JP6978906B2 - Polyacetal resin composition - Google Patents

Description

The present invention relates to a polyacetal resin composition.

Polyacetal resin is a crystalline resin and has excellent rigidity, strength, toughness, slidability, and creepability. Therefore, it has been conventionally used as a material for mechanical parts such as automobile parts, electric / electronic parts, and industrial parts. , Widely used.

In recent years, the applications of polyacetal resins have expanded and diversified, and the demand for quality has increased accordingly. Further, particularly in applications in a high temperature environment, thermal stability and long-term heat resistance aging (property that can maintain practically sufficient mechanical properties when left in a high temperature environment for a long period of time) are required. However, the conventional polyacetal resin has not reached a level that satisfies the requirement, and its use is currently limited.

As a conventional method for preventing deterioration of a molded product made of a polyacetal resin, a method of blending an additive such as a heat stabilizer or an antioxidant with the polyacetal resin is known. For example, Patent Document 1 proposes a ternary combination of amine-substituted triazines, sterically hindered phenol, and a metal-containing compound as a compounding component in a polyacetal resin. Further, Patent Document 2 proposes improvement of long-term heat-resistant aging property of a polyacetal resin by using three kinds of antioxidants in combination with a fatty acid calcium salt. Further, Patent Document 3 discloses an improvement by a combined use of a hindered phenol compound and an alkaline earth metal salt or an alkaline earth metal hydroxide of a carboxylic acid having 10 to 20 carbon atoms. Further, Patent Document 4 proposes an improvement using a hindered phenol compound and an alkaline earth metal salt of an aliphatic carboxylic acid having 22 to 36 carbon atoms.

On the other hand, in the field of automobile interior parts, there is an increasing demand for reducing the amount of volatile organic compounds (VOCs) such as formaldehyde released from molded products made of polyacetal resin.

As a means for reducing the amount of formaldehyde emitted from a polyacetal resin molded product, a technique for adding various additives is known. For example, a technique for adding a polyamide and a hydrazine derivative to a polyacetal resin (Patent Document 5), hydrazide. So far, a technique for adding a compound (Patent Document 6) and a technique for adding a nitrogen compound selected from melamine, a melamine derivative and a dicarboxylic acid hydrazide (Patent Document 7) have been proposed.
In addition, Patent Document 8 proposes the addition of a fatty acid metal salt in order to improve the acid resistance of a polyacetal resin molded product.

Special Publication No. 62-58387 Japanese Unexamined Patent Publication No. 2-209444 Special Publication No. 55-22508 Special Publication No. 60-56748 Japanese Unexamined Patent Publication No. 51-11857 Japanese Unexamined Patent Publication No. 4-345648 Japanese Patent No. 3024802 Japanese Patent No. 5297640

By the way, in recent years, in molding using polyacetal resin, there is an increasing demand for miniaturization, thinning, and precision of molded products. Therefore, there are cases where a molding method and condition setting that require a heat history more than before are adopted. is increasing. Examples of the molding method include molding with a pingate mold, high cycle molding, molding of small, thin-walled, and precision parts using a high-viscosity polyacetal resin. In these molding methods, the resin receives a higher thermal history than the usual molding method by increasing the shear rate and increasing the screw rotation and the molding temperature in order to shorten the plasticization time. Also, in other general molding methods, for example, when molding defects such as flow marks, weld lines, and jetting occur, it is often dealt with by raising the resin temperature, and this response is also higher. It becomes a factor that takes heat history. Further, when the hot runner mold is used, the resin temperature may rise due to the partial retention of the resin, and a higher heat history may be applied.
Based on the above, it is even more important to satisfy the above-mentioned requirements even when the polyacetal resin receives a higher thermal history.

Here, the fatty acid metal salt as used in the techniques described in Patent Documents 2 to 4 can contribute to the improvement of the long-term heat-resistant aging property of the polyacetal resin composition. However, if the amount of the fatty acid metal salt added is increased, there causes a problem that the resin is easily decomposed due to the heat history at the time of extrusion or the above-mentioned molding. In particular, the fatty acid metal salt as described above is a resin due to partial retention of the resin such as when small, thin-walled, precision part molding by a pingate mold or the like is adopted, or by molding using a hot runner mold or the like. When molding that can increase the temperature is adopted, decomposition may be further accelerated depending on the type of fatty acid or metal salt. This disassembly causes mold contamination (mold deposit), and causes problems such as poor appearance of the product and frequent mold maintenance. Therefore, in the above-mentioned prior art, the amount of the fatty acid metal salt used is limited.

Further, in the techniques described in Patent Documents 5 to 7, the disclosed additives cause mold contamination during molding and bleeding (precipitation) on the surface of the molded product, resulting in poor product appearance and frequent mold maintenance. Causes problems such as cost increase due to.
Further, in the technique described in Patent Document 8, there is room for improvement in terms of improving thermal stability and, by extension, suppressing the amount of formaldehyde generated.

From these facts, there is a demand for a polyacetal resin composition having an excellent balance between long-term heat resistance aging property, thermal stability, and mold stain resistance.

Therefore, the present invention can produce a molded product having less thermal decomposition of the polyacetal resin even in a high temperature environment, excellent long-term heat resistance aging property, and a reduced formaldehyde emission amount, and has a polyacetal resin composition with less mold contamination. The purpose is to provide things.

As a result of diligent research to solve the above-mentioned problems of the prior art, the present inventors added a nitrogen-containing hindered phenol compound and a nitrogen-free hindered phenol compound to the polyacetal resin in a specific ratio. Further, it was found that the long-term heat-resistant aging property can be improved and problems such as thermal stability in a high temperature environment can be solved by adding a predetermined metal salt in a specific ratio, and the present invention has been completed. rice field.

That is, the present invention is as follows.
[1]
(A) 100 parts by mass of polyacetal resin, (B) 0.001 to 0.2 parts by mass of nitrogen-containing hindered phenol compound, and (C) 0.001 to 0.4 parts by mass of nitrogen-free hindered phenol compound. , (D) A polyacetal resin composition containing 0.001 to 0.1 parts by mass of a calcium salt of a long-chain fatty acid having 22 to 30 carbon atoms.
[2]
The polyacetal resin composition according to [1], wherein the content of the (B) nitrogen-containing hindered phenol compound is 0.001 to 0.15 parts by mass with respect to 100 parts by mass of the (A) polyacetal resin.
[3]
(B) The polyacetal resin composition according to [1] or [2], wherein the nitrogen-containing hindered phenol compound contains a hydrazine structure.
[4]
The polyacetal resin composition according to any one of [1] to [3], wherein the calcium salt of the (D) long-chain fatty acid is calcium montanate.
[5]
(E) The polyacetal resin composition according to any one of [1] to [4], further containing 0.0001 to 0.01 parts by mass of calcium stearate.
[6]
(F) The stabilizer further contains at least one selected from the group consisting of an amino-substituted triazine compound, a urea derivative, a hydrazide derivative, an amide compound, a polyamide, and an acrylamide copolymer, according to [1] to [5]. The polyacetal resin composition according to any one.

According to the present invention, a polyacetal resin composition capable of producing a molded product having less thermal decomposition of the polyacetal resin even in a high temperature environment, excellent long-term heat resistance aging property, and a reduced formaldehyde emission amount, and less mold contamination. Can provide things.

Hereinafter, embodiments for carrying out the present invention (hereinafter, may be referred to as “the present embodiment”) will be described in detail.
The present invention is not limited to the following embodiments, and can be variously modified and implemented within the scope of the gist thereof.

[Polyacetal resin composition]
The polyacetal resin composition of the present embodiment is
(A) 100 parts by mass of polyacetal resin and
(B) Nitrogen-containing hindered phenol compound 0.001 to 0.2 parts by mass and
(C) Nitrogen-free hindered phenol compound 0.001 to 0.4 parts by mass and
(D) It is characterized by containing 0.001 to 0.1 parts by mass of a calcium salt of a long-chain fatty acid having 22 to 30 carbon atoms. Further, the polyacetal resin composition of the present embodiment may contain (E) calcium stearate, (F) stabilizer, and other additives, if necessary.

Hereinafter, each component constituting the polyacetal resin composition of the present embodiment will be described.

[(A) Polyacetal resin]
The (A) polyacetal resin contained in the polyacetal resin composition of the present embodiment refers to a polymer having an oximethylene group in the main chain, for example, a formaldehyde monomer, or a trimer (trioxane) or a tetramer thereof. Polyacetal homopolymer consisting substantially only of oximethylene units obtained by homopolymerizing a cyclic oligomer of formaldehyde such as (tetraoxane); formaldehyde monomer or its trimer (trioxane), tetramer (tetraoxane), etc. Formaldehyde cyclic oligomers are copolymerized with glycols such as ethylene oxide, propylene oxide, epichlorohydrin, 1,3-dioxolane and 1,4-butanediolformal, cyclic ethers such as diglycol cyclic formal, or cyclic formal. Examples thereof include the obtained polyacetal copolymer; a polyacetal copolymer having a branch obtained by copolymerizing a monofunctional glycidyl ether; and a polyacetal copolymer having a crosslinked structure obtained by copolymerizing a polyfunctional glycidyl ether.

Further, as the (A) polyacetal resin, a formaldehyde monomer or a trimer (trioxane) or a tetramer thereof (trioxane) or a tetramer thereof (in the presence of a compound having a functional group such as a hydroxyl group at both ends or one end, for example, polyalkylene glycol) Polyacetal homopolymer having a block component obtained by polymerizing a cyclic oligomer of formaldehyde such as tetraoxane); a single amount of formaldehyde in the presence of a compound having a functional group such as a hydroxyl group at both ends or one end, for example, hydrogenated polybutadiene glycol. Polyacetal copolymers having a block component obtained by copolymerizing a cyclic oligomer of formaldehyde such as a compound or a trimer (trioxane) or a tetrameric (tetraoxane) thereof with a cyclic ether or a cyclic formal can also be used.

<Polyacetal homopolymer>
The polyacetal homopolymer is produced by feeding, for example, a monomer formaldehyde, a chain transfer agent (molecular weight modifier) and a polymerization catalyst to a polymerization reactor into which a hydrocarbon-based polymerization solvent is introduced and polymerizing by a slurry polymerization method. can do.
At this time, since the raw material monomer, the chain transfer agent, and the polymerization catalyst may contain chain transferable components (components that generate unstable terminal groups) such as water, methanol, and formic acid, these chain transferable components are possible first. It is preferable to adjust the content of various components. The content of these chain transferable components is preferably in the range of 1 to 1000 ppm, more preferably 1 to 500 ppm, still more preferably 1 to 300 ppm with respect to formaldehyde as a monomer. By adjusting the content of the chain transferable component within the above range, a polyacetal resin homopolymer having excellent thermal stability can be obtained.

The molecular weight of the polyacetal homopolymer can be adjusted by chain transfer using a molecular weight modifier such as carboxylic acid anhydride or carboxylic acid. As the molecular weight modifier, propionic anhydride and acetic anhydride are particularly preferable, and acetic anhydride is more preferable.
The amount of the molecular weight modifier introduced is adjusted and determined according to the characteristics (particularly melt flow rate) of the target polyacetal homopolymer. For example, polyacetal homopolymers preferably have a melt flow rate (MFR value (based on ISO1133)) in the range of 0.1 to 100 g / 10 min, 1.0 g / 10 min to 70 g / 10. It is more preferable to make it within the range of minutes. By setting the MFR value of the polyacetal homopolymer in the above range, a polyacetal homopolymer having excellent mechanical strength can be obtained.

As the polymerization catalyst, an anionic polymerization catalyst is preferable, and the following general formula (I):
_{[R 1 R 2 R 3 R} 4 M] + X - ··· (I)
(In formula (I), R ₁ , R ₂ , R ₃ and R ₄ each independently represent an alkyl group, M represents an element having a lone pair of electrons, and X represents a nucleophilic group. ) Is more preferable.

Among onium salt-based polymerization catalysts, quaternary phosphonium salt-based compounds such as tetraethylphosphonium iodide and tributylethylphosphonium iodide, and quaternary ammonium salt-based compounds such as tetramethylammonium bromide and dimethyldistearylammonium acetate. Compounds are preferred.

The amount of the onium salt-based polymerization catalyst such as the quaternary phosphonium salt-based compound and the quaternary ammonium salt-based compound is preferably 0.0003 to 0.01 mol, more preferably 0.003 to 0.01 mol, based on 1 mol of formaldehyde. It is 0.0008 to 0.005 mol, more preferably 0.001 to 0.003 mol.

The hydrocarbon-based polymerization solvent may be any solvent that does not react with formaldehyde, and is not particularly limited. For example, a solvent such as pentane, isopentane, hexane, cyclohexane, heptane, octane, nonane, decane, and benzene. However, hexane is particularly preferable. As these hydrocarbon solvents, only one kind may be used alone, or two or more kinds may be mixed and used.

In the production of polyacetal homopolymers, it is preferable to first obtain crude polyacetal homopolymers by polymerization, and then to perform stabilization treatment on unstable terminal groups as described later.

The polymerization reactor for producing a crude polyacetal homopolymer is particularly limited as long as it is a device capable of simultaneously supplying a monomer formaldehyde, a chain transfer agent (molecular weight modifier) and a polymerization catalyst, and a hydrocarbon-based polymerization solvent. However, from the viewpoint of productivity, a continuous polymerization reactor is preferable.

The crude polyacetal homopolymer obtained by polymerization has a thermally unstable terminal group. Therefore, it is preferable to seal the unstable terminal group with an esterifying agent, an etherifying agent or the like and perform a stabilizing treatment.

For the stabilization treatment of the terminal groups of the crude polyacetal homopolymer by esterification, for example, the crude polyacetal homopolymer, the esterifying agent and the esterification catalyst are put into a terminal stabilizing reactor into which a hydrocarbon solvent is introduced. , Can be done by reacting. The reaction temperature and reaction time at this time are not limited, but for example, the reaction temperature is preferably 130 to 155 ° C, the reaction time is preferably 1 to 100 minutes, and the reaction temperature is 135 to 155 ° C. The reaction time is more preferably 5 to 100 minutes, the reaction temperature is 140 to 155 ° C., and the reaction time is further preferably 10 to 100 minutes.

As an esterifying agent that seals and stabilizes the terminal group of the crude polyacetal homopolymer, the following general formula (II):
R ₅ COOCOR ₆ ... (II)
(In formula (II), R ₅ and R ₆ each independently represent an alkyl group. R ₅ and R ₆ may be the same or different.) Can be used.

Examples of the esterifying agent include, but are not limited to, benzoic anhydride, succinic anhydride, maleic anhydride, glutaric anhydride, phthalic anhydride, propionic anhydride, and acetic anhydride, which are preferable. Is acetic anhydride. These esterifying agents may be used alone or in combination of two or more.

As the esterification catalyst, an alkali metal salt of a carboxylic acid having 1 to 18 carbon atoms is preferable, and the addition amount thereof can be appropriately selected in the range of 1 to 1000 ppm with respect to the polyacetal homopolymer. The alkali metal salt of the carboxylic acid having 1 to 18 carbon atoms is not limited to the following, and is, for example, formic acid, acetic acid, propionic acid, butyric acid, valeric acid, capric acid, enant acid, capric acid, and pelargonic acid. , Alkali metal salts of carboxylic acids such as capric acid, lauric acid, myristic acid, palmitic acid, margaric acid, stearic acid and the like, and examples of the alkali metal include lithium, sodium, potassium, rubidium and cesium. Among these carboxylic acid metal salts, lithium acetate, sodium acetate, and potassium acetate are preferable.

Examples of the etherifying agent for blocking and stabilizing the terminal group of the crude polyacetal homopolymer include an orthoester of an aliphatic or aromatic acid and an aliphatic, alicyclic or aromatic alcohol, for example, methyl ortho. It can be selected from formate or ethyl orthoformate, methyl orthoacetate or ethyl orthoacetate, methyl orthobenzoate or ethyl orthobenzoate, and orthocarbonate, specifically ethyl orthocarbonate, p-toluenesulfonic acid, acetic acid and Stabilization can be carried out using medium-strength organic acids such as oxalic acid and Lewis acid-type catalysts such as medium-strength mineral acids such as dimethylsulfate and diethylsulfate.

The solvent used for the etherification reaction when the terminal group of the crude polyacetal homopolymer is sealed and stabilized by etherification is not limited to the following, but is not limited to the following, but for example, low boiling point fats such as pentane and hexane. Examples thereof include group organic solvents; alicyclic organic solvents such as cyclohexane; aromatic organic solvents such as benzene; halogenated lower aliphatic solvents such as methylene chloride, chloroform and carbon tetrachloride; and the like.

The polyacetal homopolymer whose end group is stabilized by the above method is sealed with air or nitrogen gas adjusted to 100 to 150 ° C. using a dryer such as a hot air dryer or a vacuum dryer to remove water. And drying to obtain (A) a polyacetal homopolymer as a polyacetal resin.

<Polyacetal copolymer>
The polyacetal copolymer is not limited to the following, and uses, for example, glycols such as 1,3-dioxolane and 1,4-butanediolformal as comonomers, cyclic ethers of diglycols or cyclic formals, and trioxane and the like. Can be produced by copolymerizing with the above-mentioned monomer using a polymerization catalyst.

The proportion of the comonomer to be copolymerized is preferably 0.03 to 20 mol%, more preferably 0.03 to 7 mol%, still more preferably 0.04 to 3 mol% with respect to 1 mol of formaldehyde. .. When the proportion of comonomer is in the above range, polyacetal resin pellets having higher mechanical strength can be obtained.

Examples of the polymerization catalyst include, but are not limited to, cationically active catalysts such as Lewis acid, protonic acid and esters thereof or anhydrides thereof.
Lewis acids include, but are not limited to, halides of boric acid, tin, titanium, phosphorus, arsenic and antimony, specifically boron trifluoride, tin tetrachloride, tetrachloride. Examples thereof include titanium chloride, phosphorus pentafluoride, phosphorus pentachloride, antimony pentafluoride and complex compounds or salts thereof.
The protonic acid and its ester or anhydride are not limited to the following, but are not limited to, for example, percrolic acid, trifluoromethanesulfonic acid, perchlorolic acid-quaternary butyl ester, acetylparklorate, and trimethyloxonium hexa. Fluorophosphate and the like can be mentioned.
Among these, boron trifluoride, boron trifluoride hydrate, and a coordination complex compound of boron trifluoride and an organic compound containing an oxygen atom or a sulfur atom are preferable, for example, boron trifluoride diethyl ether. Boron trifluoride di-n-butyl ether is mentioned as more preferable.

^{The amount of boron trifluoride added is preferably 0.10 × 10 -4} mol or less, ^{more preferably 0.07 × 10 -4} mol or less, and 0.03 with respect to 1 mol of formaldehyde. It is more preferably ~ 0.05 × 10 ^{-4 mol.} When the amount of boron trifluoride added is in the above range, a polyacetal resin composition having excellent thermal stability can be provided.

The method for polymerizing the polyacetal copolymer is not particularly limited, and examples thereof include a massive polymerization method in addition to the slurry polymerization method described above for producing a polyacetal homopolymer. Further, the polymerization of the polyacetal copolymer can be applied by either a batch type or a continuous type.

The polymerization reactor is not particularly limited, and examples thereof include a self-cleaning type extrusion kneader such as a conider, a twin-screw type continuous extrusion kneader, and a twin-screw paddle type continuous mixer. The molten monomer is supplied to the above-mentioned polymerization reactor to obtain a solid massive polyacetal copolymer as the polymerization progresses.

The resulting polyacetal copolymer may have a thermally unstable terminal [-(OCH ₂ ) _n- OH group]. Therefore, it is preferable to carry out the decomposition removal treatment of the unstable end portion. Decomposition and removal of the unstable end portion can be performed by a known method.

As described above, in the present embodiment, the (A) polyacetal resin is not limited, and both polyacetal homopolymers and polyacetal copolymers can be used. Of these, polyacetal comopolymer is preferable.

[(B) Nitrogen-containing hindered phenol compound]
The polyacetal resin composition of the present embodiment contains (B) a nitrogen-containing hindered phenol compound. Here, the nitrogen-containing hindered phenol compound refers to a hindered phenol compound containing at least one nitrogen atom in its structural formula. Further, the hindered phenol compound refers to a phenol compound having a tertiary alkyl group at at least one ortho position of the hydroxyl group.

(B) The nitrogen-containing hindered phenol compound is not limited to the following, but is, for example, 1,2-bis [3- (4-hydroxy-3,5-di-t-butylphenyl) propionyl]. Hydradin, N, N'-hexamethylenebis [3- (3,5-di-t-butyl-4-hydroxyphenyl) propanamide], 1,3,5-tris [[3,5-bis (1,5-bis) 1-dimethylethyl) -4-hydroxyphenyl] methyl] -1,3,5-triazine-2,4,6 (1H, 3H, 5H) -trione, 4-[[4,6-bis (octylthio)- 1,3,5-triazin-2-yl] amino] -2,6-di-t-butylphenol and the like can be mentioned.

Among these nitrogen-containing hindered phenol compounds, 1,2-bis [3- (4-hydroxy-3,5-di-t-butylphenyl) propionyl] hydrazine, N, N'-hexamethylenebis [3-( 3,5-di-t-butyl-4-hydroxyphenyl) propanamide], is preferred. On the other hand, (B) the nitrogen-containing hindered phenol compound preferably contains a hydrazine structure. Based on these, as the (B) nitrogen-containing hindered phenol compound, 1,2-bis [3- (4-hydroxy-3,5-di-t-butylphenyl) propionyl] hydrazine is more preferable.

(B) The melting point of the nitrogen-containing hindered phenol compound is preferably 50 to 300 ° C, more preferably 100 ° C to 300 ° C, and further preferably 150 to 250 ° C from the viewpoint of further improving the thermal stability of the polyacetal resin composition. preferable.

The polyacetal resin composition of the present embodiment contains (B) a nitrogen-containing hindered phenol compound in a proportion of 0.001 to 0.2 parts by mass with respect to 100 parts by mass of the above-mentioned (A) polyacetal resin. Surprisingly, the present inventor has found from research that the content of (B) nitrogen-containing hindered phenol compound has an appropriate range in terms of the effect of improving thermal stability. When the content of (B) the nitrogen-containing hindered phenol compound is within the above range, it is possible to provide a polyacetal resin composition having less mold contamination and excellent thermal stability.
The content of the (B) nitrogen-containing hindered phenol compound in the polyacetal resin composition of the present embodiment is preferably 0.005 part by mass or more with respect to 100 parts by mass of the (A) polyacetal resin. It is more preferably 01 parts by mass or more, preferably 0.15 parts by mass or less, and more preferably 0.1 parts by mass or less.

The content of the (B) nitrogen-containing hindered phenol compound in the polyacetal resin composition of the present embodiment is measured, for example, by freeze-grinding pellets of the polyacetal resin composition and extracting socksley with a solvent such as chloroform. , GCMS, or ¹ H-NMR.

[(C) Nitrogen-free hindered phenol compound]
The polyacetal resin composition of the present embodiment contains (C) a nitrogen-free hindered phenol compound. Here, the nitrogen-free hindered phenol compound refers to a hindered phenol compound whose structural formula does not contain a nitrogen atom. Hindered phenolic compounds are generally known as antioxidants, but in this embodiment, both nitrogen-containing and nitrogen-free compounds are used in combination, which results in very good thermal stability and thus very good thermal stability. Achieve reduction of mold contamination.

(C) The nitrogen-free hindered phenol compound is not limited to the following, but is, 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-Butandiol-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. 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, more preferably
Triethylene glycol-bis- [3- (3-t-butyl-5-methyl-4-hydroxyphenyl) -propionate].

(C) The melting point of the nitrogen-free hindered phenol compound is preferably 30 to 120 ° C, more preferably 50 ° C to 120 ° C, and more preferably 50 to 100 ° C from the viewpoint of further improving the thermal stability of the polyacetal resin composition. More preferred.

The polyacetal resin composition of the present embodiment contains (C) a nitrogen-free hindered phenol compound in a proportion of 0.001 to 0.4 parts by mass with respect to 100 parts by mass of the above-mentioned (A) polyacetal resin. (C) When the content of the nitrogen-free hindered phenol compound is within the above range, a polyacetal resin composition having excellent thermal stability can be provided. From the same viewpoint, the content of the (C) nitrogen-free hindered phenol compound in the polyacetal resin composition of the present embodiment is 0.05 to 0.3 parts by mass with respect to 100 parts by mass of the (A) polyacetal resin. It is preferable to have.

The content of the (C) nitrogen-free hindered phenol compound in the polyacetal resin composition of the present embodiment was measured, for example, by freeze-grinding pellets of the polyacetal resin composition and extracting socksley with a solvent such as chloroform. Later, it can be carried out by ^{GCMS or 1 H-NMR.}

[(D) Calcium salt of long-chain fatty acid having 22 to 30 carbon atoms]
The polyacetal resin composition of the present embodiment contains (D) a calcium salt of a long-chain fatty acid having 22 to 30 carbon atoms (hereinafter, may be referred to as "(D) fatty acid calcium"). By using a long-chain fatty acid having 22 to 30 carbon atoms, heat resistance and compatibility with a polyacetal resin can be enhanced, and long-term heat resistance aging can be improved. Further, the calcium salt can reduce the thermal decomposition of the polyacetal resin, improve the long-term heat-resistant aging property, reduce the amount of formaldehyde emission, and reduce the mold contamination. As the long-chain fatty acid, saturated fatty acid is preferable, and examples thereof include behenic acid and montanic acid, and montanic acid is particularly preferable. The carbon number of the long-chain fatty acid is preferably 24 to 28, more preferably 28. The calcium fatty acid (D) is particularly preferably calcium montanate.

The polyacetal resin composition of the present embodiment contains (D) fatty acid calcium in a proportion of 0.001 to 0.1 parts by mass with respect to 100 parts by mass of the above-mentioned (A) polyacetal resin. (D) If the content of fatty acid calcium is less than 0.001 part by mass, the long-term heat resistant aging property cannot be improved, and if it is more than 0.1 part by mass, resin decomposition is likely to occur and formaldehyde. The amount of gas generated increases, and the gas causes a large amount of mold contamination. From the same viewpoint, the content of (D) fatty acid calcium in the polyacetal resin composition of the present embodiment is preferably 0.005 to 0.05 parts by mass with respect to 100 parts by mass of the (A) polyacetal resin.

[(E) Calcium stearate]
The polyacetal resin composition of the present embodiment preferably contains (E) calcium stearate. The content of calcium (E) stearate in the polyacetal resin composition of the present embodiment is preferably 0.0001 to 0.01 parts by mass with respect to 100 parts by mass of the (A) polyacetal resin, preferably 0.0005. More preferably, it is ~ 0.005 part by mass. (E) When the content of calcium stearate is within the above range, the long-term heat resistance aging property of the polyacetal resin composition can be further improved.

[(F) Stabilizer]
In the polyacetal resin composition of the present embodiment, good thermal stability is achieved by adding the above-mentioned components (B), (C), and (D) in combination, so that a stabilizer is added in addition to the composition. However, in order to further improve the thermal stability and the stability of other physical properties, various (F) stabilizers may be further contained.
Examples of the stabilizer (F) include, but are not limited to, amino-substituted triazine compounds, urea derivatives, hydrazide derivatives, amide compounds, polyamides, and acrylamide polymers. These (F) stabilizers may be used alone or in combination of two or more.

The amino-substituted triazine compound is not limited to the following, and for example, 2,4-diamino-sim-triazine, 2,4,6-triamino-sim-triazine (melamine), N-butyl melamine, and the like. N-phenylmelamine, N, N-diphenylmelamine, N, N-diallylmelamine, benzoguanamine (2,4-diamino-6-phenyl-sim-triazine), acetoganamin (2,4-diamino-6-methyl-sym) -Triazine), 2,4-diamino-6-butyl-sym-triazine and the like.

Examples of the urea derivative include, but are not limited to, N-substituted urea, urea condensate, ethylene urea, hydantoin compound, ureido compound and the like.
Examples of the N-substituted urea include, but are not limited to, methyl urea having a substituent such as an alkyl group, alkylene bisurea, and aryl substituted urea. The urea condensate is not limited to the following, and examples thereof include a condensate of urea and formaldehyde. Examples of the hydantoin compound include, but are not limited to, hydantoin, 5,5-dimethylhydantoin, 5,5-diphenylhydantoin and the like. Examples of the ureido compound include, but are not limited to, allantoin and the like.

The hydrazide derivative is not limited to the following, and examples thereof include hydrazide compounds. Examples of the hydrazide compound include a carboxylic acid monohydrazide compound, a carboxylic acid dihydrazide compound, an alkyl group-substituted monohydrazide compound, and an alkyl group-substituted dihydrazide compound, which are synthesized by a reaction between a carboxylic acid (aromatic, alicyclic) and hydrazine. And so on. The carboxylic acid may be a monocarboxylic acid, a dicarboxylic acid, or a compound having three or more carboxylic acids (polyvalent carboxylic acid). Examples of monocarboxylic acids include formic acid, acetic acid, propionic acid, butyric acid, valeric acid, caproic acid, enanthic acid, caprylic acid, lauric acid, myristic acid, palmitic acid, margaric acid, stearic acid, behenic acid, benzoic acid, Examples include salicylic acid, enanthic acid, caprylic acid, pyruvate, lactic acid and amino acids. Examples of dicarboxylic acids include oxalic acid, malonic acid, succinic acid, glutaric acid, adipic acid, pimelic acid, suberic acid, azelaic acid, sebacic acid, phthalic acid, isophthalic acid, terephthalic acid, naphthalic acid, malic acid, fumal. Examples include acid, maleic acid, tartrate acid and nitrocarboxylic acid. Examples of polyvalent carboxylic acids include mellitic acid, citric acid and aconitic acid. Examples of unsaturated carboxylic acids include oleic acid, linoleic acid, linolenic acid, arachidonic acid, docosahexaenoic acid, and eicosapentaenoic acid. Among these carboxylic acids, dicarboxylic acids such as adipic acid, sebacic acid and lauric acid are preferable. The carboxylic acid mono (di) hydrazide compounds synthesized using these carboxylic acids include, for example, carbodihydrazide, oxalic acid mono (di) hydrazide, malonic acid mono (di) hydrazide, succinic acid mono (di) hydrazide, and glutaric acid. Mono (di) hydrazide, adipic acid mono (di) hydrazide, pimelic acid mono (di) hydrazide, suberic acid mono (di) hydrazide, azelaic acid mono (di) hydrazide, sebasic acid mono (di) hydrazide, phthalic acid mono ( Di) hydrazide, isophthalic acid mono (di) hydrazide, terephthalic acid mono (di) hydrazide, 2,6-naphthalic acid mono (di) hydrazide, apple acid mono (di) hydrazide, fumaric acid mono (di) hydrazide, maleic acid Mono (di) hydrazide, tartrate mono (di) hydrazide, propionic acid monohydrazide, lauric acid monohydrazide, stearate monohydrazide, p-hydroxybenzoic hydrazine, p-hydroxybenzoic hydrazine, 1,4-cyclohexandicarboxyl Examples thereof include acid dihydrazine, acetohydrazide, acrylohydrazide, benzohydrazide, nicotine hydrazide, isonicotinohydrazide, isobutylhydrazine, oleate hydrazide and the like. Among these, as the hydrazide compound, adipic acid mono (di) hydrazide, sebacic acid mono (di) hydrazide, and lauric acid monohydrazide are preferable.

Examples of the amide compound include, but are not limited to, polyvalent carboxylic acid amides such as isophthalic acid diamide and anthranilamide.

Examples of the polyamide include polyamide resins such as nylon (registered trademark) 4-6, nylon 6, nylon 6-6, nylon 6-10, nylon 6-12, and nylon 12, and polymers thereof, for example, nylon. Examples thereof include 6 / 6-6 / 6-10 and nylon 6 / 6-12.

The acrylamide polymer is not limited to the following, but for example, acrylamide is polymerized or acrylamide is polymerized with a monomer having a vinyl group other than acrylamide by using an alkylate earth metal alcoholate as a catalyst. Examples thereof include an acrylamide polymer thus obtained. By copolymerizing acrylamide with the above-mentioned monomer having a vinyl group, a crosslinked structure can be obtained, and the extrusion productivity of the polyacetal resin composition can be improved.

Examples of the monomer having a vinyl group other than acrylamide constituting the acrylamide polymer include a monomer having one or two vinyl groups. The monomer having one vinyl group is not limited to the following, and for example, n-butyl methacrylate, isobutyl methacrylate, t-butyl methacrylate, ethyl methacrylate, cyclohexyl methacrylate, 2-ethylhexyl methacrylate, and the like. Examples thereof include cecil methacrylate, pentadecyl methacrylate, stearyl methacrylate, behenyl methacrylate, hydroxypropyl methacrylate, polypropylene glycol methacrylate, polyethylene glycol methacrylate and the like. Examples of the monomer having two vinyl groups include, but are not limited to, divinylbenzene, ethylene bisacrylamide, N, N'-methylene bisacrylamide and the like. Among these, N, N'-methylenebisacrylamide is preferable as the monomer having a vinyl group.

The amount of the monomer having a vinyl group introduced into the acrylamide polymer is preferably 0.05 to 20% by mass with respect to the total amount of the acrylamide component and the monomer having a vinyl group.

The average particle size of the acrylamide polymer is preferably 0.1 to 20 μm, more preferably 0.1 to 15 μm, and even more preferably 0.1 to 10 μm. When the average particle size of the acrylamide polymer is in the above range, a polyacetal resin composition having excellent extrusion productivity can be obtained.

Among the above (F) stabilizers, polyamide and acrylamide polymers are particularly preferable.

The amount (content) of the stabilizer added (F) is preferably 0.001 to 5 parts by mass, more preferably 0.001 to 3 parts by mass with respect to 100 parts by mass of the (A) polyacetal resin. It is preferably 0.01 to 1 part by mass, and more preferably 0.01 to 1 part by mass. (F) By setting the content of the stabilizer within the above range, a polyacetal resin composition having more excellent thermal stability can be obtained.

[Other additives]
In addition to the above-mentioned ones, the polyacetal resin composition of the present embodiment has known additives such as formic acid trapping agent, weather stabilizer, mold release agent, lubricant, conductive agent, thermoplastic resin, thermoplastic elastomer, and dyeing. It may contain a pigment, a pigment, an inorganic filler, an organic filler, or the like. These additives may be used alone or in combination of two or more.

The formic acid scavenger is not limited to the following, but is, for example, an amino-substituted triazine compound or a condensate of an amino-substituted triazine compound and formaldehyde mentioned as a specific example of (F) stabilizer, for example, melamine / formaldehyde. Condensates and the like can be mentioned.

[Manufacturing method of polyacetal resin composition]
The method for producing the polyacetal resin composition of the present embodiment is not particularly limited.
In general, (A) a polyacetal resin, (B) a nitrogen-containing hindered phenol compound, (C) a nitrogen-free hindered phenol compound, (D) fatty acid calcium, and, if necessary, the above-mentioned predetermined prescriptions described above. By mixing each component with, for example, a Henschel mixer, a tumbler, a V-shaped blender, or the like, and then kneading with a kneader such as a single-screw or multi-screw extruder, a heating roll, a kneader, or a Banbury mixer. can get. Above all, kneading by an extruder equipped with a vent depressurizing device is preferable from the viewpoint of productivity. Further, in order to stably produce a polyacetal resin composition in a large amount, a single-screw or twin-screw extruder is preferably used.
Further, without mixing in advance, each component can be continuously fed to the extruder individually or in batches of several types by a quantitative feeder or the like.
It is also possible to prepare a high-concentration masterbatch composed of each component in advance and dilute it with a polyacetal resin at the time of extrusion melt kneading.

The kneading temperature may be in accordance with the preferable processing temperature of the polyacetal resin to be used, and is generally in the range of 140 to 260 ° C, preferably in the range of 180 to 230 ° C.

〔Molding〕
The polyacetal resin composition of the present embodiment can be molded and used as a molded product. The molding method is not particularly limited, and known molding methods such as extrusion molding, injection molding, vacuum molding, blow molding, injection compression molding, decorative molding, molding of other materials, gas-assisted injection molding, and foam injection molding. , Low-pressure molding, ultra-thin wall injection molding (ultra-high-speed injection molding), in-mold composite molding (insert molding, outsert molding) and the like. Among these, the injection molding method is preferable from the viewpoint of stable productivity.

[Use]
In the polyacetal resin composition of the present embodiment, even if continuous molding is performed using, for example, a hot runner mold, the polyacetal resin is less thermally decomposed, and therefore the mold is less contaminated. Further, the polyacetal resin composition of the present embodiment has a small amount of formaldehyde emission from the obtained molded product even if it is molded under severe molding conditions.
Therefore, the polyacetal resin composition of the present embodiment can be used for molded articles for various purposes. For example, mechanical parts such as gears, cams, sliders, levers, shafts, bearings and guides; outsert molded resin parts or insert molded resin parts (chassis, trays, side plate parts); printer or copier parts. Used for digital video cameras or parts for digital video equipment; music, video or information equipment; parts for communication equipment; parts for electrical equipment; and parts for electronic equipment.

Further, the polyacetal resin composition of the present embodiment is a fuel-related part represented by a gasoline tank, a fuel pump module, valves, a gasoline tank flange, etc. as a part for an automobile; a door-related part; a seatbelt peripheral part; Combination switch parts; Suitable for switches.
Further, the polyacetal resin composition of the present embodiment can be suitably used for industrial parts typified by housing equipment.

Hereinafter, the present embodiment will be described with reference to specific examples and comparative examples thereof, but the present embodiment is not limited to the following examples.
The measurement / evaluation methods applied in the examples and comparative examples are shown below.

[Measurement / evaluation method]
<Amount of formaldehyde released from molded products>
The produced polyacetal resin pellets were molded using an IS-100GN injection molding machine manufactured by Toshiba Corporation under the setting conditions of a cylinder temperature of 220 ° C. (220 ° C. molding) and a cylinder temperature of 240 ° C. (240 ° C. molding). Molding was performed at ° C., an injection pressure of 60 MPa, an injection time of 30 seconds, and a cooling time of 15 seconds. The molded product from the start of molding to the 5th shot was discarded, and the amount of formaldehyde emitted from the molded product was measured for the 6th shot under the conditions shown below (VDA275 method).
* VDA275 method:
A test piece having a size specified as 50 mL of distilled water (length 100 mm x width 40 mm x thickness 3 mm) was placed in a polyethylene container, sealed, heated at 60 ° C. for 3 hours to extract formaldehyde into the distilled water, and then cooled to room temperature. ..
After cooling, 5 mL of a 0.4% by mass aqueous solution of acetylacetone and 5 mL of a 20% by mass aqueous solution of ammonium acetate are added to 5 mL of distilled water that has absorbed formaldehyde to obtain a mixed solution, which is heated at 40 ° C. for 15 minutes to combine formaldehyde and acetylacetone. Reaction was performed.
Further, after cooling the mixed solution to room temperature, the amount of formaldehyde in the distilled water was quantified from the absorption peak at 412 nm using a UV spectrophotometer.
The amount of formaldehyde (mg / kg) released from the molded product was calculated by the following formula.
Amount of formaldehyde released from the molded product (mg / kg)
= Amount of formaldehyde in distilled water (mg) / Mass of polyacetal resin molded product used for measurement (kg)

<Short-term thermal stability>
The prepared polyacetal resin pellets (3 ± 0.01 g) are heated to 230 ° C. under a nitrogen atmosphere (50 ml / hr) to melt them, and formaldehyde generated during a residence time of 90 minutes is converted into 1 mol / l sodium sulfite aqueous solution. The sodium hydroxide produced was titrated with sulfuric acid specified in 1/100 and converted into the amount of formaldehyde (ppm). In this titration, thymolphthalein was used as an indicator, and the end point was when the blue color became colorless. The smaller the amount of formaldehyde, the better the short-term thermal stability of the polyacetal resin composition.

<Mold deposit>
For the produced polyacetal resin pellets, injection molding was repeated using a Ti-30G injection molding machine manufactured by Toyo Kikai Metal Co., Ltd. at a cylinder temperature of 220 ° C., an injection speed of 100 mm / S, an injection pressure of 100 kg · f, and a cycle timer of 15 seconds. After 1000 shot molding, the presence or absence of deposits adhering to the low temperature mold cavity at 30 ° C. was visually observed, and the mold deposit property was evaluated in three stages according to the following criteria.
○: A state in which deposits cannot be visually confirmed ×: A state in which deposits can be clearly visually confirmed △: Between ○ and ×

<Long-term heat resistant aging property>
The produced polyacetal resin pellets were molded using an IS-100E injection molding machine manufactured by Toshiba Machine Co., Ltd., and a plurality of test pieces compliant with ISO9998-2 were produced. One of the test pieces was left for 24 hours in a constant temperature room maintained at a temperature of 23 ° C. and a humidity of 50% after molding (test piece before heating). After molding, the remaining test pieces were placed in a Tabai gear oven set at 140 ° C, taken out at different timings by one day, and then taken out in a constant temperature room maintained at a temperature of 23 ° C and a humidity of 50%. It was left for a while (test piece after heating). Next, the tensile strength of each test piece was measured using a tensile tester (manufactured by Shimadzu Corporation, AG-IS) at a tensile speed of 50 mm / min, and the average value of the three measurements was taken. I asked. Then, the tensile strength retention rate of each test piece was calculated by the following formula, and the period (days) for retaining the tensile strength retention rate of 90% was determined. The longer this period is, the better the long-term heat resistant aging property is.
Tensile strength retention rate (%)
= (Tensile strength of test piece after heating / Tensile strength of test piece before heating) × 100

[Ingredients]
The raw material components used in Examples and Comparative Examples are shown below.

<(A) Polyacetal resin>
A twin-screw paddle type continuous polymerization reactor with a jacket (manufactured by Kurimoto, Ltd., diameter 2B, L / D = 14.8) was adjusted to 80 ° C. Using this polymerization reactor, a crude polyacetal copolymer was obtained under the polymerization conditions shown below.
[Polymerization conditions]
The raw materials were supplied to the reactor at the supply rates shown below.
-Trioxane (main monomer): 3500 g / hr
-1,3-Dioxolane (comonomer): 120.9 g / hr
-Methylal (molecular weight regulator): 2.4 g / hr
-Cyclohexane (organic solvent): 6.5 g / hr
-Boron trifluoride-di-n-butyl etherate (polymerization catalyst): 0.04 g / hr (Boron trifluoride is supplied at a supply rate of ^{0.05 × 10 -4 mol with respect to 1 mol of formaldehyde).} It was set.).
Only the polymerization catalyst was fed in a separate line from the above other components.

Next, the crude polyacetal copolymer discharged from the polymerization reactor was immersed in an aqueous triethylamine solution (0.5% by mass), and then stirred at room temperature for 1 hour to stabilize unstable terminal groups. Was done. Then, it was filtered with a centrifuge and dried under nitrogen at 120 ° C. for 3 hours. Finally, a polyacetal resin ((A-1) component) having a comonomer component derived from 1,3-dioxolane of 4 mol% and an MFR value of 9 g / 10 minutes was obtained.

<(B) Nitrogen-containing hindered phenol compound>
B-1: 1,2-bis [3- (4-hydroxy-3,5-di-t-butylphenyl) propionyl] hydrazine (Irganox MD1024)
B-2: 1,3,5-Tris [[3,5-bis (1,1-dimethylethyl) -4-hydroxyphenyl] methyl] -1,3,5-triazine-2,4,6 (1H) , 3H, 5H) -Trione (Irganox 3114)

<(C) Nitrogen-free hindered phenol compound>
C-1: Triethylene glycol-bis- [3- (3-t-butyl-5-methyl-4-hydroxyphenyl) -propionate] (Irganox 245)

<(D) Fatty Acid Calcium>
D-1: Calcium montanate D-2: Calcium behenate (comparative product) D-3: Calcium laurate (comparative product) D-4: Sodium montanate: comparative product

<(E) Calcium stearate>
E-1: Calcium stearate

<(F) Stabilizer>
F-1: Acrylamide polymer (average particle size 5 μm)
F-2: Melamine F-3: Adipic acid dihydrazide

[Example 1]

<Preparation of polyacetal resin composition>
(A-1) 100 parts by mass of the polyacetal resin, 0.05 parts by mass of the (B-1) component, 0.1 parts by mass of the (C-1) component, and 0.005 parts by mass of the (D-1) component. Was uniformly mixed using a Henshell mixer to obtain a mixture. This mixture is fed from the top feed port of a twin-screw extruder with a 30 mm vent set at 200 ° C., melt-kneaded at a screw rotation speed of 80 rpm, a vent pressure reduction degree of −0.09 MPa, and a discharge rate of 5 kg / hr, and pelleted. After the conversion, the mixture was dried at a hot air temperature of 80 ° C. for 3 hours to prepare a pellet-shaped polyacetal resin composition (polyacetal resin pellets). Then, the produced polyacetal resin pellets were measured and evaluated as described above. The results are shown in Table 1.

[Examples 2 to 18, Comparative Examples 1 to 14]
The same operation as in Example 1 was carried out except that the composition was as shown in Table 1 or Table 2, to prepare a polyacetal resin pellet. Then, the produced polyacetal resin pellets were measured and evaluated as described above. The results are shown in Table 1 or Table 2.

From Tables 1 and 2, in Examples 1 to 18, the polyacetal resin was less thermally decomposed in a high temperature environment, the amount of formaldehyde generated from the molded product made of the polyacetal resin composition was small, and the mold contamination was also small. .. Further, regarding the long-term heat resistant aging property, in Examples 1 to 18, it was better than the example in which the fatty acid metal salt was not added (for example, Comparative Example 4). As is clear from Comparative Examples 10 and 11, when a sodium salt was used instead of the calcium salt, at least the long-term heat-resistant aging property could not be improved.

As shown in the examples, by using a predetermined amount of (D) a calcium salt of a long-chain fatty acid having 22 to 30 carbon atoms, long-term heat-resistant aging property can be improved, and a predetermined amount of (B) nitrogen is contained. By using the hindered phenol compound, it was possible to suppress the thermal decomposition of the polyacetal resin even in a high temperature environment. Further, by using (B) a nitrogen-containing hindered phenol compound and (C) a nitrogen-free hindered phenol compound in combination, very good thermal stability and, by extension, reduction of mold contamination could be realized. ..

The polyacetal resin composition of the present invention has industrial applicability in a wide range of fields such as automobiles, electric / electronics, and other industries.

Claims (6)

(A) 100 parts by mass of polyacetal resin, (B) 0.001 to 0.2 parts by mass of nitrogen-containing hindered phenol compound, and (C) 0.001 to 0.4 parts by mass of nitrogen-free hindered phenol compound. , (D) A polyacetal resin composition containing 0.001 to 0.1 parts by mass of a calcium salt of a long-chain fatty acid having 22 to 30 carbon atoms. The polyacetal resin composition according to claim 1, wherein the content of the (B) nitrogen-containing hindered phenol compound is 0.001 to 0.15 parts by mass with respect to 100 parts by mass of the (A) polyacetal resin. The polyacetal resin composition according to claim 1 or 2, wherein the nitrogen-containing hindered phenol compound (B) contains a hydrazine structure. The polyacetal resin composition according to any one of claims 1 to 3, wherein the calcium salt of the (D) long-chain fatty acid is calcium montanate. (E) The polyacetal resin composition according to any one of claims 1 to 4, further containing 0.0001 to 0.01 parts by mass of calcium stearate. (F) Any of claims 1 to 5, further comprising at least one selected from the group consisting of an amino-substituted triazine compound, a urea derivative, a hydrazide derivative, an amide compound, a polyamide, and an acrylamide copolymer as a stabilizer. The polyacetal resin composition according to.