JP2012246337A - Polyoxymethylene polymer pellet, method for producing the same, and method for evaluating quality of the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To suppress the adhesion of mold deposits on a metal mold and the generation of formaldehyde in molding processing of a molded article using as a raw material a polymer pellet containing a polyoxymethylene polymer.SOLUTION: The polyoxymethylene polymer pellet is constituted of (A) 100 pts.mass of a polyoxymethylene polymer, (B) 0.01 to 1.0 pt.mass of a sterically hindered phenolic antioxidant, and (C) 0.01 to 0.10 pt.mass of the total of melamine and a methylated melamine, wherein the content ratio of the methylated melamine to the melamine and the methylated melamine is regulated in a specific range.

Description

  The present invention relates to a polyoxymethylene polymer pellet, a method for producing a polyoxymethylene polymer pellet, and a quality evaluation method for a polyoxymethylene polymer pellet.

  A polyoxymethylene polymer is one of engineering plastics having excellent mechanical strength, frictional wear characteristics, and the like, and is used in various fields such as electrical and electronic equipment parts and automobile parts. This polyoxymethylene polymer is produced by polymerization of formaldehyde or trioxane, which is a cyclic oligomer thereof, or copolymerization of trioxane with a comonomer such as cyclic ether or cyclic formal.

  The polyoxymethylene polymer produced as described above has a property of being easily decomposed, and when the polyoxymethylene polymer is decomposed, harmful gases such as formaldehyde are generated. Therefore, in order to suppress the decomposition of the polyoxymethylene polymer, the end group of the polyoxymethylene polymer is stabilized, or the polyoxymethylene polymer is used in combination with additives such as an antioxidant and a heat stabilizer. Technology to do is known.

  In addition, a technique of adding cyanoguanidine, melamine or the like is known for the purpose of capturing formaldehyde generated by decomposition of a polyoxythymethylene polymer. However, by molding a polymer composition containing cyanoguanidine, melamine, etc. in a polyoxymethylene polymer over a long period of time, the mold deposit adheres to the mold and deteriorates the appearance of the molded product. In some cases, the gas vent may be blocked to cause short shots, resulting in molding processing defects. There is also a problem that these additives are oozed out when a molded product obtained by molding the polymer composition is exposed to high temperature and high humidity.

  As a technique for solving these problems, Patent Document 1 proposes a technique of blending a polyoxymethylene polymer in combination with an antioxidant and a water-insoluble melamine-formaldehyde polycondensate. .

  However, in the polymer composition proposed in Patent Document 1, the problem of adhesion of mold deposits is insufficiently improved, and further, the formaldehyde scavenging ability is poor. There is a risk of coming. Furthermore, since the melamine-formaldehyde polycondensate has a reticulated molecular structure and lacks meltability, it is difficult to melt and uniformly disperse it in the polyoxymethylene polymer.

  Further, Patent Document 2 discloses a technique for solving the above problem, but the polymer composition disclosed in Patent Document 2 is insufficient in improving the problem of mold deposit and has a formaldehyde scavenging ability. It is scarce.

JP 52-33943 A JP-A-4-81449

  The present invention has been made in order to solve the above-mentioned problems, and its purpose is to provide a mold deposit mold at the time of molding of a molded product made from polymer pellets containing a polyoxymethylene polymer. It is in suppressing adhesion of.

  Conventionally, mold deposits derived from additives are suppressed by polycondensation of melamine, but there is a problem that mold deposits are generated due to formaldehyde generation due to poor formaldehyde scavenging ability. Therefore, the present inventors have made extensive studies to solve the above problems. As a result, the mechanism of mold deposit generation when melamine is used is due to the content of melamine, the content of methylolated melamine in the raw material polyoxymethylene polymer pellets, and the amount of formaldehyde generated during molding. I found out. The main factor was that the amino group of melamine was formed by the reaction with formaldehyde rather than melamine itself. Specifically, it has been clarified that controlling the production of methylol melamine contained in the polyoxymethylene polymer pellets is effective in reducing the mole deposit, and the present invention has been completed. More specifically, the present invention provides the following.

（式（１）中の、Ｘは、前記ポリオキシメチレン重合体ペレットに含まれる水可溶成分中のトリアジン環を有する化合物の含有量であり、Ｙは前記ポリオキシメチレン重合体ペレットに含まれるメラミンの含有量であり、Ｘ−Ｙは前記ポリオキシメチレン重合体ペレットに含まれる前記メチロール化物の含有量を表す。（いずれもポリオキシメチレン重合体ペレットを１００質量部としたときの含有量） (1) (A) 0.01 to 1.0 part by mass of (B) sterically hindered phenolic antioxidant, and (C) a methylolated product of melamine and melamine with respect to 100 parts by mass of polyoxymethylene polymer. In total, 0.01 to 0.10 parts by mass of polyoxymethylene polymer pellets in which the mass of the melamine and the mass of the methylolated product satisfy the following formula (1).

(In Formula (1), X is content of the compound which has a triazine ring in the water soluble component contained in the said polyoxymethylene polymer pellet, Y is contained in the said polyoxymethylene polymer pellet. It is the content of melamine, and XY represents the content of the methylolated product contained in the polyoxymethylene polymer pellets (both content when the polyoxymethylene polymer pellets are 100 parts by mass).

  (2) Poly (1) containing 0.01 to 0.20 parts by mass of the (D) alkali metal or alkaline earth metal-containing compound with respect to 100 parts by mass of the (A) polyoxymethylene polymer. Oxymethylene polymer pellets.

  (3) (1) or (2) containing a total of 0.01 to 0.30 parts by mass of at least one of (E) fatty acid amide and fatty acid ester with respect to 100 parts by mass of the (A) polyoxymethylene polymer. A polyoxymethylene polymer pellet as described in 1.

  (4) The polyoxymethylene polymer pellet according to any one of (1) to (3), wherein the content of the methylolated product is 0.025 parts by mass or less with respect to 100 parts by mass of the polyoxymethylene polymer. .

  (5) A method for producing the polyoxymethylene polymer pellet according to any one of (1) to (4), wherein the polyoxymethylene polymer, a sterically hindered phenolic antioxidant, melamine, Is added to an extruder, and the raw material is kneaded in the extruder to obtain a pellet-like composition containing a methylolated product of melamine produced by a reaction between melamine and formaldehyde, and then a drying temperature of 60 to 145. A method for producing polyoxymethylene polymer pellets, wherein the pellet-shaped composition is dried under the conditions of C and a drying time of 3 hours or more.

（式（１）中の、Ｘは、前記ポリオキシメチレン重合体ペレットに含まれる水可溶成分中のトリアジン環を有する化合物の含有量であり、Ｙは前記ポリオキシメチレン重合体ペレット中のメラミンの含有量であり、Ｘ−Ｙは前記ポリオキシメチレン重合体ペレット中の前記メチロール化物の含有量を表す。（いずれもポリオキシメチレン重合体ペレットを１００質量部としたときの含有量） (6) Method for evaluating the quality of polyoxymethylene polymer pellets that are judged to be non-defective when the mass of melamine and the mass of methylolated melamine contained in the polyoxymethylene polymer pellet satisfy the following formula (1) .

(In the formula (1), X is the content of the compound having a triazine ring in the water-soluble component contained in the polyoxymethylene polymer pellet, and Y is the melamine in the polyoxymethylene polymer pellet. XY represents the content of the methylolated product in the polyoxymethylene polymer pellets (both content when the polyoxymethylene polymer pellets are 100 parts by mass).

  If the polyoxymethylene polymer pellet of the present invention is used as a raw material, adhesion of the mold deposit to the mold during molding of the molded product can be suppressed.

  Hereinafter, embodiments of the present invention will be described. In addition, this invention is not limited to the following embodiment.

<Polyoxymethylene polymer pellet>
The polyoxymethylene polymer pellet of the present invention contains (A) a polyoxymethylene polymer, (B) a sterically hindered phenolic antioxidant, and (C) melamine and a methylolated product of melamine. Accordingly, (D) an alkali metal or alkaline earth metal-containing compound and (E) another component such as an aliphatic amide or a fatty acid ester can be included.

[(A) polyoxymethylene polymer]
(A) A polyoxymethylene polymer is a polymer compound having an oxymethylene group (—CH ₂ O—) as a main structural unit. (A) The polyoxymethylene polymer may be any of a polyoxymethylene homopolymer, a copolymer containing a small amount of other structural units in addition to the oxymethylene group, a terpolymer, and a block copolymer. It may have a branched or crosslinked structure.

  (A) It is preferable that the number of hemi-formal end groups, the number of formyl end groups, and the weight of unstable terminal portions of the polyoxymethylene polymer are in a specific range. This is because when these amounts increase, the amount of formaldehyde generated from the polyoxymethylene polymer increases during the molding of the polyoxymethylene polymer pellets.

Here, the hemiformal end group is represented by —OCH ₂ OH, and is also referred to as a hydroxymethoxy end group or a hemiacetal end group. The number of hemi-formal terminal groups is preferably 1.0 mmol / kg or less. A more preferable hemi-formal terminal group quantity is 0.5 mmol / kg or less. Further, hemiformal terminal group number can be determined by ¹ H-NMR measurement. The specific measuring method can refer to the method described in JP-A-2001-11143. In addition, since the quantity of formaldehyde generated at the time of the shaping | molding process of a polyoxymethylene polymer pellet decreases so that there are few hemi-formal terminal group quantities, it is so preferable that the quantity of hemi-formal terminal groups in (A) polyoxymethylene polymer is small. The hemi-formal terminal group amount and formyl group terminal group amount of the polyacetal copolymer were measured according to the method described in JP-A-2001-11143 using an AVANCE400 FT-NMR apparatus manufactured by Bruker Co., Ltd. Is the value (mmol / kg) obtained by

  A formyl end group refers to -CHO. The number of formyl end groups is preferably 2.0 mmol / kg or less. A more preferable formyl end group quantity is 1.0 mmol / kg or less. The formyl end group quantity can be measured by the same method as the hemi-formal end group quantity. For the same reason as in the case of the hemi-formal end group quantity, the smaller the formyl end group quantity in the (A) polyoxymethylene polymer, the better.

  The unstable terminal group refers to a part that is present at the terminal part of the polyoxymethylene polymer and is unstable to heat and base and easily decomposes. The weight of the unstable terminal portion is preferably 0.5% by mass or less. A more preferable unstable terminal portion weight is 0.25% by mass or less. This unstable terminal part weight refers to the value derived by the method described in the examples. In addition, for the same reason as in the case of the hemiformal terminal group quantity, it is preferable that the weight of the unstable terminal portion in the (A) polyoxymethylene polymer is smaller.

  (A) The molecular weight of the polyoxymethylene polymer is not particularly limited, but is a melt index (measured at 190 ° C. under a load of 2.16 kg according to ASTM-D1238) which is an index of fluidity of the polyoxymethylene polymer during molding. ) Is preferably 1 to 50 g / 10 min.

  Although the specific example of the method of manufacturing the polyacetal polymer (A) which satisfy | fills the requirements of this invention for the following is given, it is not limited to this method at all.

First, it is important to reduce impurities such as water, alcohol (for example, methanol), and acid (for example, formic acid) contained in the monomer and comonomer, which are active impurities that form unstable terminals in the polymerization system. In addition, the total amount of these active impurities is preferably 1 × 10 ⁻² mol% or less, more preferably 5 × 10 ⁻³ mol% or less, based on all monomers in the reaction system. If the content is excessive, it is not preferable to obtain a polyacetal polymer having a small number of unstable terminal portions. It should be noted that chain transfer agents that do not form unstable ends, for example, low molecular weight linear acetals having both ends having an alkoxy group, such as methylal, are contained in an arbitrary amount to adjust the molecular weight of the polyacetal polymer. Can do.

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 5 × 10 ⁻³ to 1 × 10 ⁻² mol%, particularly 1 ×. it is preferably in the range of ^{10 -3 ~7 × 10 -3 mol%} . Setting the amount of catalyst in such a range is effective in preventing the formation of unstable end portions. If 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 it becomes difficult to obtain a polyacetal polymer having a small number of unstable end portions that satisfies the requirements of the present invention. On the other hand, if the amount of the catalyst is too small, it is not preferable because the polymerization reaction rate decreases and the polymerization yield decreases.

  The amount and type of comonomer greatly affects the thermal stability of the polyacetal polymer. As the polyacetal polymer of the present invention, trioxane and one or more compounds selected from cyclic ether and cyclic formal are used in a ratio of the former / the latter = 99.9 / 0.1 to 80.0 / 20.0 ( Copolymerized at a weight ratio), more preferably the former / the latter = 99.5 / 0.5 to 90.0 / 10.0 (weight ratio). . Further, as the compound selected from cyclic ether and cyclic formal, ethylene oxide, 1,3-dioxolane, 1,4-butanediol formal, and diethylene glycol formal are particularly preferable.

  As the polymerization method, any conventionally known method can be used, but a continuous bulk polymerization method for obtaining a solid powdery bulk polymer with the progress of polymerization using a liquid monomer is industrially preferable, and a polymerization temperature is 60 to It is desirable to maintain at 105 ° C, particularly 65 to 100 ° C.

  When a catalyst comprising boron trifluoride or a coordination compound thereof is used, as a method for deactivating the catalyst after polymerization, a method of adding the polymer after polymerization to an aqueous solution containing a basic compound or the like is possible. In order to obtain a polyacetal polymer that satisfies the requirements of the present invention, it is preferable to pulverize and subdivide the polymer obtained by the polymerization reaction and bring it into contact with a deactivator to quickly deactivate the catalyst. For example, a polymer used for deactivation of the catalyst is pulverized, and 80% by weight or more, preferably 90% by weight thereof has a particle size of 1.5 mm or less, and 15% by weight or more, preferably 20% by weight or more is 0.00. It is desirable that the particle size is 3 mm or less. Basic compounds for neutralizing and deactivating the polymerization catalyst include ammonia, amines such as triethylamine, tributylamine, triethanolamine, and tributanolamine, or oxides of alkali metals and alkaline earth metals. , Hydroxides, salts, and other known catalyst deactivators can be used. These basic compounds are preferably added in an aqueous solution of 0.001 to 0.5% by weight, particularly 0.02 to 0.3% by weight. Moreover, the temperature of the preferable aqueous solution is 10-80 degreeC, Most preferably, it is 15-60 degreeC. Further, after the polymerization is completed, it is preferable that the catalyst is deactivated by promptly adding it to these aqueous solutions.

  In addition, a hindered phenolic antioxidant is added to the monomer in an amount of 0.01 to 0.1% by weight with respect to all monomers in advance of the polymerization, and polymerization is performed in the presence of the hindered phenol in the polymerization reaction system. By uniformly presenting the dophenol antioxidant, depolymerization during polymerization can be suppressed, and post-treatment such as drying after polymerization and oxidative degradation in a stabilization step can also be suppressed.

  A polyacetal polymer with a small amount of unstable terminals can be produced by reducing impurities contained in the monomer and comonomer as described above, selecting a production process, optimizing production conditions, and the like. If necessary, it is possible to further reduce the amount of unstable terminals through the stabilization step. As the stabilization step, the polyacetal polymer is heated to a temperature equal to or higher than its melting point and processed in a molten state to decompose and remove only unstable parts, or a non-uniform system is maintained in an insoluble liquid medium at 80 ° C. or higher. For example, the unstable end portion may be decomposed and removed by heat treatment at a temperature of 5 ° C.

[(B) Steric hindrance phenolic antioxidant]
(B) The sterically hindered phenolic antioxidant is added for the purpose of suppressing the decomposition of the (A) polyoxymethylene polymer.

  Usable (B) sterically hindered phenolic antioxidants include 2,2′-methylenebis (4methyl-6-tert-butylphenol), 1,6-hexanediol-bis [3- (3,5- Di-t-butyl-4-hydroxyphenyl) propionate], pentaerythritol tetrakis [3- (3,5-di-t-butyl-4-hydroxy-phenyl) propionate], triethylene glycol-bis- [3- ( 3-tert-butyl-5-methyl-4-hydroxyphenyl) propionate], 1,3,5-trimethyl-2,4,6-tris (3,5-di-tert-butyl-4-hydroxy-benzyl) Benzene, n-octadecyl-3- (4′-hydroxy-3 ′, 5′-di-t-butylphenol) propionate, 4,4′-methylenebis (2, -Di-tert-butylphenol), 4,4'-butylidene-bis- (6-tert-butyl-3-methyl-phenol), di-stearyl-3,5-di-tert-butyl-4-hydroxybenzylphosphonate 2-t-butyl-6- (3-t-butyl-5-methyl-2-hydroxybenzyl) -4-methylphenyl acrylate, N, N′-hexamethylenebis (3,5-di-t-butyl -4-hydroxy-hydrocinnamamide) and the like.

  (B) The sterically hindered phenolic antioxidant may be produced and used by a conventionally known method, or a commercially available product may be used.

  Content of (B) sterically hindered phenolic antioxidant in a polyoxymethylene polymer is 0.01-1.0 mass part with respect to 100 mass parts of (A) polyoxymethylene polymer. When the content is less than 0.01 parts by mass, the effect of suppressing the decomposition of the (A) polyoxymethylene polymer tends to be insufficient, which is not preferable. Moreover, when the said content exceeds 1.0 mass part, since the effect which suppresses said decomposition | disassembly reaches saturation and may discolor a polyoxymethylene polymer pellet, it is unpreferable. A more preferable content is 0.04 parts by mass or more and 0.40 parts by mass or less.

[(C) Melamine and melamine methylolated product]
Melamine refers to unreacted melamine. The methylolated product refers to a methylolated product of melamine, which is methylolmelamine obtained by reacting the amino group of melamine with formaldehyde. The methylolated product is a mononuclear body that has not undergone condensation. The methylolated products are classified into monomethylol melamine, dimethylol melamine, trimethylol melamine, tetramethylol melamine, pentamethylol melamine, and hexamethylol melamine depending on the degree of methylolation.

  Melamine produced by a conventionally known method may be used, or a commercially available product may be used. The methylolated product is produced by the reaction of melamine and formaldehyde during the production of polyoxymethylene polymer pellets. In addition, this invention does not exclude using the methylolation thing manufactured by the conventionally well-known method as a raw material at the time of manufacture of a polyoxymethylene polymer pellet.

In the present invention, the content ratio of the methylolated product to the total amount of melamine and the methylolated product in the polyoxymethylene polymer pellets (in this specification, sometimes referred to as “degree of methylolation”) is in a specific range. adjust. Specifically, the methylolation degree is adjusted so as to satisfy the following formula (1). When the degree of methylol exceeds 50%, melamine is methylolated during molding of the molded product using the polyoxymethylene polymer pellets of the present invention as a raw material, and the resulting methylolated product exudes into the mold. It is not possible to sufficiently prevent the mold deposit from adhering to the surface. The methylolation degree is preferably 5% or less, but it is technically difficult to control the methylolation degree to 5% or less.

  X in Formula (1) is the content of the compound having a triazine ring in the water-soluble component contained in the polyoxymethylene polymer pellet of the present invention (when the polyoxymethylene polymer pellet is 100 parts by mass). Content). X is determined based on the absorbance obtained by separating a water-soluble component from the polyoxymethylene polymer, dissolving the water-soluble component in 1M HClaq, and measuring the absorbance. A more detailed method for determining the content of the compound having a triazine ring is described in Examples.

  Y in the formula (1) is the content of melamine contained in the polyoxymethylene polymer pellets of the invention. Y is determined by liquid chromatograph mass spectrometry (LC / MS). As described in the Examples, according to LC / MS, the content of melamine in the polyoxymethylene polymer pellet (100% of the polyoxymethylene polymer pellet was obtained using the fact that m / z of melamine was 127. The content when the content is parts by mass) can be quantified.

  (XY) in the formula (1) is the content of the methylolated product contained in the polyoxymethylene polymer pellet of the invention (content when the polyoxymethylene polymer pellet is 100 parts by mass). . Since melamine multimers such as melamine dimer are hardly soluble in water, X can be considered to be the total amount of melamine and methylolated product contained in the polyoxymethylene polymer pellet. As a result, if the content of melamine is subtracted from this total amount, the content of methylolated product is obtained.

  The total content of melamine and methylolated product contained in the polyoxymethylene polymer pellet is 0.01 to 0.10 parts by mass with respect to 100 parts by mass of (A) polyoxymethylene polymer. When the content is less than 0.01 parts by mass, the effect of trapping formaldehyde by melamine is not sufficient. When the content exceeds 0.10 parts by mass, melamine is methylolated during molding of the molded product using the pellets of the present invention, and the resulting methylolated product exudes into the mold. This is not preferable because mold deposits derived from the above are likely to occur. A more preferable content is 0.03 parts by mass or more and 0.07 parts by mass or less.

  In particular, the methylolated product content is preferably 0.025 parts by mass or less with respect to 100 parts by mass of the polyoxymethylene polymer.

[(D) Alkali metal or alkaline earth metal-containing compound]
The polyoxymethylene polymer pellets of the present invention preferably further contain (D) an alkali metal or alkaline earth metal-containing compound (hereinafter sometimes simply referred to as “metal-containing compound”). (D) By including an alkali metal or alkaline earth metal-containing compound, an effect of capturing formic acid formed by oxidation of formaldehyde generated from the polyoxymethylene polymer can be obtained. Formic acid decomposes the polyoxymethylene polymer and promotes the generation of formaldehyde, and a mold deposit derived from the polyoxymethylene polymer is deposited during the molding process.

  Usable (D) alkali metal or alkaline earth metal-containing compounds include alkali metal or alkaline earth metal hydroxides, alkali metal or alkaline earth metal carboxylates, alkali metal or alkaline earth metal Oxides, alkali metal or alkaline earth metal carbonates may be mentioned. Specifically, magnesium hydroxide, calcium hydroxide, calcium stearate, 12-hydroxycalcium stearate, calcium citrate, magnesium oxide, calcium oxide, calcium carbonate, magnesium carbonate can be used (D) alkali metal or The alkaline earth metal-containing compound is not limited to these.

  (D) As the alkali metal or alkaline earth metal-containing compound, one produced by a conventionally known method may be used, or a commercially available product may be purchased and used.

  The content of the (D) alkali metal or alkaline earth metal-containing compound in the polyoxymethylene polymer pellet is 0.005 to 0.50 parts by mass with respect to 100 parts by mass of the (A) polyoxymethylene polymer. is there. (D) If the content of the alkali metal or alkaline earth metal-containing compound is 0.005 parts by mass or more, it is preferable because it is easy to trap formic acid formed by oxidation of formaldehyde generated from the polyoxymethylene polymer. (D) When the content of the alkali metal or alkaline earth metal-containing compound is more than 0.50 parts by mass, the disproportionation reaction between formaldehyde and the metal salt and the formation of formose that causes coloring are promoted. It is not preferable for the reason. The content of the metal-containing compound (D) is more preferably 0.01 to 0.20 parts by mass.

[(E) Fatty acid amide, fatty acid ester]
The polyoxymethylene polymer of the present invention preferably contains at least one of a fatty acid amide and a fatty acid ester. By including at least one of a fatty acid amide and a fatty acid ester, an effect of improving mold release properties during molding can be obtained.

  The fatty acid amide is not particularly limited, but is preferably derived from at least one saturated or unsaturated fatty acid containing 10 or more carbon atoms and an amine or diamine.

  The fatty acid ester is preferably derived from at least one saturated or unsaturated fatty acid containing 10 or more carbon atoms and an alcohol.

  Examples of fatty acids constituting fatty acid amides and fatty acid esters include lauric acid, myristic acid, palmitic acid, stearic acid, behenic acid, montanic acid, oleic acid, etc., and examples of alcohols constituting fatty acid esters include propyl And polyhydric alcohols such as butyl, ethylene glycol, propylene glycol, glycerin and pentaerythritol, and monohydric alcohols such as propyl, butyl, lauryl, myristyl, palmityl, stearyl and behenyl. Particularly preferred fatty acid amides include ethylene bisstearyl amide and the like, and fatty acid esters include glycerin monostearate and the like.

  As fatty acid amides and fatty acid esters, those produced by a conventionally known method may be used, or commercially available products may be purchased and used.

  The content of the fatty acid amide and the fatty acid ester in the polyoxymethylene polymer pellet is not particularly limited, but is 0.01 to 0.50 parts by mass with respect to 100 parts by mass of the (A) polyoxymethylene polymer. Is preferred. If the said content is 0.01 mass part or more, it is preferable for the reason of improving the mold release property at the time of a shaping | molding process. Moreover, when the said content exceeds 0.50 mass part, it is unpreferable because the exudation of methylolated substances etc. generate | occur | produces on the molded article surface. The content is more preferably 0.05 to 0.30 parts by mass.

[Other ingredients]
The polyoxymethylene polymer pellets of the present invention may contain components other than the components (A) to (E) as long as the effects of the present invention are not impaired. Examples of other components include other polymers and general additives.

[Properties of polyoxymethylene polymer pellets]
In the polyoxymethylene polymer pellet of the present invention, the content ratio of the methylolated product to the total amount of the melamine and the methylolated product contained in the pellet is in a specific range. For this reason, at the time of the shaping | molding process of the molded article which uses the pellet of this invention as a raw material, the quantity which a mold deposit adheres to a metal mold | die can be suppressed.

  The shape of the polyoxymethylene polymer pellet of the present invention is a general pellet shape, and the size and the like can be appropriately adjusted within a conventionally known range.

<Method for producing polyoxymethylene polymer pellet>
As above-mentioned, the polyoxymethylene polymer pellet of this invention has the content ratio of the methylolation thing with respect to the total amount of a melamine and the said methylolation thing in a specific range. The methylolated product is also produced from melamine during the production of polyoxymethylene polymer pellets. Therefore, it is necessary to adjust the production conditions to adjust the content ratio of the methylolated product in the polyoxymethylene polymer pellets to a specific range.

  The method for producing the polyoxymethylene polymer pellets of the present invention will be described using a general extruder as an example. In a general extruder, a screw is disposed in a cylinder having a hopper for charging raw materials. The screw has a feed zone (feeding unit), a compression zone (compression unit), and a metering zone (measuring unit) in this order from the upstream side to the downstream side of the screw. A die is attached to the downstream end of the extruder.

  The supply unit normally has a function of transferring the raw material from the hopper side to the die direction side at a temperature setting such that the raw material does not melt, and sends the raw material to the compression unit. The compression unit melt-kneads the raw material while applying pressure to the raw material sent from the supply unit, and sends the melt-kneaded raw material to the measuring unit. The metering unit sends the melt-kneaded raw material to the die by a constant amount under a constant pressure. In addition, you may use the screw which has a mixing zone (kneading part) downstream from a measurement part.

  More specifically, first, raw materials are charged into an extruder. Here, the raw material is a polymer composition containing the above-mentioned components, and all the components may be charged into the extruder at the same time, or some of the components may be charged in the compression part and other parts. . Also, once the pellets with different compositions are prepared, the pellets are mixed (diluted) in a predetermined amount and subjected to extrusion, and polymer pellets of the desired composition are obtained after extrusion. One or more of each component is directly added to the extruder. Any method such as charging can be used. Further, in the production of polyoxymethylene polymer pellets, (A) part or all of the polyoxymethylene polymer is pulverized, mixed with other components, put into a hopper, and extruded. This is a preferable method for improving the dispersibility of the additive.

  In the compression section, as described above, the raw material is kneaded while applying pressure to the raw material. The degree of kneading depends on extrusion conditions such as the number of screw rotations. In the production of polyoxymethylene polymer pellets, the degree of kneading can be adjusted as appropriate according to the type of resin, the shape of the resin molding, and the like.

  By extruding from the die, a strand-like extrudate is obtained. This strand-shaped extrudate can be formed into a pellet by cutting by a conventionally known method (for example, a pelletizing method). By drying the composition cut into pellets, the polyoxymethylene polymer pellets of the present invention can be produced.

  The conditions for drying the pellet-like composition affect the degree of methylolation of the methylolated product because it promotes the elimination of formaldehyde from the methylolated melamine. By increasing the drying temperature or extending the drying time, the methylolation degree of the methylolated product tends to decrease. On the other hand, when the drying temperature is lowered or the drying time is shortened, the methylolation degree of the methylolated product tends to increase. In the production of the polyoxymethylene polymer pellets of the present invention, it is preferable to adjust the drying temperature in the range of 60 to 145 ° C. and the drying time of 3 hours or more. However, care should be taken because drying at a high temperature for a long time causes coloring of the pellets. The allowable long-time level and the high-temperature level vary depending on the type of resin included.

<Quality evaluation method of polyoxymethylene polymer pellet>
In the polyoxymethylene polymer pellets produced as described above, the content ratio of methylolated product to the total amount of melamine and methylolated product is in a specific range. For this reason, it is possible to suppress the adhesion of the mold deposit to the mold and the generation of formaldehyde during the molding process of a molded product made of polymer pellets containing a polyoxymethylene polymer.

  Using the above points, the quality of polyoxymethylene polymer pellets whose content ratio of methylolated product relative to the total amount of melamine and methylolated product is unknown can be evaluated. Specifically, the content ratio of the polyoxymethylene polymer pellet with the unknown content ratio is derived from the content of melamine and the content of methylolated product in the pellet, and the derived content ratio is expressed by the above formula (1 ), It is possible to evaluate the quality of the polyoxymethylene polymer pellets. In addition, content of the melamine in a pellet and content of methylolation thing can be measured by the method similar to the method described by description of the polyoxymethylene polymer pellet.

  Hereinafter, the present invention will be described in more detail with reference to examples, but the present invention is not limited to these examples.

<Material>
A-1: polyacetal copolymer (MI = 9 g / 10 min), hemi-formal terminal group quantity is 1.0 mmol / kg, formyl terminal group quantity is 2.0 mmol / kg, unstable terminal part weight is 0.5 mass% Polyoxymethylene copolymer A-2: polyacetal copolymer (MI = 9 g / 10 min) hydrolyzed, hemi-formal end group quantity 0.5 mmol / kg, formyl end group quantity 1.0 mmol / Kg, polyoxymethylene copolymer A-3 having an unstable terminal portion weight of 0.25% by mass or less; polyacetal copolymer (MI = 27 g / 10 min), hemi-formal terminal group quantity is 1.0 mmol / kg, Polyoxymethylene copolymer A-4 having a formyl terminal group quantity of 2.0 mmol / kg and an unstable terminal moiety weight of 0.5 mass%; The coalescence (MI = 27 g / 10 min) was hydrolyzed, the hemi-formal terminal group quantity was 0.5 mmol / kg, the formyl terminal group quantity was 1.0 mmol / kg, and the unstable terminal part weight was 0.25 mass%. The following polyoxymethylene copolymer B; tetrakis [methylene-3- (3,5-di-t-butyl-4-hydroxyphenyl) propionate] methane C; melamine D-1; 12-hydroxycalcium stearate D-2 Calcium stearate D-3; magnesium oxide E-1; ethylene bis stearamide E-2; glycerin monostearate

  As a polymerization method, a biaxial paddle type continuous polymerization machine was continuously supplied with a mixture of 96.7% by weight of trioxane and 3.3% by weight of 1,3-dioxolane, and 15 ppm of boron trifluoride was used as a catalyst. Polymerization was carried out by adding. The mixture of trioxane and 1,3-dioxolane used for the polymerization was 0.03% by weight of pentaerythritol-tetrakis [3- (3,5-di-t-butyl-4-hydroxyphenyl) propionate based on the total amount. ] Was contained. Further, the mixture of trioxane and 1,3-dioxolane used for polymerization contained 6 ppm water, 3.5 ppm methanol, and 5 ppm formic acid as impurities.

  Next, the polymer discharged from the polymerizer outlet is immediately added with an aqueous solution containing 1000 ppm of triethylamine and pulverized and stirred to deactivate the catalyst, and then centrifuged and dried to recover the crude polyoxymethylene copolymer. A polymer was obtained (A-1, 3). A-1 and A-3 can be produced by adjusting the polymerization conditions.

  A method for obtaining a polyoxymethylene polymer (A-2, 4) in which hemi-formal end groups, formyl end groups, and unstable end portions are further reduced is obtained by using a cylindrical pressure-resistant container that can be kept warm, from above. The pellet-shaped polymer was continuously supplied, and hydrolyzed with an aqueous solution at 135 ° C. containing 500 ppm of triethylamine from the lower part for 8 hours, followed by centrifugation and drying.

  According to ASTM-D1238, a melt index serving as an index of fluidity of the polyoxymethylene polymer was measured under the conditions of 190 ° C. and a load of 2.16 kg.

  The number of hemi-formal end groups and the number of formyl end groups of the polyoxymethylene polymers A1 to A4 were derived by the same method as the end group analysis method described in Examples of JP-A-2001-11143.

The weights of unstable terminal portions of the polyoxymethylene polymers A1 to A4 were derived by the following derivation method.
(Derivation method)
1 g of polyoxymethylene polymer is placed in a pressure-resistant sealed container together with 100 mL of 50% (volume%) aqueous methanol solution containing 0.5% (volume%) ammonium hydroxide, heat-treated at 180 ° C. for 45 minutes, and then cooled. The amount of formaldehyde decomposed and dissolved in the solution obtained by opening was quantified and expressed in parts by mass relative to 100 parts by mass of the polyoxymethylene polymer.

<Manufacture of polyoxymethylene polymer pellets>
The polyoxymethylene polymer pellets of Examples 1 to 6 and the polyoxymethylene polymer pellets of Comparative Examples 1 to 4 were produced by the following method.

First, raw materials containing the components shown in Tables 1 and 2 in the proportions shown in Tables 1 and 2 (units are parts by mass) were charged into an extruder (“TEX30α” manufactured by Nippon Steel Works). 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 to produce polyoxymethylene polymer pellets (columnar shape (diameter 1-2 mm, length 2-3 mm)). The drying conditions are shown in Tables 1 and 2.
(Extrusion conditions)
Cylinder temperature: 170-200 ° C
Extrusion amount: 18 kg / hr (using a quantitative feeder)
Rotation speed: 120rpm

<Content of compound having triazine ring>
The content (parts by mass) of the compound having a triazine ring in the water-soluble component contained in the polyoxymethylene polymer pellets of Examples and Comparative Examples was derived by the following method. The derivation results are shown in Tables 1 and 2.
(Derivation method)
A solution was obtained by dissolving 0.5 g of polyoxymethylene polymer pellets in 10 mL of hexafluoroisopropanol. About 30 mL of water was gradually added to the solution to precipitate the polymer. The solution was separated into a precipitate and a liquid by suction filtration, and the liquid was concentrated by an evaporator and dried to obtain a residue. The residue was dissolved in 1M HClaq and then made up to 50 mL, and the absorbance at 236 nm (absorption region of the compound having a triazine ring) was measured. The concentration of the compound having a triazine ring was determined from the absorbance based on a calibration curve representing the relationship between the absorbance prepared in advance and the concentration of the compound having a triazine ring. Finally, the content of the compound having a triazine ring in the water-soluble component contained in the polyoxymethylene polymer pellets of Examples and Comparative Examples was derived from this concentration.

<Melamine content>
The content (parts by mass) of melamine contained in the polyoxymethylene polymer pellets of Examples and Comparative Examples was derived by the following method. The derivation results are shown in Tables 1 and 2.
(Derivation method)
A solution was obtained by dissolving 0.1 g of polyoxymethylene polymer pellets in 1.5 mL of hexafluoroisopropanol. 15 mL of water was gradually added to the solution to precipitate a polymer. The solution was separated into a precipitate and a liquid by suction filtration, and the liquid was made up to 100 mL. The liquid was further diluted 10 times, and the diluted liquid was analyzed under the following conditions using an LC / MS analyzer, whereby the melamine contained in the polyoxymethylene polymer pellets of Examples and Comparative Examples was analyzed. The content was quantified.
(Analysis conditions)
eluent: 100 mM Ammonium form / MeCN = 10/90 → 50/50, 0.4 mL / min
column: Acquity HILIC 1.7 μm, 2.1 × 150 mm
open temp. : 40 ° C
MSD: ESI positive, capillary 15V, cone 2V, extractor 2V
m / z: 127 (melamine)

<Content of methylolated product>
By subtracting the content of melamine from the content of the compound having a triazine ring, the content of methylolated product in the polyoxymethylene polymer pellet (content when the polyoxymethylene polymer pellet is 100 parts by mass) Was derived. The derived results are also shown in Tables 1 and 2. The methylolation degree (%) is also shown in Tables 1 and 2.

<Mold deposit weight test>
First, the weight of the piece attached to the injection mold was measured in advance. Next, a molded product (2.3 mm × 3.3 mm, 1 mmt) using the polyoxymethylene polymer pellets of Examples and Comparative Examples as a raw material was continuously molded (10000 shots) under the following molding conditions with an injection molding machine. Finally, the weight of the top after the continuous molding was measured, and the weight of the mold deposit, which is a deposit of cavities in the mold, was quantified.
(Molding condition)
Injection molding machine; S-2000i 50B (manufactured by FANUC CORPORATION)
Mold: 2.3mm x 3.3mm, 1mmt
Cylinder temperature: 185-215 ° C
Injection speed: 280 mm / s
Holding pressure: 40 MPa
Mold temperature: 80 ℃

  From the above results, by adjusting the degree of methylolation within the range of 5% to 50%, the amount of mold deposit adhering to the mold can be greatly increased during the molding of the molded product made of polyoxymethylene polymer pellets. It was confirmed that it can be reduced.

Claims (6)

(A) For 100 parts by mass of the polyoxymethylene polymer,
(B) 0.01-1.0 part by mass of a sterically hindered phenolic antioxidant,
(C) A total of melamine and methylolated melamine, 0.01 to 0.10 parts by mass,
The polyoxymethylene polymer pellet with which the mass of the said melamine and the mass of the said methylolation material satisfy | fill following formula (1).

(In Formula (1), X is content of the compound which has a triazine ring in the water soluble component contained in the said polyoxymethylene polymer pellet, Y is contained in the said polyoxymethylene polymer pellet. It is the content of melamine, and XY represents the content of the methylolated product contained in the polyoxymethylene polymer pellets (both content when the polyoxymethylene polymer pellets are 100 parts by mass).   The polyoxymethylene polymer according to claim 1, comprising 0.01 to 0.20 parts by mass of (D) an alkali metal or alkaline earth metal-containing compound with respect to 100 parts by mass of the (A) polyoxymethylene polymer. pellet.   The polyoxy of Claim 1 or 2 which contains at least one of (E) fatty acid amide and fatty acid ester with respect to 100 mass parts of said (A) polyoxymethylene polymers in total 0.01-0.30 mass parts. Methylene polymer pellet.   The polyoxymethylene polymer pellet according to any one of claims 1 to 3, wherein a content of the methylolated product is 0.025 parts by mass or less with respect to 100 parts by mass of the polyoxymethylene polymer. A method for producing a polyoxymethylene polymer pellet according to any one of claims 1 to 4,
A raw material containing a polyoxymethylene polymer, a sterically hindered phenolic antioxidant, and melamine is charged into an extruder, the raw material is kneaded in the extruder, and the melamine produced by the reaction of melamine and formaldehyde A method for producing polyoxymethylene polymer pellets, which is dried under conditions of a drying temperature of 60 to 145 ° C. and a drying time of 3 hours or more after obtaining a pellet-like composition containing a methylolated product. A method for evaluating the quality of polyoxymethylene polymer pellets, which are determined to be non-defective when the mass of melamine and the mass of methylolated melamine contained in the polyoxymethylene polymer pellet satisfy the following formula (1).

(In the formula (1), X is the content of the compound having a triazine ring in the water-soluble component contained in the polyoxymethylene polymer pellet, and Y is the melamine in the polyoxymethylene polymer pellet. XY represents the content of the methylolated product in the polyoxymethylene polymer pellets (both content when the polyoxymethylene polymer pellets are 100 parts by mass).