Patent Description:
Polyacetal resins are materials that are excellent in rigidity, strength, tenacity, sliding property, and creep property. Polyacetal resins have been used over a wide range as resin materials for various mechanical members such as automobile members, electric or electronic members, and industrial members.

Polyacetal resins form formaldehyde when they are decomposed by the action of heat, light, oxygen, acid, base and the like. In particular, there is concern that formaldehyde gas generated by thermal decomposition during manufacturing or molding may deteriorate the working environment, and that formaldehyde gas generated from resin products may deteriorate the indoor environment.

A known example of methods of suppressing the generation of formaldehyde from polyacetal resins is a method of adding a hydrazide compound (<CIT> (PTL <NUM>)).

However, a polyacetal resin composition containing a hydrazide compound is likely to form mold deposits. The generation of mold deposits lowers the work efficiency and causes the deterioration of surface conditions of a molded product.

Disclosed methods of using a hydrazide compound to suppress the amount of formaldehyde emissions while also reducing mold deposits include a method of using a long-chain aliphatic hydrazide compound or an alicyclic hydrazide compound (<CIT> (PTL <NUM>)), a method of using a monohydrazide compound and a dihydrazide compound together (<CIT> (PTL <NUM>) and <CIT> (PTL <NUM>)), and a method of using two different dihydrazide compounds together (<CIT> (PTL <NUM>)). <CIT> discloses methods of using various types of hydrazide compounds to suppress the amount of formaldehyde emissions without specific focus on mold deposits.

However, the methods described in PTLs <NUM> to <NUM> above may not sufficiently suppress the amount of formaldehyde emissions and may cause mold deposits.

Accordingly, the present disclosure is made in light of the problems set forth above and aims to provide a polyacetal resin composition in which the amount of formaldehyde emissions and mold deposits are sufficiently suppressed.

We have found that both the amount of formaldehyde emissions and mold deposits can be reduced by mixing fatty acid monohydrazide compounds having different chain lengths, preferably in a specific ratio, and blending them with a polyacetal resin, and have completed the present disclosure.

We thus provide a polyacetal resin composition as defined in claims <NUM>-<NUM>.

According to the present disclosure, it is possible to provide a polyacetal resin composition in which both the amount of formaldehyde emissions and mold deposits are reduced.

The following describes an embodiment of the present disclosure (hereinafter, simply referred to as "present embodiment") in detail.

A polyacetal resin composition of the present embodiment contains (A) polyacetal resin and (B) fatty acid monohydrazide.

The following describes each component constituting the polyacetal resin composition of the present embodiment in detail.

The (A) polyacetal resin (hereinafter, may be simply referred to as "component (A)") contained in the polyacetal resin composition of the present embodiment has a repeating oxymethylene unit represented by (-CH<NUM>O-) (acetal structure) as a main constituent unit, and known ones may be used. The (A) polyacetal resin used in the present embodiment may be a homopolymer composed of only the oxymethylene unit, and may be a copolymer (including a block copolymer) or a terpolymer containing a constituent unit other than the oxymethylene unit. Further, it may have a branched or crosslinked structure as well as a linear structure.

The(A) polyacetal resin may be used alone or in combination of two or more.

The (A) polyacetal resin preferably contains <NUM> mass% to <NUM> mass%, more preferably <NUM> mass% to <NUM> mass%, and still more preferably <NUM> mass% to <NUM> mass% of polyacetal copolymer, with the total amount of the (A) polyacetal resin being <NUM> mass%.

A known method may be used to produce the (A) polyacetal resin of the present embodiment.

For example, a polyacetal homopolymer can be obtained by homopolymerizing a formaldehyde monomer or a cyclic oligomer of formaldehyde such as a trimer (trioxane) and a tetramer (tetraoxane) thereof. Further, the obtained polyacetal homopolymer can be stabilized with a known method (for example, a method of reacting the polymerization terminal with an ether group or an ester group).

The main chain of the polyacetal homopolymer consists substantially only of oxymethylene unit. That is, it is preferable to contain <NUM> mass% or more of oxymethylene unit.

In the polyacetal copolymer, a constituent unit (copolymer unit) other than the oxymethylene unit is preferably an oxyethylene unit (-CH<NUM>CH<NUM>O-).

Such a polyacetal copolymer can be obtained by copolymerizing a formaldehyde monomer or a cyclic oligomer of formaldehyde such as a trimer (trioxane) and a tetramer (tetraoxane) thereof, with a cyclic ether such as ethylene oxide or <NUM>,<NUM>-dioxolane. In a case where a polyacetal copolymer is obtained from trioxane and <NUM>,<NUM>-dioxolane, it is preferable to use <NUM> mol% to <NUM> mol%, more preferably <NUM> mol% to <NUM> mol%, and still more preferably <NUM> mol% to <NUM> mol% of <NUM>,<NUM>-dioxolane with respect to <NUM> mol% of trioxane. Further, the obtained polyacetal copolymer can be stabilized with a known method (for example, a method of melting the polyacetal copolymer in combination with a quaternary ammonium compound to decompose an unstable terminal portion).

The polyacetal copolymer preferably contains <NUM> mass% to <NUM> mass%, more preferably <NUM> mass% to <NUM> mass%, and still more preferably <NUM> mass% to <NUM> mass% of oxyethylene unit in the entire main chain of the polymer.

The melt flow rate (MFR) of the (A) polyacetal resin of the present embodiment is preferably <NUM>/<NUM> minutes to <NUM>/<NUM> minutes, more preferably <NUM>/<NUM> minutes to <NUM>/<NUM> minutes, and still more preferably <NUM>/<NUM> minutes to <NUM>/<NUM> minutes from the viewpoint of achieving both fluidity and strength.

Note that the MFR can be measured under the conditions of <NUM> and a load of <NUM> in accordance with ISO <NUM>-<NUM>.

In the present embodiment, the content of the (A) polyacetal resin in <NUM> mass% of the polyacetal resin composition is preferably <NUM> mass% or more, more preferably <NUM> mass% or more, and still more preferably <NUM> mass% or more.

The (B) fatty acid monohydrazide contained in the polyacetal resin composition of the present embodiment contains at least (B1) one type of fatty acid monohydrazide having <NUM> to <NUM> carbon atoms represented by the following general formula (<NUM>) and (B2) one type of fatty acid monohydrazide having <NUM> to <NUM> carbon atoms represented by the following general formula (<NUM>). (Hereinafter, the (B) fatty acid monohydrazide, (B1) fatty acid monohydrazide having <NUM> to <NUM> carbon atoms represented by the following general formula (<NUM>), and (B2) fatty acid monohydrazide having <NUM> to <NUM> carbon atoms represented by the following general formula (<NUM>) may be simply referred to as "component (B)", "component (B1)", and "component (B2)", respectively. )
<CHM>
(where n is an integer of <NUM> to <NUM> in the case of the component (B1), and n is an integer of <NUM> to <NUM> in the case of the component (B2).

In the present embodiment, the mass ratio (B1):(B2) of the component (B1) to the component (B2) is preferably <NUM>:<NUM> to <NUM>:<NUM>. When the mass ratio (B1):(B2) is in this range, it is possible to suppress the generation of formaldehyde and the generation of mold deposits in a molded product obtained by molding the polyacetal resin composition of the present embodiment.

The mass ratio (B1):( B2) is more preferably <NUM>: <NUM> to <NUM>:<NUM>, and still more preferably <NUM>: <NUM> to <NUM>: <NUM>. When the mass ratio (B1): (B2) is in this range, the amount of formaldehyde emissions from a molded product obtained by molding the polyacetal resin composition of the present embodiment can be suppressed, particularly in a humid atmosphere.

In the polyacetal resin composition of the present embodiment, the content of the (B) fatty acid monohydrazide is <NUM> parts by mass to <NUM> parts by mass with respect to <NUM> parts by mass of the (A) polyacetal resin. When the content of the (B) fatty acid monohydrazide is less than <NUM> parts by mass, the suppression of formaldehyde generation tends to be insufficient, and when the content exceeds <NUM> parts by mass, it cannot be sufficiently kneaded at the time of extrusion, and the fatty acid monohydrazide tends to flow out to water for cooling strands.

The content of the (B) fatty acid monohydrazide is preferably <NUM> parts by mass to <NUM> part by mass and more preferably <NUM> parts by mass to <NUM> parts by mass with respect to <NUM> parts by mass of the (A) polyacetal resin.

The component (B1) in the present embodiment is represented by the above general formula (<NUM>), where n is an integer of <NUM> to <NUM>, preferably an integer of <NUM> to <NUM>, and more preferably <NUM>.

Specific examples of the component (B1) include stearic acid hydrazide, arachidic acid hydrazide, behenic acid hydrazide, lignoceric acid hydrazide, cerotic acid hydrazide, montanic acid hydrazide, and melissic acid hydrazide. Among these, stearic acid hydrazide, arachidic acid hydrazide, and behenic acid hydrazide are preferable, and stearic acid hydrazide is more preferable.

The component (B1) may be used alone or in combination of two or more.

The component (B2) in the present embodiment is represented by the above general formula (<NUM>), where n is an integer of <NUM> to <NUM>, preferably <NUM> or an integer of <NUM> to <NUM>, and more preferably <NUM>.

Specific examples of the component (B2) include propionic acid hydrazide, butyric acid hydrazide, valeric acid hydrazide, caproic acid hydrazide, heptyl acid hydrazide, caprylic acid hydrazide, pelargonic acid hydrazide, capric acid hydrazide, lauric acid hydrazide, myristic acid hydrazide, palmitic acid hydrazide, and margaric acid hydrazide. Among these, propionic acid hydrazide, lauric acid hydrazide, myristic acid hydrazide, palmitic acid hydrazide, and margaric acid hydrazide are preferable, and palmitic acid hydrazide is more preferable.

The component (B2) may be used alone or in combination of two or more.

The polyacetal resin composition of the present embodiment may further contain (C) fatty acid dihydrazide represented by the following general formula (<NUM>) (hereinafter, may be simply referred to as "component (C)"). <CHM>
(where n is an integer of <NUM> to <NUM>.

The (C) fatty acid dihydrazide in the present embodiment is represented by the above general formula (<NUM>), where n is an integer of <NUM> to <NUM>, preferably an integer of <NUM> to <NUM>, more preferably <NUM> to <NUM>, and still more preferably <NUM> to <NUM>.

Specific examples of the (C) fatty acid dihydrazide include adipic acid dihydrazide, sebacic acid dihydrazide, and dodecane diacid dihydrazide. Among these, sebacic acid dihydrazide and dodecane diacid dihydrazide are preferable, and sebacic acid dihydrazide is more preferable.

The (C) fatty acid dihydrazide may be used alone or in combination of two or more.

In the polyacetal resin composition of the present embodiment, the content of the (C) fatty acid dihydrazide is preferably <NUM> parts by mass to <NUM> parts by mass, more preferably <NUM> parts by mass to <NUM> parts by mass, and still more preferably <NUM> parts by mass to <NUM> parts by mass with respect to <NUM> parts by mass of the (A) polyacetal resin. When the content of the (C) fatty acid dihydrazide is in the above ranges, the amount of formaldehyde emissions in a dry atmosphere can be further suppressed.

The mass ratio (B):(C) of the (B) fatty acid monohydrazide to the (C) fatty acid dihydrazide in the present embodiment is preferably <NUM>:<NUM> to <NUM>:<NUM>. When the (C) fatty acid dihydrazide is contained in the mass ratio (B):(C) in the above range, mold deposits can be further suppressed.

The mass ratio (B):(C) is more preferably <NUM>:<NUM> to <NUM>:<NUM>, and still more preferably <NUM>:<NUM> to <NUM>:<NUM>. When the mass ratio (B):(C) is in the above ranges, the amount of formaldehyde emissions in a dry atmosphere can be particularly reduced.

A conventionally known additive can be added to the polyacetal resin composition of the present embodiment, if necessary. Examples of the additive include an aging improver such as fatty acid metal salts, a sliding agent, a weather resistant agent, a light resistant agent, a release agent, a nucleating agent, a coloring agent, an organic or inorganic reinforcing agent, and various thermoplastic elastomers.

The content of the additive is preferably <NUM> mass% or less with respect to <NUM> mass% of the polyacetal resin composition.

The polyacetal resin composition of the present embodiment can be produced with a known melt-kneading method. For example, the (A) polyacetal resin, the (B) fatty acid monohydrazide, and, if necessary, the (C) fatty acid dihydrazide may be mixed by a stirrer such as a Henschel mixer, and the mixture may be supplied to a single-screw or twin-screw melt-kneading device (extruder) for melt-kneading. In addition, the (A) polyacetal resin may be supplied in the upstream side of a single-screw or twin-screw extruder and melted, and then the (B) fatty acid monohydrazide and, if necessary, the (C) fatty acid dihydrazide may be supplied in the downstream side and melt-kneaded.

A molded product can be obtained by molding the polyacetal resin composition of the present embodiment.

The method of molding the polyacetal resin composition is not particularly limited, and known molding methods such as extrusion molding, injection molding, vacuum molding, blow molding, injection compression molding, decoration molding, dual injection molding, gas-assisted injection molding, foam injection molding, low-pressure molding, ultrathin injection molding (ultrahigh-speed injection molding), in-mold composite molding (insert molding and outsert molding), and melt blow molding may be used.

The shape of the molded product is not particularly limited, and it may be, for example, an injection-molded product, a fiber or nonwoven fabric, a sheet or film, a deformed extruded product, or the like.

The use of the molded product is not particularly limited. For example, it may be used for mechanical members typified by gears, cams, sliders, levers, axes, bearings, guides and the like; resin members of outsert molding; resin members of insert molding (chassis, trays, side plates); members for printers or copiers; members for digital camera or digital video equipment; members for music, video or information equipment; members for communication equipment; members for electric equipment; and members for electronic equipment.

Further, the molded product can be suitably used as an automobile member in members around fuel typified by gasoline tanks, fuel pump modules, valves, gasoline tank flanges and the like; members around doors; peripheral members of seatbelts; combination switch members; and switches.

Moreover, the molded product also can be suitably used as an industrial member typified by house equipment.

The following describes the present disclosure in more detail with reference to Examples and Comparative Examples, yet the present disclosure is not limited thereto.

The raw material components used in Examples and Comparative Examples are as follows.

The MFR value was measured according to ISO <NUM>-<NUM> using a MELT INDEXER manufactured by Toyo Seiki Co. at a cylinder temperature of <NUM> and a load of <NUM>.

The following fatty acid monohydrazides were synthesized, mixed at the ratio listed in Table <NUM>, and used.

The method of synthesizing each fatty acid monohydrazide is as follows.

First, <NUM> of methyl stearate (manufactured by FUJIFILM Wako Pure Chemical Corporation) was added to a three-outlet flask equipped with a reflux condenser, a thermometer and a stirrer and stirred in a warm bath of <NUM> until it was completely melted. Then, <NUM> (<NUM> equivalents) of <NUM> %-hydrazine monohydrate (manufactured by Tokyo Chemical Industry Co. ) was added dropwise thereto, and the mixture was heated and stirred for <NUM> hour to obtain <NUM> of stearic acid hydrazide.

The (B1-<NUM>) behenic acid hydrazide, (B2-<NUM>) palmitic acid hydrazide, (B2-<NUM>) myristic acid hydrazide, and (B2-<NUM>) propionic acid hydrazide were obtained in the same manner as for the (B1-<NUM>) except that the methyl stearate was changed to methyl behenate, methyl palmitate, methyl myristate, and methyl propionate (all manufactured by Tokyo Chemical Industry Co. ), respectively.

Each of the synthesized fatty acid monohydrazides was dissolved in HFIP to a concentration of <NUM>/mL, and it was confirmed by GC/MS measurement that the purity was <NUM> % or more in terms of peak area ratio.

The GC/MS measurement used HP6890/<NUM> manufactured by Agilent, and DB-<NUM> manufactured by Agilent was used as the column.

The (B) fatty acid monohydrazide and the (B') aromatic monohydrazide were mixed at the ratio listed in Table <NUM> and used.

The measurement method and evaluation method used for Examples and Comparative Examples are as follows.

Test pieces (in a flat-plate shape of <NUM> × <NUM> × <NUM>) were molded from the polyacetal resin compositions obtained in Examples and Comparative Examples under conditions of a mold temperature of <NUM>, a cylinder temperature of <NUM>, an injection pressure of <NUM> MPa, an injection time of <NUM> seconds, and a cooling time of <NUM> seconds, using an injection molding machine (IS-100GN manufactured by Toshiba Machine Co.

The test piece and <NUM> of nitrogen were placed in a sampling bag with a two-way cock (smart bag PA having a capacity of <NUM> manufactured by GL Sciences Inc. ) and sealed. After heating the sampling bag at <NUM> for <NUM> hours, <NUM> of the gas inside the sampling bag was extracted through a DNPH cartridge (InertSep mini AERO DNPH manufactured by GL Sciences Inc. ) at a rate of <NUM>/min, and formaldehyde in the gas was collected. Then, the formaldehyde-DNPH in the DNPH cartridge was eluted with acetonitrile, the concentration of formaldehyde-DNPH of the eluate was determined by means of HPLC with a calibration curve method using a standard substance of formaldehyde-DNPH, and the amount of formaldehyde emissions per unit mass of the test piece (µg/g) was calculated. The smaller the value is, the more the amount of formaldehyde emissions is suppressed, which is preferable.

The amount of formaldehyde emissions from the test piece was measured according to a method described in the German Association of the Automotive Industry Standard VDA275. Specifically, the test piece was hung in a <NUM> polyethylene bottle containing <NUM> of distilled water so as not to come into contact with the distilled water, and the bottle was sealed. The bottle was heated at <NUM> for <NUM> hours and allowed to stand at room temperature for <NUM> minutes. Formaldehyde in the distilled water was reacted with acetylacetone in the presence of ammonium ions, and the reactant was measured with UV spectrometer with the wavelength of <NUM>. Note that the amount of formaldehyde emissions (µg/g) was indicated as an amount of formaldehyde with respect to <NUM> of the polyacetal resin. The smaller the value is, the more the amount of formaldehyde emissions is suppressed, which is preferable.

Pellets of the polyacetal resin compositions obtained in Examples and Comparative Examples were subjected to continuous molding to obtain molded products (in an arrowhead shape of <NUM> × <NUM> × <NUM>), and the presence or absence of mold deposits (MD) was confirmed after <NUM>, <NUM>, and <NUM> shots.

The presence or absence of mold deposits was observed in a direction perpendicular to the surface on the fixed side of the mold. When no MD was observed, it was evaluated as "good"; when any colorless MD was observed, it was evaluated as "poor"; when an interference color (interference fringes) was observed (it was presumed that the MD had a thickness of about <NUM> or more), it was evaluated as "inferior". The larger the number of molding shots is until mold deposits are observed, the more the mold deposits are suppressed, which is preferable.

The molding was performed under conditions of a mold setting temperature of <NUM>, a cylinder temperature of <NUM>, an injection pressure of <NUM> MPa, an injection time of <NUM> seconds, and a cooling time of <NUM> seconds, using an injection molding machine (Ti-<NUM> manufactured by Toyo Seiki Co.

Pellets of the polyacetal resin compositions obtained in Examples and Comparative Examples were retained in a cylinder of an injection molding machine (IS-100GN manufactured by Toshiba Machine Co. ) in a molten state for <NUM> minutes, and then the pellets were injection-molded into flat plates of <NUM> × <NUM> × <NUM> under injection conditions of an injection pressure of <NUM> MPa, an injection time of <NUM> seconds, and a cooling time of <NUM> seconds. The cylinder setting temperature was <NUM>, and the mold temperature was <NUM>.

The color tone of the central part of the obtained molded plate was measured by Lab color system using a color-difference meter (CR-<NUM> manufactured by KONICA MINOLTA, INC. ), and the color difference ΔE from a blank (molded plate obtained by normal molding without retention) was calculated according to the following formula. The lower the ΔE value is, the more the discoloration due to retention is suppressed, which is preferable. <MAT> (where the values of the blank measured by the color-difference meter are LBlank, aBlank and bBlank, and the values of the molded plate measured after retention are L, a and b.

Each component was mixed so as to have the chemical composition listed in Tables <NUM> and <NUM>, supplied to a twin-screw extruder (PCM30 manufactured by IKEGAI), melt-kneaded under the conditions of a screw rotation speed of <NUM> rpm and a cylinder setting temperature of <NUM>, and then pelletized. The obtained pellets were dried for <NUM> hours using a hot-air dryer at a temperature of <NUM>.

The evaluation results are summarized in Tables <NUM> and <NUM>.

In Comparative Example <NUM>, the polyacetal resin and the fatty acid monohydrazide were not sufficiently kneaded, and an oil film was formed on the water bath for cooling the strands. As a result, extrusion could not be performed (the materials could not be extruded).

Claim 1:
A polyacetal resin composition, comprising
<NUM> parts by mass of (A) polyacetal resin, and
<NUM> parts by mass to <NUM> parts by mass of (B) fatty acid monohydrazide, wherein
the (B) fatty acid monohydrazide comprises at least
(B1) one type of fatty acid monohydrazide having <NUM> to <NUM> carbon atoms represented by the following general formula (<NUM>), and
(B2) one type of fatty acid monohydrazide having <NUM> to <NUM> carbon atoms represented by the following general formula (<NUM>),
<CHM>
where n is an integer of <NUM> to <NUM> in a case of the component (B1), and n is an integer of <NUM> to <NUM> in a case of the component (B2).