JP2024070251A - Polyacetal resin composition and method for producing the same - Google Patents

Abstract

To provide a polyacetal resin composition which generates little formaldehyde in production, storage and/or processing while containing a polyacetal resin and a cellulose fine fiber and a method for producing the same, and a molding obtained by molding the polyacetal resin composition.SOLUTION: A resin composition contains a polyacetal resin and a cellulose fine fiber, wherein aldehyde group concentration of the cellulose fine fiber is 0.5 μmol/g to 50 μmol/g, carboxy group concentration of the cellulose fine fiber is 200 μmol/g or less, and a number average fiber diameter of the cellulose fine fiber is 1,000 nm or less.SELECTED DRAWING: None

Description

The present invention relates to a polyacetal resin composition, a method for producing the same, and a molded article obtained by molding the polyacetal resin composition.

Polyacetal resin has excellent mechanical, thermal, electrical, sliding and moldable properties, and is widely used as a structural material and mechanical parts in a wide range of applications, including electrical equipment, automotive parts and precision machinery parts.

In general, various fillers are often blended into resin-based molded bodies to improve their mechanical properties. In recent years, the use of cellulose as such a filler has been explored, focusing on the advantages of cellulose being a low specific gravity and renewable material. Among these, cellulose microfibers are advantageous in that they have a good effect on improving physical properties per unit amount used.

Cellulose is essentially hydrophilic due to its hydroxyl groups, and it is often difficult to uniformly disperse cellulose fine fibers in a resin. Therefore, various methods have been proposed to improve the dispersibility of cellulose fine fibers in a resin. For example, Patent Document 1 describes a composite composition containing a resin and a fibrous filler having an average fiber diameter of 4 to 1000 nm, and describes that the fibrous filler may be one in which some of the hydroxyl groups of the cellulose fibers have been oxidized to aldehyde and/or carboxyl groups.

JP 2010-116477 A

When a resin composition containing a polyacetal resin is produced, the polyacetal resin may be decomposed by heat, acid, etc. during production, storage, and/or processing of the resin composition, resulting in the generation of formaldehyde. The decomposition of the polyacetal resin not only reduces the mechanical properties of the polyacetal resin itself, but also leads to the problem of adverse effects of formaldehyde on the working environment. Conventionally, when producing a polyacetal resin composition, the generation of formaldehyde has been suppressed by including an antioxidant such as a hindered phenol in the resin composition, but when cellulose is used as a filler, the effect of the stabilizer is not necessarily sufficient. For example, the oxidized cellulose fiber described in Patent Document 1 may have good affinity with resins, but when combined with a polyacetal resin, it may promote the generation of formaldehyde derived from the polyacetal resin.

One aspect of the present invention aims to solve the above problems and provide a polyacetal resin composition that contains polyacetal resin and cellulose microfibers, yet generates little formaldehyde during production, storage and/or processing, and exhibits good mechanical properties, a method for producing the same, and a molded article obtained by molding the polyacetal resin composition.

This disclosure encompasses the following items.
[Item 1]
A resin composition comprising a polyacetal resin and a cellulose fine fiber,
The aldehyde group concentration of the cellulose fine fibers is 0.5 μmol/g to 50 μmol/g,
The cellulose fine fibers have a carboxy group concentration of 200 μmol/g or less,
The resin composition, wherein the cellulose fine fibers have a number average fiber diameter of 1000 nm or less.
[Item 2]
2. The resin composition according to item 1, further comprising an aldehyde group blocking agent.
[Item 3]
3. The resin composition according to item 2, wherein the aldehyde group blocking agent is at least one selected from the group consisting of aminotriazine compounds, guanamine compounds, urea derivatives, hydrazide compounds, acrylamide polymers, and polyamides.
[Item 4]
4. The resin composition according to any one of items 1 to 3, wherein the cellulose fine fibers have a weight average molecular weight of 100,000 or more.
[Item 5]
5. The resin composition according to any one of items 1 to 4, wherein the Mw/Mn of the cellulose fine fibers is 6.0 or less.
[Item 6]
Item 6. The resin composition according to any one of items 1 to 5, wherein the cellulose fine fibers have an alkali-soluble content of 10% by mass or less.
[Item 7]
7. The resin composition according to any one of items 1 to 6, wherein the cellulose fine fibers have a thermal decomposition onset temperature T _D of 200° C. or higher.
[Item 8]
8. The resin composition according to any one of items 1 to 7, wherein the halogen content H of the cellulose fine fibers is 500 ppm by mass or less.
[Item 9]
Item 9. The resin composition according to any one of items 1 to 8, wherein the cellulose fine fibers are esterified chemically modified cellulose fine fibers.
[Item 10]
Item 10. The resin composition according to item 9, wherein the esterification is acetylation.
[Item 11]
The aldehyde group concentration A per unit area of the cellulose fine fiber and the ratio (R=m/n) of the number of repeats m of the oxyethylene unit to the number of repeats n of the oxymethylene unit in the polyacetal resin satisfy the following relationship: 10 ^((R-5)/3) ≦ A ≦ 10 ^((R+3)/10)
11. The resin composition according to any one of items 1 to 10,
[Item 12]
A method for producing a resin composition according to any one of items 1 to 11,
A defibration step of defibrating the cellulose fiber raw material in a liquid medium at a liquid temperature of 85°C or less to obtain a cellulose fine fiber slurry;
a drying step of drying the cellulose fine fiber slurry to obtain a dried cellulose fine fiber body; and a mixing step of mixing a polyacetal resin with the dried cellulose fine fiber body.
A method comprising:
[Item 13]
Item 13. The method according to item 12, wherein the cellulose fine fibers in the cellulose fine fiber slurry produced in the defibration step have an aldehyde group concentration of 0.5 μmol/g to 50 μmol/g and a carboxy group concentration of 200 μmol/g or less.
[Item 14]
Item 12. A molded article obtained by molding the resin composition according to any one of items 1 to 11.
[Item 15]
Item 15. The molded article according to item 14, which is a profile extrusion molded article.
[Item 16]
A method for producing a profile extrusion molded body, comprising:
Item 12. A method comprising a step of profile extruding the resin composition according to any one of items 1 to 11.
[Item 17]
A 3D printing modeling material comprising the resin composition according to any one of items 1 to 11.
[Item 18]
Item 18. The 3D printing modeling material according to item 17, having the form of a filament or powder.
[Item 19]
Item 19. A 3D printing material according to item 17 or 18, which is used to model an object using a 3D printer.
[Item 20]
A method for manufacturing a shaped object, comprising the steps of:
A method comprising a step of modeling the 3D printing material according to item 17 or 18 using a 3D printer.

According to one aspect of the present invention, a polyacetal resin composition and a method for producing the same, as well as a molded article produced by molding the polyacetal resin composition, can be provided that contains polyacetal resin and cellulose fine fibers, yet generates little formaldehyde during production, storage and/or processing, and exhibits good mechanical properties.

FIG. 2 is a diagram illustrating an example of the arrangement of blades and grooves of a disc refiner. FIG. 2 is a diagram illustrating the blade width, groove width, and blade distance of a disc refiner. FIG. 2 is a diagram showing the cross-sectional shape of a die of a single-screw extruder used in Examples 19 to 21.

Below, we will explain exemplary embodiments of the present invention (also referred to as "present embodiments" in this disclosure), but the present invention is not limited to these embodiments.

<Polyacetal resin composition>
The polyacetal resin composition of the present embodiment contains a polyacetal resin and cellulose fine fibers, and in one aspect, the aldehyde group concentration of the cellulose fine fibers is 0.5 μmol/g to 50 μmol/g.

The present inventors have noticed that one of the reasons why the generation of formaldehyde is not sufficiently suppressed even when an antioxidant is used to suppress the decomposition of the polyacetal resin in a resin composition containing a polyacetal resin and cellulose fine fibers is the presence of aldehyde groups in the cellulose fine fibers, and have found that the decomposition of the polyacetal resin in the resin composition is suppressed well by setting the aldehyde group concentration of the cellulose fine fibers to a predetermined level or less. The hemiacetal structure at the reducing end of the cellulose molecule is usually partially ring-opened to form an aldehyde group, and therefore cellulose inherently has a certain amount of aldehyde groups. In addition, even in TEMPO-oxidized cellulose produced using free radicals such as 2,2,6,6-tetramethylpiperidine 1-oxyl (TEMPO) as a catalyst, the carboxy group at the C6 position may exist as an aldehyde group. Since the aldehyde group is highly reactive, it can become the starting point of thermal decomposition when cellulose is exposed to high temperatures. In other words, cellulose with a high aldehyde group concentration is considered to be in a state that is easily decomposed. The aldehyde group concentration can increase due to the molecular structure of cellulose (e.g., the presence of a large amount of low molecular weight components), ambient conditions (e.g., oxidizing conditions), etc.

According to the study by the present inventors, when the cellulose fine fibers and the polyacetal resin are combined at a temperature equal to or higher than the melting temperature, it is believed that the aldehyde groups of the cellulose fine fibers cleave the ether bonds of the polyacetal, promoting the decomposition of the polyacetal resin. Although the mechanism is not clear, a dehydration reaction occurs within the molecules of the cellulose fine fibers at the melting temperature of the polyacetal resin, generating water. It is believed that the combination of the water generated in the molten state of the polyacetal resin and the aldehyde groups of the cellulose fine fibers causes the formation of bonds by a dehydration reaction between the alcohol terminals formed by hydrolysis of the ether bonds of the polyacetal resin and the aldehyde groups of the cellulose fine fibers. Therefore, if the aldehyde group concentration of the cellulose fine fibers is high, the molecular weight of the polyacetal resin and the cellulose fine fibers, and therefore the physical properties of the resin composition may decrease during production, storage, and/or processing, and the generation of formaldehyde derived from the polyacetal resin is promoted. In the resin composition of this embodiment, the use of cellulose fine fibers having an aldehyde group concentration of a predetermined value or less not only inhibits the decomposition of the cellulose fine fibers themselves but also contributes to inhibiting the decomposition of the polyacetal resin, and is therefore advantageous in inhibiting the generation of formaldehyde during the production, storage and/or processing of the resin composition.
Hereinafter, preferred embodiments of the polyacetal resin composition of the present embodiment will be specifically described.

<Polyacetal resin>
Polyacetal resins are polymeric compounds whose main constituent unit is an oxymethylene group ( _-OCH2- ), and are typically polyacetal homopolymers consisting essentially of repeating oxymethylene units, and polyacetal copolymers containing oxymethylene units and other monomer units. Polyacetal resins also include copolymers into which branched and/or crosslinked structures have been introduced by copolymerizing branch-forming components and/or crosslinking components, and block or graft copolymers having a polymer portion consisting of repeating oxymethylene groups and another polymer portion.

In general, polyacetal homopolymers are produced by polymerization of one or more monomers selected from anhydrous formaldehyde and cyclic formaldehyde oligomers such as trioxane (cyclic trimer of formaldehyde) and tetraoxane (cyclic tetramer of formaldehyde). Usually, the polymerization terminals are esterified to stabilize against thermal decomposition.

Furthermore, polyacetal copolymers are generally produced by copolymerizing formaldehyde and/or a cyclic oligomer of formaldehyde represented by the general formula ( _CH2O )n [wherein n is an integer of 3 or more] (such as the above-mentioned trioxane) with a comonomer such as a cyclic ether and/or a cyclic formal (such as ethylene oxide, propylene oxide, epichlorohydrin, 1,3-dioxolane, and cyclic formals of glycols or diglycols, such as 1,4-butanediol formal). Usually, unstable terminal portions are removed by hydrolysis to stabilize the copolymer against thermal decomposition.

Further examples of polyacetal copolymers include branched polyacetal copolymers obtained by copolymerizing a formaldehyde monomer and/or a cyclic oligomer with a monofunctional glycidyl ether; and crosslinked polyacetal copolymers obtained by copolymerizing a formaldehyde monomer and/or a cyclic oligomer with a polyfunctional glycidyl ether.

Examples of polyacetal resins include polyacetal homopolymers having block components obtained by polymerizing formaldehyde monomers and/or cyclic oligomers in the presence of a compound having functional groups such as hydroxyl groups at both or one end, for example, polyalkylene glycol; and polyacetal copolymers having block components obtained by copolymerizing formaldehyde monomers and/or cyclic oligomers with cyclic ethers and/or cyclic formals in the presence of a compound having functional groups such as hydroxyl groups at both or one end, for example, hydrogenated polybutadiene glycol.

The polyacetal resin of this embodiment is preferably a polyacetal copolymer as described above, in that it generates little formaldehyde due to decomposition, and more preferably a polyacetal copolymer containing oxymethylene units ( _-OCH2- ) and _oxyethylene units ( _-OC2H5- ) as constituent units (hereinafter also referred to as an oxyethylene unit-containing copolymer). The oxyethylene unit-containing copolymer can be produced by copolymerizing formaldehyde and/or a cyclic oligomer of formaldehyde represented by the general formula ( _CH2O )n [wherein n is an integer of 3 or more] (for example, the above-mentioned trioxane), ethylene glycol or a cyclic formal thereof, and optionally other components.

In a copolymer containing oxyethylene units, the ratio of the number of repeating oxyethylene units m represented by the general formula (CH ₂ CH ₂ O) m to the number of repeating oxymethylene units n represented by the general formula (CH ₂ O) n (also referred to in this disclosure as the ethylene ratio R = m/n) preferably has a lower limit of 0.3 or 0.4 from the viewpoint of the dimensional stability of the resin composition, and an upper limit of preferably 1.8, 1.7, 1.6, or 1.5 from the viewpoint of the heat resistance and mechanical strength of the resin composition.

The polyacetal resin is preferably a copolymer of 99.9 to 90% by mass of trioxane and 0.1 to 10% by mass of a monofunctional cyclic ether. In the copolymer, the total of the alkoxy end groups and the hydroxyalkoxy end groups having at least two carbon atoms is preferably 70 to 99 mol % of all the end groups. The number of end groups can be measured using a known method (specifically, infrared absorption spectroscopy or nuclear magnetic resonance, more specifically, the methods described in JP-A-5-98028, JP-A-2001-11143, etc.).

The melt index of the polyacetal resin, measured in accordance with ASTM-D1238 under conditions of 190°C and 2.16 kgf (21.2 N), is preferably 2 g/10 min at the lower limit, 4 g/10 min at the lower limit, or 7 g/10 min at the upper limit, and is preferably 25 g/10 min at the upper limit, 20 g/10 min at the upper limit, or 18 g/10 min at the upper limit. By setting the melt index within the above range, the reinforcing effect of the cellulose microfibers can be maximized while ensuring molding fluidity.

The number average molecular weight of the polyacetal resin, in one embodiment, is 3,000 or more, or 5,000 or more, or 10,000 or more, and in one embodiment, is 1,000,000 or less, or 500,000 or less, or 200,000 or less. In addition, the weight average molecular weight, in one embodiment, is 10,000 or more, or 100,000 or more, or 200,000 or more, and in one embodiment, is 2,000,000 or less, or 1,000,000 or less, or 500,000 or less.

The aldehyde group concentration of the polyacetal resin used in the production of the resin composition is, in one embodiment, a formaldehyde concentration of 0.001 μmol/g or more, or 0.01 μmol/g or more, or 0.1 μmol/g or more, and in one embodiment, 10 μmol/g or less, or 5 μmol/g or less, or 3 μmol/g or less, or 1 μmol/g or less, or 0.5 μmol/g or less.

In the present disclosure, the aldehyde group concentration of the polyacetal resin is the amount of formaldehyde released measured by the method described in the German Automotive Industry Association standard VDA275. Specifically, first, a polyacetal resin test piece (length 100 mm x width 40 mm x thickness 3 mm) is molded using an injection molding machine under conditions conforming to JIS K7364-2 at a molding temperature of 200°C. Next, the polyacetal resin test piece is hung in a polyethylene container containing 50 mL of distilled water so as not to touch the distilled water, sealed, and heated at 60°C for 3 hours to extract formaldehyde in the distilled water, and then cooled to room temperature. After cooling, 5 mL of 0.4 mass% aqueous solution of acetylacetone and 5 mL of 20 mass% aqueous solution of ammonium acetate are added to 5 mL of distilled water that has absorbed formaldehyde to prepare a mixed solution, which is heated at 40°C for 15 minutes to cause a reaction between formaldehyde and acetylacetone. After cooling the mixture to room temperature, the amount of formaldehyde in the distilled water is quantified using a UV spectrophotometer based on the absorption peak at 412 nm. The amount of formaldehyde released from the polyacetal resin (μmol/g) is calculated using the following formula. In general, the amount of formaldehyde released is expressed in μg/g in the VDA275 test, but in this disclosure, μmol/g divided by the molecular weight of formaldehyde (30.031) is used.
Amount of formaldehyde released from polyacetal resin (μmol/g)={amount of formaldehyde in distilled water (mg)/molecular weight of formaldehyde (30.031)}/mass of polyacetal resin molded product used in measurement (g)

<Cellulose Microfibers>
The cellulose fine fibers may be obtained from various cellulose fiber raw materials selected from natural cellulose and regenerated cellulose. As the natural cellulose, wood pulp obtained from wood species (broadleaf or coniferous), non-wood pulp obtained from non-wood species (cotton, bamboo, hemp, bagasse, kenaf, cotton linters, sisal, straw, etc.), and cellulose fiber aggregates produced by animals (e.g., sea squirts, etc.), algae, and microorganisms (e.g., acetic acid bacteria, etc.) can be used. As the regenerated cellulose, regenerated cellulose fibers (viscose, cupra, Tencel, etc.), cellulose derivative fibers, and ultrafine threads of regenerated cellulose or cellulose derivatives obtained by electrospinning can be used. These raw materials can be adjusted in fiber diameter, fiber length, fibrillation degree, etc. by mechanical beating, fibrillation, and refinement using a grinder, refiner, etc., as necessary, or bleached and purified using chemicals to adjust the content of components other than cellulose (acid-insoluble components such as lignin, alkali-soluble polysaccharides such as hemicellulose, etc.). In one embodiment, the cellulose fiber raw material is pulp, and is preferably derived from linters, since the aldehyde group concentration can be easily controlled within a desired range.

[Aldehyde group concentration]
In one embodiment, the aldehyde group concentration of the cellulose fine fibers is 50 μmol/g or less, preferably 40 μmol/g or less, or 30 μmol/g or less, or 20 μmol/g or less, or 10 μmol/g or less. In terms of improving the physical properties of the resin composite by bonding between the aldehyde groups of the cellulose fine fibers and the polyacetal resin, and of ease of production of the cellulose fine fibers, the aldehyde group concentration is 0.5 μmol/g or more, preferably 1 μmol/g or more, or 2 μmol/g or more, or 3 μmol/g or more, or 4 μmol/g or more, or 5 μmol/g or more.

The aldehyde group concentration of the cellulose fiber raw material varies depending on the type, but in one embodiment, it can be about 0 μmol/g to 200 μmol/g. When cellulose fiber raw material is defibrated to obtain cellulose fine fibers, cellulose molecules may be broken due to heat, oxidative conditions, stress, etc., so the concentration of aldehyde groups at the ends of the cellulose molecules tends to be higher in cellulose fine fibers than in cellulose fiber raw materials. In addition, since the cleavage of cellulose molecules leads to a decrease in molecular weight, the molecular weight distribution expressed as weight average molecular weight (Mw)/number average molecular weight (Mn) becomes wider. That is, in one embodiment, the weight average molecular weight (Mw)/number average molecular weight (Mn) increases before and after defibration, and the preferential decomposition of low molecular weight components can significantly increase the aldehyde group concentration. In one embodiment, the cellulose fine fibers of this embodiment have an aldehyde group concentration controlled within a specific range by suppressing the increase in aldehyde group concentration during defibration. In a particularly preferred embodiment, the aldehyde group concentration of the cellulose fine fibers is controlled within a specific range by suppressing the production of low molecular weight components through highly controlled defibration conditions to produce homogeneous cellulose fine fibers.

In one embodiment, the aldehyde group concentration of the cellulose fiber raw material is 0 μmol/g or more, preferably 0.1 μmol/g or more, or 0.5 μmol/g or more, or 1 μmol/g or more, or 2 μmol/g or more, or 3 μmol/g or more, or 4 μmol/g or more, or 5 μmol/g or more, and/or 200 μmol/g or less, preferably 100 μmol/g or less, or 50 μmol/g or less, or 30 μmol/g or less, or 20 μmol/g or less, or 10 μmol/g or less, and the aldehyde group concentration of the cellulose fine fibers obtained from the cellulose fiber raw material is within the above range.

[Carboxy group concentration]
In one aspect, the carboxy group concentration of the cellulose fine fibers is, from the viewpoint of ease of production of the cellulose fine fibers, preferably 1 μmol/g or more, or 3 μmol/g or more, or 5 μmol/g or more, or 10 μmol/g or more, and from the viewpoint of maintaining the heat resistance of the cellulose fine fibers and preventing deterioration of the polyacetal resin due to the carboxy groups, in one aspect, it is 200 μmol/g or less, and preferably 150 μmol/g or less, or 100 μmol/g or less, or 80 μmol/g or less, or 50 μmol/g or less.

The carboxyl group concentration of the cellulose fiber raw material varies depending on the type, but in one embodiment, it may be about 0 μmol/g to 200 μmol/g. When cellulose fiber raw material is defibrated to obtain cellulose fine fibers, cellulose molecules may be cut or modified due to heat, oxidative conditions, stress, etc., so that the carboxyl group concentration tends to be higher in the cellulose fine fibers than in the cellulose fiber raw material. In addition, since the cutting of cellulose molecules leads to a decrease in molecular weight, the molecular weight distribution expressed by weight average molecular weight (Mw) / number average molecular weight (Mn) becomes wider. That is, in one embodiment, the weight average molecular weight (Mw) / number average molecular weight (Mn) increases before and after defibration, and the preferential decomposition of low molecular weight components can significantly increase the carboxyl group concentration. In one embodiment, the cellulose fine fibers of this embodiment have a carboxyl group concentration controlled to a specific range by suppressing the increase in the carboxyl group concentration during defibration. In a particularly preferred embodiment, the carboxyl group concentration of the cellulose fine fibers is controlled to a specific range by suppressing the generation of low molecular weight components by highly controlled defibration conditions to generate homogeneous cellulose fine fibers.

In one embodiment, the carboxyl group concentration of the cellulose fiber raw material is 0 μmol/g or more, preferably 1 μmol/g or more, or 3 μmol/g or more, or 5 μmol/g or more, or 10 μmol/g or more, and 200 μmol/g or less, or 150 μmol/g or less, or 100 μmol/g or less, or 80 μmol/g or less, or 50 μmol/g or less.

[Aldehyde group concentration and carboxyl group concentration of cellulose fiber raw material and cellulose fine fiber]
The aldehyde group concentration is determined by the following method. 60 ml of cellulose fiber raw material slurry (solid content 0.5% by mass) or cellulose fine fiber slurry (solid content 0.5% by mass) is prepared, and the pH is adjusted to about 2.5 with 0.1 M hydrochloric acid aqueous solution, and then 0.05 M sodium hydroxide aqueous solution is dropped to measure the electrical conductivity. The measurement is continued until the pH reaches about 11. The functional group amount 1 is determined using the following formula from the amount (V) of sodium hydroxide aqueous solution consumed in the neutralization stage of weak acid, where the change in electrical conductivity is gradual. The functional group amount 1 indicates the amount of carboxyl groups (carboxyl group concentration).
Amount of functional group (mmol/g)=V (ml)×0.05/mass of solid content of cellulose fine fiber (g)
Next, the cellulose fiber raw material slurry and the cellulose fine fiber slurry are further oxidized at room temperature for 48 hours in a 2% aqueous sodium chlorite solution whose pH has been adjusted to 4 to 5 with acetic acid, and the functional group amount 2 is measured again by the above method. The amount of functional groups added by this oxidation (=functional group amount 2 - functional group amount 1) is calculated and used as the aldehyde group concentration.

In one embodiment, the aldehyde group concentration of the cellulose fine fibers of the present disclosure may be the aldehyde group concentration of the cellulose fine fibers in the polyacetal resin composition. The measurement method is as follows. That is, the resin components of the polyacetal resin composition are dissolved in 1,1,1,3,3,3-hexafluoro-2-propanol, the cellulose fine fibers are extracted, and the cellulose fine fibers are thoroughly washed by repeating centrifugation and redispersion in the solvent. The washed cellulose fine fibers are further washed with water to prepare a cellulose fine fiber slurry (solid content 0.5% by mass), and the aldehyde group concentration is calculated by the above-mentioned method.

[Number average fiber length, number average fiber diameter, and L/D ratio]
In one aspect, the number average fiber length L of the cellulose fine fibers is, from the viewpoint of satisfactorily expressing the physical property improving effect of the cellulose fine fibers, preferably 100 nm or more, or 500 nm or more, 1 μm or more, or 5 μm or more, or 10 μm or more, or 20 μm or more, and, from the viewpoint of satisfactorily dispersing the cellulose fine fibers in the resin composition, preferably 1000 μm or less, or 800 μm or less, or 500 μm or less, or 400 μm or less, or 300 μm or less, or 200 μm or less.

In one embodiment, the number average fiber diameter D of the cellulose fine fibers is preferably 2 nm or more, or 4 nm or more, or 5 nm or more, or 10 nm or more, or 15 nm or more, or 20 nm or more, from the viewpoint of obtaining a good effect of improving physical properties by the cellulose fine fibers, and in one embodiment, it is 1000 nm or less, and preferably 900 nm or less, or 800 nm or less, or 700 nm or less, or 600 nm or less, or 500 nm or less, or 400 nm or less, or 300 nm or less, or 200 nm or less.

The ratio of number average fiber length L/number average fiber diameter D of the cellulose fine fibers is preferably 30 or more, or 50 or more, or 80 or more, or 100 or more, or 120 or more, or 150 or more, from the viewpoint of satisfactorily expressing the effect of improving physical properties by the cellulose fine fibers, and is preferably 5000 or less, or 3000 or less, or 2000 or less, or 1000 or less, from the viewpoint of satisfactorily dispersing the cellulose fine fibers in the resin composition.

In one embodiment, the number average fiber length L, number average fiber diameter D, and L/D ratio of the cellulose fine fibers of the present disclosure are values measured using a scanning electron microscope (SEM) according to the following procedure. An aqueous dispersion of cellulose fine fibers is replaced with tert-butanol, diluted to 0.001 to 0.1% by mass, and dispersed using a high-shear homogenizer (e.g., manufactured by IKA, product name "Ultra Turrax T18") under processing conditions: rotation speed 15,000 rpm x 3 minutes. The sample is cast on an osmium-deposited silicon substrate and air-dried to obtain a measurement sample, which is measured using a high-resolution scanning electron microscope (SEM). Specifically, the number average fiber length and number average fiber diameter of 100 randomly selected fibers are measured in an observation field where the magnification is adjusted so that at least 100 fibrous substances are observed. Then, the respective number average values are taken as the number average fiber diameter L and the number average fiber diameter D, and the ratio (L/D) is calculated.

[Specific surface area]
In one aspect, the specific surface area of the cellulose fine fibers of the present disclosure, from the viewpoint of effectively expressing the physical property improving effect of the cellulose fine fibers, is 0.1 ^m2 /g or more, or 0.5 ^m2 /g or more, or 1.0 ^m2 /g or more, or 2.0 ^m2 /g or more, or 3.0 ^m2 /g or more, and from the viewpoint of ease of production, is ⁵⁰⁰ m2/g or less, or 400 ^m2 /g or less, or 300 ^m2 /g or less, or ²⁰⁰ m2/g or less, or 100 ^m2 /g or less, or 50 ^m2 /g or less.

The specific surface area of the cellulose microfibers is measured by vacuum drying the porous sheet described below at 105°C for 5 hours using a specific surface area/pore distribution measuring device (e.g., Quantachrome Instruments, product name "Nova-4200e"), and measuring the amount of nitrogen gas adsorption at the boiling point of liquid nitrogen at 5 points in the range of relative vapor pressure (P/P0) from 0.05 to 0.2 (BET multipoint method).

[Polymorphism]
Known crystalline polymorphs of cellulose include types I, II, III, and IV, of which types I and II are particularly widely used, and types III and IV have been obtained on a laboratory scale but are not widely used on an industrial scale. When the crystalline polymorph of the cellulose fine fibers is type I or type II, the mechanical properties (strength, dimensional stability) of the fibers are high, and when the cellulose fine fibers are dispersed in a resin, the strength and dimensional stability of the resin composition are high, which is preferable.

[Crystallization degree]
The crystallinity of the cellulose fine fibers is preferably 55% or more, or 60% or more, or 65% or more, or 70% or more, or 75% or more, or 80% or more. The higher the crystallinity, the higher the mechanical properties (strength, dimensional stability) of the cellulose itself, and therefore when the cellulose fine fibers are dispersed in a resin, the strength and dimensional stability of the resin composition tend to be high. There is no particular upper limit for the crystallinity of the cellulose fine fibers, and the higher the better, but from the viewpoint of production, the preferred upper limit is 99%.

When the cellulose fine fibers are cellulose I type crystals (derived from natural cellulose), the degree of crystallinity can be calculated from the diffraction pattern (2θ/deg. is 10 to 30) obtained by measuring a sample by wide-angle X-ray diffraction using the Segal method, according to the following formula:
Crystallinity (%) = [I ₍₂₀₀₎ - I _(amorphous) ] / I ₍₂₀₀₎ x 100
I ₍₂₀₀₎ : Diffraction peak intensity due to the 200 plane (2θ = 22.5°) in cellulose I type crystals I _(amorphous) : Halo peak intensity due to amorphous in cellulose I type crystals, which is the peak intensity at an angle 4.5° lower than the diffraction angle of the 200 plane (2θ = 18.0°)

When the cellulose is cellulose II type crystal (derived from regenerated cellulose), the degree of crystallinity can be calculated from the absolute peak intensity h0 at 2θ=12.6° assigned to the (110) plane peak of cellulose II type crystal in wide-angle X-ray diffraction and the peak intensity h1 of the baseline (the line connecting 2θ=8° and 15°) at this interplanar spacing, according to the following formula:
Crystallinity (%) = (h0 - h1) / h0 × 100

[Degree of polymerization]
In addition, the degree of polymerization of the cellulose fine fibers is preferably 100 or more, or 150 or more, or 200 or more, or 300 or more, or 400 or more, or 450 or more, and preferably 3500 or less, or 3300 or less, or 3200 or less, or 3100 or less, or 3000 or less.

From the viewpoint of processability and mechanical property expression, it is desirable that the degree of polymerization of the cellulose fine fibers is within the above-mentioned range. From the viewpoint of processability, it is preferable that the degree of polymerization is not too high, and from the viewpoint of mechanical property expression, it is desirable that the degree of polymerization is not too low.

The degree of polymerization of the cellulose fine fibers means the average degree of polymerization measured according to the reduced specific viscosity method using a copper-ethylenediamine solution described in the Verification Test (3) of the "Japanese Pharmacopoeia Commentary, 15th Edition (published by Hirokawa Shoten)."
Incidentally, the degree of polymerization of the chemically modified cellulose fine fibers may not be accurately calculated due to the presence of chemically modifying groups. In such cases, the degree of polymerization of the cellulose fine fibers immediately before chemical modification, which are the raw material for the chemically modified cellulose fine fibers, or the raw cellulose fiber material immediately before chemical modification, may be regarded as the degree of polymerization of the chemically modified cellulose fine fibers.

[Mw, Mn, Mw/Mn]
In one embodiment, the weight average molecular weight (Mw) of the cellulose fine fibers is preferably 100,000 or more, or 150,000 or more, or 180,000 or more, or 200,000 or more, or 250,000 or more. In one embodiment, the number average molecular weight (Mn) of the cellulose fine fibers is preferably 10,000 or more, or 20,000 or more, or 30,000 or more, or 40,000 or more, or 50,000 or more. In one embodiment, the ratio (Mw/Mn) of the weight average molecular weight to the number average molecular weight (Mn) is preferably 6.0 or less, or 5.6 or less, or 5.4 or less. The larger the weight average molecular weight, the fewer the number of terminal groups of the cellulose molecules. In addition, since the ratio (Mw/Mn) of the weight average molecular weight to the number average molecular weight represents the width of the molecular weight distribution, the smaller the Mw/Mn, the fewer the number of terminals of the cellulose molecules. Since the end of the cellulose molecule is the starting point of thermal decomposition, when the weight average molecular weight of the cellulose molecule of the cellulose fine fiber is not only large but also has a narrow molecular weight distribution, the cellulose fine fiber has a particularly high heat resistance. From the viewpoint of the availability of the cellulose fiber raw material, the weight average molecular weight (Mw) of the cellulose fine fiber may be, for example, 600,000 or less, or 500,000 or less, or 400,000 or less. From the viewpoint of the availability of the cellulose fiber raw material, the number average molecular weight (Mn) of the cellulose fine fiber may be, for example, 200,000 or less, or 150,000 or less, or 100,000 or less, or 80,000 or less, or 60,000 or less. From the viewpoint of the ease of production of the cellulose fine fiber, the ratio (Mw/Mn) of the weight average molecular weight to the number average molecular weight (Mn) may be, for example, 1.5 or more, or 1.7 or more, or 2 or more. The Mw can be controlled within the above range by selecting a cellulose fiber raw material having an Mw appropriate for the purpose, performing physical and/or chemical treatments on the cellulose fiber raw material in an appropriate range, and particularly performing defibration under controlled and mild conditions. The Mw/Mn can also be controlled within the above range by selecting a cellulose fiber raw material having an Mw/Mn appropriate for the purpose, performing physical and/or chemical treatments on the cellulose fiber raw material in an appropriate range, and particularly performing defibration under controlled and mild conditions. In one embodiment, each of the Mw and Mw/Mn of the cellulose fiber raw material may be within the above range. In both the control of Mw and the control of Mw/Mn, examples of the physical treatment include dry or wet grinding using a microfluidizer, ball mill, disk mill, etc., and physical treatments that apply mechanical forces such as impact, shear, shear, and friction using a crusher, homomixer, high-pressure homogenizer, ultrasonic device, etc., and examples of the chemical treatment include digestion, bleaching, acid treatment, enzyme treatment, regenerated cellulose, hydrolysis, etc.
Incidentally, the Mw, Mn and Mw/Mn of the chemically modified cellulose fine fibers may not be calculated accurately due to the presence of chemically modifying groups. In this case, the Mw, Mn and Mw/Mn of the cellulose fine fibers immediately before chemical modification, which are the raw material for the chemically modified cellulose fine fibers, or the Mw, Mn and Mw/Mn of the raw cellulose fibers immediately before chemical modification may be regarded as the Mw, Mn and Mw/Mn of the chemically modified cellulose fine fibers.

The weight average molecular weight and number average molecular weight of the cellulose microfibers referred to here are values determined by dissolving the cellulose microfibers in N,N-dimethylacetamide containing lithium chloride and then performing gel permeation chromatography using N,N-dimethylacetamide as a solvent.

[Alkali-soluble polysaccharides and acid-insoluble components]
Since the cellulose fiber raw material contains alkali-soluble polysaccharides and acid-insoluble components (lignin, etc.), the alkali-soluble and sulfuric acid-insoluble components may be reduced by a purification process such as delignification by cooking and a bleaching process. On the other hand, the purification process such as delignification by cooking and the bleaching process cut the molecular chains of cellulose, changing the weight-average molecular weight and number-average molecular weight, so it is desirable to control the purification process and bleaching process of the cellulose fiber raw material so that the weight-average molecular weight of the cellulose fine fibers and the ratio of the weight-average molecular weight to the number-average molecular weight are within appropriate ranges.

There is also concern that refining processes such as delignification by cooking and bleaching processes may reduce the molecular weight of cellulose fine fibers and alter the cellulose fiber raw material, increasing the proportion of alkali-soluble matter present. Since alkali-soluble matter has poor heat resistance and increases the concentration of aldehyde groups, it is desirable that the refining and bleaching processes of cellulose fiber raw materials be controlled so that the amount of alkali-soluble matter contained in the cellulose fiber raw material is within a certain range or less.

Alkali-soluble polysaccharides that cellulose microfibers may contain include hemicellulose, β-cellulose, and γ-cellulose. Those skilled in the art will understand alkali-soluble polysaccharides as components obtained as the alkali-soluble portion of holocellulose obtained by solvent extraction and chlorine treatment of plants (e.g., wood) (i.e., components obtained by removing α-cellulose from holocellulose).

In one embodiment, the content of alkali-soluble matter in the cellulose fine fibers is preferably 20% by mass or less, or 18% by mass or less, or 15% by mass or less, or 12% by mass or less, or 10% by mass or less, or 8% by mass or less, or 6% by mass or less, based on 100% by mass of the cellulose fine fibers, from the viewpoint of maintaining the mechanical strength of the cellulose fine fibers during melt kneading, suppressing yellowing, and controlling the aldehyde group concentration within the range of the present disclosure. From the viewpoint of ease of production of the cellulose fine fibers, the above content may be 0.1% by mass or more, or 0.5% by mass or more, or 1% by mass or more, or 2% by mass or more, or 3% by mass or more.

The alkali-soluble content can be determined by the method described in the non-patent literature (Wood Science Experiment Manual, edited by the Japan Wood Research Society, pp. 92-97, 2000), by subtracting the α-cellulose content from the holocellulose content (Wise method). This method is understood in the industry as a method for measuring the amount of hemicellulose. The alkali-soluble content is calculated three times for each sample, and the number average of the calculated alkali-soluble contents is taken as the alkali-soluble content. The alkali-soluble content of chemically modified cellulose microfibers may not be calculated accurately due to the presence of chemical modification groups. In this case, the alkali-soluble content of the cellulose microfibers immediately before chemical modification, which are the raw material for the chemically modified cellulose microfibers, or the alkali-soluble content of the raw cellulose fiber immediately before chemical modification, may be considered to be the alkali-soluble content of the chemically modified cellulose microfibers.

The acid-insoluble components that cellulose microfibers may contain are understood by those skilled in the art as insoluble components that remain after a defatted sample obtained by solvent extraction of a plant (e.g., wood) is treated with sulfuric acid. Specific examples of acid-insoluble components include, but are not limited to, aromatic lignin.

In one embodiment, the average content of acid-insoluble components in the cellulose fine fibers is preferably 10% by mass or less, 5% by mass or less, or 3% by mass or less, based on 100% by mass of the cellulose fine fibers, from the viewpoint of avoiding a decrease in the heat resistance of the cellulose fine fibers and the associated discoloration. From the viewpoint of ease of production of the cellulose fine fibers, the above content may be 0.1% by mass or more, 0.2% by mass or more, or 0.3% by mass or more.

The average acid-insoluble content is determined by quantifying the acid-insoluble content using the Clason method described in the non-patent literature (Wood Science Experiment Manual, edited by the Japan Wood Research Society, pp. 92-97, 2000). This method is understood in the industry as a method for measuring the amount of lignin. The sample is stirred in a sulfuric acid solution to dissolve cellulose, hemicellulose, etc., and then filtered through a glass fiber filter. The residue obtained corresponds to the acid-insoluble component. The acid-insoluble component content is calculated from the weight of the acid-insoluble component. The acid-insoluble component content is measured three times for each sample, and the number average is taken as the average acid-insoluble component content. The average acid-insoluble component content of chemically modified cellulose microfibers may not be calculated accurately due to the presence of chemical modification groups. In this case, the acid-insoluble component content of the cellulose microfibers immediately before chemical modification, which are the raw material for chemically modified cellulose microfibers, or the acid-insoluble component content of the raw cellulose fiber immediately before chemical modification, may be considered to be the acid-insoluble component content of the chemically modified cellulose microfibers.

[Chemical modification]
The cellulose fine fibers may be chemically modified cellulose fine fibers (also referred to as chemically modified cellulose fine fibers). Examples of chemically modified cellulose fine fibers include inorganic esters such as nitrate esters, sulfate esters, phosphate esters, silicate esters, and borate esters, organic esters such as acetylation and propionylation, ethers such as methyl ether, hydroxyethyl ether, hydroxypropyl ether, hydroxybutyl ether, carboxymethyl ether, and cyanoethyl ether, and TEMPO oxides obtained by oxidizing the primary hydroxyl groups of cellulose. The chemically modified cellulose fine fibers may contain one or more types of modifying groups.

[Degree of acyl substitution (DS)]
When the cellulose fine fibers are chemically modified (for example, by hydrophobization such as acylation), the dispersibility of the cellulose fine fibers in the resin tends to be good. On the other hand, when combined with a dispersant, for example, the cellulose fine fibers can easily exhibit good dispersibility in the resin even if they are unsubstituted or have a low degree of substitution. When the cellulose fine fibers are esterified cellulose fine fibers, the acyl substitution degree (DS) is preferably 0.1 or more, or 0.2 or more, or 0.25 or more, or 0.3 or more, or 0.5 or more in terms of obtaining esterified cellulose fine fibers with a high thermal decomposition onset temperature, and is preferably 2.0 or less, or 1.8 or less, or 1.5 or less, or 1.2 or less, or 1.0 or less, or 0.8 or less, or 0.7 or less, or 0.6 or less, or 0.5 or less in terms of obtaining esterified cellulose fine fibers having both high tensile strength and dimensional stability derived from cellulose and high thermal decomposition onset temperature derived from chemical modification, since unmodified cellulose skeleton remains in the esterified cellulose fine fibers.

When the modifying group of the chemically modified cellulose fine fiber is an acyl group, the degree of acyl substitution (DS) can be calculated from the reflection infrared absorption spectrum of the esterified cellulose fine fiber based on the peak intensity ratio between the peak derived from the acyl group and the peak derived from the cellulose skeleton. The peak of the absorption band of C=O based on the acyl group appears at 1730 cm ^-1 , and the peak of the absorption band of C-O based on the cellulose skeleton appears at 1030 cm ^-1 . The DS of the esterified cellulose fine fiber is calculated by preparing a correlation graph between the DS obtained from the solid-state NMR measurement of the esterified cellulose fine fiber described later and the modification ratio (IR index 1030) defined as the ratio of the peak intensity of the absorption band of C=O based on the acyl group to the peak intensity of the absorption band of C-O of the cellulose skeleton, and calculating the calibration curve substitution degree DS=4.13×IR index (1030) from the correlation graph.
It can be found by using
IR index(1030) = H1730/H1030
In the formula, H1730 and H1030 are the absorbances at 1730 cm ^-1 and 1030 cm ^-1 (absorption bands of C-O stretching vibration of the cellulose backbone chain), respectively, where the lines connecting 1900 cm ^-1 and 1500 cm ^-1 and 800 cm ^-1 and 1500 cm ^-1 are taken as baselines, and these mean the absorbances when these baselines are taken as absorbance 0.

The DS of the esterified cellulose fine fibers can be calculated by solid-state NMR by performing ^13C solid-state NMR measurement on the frozen and pulverized esterified cellulose fine fibers, and calculating the DS from the total intensity (Inp) of the signals assigned to carbons C1 to C6 derived from the pyranose ring of cellulose appearing in the range from 50 ppm to 110 ppm relative to the intensity (Inf) of a signal assigned to one carbon atom derived from the modifying group, according to the following formula:
DS = (Inf) x 6 / (Inp)
For example, when the modifying group is an acetyl group, the signal at 23 ppm assigned to _--CH.sub.3 may be used.
The conditions for the ¹³ C solid state NMR measurement are, for example, as follows:
Equipment: Bruker Biospin Avance 500WB
Frequency: 125.77MHz
Measurement method: DD/MAS method Waiting time: 75 sec
NMR sample tube: 4 mm diameter
Total number of times: 640 times (approximately 14 hours)
MAS: 14,500Hz
Chemical shift reference: glycine (external reference: 176.03 ppm)

[Thermal decomposition onset temperature (T _D )]
From the viewpoint of avoiding thermal degradation during melt-kneading and exhibiting mechanical strength, the thermal decomposition onset temperature (T _D ) of the cellulose fine fibers in one embodiment is preferably 200° C. or higher, or 210° C. or higher, 220° C. or higher, or 230° C. or higher, or 240° C. or higher, or 250° C. or higher, or 260° C. or higher, or 270° C. or higher, or 275° C. or higher, or 280° C. or higher, or 285° C. or higher. The higher the thermal decomposition onset temperature, the more preferable it is, but from the viewpoint of ease of production of the cellulose fine fibers, it may be, for example, 320° C. or lower, 310° C. or lower, or 300° C. or lower.

[Temperature at 1% weight loss (T _1% ), weight loss rate at 250°C (T _250°C )]
From the viewpoint of avoiding thermal degradation during melt-kneading and exhibiting mechanical strength, the temperature at which the cellulose fine fibers lose 1 wt % weight (T _1% ) is, in one embodiment, preferably 230° C. or more, or 240° C. or more, or 250° C. or more, or 260° C. or more, or 270° C. or more, or 275° C. or more, or 280° C. or more, or 285° C. or more, or 290° C. or more. The higher _{T 1%} is, the more preferable, but from the viewpoint of ease of production of the cellulose fine fibers, it may be, for example, 330° C. or less, 320° C. or less, or 310° C. or less.

From the viewpoint of avoiding thermal degradation during melt kneading and exhibiting mechanical strength, the 250°C weight loss rate (T250 _°C ) of the cellulose fine fibers is preferably 15% or less, or 12% or less, or 10% or less, or 8% or less, or 6% or less, or 5% or less, or 4% or less, or 3% or less in one embodiment. The lower _{the T250°C} , the more preferable it is, but from the viewpoint of ease of production of the cellulose fine fibers, it may be, for example, 0.1% or more, or 0.5% or more, or 0.7% or more, or 1.0% or more.

In this disclosure, T _D is a value obtained from a graph in which the horizontal axis is temperature and the vertical axis is weight residual percentage in a thermogravimetric (TG) analysis under nitrogen flow. A porous sheet of cellulose fine fibers described later is heated from room temperature to 150° C. at a heating rate of 10° C./min in a nitrogen flow of 100 ml/min, and then held at 150° C. for 1 hour, and then heated to 450° C. at a heating rate of 10° C./min. Starting from the weight (weight loss of 0 wt%) at 150° C. (state in which moisture is almost completely removed), a straight line is obtained that passes through the temperature at 1 wt% weight loss (T _1% ) and the temperature at 2 wt% weight loss (T _2% ). The temperature at the point where this straight line intersects with a horizontal line (baseline) that passes through the starting point of the weight loss of 0 wt% is defined as T _D.

The 1% weight loss temperature (T _1% ) is the temperature at which a 1% weight loss occurs, starting from a weight of 150° C., when the temperature is continued to be raised by the above-mentioned T _D method.

The 250°C weight loss rate ( _T250°C ) of the cellulose fine fibers is the weight loss rate when the cellulose fine fibers are held at 250°C under nitrogen flow for 2 hours in TG analysis. The cellulose fine fibers are heated from room temperature to 150°C at a heating rate of 10°C/min in a nitrogen flow of 100 ml/min, held at 150°C for 1 hour, then heated from 150°C to 250°C at a heating rate of 10°C/min, and held at 250°C for 2 hours. The weight W0 at the time when 250°C is reached is taken as the starting point, and the weight after holding at 250°C for 2 hours is taken as W1, and is calculated from the following formula.
Weight change rate at 250°C (%): (W1-W0)/W0 x 100

[Halogen content H]
In the cellulose fine fibers of this embodiment, the content of halogen bonded to cellulose is preferably 500 ppm by mass or less, or 400 ppm by mass or less, or 300 ppm by mass or less, or 250 ppm by mass or less. In the cellulose fine fibers according to one embodiment, the content of chlorine bonded to cellulose is preferably 500 ppm by mass or less, or 400 ppm by mass or less, or 300 ppm by mass or less, or 250 ppm by mass or less. In this disclosure, the content of halogen bonded to cellulose in the cellulose fine fibers (chlorine in one embodiment) means the halogen content H (chlorine content in one embodiment) after the cellulose fine fibers are subjected to the following [immersion and filtration treatment]. In this disclosure, the content of halogen (chlorine in one embodiment) is a value measured according to the following [halogen content H measurement]. By setting the content of halogen (chlorine in one embodiment) bonded to cellulose in the above range, thermal deterioration of the cellulose fine fibers can be suppressed when the cellulose fine fibers are composited with the polyacetal resin, and therefore a polyacetal resin composition can be obtained that is excellent in stability during long-term storage and stable even after multiple thermal histories associated with melt-kneading, such as material recycling. Furthermore, a halogen content H (chlorine content in one embodiment) in the above range is also advantageous for suppressing corrosion inside equipment such as kneading equipment and molding equipment.

When halogens are present in the cellulose fine fibers, the halogens may be strongly bound to the cellulose by chemical or physical bonds. In one aspect, when the cellulose fine fibers are immersed in pure water at 25°C for 48 hours, followed by filtration and drying, as in the [immersion and filtration treatment] of the present disclosure, 80% or more by mass of the halogens before the treatment may remain in the cellulose fine fibers. Due to the strong bond with cellulose, such halogens continue to remain even when the cellulose fine fibers are composited with a resin, resulting in inconveniences such as decomposition of the resin and corrosion of the device. In one aspect, the cellulose fine fibers of the present embodiment may be characterized by a low content of halogens firmly bound to cellulose, and the content of halogens still remaining in the cellulose fine fibers after the treatment according to the [immersion and filtration treatment] of the present disclosure is used as an indicator of this.

[Immersion and filtration process]
The cellulose fine fibers are immersed in pure water at 25°C for 48 hours. Specifically, the cellulose fine fiber porous sheet described later is immersed in pure water at a solid content of 2% by mass in a glass beaker with a total volume of 200 mL, stirred for 1 hour with a 3-1 motor (HEIDON BL-600 type, SUS propeller blade, 100 rpm), and then allowed to stand. Next, the mixture is filtered under reduced pressure using a Teflon (registered trademark) membrane filter (1 μm mesh size) to prepare a sheet with a basis weight of 10 g/m ² , and filtered and dried in a ventilated oven at 70°C until the moisture content is 10% by mass or less to obtain cellulose fine fibers after treatment. Here, the moisture content is measured by the following method. 2.00 g of a cellulose sample is introduced into a glass weighing bottle, dried at 60°C for 15 hours and then at 105°C for 2 hours, weighed to a constant weight in a desiccator, and then the weight is measured and calculated by the following formula.
Moisture content (mass%)=(sample weight before drying−sample weight after drying)/(sample weight before drying)×100

[Halogen content H measurement]
50 mg of the above-mentioned treated cellulose fine fibers are weighed out in a quartz sample boat. The sample boat is set in an electric furnace (for example, manufactured by Mitsubishi Chemical Analytical Co., Ltd.) and burned at 1000°C. The gas generated by the combustion is cooled to room temperature through a cooling section and bubbled through a fluororesin tube into an absorbing liquid (the absorbing liquid is a solution of 10 mg/L of tartrate ions, 600 mg/L of hydrogen peroxide, 2.7 mmol/L of sodium carbonate, and 0.3 mmol/L of sodium bicarbonate dissolved in ion-exchanged water). This absorbing liquid is passed through a fluororesin tube and the halogen is quantified using an ion chromatograph (INTEGRION CT type manufactured by THERMOFISHER). At this time, the moisture amount obtained by the above-mentioned measurement is subtracted from the treated cellulose fine fibers. Finally, the value (ppm by mass) converted per dry mass (i.e., water-free state) of the treated cellulose fine fibers is taken as the content of halogen bonded to the cellulose of this embodiment.

The halogen that may be contained in the cellulose fine fibers of this embodiment may be in the form of a compound containing fluorine, chlorine, bromine, iodine, and/or astatine (i.e., a halogen compound). The halogen compound may be a halide (i.e., a compound of a halogen and an element having a lower electronegativity than the halogen), a halogen salt, or the like, and may be an inorganic halogen compound or an organic halogen compound. Considering bleaching and the like in the manufacturing process of the cellulose fiber raw material, the cellulose fine fibers often contain fluorine and/or chlorine among the halogens, and particularly often contain chlorine. When a cellulose fiber raw material having a high halogen content H (chlorine content in one embodiment) is used, the advantage of reducing the halogen content H (chlorine content in one embodiment) in the manufacturing process of the cellulose fine fibers is more pronounced.

[Porous sheet]
Measurements of the properties of cellulose fine fibers (crystallinity, crystal polymorphism, degree of polymerization, Mw, Mn, Mw/Mn, alkali-soluble content, average acid-insoluble content, T _D , T _1% , T _250°C , etc.) can vary greatly depending on the form of the measurement sample. To ensure stable and reproducible measurements, a distortion-free porous sheet is used as the measurement sample. The porous sheet is prepared as follows.

First, a concentrated cake of cellulose fine fibers with a solid content of 10% by mass or more is added to tert-butanol, and a dispersion process is performed using a mixer or the like until no aggregates are present. The concentration is adjusted to 0.5% by mass for 0.5 g of cellulose fine fiber solid content. 100 g of the obtained tert-butanol dispersion is filtered on filter paper. The filtered material is not peeled off from the filter paper, but is sandwiched between two sheets of larger filter paper, and the edges of the larger filter paper are pressed down with a weight and dried in an oven at 150 ° C. for 5 minutes. The filter paper is then peeled off to obtain a porous sheet with little distortion. The sheet with an air resistance R of 100 sec/100 ml or less per 10 g/ ^m2 of sheet basis weight is used as a porous sheet and is used as a measurement sample.

The air resistance R is measured by measuring the basis weight W (g/ ^m2 ) of a porous sheet sample that has been left to stand for one day in an environment of 23°C and 50% RH, and then measuring the air resistance R (sec/100 ml) using an Oken air resistance tester (e.g., Model EG01, manufactured by Asahi Seiko Co., Ltd.). At this time, the value per basis weight of 10 g/ ^m2 is calculated according to the following formula.
Air resistance per unit area of 10 g/ ^m2 (sec/100 ml) = R/W x 10

[Physical properties of cellulose fiber raw materials]
The various physical properties of the cellulose fine fibers described above are measured using the same methods as those for the raw cellulose fiber materials.

[Physical properties of cellulose fine fibers in resin composition]
Various physical properties (number average fiber length, number average fiber diameter, L/D ratio, crystallinity, crystal polymorphism, degree of polymerization, Mw, Mn, Mw/Mn, alkali soluble content, average acid insoluble content, T _D , T _1% , T _{250° C.} , DS, etc.) of the cellulose fine fibers in the resin composition are analyzed by the following method. The resin components in the resin composition are dissolved in an organic or inorganic solvent capable of dissolving the resin components of the resin composition, the cellulose fine fibers are extracted, and the cellulose fine fibers are thoroughly washed with the solvent, and then the solvent is replaced with tert-butanol. In the case of acetal resin, 1,1,1,3,3,3-hexafluoro-2-propanol is suitable as the dissolving solvent. Thereafter, the cellulose fine fiber tert-butanol slurry is analyzed using the same measurement method as the above-mentioned method, and various physical properties of the cellulose fine fibers in the resin composition are calculated.

[Cellulose fine fiber content]
The amount of cellulose fine fibers per 100 parts by mass of polyacetal resin in the resin composition is, from the viewpoint of obtaining a good reinforcing effect, preferably 0.001 parts by mass or more, or 0.01 parts by mass or more, or 0.1 parts by mass or more, or 1 part by mass or more, and from the viewpoint of stably achieving good dispersion of the cellulose fine fibers in the resin composition, preferably 100 parts by mass or less, or 80 parts by mass or less, or 70 parts by mass or less, or 50 parts by mass or less, or 30 parts by mass or less.

The amount of cellulose microfibers relative to 100% by mass of the resin composition is preferably 0.001% by mass or more, or 0.01% by mass or more, or 0.1% by mass or more, or 1% by mass or more, from the viewpoint of obtaining a good reinforcing effect, and is preferably 50% by mass or less, or 40% by mass or less, or 30% by mass or less, or 20% by mass or less, from the viewpoint of stably achieving good dispersion of the cellulose microfibers in the resin composition.

<Additional Ingredients>
The polyacetal resin composition of the present embodiment may contain additional components in addition to the above-mentioned components. Examples of the additional components include aldehyde group blocking agents, formic acid scavengers, antioxidants, weathering stabilizers, dispersants, release agents, lubricants, conductive agents, thermoplastic resins, thermoplastic elastomers, dyes and pigments, pigments, inorganic fillers, or organic fillers. These additives may be used alone or in combination of two or more.

[Aldehyde group blocking agent]
The resin composition preferably contains an aldehyde group blocking agent. The aldehyde group blocking agent can inhibit the decomposition of the polyacetal resin by blocking the aldehyde groups of the cellulose fine fibers, and can also block the aldehyde groups of the formaldehyde generated by the decomposition of the polyacetal resin. In one embodiment, the aldehyde group blocking agent is a compound capable of undergoing a dehydration condensation reaction with the aldehyde group, and in one embodiment, is a nitrogen-containing compound.

Examples of the nitrogen-containing compound include aminotriazine compounds, guanamine compounds, urea derivatives, hydrazide compounds, amide compounds (e.g., acrylamide polymers), polyamides, etc., which can be used alone or in combination of two or more. In a preferred embodiment, the nitrogen-containing compound is at least one selected from the group consisting of aminotriazine compounds, guanamine compounds, hydrazide compounds, and polyamides.

Examples of the aminotriazine compounds include melamine, 2,4-diamino-sym-triazine, 2,4,6-triamino-sym-triazine, N-butylmelamine, N-phenylmelamine, N,N-diphenylmelamine, N,N-diallylmelamine, benzoguanamine (2,4-diamino-6-phenyl-sym-triazine), acetoguanamine (2,4-diamino-6-methyl-sym-triazine), 2,4-diamino-6-butyl-sym-triazine, etc.

Examples of the guanamine compounds include aliphatic guanamine compounds (monoguanamines, alkylenebisguanamines, etc.), alicyclic guanamine compounds (monoguanamines, etc.), aromatic guanamine compounds [for example, monoguanamines (benzoguanamine and its functional group-substituted derivatives, etc.), α- or β-naphthoguanamine and their functional group-substituted derivatives, polyguanamines, aralkyl or aralkyleneguanamines, etc.], and heteroatom-containing guanamine compounds [for example, acetal group-containing guanamines, tetraoxospiro ring-containing guanamines (CTU-guanamine, CMTU-guanamine, etc.), isocyanuric ring-containing guanamines, imidazole ring-containing guanamines, etc.].

Examples of the urea derivatives include N-substituted ureas, urea condensates, ethylene ureas, hydantoin compounds, and ureido compounds.
Examples of the N-substituted urea include methyl urea having a substituent such as an alkyl group, alkylene bis urea, and aryl substituted urea.
The urea condensate may, for example, be a condensate of urea and formaldehyde.
Examples of the hydantoin compound include hydantoin, 5,5-dimethylhydantoin, and 5,5-diphenylhydantoin.
The ureido compounds include, for example, allantoin.

The hydrazide compound may be a carboxylic acid mono/dihydrazide compound synthesized by reacting a carboxylic acid (containing an aromatic ring and/or an alicyclic ring) with hydrazine, or an alkyl group-substituted mono/dihydrazide compound. Carboxylic acids constituting the carboxylic acid mono/dihydrazide compound include monocarboxylic acids and dicarboxylic acids, which may be saturated or unsaturated. Examples of monocarboxylic acids include formic acid, acetic acid, propionic acid, butyric acid, valeric acid, caproic acid, enanthic acid, caprylic acid, lauric acid, myristic acid, palmitic acid, margaric acid, stearic acid, and behenic acid. Examples of dicarboxylic acids include oxalic acid, malonic acid, succinic acid, glutaric acid, adipic acid, pimelic acid, suberic acid, azelaic acid, sebacic acid, benzoic acid, phthalic acid, isophthalic acid, terephthalic acid, naphthalic acid, salicylic acid, gallic acid, mellitic acid, cinnamic acid, pyruvic acid, lactic acid, malic acid, citric acid, fumaric acid, maleic acid, aconitic acid, amino acids, nitrocarboxylic acids, etc. Examples of unsaturated carboxylic acids include oleic acid, linoleic acid, linolenic acid, arachidonic acid, docosahexaenoic acid, eicosapentaenoic acid, etc. Examples of carboxylic acid mono(di)hydrazide compounds synthesized using these carboxylic acids include carbodihydrazine, oxalic acid mono(di)hydrazide, malonic acid mono(di)hydrazide, succinic acid mono(di)hydrazide, glutaric acid mono(di)hydrazide, adipic acid mono(di)hydrazide, sebacic acid mono(di)hydrazide, lauric acid mono(di)hydrazide, malic acid dihydrazide, tartaric acid dihydrazide, propionic acid monohydrazide, lauric acid monohydrazide, and stearic acid monohydrazide. Examples of the carboxylic acid hydrazide include azide, phthalic acid dihydrazide, isophthalic acid dihydrazide, terephthalic acid dihydrazide, 2,6-naphthalic acid dihydrazide, p-hydroxybenzoic hydrazine, p-hydroxybenzoic hydrazine, 1,4-cyclohexanedicarboxylic acid dihydrazine, acetohydrazide, acrylohydrazide, maleic acid dihydrazide, fumaric acid dihydrazide, benzohydrazide, nicotinohydrazide, isonicotinohydrazide, isobutylhydrazine, and oleic acid hydrazide. Among these carboxylic acids, dicarboxylic acids such as adipic acid, sebacic acid, and lauric acid are preferred, and adipic acid mono(di)hydrazide, sebacic acid mono(di)hydrazide, and lauric acid mono(di)hydrazide are the most preferred carboxylic acid hydrazide compounds.

Among these carboxylic acid hydrazide compounds, when the content of the monohydrazide compound and the dihydrazide compound is within a specific range, it is preferable in terms of suppressing the generation of formaldehyde, and further, it is also preferable in terms of suppressing the generation of carbonized products and modified products that occur during long-term continuous molding, and suppressing mold contamination. The content of the carboxylic acid monohydrazide compound relative to the total of 100 mass% of the carboxylic acid monohydrazide compound and the carboxylic acid dihydrazide compound is preferably 0.0001 to 1.0 mass%, or 0.0001 to 0.5 mass%, or 0.0001 to 0.1 mass%.

Methods for adjusting the above content of the carboxylic acid monohydrazide compound include a method of adjusting the content by adding a monohydrazide compound to the carboxylic acid dihydrazide compound, and a method of adjusting the synthesis reaction conditions when synthesizing by the reaction of the above-mentioned carboxylic acid and hydrazine. In the method of adjusting the synthesis reaction conditions of the carboxylic acid and hydrazine, a monohydrazide compound is generated as an intermediate during the synthesis reaction. The content of the monohydrazide compound can be adjusted by washing and removing this monohydrazide compound.

Examples of the amide compound include polycarboxylic acid amides such as isophthalic acid diamide, anthranilamide, and polyacrylamide polymers.
The acrylamide polymer is preferably a particulate polymer having 30 to 70 mol% primary amide groups and an average particle size of 0.1 to 10 μm. Among them, a preferred acrylamide polymer is a crosslinked acrylamide polymer having an average particle size of 10 μm or less. More preferred is an acrylamide polymer having an average particle size of 5 μm or less, and most preferred is a crosslinked acrylamide polymer having an average particle size of 3 μm or less.

Polyamides include polyamides derived from diamines and dicarboxylic acids; polyamides obtained by using aminocarboxylic acids, optionally in combination with diamines and/or dicarboxylic acids; and polyamides derived by using lactams, optionally in combination with diamines and/or dicarboxylic acids. Also included are copolymerized polyamides formed from two or more different polyamide-forming components.

From the viewpoint of mold depositability and reducing color difference change after residence in the molding machine, the melting point of the polyamide is preferably 240°C or higher, or 245°C or higher, or 250°C or higher. Examples of polyamides having a melting point of 240°C or higher include polyamide 66, polyamide 46, polyamide 66/6T, polyamide 66/6I/6T, etc. Among these polyamides, polyamide 66, polyamide 66/6T, and polyamide 66/6I/6T are preferred, and polyamide 66 is more preferred.

The amount of the aldehyde group blocking agent in the resin composition is preferably 0.001 parts by mass or more, or 0.005 parts by mass or more, or 0.01 parts by mass or more, or 0.05 parts by mass or more, or 0.1 parts by mass or more, relative to 100 parts by mass of the total of the polyacetal resin and the cellulose fine fibers, from the viewpoint of obtaining a good formaldehyde generation suppression effect and from the viewpoint of good physical properties of the resin composition, and is preferably 3 parts by mass or less, or 2 parts by mass or less, or 1 part by mass or less, or 0.7 parts by mass or less, or 0.5 parts by mass or less, or 0.3 parts by mass or less, from the viewpoint of suppressing mold deposits on the mold in advance, maintaining color tone and thermal stability, suppressing odor during processing, and mechanical properties.

When the aldehyde group blocking agent is a nitrogen-containing compound, the amount of the nitrogen-containing compound relative to 100 parts by mass of the polyacetal resin is preferably 0.001 parts by mass or more, or 0.005 parts by mass or more, or 0.01 parts by mass or more from the viewpoints of color tone, maintenance of thermal stability, suppression of odor during processing, and mechanical properties, and is preferably 3 parts by mass or less, or 2 parts by mass or less, or 1 part by mass or less, or 0.7 parts by mass or less, or 0.5 parts by mass or less, or 0.3 parts by mass or less from the viewpoints of suppressing mold deposits on the mold in advance, and of maintaining color tone, thermal stability, suppression of odor during processing, and mechanical properties.

The process for mixing the aldehyde group blocking agent is not particularly limited, but is preferably a drying process or a mixing process, and particularly preferably a drying process, from the viewpoint of obtaining a good formaldehyde generation suppression effect and good physical properties of the resin composition. Although the mechanism is not clear, when added in the drying process, the aldehyde group blocking agent is present in high concentration near the aldehyde groups, and it is presumed that the aldehyde groups can be blocked with high efficiency when the cellulose fine fibers are dispersed in the polyacetal resin by melt kneading. In addition, heating is performed to remove water in the drying process, and it is presumed that the aldehyde groups are blocked due to the presence of the aldehyde group blocking agent in high concentration near the aldehyde groups of the cellulose fine fibers, and the aldehyde group concentration may be reduced.

[Formic acid scavengers]
The resin composition preferably contains a formic acid scavenger. When the polyacetal resin decomposes, formaldehyde is produced, and the formaldehyde is easily oxidized to formic acid. Formic acid promotes further decomposition of the polyacetal resin and also promotes decomposition of the cellulose fine fibers. It is advantageous for the resin composition to contain a formic acid scavenger in terms of suppressing the decomposition of the polyacetal resin and the cellulose fine fibers and maintaining good mechanical properties of the resin composition. Examples of the formic acid scavenger include hydroxides, inorganic acid salts, carboxylates, and alkoxides of alkali metals or alkaline earth metals. For example, hydroxides of sodium, potassium, magnesium, calcium, or barium; carbonates, phosphates, silicates, borates, carboxylates, and layered double hydroxides of the above metals are included.

The carboxylic acid of the carboxylate is preferably a saturated or unsaturated aliphatic carboxylic acid having 10 to 36 carbon atoms, and these carboxylic acids may be substituted with a hydroxyl group. Examples of the saturated or unsaturated aliphatic carboxylate include, but are not limited to, calcium dimyristate, calcium dipalmitate, calcium distearate, calcium (myristate-palmitate), calcium (myristate-stearate), calcium (palmitate-stearate), and calcium 12-hydroxystearate, and among these, calcium dipalmitate, calcium distearate, and calcium 12-hydroxydistearate are preferred.
The formic acid scavenger may be used alone or in combination of two or more kinds.

The amount of formic acid scavenger in the resin composition is preferably 0.001 parts by mass or more, or 0.005 parts by mass or more, or 0.01 parts by mass or more, or 0.05 parts by mass or more, or 0.1 parts by mass or more, and is preferably 3 parts by mass or less, or 2 parts by mass or less, or 1 part by mass or less, or 0.7 parts by mass or less, or 0.5 parts by mass or less, or 0.3 parts by mass or less, per 100 parts by mass of polyacetal resin.

[Antioxidant]
The antioxidant may be a hindered phenol-based antioxidant, etc. The antioxidant is useful for suppressing thermal decomposition or hydrolysis of the polyacetal resin, particularly suppressing the generation of formaldehyde due to the thermal decomposition or hydrolysis.

Examples of hindered phenol antioxidants include n-octadecyl-3-(3',5'-di-t-butyl-4'-hydroxyphenyl)-propionate, n-octadecyl-3-(3'-methyl-5'-t-butyl-4'-hydroxyphenyl)-propionate, n-tetradecyl-3-(3',5'-di-t-butyl-4'-hydroxyphenyl)-propionate, 1,6-hexanediol-bis-[3-(3,5-di-t-butyl-4-hydroxyphenyl)-propionate], 1,4-butanediol-bis-[3-(3,5-di-t-butyl-4-hydroxyphenyl)-propionate], triethylene glycol-bis-[3-(3-t-butyl-5-methyl-4-hydroxyphenyl)-propionate], nyl)-propionate], pentaerythritol tetrakis[methylene-3-(3',5'-di-t-butyl-4'-hydroxyphenyl)propionate]methane, 1,2-bis[3-(4-hydroxy-3,5-di-t-butylphenyl)propionyl]hydrazine, N,N'-hexamethylenebis[3-(3,5-di-t-butyl-4-hydroxyphenyl)propanamide], 1,3,5-tris[[3,5-bis(1,1-dimethylethyl)-4-hydroxyphenyl]methyl]-1,3,5-triazine-2,4,6(1H,3H,5H)-trione, 4-[[4,6-bis(octylthio)-1,3,5-triazin-2-yl]amino]-2,6-di-t-butylphenol, and the like.

The antioxidant is preferably triethylene glycol-bis-[3-(3-t-butyl-5-methyl-4-hydroxyphenyl)-propionate], pentaerythritol tetrakis[methylene-3-(3',5'-di-t-butyl-4'-hydroxyphenyl)propionate]methane, 1,2-bis[3-(4-hydroxy-3,5-di-t-butylphenyl)propionyl]hydrazine, N,N'-hexamethylene bis[3-(3,5-di-t-butyl-4-hydroxyphenyl)propanamide], etc., and among these, nitrogen-containing hindered phenol-based antioxidants are particularly preferred from the viewpoint of improving the thermal stability of the polyacetal resin.

The nitrogen-containing hindered phenol-based antioxidant preferably contains a hydrazine structure, and is more preferably 1,2-bis[3-(4-hydroxy-3,5-di-t-butylphenyl)propionyl]hydrazine, in terms of mold deposit properties during long-term continuous molding, the appearance of the molded product, and reducing color difference changes after retention in the molding machine.

The melting point of the hindered phenol-based antioxidant is preferably 50°C or higher, or 150°C or higher, or 200°C or higher, or 225°C or higher from the viewpoint of the thermal stability of the polyacetal resin composition, and is preferably 300°C or lower, or 250°C or lower from the viewpoint of the availability of the antioxidant. In this disclosure, the melting point is a value measured using a differential scanning calorimeter (DSC) at a heating rate of 10°C/min.

From the viewpoint of moldability, the amount of antioxidant per 100 parts by mass of polyacetal resin is preferably 0.01 parts by mass or more, or 0.02 parts by mass or more, or 0.03 parts by mass or more, and is preferably 3 parts by mass or less, 2 parts by mass or less, or 1 part by mass or less.

[Weather resistance stabilizer]
The weather resistance stabilizer is not limited to the following, but preferred examples include at least one selected from the group consisting of benzotriazole-based compounds, oxalic acid anilide-based compounds, and hindered amine-based light stabilizers.

The above benzotriazole compounds include, but are not limited to, 2-(2'-hydroxy-5'-methyl-phenyl)benzotriazole, 2-(2'-hydroxy-3,5-di-t-butyl-phenyl)benzotriazole, 2-[2'-hydroxy-3,5-bis(α,α-dimethylbenzyl)phenyl]benzotriazole, 2-(2'-hydroxy-3,5-di-t-amylphenyl]benzotriazole, 2-(2'-hydroxy-3,5-di-isoamyl-phenyl)benzotriazole, 2-[2'-hydroxy-3,5-bis-(α,α-dimethylbenzyl)phenyl]-2H-benzotriazole, and 2-(2'-hydroxy-4'-octoxyphenyl)benzotriazole. Each of these compounds may be used alone or in combination of two or more.

The oxalic acid anilide compounds include, but are not limited to, 2-ethoxy-2'-ethyloxalic acid bisanilide, 2-ethoxy-5-t-butyl-2'-ethyloxalic acid bisanilide, 2-ethoxy-3'-dodecyloxalic acid bisanilide, etc. These compounds may be used alone or in combination of two or more.

Examples of the hindered amine light stabilizer include, but are not limited to, 4-acetoxy-2,2,6,6-tetramethylpiperidine, 4-stearoyloxy-2,2,6,6-tetramethylpiperidine, 4-acryloyloxy-2,2,6,6-tetramethylpiperidine, 4-(phenylethoxy)-2,2,6,6-tetramethylpiperidine, 4-benzoyloxy-2,2,6,6-tetramethylpiperidine, 4-methoxy-2,2,6,6-tetramethylpiperidine, 4-stearyloxy-2,2,6,6-tetramethylpiperidine, 4-cyclohexyloxy-2,2,6,6-tetramethylpiperidine, 4-benzyloxy-2,2,6,6-tetramethylpiperidine, Methylpiperidine, 4-phenoxy-2,2,6,6-tetramethylpiperidine, 4-(ethylcarbamoyloxy)-2,2,6,6-tetramethylpiperidine, 4-(cyclohexylcarbamoyloxy)-2,2,6,6-tetramethylpiperidine, 4-(phenylcarbamoyloxy)-2,2,6,6-tetramethylpiperidine, bis(2,2,6,6-tetramethyl-4-piperidyl)-carbonate, bis(2,2,6,6-tetramethyl-4-piperidyl)-oxalate, bis(2,2,6,6-tetramethyl-4-piperidyl)-malonate, bis(1,2,2,6,6-pentamethyl-4-piperidinyl)sebacate, bis-(N-methyl-2,2,6,6-tetramethyl-4-piperidinyl) tetramethyl-4-piperidinyl) sebacate, bis(2,2,6,6-tetramethyl-4-piperidyl) sebacate, bis(2,2,6,6-tetramethyl-4-piperidyl) adipate, bis(2,2,6,6-tetramethyl-4-piperidyl) terephthalate, 1,2-bis(2,2,6,6-tetramethyl-4-piperidyloxy) ethane, α,α'-bis(2,2,6,6-tetramethyl-4-piperidyloxy) p-xylene, bis(2,2,6,6-tetramethyl-4-piperidyl tolylene-2,4-dicarbamate, bis(2,2,6,6-tetramethyl-4-piperidyl) hexamethylene-1,6-dicarbamate, tris(2,2,6,6-tetramethyl -4-piperidyl)-benzene-1,3,5-tricarboxylate, tris(2,2,6,6-tetramethyl-4-piperidyl)-benzene-1,3,4-tricarboxylate, 1-[2-{3-(3,5-di-t-butyl-4-hydroxyphenyl)propionyloxy}butyl]-4-[3-(3,5-di-t-butyl-4-hydroxyphenyl)propionyloxy]2,2,6,6-tetramethylpiperidine, condensation product of 1,2,3,4-butanetetracarboxylic acid, 1,2,2,6,6-pentamethyl-4-piperidinol, and β,β,β',β'-tetramethyl-3,9-[2,4,8,10-tetraoxaspiro(5,5)undecane]diethanol, etc. The above hindered amine light stabilizers may be used alone or in combination of two or more.

Among them, the most preferred weathering stabilizers are 2-[2'-hydroxy-3,5-bis(α,α-dimethylbenzyl)phenyl]benzotriazole, 2-(2'-hydroxy-3,5-di-t-butylphenyl)benzotriazole, 2-(2'-hydroxy-3,5-di-t-amylphenyl]benzotriazole, bis(1,2,2,6,6-pentamethyl-4-piperidinyl)sebacate, bis-(N-methyl-2,2,6,6-tetramethyl-4-piperidinyl)sebacate, bis(2,2,6,6-tetramethyl-4-piperidinyl)sebacate, and a condensate of 1,2,3,4-butanetetracarboxylic acid, 1,2,2,6,6-pentamethyl-4-piperidinol, and β,β,β',β'-tetramethyl-3,9-[2,4,8,10-tetraoxaspiro(5,5)undecane]diethanol.

[Dispersant]
<Amphiphilic molecules>
In one embodiment, the dispersant preferably has a hydrophilic segment and a hydrophobic segment in the same molecule (i.e., is an amphiphilic molecule) from the viewpoint of dispersing the cellulose fine fibers more uniformly in the resin.

The hydrophilic segment is a portion that exhibits good affinity with cellulose fine fibers by containing a hydrophilic structure. The hydrophilic structure includes hydroxyl groups, thiol groups, carboxy groups, sulfonic acid groups, sulfate groups, phosphate groups, boronic acid groups, silanol groups, groups derived from sugars such as sorbitan and sucrose, groups derived from glycerin, groups represented by -OM, -COOM, -SO ₃ M, -OSO ₃ M, -HMPO ₄ , and -M ₂ PO ₄ (wherein M represents an alkali metal or an alkaline earth metal), as well as primary to tertiary amines and quaternary ammonium salts. Examples of the counter anion of the quaternary ammonium salt include one or more hydrophilic groups selected from the group consisting of hydroxide ions, fluoride ions, chloride ions, bromide ions, iodide ions, and other halide ions, as well as nitrate ions, formate ions, acetate ions, trifluoroacetate ions, p-toluenesulfonate ions, hexafluorophosphate, and tetrafluoroborate.

Examples of hydrophilic segments include polyethylene glycol segments, segments containing repeating units containing a quaternary ammonium salt structure, polyvinyl alcohol segments, polyvinylpyrrolidone segments, polyacrylic acid segments, carboxyvinyl polymer segments, cationized guar gum segments, hydroxyethyl cellulose segments, methyl cellulose segments, carboxymethyl cellulose segments, and polyurethane soft segments (specifically diol segments). Nonionic polyoxyethylene derivatives are particularly preferred, and the polyoxyethylene chain length of the polyoxyethylene derivative may be 3 or more, or 5 or more, or 10 or more, or 15 or more. The longer the chain length, the higher the affinity with cellulose fine fibers, but from the viewpoint of balance with the desired properties (e.g., mechanical properties) of the resin molded body, the polyoxyethylene chain length may be 60 or less, or 50 or less, or 40 or less, or 30 or less, or 20 or less.

Examples of hydrophobic segments include segments having a hydrocarbon, segments having an alkylene oxide unit having 3 or more carbon atoms (for example, a PPG block), and segments containing a polymer structure.
Preferred examples of the segment having a hydrocarbon include alkyl, alkenyl, alkyl ether, alkenyl ether, alkyl phenyl ether, alkenyl phenyl ether, rosin ester, bisphenol A, β-naphthyl, styrenated phenyl, and hydrogenated castor oil. The number of carbon atoms in the alkyl or alkenyl chain of the hydrophobic group (the number of carbon atoms excluding the phenyl group in the case of alkylphenyl or alkenylphenyl) is preferably 5 or more, or 10 or more, or 12 or more, or 16 or more.
Examples of the segment containing a polymer structure include acrylic polymers, styrene resins, vinyl chloride resins, vinylidene chloride resins, polyolefin resins, polyhexamethylene adipamide (6,6 nylon), polyhexamethylene azelamide (6,9 nylon), polyhexamethylene sebacamide (6,10 nylon), polyhexamethylene dodecanoamide (6,12 nylon), polybis(4-aminocyclohexyl)methanedodecane, and other polycondensates of organic dicarboxylic acids having 4 to 12 carbon atoms and organic diamines having 2 to 13 carbon atoms, and polycondensates of ω-amino acids (for example, ω-aminoundecanoic acid) (for example, polyundecane, Preferred are amino acid lactams containing ring-opening polymerization products of lactams such as polycapramide (nylon 6) which is a ring-opening polymerization product of ε-aminocaprolactam, and polylauric lactam (nylon 12) which is a ring-opening polymerization product of ε-aminolaurolactam, polymers composed of diamines and dicarboxylic acids, polyacetal resins, polycarbonate resins, polyester resins, polyphenylene sulfide resins, polysulfone resins, polyether ketone resins, polyimide resins, fluorine resins, hydrophobic silicone resins, melamine resins, epoxy resins, and phenolic resins.

The structure of the amphiphilic molecule is not particularly limited, but when the hydrophilic segment is A and the hydrophobic segment is B, examples include AB block copolymers, ABA block copolymers, BAB block copolymers, ABAB block copolymers, ABABA block copolymers, BABAB block copolymers, tri-branched copolymers containing A and B, tetra-branched copolymers containing A and B, star copolymers containing A and B, monocyclic copolymers containing A and B, polycyclic copolymers containing A and B, and cage copolymers containing A and B.

In one embodiment, the amphiphilic molecule may be any of anionic surfactants, nonionic surfactants, cationic surfactants, and amphoteric surfactants. The dispersant may be a polymeric surfactant, a reactive surfactant, or the like. In terms of affinity with cellulose fine fibers, cationic surfactants and nonionic ionic surfactants are preferred, and in terms of heat resistance, nonionic surfactants are more preferred.

<Hydrophilic polymer>
In one embodiment, the dispersant is preferably a hydrophilic polymer. As the hydrophilic polymer, one or more selected from the group consisting of cellulose derivatives (hydroxyethyl cellulose, methyl cellulose, carboxymethyl cellulose, etc.), polyalkylene glycol, polyvinyl alcohol, polyvinylpyrrolidone, polyacrylic acid, carboxyvinyl polymer, cationized guar gum, water-soluble polyurethane, polymers containing a quaternary ammonium salt structure, amides, amines, etc. can be used. Among them, cellulose derivatives and polyalkylene glycols are more preferred, and polyalkylene glycols are particularly preferred.

Cellulose derivatives are preferred because they are cellulose-based substances and therefore have a high affinity with cellulose, but because they are also thermoplastic resins, they are highly effective in improving the dispersion stability of cellulose in resin compositions.

Polyalkylene glycols are obtained by the addition of alkylene oxides having 2 to 4 carbon atoms, and polyethylene glycols having 2 carbon atoms are preferred because they have good affinity with both polyacetal resins, particularly polyacetal resins having oxyethylene units, and cellulose microfibers. The number of repeating oxyalkylene units is preferably 10 or more, or 20 or more, or 30 or more, or 40 or more, or 50 or more, or 60 or more, or 70 or more, or 80 or more, or 85 or more, or 90 or more, or 95 or more, or 100 or more in terms of increasing high-temperature rigidity, and is preferably 1000 or less, or 900 or less, or 800 or less, or 700 or less, or 600 or less, or 550 or less, or 500 or less in terms of processability.

In one embodiment, the ethylene ratio R, which is the ratio of the number of oxyethylene units to the number of oxymethylene units of the polyacetal resin, and the number n of oxyethylene repeating units of the polyethylene glycol are expressed by the following formula:
(R+0.5)/0.015≦n≦(R+10)/0.015
When the above formula is satisfied, the high affinity between the polyacetal resin and the polyethylene glycol contributes to improving the affinity between the polyacetal resin and the cellulose fine fibers, and therefore high dispersion of the cellulose fine fibers in the polyacetal resin is achieved, and good mechanical properties (e.g., rigidity and toughness) of the polyacetal resin composition are obtained. The above n is more preferably (R+0.6)/0.015 or more, or (R+0.7)/0.015 or more, and more preferably (R+9)/0.015 or less, or (R+8)/0.015 or less.

<Liquid Polymer>
In one embodiment, the dispersant is preferably a liquid polymer. Specific examples of the liquid polymer include liquid rubber, liquid polyolefin, liquid acrylic polymer, and liquid paraffin.

<Liquid rubber>
Liquid rubber means a substance that has fluidity at 23°C and forms a rubber elastomer by crosslinking (more specifically, vulcanization) and/or chain extension. That is, liquid rubber is an uncured material in one embodiment. Also, having fluidity means that, in one embodiment, liquid rubber dissolved in cyclohexane is placed in a vial with a body diameter of 21 mm and a total length of 50 mm at 23°C, dried, the liquid rubber is filled in the vial to a height of 1 mm, sealed, and the vial is left standing upside down for 24 hours, and a movement of the substance in the vertical direction of 0.1 mm or more can be confirmed.

In one embodiment, the liquid rubber includes a diene rubber, and in another embodiment, a conjugated diene polymer or a non-conjugated diene polymer or a hydrogenated product thereof. The above polymer or hydrogenated product may be an oligomer, a random copolymer, or a block copolymer. The monomers constituting the liquid rubber may be unmodified or modified (e.g., acid modified, hydroxyl modified, etc.). In one embodiment, the liquid rubber may have reactive groups (e.g., one or more selected from the group consisting of hydroxyl groups, carboxy groups, isocyanato groups, thio groups, amino groups, and halo groups) at both ends, and therefore may be bifunctional.

Examples of conjugated diene polymers include polybutadiene, butadiene-styrene copolymers, polyisoprene, acrylonitrile-butadiene copolymers, and polychloroprene, as well as derivatives thereof (e.g., maleic anhydride modified products, methacrylic acid modified products, terminal hydroxyl group modified products, hydrogenated products, and combinations thereof).

Non-conjugated diene polymers include olefin polymers such as ethylene-propylene rubber, ethylene-propylene-diene rubber, ethylene-butene-diene rubber, and ethylene-α-olefin copolymers, butyl rubber, brominated butyl rubber, acrylic rubber, fluororubber, silicone rubber, chlorinated polyethylene rubber, epichlorohydrin rubber, α,β-unsaturated nitrile-acrylate-conjugated diene copolymer rubber, urethane rubber, and polysulfide rubber.

The amount of dispersant per 100 parts by mass of polyacetal resin is preferably 0.1 parts by mass or more, or 1 part by mass or more, or 2 parts by mass or more, or 3 parts by mass or more, or 4 parts by mass or more, or 5 parts by mass or more, from the viewpoint of obtaining a good effect of improving the dispersibility of cellulose fine fibers in the resin composition, and is preferably 100 parts by mass or less, or 80 parts by mass or less, or 50 parts by mass or less, or 20 parts by mass or less, or 10 parts by mass or less, from the viewpoint of avoiding inconveniences such as plasticization of the resin composition due to excess dispersant.

[Release agents and lubricants]
The release agent and lubricant are not limited to the following, but preferred examples include alcohols, fatty acids and their esters (i.e., fatty acid esters of alcohols), olefin compounds having an average degree of polymerization of 10 to 500, and silicones. The release agent and lubricant may be used alone or in combination of two or more. In one embodiment, the total amount of the release agent and lubricant relative to 100 parts by mass of the polyacetal resin may be 0.01 parts by mass to 10 parts by mass.

[Conductive agent]
The conductive agent is not limited to the following, but examples thereof include conductive carbon black, metal powder, and fibers. The conductive agent may be used alone or in combination of two or more. In one embodiment, the amount of the conductive agent relative to 100 parts by mass of the polyacetal resin may be 0.01 parts by mass to 10 parts by mass.

[Thermoplastic resin]
Examples of the thermoplastic resin include, but are not limited to, polyolefin resin, acrylic resin, styrene resin, polycarbonate resin, and uncured epoxy resin. Only one type of thermoplastic resin may be used alone, or two or more types may be used in combination. The thermoplastic resin also includes modified products of the above-mentioned resins. In one embodiment, the amount of the thermoplastic resin relative to 100 parts by mass of the polyacetal resin may be 0.01 parts by mass to 10 parts by mass.

[Thermoplastic elastomer]
Examples of the thermoplastic elastomer include, but are not limited to, polyurethane elastomers, polyester elastomers, polystyrene elastomers, and polyamide elastomers. Only one type of thermoplastic elastomer may be used alone, or two or more types may be used in combination. In one embodiment, the amount of the thermoplastic elastomer relative to 100 parts by mass of the polyacetal resin may be 0.01 parts by mass to 10 parts by mass.

[Dye and pigment]
Examples of the dyes and pigments include, but are not limited to, inorganic pigments, organic pigments, metallic pigments, fluorescent pigments, and the like.
The inorganic pigment may be any pigment commonly used for coloring resins, and examples thereof include, but are not limited to, zinc sulfide, titanium oxide, barium sulfate, titanium yellow, cobalt blue, combustion pigments, carbonates, phosphates, acetates, carbon black, acetylene black, lamp black, and the like.
Examples of organic pigments include, but are not limited to, condensed azo, ynone, monoazo, diazo, polyazo, anthraquinone, heterocyclic, pennone, quinacridone, thioindigo, perylene, dioxazine, and phthalocyanine pigments.
The dyes and pigments may be used alone or in combination of two or more kinds.

The proportion of dyes and pigments added varies greatly depending on the desired color tone, so it is difficult to specify a general ratio, but generally, they are used in the range of 0.05 to 5 parts by weight per 100 parts by weight of polyacetal resin.

[filler]
The inorganic filler is not limited to the following, but for example, a fibrous, powdery, plate-like or hollow filler is used.
Examples of fibrous fillers include, but are not limited to, inorganic fibers such as glass fibers, carbon fibers, silicone fibers, silica-alumina fibers, zirconia fibers, boron nitride fibers, silicon nitride fibers, boron fibers, potassium titanate fibers, and metal fibers such as stainless steel, aluminum, titanium, copper, and brass. Also included are short whiskers such as potassium titanate whiskers and zinc oxide whiskers.
Examples of powdery particulate fillers include, but are not limited to, talc; carbon black; silica; quartz powder; glass beads; glass powder; silicates such as calcium silicate, magnesium silicate, aluminum silicate, kaolin, clay, diatomaceous earth, and wollastonite; metal oxides such as iron oxide, titanium oxide, and alumina; metal sulfates such as calcium sulfate and barium sulfate; carbonates such as magnesium carbonate and dolomite; silicon carbide; silicon nitride; boron nitride; and various metal powders.
Examples of the plate-like filler include, but are not limited to, mica, glass flakes, and various metal foils.
Examples of hollow fillers include, but are not limited to, glass balloons, silica balloons, shirasu balloons, and metal balloons.

Organic fillers include, but are not limited to, high melting point organic fibrous fillers such as aromatic polyamide resins, fluororesins, and acrylic resins.

The inorganic or organic fillers may be used alone or in combination of two or more. These fillers may be either surface-treated or untreated, but from the viewpoint of the surface smoothness and mechanical properties of the molded article obtained using the polyacetal resin composition, it may be preferable to use fillers that have been surface-treated with a surface treatment agent.

The surface treatment agent is not particularly limited, and conventionally known surface treatment agents can be used. Examples of surface treatment agents that can be used include, but are not limited to, various coupling treatment agents such as silane-based, titanate-based, aluminum-based, and zirconium-based agents, resin acids, organic carboxylic acids, organic carboxylates, and surfactants. Specific examples of surface treatment agents that can be used include, but are not limited to, N-(2-aminoethyl)-3-aminopropyltriethoxysilane, 3-glycidoxypropyltrimethoxysilane, isopropyltristearoyltitanate, diisopropoxyammoniumethylacetate, and n-butylzirconate.

In one embodiment, the amount of filler per 100 parts by mass of polyacetal resin may be 0.01 parts by mass to 10 parts by mass.

<<Method for producing polyacetal resin composition>>
In one embodiment, the polyacetal resin composition can be produced by a method including mixing a polyacetal resin, cellulose fine fibers, and optionally additional components.
(1) A method of melt-kneading kneading components containing a polyacetal resin and a cellulose fiber raw material, and forming a resin composition while defibrating the cellulose fiber raw material by the shear force during the melt-kneading to generate cellulose fine fibers;
(2) a method including a defibration step of defibrating a cellulose fiber raw material to obtain cellulose fine fibers, and a mixing step of mixing a polyacetal resin and cellulose fine fibers, and (3) a method including a defibration step of defibrating a cellulose fiber raw material in a liquid medium to obtain a cellulose fine fiber slurry, a drying step of drying the cellulose fine fiber slurry to obtain a dried cellulose fine fiber body, and a mixing step of mixing a polyacetal resin and a dried cellulose fine fiber body. From the viewpoint of obtaining a resin composition in which the cellulose fine fibers are highly dispersed, the above method (3) is preferred. Preferred examples of the above methods (2) and (3) are described below.

<Defibrillation process>
In this process, the cellulose fiber raw material is defibrated to obtain cellulose fine fibers. The cellulose fiber raw material may be subjected to a pretreatment before defibration. By adjusting the fiber shape, particularly the fiber length, through the pretreatment, fine and homogeneous cellulose fine fibers can be obtained even if the subsequent defibration process is performed under relatively mild defibration conditions. In one embodiment, the cellulose fine fibers produced in the defibration process have an aldehyde group concentration within the range of the present disclosure, particularly 0.5 μmol/g to 50 μmol/g.

In the defibration process, the temperature of the cellulose fiber raw material or the defibrated product thereof is preferably 90°C or less, or 85°C or less, or 80°C or less, or 75°C or less, or 70°C or less, or 60°C or less. Defibration under such gentle conditions is advantageous in terms of suppressing an increase in the concentration of aldehyde groups in the cellulose during defibration. In one embodiment, the temperature of the cellulose fiber raw material or the defibrated product thereof may be 0°C or more, or 1°C or more, or 5°C or more, or 10°C or more, or 15°C or more, or 20°C or more, or 30°C or more.

In one embodiment, the defibration process is carried out under conditions in which the pressure applied to the cellulose fiber raw material or its defibrated product is maintained at 300 MPa or less, or 250 MPa or less, or 200 MPa or less throughout the process. Defibration under such gentle conditions is advantageous in terms of suppressing an increase in the aldehyde group concentration in the cellulose during defibration. In one embodiment, the pressure applied to the cellulose fiber raw material or its defibrated product may be 30 MPa or more, or 50 MPa or more, or 80 MPa or more during part or all of the defibration process.

[Preprocessing]
In one embodiment, the pretreatment may be one or more selected from pulverization, grinding, and classification. Grinding is a process of grinding the cellulose fiber raw material in a dry manner. Grinding is a process of grinding a slurry obtained by dispersing the cellulose fiber raw material in a liquid medium, and is distinguished from the above-mentioned grinding in that it is a wet process. Classification is a separation operation for aligning the fiber length of the cellulose fiber raw material, and may be dry classification or wet classification. When performing pretreatment, even if the slurry has a relatively high solid content concentration (for example, 0.5 mass% or more, 1.0 mass% or more, 1.5 mass% or more, or 2.0 mass% or more), it is preferable because defibration can be performed in a short time without trouble such as clogging of the defibration device.

[solvent]
The liquid medium may include water and/or other media (eg, organic solvents, inorganic acids, bases, and/or ionic liquids) and may include one or more types of media.

The organic solvent is not particularly limited, but examples thereof include alcohols having 1 to 20 carbon atoms, preferably 1 to 4 carbon atoms, such as methanol, ethanol, and propanol; glycol ethers having 2 to 20 carbon atoms, preferably 2 to 6 carbon atoms, such as methyl cellosolve and propylene glycol monomethyl ether; ethers having 2 to 20 carbon atoms, preferably 2 to 8 carbon atoms, such as propylene glycol monomethyl ether, 1,2-dimethoxyethane, diisopropyl ether, tetrahydrofuran, and 1,4-dioxane; acetone, methyl ethyl ketone, methyl isobutyl ether, and the like. Examples include ketones having 3 to 20 carbon atoms, preferably 3 to 6 carbon atoms, such as ketones with 3 to 6 carbon atoms; linear or branched saturated or unsaturated hydrocarbons having 1 to 20 carbon atoms, preferably 1 to 8 carbon atoms; aromatic hydrocarbons such as benzene and toluene; halogenated hydrocarbons such as methylene chloride and chloroform; carboxylic acids having 1 to 20 carbon atoms, such as formic acid, acetic acid, and lactic acid; esters having 2 to 20 carbon atoms, preferably 2 to 6 carbon atoms, such as ethyl acetate and vinyl acetate; nitrogen-containing solvents such as dimethylformamide, dimethylacetamide, and N-methylpyrrolidone; and sulfur-containing solvents such as dimethylsulfoxide. These can be used alone or in combination of two or more kinds, but from the viewpoint of operability of the defibration treatment, alcohols having 1 to 6 carbon atoms, glycol ethers having 2 to 6 carbon atoms, ethers having 2 to 8 carbon atoms, ketones having 3 to 6 carbon atoms, lower alkyl ethers having 2 to 5 carbon atoms, carboxylic acids having 1 to 8 carbon atoms, esters having 2 to 6 carbon atoms, dimethylformamide, dimethylacetamide, N-methylpyrrolidone, dimethylsulfoxide, etc. are preferred.

Examples of inorganic acids include hydrochloric acid, sulfuric acid, phosphoric acid, nitric acid, boric acid, etc., but from the viewpoint of defibration efficiency and ease of handling, one or more acids selected from the group consisting of hydrochloric acid, sulfuric acid, and phosphoric acid are preferred.

Examples of bases include hydroxides such as sodium hydroxide, potassium hydroxide, and calcium hydroxide, carbonates such as sodium carbonate, potassium carbonate, and calcium carbonate, and organic amines such as ammonia, triethylamine, and triethanolamine. From the viewpoint of defibration efficiency and ease of handling, the base is preferably one or more selected from the group consisting of hydroxides, carbonates, and organic amines.

In this disclosure, an ionic liquid refers to a liquid salt containing an organic ion in at least one of the cation and anion parts, and the melting point of the ion alone is 100°C or less. The cation part of the ionic liquid preferably has at least one cation selected from the group consisting of imidazolium cation, pyrrolidinium cation, piperidinium cation, morpholinium cation, pyridinium cation, quaternary ammonium cation, and phosphonium cation.

Examples of anion components include halide ions (Cl ^- , Br ^- , I ^- , etc.), carboxylate anions (for example, carboxylate anions having a total of 1 to 3 carbon atoms, such as C ₂ H ₅ CO ₂ ^- , CH ₃ CO ₂ ^- , HCO ₂ ^- , etc.), pseudohalide ions (i.e., ions that are monovalent and have properties similar to those of halide ions, such as CN ^- , SCN ^- , OCN ^- , ONC ^- , N ₃ ^- , etc.), sulfonate anions, organic sulfonate anions (methanesulfonate anion, etc.), phosphate anions (ethyl phosphate anion, methyl phosphate anion, hexafluorophosphate anion, etc.), borate anions (tetrafluoroborate anion, etc.), perchlorate anions, etc., and from the viewpoint of defibration ability, halide ions and carboxylate anions are preferred.

Examples of imidazolium ionic liquids include 1-ethyl-3-methylimidazolium acetate, 1-ethyl-3-methylimidazolium formate, 1-allyl-3-methylimidazolium chloride, 1-allyl-3-methylimidazolium bromide, 1-ethyl-3-methylimidazolium dimethyl phosphate, 1-butyl-3-methylimidazolium acetate, 1-butyl-3-methylimidazolium chloride, 1-butyl-3-methylimidazolium bromide, 1-ethyl-3-methylimidazolium diethyl phosphate, 1,3-dimethylimidazolium acetate, 1-ethyl-3-methylimidazolium propionate, 1-propyl-3-methylimidazolium chloride, and 1-propyl-3-methylimidazolium bromide.

In one embodiment, the liquid medium is an aqueous medium, and examples of the liquid medium include water alone or a mixture of water and one or more organic solvents selected from the group consisting of monohydric alcohols such as ethanol, n-propanol, isopropanol, and butanol, polyhydric alcohols such as ethylene glycol, diethylene glycol, and glycerin, ketones such as acetone, nitrile solvents such as acetonitrile, and pyrrolidone solvents. The ratio of the organic solvent in the mixture of the organic solvent and water is preferably less than 50% by mass, or 30% by mass or less, or 20% by mass or less. When the water ratio is high, the grindability tends to be good, and when the organic solvent ratio is high, the aggregation of the cellulose fibers after grinding tends to be suppressed. It is preferable that the ratio of the organic solvent is set in consideration of the balance between the grindability and the suppression of aggregation.

[Defibrillation]
The cellulose fiber raw material is optionally subjected to the above-mentioned pretreatment and then subjected to defibration. The defibration may be a dry or wet mechanical treatment. For the defibration treatment, a single device may be used once or more, or multiple devices may be used once or more. The device used for defibration is not particularly limited, and examples thereof include devices of the type such as high-speed rotation, colloid mill, high-pressure, roll mill, and ultrasonic types. Examples of the device that can be used include high-pressure or ultra-high-pressure homogenizers, refiners, beaters, PFI mills, kneaders, dispersers, high-speed defibrators, grinders (stone-type grinders), ball mills, vibration mills, bead mills, conical refiners, disk refiners, single-axis, twin-axis, or multi-axis kneaders/extruders, homomixers under high-speed rotation, refiners, defibrators, beaters, friction grinders, high-shear fibrilators (e.g., Cavitron rotor/starter devices), dispergers, and homogenizers (e.g., microfluidizers), which act on pulp fibers with a metal or blade around a rotating shaft, or devices that use friction between pulp fibers. In this embodiment, from the viewpoint of controlling the aldehyde group concentration of the cellulose fine fibers within a desired range, a defibration method that does not apply high temperature and/or high pressure to the cellulose fiber raw material is preferred, and for example, a conical refiner, a disc refiner, etc. are suitable.

When the defibration process is a wet process, the liquid medium may be one of those exemplified above. The liquid temperature of the cellulose fiber raw material slurry in this case is preferably 85°C or less, or 80°C or less, or 75°C or less, or 70°C or less. In order to prevent the slurry from freezing and to reduce the cost of heat exchange, the liquid temperature of the slurry is preferably 1°C or more, or 5°C or more, or 10°C or more, or 15°C or more.

The defibration process may be performed in one stage or multiple stages. In the case of multiple stages, the same device may be used multiple times, or different devices may be used in combination. In the case of multiple stages, it is effective to combine two or more types of defibration devices with different defibration mechanisms or shear rates. The multi-stage method is preferably a method using disc refiners with different disc configurations, since the degree of defibration can be precisely controlled, making it easy to control the aldehyde group concentration of the cellulose fine fibers. Examples of disc refiners include single disc refiners, double disc refiners, and conical refiners, but from the perspective of highly controlling defibration, single disc refiners are preferred, as they provide high precision control of the blade distance between the fixed blade and the rotary blade.

When using a disc refiner, a slurry in which cellulose fiber raw material is dispersed in a defibrating solvent at an appropriate solid content concentration is stored in a tank, and the slurry is supplied to the disc refiner for defibration. The solid content concentration of the slurry is preferably 0.1% by mass or more, or 0.3% by mass or more, or 0.5% by mass or more, or 0.8% by mass or more, or 1.0% by mass or more, and is preferably 6% by mass or less, or 3.5% by mass or less, or 3% by mass or less. The water used as the slurry medium is advantageously high-purity water such as distilled water or ion-exchanged water.

In operating the disc refiner, the defibration process may be performed by a continuous circulation process in which the slurry stored in a tank is returned to the original tank via the disc refiner. However, it is preferable to prepare two tanks connected by piping via the disc refiner (hereinafter referred to as Tank A and Tank B), and first transfer the slurry from Tank A to Tank B via the disc refiner and store it there. When the processing of the slurry in Tank A is completed, the process is switched to continuously transfer the slurry from Tank B to Tank A via the disc refiner and store it there. Thereafter, if the defibration is performed by a continuous process in which these steps are alternately repeated, the slurry is reliably passed through the disc refiner in each processing, and a uniform number of passes can be performed on the entire amount of slurry, which is more preferable from the viewpoint of the uniformity of the degree of defibration, i.e., the quality stability of the cellulose fine fibers.

During operation of the disc refiner, the liquid temperature of the slurry rises. From the viewpoint of suppressing an increase in the concentration of aldehyde groups in the cellulose during defibration, it is preferable to control the liquid temperature of the slurry using a heat exchanger or the like. The liquid temperature is preferably 85°C or less, or 80°C or less, or 75°C or less, or 70°C or less. In addition, from the viewpoint of preventing the slurry from freezing and suppressing the cost of heat exchange, the liquid temperature is preferably 1°C or more, or 5°C or more, or 10°C or more, or 15°C or more.

When using a disc refiner for fiber defibration, it can be done in multiple stages (processing with multiple types of blades) or in one stage (processing with one type of blade).

Fig. 1 is a diagram for explaining an example of the arrangement of the blades and grooves of a disc refiner, and Fig. 2 is a diagram for explaining the blade width, groove width, and blade distance of a disc refiner. When multiple disc refiners are used for multi-stage defibration, it is preferable to use a refiner having at least two different types of blades. With reference to Figs. 1 and 2, as a specific blade configuration, in a disc refiner having a blade 11 and a groove 12 as shown in Fig. 1, the blade width W _B , the groove width W _G , and the value obtained by dividing the blade width W _B by the groove width W _G (hereinafter also referred to as the blade groove ratio) shown in Fig. 2 are important, and it is particularly preferable to perform defibration processing (hereinafter also referred to as the front stage) using a refiner equipped with a blade having a blade width of 1.5 mm or more and 5 mm or less and a blade groove ratio of 0.1 or more and 1.0 or less, and then perform defibration processing (hereinafter also referred to as the back stage) using a refiner having a blade having a blade width of 0.1 mm or more and 1.0 mm or less and a blade groove ratio of 0.5 or more and 1.0 or less. Defibration using a disc refiner of this configuration reduces the number of long fibers that cause aggregation in the resin, and produces cellulose fibers with a low fibrillation rate (i.e., less fluff). In this case, a separate defibration treatment may be added between the front and rear stages.

When using one type of blade to perform disc refiner processing in one stage, it is particularly preferable to perform the fiberization process using a refiner having a blade with a blade width of 0.1 mm or more and 1.0 mm or less, and a blade groove ratio of 0.5 or more and 1.0 or less.

[Blade distance in disc refiner treatment]
Also, referring to FIG. 2, in defibration using a disc refiner, it is advantageous to control the blade distance W _L (hereinafter simply referred to as the blade distance) between two blades (specifically, the rotary blade 21 and the fixed blade 22 in FIG. 2). By controlling the blade distance, it is possible to control the fiber length and defibration degree of the cellulose fine fibers. The blade distance is preferably 0.01 mm or more, 0.05 mm or more, and preferably 0.5 mm or less, or 0.3 mm or less. When performing multi-stage processing, it is preferable to set the blade distance to 0.01 mm or more and 0.5 mm or less in the first stage processing, and to 0.05 mm or more and 0.3 mm or less in the second stage processing. When performing single-stage processing, it is preferable to set the blade distance to 0.01 mm or more and 0.5 mm or less. When adjusting the blade distance, it is preferable to gradually narrow the blade distance from a wide blade distance while suppressing the current value of the device to a certain value or less. By such control, clogging or overloading of the device is prevented, and highly homogeneous cellulose fine fibers are obtained.

Highly controlling the blade distance between the fixed blade and the rotary blade as described above is advantageous in producing cellulose fine fibers with a controlled aldehyde group concentration. For example, in the blade distance adjustment of a conventional single disc refiner, a screw-type screw jack or the like is usually used, and since there is play in the runner part that fixes the rotary blade, if the runner part is pulled strongly in the thrust direction, it moves about 0.3 mm. From the viewpoint of precisely controlling the defibration property to obtain homogeneous cellulose fine fibers, it is advantageous that this movement amount (play) is small, and is preferably 0.1 mm or less, 0.08 mm or less, or 0.05 mm or less. In one embodiment, a single disc refiner in which the blade distance adjustment mechanism is a ball screw jack and the above-mentioned movement amount in the thrust direction is 0.03 mm may be used. Furthermore, in order to precisely adjust the blade distance, it is preferable to attach a reducer to the ball screw jack so that fine adjustment of the blade distance can be performed. By using such a single disc refiner, it is possible to finely adjust the blade distance and maintain a constant blade distance without blade vibration during the defibration process. This prevents the blades from coming into contact with each other when the blade distance is reduced, preventing the fiber length from becoming too short and reducing coarse fibers. The cellulose fine fibers obtained in this way and with a uniform degree of defibration can have a reduced aldehyde group concentration within the desired range.

[Number of passes in disc refiner processing]
The degree of defibration can also be controlled by the number of times the cellulose fibers pass between the rotary blade and the fixed blade (hereinafter also referred to as the number of passes), and by increasing the number of passes, cellulose fine fibers with a uniform fiber length distribution can be produced. Such cellulose fine fibers can have a reduced aldehyde group concentration within a desired range. Here, the number of passes means the number of times the refining process is performed (i.e., the number of passes between the rotary blade and the fixed blade) after the aforementioned blade distance is reduced to the desired blade distance.

The number of passes through the disc refiner is preferably 5 or more, 20 or more, or 40 or more. Since the fiber shape distribution converges as the number of passes increases, a larger number of passes is preferable, but considering productivity, the upper limit of the number of passes is preferably 300 or less.

[Method of determining defibration conditions using a disc refiner]
The shape of the cellulose fine fibers obtained by the disc refiner treatment is controlled by the combined effects of the above-mentioned type of disc refiner blade, blade distance, number of passes, concentration, etc. In order to obtain a shape of cellulose fine fibers that is preferable for use in a resin composition, it is preferable to increase the number of passes under viscous beating conditions. Viscous beating is a beating method that tends to fluff and defibrate the fibers. On the other hand, a beating method that tends to cause cutting in the fiber length direction is called free beating. As for the configuration of the disc refiner blade, the more the number of blades, the longer the blade length, the larger the ratio of the blade width to the groove width (blade groove ratio), and the larger the contact angle, the more the number of intersections of the blades between the rotating blade and the fixed blade increases, so that the force applied to the fiber at one intersection is dispersed, and the number of impacts on the fiber increases, resulting in a tendency to viscous beating. On the other hand, when the above conditions are reversed, a tendency to free beating is shown. The blade distance of the disc refiner is preferably widened when a blade showing a tendency to free beating is used, and is preferably narrowed when a blade showing a tendency to free beating is used, but narrowing the blade distance too much leads to clogging, fiber shortening due to cutting of fiber length, and excessive defibration, so the blade distance is preferably 0.05 mm or more. The aldehyde group concentration of the cellulose fine fibers can be controlled within a desired range by adjusting the blade distance and the number of passes described above depending on the shape (fiber length and fiber diameter) of the cellulose fiber raw material, the treatment concentration, and the blade used to control the defibration state of the cellulose fine fibers.

[Multi-stage beating process using a combination of a disc refiner and a high-pressure homogenizer]
It is also a preferred embodiment to subject the cellulose fibers beaten by the disc refiner to a further beating treatment by a high-pressure homogenizer. The high-pressure homogenizer has a greater effect of thinning the fibers than the disc refiner. The high-pressure homogenizer treatment is preferably carried out at a pressure of 30 MPa or more, more preferably 50 MPa or more, and more preferably 80 MPa or more. The upper limit of the pressure may be preferably 300 MPa or less, more preferably 250 MPa or less, and even more preferably 150 MPa or less, depending on the characteristics of the device.

Examples of high-pressure homogenizers include the NS-type high-pressure homogenizer from Nilo Soavi (Italy), the Lanier-type (R model) pressure homogenizer from SMT Co., Ltd., and the high-pressure homogenizer from Sanwa Machine Co., Ltd., while examples of ultra-high-pressure homogenizers include high-pressure collision type beating machines such as the Microfluidizer from Mizuho Kogyo Co., Ltd., the Nanomizer from Yoshida Kikai Kogyo Co., Ltd., and the Ultimizer from Sugino Machine Co., Ltd., but other devices may also be used as long as they perform micronization using a mechanism similar to that of these devices.

In the high-pressure homogenizer treatment, as in the disc refiner treatment, the defibration treatment may be performed in a continuous circulating treatment process in which the slurry stored in a tank is returned to the original tank via the high-pressure homogenizer. However, it is preferable to prepare two tanks (Tank A and Tank B) connected by piping via a high-pressure homogenizer, and first transfer the slurry from Tank A to Tank B via the high-pressure homogenizer and store it there. When the processing of the slurry in Tank A is completed, the slurry is continuously transferred from Tank B to Tank A via the high-pressure homogenizer and stored there. If the defibration treatment is performed in a continuous treatment process in which these steps are repeated alternately, the slurry is reliably passed through the high-pressure homogenizer in each treatment, and a uniform number of passes can be performed on the entire amount of slurry, which is more preferable from the viewpoint of the uniformity of the degree of defibration, i.e., the quality stability of the cellulose fine fibers.

The liquid temperature of the slurry also rises during high-pressure homogenizer treatment. From the viewpoint of suppressing an increase in the concentration of aldehyde groups in the cellulose during defibration, it is preferable to control the liquid temperature of the slurry using a heat exchanger or the like. The liquid temperature is preferably 85°C or less, or 80°C or less, or 75°C or less, or 70°C or less. In addition, from the viewpoint of preventing the slurry from freezing and suppressing the cost of heat exchange, it is preferably 1°C or more, or 5°C or more, or 10°C or more, or 15°C or more.

Even with high-pressure homogenizer treatment, pressure and heat are applied to the cellulose fibers, so an increase in the aldehyde group concentration may be observed, but high-pressure homogenizer treatment is a method that can efficiently refine cellulose fibers and requires fewer passes than disc refiner treatment. Therefore, surprisingly, high-pressure homogenizer treatment is unlikely to be the main cause of an increase in the aldehyde group concentration, while the selection of disc refiner treatment conditions has a strong influence on the determination of the aldehyde group concentration.

The cellulose fine fibers produced in the defibration process, and in one embodiment, the cellulose fine fibers in the cellulose fine fiber slurry, can have an aldehyde group concentration within the range of the present disclosure, particularly 0.5 μmol/g to 50 μmol/g, and can have a carboxy group concentration within the range of the present disclosure, particularly 200 μmol/g or less.

<Chemical modification step>
The cellulose fine fibers may be chemically modified with a modifying agent, for example, at the stage of raw cellulose fiber material, during or after the defibration process, or may be chemically modified during or after the preparation of a slurry containing the cellulose fine fibers, or during or after the drying and granulation process.

As a modification agent for cellulose fine fibers, a compound that reacts with the hydroxyl groups of cellulose can be used, and examples thereof include inorganic esterifying agents (nitrate esters, sulfate esters, phosphate esters, silicate esters, borate esters, etc.), organic esterifying agents (acetylating agents, propionylating agents, etc.), etherifying agents (methyl ether, hydroxyethyl ether, hydroxypropyl ether, hydroxybutyl ether, carboxymethyl ether, cyanoethyl ether, etc.), silylation agents, and TEMPO oxidation catalysts (oxidizing the primary hydroxyl groups of cellulose). In a preferred embodiment, the chemical modification is esterification, specifically esterification (acylation) using an organic esterifying agent, and particularly preferably acetylation. As organic esterifying agents, acid halides, acid anhydrides, vinyl carboxylates, and carboxylic acids are preferred.

The acid halide may be at least one selected from the group consisting of compounds represented by the following formula:
R ¹ -C(=O)-X
(In the formula, ^R1 represents an alkyl group having 1 to 24 carbon atoms, an alkenyl group having 2 to 24 carbon atoms, a cycloalkyl group having 3 to 24 carbon atoms, or an aryl group having 6 to 24 carbon atoms, and X represents Cl, Br, or I.)
Specific examples of acid halides include, but are not limited to, acetyl chloride, acetyl bromide, acetyl iodide, propionyl chloride, propionyl bromide, propionyl iodide, butyryl chloride, butyryl bromide, butyryl iodide, benzoyl chloride, benzoyl bromide, and benzoyl iodide. Among them, acid chlorides can be preferably used in terms of reactivity and handling. In addition, in the reaction of acid halides, one or more alkaline compounds may be added to act as a catalyst and neutralize the by-product acidic substances. Specific examples of alkaline compounds include, but are not limited to, tertiary amine compounds such as triethylamine and trimethylamine; and nitrogen-containing aromatic compounds such as pyridine and dimethylaminopyridine.

As the acid anhydride, any suitable acid anhydride can be used. For example,
Saturated aliphatic monocarboxylic acid anhydrides, such as acetic acid, propionic acid, (iso)butyric acid, and valeric acid; unsaturated aliphatic monocarboxylic acid anhydrides, such as (meth)acrylic acid and oleic acid;
Alicyclic monocarboxylic acid anhydrides such as cyclohexanecarboxylic acid and tetrahydrobenzoic acid;
Aromatic monocarboxylic acid anhydrides such as benzoic acid and 4-methylbenzoic acid;
Examples of dibasic carboxylic acid anhydrides include saturated aliphatic dicarboxylic acid anhydrides such as succinic anhydride and adipic acid, unsaturated aliphatic dicarboxylic acid anhydrides such as maleic anhydride and itaconic anhydride, alicyclic dicarboxylic acid anhydrides such as 1-cyclohexene-1,2-dicarboxylic acid anhydride, hexahydrophthalic anhydride and methyltetrahydrophthalic anhydride, and aromatic dicarboxylic acid anhydrides such as phthalic anhydride and naphthalic anhydride;
Examples of the polybasic carboxylic acid anhydrides having three or more bases include polycarboxylic acids (anhydrides) such as trimellitic anhydride and pyromellitic anhydride.
In addition, in the reaction of an acid anhydride, one or more types of acidic compounds such as sulfuric acid, hydrochloric acid, phosphoric acid, etc., or Lewis acids (for example, Lewis acid compounds represented by MYn, where M represents a semimetal element such as B, As, Ge, etc., or a base metal element such as Al, Bi, In, etc., or a transition metal element such as Ti, Zn, Cu, etc., or a lanthanoid element, n is an integer corresponding to the atomic valence of M and represents 2 or 3, and Y represents a halogen atom, OAc, _OCOCF3 , _ClO4 , _SbF6 , _PF6 , or _OSO2CF3 (OTf)), or alkaline compounds such as triethylamine, pyridine, etc. may be added as _a catalyst.

The vinyl carboxylate may be represented by the following formula:
R-COO-CH= _CH2
{wherein R is any one of an alkyl group having 1 to 24 carbon atoms, an alkenyl group having 2 to 24 carbon atoms, a cycloalkyl group having 3 to 16 carbon atoms, and an aryl group having 6 to 24 carbon atoms.} is preferred. The vinyl carboxylate is more preferably at least one selected from the group consisting of vinyl acetate, vinyl propionate, vinyl butyrate, vinyl caproate, vinyl cyclohexanecarboxylate, vinyl caprylate, vinyl caprate, vinyl laurate, vinyl myristate, vinyl palmitate, vinyl stearate, vinyl pivalate, vinyl octylate, divinyl adipate, vinyl methacrylate, vinyl crotonate, vinyl octylate, vinyl benzoate, and vinyl cinnamate. In the esterification reaction with a vinyl carboxylate, one or more catalysts selected from the group consisting of alkali metal hydroxides, alkaline earth metal hydroxides, alkali metal carbonates, alkaline earth metal carbonates, alkali metal hydrogencarbonates, primary to tertiary amines, quaternary ammonium salts, imidazole and derivatives thereof, pyridine and derivatives thereof, and alkoxides may be added.

Examples of alkali metal hydroxides and alkaline earth metal hydroxides include sodium hydroxide, potassium hydroxide, lithium hydroxide, calcium hydroxide, barium hydroxide, etc. Examples of alkali metal carbonates, alkaline earth metal carbonates, and alkali metal hydrogen carbonates include lithium carbonate, sodium carbonate, potassium carbonate, cesium carbonate, magnesium carbonate, calcium carbonate, barium carbonate, lithium hydrogen carbonate, sodium hydrogen carbonate, potassium hydrogen carbonate, and cesium hydrogen carbonate, etc.

Primary, secondary and tertiary amines refer to primary, secondary and tertiary amines, and specific examples include ethylenediamine, diethylamine, proline, N,N,N',N'-tetramethylethylenediamine, N,N,N',N'-tetramethyl-1,3-propanediamine, N,N,N',N'-tetramethyl-1,6-hexanediamine, tris(3-dimethylaminopropyl)amine, N,N-dimethylcyclohexylamine and triethylamine.

Imidazole and its derivatives include 1-methylimidazole, 3-aminopropylimidazole, carbonyldiimidazole, etc.

Examples of pyridine and its derivatives include N,N-dimethyl-4-aminopyridine and picoline.

Examples of alkoxides include sodium methoxide, sodium ethoxide, and potassium t-butoxide.

The carboxylic acid may be at least one selected from the group consisting of compounds represented by the following formulas:
R-COOH
(In the formula, R represents an alkyl group having 1 to 16 carbon atoms, an alkenyl group having 2 to 16 carbon atoms, a cycloalkyl group having 3 to 16 carbon atoms, or an aryl group having 6 to 16 carbon atoms.)

Specific examples of carboxylic acids include at least one selected from the group consisting of acetic acid, propionic acid, butyric acid, caproic acid, cyclohexane carboxylic acid, caprylic acid, capric acid, lauric acid, myristic acid, palmitic acid, stearic acid, pivalic acid, methacrylic acid, crotonic acid, octylic acid, benzoic acid, and cinnamic acid.

Among these carboxylic acids, at least one selected from the group consisting of acetic acid, propionic acid, and butyric acid, and particularly acetic acid, is preferred from the viewpoint of reaction efficiency.
In addition, in the reaction of carboxylic acid, one or more types of acidic compounds such as sulfuric acid, hydrochloric acid, phosphoric acid, etc., or Lewis acids (for example, Lewis acid compounds represented by MYn, where M represents a semimetal element such as B, As, Ge, etc., or a base metal element such as Al, Bi, In, etc., or a transition metal element such as Ti, Zn, Cu, etc., or a lanthanoid element, n is an integer corresponding to the atomic valence of M and represents 2 or 3, and Y represents a halogen atom, OAc, _OCOCF3 , _ClO4 , _SbF6 , _PF6 , or _OSO2CF3 ( _OTf )), or alkaline compounds such as triethylamine, pyridine, etc. may be added as a catalyst.

Among these esterification reactants, at least one selected from the group consisting of acetic anhydride, propionic anhydride, butyric anhydride, vinyl acetate, vinyl propionate, vinyl butyrate, and acetic acid, and among these, acetic anhydride and vinyl acetate are preferred from the viewpoint of reaction efficiency.

<Drying process>
In this step, the cellulose fine fiber slurry in which the cellulose fine fibers are dispersed in a liquid medium is dried to prepare a dried cellulose fine fiber body.
The dryer is not particularly limited, but examples thereof include a kneader, a planetary mixer, a Henschel mixer, a high-speed mixer, a propeller mixer, a ribbon mixer, a single-screw or twin-screw extruder, a Banbury mixer, a freeze dryer, a shelf dryer, a spray dryer, a fluidized bed dryer, and a drum dryer.

The drying temperature may be, for example, 20°C or more, or 30°C or more, or 40°C or more, or 50°C or more from the viewpoint of drying efficiency, and of forming a dried body with powder properties excellent in nano-dispersibility and macro-dispersibility of the cellulose fine fibers in the resin composition, and may be, for example, 200°C or less, or 180°C or less, or 160°C or less, or 140°C or less, or 120°C or less, or 100°C or less from the viewpoint of making it difficult for thermal deterioration of the cellulose fine fibers and additional components to occur, and from the viewpoint of avoiding excessive pulverization of the dried body due to rapid drying of the slurry.
The drying temperature is the temperature of the heat source in contact with the slurry, and is defined, for example, as the surface temperature of the temperature-regulating jacket of the drying device, the surface temperature of the heating cylinder, or the temperature of the hot air.

The degree of reduced pressure may be either atmospheric pressure or reduced pressure, but from the viewpoint of forming a dried body with powder characteristics excellent in drying efficiency and nano-dispersibility and macro-dispersibility of the cellulose fine fibers in the resin composition, it may be -1 kPa or less, or -10 kPa or less, or -20 kPa or less, or -30 kPa or less, or -40 kPa or less, or -50 kPa or less, and from the viewpoint of avoiding excessive pulverization of the dried body due to rapid drying of the slurry, it may be -100 kPa or more, or -95 kPa or more, or -90 kPa or more.

The concentration of cellulose fine fibers in the cellulose fine fiber slurry to be subjected to the drying step is preferably 1% by mass or more, or 2% by mass or more, or 3% by mass or more, or 5% by mass or more, or 10% by mass or more, or 15% by mass or more, or 20% by mass or more, or 25% by mass or more from the viewpoint of process efficiency during drying, and is preferably 60% by mass or less, or 55% by mass or less, or 50% by mass or less, or 45% by mass or less, or 40% by mass or less, or 35% by mass or less from the viewpoint of avoiding an excessive increase in the viscosity of the slurry and solidification due to aggregation and maintaining good handleability. For example, the production of cellulose fine fibers is often carried out in a dilute dispersion, and the cellulose fine fiber concentration in the slurry may be adjusted to the above-mentioned preferred range by concentrating such a dilute dispersion. For concentration, methods such as suction filtration, pressure filtration, centrifugal deliquation, and heating can be used.

Any additional ingredients other than the cellulose microfibers (e.g., dispersants as described above) may be added before, during, and/or after drying of the cellulose microfiber slurry.

One aspect of the present invention also provides a dried cellulose fine fiber body containing cellulose fine fibers having an aldehyde group concentration of 0.5 μmol/g to 50 μmol/g. The number average fiber diameter of the cellulose fine fibers may be within the range disclosed herein.

[Moisture percentage]
The liquid medium content of the dried body may be preferably 50% by mass or less, or 40% by mass or less, or 30% by mass or less, or 20% by mass or less, or 10% by mass or less. The liquid medium content may be 0% by mass, but from the viewpoint of ease of production of the dried body, it may be, for example, 0.1% by mass or more, 1% by mass or more, or 1.5% by mass or more. The liquid medium content is a value measured using an infrared heating type moisture meter.

[Average particle size]
The average particle size of the dried product is preferably 1 μm or more, or 10 μm or more, 50 μm or more, or 100 μm or more, or 200 μm or more, or 500 μm or more, and is preferably 5000 μm or less, or 4000 μm or less, or 3000 μm or less, or 2000 μm or less. The average particle size is a value measured by a dynamic image analysis type particle size distribution measuring device (CAMSIZER X2 manufactured by Microtrac).

[Loose bulk density]
In one aspect, the loose bulk density of the dried body is preferably 0.01 g / cm 3 or more, or 0.05 g / cm 3 or more, or 0.10 g / cm ³ or more, or 0.15 g / cm ³ or more, or 0.20 g / cm 3 or more, or 0.25 g / cm ³ or more, or 0.30 g / cm ³ or more, or 0.35 g / cm ³ or more, or 0.40 g / cm ^{3 or} more, or 0.45 g / cm ³ or more, or 0.50 g / cm ^{3 or} more, from the viewpoint of good fluidity of the dried body and excellent feedability to the twin ^- screw extruder and suppression of migration of the dispersant to the resin, and the dried body is easily disintegrated in the resin so that the cellulose fine fibers can be well dispersed in the resin, and the dried body is not too heavy and poor mixing of the dried body and the resin can be avoided. It is preferably 0.85 g / cm ³ or less, or 0.80 g / cm ³ or less, or 0.75 g / cm ³ or less.

[Hard bulk density]
The hard bulk density of the dried body is controlled to a range that is useful for controlling the loose bulk density and compressibility within the ranges of the present disclosure, and in one aspect is preferably 0.01 g/cm ³ or more, or 0.1 g/cm ³ or more, or 0.15 g/cm ³ or more, or 0.2 g/cm ³ or more, or 0.3 g/cm ³ or more, or 0.4 g/cm ³ or more, or 0.5 g/cm ^{3 or more, or 0.6 g/cm 3 or} more, and preferably 0.95 g/cm ³ or less, or 0.9 g/cm ³ or less, or 0.85 g/cm ³ or less.

[Compression level]
The degree of compression is calculated by the formula: degree of compression = (hardened bulk density - loose bulk density) / hardened bulk density. The loose bulk density and hardened bulk density are values measured by the method described in the [Examples] section of this disclosure.
In one embodiment, the compression degree represents the degree of bulk loss. In one embodiment, the compression degree of the dried body is preferably 1% or more, or 5% or more, or 10% or more, or 15% or more, or 20% or more, or 25% or more, in terms of the fluidity of the dried body not being too high. In addition, in terms of the fluidity of the dried body being good and excellent in feedability to a twin-screw extruder, and excellent handling (specifically, scattering, floating, or dust formation is unlikely to occur), in terms of dispersing the dried body well in a thermoplastic resin, and in terms of suppressing migration of the dispersant to the resin, the compression degree is preferably 50% or less, or 45% or less, or 40% or less, or 35% or less, or 30% or less.

The loose bulk density, hardened bulk density, and compressibility are measured using a powder tester (model: PT-X) manufactured by Hosokawa Micron Corporation. The hardened bulk density is measured by tapping 180 times.

<Mixing step>
In this step, a mixture of components including a polyacetal resin, a dried cellulose fine fiber obtained in the drying step, and an optional additional component is mixed. The mixing may be performed using a stirring means such as a rotation/revolution mixer, a planetary mixer, a homogenizer, a propeller type stirring device, a rotary stirring device, an electromagnetic stirring device, an open roll, a Banbury mixer, a single screw extruder, or a twin screw extruder. In one embodiment, the mixing is melt kneading using an extruder. As the extruder, a unidirectional rotating twin screw extruder is preferable from the viewpoint of improving the dispersibility of the cellulose fine fiber. In one embodiment, L/D obtained by dividing the cylinder length (L) of the extruder by the screw diameter (D) may be 40 or more, or 50 or more. In one embodiment, the screw rotation speed may be 50 ppm or more, 100 ppm or more, or 150 ppm or more, and 800 rpm or less, or 600 rpm or less. Each screw in the cylinder of the extruder may be optimized by combining a conveying screw having an elliptical two-wing screw shape, a kneading element called a kneading disk, or the like.

The temperature of the mixed components during mixing is preferably 170°C or higher, or 180°C or higher, or 190°C or higher from the viewpoint of high dispersion of the cellulose fine fibers, and is preferably 250°C or lower, or 240°C or lower, or 230°C or lower from the viewpoint of suppressing decomposition of the mixed components, particularly suppressing decomposition of the polyacetal resin and the cellulose fine fibers and thereby suppressing an increase in the aldehyde group concentration of these.

The pressure applied to the mixed components is preferably maintained at 30 MPa or less, or 20 MPa or less, or 10 MPa or less throughout the mixing process, from the viewpoint of suppressing the generation of low molecular weight components due to cleavage of cellulose molecules and effectively controlling the aldehyde group concentration of the cellulose microfibers. From the viewpoint of highly dispersing the cellulose microfibers, the pressure applied to the mixed components may be preferably 0.0 MPa or more, or 0.1 MPa or more, or 0.2 MPa or more, or 0.5 MPa or more in part or all of the mixing process.

<Shape of polyacetal resin composition>
The polyacetal resin composition of the present embodiment can be provided in various shapes. Specifically, resin pellets, sheets, fibers, plates, rods, etc. can be mentioned, but the resin pellet shape is preferred from the viewpoint of ease of post-processing and ease of transportation. Preferred resin pellet shapes include round, elliptical, and cylindrical shapes, and the shape may vary depending on the cutting method used during extrusion processing. For example, pellets cut by a cutting method called underwater cutting are often round, pellets cut by a cutting method called hot cutting are often round or elliptical, and pellets cut by a cutting method called strand cutting are often cylindrical. The preferred pellet diameter of round pellets is 1 mm or more and 3 mm or less. The preferred diameter of cylindrical pellets is 1 mm or more and 3 mm or less, and the preferred length is 2 mm or more and 10 mm or less. It is desirable to set the above diameter and length to be equal to or greater than the lower limit from the viewpoint of operational stability during extrusion, and it is desirable to set them to be equal to or less than the upper limit from the viewpoint of bite into the molding machine during post-processing.

<Molded body and its uses>
Another aspect of the present invention provides a molded article obtained by molding the polyacetal resin composition of the present disclosure. The polyacetal resin composition can be molded into various molded articles by a conventionally known molding method (e.g., injection molding, extrusion molding, compression molding, blow molding, vacuum molding, foam molding, rotational molding, gas injection molding, etc.), and is particularly suitable for injection molding.

In one aspect, the molding method may be a profile molding. That is, in one aspect, the molded body of this embodiment may be a profile shaped body. One aspect of the present invention also provides a method for producing a profile extrusion molded body, which includes a step of profile extruding the polyacetal resin composition of this embodiment.

A known method can be used for the contour extrusion molding. A specific example of the contour extrusion molding method is to feed a polyacetal resin composition into an extrusion molding machine, knead it while heating it inside, and extrude it from a contour extrusion die to obtain an uncooled molded product. The uncooled molded product is then continuously guided to a cooling zone and cooled to obtain a contour extrusion molded product.
Another example is a method in which melt kneading is performed to obtain a polyacetal resin composition, and then the composition is extruded using a die of the kneading machine as a die for profile extrusion to obtain an uncooled molded product, and then the uncooled molded product is continuously guided to a cooling zone and cooled to obtain a profile extrusion molded product.

The lower limit of the extrusion temperature during profile extrusion is preferably +5°C, more preferably +10°C, relative to the melting point when the thermoplastic resin in the polyacetal resin composition is a crystalline resin, or +10°C, more preferably relative to the glass transition point when the thermoplastic resin in the polyacetal resin composition is an amorphous resin. By controlling the lower limit within this range, the productivity of profile extrusion can be improved. The upper limit of the extrusion temperature during profile extrusion is preferably +100°C, more preferably +80°C, more preferably +70°C, and more preferably +60°C, relative to the melting point when the thermoplastic resin in the polyacetal resin composition is a crystalline resin, or +100°C, more preferably +80°C, more preferably +70°C, and more preferably +60°C, respectively, relative to the glass transition point when the thermoplastic resin in the polyacetal resin composition is an amorphous resin. By controlling the upper limit within this range, the deterioration of the cellulose fine fibers can be suppressed, so that the mechanical properties of the polyacetal resin composition can be maintained, and the drawdown of the resin between the profile extrusion die and the cooling zone can be suppressed, so that the dimensional accuracy of the profile extrusion molded product is good.

The cross-sectional shape of the profiled extrusion molded product is not particularly limited, but the cross-sectional shapes are preferably sheet, pipe, tube, and angular. In the case of a sheet, the sheet thickness can be 0.2 to 50 mm, and the sheet width can be 10 to 1500 mm. In the case of a pipe or tube, the thickness can be 0.1 to 30 mm, and the inner diameter can be 1 to 1000 mm. In the case of an angular shape, the angle of the corner can be 30 to 150°. The minimum radius of curvature on the valley side of the corner can be 0.1 mm.

The resulting molded articles can be used for a variety of purposes, including automobile parts, electrical and electronic parts, building materials, lifestyle, cosmetic and medical parts, rails, pipes, sashes, door frames, window frames, handrails, deck materials, fences and various building materials.

Specific examples of automotive parts include interior parts such as inner handles, fuel trunk openers, seat belt buckles, assist wraps, various switches, knobs, levers, and clips, electrical system parts such as meters and connectors, in-vehicle electrical and electronic parts such as audio equipment and car navigation equipment, parts that come into contact with metal such as window regulator carrier plates, door lock actuator parts, mirror parts, wiper motor system parts, and mechanical parts such as fuel system parts.

Electrical and electronic parts include parts or components of equipment that are made of polyacetal resin molded bodies and have many metal contacts, such as audio equipment, video equipment, office automation equipment such as telephones, copy machines, facsimiles, word processors, and computers, and parts or components of toys, specifically chassis, gears, levers, cams, pulleys, bearings, etc.

Furthermore, the material can be suitably used in a wide range of lifestyle-related, cosmetic-related, and medical-related parts, such as lighting fixtures, fittings, piping, cocks, faucets, toilet peripheral parts, and other building materials and piping parts, fasteners, stationery, lip balm and lipstick containers, cleaning devices, water purifiers, spray nozzles, spray containers, aerosol containers, general containers, and syringe needle holders.
Among these, it is more preferably usable for gears, which are used in high-temperature environments and subject to high loads.

<Characteristics of polyacetal resin composition>
[Tensile yield strength]
The tensile yield strength of the polyacetal resin composition of the present embodiment may be 50 MPa or more, or 60 MPa or more, or 65 MPa or more, or 70 MPa or more, or 73 MPa or more, or 75 MPa or more, or 80 MPa or more from the viewpoint of obtaining good durability of a molded article, for example, a sliding article, and may be 300 MPa or less, or 200 MPa or less, or 150 MPa or less from the viewpoint of ease of production of the resin composition.

[Tensile elongation at break]
The tensile elongation at break of the polyacetal resin composition of the present embodiment may be 1.0% or more, or 2.0% or more, or 3.0% or more, or 4.0% or more, or 5.0% or more, or 6.0% or more from the viewpoint of obtaining good durability of a molded article, such as a sliding article, and may be 1000% or less, or 500% or less, or 300% or less, or 200% or less from the viewpoint of ease of production of the resin composition.

[Flexural modulus]
The flexural modulus of the polyacetal resin composition is preferably 3.0 GPa or more, or 4.0 GPa or more, or 4.5 GPa or more, or 5.0 GPa or more from the viewpoint of obtaining good durability of a molded article, for example, a sliding article, and may be, for example, 20 GPa or less, or 15 GPa or less, or 12 GPa or less, or 10 GPa or less, or 8 GPa or less, or 7 GPa or less from the viewpoint of ease of production of the resin composition.
The tensile yield strength, tensile elongation at break, and flexural modulus of the present disclosure are measured in accordance with ISO 527 and ISO 178 after molding a multipurpose test piece conforming to ISO 294-3 under conditions conforming to JIS K7364-2 at a molding temperature of 200°C.

[Rigidity at high temperatures]
The polyacetal resin composition of the present embodiment preferably has a feature of high high-temperature rigidity in order to suppress deformation due to load when in contact with other members at high temperatures (for example, meshing of gears). Specifically, the storage modulus of the polyacetal resin composition at 120°C is preferably 1000 MPa or more, or 1200 MPa or more, or 1300 MPa or more, or 1400 MPa or more, or 1500 MPa or more, or 1700 MPa or more, from the viewpoint of suppressing deformation when in contact with other members. There is no particular upper limit, but it is preferably 3000 MPa or less from the viewpoint of maintaining toughness.

In addition, in this embodiment, it is desirable that the polyacetal resin composition has a component composition (i.e., the type and amount of the components of the polyacetal resin composition) such that the ratio of the storage modulus at 120 ° C to the storage modulus at 23 ° C when 10% by mass of cellulose fine fibers is blended is 0.4 or more. This index is an index of the dispersibility of the cellulose fine fibers in the polyacetal resin composition, the 3D printing modeling material, or the modeled object. The higher the dispersibility, the larger the above ratio tends to be. For example, when no cellulose fine fibers are included, the ratio of the storage modulus at 120 ° C to the storage modulus at 23 ° C is less than 0.3. Also, when cellulose fibers with an average fiber diameter of 1000 nm or more are blended, the above ratio is less than 0.4. From the viewpoint of increasing high-temperature rigidity with a smaller amount of cellulose fine fibers, the ratio of the storage modulus at 120 ° C to the storage modulus at 23 ° C is preferably 0.4 or more, or 0.45 or more, or 0.5 or more. There is no particular upper limit, but from the viewpoint of processability, it is preferably 1.5 or less.

The storage modulus is the storage modulus measured using an ISO multipurpose test piece 10 mm wide and 4 mm thick with a solid viscoelasticity measuring device under the following conditions: temperature range 0°C to 150°C (heating rate: 2°C/min), tensile mode, vibration frequency 10 Hz, static load strain 0.5%, and dynamic load strain 0.3%. The temperatures of 23°C and 120°C are calculated by interpolating the measured temperatures before and after them.

[Formaldehyde emission amount]
The polyacetal resin composition of the present embodiment has a lower formaldehyde emission amount, and from the viewpoint of ease of production, it is preferably 0.001 μmol/g or more, or 0.01 μmol/g or more, or 0.05 μmol/g or more, or 0.1 μmol/g or more, and in one embodiment, from the viewpoint of preserving the working environment during molding and reducing health hazards to users when using the molded product, it is preferably 5 μmol/g or less, or 4 μmol/g or less, or 3.5 μmol/g or less, or 3 μmol/g or less. The formaldehyde emission amount is calculated by the method described above.

[Gear Duration]
The polyacetal resin composition of the present embodiment is preferably highly durable for long-term use, for example, when it is assumed to be used as a sliding member. Specifically, in a gear durability test for evaluating the time until a gear molded from the polyacetal resin composition breaks, the gear durability time is preferably 100 hours or more, or 120 hours or more, or 140 hours or more, or 150 hours or more, or 160 hours or more, or 170 hours or more. There is no particular upper limit, but from the viewpoint of ease of production, it is preferably 1000 hours or less, or 500 hours or less. The gear durability time is measured using the method described in the examples.

[Relationship between aldehyde group concentration A of cellulose fine fiber per unit area and ethylene ratio R of polyacetal resin]
In one aspect of the polyacetal resin composition of this embodiment, it is preferable that the aldehyde group concentration A of the cellulose fine fibers per unit area (μmol/ ^m2 ) and the ethylene ratio R of the polyacetal resin (ratio of the number of repeating oxyethylene units m to the number of repeating oxymethylene units n (R=m/n)) satisfy the following relationship: The aldehyde group concentration A of the cellulose fine fibers per unit area is the value obtained by dividing the aldehyde group concentration (μmol/g) of the cellulose fine fibers by the specific surface area ( ^m2 /g) of the cellulose fine fibers.
10 ^((R-5)/3) ≦ A ≦ 10 ^((R+3)/10)

When the above formula is satisfied, the mechanical properties are improved by the bond between the aldehyde groups on the surface of the cellulose fine fibers and the polyacetal resin, and the decomposition of the polyacetal resin by the aldehyde groups is suppressed, so that the polyacetal resin composition has good mechanical properties (for example, rigidity and toughness). The reason for this relationship is presumed to be as follows. In the polyacetal resin, the oxymethylene chain is relatively unstable, and the oxyethylene chain is stable. The higher the oxymethylene chain ratio, the easier it is to decompose as a polyacetal resin, but if the amount of aldehyde groups is large here, the decomposition of the polyacetal resin accelerates, and the mechanical properties tend to deteriorate. On the other hand, if the ratio of oxyethylene chains increases, the polyacetal resin becomes less likely to decompose, but if the amount of aldehyde groups is small here, the interface strengthening by the bond between the cellulose fine fibers and the polyacetal resin is difficult to occur, and the mechanical properties tend to be difficult to improve.
More preferably, 10 ^((R-4)/3) ≦A≦10 ^((R/10) , or 10 ^((R-3)/3) ≦A≦10 ^((R-1)/10) .

[Relationship between aldehyde group concentration A and halogen content H of cellulose fine fiber per unit area]
In one aspect of the polyacetal resin composition of the present embodiment, it is preferable that the aldehyde group concentration A (μmol/m ² ) per unit area of the cellulose fine fibers and the halogen content H (ppm by mass) of the cellulose fine fibers satisfy the following relationship.
50≦H/A≦1000

When the above formula is satisfied, the polyacetal resin composition has good mechanical properties (e.g., gear durability) due to the high molecular weight of the polyacetal resin and the reinforcement of the interface between the cellulose fine fiber and the polyacetal resin. In particular, in applications such as gears that require long-term durability, it is possible to suppress the low molecular weight of the matrix resin during long-term use and the interfacial peeling between the filler and the matrix resin. The reason why such a relationship is established is presumed to be as follows. The aldehyde group is the starting point for decomposing the polyacetal resin and promotes the low molecular weight, while it also contributes to the interfacial reinforcement of the resin composition by bonding the cellulose fine fiber and the polyacetal resin. On the other hand, the halogen compound contained in the cellulose fine fiber plays a role as a polymerization catalyst for the polyacetal resin. Therefore, when the halogen content H is significantly larger than the aldehyde group concentration A and H/A exceeds 1000, the polyacetal resin has a high molecular weight but the interface is not reinforced and the long-term physical properties tend to be poor. On the other hand, when the halogen content H is significantly smaller than the aldehyde group concentration A and falls below 50, the interface is easily reinforced, but the molecular weight of the polyacetal resin becomes significantly low and the long-term physical properties tend to be poor.
The value of H/A is preferably 50 or more, or 60 or more, or 70 or more, and is preferably 1000 or less, or 500 or less, or 300 or less.

<3D printing materials and objects>
<3D printing modeling material and its manufacturing method>
One aspect of the present invention provides a 3D printing modeling material composed of the polyacetal resin composition of the present embodiment. In one aspect, the 3D printing modeling material may have a desired form such as a filament or powder, and is preferably in the form of a filament or powder. A known method can be used to mold the polyacetal resin composition into a 3D printing modeling material of a desired form. For example, the filament may be a monofilament or a multifilament, but a monofilament is preferred from the viewpoint of ease of molding.

The diameter of the filamentary modeling material is preferably 0.5 to 5.0 mm, more preferably 1.0 to 3.5 mm, and most preferably 1.5 to 3.0 mm. The length of the filamentary modeling material is preferably more than 1 m, more preferably more than 10 m, more preferably more than 100 m, and most preferably more than 300 m. By controlling the shape of the filamentary modeling material within this range, it becomes possible to select a wide range of applicable 3D printers, and it becomes possible to appropriately design the modeling time, size, and sophistication of the modeled object. In one embodiment, the length of the filamentary modeling material may be 20,000 m or less.

In one embodiment, the filament-shaped modeling material can be produced by heating and melting the polyacetal resin composition, passing it through a fine hole such as a nozzle, cooling it, and winding it up. The diameter of the fine hole can be appropriately selected according to the diameter of the filament and the winding speed, but from the viewpoint of production efficiency and the frequency of occurrence of thread breakage defects, it is preferably 0.5 to 10.0 mm, more preferably 0.8 to 5.0 mm, and most preferably 1.0 to 3.0 mm. As a cooling method, a known method such as air cooling or water cooling can be appropriately selected, but air cooling is preferred from the viewpoint of preventing water absorption due to the hydrophilicity of the cellulose fine fibers. From the viewpoint of production efficiency and the frequency of occurrence of thread breakage defects, the winding speed of the filament is preferably 0.1 to 10 m/sec, more preferably 0.15 to 5 m/sec, and most preferably 0.2 to 1 m/sec. The manufacturing device for the filament-shaped modeling material and the manufacturing device for the polyacetal resin composition may be the same or different.

The particle size, particle shape, and aspect ratio of the powdered modeling material can be appropriately selected depending on the 3D printer to be used. In one embodiment, the particle size is preferably 1 to 10,000 μm, more preferably 10 to 500 μm, and most preferably 30 to 200 μm, from the viewpoints of handling as a modeling material and surface smoothness of the modeled object. The particle shape may be spherical or irregular, but irregular shape is preferable from the viewpoint of suppressing voids during modeling. The aspect ratio is preferably 1.001 to 3.0, preferably 1.01 to 2.0, and most preferably 1.1 to 1.8, from the viewpoint of suppressing voids by reducing interparticle gaps.

In one embodiment, the powdered modeling material can be produced by pulverizing or reprecipitating the polyacetal resin composition. The method for pulverizing the polyacetal resin composition is not particularly limited, and may be wet pulverization, dry pulverization, low-temperature pulverization, freeze pulverization, heat pulverization, or the like. A grinding medium may be used for the purpose of controlling the shape of the powdered modeling material.

<Model and its manufacturing method>
One aspect of the present invention provides a modeled object produced by using the 3D printing material of the present embodiment with a 3D printer. Another aspect of the present invention provides a method for producing a modeled object, including a step of using the 3D printing material of the present embodiment with a 3D printer. Modeling methods for 3D printers include fused deposition modeling, stereolithography, material injection, powder bonding, powder bed fusion, and the like. When a filamentary modeling material is used, the fused deposition modeling is preferred, and when a powdered modeling material is used, the powder bonding and powder bed fusion are preferred.

<Uses of 3D printing materials and objects>
The shaped object may be directly applied to various applications, or may be molded into a desired shape alone or together with other components to produce a desired molded body. The method of combining the components and the molding method are not particularly limited and may be selected according to the desired molded body. The molding method may be, but is not limited to, a cutting molding method, a foam molding method, or the like. The shaped object or molded body is useful as a substitute for steel plates, fiber-reinforced plastics (e.g., carbon fiber reinforced plastics, glass fiber reinforced plastics, etc.), resin composites containing inorganic fillers, etc. Suitable applications of the 3D printing molding material, shaped object, or molded body include industrial machine parts, general machine parts, automobiles, railways, vehicles, ships, and aerospace-related parts, electronic and electrical parts, building and civil engineering materials, daily necessities, sports and leisure goods, wind power generation housing parts, containers and packaging parts, etc.

<<Characteristics of polyacetal resin composition, 3D printing material, and modeled object>>
In one embodiment, the polyacetal resin composition, the 3D printing modeling material, and the modeled object can have the following characteristics.

[Tensile yield strength]
In one embodiment, the tensile yield strength of the polyacetal resin composition, 3D printing modeling material, or modeled object may be 20 MPa or more, or 50 MPa or more, or 60 MPa or more, or 65 MPa or more, or 70 MPa or more, or 73 MPa or more, or 75 MPa or more, or 80 MPa or more, and may be 300 MPa or less, or 200 MPa or less, or 150 MPa or less.

[Tensile elongation at break]
In one embodiment, the tensile elongation at break of the polyacetal resin composition, the 3D printing modeling material, or the modeled object may be 2.0% or more, or 3.0% or more, or 4.0% or more, or 5.0% or more, or 6.0% or more, and may be 1000% or less, or 500% or less, or 300% or less, or 200% or less.

[Flexural modulus]
In one embodiment, the flexural modulus of the polyacetal resin composition, 3D printing modeling material, or modeled object may be 2.0 GPa or more, or 2.5 GPa or more, or 3.0 GPa or more, or 3.5 GPa or more, or 3.7 GPa or more, or 3.9 GPa or more, and may be 20.0 GPa or less, or 10.0 GPa or less, or 8.0 GPa or less.

[Weight loss rate at 250°C (T250°C)]
The 250°C weight loss rate ( _T250°C ) of the polyacetal resin composition, the 3D printing modeling material, or the modeled object is preferably 1.5% or less, or 1.4% or less, or 1.3% or less, from the viewpoint of avoiding thermal deterioration during molding and improving the mechanical strength of the modeled object. The 250°C weight loss rate is preferably low, but from the viewpoint of ease of production of the polyacetal resin composition, the 3D printing modeling material, or the modeled object, in one embodiment, it may be 0.01% or more, or 0.1% or more, or 0.3% or more. The 250°C weight loss rate ( _T250°C ) of the polyacetal resin composition, the 3D printing modeling material, or the modeled object is the weight loss rate when a sample of the polyacetal resin composition, the 3D printing modeling material, or the modeled object is held at 250°C under nitrogen flow for 2 hours in TG analysis. The sample is heated from room temperature to 150° C. at a rate of 10° C./min in a nitrogen flow of 100 ml/min, held at 150° C. for 1 hour, then heated from 150° C. to 250° C. at a rate of 10° C./min, and held at 250° C. for 2 hours. The weight W0 at the time when 250° C. is reached is taken as the starting point, and the weight W1 after holding at 250° C. for 2 hours is calculated using the following formula.
Weight change rate at 250°C (%): (W1-W0)/W0 x 100

[Surface roughness]
The polyacetal resin composition, 3D printing material, or shaped object of the present embodiment has low surface roughness, and thus has excellent decorative properties and appearance. The arithmetic mean surface roughness Ra of the polyacetal resin composition, 3D printing material, or shaped object is preferably 0.5 μm or less, or 0.4 μm or less, or 0.3 μm or less. In one aspect, the arithmetic mean surface roughness Ra may be 0.001 μm or more, or 0.01 μm or more, or 0.1 μm or more, from the viewpoint of ease of production of the polyacetal resin composition, 3D printing material, or shaped object.

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

Evaluation method
<Cellulose fiber raw material and cellulose fine fibers>
[Aldehyde group concentration and carboxyl concentration of cellulose fine fibers]
60 ml of cellulose fine fiber slurry (solid content: 0.5% by mass) was prepared, and the pH was adjusted to about 2.5 with 0.1 M aqueous hydrochloric acid, and then 0.05 M aqueous sodium hydroxide was added dropwise to measure the electrical conductivity. The measurement was continued until the pH reached about 11. The functional group amount 1 (carboxy group concentration) was determined using the following formula from the amount (V) of aqueous sodium hydroxide consumed in the neutralization stage of the weak acid, where the change in electrical conductivity is gradual.
Amount of functional group (mmol/g)=V (ml)×0.05/mass of solid content of cellulose fine fiber (g)
Next, the cellulose fine fiber slurry was further oxidized at room temperature for 48 hours in a 2% by mass aqueous solution of sodium chlorite adjusted to pH 4.5 with acetic acid, and the functional group amount 2 was measured again by the above method. The amount of functional groups added by this oxidation (=functional group amount 2-functional group amount 1) was calculated and used as the aldehyde group concentration.
The same method was also used to measure the various pulps used as cellulose fiber raw materials.

[Preparation of porous sheet]
A porous sheet of cellulose fine fibers was prepared to carry out various evaluations described later. First, a concentrated cake was prepared by concentrating cellulose fine fibers (solid content rate of 1% by mass) to a solid content rate of 10% by mass using a Buchner funnel. Next, the concentrated cake was added to tert-butanol, and further dispersed in a mixer or the like until no aggregates were present. The concentration was adjusted to 0.5% by mass per 0.5 g of cellulose fine fiber solid content. 100 g of the obtained tert-butanol dispersion was filtered on filter paper. The filtrate was not peeled off from the filter paper, but was sandwiched together with the filter paper between two sheets of larger filter paper, and the edges of the larger filter paper were pressed down with a weight and dried for 5 minutes in an oven at 150 ° C. Thereafter, the filter paper was peeled off to obtain a porous sheet with little distortion. The sheet with an air resistance of 100 sec/100 ml or less per 10 g/ ^m2 sheet basis weight was used as a porous sheet and was used as a measurement sample.
After measuring the basis weight W (g/ ^m2 ) of the sample left to stand for one day in an environment of 23°C and 50% RH, the air resistance R (sec/100 ml) was measured using an Oken type air resistance tester (manufactured by Asahi Seiko Co., Ltd., model EG01). At this time, the value per basis weight of 10 g/ ^m2 was calculated according to the following formula.
Air resistance per unit area of 10 g/ ^m2 (sec/100 ml) = R/W x 10

[Number average fiber diameter D and L/D of cellulose fine fibers]
The concentrated cake was diluted to 0.01% by mass with tert-butanol, dispersed using a high-shear homogenizer (manufactured by IKA, product name "Ultra Turrax T18") under processing conditions: rotation speed 15,000 rpm x 3 minutes, cast onto an osmium-deposited silicon substrate, air-dried, and measured with a high-resolution scanning electron microscope (manufactured by Hitachi High-Technologies Corporation, Regulus 8220). The measurement was performed by adjusting the magnification so that at least 100 cellulose fibers were observed, and the minor diameter (number average fiber diameter D) of 100 randomly selected cellulose fibers was measured, and the arithmetic average of the 100 cellulose fibers was calculated.

[Degree of acetyl substitution of hydrophobized cellulose fine fibers DS]
The infrared spectrum of the porous sheet at five points was measured by ATR-IR using a Fourier transform infrared spectrophotometer (FT/IR-6200 manufactured by JASCO Corp.) The infrared spectrum measurement was carried out under the following conditions.
Number of times: 64
Wave number resolution: ⁴ cm
Measurement wave number range: 4000 to 600 cm ^-1 ,
ATR crystal: Diamond,
Incident angle: 45°
From the obtained IR spectrum, the IR index was calculated according to the following formula:
IR index = H1730/H1030
In the formula, H1730 and H1030 are the absorbances at 1730 cm ^-1 and 1030 cm ^-1 (absorption bands of C-O stretching vibration of the cellulose backbone chain). However, the lines connecting 1900 cm ^-1 and 1500 cm ^-1 and the line connecting 800 cm ^-1 and 1500 cm ^-1 are taken as baselines, and the absorbances are calculated based on these baselines as 0 absorbance.
The average degree of substitution at each measurement site was calculated from the IR index according to the following formula, and the average value was taken as DS.
DS = 4.13 x IR index

[Weight average molecular weight (Mw), number average molecular weight (Mn) and Mw/Mn ratio]
0.88 g of the porous sheet was weighed, cut into small pieces with scissors, lightly stirred, and then 20 mL of pure water was added and left for one day. Next, water and solids were separated by centrifugation. Then, 20 mL of acetone was added, lightly stirred, and left for one day. Next, acetone and solids were separated by centrifugation. Then, 20 mL of N,N-dimethylacetamide was added, lightly stirred, and left for one day. N,N-dimethylacetamide and solids were separated again by centrifugation, and then 20 mL of N,N-dimethylacetamide was added, lightly stirred, and left for one day. N,N-dimethylacetamide and solids were separated by centrifugation, and 19.2 g of N,N-dimethylacetamide solution prepared so that lithium chloride was 8 mass percent was added to the solids, and the mixture was stirred with a stirrer, and it was confirmed that it was dissolved by visual observation. The solution in which cellulose was dissolved was filtered through a 0.45 μm filter, and the filtrate was used as a sample for gel permeation chromatography. The equipment and measurement conditions used are as follows.

Equipment: Tosoh HLC-8120
Column: TSKgel SuperAWM-H (6.0 mm ID x 15 cm) x 2 Detector: RI detector Eluent: N,N-dimethylacetamide (lithium chloride 0.2%)
Flow rate: 0.6 mL/min. Calibration curve: Pullulan equivalent

[Alkali soluble content]
The alkali-soluble content was determined by subtracting the α-cellulose content from the holocellulose content (Wise method) according to the method described in the non-patent literature (Wood Science Experiment Manual, edited by the Japan Wood Research Society, pp. 92-97, 2000) for cellulose fine fibers. The alkali-soluble content was calculated three times for each sample, and the number average was taken as the alkali-soluble content of the cellulose fine fibers.
The same method was also used to measure the various pulps used as cellulose fiber raw materials.

[Specific surface area of cellulose fine fibers]
The specific surface area of the cellulose fine fibers was measured using a specific surface area/pore distribution measuring device (Nova-4200e, manufactured by Quantachrome Instruments) by drying approximately 0.2 g of a porous sheet sample under vacuum at 105°C for 5 hours, measuring the amount of nitrogen gas adsorption at the boiling point of liquid nitrogen at five points in the range of relative vapor pressure (P/P0) of 0.05 or more and 0.2 or less (multipoint method), and then calculating the BET specific surface area ( ^m2 /g) using the device program.

[Thermal decomposition onset temperature of cellulose fine fibers (T _D )]
The _TD of the cellulose fine fibers was evaluated for the porous sheet by the following measurement method.
Apparatus: Thermo plus EVO2, manufactured by Rigaku Corporation
Sample: A circular sample was cut out from the porous sheet and placed in an aluminum sample pan in a pile of 10 mg.
Sample amount: 10 mg
Measurement conditions: In a nitrogen flow of 100 ml/min, the temperature was increased from room temperature to 150° C. at a rate of 10° C./min, and after holding at 150° C. for 1 hour, the temperature was increased to 450° C. at a rate of 10° C./min.
_TD calculation method: Calculated from a graph with temperature on the horizontal axis and weight remaining rate % on the vertical axis. Starting from the weight (weight loss 0 wt%) of the porous sheet at 150°C (state where moisture is almost completely removed), the temperature was further increased to obtain a straight line passing through the temperature at 1 wt% weight loss and the temperature at 2 wt% weight loss. The temperature at the point where this straight line intersects with the horizontal line (baseline) passing through the starting point of 0 wt% weight loss was determined as the thermal decomposition onset temperature ( _TD ).

[Halogen content H in cellulose fine fibers]
The air-dried porous sheet of cellulose fine fibers was immersed in pure water at 25° C. with a solid content of 2% by mass in a glass beaker with a total volume of 200 mL, stirred for 1 hour with a 3-1 motor (HEIDON BL-600 type, SUS propeller blade, 100 rpm), and then allowed to stand for 48 hours at 25° C. Next, the mixture was filtered under reduced pressure using a Teflon (registered trademark) membrane filter (1 μm mesh size) to prepare a sheet with a basis weight of 10 g/m ² , which was then filtered and dried in a ventilated oven at 70° C. until the moisture content was 10% by mass or less, to obtain a cellulose sheet.

Next, 50 mg of the cellulose sheet was placed in a quartz sample boat, set in an electric furnace (manufactured by Mitsubishi Chemical Analytical Co., Ltd.), and burned at 1000°C. The gas generated by the combustion was cooled to room temperature through a cooling section, and was bubbled through a fluororesin tube into an absorption liquid (the absorption liquid was prepared by dissolving 10 mg/L of tartrate ions, 600 mg/L of hydrogen peroxide, 2.7 mmol/L of sodium carbonate, and 0.3 mmol/L of sodium bicarbonate in ion-exchanged water). This absorption liquid was passed through a fluororesin tube and the halogen was quantified using an ion chromatograph (INTEGRION CT model manufactured by THERMOFISHER). At this time, the moisture content of the cellulose sheet measured by the loss on drying method described later was subtracted from the weight of the cellulose sheet to determine the dry mass of the cellulose sheet. Finally, the value (ppm by mass) converted to the dry mass of the cellulose sheet (i.e., the state without water) was determined as the content of halogen bonded to the cellulose of this embodiment.

(Loss on drying method)
2.00 g of the cellulose sheet was placed in a glass weighing bottle, dried at 60° C. for 15 hours and then at 105° C. for 2 hours, weighed to a constant weight in a desiccator, and the moisture content was calculated using the following formula.
Moisture content (mass%)=(sample weight before drying−sample weight after drying)/(sample weight before drying)×100
The same method was also used to measure the various pulps used as cellulose fiber raw materials.

<Polyacetal resin>
[Melt flow rate (MFR)
Measurement was performed in accordance with ISO 1133 (condition D, load 2.16 kg, cylinder temperature 190° C.).

[Formaldehyde emission amount]
The amount of formaldehyde released was measured by the method described in the German Automotive Industry Association standard VDA275. Specifically, first, a polyacetal resin test piece (length 100 mm x width 40 mm x thickness 3 mm) was molded using an injection molding machine under conditions conforming to JIS K7364-2. The molding temperature was set to 200°C. Next, the polyacetal resin test piece was suspended in a polyethylene container containing 50 mL of distilled water so as not to touch the distilled water, and sealed, and formaldehyde was extracted into the distilled water while heating at 60°C for 3 hours, and then cooled to room temperature. After cooling, 5 mL of 0.4 mass% aqueous solution of acetylacetone and 5 mL of 20 mass% aqueous solution of ammonium acetate were added to 5 mL of distilled water that had absorbed formaldehyde to prepare a mixed liquid, which was heated at 40°C for 15 minutes to cause a reaction between formaldehyde and acetylacetone. After the mixture was cooled to room temperature, the amount of formaldehyde in the distilled water was quantified using a UV spectrophotometer from the absorption peak at 412 nm. The amount of formaldehyde released from the polyacetal resin (μmol/g) was calculated using the following formula. In general, the amount of formaldehyde released is expressed in μg/g in the VDA275 test, but in this disclosure, μmol/g divided by the molecular weight of formaldehyde (30.031) was used.
Amount of formaldehyde released from polyacetal resin (μmol/g)={amount of formaldehyde in distilled water (mg)/molecular weight of formaldehyde (30.031)}/mass of polyacetal resin molded product used in measurement (g)

<Resin Composition>
[Formaldehyde emission amount]
The polyacetal resin was measured in the same manner as described above.

[Tensile properties]
Multipurpose test pieces conforming to ISO 294-3 were molded under conditions conforming to JIS K7364-2 using an injection molding machine. The molding temperature was set to 200° C. Tensile tests were carried out on the molded test pieces conforming to ISO 527 to measure the tensile stress at break and the tensile strain at break.

[Storage modulus]
Using an injection molding machine, a multipurpose test piece conforming to ISO294-3 was molded under conditions conforming to JIS K7364-2. The storage modulus was measured under the conditions of tensile mode, measurement temperature range -100 ° C to 150 ° C, heating rate: 2 ° C / min, vibration frequency 10 Hz, static load strain 0.5%, and dynamic load strain 0.3%. The storage modulus at 23 ° C is E' (23 ° C), and the storage modulus at 120 ° C is E' (120 ° C), and are listed in Tables 2 to 4, respectively. In addition, the ratio of the storage modulus at 120 ° C to the storage modulus at 23 ° C is listed in the table as RATIO (120 ° C / 23 ° C).

[Gear durability test]
Using an injection molding machine manufactured by FANUC LTD. (product name "α50i-A injection molding machine"), the resin composition was injection molded under the following injection conditions: cylinder temperature 200°C, mold temperature 80°C, maximum injection pressure 120MPa, injection time 10 seconds, and cooling time 60 seconds, to obtain a worm wheel gear having a module of 3.0, 50 teeth, tooth thickness 5mm, and tooth width 15mm. Next, the worm and the resin worm wheel gear were combined and installed in a gear durability tester manufactured by Toshiba Machine Co., Ltd. The driving side was the worm wheel gear, and the driven side was the worm. In addition, grease (Multemp CPL manufactured by Kyodo Yushi Co., Ltd.) was applied to the meshing portion, and the grease was applied to the entire worm and worm wheel gear by rotating it by hand. Next, the driving side gear was rotated under the following conditions, and the time (durability time) until the gear broke was measured.
Durability test: temperature 23°C, humidity 50%, torque 25N/m, rotation speed 30rpm
After each rotation in the forward and backward directions, a 10-second interval was allowed before a rotation in the opposite direction was performed.

Grease: Multemp CPL
Base oil (ester-based synthetic oil) 60-70% by mass
Thickener (urea derivative) 10-20% by weight
Extreme pressure agent (polytetrafluoroethylene) 15 to 25% by mass
Others (antioxidants) 5% by weight or less

Materials used:
<Production of Cellulose Fine Fibers (CNF)>
[CNF Production Example 1] (Production of Cellulose Fine Fibers CNF-A)
(Pretreatment by grinding)
Cotton linter pulp (CLP) bales (aldehyde group concentration 0.3 μmol/g, alkali soluble content 2.0 mass%, halogen content H 60 mass ppm) obtained from Japan Pulp and Paper Co., Ltd. were shredded into 5 mm squares using a shredder.

(Beating)
The ground material was immersed in water to a solid content of 1.0% by mass, and dispersed using a lab pulper (manufactured by Aikawa Iron Works, Ltd.) to obtain a slurry of pretreated cellulose fiber raw material. The slurry was defibrated using a single disc refiner (manufactured by Aikawa Iron Works, SDR14 type lab refiner, pressurized DISK type). This disc refiner has two tanks (tank A and tank B) connected by piping through a device. First, the slurry was fed from tank A into which the slurry was charged, and sent to tank B via the disc refiner and stored therein. At the stage where the processing of the slurry in tank A was completed, the slurry was continuously sent from tank B to tank A via the disc refiner and stored therein. The number of times the slurry passed through the disc refiner (number of passes) was controlled and processing was performed. The blade gap adjustment mechanism of the disc refiner is provided with a ball screw type jack and a reducer, and strict blade gap adjustment can be performed with micrometer accuracy. In addition, the deviation of the blade distance during the beating process after the target blade distance was reached was 0.005 mm or less as measured by a displacement sensor. As the blade of the disc refiner, a blade with a blade width of 4.0 mm and a blade groove ratio of 0.89 was used in the first stage, and 30 passes were made with a blade distance of 0.25 mm, and then a blade with a blade width of 0.8 mm and a blade groove ratio of 0.53 was used in the second stage, and 30 passes were made with a blade distance of 0.30 mm. The slurry temperature during the disc refiner treatment was adjusted to 5° C. using a heat exchanger.

(Defibrilization)
The obtained slurry was subjected to 10 passes at 80 MPa using a high-pressure homogenizer (NS3015H, manufactured by Niro Soavi). The high-pressure homogenizer treatment was also performed using two tanks in the same manner as the above-mentioned disc refiner treatment, and the number of passes was controlled to produce cellulose fine fibers (CNF-A). The production conditions and properties of the cellulose fine fibers are shown in Table 1.

[CNF Production Example 2] (Production of Cellulose Fine Fibers CNF-B)
Cellulose fine fibers (CNF-B) were produced in the same manner as in CNF Production Example 1, except that the slurry temperature was adjusted to 50°C.

[CNF Production Example 3] (Production of cellulose fine fibers CNF-C)
Cellulose fine fibers (CNF-C) were produced in the same manner as in CNF Production Example 1, except that the slurry temperature was adjusted to 80°C.

[CNF Production Example 4] (Production of cellulose fine fibers CNF-D)
Cellulose fine fibers (CNF-D) were produced in the same manner as in CNF Production Example 2, except that the pulp was changed to conifer-derived bleached kraft pulp (NBKP) bale (aldehyde group concentration 20 μmol/g, alkali-soluble content 8.0 mass%, halogen content H 100 mass ppm) NBKP obtained from Japan Pulp and Paper Co., Ltd.

[CNF Production Example 5] (Production of cellulose fine fibers CNF-E)
Cellulose fine fibers (CNF-E) were produced in the same manner as in CNF Production Example 4, except that the slurry temperature was adjusted to 85°C.

[CNF Production Example 6] (Production of cellulose fine fibers CNF-F)
Cellulose fine fibers (CNF-F) were produced in the same manner as in CNF Production Example 4, except that the number of passes in the first and second stages of the disc refiner treatment was adjusted to 10, respectively. By reducing the number of passes, the number average fiber diameter of the cellulose fine fibers increased, while the aldehyde group concentration decreased compared to CNF Production Example 4.

[CNF Production Example 7] (Production of cellulose fine fibers CNF-G)
Cellulose fine fibers (CNF-G) were produced in the same manner as in CNF Production Example 4, except that bleached kraft pulp, which will be described later, was used as the raw pulp used. The halogen content H of the bleached kraft pulp was high, and the halogen content H of the CNF was also high.

<Example of bleached kraft pulp production>
Softwood chips were dry screened, and the 2-8 mm fraction was collected to obtain groundwood pulp. The groundwood pulp was introduced into an autoclave and cooked for 90 minutes at an active alkali addition rate of 18 ((NaOH (g) + Na ₂ S (g)) / water (L)), a sulfidity of 28% (Na ₂ S (g) / total alkali (g) × 100), a liquid ratio of 4.5 (liquid / solids), an initial temperature of 90 ° C., and a cooking temperature of 155 ° C. After cooking, the pulp was diluted 10 times (by mass) with pure water and washed by repeating decantation four times. Next, the solids were dehydrated to 25 mass % with a center type dehydrator (equipped with a filter cloth with a mesh size of 200 μm) to obtain unbleached kraft pulp. The unbleached kraft pulp was adjusted by adding pure water to a pulp concentration of 10 mass %, and 5 mass % sodium hypochlorite was added and treated at 50 ° C. The sodium hypochlorite-treated pulp was diluted 10-fold (by mass) with pure water and washed by decantation four times, then dehydrated to a solid content of 25% by mass using a centrifugal dehydrator (equipped with a filter cloth with a mesh size of 200 μm), and then dried in a steam oven at 60° C. to obtain bleached kraft pulp (aldehyde group concentration 20 μmol/g, alkali soluble content 8.0% by mass, halogen content H 510 ppm by mass).

[CNF Production Example 8] (Production of cellulose fine fibers CNF-H)
Cellulose fine fibers (CNF-H) were produced in the same manner as in CNF Production Example 1, except that the slurry temperature was adjusted to 90°C.

[CNF Production Example 9] (Production of Cellulose Fine Fibers CNF-I)
Cellulose fine fibers (CNF-I) were produced in the same manner as in CNF Production Example 4, except that the slurry temperature was adjusted to 90°C.

From CNF production examples 1 to 5, 8, and 9, the higher the slurry temperature, the higher the aldehyde group concentration, and when it exceeded 90°C, it reached 50 μmol/g or more. In addition, as the slurry temperature increased, the Mw/Mn became less dispersed, the Mw became lower in molecular weight, and the alkali-soluble content increased.

[CNF Production Example 10] (Production of acetylated cellulose fine fibers CNF-J)
Cellulose fine fibers (CNF-J) were produced in the same manner as in CNF Production Example 2, except that the slurry of the pretreated cellulose fiber raw material was changed to the acetylated pulp slurry described below.

<Acetylated pulp>
The ground cotton linter pulp described in CNF Production Example 1 was dispersed in dimethyl sulfoxide (DMSO) so that the pulp was 5.8% by mass solids and potassium carbonate was 1.1% by mass, and 30 L of this slurry was charged into a reaction vessel with a total volume of 50 L and heated to 60 ° C. while stirring homogeneously. Vinyl acetate (4.4% by mass relative to the reaction solution) was added thereto, and acetylation was performed until a predetermined degree of substitution was reached. During the reaction, DS was appropriately measured, and when DS reached 1.0 or more, 3 L of water was added to terminate the reaction. This reaction solution was stirred and filtered using pure water 50 times by mass relative to the cellulose solid content in a pressure filter to thoroughly wash out the solvent, etc., to obtain a wet cake of acetylated pulp. Next, this cake was dispersed in pure water so that the solid content was 1% by mass, to produce an acetylated pulp slurry.

[CNF Production Example 11] (Production of cellulose fine fibers CNF-K)
Cellulose fine fibers (CNF-K) were produced in the same manner as in CNF Production Example 4, except that the number of passes in the first and second stages of the disc refiner treatment was adjusted to 20 times each, and the slurry temperature was set to 5° C. By reducing the number of passes and setting the slurry temperature to 5° C., the number average fiber diameter of the cellulose fine fibers increased, while the aldehyde group concentration was significantly reduced compared to CNF Production Example 4.

[CNF Production Example 12] (Production of Cellulose Fine Fibers CNF-L)
Cellulose fine fibers (CNF-L) were produced in the same manner as in CNF Production Example 2, except that the blade distance in the second stage of the disc refiner treatment was set to 0.51 mm. The wider blade distance reduced the defibration efficiency and increased the number average fiber diameter, while suppressing the increase in the aldehyde group concentration.

[CNF Production Example 13] (Production of cellulose fine fibers CNF-M)
Cellulose fine fibers (CNF-M) were produced in the same manner as in CNF Production Example 4, except that the blade distance in the second stage of the disc refiner treatment was set to 0.04 mm. After production, the discs of the disc refiner were checked and clogging was confirmed between the blades. Clogging was also confirmed in the high-pressure homogenizer treatment, and the aldehyde group concentration increased. It is estimated that an excessive load was applied to the clogged fibers, causing the aldehyde group concentration to increase to more than 50 μmol/g.

[CNF Production Example 14] (Production of cellulose fine fibers CNF-N)
Cellulose fine fibers (CNF-N) were produced in the same manner as in CNF Production Example 4, except that the cutting groove ratios in the first and second stages of the disc refiner treatment were 1.3 and 1.1, respectively. By increasing the cutting groove ratio, the number of disc blades increased and the defibration efficiency improved, while the aldehyde group concentration increased to over 50 μmol/g.

[CNF Production Example 15] (Production of cellulose fine fibers CNF-O)
Cellulose fine fibers (CNF-O) were produced in the same manner as in CNF Production Example 4, except that the cutting groove ratio in the first and second stages of the disc refiner treatment was set to 0.09, respectively. The smaller cutting groove ratio reduced the number of disk blades, worsening the defibration efficiency and increasing the number average fiber diameter to over 1000 nm, while the increase in the aldehyde group concentration was limited.

[CNF Production Example 15] (Production of cellulose fine fibers CNF-P)
Cellulose fine fibers (CNF-P) were produced in the same manner as in CNF Production Example 4, except that the groove ratio in the first and second stages of the disk refiner treatment was 0.09, and the number of passes was 300. The number of disk blades was reduced by decreasing the groove ratio, but the number of passes was increased to fine fibers with a number average fiber diameter of 48 nm. However, the aldehyde group concentration increased to over 50 μmol/g.

[CNF Production Example 16] (Production of Cellulose Fine Fibers CNF-Q)
Cellulose fine fibers (CNF-Q) were produced in the same manner as in CNF Production Example 4, except that the blade widths in the first and second stages of the disc refiner treatment were 0.51 mm and 1.1 mm, respectively. As the blade width increased, the number of disk blades decreased, the defibration efficiency deteriorated, and the number average fiber diameter increased to over 1000 nm, but the increase in the aldehyde group concentration was limited.

[CNF Production Example 17] (Production of cellulose fine fibers CNF-R)
Cellulose fine fibers (CNF-R) were produced in the same manner as in CNF Production Example 4, except that the blade widths in the first and second stages of the disk refiner treatment were 5.1 mm and 1.1 mm, respectively, and the number of passes was 300. Although the number of disk blades was reduced and the defibration efficiency deteriorated due to the increased blade width, the number average fiber diameter could be thinned to 243 nm by increasing the number of passes. However, the aldehyde group concentration increased to over 50 μmol/g.

[CNF Production Example 18] (Production of cellulose fine fibers CNF-S)
Cellulose fine fibers (CNF-S) were produced in the same manner as in CNF Production Example 4, except that the blade distance in the second stage of the disc refiner treatment was set to 1.4 mm and 0.09 mm, respectively. The number of disk blades increased by reducing the blade width, improving the defibration efficiency, while the aldehyde group concentration increased to over 50 μmol/g.

[CNF Production Example 19] (Production of TEMPO oxidized cellulose fine fibers CNF-T)
The pulverized pulp in CNF Production Example 1 equivalent to 2 parts by weight in dry weight, 0.003 parts by weight of TEMPO (2,2,6,6-tetramethyl-1-piperidine-N-oxyl), and 0.03 parts by weight of sodium bromide were dispersed in 150 parts by weight of water, and then a 13% by weight aqueous solution of sodium hypochlorite was added so that the amount of sodium hypochlorite per 1 g of pulp was 2.5 mmol, to start the reaction. During the reaction, an automatic titrator was used to drop a 0.5 M aqueous solution of sodium hydroxide to maintain the pH at 10.5. The reaction was deemed to be complete when no change in pH was observed, and the reaction product was neutralized to pH 7 with a 0.5 M aqueous solution of hydrochloric acid, filtered, and then washed with a sufficient amount of water and filtered six times to obtain TEMPO-oxidized cellulose fibers impregnated with water having a solid content of 2% by weight. Next, water was added to the TEMPO oxidation-treated cellulose fibers to prepare a 1.0 mass% mixed solution, which was then defibrated using the high-pressure homogenizer described in CNF Production Example 1 to produce TEMPO-oxidized cellulose fine fibers (CNF-T). As a result of the TEMPO oxidation, the aldehyde group concentration increased to 40 μmol/g, the carboxyl group concentration increased to 220 μmol/g, and the halogen content H increased to 320 ppm by mass.

<Polyacetal resin>
[Preparation Example A-1]
A jacketed twin-shaft paddle-type continuous polymerization reactor (Kurimoto Iron Works, Ltd., diameter 2B, L/D = 14.8) was adjusted to 80°C, and raw materials and the like were fed under the polymerization conditions (feed rate) shown below to polymerize a polyacetal copolymer. The unstable terminal groups of the obtained crude polymer were removed under the terminal stabilization conditions shown below to obtain a polyacetal copolymer in which the content of the comonomer component derived from 1,3-dioxolane was 0.5 mol % relative to the number of moles of _trioxane (( _CH2CH2 )/( _CH2 ) = 0.5).

(Polymerization conditions)
The materials were fed to the reactor at the following feed rates:
Trioxane (main monomer): 3,500 gr/hr
1,3-dioxolane (comonomer): 14.4 gr/hr
Methylal (low molecular weight acetal compound): 2.4 gr/hr
Cyclohexane (organic solvent): 6.5 g/hr
Boron trifluoride-di-n-butyl etherate (polymerization catalyst): 0.15 g/hr (the supply rate was set so that the amount of boron trifluoride was 0.2×10 ⁻⁴ mol per 1 mol of trioxane.)
The polymerization catalyst alone was fed in a line separate from the other components.

(Terminal stabilization conditions)
The crude polyacetal copolymer discharged from the polymerization reactor was immersed in an aqueous triethylamine solution (0.5% by mass), then stirred at room temperature for 1 hour, filtered with a centrifuge, dried under nitrogen for 120°C for 3 hours, and then fed to a vented twin-screw extruder (L/D=40) set at 200°C, and a 0.8% by mass aqueous triethylamine solution was added to the terminal stabilization zone so that the amount was 20 ppm by mass in terms of the mass of nitrogen, and the mixture was stabilized while being degassed under reduced pressure at 90 kPa, and pelletized with a pelletizer. The mixture was then dried at 100°C for 2 hours to obtain polyacetal resin A-1. The melt flow rate (MFR) of the obtained polyacetal resin was 8 g/10 min, and the formaldehyde emission amount was 0.03 μmol/g.

[Preparation Example A-2]
By adjusting the amount of 1,3-dioxolane added, polyacetal resin A-2 having a different ethylene ratio was obtained.
( _CH2CH2 )/( _CH2 )=1.5, MFR: 10g/10min, formaldehyde release amount: 0.04 _μmol /g

[Polyacetal homopolymer (A-3)]
Tenac 4010 manufactured by Asahi Kasei Corporation (homopolymer (CH ₂ CH ₂ )/(CH ₂ )=0, MFR: 10 g/10 min, formaldehyde release amount: 0.05 μmol/g) was used as polyacetal resin A-3.

<Aldehyde group blocking agent>
Melamine (Nissan Chemical Co., Ltd.)

<Dispersant: Polyethylene glycol>
PEG50 Mn = approx. 2,200 Number of oxyethylene repeat units = 50
PEG85 Mn = approx. 3,740 Number of oxyethylene repeat units = 85
PEG200 Mn = approx. 8,800 Number of oxyethylene repeat units = 200
PEG500 Mn = approx. 22,000 Number of oxyethylene repeat units = 500
PEG700 Mn = approx. 30,000 Number of oxyethylene repeat units = 700
PEG900 Mn = approx. 41,000 Number of oxyethylene repeat units = 900

<Hindered phenol antioxidant>
Irganox 1010 (pentaerythritol tetrakis[3-(3,5-di-t-butyl-4-hydroxyphenyl)propionate], manufactured by BASF Japan Ltd.)

[Examples 1 to 18, Comparative Examples 1 to 11]
<Production of dried cellulose fine fiber body>
The cellulose fine fiber slurry (solid content 1.0% by mass) produced above was filtered to obtain a concentrated cake (solid content 10% by mass). Cellulose fine fibers and a dispersant were added to a planetary mixer in the compositions shown in Tables 2 to 4, and dried under the conditions below to obtain a dried cellulose fine fiber body. The end point of drying was the point at which the moisture content of the dried cellulose fine fiber body became 3% by mass or less (solid content 97% by mass or more), and the moisture content was measured using an infrared heating moisture meter (MX-50 (manufactured by A&D)).
Equipment: Primix Corporation Hivismix 2P-1
Jacket temperature: 80°C
Degree of vacuum: -0.1MPa
Stirring speed: 50 rpm

<Production of Resin Composition>
The cylinder temperature of a co-rotating twin-screw extruder ZSK26MC (manufactured by Coperion) with L/D=48 and one inlet on the upstream side and one in the center of the extruder was set to 200°C, a dry blend of polyacetal resin, aldehyde group blocking agent, and hindered phenol-based antioxidant was fed at a fixed amount from a loss-in-weight feeder installed at the upstream inlet, and each of the above dried cellulose fine fibers was fed at a fixed amount so as to have the composition shown in Tables 2 to 4 from a loss-in-weight feeder installed at the central inlet of the extruder, melt-kneaded, extruded into a strand shape, and cooled and cut to obtain a pellet-shaped polyacetal resin composition. The downstream of the extruder was made capable of degassing under reduced pressure, and the air and generated gas in the extruder were removed.

The screw configuration was designed so that three RKDs were placed upstream of the central supply port of the extruder, and three RKDs and one LKD were placed in that order downstream just before the reduced pressure degassing. The screw rotation speed of the extruder was set to 150 rpm, and the supply unit was set so that the total extrusion output was 5 kg/hour. Various tests were carried out using the obtained pellets. The results are shown in Tables 2 to 4.

<Production of profile extrusion molded body>
[Example 19]
Using the resin composition pellets of Example 2, irregular extrusion molding was performed. Using a single-screw extruder with a diameter of 40 mm equipped with a die having a cross-sectional shape shown in FIG. 3 (the numerical values in the figure are in millimeters), the pellets were extruded at a molding temperature of 190° C. and a screw rotation speed of 20 rpm, and then shaped using a sizing die having the same cross section as the die in a 2 m long water tank containing cooling water at a water temperature of 25° C. to obtain an irregular extrusion molded product. This confirmed that an irregular extrusion molded product could be formed without any problems using the resin composition of this embodiment.

[Example 20]
The polyacetal resin of Example 2 was changed to a glass fiber reinforced polyacetal resin (Tenac-C GN752, manufactured by Asahi Kasei Co., Ltd.), and the amount of cellulose fine fibers in the composition was 5% by mass. Using the resin composition pellets, irregular extrusion molding was performed in the same manner as in Example 19 to obtain an irregular extrusion molded article. This confirmed that an irregular extrusion molded article could be formed without any problems using the resin composition of this embodiment.

[Example 21]
As in Example 2, the amount of carbon fiber (Toray, Torayca T300) in the composition was changed to 10 mass% and the amount of cellulose fine fiber in the composition was changed to 5 mass%, and the resin composition pellets were subjected to irregular extrusion molding in the same manner as in Example 19 to obtain an irregular extrusion molded article. This confirmed that an irregular extrusion molded article could be formed without any problems using the resin composition of this embodiment.

<Manufacturing objects by 3D printing>
[Example 22]
Using the resin composition pellets of Example 2, a 3devo filament extruder (nozzle diameter 1.7 mm) manufactured by 3D Printing Corporation was used, and the extruder was pulled under automatically controlled conditions of a nozzle temperature of 210°C, a screw rotation speed of 3.5 rpm, and a winding speed of 0.02 to 0.1 m/s under air-cooled conditions to obtain a monofilament of a filament-like modeling material.
Next, the filamentous modeling material was used to obtain a model of the same shape as the multipurpose test piece conforming to ISO294-3 using a FUNMAT HT fused deposition modeling 3D printer manufactured by Canon Inc. under the conditions of a nozzle temperature of 210°C, a platform temperature of 80°C, a layer pitch of 0.3 mm, and a modeling speed of 30 mm/sec. The modeling was possible without any problems.

From Examples 1 to 5 and Comparative Examples 1, 2, 4, 5, 7, 9, and 10, it is seen that the higher the aldehyde group concentration of the cellulose fine fibers, the lower the physical properties of the resin composition and the higher the amount of formaldehyde released. It is also seen that Comparative Examples 1, 2, 4, 5, 7, 9, and 10, in which the aldehyde group concentration exceeds 50 μmol/g, show a significant decrease in physical properties.
In Comparative Example 3, the aldehyde group concentration of the cellulose fine fibers is quite small at 0.4 μmol/g, and the formaldehyde emission amount is also small. However, it is presumed that the amount of bonding between the cellulose fine fibers and the polyacetal resin is too small, and it is understood that the physical properties of the resin composition are deteriorated.

In Comparative Examples 6 and 8, the aldehyde group concentration of the cellulose fine fibers was 50 μmol/g or less, but the number average fiber diameter was more than 1000 μm, and it is clear that the physical properties of the resin composition were significantly deteriorated.

In Comparative Example 11, the carboxyl group concentration is very high at 220 μmol/g, and the thermal decomposition onset temperature T _D is very low at 190° C., so that the physical properties of the resin composition are deteriorated and the amount of formaldehyde emitted is increased.

Comparing Examples 4 and 6, it is evident that the inclusion of an aldehyde group blocking agent in the resin composition can suppress the deterioration of physical properties.
Comparing Examples 4 and 7, the aldehyde group concentration in the cellulose fine fibers in Example 7 is low, but the physical properties of the resin composition tend to be low. In Example 7, the aldehyde group concentration A in the cellulose fine fibers per unit area is quite high, and the aldehyde groups in the cellulose fine fibers, which are thought to contribute to the decomposition of the polyacetal resin, are high density, so that even though the overall aldehyde group concentration is low, there is a tendency for the physical properties of the resin composition to deteriorate and the amount of formaldehyde emitted to increase.
Comparing Examples 4 and 8, although the aldehyde group concentrations of the cellulose fine fibers were comparable, the resin composition of Example 8 clearly showed significant yellowing, and it is presumed that the high halogen content H caused the thermal degradation of the cellulose fine fibers to progress, confirming a tendency for the physical properties of the resin composition to deteriorate.

In Examples 9 to 13 and Examples 14 to 16, the aldehyde group concentration of the cellulose fine fibers was low, and therefore the resin physical properties were generally excellent. However, the relationship between the ethylene ratio R, which is the ratio of the number of oxyethylene units to the number of oxymethylene units of the polyacetal resin, and the number of oxyethylene repeating units n of the polyethylene glycol did not satisfy the following formula: (R+0.5)/0.015≦n≦(R+10)/0.015
The resin composition satisfying the above (Examples 9 to 11 and 14) has excellent physical properties.

Compared to Example 14, the aldehyde group concentration of the cellulose fine fibers in Example 17 is sufficiently small. However, the aldehyde group concentration A of the cellulose fine fibers per unit area is too small, and although the amount of formaldehyde released is small, it is presumed that the amount of bonding between the cellulose fine fibers and the polyacetal resin is too small, and the physical properties of the resin composition tend to deteriorate.

In Examples 1, 7, and 17, the aldehyde group concentration of the cellulose fine fibers was low, and therefore the resin physical properties were generally excellent; however, the following relationship between the aldehyde group concentration A of the cellulose fine fibers per unit area and the halogen content H of the cellulose fine fibers was not satisfied, and the gear durability time tended to be shorter than in the other Examples.
50≦H/A≦1000
Example 1 has a small amount of formaldehyde emission and is excellent in various mechanical properties, but the gear durability tends to be poor. This is presumed to be because, while the polyacetal resin has a high molecular weight due to the H/A exceeding 1000 and the mechanical properties have been improved, the gear durability time, which is a long-term property, has deteriorated because the interface has not been reinforced. Example 17 has low mechanical properties due to the high cellulose fine fiber aldehyde group concentration A per unit area compared to Example 1, and it is presumed that the long-term properties have deteriorated due to the H/A exceeding 1000. Example 7 has excellent long-term properties compared to Examples 1 and 17 due to the interface reinforcement with an H/A of less than 50, but the mechanical properties have decreased due to the low molecular weight and the amount of formaldehyde emission has increased.

The composition containing polyacetal resin and cellulose fine fibers provided by one aspect of the present invention can be suitably used in a wide range of applications, particularly in high-load applications in high-temperature environments.

Claims (20)

A resin composition comprising a polyacetal resin and a cellulose fine fiber,
The aldehyde group concentration of the cellulose fine fibers is 0.5 μmol/g to 50 μmol/g,
The cellulose fine fibers have a carboxy group concentration of 200 μmol/g or less,
The resin composition, wherein the cellulose fine fibers have a number average fiber diameter of 1000 nm or less. The resin composition according to claim 1, further comprising an aldehyde group blocking agent. The resin composition according to claim 2, wherein the aldehyde group blocking agent is at least one selected from the group consisting of aminotriazine compounds, guanamine compounds, urea derivatives, hydrazide compounds, acrylamide polymers, and polyamides. The resin composition according to claim 1, wherein the weight average molecular weight of the cellulose microfibers is 100,000 or more. The resin composition according to claim 1, wherein the Mw/Mn of the cellulose fine fibers is 6.0 or less. The resin composition according to claim 1, wherein the alkali-soluble content in the cellulose fine fibers is 10% by mass or less. The resin composition according to claim 1, wherein the cellulose fine fibers have a thermal decomposition onset temperature T _D of 200° C. or higher. The resin composition according to claim 1, wherein the halogen content H of the cellulose fine fibers is 500 ppm by mass or less. The resin composition according to claim 1, wherein the cellulose fine fibers are esterified chemically modified cellulose fine fibers. The resin composition according to claim 9, wherein the esterification is acetylation. The aldehyde group concentration A per unit area of the cellulose fine fiber and the ratio (R=m/n) of the number of repeats m of the oxyethylene unit to the number of repeats n of the oxymethylene unit in the polyacetal resin satisfy the following relationship: 10 ^((R-5)/3) ≦ A ≦ 10 ^((R+3)/10)
The resin composition according to claim 1, which satisfies the above. A method for producing the resin composition according to any one of claims 1 to 11,
A defibration step of defibrating the cellulose fiber raw material in a liquid medium at a liquid temperature of 85°C or less to obtain a cellulose fine fiber slurry;
a drying step of drying the cellulose fine fiber slurry to obtain a dried cellulose fine fiber body; and a mixing step of mixing a polyacetal resin with the dried cellulose fine fiber body.
A method comprising: The method according to claim 12, wherein the cellulose fine fibers in the cellulose fine fiber slurry produced in the defibration step have an aldehyde group concentration of 0.5 μmol/g to 50 μmol/g and a carboxy group concentration of 200 μmol/g or less. A molded body obtained by molding the resin composition according to any one of claims 1 to 11. The molded article according to claim 14, which is a profile extrusion molded article. A method for producing a profile extrusion molded body, comprising:
A method comprising the step of profile extruding the resin composition according to any one of claims 1 to 11. A 3D printing modeling material comprising the resin composition according to any one of claims 1 to 11. The 3D printing modeling material according to claim 17, which has the form of a filament or powder. A modeled object produced by using a 3D printer with the 3D printing material according to claim 17. A method for manufacturing a shaped object, comprising the steps of:
A method comprising the step of modeling the 3D printing material according to claim 17 using a 3D printer.

Images