Low-formaldehyde content polyacetal fiber manufacturing method, and fiber

Abstract

To provide a manufacturing method for a low-formaldehyde content POM fiber that generates a small amount of formaldehyde from the fiber, and the POM fiber manufactured by the method.SOLUTION: There is provided a method that involves adding 0.1 to 5 wt.% of melamine or a melamine derivative, 0.01 to 5 wt.% of an alkaline earth metal hydroxide, and 0.01 to 5 wt.% of an antioxidant to a crude polymer after a POM polymerization reaction to obtain a heat-stabilized POM resin, and then adding 0.01 to 5 wt.% of a formalin scavenger to a resulting POM resin and melt-spinning a resulting resin to obtain a POM fiber with a low formaldehyde content. When spinning an alloy of POM and a biodegradable polyester resin such as PBS or PLA, a safely performed fiber with a low formaldehyde content can be obtained by further adding 0.1 to 5 wt.% of a carbodiimide compound.SELECTED DRAWING: None

Description

Technical Field

[0001] The present invention relates to a method for producing POM fibers and fibers, in which single-layer or multi-layer synthetic fibers mainly composed of polyacetal resin (hereinafter referred to as POM) have a free formaldehyde content of 16 ppm or less when measured for free formaldehyde in accordance with JIS L1041.

Background Art

[0002] POM is an engineering plastic with well-balanced mechanical properties, good wear resistance, heat resistance, electrical properties, and chemical resistance, and is widely used in various mechanical parts and electrical parts.

[0003] On the other hand, unlike nylon and polyester, POM has not been widely used as a fiber. This is because problems such as the difficulty of dyeing POM fibers and the relatively large unevenness in the longitudinal thickness of the fibers due to the high crystallization rate during spinning have been pointed out.

[0004] In addition, since the main raw material of the monomer of POM is formaldehyde, a very small amount of formaldehyde is generated by a slight thermal decomposition reaction during the polymerization of the resin or the heat history during molding processing, etc., so there is a problem that the regulation of free formaldehyde when used as a fiber product is exceeded.

[0005] When POM is applied as an industrial part by injection molding or extrusion molding, many nitrogen-based compounds such as melamine-based compounds, hydrazine-based compounds, urea-based compounds, amine-based and amide-based compounds, and additives combined with sterically hindered phenol (hindered phenol)-based antioxidants have been proposed as additives for suppressing the amount of formaldehyde generated.

[0006] For example, Patent Document 1 proposes a stabilized POM composition obtained by adding alkylene urethane, polybasic carboxylic acid amide and / or urea, and hindered phenol to a POM resin. However, it is not a patent for POM fibers.

[0007] Patent Document 2 provides a POM resin having excellent friction and wear characteristics and little mold deposit, and proposes a combination of an olefin polymer, at least one vinyl polymer, a melamine-formaldehyde polycondensate, and an antioxidant as additives. This patent is an invention of a composition for injection molding applications.

[0008] Patent Document 3 proposes a combination of a sterically hindered phenolic antioxidant, a specific nitrogen-containing compound, and a borate, which results in little exudation of additives from a POM resin molded article and little mold fouling even with continuity. This patent also targets POM for injection molding.

[0009] Patent Document 4 proposes a fiber in which an aliphatic or aromatic dihydrazide compound and a sterically hindered phenol are added for the purpose of suppressing formaldehyde generated during the production of POM resin fibers and improving the working environment during production. However, the free formaldehyde concentration that can be used as a fiber is not mentioned.

[0010] Patent Document 5 proposes a POM fiber containing 0.05 to 1.3 parts by weight of an inorganic filler in the POM resin, and the inorganic filler is a POM fiber containing at least one of magnesium and silicon, but nothing is written about free formaldehyde.

[0011] All of these patents propose improvements in the working environment during injection molding for the purpose of improving the thermal stability of POM resin, but they do not propose a technology related to POM fibers in which the formaldehyde content of the fibers is 16 ppm or less when measured in accordance with JIS L1041 for using POM as a fiber.

Prior Art Documents

Patent Documents

[0012]

Patent Document 1

[0013] The present invention relates to a method for producing low-formaldehyde-containing POM fibers that can be used as fibers for clothing and industrial materials, and POM fibers produced by the method. Generally, when producing fibers by melt-spinning a thermoplastic resin, compared to injection molding, sheet, or film molding, it takes a long time for the molten resin to pass through the melt resin pipe from the extruder, be pressurized by a gear pump, and reach the die. In normal injection molding or sheet / film molding, the residence time of the molten resin is 1 minute to 20 minutes, usually about 3 minutes to 10 minutes, whereas in spinning, the residence time is 20 minutes to 90 minutes, usually 20 minutes to 60 minutes. Since the resin temperature during spinning is usually controlled at 190°C to 250°C, preferably 190°C to 220°C, the POM resin does not decompose violently. However, even if there is a very small amount of decomposition, if the residual formaldehyde in the fiber is not below the JIS standard value, general use as a fiber is not permitted.

[0014] The method for analyzing free formaldehyde according to JIS L1041 is as follows: (1) Collect fabric parts from clothing and cut them finely. (2) Put 2.5 g of the sample into a glass container, add 100 ml of water, and perform extraction in a warm bath at 40°C. (3) Add an acetylacetone test solution to the extract and react it in a warm bath at 40°C. Similarly, add an ammonium acetate buffer solution to the extract and react it in a warm bath at 40°C. Pure water and each test solution are also subjected to the same operation as a control. (4) If the extract contains formaldehyde, it reacts with the acetylacetone solution and a yellow color development can be observed. (5) Analyze the reaction solution with a spectrophotometer and measure the absorbance at 412 - 415 nm. For the control, use pure water and each test solution, and measure the absorbance of the one reacted with the acetylacetone test solution as A and the one reacted with the buffer solution as A0. (6) If the absorbance difference A - A0 is 0.05 or less, it is within the standard (16 ppm or less). There has been no mention in the literature so far about a method for POM fibers produced by melt spinning to meet this standard.

Means for Solving the Problem

[0015] The present invention relates to a fiber in which the contained formaldehyde in the fiber is 10 ppm or less when a single-layer or multi-layer synthetic fiber made of POM or an alloy of 50 - 100 wt% of POM and 0 - 50 wt% of a biodegradable polyester resin measures free formaldehyde in accordance with JIS L1041. The synthetic fiber made of POM or an alloy of POM and a biodegradable polyester according to the present invention can be used in the form of knitted fabrics, woven fabrics, non-woven fabrics, webs, etc. as textiles, and can be widely used in clothing, bedding, interior, etc.

[0016] The synthetic fibers composed of POM or an alloy of POM and a biodegradable polyester resin proposed by the inventors of the present invention can be manufactured by the ordinary melt spinning method. Single-layer or multi-layer synthetic fibers with a fiber diameter of 0.5 to 100 μm can be processed to a fiber diameter of 0.5 to 100 μm by once melt spinning fibers with a fiber diameter of 20 to 500 μm and stretching them in one or multiple steps. It is possible to manufacture using a melt spinning apparatus for thermoplastic resins that has been widely used conventionally, and it is possible to perform spinning by controlling the molten resin temperature to 190°C to 250°C, preferably 190°C to 220°C.

[0017] That is, the present invention is as follows. 1) As a first step, 0.1 to 5% wt% of melamine or a melamine derivative, 0.01 to 5 wt% of an alkaline earth metal hydroxide, and 0.01 to 5 wt% of an antioxidant are added to a polyacetal (POM) crude polymer having an oxymethylene terminal with a thermally unstable molecular chain end obtained by copolymerizing trioxane, which is a trimer of formaldehyde, and a cyclic oligomer containing an oxyalkylene group having 2 to 4 carbon atoms such as ethylene oxide, 1,3-dioxolane, 1,3,6-trioxocane, 1,3-dioxepane. The POM crude polymer is heated to 190°C to 250°C and melted to decompose the thermally unstable oxymethylene molecular chain end, and the generated formaldehyde is separated and removed to obtain a POM resin having a thermally stable oxyethylene terminal at the molecular chain end. Then, as a second step, a method for producing a low-formaldehyde-containing POM fiber with a free formaldehyde content of 16 ppm or less by melt spinning a POM resin added with 0.01 to 5 wt% of a formaldehyde scavenger (absorbent) at a resin temperature of 190 to 250°C is proposed.

[0018] 2) Alternatively, as the first step, a polyacetal (POM) crude polymer having an oxymethylene terminal with a thermally unstable molecular chain end obtained by copolymerizing trioxane, which is a trimer of formaldehyde, with a cyclic oligomer containing an oxyalkylene group having 2 to 4 carbon atoms such as ethylene oxide, 1,3-dioxolane, 1,3,6-trioxocane, 1,3-dioxepane, etc., is added with 0.1 to 5% wt of melamine or a melamine derivative, 0.01 to 5 wt% of an alkaline earth metal hydroxide, and 0.01 to 5 wt% of an antioxidant. The POM crude polymer is heated to 190°C to 250°C to be melted, and the thermally unstable oxymethylene molecular chain end is decomposed to separate and remove the generated formaldehyde, obtaining a POM resin with a thermally stable oxyethylene terminal at the molecular chain end. Then, as the second step, 0 to 50 t% of a biodegradable polyester resin is added to the POM resin based on 50 to 100 wt%, and 0.01 to 5 wt% of a formaldehyde scavenger and 0.1 to 5 wt% of a monocarboxydiimide or a polycarboxydiimide compound are added, and melt-spun at a resin temperature of 190 to 250°C to obtain a low-formaldehyde-containing POM alloy fiber with a free formaldehyde content of 16 ppm or less.

[0019] 3) A single-layer or multi-layer synthetic fiber with a fiber diameter of 0.5 to 100 μm obtained by melt-spinning 50 to 100 wt% of a POM containing one or more structural units other than the oxymethylene group (-CH2O-) and 0 to 50 wt% of a biodegradable polyester resin, which contains 0.1 to 5 wt% of melamine or a melamine derivative, 0.01 to 5 wt% of an alkaline earth metal hydroxide, 0.01 to 5 wt% of an antioxidant, and 0.01 to5 wt% of a formaldehyde scavenger and has a free formaldehyde content of 16 ppm or less, and a fiber according to the present invention.

[0020] 4) As the melamine derivative, a method for producing a low-formaldehyde-containing POM fiber using one or more of methylol melamine, guanamine, melamine cyanurate, and a melamine-formaldehyde polycondensate is shown, as well as the POM fiber.

[0021] 5) A method for producing low-formaldehyde-containing POM fibers in which the alkaline earth metal hydroxide is calcium hydroxide or magnesium hydroxide, and the POM fibers are shown.

[0022] 6) Examples of useful formaldehyde scavengers include dihydrazide compounds. Specifically, it is at least one dihydrazide compound selected from aromatic dihydrazides and aliphatic dihydrazides, and a method for producing low-formaldehyde-containing POM fibers and the fibers, which are at least one selected from the group consisting of dihydrazide propionate, dihydrazide thiocarboxylic acid, dihydrazide oxalic acid, dihydrazide sebacic acid, dihydrazide naphthalic acid, dihydrazide terephthalic acid, dihydrazide isophthalic acid, dihydrazide sebacic acid, dihydrazide adipic acid, and dihydrazide dodecanedioic acid.

[0023] 7) Examples of the biodegradable polyester resin include one or more resins selected from the group consisting of polylactic acid (hereinafter referred to as PLA), polybutylene succinate (hereinafter referred to as PBS), polybutylene succinate adipate (PBSA), polyhydroxybutyrate (PHB), polyhydroxybutyrate-co-hydroxyvalerate (PHBV), polybutylene adipate-terephthalate (PBAT), and polyhydroxybutyric acid-hydroxyhexanoic acid (PHBH). A method for producing POM fibers and the POM fibers are provided.

[0024] 8) When melt-spinning an alloy of 50 to 100 wt% of POM and 0 to 50 wt% of the biodegradable polyester resin, it is preferable to add 0.1 to 5 wt% of a monocarboxydiimide or a polycarboxydiimide compound in order to suppress the hydrolysis of the biodegradable polyester.

[0025] 9) Examples of the monocarboxylic diimide compound include aromatic monocarboxylic diimide compounds such as diphenylcarbodiimide, di-2,6-dimethylphenylcarbodiimide, di-2,6-diethylphenylcarbodiimide, di-2,6-diisopropylphenylcarbodiimide, di-2,6-di-tert-butylphenylcarbodiimide, di-o-tolylcarbodiimide, di-p-tolylcarbodiimide, di-2,4,6-trimethylphenylcarbodiimide, di-2,4,6-triisopropylphenylcarbodiimide, di-2,4,6-triisobutylphenylcarbodiimide; alicyclic monocarboxylic diimide compounds such as dicyclohexylcarbodiimide, dicyclohexylmethanecarbodiimide; and aliphatic monocarboxylic diimide compounds such as diisopropylcarbodiimide, dioctadecylcarbodiimide, etc.

[0026] 10) Examples of the polycarboxylic diimide include aromatic polycarboxylic diimides such as poly(4,4'-diphenylmethanecarbodiimide), poly(p-phenylene carbodiimide), poly(m-phenylene carbodiimide), poly(diisopropylphenylcarbodiimide), poly(triisopropylphenylcarbodiimide); and alicyclic polycarboxylic diimides such as poly(dicyclohexylmethanecarbodiimide).

Advantages of the Invention

[0027] The present invention relates to a low-formaldehyde-containing polyacetal fiber that can be used as a fiber for clothing and industrial materials. POM resin has been widely used in industrial parts and life-related parts by injection molding and extrusion molding, but it has been used very little as a fiber. To be used as a fiber product, a melt spinning process is essential. Generally, when producing a fiber by melt spinning a thermoplastic resin, compared with injection molding, sheet or film molding, when the molten resin passes through the melt resin pipe from the extruder and reaches the die after being pressurized by a gear pump, it takes a long time. In normal injection molding or sheet / film molding, the residence time of the molten resin is 1 minute to 20 minutes, usually about 3 minutes to 10 minutes, while in spinning, the residence time is 20 minutes to 90 minutes, usually 20 minutes to 60 minutes. Since the resin temperature during spinning is usually controlled at 190°C to 250°C, preferably 190°C to 220°C, the POM resin does not decompose violently. However, even if there is a very small amount of decomposition, if the residual formaldehyde in the fiber is not below the JIS standard value, general use is not permitted. When measuring the free formaldehyde in accordance with JIS L1041 for the fibers composed of POM of the present invention and the alloy of POM and a biodegradable polyester resin, the formaldehyde content in the fiber is 16 ppm or less of the reference value, and it can be used in the form of knitted fabrics, woven fabrics, non-woven fabrics, webs, etc. as a fabric.

Embodiments for Carrying Out the Invention

[0028] A method for producing a fiber composed of POM used in the fiber of the present invention, or an alloy of POM and a biodegradable polyester resin, such as PBS or a resin with a similar structure to PBS or PLA, can be produced by a known melt spinning method. The spinning machine is equipped with a single-screw or twin-screw extruder for melt-extruding the POM resin and one or more gear pumps for pressurizing the molten resin and guiding it to the spinning head.

[0029] In order to adjust the fiber to the desired fineness, stretching can be carried out by winding up the once-spun POM fiber and then applying it to a stretching machine. However, usually, the spinning machine and the stretching machine are directly connected, and the stretching process can be carried out simultaneously with spinning. The stretching process can be carried out by known stretching methods. As an example, there are stretching methods such as wet stretching carried out in a warm water bath, dry stretching carried out in dry air or using a heated metal roll, and steam stretching carried out in a superheated steam atmosphere heated to a temperature of 100 °C or higher. Among these, when manufacturing the polyacetal resin (POM) composition fiber of the present invention, it is preferable to carry out wet stretching in a warm water bath at 40 to 100 °C, preferably in a warm water bath at 50 to 90 °C. Alternatively, the extruded fiber can be brought into contact with a hot plate at 80 to 120 °C and stretched dry.

[0030] Synthetic fibers obtained from POM fibers or an alloy of POM and a biodegradable polyester resin are produced as monofilament or multifilament fibers. As a method for producing ultra-fine fibers, a method for producing multifilament fibers is preferable. The production of multifilament involves extruding and cooling the molten resin from a plurality of die holes, winding up the obtained fibers with a take-up roll, and then stretching the fibers with a stretching roll. Alternatively, fibers with a melt-spun fiber diameter of 20 to 100 μm can be wound up once and then made into fibers with a fiber diameter of 0.5 to 20 μm by another stretching machine.

[0031] The POM used in the present invention is an acetal copolymer having a copolymer and a terpolymer containing one or more structural units other than the oxymethylene group and the oxymethylene group as the main structural units. In the melt spinning of POM, since the residence time during melting is 20 minutes to 90 minutes, usually 20 minutes to 60 minutes, it is preferable to use an acetal copolymer having excellent thermal stability.

[0032] The POM copolymer can be used alone or by mixing POM copolymers with different types and contents of comonomers. The POM copolymer has, in addition to oxymethylene units in the molecule, oxyalkylene units represented by the following formula (1). Here, polyacetal resin and polyoxymethylene resin are synonymous. [Chemical formula] In the acetal copolymer used in the present invention, the proportion of the oxyalkylene unit represented by the general formula (1) needs to be 0.5 to 10 moles per 100 moles of oxymethylene units, preferably 1.2 to 10 moles per 100 moles of oxymethylene units, and particularly preferably 2 to 6 moles. When the proportion of the oxyalkylene unit is less than 1.2 moles, the crystallization rate of the polyoxymethylene copolymer becomes fast, aggregates of crystals are formed in the fiber, and the fiber is easily broken. Also, the USTER value showing the variation in the thickness in the longitudinal direction of the fiber becomes 1.5 or more, and unevenness in the thickness and dyeing of the fabric increases. When the proportion of the oxyalkylene unit exceeds 10 moles, the achieved crystallinity decreases and high-strength fibers cannot be obtained. (In the formula, R0 and R0’ may be the same or different and are a hydrogen atom, an alkyl group, a phenyl group, or an alkyl group interrupted by one or more ether bonds, and m is an integer of 2 to 6)

[0033] The alkyl group is an unsubstituted or substituted linear or branched alkyl group having 1 to 20 carbon atoms, and a linear or branched alkyl group having 1 to 4 carbon atoms is preferred. Examples of the alkyl group include methyl, ethyl, n-propyl, i-propyl, n-butyl, i-butyl, t-butyl, pentyl, hexyl, decyl, dodecyl, and octadecyl. Examples of the substituent include a hydroxy group, an amino group, an alkoxy group, an alkenyloxymethyl group, and a halogen. Here, examples of the alkoxy group include methoxy, ethoxy, and propoxy. Also, examples of the alkenyloxymethyl group include allyloxymethyl.

[0034] The phenyl group is unsubstituted, or an unsubstituted or substituted alkyl group, an unsubstituted or substituted aryl group, or a phenyl group substituted with a halogen. Here, examples of the aryl group include phenyl, naphthyl, anthracyl, and the like.

[0035] Examples of the alkyl group interrupted by one or more ether bonds include a group represented by the following formula (2). -CH2-O-(R3-O)P-R4 (2) (In the formula, R3 is an alkylene group, P represents an integer from 0 to 20, R4 is a hydrogen atom, an alkyl group, a phenyl group, or a glycidyl group, and here each (R3-O) unit may be the same or different)

[0036] The alkylene group is linear or branched, an unsubstituted or substituted alkylene group having 2 to 20 carbon atoms, and examples include ethylene, propylene, butylene, and 2-ethylhexylene. As the alkylene for R1, ethylene and propylene are preferred.

[0037] R0 and R0’ are preferably the same and are a hydrogen atom. Examples of the oxyalkylene unit represented by formula (1) include an oxyethylene unit, an oxypropylene unit, an oxybutylene unit, an oxypentylene unit, and an oxyhexylene unit, preferably an oxyethylene unit, an oxypropylene unit, and an oxybutylene unit, and more preferably an oxydimethylene unit, an oxytrimethylene unit, and an oxytetramethylene unit.

[0038] The polyoxymethylene (POM) copolymer can further have a unit represented by the following formula (3). -CH(CH3)-CHR5- (3) (In the formula, R5 is a group represented by the following formula (4)) -O-(R3-O)P-R6 (4) (In the formula, R6 is a hydrogen atom, an alkyl group, an alkenyl group, a phenyl group or a phenylalkyl group, and R3 and P are as defined in formula (2).)

[0039] The alkenyl group is a straight-chain or branched, unsubstituted or substituted alkenyl group having 2 to 20 carbon atoms, and examples thereof include vinyl, allyl, and 3-butenyl. Examples of the alkyl moiety and the phenyl moiety in the phenylalkyl group are as exemplified for the above alkyl group and phenyl group. Examples of the phenylalkyl group include benzyl, phenylethyl, phenylbutyl, 2-methoxybenzyl, 4-methoxybenzyl, and 4-(allyloxymethyl)benzyl. In the present invention, when present, the alkenyl group and the glycidyl group in the group represented by formula (2), or the alkenyl group in the group represented by formula (4) can serve as crosslinking points in a further polymerization reaction, whereby a crosslinked structure is formed.

[0040] The method for producing the polyoxymethylene (POM) copolymer is not particularly limited. For example, there is a method of bulk-polymerizing trioxane, which is a trimer of formaldehyde, and a comonomer using a cationic polymerization catalyst such as boron trifluoride as necessary. Examples of the comonomer include cyclic ethers having 2 to 8 carbon atoms such as ethylene oxide, 1,3-dioxolane, 1,3,5-trioxepane, and 1,3,6-trioxocane, cyclic formals of glycols having 2 to 8 carbon atoms such as cyclic formal of glycol and cyclic formal of diglycol. By these comonomers, an oxyalkylene unit represented by formula (1) in which R0 and R0' are the same and are hydrogen atoms is formed.

[0041] The melt polymerization method in which a monomer and a comonomer are dissolved in an organic solvent and polymerized is a classical method, but it is necessary to recover the solvent and unreacted monomer. On the other hand, the bulk polymerization method without using a solvent is more economical. However, the polymerization catalyst remains in the polymer after polymerization, which causes depolymerization. Therefore, a catalyst deactivator is added at the end of the polymerization reaction. When a cationic polymerization catalyst such as boron trifluoride is used as the polymerization catalyst for this deactivator, triphenylphosphine and hindered amine are used.

[0042] In the present invention, the polyoxymethylene (POM) copolymer includes a binary copolymer and a multi-component copolymer. Therefore, as the POM copolymer of the present invention, a POM copolymer having an oxymethylene unit and an oxyalkylene unit represented by the above formula (1), a POM copolymer including an oxymethylene unit, an oxyalkylene unit represented by the above formula (1), and a unit represented by the formula (3), and the copolymer having a crosslinked structure can be widely used. In the present invention, a unit represented by the formula (1) in which R0 and R0' are not simultaneously hydrogen atoms can be formed, for example, by copolymerizing a glycidyl ether compound or an epoxy compound, and a unit represented by the formula (3) can be formed, for example, by copolymerizing an allyl ether compound.

[0043] The glycidyl ether and the epoxy compound are not particularly limited, and examples thereof include epichlorohydrin; alkyl glycidyl formals such as methyl glycidyl formal, ethyl glycidyl formal, propyl glycidyl formal, and butyl glycidyl formal; diglycidyl ethers such as ethylene glycol diglycidyl ether, propylene glycol diglycidyl ether, 1,4-butanediol diglycidyl ether, hexamethylene glycol diglycidyl ether, resorcinol diglycidyl ether, bisphenol A diglycidyl ether, hydroquinone diglycidyl ether, polyethylene glycol diglycidyl ether, polypropylene glycol diglycidyl ether, and polybutylene glycol diglycidyl ether; triglycidyl ethers such as glycerin triglycidyl ether and trimethylolpropane triglycidyl ether; and tetraglycidyl ethers such as pentaerythritol tetraglycidyl ether.

[0044] Examples of allyl ether compounds include polyethylene glycol allyl ether, methoxypolyethylene glycol allyl ether, polyethylene glycol - polypropylene glycol allyl ether, polypropylene glycol allyl ether, butoxypolyethylene glycol - polypropylene glycol allyl ether, polypropylene glycol diallyl ether, phenylethyl allyl ether, phenylbutyl allyl ether, 4 - methoxybenzyl allyl ether, 2 - methoxybenzyl allyl ether, and 1,4 - diallyloxymethylbenzene.

[0045] Among them, from the viewpoints of mass - productivity and thermal stability, a polypolyoxymethylene (POM) copolymer obtained by adding 0.5 to 30 parts by weight, preferably 1 to 15 parts by weight, of a comonomer composed of one or more cyclic ethers and / or cyclic formaldehyde other than trioxane to 100 parts by weight of trioxane is preferred. If the comonomer is 0.5 parts by weight or more, the heat resistance required for melt - spinning is sufficient, and decomposition and foaming of the POM copolymer are less likely to occur in the residence parts inside the extruder and the spinning nozzle, and the processability is excellent. If it is 30 parts by weight or less, the yield in manufacturing the POM copolymer is improved. Also, the amounts of glycidyl ether compounds, epoxy compounds, and allyl ether compounds are not particularly limited, but preferably, 0.05 to 20 parts by weight of glycidyl ether compounds, epoxy compounds, and allyl ether compounds can be added to 100 parts by weight of trioxane.

[0046] In addition, the acetal copolymer used in the present invention needs to have a melt index (MI) measured at 190 °C under a load of 2160 g in accordance with ASTM D - 1238 of 0.3 to 50 g / 10 minutes, preferably 1.0 to 35 g / 10 minutes. If the melt index (MI) is too small, it becomes difficult to discharge from the spinning nozzle used during spinning, and particularly when the number of nozzles is 100 or more, the discharge amount from each nozzle is likely to vary. On the other hand, if the melt index (MI) is too large, the winding of the fiber becomes unstable due to draw - down of the resin.

[0047] The method for producing the acetal copolymer used in the present invention is not particularly limited. Generally, it can be obtained by bulk-polymerizing trioxane and a comonomer, which is a cyclic ether compound or a cyclic formal compound, mainly using a cationic polymerization catalyst. As the polymerization apparatus, any known apparatus such as a batch type or a continuous type can be used. The molecular weight of the polymer can be controlled by adjusting the addition amount of a chain transfer agent, for example, methylal.

[0048] The acetal copolymer thus obtained and used in the present invention preferably has an amount of oxymethylene end groups detected by 1H-NMR of 0 to 4 mmol / Kg, and particularly preferably 0 to 2 mmol / Kg. When the amount of oxymethylene end groups exceeds 4 mmol / Kg, it is difficult to sufficiently thermally stabilize the polymer due to foaming or the like accompanying the decomposition of the polymer during thermal stabilization. In order to control the amount of oxymethylene end groups within the above range, it is preferable that the impurities, particularly water, in the total amount of the monomers and comonomers used for polymerization be 20 ppm or less, and particularly preferably controlled to 10 ppm or less.

[0049] In order to thermally stabilize an acetal copolymer containing an oxymethylene end group amount of 0 to 4 mmol / Kg (this is called a crude polymer), the step of decomposing and removing this end group to make the molecular chain end an oxyalkylene group and obtaining a polyacetal resin that can be safely used as a molding material is called a thermal stabilization step. There are two methods for this thermal stabilization method: a hydrolysis method and a melt thermal stabilization method. The hydrolysis method suspends the crude polymer in water, adds a basic substance such as sodium hydroxide, ammonia, methylamine, ethylamine, ethanolamine, etc., and decomposes and removes the oxy end groups in the range of 100°C or higher, preferably 120 to 150°C. This requires a large amount of water, and after separating the stabilized acetal copolymer and water after the decomposition reaction, it is necessary to dry the polymer.

[0050] In contrast, in the present invention, 0.1 to 5% wt% of melamine or a melamine derivative and 0.01 to 5 wt% of an alkaline earth metal hydroxide are added to a polyacetal (POM) crude polymer having an oxymethylene terminal that is thermally unstable at the molecular chain end. At this time, it is preferable to add 0.1 to 5 wt% of an antioxidant, namely, a hindered phenol compound. The crude polymer is heated to 190°C to 250°C and melted to decompose the thermally unstable oxymethylene, and the generated formaldehyde is separated and removed. After the molecular chain end becomes a thermally stable oxyalkylene terminal, at least one hydrazide compound selected from aromatic dihydrazide, aliphatic dihydrazide, and carbodiimide compounds is added as a formaldehyde scavenger.

[0051] That is, in the first step, in order to remove the thermally unstable oxymethylene from the crude polymer, a surface renewal type stirrer for removing the formaldehyde generated by decomposing the thermally unstable oxymethylene from the molten resin by evacuation is used. 0.1 to 5% wt% of melamine or a melamine derivative, 0.01 to 5 wt% of an alkaline earth metal hydroxide, and 0.01 to 5 wt% of an antioxidant are added to the crude polymer. The oxymethylene end groups are removed at a melting temperature of 190 to 250°C and a residence time of 1 to 60 minutes, preferably 5 to 30 minutes, to become thermally stable oxyalkylene end groups. The molten resin withdrawn from this surface renewal type stirrer is pressurized and led to a die, and pellets are produced by strand cutting or hot cutting.

[0052] Next, in the second step, 0.01 to 5 wt% of aromatic dihydrazide and aliphatic dihydrazide are added during the spinning of the stabilized POM. Specifically, at least one selected from the group consisting of dihydrazide propionate, thiocarbohydrazide, carbodihydrazide, dihydrazide oxalate, dihydrazide sebacate, dihydrazide naphthalene, dihydrazide terephthalic acid, dihydrazide isophthalic acid, dihydrazide sebacate, and dihydrazide dodecanedioic acid is added. POM and additives are added and melt-spun at 190 to 250°C.

[0053] When melt-spinning an alloy of 50 to 100 wt% of POM and 0 to 50 wt% of a biodegradable polyester resin, in the second step, a predetermined amount of a biodegradable resin, 0.01 to 5 wt% of an aromatic dihydrazide and an aliphatic dihydrazide, and 0.1 to 5 wt% of a carbodiimide compound are added to the POM. The carbodiimide compound may be a monocarboxydiimide or a polycarbodiimide compound may be used. The carbodiimide compound is particularly effective in preventing the hydrolysis of the biodegradable polyester. The second step can be divided into two steps to separately prepare a compound of POM and a biodegradable resin, and 0.01 to 5 wt% of an aromatic dihydrazide and an aliphatic dihydrazide, and 0.1 to 5 wt% of a carbodiimide compound are added to the obtained pellets, and melt-spinning can be carried out at 190 to 250 °C.

[0054] Furthermore, to the acetal copolymer used in the present invention, if necessary, one or more general additives for thermoplastic resins, such as colorants such as dyes and pigments, lubricants, nucleating agents, mold release agents, antistatic agents, surfactants, inorganic or organic fibrous, plate-like, powdery or granular fillers, etc., can be added within a range that does not inhibit the object of the present invention. However, when adding organic and inorganic substances that generally do not melt in the POM resin, since the nozzle diameter of the spinning nozzle is usually 100 μm to 1 mm, it is necessary to sufficiently reduce the particle size to prevent clogging of the nozzle.

[0055] The biodegradable polyester resin for melt-kneading with 50 to 100 wt% of POM to form an alloy can be polylactic acid (hereinafter referred to as PLA), polybutylene succinate (hereinafter referred to as PBS), polybutylene succinate adipate (PBSA), polyhydroxybutyrate (PHB), polyhydroxybutyrate-co-hydroxyvalerate (PHBV), polybutylene adipate-terephthalate (PBAT), polyhydroxybutyric acid-hydroxyhexanoic acid (PHBH). It is preferable to melt-knead the polymer alloy separately with an extruder before spinning.

[0056] Examples of products (commercially available products) that can be used as PBS-based resins include Mitsubishi Chemical's "BioPBS (Bio-PBS)" (registered trademark), "Bionole" (registered trademark) manufactured by Showa Denko KK, PBS resin manufactured by Shandong Fuwin New Material Co., Ltd., and polybutylene adipate terephthalate-based resin "Ecoflex" (registered trademark) manufactured by BASF Co., Ltd.

[0057] There are resins with similar structures (similar-structure resins) in PBS-based resins. Examples of similar-structure resins include polybutylene succinate adipate (PBSA), polyhydroxybutyrate (PHB), polyhydroxybutyrate-co-hydroxyvalerate (PHBV), polybutylene adipate-terephthalate (PBAT), and polyhydroxybutyric acid-hydroxyhexanoic acid (PHBH). In the resin composition of the present invention, they can be treated equivalently to polybutylene succinate resin (PBS).

[0058] The optimal MFR of PBS or its analogs is 4 to 30 g / 10 min. When the molecular weight is high with an MFR of 4 g / 10 min or less, or when the molecular weight is low with an MFR of 30 g / 10 min or more, the compatibility between the resin and POM is poor, and a high draw ratio cannot be imparted to the fibers.

[0059] PLA is manufactured by Cargill Dow LLC in the United States and supplied under the trade name Nature Works. It is imported and processed in Japan by Kanebo Gohsen Co., Ltd., Kuraray Co., Ltd., Unitika Ltd., and Mitsui Chemicals, Inc., and sold in a wide range of applications such as packaging containers, agricultural civil engineering, compost-related, sports wear, and bedding products. PLA is commercially available from Unitika Ltd. under the name "Terramac" (registered trademark).

Examples

[0060] The present invention will be described more specifically below with reference to examples and comparative examples, but the present invention is not limited to the examples shown below as long as the gist of the invention is not exceeded. <Examples and Comparative Examples>

Table 1

Table 2

[0061] <Manufacture of POM Resin> 100 parts by weight of trioxane with a water content of 20 ppm or less and 4.0 parts by weight of 1,3-dioxolane containing the same amount of water were mixed, and 0.045 mmol of boron trifluoride diethyl etherate per mole of trioxane was supplied as a catalyst, and polymerization was carried out in a twin-screw kneader having paddle-shaped convex lenses that clean each other's surfaces. At this time, 0.12 parts by weight of methylal was added as a molecular weight regulator to 100 parts by weight of trioxane. After the polymerization was completed, triphenylphosphine was added as a catalyst deactivator to stop the polymerization, and the polymer was pulverized to obtain a crude polymer. To 100 parts by weight of this crude polymer, 0.2 parts by weight of melamine, or methylol melamine, guanamine, melamine cyanurate, or a melamine-formaldehyde polycondensate was added, and further 0.5 parts by weight of a hindered phenol, 0.5 parts by weight of magnesium hydroxide, or calcium hydroxide was added, and the obtained blend was fed to a co-rotating twin-screw extruder (manufactured by Nippon Steel Works, inner diameter 69 mm, L / D = 31.5) and melt-kneaded. A surface-renewing horizontal twin-screw kneader (effective volume 60 L) was directly connected to this twin-screw extruder, and a formaldehyde removal treatment was carried out under a reduced pressure of 20 KPa at a resin temperature of 220°C and a residence time of 20 minutes to obtain a stabilized POM resin. When the MI value of this POM resin was measured in accordance with JIS K7210, it was 9.0 g / 10 min.

[0062] <Mixing of Additives> 0.1 to 5 wt% of a hydrazide compound was added to the thus thermally stabilized POM resin and mixed in a tumbler. In addition to these, an internal lubricant, an antistatic agent, an ultraviolet absorber, a dye or pigment, etc. can also be added as necessary. After mixing in a tumbler it was put into the hopper of a spinning machine. The internal lubricant and pigment When the dispersion of the dye is a problem, after mixing in a tumbler, melt-knead at a resin temperature of 190 to 250 °C using a single-screw or twin-screw extruder to produce pellets, and these can also be fed into the hopper of a spinning machine for melt spinning.

[0063] <Melt Spinning of POM> For melt spinning, a horizontal single-screw extruder with a screw diameter of 45 mm was used as the spinning machine. From the die at the tip of the extruder, a pipe with an inner diameter of 10 mm has 10 branches, and a gear pump is directly connected to each, and the molten resin is led to each spinning nozzle. The die holes have 24 holes arranged in a circular pattern, and the inner diameter of the die holes is 300 μm. That is, 10 multi-filaments of 24 strands can be melt-spun simultaneously. The temperatures of the extruder and the die can be controlled from 160 to 250 °C according to the melting temperature of the resin used. The 240 fibers discharged from the nozzle are taken up using a plurality of rollers, and usually, the stretching can be carried out by sequentially increasing the rotational speed of each roller. In this case, it is effective to control the surface temperature of the rollers at 80 to 120 °C. Fibers with a fiber diameter of 20 to 100 μm were produced in this way. Furthermore, the wound fibers can be reheated and stretched again to produce fibers with a fiber diameter of 0.5 to 20 μm. The fibers wound on the bobbin are led to a stretching device, and the draw ratio is adjusted by the difference in the rotational speed and diameter between the rotating roll before the heating device for stretching and the winding roll after the heating device. The heating device used the method of passing through an air-type heater at 100 to 140 °C. In addition, other methods such as passing through a hot water bath or an oil bath are also effective. The heating device can be single-stage or multiple-stage can be used to increase to the desired draw ratio.

[0064] <Melt Spinning of Polymer Alloy> In the case of melt spinning of the polymer alloy, Bio BPS FZ91 manufactured by Mitsubishi Chemical with an MI value of 5.0 was used as the polybutylene succinate (PBS) resin. As the polylactic acid resin (PLA), Terramac TP-4000 manufactured by Unitika with an MI value of 5.0 was used. Heat-stabilized POM was charged into a tumbler at a predetermined ratio together with PBS or PLA, and at the same time, 0.1 to 5 wt% of a hydrazide compound, 0.1 to 5 wt% of a monocarboxydiimide, or a polycarboxydiimide compound was added. The mixture thus prepared was charged into the hopper of a spinning machine and melt-spun. Although it is also possible to directly spin by mixing the additive and the resin pellets in a tumbler in this way, once a predetermined amount of POM, PBS or PLA, 0.1 to 5 wt% of a hydrazide compound, 0.1 to 5 wt% of a monocarboxydiimide, or a polycarboxydiimide compound is added and melt-kneaded at a resin temperature of 190 to 250 °C using a single-screw or twin-screw extruder to obtain pellets, these can also be charged into the hopper of a spinning machine and melt-spun.

[0065] <Measurement of residence time> The residence time of the molten resin in the spinning machine was measured by a tracer response test. POM pellets colored with carbon black were charged into the hopper of the extruder, and the time of charging was set to zero. The fibers discharged from the nozzle of the spinning machine were sampled every minute. 5 g of this fiber was taken, sandwiched between chromium-plated steel plates heated to 220 °C, and a film with a thickness of 0.5 mm was prepared. The light transmittance of this film was measured, and the time when the color was darkest was taken as the residence time.

[0066] As examples, the results of the formaldehyde content of the POM fibers according to the present invention measured in accordance with JIS L1041 are shown in Tables 1-a to 1-l.

[0067] As comparative examples, the results of the formaldehyde content of the POM fibers by the method without using the additive according to the present invention are shown in Tables 2-a to 2-j.

Claims

1. As a first step, 0.1 to 5% wt% of melamine or a melamine derivative, 0.01 to 5 wt% of an alkaline earth metal hydroxide, and 0.01 to 5 wt% of an antioxidant are added to a polyacetal (POM) crude polymer having oxy-methylene terminals obtained by copolymerizing trioxane, which is a trimer of formaldehyde, with a cyclic oligomer containing an oxyalkylene group having 2 to 4 carbon atoms such as ethylene oxide, 1,3-dioxolane, 1,3,6-trioxocane, 1,3-dioxepane. The POM crude polymer is heated and melted at 190°C to 250°C to decompose the oxy-methylene molecular chain terminals, and the generated formaldehyde is separated and removed to obtain a POM resin having oxy-ethylene terminals at the molecular chain terminals. Then, as a second step, a formaldehyde scavenger of 0.01 to 5 wt% is added to the POM resin, and the resin is melt-spun at a resin temperature of 190 to 250°C to produce a low-formaldehyde-containing POM fiber. A method for producing a POM fiber.

2. As a first step, 0.1 to 5% wt% of melamine or a melamine derivative, 0.01 to 5 wt% of an alkaline earth metal hydroxide, and 0.01 to 5 wt% of an antioxidant are added to a polyacetal (POM) crude polymer having oxy-methylene terminals obtained by copolymerizing trioxane, which is a trimer of formaldehyde, with a cyclic oligomer containing an oxyalkylene group having 2 to 4 carbon atoms such as ethylene oxide, 1,3-dioxolane, 1,3,6-trioxocane, 1,3-dioxepane. The POM crude polymer is heated and melted at 190°C to 250°C to decompose the oxy-methylene molecular chain terminals, and the generated formaldehyde is separated and removed to obtain a POM resin having oxy-ethylene terminals at the molecular chain terminals. Then, as a second step, 0 to 50 t% of a biodegradable polyester resin is added to 50 to 100 wt% of the POM resin, 0.01 to 5 wt% of a formaldehyde scavenger is added, and the resin is melt-spun at a resin temperature of 190 to 250°C to produce a low-formaldehyde-containing POM alloy fiber. A method for producing a POM alloy fiber.

3. A single-layer or multi-layer synthetic fiber with a fiber diameter of 0.5 to 100 μm obtained by melt spinning 50 to 100 wt% of a POM containing an oxymethylene group (—CH₂O—) and one or more constitutional units other than the oxymethylene group and 0 to 50 wt% of a biodegradable polyester resin, wherein the free formaldehyde containing 0.1 to 5 wt% of melamine or a melamine derivative, 0.01 to 5 wt% of an alkaline earth metal hydroxide, 0.01 to 5 wt% of an antioxidant, and 0.01 to 5 wt% of a formaldehyde scavenger is 16 ppm or less.

4. The method for producing a low-formaldehyde-containing POM fiber and the POM fiber according to claims 1 to 3, wherein the melamine derivative is methylol melamine, guanamine, melamine cyanurate, or a melamine-formaldehyde polycondensate.

5. The method for producing a low-formaldehyde-containing POM fiber and the POM fiber according to claims 1 to 3, wherein the alkaline earth metal hydroxide is calcium hydroxide or magnesium hydroxide.

6. The method for producing a low-formaldehyde-containing POM fiber and the POM fiber according to claims 1 to 3, wherein the formaldehyde scavenger is at least one selected from the group consisting of dihydrazide propionate, dihydrazide thiocarboxylic acid, dihydrazide oxalic acid, dihydrazide sebacic acid, dihydrazide naphthalate, dihydrazide terephthalic acid, dihydrazide isophthalic acid, dihydrazide sebacic acid, dihydrazide adipic acid, and dihydrazide dodecanedioic acid.

7. The method for producing a low-formaldehyde-containing POM fiber and the POM fiber according to claims 2 to 3, wherein the biodegradable polyester resin is one or more resins selected from the group consisting of polylactic acid (hereinafter referred to as PLA), polybutylene succinate (hereinafter referred to as PBS), polybutylene succinate adipate (PBSA), polyhydroxybutyrate (PHB), polyhydroxybutyrate-co-hydroxyvalerate (PHBV), polybutylene adipate-terephthalate (PBAT), and polyhydroxybutyric acid-hydroxyhexanoic acid (PHBH).

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