Method for producing polyacetal resin composition and polyacetal resin composition

Abstract

Provided are a method for producing a polyacetal resin composition in which the amount of formaldehyde generated and mold deposits are reduced, and a polyacetal resin composition. More specifically, the present invention provides a method for producing a polyacetal resin composition containing 100 parts by mass of a polyacetal resin and 0.2-0.5 parts by mass of ethylene urea, wherein the method includes a kneading step for kneading the ethylene urea into the polyacetal resin, the heating / melting / kneading time when kneading the ethylene urea into the polyacetal resin in the kneading step is 10-60 minutes, and the heating / melting / kneading temperature is 220°C-240°C.

Description

Method for producing polyacetal resin composition and polyacetal resin composition

[0001] The present invention relates to a method for producing a polyacetal resin composition and a polyacetal resin composition. More specifically, the present invention relates to a method for producing a polyacetal resin composition and a polyacetal resin composition that reduce formaldehyde emissions and mold deposits. The present invention also relates to pellets, molded articles, vehicle components, and the like formed from the polyacetal resin composition.

[0002] Polyacetal resin, also known as oxymethylene polymer, is available in homopolymers formed by polymerization of formaldehyde and copolymers formed by polymerization of cyclic oligomers such as trioxane with comonomers. Polyacetal resin offers an excellent balance of mechanical properties, chemical resistance, and sliding properties, and is easy to process. For these reasons, it is widely used as a representative engineering plastic, primarily in electrical and electronic components, automotive parts, and various other mechanical components.

[0003] However, polyacetal resin undergoes slight thermal decomposition due to thermal history during resin production, processing, and molding. As a result, very small amounts of formaldehyde are generated, which contaminates molding dies and worsens the working (hygienic) environment during molding operations. Furthermore, formaldehyde generated from resin products is said to potentially cause sick building syndrome and other conditions. In response to this situation, the Ministry of Health, Labor, and Welfare has issued guideline values ​​for formaldehyde concentrations in buildings (upper limit 0.08 ppm), calling for further reductions in the amount of formaldehyde generated from polyacetal resin molded products.

[0004] Various methods have been proposed to improve the thermal stability of polyoxymethylene copolymers. One proposed method for improving thermal stability is the addition of additives such as amines, amides, and hydrazines that can react with decomposition gases, such as formaldehyde, generated by thermal decomposition. It is well known that adding additives to polyacetal resins can suppress formaldehyde generation from pellets and molded articles, and various additives have been investigated. Examples of additives proposed include melamine-formaldehyde polymers (Patent Document 1), polyamine reactants obtained by reacting ammonia or a derivative thereof with a reaction product of polyamine and cyanuric chloride (Patent Document 2), dicyandiamide compounds (Patent Document 3), silane compounds (Patent Document 4), nitrogen-containing compound-borate salts (Patent Document 5), glyoxydiureido compounds (Patent Document 6), urea derivatives and / or amidine derivatives (Patent Document 7), condensates of phenols, basic nitrogen-containing compounds, and aldehydes (Patent Document 8), and triazine ring-containing spiro compounds (Patent Document 9).

[0005] However, the above-mentioned methods only solve one of the problems of suppressing the generation of formaldehyde or improving moldability by suppressing the generation of mold deposits due to bleeding out of additives.

[0006] Therefore, there is a demand for the development of a polyacetal resin composition that reduces the amount of formaldehyde emitted and reduces mold deposits.

[0007] JP 5-271516 JP 7-207118 JP 8-208946 JP 9-235447 JP 10-3663 No. 0 JP 10-182928 JP 2000-34417 JP 2002-212384 JP 2003-113289

[0008] The present invention provides a method for producing a polyacetal resin composition that reduces formaldehyde emissions and mold deposits, and the polyacetal resin composition.

[0009] As a result of extensive research, the present inventors have developed a method for producing a polyacetal resin composition and a polyacetal resin composition that reduce formaldehyde emissions and mold deposits. Specifically, the present invention includes the following aspects: <1> A method for producing a polyacetal resin composition containing 100 parts by mass of a polyacetal resin and 0.2 to 0.5 parts by mass of ethylene urea, the method including a kneading step of kneading the ethylene urea into the polyacetal resin, wherein, in the kneading step, the heat-melt-kneading time when kneading the ethylene urea into the polyacetal resin is 10 to 60 minutes and the heat-melt-kneading temperature is 220°C to 240°C. <2> The method for producing the polyacetal resin composition according to <1>, wherein the amount of ethylene urea extracted with hot water when the polyacetal resin composition is freeze-pulverized and then subjected to hot water extraction at 120°C for 3 hours is 0.10 mass% or less, based on the total amount of the polyacetal resin composition. <3> The method for producing the polyacetal resin composition according to <1> or <2>, wherein the amount of formaldehyde emitted from the polyacetal resin composition is 3 ppm or less, as measured in accordance with German Automotive Industry Standard VDA 275. <4> A polyacetal resin composition produced by the method according to any one of <1> to <3>. <5> A polyacetal resin composition comprising 100 parts by mass of a polyacetal resin and 0.2 to 0.5 parts by mass of ethylene urea, wherein the amount of ethylene urea extracted with hot water when the polyacetal resin composition is freeze-pulverized and then subjected to hot water extraction at 120°C for 3 hours is 0.10% by mass or less, based on the total amount of the polyacetal resin composition. <6> The polyacetal resin composition according to <5>, wherein the amount of formaldehyde emitted from the polyacetal resin composition is 3 ppm or less, as measured in accordance with German Automotive Industry Standard VDA 275. <7> The polyacetal resin composition according to <5> or <6>, which is produced by kneading ethylene urea into a polyacetal resin, and wherein the heat-melt kneading time when kneading the ethylene urea into the polyacetal resin is 10 to 60 minutes.<8> The polyacetal resin composition according to any one of <5> to <7>, which is produced by kneading ethylene urea into a polyacetal resin, and the heating / melting temperature when kneading the ethylene urea into the polyacetal resin is 220°C to 240°C. <9> Pellets formed from the polyacetal resin composition according to any one of <4> to <8>. <10> A molded product formed from the polyacetal resin composition according to any one of <4> to <8>. <11> A vehicle member formed from the polyacetal resin composition according to any one of <4> to <8>.

[0010] By using the method for producing a polyacetal resin composition of the present invention, it is possible to produce a polyacetal resin composition with reduced formaldehyde generation and reduced mold deposits.

[0011] The resin composition is introduced through gate G, and the mold is teardrop-shaped and designed so that generated gas can easily accumulate at tip P.

[0012] The present invention will be described in detail below. However, the following description is not intended to limit the present invention.

[0013] <1> Polyacetal Resin Composition The polyacetal resin composition of the present invention contains a polyacetal resin and ethylene urea. Each component will be described below.

[0014] <1-1> Polyacetal Resin The polyacetal resin used in the present invention is a -(-O-CRH-) n It is a polymer having a repeating acetal structure represented by the formula - (where R represents a hydrogen atom or an organic group), and typically has an oxymethylene group (-CHO-) where R is a hydrogen atom as the main structural unit. The polyacetal resin used in the present invention may be a homopolymer consisting only of this oxymethylene unit, or may be a copolymer (block copolymer) or terpolymer containing structural units other than oxymethylene units, and may have not only a linear structure but also a branched or crosslinked structure.

[0015] Examples of structural units other than the oxymethylene unit include oxyalkylene groups having 2 to 10 carbon atoms, which may be branched, such as an oxyethylene group (-CH2CHO-), an oxypropylene group (-CH2CH2CHO-), and an oxybutylene group (-CH2CH2CH2CHO-). Of these, an oxyalkylene group having 2 to 4 carbon atoms, which may be branched, is preferred, with an oxyethylene group being particularly preferred. The content of oxyalkylene groups other than oxymethylene groups in the polyacetal resin is usually 0.1 to 20% by mass. The content of oxyalkylene groups having 2 or more carbon atoms in the oxymethylene polymer is １ It can be measured by H-NMR.

[0016] Many methods for producing polyacetal resins are known, and polyacetal resins produced by any of these methods can be used in the present invention. For example, polyacetal resins having oxymethylene groups and oxyalkylene groups having 2 to 4 carbon atoms as structural units can be produced by copolymerizing a cyclic oligomer of oxymethylene groups, such as a formaldehyde trimer (trioxane) or tetramer (tetraoxane), 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, or 1,3-dioxepane. As the polyacetal resin, a copolymer of a cyclic oligomer such as trioxane or tetraoxane with ethylene oxide or 1,3-dioxolane is preferred, and a copolymer of trioxane and 1,3-dioxolane is particularly preferred. The melt index of the polyacetal resin (ASTM-D1238 standard: 190° C., 2.16 kg) is usually 1 to 100 g / 10 min, preferably 0.5 to 80 g / 10 min.

[0017] <1-2> Ethylene urea Ethylene urea is added as a formaldehyde scavenger. The addition of ethylene urea can reduce the amount of formaldehyde emitted from pellets and molded pieces of the polyacetal resin composition.

[0018] Ethylene urea can be produced by a conventional method by reacting 1,2-ethylenediamine with urea, and may be in the form of flakes, pellets, or particles. The content is not limited, but can be 0.001 to 2 parts by mass, specifically 0.01 to 1 part by mass, more specifically 0.1 to 1 part by mass, and even more preferably 0.2 to 0.5 parts by mass, per 100 parts by mass of polyoxymethylene copolymer. When the ethylene urea content is within the above range, the amount of formaldehyde generated in pellets and molded pieces of the polyacetal resin composition can be reduced. The product and the oxymethylene polymer obtained by melt-kneading are less susceptible to decomposition and degradation, thereby reducing the amount of formaldehyde generated. Furthermore, the condensation reaction of ethylene urea with formaldehyde reduces the volatility of ethylene urea, thereby reducing the amount of mold deposits.

[0019] In a preferred embodiment of the present invention, the polyacetal resin composition contains 0.2 to 0.5 parts by mass of ethylene urea relative to 100 parts by mass of the polyacetal resin. In the embodiment of the present invention, the amount of ethylene urea relative to 100 parts by mass of the polyacetal resin may be, for example, 0.20 parts by mass, 0.25 parts by mass, 0.30 parts by mass, 0.35 parts by mass, 0.40 parts by mass, 0.45 parts by mass, or 0.50 parts by mass. In one embodiment of the present invention, the ethylene urea is used in an amount of, for example, 0.20 parts by mass to 0.25 parts by mass, 0.20 parts by mass to 0.30 parts by mass, 0.20 parts by mass to 0.35 parts by mass, 0.20 parts by mass to 0.40 parts by mass, 0.20 parts by mass to 0.45 parts by mass, 0.20 parts by mass to 0.50 parts by mass; 0.25 parts by mass to 0.30 parts by mass, 0.25 parts by mass to 0.35 parts by mass, 0.25 parts by mass to 0.4 parts by mass, 0.25 parts by mass to 0.45 parts by mass, 0.25 parts by mass to 0.50 parts by mass; 0.30 parts by mass to 0.35 parts by mass, 0.3 parts by mass to 0.40 parts by mass, 0.30 parts by mass to 0.45 parts by mass, 0.30 parts by mass to 0.50 parts by mass; 0.35 parts by mass to 0.40 parts by mass, 0.35 parts by mass to 0.45 parts by mass, 0.35 parts by mass to 0.50 parts by mass; 0.40 parts by mass to 0.45 parts by mass, 0.40 parts by mass to 0.50 parts by mass; 0.45 parts by mass to 0.50 parts by mass; May be.

[0020] In a preferred embodiment of the present invention, there is provided a polyacetal resin composition containing 0.2 to 0.5 parts by mass of ethylene urea per 100 parts by mass of polyacetal resin.

[0021] <1-3> Other Components The polyacetal resin composition of the present invention may further contain hydroxides of alkali metals or alkaline earth metals (calcium hydroxide, magnesium hydroxide, calcium carbonate, magnesium carbonate, etc.), inorganic acid salts or alkoxides, etc. For example, hydroxides of sodium, potassium, calcium, magnesium, etc., inorganic acid salts such as carbonates, phosphates, silicates, and borates, and alkoxides such as methoxides and ethoxides may be blended.

[0022] In addition to the above-mentioned components, the polyacetal resin composition of the present invention may contain various known additives and fillers, if necessary, within the scope of the object of the present invention. Examples of additives include antioxidants, formaldehyde or formic acid scavengers, end group stabilizers, fillers, colorants, lubricants, mold release agents, antistatic agents, flame retardants, reinforcing agents, light stabilizers, and pigments. Examples of fillers include glass fibers, glass flakes, glass beads, talc, mica, and potassium titanate whiskers.

[0023] <2> Method for Producing Polyacetal Resin Composition The method for producing a polyacetal resin composition of the present invention is a method for producing a polyacetal resin composition containing a polyacetal resin and ethylene urea, and includes a kneading step of kneading the ethylene urea into the polyacetal resin.

[0024] After being discharged from the polymerization machine, the polyacetal resin (oxymethylene polymer) may be pulverized, if necessary, by a turbo mill or the like before being heated, melted, and kneaded (or before being blended, if blending is performed).

[0025] When blending the crude polymer and the stabilizer, the blending may be carried out by a known method, for example, by melt-kneading using a mixer connected in series to the above-mentioned polymerizer, which has mixed the product and the terminator. The melt-kneading device preferably has a vent function, and examples of such devices include a single-screw or multi-screw continuous extrusion kneader having at least one vent hole, a two-screw surface-renewing horizontal kneader, etc. These devices may be used alone or in combination of two or more devices.

[0026] When the crude polymer and the stabilizer are not blended in advance, the stabilizer may be continuously fed to the crude polymer line, or the crude polymer and the stabilizer may be fed to a twin-screw extruder in separate lines and then heated, melted, and kneaded in the twin-screw extruder.

[0027] Examples of known stabilizers that can be used include antioxidants such as triethylene glycol-bis[3-(3-t-butyl-4-hydroxy-5-methylphenyl)propionate] (sometimes referred to as ethylenebis(oxyethylene)bis[3-(5-tert-butyl-4-hydroxy-m-tolyl)propionate]), heat stabilizers such as melamine, additional formaldehyde scavengers, acid scavengers, etc. Furthermore, additives such as inorganic fillers such as glass fiber, crystallization accelerators (nucleating agents), mold release agents, sliding agents, and colorants may also be added.

[0028] In the stabilization step, a layered double hydroxide such as hydrotalcite may be used in place of or in addition to a known stabilizer, from the viewpoint of more effectively suppressing odors generated during molding and odors generated from the molded body.

[0029] The amount of layered double hydroxide added is determined appropriately, but is preferably 0.003 to 1 part by mass, more preferably 0.003 to 0.6 parts by mass, 0.004 to 0.6 parts by mass, or 0.005 to 0.5 parts by mass, still more preferably 0.005 to 0.2 parts by mass, and particularly preferably 0.01 to 0.2 parts by mass, per 100 parts by mass of the oxymethylene polymer.

[0030] Like the stabilizer, the layered double hydroxide may be blended with the crude polymer and then heated and melted and kneaded, or may be continuously fed to the crude polymer line, or may be continuously fed to a twin-screw extruder in a line separate from the crude polymer line. The layered double hydroxide may be added simultaneously with a known stabilizer, or may be added separately.

[0031] In the kneading step, the heating, melting, and kneading time when kneading ethylene urea into the polyacetal resin is not particularly limited, but is preferably 5 to 60 minutes, more preferably 10 to 60 minutes. If the heating, melting, and kneading time when kneading ethylene urea into the polyacetal resin in the kneading step is within the above range, the product and the oxymethylene polymer obtained by melt kneading are less likely to decompose and deteriorate, thereby reducing the amount of formaldehyde generated, and the volatility of ethylene urea is reduced by the condensation reaction of ethylene urea and formaldehyde, thereby reducing the amount of mold deposits.

[0032] In an embodiment of the present invention, the heating, melting, and kneading time may be, for example, 5 minutes, 10 minutes, 15 minutes, 20 minutes, 25 minutes, 30 minutes, 35 minutes, 40 minutes, 45 minutes, 50 minutes, 55 minutes, or 60 minutes. In one embodiment of the present invention, the heating, melting, and kneading time is, for example, 5 to 10 minutes, 5 to 15 minutes, 5 to 20 minutes, 5 to 25 minutes, 5 to 30 minutes, 5 to 35 minutes, 5 to 40 minutes, 5 to 45 minutes, 5 to 50 minutes, 5 to 55 minutes, or 5 to 60 minutes; 10 to 15 minutes, 10 to 20 minutes, 10 to 25 minutes, 10 to 30 minutes, 10 to 35 minutes, 10 to 40 minutes, 10 to 45 minutes, 10 to 50 minutes, 10 to 55 minutes, or 10 to 60 minutes; 15 to 20 minutes, 15 to 25 minutes, 15 to 30 minutes, 15 to 35 minutes, 15 to 40 minutes, 15 to 45 minutes, 15 to 50 minutes, 15 to 55 minutes, or 15 to 60 minutes; 20-25 minutes, 20-30 minutes, 20-35 minutes, 20-40 minutes, 20-45 minutes, 20-50 minutes, 20-55 minutes, 20-60 minutes; 25-30 minutes, 25-35 minutes, 25-40 minutes, 25-45 minutes, 25-50 minutes, 25-55 minutes, 25-60 minutes; 30-35 minutes, 30-40 minutes, 30-45 minutes, 30-50 minutes, 30-55 minutes, 30-60 minutes; 35-40 minutes, 35-45 minutes, 35-50 minutes, 35-55 minutes, 35-60 minutes; 40-45 minutes, 40-50 minutes, 40-55 minutes, 40-60 minutes; 45 minutes to 50 minutes, 45 minutes to 55 minutes, 45 minutes to 60 minutes; 50 minutes to 55 minutes, 50 minutes to 60 minutes; 55 minutes to 60 minutes;

[0033] In a preferred embodiment of the present invention, the heating, melting, and kneading time is 5 to 60 minutes. In a preferred embodiment of the present invention, there is provided a method for producing a polyacetal resin composition, in which the heating, melting, and kneading time is 5 to 60 minutes. In a more preferred embodiment of the present invention, there is provided a method for producing a polyacetal resin composition, in which the heating, melting, and kneading time is 10 to 60 minutes. In a more preferred embodiment of the present invention, there is provided a method for producing a polyacetal resin composition, in which the heating, melting, and kneading time is 10 to 60 minutes.

[0034] In a preferred embodiment of the present invention, there is provided a polyacetal resin composition produced by kneading ethylene urea with a polyacetal resin, wherein the heat-melt-kneading time is 10 to 60 minutes.

[0035] In the kneading step, the kneading temperature when kneading ethylene urea into the polyacetal resin is not particularly limited as long as it is equal to or higher than the melting point of the product obtained by the polymerization reaction, but is preferably 220° C. to 240° C. If the kneading temperature when kneading ethylene urea into the polyacetal resin in the kneading step is within the above range, decomposition and deterioration of the product and the oxymethylene polymer obtained by melt-kneading are less likely to occur, thereby reducing the amount of formaldehyde generated, and the volatility of ethylene urea is reduced by the condensation reaction of ethylene urea and formaldehyde, thereby reducing the amount of mold deposits.

[0036] In an embodiment of the present invention, the kneading temperature may be, for example, 220°C, 225°C, 230°C, 235°C, 240°C, etc. In one embodiment of the present invention, the kneading temperature may be, for example, 220°C to 225°C, 220°C to 230°C, 220°C to 235°C, 220°C to 240°C; 225°C to 230°C, 225°C to 235°C, 225°C to 240°C; 230°C to 235°C, 230°C to 240°C; 235°C to 240°C.

[0037] In a preferred embodiment of the present invention, there is provided a method for producing a polyacetal resin composition, wherein the kneading temperature is 220°C to 240°C.

[0038] In a preferred embodiment of the present invention, there is provided a polyacetal resin composition produced by kneading ethylene urea into a polyacetal resin, wherein the heat-melt kneading temperature when kneading the ethylene urea into the polyacetal resin is 220°C to 240°C.

[0039] In an embodiment of the present invention, there is provided a method for producing the polyacetal resin composition, which is produced by kneading ethylene urea into a polyacetal resin, wherein the heating and melting kneading time when kneading the ethylene urea into the polyacetal resin is 10 minutes to 60 minutes, and the heating and melting kneading temperature when kneading the ethylene urea into the polyacetal resin is 220°C to 240°C.

[0040] In an embodiment of the present invention, there is provided the above polyacetal resin composition, which is produced by kneading ethylene urea into a polyacetal resin, wherein the heat-melt-kneading time when kneading the ethylene urea into the polyacetal resin is 10 minutes to 60 minutes, and the heat-melt-kneading temperature when kneading the ethylene urea into the polyacetal resin is 220°C to 240°C.

[0041] The pressure during melt-kneading is not particularly limited, but is preferably carried out under reduced pressure together with degassing treatment in order to remove unreacted raw material cyclic oligomers, formaldehyde components derived from cyclic oligomers, and formaldehyde derived from hemiformal terminals. Degassing under reduced pressure is carried out through the vent hole described above. Therefore, the pressure during melt-kneading is preferably in the range of 10 to 100 kPa, more preferably 10 to 70 kPa, and particularly preferably 10 to 50 kPa, assuming atmospheric pressure to be 100 kPa. The rotation speed of the stirring blades during melt-kneading is preferably 50 to 200 rpm in a twin-screw extruder. In a twin-screw horizontal kneader with surface renewal, it is preferably 1 to 100 rpm.

[0042] In a preferred embodiment of the present invention, there is provided a method for producing a polyacetal resin composition containing 100 parts by mass of a polyacetal resin and 0.2 to 0.5 parts by mass of ethylene urea, the method including a kneading step of kneading the ethylene urea into the polyacetal resin, wherein in the kneading step, a heat-melt-kneading time when kneading the ethylene urea into the polyacetal resin is 10 minutes to 60 minutes and the heat-melt-kneading temperature is 220°C to 240°C.

[0043] Thus, the desired polyacetal resin (oxymethylene polymer) composition is obtained.

[0044] The above-described production process is an example, and steps may be added or omitted as appropriate, and the content of each step may be changed. For example, after the polymerization reaction is stopped and before stabilization, the crude polymer may be washed, unreacted monomers may be separated and recovered, dried, etc., as needed. Furthermore, if purification is required, washing, unreacted monomers may be separated and recovered, drying, etc. may be performed after stabilization.

[0045] In addition to the above-mentioned materials, known materials such as additives may be used within the scope of the present invention. Furthermore, within the scope of the present invention, the above-mentioned materials may be used in a step other than the above-mentioned step. For example, an antioxidant or a heat stabilizer that can be used in the stabilization step may be used in the polymerization termination step.

[0046] <3> Physical Properties of Polyacetal Resin Composition <3-1> Formaldehyde Emission Amount As mentioned above, there is a demand for further reduction in the amount of formaldehyde emitted from polyacetal resin molded articles. The amount of formaldehyde emitted from polyacetal resin molded articles can be measured, for example, in accordance with the German Automobile Industry Standard VDA275, but the measurement method is not limited thereto. In the method of the present invention, the amount of formaldehyde emitted was measured in accordance with the German Automobile Industry Standard VDA275.

[0047] In an embodiment of the present invention, the polyacetal resin composition has a formaldehyde emission amount of 3 ppm or less as measured in accordance with German Automobile Industry Standard VDA 275. In an embodiment of the present invention, the formaldehyde emission amount of the polyacetal resin composition as measured in accordance with German Automobile Industry Standard VDA 275 is preferably as small as possible, for example, 3 ppm or less, 2.5 ppm or less, 2 ppm or less, 1.5 ppm or less, 1 ppm or less, 0.5 ppm or less, 0.4 ppm or less, 0.3 ppm or less, 0.2 ppm or less, or 0.1 ppm or less. In an embodiment of the present invention, the polyacetal resin composition has a formaldehyde emission level of, for example, 3 ppm, 2.5 ppm, 2 ppm, 1.5 ppm, 1 ppm, 0.5 ppm, 0.4 ppm, 0.3 ppm, 0.2 ppm, 0.1 ppm, or 0 ppm, as measured in accordance with German Automobile Industry Standard VDA 275. In another embodiment of the present invention, there is provided a method for producing the polyacetal resin composition, in which the formaldehyde emission level of the polyacetal resin composition is 3 ppm or less, as measured in accordance with German Automobile Industry Standard VDA 275.

[0048] In an embodiment of the present invention, there is provided a polyacetal resin composition comprising 100 parts by mass of a polyacetal resin and 0.2 to 0.5 parts by mass of ethylene urea, wherein the polyacetal resin composition emits formaldehyde in an amount of 3 ppm or less as measured in accordance with German Automotive Industry Standard VDA275.

[0049] By reducing the amount of formaldehyde generated, it is possible to improve the contamination of molding dies and the deterioration of the working (hygienic) environment during molding work, and to reduce the possibility of causing sick house syndrome and the like.

[0050] <3-2> Amount of Hot Water Extraction Extraction of unreacted ethylene urea from the polyacetal resin composition produced by the method of the present invention was carried out by hot water extraction. More specifically, the polyacetal resin composition was freeze-pulverized, and then subjected to hot water extraction at 120°C for 3 hours, and the amount of ethylene urea extracted with hot water was measured.

[0051] In an embodiment of the present invention, the hot water extractable amount of ethylene urea measured by the hot water extraction method is 0.10 mass% or less, relative to the total amount of the polyacetal resin composition. In an embodiment of the present invention, the hot water extractable amount of ethylene urea measured by the hot water extraction method is, for example, 0.10 mass% or less, 0.09 mass% or less, 0.08 mass% or less, 0.07 mass% or less, 0.06 mass% or less, 0.05 mass% or less, 0.04 mass% or less, 0.03 mass% or less, 0.02 mass% or less, or 0.01 mass% or less, relative to the total amount of the polyacetal resin composition. In an embodiment of the present invention, the hot water extractable amount of ethylene urea measured by the above-mentioned hot water extraction method is, for example, 0.10 mass%, 0.09 mass%, 0.08 mass%, 0.07 mass%, 0.06 mass%, 0.05 mass%, 0.04 mass%, 0.03 mass%, 0.02 mass%, 0.01 mass%, or 0 mass% relative to the total amount of the polyacetal resin composition.

[0052] In one embodiment of the present invention, there is provided a method for producing the polyacetal resin composition, wherein the amount of ethylene urea extracted with hot water when the polyacetal resin composition is freeze-pulverized and then subjected to hot water extraction at 120°C for 3 hours is 0.10 mass% or less, based on the total amount of the polyacetal resin composition.

[0053] In an embodiment of the present invention, there is provided a polyacetal resin composition comprising 100 parts by mass of a polyacetal resin and 0.2 to 0.5 parts by mass of ethylene urea, wherein when the polyacetal resin composition is freeze-pulverized and then subjected to hot water extraction at 120°C for 3 hours, the amount of ethylene urea extracted with hot water is 0.10% by mass or less relative to the total amount of the polyacetal resin composition.

[0054] <3-3> Mold deposit (MD, mold adhesion) Mold deposit is material adhering to the mold used during molding, significantly degrading the working environment during molding of a thermoplastic resin composition. The fewer mold deposits there are, the better the molding processability. Mold deposit properties can be determined, for example, using a Minimat M14 / 7B manufactured by Sumitomo Heavy Industries, Ltd. and a teardrop-shaped mold as shown in the figure, but are not limited to this method.

[0055] <4> Polyacetal resin composition produced by the production method of the present invention In an embodiment of the present invention, there is provided a polyacetal resin composition produced by the above-mentioned method for producing a polyacetal resin composition.

[0056] In an embodiment of the present invention, the polyacetal resin composition comprises 100 parts by mass of a polyacetal resin and 0.2 to 0.5 parts by mass of ethylene urea, and when the polyacetal resin composition is freeze-pulverized and then subjected to hot water extraction at 120°C for 3 hours, the amount of ethylene urea extracted with hot water is 0.10% by mass or less relative to the total amount of the polyacetal resin composition.

[0057] In an embodiment of the present invention, the polyacetal resin composition is produced by kneading ethylene urea into a polyacetal resin, and the heat-melt kneading time when kneading the ethylene urea into the polyacetal resin is 10 to 60 minutes.

[0058] In an embodiment of the present invention, the polyacetal resin composition is produced by kneading ethylene urea into a polyacetal resin, and the heat-melt kneading temperature when kneading the ethylene urea into the polyacetal resin is 220°C to 240°C.

[0059] In an embodiment of the present invention, the polyacetal resin composition is produced by kneading ethylene urea into a polyacetal resin, and the heat-melt-kneading time when kneading the ethylene urea into the polyacetal resin is 10 minutes to 60 minutes, and the heat-melt-kneading temperature when kneading the ethylene urea into the polyacetal resin is 220°C to 240°C.

[0060] <5> Molded Article The present invention provides a molded article formed from the polyacetal resin composition of the present invention. The polyacetal resin composition of the present invention can be molded according to a molding method for polyacetal resins known in the art. Molding methods include, but are not limited to, injection molding, extrusion molding, blow molding, vacuum molding, compression molding, press molding, 3D printing, etc.

[0061] <5-1> Examples of molded articles formed from the polyacetal resin composition of the present invention include various products that are conventionally known to be uses of polyacetal resins, such as pellets, round bars, thick plates, and other raw materials, sheets, tubes, various containers, various parts for machinery, electrical equipment, automobiles, and building materials, and vehicle components. The polyacetal resin composition of the present invention can be used for, for example, automobile parts, clothing parts, molded parts for electrical and electronic applications, molded parts for information recording devices, molded parts for medical devices, molded parts for household use, rotating parts such as gears, bearing members, sliding members, press-fit parts, hinge parts, automobile fuel-related parts, insert parts, snap-fit ​​parts, plumbing parts, various handles, various handrails, various chassis, side panel parts, spring parts, seat belt parts, automobile carrier plates, automobile combination switches, clips, pipe holders, electric wire holders, connectors, assist clips, bumper storage materials, console boxes, door trims, door checkers, ball joints, undercut parts, storage cases for optical fiber core wire connections, disk cartridges, tape cassettes, trays for disc-shaped recording media, toner, film holders, protective covers, artificial joints, medical treatment tool insertion valves, blood vessel insertion tools, caps, compact containers, fastener parts, card cases, toothbrushes, eating and drinking utensils, curtain rails with covers, curtain rail caps, lids for liquid containers, writing instruments, foldable storage frames, baskets and their handles, etc.

[0062] <5-2> Pellets The polyacetal resin composition of the present invention can be molded into pellets according to a molding method for polyacetal resins known in the art. The present invention provides pellets formed from the polyacetal resin composition of the present invention.

[0063] <5-3> Vehicle Components The polyacetal resin composition of the present invention can be molded into vehicle components according to polyacetal resin molding methods known in the art. The present invention provides a vehicle component formed from the polyacetal resin composition of the present invention. Examples of vehicle components include, but are not limited to, automobile parts, molded electrical and electronic components, molded information recording device components, rotating parts such as gears, bearings, sliding components, press-fit components, hinge components, automobile fuel-related components, insert components, snap-fit ​​components, plumbing components, various handles, various handrails, various chassis, side panel components, spring components, seatbelt components, automobile carrier plates, automobile combination switches, clips, pipe holders, electric wire holders, connectors, assist clips, bumper storage materials, console boxes, door trim, door checkers, and the like.

[0064] The present invention will be described below based on examples. However, the following examples are merely illustrative and are not intended to limit the scope of the present invention.

[0065] <Production of Crude Oxymethylene Copolymer> 4.2 parts by mass of 1,3-dioxolane per 100 parts by mass of trioxane, 0.03 mmol of the polymerization catalyst boron trifluoride diethyl etherate per 1 mole of trioxane, and 0.6 mmol of methylal as a molecular weight modifier were continuously added to a twin-screw continuous polymerization reactor equipped with self-cleaning paddles set at 85°C. The polymerization reaction was carried out continuously so that the residence time of the polymerization reaction product in the continuous polymerization reactor was 15 minutes. The polymerization terminator N,N-diethylhydroxylamine was added to the resulting polymerization reaction product in an amount twice the molar amount of the polymerization catalyst, and the mixture was then pulverized to obtain a crude oxymethylene copolymer.

[0066] <Evaluation Method 1: Amount of Formaldehyde Generated> The amount of formaldehyde generated was measured as the amount generated per 1 g of oxymethylene copolymer resin (unit: μg / g) by the following procedure. 1) The oxymethylene copolymer resin composition was pre-dried at 80°C for 3 hours and molded into a circular test piece having a diameter of 50 mm and a thickness of 3 mm using a Yamashiro SAV-30-30 molding machine at a cylinder temperature of 215°C. 2) Using the obtained test piece, the amount of formaldehyde generated was measured on the day after molding in accordance with the method described in the German Association of the Automotive Industry Standard VDA275 (Automotive interior parts - Determination of formaldehyde emission amount by the revised flask method).

[0067] A product in which the amount of formaldehyde generated per 1 g of oxymethylene copolymer resin was 3 μg / g was judged to be acceptable.

[0068] <Evaluation Method 2: Hot Water Extraction Amount> The extraction of ethylene urea in the pellets was measured as the hot water extraction amount (phr) per 100 parts by mass of the oxymethylene copolymer resin composition using the following procedure. 1) After freeze-pulverizing the pellets, 2 g of the powder that passed through a 60-mesh metal screen was refluxed in 25 mL of pure water at 120°C for 3 hours. 2) After refluxing, the extract was subjected to suction filtration to remove the powder, and the ethylene urea in the extract was quantified by liquid chromatography. The liquid chromatography measurement conditions are shown below. Apparatus: SHIMADZU LC-10AD Column: L-column 2 ODS (particle size 5 μm, φ4.6 mm × 250 mm) Column temperature: 40°C Mobile phase: 10 mM potassium dihydrogen phosphate aqueous solution (potassium dihydrogen phosphate 5 mM + phosphoric acid 5 mM) / acetonitrile = 25:2 (v / v) Flow rate: 0.5 mL / min Detector: UV-visible detector (detection wavelength: 215 nm)

[0069] Those having an extractable amount of 0.1 phr or less per 100 parts by mass of the oxymethylene copolymer resin composition were rated as passing.

[0070] <Evaluation method 3: Mold deposit (MD, mold adhesion)> Using an injection molding machine: Minimat M14 / 7B manufactured by Sumitomo Heavy Industries, Ltd. and a teardrop-shaped mold as shown in the figure, 4,000 shots were continuously molded under conditions of a cylinder temperature of 220°C and a mold temperature of 40°C, and the amount of adhesion to the mold was evaluated on a 4-point scale from A to D.

[0071] The teardrop-shaped mold in Figure 1 is designed so that the resin composition is introduced through gate G and the generated gas is easily accumulated at tip P. Gate G has a width of 1 mm and a thickness of 1 mm, and in Figure 1, width h1 is 14.5 mm, length h2 is 7 mm, length h3 is 27 mm, and the thickness of the molded portion is 3 mm.

[0072] Those with A or B below were judged to be acceptable. A: No mold deposits at all, and the mold contamination suppression effect was extremely good. B: Almost no mold deposits, and the mold contamination suppression effect was extremely good. C: Some mold deposits were found, but the mold contamination suppression effect was good. D: Much mold deposits were found, and the mold contamination suppression effect was poor.

[0073] Examples 1 to 9, Comparative Examples 1 to 5 To 100 parts by mass of the crude oxymethylene copolymer, 0.3 parts by mass of ethylene bis(oxyethylene)bis[3-(5-tert-butyl-4-hydroxy-m-tolyl)propionate (IRGANOX® 245, manufactured by BASF) as a stabilizer, 0.05 parts by mass of melamine (manufactured by Mitsui Chemicals), and the formulations described in each Example and Comparative Example were added, and the mixture was premixed using a Henschel mixer. The premixed crude oxymethylene copolymer was introduced from a hopper equipped with an automatic quantitative feed function into a co-rotating twin-screw extruder (inner diameter 69 mm, L / D = 31.5) at a rate of 60 kg / h, and the crude oxymethylene copolymer was melted at 220 to 250°C and continuously introduced into a twin-screw, surface-renewal horizontal kneader. The molten resin was continuously extracted by a gear pump and immersed in a water bath for cooling as a strand, which was then fed to a pelletizer to be pelletized. The pellets obtained were dried in a hot air dryer at 120°C for 12 hours to prepare the final sample.

[0074] Comparative Example 6 To 100 parts by mass of the crude oxymethylene copolymer, 0.3 parts by mass of ethylene bis(oxyethylene)bis[3-(5-tert-butyl-4-hydroxy-m-tolyl)propionate (IRGANOX® 245, manufactured by BASF) as a stabilizer, 0.05 parts by mass of melamine (manufactured by Mitsui Chemicals), and the formulations described in each Example and Comparative Example were added, and the mixture was premixed using a Henschel mixer. The premixed crude oxymethylene copolymer was introduced at 10 kg / h from a hopper equipped with an automatic quantitative feed function into a co-rotating twin-screw extruder (inner diameter 29 mm, L / D = 18). The crude oxymethylene copolymer was melted at 220°C, and the molten resin extruded through the die holes was immersed as strands in a cooling water bath and then fed to a pelletizer for pelletization. The resulting pellets were dried in a hot air dryer at 120°C for 12 hours to prepare a final sample.

[0075] For Examples 1 to 9 and Comparative Examples 1 to 6, the amounts of each component, the resin composition production method, kneading time, kneading temperature, and the evaluation results of the amount of formaldehyde generated, the amount of hot water extraction, and mold deposit (MD) are shown in Tables 1 and 2 below.

[0076]

[0077]

[0078] As described above, it has been demonstrated that the polyacetal resin production method of the present invention can produce a polyacetal resin composition with reduced formaldehyde emissions and reduced mold deposits. The method of the present invention not only improves the working environment, but also reduces the amount of formaldehyde emitted from the polyacetal resin composition and molded articles using the same, thereby improving moldability through reduced mold deposits. Therefore, the polyacetal resin composition can be suitably used as a countermeasure against so-called sick house syndrome in automobile interior parts, interior parts for houses and the like (hot water mixer taps, etc.), clothing parts (zippers, belt buckles, etc.), building materials (pipes, pump parts, etc.), and machine parts (gears, etc.).

[0079] G Gate P Tip h1 Width h2 Length (distance from gate G to the part with width h1) h3 Length (total length)

Claims

1. A method for producing a polyacetal resin composition containing 100 parts by mass of polyacetal resin and 0.2 to 0.5 parts by mass of ethylene urea, the method including a kneading step of kneading ethylene urea into the polyacetal resin, the kneading step including kneading the ethylene urea into the polyacetal resin for a heating and melting kneading time of 10 minutes to 60 minutes and a heating and melting kneading temperature of 220°C to 240°C.

2. A method for producing the polyacetal resin composition described in claim 1, wherein the amount of ethylene urea extracted with hot water when the polyacetal resin composition is freeze-pulverized and then subjected to hot water extraction at 120°C for 3 hours is 0.10 mass% or less relative to the total amount of the polyacetal resin composition.

3. A method for producing the polyacetal resin composition according to claim 1 or 2, wherein the amount of formaldehyde emitted from the polyacetal resin composition as measured in accordance with the German Automotive Industry Association standard VDA275 is 3 ppm or less.

4. A polyacetal resin composition produced by the method according to any one of claims 1 to 3.

5. A polyacetal resin composition comprising 100 parts by mass of polyacetal resin and 0.2 to 0.5 parts by mass of ethylene urea, wherein the amount of ethylene urea extracted with hot water when the polyacetal resin composition is freeze-pulverized and then subjected to hot water extraction at 120°C for 3 hours is 0.10 mass% or less relative to the total amount of the polyacetal resin composition.

6. The polyacetal resin composition according to claim 5, wherein the amount of formaldehyde emitted from the polyacetal resin composition as measured in accordance with the German Automotive Industry Association standard VDA275 is 3 ppm or less.

7. The polyacetal resin composition according to claim 5 or 6, which is produced by kneading ethylene urea into a polyacetal resin, and the heating, melting and kneading time when kneading the ethylene urea into the polyacetal resin is 10 to 60 minutes.

8. The polyacetal resin composition according to any one of claims 5 to 7, which is produced by kneading ethylene urea into a polyacetal resin, and the heating, melting and kneading temperature when kneading the ethylene urea into the polyacetal resin is 220°C to 240°C.

9. A pellet formed from the polyacetal resin composition according to any one of claims 4 to 8.

10. A molded article formed from the polyacetal resin composition according to any one of claims 4 to 8.

11. A vehicle component formed from the polyacetal resin composition according to any one of claims 4 to 8.

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