JP2019056118A - Method for producing polyoxymethylene resin composition - Google Patents

Abstract

To provide a polyoxymethylene resin composition that can sufficiently suppress a generation amount of formaldehyde during molding without performing stabilization treatment for stabilizing an unstable terminal group of a crude oxymethylene copolymer.SOLUTION: The polyoxymethylene resin composition is produced by melting and kneading a hindered phenolic antioxidant and an ethylene methacrylic acid copolymer resin or an ethylene acrylic acid copolymer resin or a salt thereof with a crude oxymethylene copolymer having an unstable terminal group which has not been stabilized although a polymerization catalyst is deactivated after finishing the copolymerization without performing stabilization treatment for stabilizing the unstable terminal group. The thus-produced polyoxymethylene resin composition is suitably used for forming an extruded molded article because long-term discoloration and long-term degradation in physical properties is suppressed when the polyoxymethylene resin composition is extrusion-molded.SELECTED DRAWING: None

Description

  The present invention relates to a method for producing a polyoxymethylene resin composition.

  Polyoxymethylene (also referred to as polyacetal, also abbreviated as POM) resin is a typical resin that has an excellent balance of mechanical properties, chemical resistance, slidability, and the like, and is easy to process. As an engineering plastic, it is widely used mainly for electrical / electronic parts, automobile parts, and other various machine parts.

  There is a copolymer as a polyoxymethylene polymer, and the copolymer is produced by polymerizing in the presence of a catalyst using formaldehyde or a cyclic multimer thereof as a main monomer and using a cyclic ether and / or a cyclic formal as a comonomer.

  However, the resulting crude polyoxymethylene copolymer is thermally unstable because some of its molecular ends are unstable terminal groups, and formaldehyde is generated by thermal decomposition during molding. Can be. Further, the generated formaldehyde is oxidized during molding to form formic acid, which may cause problems such as decomposition of the polyoxymethylene copolymer and foaming of the resin molded product. Furthermore, formic acid can be a factor that corrodes metal parts in contact with the resin molded product.

  In response to the above, in order to obtain polyoxymethylene resin pellets by adding various additives such as formaldehyde scavenger, antioxidant, processing stabilizer and heat stabilizer to oxymethylene copolymer, The unstable terminal group of the copolymer is stabilized, and the above-mentioned additive is added to the stabilized polyoxymethylene copolymer obtained by this stabilization to obtain polyoxymethylene resin pellets.

  As a method for stabilizing a crude polyoxymethylene copolymer, a method in which an unstable terminal group and a subsequent unstable terminal are decomposed and removed are known.

  For example, hydrolyzing a crude polyoxymethylene copolymer, more specifically, by heating the crude polyoxymethylene copolymer to a temperature above its melting point and treating it in a molten state, Decomposing and removing unstable terminal groups, or heating a crude polyoxymethylene copolymer at a temperature of 80 ° C. or higher while maintaining a heterogeneous system in an insoluble liquid medium, It is known to decompose and remove groups (see Patent Document 1).

  In addition, ammonia, triethylamine, aliphatic amines such as tri-n-butylamine or triethanolamine, quaternary ammonium salts such as tetrabutylammonium hydroxide, alkali metal or alkaline earth metal hydroxides, inorganic weak acid salts or It is also known that an unstable salt is decomposed in the presence of an organic acid salt or the like (see Patent Document 2). It has also been proposed to decompose unstable terminal portions in the presence of quaternary phosphonium salts, PN bond-containing compounds, heterocyclic quaternary ammonium salts, betaines, betaine derivatives, amine oxides or hydrazinium salts (patents) Reference 2-5).

JP 2010-37445 A JP 2008-1850 A JP 2008-31348 A JP 2007-332227 A JP 2007-112959 A

  However, if the addition of various additives to the crude oxymethylene copolymer without any stabilization treatment to stabilize unstable terminal groups can be supplied as a polyoxymethylene resin composition, the production process will be greatly increased. This is preferable because it can be simplified.

  An object of the present invention is to provide a polyoxymethylene resin composition in which the amount of formaldehyde generated during molding is sufficiently suppressed without performing the stabilization treatment.

  As a result of intensive studies to solve the above problems, the present inventors have found that the above problems can be solved by using specific additives, and have completed the present invention. Specifically, the present invention provides the following.

  (1) The present invention stabilizes the unstable terminal group with respect to a crude oxymethylene copolymer in which the polymerization catalyst is deactivated after completion of the copolymerization but the unstable terminal group is not stabilized. A polyoxymethylene resin is obtained by melt-kneading a hindered phenolic antioxidant, an ethylene methacrylic acid copolymer resin or an ethylene acrylic acid copolymer resin or a salt thereof, and an alkaline earth metal compound without any treatment. A method for producing a composition.

  (2) Moreover, this invention is a manufacturing method as described in (1) whose said alkaline-earth metal compound is a salt or oxide of an aliphatic carboxylic acid metal.

  (3) Further, in the present invention, the alkaline earth metal compound is calcium stearate, and the calcium stearate is 0.003% by weight or more and 0.020% by weight or less with respect to the crude oxymethylene copolymer. The production method according to (1) or (2), which is used in a range.

  (4) Moreover, this invention is a manufacturing method in any one of (1) to (3) whose said polyoxymethylene resin composition is an object for extrusion molding formation.

  According to the present invention, a polyoxymethylene resin composition in which the amount of formaldehyde generated during molding is sufficiently suppressed can be provided without performing the stabilization treatment.

  Hereinafter, specific embodiments of the present invention will be described in detail. However, the present invention is not limited to the following embodiments, and may be implemented with appropriate modifications within the scope of the object of the present invention. can do.

<Method for producing polyoxymethylene resin composition>
The present invention deactivates the polymerization catalyst after completion of the copolymerization, but the hindered phenol-based oxidation is carried out on the crude oxymethylene copolymer in which the unstable end group is not stabilized without performing the above stabilization treatment. An inhibitor, an ethylene methacrylic acid copolymer resin or an ethylene acrylic acid copolymer resin or a salt thereof, and an alkaline earth metal compound are melt-kneaded to produce a polyoxymethylene resin composition.

[Crude oxymethylene copolymer]

  In the present invention, the copolymer as a raw material is a crude copolymer in which the polymerization catalyst is deactivated after completion of the copolymerization, but the unstable terminal groups are not stabilized.

The crude oxymethylene copolymer is a resin having an oxymethylene group (—OCH ₂ —) as a main structural unit and other comonomer units in addition to the oxymethylene units. Generally, a crude oxymethylene copolymer is produced by copolymerizing formaldehyde or a cyclic oligomer of formaldehyde as a main monomer and a compound selected from cyclic ether or cyclic formal as a comonomer.

  As the main monomer, trioxane, which is a cyclic trimer of formaldehyde, is generally used. Trioxane is generally obtained by reacting an aqueous formaldehyde solution in the presence of an acidic catalyst, and is used after being purified by a method such as distillation.

  The cyclic ether and cyclic formal which are comonomers include ethylene oxide, propylene oxide, butylene oxide, cyclohexene oxide, oxetane, tetrahydrofuran, trioxepane, 1,3-dioxane, 1,3-dioxolane, propylene glycol formal, diethylene glycol formal, triethylene glycol. Formal, 1,4-butanediol formal, 1,6-hexanediol formal and the like can be mentioned. Further, a compound capable of forming a branched structure or a crosslinked structure can be used as a comonomer (or termonomer). Examples of such a compound include methyl glycidyl ether, ethyl glycidyl ether, butyl glycidyl ether, and 2-ethyl-hexyl. Alkyl or aryl glycidyl ethers such as glycidyl ether and phenyl glycidyl ether, alkylene glycols such as ethylene glycol diglycidyl ether, triethylene glycol diglycidyl ether, and butanediol diglycidyl ether, and diglycidyl ethers of polyalkylene glycols.

  Among these, the comonomer is preferably ethylene oxide, 1,3-dioxolane, 1,4-butanediol formal, or diethylene glycol formal in that the thermal stability of the crude polyoxymethylene copolymer is suitable. These comonomers can be used alone or in combination of two or more.

  The amount of comonomer greatly affects the thermal stability of the crude polyoxymethylene copolymer. The weight ratio of the main monomer to the comonomer is preferably 99.9: 0.1 to 80.0: 20.0, and preferably 99.5: 0.5 to 90.0: 10.0. More preferred.

By the way, in both the main monomer and the comonomer, it is preferable that the content of impurities such as water, methanol and formic acid is as small as possible. The impurities are for forming unstable terminals in the polymerization system. The total amount of impurities is preferably 1 × 10 ⁻² mol% or less, and more preferably 5 × 10 ⁻³ mol% or less, based on all monomers in the reaction system.

  The crude oxymethylene copolymer can be generally obtained by adding a suitable amount of molecular weight regulator and performing cationic polymerization using a cationic polymerization catalyst. Molecular weight regulators, cationic polymerization catalysts, polymerization methods, polymerization apparatuses and the like used are known from many literatures, and basically any of them can be used. For example, a low molecular weight linear acetal having both alkoxy groups at both ends, such as methylal, does not form an unstable end, and therefore may contain an arbitrary amount for the purpose of adjusting the molecular weight of the crude polyoxymethylene copolymer. it can.

  The catalyst used in the polymerization reaction is lead tetrachloride, tin tetrachloride, titanium tetrachloride, aluminum trichloride, zinc chloride, vanadium trichloride, antimony trichloride, phosphorus pentafluoride, antimony pentafluoride, boron trifluoride. Boron trifluoride coordination compounds such as boron trifluoride diethyl etherate, boron trifluoride dibutyl etherate, boron trifluoride dioxanate, boron trifluoride acetate anhydrate, boron trifluoride triethylamine complex, Inorganic and organic acids such as perchloric acid, acetyl perchlorate, t-butyl perchlorate, hydroxyacetic acid, trichloroacetic acid, trifluoroacetic acid, trifluoromethanesulfonic acid, p-toluenesulfonic acid, triethyloxonium tetrafluoroborate, triphenyl Methyl hexafluoroantimonate , Allyl diazonium hexafluorophosphate, complex salt compounds such as allyl diazonium tetrafluoroborate, diethyl zinc, triethyl aluminum, alkali metal salts such as diethyl aluminum chloride, heteropoly acid and isopoly acid. Of these, boron trifluoride, boron trifluoride coordination compound, heteropolyacid, and trifluoromethanesulfonic acid are particularly preferable. These catalysts may be used after diluting with an organic solvent or the like.

When using a catalyst comprising boron trifluoride or a coordination compound thereof, the amount of the catalyst is preferably in the range of 1 × 10 ⁻³ mol% or more and 1 × 10 ⁻² mol% or less based on the total monomers, A range of 5 × 10 ⁻³ mol% or more and 7 × 10 ⁻³ mol% or less is more preferable. Setting the amount of catalyst in such a limited range is effective in preventing the formation of unstable end portions. When the amount of the catalyst is too large, it is difficult to properly control the polymerization temperature, the decomposition reaction during the polymerization becomes dominant, and as a result, a large number of unstable terminal portions are excessively generated. On the other hand, if the amount of the catalyst is too small, it is not preferable because the polymerization reaction rate may decrease and the polymerization yield may decrease.

  Any conventionally known method can be used as the polymerization method, but a continuous bulk polymerization method that uses a liquid monomer to obtain a solid powdery polymer as the polymerization proceeds is industrially preferable. The polymerization temperature is preferably maintained at 60 ° C. or higher and 105 ° C. or lower, and particularly preferably 65 ° C. or higher and 100 ° C. or lower.

  The method for deactivating the catalyst after polymerization is not particularly limited, and any conventionally known method can be used. For example, when a catalyst comprising boron trifluoride or a coordination compound thereof is used, a method such as adding a polymer after polymerization to an aqueous solution containing a basic compound is possible. As the basic compound, ammonia, amines such as triethylamine, tributylamine, triethanolamine, tributanolamine, oxides, hydroxides or salts of alkali metals or alkaline earth metals, or other known compounds And a catalyst deactivator. The basic compound is preferably added as an aqueous solution having a concentration of 0.001% to 0.5% by weight, particularly preferably 0.02% to 0.3% by weight. Moreover, it is preferable that the temperature of aqueous solution is 10 to 80 degreeC, Most preferably, it is 15 to 60 degreeC. Further, after the polymerization is completed, it is preferable that the catalyst is deactivated by promptly adding it to these aqueous solutions.

  The molecular weight of the crude oxymethylene copolymer is not particularly limited, but those having a weight average molecular weight of 10,000 or more and 400,000 or less are preferable. Moreover, the thing whose melt index used as the parameter | index of the fluidity | liquidity of resin is 0.1 / 10min or more and 100g / 10min or less is preferable, More preferably, it is 0.5 / 10min or more and 80g / 10min or less. In this specification, a melt index shall be a value when measured by 190 degreeC and load 2.16kg according to ASTM-D1238.

[Rough Oxymethylene Copolymer not Stabilized]
In the present invention, the crude oxymethylene copolymer deactivates the polymerization catalyst after completion of the copolymerization but does not stabilize unstable terminal groups. And a crude oxymethylene copolymer and various additives are melt-kneaded without performing the stabilization process which stabilizes an unstable terminal group.

Here, the stabilization process of the terminal group of a crude oxymethylene copolymer and an unstable terminal group is demonstrated. The stable end group of the crude oxymethylene copolymer includes an alkoxy group such as a methoxy group (—OCH ₃ ), a hydroxyethyl group (—CH ₂ CH ₂ OH), a hydroxybutyl group (—CH ₂ CH ₂ CH ₂ CH _2). A hydroxyalkyl group having 2 or more carbon atoms, such as (OH). On the other hand, the unstable end groups of the crude oxymethylene copolymer include hemiacetal end groups (also referred to as hydroxymethoxy end groups and hemiformal end groups, represented by —OCH ₂ OH) and formyl end groups (in —CHO). It is expressed.)

  Generally, through the stabilization step, the proportion of unstable end groups contained in the oxymethylene copolymer can be reduced, and a stabilized oxymethylene copolymer is obtained. As a stabilization treatment, the polyoxymethylene copolymer is heated to a temperature equal to or higher than its melting point and treated in a molten state to decompose and remove only unstable parts, or to maintain a heterogeneous system in an insoluble liquid medium. It is known that only unstable terminal portions are decomposed and removed by heat treatment at a temperature of ℃ or higher.

  It is also known that a crude polyoxymethylene copolymer is heat-treated in the presence of an unstable terminal group decomposition treatment agent. As unstable end group decomposition treatment agents, aliphatic amines such as ammonia, triethylamine, tri-n-butylamine and triethanolamine, quaternary ammonium salts such as tetrabutylammonium hydroxide, hydroxylation of alkali metals or alkaline earth metals Quaternary phosphonium salts, PN bond-containing compounds, heterocyclic quaternary ammonium salts, betaines, betaine derivatives, amine oxides or hydrazinium salts, etc., in addition to products, inorganic weak acid salts or organic acid salts (Patent Documents) 2-5).

  The present invention is characterized in that a polyoxymethylene resin composition is obtained by adding a specific additive to a crude oxymethylene copolymer without performing these stabilization treatments. Below, the specific additive is demonstrated.

[Hindered phenolic antioxidants]
In the present invention, a hindered phenol-based antioxidant is added to the above crude oxymethylene copolymer.

  Examples of the hindered phenol antioxidant used in the present invention include a monocyclic hindered phenol compound, a polycyclic hindered phenol compound linked by a hydrocarbon group or a group containing a sulfur atom, an ester group or an amide group. The hindered phenol compound etc. which have are mentioned.

  Specific examples of these compounds include 2,6-di-t-butyl-p-cresol, 2,2′-methylenebis (4-methyl-6-t-butylphenol), 4,4′-methylenebis (2,6 -Di-t-butylphenol), 1,1,3-tris (2-methyl-4-hydroxy-5-t-butylphenyl) butane, 4,4'-butylidenebis (3-methyl-6-t-butylphenol) 1,3,5-trimethyl-2,4,6-tris (3,5-di-tert-butyl-4-hydroxybenzyl) benzene, 4,4′-thiobis (3-methyl-6-tert-butylphenol) ), N-octadecyl-3- (4′-hydroxy-3 ′, 5′-di-t-butylphenyl) propionate, n-octadecyl-2- (4′-hydroxy-3 ′, 5′-di-t) -Butyl fluoride Nyl) propionate, 1,6-hexanediol-bis [3- (3,5-di-tert-butyl-4-hydroxyphenyl) propionate], ethylenebis (oxyethylene) bis [3- (5-tert-butyl) -4-hydroxy-m-tolyl) propionate], pentaerythritol tetrakis [3- (3,5-di-t-butyl-4-hydroxyphenyl) propionate], 3,9-bis [2- {3- (3 -T-butyl-4-hydroxy-5-methylphenyl) propionyloxy} -1,1-dimethylethyl] -2,4,8,10-tetraoxaspiro [5.5] undecane, 2-t-butyl- 6- (3′-t-butyl-5′-methyl-2′-hydroxybenzyl) -4-methylphenyl acrylate, 2- [1- (2-hydroxy 3,5-di-t-pentylphenyl) ethyl] -4,6-di-t-pentylphenyl acrylate, di-n-octadecyl-3,5-di-t-butyl-4-hydroxybenzylphosphonate, N, N′-hexamethylenebis (3,5-di-t-butyl-4-hydroxy-dihydrocinnamamide), N, N′-ethylenebis [3- (3,5-di-t-butyl-4- Hydroxyphenyl) propionamide], N, N′-tetramethylenebis [3- (3,5-di-t-butyl-4-hydroxyphenyl) propionamide], N, N′-hexamethylenebis [3- ( 3,5-di-t-butyl-4-hydroxyphenyl) propionamide], N, N′-ethylenebis [3- (3-t-butyl-5-methyl-4-hydroxyphenyl) propion Amido], N, N′-hexamethylenebis [3- (3-tert-butyl-5-methyl-4-hydroxyphenyl) propionamide], N, N′-bis [3- (3,5-di-) t-butyl-4-hydroxyphenyl) propionyl] hydrazine, N, N′-bis [3- (3-t-butyl-5-methyl-4-hydroxyphenyl) propionyl] hydrazine, 1,3,5-tris ( 3,5-di-tert-butyl-4-hydroxybenzyl) isocyanurate, 1,3,5-tris (4-tert-butyl-3-hydroxy-2,6-dimethylbenzyl) isocyanurate, etc. Can do.

  These hindered phenolic antioxidants can be used alone or in combination of two or more. The addition amount of the hindered phenolic antioxidant is not particularly limited, but is preferably 0.01% by weight or more and 3% by weight or less, and 0.05% by weight or more with respect to the crude oxymethylene copolymer. More preferably, it is 2% by weight or less. If the amount of the hindered phenol-based antioxidant is less than 0.01% by weight, workability and material properties during long-term use may be deteriorated, which is not preferable. If the amount of the hindered phenol-based antioxidant exceeds 3% by weight, it may ooze out from the molded product, and this is not preferable from the viewpoint of cost.

  By the way, as an antioxidant, besides a hindered phenol-based antioxidant, a hindered amine-based antioxidant, a phosphorus-based secondary antioxidant, and a sulfur-based secondary antioxidant are also known. The present invention does not prevent the addition of these antioxidants, and a hindered amine antioxidant may be added in addition to the hindered phenol antioxidant.

[Ethylene methacrylic acid copolymer resin or ethylene acrylic acid copolymer resin or salts thereof]
In the present invention, an ethylene methacrylic acid copolymer resin or an ethylene acrylic acid copolymer resin or a salt thereof is added to the above crude oxymethylene copolymer. Even if an additive is added to the crude oxymethylene copolymer without adding a stabilization treatment by adding an ethylene methacrylic acid copolymer resin or an ethylene acrylic acid copolymer resin or a salt thereof, the resin composition The amount of formaldehyde generated when molding a product can be suitably suppressed.

  The ethylene methacrylic acid copolymer resin or the ethylene acrylic acid copolymer resin or a salt thereof can be used alone or in combination of two or more. The addition amount of the ethylene methacrylic acid copolymer resin or the ethylene acrylic acid copolymer resin or each salt is not particularly limited, but is 0.01% by weight or more and 2% by weight or less based on the crude oxymethylene copolymer. It is preferably 0.015% by weight or more and 1% by weight or less. If the added amount of the ethylene methacrylic acid copolymer resin or the ethylene acrylic acid copolymer resin or each salt is less than 0.01% by weight, a sufficient effect cannot be obtained, which is not preferable. When the addition amount of the ethylene methacrylic acid copolymer resin or a salt thereof exceeds 2% by weight, peeling from the molded product may occur, which is not preferable.

[Alkaline earth metal compounds]
Examples of alkaline earth metal compounds include salts of alkaline earth metals (calcium, magnesium, etc.) and organic carboxylic acids; metal oxides such as CaO and MgO; metal carbonates such as CaCO ₃ and MgCO ₃ ; alkaline earth metals Examples thereof include metal inorganic acid salts such as salts of (calcium, magnesium, etc.) and boric acid or phosphoric acid.

  As the carboxylic acid constituting the carboxylic acid metal salt, a saturated or unsaturated aliphatic carboxylic acid having 1 to 36 carbon atoms can be used. Further, these aliphatic carboxylic acids may have a hydroxyl group.

  Examples of the saturated aliphatic carboxylic acid include acetic acid, propionic acid, butyric acid, caproic acid, caprylic acid, capric acid, lauric acid, myristic acid, palmitic acid, stearic acid, arachidic acid, behenic acid, lignoceric acid, serotic acid, montan Saturated C1-36 monocarboxylic acids such as acid, melicic acid, and celloplastic acid, saturated C6-36 dicarboxylic acids such as oxalic acid, malonic acid, succinic acid, and adipic acid, saturated C6- such as tricarballylic acid, butanetricarboxylic acid Examples thereof include polyvalent carboxylic acids such as 36 tricarboxylic acid, or oxyacids thereof (for example, lactic acid, hydroxybutyric acid, hydroxylauric acid, hydroxypalmitic acid, hydroxystearic acid, malic acid, citric acid, etc.).

  Examples of the unsaturated aliphatic carboxylic acid include unsaturated C3-36 carboxylic acids such as undecylenic acid, oleic acid, elaidic acid, celetic acid, erucic acid, brassic acid, sorbic acid, linoleic acid, linolenic acid, arachidonic acid, and the like And oxyacids (for example, propiolic acid, stearic acid, etc.)

  As the aliphatic carboxylic acid, calcium stearate is preferably used.

  The alkaline earth metal compounds can be used alone or in combination of two or more, and the ratio is preferably 0.001 wt% or more and 2 wt% or less with respect to the crude oxymethylene copolymer, more preferably. The range is 0.003% to 0.020% by weight.

  As formaldehyde scavengers, aminotriazine compounds such as melamine, urea compounds, carboxylic acid hydrazide compounds, polyurethane resins, polyacrylamide resins and polyamide resins are known. The present invention does not prevent the addition of these formaldehyde scavengers.

[Other additives]
A known additive can be further used for the crude polyoxymethylene copolymer of the present invention.

  When used in extrusion molding applications, as slidability improvers, olefin polymers (polyethylene, polypropylene, copolymers of ethylene and α-olefin, modified products thereof with acids, etc.), waxes (polyethylene wax, etc.) ), Silicone oil, silicone resin, fluorine resin (polytetrafluoroethylene, etc.), fatty acid ester, and the like.

  Furthermore, known lubricants, anti-glare (light) stabilizers, impact resistance improvers, gloss control agents, fillers, colorants, nucleating agents, antistatic agents, surfactants, antibacterial agents, antifungal agents, fragrances , Foaming agents, compatibilizers, physical property improvers (boric acid or its derivatives, etc.), fragrances, etc. can be blended, and various properties according to each additive without impairing the object of the present invention Can be improved.

[Production of polyoxymethylene resin composition]
The manufacturing method of a polyoxymethylene resin composition is not specifically limited, It can prepare by the various methods conventionally known as a preparation method of a resin composition. For example, (1) a method in which all components constituting the composition are mixed, and this is supplied to an extruder and melt-kneaded to obtain a pellet-like composition; (2) a part of the components constituting the composition The remaining components are fed from the main feed port of the extruder through the side feed port and melt-kneaded to obtain a pellet-like composition. (3) Once the pellets having different compositions are prepared by extrusion or the like, the pellets are mixed And a method of adjusting to a predetermined composition.

  In the preparation of the composition using an extruder, it is preferable to use an extruder having one or more devolatilization vent ports, and further, water or a low boiling point at any location from the main feed port to the devolatilization vent port. Alcohol is supplied in the range of 0.1 to 10 parts by weight with respect to 100 parts by weight of the crude oxymethylene copolymer, and formaldehyde generated in the extrusion process is devolatilized with water and low-boiling alcohols. It is preferable to volatilize and remove from the vent port. Thereby, the amount of formaldehyde generated from the polyoxymethylene resin composition and its molded product can be reduced.

  In addition, when forming a resin molded product, it is suitable that the polyoxymethylene resin composition of this invention is a pellet shape at the point which is easy to process.

[Formation of resin molded product using polyoxymethylene resin composition]
Conventionally, injection molding, extrusion molding, compression molding, blow molding, vacuum molding, foam molding, rotational molding, and the like are known as methods for forming a resin molded product using a resin composition. When forming a molded article using the resin composition according to the present invention, the molded article can be suitably formed by any of these conventional molding methods.

  By the way, the extrusion molding can form a resin molded product having a complicated cross-sectional shape, and since the stress applied to the resin composition is only compression stress and shear stress, it is suitably molded even if the resin composition is a fragile material. There are advantages such that the surface of the molded product after extrusion can be made very smooth and a finishing treatment is unnecessary. On the other hand, while the resin composition stays inside the molding machine, there is a drawback that deterioration of the compounding components and side reaction with formaldehyde occur, which may cause defective appearance such as yellowing of the resin molded product. Have.

  When the polyoxymethylene resin composition of the present invention is used, even when extrusion molding is performed, alteration of the compounding components and side reaction with formaldehyde can be prevented. Therefore, it is preferable that the polyoxymethylene resin composition of the present invention is particularly used for forming an extruded product.

EXAMPLES Hereinafter, the present invention will be specifically described with reference to examples, but the present invention is not limited thereto.

<Preparation of crude oxymethylene copolymer>
A barrel having a cross-sectional shape in which two circles partially overlap, and a barrel having a jacket for passing a heat (cooling) medium on the outside, and two barrels each having a stirring and propulsion paddle in the longitudinal direction inside the barrel The polymerization reaction was performed as follows using a continuous mixing reactor having a rotating shaft.

  Warm water at 80 ° C. was passed through the jacket, the two rotating shafts were rotated at a speed of 100 rpm, and 0.05% by weight of triethylene glycol-bis [3- (3-tert-butyl-5-methyl) was used as an antioxidant. -4-hydroxyphenyl) propionate], trioxane containing 3.3% by weight of 1,3-dioxolane as comonomer and 700 ppm (by weight) of methylal as chain transfer agent are continuously fed to the reactor and in parallel Then, a solution of boron trifluoride / dibutyl etherate dissolved in cyclohexane (concentration of 1% by weight) is 10 ppm (weight) as boron trifluoride with respect to all monomers (total amount of trioxane and 1,3-dioxolane). Copolymerization was carried out with continuous addition at a standard) concentration. Subsequently, the crude polyoxymethylene copolymer discharged from the discharge port of the reactor was added to an aqueous solution containing 0.1% by weight of triethylamine to deactivate the catalyst. This mixture was centrifuged and further dried to obtain a crude oxymethylene copolymer.

  The crude oxymethylene copolymer had a hemiacetal terminal group amount of 2.2 mmol / kg, a formyl terminal group amount of 1.7 mmol / kg, and an unstable terminal amount (amount of terminal unstable parts) of 1.18% by weight. there were.

In the present invention, the amount of hemiacetal end group and formyl end group are evaluated by the following methods.
Dissolve the crude oxymethylene copolymer in hexafluoroisopropyl alcohol, add N, O-bis (trimethylsilyl) trifluoroacetamide and pyridine for reaction, air dry, and then vacuum dry at 40 ° C. To remove residual solvent and unreacted material. The obtained reaction product was dissolved in deuterated hexafluoroisopropyl alcohol at a concentration of 5% by weight as a solvent, the solution was filled in an NMR sample tube, and an NMR spectrum was measured at room temperature (Japanese Patent Laid-Open No. 2001-11143). No. publication).
The amount of hemiacetal end groups (mmol / kg) and the amount of formyl end groups (mmol / kg) are calculated based on the corresponding NMR absorption peaks.
NMR apparatus: Bruker, AVANCE400 type FT-NMR
Measurement conditions: Pulse flip angle 30 °, integration repetition time 10 sec, integration count 128 times

In the present invention, the amount of unstable terminal (the amount of unstable part at the terminal) is evaluated by the following method.
About 1 g of the crude oxymethylene copolymer was precisely weighed and placed in a pressure-resistant sealed container together with 100 ml of a 60 volume% methanol aqueous solution containing 15 mg of calcium hydroxide and 0.5 volume% ammonium hydroxide, and heat-treated at 170 ° C. for 60 minutes. Then, it is cooled and opened to take out the inner solution. The amount of formaldehyde generated by the decomposition of the unstable terminal portion and dissolved in the solution is quantified according to JIS K0102, item 29.1 acetylacetone absorptiometry, and the ratio to the crude oxymethylene copolymer is calculated as wt%.

<Preparation of stabilized oxymethylene copolymer>
0.01 parts by weight of triethylene glycol-bis [3- (3-tert-butyl-5-methyl-4-hydroxyphenyl) propionate] and 2 parts by weight per 100 parts by weight of the crude polyoxymethylene copolymer Part of a triethylamine aqueous solution (0.72 wt% concentration: triethylamine is 1.4 mmol in terms of tertiary amine nitrogen per kg of the crude polyoxymethylene copolymer) is added and mixed uniformly.
Next, this mixture was supplied to the above-described twin screw extruder with a devolatilization port, and volatiles were vented at a vent vacuum of 20 mmHg (2.7 kPa), a cylinder temperature of 200 ° C., and an average residence time of 300 seconds. While being removed from the devolatilization port, the mixture was melt-kneaded to obtain a pelletized stabilized oxymethylene copolymer.

  The stabilized oxymethylene copolymer has a hemiacetal end group amount of 1.2 mmol / kg, a formyl end group amount of 1.3 mmol / kg, and an unstable end amount (amount of terminal unstable portion) of 0.56% by weight. Met.

<Examples, reference examples and comparative examples>

In Table 1, various materials are as follows.
1. Crude POM Copolymer Crude oxymethylene copolymer obtained by <Preparation of Crude Oxymethylene Copolymer> 2. 2. Stabilized POM copolymer Stabilized oxymethylene copolymer obtained by the above <Preparation of stabilized oxymethylene copolymer>. Hindered phenolic antioxidant pentaerythritol tetrakis [3- (3,5-di-tert-butyl-4-hydroxyphenyl) propionate] (Product name: Irganox 1010, manufactured by BASF Japan Ltd.)
4). Ethylene methacrylic acid copolymer resin Ethylene methacrylic acid copolymer resin (Product name: Nucrel N1525, manufactured by Mitsui & DuPont Polychemicals)
5. Ethylene acrylic acid copolymer resin (Product name: Primacol 3460, manufactured by Dow Chemical Company)
6). 6. Zinc salt of ethylene methacrylic acid copolymer resin 7. alkaline earth metal compound calcium stearate magnesium oxide Sliding property improving agent Low molecular weight polyethylene (Product name: Sunwax 161-P, manufactured by Sanyo Chemical Industries)

The materials shown in Table 1 were charged into an extruder TEX30α (manufactured by Nippon Steel Works) at the ratio shown in Table 1 (unit: parts by weight). Subsequently, the above-described raw materials charged into the extruder were kneaded under the following extrusion conditions. Next, the kneaded raw materials were extruded into strands, cooled, cut into pellets, and dried at 140 ° C. for 4 hours. Thus, polyoxymethylene resin composition pellets (diameter: 1 to 2 mm, length: 2 to 3 mm) according to Examples and Comparative Examples were produced.
(Extrusion conditions)
Cylinder temperature: 170-200 ° C
Extrusion amount: 18 kg / hr (using a quantitative feeder)
Rotation speed: 120rpm

<Evaluation>
[Formaldehyde generation amount from melt]
5 g of the pellet is accurately weighed and held in a metal container at 200 ° C. for 5 minutes, and then the atmosphere in the container is absorbed into distilled water. The amount of formaldehyde in this aqueous solution was adjusted to JISK0102, 29. The amount of formaldehyde gas (ppm) generated from the pellet was calculated according to (formaldehyde term). The case where the amount of formaldehyde gas was less than 70 ppm was designated as “◯”, and the case where it was 70 ppm or more was designated as “x”. The results are shown in Table 2.

[Long-term hue stability (ΔE)]
Using the above-described composition pellets, a φ140 round bar was solid-extruded using a 30 mm uniaxial solidification extruder at an extrusion speed of 5 mm / min. And the test piece according to ISO 527-1 type 1B was cut out from the obtained round bar.

Then, the said test piece was hold | maintained for a long time in 140 degreeC oven, and the hue was evaluated with the color difference meter. The degree of color change (ΔE) was calculated by the following formula.
ΔE = [(L ₁ −L ₀ ) ² + (a ₁ −a ₀ ) ² + (b ₁ −b ₀ ) ² ] ^1/2
In the formula, L, a, and b are the color values measured by the color difference meter, respectively, and the subscript 1 of L, a, and b is the hue after being kept in an oven at 140 ° C. for 20 days. The suffix 0 means the hue just before entering the oven.

  A case where the calculated result is less than 10 is “◎”, and a case where the calculated result is 10 or more and 15 or less is “◯”. The results are shown in Table 2.

  The test piece produced by the above [Long-term hue stability (ΔE)] was held in a 140 ° C. oven for 20 days, and the tensile strength was evaluated. Evaluation conforms to ISO527. With respect to the tensile strength before long-term holding, the case where the tensile holding ratio after long-term holding was 100% or more was “◯”, and the case where the tensile holding ratio was less than 100% was “x”. The results are shown in Table 2.

  When Examples 1 to 6 and Reference Example 1 are compared, as a material for forming a resin molded product, a hindered phenol-based antioxidant and an ethylene methacrylic acid copolymer resin or ethylene are used with respect to the crude oxymethylene copolymer. In the case of using a polyoxymethylene resin composition obtained by melt-kneading an acrylic acid copolymer resin or a salt thereof, the stabilization treatment for stabilizing unstable terminal groups is not performed. It can be said that the amount of formaldehyde generated can be suppressed to about the same level as in the case of using a polyoxymethylene resin composition obtained from a stabilized oxymethylene copolymer that has undergone stabilization treatment. From this, it can be said that according to the present invention, a polyoxymethylene resin composition in which the amount of formaldehyde generated during molding is sufficiently suppressed can be provided without performing the stabilization treatment.

  Further, even if the polyoxymethylene resin composition is extruded, long-term discoloration and long-term physical property deterioration can be suppressed, and therefore the polyoxymethylene resin composition of the present invention is also suitable for forming an extruded product (Examples). 1-6).

  On the other hand, when an ethylene methacrylic acid copolymer resin is used alone as an additive, further reduction in long-term physical property retention cannot be suppressed when a polyoxymethylene resin composition is extruded (Comparative Example 1). Even if an alkaline earth metal compound is used, the amount of formaldehyde generated cannot be suitably suppressed, which may be inappropriate (Comparative Example 2).

Claims (2)

  The polymerization catalyst is deactivated after completion of the copolymerization, but the hindered oxymethylene copolymer, which does not stabilize the unstable end groups, is subjected to a hindering treatment without stabilizing the unstable end groups. A dophenol-based antioxidant, an ethylene methacrylic acid copolymer resin or an ethylene acrylic acid copolymer resin, and calcium stearate are used using an extruder having one or more devolatilization vent ports, and further from the main feed port. At least one selected from water and low-boiling point alcohols at an arbitrary location up to the devolatilization vent port is in the range of 0.1 to 10 parts by weight with respect to 100 parts by weight of the crude oxymethylene copolymer. A method for producing a polyoxymethylene resin composition that is supplied and melt-kneaded.   The crude oxymethylene copolymer has a hemi-formal end group content exceeding 1.2 mmol / kg, a formyl end group amount exceeding 1.3 mmol / kg, and an unstable end group amount exceeding 0.56 wt%. A method for producing a polyoxymethylene resin composition, which is a methylene copolymer.