyoxymethylene resin composition and the production of the polyoxymethylene resin composition. The sex was evaluated. The evaluation results are shown in Table 2.

(1. Productivity evaluation of polyoxymethylene resin)
The productivity evaluation of the polyoxymethylene resin was comprehensively performed based on the average granulation amount of the polyoxymethylene resin per unit time in the (granulation step), the state of the strands, and the appearance quality and odor of the pellets. As a guideline for evaluation, a commercially available polyacetal resin Tenac 4520 (manufactured by Asahi Kasei Corporation / general copolymer MFR = 9, and the number average molecular weight was measured by the same method as described above, Mn was 75,000. Was compared with the productivity when the (granulation step) was performed instead of the stabilized polyoxymethylene resin (A). The evaluation results are shown in Table 2.
((Evaluation criteria))
◯: When it is good compared to the productivity of the reference example ◇: When it is at the same level as the productivity of the reference example △: When it is slightly lower than the productivity of the reference example X: When the productivity is lower than that of the reference example The above "good" means that the increase in the average granulation amount per unit time is 20% by mass or more when compared with the reference example. Say.
The above-mentioned "equivalent level" means a state in which the increase in the average granulation amount per unit time is more than -20% by mass and less than 20% by mass when compared with the reference example.
The above-mentioned "slight decrease" means that the decrease in the average granulation amount per unit time is 20% by mass or less and less than 50% by mass, or the obtained strand has no blisters or breaks when compared with the reference example. It is a state in which stable winding is possible and workability is not deteriorated, but the obtained pellets have some facets or odors.
The above-mentioned "decrease" means that, when compared with the reference example, the decrease in the average granulation amount per unit time is 50% or more, or the obtained strand has blisters or breaks, and stable winding is not possible. It refers to what was possible, and the pellets obtained had many facets and a strong odor.

(2. Productivity evaluation of polyoxymethylene resin composition)
The productivity evaluation of the polyoxymethylene resin composition was comprehensively carried out based on the state and odor of the flakes of the polyoxymethylene resin composition for molding obtained in the manufacturing process of the composition. The evaluation results are shown in Table 2.
((Evaluation criteria))
◯: When the inorganic substance and polyoxymethylene resin are integrated and the odor is not a concern ◇: When some separated inorganic substance powder is seen or some odor is felt △: Separated inorganic substance When powder is seen or a strong odor is felt ×: When the inorganic substance and polyoxymethylene resin are not uniformly integrated

<Evaluation of polyoxymethylene resin molded product>
The productivity, quality, and dimensional stability of the polyoxymethylene resin molded products used in Examples and Comparative Examples were evaluated. The evaluation results are shown in Table 2.

(1. Productivity of molded product)
The productivity of the polyoxymethylene resin molded product was evaluated based on the state of formation of the mold deposit (MD) on the mold in the manufacturing process of the molded product.
◯: When MD to the mold after 200 shots was hardly seen ◇: When MD to the mold after 200 shots was seen in the gas vent △: MD to the mold after 200 shots When it is confirmed in the cavity, but it can be easily removed with water etc. ×: When MD to the mold after 200 shots is confirmed in the cavity and it cannot be easily removed.

(2. Quality of molded product)
The quality of the polyoxymethylene resin molded product was evaluated by observing the obtained flat plate-shaped molded product. The evaluation was carried out by sampling N = 5 from the 50th shot of molding. The evaluation results are shown in Table 2.
◯: When there is no blistering, silver, color unevenness, etc. on the surface of the molded body and sufficient texture is obtained ◇: When some blistering, silver, color unevenness, etc. are confirmed on the surface of the molded body △: The surface of the molded body When obvious blisters, silver, color unevenness, etc. are confirmed, or when the texture is slightly impaired ×: When the shape of the molded product is not stable or the texture is impaired (3. Dimensional stability of the molded product) sex)
The dimensional stability of the polyoxymethylene resin molded product was evaluated by changing the dimensions of the obtained plate-shaped molded product. Specifically, the product dimensions were measured after being left in an oven at 80 ° C. for 24 hours after molding, and the rate of change with respect to the mold dimension of 50 mm in the length direction was determined. The evaluation was carried out by sampling N = 5 from the 50th shot of molding. The evaluation results are shown in Table 2.
◯: When the dimensional change rate is less than 1.2% with respect to the mold dimensions ◇: When the dimensional change rate is 1.2% or more and less than 1.4% with respect to the mold dimensions Δ: The dimensional change rate is When 1.4% or more and less than 1.6% with respect to the mold dimensions ×: When the dimensional change rate is 1.6% or more with respect to the mold dimensions

[Examples 1 to 3, Comparative Examples 1 and 2]
The polyoxymethylene resin compositions used in Examples 1 to 3 and Comparative Examples 1 and 2 are shown in Table 1, and the evaluation results are shown in Table 2.
From these results using the resin compositions P1 to P5 having different weight reduction rates, the polyoxymethylene resin molded product obtained by setting the resin composition to the weight reduction rate specified in the present embodiment has the quality and quality. It can be seen that while improving the appearance, it is possible to maintain sufficient productivity for practical use and improve the dimensional accuracy and quality of the molded product.
On the other hand, if the weight reduction rate of the resin composition is smaller than the specification of the present embodiment, the texture of the molded product is deteriorated, and if it is too large, the composition cannot be obtained or it becomes difficult to maintain the shape of the molded product. It can be seen that it shows a tendency to do.

[Examples 2, 4 to 6, Comparative Example 3]
The polyoxymethylene resin compositions used in Examples 2, 4 to 6 and Comparative Example 3 are shown in Table 1, and the evaluation results thereof are shown in Table 2.
From these results using the resin compositions P3 and P6 to P9 having different weight reduction rates, the polyoxymethylene resin molded product obtained by setting the resin composition to the weight reduction rate specified in the present embodiment can be obtained. While improving the quality and appearance, it tends to be possible to maintain sufficient productivity for practical use and improve the dimensional accuracy and quality of the molded product.
On the other hand, it can be seen that when the weight reduction rate of the resin composition is larger than the specified value, it tends to be difficult to maintain the quality and appearance of the molded product.

[Examples 2, 7, 8, Comparative Examples 4, 5]
The polyoxymethylene resin compositions used in Examples 2, 7, 8 and Comparative Examples 4 and 5 are shown in Table 1, and the evaluation results thereof are shown in Table 2.
Based on these results using resin compositions P3 and P10 to P13 having different number average molecular weights of the contained polyoxymethylene resins, the polyoxymethylene resin was set to the number average molecular weight specified in the present embodiment. It can be seen that the obtained polyoxymethylene resin molded product tends to be able to maintain sufficient productivity for practical use while improving the quality and appearance, and to improve the dimensional accuracy and quality of the molded product.
On the other hand, if the number average molecular weight of the polyoxymethylene resin contained in the resin composition is larger than the specified value, it becomes difficult to maintain the quality and appearance of the molded product, and if it is smaller, the productivity of the polyoxymethylene resin tends to decrease. It can be seen that

[Examples 2, 9 to 12]
The polyoxymethylene resin compositions used in Examples 2 and 9 to 12 are shown in Table 1, and the evaluation results thereof are shown in Table 2.
From these results using the resin compositions P3 and P14 to P17 having different crystallization start temperatures, the polyoxymethylene resin molding obtained by setting the resin composition to a preferable crystallization start temperature specified in the present embodiment. It can be seen that the body tends to be able to maintain sufficient productivity for practical use and improve the dimensional accuracy and quality of the molded product while improving the quality and appearance.
On the other hand, it can be seen that when the crystallization start temperature of the resin composition deviates from the specified value, it tends to be difficult to maintain productivity.

[Examples 2, 13 to 15]
The polyoxymethylene resin compositions used in Examples 2 and 13 to 15 are shown in Table 1, and the evaluation results thereof are shown in Table 2.
From these results using the resin compositions P3 and P18 to P20 having different types and blending ratios of the additives, the resin composition was obtained by containing two or more kinds of formaldehyde scavengers specified in the present embodiment. It can be seen that the polyoxymethylene resin molded product tends to be able to maintain sufficient productivity for practical use and improve the dimensional accuracy and quality of the molded product while improving the quality and appearance.

[Examples 2, 16, 17]
The polyoxymethylene resin compositions used in Examples 2, 16 and 17 are shown in Table 1, and the evaluation results thereof are shown in Table 2.
From these results using resin compositions P3, P21, and P22 having different types of inorganic substances, the polyoxymethylene resin molded product obtained by using the polyoxymethylene resin composition of the present embodiment has a quality and quality. It can be seen that while improving the appearance, it is possible to maintain sufficient productivity for practical use and improve the dimensional accuracy and quality of the molded product.

The polyoxymethylene resin molded body of the present embodiment is a mechanical part or a sliding part in fields such as precision equipment, home appliances / OA equipment, automobiles, industrial applications and miscellaneous goods; design parts such as emblems and logo marks; balancers, weights and the like. Specific gravity adjusting parts; Drive equipment / acoustic equipment and surrounding covers and cases; Precision parts such as OA equipment and optical equipment; Containers that control X-rays and electromagnetic waves; Heat dissipation plates and heat insulating plates; Ceramics / pottery parts It can be suitably used as a substitute for metal parts and the like.
The polyoxymethylene resin molded product of the present embodiment can also be used as an injection molded product (green part) as an intermediate product for a sintered product for manufacturing a sintered product (white part) such as a metal part or a ceramic part. It can be preferably used.
The polyoxymethylene resin composition of the present embodiment can be used for producing a polyoxymethylene resin molded product of the present embodiment that can be suitably used for the above-mentioned applications.

Claims (6)

A polyoxymethylene resin composition for sintered products containing an inorganic substance and a polyoxymethylene resin.
The contained polyoxymethylene resin has a number average molecular weight of 30,000 to 65,000.
The weight loss rate measured by thermogravimetric analysis by holding in air at 230 ° C. for 150 minutes was 5 to 30%.
Ri weight loss rate is 4.4% / min der less at weight loss reaching 50% when the weight loss corresponding to the weight reduction rate is 100%,
The inorganic substances include aluminum (excluding aluminum hydroxide), cobalt, zinc, copper, nickel, iron, silicon, titanium, tungsten, and metal compounds and alloys based on these, or zinc oxide. aluminum oxide, zirconia, hydroxyapatite, silicon carbide, silicon nitride, and wherein boron nitride, fluorite, steatite, barium titanate, lead zirconate titanate, at least one der Rukoto selected from the group consisting of ferrite Polyoxymethylene resin composition. The polyoxymethylene resin composition according to claim 1, which has a crystallization start temperature of 142 ° C. to 154 ° C. The polyoxymethylene resin composition according to claim 1 or 2, further comprising two or more types of formaldehyde scavengers. The polyoxymethylene resin composition according to any one of claims 1 to 3, wherein the inorganic substance contains a metal. The polyoxymethylene resin composition according to any one of claims 1 to 3, wherein the inorganic substance contains ceramics. An injection-molded product as an intermediate product for a sintered product , which comprises the polyoxymethylene resin composition according to any one of claims 1 to 5.

Images