Manufacturing method of dry powder of cellulose fiber

Abstract

To provide a manufacturing method of a dry powder of a cellulose fiber showing excellent redispersibility, and a manufacturing method of a resin composite containing using the dry powder prepared by the method.SOLUTION: A method for manufacturing a dry powder of a cellulose fiber, comprising a slurry preparation step for preparing a slurry comprising the cellulose fibers and water, and a granulation step for agitating the slurry under reduced pressure to form a dry powder of the cellulose fibers, in which the granulation step comprises forming the particles of the cellulose fibers by stirring and chopper pulverizing the particles.SELECTED DRAWING: None

Description

Technical Field

[0001] The present invention relates to a method for producing a dry powder of cellulose fibers and a method for producing a composite (also referred to as a resin composite in the present disclosure) containing cellulose fibers and a resin.

Background Art

[0002] Since thermoplastic resins are light and have excellent processing characteristics, they are widely used in various fields such as automotive members, electrical and electronic members, office equipment housings, and precision parts. However, in many cases, the mechanical properties, dimensional stability, etc. of the resin alone are insufficient. Therefore, a composite of a resin and various fillers is generally used. In recent years, the use of nanofibers such as cellulose nanofibers (CNF) as such fillers has been studied. Nanofibers including CNF have the property of being easily aggregated in a dry state, and thus are produced as a dispersion liquid capable of stable dispersion. When applying cellulose nanofibers to various uses, there are cases where the above dispersion liquid is once dried and then redispersed in a dispersion medium to prepare a redispersion liquid.

[0003] Patent Document 1 describes a method for redispersing a cellulose nanofiber dispersion liquid, in which powder particles of cellulose nanofibers produced by drying a produced cellulose nanofiber dispersion liquid are redispersed in an aqueous solvent, and when redispersing the powder particles of cellulose nanofibers in the aqueous solvent, stirring is performed and mechanical shear force is applied.

[0004] Patent Document 2 describes a method for treating chemically modified fibrillated cellulose, which includes introducing a chemically modified fibrillated cellulose material into a heat drying device (20) including a belt (22), forming at least one rod-shaped body of the fibrillated cellulose material on the belt (22), dehydrating the chemically modified fibrillated cellulose material on the belt (22) using a heated air flow having a temperature of at least 40°C, and concentrating and / or drying the chemically modified fibrillated cellulose material such that the dry solid content of the fibrillated cellulose material is at least 10% after the heat drying device (20).

[0005] Patent Document 3 describes a powdery nanofiber characterized in that (A) a powdery nanofiber is blended with (B) a dispersant in an amount of 1 to 40% by weight in terms of solid content and has a bulk density of 90 to 200 g / L.

[0006] Patent Document 4 describes a method for producing dried microfibers having a moisture content of 0 to 1% by mass, which includes homogenizing cellulose nanofibers in the presence of an organic solvent and then removing the organic solvent.

Prior Art Documents

Patent Documents

[0007]

Patent Document 1

Patent Document 2

Patent Document 3

Patent Document 4

Summary of the Invention

Problems to be Solved by the Invention

[0008] When storing or transporting cellulose fibers, especially cellulose nanofibers, in the form of a dispersion, the cellulose fibers are likely to deteriorate (such as rot) because they are placed in a wet environment, and the increase in storage and transportation costs due to the extra volume and weight occupied by the dispersion medium becomes a problem. If the cellulose fibers are stored and transported in a dry state, the volume and weight can be reduced, and the advantage that it is easy to compound with other materials according to the application can also be obtained. However, once the cellulose fibers are dried from the dispersion state, it has been difficult to reproduce the good dispersion state of the cellulose fibers before drying (that is, to obtain good redispersibility) even if they are redispersed in the dispersion medium later.

[0009] The present invention aims to solve the above problems and provides a method for producing a dry powder of cellulose fibers exhibiting good redispersibility, and a method for producing a resin composite including using the dry powder prepared by the method.

Means for Solving the Problems

[0010] As a result of intensive studies to solve the above problems, the present inventor has found that when producing a dry powder of cellulose fibers under specific drying conditions, a dry powder of cellulose fibers with excellent redispersibility can be produced, and thus the present invention has been completed. That is, the present invention includes the following aspects.

[0011] [1] A method for producing a dry powder of cellulose fibers, comprising: a slurry preparation step of preparing a slurry containing cellulose fibers and water, and a granulation step of stirring the slurry under reduced pressure to form the dry powder of the cellulose fibers, wherein the granulation step includes forming the particles of the cellulose fibers by the stirring and chopping and pulverizing the particles, a method. [2] The method according to the above aspect 1, wherein the slurry contains 5% by mass or more of water at the start of the granulation step. [3] The method according to aspect 1 or 2 above, wherein in the granulation step, an additional medium, which is a liquid medium different from water, is added to the slurry. [4] The method according to aspect 3 above, wherein in the granulation step, an additional medium, which is a liquid medium different from water, is added to the slurry in two or more times. [5] The method according to aspect 3 or 4 above, wherein the additional medium is selected from the group consisting of: an alcohol having a boiling point of 50°C to 170°C; an ether; a carboxylic acid; an ester; a ketone; and a nitrogen-containing solvent. [6] The method according to any one of aspects 3 to 5 above, wherein the additional medium is a substance that forms an azeotropic mixture with water. [7] The method according to aspect 6 above, wherein the additional medium is added to the slurry at a ratio higher than the azeotropic composition ratio with water. [8] The method according to any one of aspects 3 to 7 above, wherein the additional medium is added to the slurry in a range of a mass ratio of water: additional medium in the slurry of 1:99 to 90:10. [9] A method for producing a dry powder of cellulose fiber, comprising: a slurry preparation step of preparing a slurry containing cellulose fiber and a liquid medium, and a granulation step of stirring the slurry under reduced pressure to form the dry powder of the cellulose fiber, wherein the granulation step includes forming particles of the cellulose fiber by the stirring and chopping and pulverizing the particles.

[10] The method according to aspect 9 above, wherein the liquid medium is one or more selected from the group consisting of: an alcohol having a boiling point of 50°C to 170°C; an ether; a carboxylic acid; an ester; a ketone; and a nitrogen-containing solvent.

[11] The method according to any one of aspects 1 to 10 above, wherein in the slurry preparation step and / or the granulation step, a binder is added to the slurry.

[12] The method according to aspect 11 above, wherein the binder is selected from the group consisting of a polyalkylene oxide, a cellulose ether, and a cellulose ester.

[13] The method according to aspect 11 or 12 above, wherein in the slurry preparation step and / or the granulation step, the binder is dissolved in a medium and added to the slurry.

[14] The granulation step is carried out in a granulator equipped with a stirring blade, a chopper blade and a decompression mechanism, In the granulation step, the stirring is carried out by rotating the stirring blade at a peripheral speed of 0.5 m / sec to 40 m / sec, and the chopper pulverization is carried out by rotating the chopper blade at 100 rpm to 6000 rpm, The granulator is configured such that the particles pulverized by the chopper are further subjected to the stirring. The method according to any one of aspects 1 to 13 above.

[15] The granulation step is carried out in a granulator equipped with a stirring blade, a chopper blade and a decompression mechanism, In the granulation step, the stirring is carried out by rotating the stirring blade at a peripheral speed of 0.5 m / sec to 40 m / sec, and the chopper pulverization is carried out by rotating the chopper blade at a peripheral speed of 0.5 m / sec to 40 m / sec, The granulator is configured such that the particles pulverized by the chopper are further subjected to the stirring. The method according to any one of aspects 1 to 14 above.

[16] The method according to aspect 15 above, wherein the peripheral speed of the chopper blade is equal to or less than the peripheral speed of the stirring blade.

[17] The granulation step is carried out at a temperature of 20 to 160 °C and a degree of decompression of -100 kPa to -1 kPa. The method according to any one of aspects 1 to 16 above.

[18] The bulk density of the dried powder is 0.05 g / mL to 1.0 g / mL. The method according to any one of aspects 1 to 17 above.

[19] Using cellulose fibers derived from cotton linter. The method according to any one of aspects 1 to 18 above.

[20] Using chemically modified cellulose fibers. The method according to any one of aspects 1 to 19 above.

[21] Using cellulose fibers chemically modified with a hydrophobic substituent. The method according to any one of aspects 1 to 20 above.

[22] The method according to any one of the above aspects 1 to 21, wherein the number average fiber diameter of the cellulose fiber is 10 nm or more and 1000 nm or less.

[23] A method for producing a composite containing cellulose fiber and resin, the method comprising preparing a dry powder by the method according to any one of the above aspects 1 to 22, and mixing the dry powder and the resin.

[24] The resin is a thermoplastic resin, The method according to the above aspect 23, wherein the dry powder and the resin are mixed by melt kneading. [Advantages of the Invention]

[0012] According to one aspect of the present invention, there can be provided a method for producing a dry powder of cellulose fiber exhibiting good redispersibility, and a method for producing a resin composite including using the dry powder prepared by the method. [Brief Description of the Drawings]

[0013]

Figure 1

Figure 2

[0014] Exemplary aspects of the present invention will be specifically described below, but the present invention is not limited to these aspects.

[0015] ≪Method for Producing Dry Powder of Cellulose Fiber≫ One aspect of the present invention includes a slurry preparation step of preparing a dispersion (slurry) containing cellulose fiber and a liquid medium (in one aspect, a liquid medium containing water), and a granulation step of stirring the slurry under reduced pressure to form a dry powder of the cellulose fiber. The granulation step includes forming particles of the cellulose fiber by stirring and chopping and pulverizing the particles. A method for producing a dry powder of cellulose fiber is provided.

[0016] <Slurry Preparation Process> In this process, a slurry containing cellulose fibers and a liquid medium (in one embodiment, a liquid medium containing water) is prepared. As raw materials for the cellulose fibers, natural cellulose and regenerated cellulose can be used. As natural cellulose, wood pulp obtained from wood species (hardwood or softwood), non-wood pulp obtained from non-wood species (cotton, bamboo, hemp, bagasse, kenaf, cotton linter, sisal, straw, etc.), cellulose fiber aggregates produced by animals (e.g., tunicates), algae, and microorganisms (e.g., acetic acid bacteria) can be used. As regenerated cellulose, regenerated cellulose fibers (viscose, cupra, tencel, etc.), cellulose derivative fibers, regenerated cellulose or ultrafine fibers of cellulose derivatives obtained by the electrospinning method can be used. Non-wood pulp obtained from cotton linter is preferred in that high-purity and highly crystallized cellulose fibers can be obtained.

[0017] In one embodiment, the cellulose fibers are cellulose nanofibers. Cellulose nanofibers refer to fine cellulose obtained by treating pulp or the like with hot water at 100 °C or higher to hydrolyze hemicellulose and weaken it, and then defibrating it by a pulverization method using a high-pressure homogenizer, a microfluidizer, a ball mill, a disk mill, a mixer (e.g., a homomixer), or the like. In one embodiment, the cellulose nanofibers have a number average fiber diameter of 1 nm or more and 1000 nm or less. The cellulose fibers may be chemically modified as described below.

[0018] The slurry can be prepared by dispersing cellulose fibers (for example, the cellulose nanofibers obtained through the above fibrillation) in a liquid medium. The dispersion can be carried out using a high-pressure homogenizer, a microfluidizer, a ball mill, a disk mill, a mixer (for example, a homomixer), etc. For example, the product of the above fibrillation may be obtained as the product of the slurry preparation step of the present disclosure. The liquid medium in the slurry can contain water in one aspect and can be free of water in another aspect. In one aspect, the liquid medium can contain water and optionally other liquid media (for example, organic solvents) singly or in combination of two or more. As the organic solvent, generally used water-miscible organic solvents can be used, for example: alcohols with a boiling point of 50°C to 170°C (for example, methanol, ethanol, n-propanol, i-propanol, n-butanol, i-butanol, s-butanol, t-butanol, etc.); ethers (for example, propylene glycol monomethyl ether, 1,2-dimethoxyethane, diisopropyl ether, tetrahydrofuran, 1,4-dioxane, etc.); carboxylic acids (for example, formic acid, acetic acid, lactic acid, etc.); esters (for example, ethyl acetate, vinyl acetate, etc.); ketones (for example, acetone, methyl ethyl ketone, methyl isobutyl ketone, cyclopentanone, cyclohexanone, etc.); nitrogen-containing solvents (dimethylformamide, dimethylacetamide, acetonitrile, etc.), etc. It is preferable that these organic solvents are substances that form an azeotropic mixture with water. In particular, it is more preferable that the azeotropic mixture has a minimum azeotropic point at which the boiling point is lower than the boiling points of water and the organic solvent alone, because it is easy to dry moisture even when the degree of vacuum and / or temperature is low. In a typical aspect, the liquid medium in the slurry is substantially only water.

[0019] When the liquid medium does not contain water, the liquid medium is a commonly used water-miscible organic solvent, such as: alcohols with a boiling point of 50 °C to 170 °C (such as methanol, ethanol, n-propanol, i-propanol, n-butanol, i-butanol, s-butanol, t-butanol, etc.); ethers (such as propylene glycol monomethyl ether, 1,2-dimethoxyethane, diisopropyl ether, tetrahydrofuran, 1,4-dioxane, etc.); carboxylic acids (such as formic acid, acetic acid, lactic acid, etc.); esters (such as ethyl acetate, vinyl acetate, etc.); ketones (such as acetone, methyl ethyl ketone, methyl isobutyl ketone, cyclopentanone, cyclohexanone, etc.); nitrogen-containing solvents (dimethylformamide, dimethylacetamide, acetonitrile, etc.) and hydrophobic organic solvents, such as aromatic hydrocarbons (benzene, toluene, xylene, etc.); aliphatic hydrocarbons (hexane, heptane, octane, decane, etc.); halogenated hydrocarbons (carbon tetrachloride, chloroform, dichloromethane, chloroethane, etc.), etc., and may be one or more selected from the group consisting of them.

[0020] In addition to the cellulose fibers and the liquid medium, the slurry may contain additives (such as binders, dispersants, antioxidants, preservatives, thickeners, etc.).

[0021] Since the cellulose raw material contains an alkali-soluble component and a sulfuric acid-insoluble component (such as lignin), through a purification process such as delignification by cooking treatment and a bleaching process, the alkali-soluble component and the sulfuric acid-insoluble component may be reduced. On the other hand, the purification process such as delignification by cooking treatment and the bleaching process cut the molecular chain of cellulose and change the weight-average molecular weight and the number-average molecular weight. Therefore, it is desirable that the purification process and the bleaching process of the cellulose raw material are controlled so that the weight-average molecular weight of cellulose and the ratio of the weight-average molecular weight to the number-average molecular weight do not deviate from an appropriate range.

[0022] In addition, since the purification process such as delignification and the bleaching process by steaming treatment reduce the molecular weight of cellulose molecules, there is a concern that these processes may result in the reduction of the molecular weight of cellulose and the alteration of the cellulose raw material, leading to an increase in the proportion of alkali-soluble components. Since the alkali-soluble components are inferior in heat resistance, it is desirable that the purification process and the bleaching process of the cellulose raw material be controlled so that the amount of alkali-soluble components contained in the cellulose raw material is within a certain range or less.

[0023] In one aspect, the number average fiber diameter (D) of the cellulose fiber is preferably 2 to 1000 nm from the viewpoint of obtaining a good physical property improvement effect by the cellulose fiber. The number average fiber diameter of the cellulose fiber is more preferably 4 nm or more, or 5 nm or more, or 10 nm or more, or 15 nm or more, or 20 nm or more, and more preferably 500 nm or less, or 450 nm or less, or 400 nm or less, or 350 nm or less, or 300 nm or less, or 250 nm or less.

[0024] In one aspect, the number average fiber length (L) of the cellulose fiber is preferably 100 nm to 1000 μm from the viewpoint of obtaining a good physical property improvement effect by the cellulose fiber. The number average fiber length of the cellulose fiber is more preferably 200 nm or more, or 500 nm or more, or 1 μm or more, or 10 μm or more, or 100 μm or more, and more preferably 500 μm or less, or 300 μm or less, or 200 μm or less.

[0025] The average L / D of the cellulose fiber is preferably 50 or more, or 80 or more, or 100 or more, or 120 or more, or 150 or more from the viewpoint of improving the mechanical properties of the resin composite containing the cellulose fiber well with a small amount of cellulose fiber. The upper limit is not particularly limited, but is preferably 5000 or less from the viewpoint of handleability.

[0026] In one aspect, the number average fiber diameter (D), number average fiber length (L), and L / D ratio of the cellulose fibers of the present disclosure are values measured by the following procedure using a scanning electron microscope (SEM). The aqueous dispersion of cellulose fibers is replaced with t-butanol, diluted to 0.001 to 0.1% by mass, and dispersed using a high-shear homogenizer (for example, manufactured by IKA, trade name "Ultra Turrax T18") under the treatment conditions: rotation speed 15,000 rpm × 3 minutes. The sample is cast on an osmium-evaporated silicon substrate and air-dried, and the measurement sample is measured with a high-resolution scanning electron microscope (SEM). Specifically, in an observation field with the magnification adjusted so that at least 100 fibrous substances are observed, the lengths (L) and diameters (D) of 100 randomly selected fibrous substances are measured, and the ratio (L / D) is calculated. For the cellulose fibers, the number average value of the length (L), the number average value of the diameter (D), and the number average value of the ratio (L / D) are calculated.

[0027] In another aspect, the number average fiber diameter of the cellulose fibers of the present disclosure is the number average fiber diameter calculated from the specific surface area obtained by the BET method by nitrogen adsorption. When the average fiber diameter is 1000 nm or less, it corresponds to a specific surface area of 2.667 m 2 / g or more.

[0028] The method for calculating the number average fiber diameter by nitrogen adsorption is as follows. That is, after replacing the aqueous dispersion of cellulose fibers with t-butanol, it is filtered, concentrated, and dried to produce a porous sheet, and the specific surface area of the porous sheet is measured using the BET method by nitrogen adsorption. When cellulose is in an ideal state where no fusion occurs between fibers and the cellulose density is d (g / cm 3 ), and the fiber diameter is a cylinder with D (nm), the relationship between the specific surface area and the fiber diameter is expressed by the following formula. Specific surface area (m 2 / g) = 4000 / (dD) And when the cellulose density is 1.50 g / cm 3 , the number average fiber diameter is expressed by the following formula. D (nm) = 2667 / specific surface area (m 2 / g) Therefore, when D is 1000 nm, the specific surface area is 2.667 m 2 / g.

[0029] In addition, the length, diameter, and L / D ratio of the cellulose fibers in the resin composite described below are obtained by dissolving the resin component in the resin composite in an organic or inorganic solvent that can dissolve the resin component of the resin composite, separating the cellulose fibers, thoroughly washing them with the solvent, substituting them with t-butanol, preparing a 0.001 to 0.1 mass% dispersion, and redispersing them with a high-shear homogenizer (for example, manufactured by IKA, trade name "Ultra Turrax T18").

[0030] The crystallinity of the cellulose fiber is preferably 55% or more. When the crystallinity is within this range, the mechanical properties (strength, dimensional stability) of the cellulose fiber itself are high. Therefore, when the cellulose fiber is dispersed in the resin, the strength and dimensional stability of the resin composite tend to be high. The lower limit of the more preferable crystallinity is 60%, even more preferably 70%, and most preferably 80%. The upper limit of the crystallinity of the cellulose fiber is not particularly limited, and a higher value is preferable, but from the perspective of production, the preferable upper limit is 99%.

[0031] Between the microfibrils of plant-derived cellulose and between the microfibril bundles, there are alkali-soluble polysaccharides such as hemicellulose and acid-insoluble components such as lignin. Hemicellulose is a polysaccharide composed of sugars such as mannan and xylan, and forms a hydrogen bond with cellulose to play a role in connecting between microfibrils. Lignin is a compound having an aromatic ring and is known to be covalently bonded to hemicellulose in the plant cell wall. If the remaining amount of impurities such as lignin in the cellulose fiber is large, it may cause discoloration due to heat during processing. Therefore, from the perspective of suppressing the discoloration of the resin composite during extrusion processing and molding processing, it is desirable that the crystallinity of the cellulose fiber be within the above range.

[0032] The crystallinity referred to here is determined by the Segal method from the diffraction pattern (2θ / deg. being 10 to 30) when the sample is measured by wide-angle X-ray diffraction, in the case where the cellulose fiber is cellulose I crystal (derived from natural cellulose), by the following formula. Crystallinity (%) = ([Diffraction intensity due to the (200) plane at 2θ / deg. = 22.5] - [Diffraction intensity due to the amorphous at 2θ / deg. = 18]) / [Diffraction intensity due to the (200) plane at 2θ / deg. = 22.5] × 100

[0033] Also, the crystallinity, in the case where the cellulose fiber is cellulose II crystal (derived from regenerated cellulose), is determined by the following formula from the absolute peak intensity h0 at 2θ = 12.6° attributed to the (110) plane peak of the cellulose II crystal and the peak intensity h1 from the baseline at this plane spacing in wide-angle X-ray diffraction. Crystallinity (%) = h1 / h0 × 100 Note that the porous sheet described above is used as the measurement sample.

[0034] As crystal forms of cellulose, type I, type II, type III, type IV, etc. are known. Among them, in particular, type I and type II are widely used. Although type III and type IV are obtained on a laboratory scale, they are not widely used on an industrial scale. As the cellulose fiber of the present disclosure, since the structural mobility is relatively high, and by dispersing the cellulose fiber in a resin, a resin composite having a lower linear expansion coefficient and more excellent strength and elongation during tensile and bending deformation can be obtained, cellulose fibers containing cellulose I crystal or cellulose II crystal are preferred, and cellulose fibers containing cellulose I crystal and having a crystallinity of 55% or more are more preferred.

[0035] Also, the degree of polymerization of the cellulose fiber is preferably 100 or more, more preferably 150 or more, still more preferably 200 or more, still more preferably 300 or more, still more preferably 400 or more, still more preferably 450 or more, and preferably 3500 or less, more preferably 3300 or less, still more preferably 3200 or less, still more preferably 3100 or less, still more preferably 3000 or less.

[0036] From the viewpoints of processability and manifestation of mechanical properties, it is desirable that the degree of polymerization of the cellulose fiber be within the above range. From the viewpoint of processability, it is preferable that the degree of polymerization is not too high, and from the viewpoint of manifestation of mechanical properties, it is desirable that it is not too low.

[0037] The degree of polymerization of the cellulose fiber means the average degree of polymerization measured according to the reduced specific viscosity method using a copper ethylenediamine solution described in the confirmation test (3) of the "Fifteenth Revised Japanese Pharmacopoeia Explanation Book (published by Hirokawa Shoten)".

[0038] In one aspect, the weight average molecular weight (Mw) of the cellulose fiber is 100,000 or more, more preferably 200,000 or more. The ratio (Mw / Mn) of the weight average molecular weight to the number average molecular weight (Mn) is 6 or less, preferably 5.4 or less. A larger weight average molecular weight means fewer end groups of the cellulose molecules. Also, since the ratio (Mw / Mn) of the weight average molecular weight to the number average molecular weight represents the width of the molecular weight distribution, a smaller Mw / Mn means fewer ends of the cellulose molecules. Since the ends of the cellulose molecules serve as the starting points for thermal decomposition, particularly highly heat-resistant cellulose fibers and resin composites containing cellulose fibers and resins can be obtained when the weight average molecular weight of the cellulose molecules in the cellulose fiber is not only large but also the width of the molecular weight distribution is narrow while the weight average molecular weight is large. The weight average molecular weight (Mw) of the cellulose fiber may be, for example, 600,000 or less, or 500,000 or less, from the viewpoint of the availability of the cellulose raw material. The ratio (Mw / Mn) of the weight average molecular weight to the number average molecular weight (Mn) may be, for example, 1.5 or more, or 2 or more, from the viewpoint of the ease of manufacturing the cellulose fiber. Mw can be controlled within the above range by selecting a cellulose raw material having an Mw suitable for the purpose, appropriately performing physical and / or chemical treatments on the cellulose raw material within an appropriate range, and the like. Mw / Mn can also be controlled within the above range by selecting a cellulose raw material having an Mw / Mn suitable for the purpose, appropriately performing physical and / or chemical treatments on the cellulose raw material within an appropriate range, and the like. In both the control of Mw and the control of Mw / Mn, examples of the above physical treatments include physical treatments that apply mechanical forces such as impact, shear, shear, and friction by a microfluidizer, ball mill, disk mill, etc. for dry or wet grinding, a crusher, a homomixer, a high-pressure homogenizer, an ultrasonic device, etc. Examples of the above chemical treatments include cooking, bleaching, acid treatment, regeneration of cellulose, etc.

[0039] The weight-average molecular weight and number-average molecular weight of cellulose referred to herein are values obtained by dissolving cellulose in N,N-dimethylacetamide added with lithium chloride and then determining them by gel permeation chromatography using N,N-dimethylacetamide as a solvent.

[0040] Examples of methods for controlling the degree of polymerization (i.e., average degree of polymerization) or molecular weight of cellulose fibers include hydrolysis treatment. By hydrolysis treatment, the depolymerization of amorphous cellulose inside the cellulose fibers proceeds, and the average degree of polymerization decreases. At the same time, by hydrolysis treatment, in addition to the above-mentioned amorphous cellulose, impurities such as hemicellulose and lignin are also removed, so that the inside of the fibrous material becomes porous.

[0041] The method of hydrolysis is not particularly limited, and examples include acid hydrolysis, alkali hydrolysis, hydrothermal hydrolysis, steam explosion, microwave decomposition, etc. These methods may be used alone or in combination of two or more. In the method of acid hydrolysis, for example, using α-cellulose obtained as pulp from fibrous plants as a cellulose raw material, dispersing it in an aqueous medium, adding an appropriate amount of a protonic acid, carboxylic acid, Lewis acid, heteropolyacid, etc., and heating with stirring, the average degree of polymerization can be easily controlled. The reaction conditions such as temperature, pressure, and time at this time vary depending on the cellulose species, cellulose concentration, acid species, acid concentration, etc., but are appropriately adjusted so that the target average degree of polymerization is achieved. For example, conditions such as using an aqueous solution of a mineral acid of 2% by mass or less, treating cellulose at 100°C or higher under pressure for 10 minutes or more can be mentioned. Under these conditions, the catalyst component such as an acid penetrates into the cellulose fibers, hydrolysis is promoted, the amount of the catalyst component used is reduced, and subsequent purification becomes easy. In addition, the dispersion of the cellulose raw material during hydrolysis may contain a small amount of an organic solvent within a range that does not impair the effects of the present invention in addition to water.

[0042] Alkaline-soluble polysaccharides that may be contained in cellulose fibers include, in addition to hemicellulose, β-cellulose and γ-cellulose. Alkaline-soluble polysaccharides are understood by those skilled in the art as components obtained as the alkaline-soluble part of holocellulose obtained by solvent extraction and chlorination treatment of plants (e.g., wood) (i.e., components obtained by removing α-cellulose from holocellulose). Alkaline-soluble polysaccharides are polysaccharides containing hydroxyl groups, have poor heat resistance, may decompose when heated, cause yellowing during heat aging, and may cause disadvantages such as a decrease in the strength of cellulose fibers. Therefore, it is preferable that the content of alkaline-soluble polysaccharides in cellulose fibers is low.

[0043] In one aspect, from the viewpoint of obtaining good dispersibility of cellulose fibers, the average content rate of alkaline-soluble polysaccharides in cellulose fibers is preferably 20% by mass or less, or 18% by mass or less, or 15% by mass or less, or 12% by mass or less with respect to 100% by mass of cellulose fibers. From the viewpoint of the ease of manufacturing cellulose fibers, the above content rate may be 1% by mass or more, or 2% by mass or more, or 3% by mass or more.

[0044] The average content rate of alkaline-soluble polysaccharides can be determined by the method described in a non-patent document (Wood Science Experiment Manual, edited by the Japanese Wood Research Society, pages 92-97, 2000), and is determined by subtracting the α-cellulose content rate from the holocellulose content rate (Wise method). This method is understood in the art as a method for measuring the amount of hemicellulose. Calculate the alkaline-soluble polysaccharide content rate three times for one sample, and take the number average of the calculated alkaline-soluble polysaccharide content rates as the average content rate of alkaline-soluble polysaccharides.

[0045] In one aspect, from the viewpoint of avoiding a decrease in the heat resistance of cellulose fibers and the accompanying discoloration, the average content rate of acid-insoluble components in cellulose fibers is preferably 10% by mass or less, or 5% by mass or less, or 3% by mass or less with respect to 100% by mass of cellulose fibers. From the viewpoint of the ease of manufacturing cellulose fibers, the above content rate may be 0.1% by mass or more, or 0.2% by mass or more, or 0.3% by mass or more.

[0046] The average content rate of acid-insoluble components is determined by quantifying the acid-insoluble components using the Klason method described in the non-patent literature (Wood Science Experiment Manual, edited by the Japanese Wood Research Society, pages 92-97, 2000). This method is understood in the art as a method for measuring the amount of lignin. After stirring the sample in a sulfuric acid solution to dissolve cellulose, hemicellulose, etc., it is filtered through a glass fiber filter paper, and the obtained residue corresponds to the acid-insoluble components. The acid-insoluble component content rate is calculated from the weight of the acid-insoluble components, and the number average of the acid-insoluble component content rates calculated for 3 samples is taken as the average acid-insoluble component content rate.

[0047] The thermal decomposition start temperature (T D ) is, from the viewpoint of exhibiting heat resistance and mechanical strength desired for in-vehicle applications, etc., in one aspect, 270 °C or higher, preferably 275 °C or higher, more preferably 280 °C or higher, and still more preferably 285 °C or higher. Although a higher thermal decomposition start temperature is more preferable, from the viewpoint of ease of manufacturing the cellulose fibers, it may be, for example, 320 °C or lower, or 300 °C or lower.

[0048] In the present disclosure, T D is, as shown in the explanatory diagram of FIG. 2, a value obtained from a graph in thermogravimetric (TG) analysis where the horizontal axis is temperature and the vertical axis is the weight retention rate %. (Note that FIG. 2(B) is an enlarged view of FIG. 2(A).) Starting from the weight of the cellulose fibers at 150 °C (state where moisture is almost removed) (weight reduction amount 0 wt%), the temperature is further increased, and a straight line passing through the temperature (T 1% ) at 1 wt% weight reduction and the temperature (T 2% ) at 2 wt% weight reduction is obtained. The temperature at the point where this straight line intersects the horizontal line (baseline) passing through the starting point of 0 wt% weight reduction amount is defined as T D .

[0049] The 1% weight reduction temperature (T 1% ) is the temperature at 1 wt% weight reduction starting from the weight at 150 °C when the temperature increase is continued by the method of the above T D .

[0050] The 250 °C weight loss rate (T 250℃ ) of the cellulose fiber is the weight loss rate when the cellulose fiber is held at 250 °C for 2 hours under a nitrogen flow in TG analysis.

[0051] From the viewpoint of process efficiency in the subsequent granulation process, the concentration of the cellulose fiber in the slurry to be subjected to the process of the present invention is preferably 5% by mass or more, or 10% by mass or more, or 15% by mass or more, or 20% by mass or more, or 25% by mass or more. From the viewpoint of avoiding an excessive increase in the viscosity of the slurry and solidification due to aggregation and maintaining good handleability, it is preferably 60% by mass or less, or 55% by mass or less, or 50% by mass or less, or 45% by mass or less. Generally, the production of cellulose nanofibers is often carried out in a dilute dispersion, but the cellulose concentration in the slurry may be adjusted to the above preferred range by concentrating such a dilute dispersion. For concentration, methods such as suction filtration, pressure filtration, centrifugal dewatering, and heating can be used.

[0052] <Granulation process> In this step, the slurry obtained in the slurry preparation step is stirred under reduced pressure to form a dry powder of cellulose fiber. The granulation process can be carried out, for example, using a high-speed stirring granulator equipped with stirring blades, chopper blades, and a decompression mechanism, and includes forming particles of cellulose fiber by stirring and chopping the particles.

[0053] The stirring blades and the chopper blades may have different or the same rotation axes.

[0054] A granulator in which the stirring blades and the chopper blades have different rotation axes may include, for example, a vertical or horizontal can body having a material inlet at the upper part, a combination of low-speed rotating stirring blades arranged at the bottom of the can body and high-speed rotating chopper blades arranged at the side of the can body, a decompression mechanism, and optionally a temperature adjustment mechanism.

[0055] A granulator in which the stirring blade and the chopper blade have the same rotation axis may include, for example, a vertical or horizontal can body having a material inlet at the upper part, a combination of a stirring blade disposed at the bottom of the can body and a chopper blade disposed above the same rotation axis, a decompression mechanism, and optionally a temperature adjustment mechanism. When the measured slurry is introduced into the can body from the material supply port, the slurry is dried under reduced pressure while undergoing convection in the can body due to the centrifugal force and upward propulsion force of the stirring blade, and particles are generated. The particles move within the can body, hit the chopper blade having a strong shearing force, are pulverized, and then return to the vicinity of the stirring blade and are stirred again to increase the particle size. In this way, by repeatedly subjecting the particles to stirring and chopper pulverization, it is possible to produce a dried powder of cellulose fibers that have been sized (i.e., have a small variation in particle size).

[0056] The stirring blade may be a rotating blade such as a two-blade, three-blade, or four-blade, or may be a rotating blade in which a plurality of blades are connected in a ring shape and integrated. Also, the rotating blade may have a multi-stage structure of an upper blade and a lower blade. The blade surface of the rotating blade may be perpendicular or inclined with respect to the rotation axis, and may be a flat surface, a curved surface, or a combination thereof. From the viewpoint of obtaining good stirring efficiency, preferably, the rotating blade is arranged along the bottom surface and the side wall of the can body, and the clearance between the tip of the rotating blade and the bottom surface and the side wall of the can body is minimized within the limit that does not hinder the rotation of the rotating blade. The stirring blade generates particles by imparting centrifugal force and upward propulsion force to the slurry.

[0057] As the rotation conditions of the rotating blade, the lower limit of the peripheral speed is preferably 0.5 m / sec, or 0.7 m / sec, or 1 m / sec, or 3 m / sec, or 6 m / sec, and the upper limit is preferably 40 m / sec, or 30 m / sec, or 20 m / sec, or 15 m / sec, or 14 m / sec, or 13 m / sec, or 12 m / sec. The peripheral speed does not necessarily have to be constant at all times during the granulation process and may be varied within a preferable range. By setting the peripheral speed within the preferable range, a dry powder of cellulose fibers excellent in redispersibility can be obtained. The fact that the peripheral speed is below the upper limit is preferable from the viewpoint of preventing deterioration of physical properties due to a decrease in the crystallinity of cellulose. The fact that the peripheral speed is above the lower limit is preferable from the viewpoint of improving the efficiency of pulverizing the slurry during drying with the chopper blades.

[0058] The shear rate applied to the slurry by the stirring blades is 50 sec -1 ~7000 sec ‐1 or 150 sec -1 ~5000 sec ‐1 or 250 sec -1 ~3500 sec ‐1 can be exemplified.

[0059] The chopper blades may have one or a plurality of chopper blades extending outward from the rotation axis, and the plurality of chopper blades may have a multi-stage structure. The rotation axis may protrude inwardly from the side wall of the can body in a cantilever manner, or may penetrate the can body in the horizontal direction (that is, may constitute a through-type chopper blade). A plurality of chopper blades may be arranged at predetermined intervals in the rotation axis direction.

[0060] As the pulverization conditions by the chopper blades, the lower limit of the chopper rotation speed is preferably 10 rpm, or 50 rpm, or 100 rpm, or 200 rpm, or 500 rpm, or 1000 rpm, and the upper limit is preferably 6000 rpm, or 5000 rpm, or 4500 rpm, or 4000 rpm. By setting the chopper rotation speed within the preferable range, a dry powder of cellulose fibers excellent in redispersibility can be obtained. The fact that the chopper rotation speed is below the upper limit is preferable from the viewpoint of preventing deterioration of physical properties due to a decrease in the crystallinity of cellulose. The fact that the chopper rotation speed is above the lower limit is preferable from the viewpoint of obtaining a good pulverization effect of the chopper.

[0061] In one aspect, the lower limit of the peripheral speed of the chopper blade is preferably 0.5 m / sec, or 0.7 m / sec, or 1 m / sec, or 3 m / sec, or 6 m / sec, and the upper limit is preferably 40 m / sec, 30 m / sec, 20 m / sec, 15 m / sec, or 14 m / sec, or 13 m / sec, or 12 m / sec. By setting the peripheral speed of the chopper blade within a preferable range, a dry powder of cellulose fiber excellent in redispersibility can be obtained. The fact that the peripheral speed of the chopper blade is below the upper limit is preferable from the viewpoint of preventing deterioration of physical properties due to a decrease in the crystallinity of cellulose. The fact that the peripheral speed of the chopper blade is above the lower limit is preferable from the viewpoint of obtaining a good pulverizing effect of the chopper.

[0062] When the chopper blade and the stirring blade are on different rotation axes, the chopper blade / stirring blade ratio of each of the rotational diameter and the peripheral speed may be arbitrarily set as desired. For example, it may be 1.0 / 1.0 to 0.1 / 1.0, or 0.5 / 1.0 to 0.1 / 1.0, or 0.5 / 1.0 to 0.2 / 1.0, or 0.5 / 1.0 to 0.3 / 1.0. In one aspect, the peripheral speed of the chopper blade is equal to or lower than the peripheral speed of the stirring blade. When the diameter and the peripheral speed of the chopper blade are equal to or lower than the diameter and the peripheral speed of the stirring blade, the convection of the slurry by the stirring blade is not disturbed, and it is preferable because the control of the powder shape is easy. When the diameter and the peripheral speed of the chopper blade are 1 / 10 or more of the diameter and the peripheral speed of the stirring blade, the pulverizing effect by the chopper blade is high and preferable.

[0063] On the one hand, when the chopper blade and the stirring blade are on the same rotation axis, it is preferable that their rotation speeds are equal. Also, it is preferable that the rotation diameter of the chopper blade is equal to or less than the rotation diameter of the stirring blade, and it is preferable that the peripheral speed of the chopper blade is equal to or less than the peripheral speed of the stirring blade. When the rotation diameter of the chopper blade is larger than the rotation diameter of the stirring blade, and when the peripheral speed of the chopper blade is larger than the peripheral speed of the stirring blade, the upward propulsion force by the stirring blade decreases, and the stirring efficiency tends to be low. When the chopper blade and the stirring blade are on the same rotation axis, the chopper blade / stirring blade ratio of each of the rotation diameter and the peripheral speed is preferably 1.0 / 1.0 to 0.5 / 1.0, or 0.95 / 1.0 to 0.5 / 1.0, or 0.95 / 1.0 to 0.6 / 1.0. In one aspect, the peripheral speed of the chopper blade is equal to or less than the peripheral speed of the stirring blade, or is smaller than the peripheral speed of the stirring blade.

[0064] Even when the chopper blade and the stirring blade are on the same rotation axis, the slurry or particles convect in the can body due to the centrifugal force and upward propulsion force of the lower blade corresponding to the stirring blade, and are dried under reduced pressure to generate particles. In the process, they are crushed by the shearing force of the upper blade corresponding to the chopper blade, and the crushed particles return to the vicinity of the stirring blade and are stirred again, so that the particle size increases and granulation gradually occurs. Therefore, even if there are two or more blades on the same rotation axis, the lower blade has the role of the stirring blade, and the upper blade has the role of the chopper blade. When the diameter and peripheral speed of the chopper blade are equal to or less than the diameter and peripheral speed of the stirring blade, it is preferable because it is easy to generate convection of the slurry by the stirring blade, and the slurry remaining in the corner of the can body is less likely to remain. When the diameter and peripheral speed of the chopper blade are at least half of the diameter and peripheral speed of the stirring blade, the crushing effect by the chopper blade is high, which is preferable.

[0065] As the conditions for vacuum drying in the granulation process, from the viewpoint of increasing the drying rate and enhancing the production efficiency, the lower limit of the jacket temperature is preferably 20°C or higher, or 30°C or higher, or 40°C or higher, or 50°C or higher. From the viewpoint of the thermal stability of the cellulose fiber and the additive, the upper limit is 160°C or lower, or 150°C or lower, or 140°C or lower, or 130°C or lower. The lower limit of the degree of vacuum is preferably -1 kPa or higher, or -10 kPa or higher, -20 kPa or higher, -30 kPa or higher, -40 kPa or higher, -50 kPa or higher, and the upper limit is preferably -100 kPa or lower, -95 kPa or lower, -90 kPa or lower. For the pressure adjustment, a vacuum pump with appropriate exhaust capacity may be fully operated, or air and / or an inert gas may be intentionally introduced using a vacuum regulator, a leak valve, etc. When introducing air and / or an inert gas, it is preferable to provide an intake section at the can body or upstream of the can body because the medium vapor can be efficiently exhausted.

[0066] Since cellulose fibers are extremely prone to aggregation in the dry state, in the dry powder of ordinary cellulose fibers, the cellulose fibers are strongly aggregated with each other and are not easily redispersed even when the dry powder is redispersed in a dispersion medium. In the granulation process of the method of the present disclosure, since granulation is performed by stirring, the shearing force applied to the slurry and the generated particles is relatively small, and the cellulose fibers aggregate to generate coarse particles. The generated coarse particles are refined by chopper grinding, but the particles after refinement are further subjected to stirring to increase their particle size. If coarse particles are generated by this stirring, they are refined again by chopper grinding. In chopper grinding, although the coarse particles are ground, the particles that are originally refined are not ground any further. Therefore, by repeating the particle generation by stirring and chopper grinding, a dry powder with reduced particle size variation can be obtained. In addition, by chopper grinding the particles of cellulose fiber, the cellulose fibers on the particle surface can be made to stand up (that is, a sparse structure is formed on the particle surface). By repeating such chopper grinding and stirring, a dry powder with a desired particle size and a sparse (that is, low bulk density) can be generated.

[0067] The slurry at the start of the granulation process preferably contains 5 mass% or more, or 20 mass% or more, or 40 mass% or more, or 60 mass% or more of a liquid medium from the viewpoint of stirring efficiency. The amount of the liquid medium in the slurry at the start of the granulation process may be 95 mass% or less, or 90 mass% or less, or 80 mass% or less from the viewpoint of process efficiency.

[0068] The slurry at the start of the granulation process preferably contains 5 mass% or more, or 20 mass% or more, or 40 mass% or more, or 60 mass% or more of water from the viewpoint of stirring efficiency. The amount of water in the slurry at the start of the granulation process may be 95 mass% or less, or 90 mass% or less, or 80 mass% or less from the viewpoint of process efficiency.

[0069] In the granulation step when the liquid medium in the slurry contains water, it is preferable to add an additional medium which is a liquid medium different from water to the slurry. Examples of the additional medium include various organic solvents as exemplified in the section of <Slurry preparation step>. The additional medium is preferably: alcohols having a boiling point of 50°C to 170°C (e.g., methanol, ethanol, n-propanol, i-propanol, n-butanol, i-butanol, s-butanol, t-butanol, etc.); ethers (e.g., propylene glycol monomethyl ether, 1,2-dimethoxyethane, diisopropyl ether, tetrahydrofuran, 1,4-dioxane, etc.); carboxylic acids (e.g., formic acid, acetic acid, lactic acid, etc.); esters (e.g., ethyl acetate, vinyl acetate, etc.); ketones (e.g., acetone, methyl ethyl ketone, methyl isobutyl ketone, cyclopentanone, cyclohexanone, etc.); and nitrogen-containing solvents (dimethylformamide, dimethylacetamide, acetonitrile, etc.), and one or more media selected from the group consisting of t-butanol, s-butanol, i-butanol, acetone, etc. are more preferable. In addition, it is preferable that these organic solvents are substances that form an azeotropic mixture with water. In particular, it is more preferable to have a minimum azeotropic point at which the boiling point of the azeotropic mixture is lower than the boiling points of water and the organic solvent alone, because moisture can be easily dried even when the degree of vacuum and / or temperature is low. The timing of addition is preferably during the granulation step, for example, after the water in the slurry has progressed to 80% by mass or less, or 70% by mass or less, or 60% by mass or less, or 50% by mass or less, or 40% by mass or less, or 30% by mass or less, or 20% by mass or less, or 10% by mass or less. The remaining water at these ratios causes the additional medium to be substituted for water, suppressing the aggregation of cellulose fibers and enabling the formation of a dry powder having a desired particle size and good redispersibility.

[0070] In a preferred embodiment, an additional medium is added to the slurry in a mass ratio of water in the slurry: additional medium of 1:99 to 90:10. The mass ratio is more preferably 1:99 to 80:20, or 1:99 to 70:30, or 5:95 to 70:30, or 5:95 to 60:40, or 10:90 to 60:40. By adding the additional medium at the ratio within the above range, strong aggregation between cellulose fibers at a microscopic level, such as 10 μm or less, can be suppressed, while granulation at a level of more than 10 μm to 1000 μm or less can be promoted. Therefore, it becomes possible to achieve both good progress of the granulation process and good redispersibility of the obtained dry powder. When the additional medium is a substance that forms an azeotropic mixture with water, it is preferable to add the additional medium to the slurry at a ratio higher than the azeotropic composition ratio with water (i.e., the minimum ratio of the additional medium that can form an azeotropic mixture with water).

[0071] In another preferred embodiment, the additional medium is added to the slurry in two or more times. By repeating the addition and drying of the additional medium in the granulation process, the replacement of moisture and the additional medium progresses, and additives such as binders are uniformly mixed with the cellulose fibers, making it possible to achieve both good redispersibility of the obtained dry powder and the function of the binder.

[0072] In another aspect, from the viewpoints of reducing the usage amount of the additional medium and reducing the drying time, it is preferable that the granulation process includes a step of adding the additional medium at a flow rate per unit time while continuing vacuum drying. In this step, it is particularly preferable to add the additional medium at a flow rate per unit time so that the total liquid amount in the slurry (i.e., the total amount of water and the additional medium) is maintained constant. Depending on the type of the additional medium, the total liquid amount in the slurry may be increased or decreased. After such a step, vacuum drying can be further performed to reduce the total liquid amount to obtain the target dry powder.

[0073] In the granulation process, when forming a slurry with an arbitrary water: additional medium ratio, it is preferable in terms of the process to add the additional medium while volatilizing water rather than adding the entire amount of the additional medium at once, because the total added amount of the additional medium can be reduced. Also, since the additional medium can be added while granulating, the replacement of water with the additional medium proceeds easily, and the powder is likely to have good redispersibility. The additional liquid may be added, for example, in the form of droplets, mist, or the like.

[0074] The moisture content of the slurry in the granulation process can be measured with a heat drying type moisture meter or a Karl Fischer moisture meter. Also, the mass ratio of water to the additional medium in the slurry after adding the additional medium is, for example, i) A method of measuring the moisture content of the slurry with a Karl Fischer moisture meter and measuring and calculating the liquid ratio of the volatile components (water and the additional medium) in the slurry with a heat drying type moisture meter ii) A method of extracting the additional medium in the slurry with a different solvent capable of dissolving the additional medium, measuring the content rate of the additional medium by gas chromatography, and measuring and calculating the total liquid ratio of the volatile components (water and the additional medium) in the slurry with a heat drying type moisture meter iii) A method of extracting water and the additional medium in the slurry with a heavy solvent and calculating by solution NMR, etc. can be mentioned.

[0075] Also, in an embodiment where the liquid medium in the slurry prepared in the slurry preparation step does not contain water, an additional medium may be added in the granulation step. As the additional medium, generally used water-miscible organic solvents such as: alcohols with a boiling point of 50°C to 170°C (e.g., methanol, ethanol, n-propanol, i-propanol, n-butanol, i-butanol, s-butanol, t-butanol, etc.); ethers (e.g., propylene glycol monomethyl ether, 1,2-dimethoxyethane, diisopropyl ether, tetrahydrofuran, 1,4-dioxane, etc.); carboxylic acids (e.g., formic acid, acetic acid, lactic acid, etc.); esters (e.g., ethyl acetate, vinyl acetate, etc.); ketones (e.g., acetone, methyl ethyl ketone, methyl isobutyl ketone, cyclopentanone, cyclohexanone, etc.); nitrogen-containing solvents (dimethylformamide, dimethylacetamide, acetonitrile, etc.) and hydrophobic organic solvents such as aromatic hydrocarbons (benzene, toluene, xylene, etc.); aliphatic hydrocarbons (hexane, heptane, octane, decane, etc.); halogenated hydrocarbons (carbon tetrachloride, chloroform, dichloromethane, chloroethane, etc.), etc. One or more selected from the group may be used. As a preferred addition mode of the additional medium, it may be added once or divided into multiple times before or after the start of granulation. The additional medium may be added, for example, in the form of droplets or mist while drying under reduced pressure during granulation.

[0076] In one embodiment, the average particle size of the dry powder of cellulose fibers 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 a value measured by the laser diffraction / scattering method or the dry sieving method.

[0077] In one aspect, the bulk density of the dry powder of cellulose fibers is 0.05 g / mL or more, or 0.06 g / mL or more, or 0.07 g / mL or more, or 0.08 g / mL or more, or 0.09 g / mL or more, or 0.10 g / mL or more from the viewpoint of ease of production and transportation efficiency of the dry powder, and is 1.0 g / mL or less, or 0.9 g / mL or less, or 0.8 g / mL or less, or 0.7 g / mL or less, or 0.6 g / mL or less in terms of good redispersibility of the dry powder. The bulk density of the present disclosure is a value measured by a loose bulk density measurement method.

[0078] <Chemical modification> In one aspect, chemically modified cellulose fibers are used as the cellulose fibers. The cellulose fibers may be those previously chemically modified, for example, at the stage of raw material pulp or linter, during fibrillation treatment, or after fibrillation treatment, or may be chemically modified during the slurry preparation process, during the granulation process, or after the granulation process. In a preferred aspect, the chemical modification is a chemical modification with a hydrophobic substituent.

[0079] As a modifier for cellulose, a compound that reacts with the hydroxyl group of cellulose can be used, and examples include an esterifying agent, an etherifying agent, and a silylating agent. In a preferred aspect, the chemical modification is acylation using an esterifying agent. Preferred esterifying agents include acid halides, acid anhydrides, and vinyl esters of carboxylic acids, carboxylic acids.

[0080] The acid halide may be at least one selected from the group consisting of compounds represented by the following formula (1). R 1 -C(=O)-X (1) (In the formula, R 1 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, benzoyl iodide, etc. Among these, acid chlorides can be preferably employed from the viewpoints of reactivity and handleability. In the reaction of acid halides, one or more alkaline compounds may be added for the purpose of neutralizing acidic substances that act as catalysts and are 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.

[0081] As the acid anhydride, any suitable acid anhydrides can be used. For example, saturated aliphatic monocarboxylic acid anhydrides such as acetic anhydride, propionic anhydride, (iso)butyric anhydride, and valeric anhydride; unsaturated aliphatic monocarboxylic acid anhydrides such as (meth)acrylic anhydride and oleic anhydride; alicyclic monocarboxylic acid anhydrides such as cyclohexanecarboxylic anhydride and tetrahydrobenzoic anhydride; aromatic monocarboxylic acid anhydrides such as benzoic anhydride and 4-methylbenzoic anhydride; As the dibasic carboxylic acid anhydride, for example, anhydrous saturated aliphatic dicarboxylic acids such as succinic anhydride and adipic anhydride, anhydrous unsaturated aliphatic dicarboxylic acid anhydrides such as maleic anhydride and itaconic anhydride, anhydrous alicyclic dicarboxylic acids such as 1-cyclohexene-1,2-dicarboxylic anhydride, hexahydrophthalic anhydride, and methyltetrahydrophthalic anhydride, and anhydrous aromatic dicarboxylic acid anhydrides such as phthalic anhydride and naphthalic anhydride; Examples of polybasic carboxylic acid anhydrides having three or more basic groups include (anhydrous) polycarboxylic acids such as trimellitic anhydride and pyromellitic anhydride. In the reaction of acid anhydrides, as a catalyst, an acidic compound such as sulfuric acid, hydrochloric acid, or phosphoric acid, or a Lewis acid (for example, a Lewis acid compound represented by 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 lanthanoid 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 an alkaline compound such as triethylamine or pyridine may be added singly or in combination of two or more.

[0082] As the vinyl carboxylate, the following formula (1): R-COO-CH=CH2…Formula (1) {In the formula, R is any one of an alkyl group having 1 to 24 carbon atoms, an alkenyl group having 2 to 24 carbon atoms, a cycloalkyl group having 3 to 16 carbon atoms, or an aryl group having 6 to 24 carbon atoms.} The vinyl carboxylate represented by the formula is preferred. The vinyl carboxylate is more preferably at least one selected from the group consisting of vinyl acetate, vinyl propionate, vinyl butyrate, vinyl caproate, vinyl cyclohexanecarboxylate, vinyl caprylate, vinyl caprate, vinyl laurate, vinyl myristate, vinyl palmitate, vinyl stearate, vinyl pivalate, vinyl octylate, divinyl adipate, vinyl methacrylate, vinyl crotonate, vinyl pivalate, vinyl octylate, vinyl benzoate, and vinyl cinnamate. In the esterification reaction with the vinyl carboxylate, as a catalyst, one or more selected from the group consisting of alkali metal hydroxides, alkaline earth metal hydroxides, alkali metal carbonates, alkaline earth metal carbonates, alkali metal hydrogen carbonates, primary to tertiary amines, quaternary ammonium salts, imidazole and its derivatives, pyridine and its derivatives, and alkoxides may be added.

[0083] Examples of the alkali metal hydroxides and alkaline earth metal hydroxides include sodium hydroxide, potassium hydroxide, lithium hydroxide, calcium hydroxide, barium hydroxide and the like. Examples of the alkali metal carbonates, alkaline earth metal carbonates and alkali metal hydrogen carbonates include lithium carbonate, sodium carbonate, potassium carbonate, cesium carbonate, magnesium carbonate, calcium carbonate, barium carbonate, lithium hydrogen carbonate, sodium hydrogen carbonate, potassium hydrogen carbonate, cesium hydrogen carbonate and the like.

[0084] The primary, secondary and tertiary amines refer to primary amines, secondary amines 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 the like.

[0085] Examples of imidazole and its derivatives include 1-methylimidazole, 3-aminopropylimidazole, carbonyldiimidazole and the like.

[0086] Examples of pyridine and its derivatives include N,N-dimethyl-4-aminopyridine, picoline and the like.

[0087] Examples of alkoxides include sodium methoxide, sodium ethoxide, potassium-t-butoxide and the like.

[0088] Examples of the carboxylic acid include at least one selected from the group consisting of the compounds represented by the following formula (1). R-COOH …(1) (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.)

[0089] Specific examples of the carboxylic acid 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, octylic acid, benzoic acid, and cinnamic acid.

[0090] Among these carboxylic acids, at least one selected from the group consisting of acetic acid, propionic acid, and butyric acid, particularly acetic acid, is preferable from the viewpoint of reaction efficiency. In the reaction of the carboxylic acid, as a catalyst, an acidic compound such as sulfuric acid, hydrochloric acid, or phosphoric acid, or a Lewis acid (for example, a Lewis acid compound represented by 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 lanthanoid 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 an alkaline compound such as triethylamine or pyridine may be added singly or in combination of two or more.

[0091] Among these esterifying agents, in particular, at least one selected from the group consisting of acetic anhydride, propionic anhydride, butyric anhydride, vinyl acetate, vinyl propionate, vinyl butyrate, and acetic acid, and among them, acetic anhydride and vinyl acetate are preferable from the viewpoint of reaction efficiency.

[0092] When the cellulose fibers are hydrophobized (e.g., by chemical modification such as acylation), the dry powder of the cellulose fibers tends to have good redispersibility. However, the dry powder of the cellulose fibers obtained by the method of the present disclosure is advantageous in that it can exhibit good redispersibility even when it is unsubstituted or has a low degree of substitution. Therefore, in one aspect, the average degree of substitution (DS) (the average number of substituted hydroxyl groups per glucose, which is the basic structural unit of cellulose) of the dry powder of the cellulose fibers can be 0.5 or less, or 0.3 or less, or 0. On the other hand, the average degree of substitution (DS) may be 0.2 or more, or 0.4 or more, or 0.6 or more depending on the intended use of the cellulose fibers.

[0093] When the modifying group of the chemically modified cellulose fiber is an acyl group, the degree of acyl substitution (DS) can be calculated from the peak intensity ratio between the peak derived from the acyl group and the peak derived from the cellulose backbone in the reflectance infrared absorption spectrum of the esterified cellulose fiber. The peak of the absorption band of C=O based on the acyl group appears at 1730 cm -1 and the peak of the absorption band of C-O based on the cellulose backbone chain appears at 1030 cm -1 (see Figure 1). The DS of the esterified cellulose fiber is defined by the correlation graph between the DS obtained from the solid NMR measurement of the esterified cellulose fiber described below and the modification rate (IR index 1030) defined by the ratio of the peak intensity of the absorption band of C=O based on the acyl group to the peak intensity of the absorption band of C-O of the cellulose backbone chain. By preparing a calibration curve Degree of substitution DS = 4.13 × IR index (1030) it can be determined by using.

[0094] The method for calculating the DS of the esterified cellulose fiber by solid NMR is as follows for the freeze-ground esterified cellulose fiber 13 perform 13C solid NMR measurement, and it can be obtained by the following formula from the area intensity (Inf) of the signal attributed to one carbon atom derived from the modifying group with respect to the total area intensity (Inp) of the signals attributed to the carbon C1-C6 derived from the pyranose ring of cellulose that appears in the range of 50 ppm to 110 ppm. DS = (Inf) × 6 / (Inp) For example, when the modifying group is an acetyl group, the signal at 23 ppm attributed to -CH3 can be used. Use 13 The conditions for solid-state C NMR measurement are as follows, for example. Apparatus: Bruker Biospin Avance500WB Frequency: 125.77 MHz Measurement method: DD / MAS method Waiting time: 75 sec NMR sample tube: 4 mm φ Number of integrations: 640 times (about 14 Hr) MAS: 14,500 Hz Chemical shift reference: Glycine (external reference: 176.03 ppm)

[0095] The DS non-uniform ratio (DSs / DSt), which is defined as the ratio of the degree of modification (DSs) on the fiber surface to the degree of modification (DSt) of the entire chemically modified cellulose fiber (which is synonymous with the above acyl substitution degree (DS)), is preferably 1.05 or more. The larger the value of the DS non-uniform ratio, the more prominent the sheath-core structure-like non-uniform structure (that is, a structure in which the fiber surface layer is highly chemically modified while the fiber core part retains a cellulose structure close to the original unmodified state). While having high tensile strength and dimensional stability derived from cellulose, it is possible to improve the affinity with the resin during the composite formation with the resin and improve the dimensional stability of the resin composition. The DS non-uniform ratio is more preferably 1.1 or more, or 1.2 or more, or 1.3 or more, or 1.5 or more, or 2.0 or more, and from the viewpoint of the ease of manufacturing chemically modified cellulose fibers, it is preferably 30 or less, or 20 or less, or 10 or less, or 6 or less, or 4 or less, or 3 or less. The value of DSs varies according to the degree of modification of esterified cellulose. As an example, it is preferably 0.1 or more, more preferably 0.2 or more, still more preferably 0.3 or more, still more preferably 0.5 or more, preferably 3.0 or less, more preferably 2.5 or less, particularly preferably 2.0 or less, still more preferably 1.5 or less, particularly preferably 1.2 or less, and most preferably 1.0 or less. The preferred range of DSt is as described above for the acyl substituent (DS).

[0096] The coefficient of variation (CV) of the DS non-uniform ratio of chemically modified cellulose fibers is preferably as small as possible because the variations in various physical properties of the resin composition become smaller. The coefficient of variation is preferably 50% or less, or 40% or less, or 30% or less, or 20% or less. The coefficient of variation can be reduced more, for example, by a method of obtaining chemically modified cellulose fibers by performing chemical modification after defibrating the cellulose raw material (i.e., the sequential method), while it can be increased by a method of performing defibrating and chemical modification of the cellulose raw material simultaneously (i.e., the simultaneous method). Although the mechanism of this action is not clear, in the simultaneous method, chemical modification progresses more easily in the thin fibers generated at the initial stage of defibrating, and as the hydrogen bonds between cellulose microfibrils decrease due to chemical modification, defibrating further progresses, resulting in an increase in the coefficient of variation of the DS non-uniform ratio.

[0097] The coefficient of variation (CV) of the DS non-uniform ratio can be calculated by the following formula from the standard deviation (σ) and arithmetic mean (μ) of the DS non-uniform ratio among 10 samples obtained after calculating the DS non-uniform ratio from DSt and DSs of 10 samples, by collecting 100 g of an aqueous dispersion of chemically modified cellulose fibers (solid content rate of 10 mass% or more), using the frozen and pulverized samples taken in 10 g portions as measurement samples. DS non-uniform ratio = DSs / DSt Coefficient of variation (%) = standard deviation σ / arithmetic mean μ × 100

[0098] The method for calculating DSs is as follows. That is, the esterified cellulose powdered by cryogenic grinding is placed on a dish-shaped sample stage with a diameter of 2.5 mm, the surface is pressed down to make it flat, and measurement is performed by X-ray photoelectron spectroscopy (XPS). The XPS spectrum reflects the constituent elements and chemical bonding states only in the surface layer of the sample (typically about several nm). For the obtained C1s spectrum, peak separation is performed, and it can be obtained by the following formula from the area intensity (Ixf) of the peak attributed to one carbon atom derived from the modifying group with respect to the area intensity (Ixp) of the peak (289 eV, C-C bond) attributed to the carbon C2-C6 derived from the pyranose ring of cellulose. DSs = (Ixf) × 5 / (Ixp) For example, when the modifying group is an acetyl group, after peak separation of the C1s spectrum at 285 eV, 286 eV, 288 eV, and 289 eV, the peak at 289 eV can be used for Ixp, and the peak (286 eV) derived from the O-C=O bond of the acetyl group can be used for Ixf. The conditions for the XPS measurement to be used are as follows, for example. Equipment used: ULVAC-PHI VersaProbeII Excitation source: mono.AlKα 15 kV × 3.33 mA Analysis size: approximately 200 μmφ Photoelectron extraction angle: 45° Capture region Narrow scan: C 1s, O 1s Pass Energy: 23.5 eV

[0099] <Addition of binder> In one aspect, in the slurry preparation step and / or the granulation step, a binder can be added to the slurry. The binder contributes to improving the affinity between the cellulose fiber and the resin in the composite. Examples of the binder include polymers having hydrophilic groups (e.g., hydroxyl groups, amino groups, etc.) (e.g., polyacrylamide, polyalkylene oxide, polyacrylic acid and its salts, polysaccharides (e.g., cellulose derivatives, starch, alginic acid and its salts (e.g., sodium alginate), guar gum, gellan gum, gelatin, etc.), polyvinyl alcohol, etc.), and monomers having hydrophilic groups (e.g., propylene glycol, N-vinylacetamide, etc.).

[0100] Examples of the alkylene oxide unit of the polyalkylene oxide include alkylene oxides having 2 to 4 carbon atoms, preferably ethylene oxide and propylene oxide. In a preferred embodiment, the polyalkylene oxide is composed of ethylene oxide units and / or propylene oxide units. A particularly preferred polyalkylene oxide is polyethylene oxide.

[0101] Examples of the cellulose derivative include cellulose ethers (e.g., methyl cellulose, carboxymethyl cellulose, carboxyethyl cellulose, hydroxymethyl cellulose, hydroxyethyl cellulose, hydroxypropyl cellulose, hydroxypropyl methyl cellulose, etc.).

[0102] The weight average molecular weight of the binder is preferably 1000 or more, more preferably 5000 or more, still more preferably 10000 or more, and preferably 5×10 8 or less, more preferably 1×10 8 or less, still more preferably 5×10 7 or less.

[0103] In one aspect, the binder is a surfactant. The surfactant has a chemical structure in which a hydrophilic substituent-bearing site and a hydrophobic substituent-bearing site are covalently bonded. As the surfactant, any of an anionic surfactant, a nonionic surfactant, an amphoteric ion surfactant, and a cationic surfactant can be used, but a nonionic surfactant is preferred in terms of obtaining good dispersibility of cellulose fibers.

[0104] As the hydrophilic group of the surfactant, a polyoxyethylene chain, a carboxyl group, and a hydroxyl group are preferred from the viewpoint of affinity with cellulose fibers, and a polyoxyethylene chain is particularly preferred. A nonionic polyoxyethylene derivative is particularly preferred. The polyoxyethylene chain length of the polyoxyethylene derivative may be 1 or more, or 4 or more, or 10 or more, or 15 or more. The longer the chain length, the higher the affinity for hydrophobic cellulose fibers, but from the viewpoint of balance with the properties of the resin composite (such as mechanical properties, etc.), the polyoxyethylene chain length may be 60 or less, or 50 or less, or 40 or less, or 30 or less, or 20 or less.

[0105] As the structure of the hydrophobic group of the surfactant, an alkyl ether type, an alkyl phenyl ether type, a rosin ester type, a bisphenol A type, a β-naphthyl type, a styrenated phenyl type, and a hydrogenated castor oil type are preferred from the viewpoint of high affinity with the resin. The number of carbon atoms in the alkyl chain of the hydrophobic group (in the case of alkyl phenyl, the number of carbon atoms excluding the phenyl group) is preferably 5 or more, or 10 or more, or 12 or more, or 16 or more. For example, when the resin is a polyolefin-based resin, the higher the number of carbon atoms of the surfactant, the higher the affinity with the resin. The above number of carbon atoms may be, for example, 30 or less, or 25 or less.

[0106] In a preferred embodiment, the binder is one or more compounds selected from the group consisting of polyalkylene oxide and cellulose derivatives, and particularly preferably one or more compounds selected from the group consisting of polyalkylene oxide, cellulose ether, and cellulose ester.

[0107] From the viewpoint of facilitating uniform mixing in the slurry preparation step and / or the granulation step, the binder is preferably dissolved in a medium and added to the slurry. The medium to be used can be selected from water and those exemplified as additional media in the present disclosure. When the binder is added in the slurry preparation step, it is preferably of the same composition as the medium used in the slurry preparation step, and when the binder is added in the granulation step, it is preferably of the same composition as the medium used in the granulation step.

[0108] The amount of the binder may preferably be 5 parts by mass or more, or 10 parts by mass or more, or 20 parts by mass or more, or 30 parts by mass or more, or 40 parts by mass or more, and preferably 100 parts by mass or less, or 70 parts by mass or less, or 50 parts by mass or less, based on 100 parts by mass of the cellulose fiber.

[0109] The dry powder produced by the method of the present disclosure and having good redispersibility in the dispersion medium can be well dispersed in the resin, for example, even when the cellulose fiber and the resin are compounded. Therefore, it is excellent in the effect of improving the physical properties of the resin composite containing the cellulose fiber and the resin. Further, in one aspect, the dry powder of the cellulose fiber of the present disclosure is likely to have fiber hairs remaining on the powder surface after being chopped and pulverized. Such a sparse structure on the powder surface can promote the penetration of the dispersion medium into the powder during redispersion, contributing to the improvement of redispersibility.

[0110] In one aspect, when a redispersion liquid is prepared by dispersing the dry powder in the same type and amount of liquid medium as the slurry produced in the slurry preparation step, the viscosity of the redispersion liquid at a shear rate of 100 s -1 is 30% or more of the above-mentioned viscosity at a shear rate of 100 s -1 of the slurry obtained in the slurry preparation step. The above ratio is an index indicating how well the dispersibility of the cellulose fiber before drying can be reproduced after redispersion (i.e., redispersibility). The above ratio is preferably 40% or more, or 50% or more, or 60% or more. The higher the above ratio, the more preferable it is, and most preferably it is 100%. However, from the viewpoint of ease of manufacturing the cellulose fiber, it may be, for example, 90% or less, or 80% or less.

[0111] Share rate of the redispersion liquid for 100 s -1 The viscosity at [the time of -1 ] is preferably 6 mPa·s or more, or 7.5 mPa·s or more, or 9 mPa·s or more in that the cellulose fibers are highly dispersed, and is preferably 13.5 mPa·s or less, or 12 mPa·s or less in that the redispersion liquid can be suitably used, for example, in the production of a resin composite.

[0112] ≪Method for producing resin composite≫ One aspect of the present invention provides a method for producing a resin composite including cellulose fibers and a resin. The method includes preparing a dry powder of cellulose fibers by the method as described above, and mixing the dry powder and the resin.

[0113] <Resin> As the resin, a thermoplastic resin, a thermosetting resin, and a photocurable resin can be used. The resin may be an elastomer. From the viewpoints of moldability and productivity, a thermoplastic resin is more preferable.

[0114] (Thermoplastic resin) When the resin is a thermoplastic resin, the melting point of the thermoplastic resin may be appropriately selected according to the use of the resin composite and the like. Examples of the melting point of the thermoplastic resin include 150°C to 190°C, or 160°C to 180°C for a resin with a relatively low melting point (for example, a polyolefin resin), and 220°C to 350°C, or 230°C to 320°C for a resin with a relatively high melting point (for example, a polyamide resin).

[0115] The thermoplastic resin can preferably be at least one selected from the group consisting of a polyolefin resin, a polyacetate resin, a polycarbonate resin, a polyamide resin, a polyester resin, a polyphenylene ether resin, and an acrylic resin.

[0116] Preferred polyolefin resins as thermoplastic resins are polymers obtained by polymerizing olefins (e.g., α-olefins) and / or alkenes as monomer units. Specific examples of polyolefin resins include ethylene-based (co)polymers exemplified by low-density polyethylene (e.g., linear low-density polyethylene), high-density polyethylene, ultra-low-density polyethylene, ultra-high molecular weight polyethylene, etc., polypropylene-based (co)polymers exemplified by polypropylene, ethylene-propylene copolymer, ethylene-propylene-diene copolymer, etc., and copolymers of ethylene and α-olefins represented by ethylene-acrylic acid copolymer, ethylene-methyl methacrylate copolymer, ethylene-glycidyl methacrylate copolymer, etc.

[0117] Here, the most preferred polyolefin resin is polypropylene. In particular, polypropylene having a melt mass flow rate (MFR) measured at 230 °C and a load of 21.2 N in accordance with ISO 1133 of 3 g / 10 min or more and 30 g / 10 min or less is preferred. The lower limit value of MFR is more preferably 5 g / 10 min, even more preferably 6 g / 10 min, and most preferably 8 g / 10 min. Also, the upper limit value is more preferably 25 g / 10 min, even more preferably 20 g / 10 min, and most preferably 18 g / 10 min. It is desirable that MFR does not exceed the above upper limit value from the viewpoint of improving the toughness of the resin composite, and it is desirable that MFR does not exceed the above lower limit value from the viewpoint of the fluidity of the resin composite.

[0118] In addition, in order to enhance the affinity with cellulose fibers, an acid-modified polyolefin resin can also be preferably used. As the acid used for acid modification, mono- or polycarboxylic acids can be used, and examples thereof include maleic acid, fumaric acid, succinic acid, phthalic acid and their anhydrides, and citric acid. From the viewpoint of ease of increasing the modification rate, maleic acid or its anhydride is particularly preferred. There is no particular limitation on the modification method, but a method of heating the polyolefin resin above its melting point and melt-kneading it in the presence or absence of a peroxide is common. As the polyolefin resin to be acid-modified, all of the above-mentioned polyolefin resins can be used, but polypropylene is particularly preferred. The acid-modified polypropylene resin may be used alone, but in order to adjust the modification rate of the entire resin, it is more preferably used by mixing with an unmodified polypropylene resin. The ratio of the acid-modified polypropylene resin to all the polypropylene resins at this time is preferably 0.5% by mass 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. Also, 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. In order to maintain the interfacial strength between the resin and the cellulose fibers, it is preferably above the lower limit, and in order to maintain the ductility of the resin, it is preferably below the upper limit.

[0119] The melt mass flow rate (MFR) of the acid-modified polypropylene resin, measured at 230 °C and a load of 21.2 N in accordance with ISO 1133, is preferably 50 g / 10 min or more, or 100 g / 10 min or more, or 150 g / 10 min or more, or 200 g / 10 min or more from the viewpoint of enhancing the affinity at the interface between the resin and the cellulose fibers. The upper limit is not particularly limited, but from the viewpoint of maintaining the mechanical strength, it is preferably 500 g / 10 min.

[0120] Preferred polyamide resins as thermoplastic resins include: polyamides obtained by polycondensation reaction 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., butanedioic acid, pentanedioic acid, hexanedioic acid, heptanedioic acid, octanedioic acid, nonanedioic acid, decanedioic 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.) copolymers obtained as polyamides (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 in which these are copolymerized respectively (e.g., polyamide 6,T / 6,I, etc.).

[0121] Among these polyamide resins, aliphatic polyamides such as polyamide 6, polyamide 11, polyamide 12, polyamide 6,6, polyamide 6,10, polyamide 6,11, polyamide 6,12, etc., and alicyclic polyamides such as polyamide 6,C, polyamide 2M5,C, etc. are more preferred.

[0122] From the viewpoint of improving the heat resistance of the resin composite, the melting point of the polyamide resin is preferably 220 °C or higher, or 230 °C or higher, or 240 °C or higher, or 245 °C or higher, or 250 °C or higher, and from the viewpoint of the ease of manufacturing the resin composite, the above melting point is preferably 350 °C or lower, or 320 °C or lower, or 300 °C or lower.

[0123] There is no particular limitation on the terminal carboxyl group concentration of the polyamide resin, but preferably it is 20 μmol / g or more, or 30 μmol / g or more, and preferably it is 150 μmol / g or less, or 100 μmol / g or less, or 80 μmol / g or less.

[0124] In the polyamide resin, the carboxyl terminal group ratio ([COOH] / [total terminal groups]) to all terminal groups is preferably 0.30 or more, or 0.35 or more, or 0.40 or more, or 0.45 or more from the viewpoint of the dispersibility in the resin composite of the cellulose fiber, and preferably 0.95 or less, or 0.90 or less, or 0.85 or less, or 0.80 or less from the viewpoint of the color tone of the resin composite.

[0125] The terminal group concentration of the polyamide resin can be adjusted by a known method. As the adjustment method, a method of adding a terminal adjusting agent (for example, diamine compound, monoamine compound, dicarboxylic acid compound, monocarboxylic acid compound, acid anhydride, monoisocyanate, monoacid halide, monoester, monoalcohol, etc.) that reacts with the terminal group so as to have a predetermined terminal group concentration to the polymerization solution during the polymerization of the polyamide can be mentioned.

[0126] Examples of the terminal adjusting agent that reacts with the terminal amino group include aliphatic monocarboxylic acids such as acetic acid, propionic acid, butyric acid, valeric acid, caproic acid, caprylic acid, lauric acid, tridecanoic acid, myristic acid, palmitic acid, stearic acid, pivalic acid, and isobutyric acid; alicyclic monocarboxylic acids such as cyclohexanecarboxylic acid; aromatic monocarboxylic acids such as benzoic acid, toluic acid, α-naphthalenecarboxylic acid, β-naphthalenecarboxylic acid, methylnaphthalenecarboxylic acid, and phenylacetic acid; and a plurality of mixtures arbitrarily selected from these. Among these, from the viewpoints of reactivity, stability of the blocked terminal, price, etc., one or more terminal adjusting agents selected from the group consisting of acetic acid, propionic acid, butyric acid, valeric acid, caproic acid, caprylic acid, lauric acid, tridecanoic acid, myristic acid, palmitic acid, stearic acid, and benzoic acid are preferable, and acetic acid is most preferable.

[0127] As the terminal modifier that reacts with the terminal carboxyl group, there are aliphatic monoamines such as methylamine, ethylamine, propylamine, butylamine, hexylamine, octylamine, decylamine, stearylamine, dimethylamine, diethylamine, dipropylamine, dibutylamine; cycloaliphatic monoamines such as cyclohexylamine, dicyclohexylamine; aromatic monoamines such as aniline, toluidine, diphenylamine, naphthylamine, and any mixture thereof. Among these, from the viewpoints of reactivity, boiling point, stability of the capped terminal, price, etc., one or more terminal modifiers selected from the group consisting of butylamine, hexylamine, octylamine, decylamine, stearylamine, cyclohexylamine, and aniline are preferred.

[0128] The concentrations of the amino terminal group and the carboxyl terminal group of the polyamide resin 1 can be determined from the integral values of the characteristic signals corresponding to each terminal group by 1H-NMR. This method is preferable in terms of accuracy and simplicity. More specifically, it is recommended to use the method described in JP-A-7-228775, use heavy trifluoroacetic acid as the measurement solvent, and set the number of integrations to 300 scans or more.

[0129] The intrinsic viscosity [η] of the polyamide resin measured under the condition of 30 °C in concentrated sulfuric acid is preferably 0.6 to 2.0 dL / g, or 0.7 to 1.4 dL / g, or 0.7 to 1.2 dL / g, or 0.7 to 1.0 dL / g from the viewpoint of good fluidity in the mold and good appearance of the molded piece when, for example, injecting and molding the resin composite. In the present disclosure, the "intrinsic viscosity" is synonymous with the viscosity generally called the limiting viscosity. The intrinsic viscosity is determined by measuring ηsp / c of several measurement solvents with different concentrations in 96% concentrated sulfuric acid under the temperature condition of 30 °C, deriving the relational expression between each ηsp / c and the concentration (c), and extrapolating the concentration to zero. The value extrapolated to zero is the intrinsic viscosity. Details of the above method are described, for example, on pages 291 to 294 of Polymer Process Engineering (Prentice-Hall, Inc 1994). It is desirable from the viewpoint of accuracy that the concentrations in several measurement solvents with different concentrations be at least 4 points (for example, 0.05 g / dL, 0.1 g / dL, 0.2 g / dL, 0.4 g / dL).

[0130] As the polyester resin preferably used as the thermoplastic resin, one or more selected from polyethylene terephthalate (PET), polyethylene naphthalate (PEN), polybutylene terephthalate (PBT), polybutylene succinate (PBS), polybutylene succinate adipate (PBSA), polybutylene adipate terephthalate (PBAT), polyhydroxyalkanoic acid (PHA), polylactic acid (PLA), polyarylate (PAR), etc. can be used. Among them, PET, PBS, PBSA, PBT and PEN are more preferable, and PBS, PBSA and PBT are particularly preferable.

[0131] The end groups of the polyester resin can be arbitrarily changed depending on the monomer ratio during polymerization, the presence or absence and amount of the end stabilizer, etc. The carboxyl end group ratio ([COOH] / [total end groups]) with respect to all the end groups of the polyester resin is preferably 0.30 or more, or 0.35 or more, or 0.40 or more, or 0.45 or more from the viewpoint of the dispersibility of the cellulose fibers in the resin composite, and preferably 0.95 or less, or 0.90 or less, or 0.85 or less, or 0.80 or less from the viewpoint of the color tone of the resin composite.

[0132] Preferred polyacetal resins as the thermoplastic resin include homopolyacetals made from formaldehyde and copolyacetals having trioxane as the main monomer and containing 1,3-dioxolane as the comonomer component. Both can be used, but copolyacetals are preferred from the viewpoint of thermal stability during processing. The amount of the structure derived from the comonomer component (for example, 1,3-dioxolane) is preferably 0.01 mol% or more, or 0.05 mol% or more, or 0.1 mol% or more, or 0.2 mol% or more from the viewpoint of thermal stability during extrusion and molding processes, and preferably 4 mol% or less, or 3.5 mol% or less, or 3.0 mol% or less, or 2.5 mol% or less, or 2.3 mol% or less from the viewpoint of mechanical strength.

[0133] (Thermosetting resin) Examples of the thermosetting resin include bisphenol type epoxy resins such as bisphenol A epoxy resin, bisphenol F epoxy resin, bisphenol S epoxy resin, bisphenol E epoxy resin, bisphenol M epoxy resin, bisphenol P epoxy resin, and bisphenol Z epoxy resin; novolac type epoxy resins such as bisphenol A novolac epoxy resin, phenol novolac epoxy resin, and cresol novolac epoxy resin; biphenyl type epoxy resin, biphenyl aralkyl type epoxy resin, aryl alkylene type epoxy resin, tetraphenylol ethane type epoxy resin, naphthalene type epoxy resin, anthracene type epoxy resin, phenoxy type epoxy resin, dicyclopentadiene type epoxy resin, norbornene type epoxy resin, adamantane type epoxy resin, fluorene type epoxy resin, glycidyl methacrylate copolymer type epoxy resin, copolymer epoxy resin of cyclohexyl maleimide and glycidyl methacrylate, epoxy modified polybutadiene rubber derivative, CTBN modified epoxy resin, trimethylolpropane polyglycidyl ether, phenyl-1,3-diglycidyl ether, biphenyl-4,4'-diglycidyl ether, 1,6-hexanediol diglycidyl ether, diglycidyl ether of ethylene glycol or propylene glycol, sorbitol polyglycidyl ether, tris(2,3-epoxypropyl) isocyanurate, triglycidyl tris(2-hydroxyethyl) isocyanurate, novolac type phenol resins such as phenol novolac resin, cresol novolac resin, and bisphenol A novolac resin; resol type phenol resins such as unmodified resol phenol resin and oil-modified resol phenol resin modified with tung oil, linseed oil, walnut oil, etc.; phenol resins such as phenoxy resin, triazine ring-containing resins such as urea (urea) resin and melamine resin, unsaturated polyester resin, bismaleimide resin, diallyl phthalate resin, silicone resin, resin having a benzoxazine ring, norbornene resin, cyanate resin, isocyanate resin, urethane resin, benzocyclobutene resin, maleimide resin, bismaleimide triazine resin, polyazomethine resin, thermosetting polyimide, etc.

[0134] (Photocurable resin) Examples of the photocurable resin include (meth)acrylate resins, vinyl resins, epoxy resins, etc. These are generally classified into a radical reaction type in which monomers react with radicals generated by light and a cation reaction type in which monomers undergo cationic polymerization, depending on the reaction mechanism. Examples of monomers of the radical reaction type include (meth)acrylate compounds and vinyl compounds (e.g., certain vinyl ethers). Examples of the cation reaction type include epoxy compounds and certain vinyl ethers. Note that, for example, an epoxy compound that can be used as the cation reaction type can be a monomer for both thermosetting resins and photocurable resins.

[0135] (meth)acrylate compound is a compound having one or more (meth)acrylate groups in the molecule. Examples of the (meth)acrylate compound include monofunctional (meth)acrylate, polyfunctional (meth)acrylate, epoxy acrylate, polyester acrylate, urethane acrylate, etc.

[0136] Examples of the vinyl compound include vinyl ether, styrene, and styrene derivatives. Examples of the vinyl ether include ethyl vinyl ether, propyl vinyl ether, hydroxyethyl vinyl ether, ethylene glycol divinyl ether, etc. Examples of the styrene derivative include methyl styrene, ethyl styrene, etc. Examples of other vinyl compounds include triallyl isocyanurate, trimethallyl isocyanurate, etc.

[0137] As a raw material for the photocurable resin, a so-called reactive oligomer may be used. Examples of the reactive oligomer include an oligomer having any combination selected from (meth)acrylate groups, epoxy groups, urethane bonds, and ester bonds in the same molecule, for example, urethane acrylate having both a (meth)acrylate group and a urethane bond in the same molecule, polyester acrylate having both a (meth)acrylate group and an ester bond in the same molecule, epoxy acrylate derived from an epoxy resin and having both an epoxy group and a (meth)acrylate group in the same molecule, and the like.

[0138] (Elastomer) Examples of the elastomer (i.e., rubber) include natural rubber (NR), butadiene rubber (BR), styrene-butadiene copolymer rubber (SBR), isoprene rubber (IR), butyl rubber (IIR), acrylonitrile-butadiene rubber (NBR), acrylonitrile-styrene-butadiene copolymer rubber, chloroprene rubber, styrene-isoprene copolymer rubber, styrene-isoprene-butadiene copolymer rubber, isoprene-butadiene copolymer rubber, chlorosulfonated polyethylene rubber, modified natural rubber (epoxidized natural rubber (ENR), hydrogenated natural rubber, protein-free natural rubber, etc.), ethylene-propylene copolymer rubber, acrylic rubber, epichlorohydrin rubber, polysulfide rubber, silicone rubber, fluororubber, urethane rubber, and the like.

[0139] When the resin is a thermoplastic resin, a resin composite can be produced by melt-kneading cellulose fibers (which may be in the form of the dry powder of the present disclosure or a redispersion liquid obtained by dispersing the dry powder in a dispersion medium) with the thermoplastic resin. As a more specific method for producing the resin composite, - A method in which a resin monomer and cellulose fibers are mixed, a polymerization reaction is carried out, the obtained resin composite is extruded in a strand shape, and cooled and solidified in a water bath to obtain a pellet-shaped molded body. - A method in which a mixture of a resin and cellulose fibers is melt-kneaded using a single-screw or twin-screw extruder, extruded in a strand shape, and cooled and solidified in a water bath to obtain a pellet-shaped molded body. - A method of melt-kneading a mixture of a resin and cellulose fibers using a single-screw or twin-screw extruder, and extruding and cooling it in a rod shape or a cylindrical shape to obtain an extruded molded body. - A method of melt-kneading a mixture of a resin and cellulose fibers using a single-screw or twin-screw extruder, and extruding a sheet or a film-shaped molded body from a T-die. Examples include the above. In a preferred embodiment, a mixture of a resin and cellulose fibers is melt-kneaded using a single-screw or twin-screw extruder, extruded in a strand shape, cooled and solidified in a water bath, and a pellet-shaped molded body is obtained. As a specific example of the method for melt-kneading a resin and cellulose fibers, there is a method of mixing a resin and cellulose fibers conveyed at a desired ratio and then performing melt-kneading. When the resin is a thermoplastic resin, the minimum processing temperature recommended by the thermoplastic resin supplier is 255 - 270 °C for nylon 66, 225 - 240 °C for nylon 6, 170 - 190 °C for polyacetal resin, and 160 - 180 °C for polypropylene. The heating set temperature is preferably in the range 20 °C higher than these recommended minimum processing temperatures. By setting the mixing temperature within this temperature range, the cellulose fibers and the resin can be uniformly mixed.

[0140] A resin composite containing a thermoplastic resin as a resin can be provided in various shapes. Specifically, examples include resin pellet form, sheet form, fiber form, plate form, rod form, etc. Among them, the resin pellet shape is more preferable from the viewpoints of ease of post-processing and ease of transportation. Preferred pellet shapes in this case include round shape, elliptical shape, cylindrical shape, etc., and these differ depending on the cutting method during extrusion processing. Pellets cut by a cutting method called underwater cut often become round, pellets cut by a cutting method called hot cut often become square or elliptical, and pellets cut by a cutting method called strand cut often become cylindrical. In the case of round pellets, the preferred size is 1 mm or more and 3 mm or less as the pellet diameter. Also, in the case of cylindrical pellets, the preferred diameter is 1 mm or more and 3 mm or less, and the preferred length is 2 mm or more and 10 mm or less. From the viewpoint of operation stability during extrusion, it is desirable that the above diameter and length be equal to or greater than the lower limit, and from the viewpoint of bite-in property into the molding machine in post-processing, it is desirable that they be equal to or less than the upper limit.

[0141] A resin composite containing a thermoplastic resin as a resin can be used as various resin molded articles. There are no particular restrictions on the method for manufacturing the resin molded article, and any manufacturing method may be used. However, injection molding methods, extrusion molding methods, blow molding methods, inflation molding methods, foam molding methods, etc. can be used. Among these, the injection molding method is most preferable from the viewpoints of designability and cost.

[0142] When the resin is a thermosetting resin or a photocurable resin, for example, a method of sufficiently dispersing cellulose fibers in a resin solution or a resin powder dispersion and drying, a method of sufficiently dispersing cellulose fibers in a resin monomer solution and polymerizing by heat, UV irradiation, a polymerization initiator, etc., a method of sufficiently impregnating a dried powder of cellulose fibers with a resin solution or a resin powder dispersion and drying, a method of sufficiently impregnating a dried powder of cellulose fibers with a resin monomer solution and polymerizing by heat, UV irradiation, a polymerization initiator, etc. can be used to produce a resin composite. During curing, various polymerization initiators, curing agents, curing accelerators, polymerization inhibitors, etc. can be blended.

[0143] When the resin is a thermosetting resin or a photocurable resin, after producing a sheet called an uncured or semi-cured prepreg, the prepreg may be made into a single layer or laminated, and a method of curing and molding the resin by pressurization and heating may be used. Examples of the methods of pressurization and heating include a press molding method, an autoclave molding method, a bagging molding method, a wrapping tape method, an internal pressure molding method, and the like.

[0144] When the resin is a photocurable resin, a resin molded body can be manufactured using various curing methods using active energy rays.

[0145] When the resin is an elastomer, a resin composite can be manufactured by a method of dry-kneading a dry powder of cellulose fiber and a raw rubber, a method of dispersing or dissolving the cellulose fiber and the raw rubber in a dispersion medium and then drying and mixing them, and the like. As the mixing method, a mixing method using a homogenizer is preferable in that high shearing force and pressure can be applied to promote dispersion, but other methods such as a propeller type stirring device, a rotary stirring device, an electromagnetic stirring device, and manual stirring can also be used. The resin composite containing an elastomer is molded using a desired molding method such as die molding, injection molding, extrusion molding, blow molding, foam molding, etc., to obtain an uncured molded body having a desired shape such as a sheet, pellet, powder, etc. The uncured molded body can be vulcanized by heat treatment or the like as necessary to obtain a resin molded body.

[0146] For a resin molded body containing a thermoplastic resin or an elastomer, a part thereof (for example, several places) may be heat-treated and melted, and then adhered to a substrate such as a resin or metal and used. Further, the resin molded body may be a coating film applied to a substrate of a resin or metal, or may form a laminate with the substrate. Further, secondary processing such as annealing treatment, etching treatment, corona treatment, plasma treatment, embossing transfer, cutting, surface polishing, etc. may be performed on the resin molded body in the form of a sheet, film or fiber.

[0147] In the resin composite, the amount of cellulose fiber with respect to 100 parts by mass of the resin may preferably be 0.001 part by mass or more, or 0.01 part by mass or more, or 0.1 part by mass or more, or 1 part by mass or more, and may preferably be 100 parts by mass or less, or 80 parts by mass or less, or 70 parts by mass or less, or 50 parts by mass or less, from the viewpoint of the balance between processability and mechanical properties.

Example

[0148] The present invention will be further described based on examples, but the present invention is not limited to these examples.

[0149] ≪Production of Wet Cake of Cellulose Fiber≫ <Cellulose Fiber 1> Cellish KY-100G (solid content concentration: 10% by mass) manufactured by Daicel Finechem Ltd. was used as it was.

[0150] <Cellulose Fiber 2> After cutting cotton linter pulp, the purified pulp washed with water to remove impurities was added to pure water so that the solid content ratio became 1.5% by mass, and was highly short-fiberized and fibrillated by beating treatment to obtain defibrated cellulose. Here, in the beating treatment, a disk refiner was used, and after treating for 2.5 hours with a beating blade having a high cutting function, beating was further carried out for 2 hours using a beating blade having a high defibrating function, and the slurry was filtered and concentrated, and the obtained cellulose fiber (solid content concentration: 20% by mass) was used.

[0151] <Cellulose Fiber 3> 1 kg of linter pulp and 19 kg of DMSO were charged into a KAPPA VITA (registered trademark) homomixer (tank size: 35 L) manufactured by NETZSCH Vakumix, and defibrated at a homomixer rotation speed of 6000 rpm (circumferential speed: 29 m / s) for 8 hours. Then, 0.321 kg of sodium bicarbonate and 2.1 kg of vinyl acetate were added, and acetylation was carried out at 60°C for 4 hours. During acetylation, in order to prevent retention in the circulation line, the rotation speed of the homomixer was set to 2500 rpm (circumferential speed: 12 m / s) before the shear force increased. The reaction mixture was washed with water and then filtered and concentrated, and acetylated cellulose fibers with a degree of substitution of 1.0 (solid content concentration: 15% by mass) thus obtained were used.

[0152] ≪Production of Dry Powder of Cellulose Fibers≫ [Example 1] Using the cellulose fiber wet cake prepared above, dry powder was produced according to the following procedure. Apparatus: High-speed mixer (model number: FS10) manufactured by Earth Technica Co., Ltd. Raw material: Cellulose fiber 1 (5 kg) Conditions: While stirring with a jacket temperature of 70°C, an agitator (peripheral speed: 2 m / s), and a chopper (rotation speed: 3500 rpm), the pressure was reduced to -70 kPa with a vacuum pump. When the pressure-reducing drying was carried out until the moisture content reached 50% by mass, t-butanol (1 kg) was added, and the pressure-reducing drying was continued until the product temperature reached 60°C and the moisture content was less than 5% by mass.

[0153] [Example 2] Using the cellulose fiber wet cake prepared above, dry powder was produced according to the following procedure. Apparatus: High-speed mixer (model number: FS10) manufactured by Earth Technica Co., Ltd. Raw material: Cellulose fiber 1 (5 kg) + Sunnex GL-3000 manufactured by Sanyo Chemical Industries, Ltd. (214 g) Conditions: While stirring with a jacket temperature of 70°C, an agitator (peripheral speed: 1 m / s), and a chopper (rotation speed: 3500 rpm), the pressure was reduced to -70 kPa with a vacuum pump, and the pressure-reducing drying was carried out until the product temperature reached 60°C.

[0154] [Example 3] Using the cellulose fiber wet cake prepared above, dry powder was produced according to the following procedure. Apparatus: Lodige mixer (model number: M20) manufactured by Chuo Kiko Co., Ltd. Raw material: Cellulose fiber 1 (5 kg) + Sunnex GL-3000 manufactured by Sanyo Chemical Industries, Ltd. (214 g) Condition: While stirring with a jacket temperature of 100 °C, an agitator (peripheral speed 4 m / s), and a chopper (rotation speed 5000 rpm), the pressure was reduced to -90 kPa with a vacuum pump, and vacuum drying was carried out until the product temperature reached 90 °C.

[0155] [Example 4] Vacuum drying was carried out in the same manner as in Example 2, except that cellulose fiber 2 (2.5 kg) was used instead of cellulose fiber 1.

[0156] [Example 5] Vacuum drying was carried out in the same manner as in Example 1, except that cellulose fiber 3 (3.3 kg) was used instead of cellulose fiber 1.

[0157] [Example 6] Vacuum drying was carried out in the same manner as in Example 2, except that cellulose fiber 3 (3.3 kg) was used instead of cellulose fiber 1.

[0158] [Example 7] Using the cellulose fiber wet cake prepared above, dry powder was produced by the following procedure. Apparatus: High-speed mixer (model number: FS10) manufactured by Earth Technica Co., Ltd. Raw materials: Cellulose fiber 3 (3.3 kg) + 5 mass% acetone solution of CAB381-20 (214 g) manufactured by Eastman Chemical Company Condition: While stirring with a jacket temperature of 70 °C, an agitator (peripheral speed 1 m / s), and a chopper (3500 rpm), the pressure was reduced to -70 kPa with a vacuum pump. Acetone (1 kg) was added at the stage when vacuum drying was carried out until the moisture content reached 50 mass%, and vacuum drying was carried out until the product temperature reached 60 °C and the residual solvent fraction was less than 3 mass%.

[0159] [Example 8] Vacuum drying was carried out in the same manner as in Example 2, except that the peripheral speed of the agitator was 15 m / s.

[0160] [Example 9] The pressure-reducing drying was carried out in the same manner as in Example 2, except that the peripheral speed of the agitator stirring was 0.5 m / s.

[0161] [Example 10] The pressure-reducing drying was carried out in the same manner as in Example 3, except that the peripheral speed of the agitator was 1 m / s and the rotation speed of the chopper was 6000 rpm.

[0162] [Example 11] The pressure-reducing drying was carried out in the same manner as in Example 2, except that the rotation speed of the chopper was 200 rpm.

[0163] [Example 12] Using the cellulose fiber wet cake prepared above, a dried powder was produced by the following procedure. Apparatus: High-speed mixer (model number: FS10) manufactured by Earth Technica Co., Ltd. Raw material: Cellulose fiber 3 (3.3 kg) Conditions: While stirring with a jacket temperature of 70 °C, an agitator (peripheral speed 2 m / s), and a chopper (3500 rpm), the pressure was reduced to -70 kPa with a vacuum pump. At the stage where the pressure-reducing drying was carried out until the moisture content reached 50% by mass, t-butanol (1 kg) was added as the first additional medium, and the pressure-reducing drying was continued. At the stage where the pressure-reducing drying was carried out until the moisture content reached 20% by mass, t-butanol (1 kg) was added as the second additional medium, and the pressure-reducing drying was carried out until the product temperature reached 60 °C and the residual solvent fraction was less than 3% by mass.

[0164] [Example 13] Using the cellulose fiber wet cake prepared above, a dried powder was produced by the following procedure. Apparatus: High-speed mixer (model number: FS10) manufactured by Earth Technica Co., Ltd. Raw material: Cellulose fiber 3 (3.3 kg) Condition: While stirring at a jacket temperature of 70 °C, with an agitator (peripheral speed 2 m / s) and a chopper (3500 rpm), the pressure was reduced to -70 kPa using a vacuum pump. When the pressure reduction drying was carried out until the moisture content reached 50% by mass, 1-methoxy-2-propanol (1 kg) was added as the first additional medium, and the pressure reduction drying was continued. When the pressure reduction drying was carried out until the moisture content reached 10% by mass, t-butanol (1 kg) was added as the second additional medium, and the pressure reduction drying was carried out until the product temperature reached 60 °C and the residual solvent fraction was less than 3% by mass.

[0165] [Example 14] Using the cellulose fiber wet cake prepared above, a dry powder was produced according to the following procedure. Apparatus: High-speed mixer (model number: FS10) manufactured by Earth Technica Co., Ltd. Raw material: Cellulose fiber 3 (3.3 kg) Condition: While stirring at a jacket temperature of 100 °C, with an agitator (peripheral speed 2 m / s) and a chopper (3500 rpm), the pressure was reduced to -70 kPa using a vacuum pump. When the pressure reduction drying was carried out until the moisture content reached 75% by mass, 2.0 kg of i-butanol was added dropwise as an additional medium over 30 minutes. During this time, the pressure reduction drying was continued, and the total liquid ratio at the end of the dropwise addition (the total liquid ratio of both water and i-butanol measured by a heat drying type moisture meter) was 72% by mass. Also, when calculating the mass ratio of water:i-butanol at the end of the dropwise addition using gas chromatography, it was 67:33. After the end of the dropwise addition, the pressure reduction drying was continued, and finally, the product temperature reached 70 °C and the residual solvent fraction was less than 3% by mass.

[0166] [Example 15] Pressure reduction drying was carried out in the same manner as in Example 14 except that the dropwise addition amount of i-butanol was 3.0 kg and the dropwise addition time was 45 minutes. The total liquid ratio at the end of the dropwise addition was 74% by mass, and the mass ratio of water:i-butanol was 31:69.

[0167] [Example 16] Except for changing the amount of i-butanol dropped to 4.0 kg and the dropping time to 60 minutes, drying under reduced pressure was carried out in the same manner as in Example 14. At the end of the dropping, the total liquid ratio was 73 mass%, and the mass ratio of water:i-butanol was 4:96.

[0168] [Example 17] The cellulose fiber wet cake prepared above was used to produce a dry powder according to the following procedure. Equipment: Nippon Coke & Engineering Co., Ltd. Henschel mixer (model: FM20) Raw material: cellulose fiber 1 (5 kg) Conditions: Jacket temperature 70°C, stirring with an agitator (circumferential speed 8 m / s) and chopper (circumferential speed 8 m / s), pressure reduced to -70 kPa with a vacuum pump. Drying under reduced pressure was continued until the moisture content reached 50% by mass, at which point t-butanol (1 kg) was added, and drying under reduced pressure was continued until the product temperature reached 60°C and the moisture content was less than 5% by mass.

[0169] [Comparative Example 1] The cellulose fiber wet cake prepared above was used to produce a dry powder according to the following procedure. Equipment: Primix Hi-Vismix (Model: 2P-1) Raw materials: Cellulose fiber 1 (0.3 kg) + Sannix GL-3000 (13 g) manufactured by Sanyo Chemical Industries, Ltd. Conditions: jacket temperature 70°C, stirring with two blades (planetary rotation at 50 rpm), reducing the pressure to -95 kPa with a vacuum pump, and drying under reduced pressure was performed until the residual moisture content reached less than 5% by mass.

[0170] [Comparative Example 2] Except for stopping the agitator and only performing chopper stirring, drying under reduced pressure was performed in the same manner as in Example 1. Most of the cellulose fibers were dried without coming into contact with the chopper, making it difficult to redisperse them and measure their viscosity using the method described below.

[0171] [Comparative Example 3] The cellulose fiber wet cake prepared above was used to produce a dry powder according to the following procedure. Apparatus: Constant temperature machine (model number: SPH-201) manufactured by Espec Corporation Raw material: Cellulose fiber 1 (0.3 kg) Condition: Heated at a temperature of 105°C, without stirring, and at normal pressure until the residual moisture content reached less than 5% by mass. The cellulose fibers aggregated and dried, making it difficult to redisperse and measure the viscosity by the method described below.

[0172] <<Manufacture of resin composite>> The dried powder of the cellulose fiber produced above and the thermoplastic resin (UBE Nylon 1013B manufactured by Ube Industries, Ltd.) were blended at a ratio such that the cellulose fiber was 10% by mass in the resin composite, and the resin composite was manufactured by the following procedure. Using a small kneader (manufactured by Xplore instruments, product name "Xplore"), circulation kneading was performed at 260°C and 200 rpm (shear rate 1570 (1 / s)) for 5 minutes to check the torque. The better the dispersibility of the cellulose fiber in the thermoplastic resin, the higher the melt viscosity. Subsequently, the molten resin was directly transferred to the attached injection molding machine to produce dumbbell-shaped test pieces according to ISO037-3 standard and used for evaluation.

[0173] [Comparative Example 4] The torque was observed when only the thermoplastic resin (UBE Nylon 1013B manufactured by Ube Industries, Ltd.) was kneaded without using the dried powder of the cellulose fiber.

[0174] <<Evaluation>> [Evaluation of cellulose fiber] [Production of porous sheet] First, the wet cake was added to t-butanol, and further dispersion treatment was performed with a mixer or the like until there were no aggregates. It was adjusted so that the concentration was 0.5% by mass with respect to 0.5 g of the cellulose fiber solid content weight. 100 g of the obtained t-butanol dispersion was filtered on filter paper and dried at 150°C, and then the filter paper was peeled off to obtain a sheet. The porous sheet was a sheet having an air permeability resistance of 100 sec / 100 ml or less per sheet basis weight of 10 g / m 2 and was used as a measurement sample. The basis weight W (g / m 2 ) of the sample left standing for one day in an environment of 23°C and 50% RH was measured, and then the air permeability resistance R (sec / 100 ml) was measured using the Wang Research air permeability resistance tester (manufactured by Asahi Seiko Co., Ltd., model EG01). At this time, according to the following formula, the value per unit basis weight was calculated for 10 g / m 2 . Air permeability resistance per 10 g / m 2 basis weight (sec / 100 ml) = R / W × 10

[0175] [Degree of acyl substitution (DS)] Infrared spectra of five locations on the porous sheet by the ATR-IR method were measured using a Fourier transform infrared spectrophotometer (FT / IR-6200 manufactured by JASCO Corporation). The infrared spectrum measurement was carried out under the following conditions. Number of accumulations: 64 times, Wavenumber resolution: 4 cm -1 , Measurement wavenumber range: 4000~600 cm -1 , ATR crystal: diamond, Incident angle: 45° From the obtained IR spectrum, the IR index was calculated according to the following formula (1): IR index = H1730 / H1030 ··· (1) In the formula, H1730 and H1030 are the absorbances at 1730 cm -1 , 1030 cm -1 (absorption band of cellulose backbone chain C-O stretching vibration). However, they are the absorbances when the baseline is set to the absorbance of 0, with the baseline being the line connecting 1900 cm -1 and 1500 cm -1 and the line connecting 800 cm -1 and 1500 cm -1 . Then, the average degree of substitution at each measurement location was calculated from the IR index according to the following formula (2), and the average value was taken as DS. DS = 4.13 × IR index ··· (2)

[0176] [Coefficient of variation of DS (CV)] The porous sheet on which the above ATR-IR measurement was performed was cryogenically pulverized to prepare a powder sample of cellulose fibers. The powder was placed on 10 dish-shaped sample holders with a diameter of 2.5 mm, the surface was pressed down to make it flat, and XPS measurements were performed on each of them. For the obtained C1s spectrum, peak separation was performed, and the degree of substitution (DSs) of each sample was determined by the following formula from the area intensity (Ixf) of the peak (286 eV) derived from the O-C=O bond of the acetyl group with respect to the area intensity (Ixp) of the peak (289 eV, C-C bond) attributed to the carbons C2-C6 derived from the pyranose ring of cellulose, and the average was taken as the DSs of the cellulose fibers. DSs=(Ixf)×5 / (Ixp)

[0177] The conditions of the XPS measurement used were as follows. Equipment used: ULVAC-PHI VersaProbeII Excitation source: mono.AlKα 15 kV×3.33 mA Analysis size: approximately 200 μmφ Photoelectron extraction angle: 45° Capture region Narrow scan: C 1s, O 1s Pass Energy: 23.5 eV

[0178] Based on the above DS and DSs, the DS non-uniformity ratio (CV) was calculated according to the following formula. DS non-uniformity ratio (CV)=DSs / DS

[0179] [Average fiber diameter equivalent to specific surface area] Using a specific surface area and pore size distribution measuring device (Nova-4200e, manufactured by Quantachrome Instruments), after drying approximately 0.2 g of the porous sheet sample under vacuum at 150 °C for 2 hours, the nitrogen gas adsorption amount at the boiling point of liquid nitrogen was measured at 5 points in the range where the relative vapor pressure (P / P0) was 0.05 or more and 0.2 or less (multi-point method), and then the BET specific surface area (m 2 / g) was calculated. Then, the average fiber diameter equivalent to the specific surface area was calculated from the following formula and taken as the average fiber diameter D of cellulose. D(nm)=2667 / specific surface area (m 2 / g)

[0180] [Average fiber diameter based on electron microscope image] The wet cake was diluted with t-butanol to 0.01% by mass, dispersed using a high-shear homogenizer (manufactured by IKA, trade name "Ultra Turrax T18") under the treatment conditions: rotation speed 15,000 rpm × 3 minutes, cast onto an osmium-evaporated silicon substrate, air-dried, and measured with a high-resolution scanning electron microscope (manufactured by Hitachi High-Tech Corporation, Regulus8220). The measurement was carried out by adjusting the magnification so that at least 100 cellulose fibers were observed, measuring the minor axis (D) of 100 randomly selected cellulose fibers, and calculating the additive average of the 100 cellulose fibers.

[0181] [Weight-average molecular weight (Mw), number-average molecular weight (Mn), and Mw / Mn ratio] Weighed 0.88 g of the porous sheet, cut it into small pieces with scissors, gently stirred it, added 20 mL of pure water, and left it for 1 day. Next, the water and solid content were separated by centrifugation. Subsequently, 20 mL of acetone was added, gently stirred, and left for 1 day. Next, the acetone and solid content were separated by centrifugation. Subsequently, 20 mL of N,N-dimethylacetamide was added, gently stirred, and left for 1 day. Again, after separating the N,N-dimethylacetamide and solid content by centrifugation, 20 mL of N,N-dimethylacetamide was added, gently stirred, and left for 1 day. After separating the N,N-dimethylacetamide and solid content by centrifugation, 19.2 g of an N,N-dimethylacetamide solution adjusted to 8 mass percent lithium chloride in the solid content was added, stirred with a stirrer, and visually confirmed to dissolve. The solution in which cellulose was dissolved was filtered through a 0.45 μm filter, and the filtrate was used as a sample for gel permeation chromatography. The apparatus and measurement conditions used are as follows. Apparatus: Tosoh Corporation HLC-8120 Column: TSKgel SuperAWM-H (6.0 mm I.D. × 15 cm) × 2 columns Detector: RI detector Eluent: N,N-dimethylacetamide (0.2% lithium chloride) Flow rate: 0.6 mL / min Calibration curve: Pullulan conversion

[0182] [Average content rate of alkali-soluble polysaccharides] The content rate of alkali-soluble polysaccharides was determined by subtracting the α-cellulose content rate from the holocellulose content rate (Wise method) using the method described in the non-patent literature (Wood Science Experiment Manual, edited by the Japanese Wood Research Society, pages 92 - 97, 2000) for cellulose fibers. The content rate of alkali-soluble polysaccharides was calculated three times for one sample, and the number average of the calculated content rates of alkali-soluble polysaccharides was taken as the average content rate of alkali-soluble polysaccharides of the cellulose fibers.

[0183] [Average content rate of acid-insoluble components] The quantification of acid-insoluble components was performed by the Klason method described in the non-patent literature (Wood Science Experiment Manual, edited by the Japanese Wood Research Society, pages 92 - 97, 2000) for cellulose fibers. The air-dried cellulose fibers were precisely weighed, placed in a predetermined container, and 72 mass% sulfuric acid was added. After appropriately pressing with a glass rod so that the contents became uniform, they were autoclaved to dissolve cellulose and hemicellulose in the acid solution. After allowing to cool, the contents were filtered through glass fiber filter paper, and the acid-insoluble components were obtained as residues. The acid-insoluble component content rate was calculated from the weight of this acid-insoluble component, and the number average of the acid-insoluble component content rates calculated for three samples was taken as the average content rate of acid-insoluble components.

[0184] [Thermal decomposition start temperature (T D )] The thermal analysis of the porous sheet was evaluated by the following measurement method. Apparatus: Thermo plus EVO2 manufactured by Rigaku Sample: Circularly cut out from the porous sheet and 10 mg were stacked and placed in an aluminum sample pan. Sample amount: 10 mg Measurement conditions: In a nitrogen flow of 100 ml / min, the temperature was raised from room temperature to 150 °C at a heating rate of 10 °C / min, held at 150 °C for 1 hour, and then cooled to 30 °C. Subsequently, the temperature was raised from 30 °C to 450 °C at a heating rate of 10 °C / min as it was. T D Calculation method: Obtained from a graph with temperature on the horizontal axis and weight retention rate (%) on the vertical axis. Starting from the weight of the porous sheet at 150 °C (state where moisture is almost removed) (weight loss amount 0 wt%), the temperature was further increased, and a straight line passing through the temperature at 1 wt% weight loss and the temperature at 2 wt% weight loss was obtained. The temperature at the point where this straight line intersects the horizontal line (baseline) passing through the starting point of 0 wt% weight loss amount was defined as the thermal decomposition start temperature (T D ).

[0185] [Temperature at 1 wt% weight loss] Calculation method for temperature at 1 wt% weight loss: The temperature at 1 wt% weight loss used in the above T D calculation was defined as the temperature at 1 wt% weight loss.

[0186] [Weight loss rate at 250 °C] Apparatus: Thermo plus EVO2 manufactured by Rigaku Sample: A circular piece cut from the porous sheet was stacked and placed in an aluminum sample pan at 10 mg portions. Sample amount: 10 mg Measurement conditions: In a nitrogen flow of 100 ml / min, the temperature was increased from room temperature to 150 °C at a heating rate of 10 °C / min, held at 150 °C for 1 hour, then the temperature was increased from 150 °C to 250 °C at a heating rate of 10 °C / min, and held at 250 °C for 2 hours as it was. Calculation method for weight change rate at 250 °C: Starting from the weight W0 at the time of reaching 250 °C, after holding at 250 °C for 2 hours, the weight was defined as W1, and calculated from the following formula. Weight change rate at 250 °C (%): (W1 - W0) / W0 × 100

[0187] <Bulk density of dry powder of cellulose fiber> A 100 mL cylindrical container made of stainless steel was filled with the dry powder of cellulose fiber until it overflowed. After rubbing the dry powder, the weight was measured and calculated.

[0188] <Viscosity of cellulose fiber slurry and redispersion liquid> The sample solution prepared by dispersing cellulose fibers before drying or dry powder with a homogenizer to form a 0.5% by mass aqueous dispersion was subjected to viscosity measurement using a coaxial cylinder configuration with a Thermo Fisher Scientific rheometer HAAKE MARS. When reading the viscosity at a shear rate of 100 s -1 −1, in order to suppress data scatter, the viscosity at a shear rate of 100 s -1 −1 was read after applying a certain shear history. Specifically, after putting the 0.5% by mass sample solution into the coaxial cylinder cup, the shear rate was increased from 1 s -1 −1 to 100 s -1 −1 over 100 seconds using the rheometer, and then the shear rate was decreased from 100 s -1 −1 to 1 s -1 −1 over 100 seconds, and then the shear rate was increased again from 1 s -1 −1 to 100 s -1 −1 over 100 seconds, and the viscosity at the time when 100 s -1 −1 was reached was read.

[0189] <Water content and total liquid ratio of CNF slurry and dry powder> A heat drying type moisture meter (manufactured by A&D Company, MX-50) was used. 5 g of the slurry and dry powder were placed in an aluminum dish, heated at 150 °C, and the moisture content was measured. When the slurry contained a volatile organic solvent, the total liquid ratio was measured as the sum of water and the organic solvent.

[0190] <Water:i-butanol ratio of CNF slurry> After preparing a DMF solution by diluting the CNF slurry to 0.1% by mass with dimethylformamide (DMF), solids were removed using a 0.2 μm syringe filter. The obtained DMF solution was measured by gas chromatography. From the peak area of the obtained chromatogram, the mass percentage of i-butanol in the DMF solution was calculated, and then the mass percentage of i-butanol in each CNF slurry was calculated from the dilution ratio of the CNF slurry. In calculating the mass percentage of i-butanol from the peak area, a calibration curve was prepared in advance using DMF standard solutions containing i-butanol with different concentrations (i-butanol concentrations were 50 ppm by mass, 100 ppm by mass, and 500 ppm by mass). Finally, the total liquid ratio (total of both water and i-butanol) of the CNF slurry was measured using a heat drying type moisture meter, and the water:i-butanol ratio was calculated from the following formula. Water:i-butanol = (total liquid ratio (mass%)) - (i-butanol mass%):i-butanol mass% The measurement by gas chromatography was carried out under the following conditions. Apparatus: GC-2010 manufactured by Shimadzu Corporation Column: DB-WAX (30 m × 0.25 mm, film thickness 0.25 μm) Column temperature: 40°C → heated to 100°C at 15°C / min → heated to 200°C at 20°C / min Column flow rate: 1.0 ml / min Inlet temperature: 200°C Injection method: Split method (1:50) Detector temperature: 230°C Injection volume: 1 μl

[0191] <Tensile strength and elongation at break of the resin composite> For the obtained test pieces, in accordance with ISO527-1, the tensile yield strength and elongation at break were measured. For the molded pieces that broke before reaching yield, the maximum strength was substituted.

[0192] [Table 1]

[0193] [Table 2]

Industrial Applicability

[0194] According to the present invention, it is possible to produce a dry powder of cellulose fiber which can be provided as a dry powder showing good redispersibility, is excellent in storage and transportation costs, and is extremely useful as a physical property improver for resin composites.

Claims

1. 1. A method for producing a dry powder of cellulose fibers, comprising the steps of: A slurry preparation step of preparing a slurry containing cellulose fibers and water; and a granulation step of agitating the slurry under reduced pressure to form a dry powder of the cellulose fibers; Including, The method, wherein the granulating step comprises forming particles of the cellulose fibers by the agitation and chopping the particles.

2. 10. The method of claim 1, wherein the slurry contains 5% or more by weight water at the start of the granulation step.

3. 3. The method of claim 1 or 2, wherein an additional medium, which is a liquid medium other than water, is added to the slurry in the granulation step.

4. 4. The method of claim 3, wherein an additional medium, which is a liquid medium other than water, is added to the slurry in two or more portions during the granulation step.

5. The method according to claim 3 or 4, wherein the additional medium is selected from the group consisting of: alcohols having a boiling point of 50° C. to 170° C.; ethers; carboxylic acids; esters; ketones; and nitrogen-containing solvents.

6. The method according to any one of claims 3 to 5, wherein the additional medium is a substance which forms an azeotrope with water.

7. 7. The method of claim 6, wherein the additional medium is added to the slurry in a proportion greater than the azeotropic composition with water.

8. The method according to any one of claims 3 to 7, wherein the additional medium is added to the slurry in a mass ratio of water:additional medium in the slurry ranging from 1:99 to 90:

10.

9. 1. A method for producing a dry powder of cellulose fibers, comprising the steps of: A slurry preparation step of preparing a slurry comprising cellulose fibers and a liquid medium; and a granulation step of agitating the slurry under reduced pressure to form a dry powder of the cellulose fibers; Including, The method, wherein the granulating step comprises forming particles of the cellulose fibers by the agitation and chopping the particles.

10. 10. The method of claim 9, wherein the liquid medium is at least one selected from the group consisting of alcohols having a boiling point of 50° C. to 170° C.; ethers; carboxylic acids; esters; ketones; and nitrogen-containing solvents.

11. The method according to any one of claims 1 to 10, wherein a binder is added to the slurry in the slurry preparation step and / or the granulation step.

12. The method of claim 11 , wherein the binder is selected from the group consisting of polyalkylene oxides, cellulose ethers, and cellulose esters.

13. The method according to claim 11 or 12, wherein the binder is dissolved in a medium and added to the slurry in the slurry preparation step and / or the granulation step.

14. The granulation step is carried out in a granulator equipped with an agitator blade, a chopper blade, and a pressure reducing mechanism, In the granulation step, the stirring is performed by rotating the stirring blade at a peripheral speed of 0.5 m / sec to 40 m / sec, and the chopper pulverization is performed by rotating the chopper blade at a speed of 100 rpm to 6000 rpm; The method according to any one of claims 1 to 13, wherein the granulator is configured such that the chopper-milled particles are further subjected to said agitation.

15. The granulation step is carried out in a granulator equipped with an agitator blade, a chopper blade, and a pressure reducing mechanism, In the granulation step, the stirring is performed by rotating the stirring blade at a peripheral speed of 0.5 m / sec to 40 m / sec, and the chopper pulverization is performed by rotating the chopper blade at a peripheral speed of 0.5 m / sec to 40 m / sec, The method according to any one of claims 1 to 14, wherein the granulator is configured such that the chopper-milled particles are further subjected to said agitation.

16. 16. The method of claim 15, wherein the peripheral speed of the chopper blade is less than or equal to the peripheral speed of the agitator blade.

17. The method according to any one of claims 1 to 16, wherein the granulation step is carried out at a temperature of 20 to 160°C and a reduced pressure of -100 kPa to -1 kPa.

18. 18. The method of any one of claims 1 to 17, wherein the bulk density of the dry powder is from 0.05 g / mL to 1.0 g / mL.

19. The method according to any one of the preceding claims, wherein cellulose fibres derived from cotton linters are used.

20. The method according to any one of claims 1 to 19, wherein chemically modified cellulose fibres are used.

21. The method according to any one of claims 1 to 20, wherein cellulose fibres are used which are chemically modified with hydrophobic substituents.

22. The method according to any one of claims 1 to 21, wherein the number average fiber diameter of the cellulose fibers is 10 nm or more and 1000 nm or less.

23. 23. A method for producing a composite comprising cellulose fibers and a resin, the method comprising preparing a dry powder by the method according to any one of claims 1 to 22, and mixing the dry powder with the resin.

24. The resin is a thermoplastic resin, 24. The method of claim 23, wherein the dry powder and the resin are mixed by melt kneading.

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