JP7850563B2 - Method for producing a concentrated cellulose microfiber dispersion, and method for producing a resin composition - Google Patents

Description

This invention relates to a method for producing a concentrated cellulose microfiber dispersion and a method for producing a resin composition.

Thermoplastic resins are lightweight and have excellent processing properties, making them widely used in various applications such as automotive components, electrical and electronic components, office equipment housings, and precision parts. However, since resins alone often have insufficient mechanical properties and dimensional stability, composite resins with various fillers are commonly used. In recent years, the use of organic fibers such as cellulose fibers as such fillers has been investigated. Cellulose is a promising filler for environmentally friendly resin compositions because it is an environmentally friendly material, has a low specific gravity, and can have an excellent effect on improving the physical properties of resin compositions. In particular, cellulose microfibers can show an excellent reinforcing effect on resin compositions even in small amounts due to their microstructure, and their use as a filler for resin compositions has been investigated in recent years. As a method for producing cellulose microfibers, a dilute dispersion with a low solid content is generally used, which involves processing it with a refiner, high-pressure homogenizer, etc. Since dilute dispersions are difficult to mix with resin as fillers in their original state, they need to be concentrated. However, cellulose microfibers are extremely prone to aggregation due to hydrogen bonding between cellulose molecules, and excessive concentration reduces their redispersibility, making uniform dispersion in the resin difficult. Therefore, various cellulose microfiber concentration techniques have been proposed to achieve good dispersion of these microfibers in the resin while simultaneously exhibiting excellent reinforcing effects.

For example, Patent Document 1 describes a method of obtaining a molded article as a mixture of cellulose microfibers and resin by adding a resin emulsion to a dispersion of cellulose microfibers, and then crushing the molded article and melt-kneading it with a main resin.

Patent document 2 describes a method for dewatering a chemically modified pulp aqueous dispersion by pressing it under processing conditions of 2 to 10 MPa.

International Publication No. 2013/137449 Japanese Patent Publication No. 2017-95813

When mixing cellulose microfibers with resin, it is necessary to remove the dispersion medium from the cellulose microfiber dispersion. However, since this dispersion is generally dilute, in industrial processes using large quantities of cellulose microfibers, the amount of dispersion medium to be removed is enormous, making batch processes extremely inefficient. Furthermore, there were problems with the solid content of the resulting concentrate varying from batch to batch, and even within the same batch, some cellulose microfibers were locally concentrated to a high solid content, resulting in a non-uniform state. Due to this variation in solid content, defects were likely to occur when used as a filler for filler-reinforced resins, making conventional methods unsuitable for mass production. Additionally, for example, the papermaking process widely used in the paper industry includes a heat drying step. The dried material obtained in this process has poor redispersibility when mixed with resin, making it difficult to exhibit its performance as a filler for filler-reinforced resins.

Patent Document 1 describes a manufacturing method in which a resin emulsion is added to a dispersion of cellulose microfibers, and papermaking is performed using a mixture of cellulose microfibers and resin to obtain a concentrated cellulose microfiber composition as an intermediate. However, depending on the properties of the resin emulsion and the coarseness of the papermaking machine, the added resin emulsion may not be 100% utilized and may be discharged in wastewater, potentially leading to increased energy consumption when disposing of it as industrial waste. Therefore, the above technology cannot be considered suitable as an industrial process from the standpoint of cost and environmental impact.

On the other hand, Patent Document 2 describes a method for dewatering a dispersion of chemically modified pulp by pressurization, but the pressurization method is difficult to implement as a continuous process. Cellulose microfiber compositions are more prone to filter clogging than pulp, and in the pressurization method, the cake layer formed in the early stages of the process is densely compressed. As a result, the above technology is prone to the problem of products with different solid content ratios being mixed within the batch.

The present invention aims to solve the above problems and provide a method for producing a concentrated cellulose microfiber dispersion, and a method for producing a resin composition using said concentrate, which allows for the production of a concentrated concentrate with low environmental impact and minimal variation in solid content, even when using a dilute cellulose microfiber dispersion.

This disclosure includes the following aspects:
[1] A method for producing a concentrated cellulose microfiber dispersion,
The method includes a concentration step of deliquing the cellulose fine fiber dispersion to obtain the concentrate,
The average fiber diameter of the cellulose microfibers in the cellulose microfiber dispersion is 50 to 1000 nm.
In the concentration step, the cellulose fine fiber dispersion is continuously deliquidated at a processing rate of 1.0 kg-DS/h or more and less than 45.0 kg-DS/h.
In the concentration step, when the solid content of the concentrate is sampled and measured 10 times, the average value of the solid content is 5% by mass or more and 60% by mass or less, and the CV value (standard deviation/mean value) of the solid content is 0.001 or more and 0.300 or less.
method.
[2] The method according to embodiment 1, wherein a cellulose fine fiber dispersion, which has been stirred at a peripheral speed of 0.01 m/sec to 6.00 m/sec, is supplied to the concentration step.
[3] The method according to embodiment 1 or 2 above, wherein the concentration step is carried out at 80°C or below.
[4] The method according to any one of embodiments 1 to 3, wherein the cellulose microfibers in the cellulose microfiber dispersion contain 70% or more of fibers with a fiber length of less than 0.1 mm, based on the number of fibers.
[5] The method according to any one of embodiments 1 to 4, wherein in the cellulose microfiber dispersion subjected to the concentration step, the content of cellulose microfibers is 75% by mass or more with respect to 100% by mass of the total content of nonvolatile components.
[6] The method according to any one of embodiments 1 to 5, wherein the cellulose microfibers in the cellulose microfiber dispersion are chemically modified with hydrophobic substituents.
[7] The method according to any one of embodiments 1 to 6, wherein the cellulose microfibers in the cellulose microfiber dispersion are chemically modified with acetyl groups.
[8] The method according to any one of embodiments 1 to 7, wherein the cellulose fine fibers subjected to the concentration step are made from cotton linters.
[9] A step of producing a concentrate of cellulose fine fiber dispersion by any of the methods described in any of embodiments 1 to 8 above,
A step of drying the aforementioned concentrate to produce a cellulose microfiber dry body,
A method for producing a dried cellulose microfiber body, including the above.
[10] A step of producing a concentrated cellulose microfiber dispersion by the method of any one of the above embodiments 1 to 8, or producing a dried cellulose microfiber by the method of the above embodiment 9,
A step of producing a resin composition by mixing a concentrate of the cellulose microfiber dispersion or the dried cellulose microfiber with a thermoplastic resin,
A method for producing a resin composition containing [the specified element].

According to one aspect of the present invention, a method for producing a concentrated cellulose microfiber dispersion and a method for producing a resin composition using the concentrated cellulose microfiber are provided, which enable the production of a concentrated cellulose microfiber dispersion with low environmental impact, even when using a dilute cellulose microfiber dispersion, and produce a concentrated cellulose microfiber dispersion with low solid content variation.

This diagram illustrates an example of the arrangement of blades and grooves in a disc refiner. This diagram illustrates the blade width, groove width, and inter-blade distance of a disc refiner. This diagram illustrates an example of the configuration of a continuous concentration apparatus.

The following describes exemplary embodiments of the present invention (hereinafter abbreviated as "Embodiments"), but the present invention is not limited to these embodiments. Unless otherwise specified, the characteristic values in this disclosure are those measured by the methods described in the "Examples" section of this disclosure or by methods that would be understood to those skilled in the art to be equivalent thereto.

≪Method for producing concentrated cellulose microfiber dispersions≫
One aspect of the present invention provides a method for producing a concentrate of a cellulose microfiber dispersion (hereinafter also simply referred to as a concentrate). In one aspect, the method includes a concentration step of deliquing the cellulose microfiber dispersion to obtain a concentrate. In one aspect, in the concentration step, the cellulose microfiber dispersion is continuously deliqued in a concentrator at a processing rate of 1.0 kg-DS/h or more and less than 45.0 kg-DS/h. In the concentration step according to one aspect, the average solid content of the concentrate is 5% by mass or more and 60% by mass or less. In one aspect, the CV value (standard deviation/mean value) of the solid content is 0.001 or more and 0.300 or less. In one aspect, the average fiber diameter of the cellulose microfibers in the cellulose microfiber dispersion is 50 to 1000 nm. In one aspect, the method may include a defibration step of beating and/or defibrating a cellulose raw material (e.g., pulp) in the dispersion to produce a cellulose microfiber dispersion.

Cellulose microfibers are materials primarily composed of cellulose naturally produced by plants, and their use is expected to provide environmentally friendly and sustainable industrial products. One example is their use as a filler to enhance the properties of resins. However, mixing with resins requires removing water from the dilute dispersion of cellulose microfibers. Furthermore, while cellulose microfibers maintain a stable dispersion in a dilute dispersion, removing the dispersion medium causes the microfibers to converge and bond strongly through hydrogen bonding, making redispersion difficult. This can lead to defects in physical properties and inconsistent quality.

The inventors have found that, in a specific manner, when a dispersion of cellulose microfibers having a predetermined average fiber diameter is concentrated to a predetermined solid content using a continuous deliquidation device, it is easy to handle, variations in solid content are suppressed, and good physical properties and uniform quality can be achieved when used as a filler for filler-reinforced resins. If the solid content of the concentrated cellulose microfiber dispersion is lower than the appropriate range, the cellulose microfibers tend to adhere to the deliquidation device, which can lead to a decrease in the yield of the concentrate and contamination of the concentrate with solid foreign matter that has solidified while adhering to the device and can no longer be redispersed. On the other hand, if the solid content of the concentrate is higher than the appropriate range, the concentration is excessive and the redispersibility of the cellulose microfibers decreases. In particular, when the concentration progresses to a state close to dryness, the variation in the solid content of the concentrate decreases, but the redispersibility decreases significantly. For example, in batch-type and batch-operated deliquidation systems, localized variations in solid content within a batch can easily occur, resulting in problems such as a decrease in the physical properties of filler-reinforced resins when the product is used as a filler, and a decrease in yield due to the removal of substandard products from the product to suppress variations in solid content between batches. On the other hand, the method of this embodiment allows for the concentration of a cellulose microfiber dispersion at a solid content ratio that maintains redispersibility, making it possible to mass-produce a concentrate with minimal variation in solid content.

The method for producing a concentrated cellulose microfiber dispersion according to this embodiment includes a concentration step, and typically includes a defibration step and a concentration step. Each step will be described below.

<Defibration process>
In this process, cellulose raw materials (e.g., pulp containing cellulose) are beaten and/or defibrated in a dilute dispersion to obtain fine cellulose fibers. As cellulose raw materials, wood pulp obtained from wood species (hardwood or softwood), non-wood pulp obtained from non-wood species (bamboo, hemp fibers, bagasse, kenaf, linter, etc.), and refined pulps of these (refined linter, etc.) can be used. As non-wood pulps, cotton-derived pulp including cotton linter pulp, hemp-derived pulp, bagasse-derived pulp, kenaf-derived pulp, bamboo-derived pulp, straw-derived pulp, etc. can be used. Cotton-derived pulp, hemp-derived pulp, bagasse-derived pulp, kenaf-derived pulp, bamboo-derived pulp, and straw-derived pulp may each be refined pulp obtained from raw materials such as cotton lint, cotton linters, hemp-based abaca (e.g., from Ecuador or the Philippines), sisal, bagasse, kenaf, bamboo, and straw through purification processes such as deligninization by pulping, bleaching processes, etc. The cellulose raw material is preferably derived from cotton linters (e.g., cotton linter-derived pulp) because it has a high degree of crystallinity and can produce cellulose fine fibers with excellent mechanical properties when used as a filler for filler-reinforced resins.

Cellulose microfibers may be chemically modified. Chemical modification may be performed on the cellulose raw material (e.g., pulp) and/or on the cellulose microfibers, but in a preferred embodiment, it is performed on the pulp. Chemical modification may involve the introduction of hydrophilic substituents or hydrophobic substituents, and can be appropriately selected depending on the application. Methods for introducing hydrophilic substituents include TEMPO oxidation, carboxymethylation, phosphate esterification, and sulfuric acid esterification. Methods for introducing hydrophobic substituents include esterification (acylation), etherification, and silylation.

When using cellulose microfibers as a filler for filler-reinforced resins, chemical modification by introducing hydrophobic substituents to the cellulose is preferred. Esterification is more preferable because it does not disrupt the type I crystalline structure of natural cellulose and has good reactivity, while acetylation is particularly preferable from the viewpoint of ease of reaction and cost. Therefore, the hydrophobic substituent is preferably one or more selected from the group consisting of acyl groups, ether groups, and silyl groups, more preferably an acyl group, and particularly preferably an acetyl group. While chemical modification, especially the introduction of hydrophobic substituents, can lower the affinity between cellulose microfibers and the dispersion medium (especially water), making the cellulose microfibers more likely to separate from the dispersion medium, the concentrated product obtained by the method of this embodiment, which has little variation in solid content, allows for a good improvement in the physical properties and quality stability of the resin composition due to chemical modification.

The esterification reaction may be carried out in a solvent in the presence of an esterifying agent. The solvent used for esterification (hereinafter also referred to as the esterification solvent) can be aprotic solvents, such as alkyl sulfoxides, alkylamides, pyrrolidones, etc., which can be used alone or in combination of two or more.

Examples of alkyl sulfoxides include _diC1-4 alkyl sulfoxides such as dimethyl sulfoxide (DMSO), methyl ethyl sulfoxide, and diethyl sulfoxide.

Examples of alkylamides include N,N- _diC1-4 alkylformamides such as N,N-dimethylformamide (DMF) and N,N-diethylformamide; and N,N-diC1-4 alkylacetamides such as N,N-dimethylacetamide (DMAc) and N,N- _{diethylacetamide} .

Examples of pyrrolidones include pyrrolidones such as 2-pyrrolidone and 3-pyrrolidone; and N- _C1-4 alkylpyrrolidones such as N-methyl-2-pyrrolidone (NMP).

From the viewpoint of obtaining good esterification efficiency, dimethyl sulfoxide (DMSO) is particularly preferred as the esterification solvent.

As esterifying agents, acid halides, acid anhydrides, and vinyl carboxylates are preferred, with vinyl carboxylates being particularly preferred from the viewpoint of esterification efficiency.

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 is 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 these, acid chlorides are particularly suitable due to their reactivity and ease of handling. Furthermore, in the reaction of acid halides, one or more alkaline compounds may be added to act as a catalyst and neutralize the acidic by-products. 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.

Any suitable acid anhydride can be used as the acid anhydride. For example,
Anhydrides of saturated aliphatic monocarboxylic acids such as acetic acid, propionic acid, (iso)butyric acid, and valeric acid; anhydrides of unsaturated aliphatic monocarboxylic acids such as (meth)acrylic acid and oleic acid;
Anhydrides of alicyclic monocarboxylic acids such as cyclohexanecarboxylic acid and tetrahydrobenzoic acid;
Anhydrides of aromatic monocarboxylic acids such as benzoic acid and 4-methylbenzoic acid;
Examples of dibasic carboxylic acid anhydrides include saturated aliphatic dicarboxylic anhydrides such as succinic anhydride and adipic acid, unsaturated aliphatic dicarboxylic anhydrides such as maleic anhydride and itaconic anhydride, alicyclic dicarboxylic anhydrides such as 1-cyclohexene-1,2-dicarboxylic anhydride, hexahydrophthalic anhydride and methyltetrahydrophthalic anhydride, and aromatic dicarboxylic anhydrides such as phthalic anhydride and naphthalic anhydride;
Examples of polybasic carboxylic acid anhydrides with three or more bases include (anhydride) polycarboxylic acids such as trimellitic anhydride and pyromellitic anhydride.

Furthermore, in the reaction of acid anhydrides, one or more acidic compounds such as sulfuric acid, hydrochloric acid, or phosphoric acid, or Lewis acids (for example, Lewis acid compounds represented as MYn, where M represents a metalloid element such as B, As, or Ge, or a base metal element such as Al, Bi, or In, or a transition metal element such as Ti, Zn, or Cu, or a lanthanide element; n is an integer corresponding to the valence of M, representing 2 or 3; and Y represents a halogen atom, OAc, _OCOCF3 , _ClO4 , _SbF6 , _PF6 , or _OSO2CF3 ( _OTf )), or alkaline compounds such as triethylamine or pyridine may be added as catalysts.

Examples of vinyl carboxylates include those with the following formula:
R-COO-CH=CH ₂
A vinyl carboxylate ester represented by the formula {wherein R is any 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, or an aryl group having 6 to 24 carbon atoms} is preferred. The vinyl carboxylate ester 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 octoate, vinyl adipate, vinyl methacrylate, vinyl crotate, vinyl pivalate, vinyl octoate, vinyl benzoate, and vinyl cinnamate. In esterification reactions with vinyl carboxylates, 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 bicarbonates, primary to tertiary amines, quaternary ammonium salts, imidazoles and their derivatives, pyridines and their derivatives, and alkoxides may be added.

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

Primary, secondary, and tertiary amines refer to primary, secondary, and tertiary amines. 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, triethylamine, and diazabicycloundecene.

Examples of imidazoles and their derivatives include 1-methylimidazole, 3-aminopropylimidazole, and carbonyldiimidazole.

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 is selected from the group consisting of compounds represented by the following formula.
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, cyclohexanecarboxylic acid, caprylic acid, capric acid, lauric acid, myristic acid, palmitic acid, stearic acid, pivalic acid, methacrylic acid, crotonic acid, pivalic acid, octic 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, particularly acetic acid, is preferred from the viewpoint of reaction efficiency.

Furthermore, in the reaction of carboxylic acids, one or more acidic compounds such as sulfuric acid, hydrochloric acid, or phosphoric acid, or Lewis acids (for example, Lewis acid compounds represented as MYn, where M represents a metalloid element such as B, As, or Ge, or a base metal element such as Al, Bi, or In, or a transition metal element such as Ti, Zn, or Cu, or a lanthanide element; n is an integer corresponding to the valence of M, representing 2 or 3; and Y represents a halogen atom, _OAc , _OCOCF3 , _ClO4 , _SbF6 , _PF6 , or _OSO2CF3 (OTf)), or alkaline compounds such as triethylamine or pyridine may be added as catalysts.

Among these esterifying agents, at least one selected from the group consisting of acetic anhydride, propionic anhydride, butyric anhydride, vinyl acetate, vinyl propionate, vinyl butyrate, and acetic acid, with acetic anhydride and vinyl acetate being particularly preferred from the viewpoint of reaction efficiency, is preferred.

The degree of substitution (DS) of chemically modified cellulose raw materials (e.g., pulp) or chemically modified cellulose microfibers, such as the degree of esterification of esterified products, is, in one embodiment, greater than 0.5, or 0.6 or greater, or 0.7 or greater, from the viewpoint of obtaining chemically modified (e.g., esterified) cellulose microfibers with excellent dispersibility in resins, heat resistance, etc., and in one embodiment, less than or equal to 2.0, or less than or equal to 1.9, or less than or equal to 1.8, from the viewpoint of obtaining chemically modified (e.g., esterified) cellulose microfibers that retain the good mechanical properties inherent to cellulose after defibration.

For example, the degree of esterification, which is the degree of substitution (DS) of an esterified product, can be calculated from the reflectivity infrared absorption spectrum of esterified cellulose raw material (e.g., pulp) or esterified cellulose fine fibers (hereinafter collectively referred to as esterified cellulose) based on the peak intensity ratio of the peak derived from the acyl group and the peak derived from the cellulose skeleton. The peak of the C=O absorption band based on the acyl group appears at 1730 ^cm⁻¹ , and the peak of the C-O absorption band based on the cellulose skeleton chain appears at 1030 ^cm⁻¹ . The DS of esterified cellulose is calculated by creating a correlation graph between the DS obtained from solid-state NMR measurement (described later) and the modification rate (IR index 1030), which is defined as the ratio of the peak intensity of the C=O absorption band based on the acyl group to the peak intensity of the C-O absorption band of the cellulose skeleton chain. The calibration curve substitution degree DS = 4.13 × IR index (1030) is calculated from the correlation graph.
This can be obtained by using [this method].

If appropriate measurement is difficult using the above-mentioned reflection-type infrared absorption spectrum, solid-state NMR may be used. The method for calculating DS by solid-state NMR involves performing ^13C solid-state NMR measurements on freeze-pulverized esterified cellulose, and calculating it using the following formula based on the ratio of the area intensity (Inf) of the signal attributed to a single carbon atom derived from the modifying group to the total area intensity (Inp) of the signals attributed to carbon atoms C1-C6 derived from the pyranose ring of cellulose that appear in the range of 50 ppm to 110 ppm.
DS=(Inf)×6/(Inp)
For example, if the modifying group is an acetyl group, you can use the 23 ppm signal assigned to _-CH3 .

The conditions used for ^13C solid-state NMR measurement are, for example, as follows:
Equipment: Bruker Biospin Avance500WB
Frequency: 125.77 MHz
Measurement method: DD/MAS method Waiting time: 75 seconds
NMR sample tube: 4 mm diameter
Total number of times: 640 (approximately 14 hours)
MAS: 14,500Hz
Chemical shift standard: Glycine (External standard: 176.03 ppm)

Known crystalline forms of cellulose raw materials or cellulose microfibers include Type I, Type II, Type III, and Type IV. Types I and II are commonly used, while Types III and IV are not widely used on an industrial scale. The crystalline form of cellulose raw materials or cellulose microfibers is preferably Type I or Type II, more preferably Type I, due to its high structural mobility, low coefficient of thermal expansion, and high tensile strength, flexural strength, and flexural elongation.

The degree of crystallinity of the cellulose raw material or cellulose microfibers may, in one embodiment, be 50% or more, 60% or more, 70% or more, 73% or more, or 75% or more, and in one embodiment, it may be 95% or less, 90% or less, or 85% or less.
The above degree of crystallinity is, in one embodiment, the degree of crystallinity of cellulose type I.

In this disclosure, the degree of crystallinity, when the cellulose is cellulose type I crystal (derived from natural cellulose), is determined by the Segal method from the diffraction pattern (2θ/deg. is 10 to 30) obtained by measuring the sample by wide-angle X-ray diffraction, using 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 a cellulose type I crystal. I(amorphous): Halo peak intensity due to amorphous material in a cellulose type I crystal, at a diffraction angle 4.5° lower than the 200 plane (2θ = 18.0°).

Furthermore, if the cellulose is a type II cellulose crystal (derived from regenerated cellulose), the degree of crystallinity can be determined by the following formula using wide-angle X-ray diffraction, from the absolute peak intensity h0 at 2θ = 12.6°, which is attributed to the (110) plane peak of the type II cellulose crystal, and the peak intensity h1 from the baseline at this interplanar spacing.
Crystallinity (%) = h1 /h0 ×100

In this process, cellulose raw material (e.g., pulp) is beaten and/or defibrated to produce cellulose fine fibers. In one embodiment, beating and/or defibration is performed in a solvent (hereinafter also referred to as a defibration solvent). For example, cellulose raw material (e.g., pulp), typically in slurry form, is processed in a defibration solvent using a beating device such as a single-disc refiner, double-disc refiner, conical refiner, Niagara beater, or PFI mill, and a defibration device such as a high-pressure homogenizer, microfluidizer, ball mill, bead mill, disc mill, or wet pulverizer to obtain cellulose fine fibers. These processes may be performed individually or in combination.

Examples of defibrillating solvents include water, DMSO (dimethyl sulfoxide), DMF (dimethylformamide), DMAc (dimethylacetamide), NMP (N-methylpyrrolidone), and acetic acid. Two or more of these solvents may also be used in mixture form.

Furthermore, it is preferable to homogeneously disperse the raw materials in a defibration solvent using a pulper or homomixer before the beating and/or defibration process. In particular, when chemically modifying the cellulose raw material before the defibration process, it is preferable to perform dispersion using a mixer such as a homomixer with a peripheral speed of preferably 10 m/s or more, more preferably 20 m/s or more, more preferably 25 m/s or more, preferably 90 m/s or less, more preferably 80 m/s or less, and more preferably 50 m/s or less, because the hydrophilicity of the cellulose raw material is reduced. By reducing clumps and other impurities as a pretreatment, homogeneous cellulose fine fibers can be obtained through a homogeneous defibration process. When using water as the solvent in this process, using highly purified water such as distilled water or ion-exchanged water may be effective.

When producing cellulose fine fibers using multiple beating and/or defibration processes, it is effective to combine two or more processes with different refinement mechanisms or shear rates. As described above, a multi-stage refinement method is preferable, either by using disc refiners with different disc configurations, or by performing refinement in a high-pressure homogenizer after refinement in a disc refiner. While single-disc refiners, double-disc refiners, or conical refiners may be used, a single-disc refiner with high clearance accuracy between the fixed and rotating blades is preferable for highly controlled refinement.

(Miniaturization using a disc refiner)
When performing micronization using a disc refiner, for example, purified cellulose fibers in the form of pulp or cotton are dispersed and stored in a tank in a defibration solvent at a solid content concentration of 0.5% to 6% by mass, preferably 0.8% to 3.5% by mass, and more preferably 1% to 3% by mass, and then micronized using a disc refiner. When water is used as the solvent in this process, it may be effective to use highly purified water such as distilled water or ion-exchanged water.

In the operation of the disc refiner, defibration can be performed in a continuous circulating process where the slurry stored in the 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 (let's call them Tank A and Tank B), first supplying the slurry to Tank A, then transferring it to Tank B via the disc refiner for storage. Once the processing of the slurry in Tank A is complete, the process switches to continuously transferring the slurry from Tank B to Tank A via the disc refiner for storage. This process is then repeated alternately in a continuous processing manner. This ensures that the slurry is reliably passed through the disc refiner each time, allowing for a uniform number of passes across the entire slurry volume. This is preferable from the viewpoint of uniformity in the degree of defibration, i.e., the quality stability of cellulose fine fibers.

Figure 1 is a diagram illustrating an example of the arrangement of blades and grooves in a disc refiner, and Figure 2 is a diagram illustrating the blade width, groove width, and inter-blade distance of a disc refiner. When performing multi-stage refinement using multiple disc refiners, it is preferable to use refiners having at least two different types of blades. Referring to Figures 1 and 2, as a specific blade configuration, in a disc refiner having blades 11 and grooves 12 as shown in Figure 1, it is important to appropriately adjust the blade width _WB , groove width _WG , and the value obtained by dividing the blade width _WB by the groove width WG (hereinafter referred to as the blade-to-groove ratio) as shown in Figure _2. It is particularly preferable to perform a refinement process (hereinafter referred to as the first stage) with a refiner equipped with blades having a blade width of 1.5 mm or more and 5 mm or less and a blade-to-groove ratio of 0.1 or more and 1.0 or less, and then perform a refinement process (hereinafter referred to as the second stage) with a refiner having blades having a blade width of 0.1 mm or more and 1.0 mm or less and a blade-to-groove ratio of 0.5 or more and 1.0 or less. By using a disc refiner with this configuration to defibrate the resin, the number of long fibers that cause aggregation in the resin is reduced, and cellulose fibers with a low fibrillation rate can be obtained. At this time, another refinement step may be added between the preceding and succeeding steps.

Furthermore, when disc refiner processing is performed in a single stage using one type of blade, it is particularly preferable to perform the fine processing with a refiner 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. In this case, the fiber length of the raw material used, as measured by a length-weighted average fiber length using an automated fiber shape analyzer (specifically, a Morfi Neo manufactured by Techpap), is preferably 500 μm or more, more preferably 700 μm or more, even more preferably 900 μm or more, preferably 3000 μm or less, more preferably 2000 μm or less, more preferably 1500 μm or less, and even more preferably 1300 μm or less. By using raw materials within this range, it is possible to efficiently reduce long fibers that cause aggregation in the resin in a single stage, and to obtain cellulose fine fibers with a low fibril content.

(Distance between blades in disc refiner processing)
Referring to Figure 2, in the miniaturization process using a disc refiner, it is important to control the distance _WL (clearance) between the two blades (specifically, the rotating blade 21 and the stationary blade 22 in Figure 2) (hereinafter simply referred to as the inter-blade distance). By controlling the inter-blade distance, it is possible to control the fiber length and degree of beating of the cellulose fibers. When processing in multiple stages, it is preferable to set the inter-blade distance to 0.05 mm or more and 0.5 mm or less in the first stage of processing, and to set the inter-blade distance to 0.05 mm or more and 0.3 mm or less in the second stage of processing. When processing in a single stage, it is preferable to set the inter-blade distance to 0.05 mm or more and 0.3 mm or less. When adjusting the inter-blade distance, it is preferable to gradually reduce the distance between the blades from a wider inter-blade distance while keeping the current value of the device below a certain level. By controlling it in this way, clogging and overload of the device can be prevented, and highly homogeneous cellulose fibers can be obtained.

Thus, in the cellulose refining process using a disc refiner, precisely controlling the distance between the fixed blade and the rotating blade is advantageous for producing homogeneous cellulose fine fibers with good mechanical properties as a filler. For example, conventional single disc refiners use a screw-type screw jack to adjust the blade distance, resulting in play in the runner that fixes the rotating blade. Therefore, if the runner is strongly pulled in the thrust direction, it moves by about 0.3 mm. For this reason, in order to obtain cellulose fine fibers with good accuracy and reproducibility, it is preferable to have a small amount of movement (play). In one embodiment, the amount of movement (play) is preferably 0.10 mm or less, more preferably 0.08 mm or less, and even more preferably 0.05 mm or less. Furthermore, it is preferable that the accuracy of closing the blade distance be 5 μm or less, more preferably 3 μm or less, and most preferably 1 μm or less. In one embodiment, by using a ball screw type jack as the blade distance adjustment mechanism, a single disc refiner with the above-mentioned thrust direction movement of 0.03 mm can be used. Furthermore, by attaching a reduction gear to the ball screw jack, the blade distance can be adjusted in increments of 1 μm. In addition, any mechanism is acceptable as long as it provides sufficient precision in adjusting the runner's movement and blade distance, such as combining a ball screw jack with a servo motor.

By using a single-disc refiner in this way, high-precision adjustment of the blade spacing becomes possible. Furthermore, it becomes possible to maintain a constant blade spacing without blade wobble during the refinement process. This also prevents the fixed and rotating blades from contacting each other when the blade spacing is reduced, thus preventing the cellulose microfibers from becoming too short and reducing the amount of coarse fibers due to insufficient defibration. As a result, cellulose microfibers with highly uniform shape distribution can be reliably manufactured, resulting in a filler that exhibits excellent mechanical properties when compounded with resin.

(Number of passes in the discriminator process)
The refinement process can also be controlled by the number of times the cellulose fibers pass between the rotating blade and the stationary blade (hereinafter referred to as the number of passes). By increasing the number of passes, cellulose fibers with a homogeneous fiber diameter and fiber length distribution can be obtained. Here, the number of passes refers to the number of times the refiner treatment (passing between the rotating blade and the stationary blade) is performed after the blade distance has been reduced to the desired blade distance.

The number of passes for the disc refiner is preferably 5 or more, more preferably 20 or more, and even more preferably 40 or more. While a higher number of passes is preferable because the distribution of fiber shapes gradually converges to a more consistent pattern, considering productivity, the upper limit of the number of passes may be 300 or less.

(Method for determining miniaturization conditions using a disc refiner)
The shape of cellulose fine fibers obtained by disc refiner processing is controlled by a combination of factors, including the type of disc refiner blades, the distance between blades, the number of passes, and the concentration. To obtain a desirable cellulose fiber shape for use in fiber-reinforced resins, it is preferable to increase the number of passes under viscous beating conditions. Viscous beating is a beating method that tends to make the fibers finer by fluffing them up, while a beating method that tends to cut the fibers is called free beating. In terms of the disc refiner blade configuration, the more blades there are, the longer the blade length, the larger the blade width to groove width ratio (blade-to-groove ratio), and the larger the contact angle, the more the number of intersections between the rotating blades and the stationary blades increases. As a result, the force applied to the fibers at each intersection is dispersed, and the number of impacts on the fibers increases, which tends to result in viscous beating. Conversely, when this is not the case, it tends to result in free beating. When using blades that exhibit a free beating tendency, it is preferable to widen the inter-blade distance of the disc refiner, and when using blades that exhibit a viscous beating tendency, it is preferable to narrow the inter-blade distance. However, if the inter-blade distance is narrowed too much, clogging occurs, the fibers are shortened due to cutting of the fiber length, and the performance as a filler deteriorates due to excessive fineness, so it is preferable that the inter-blade distance be 0.05 mm or more. Depending on the shape of the cellulose raw material (e.g., pulp) (fiber length and fiber diameter), the processing concentration, and the blades used, it is possible to control the fiber shape, such as the average fiber diameter and fiber length distribution, to a desirable range by adjusting the aforementioned inter-blade distance and/or the number of passes.

(Multi-stage miniaturization process using a combination of a disc refiner and a high-pressure homogenizer)
In addition to the cellulose fibers refined by the disc refiner, further refinement is performed using a high-pressure homogenizer. Compared to the disc refiner, the high-pressure homogenizer has a greater effect in thinning the fibers. The high-pressure homogenizer treatment is preferably performed at a pressure of 30 MPa or higher, more preferably 50 MPa or higher, and more preferably 80 MPa or higher. The upper limit may be 300 MPa or lower, or 250 MPa or lower, or 150 MPa or lower, depending on the characteristics of the apparatus.

Examples of high-pressure homogenizers include the NS-type high-pressure homogenizer from Nilo Soavi GmbH (Italy), the Lanier-type (R-model) pressure homogenizer from SMT Corporation, and the high-pressure homogenizer from Sanwa Machinery Co., Ltd. Examples of ultra-high-pressure homogenizers include the microfluidizer from Mizuho Industries Co., Ltd., the nanomizer from Yoshida Machinery Industry Co., Ltd., and the ultimateizer from Sugino Machine Co., Ltd. However, any device that performs micronization using a mechanism nearly identical to these may also be used.

In high-pressure homogenizer processing, as in disc refiner processing, defibration can be performed in a continuous circulating process where the slurry stored in a tank is returned to the original tank via a high-pressure homogenizer. However, it is preferable to prepare two tanks connected by piping via a high-pressure homogenizer (let's call them Tank A and Tank B). First, the slurry is introduced into Tank A, sent to Tank B via the high-pressure homogenizer for storage, and once the processing of the slurry in Tank A is complete, the process switches to continuously sending the slurry from Tank B to Tank A via the high-pressure homogenizer for storage. This process is then repeated alternately in a continuous processing step. This ensures that the slurry passes through the high-pressure homogenizer reliably in each pass, allowing for a uniform number of passes across the entire slurry volume. This is more preferable from the viewpoint of uniformity in the degree of defibration, i.e., quality stability of cellulose fine fibers.

<Concentration process>
In this step, for example, a dispersion of cellulose microfibers defibrated by the above-described defibration step is dehydrated to obtain a concentrate. As the cellulose microfiber dispersion, the cellulose microfiber slurry obtained in the defibration step can be used as is or diluted. As the dilution solvent, the same solvents as those exemplified above as defibration solvents can be used, and more preferably, water, or a mixed solvent of water and one or more of the organic solvents exemplified as defibration solvents.

The solid content of the cellulose fine fiber dispersion supplied to the concentration process is, in one embodiment, 0.1% by mass or more, or 0.3% by mass or more, or 0.5% by mass or more, or 0.7% by mass or more, or 1.0% by mass or more, or 1.5% by mass or more, and in one embodiment, 5.0% by mass or less, or 4.0% by mass or less, or 3.0% by mass or less, or 2.5% by mass or less.

In the cellulose microfiber dispersion supplied to the concentration process, the content of cellulose microfibers relative to 100% by mass of the total content of nonvolatile components may, in one embodiment, be 75% by mass or more, 80% by mass or more, 90% by mass or more, or 100% by mass. If the nonvolatile components also include components other than cellulose microfibers, the above content of cellulose microfibers may, in one embodiment, be 99% by mass or less, 95% by mass or less, or 90% by mass or less. In addition to cellulose microfibers, other nonvolatile components that may be present include, for example, one or more selected from the group consisting of dispersants; filler components other than cellulose; compatibilizers; plasticizers; polysaccharides such as starches and alginic acid; natural proteins such as gelatin, glue, and casein; inorganic compounds such as zeolites, ceramics, talc, silica, metal oxides, and metal powders; colorants; fragrances; pigments; flow regulators; leveling agents; conductive agents; antioxidants; antistatic agents; ultraviolet absorbers; ultraviolet dispersants; and deodorants. Preferred examples of each of the above components may be the same as those described later in the section on <additional components> in the resin composition. The content of cellulose microfibers relative to 100% by mass of the total nonvolatile components is determined by drying the cellulose microfiber dispersion or concentrate of the cellulose microfiber dispersion in an oven and/or vacuum dryer at 110°C to remove the solvent. If additional components are soluble in the solvent, they can be extracted by solvent extraction; if insoluble in the solvent, they can be calculated by comparing nuclear magnetic resonance (NMR) or infrared (IR) spectroscopy spectra with a standard sample; if inorganic, they can be measured by ash content; or a combination of these methods can be used. However, when a mixture of a dispersion of cellulose microfibers and solvent with additional components is subjected to the concentration process, the content of cellulose microfibers relative to 100% by mass of the total nonvolatile components can be calculated from the amount charged.

A concentration device (more specifically, a deliquidation device) for concentrating a cellulose microfiber dispersion is advantageously continuous in order to reduce variations in the solid content of the concentrated cellulose microfiber dispersion. The concentration device includes a concentration mechanism that receives and deliquidates the cellulose microfiber dispersion. An example of the concentration mechanism is a combination of a filter substrate that holds the cellulose microfiber dispersion on it and a suction unit that deliquidates the dispersion from the filter substrate by reducing the pressure. Other examples of concentration mechanisms include deliquidation by gravity from the cellulose microfiber dispersion on the filter substrate, deliquidation by compressing the cellulose microfibers between two filter substrates, and deliquidation by compression and shearing using a cylindrical screen and a screw inside the cylinder. The concentration mechanism combining the filter substrate and suction unit described above is preferable because it is less prone to leakage from the ends of the filter substrate and can concentrate even highly fluid, dilute dispersions. The procedure of this embodiment will be described below using a continuous concentration device equipped with this concentration mechanism as an example.

Figure 3 illustrates an example of the configuration of a continuous concentration apparatus. In one embodiment, the continuous concentration apparatus 300 comprises a tank 301 for storing a cellulose microfiber dispersion D, a suction unit 303, a pump 302 for supplying the cellulose microfiber dispersion from the tank 301 to the suction unit 303, a filtration substrate 304 for solid-liquid separation of the cellulose microfiber dispersion, a feeding mechanism 305 for continuously feeding/or circulating the filtration substrate 304, a transfer body 306 for receiving the concentrate C of the cellulose microfiber dispersion from the filtration substrate 304 by transfer, a scraper 307 for separating the concentrate C from the transfer body 306, and a recovery container 308 for recovering the concentrate C.

From the viewpoint of uniformity of the concentrate, it is preferable to supply a cellulose fine fiber dispersion, stirred at a peripheral speed of 0.01 m/sec to 6.00 m/sec, to the concentration process. For example, it is preferable that the tank 301 is equipped with a stirring device 309 that stirs the dispersion to maintain a uniform concentration. The stirring device 309 may have a configuration in which, for example, a stirring blade 309b is attached to a stirrer 309a. When stirring the dispersion, the stirring speed is preferably a peripheral speed of 0.01 m/sec or more, or 0.05 m/sec or more, or 0.10 m/sec or more, or 0.25 m/sec or more, or 0.50 m/sec or more, or 0.70 m/sec or more, or 1.00 m/sec or more, or 1.50 m/sec or more, and preferably 6.00 m/sec or less, or 5.00 m/sec or less, or 4.00 m/sec or less, or 3.00 m/sec or less. When the peripheral speed is above the lower limit of the above, it is less likely that a concentration distribution will occur inside the tank due to flocculation or sedimentation of cellulose microfibers, and the concentration will be uniform. When the peripheral speed is below the above upper limit, problems such as foam formation due to stirring, the dispersion splashing and adhering to a position above the liquid surface in the tank, and the detachment and mixing of dried solid particles that have lost their redispersibility, resulting in uneven concentration, are less likely to occur.

Examples of pumps 302 that supply the dispersion liquid from tank 301 to suction section 303 include piston pumps, diaphragm pumps, plunger pumps, mono pumps, hose pumps, and rotary pumps. A mono pump, which is pulsation-free and offers excellent quantitative liquid delivery, is preferably used.

The concentration of cellulose microfibers in the dispersion supplied to the continuous concentration device 300, more specifically the dispersion supplied to the suction section 303, is preferably 0.1% by mass or more, or 0.3% by mass or more, or 0.5% by mass or more, or 0.7% by mass or more, or 1.0% by mass or more, or 1.5% by mass or more, and preferably 5% by mass or less, or 4% by mass or less, or 3% by mass or less, or 2.5% by mass or less. When the cellulose microfiber concentration is above the lower limit, the film of the concentrated cellulose microfiber dispersion produced in the suction section does not become too thin, making it less likely for pinholes to occur in the film and easier to achieve a uniform state, as well as easier recovery from the filter substrate. When the cellulose microfiber concentration is below the upper limit, the thixotropy or viscosity of the dispersion does not become too high, resulting in a constant liquid thickness of the dispersion supplied to the suction section, and making it less likely for variations in the solid content of the concentrated dispersion to occur.

The filtration substrate 304 for solid-liquid separation of the cellulose microfiber dispersion may be any substrate that allows solvent to pass through but can hold the cellulose microfibers, such as wire (mesh), or porous materials such as woven or nonwoven fabrics. The wire material may be metal or plastic. Examples of porous materials include unmodified cellulose, modified cellulose, regenerated cellulose, polyester, polypropylene, polyethylene, polyamide, and glass fiber, and combinations of multiple materials, such as mixed sheets, may also be used. These filtration substrates may be used individually or two or more substrates may be laminated together. Examples of filtration substrates include, but are not limited to, TETEXMONODLW07-8435-SK010 (made of PET (polyethylene terephthalate)) from SEFAR GmbH (Switzerland), LTT-9FE (made of polyester) from Nippon Philcon Co., Ltd., NT20 (PET/nylon blend), TT30 (made of PET) from Shikishima Canvas Co., Ltd., and ultra-strong Japanese paper from Nakamura Paper Co., Ltd. The filtration substrate 304 may be held on a support 310 such as a wire. When two or more types of filtration substrates are used in a laminated manner, a different filtration substrate from the filtration substrate 304 may be used as the support 310. The support 310 may be equipped with a drive mechanism 311 and may be used in a circulating manner.

The feeding mechanism 305 for continuously feeding/circulating the filtration substrate 304 may be a roll-to-roll mechanism for feeding and winding the filtration substrate 304 (as shown in Figure 3), a mechanism for circulating the filtration substrate with both ends connected by a roll drive, etc. When using a mechanism for circulating the filtration substrate, it is preferable to also provide a cleaning mechanism (not shown) for cleaning the filtration substrate along the circulation path to prevent clogging. By continuously concentrating the cellulose microfiber dispersion using a continuous (i.e., non-batch) concentration apparatus equipped with the above feeding mechanism, fluctuations in the dispersion concentration immediately after the start of concentration and immediately before the end of concentration, as well as variations in the solid content of the concentrate, can be reduced, thereby increasing the uniformity of the concentrated cellulose microfiber dispersion.

The suction section 303 concentrates the cellulose microfiber dispersion on the filter substrate 304 by removing the solvent (de-solvent) under reduced pressure. There may be one or more suction sections. Using multiple suction sections in combination to control solvent removal is preferable because it allows for precise concentration of the cellulose microfiber dispersion, resulting in a concentrate with less variation in solid content. Reduced pressure in the suction section may be achieved by a vacuum mechanism 312. Furthermore, to improve concentration efficiency, the continuous concentration apparatus may include a mechanism that presses the cellulose microfiber dispersion while reducing pressure; for example, a vacuum pump as the vacuum mechanism 312 and a roll as the press mechanism (not shown) may be combined.

The processing rate for concentrating the cellulose microfiber dispersion is, in one embodiment, 1.0 kg-DS/h or more, or 1.5 kg-DS/h or more, or 2.0 kg-DS/h or more, or 3.0 kg-DS/h or more, or 5.0 kg-DS/h or more, or 10.0 kg-DS/h or more, from the viewpoint of productivity and reducing variability in the solid content of the concentrate, and in one embodiment, less than 45.0 kg-DS/h, or 40.0 kg-DS/h or less, or 35.0 kg-DS/h or less, or 30.0 kg-DS/h or less. Here, kg-DS represents the oven-dry weight of the cellulose microfibers. The above processing rate may be determined from the weight of concentrate produced per unit time. Specifically, it is determined by measuring the solid content of the concentrate collected from the recovery container 308 using an infrared (IR) moisture meter. However, when the dispersion medium contains an organic solvent, the solid content is calculated from the weight of the solids dried in a vacuum dryer for safety reasons. Concentration at a processing speed within the above range ensures a uniform fiber size distribution of cellulose microfibers (for example, the fiber size distribution of cellulose microfibers in the thickness direction of the concentrate formed on the filter substrate). When the processing speed is above the lower limit, variations in distribution due to sedimentation of cellulose microfibers with large fiber diameters and/or fiber lengths are less likely to occur, resulting in uniform deliquescence (more specifically, deliquescence in the suction section), which is preferable. When the processing speed is below the upper limit, deliquescence is performed well, resulting in a high recovery rate of the concentrate and smaller variations in the solid content of the concentrate, which is preferable.

The processing speed described above can be controlled within a predetermined range by adjusting, for example, the width of the filtration substrate (i.e., the dimension perpendicular to the direction of travel), the temperature, the degree of pressure reduction applied by the suction section, the supply speed of the dispersion, and the travel speed of the filtration substrate. In this case, continuing to stir the tank to maintain the uniformity of the dispersion throughout the concentration process is useful in reliably controlling the processing speed within the desired range.

The concentrated material C deposited on the filtration substrate 304 may be transferred to a transfer body 306, which may be, for example, a transfer roll or a transfer film, to detach it from the filtration substrate, and then collected and recovered from the transfer body. As a recovery method, a scraper 307 can be installed in the direction of travel of the filtration substrate to scrape off the concentrated material. Alternatively, the concentrated material C may be directly scraped off and recovered from the filtration substrate.

The solid content of the concentrated cellulose microfiber dispersion obtained in the concentration process is determined by taking 10 samples at any point during the continuous concentration process. The solid content of each sample is measured using an IR moisture meter (however, if the dispersion medium contains an organic solvent, a vacuum dryer is used), and the number mean and standard deviation of the solid content are determined, and the CV value is then calculated. In one embodiment, sampling is performed at 15-minute intervals. However, if the continuous operation time is shorter than 150 minutes, sampling is performed at 1/10 of the continuous operation time. For example, if the continuous operation time is 100 minutes, sampling is performed at 10-minute intervals.
Here, the CV value (coefficient of variation) is calculated using the following formula.
CV value = Standard deviation / Mean value

The average solid content of the concentrate of the cellulose microfiber dispersion is, in one embodiment, 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, or 30% by mass or more, and in another embodiment, 60% by mass or less, or 50% by mass or less, or 45% by mass or less, or 40% by mass or less. When the average solid content of the concentrate of the cellulose microfiber dispersion is above the lower limit, the solid content is easy to control, there is little variation, and residue is less likely to adhere to the filter substrate, resulting in a high recovery rate. On the other hand, when the average solid content of the concentrate of the cellulose microfiber dispersion is below the upper limit, the adhesion between the concentrate and the filter substrate does not become too strong, making recovery easy. Furthermore, in this case, aggregation between cellulose microfibers is minimal and redispersibility is good, resulting in a good reinforcing effect when used as a filler in resin compositions.

The CV value of the solid content of the concentrated cellulose microfiber dispersion is, in one embodiment, 0.001 or higher, or 0.005 or higher, or 0.010 or higher, or 0.020 or higher, or 0.050 or higher, or 0.070 or higher, or 0.090 or higher, and preferably 0.300 or lower, or 0.250 or lower, or 0.200 or lower, or 0.150 or lower, or 0.100 or lower. Because the CV value is within the above range, the concentrated cellulose microfiber dispersion exhibits excellent quantitative accuracy even though it still contains a large amount of dispersion medium. Therefore, when using this concentrate as a raw material for manufacturing fillers for resin reinforcement, and when manufacturing filler-reinforced resins using this filler, the amount of cellulose microfibers packed can be accurately controlled, resulting in stable quality and reduced defects when mass-producing filler-reinforced resins. While drying cellulose microfibers, i.e., using a very small amount of dispersion medium such as water, reduces variations in solid content and thus lowers the CV value, handling them in a concentrated form is advantageous in terms of redispersibility of cellulose microfibers in subsequent processes.

The concentration process is preferably carried out at 80°C or below, more preferably at 70°C or below, even more preferably at 60°C or below, and particularly preferably at 50°C or below. When the temperature of the concentration process is maintained below the above upper limit, drying from the surface of the concentrated cellulose microfiber dispersion can be suppressed, and variations in the solid content can be reduced. In this case, aggregation of cellulose microfibers due to excessive drying of the concentrate can be prevented, thus maintaining good redispersibility. The lower limit of the temperature in the concentration process is preferably 5°C or above, more preferably 10°C or above, and even more preferably 20°C or above. When the temperature of the concentration process is maintained above the above lower limit, the refrigerant temperature can be prevented from falling below the set temperature in order to lower the overall system temperature, thus making it less likely for the dispersion medium, such as water, to freeze due to localized overcooling. If the dispersion medium freezes, aggregation of cellulose microfibers occurs during thawing, reducing redispersibility; therefore, it is preferable to avoid freezing of the dispersion medium. When the temperature of the concentration process is adjusted by a heating mechanism such as hot air, infrared radiation, or microwaves, the temperature during heating should be measured. If temperature control is not performed by a heating mechanism, the temperature is evaluated as the temperature of the cellulose microfiber dispersion in the tank and the concentrated cellulose microfiber dispersion immediately after dewatering.

≪Method for producing dried cellulose microfibers≫
One aspect of the present invention also provides a method for producing a dried cellulose microfiber, comprising the steps of producing a concentrate of a cellulose microfiber dispersion by the method of the present disclosure, and drying the concentrate to produce a dried cellulose microfiber. Such a dried body is preferable because it can be easily mixed with a resin in the production of a resin composition containing cellulose microfibers and a resin.

For drying the concentrate, drying equipment such as a kneader, planetary mixer, Henschel mixer, high-speed mixer, propeller mixer, ribbon mixer, single-screw or twin-screw extruder, Banbury mixer, freeze dryer, shelf dryer, spray dryer, and fluidized bed dryer can be used. For example, when producing a dried product containing additional components (e.g., dispersants as illustrated in this disclosure) by adding them to the concentrate and then drying, dynamic dryers such as extruders, mixers, spray dryers, and fluidized bed dryers are preferred from the viewpoint of uniformly dispersing the additional components in the dried product. From the viewpoint of productivity, extruders and mixers that can easily stir and knead even high-viscosity products are preferred. Granulation may also be performed during drying to form particle shapes of a desired size.

The drying temperature may be, for example, 20°C or higher, 30°C or higher, 40°C or higher, or 50°C or higher, from the viewpoint of obtaining a dried product with excellent drying efficiency and dispersibility in the resin. From the viewpoint of minimizing thermal degradation of cellulose microfibers and additional components, it may be, for example, 160°C or lower, 150°C or lower, 140°C or lower, 130°C or lower, or 100°C or lower. The drying temperature is the temperature of the heat source in contact with the concentrate, and is defined, for example, by the surface temperature of the temperature-controlled jacket of the drying apparatus, the surface temperature of the heating cylinder, the temperature of the hot air, etc.

The drying pressure may be atmospheric pressure or reduced pressure. However, from the viewpoint of obtaining a dried product with excellent drying efficiency and dispersibility in the resin, it may be -1 kPa or less, -10 kPa or less, -20 kPa or less, -30 kPa or less, -40 kPa or less, or -50 kPa or less. From the viewpoint of avoiding excessive pulverization of the dried product due to rapid drying of the concentrate, it may be -100 kPa or more, -95 kPa or more, or -90 kPa or more. The pressure may be adjusted by methods such as operating a vacuum pump with appropriate exhaust capacity at full capacity, or by intentionally introducing air and/or inert gas using a vacuum regulator, leak valve, etc.

In one embodiment, the residence time of the concentrate at a temperature of 40°C to 100°C during the drying process may be, for example, 30 minutes to 600 minutes, 45 minutes to 300 minutes, or 60 minutes to 200 minutes.

In one embodiment, the dried cellulose microfiber may be particulate. In this case, the average particle size is preferably 1 μm or more, or 10 μm or more, or 50 μm or more, or 100 μm or more, or 200 μm or more, or 500 μm or more, and preferably 5000 μm or less, or 4000 μm or less, or 3000 μm or less, or 2000 μm or less. The above average particle size is measured by laser diffraction/scattering.

<BET specific surface area>
In one embodiment, the BET specific surface area of the dried cellulose microfiber is preferably 1 ^{m²/g or more, or 3 m²} /g or more, or 5 ^m² /g or more, or 8 ^m² /g or more, or 10 ^m² /g or more, or 12 ^m² /g or more, from the viewpoint of dispersibility of the cellulose microfiber in the resin composition, and preferably 50 ^m² /g or less, or 40 ^m² /g or less, or 30 ^m² /g or less, or 25 ^m² /g or less, or ^{20 m² /} g or less, from the viewpoint of ease of manufacturing the dried product. The specific surface area is obtained by using a specific surface area and pore distribution analyzer (e.g., Nova-4200e, manufactured by Quantachrome Instruments) to dry approximately 0.2 g of the dried material under vacuum at 120°C for 5 hours, then measuring the amount of nitrogen gas adsorbed at the boiling point of liquid nitrogen at five points within a relative vapor pressure (P/P ₀ ) range of 0.05 to 0.2 (multi-point method), and finally calculating the BET specific surface area ( ^m² /g) using the program of the same analyzer.

≪Characteristics of Cellulose Raw Materials and Cellulose Microfibers≫
The following describes exemplary embodiments of the properties of the cellulose raw materials and cellulose microfibers of this disclosure. Unless otherwise specified, the following properties may relate to the cellulose microfibers in the cellulose microfiber dispersion of this disclosure (which may also be referred to as cellulose microfibers before concentration in this disclosure), the cellulose microfibers in the concentrate of this disclosure (which may also be referred to as cellulose microfibers after concentration in this disclosure), or the cellulose microfibers in the dried product of this disclosure.

The average fiber diameter of the cellulose microfibers is, in one embodiment, 50 to 1000 nm, preferably 55 nm or more, or 60 nm or more, or 65 nm or more, or 70 nm or more, or 75 nm or more, 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. When the average fiber diameter of the cellulose microfibers is within the above range, concentration with little variation in solid content is possible, even for cellulose microfibers with increased surface hydrophobicity due to chemical modification, as well as unmodified cellulose microfibers. When the average fiber diameter is above the lower limit, the water retention is not excessively high, making dewatering from the cellulose microfiber dispersion easy, and clogging of the concentration device and a decrease in recovery rate are less likely to occur. On the other hand, when the average fiber diameter is below the upper limit, the cellulose microfibers are less likely to settle in the dispersion, thus reducing concentration unevenness due to sedimentation.

In one embodiment, the number-average fiber diameter (D) of cellulose microfibers is a value measured using a scanning electron microscope (SEM) by the following procedure. Cellulose microfibers before or after concentration are diluted with tert-butanol to 0.1–0.5% by mass, and a sheet prepared by suction filtration is dried in a 150°C oven for 5 minutes. This sheet is used as the measurement sample, and the number-average diameter is determined from a 10,000x magnification image observed with a high-resolution scanning electron microscope (SEM). Specifically, three lines are drawn arbitrarily passing through the center point of the observed image, and the width of the fibers intersecting these lines is determined for at least 100 fibers, and the number-average value is calculated.

From the viewpoint of obtaining a resin composition with excellent heat resistance, mechanical strength, and dimensional stability, the crystallinity of the cellulose raw material or cellulose microfibers is preferably 55% or higher, 60% or higher, 70% or higher, 73% or higher, or 75% or higher. When the crystallinity is within this range, the mechanical properties (heat resistance, strength, and dimensional stability) of the cellulose itself are high, and therefore, when cellulose is dispersed in the resin, the resulting resin composition tends to have high heat resistance, strength, and dimensional stability. While a higher crystallinity is preferable, from a production standpoint, the preferred upper limit is 99%.

From the viewpoint of mechanical property development, the degree of polymerization of the cellulose raw material or cellulose microfibers is preferably 100 or more, 150 or more, 200 or more, 300 or more, or 400 or more. From the viewpoint of processability, it is preferably 3500 or less, 3300 or less, 3200 or less, 3100 or less, or 3000 or less.

The degree of polymerization of cellulose refers to the average degree of polymerization measured according to the reduction ratio viscosity method using copper ethylenediamine solution, as described in the confirmation test (3) of the "Fifteenth Revised Japanese Pharmacopoeia Commentary (published by Hirokawa Shoten)".

In one embodiment, the weight-average molecular weight (Mw) of the cellulose raw material or cellulose microfibers is 100,000 or more, more preferably 200,000 or more. The ratio of weight-average molecular weight to number-average molecular weight (Mn) (Mw/Mn) is 6 or less, preferably 5.4 or less. A larger weight-average molecular weight means fewer end groups in the cellulose molecule. Also, since the ratio of weight-average molecular weight to number-average molecular weight (Mw/Mn) represents the width of the molecular weight distribution, a smaller Mw/Mn means fewer end groups in the cellulose molecule. Since the end groups of cellulose molecules are the starting points for thermal decomposition, a particularly heat-resistant cellulose and a resin composition containing cellulose and resin can be obtained when the weight-average molecular weight of the cellulose molecule is large, and at the same time the width of the molecular weight distribution is narrow. From the viewpoint of the availability of cellulose raw materials, the weight-average molecular weight (Mw) of the cellulose microfibers may be, for example, 600,000 or less, or 500,000 or less. The ratio of weight-average molecular weight to number-average molecular weight (Mn) (Mw/Mn) may be, for example, 1.5 or higher, or 2 or higher, from the viewpoint of ease of manufacturing cellulose fine fibers. Mw can be controlled within the above range by selecting a cellulose raw material having an Mw appropriate to the purpose, and by appropriately performing physical and/or chemical treatments on the cellulose raw material within an appropriate range. Mw/Mn can also be controlled within the above range by selecting a cellulose raw material having an Mw/Mn appropriate to the purpose, and by appropriately performing physical and/or chemical treatments on the cellulose raw material within an appropriate range. Examples of physical treatments for both Mw and Mw/Mn control include dry or wet grinding using microfrudizers, ball mills, disc mills, etc., and applying mechanical forces such as impact, shear, shatter, and friction using grinders, homomixers, high-pressure homogenizers, ultrasonic devices, etc. Examples of chemical treatments include pulverization, bleaching, acid treatment, and regenerative celluloseization.

The weight-average molecular weight and number-average molecular weight referred to here are values obtained by dissolving cellulose raw materials or cellulose fine fibers in N,N-dimethylacetamide to which lithium chloride has been added, and then determining them by gel permeation chromatography using N,N-dimethylacetamide as the solvent.

Methods for controlling the degree of polymerization (i.e., average degree of polymerization) or molecular weight of cellulose microfibers include hydrolysis treatment after the defibrillation process. Hydrolysis treatment promotes the depolymerization of amorphous cellulose within the cellulose, reducing the average degree of polymerization. Simultaneously, hydrolysis removes impurities such as hemicellulose and lignin in addition to amorphous cellulose, resulting in a porous structure within the fibrous material. This makes the cellulose more susceptible to mechanical processing during processes that apply mechanical shear force to it, such as the kneading process described later, and facilitates fine dispersion of the cellulose.

Cellulose microfibers can have a high aspect ratio shape, where the fiber length is long relative to the fiber diameter, and can also be bent. Therefore, quantitatively measuring the fiber length is difficult. However, using an automated fiber shape analyzer (e.g., Morfi Neo from Techpap), the fineness ratio, which reflects the fiber length distribution, can be determined. In this disclosure, the fineness ratio is defined and calculated as the percentage of fibers with a length-weighted fiber length of less than 0.1 mm.

(Automatic fiber shape analyzer)
The measurement procedure for the automated fiber shape analyzer (Techpap Morfi Neo) is described below. For measurement, the fiber parameter is defined with a fiber length of 0.1 mm as the threshold. Cellulose microfibers above the threshold are defined as normal fibers, and fibers below the threshold are defined as fine fibers.

Prepare a 1 L aqueous dispersion by dispersing cellulose microfibers in pure water to a solid content concentration of 0.003 to 0.005% by mass. If the aqueous dispersion of cellulose microfibers before dilution is 2% by mass or less, it is sufficient to simply mix it with a spatula or the like. However, if the aqueous dispersion is 2% by mass or more, or if it is in the form of a water-containing cake or powder, dispersion treatment should be performed using a high-shear homogenizer (IKA, product name "Ultra-Turrax T18") under the following conditions: rotation speed 25,000 rpm x 5 minutes. If dispersed in a medium other than water, the material is dispersed in a sufficient amount of pure water using a high-shear homogenizer (e.g., IKA product, "Ultra-Turrax T18") under the following conditions: rotation speed 25,000 rpm x 5 minutes. After dispersing, the medium is removed by means of suction filtration or other means. Then, the material is dispersed again in pure water using a high-shear homogenizer (e.g., IKA product, "Ultra-Turrax T18") under the following conditions: rotation speed 25,000 rpm x 5 minutes, so that the solid content concentration is 0.003 to 0.005 mass%, thereby replacing the medium with water. The aqueous dispersion prepared as described above is subjected to measurement using an autosampler, and each shape parameter is extracted or calculated from the results. Note that in measuring the fiber length distribution with this instrument, the data interval can be set arbitrarily, so any setting is acceptable as long as the distribution of fibers with the aforementioned fiber length can be confirmed.
The following provides a detailed explanation of each shape parameter.

(Length-weighted average fiber length)
Length-weighted average fiber length was measured using an automated fiber shape analyzer in accordance with the method defined in ISO/FDIS 16065-2:2006, and the average value was calculated for fibers with a length of 0.1 mm or more. For bent fibers, the average value represents the fiber length corresponding to the actual fiber length, taking into account the bent shape.

(Fine rate)
This is the percentage of fine fibers (fibers with a length of less than 0.1 mm) out of the total number of cellulose microfibers observed by an automated fiber shape analyzer. In one embodiment, the fine ratio is preferably 70% or more, or 80% or more, or 90% or more, and preferably 99% or less, or 98% or less, or 97% or less. By controlling the fine ratio within the above range, a good reinforcing effect can be obtained when cellulose microfibers are used as a filler for filler-reinforced resins. When the fine ratio is above the lower limit, it tends to indicate that the cellulose microfibers are defibrated well, and since the cellulose microfibers are less likely to settle in the dispersion, uneven concentration due to settling is less likely to occur, which is preferable. In this case, the reinforcing effect as a filler for filler-reinforced resins is also good. On the other hand, when the fine ratio is below the upper limit, it tends to indicate that the cellulose microfibers are not defibrated excessively, and problems such as passing through the filtration substrate or clogging the filtration substrate in the concentration process are less likely to occur, which is preferable. Furthermore, in this case, excessive defibration is less likely to cause a decrease in the heat resistance of the cellulose microfibers, which is preferable because it is less likely to cause severe discoloration or deterioration of physical properties due to thermal degradation as a filler for filler-reinforced resins.

(Fine fiber area ratio)
The fine fiber area ratio is the ratio of the total area of fine fibers with a fiber length of less than 0.1 mm to the total area of all cellulose microfibers observed (area of normal fibers + area of fine fibers). The fine fiber area ratio is preferably 90% or less, or 80% or less, or 70% or less, or 60% or less, and preferably 5% or more, or 10% or more, or 20% or more, or 25% or more, or 30% or more. Having a fine fiber area ratio within a preferred range makes it easier to concentrate with less variation in solid content during the concentration process.

(Fibrillation rate)
The fibrillation rate, in a fiber having a branched structure in which at least a portion is branched, refers to the total length of the n branched side chains L (Sub) relative to the main chain length L (Main) of the main chain, which has the largest diameter, and is defined by the following formula.

The fibrillation rate of cellulose microfibers is preferably 0.5% or more, or 0.7% or more, or 0.8% or more, or 0.9% or more, or 1.0% or more, or 1.2% or more, or 1.5% or more, and preferably 3.5% or less, or 3.0% or less, or 2.5% or less, or 2.0% or less. Having the fibrillation rate within this range ensures that when cellulose microfibers are used as a filler for filler-reinforced resins, the interface area between the cellulose microfibers and the resin in the resin composition is within an appropriate range, reducing the number of fracture initiation points and thus increasing the fracture strain.

In one embodiment, cellulose microfibers may contain alkali-soluble polysaccharides. These alkali-soluble polysaccharides include hemicellulose, as well as β-cellulose and γ-cellulose. Alkali-soluble polysaccharides are understood by those skilled in the art as components obtained as the alkali-soluble portion of holocellulose obtained by solvent extraction and chlorination of plants (e.g., wood) (i.e., components obtained by removing α-cellulose from holocellulose). Since alkali-soluble polysaccharides are polysaccharides containing hydroxyl groups, they can cause a decrease in the heat resistance, physical properties, discoloration, and dispersibility in resins of cellulose microfibers; therefore, a low content of alkali-soluble polysaccharides in cellulose microfibers is preferable.

In one embodiment, the average content of alkali-soluble polysaccharides in cellulose microfibers is preferably 20% by mass or less, 18% by mass or less, 15% by mass or less, 12% by mass or less, 11% by mass or less, or 8% by mass or less, based on 100% by mass of cellulose microfibers, from the viewpoint of maintaining good functionality of the cellulose microfibers. From the viewpoint of ease of manufacturing cellulose microfibers, the above content may be 1% by mass or more, 2% by mass or more, 3% by mass or more, or 6% by mass or more. In one embodiment, the average content of alkali-soluble polysaccharides in the cellulose raw material may be 13% by mass or less, 12% by mass or less, 11% by mass or less, or 8% by mass or less, most preferably 0% by mass, but from the viewpoint of ease of obtaining cellulose raw materials, it may be, for example, 3% by mass or more, or 6% by mass or more.

The average alkali-soluble polysaccharide content can be determined using the method described in the non-patent literature (Wood Science Experiment Manual, edited by the Japan Wood Research Society, pp. 92-97, 2000). It is calculated by subtracting the α-cellulose content from the holocellulose content (Wise method). This method is understood in this industry as a method for measuring hemicellulose content. The alkali-soluble polysaccharide content is calculated three times for each sample, and the number average of these calculated alkali-soluble polysaccharide content values is taken as the average alkali-soluble polysaccharide content.

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

The average acid-insoluble component content is determined using the Claesson 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 this industry as a method for measuring lignin content. The sample is stirred in sulfuric acid solution to dissolve cellulose and hemicellulose, etc., and then filtered through glass fiber filter paper. The resulting residue contains the acid-insoluble components. The acid-insoluble component content is calculated from the weight of these components, and the average of the number of acid-insoluble component content values calculated for three samples is taken as the average acid-insoluble component content.

≪Method for manufacturing resin compositions≫
One aspect of the present invention also provides a method for producing a resin composition comprising cellulose microfibers and a thermoplastic resin. In one aspect, the method includes the steps of producing a concentrate of cellulose microfiber dispersion using the method for producing a concentrate of cellulose microfiber dispersion of the present disclosure, or producing a dried cellulose microfiber using the method for producing a dried cellulose microfiber of the present disclosure, and mixing (typically by melt-kneading) the concentrate of cellulose microfiber dispersion or the dried cellulose microfiber with a thermoplastic resin to produce a resin composition.

For melt kneading, extruders such as single-screw extruders and twin-screw extruders can be used, but twin-screw extruders are preferred for controlling the dispersibility of cellulose fine fibers. The L/D ratio, obtained by dividing the extruder cylinder length (L) by the screw diameter (D), is preferably 30 or more, and particularly preferably 40 or more. Furthermore, the screw rotation speed during kneading is preferably in the range of 50 to 800 rpm, and more preferably in the range of 100 to 600 rpm. Each screw within the extruder cylinder is optimized by combining a conveying screw with an elliptical two-blade screw shape, a kneading element called a kneading disc, and the like.

<Thermoplastic resin>
The thermoplastic resin is appropriately selected according to the intended use of the resin composition, and may be, for example, a crystalline thermoplastic resin having a melting point in the range of 100°C to 350°C, or an amorphous thermoplastic resin having a glass transition temperature in the range of 100°C to 250°C. Examples of resins include polyolefin resins, polyamide resins, polyester resins, polyacetal resins, polyphenylene ether resins, polyphenylene sulfide resins, and mixtures of two or more of these. From the viewpoint of ease of handling and cost, polyolefin resins, polyamide resins, polyester resins, polyacetal resins, etc. are preferred, polyamide resins, polyolefin resins and polyacetal resins are more preferred, and polyamide resins and polyacetal resins are particularly preferred. From the viewpoint of improving the heat resistance of the resin composition, the melting point of thermoplastic resins (especially crystalline resins) is preferably 140°C or higher, or 150°C or higher, or 160°C or higher, or 170°C or higher, or 180°C or higher, or 190°C or higher, or 200°C or higher, or 210°C or higher, or 220°C or higher, or 230°C or higher, or 240°C or higher, or 245°C or higher, or 250°C or higher.

Examples of melting points for thermoplastic resins include, for example, 150°C to 190°C or 160°C to 180°C for resins with relatively low melting points (e.g., polyolefin resins), and 220°C to 350°C or 230°C to 320°C for resins with relatively high melting points (e.g., polyamide resins).

In this disclosure, the melting point of the resin refers to the peak top temperature of the endothermic peak that appears when the temperature is increased from 23°C at a heating rate of 10°C/min using a differential scanning calorimetry (DSC). If two or more endothermic peaks appear, the peak top temperature of the highest-temperature endothermic peak is referred to.

In this disclosure, the glass transition temperature of a resin refers to the temperature at which the storage modulus decreases significantly and the loss modulus reaches its maximum, measured using a dynamic viscoelasticity measuring device at an applied frequency of 10 Hz while increasing the temperature from 23°C at a heating rate of 2°C/min. If two or more peaks in the loss modulus appear, the peak top temperature of the highest-temperature peak is referred to.

Preferred polyolefin resins as thermoplastic resins are polymers obtained by polymerizing olefins (e.g., α-olefins) or alkenes as monomer units. Specific examples of polyolefin resins include ethylene-based (co)polymers such as low-density polyethylene (e.g., linear low-density polyethylene), high-density polyethylene, ultra-low-density polyethylene, and ultra-high molecular weight polyethylene; polypropylene-based (co)polymers such as polypropylene, ethylene-propylene copolymer, and ethylene-propylene-diene copolymer; and copolymers of ethylene and other α-olefins, such as ethylene-acrylic acid copolymer, ethylene-methyl methacrylate copolymer, and ethylene-glycidyl methacrylate copolymer.

The most preferred polyolefin resin here is polypropylene. In particular, polypropylene with a melt mass flow rate (MFR) of 3 g/10 min or more and 30 g/10 min or less, measured at 230°C and a load of 21.2 N in accordance with ISO 1133, is preferred. The lower limit of the MFR is more preferably 5 g/10 min, even more preferably 6 g/10 min, and most preferably 8 g/10 min. The upper limit is more preferably 25 g/10 min, even more preferably 20 g/10 min, and most preferably 18 g/10 min. From the viewpoint of improving the toughness of the composition, it is desirable that the MFR does not exceed the upper limit, and from the viewpoint of the fluidity of the composition, it is desirable that it does not fall below the lower limit.

Furthermore, to enhance affinity with fine cellulose fibers, acid-modified polyolefin resins can also be suitably used. Mono- or polycarboxylic acids can be used as the acid for acid modification; examples include maleic acid, fumaric acid, succinic acid, phthalic acid and their anhydrides, as well as citric acid. Maleic acid or its anhydride is particularly preferred due to its ease of increasing the modification rate. While there are no particular restrictions on the modification method, a common method involves heating the polyolefin resin above its melting point in the presence or absence of a peroxide and then melt-kneading it. All of the aforementioned polyolefin resins can be used for acid modification, but polypropylene is particularly preferred. Acid-modified polypropylene resin may be used alone, but it is more preferable to mix it with unmodified polypropylene resin to adjust the overall modification rate of the resin. In this case, the ratio of acid-modified polypropylene resin to the total polypropylene resin is preferably 0.5% to 50% by mass. A more preferable lower limit is 1% by mass, or 2% by mass, or 3% by mass, or 4% by mass, or 5% by mass. A more preferable upper limit is 45% by mass, or 40% by mass, or 35% by mass, or 30% by mass, or 20% by mass. To maintain the interfacial strength between the resin and the fine cellulose fibers, a value above the lower limit is preferable, while to maintain the ductility of the resin, a value below the upper limit is preferable.

The melt mass flow rate (MFR) of acid-modified polypropylene, measured at 230°C and under a load of 21.2 N in accordance with ISO 1133, is preferably 50 g/10 min or higher to enhance affinity with the cellulose interface. A more preferable lower limit is 100 g/10 min, even more preferably 150 g/10 min, and most preferably 200 g/10 min. There is no particular upper limit, but 500 g/10 min is recommended for maintaining mechanical strength. By keeping the MFR within this range, when acid-modified and unmodified polypropylene are used together, the advantage of the acid-modified polypropylene being more readily present at the cellulose-resin interface can be enjoyed.

Preferred polyamide resins as thermoplastic resins include: polyamides obtained by polycondensation reactions of lactams (e.g., polyamide 6, polyamide 11, polyamide 12, etc.); diamines (e.g., 1,6-hexanediamine, 2-methyl-1,5-pentanediamine, 1,7-heptanediamine, 2-methyl-1-6-hexanediamine, 1,8-octanediamine, 2-methyl-1,7-heptanediamine, 1,9-nonanediamine, 2-methyl-1,8-octanediamine, 1,10-decanediamine, 1,11-undecanediamine, 1,12-dodecanediamine, m-xylylenediamine, etc.) and dicarboxylic acids (e.g., butanediamine, pentanediamine, hexanediamine) Examples include polyamides obtained as copolymers with heptanediic acid, octanedioic acid, nonanediic acid, decanediic acid, benzene-1,2-dicarboxylic acid, benzene-1,3-dicarboxylic acid, benzene-1,4-dicarboxylic acid, cyclohexane-1,3-dicarboxylic acid, cyclohexane-1,4-dicarboxylic acid, etc. (e.g., polyamide 6,6, polyamide 6,10, polyamide 6,11, polyamide 6,12, polyamide 6,T, polyamide 6,I, polyamide 9,T, polyamide 10,T, polyamide 2M5,T, polyamide MXD,6, polyamide 6,C, polyamide 2M5,C, etc.); and copolymers obtained by copolymerizing these (e.g., polyamide 6,T/6,I, etc.).

Among these polyamide resins, aliphatic polyamides such as polyamide 6, polyamide 11, polyamide 12, polyamide 6,6, polyamide 6,10, polyamide 6,11, and polyamide 6,12, and alicyclic polyamides such as polyamide 6,C and polyamide 2M5,C are more preferred.

There are no particular restrictions on the concentration of terminal carboxyl groups in the polyamide resin, but it is preferably 20 μmol/g or more, or 25 μmol/g or more, and preferably 150 μmol/g or less, or 100 μmol/g or less.

The concentration of terminal amino groups in the polyamide resin is preferably 20 μmol/g or more, or 30 μmol/g or more, and preferably 150 μmol/g or less, or 100 μmol/g or less.

There are no particular restrictions on the total concentration of terminal amino groups and terminal carboxyl groups in the polyamide resin, but it is preferably 10 μmol/g or more, or 50 μmol/g or more, or 100 μmol/g or more, or 135 μmol/g or more. From the viewpoint of preventing viscosity reduction due to the resin becoming excessively low molecular weight and suppressing the generation of burrs during molding, it is preferably 500 μmol/g or less, or 300 μmol/g or less, or 135 μmol/g or less, or 100 μmol/g or less.

The ratio of amino-terminal groups to carboxyl-terminal groups ([ _NH₂ ]/[COOH]) of the polyamide resin is preferably greater than 1.00, or 1.01 or more, or 1.05 or more, or 1.10 or more. There is no particular upper limit to the amino-terminal group ratio, but from the viewpoint of maintaining a good color tone of the resin composition, it may preferably be 10,000 or less, or 1,000 or less, or 10 or less.

The end group concentration of polyamide resins can be adjusted by known methods. One such method involves adding an end group adjusting agent (e.g., diamine compounds, monoamine compounds, dicarboxylic acid compounds, monocarboxylic acid compounds, acid anhydrides, monoisocyanates, monoacid halides, monoesters, monoalcohols, etc.) to the polymerization solution during the polymerization of the polyamide, so that a predetermined end group concentration is achieved.

The concentrations of amino-terminated and carboxyl-terminated groups in polyamide resins can be determined by ^1H -NMR from the integrated values of the characteristic signals corresponding to each terminus. This method is preferred in terms of accuracy and simplicity. More specifically, it is recommended to use the method described in Japanese Patent Publication No. 7-228775, using deuterated trifluoroacetic acid as the measurement solvent and performing 300 or more scans for integration.

The intrinsic viscosity [η] of polyamide resins, measured under conditions of 30°C in concentrated sulfuric acid, is preferably 0.6 to 2.0 dL/g, 0.7 to 1.4 dL/g, 0.7 to 1.2 dL/g, or 0.7 to 1.0 dL/g, from the viewpoint of good in-mold fluidity and good appearance of molded pieces when the resin composition is, for example, injection molded. In this disclosure, "intrinsic viscosity" is synonymous with viscosity generally called intrinsic viscosity. The intrinsic viscosity is determined by measuring the ηsp/c of several measurement solvents of different concentrations under conditions of 30°C in 96% concentrated sulfuric acid, deriving a relationship between each ηsp/c and the concentration (c), and extrapolating the concentration to zero. This extrapolated value is the intrinsic viscosity. Details of the above method are described, for example, on pages 291-294 of Polymer Process Engineering (Prentice-Hall, Inc. 1994). From the standpoint of accuracy, it is desirable to use at least four different concentrations of the measurement solvent (e.g., 0.05 g/dL, 0.1 g/dL, 0.2 g/dL, 0.4 g/dL).

As the polyester resin, one or more selected from polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polyethylene naphthalate (PEN), polybutylene succinate (PBS), polybutylene succinate adipate (PBSA), polybutylene adipate terephthalate (PBAT), polyhydroxyalkanoic acid (PHA), polylactic acid (PLA), polyarylate (PAR), polycarbonate (PC), etc., can be used. More preferably, the polyester resin is PET, PBS, PBSA, PBT, or PEN, and even more preferably, PBS, PBSA, or PBT.

Furthermore, while the end groups of polyester resins can be freely altered by changing the monomer ratio during polymerization and the presence or absence and amount of end stabilizers added, it is more preferable that the ratio of carboxyl end groups to the total end groups of the polyester resin ([COOH]/[total end groups]) is 0.30 to 0.95. The lower limit of the carboxyl end group ratio is more preferably 0.35, even more preferably 0.40, and most preferably 0.45. The upper limit of the carboxyl end group ratio is more preferably 0.90, even more preferably 0.85, and most preferably 0.80. From the viewpoint of dispersibility in the cellulose composition, it is desirable that the above carboxyl end group ratio be 0.30 or higher, and from the viewpoint of the color tone of the resulting composition, it is desirable that it be 0.95 or lower.

Common polyacetal resins include homopolyacetals derived from formaldehyde and copolyacetals, which primarily use trioxane as a monomer and contain 1,3-dioxolane as a comonomer. Both are usable, but copolyacetals are preferred from the viewpoint of thermal stability during processing. In particular, the amount of structure derived from the comonomer component (e.g., 1,3-dioxolane) is more preferably in the range of 0.01 to 4 mol%. The preferred lower limit of the amount of structure derived from the comonomer component is 0.05 mol%, more preferably 0.1 mol%, and even more preferably 0.2 mol%. The preferred upper limit is 3.5 mol%, more preferably 3.0 mol%, even more preferably 2.5 mol%, and most preferably 2.3 mol%.

From the viewpoint of thermal stability during extrusion and molding processes, it is desirable that the lower limit be within the above-mentioned range, and from the viewpoint of mechanical strength, it is desirable that the upper limit be within the above-mentioned range.

From the viewpoint of affinity with cellulose, resins having hydrophilic groups (for example, one or more selected from hydroxyl groups, ether groups, ester groups, amino groups, and carboxyl groups) are particularly preferred. Preferred examples of resins having hydrophilic groups are one or more selected from the group consisting of acid-modified polyolefin resins, polyacetal resins, polycarbonate resins, polyamide resins, polyester resins, polyphenylene ether resins, and acrylic resins. Among these, polyamide resins and maleated polypropylene are preferred.

<Additional ingredients>
The resin composition of this embodiment may further contain additional components as needed to improve its performance. Examples of additional components include dispersants; filler components other than cellulose; compatibilizers; plasticizers; polysaccharides such as starches and alginic acid; natural proteins such as gelatin, glue, and casein; inorganic compounds such as zeolites, ceramics, talc, silica, metal oxides, and metal powders; colorants; fragrances; pigments; flow regulators; leveling agents; conductive agents; antioxidants; antistatic agents; ultraviolet absorbers; ultraviolet dispersants; and deodorants. The content ratio of any additional component in the resin composition is appropriately selected within a range that does not impair the desired effects of the present invention, but may be, for example, 0.01 to 50% by mass, or 0.1 to 30% by mass.

As a dispersant, one can be used that suppresses the aggregation and solidification of cellulose when mixed with concentrated cellulose microfibers to form a dried cellulose microfiber body, and improves the dispersion stability of cellulose microfibers in the resin composition obtained by kneading the resin and the dried cellulose microfiber body. It may be hydrophilic or hydrophobic. Preferred examples of dispersants are one or more selected from the group consisting of cellulose derivatives, polyalkylene oxides, amides, and amines, but are not limited thereto. Among these, cellulose derivatives are preferred because they are cellulosic substances and therefore have high affinity with cellulose microfibers, while also being thermoplastic resins, thus providing a high effect in improving the dispersion stability of cellulose microfibers in the resin composition. It is preferable that the dispersant has a boiling point higher than that of water. A boiling point higher than that of water refers to a boiling point higher than the boiling point at each pressure on the water vapor pressure curve (for example, 100°C at 1 atmosphere). It is more preferable, and the higher the boiling point, the higher the boiling point of the dispersant. The boiling point of the dispersant may be, for example, 130°C or higher, 140°C or higher, 150°C or higher, 160°C or higher, 170°C or higher, or 180°C or higher, and a dispersant with a boiling point higher than the planned mixing temperature may be selected. Alternatively, the dispersant may decompose thermally without having a boiling point. In this case, the thermal decomposition temperature of the dispersant is preferably higher than the resin temperature during mixing, and in one embodiment, it may have a thermal decomposition temperature similar to the preferred boiling point described above.

The amount of cellulose microfibers relative to 100% by mass of the entire resin composition is preferably 0.1% by mass or more, 0.5% by mass or more, 1% by mass or more, or 3% by mass or more, from the viewpoint of obtaining a good reinforcing effect from the cellulose microfibers. From the viewpoint of maintaining the inherent properties of the resin well, it is preferably 30% by mass or less, 25% by mass or less, 20% by mass or less, or 15% by mass or less. It is preferable that the cellulose microfiber content is evenly distributed throughout the molded product of the resin composition. If there are areas with locally low or high cellulose microfiber content, these areas may reduce the reinforcing effect of the molded product or cause it to break. This may lead to an increase in defective products, especially when manufacturing small molded products.

The amount of resin relative to 100% by mass of the entire resin composition is preferably 20% by mass or more, or 30% by mass or more, or 40% by mass or more, or 50% by mass or more, or 60% by mass or more, or 70% by mass or more, or 75% by mass or more, or 80% by mass or more, or 85% by mass or more, from the viewpoint of maintaining the inherent properties of the resin well. From the viewpoint of obtaining the effects of other components well, it is preferably 99.9% by mass or less, or 99.5% by mass or less, or 99% by mass or less, or 97% by mass or less, or 95% by mass or less, or 90% by mass or less.

In the resin composition, the amount of dispersant per 100 parts by mass of cellulose fine fibers is preferably 1 part by mass or more, 5 parts by mass or more, 10 parts by mass or more, 20 parts by mass or more, or 30 parts by mass or more, from the viewpoint of good dispersion of cellulose and network formation. From the viewpoint of reducing variability in the performance of the resin composition, it is preferably 500 parts by mass or less, 300 parts by mass or less, 200 parts by mass or less, or 100 parts by mass or less.

The resin composition of this embodiment can be used as various resin molded articles. There are no particular restrictions on the method of manufacturing the resin molded articles, but injection molding, extrusion molding, blow molding, inflation molding, and foam molding methods can be used. Among these, injection molding is particularly preferred from the viewpoint of design and cost.

Uses of resin compositions
The resin composition obtained by the method of this embodiment 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 resin composition include industrial machine parts, general machine parts, automobile, railway, vehicle, ship, and aerospace-related parts, electronic and electrical components, building and civil engineering materials, household goods, sports and leisure goods, wind turbine housing components, containers and packaging components, etc.

The following describes illustrative embodiments of the present invention with reference to examples, but the present invention is not limited to the following embodiments.

≪Evaluation Method≫
<Evaluation of fine fiber content, fine fiber area ratio, and fibrillation rate using an automated fiber shape analyzer>
The measurement procedure using the automated fiber shape analyzer (Techpap Morfi Neo) is described below. For measurement, a fiber length of 0.1 mm is used as the threshold for fiber parameters. Cellulose microfibers above this threshold are defined as normal fibers, and fibers below this threshold are defined as fine fibers. The following shape parameters were extracted or calculated from the measurement results obtained using the automated fiber shape analyzer.
Fine content: The percentage of fine fibers (fibers with a length of less than 0.1 mm) out of the total number of cellulose microfibers. Fine fiber area ratio: Fine content, % in area [%]
Fibrillation rate: MacroFibrillation index [%]

A 1 L aqueous dispersion was prepared by diluting a cellulose microfiber dispersion with pure water to a solid content concentration of 0.003–0.005% by mass. This aqueous dispersion was subjected to dispersion treatment using a high-shear homogenizer (IKA, product name "Ultra-Turrax T18") under the following conditions: rotation speed 25,000 rpm for 5 minutes. The aqueous dispersion prepared as described above was subjected to measurement using an autosampler, and the fineness ratio was calculated from the results.

<Preparation of porous sheets from pulp and cellulose microfibers>
Approximately 3.3 g (equivalent to 0.5 g of solids) of the hydrated acetylated pulp obtained by the method described later, or approximately 35 g (equivalent to 0.5 g of solids) of the cellulose fine fiber dispersion obtained in the production example described later, were taken and filtered by suction. The filtrate was added to tert-butanol, and the mixture was further dispersed in a mixer until no aggregates remained. The concentration was adjusted to 0.5% by mass per 0.5 g of cellulose solids. 100 g of the obtained tert-butanol dispersion was filtered on filter paper, dried at 150°C, and then the filter paper was peeled off to obtain a porous sheet.

<Average fiber diameter (D) of cellulose microfibers>
The number-average fiber diameter (D) of cellulose microfibers was measured using a scanning electron microscope (SEM) according to the following procedure. A porous sheet was prepared using the method described above and used as a measurement sample. The number-average diameter was determined from images at 10,000x or 50,000x magnification observed with a high-resolution scanning electron microscope (SEM). Specifically, three straight lines were drawn arbitrarily through the center point of the observed image, and the width of the fibers intersecting these lines was determined for at least 100 fibers. The number-average value was then calculated.

<Degree of crystallinity of cellulose microfibers>
The diffraction pattern (2θ/deg. 10-30) obtained by measuring the porous sheet prepared using the above method with wide-angle X-ray diffraction was analyzed using the Segal method and the following formula was obtained.
Crystallinity (%) = [I (200) - I (amorphous)] / I (200) x 100
I(200): Diffraction peak intensity due to the 200 plane (2θ = 22.5°) in a cellulose type I crystal. I(amorphous): Halo peak intensity due to amorphous material in a cellulose type I crystal, at a diffraction angle 4.5° lower than the 200 plane (2θ = 18.0°).

(X-ray diffraction measurement conditions)
Device: MiniFlex (manufactured by Rigaku Corporation)
Operation axis 2θ/θ
Radiation source CuKα
Measurement method: Continuous; Voltage: 40kV
Current 15mA
Starting angle 2θ=5°
Ending angle 2θ = 30°
Sampling width 0.020°
Scan speed: 2.0°/min
Sample: A porous sheet is attached to the sample holder.

<Degree of substitution (DS) of acetylated pulp and acetylated cellulose microfibers>
For acetylated pulp and acetylated cellulose microfibers, the degree of substitution (DS) was calculated from the reflective infrared absorption spectra of porous sheets prepared by the respective methods described above, based on the peak intensity ratio between the peak derived from the acetyl group and the peak derived from the cellulose skeleton. The peak of the C=O absorption band based on the acetyl group appears at 1730 ^cm⁻¹ , and the peak of the C-O absorption band based on the cellulose skeleton chain appears at 1030 ^cm⁻¹ . For acetylated cellulose, a correlation graph was created between the DS obtained from solid NMR measurements of acetylated cellulose (described later) and the modification rate (IR index 1030), which is defined as the ratio of the peak intensity of the C=O absorption band based on the acetyl group to the peak intensity of the C-O absorption band of the cellulose skeleton chain. The calibration curve of substitution DS calculated from the correlation graph was: DS = 4.13 × IR index (1030).
This was obtained by using [a specific method/tool].

(Measurement conditions for reflected infrared spectrum)
Equipment: Fourier transform infrared spectrophotometer (Nicolet Summit Pro, manufactured by ThermoFisher Scientific)
Total number of times: 16
Wavenumber resolution: 4cm ^-1
ATR crystal: Diamond; Angle of incidence: 45°

The method for calculating the DS of acetylated cellulose by solid NMR involved performing ^13C solid NMR measurements on freeze-ground acetylated pulp and acetylated fine cellulose fibers, and determining the DS using the following formula, which is calculated by comparing the area intensity (Inf) of the signal attributed to a single carbon atom derived from the modifying group with the total area intensity (Inp) of the signals attributed to carbon atoms C1-C6 derived from the pyranose ring of cellulose appearing in the range of 50 ppm to 110 ppm.
DS=(Inf)×6/(Inp)
For the acetyl group, a 23 ppm signal attributed to _-CH3 was used.

The conditions used for ^{the 13C} solid-state NMR measurement were as follows:
Equipment: Bruker Biospin Avance500WB
Frequency: 125.77 MHz
Measurement method: DD/MAS method Waiting time: 75 seconds
NMR sample tube: 4 mm diameter
Total number of times: 640 (approximately 14 hours)
MAS: 14,500Hz
Chemical shift standard: Glycine (External standard: 176.03 ppm)

<Number of moles of substituents>
The dispersion of cellulose microfibers obtained in the manufacturing example was subjected to conductivity titration according to the method described in non-patent literature (Biomacromolecules 2004, 5, 1983-1989) to determine the number of moles of carboxyl groups per unit mass of carboxylated cellulose microfibers.
Furthermore, regarding acetylated cellulose microfibers, the number of moles of acetyl groups per unit mass of acetylated cellulose microfibers was determined using the following formula, based on the DS measurement results mentioned above.
{1/[(162-DS) + (molecular weight of acetyl group × DS)]} × DS

<Content of cellulose microfibers relative to 100% by mass of nonvolatile components in the dispersion subjected to the concentration process>
It was calculated from the amount of each ingredient used.

<Processing speed>
Starting from the point when the cellulose microfiber dispersion was supplied to the continuous concentration device, the weight and solid content of the cellulose microfiber concentrate collected in the recovery container after 30 minutes of operation were measured, the solid content weight was calculated, and this was converted into a processing rate per hour.

<Solid content of concentrate>
Five g of the concentrate was taken and dried at 150°C using an IR moisture meter (MX-50 (manufactured by A&D)) to determine the solid content. For each example, ten samples were taken every 15 minutes during the concentration process, and the numerical mean and CV value (standard deviation/numerical mean) of the ten samples were calculated.

<Handling>
The handling characteristics in the concentration process were evaluated according to the following criteria.
×: One or more of the following problems (1) to (3) occurred. ○: None of the following problems (1) to (3) occurred. (1) Continuous concentration was impossible due to clogging of cellulose microfibers.
(2) Because it was difficult to separate the concentrate from the filter substrate, the residue remained attached to the filter substrate, resulting in a reduced recovery rate or making recovery impossible.
(3) The recovered cellulose microfibers did not allow the dispersant and molten resin to penetrate due to aggregation.

<Tensile yield strength and tensile elongation at break of resin compositions>
Resin composition pellets were molded using an injection molding machine under conditions compliant with JIS K6920-2 to produce multipurpose test specimens compliant with ISO 294-3. The injection molding temperatures were 260°C for PA6, 280°C for PA66, 210°C for POM, and 200°C for PP.

<Cellulose microfiber content in resin composition>
To quantify the cellulose microfibers in the resin composition, pellets of the resin composition were weighed, and the composition was dissolved and dispersed in a solvent that dissolves the resin and dispersant but not the cellulose microfibers. The insoluble matter recovered by centrifugation and filtration was washed in the same solvent, ethanol, and water in that order, and the sample was weighed after drying in an oven at 110°C. Five samples were weighed for each resin composition. The maximum and minimum values obtained are shown in Table 3.

As the solvent, hexafluoroisopropanol at room temperature was used when the resin was polyamide 6, polyamide 66, or polyacetal, and hot xylene at 140°C was used when the resin was polypropylene. Five thin sections were cut from the resin composition pellets for each resin composition, and each was subjected to the following treatment. 1 g of the sample was weighed using a precision balance, 30 mL of solvent (i.e., hexafluoroisopropanol or hot xylene) was added, and the resin was dissolved by ultrasonic irradiation using an ultrasonic cleaner. The mixture was pressure filtered through a PTFE membrane filter, and the residue was washed by pressure filtration twice with the solvent (i.e., hexafluoroisopropanol or hot xylene), twice with ethanol, and twice with water. The residue was dried at 110°C for 1 hour, and its weight was measured using a precision balance to calculate the cellulose microfiber content in the resin composition.

≪Materials used≫
<Resin>
Polyamide 6 (manufactured by Ube Industries, Ltd., UBE NYLON 1013B), melting point 225°C
Polyamide 66 (manufactured by Asahi Kasei Corporation, LEONA 1300), melting point 265°C
Polypropylene (manufactured by Prime Polymer Co., Ltd., J106G), melting point 160°C
Polyacetal (manufactured by Asahi Kasei Corporation, TENAC HC450), melting point 165°C

<Pulp>
Cotton linter pulp: Cotton linter pulp sheets obtained from Nippon Paper Pulp Trading Co., Ltd. were used.

<Manufacturing of acetylated pulp>
Dimethyl sulfoxide (30 kg) was added to a 40 L reaction vessel with a jacket, and the catalyst sodium bicarbonate (0.48 kg) and pulp (1.5 kg) were added and stirred. Hot water was circulated through the jacket to heat the liquid to 60°C. The inside of the reaction vessel was purged with nitrogen and vinyl acetate (1.4 kg) was added. The reaction was carried out for 2 hours, and the reaction was stopped by adding pure water (10 kg). A filter cloth (PP9B, available from Nakao Filter Industry Co., Ltd.) was set in a 100 L Nutsche filter, and pure water (50 kg) and the reaction solution were added and pressure filtration was performed (first filtration). Further pressure filtration with pure water (50 kg) was repeated five times at room temperature (second to sixth filtration), for a total of six pressure filters to obtain acetylated pulp with a solid content of 15% by mass in a water-containing state, which was used in the next process without drying. At this time, the DS of the pulp surface, determined by reflection infrared spectroscopy, was 1.50.

<Manufacturing Example 1> (Manufacturing of Cellulose Microfiber Dispersion A)
Defibration was performed using a defibration apparatus equipped with two tanks (Tank A and Tank B) connected by piping via a disc refiner. Cotton linter pulp sheets were immersed in water to a solid content concentration of 1.5% by mass, and a total of 20 kg of cotton linter pulp sheets were dispersed using a lab pulper (manufactured by Aikawa Iron Works Co., Ltd.). The liquid was then sent to Tank A and processed using a single disc refiner (manufactured by Aikawa Iron Works Co., Ltd., SDR14 type lab refiner, pressurized disc type). First, the slurry was introduced into Tank A, and then sent to Tank B via the disc refiner for storage. Once the processing of the slurry in Tank A was complete, the liquid was continuously sent from Tank B to Tank A via the disc refiner for storage, thereby controlling the number of times the slurry passed through the disc refiner (number of passes). Furthermore, the disc refiner's blade spacing adjustment mechanism is equipped with a ball screw type jack and a reduction gear. The deviation in the blade spacing during the beating process after reaching the desired blade spacing was 0.005 mm or less, as measured by a displacement sensor. The disc refiner used blades with a blade width of 4.0 mm and a groove ratio of 0.89, performing 30 passes with a blade spacing of 0.25 mm, followed by 30 passes using blades with a blade width of 0.8 mm and a groove ratio of 0.53, also maintaining a blade spacing of 0.25 mm.

The obtained slurry was subjected to 10 passes at 80 MPa using a high-pressure homogenizer (NS3015H, manufactured by Nilo Soavi). Similar to the disc refiner treatment described above, the high-pressure homogenizer treatment was carried out using two tanks, controlling the number of passes. A dispersion A of cellulose microfibers with a cellulose microfiber content of 100% by mass relative to 100% by mass of non-volatile components and an average fiber diameter of 95 nm was obtained.

<Manufacturing Example 2> (Manufacturing of dispersion B of acetylated cellulose microfibers)
Using 40 kg of acetylated pulp produced by repeating the above method multiple times as the raw material, the disc refiner treatment was carried out in the same manner as in Production Example 1, except that the number of passes for the high-pressure homogenizer treatment was 3, with a blade width of 0.8 mm and a blade groove ratio of 0.53, and a blade inter-blade distance of 0.25 mm. A dispersion B of acetylated cellulose fine fibers was obtained, with a cellulose fine fiber content of 100% by mass relative to 100% by mass of nonvolatile components, a DS of 0.78, and an average fiber diameter of 150 nm.

<Manufacturing Example 3> (Manufacturing of dispersion C of acetylated cellulose microfibers)
Using 75 kg of acetylated pulp produced by repeating the above method multiple times as raw material, the disc refiner treatment was carried out in the same manner as in Production Example 1, except that a blade with a blade width of 0.8 mm and a blade groove ratio of 0.53 was used, with a blade inter-blade distance of 0.30 mm and 20 passes in one stage. Without high-pressure homogenizer treatment, a dispersion C of acetylated cellulose fine fibers was obtained with a cellulose fine fiber content of 100% by mass relative to 100% by mass of nonvolatile components, DS = 0.88, and average fiber diameter of 450 nm.

<Manufacturing Example 4> (Manufacturing of Cellulose Microfiber Dispersion D)
Except for using 75 kg of unmodified cotton linter pulp, the procedure was carried out in the same manner as in Production Example 2 to obtain a dispersion of cellulose microfibers D with a cellulose microfiber content of 100% by mass relative to 100% by mass of nonvolatile components and an average fiber diameter of 178 nm.

<Manufacturing Example 5> (Manufacturing of dispersion E of acetylated cellulose microfibers)
Using 20 kg of acetylated pulp produced by repeating the above method multiple times as the raw material, the disc refiner treatment was carried out in the same manner as in Production Example 1, except that the number of passes for the high-pressure homogenizer treatment was 3, with a blade width of 4.0 mm and a blade groove ratio of 0.89, a blade inter-blade distance of 0.25 mm, and 30 passes. A dispersion E of acetylated cellulose fine fibers was obtained, with a cellulose fine fiber content of 100% by mass relative to 100% by mass of nonvolatile components, a DS of 0.80, and an average fiber diameter of 275 nm.

<Manufacturing Example 6> (Manufacturing of Acetylated Cellulose Microfiber Dispersion F)
Using 10 kg of acetylated pulp produced by repeating the above method multiple times as the raw material, the disc refiner treatment was carried out in the same manner as in Production Example 1, except that a blade with a blade width of 4.0 mm and a blade groove ratio of 0.89 was used, and the treatment was performed in one stage of 20 passes with a blade inter-blade distance of 0.30 mm. Without high-pressure homogenizer treatment, a dispersion F of acetylated cellulose fine fibers with DS = 0.88 and an average fiber diameter of 660 nm was obtained.

<Manufacturing Example 7> (Manufacturing of dispersion G of oxidized cellulose microfibers)
5 kg of bleached kraft pulp derived from coniferous trees was added to 500 L of an aqueous solution containing 78 g of TEMPO (available from Sigma Aldrich) and 754 g of sodium bromide, and stirred. 18 L of an aqueous sodium hypochlorite solution (5% available chlorine) was added, and the oxidation reaction was started at room temperature. During the reaction, 1 mol/L aqueous sodium hydroxide solution was added as needed to adjust the pH to 10. The reaction was carried out for 2 hours, and the mixture after the reaction was washed with water to obtain oxidized pulp (carboxylated cellulose). Water was added to adjust the concentration to 1.0% by mass, and the mixture was subjected to a 3-pass treatment in a high-pressure homogenizer to obtain a dispersion G of oxidized cellulose fine fibers with a cellulose fine fiber content of 100% by mass relative to 100% by mass of nonvolatile components and an average fiber diameter of 5 nm.

The properties of the cellulose microfibers in the obtained dispersion are summarized in Table 1.

<Example 1>
The cellulose microfiber dispersion A prepared in Production Example 1 was dehydrated and concentrated using the continuous concentration apparatus shown in Figure 3. The dispersion was diluted with pure water to a solid content of 0.50% by mass and poured into a 1.5 ^m³ tank equipped with stirring blades. Stirring was continued at a peripheral speed of 0.7 m/sec to maintain a homogeneous dispersion. A filtration substrate (cellulose and polyester blended nonwoven fabric) was placed on a circulating papermaking wire and fed at a speed of 5 m/min. The dispersion was supplied onto the filtration substrate by a mono pump at a speed of 17 L/min. After deliquing in a -20 kPa suction section to concentrate the cellulose microfibers in layers, the material was transferred from the filtration substrate to a transfer roll, scraped off with a scraper on the top of the transfer roll, and the concentrate was recovered. Throughout the process, the processing speed was maintained at 5.0 kg-DS/hr and the temperature at 20°C to 25°C. Note that the temperature is the temperature of the dispersion in the tank (the same applies to the following examples).

<Example 2>
The dispersion B of acetylated cellulose microfibers prepared in Production Example 2 was dehydrated and concentrated using the continuous concentration apparatus shown in Figure 3. The concentrate was recovered in the same manner as in Example 1, except that the dispersion was diluted with pure water to a solid content of 0.35% by mass. Throughout the process, the processing rate was maintained at 3.5 kg-DS/hr and the temperature at 20°C to 25°C.

<Example 3>
The dispersion C of acetylated cellulose microfibers prepared in Production Example 3 was dehydrated and concentrated using the continuous concentration apparatus shown in Figure 3. The dispersion was used without dilution, maintaining a solid content of 1.5% by mass. The procedure was carried out in the same manner as in Example 1, except that the dispersion supply rate was set to 28 L/min and the suction section pressure was set to -40 kPa. The concentrate was recovered. Throughout the process, the processing rate was maintained at 25.0 kg-DS/hr and the temperature at 20°C to 25°C.

<Example 4>
The cellulose microfiber dispersion D prepared in Production Example 4 was dehydrated and concentrated using the continuous concentration apparatus shown in Figure 3. The dispersion was used without dilution, maintaining a solid content of 1.5% by mass. The process was carried out in the same manner as in Example 1, except that the suction section was set to -30 kPa for deliquidation, and the concentrated product was recovered. Throughout the process, the processing rate was maintained at 15.0 kg-DS/hr and the temperature at 20°C to 25°C.

<Example 5>
The dispersion B of acetylated cellulose microfibers prepared in Production Example 2 was dehydrated and concentrated using the continuous concentration apparatus shown in Figure 3. The dispersion was diluted with pure water to a solid content of 0.35% by mass, and the concentrate was recovered in the same manner as in Example 1, except that the feed rate of the filter substrate was set to 4 m/sec and the suction section to -25 kPa. Throughout the process, the processing rate was maintained at 3.4 kg-DS/hr and the temperature was maintained between 20°C and 25°C.

<Example 6>
The dispersion E of acetylated cellulose microfibers prepared in Production Example 5 was dehydrated and concentrated using the continuous concentration apparatus shown in Figure 3. The dispersion was diluted with pure water to a solid content of 0.35% by mass, and the procedure was carried out in the same manner as in Example 1, except that the feed rate of the filter substrate was 3 m/sec, the dispersion supply rate was 11 L/min, and two suction sections were provided at -25 kPa and -1.8 kPa. The concentrate was recovered. Throughout the process, the processing rate was maintained at 2.3 kg-DS/hr and the temperature was maintained between 20°C and 25°C.

<Example 7>
The dispersion E of acetylated cellulose microfibers prepared in Production Example 5 was dehydrated and concentrated using the continuous concentration apparatus shown in Figure 3. The dispersion was diluted with pure water to a solid content of 0.50% by mass, and the concentrate was recovered in the same manner as in Example 1, except that the feed rate of the filter substrate was 3 m/sec, the dispersion supply rate was 11 L/min, and the suction section was -25 kPa. Throughout the process, the processing rate was maintained at 3.2 kg-DS/hr and the temperature was maintained between 20°C and 25°C.

<Example 8>
The cellulose microfiber dispersion D prepared in Production Example 4 was dehydrated and concentrated using the continuous concentration apparatus shown in Figure 3. The dehydration process was carried out in the same manner as in Example 1, except that the dispersion supply rate was 7 L/min and the suction pressure was set to -25 kPa. The concentrated product was recovered. Throughout the process, the processing rate was maintained at 2.0 kg-DS/hr and the temperature was maintained between 20°C and 25°C.

<Example 9>
The dispersion F of acetylated cellulose microfibers prepared in Production Example 6 was dehydrated and concentrated using the continuous concentration apparatus shown in Figure 3. The dispersion was diluted with pure water to a solid content of 0.35% by mass, and the concentrate was recovered in the same manner as in Example 1, except that the feed rate of the filter substrate was 3 m/sec, the dispersion supply rate was 7 L/min, and the suction section was set to -30 kPa. Throughout the process, the processing rate was maintained at 1.4 kg-DS/hr and the temperature was maintained between 20°C and 25°C.

<Example 10>
Dispersion B of acetylated cellulose microfibers prepared in Production Example 2 and powdered cellulose acetate butyrate (CAB, Eastman Chemical Co., Ltd., product name: CAB381-0.1) were dehydrated and concentrated using the continuous concentrator shown in Figure 3. After diluting dispersion B with pure water to a solid content of 0.35% by mass, CAB was added so that the ratio of CAB to the total solid content of acetylated cellulose microfibers and CAB (100% by mass) was 10% by mass (i.e., the ratio of acetylated cellulose microfibers to 100% by mass of nonvolatile components was 90% by mass). The mixture was stirred and then subjected to dehydration and concentration, and the procedure was carried out in the same manner as in Example 1, except that the concentrate was recovered. Throughout the process, the processing rate was maintained at 3.7 kg-DS/hr and the temperature at 20°C to 25°C.

<Comparative Example 1>
The dispersion G of oxidized cellulose microfibers prepared in Production Example 7 was dehydrated and concentrated using the continuous concentration apparatus shown in Figure 3. The procedure was the same as in Example 9, except that the above dispersion was used, but the fibers were too fine, causing the filter substrate to become clogged and concentration impossible.

<Comparative Example 2>
Dispersion B of acetylated cellulose microfibers prepared in Production Example 2 was dehydrated and concentrated using the continuous concentrator shown in Figure 3. The procedure was the same as in Example 1, except that the dispersion was used at a solid content of 1.5% by mass without dilution and the dispersion supply rate was set to 50 L/min. However, due to insufficient dewatering, the solid content could only be concentrated to 4.5% by mass, resulting in poor transferability of the concentrate to the transfer roll and making recovery difficult. Furthermore, the recovered cellulose microfibers contained a large amount of water, and the CV value of the solid content was high at 0.32.

<Comparative Example 3>
The dispersion A of cellulose microfibers prepared in Production Example 1 was used in a continuous paper machine equipped with a wire section, a press section, and a dryer section. The processing speed was maintained at 1.3 kg-DS/hr throughout the process. The drying temperature in the dryer section was adjusted to 110°C to remove moisture. The material was dehydrated to a solid content of 93% by mass, and the CV value of the solid content was 0.010. An attempt was made to mix the obtained product with a dispersant in the same manner as in Example 11 described below, but the cellulose microfibers were aggregated to a state where redispersion was difficult, making it difficult to knead them with a thermoplastic resin as cellulose microfibers.

<Comparative Example 4>
The dispersion E of acetylated cellulose microfibers prepared in Production Example 5 was dehydrated and concentrated at 20°C to 25°C using a batch-type pressure filter, a 100L Nütsche filter. A filter cloth (PP9B, available from Nakao Filter Industry Co., Ltd.) was set in the filter disc, and the dispersion was injected without dilution. The mixture was then filtered under nitrogen pressure of 0.18 MPa. A layer of tightly compressed cellulose microfibers was found directly above the filter cloth, with a layer of soft, water-containing cellulose microfibers on top of that. The CV value of the solids content was high at 0.44.

<Example 11>
0.7 kg of the solid content of the concentrate obtained in Example 1 was weighed, and 0.3 kg of polyethylene oxide-polypropylene oxide copolymer (Sanyo Chemical Industries: GL-3000) was added as a dispersant. The mixture was thoroughly stirred using a commercial mixer (Kenmix Aiko Chef PRO) manufactured by Aikosha Seisakusho Co., Ltd. to obtain a concentrated cake with the dispersant. Using a high-speed vacuum dryer (model: FS10) manufactured by Earth Technica Co., Ltd., the jacket temperature was set to 80°C, and the mixture was stirred with an agitator (peripheral speed 2 m/sec) and a chopper (3500 rpm). The pressure was reduced to -70 kPa with a vacuum pump, and vacuum drying was carried out until the product temperature reached 70°C. The moisture content was measured using an infrared heating type moisture meter (MX-50 (A&D Co., Ltd.)) and it was confirmed that the moisture content was 7% by mass or less (solid content mass 93% or more), at which point the drying process was terminated.

The dried powder containing cellulose microfibers and a dispersant obtained by the above method, and PA6 pellets as a thermoplastic resin, were weighed so that the cellulose microfiber content was 10% by mass of the resin composition. Each was fed into a twin-screw extruder using separate feeders, and the mixture was melt-kneaded at a cylinder temperature of 250°C and a rotation speed of 250 rpm to extrude it into strands. The mixture was then water-cooled and cut to obtain pellets.

Using the obtained resin composition pellets, the tensile yield strength and tensile elongation at break were measured, and the content of cellulose fine fibers in the resin composition was measured according to the procedure described above.

<Example 12>
Except for using the concentrated acetylated cellulose microfibers from Example 2, the resin composition was manufactured and evaluated in the same manner as in Example 11.

<Example 13>
Except for using the concentrated acetylated cellulose microfibers from Example 3, the resin composition was manufactured and evaluated in the same manner as in Example 11.

<Example 14>
Except for using the concentrated cellulose microfibers from Example 4, the resin composition was manufactured and evaluated in the same manner as in Example 11.

<Example 15>
Except for using the concentrated acetylated cellulose microfibers from Example 5, the resin composition was manufactured and evaluated in the same manner as in Example 11.

<Example 16>
The resin composition was manufactured and evaluated in the same manner as in Example 11, except that concentrated acetylated cellulose microfibers from Example 5 were used, liquid rubber (Ricon 181, manufactured by Clay Valley Corporation) was used as a dispersant, and PP pellets were used as the thermoplastic resin, and the kneading and molding were carried out at 200°C.

<Example 17>
The resin composition was manufactured and evaluated in the same manner as in Example 11, except that concentrated acetylated cellulose microfibers were used in Example 5, POM pellets were used as the thermoplastic resin, and the kneading and molding were performed at 210°C.

<Example 18>
The resin composition was manufactured and evaluated in the same manner as in Example 11, except that the concentrated acetylated cellulose fine fibers from Example 5 were used, PA66 pellets were used as the thermoplastic resin, and the kneading and molding were performed at 280°C.

<Example 19>
Except for using the concentrated acetylated cellulose microfibers from Example 6, the resin composition was manufactured and evaluated in the same manner as in Example 11.

<Example 20>
Except for using the concentrated acetylated cellulose microfibers from Example 7, the resin composition was manufactured and evaluated in the same manner as in Example 11.

<Example 21>
The resin composition was manufactured and evaluated in the same manner as in Example 11, except that concentrated acetylated cellulose microfibers were used in Example 8.

<Example 22>
The resin composition was manufactured and evaluated in the same manner as in Example 11, except that concentrated acetylated cellulose microfibers were used in Example 9.

<Example 23>
The resin composition was manufactured and evaluated in the same manner as in Example 11, except that a mixture of concentrated acetylated cellulose microfibers and CAB was used in Example 10.

<Comparative Example 5>
The resin composition was manufactured and evaluated in the same manner as in Example 10, except that concentrated acetylated cellulose microfibers were used in Comparative Example 2.

<Comparative Example 6>
The resin composition was manufactured and evaluated in the same manner as in Example 10, except that the concentrated cellulose microfibers used in Comparative Example 3 were employed.

<Comparative Example 7>
The resin composition was manufactured and evaluated in the same manner as in Example 10, except that concentrated acetylated cellulose microfibers were used in Comparative Example 4.

<Comparative Example 8>
Multipurpose test specimens were prepared and evaluated by injection molding using PA6 pellets as they were.

<Comparative Example 9>
Multipurpose test specimens were prepared and evaluated by injection molding using PP pellets as they were.

<Comparative Example 10>
Multipurpose test specimens were prepared and evaluated by injection molding using POM pellets as they were.

<Comparative Example 11>
PA66 pellets were used directly for injection molding to create multi-purpose test specimens, which were then evaluated.

The results are shown in Tables 2 and 3.

As shown in Tables 1-3, the cellulose microfibers concentrated by the method of this disclosure have their solid content and CV value controlled within a predetermined range, demonstrating both improved physical properties and stable fiber content when used as a filler in filler-reinforced resin compositions.

The concentrates and dried cellulose microfiber dispersions produced by the method of this disclosure contain a dispersion medium (particularly water) at a predetermined concentration while exhibiting minimal variation in solid content. Therefore, they can be mass-produced while maintaining desired quality when used in applications requiring redispersion of cellulose microfibers or uniform mixing with other materials. Consequently, these concentrates and dried cellulose microfibers are suitably applicable to a wide range of applications utilizing resin compositions reinforced with cellulose microfibers, including industrial machinery parts, general machinery parts, automotive, railway, vehicle, ship, and aerospace components, electronic and electrical components, building and civil engineering materials, consumer goods, sports and leisure goods, wind turbine housing components, containers and packaging materials, and more.

11 Blade 12 Groove 21 Rotating blade 22 Fixed blade 300 Continuous concentration device 301 Tank 302 Pump 303 Suction section 304 Filtration substrate 305 Feeding mechanism 306 Transfer body 307 Scraper 308 Recovery container 309 Agitator 309a Agitator 309b Agitator blade 310 Support 311 Drive mechanism 312 Pressure reduction mechanism

Claims (10)

A method for producing a concentrated cellulose microfiber dispersion,
The method includes a concentration step of deliquing the cellulose fine fiber dispersion to obtain the concentrate,
The average fiber diameter of the cellulose microfibers in the cellulose microfiber dispersion is 50 to 1000 nm.
In the concentration step, the cellulose fine fiber dispersion is continuously deliquidated at a processing rate of 1.0 kg-DS/h or more and less than 45.0 kg-DS/h.
In the concentration step, when the solid content of the concentrate is sampled and measured 10 times, the average value of the solid content is 5% by mass or more and 60% by mass or less, and the CV value (standard deviation/mean value) of the solid content is 0.001 or more and 0.300 or less.
method. The method according to claim 1, wherein a cellulose fine fiber dispersion, stirred at a peripheral speed of 0.01 m/sec to 6.00 m/sec, is supplied to the concentration step. The method according to claim 1 or 2, wherein the concentration step is performed at a temperature of 80°C or lower. The method according to any one of claims 1 to 3, wherein the cellulose microfibers in the cellulose microfiber dispersion contain 70% or more of fibers with a fiber length of less than 0.1 mm, based on the number of fibers. The method according to any one of claims 1 to 4, wherein the cellulose microfiber dispersion subjected to the concentration step has a content of 75% by mass or more of cellulose microfibers relative to a total content of 100% by mass of nonvolatile components. The method according to any one of claims 1 to 5, wherein the cellulose microfibers in the cellulose microfiber dispersion are chemically modified with hydrophobic substituents. The method according to any one of claims 1 to 6, wherein the cellulose microfibers in the cellulose microfiber dispersion are chemically modified with acetyl groups. The method according to any one of claims 1 to 7, wherein the cellulose fine fibers subjected to the concentration step are made from cotton linters. A step of producing a concentrate of cellulose microfiber dispersion by the method of any one of claims 1 to 8,
A step of drying the aforementioned concentrate to produce a cellulose microfiber dry body,
A method for producing a dried cellulose microfiber body, including the above. A step of producing a concentrated cellulose microfiber dispersion by the method of any one of claims 1 to 8, or producing a dried cellulose microfiber by the method of claim 9,
A step of producing a resin composition by mixing a concentrate of the cellulose microfiber dispersion or the dried cellulose microfiber with a thermoplastic resin,
A method for producing a resin composition containing [the specified element].