Cellulose fine fibers and their manufacturing method, nonwoven fabric, and fiber-reinforced resin and its manufacturing method

Abstract

Cellulose fine fibers can be provided that provide fiber reinforced resins that are excellent in all of strength, modulus, and strain at break. [Solution] In one aspect, cellulose fine fibers can be provided which, when measured with an automatic fiber shape analyzer, satisfy all of the following: (i) a length-weighted average fiber length of fibers having a fiber length of 100 μm or more is 110 μm or more and 500 μm or less; (ii) an average fiber diameter of 42.5 μm or less; (iii) a fine fiber area ratio of 90% or less; (iv) among fibers having a fiber length of less than 100 μm, the number frequency of fibers having a fiber length of 20 μm or more and 56 μm or less is 97% or less; (v) among fibers having a fiber length of 100 μm or more, the number frequency of fibers having a fiber length of 411 μm or more is 54% or less; and (vi) an average fiber diameter when converted into a specific surface area of ​​20 to 150 nm.

Description

Technical Field

[0001] The present invention relates to cellulose microfibers, a method for producing the same, non-woven fabrics, and a fiber-reinforced resin using the same and a method for producing the same.

Background Art

[0002] In recent years, from the viewpoint of environmental protection and from the viewpoint of performance expression with various characteristics, cellulose fibers, particularly cellulose microfibers, can be effectively utilized as plant resources in a wide range of application fields, and also have a high elastic modulus and excellent thermal dimensional stability. As a material, for example, it has attracted attention as a raw material for fillers for automotive composites or core materials for fiber-reinforced plastics (FRP). However, the resin containing cellulose microfibers has high brittleness and is easily broken even by a small change, so there are still problems from the viewpoints of strength and impact resistance.

[0003] Patent Document 1 describes a technique for improving flexural strength and flexural modulus while maintaining impact resistance by compounding a resin having a specific relative viscosity and carboxy terminal concentration with acetylated microfibrillated cellulose fibers.

[0004] Patent Document 2 describes microfibrillated cellulose having an average fiber length of 0.02 to 3.0 mm, an average fiber diameter of 0.1 μm or more, and a fibrillation rate of 1.0% or more. After subjecting this to a hydrophobization treatment and then blending it with a resin, a technique for increasing the flexural modulus of the fiber-reinforced composite resin is described.

[0005] Patent Document 3 shows a composite material composed of three components: microfibrillated cellulose, an elastomer, and a resin. It is described that the impact resistance can be improved by using a core-shell type elastomer having a shell portion having reactivity with the hydroxyl group of cellulose.

Prior Art Documents

Patent Documents

[0006] [Patent Document 1] International Publication No. 2016 / 148233 [Patent Document 2] International Publication No. 2019 / 230573 [Patent Document 3] Japanese Patent Publication No. 2010-31093 [Overview of the project] [Problems that the invention aims to solve]

[0007] However, the technology described in Patent Document 1 uses pulp with a certain amount of lignin remaining, known as lignocellulose, which presents challenges in heat resistance during melt-mixing. In addition, because defibration is performed under the constrained shear conditions of the kneading extrusion process, sufficient defibration for performance development does not occur, and even if the properties of the resin are improved, the strength and elastic modulus of the composite of the resin and cellulose remain insufficient. Furthermore, in Patent Document 2, achieving high levels of strength, elastic modulus, and fracture strain has not been sufficiently considered. Thus, conventional technologies have not yielded a fiber-reinforced resin that simultaneously satisfies high levels of strength, elastic modulus, and fracture strain.

[0008] Therefore, the problem that the present invention aims to solve is to provide cellulose microfibers that give a fiber-reinforced resin that is superior in strength, elastic modulus, and fracture strain. [Means for solving the problem]

[0009] This disclosure includes the following items: [1] In the measurement of fiber shape using an automated fiber shape analyzer, (i) The length-weighted average fiber length of fibers with a fiber length of 100 μm or more is between 110 μm and 500 μm. (ii) Average fiber diameter is 42.5 μm or less, (iii) Fine fiber area ratio is 90% or less, (iv) Among fibers with a fiber length of less than 100 μm, the number frequency of fibers with a fiber length of 20 μm or more and 56 μm or less is 97% or less. (v) Among fibers with a fiber length of 100 μm or more, the number frequency of fibers with a fiber length of 411 μm or more is 54% or less, (vi) When converted by specific surface area, the average fiber diameter is 20-150 nm. Cellulose microfibers that meet all of these requirements. [2] Cellulose microfibers as described in item 1, having an average fiber length of 110 μm or more and 500 μm or less. [3] In the measurement of fiber shape using an automated fiber shape analyzer, (i) Average fiber length is 130 μm or more and 350 μm or less. (ii) Average fiber diameter is 35 μm or less, (iii) Fine fiber area ratio is 75% or less, (iv) Among fibers with a fiber length of less than 100 μm, the number frequency of fibers with a fiber length of 20 μm or more and 56 μm or less is 75% or less. (v) Among fibers with a fiber length of 100 μm or more, the number frequency of fibers with a fiber length of 411 μm or more is 30% or less, (vi) Fibrillation rate is 5% or less, Cellulose microfibers as described in item 1 or 2, which satisfy all of the following conditions. [4] Cellulose microfibers as described in any of items 1 to 3, having a glucose content of 90% by mass or more in the constituent sugar analysis. [5] In a scanning electron microscope (SEM) image of the surface of a sample obtained by casting and drying a 5 ppm DMSO dispersion of cellulose microfibers, the occupied area relative to the total area occupied by the cellulose microfibers was 15 μm². 2 Cellulose microfibers as described in any of items 1 to 4, wherein the proportion of the total occupied area of ​​ultrafine fibers that are less than 10% is between 10% and 80%. [6] Cellulose microfibers having a cellulose type I crystalline structure, as described in any of items 1 to 5. [7] Cellulose microfibers described in any of items 1 to 6, having a crystallinity of 60% or higher. [8] Cellulose microfibers as described in any of items 1 to 7, having a halogen content of 250 ppm by mass or less. [9] Cellulose microfibers described in any of items 1-8, with a whiteness of 50% or more.

[10] Cellulose microfibers as described in any of items 1 to 9, wherein the length-weighted average fiber length of fibers with a fiber length of 100 μm or more is between 130 μm and 350 μm.

[11] Cellulose microfibers as described in any of items 1 to 10, wherein, among fibers with a fiber length of 100 μm or more, the frequency of fibers with a fiber length of 411 μm or more is 30% or less.

[12] Cellulose microfibers as described in any of items 1 to 11, having a fine fiber area ratio of 75% or less.

[13] Cellulose microfibers as described in any of items 1 to 12, wherein, among fibers with a fiber length of less than 100 μm, the frequency of fibers with a fiber length of 20 μm to 56 μm is 30% to 75%.

[14] Cellulose microfibers as described in any of items 1 to 13, having a fibrillation rate of 5% or less.

[15] Cellulose microfibers as described in any of items 1 to 14, wherein at least the surface of the cellulose microfibers is chemically modified.

[16] Cellulose microfibers as described in item 15, wherein the chemical modification is acetylation, and the degree of acetylation is 0.5 to 1.3.

[17] In measurements using an automated fiber shape analyzer (iv) Among fibers with a fiber length of less than 100 μm, the number frequency of fibers with a fiber length of 20 μm or more and 56 μm or less is 30% or more and 97% or less, (vi) Fibrillation rate is 5% or less, Cellulose microfibers as described in any of items 1-16, which further satisfy the above conditions.

[18] A method for producing cellulose microfibers as described in any of items 1 to 17, The halogen content of the cellulose fine fibers is 250 ppm by mass or less, and the method is A method for producing cellulose microfibers, comprising a step of defibrating a cellulose raw material having a halogen content of 300 ppm by mass or less.

[19] A fiber-reinforced resin comprising cellulose microfibers as described in any of items 1 to 17 and a resin.

[20] The fiber-reinforced resin according to item 19, wherein the resin has a melting point of 200°C or higher. [twenty one] The fiber-reinforced resin according to item 19 or 20, comprising 1% by mass or more of the aforementioned cellulose fine fibers. [twenty two] Nonwoven fabric containing cellulose microfibers as described in any of items 1-17. [twenty three] A nonwoven fabric as described in item 22, containing 50% by mass or more of synthetic fibers with a melting point of 300°C or lower. [twenty four] The nonwoven fabric according to item 22 or 23, comprising 1% by mass or more of the cellulose fine fibers. [twenty five] A fiber-reinforced resin comprising a nonwoven fabric described in any of items 22 to 24 and a resin impregnated in the nonwoven fabric.

[26] A method for producing a fiber-reinforced resin containing cellulose microfibers and resin, The process includes a step of obtaining a fiber-reinforced resin by heat-pressing a nonwoven fabric described in any of items 22 to 24, A method for producing a fiber-reinforced resin, wherein the nonwoven fabric contains synthetic fibers, and the heat pressing is performed at a temperature above the melting point of the synthetic fibers. [Effects of the Invention]

[0010] One aspect of the present invention provides cellulose microfibers that give a fiber-reinforced resin that is excellent in strength, elastic modulus, and fracture strain. [Brief explanation of the drawing]

[0011] [Figure 1]This is an explanatory diagram of the calculation methods for IR Index 1730 and IR Index 1030. [Figure 2] This diagram illustrates an example of the arrangement of blades and grooves in a disc refiner. [Figure 3] This diagram illustrates the blade width, groove width, and inter-blade distance of a disc refiner. [Modes for carrying out the invention]

[0012] The following describes exemplary embodiments of the present invention (hereinafter also referred to as these embodiments), but the present invention is not limited to these embodiments and can be implemented in various ways within the scope of its gist.

[0013] ≪Cellulose microfibers≫ <Shape of cellulose microfibers> Cellulose microfibers according to one embodiment are measured by an automated fiber shape analyzer. (i) The length-weighted average fiber length of fibers with a fiber length of 100 μm or more is between 110 μm and 500 μm. (ii) Average fiber diameter is 42.5 μm or less, (iii) Fine fiber area ratio is 90% or less, (iv) Among fibers with a fiber length of less than 100 μm, the number frequency of fibers with a fiber length of 20 μm or more and 56 μm or less is 97% or less, (v) Among fibers with a fiber length of 100 μm or more, the number frequency of fibers with a fiber length of 411 μm or more is 54% or less. It satisfies all of the following requirements.

[0014] In one embodiment, the average fiber length of the cellulose microfibers is 110 μm or more and 500 μm or less.

[0015] Cellulose microfibers according to one embodiment are, in an automated fiber shape analyzer, (i) Average fiber length is 130 μm or more and 350 μm or less. (ii) Average fiber diameter is 35 μm or less, (iii) The ratio of fine fiber area is 75% or less. (iv) Among fibers with a fiber length of less than 100 μm, the number frequency of fibers with a fiber length of 20 μm or more and 56 μm or less is 75% or less. (v) Among fibers with a fiber length of 100 μm or more, the number frequency of fibers with a fiber length of 411 μm or more is 30% or less, (vi) Fibrillation rate is 5% or less, It satisfies all of the following requirements.

[0016] A cellulose microfiber according to one embodiment is obtained by micronizing a cellulose raw material using at least one type of physical means, and is generally referred to as cellulose nanofiber, CNF, CeNF, or micronized cellulose fiber.

[0017] In one embodiment, the cellulose microfiber is a chemically modified cellulose microfiber. In this disclosure, a chemically modified cellulose microfiber means a cellulose microfiber in which at least a portion of the three hydroxyl groups contained in the glucopyranose units in the cellulose molecular backbone present in the cellulose microfiber is chemically modified. Here, "a portion" means that at least one hydroxyl group of at least one glucopyranose unit in the cellulose structure formed by the polymerization of multiple glucopyranose units is chemically modified. In a typical embodiment, the entire cellulose is not chemically modified, and the chemically modified cellulose microfiber retains the crystalline structure of the cellulose before chemical modification. For example, the crystalline structure of cellulose type I can be confirmed when analyzed by X-ray diffraction (XRD).

[0018] In one embodiment, the cellulose microfibers are chemically modified at least on their surface. The cellulose microfibers, whose surface is chemically modified at least on their surface, may have a length-weighted average fiber length of 110 μm or more and 500 μm or less when measured with an automated fiber shape analyzer, and the number frequency of fibers with a fiber length of 411 μm or more among fibers with a fiber length of 100 μm or more may be 54% or less.

[0019] Here, a cellulose microfiber with at least a chemically modified surface means a cellulose microfiber in which at least a portion of the hydroxyl groups in the cellulose backbone are chemically modified. Chemically modified cellulose microfibers are usually either chemically modified throughout their entire structure from the surface to the interior, or their surface is chemically modified but they have regions that are not chemically modified. In one embodiment, a cellulose microfiber has a chemically modified surface and also has regions that are not chemically modified. In one embodiment, even if the surface of a cellulose microfiber is chemically modified, the overall crystalline structure of the cellulose microfiber remains unchanged and retains the crystalline structure before chemical modification (for example, when the cellulose microfiber is analyzed by XRD, it can be confirmed that it has a cellulose type I crystalline structure). Such a cellulose microfiber can be determined to be a cellulose microfiber with a chemically modified surface and also having regions that are not chemically modified. That is, in one embodiment, the cellulose microfiber has a cellulose type I crystalline structure.

[0020] Cellulose microfibers according to one embodiment are analyzed by an automated fiber shape analyzer using the following fiber shape parameters: (1) Average fiber diameter is 42.5 μm or less, (2) Fine fiber area ratio is 90% or less, (3) Among fibers with a fiber length of less than 100 μm, the number frequency of fibers with a fiber length of 20 μm or more and 56 μm or less is 30% or more and 97% or less, (4) Fibrillation rate is 5% or less, It is preferable that the following conditions be met.

[0021] Furthermore, in scanning electron microscope (SEM) images of the surface of a sample obtained by casting a 5 ppm by mass dimethyl sulfoxide (DMSO) dispersion of cellulose microfibers onto a smooth substrate and drying it, the occupied area of ​​the cellulose microfibers was 15 μm² relative to the total area occupied by the cellulose microfibers. 2 Preferably, the proportion of the total occupied area of ​​the ultrafine fibers is between 10% and 80%.

[0022] (Automatic fiber shape analyzer) The various characteristics of the cellulose microfibers in this embodiment are determined using an automated fiber shape analyzer (in one embodiment, a Morfi Neo manufactured by Techpap). The measurement procedure is described below. For the fiber parameters during measurement, a fiber length of 100 μm is used as the threshold, with fibers of 100 μm or longer defined as normal fibers and fibers of less than 100 μm defined as fine fibers. 1. Disperse cellulose microfibers in pure water to prepare a 1 L aqueous dispersion. Here, the final solid content concentration of the cellulose microfibers should be 0.003 to 0.005 mass%. If the aqueous dispersion of cellulose microfibers before dilution is less than 2 mass%, it is sufficient to simply mix it with a spatula or the like. However, if the aqueous dispersion is 2 mass or more, or if it is a water-containing cake or powder, the dispersion treatment should be performed using a high-shear homogenizer (in one embodiment, manufactured by IKA, trade name "Ultra-Turrax T18") under the following conditions: rotation speed 25,000 rpm for 5 minutes. If dispersed in a medium other than water, the medium is dispersed in a sufficient amount of pure water using the high-shear homogenizer described above under the following conditions: rotation speed 25,000 rpm for 5 minutes. After dispersing, the medium is removed by means of suction filtration or other means. Then, the medium is dispersed again in pure water using the high-shear homogenizer described above under the following conditions: rotation speed 25,000 rpm for 5 minutes, so that the final solid content concentration is 0.003 to 0.005 mass%, thereby replacing the medium with water. 2. The aqueous dispersion prepared in step 1 is subjected to an autosampler and measured. 3. Output the measurement results in txt format (or csv format). 4. Extract or calculate each shape parameter from the measurement results. The following values ​​from the measurement results will be used for each parameter.

[0023] (1) Mean arithmetic length [μm] (2) Mean length-weighted length [μm] for ordinary fibers (fibers with a length of 100 μm or more) (3) Number frequency of fibers with a fiber length of 411 μm or more in normal fibers (fibers with a fiber length of 100 μm or more): Calculated from the length-weighted fiber length distribution (length-weighted fiber length, μm) of normal fibers. (4) Mean fiber width [μm] (5) Fine fiber area ratio: Fine content, % in Area (6) Number frequency of fibers with a fiber length of 20 μm or more and 56 μm or less in fine fibers (fibers with a fiber length of less than 100 μm): Calculated from the fiber length distribution of fine fibers (Fine length, μm: FL). (7) Fibrillation rate: MacroFibrillation index [%]

[0024] Furthermore, since the data interval can be arbitrarily set when measuring the fiber length distribution with this device, any setting is acceptable as long as it allows the distribution of fibers with the aforementioned fiber lengths to be confirmed.

[0025] The following provides a detailed explanation of each shape parameter.

[0026] (Average fiber length) In one embodiment, the cellulose microfibers have an average fiber length of 110 μm to 500 μm, or 130 μm to 350 μm, as measured by an automated fiber shape analyzer. Here, the average fiber length is the mean arithmetic fiber length, which in the case of bent fibers means the length of the straight line connecting the ends of the fibers. Having an average fiber length within this range allows for uniform dispersion when compounded into a resin, improving stress transmission and thus increasing strength and fracture strain. The average fiber length of the cellulose microfibers is preferably 150 μm to 250 μm, and more preferably 160 μm to 200 μm.

[0027] (Length-weighted average fiber length) In one embodiment, the cellulose microfibers, as measured by an automated fiber shape analyzer, have a length-weighted average fiber length of 110 μm to 500 μm, more preferably 120 μm to 400 μm, and even more preferably 130 μm to 350 μm. The length-weighted average fiber length is defined in ISO / FDIS 16065-2:2006 and, in the case of bent fibers, is the average value of the fiber length corresponding to the actual fiber length considering the bent shape. It is particularly advantageous to control the fiber length of the normal fibers within the cellulose microfibers to a specific range. That is, when the fiber length of the normal fibers is within this range, the fibers that are too long do not entangle and form aggregates when compounded in resin, allowing for uniform dispersion and improved stress transmission, resulting in increased strength and fracture strain.

[0028] (Fiber length distribution of typical fibers) In one embodiment, the cellulose microfibers, when measured with an automated fiber shape analyzer, have a number frequency of 54% or less of fibers with a fiber length of 411 μm or more among the normal fibers (fibers with a fiber length of 100 μm or more). This number frequency can be calculated from the length-weighted fiber length distribution described above. The length-weighted fiber length is the fiber length that corresponds to the actual fiber length considering the bending shape of the bent fiber. When the fiber length of the normal fibers is within this range, the fibers that are too long do not entangle and form aggregates when compounded with resin, allowing for uniform dispersion and improved stress transmission, resulting in increased strength and fracture strain. The number frequency of fibers with a fiber length of 411 μm or more among the normal fibers is preferably 40% or less, more preferably 30% or less. The lower limit is not particularly limited and is 0% or more.

[0029] (Average fiber diameter) The cellulose microfibers of this embodiment have an average fiber diameter of 42.5 μm or less, or 41.5 μm or less, or 40 μm or less, or 38 μm or less, or 35 μm or less, or 30 μm or less, or 25 μm or less, as measured by an automatic fiber shape analyzer. The fact that the length-weighted average fiber length and / or average fiber length are within the above range, along with the average fiber diameter being within this range, means that the L / D ratio of individual cellulose microfibers is sufficiently large. A larger L / D ratio causes entanglement among the cellulose microfibers within the resin, thereby increasing the strength of the fiber-reinforced resin. A thinner fiber diameter is preferable because it results in a larger L / D ratio, but due to the resolution of the measuring device, it may be 1.5 μm or larger. Furthermore, from the viewpoint that a certain thickness is advantageous for increasing the flexural elasticity of the fiber-reinforced resin, a diameter of 15 μm or larger is preferable.

[0030] (Average fiber diameter calculated using specific surface area) In cellulose microfibers, the specific surface area generally corresponds to the average fiber diameter in one embodiment, and the specific surface area increases as the average fiber diameter decreases. In one embodiment, the specific surface area is preferably 20 m² from the viewpoint of increasing the strength of the fiber-reinforced resin. 2 / g or more, or 30m 2 / g or more, or 40m 2 It is 100m or more, and from the viewpoint of increasing the flexural elasticity of the fiber-reinforced resin, it is preferably 100m 2 / g or less, or 80m 2 / g or less, or 60m 2 It is less than / g.

[0031] The average fiber diameter (also referred to in this disclosure as the converted average fiber diameter) calculated from the specific surface area by the procedure described in the [Examples] section of this disclosure is, in one embodiment, 20 nm or more, or 30 nm or more, from the viewpoint of increasing the flexural elasticity of the fiber-reinforced resin, and in one embodiment, 150 nm or less, 130 nm or less, or 100 nm or less, in order to increase the strength of the fiber-reinforced resin by causing entanglement of cellulose fine fibers within the resin.

[0032] (Fine fiber area ratio) In this embodiment, the cellulose microfibers have a fine fiber area ratio, as measured by an automated fiber shape analyzer, preferably 90% or less, 85% or less, 80% or less, 75% or less, 60% or less, or 50% or less. Here, the fine fiber area ratio is the ratio of the total area of ​​the observed images of fine fibers with a fiber length of less than 100 μm to the total area of ​​the observed images of all fibers (area of ​​normal fibers + area of ​​fine fibers). When the fine fiber area ratio is within this range, there are not too many fragile interfaces between cellulose and resin in the resin, and the number of fracture initiation points is reduced, resulting in greater fracture strain. The fine fiber area ratio is preferably 5% or more, 10% or more, 20% or more, or 30% or more, as this facilitates orientation when compounded with resin and has a good effect on improving the strength and elastic modulus of the fiber-reinforced resin.

[0033] (Fiber length distribution of fine fibers) In this embodiment, the cellulose microfibers, as measured by an automated fiber shape analyzer, preferably have a fiber frequency of 20 μm to 56 μm in length among the fine fibers (fibers with a fiber length of less than 100 μm) that is 97% or less, 90% or less, 85% or less, 80% or less, 75% or less, 70% or less, or 65% or less. Because these fine fibers are too short, they have poor stress transmission and tend to contribute little to strength improvement. A particularly effective reinforcing effect can be obtained by controlling the frequency of these fine fibers within a predetermined range. Fine fibers with a fiber length of 20 μm to 56 μm are inevitably generated in some quantities as a result of the micronization process of the cellulose raw material, so their frequency may be 5% or more in one embodiment, and may be 30% or more, 50% or more, 55% or more, or 60% or more in another embodiment.

[0034] In one preferred embodiment, the frequency of fibers with a fiber length of 20 μm to 56 μm among fine fibers (fibers with a fiber length of less than 100 μm) is within the above range, while the frequency of fibers with a fiber length of 411 μm or more among normal fibers (fibers with a fiber length of 100 μm or more) is 30% or less. Fibers with a fiber length of 411 μm or more are too long and easily aggregate in the resin, thus contributing little to improving the elastic modulus. Therefore, it is effective to control the frequency of fibers with a fiber length of 411 μm or more to a low level, preferably 10% or less, more preferably 5% or less. The lower limit is not particularly limited, but since it is difficult to completely eliminate fibers with a fiber length of 411 μm or more, in one embodiment it may be 1% or more.

[0035] (Fibrillation rate) The cellulose microfibers of this embodiment preferably have a fibrillation rate of 5% or less as measured by an automated fiber shape analyzer. Here, the fibrillation rate is the ratio of the total length of the n branched side chains L(Sub) to the main chain length L(Main) of a fiber having a branched structure in which at least a portion is branched, with the largest diameter portion being the main chain, and is defined by the following formula.

number

[0036] When the fibrillation rate is within this range, the surface area of ​​each cellulose microfiber becomes small, preventing an excessive number of fragile interfaces between cellulose and resin in the resin, thus reducing the number of fracture initiation points and increasing fracture strain. The fibrillation rate of the cellulose microfiber is preferably 4% or less, or 3% or less, or 2.5% or less, or 2% or less. The lower limit is not particularly limited, and in one embodiment it is 0% or more, or 0.01% or more, or 0.1% or more.

[0037] (Ratio of area occupied by microfibers in SEM images) In a scanning electron microscope (SEM) image of the surface of a sample obtained by casting and drying a cellulose microfiber as a 5 ppm by mass dimethyl sulfoxide (DMSO) dispersion on a smooth substrate, the ratio of the total occupied area of cellulose microfibers to the occupied area of microfibers with an area of 15 μm 2 The ratio of the total occupied area of ultrafine fibers, that is, the occupied area ratio of ultrafine fibers, which is as follows, is preferably 10% or more and 80% or less. These ultrafine fibers are fibers in a region that cannot be measured by the resolution of the element in a fiber shape automatic analyzer. If the occupied area ratio of these ultrafine fibers is too large, there are too many nano-sized fibers, so aggregation of ultrafine fibers in the resin is likely to occur, which may become a starting point for fracture. On the other hand, if the occupied area ratio of ultrafine fibers is too small, there are too few nano-sized fibers, so a good nano-network cannot be obtained and the strength tends to be low. From the above viewpoints, the occupied area ratio of ultrafine fibers is more preferably 15% or more and 75% or less, more preferably 20% or more and 70% or less, and most preferably 20% or more and 65% or less. The cellulose microfibers with the occupied area ratio of ultrafine fibers within the above range may be those refined using at least one physical method, and are generally referred to as cellulose nanofibers, CNF, CeNF, refined cellulose microfibers, and the like. The occupied area ratio of ultrafine fibers is measured by the following procedure.

[0038] 1. Dilute a cellulose microfiber aqueous dispersion with a solid content concentration of 0.2 to 2% by mass to 5 ppm by mass with dimethyl sulfoxide (DMSO), and stir at 3000 rpm for 30 seconds using a homogenizer (in one aspect, manufactured by IKA, trade name "Ultra Turrax T18") to obtain a DMSO dispersion. 2. Apply osmium plasma coating to a smooth substrate (silicon wafer or glass substrate) and heat it to 130 °C on a hot plate. 3. Drop 7 μL of the DMSO dispersion onto the center of the heated smooth substrate, and leave it to dry under heating to fix the cellulose microfibers on the substrate. 4. Using a scanning electron microscope (SEM), four images are taken of the substrate on which the obtained cellulose microfibers are immobilized, at arbitrary different locations on the substrate, with an acceleration voltage of 1.5 kV, an observation magnification of 400x, and a resolution of 400 pixels or more per 100 μm. 5. The threshold value of 15 μm is determined from the number of pixels in the scale bar of the SEM image. 2 Calculate the number of pixels corresponding to this. 6. From the acquired SEM images, a binarized image is created using the MaxEntropy method with the image processing software ImageJ. 7. The binarized image is analyzed using ImageJ's Analyze Particle function to calculate the area (pixels) of individual cellulose microfibers. 8. The particle analysis results of the four captured images are combined, pixels smaller than 2 pixels are removed as noise, and a threshold of 15 μm area is set. 2 Fibers smaller than 15 μm are considered ultrafine fibers, and 15 μm is the total area of ​​cellulose microfibers. 2 Calculate the ratio of the area of ​​extremely small fibers (less than 100%).

[0039] <Controlling the fiber shape of cellulose microfibers> As a method for realizing the unique fiber shape of the cellulose microfibers of this embodiment, more specifically, in one embodiment, a fiber shape in which the length-weighted fiber length of normal fibers, average fiber length, average fiber diameter, fine fiber area ratio, fine fiber fiber length, fibrillation rate, and / or area ratio of ultrafine fibers are within the range of this embodiment, or in one embodiment, a fiber shape in which the average fiber length, average fiber diameter, fine fiber area ratio (area ratio of ultrafine fibers), the number frequency of fibers having a fiber length of 20 μm or more and 56 μm or less among fibers with a fiber length of less than 100 μm, the number frequency of fibers having a fiber length of 411 μm or more among fibers with a fiber length of 100 μm or more, and / or fibrillation rate are within the range of this embodiment, one or more of the methods exemplified below may be used. Using a disc refiner when refining the cellulose raw material, more specifically, adjusting the disc configuration and / or usage conditions of the disc refiner may be particularly advantageous in realizing the desired fiber shape of this embodiment.

[0040] (Cellulose raw material) The raw materials for cellulose microfibers are not particularly limited, and wood-based cellulose raw materials (e.g., coniferous tree chips and hardwood chips) or non-wood-based cellulose raw materials (such as those derived from cotton, hemp, bagasse, kenaf, bamboo, straw, seaweed, algae, sea squirts, and bacterial cellulose) can be used. It is preferable to use cellulose raw materials with a high degree of type I crystallinity, such as so-called wood pulp like coniferous tree pulp and hardwood pulp, and non-wood pulp like cotton linter pulp, hemp pulp, bagasse pulp, kenaf pulp, bamboo pulp, and straw pulp. In a preferred embodiment, the cellulose microfibers are plant-derived.

[0041] In one embodiment, the cellulose raw material has an average fiber length (specifically, a length-weighted average fiber length) of 3 mm or less as measured by an automated fiber shape analyzer, and / or the number percentage of fibers with a fiber length of 3 mm or more is 20% or less. Having a specific fiber length distribution in the cellulose raw material allows for good energy transfer in the fine-grinding or beating section during the defibration process (e.g., beating using a disc refiner or high-pressure homogenizer), and further reduces clogging, thus achieving stable defibration even when the cellulose concentration is relatively high.

[0042] The average fiber length is more preferably 2.5 mm or less, even more preferably 2.0 mm or less, and particularly preferably 1.6 mm or less. Since the above effects are enhanced as the average fiber length decreases, there is no particular lower limit, but considering the mechanical properties when using cellulose fine fibers after beating as a resin filler, 0.1 mm or more is preferred, and 0.5 mm or more is more preferred.

[0043] The percentage of fibers with a length of 3 mm or more is more preferably 15% or less, and even more preferably 10% or less. The lower limit is not particularly limited, as a smaller value enhances the above-mentioned effects, but a range of 0.5% or more and more preferably 1% or more is preferable for practical pretreatment. The fiber length of the cellulose raw material mentioned above can be measured using an automated fiber shape analyzer (Morfi Neo, manufactured by Techpap). The measurement procedure is described below.

[0044] Disperse the cellulose raw material in pure water to prepare a 1 L aqueous dispersion. Here, the final solid content concentration of the cellulose raw material should be 0.003 to 0.005 mass%. If the cellulose raw material before dilution is an aqueous dispersion of less than 2 mass%, it is sufficient to simply mix it with a spatula or the like. However, if it is an aqueous dispersion of 2 mass or more, a hydrated cake, or a powder, the dispersion treatment should be performed using a high-shear homogenizer (IKA, product name "Ultra-Turrax T18") under the following conditions: rotation speed 25,000 rpm for 5 minutes. If dispersed in a medium other than water, the medium is dispersed in a sufficient amount of pure water using a high-shear homogenizer (IKA, product name "Ultra-Turrax T18") under the following conditions: rotation speed 25,000 rpm for 5 minutes. After dispersing, the medium is removed by means of suction filtration or other means. Then, the medium is dispersed again in pure water using the high-shear homogenizer (IKA, product name "Ultra-Turrax T18") under the following conditions: rotation speed 25,000 rpm for 5 minutes, so that the final solid content concentration is 0.003 to 0.005 mass%, thereby replacing the medium with water.

[0045] Next, the aqueous dispersion prepared above is subjected to an autosampler and measured. The obtained measurement results are output in txt format (or csv format), and each shape parameter is extracted or calculated from the measurement results. The following values ​​from the measurement results will be used for each parameter.

[0046] 1) Length-weighted average fiber length: Mean length-weighted length [μm] 2) Percentage of fibers with a fiber length of 3 mm or more: From the histogram of the fiber length distribution in 1), the percentage of fibers with a fiber length of 3 mm or more out of the total number of fibers is calculated using the following formula. Percentage of fibers with a length of 3 mm or more (%) = Number of fibers with a length of 3 mm or more / Total number of measured fibers x 100 3) Mean fiber width [μm]

[0047] (Pretreatment of cellulose raw materials) The cellulose raw material of this embodiment may be subjected to one or more pretreatments selected from crushing, grinding, and classification in order to control its fiber length within a specific range, and then used for defibration (e.g., beating). One pretreatment according to one embodiment is a process that produces a pretreated cellulose raw material in which the average fiber length is 3 mm or less and / or the number percentage of fibers with a fiber length of 3 mm or more is 20% or less, from a cellulose raw material in which the average fiber length is greater than 3 mm and the number percentage of fibers with a fiber length of 3 mm or more is greater than 20%.

[0048] The pulverization process in this embodiment is a process of dry pulverizing the cellulose raw material, and as the pulverizer, a coarse pulverizer, an intermediate pulverizer, a fine pulverizer, etc., can be used.

[0049] Examples of coarse crushers include jaw crushers (i.e., crushers that grip the raw material between a fixed plate and a movable plate and crush it with a strong compressive force), gyretricrusher (i.e., crushers that grip the raw material between a fixed concave and an eccentrically rotating mantle and crush it with a compressive force), and impact crushers (i.e., crushers that pulverize the raw material by striking it with impact blades attached to a high-speed rotating cylindrical rotor, and further pulverize it by striking the material against a rebound plate at high speed).

[0050] Examples of intermediate grinders include roll crushers (i.e., grinders that use multiple cylindrical horizontal rolls, passing the raw material through the gaps between them and grinding it using the pressure of two rolls rotating in different directions and at different speeds), edge runners (i.e., grinders that use two heavy rollers with a large diameter rolling on a horizontal disc to compress and shear the raw material, thereby grinding, mixing, and kneading it), disintegrators (i.e., grinders that use two steel cage-type rotors that rotate in opposite directions around a concentric axis, applying impact force to the raw material supplied from the inner rotor through centrifugal force and rotational action to grind it), SAG (Semi-Autogenous Grinding mill) mills, and self-grinding mills.

[0051] A SAG mill is a type of grinder that uses both large stones and metal balls for crushing. Typically, SAG mills use the smallest balls with a charge of 6-15%. The rotation of the drum throws the large stones and metal balls into the air, causing them to collide with and crush the material. During this process, friction further reduces the particle size. SAG mills are characterized by their large diameter and short cylinder, and the interior of the mill is lined with plates for mixing the materials.

[0052] In a self-sustaining mill (also known as a Run of Mine (ROM) mill), large stones are thrown up by a rotating drum, and the stones collide with each other, compressing the particles. The principle is similar to the SAG mill described above, but it differs in that it does not use metal balls.

[0053] Examples of fine grinding machines include screen type (screen mill), rotary disc type, axial flow type, ball mill type grinders, rod mills, jet mills, and others.

[0054] In a ball mill type grinder, sand or metal balls are typically packed inside a cylinder that rotates horizontally or at a slight incline, and grinding is performed by collision and friction with the balls. The material to be ground is supplied from one end of the cylinder, and the ground product is discharged from the other end.

[0055] A rod mill has a structure very similar to a ball mill, but instead of balls, it uses rods (metal cylinders) as the grinding medium. The material to be ground is ground by the impact of the rods on the rotating drum (body). Compared to a ball mill, it is less prone to over-grinding, and a relatively uniform particle size can be obtained from the ground product.

[0056] In a jet mill, compressed air is used to generate a supersonic airflow, which is then used to pulverize the material to be pulverized. There are two types of jet mills: a pancake type, in which jet nozzles are arranged in a spiral, and an impact type, in which the supersonic airflow from the jet nozzles is injected onto an impact plate.

[0057] For processing the cellulose raw material in this embodiment, an intermediate grinder or a fine grinder is preferred among the above, and a fine grinder is more preferred. Among the fine grinders, the screen type is preferred because it is superior in terms of processing capacity.

[0058] Next, the grinding process in this embodiment is a process in which cellulose raw material is dispersed in an aqueous medium and the aqueous dispersion is subjected to a grinding process, and is distinguished from the grinding process in this embodiment by being a wet process. Examples of aqueous mediums include water itself, or a mixed medium of water and an organic solvent, which is one or more of the following: monohydric alcohols such as ethanol, n-propanol, isopropanol, and butanol; polyhydric alcohols such as ethylene glycol, diethylene glycol, and glycerin; ketones such as acetone; nitrile solvents such as acetonitrile; pyrrolidone solvents, etc. The blending ratio of the organic solvent in the above-mentioned mixture of organic solvent and water is preferably less than 50% by mass, more preferably 30% by mass or less, and particularly preferably 20% by mass or less. The higher the water ratio, the better the grinding performance, and the higher the organic solvent ratio, the more the aggregation of fine fibers in the drying process after grinding is suppressed. Therefore, it is preferable to set the ratio of the organic solvent in consideration of the balance between grinding performance and aggregation suppression. Examples of grinders that can be used in this embodiment include rotary millstones, grinders, planetary mixers, single-screw extruders, twin-screw extruders, and bead mills.

[0059] A bead mill is a media stirring mill that uses beads to nano-disperse or finely grind powders. The material to be processed and beads (media) are placed in a grinding chamber (vessel), and the stirring mechanism rotates at high speed to impart energy to the beads by centrifugal force, grinding the material particles through shear stress, friction, and impact force.

[0060] Among these grinders, rotary millstones, grinders, or planetary mixers are preferred because they offer excellent control over the fiber length distribution. Furthermore, the cellulose concentration in the aqueous dispersion used for grinding is preferably 50% by mass or less, more preferably 25% by mass or less, and particularly preferably 20% by mass or less. As a lower limit, considering the grinding efficiency, it is preferably 1% by mass or more, more preferably 2% by mass or more, even more preferably 5% by mass or more, and particularly preferably 10% by mass or more.

[0061] Furthermore, the classification process in this embodiment is an operation to separate cellulose raw materials by fiber length with the aim of standardizing their fiber lengths, and either dry classification or wet classification methods can be used. Examples of dry classification include gravity field classification, inertial force field classification, and centrifugal force field classification (natural vortex type or forced vortex type), while examples of wet classification include gravity field classification, centrifugal force field classification (free vortex type), and centrifugal force field classification (forced vortex type), and all of these can be used. Classification using mesh sizes of sieves, screens, wires (edge ​​wires), nets, etc., and classification by centrifugal separation can also be used. Considering production efficiency, classification using mesh sizes is preferred, and among these, it is more preferable to use a dry cyclone or screen, or a wet screen or edge wire, even more preferable to use a wet screen or edge wire, and particularly preferable to use a wet edge wire.

[0062] To suppress discoloration and deterioration of physical properties due to heat during compounding with resin, the glucose content of the cellulose raw material and / or cellulose microfibers in this embodiment, as determined by constituent sugar analysis, is preferably 80% by mass or more. Similarly, the cellulose fiber raw material for producing cellulose microfibers also preferably has a glucose content of 80% by mass or more, as determined by constituent sugar analysis. More preferably, these glucose content percentages are 85% by mass or more, or 90% by mass or more, or 91% by mass or more, or 93% by mass or more. Due to the limitations of impurities (e.g., oily components other than polysaccharides and various contaminants) that may be introduced during the harvesting or refining process of the cellulose raw material, or during the production process of cellulose microfibers, the glucose content is preferably 99.5% by mass or less, or 99% by mass or less. A high glucose content in cellulose microfibers usually indicates high cellulose purity, meaning that there is a small amount of lignin, hemicellulose, and other components that can reduce the high modulus of elasticity and high heat resistance of cellulose microfibers.

[0063] In this disclosure, the method for measuring glucose content in structural sugar analysis is as follows. Structural sugar analysis can be performed by referring to the analytical procedure of the National Renewable Energy Laboratory of the U.S. Department of Energy (Sluiter, A., Hames, B., Ruiz, R., Scarlata, C., Sluiter, J., Templeton, D., Crocker, D.: Determination of structural carbohydrates and lignin in biomass. National Renewable Energy Laboratory (NREL), USA, 2008.). Add 3 ml of 72% sulfuric acid to 200 mg of the sample and swell at 30°C for 1 hour. Then, pour 84 ml of pure water into a 125 ml pressure bottle and hydrolyze at 120°C for 1 hour. After that, suction filtration is performed while still hot using a 1G-3 glass filter (constantly weighed at 105°C), and after solid-liquid separation, the filtrate is reduced to a volume of 100 ml, and the constituent sugars can be quantified by high-performance liquid chromatography (HPLC) (FL detection method).

[0064] A preferred example of a cellulose raw material is refined cellulose fiber. Refined cellulose fiber refers to refined cellulose raw materials such as refined pulp or cotton-like refined products obtained from coniferous tree chips, hardwood chips, or non-wood cellulose raw materials (such as cotton-derived, hemp-derived, bagasse-derived, kenaf-derived, bamboo-derived, straw-derived, seaweed-derived, algae-derived, sea squirt-derived, and bacterial cellulose-derived) through a purification process and bleaching process aimed at deligninization by pulping and removal of hemicellulose. Among these, cotton fibers or cellulose raw materials derived from cotton linters or bacteria are particularly preferred due to their high cellulose purity. Furthermore, cut yarn of regenerated cellulose fiber can also be used as a raw material for cellulose microfibers, and cut yarn of regenerated cellulose obtained by the electrospinning method can also be used as a refined cellulose fiber raw material for cellulose microfibers. It is preferable to set appropriate purification conditions (pulping temperature, alkali concentration during pulping, bleaching agent concentration and bleaching time) according to the type of cellulose raw material selected from these, in order to produce refined cellulose fiber with high cellulose purity and use it as a raw material.

[0065] In response to the growing demand for a sustainable society, recycled materials such as recycled cotton and recycled wood can be used as cellulose raw materials. Recycled cotton, as used here, refers to fibers made by collecting and crushing cotton scraps and waste cotton that were discarded at spinning and sewing factories, or fibers obtained by crushing cotton that has been processed into the form of cloth, clothing, etc. Recycled wood refers to wood that has been chipped from sawmill residues, construction waste, thinned wood, and forest residues, and then pulped using conventional methods. Among the recycled materials mentioned above, recycled cotton is preferred as a cellulose raw material.

[0066] Furthermore, to obtain high-purity purified cellulose fibers, it may also be effective to further impregnate the cellulose fibers or the purified cellulose fibers described above in water and heat-treat them at a temperature of 100°C or higher; to impregnate the cellulose fibers or the purified cellulose fibers described above in a strong alkaline aqueous solution such as sodium hydroxide (alkali concentration: 1% to 10% by mass), allow it to stand or stir for a certain period of time in the range of 0°C to 60°C, and then repeat the washing with water in an alkaline treatment; to further impregnate the cellulose fibers or the purified cellulose fibers described above in water and treat them with hemicellulose-degrading enzymes such as xylase or mannanase or cellulase in the range of 35°C to 55°C; or to purify them by combining several of the above three treatments. These treatments not only reduce the burden of the micronization treatment, but also have the effect of removing impurities such as lignin and hemicellulose present on the surface and in the gaps of the microfibrils that make up the cellulose fibers into the aqueous phase, thereby increasing the cellulose purity of the purified cellulose fibers, and can therefore be very effective. In particular, when using bacterial cellulose as a raw material, washing with cold water in the range of 2°C to 10°C can remove water-soluble polysaccharide components produced simultaneously with the bacterial cellulose, and can be an effective purification method.

[0067] (Degree of crystallinity) In one embodiment, the cellulose raw material and / or cellulose microfibers may have a cellulose type I crystalline structure or a cellulose type II crystalline structure. In a preferred embodiment, the cellulose microfibers have a cellulose type I crystalline structure. The degree of crystallinity of the cellulose raw material or cellulose microfibers in this embodiment is preferably 55% or more, or 60% or more. When the degree of crystallinity is within this range, the mechanical properties (especially strength and dimensional stability) of the cellulose microfibers themselves are enhanced, and the strength and dimensional stability of the fiber-reinforced resin formed by dispersing the cellulose microfibers in the resin tend to be enhanced. The degree of crystallinity of the cellulose raw material or cellulose microfibers is preferably 65% ​​or more, more preferably 70% or more, and most preferably 80% or more. Since a higher degree of crystallinity tends to be preferable, there is no particular upper limit, but from a production standpoint, 99% is a preferred upper limit.

[0068] Between the microfibrils of plant-derived cellulose, and between the bundles of microfibrils, 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 plays a role in linking microfibrils together by hydrogen bonding with cellulose. Lignin is a compound with an aromatic ring and is known to be covalently bonded to hemicellulose in the cell walls of plants. If the amount of impurities such as lignin remaining in the cellulose microfibers is high, discoloration may occur due to the heat during processing. Therefore, from the viewpoint of suppressing discoloration of fiber-reinforced resins during extrusion and molding, it is desirable to keep the crystallinity of the cellulose microfibers within the above-mentioned range.

[0069] The degree of crystallinity, when the cellulose is cellulose type 1 crystal (derived from natural cellulose), can be determined by the Segal method using the following formula based on the diffraction pattern (2θ / deg. of 10 to 30) obtained by measuring the sample by wide-angle X-ray diffraction. Crystallinity (%)=[I (200) -I (amorphous) ] / I (200) ×100 I (200):Diffraction peak intensity at the 200 plane (2θ=22.5°) in cellulose type I crystals I (amorphous) : The halo peak intensity due to amorphous material in type I cellulose crystals, specifically the peak intensity at an angle 4.5° lower than the diffraction angle of the 200 plane (2θ = 18.0°).

[0070] Furthermore, if the cellulose is a type II cellulose crystal (derived from regenerated cellulose), the degree of crystallinity can be determined by the following formula using wide-angle X-ray diffraction, from the absolute peak intensity h0 at 2θ=12.6°, which is attributed to the (110) plane peak of the type II cellulose crystal, and the peak intensity h1 from the baseline at this interplanar spacing. Crystallinity (%) =h1 / h0 ×100

[0071] Known crystalline forms of cellulose include Type I, Type II, Type III, and Type IV. Among these, Type I and Type II are particularly widely used, while Type III and Type IV, although obtained on a laboratory scale, are not widely used on an industrial scale. The cellulose raw material or cellulose microfibers of this disclosure have relatively high structural mobility, and by dispersing the cellulose microfibers in a resin, a resin composition with a lower coefficient of thermal expansion and superior strength and elongation during tensile and bending deformation can be obtained. Therefore, materials containing Type I or Type II cellulose crystals are preferred, and materials containing Type I cellulose crystals with a crystallinity of 55% or higher are more preferred.

[0072] (chemical modification) The cellulose microfibers of this embodiment are cellulose microfibers whose hydroxyl groups on the surface have been modified by chemical modification. Chemical modification may be performed in the pre-defibration state (in one embodiment, in the pulp state) before the micronization treatment described later, or chemical modification may be performed after the micronization treatment has been performed to form cellulose microfibers. When obtaining low-halogen cellulose microfibers, it is preferable to perform chemical modification in the pre-defibration state and then the defibration treatment described later. Furthermore, when pre-treatment is performed before defibration, this chemical modification can be performed before the pre-treatment, but it is easier and preferable to perform it after the pre-treatment.

[0073] Methods of chemical modification include esterification, etherification, and urethaneification, but esterification is preferred. Among these, saturated monocarboxylic acid esterification such as acetate esterification (acetylation), propionic acid esterification, pentanoic acid (valeric acid) esterification, and hexanoic acid (caproic acid) esterification are preferred, and among these, acetate esterification (acetylation) is preferred due to the heat resistance of the cellulose microfibers after modification (i.e., chemical modification), but esterification using dicarboxylic acids such as phthalic acid esterification may also be used. For chemical modification, general esterification reaction methods using saturated carboxylic acids or their acid anhydrides or acid chlorides, vinyl acetate, vinyl propionate, and other saturated vinyl monocarboxylates can be used.

[0074] When chemically modifying cellulose raw materials (e.g., pulp) before micronization, it is preferable to perform the chemical modification under a solvent that well swells the cellulose raw materials in order to chemically modify the fiber surface inside the cellulose raw materials. In one embodiment, the solvent that well swells the cellulose raw materials is an aprotic polar solvent, and is preferably dimethyl sulfoxide (DMSO), N-methyl-2-pyrrolidone (NMP), N,N-dimethylformamide (DMF), N,N-dimethylacetamide (DMAc), or a mixture of any of these.

[0075] On the other hand, when chemical modification is performed after micronization, the cellulose microfibers are concentrated by suction filtration or the like to form a moist cake, which is then diluted and dispersed in a solvent for chemical modification. The method of chemical modification may be the same as that for chemical modification of cellulose raw materials. In this case, if the material is dried too much, aggregation of cellulose microfibers will occur, so the cellulose solid content concentration is preferably 30% by mass or less, and more preferably 20% by mass or less. Also, when using an esterifying agent, since the esterifying agent also reacts with water, it is better to keep the amount of moisture introduced low, and the lower limit of the cellulose solid content concentration is preferably 5% by mass or more, or more preferably 10% by mass or more. If chemical modification is difficult due to the presence of moisture, it is advisable to repeat the process of suction filtration of the dispersed slurry diluted and dispersed in the above solvent, and then adding more solvent to reduce the amount of moisture in the system before performing chemical modification. Also, when chemical modification is performed after micronization, in order to perform homogeneous chemical modification, it is preferable to use a solvent that swells the pulp well as described above, but since the surface of the cellulose microfibers is exposed, solvents other than those described above can also be used.

[0076] When the group introduced by chemical modification is an acyl group (e.g., an acetyl group), the degree of substitution (DS) (degree of acylation, e.g., degree of acetylation) of the acyl group is preferably 0.5 or higher, more preferably 0.6 or higher, and even more preferably 0.7 or higher. The upper limit is preferably 1.3 or lower, more preferably 1.1 or lower, and even more preferably 1.0 or lower, because if the DS is too high, the degree of crystallinity decreases, and the mechanical properties of the resin composition obtained by compounding cellulose microfibers with the resin tend to decrease.

[0077] The degree of acyl substitution (DS) can be calculated from the reflectance infrared absorption spectrum of esterified cellulose microfibers based on the peak intensity ratio between the peak derived from the acyl group and the peak derived from the cellulose backbone. The peak of the C=O absorption band based on the acyl group is at 1730 cm⁻¹. -1 The peak of the CO absorption band based on the cellulose backbone chain appears at 1030 cm⁻¹. -1It appears in (see Figure 1). The DS of esterified cellulose microfibers was obtained by creating a correlation graph between the DS obtained from solid-state NMR measurements of esterified cellulose microfibers (described later) and the modification rate (IR index 1030), which is defined as the ratio of the peak intensity of the absorption band of C=O based on acetyl groups to the peak intensity of the absorption band of CO in the cellulose backbone chain, and a calibration curve was calculated from the correlation graph. Degree of substitution DS = 4.13 × IR index (1030) This can be obtained by using [this method].

[0078] The method for calculating the DS of esterified cellulose microfibers using solid-state NMR is described below for freeze-pulverized esterified cellulose microfibers. 13 The following formula can be used to determine the signal intensity (Inf) from a single carbon atom derived from the modifying group, based on the total area intensity (Inp) of the signals attributed to carbon atoms C1-C6 derived from the pyranose ring of cellulose, which appear in the range of 50 ppm to 110 ppm. DS = (Inf) × 6 / (Inp) For example, if the modifying group is an acetyl group, you can use the 23 ppm signal assigned to -CH3.

[0079] Use 13 The conditions for 13C solid-state NMR measurement are as follows, for example: Equipment:Bruker Biospin Avance500WB Frequency: 125.77MHz Measurement method: DD / MAS method Waiting time: 75 seconds NMR sample tube: 4mmφ Total number of times: 640 (approximately 14 hours) MAS: 14,500Hz Chemical shift reference: Glycine (External reference: 176.03 ppm)

[0080] (DS of cellulose fibers) s / DS) In one embodiment, the cellulose fiber may be a cellulose microfiber with a chemically modified surface. In one embodiment, the DS non-uniformity ratio (DSs / DS), defined as the ratio of the degree of substitution of the fiber surface (DSs) to the degree of substitution of the entire fiber (DS) of the chemically modified cellulose microfiber, is 1.05 or greater.

[0081] When the chemically modifying group is an acyl group, the DS non-uniformity ratio (DSs / DS), defined as the ratio of the degree of acyl substitution on the fiber surface (DSs) to the degree of acyl substitution of the entire fiber (DS), is preferably 1.05 or higher. The larger the value of the DS non-uniformity ratio, the more pronounced the sheath-core-like non-uniform structure (i.e., a structure in which the fiber surface is highly chemically modified while the fiber core retains a structure close to the original unmodified cellulose), allowing for high tensile strength and dimensional stability derived from cellulose, as well as improved affinity with resins during composite formation and improved dimensional stability of the resin composition. The DS non-uniformity ratio is more preferably 1.1 or higher, or 1.2 or higher, or 1.3 or higher, or 1.5 or higher, or 2.0 or higher, and from the viewpoint of ease of manufacturing chemically modified cellulose fine fibers, it is preferably 30 or lower, or 20 or lower, or 10 or lower, or 6 or lower, or 4 or lower, or 3 or lower.

[0082] DS s The value of varies depending on DS, but as an example, it is preferably 0.1 or higher, or 0.2 or higher, or 0.3 or higher, or 0.5 or higher, and preferably 3.0 or lower, or 2.5 or lower, or 2.0 or lower, or 1.5 or lower, or 1.2 or lower, or 1.0 or lower.

[0083] DSs is determined by the following method: Esterified cellulose fine fibers, powdered by freeze-grinding, are placed on a 2.5 mmφ dish-shaped sample stage, the surface is pressed down to flatten it, and X-ray photoelectron spectroscopy (XPS) is performed. The XPS spectrum reflects only the constituent elements and chemical bonding state of the surface layer of the sample (typically a few nm). Peak separation is performed on the obtained C1s spectrum, and the area intensity (Ixp) of the peak attributed to a single carbon atom derived from the chemical modification group is used to determine the DSs using the following formula: the area intensity (Ixf) of the peak attributed to a single carbon atom derived from the pyranose ring of cellulose (289 eV, CC bond) versus the area intensity (Ixp) of the peak attributed to a carbon atom C2-C6 derived from the pyranose ring of cellulose. DSs = (Ixf) × 5 / (Ixp) If the chemically modified group is an acetyl group, after separating the C1s spectrum at 285eV, 286eV, 288eV, and 289eV, the 289eV peak should be used for Ixp and the peak derived from the OC=O bond of the acetyl group (286eV) should be used for Ixf. The conditions used for XPS measurement are as follows, for example: Equipment used: ULVAC-FI VersaProbeII Excitation source: mono.AlKα 15kV × 3.33mA Analysis size: Approximately 200 μmφ Photoelectron extraction angle: 45° Capture area Narrow scan: C 1s, O 1s Pass Energy: 23.5 eV

[0084] (Changes in the morphology of cellulose raw materials or cellulose microfibers before and after chemical modification) In the chemical modification of this embodiment, stirring conditions, temperature, etc., are adjusted as appropriate, but the retention rate of fiber length of the cellulose raw material or cellulose microfibers before and after chemical modification (retention rate of fiber length (%) = average fiber length after modification (nm) / average fiber length before modification (nm) x 100) is preferably 70% or more, more preferably 80% or more, and particularly preferably 90% or more. The average fiber length referred to here is the length-weighted average fiber length measured using an automated fiber shape analyzer (Morfi Neo, manufactured by Techpap). If the fiber length is maintained for a long time after chemical modification, the fiber length of the resulting cellulose microfibers will be maintained for a long time, which is advantageous for increasing the strength and heat resistance of the resin composition obtained by compounding the cellulose microfibers with the resin. The higher the fiber length retention rate, the greater the effect, so there is no particular upper limit, but considering a realistic modification process, 99.5% or less is preferable.

[0085] (Fine cellulose fragmentation) Cellulose microfibers can be obtained by micronizing the raw materials described above. In the micronization process, the raw material pulp sheet, etc., is dispersed in water using a pulper or the like, and then micronized using micronization equipment such as a beater, disc refiner, high-pressure homogenizer, water jet, disc mill, ball mill, bead mill, mascolloider, or homomixer. In one embodiment, the micronization may be a beating process. The micronization process may be carried out in one stage (processing with one type of blade) or in multiple stages (processing with multiple types of blades), and in the case of multi-stage processing, the same equipment may be used multiple times, or different equipment may be used in combination. In one embodiment, multi-stage processing is preferred.

[0086] Furthermore, it is preferable to homogenize the raw materials in water using a pulper or homomixer before the micronization process. In particular, when chemically modifying the pulp before micronization, the hydrophilicity of the pulp is reduced, so it is preferable to perform dispersion using a mixer such as a homomixer at a peripheral speed of, for example, 10 m / s or more, preferably 20 m / s or more, more preferably 25 m / s or more, for example 90 m / s or less, preferably 80 m / s or less, and more preferably 50 m / s or less. By reducing clumps and the like as a pretreatment, homogeneous micronized cellulose fine fibers can be obtained through a homogeneous micronization process. It should be noted that using highly purified water such as distilled water or ion-exchanged water at this time can be effective.

[0087] (Multi-stage miniaturization) When cellulose is refined in multiple stages, it is effective to combine two or more refinement devices with different refinement mechanisms or shear rates. Here, as a method of multi-stage refinement, it is preferable to perform multi-stage refinement using disc refiners with different disc configurations, or to perform refinement with a high-pressure homogenizer after refinement with a disc refiner. Here, any of single disc refiners, double disc refiners, or conical refiners may be used as disc refiners. In one embodiment, a single disc refiner with high clearance controllability between the fixed blade and the rotating blade is preferred in order to highly control the refinement.

[0088] (Miniaturization using a disc refiner) When performing micronization using a disc refiner, pulp or cotton-like cellulose fibers (e.g., purified cellulose fibers) are dispersed and stored in a tank in an aqueous medium at a solid content concentration of, for example, 0.5% to 6% by mass, preferably 0.8% to 3.5% by mass, and more preferably 1% to 3% by mass, and then micronized using a disc refiner. Using highly purified water such as distilled water or ion-exchanged water in this process can be effective.

[0089] In the operation of the disc refiner, defibration can be performed in a continuous circulating process where the slurry stored in the tank is returned to the original tank via the disc refiner. However, it is preferable to prepare two tanks connected by piping via the disc refiner (let's call them Tank A and Tank B), first supplying slurry to Tank A, then transferring it to Tank B via the disc refiner for storage, and once the processing of the slurry in Tank A is complete, switching to a process where the slurry is continuously transferred from Tank B to Tank A via the disc refiner for storage. Subsequently, performing defibration in a continuous process that alternates between these steps ensures that the slurry is reliably passed through the disc refiner each time, allowing for a uniform number of passes across the entire slurry volume. This is more preferable from the viewpoint of uniformity in the degree of defibration, i.e., quality stability of cellulose fine fibers.

[0090] Figure 2 is a diagram illustrating an example of the arrangement of blades and grooves of a disc refiner, and Figure 3 is a diagram illustrating the blade width, groove width, and inter-blade distance of a disc refiner. When using multiple disc refiners for multi-stage refinement, there may be one or more types of blades, but it is preferable to use a refiner with at least two different types of blades. Referring to Figures 2 and 3, a specific blade configuration is a disc refiner having blades 11 and grooves 12 as shown in Figure 2, with a blade width W as shown in Figure 3. B , groove width W G , and blade width W B groove width W GIt is important to appropriately adjust the value obtained by dividing by (hereinafter referred to as the blade groove ratio). It is particularly preferable to perform a fine-grinding treatment (hereinafter referred to as the pre-stage) using a refiner equipped with blades having a blade width of 1.5 mm or more and 5 mm or less, and a blade groove ratio of 0.1 or more and 1.0 or less, and then perform a fine-grinding treatment (hereinafter referred to as the post-stage) using a refiner having blades having a blade width of 0.1 mm or more and 1.0 mm or less, and a blade groove ratio of 0.5 or more and 1.0 or less. By defibrating with a disc refiner with such a configuration, the number of fibers with long fiber lengths (fiber lengths of 411 μm or more in one embodiment) that cause aggregation in the resin is reduced, and cellulose fine fibers with a low fibrillation rate (i.e., less fluff) can be obtained. In addition, in one embodiment, the generation of fibers with a fiber length of 20 μm or more and 56 μm or less, which have little reinforcing effect, can be suppressed. Another fine-grinding step may be added between the pre-stage and the post-stage.

[0091] Furthermore, when disc refiner processing is performed in one stage using one type of blade, it is particularly preferable to perform the fine processing with a refiner having a blade with a blade width of 0.1 mm or more and 1.0 mm or less, and a blade groove ratio of 0.5 or more and 1.0 or less. In this case, the fiber length of the raw material used is preferably 500 μm or more, more preferably 700 μm or more, even more preferably 900 μm or more, preferably 3000 μm or less, more preferably 2000 μm or less, more preferably 1500 μm or less, and even more preferably 1300 μm or less, as measured by the length-weighted average fiber length measured by the aforementioned automatic fiber shape analyzer (in one embodiment, the Morfi Neo manufactured by Techpap). By using a raw material with a fiber length within the above range, fibers with a fiber length of 411 μm or more, which cause aggregation in the resin, can be efficiently reduced in one stage, and cellulose fine fibers with a low fibrillation rate can be obtained.

[0092] (Distinguishing distance between blades in disc refiner processing) Also, referring to Figure 3, in the miniaturization process using a disc refiner, the distance W between the two blades (specifically, the rotating blade 21 and the fixed blade 22 in Figure 3) is... LIt is advantageous to control the clearance (hereinafter simply referred to as the inter-blade distance). By controlling the inter-blade distance, it is possible to control the fiber length and degree of beating of cellulose microfibers. When processing in multiple stages, it is preferable to set the inter-blade distance to 0.05 mm or more and 0.5 mm or less in the first stage of processing, and to set the inter-blade distance to 0.05 mm or more and 0.3 mm or less in the second stage of processing. When processing in one stage, it is preferable to set the inter-blade distance to 0.05 mm or more and 0.3 mm or less. When adjusting the inter-blade distance, it is preferable to gradually reduce the distance from a wider inter-blade distance while keeping the current value of the device below a certain level. By controlling it in this way, clogging and overload of the device can be prevented, and highly homogeneous cellulose microfibers can be obtained.

[0093] Thus, in the cellulose refining process using a disc refiner, precise control of the distance between the fixed blade and the rotating blade is advantageous for producing homogeneous cellulose fine fibers with good mechanical properties as a filler. For example, conventional single disc refiners use a screw-type jack or the like to adjust the blade distance, resulting in play in the runner that fixes the rotating blade. Therefore, if the runner is strongly pulled in the thrust direction, it will move by about 0.3 mm. For this reason, it is preferable to minimize this movement (play) in order to obtain finely reproducible cellulose with high accuracy, and the amount of movement is preferably 0.1 mm or less, more preferably 0.08 mm or less, and even more preferably 0.05 mm or less. Furthermore, it is preferable to be able to finely reduce the blade distance to 5 μm or less, more preferably 3 μm or less, and most preferably 1 μm or less. In one embodiment, a single disc refiner with a thrust direction movement of 0.03 mm may be used by using a ball screw type jack as the blade distance adjustment mechanism. Furthermore, in order to adjust the blade distance with high precision, it is preferable to attach a reduction gear to the ball screw type jack so that fine adjustment of the blade distance can be performed. By using such a single disc refiner, fine adjustment of the blade distance becomes possible, and it becomes possible to perform beating while maintaining a constant blade distance without blade wobble during the beating process. In the [Examples] section of this disclosure, an example is shown in which a single disc refiner with a truss direction movement amount of 0.03 mm is used by making the blade distance adjustment mechanism a ball screw type jack, and furthermore, a reduction gear is attached to the ball screw type jack so that the blade distance can be finely adjusted in units of 1 μm. However, any mechanism can be used as long as the amount of movement of the runner part or the precision of reducing the blade distance can be obtained, such as combining a ball screw type jack and a servo motor.

[0094] Using such a single-disc refiner allows for fine adjustment of the blade spacing. Furthermore, it enables fine refining while maintaining a constant blade spacing without blade wobble during the refining process. This prevents contact between blades when the spacing is narrowed, thus preventing the fiber length from becoming too short and reducing the amount of coarse fibers. As a result, it becomes possible to reliably produce cellulose microfibers with high shape distribution uniformity, which imparts excellent mechanical properties to fiber-reinforced resins obtained by compounding cellulose microfibers with resin.

[0095] (Number of passes in the discriminator process) The degree of refinement can also be controlled by the number of times the cellulose microfibers pass through the disc portion, i.e., between the rotating blade and the stationary blade (hereinafter referred to as the number of passes). By increasing the number of passes, cellulose microfibers with a homogeneous fiber diameter and fiber length distribution can be obtained. Here, the number of passes refers to the number of times the refiner process is performed after the blade distance is reduced to the desired blade distance (i.e., the material passes between the rotating field and the stationary field). The number of passes for the disc refiner is preferably 5 or more, more preferably 20 or more, and even more preferably 40 or more. A higher number of passes is preferable because the distribution of fiber shape gradually converges to a constant value as the number of passes increases, but considering productivity, the upper limit of the number of passes is preferably 300 or less.

[0096] (Method for determining miniaturization conditions using a disc refiner) The shape of cellulose microfibers obtained by disc refiner processing is controlled by a combination of factors, including the disc refiner configuration (type and number of blades), inter-blade distance, number of passes, and concentration. To obtain a desirable cellulose microfiber shape for use in fiber-reinforced resins, it is preferable to increase the number of passes under relatively low-intensity processing conditions. Here, the intensity of the processing is determined by the disc refiner blade configuration and inter-blade distance. With respect to the blade configuration, a larger blade width and blade groove ratio decrease the processing intensity, while a smaller ratio increases the processing intensity. Similarly, a larger inter-blade distance decreases the processing intensity, while a smaller inter-blade distance increases it. Therefore, when using a blade configuration that increases processing intensity, it is preferable to increase the inter-blade distance, and conversely, when using a blade configuration that decreases processing intensity, it is preferable to decrease the inter-blade distance. More preferably, a method is used where the inter-blade distance is increased with a blade configuration that increases processing intensity, and by using the aforementioned number of passes under these processing conditions, it is possible to control the average fiber length and fiber length distribution within a desirable range. In one embodiment, to obtain a desirable cellulose fine fiber shape for use in fiber-reinforced resins, it is preferable to increase the number of passes under viscous beating conditions. Viscous beating is a beating method that tends to make the fibers finer by fluffing them up, while a beating method that tends to cause cutting in the fiber direction is called free beating. In terms of the blade configuration of a disc refiner, the more blades there are, the longer the blade length, the larger the ratio of blade width to groove width (blade-to-groove ratio), and the larger the contact angle, the more the number of intersections between the rotating blade and the stationary blade increases. As a result, the force applied to the fiber at one intersection is dispersed, and the number of impacts on the fiber increases, leading to a tendency towards viscous beating. On the other hand, if the above conditions are reversed, a tendency towards free beating is observed. The inter-blade distance of a disc refiner is preferably widened when using blades that tend towards free beating, and preferably narrowed when using blades that tend towards viscous beating. However, if the inter-blade distance is too narrow, clogging occurs, the fibers become shorter due to cutting in the fiber direction, and the fibers become too fine, so the inter-blade distance is preferably 0.05 mm or more. By adjusting the aforementioned inter-blade distance and number of passes depending on the shape (fiber length and fiber diameter) of the cellulose raw material (e.g., pulp), the processing concentration, and the blades used, it is possible to control the fiber shape, such as the average fiber diameter and fiber length distribution, to a desirable range.

[0097] (Method for controlling the number of passes in the discriminator process) Here, as a method for controlling the number of passes, one method may be used in which one refiner is connected to one tank, the slurry is simply circulated, and the number of passes is controlled based on the flow rate, or two tanks are connected to one refiner, and the slurry is passed back and forth between the tanks during the refiner treatment. In the former case, the equipment can be simplified. On the other hand, in the latter case, since the cellulose microfibers are reliably passed through the disc section in each treatment, more uniform cellulose microfibers can be obtained. From the viewpoint of stably obtaining cellulose microfibers of this embodiment that have a good reinforcing effect on the resin, that is, cellulose microfibers with a uniform fiber shape, the latter method is preferred.

[0098] (Multi-stage miniaturization process using a combination of a disc refiner and a high-pressure homogenizer) It is also preferable to further refine the cellulose microfibers, which have been refined by a disc refiner, using a high-pressure homogenizer. A high-pressure homogenizer has a greater effect on thinning the fibers compared to a disc refiner. By combining a disc refiner and a high-pressure homogenizer, elongated cellulose microfibers can be obtained. The high-pressure homogenizer treatment is preferably carried out at a pressure of 30 MPa or higher, more preferably 50 MPa or higher, and more preferably 80 MPa or higher. The upper limit of the pressure may be preferably 300 MPa or lower, more preferably 250 MPa or lower, and more preferably 150 MPa or lower, depending on the characteristics of the equipment.

[0099] Examples of high-pressure homogenizers include the NS-type high-pressure homogenizer from Nilo Soavi GmbH (Italy), the Lanier-type (R model) pressure homogenizer from SMT Corporation, and the high-pressure homogenizer from Sanwa Machinery Co., Ltd. Examples of ultra-high-pressure homogenizers include the microfluidizer from Mizuho Industries Co., Ltd., the nanomizer from Yoshida Machinery Industry Co., Ltd., and the ultimateizer from Sugino Machine Co., Ltd., which are high-pressure impact type micronization processing machines. However, any device that performs micronization with a mechanism almost identical to these devices may be used.

[0100] In high-pressure homogenizer processing, as in disc refiner processing, defibration can be performed in a continuous circulating process where the slurry stored in a tank is returned to the original tank via a high-pressure homogenizer. However, it is preferable to prepare two tanks connected by piping via a high-pressure homogenizer (let's call them Tank A and Tank B), first supplying slurry to Tank A, then transferring it to Tank B via the high-pressure homogenizer for storage, and once the processing of the slurry in Tank A is complete, switching to a process where the slurry is continuously transferred from Tank B to Tank A via the high-pressure homogenizer for storage. Subsequently, performing defibration in a continuous process that alternates between these steps ensures that the slurry is reliably passed through each high-pressure homogenizer treatment, allowing for a uniform number of passes for the entire amount of slurry. This is more preferable from the viewpoint of uniformity in the degree of defibration, i.e., quality stability of cellulose fine fibers.

[0101] (Process to accelerate the refinement of cellulose raw materials) In one embodiment, a pretreatment step may be performed before the micronization process. Examples of pretreatment methods include autoclaving under water impregnation at a temperature of 100-150°C, enzymatic treatment, immersion in an aqueous sodium hydroxide solution, or a combination thereof. All of these pretreatments have the effect of breaking hydrogen bonds between cellulose microfibrils, which not only reduces the burden of the micronization process but also discharges impurities such as lignin and hemicellulose present on the surface and in the gaps of the microfibrils constituting the cellulose microfibers into the aqueous phase. As a result, they also have the effect of increasing the α-cellulose purity of the micronized fibers, and may be effective in improving the heat resistance of the cellulose microfibers.

[0102] (Concentration and drying of cellulose microfibers) The cellulose microfibers of this embodiment can be obtained as a wet molded body (wet cake) by dewatering the slurry using a filter or a paper machine. Among these methods, the papermaking method using a paper machine is advantageous in that it reduces drying shrinkage between the cellulose microfibers. In one embodiment, dewatering is performed by filtering the slurry on a porous substrate. In the papermaking method, any paper machine equipped with wires of a mesh size that dewaters the slurry and holds the cellulose microfibers can be used. As for the papermaking apparatus, when obtaining a fiber-reinforced resin in the shape of a flat sheet, an inclined wire paper machine, a long wire paper machine, or a cylinder wire paper machine can be used.

[0103] Cellulose microfibers can also be used as a dry filler. In this case, drying can be done using known drying equipment such as a hot air dryer or a spray dryer. Cellulose tends to aggregate during the drying process and is difficult to redisperse afterward, so it is preferable to use a dispersant. By improving redispersibility, the mechanical properties and stability of the resulting resin composition can be improved. It is desirable to add a dispersant to an aqueous dispersion of cellulose microfibers and then dry it while applying shear to obtain cellulose powder.

[0104] The dispersant may be at least one selected from the group consisting of surfactants, organic compounds with a boiling point of 100°C or higher, and resins having a chemical structure capable of highly dispersing cellulose.

[0105] A surfactant only needs to have a chemical structure in which a hydrophilic substituent and a hydrophobic substituent are covalently bonded. Surfactants used in various applications, such as food and industrial uses, can be used. For example, the following can be used individually or in combination of two or more:

[0106] Any of the following surfactants can be used: anionic surfactants, nonionic surfactants, amphoteric surfactants, and cationic surfactants. However, in terms of affinity with cellulose, anionic surfactants and nonionic surfactants are preferred, and nonionic surfactants are more preferred.

[0107] Among the above, surfactants having a polyoxyethylene chain, carboxyl group, or hydroxyl group as a hydrophilic group are preferred in terms of affinity with cellulose, polyoxyethylene-based surfactants (polyoxyethylene derivatives) having a polyoxyethylene chain as a hydrophilic group are more preferred, and nonionic polyoxyethylene derivatives are even more preferred. The polyoxyethylene chain length of the polyoxyethylene derivative is preferably 3 or more, more preferably 5 or more, even more preferably 10 or more, and particularly preferably 15 or more. The longer the chain length, the higher the affinity with cellulose, but in terms of balancing with coating properties, the upper limit is preferably 60 or less, more preferably 50 or less, even more preferably 40 or less, particularly preferably 30 or less, and most preferably 20 or less.

[0108] Among the surfactants mentioned above, alkyl ether type, alkylphenyl ether type, rosin ester type, bisphenol A type, β-naphthyl type, styrene-phenyl type, and hydrogenated castor oil type are particularly suitable as hydrophobic groups due to their high affinity with resins. The preferred alkyl chain length (in the case of alkylphenyl, the number of carbon atoms excluding the phenyl group) is preferably 5 or more, more preferably 10 or more, even more preferably 12 or more, and particularly preferably 16 or more. The higher the number of carbon atoms in the alkyl chain, the higher the affinity with general resins. For example, when the resin is a polyolefin, the higher the number of carbon atoms in the surfactant, the higher the affinity with the resin. Therefore, there is no upper limit to the number of carbon atoms, but it is preferably 30 or less, and more preferably 25 or less.

[0109] Among these hydrophobic groups, those having a cyclic structure or a bulky polyfunctional structure are preferred. Among those having a cyclic structure, alkylphenyl ether type, rosin ester type, bisphenol A type, β-naphthyl type, and styrene-phenyl type are preferred, and among those having a polyfunctional structure, hydrogenated castor oil type is preferred. Of these, rosin ester type and hydrogenated castor oil type are particularly preferred.

[0110] Furthermore, organic compounds with a boiling point of 100°C or higher can be effective as non-surfactant dispersants. Examples of such organic compounds include polyethylene glycol, polypropylene glycol, and organic compounds having a glycerin structure. Depending on the type of resin, for example, if the resin is a polyolefin, high-boiling point organic solvents such as liquid paraffin and decalin are effective. In the case of polar resins such as nylon and polyacetate, it may be effective to use a solvent similar to the aprotic solvents that can be used when manufacturing cellulose microfibers, such as dimethyl sulfoxide.

[0111] <Rheological properties of cellulose microfibers> In this embodiment, the rheological properties of the cellulose microfibers are such that, in strain-dispersion measurements of an aqueous dispersion with a cellulose concentration of 0.75% by mass, the reciprocal of the yield strain, 1 / γ, is preferably 200 or higher, and more preferably 250 or higher. If this parameter is within this range, the effect of improving the dynamic viscoelasticity at high temperatures when cellulose microfibers are added to the resin is significant, that is, the storage modulus is high in the high-temperature range. Cellulose microfibers are said to form a pseudo-crosslinked structure in water through inter-fiber entanglement and hydrogen bonding between cellulose molecules, and the interactions between cellulose microfibers in water are thought to partially reflect the interactions between cellulose microfibers in the resin. Generally, in crosslinked bodies such as gels, the greater the distance between crosslinking points and the greater the number of crosslinks, the higher the elastic modulus and strength of the crosslinked body, and cellulose microfibers whose yield strain falls within the above range are thought to interact strongly in the resin. In one embodiment, the upper limit of 1 / γ may be 1000 or less. The measurement conditions and measurement method are described below. [Measurement conditions] Measuring instrument: Rheometer HAAKE MERS (manufactured by Thermo Fisher Scientific) Measuring jig: Coaxial double cylinder (Cup: CCB25 DIN, Rotor: CC25 DIN Ti) Measurement mode: Oscillation Control method: Stress control Control range: 0.01 ~ 100 Pa Temperature: 25℃

[0112] 1. Disperse the cellulose microfibers in pure water. Here, the final solid content concentration of the cellulose microfibers is 0.75% by mass. If the cellulose microfibers before dilution are an aqueous dispersion with a solid content concentration of 2% by mass or less, the dispersion is performed by shaking in a sealed container with a filling rate of 75% by volume or less. If the material is an aqueous dispersion with a solid content concentration of 2% by mass or more, a hydrated cake, or a powder, the dispersion is performed using a high-shear homogenizer (in one embodiment, manufactured by IKA, trade name "Ultra-Turrax T18") under the following conditions: rotation speed 25,000 rpm × 5 minutes. If dispersed in a medium other than water, the medium is dispersed in a sufficient amount of pure water using the high-shear homogenizer described above under the following conditions: rotation speed 25,000 rpm for 5 minutes. After dispersing, the medium is removed by means of suction filtration or other means, and then the medium is replaced with water by dispersing again in pure water using the high-shear homogenizer under the following conditions: rotation speed 25,000 rpm for 5 minutes, so that the final solid content concentration is 0.75% by mass. 2. Allow the aqueous dispersion prepared in step 1 to stand at 25°C for at least 24 hours. 3. Attach the jig to the rheometer and load 17.0 ± 1.0 g of cellulose microfiber aqueous dispersion using a pipette or dropper. 4. Measurements are taken based on the settings, and the reciprocal of the yield strain (1 / γ) is calculated from the analysis results (LVE analysis).

[0113] <Surface treatment of cellulose microfibers> The cellulose microfibers of this embodiment may have their surface layers modified as needed. Methods of modification include esterification, etherification, and urethaneification. The preferred method of modification is esterification, and among these, esterification using saturated monocarboxylic acids is preferred. Examples of esterifying agents include relatively short-chain agents such as acetic acid, propionic acid, pentanoic acid (valeric acid), and hexanoic acid (caproic acid), as well as long-chain agents such as palmitic acid and stearic acid. However, from the viewpoint of heat resistance of the modified cellulose microfibers, it is more preferable to use agents with shorter chain lengths, such as acetic acid and propionic acid.

[0114] <Surface potential of cellulose microfibers> In this embodiment, the cellulose microfibers preferably have a zeta potential of -50mV or more and 50mV or less. Having a zeta potential within this range allows for low reactivity control, making thermal decomposition less likely and reducing the coloring and reinforcing effects when compounded with resins and the like. Originally, cellulose microfibers have a weak negative zeta potential of about -20mV to 30mV, but even when performing the surface treatment described above, it is preferable to ensure that the zeta potential of the modified cellulose microfibers falls within the above range.

[0115] <Cellulose microfibers with halogen content of 250 ppm by mass or less> One embodiment of the cellulose microfiber may be a cellulose microfiber having a halogen content of 250 ppm by mass or less (hereinafter also referred to as a low-halogen cellulose microfiber). When plant-derived cellulose microfibers are compounded with a resin, the presence of the cellulose microfibers can lead to problems such as resin decomposition and corrosion of the inside of equipment such as kneading equipment and molding equipment. Low-halogen cellulose microfibers, by having a halogen content below a certain level, can suppress resin decomposition during compounding with resin, even if they are plant-derived. Fiber-reinforced resins obtained using low-halogen cellulose microfibers have excellent stability during long-term storage and can remain stable even after undergoing multiple thermal histories associated with melt kneading, such as in material recycling. Furthermore, low-halogen cellulose microfibers can also suppress corrosion of equipment caused by the cellulose microfibers.

[0116] In one embodiment, low-halogen cellulose microfibers may include both unmodified and chemically modified cellulose microfibers. In this disclosure, the halogen content in low-halogen cellulose microfibers refers to the halogen content remaining in the cellulose microfibers after subjecting them to the [immersion and filtration treatment] described below. In this disclosure, the halogen content is a value measured according to the [halogen content measurement] described below. Having the halogen content of the cellulose microfibers within the above range suppresses the decomposition of the resin when compounding the cellulose microfibers with the resin, resulting in excellent stability during long-term storage and enabling the acquisition of a stable resin composition even after undergoing multiple thermal histories associated with melt kneading, such as in material recycling. Furthermore, a halogen content within the above range is also advantageous in suppressing corrosion inside equipment such as kneading equipment and molding equipment.

[0117] When halogens are present in cellulose microfibers, these halogens may be strongly bound to the cellulose by chemical or physical bonds. In one embodiment, when cellulose microfibers are subjected to a treatment such as the [immersion and filtration treatment] of this disclosure, which involves immersing them in pure water at 25°C for 48 hours and then filtering and drying, more than 80% by mass of halogens may remain in the cellulose microfibers. Due to their strong bond with cellulose, such halogens remain even when the cellulose microfibers are compounded with resin, leading to problems such as resin decomposition and equipment corrosion. The cellulose microfibers of this embodiment are characterized by having a low content of halogens strongly bound to cellulose, and as an indicator of this, the amount of halogens still remaining in the cellulose microfibers after treatment according to the [immersion and filtration treatment] of this disclosure is used.

[0118] [Immersion and filtration treatment] Cellulose microfibers are immersed in pure water at 25°C for 48 hours. Specifically, cellulose microfibers are immersed in pure water with a solid content of 2% by mass in a 200 mL glass beaker, stirred for 1 hour with a 3-1 motor (HEIDON BL-600 model, SUS propeller blades, 100 rpm), and then allowed to stand. Next, the mixture is filtered under reduced pressure using a Teflon® membrane filter (mesh size 1 μm), resulting in a basis weight of 10 g / m². 2 A sheet is prepared and filtered and dried in a ventilated oven at 70°C until the moisture content is 10% by mass or less, thereby obtaining cellulose fine fibers. Here, the moisture content is measured by the following method: 2.00 g of the cellulose sample is placed in a glass weighing bottle, dried at 60°C for 15 hours, then at 105°C for 2 hours, and weighed in a desiccator. The weight is then measured and calculated using the following formula: Moisture content (mass%) = (weight of sample before drying - weight of sample after drying) / (weight of sample before drying) x 100

[0119] [Halogen content measurement] 50 mg of the cellulose microfibers after the above treatment are weighed into a quartz sample boat. The sample boat is placed in an electric furnace (manufactured by Mitsubishi Chemical Analytic Corporation) and burned at 1000°C. The gas generated by the combustion cools to room temperature via a cooling section and is bubbling through a fluororesin tube into an absorption solution (the absorption solution is a solution of 10 mg / L tartrate ions, 600 mg / L hydrogen peroxide, 2.7 mmol / L sodium carbonate, and 0.3 mmol / L sodium bicarbonate dissolved in deionized water). The halogen content of this absorption solution is quantified using an ion chromatograph (THERMOFISHER INTEGRION CT type) through a fluororesin tube. The quantification is performed based on a calibration curve created with samples of various halogen content. At this time, the amount of water obtained in the above measurement is subtracted from the cellulose microfibers after treatment. Finally, the value (mass ppm) converted to the dry mass (i.e., water-free state) of the cellulose microfibers after treatment is taken as the halogen content of the cellulose microfibers in this embodiment.

[0120] The halogens that the cellulose microfibers of this embodiment may contain may, in one embodiment, be in the form of compounds containing fluorine, chlorine, bromine, iodine, and / or astatine (i.e., halogen compounds). The halogen compounds may be halides (i.e., compounds of halogens with elements of lower electronegativity), halogen salts, etc., and may be inorganic halogen compounds or organic halogen compounds. Considering bleaching and other processes in the manufacturing process of cellulose raw materials, cellulose microfibers often contain fluorine and / or chlorine among halogens, and particularly often chlorine. When using cellulose raw materials with a high halogen content, the advantages of reducing the halogen content in the manufacturing process of cellulose microfibers become even more pronounced.

[0121] Low-halogen cellulose microfibers are, in one embodiment, chemically modified cellulose microfibers.

[0122] The cellulose raw material for obtaining low-halogen cellulose fine fibers is, in one embodiment, plant-derived, and in another embodiment, coniferous tree chips, hardwood chips, or non-wood cellulose raw material (such as cotton-derived, hemp-derived, bagasse-derived, kenaf-derived, bamboo-derived, or straw-derived). It is preferable to use a cellulose raw material with a high degree of type I crystallinity.

[0123] Furthermore, in order to suppress discoloration and deterioration of physical properties due to heat when compounding cellulose microfibers with resin, the glucose content of the cellulose raw material for obtaining low-halogen cellulose microfibers, as determined by constituent sugar analysis, is preferably 90% by mass or more, more preferably 91% by mass or more, and even more preferably 93% by mass or more. There is no particular upper limit to the glucose content, but considering the limits of impurities (for example, components other than polysaccharides, such as oil and fat components, various contaminants, etc.) that may be introduced during the harvesting or purification process of the cellulose raw material, or during the manufacturing process of cellulose microfibers, it is preferable that it be 99.5% by mass or less.

[0124] The glucose content determined by constituent sugar analysis is preferably high not only in cellulose raw materials but also in cellulose microfibers. The glucose content of cellulose microfibers is preferably 85% by mass or more, more preferably 90% by mass or more, and there is no particular upper limit, but in one embodiment it is 99.5% by mass or less.

[0125] In one embodiment, the cellulose raw material for obtaining low-halogen cellulose fine fibers may be a plant-derived purified cellulose fiber, i.e., coniferous tree chips, hardwood chips, or a non-wood cellulose raw material (such as cotton-derived, hemp-derived, bagasse-derived, kenaf-derived, bamboo-derived, or straw-derived) obtained through the aforementioned process. Among these, from the viewpoint of high cellulose purity, industrial availability, and quality stability, a cellulose raw material derived from cotton (cotton lint or cotton linter) is preferred, and cotton linter pulp is particularly preferred. In one embodiment, the cellulose raw material for obtaining low-halogen cellulose fine fibers may be the recycled material mentioned above, preferably recycled cotton.

[0126] Furthermore, immersing the cellulose raw material or the aforementioned refined cellulose raw material (e.g., refined pulp) in water and performing heat treatment at a temperature of 100°C or higher, and performing alkaline treatment by immersing the cellulose raw material or the aforementioned refined cellulose raw material in a strong alkaline aqueous solution (alkaline concentration: 1% to 10% by mass) such as an aqueous sodium hydroxide solution, allowing it to stand or stir for a certain period of time in the range of 0°C to 60°C, and then repeatedly washing it with water, are effective in reducing the halogen content in the cellulose raw material. In addition, immersing the cellulose raw material or the aforementioned refined cellulose raw material in water and performing enzymatic treatment by reacting it with a hemicellulose-degrading enzyme such as xylase or mannanase or cellulase in the range of 35°C to 55°C may also be effective in obtaining a high-purity refined cellulose raw material. In particular, combining several of the above-mentioned heat treatment, alkaline treatment, and enzymatic treatment may be effective in obtaining a higher-purity refined cellulose raw material. These processes not only reduce the burden of the micronization process, but also have the effect of removing impurities such as lignin and hemicellulose present on the surface and in the spaces between the microfibrils that make up the cellulose raw material into the aqueous phase, thereby increasing the cellulose purity of the purified cellulose raw material. Therefore, they can be remarkably effective.

[0127] (Halogen content of cellulose raw materials) From the viewpoint of achieving the aforementioned halogen content of cellulose fibers and the whiteness described later, the halogen content (in one embodiment, chlorine content) in the cellulose raw material subjected to defibration is preferably 300 ppm by mass or less, more preferably 250 ppm by mass or less, even more preferably 200 ppm by mass or less, particularly preferably 150 ppm by mass or less, and exceptionally preferably 100 ppm by mass or less. A lower halogen content (in one embodiment, chlorine content) in the cellulose raw material is desirable, but from the viewpoint of the production efficiency of cellulose fine fibers, in one embodiment, it may be 10 ppm by mass or more, or 25 ppm by mass or more. The above halogen content is the amount per unit dry mass of the cellulose raw material, measured by the same method as described above for cellulose fine fibers.

[0128] <Whiteness> Cellulose microfibers, particularly low-halogen cellulose microfibers, preferably have a whiteness of 50% or higher. Here, whiteness refers to the value measured using a spectrophotometer / colorimeter (PF700 model, manufactured by Nippon Denshoku Industries Co., Ltd.) according to the "Method for Measuring the Diffuse Blue Light Reflectance of Paper, Cardboard, and Pulp (JIS P8148, ISO 2470)". If the cellulose raw material or cellulose microfibers are obtained in sheet form, they are used directly for measurement. On the other hand, in a wet state, the cellulose raw material or cellulose microfibers are measured at a basis weight of 50 g / m². 2 As described above, papermaking is performed using a suction filtration apparatus equipped with a polytetrafluoroethylene (PTFE) membrane filter, and the cellulose sheet is dried at 80°C until equilibrium moisture content is reached. This sheet is then used to measure the whiteness using the apparatus described above. Higher whiteness is preferable because it indicates superior heat resistance of the cellulose microfibers, thereby improving the strength, elastic modulus, and dimensional stability when the resin composition obtained by compounding with the resin through melt kneading is mechanically recycled. The whiteness of the cellulose microfibers is more preferably 60% or higher, even more preferably 70% or higher, particularly preferably 80% or higher, exceptionally preferably 90% or higher, and most preferably 95% or higher. The higher this value, the greater the effect of this embodiment, so there is no upper limit, but a substantially obtainable range of 99% or less is preferable.

[0129] To achieve the whiteness of the cellulose microfibers described above, it is preferable that the cellulose raw material be subjected to bleaching or other treatments prior to the defibration process. In the defibration process of this embodiment, the whiteness does not decrease significantly, so the whiteness of the cellulose raw material subjected to defibration matches the whiteness of the cellulose microfibers. That is, the whiteness of the cellulose raw material is preferably 50% or more, more preferably 60% or more, even more preferably 70% or more, particularly preferably 80% or more, exceptionally preferably 90% or more, and most preferably 95% or more. The higher this value, the greater the effect of this embodiment, so there is no upper limit, but a substantially obtainable range of 99% or less is preferable.

[0130] <Control of halogen content> (Bleaching method for cellulose raw materials) In one embodiment, one or more methods selected from the group consisting of chlorine treatment, alkaline extraction treatment, hypochlorite treatment, chlorine dioxide treatment, oxygen bleaching treatment, hydrogen peroxide bleaching treatment, and ozone bleaching treatment can be used as the bleaching method for the cellulose raw material.

[0131] Chlorine treatment (hereinafter also referred to as "C" treatment) is a bleaching method using chlorine gas, which solubilizes lignin in plant-derived cellulose raw materials (typically unbleached pulp) by chlorinating it.

[0132] Alkaline extraction (hereinafter also referred to as "E" treatment) is a process in which alkali-soluble chlorinated lignin is dissolved and extracted using an alkali (such as caustic soda).

[0133] Hypochlorite treatment (hereinafter also referred to as "H" treatment) is a treatment that bleaches carbohydrates such as cellulose and hemicellulose using sodium hypochlorite.

[0134] Chlorine dioxide treatment (hereinafter also referred to as "D treatment") is a process that uses chlorine dioxide to selectively decompose and remove lignin without destroying carbohydrates.

[0135] Oxygen bleaching (hereinafter also referred to as "O" treatment) is a process that involves the oxidative decomposition and extraction of lignin using oxygen.

[0136] Hydrogen peroxide bleaching treatment (hereinafter also referred to as "P treatment") is a process that involves the oxidative decomposition and extraction of lignin using hydrogen peroxide.

[0137] Ozone bleaching (hereinafter also referred to as "Z" treatment) is a process that uses ozone to oxidize, decompose, and extract lignin.

[0138] Effective combinations of bleaching methods include CEH treatment, CEHH treatment, CEHD treatment, CEHED treatment, CEHDED treatment, and CEDED treatment. The sequence of letters indicates the sequence of each treatment, but the order may be changed depending on the purpose. Furthermore, there are C / D treatments in which some of the chlorine used in chlorine treatment is replaced with chlorine dioxide (where " / " means that both treatments on either side are performed simultaneously), treatments in which C in the above sequence treatment is replaced with C / D, E / O treatments or E / P treatments in which a small amount of oxygen or hydrogen peroxide is added to strengthen the alkali during E treatment, treatments in which E in the above sequence treatment is replaced with E / O treatment or E / P treatment, treatments in which oxygen is further added to E / O treatment or E / P treatment, and treatments in which E in the above sequence treatment is replaced with E / OH treatment, and so on. These can be appropriately combined according to the application and purpose.

[0139] Alternatively, equivalent treatments such as ECF (Elemental Chlorine Free, i.e., DE / ODD, E / OEDP) and TCF (Total Chlorine Free, i.e., E / OP-ZP) can also be used.

[0140] To reduce the halogen concentration in the cellulose raw material, treatments that do not use chlorine as much as possible are preferable. From this viewpoint, alkaline extraction treatment, oxygen treatment, ozone treatment, chlorine dioxide treatment, hypochlorite treatment, or a combination thereof, ECF treatment, or TCF treatment are preferred. To achieve high whiteness while maintaining the degree of polymerization, i.e., strength, of the cellulose raw material, alkaline extraction treatment, ozone treatment, ECF treatment, or TCF treatment are preferred, with ECF treatment or TCF treatment being more preferred.

[0141] The defibration of the cellulose raw material to obtain low-halogen cellulose fine fibers may be performed on the cellulose raw material with or without the pretreatment of this embodiment, but is preferably performed on the cellulose raw material that has undergone pretreatment. In one embodiment, the cellulose raw material, which has been adjusted by the pretreatment step to a specific fiber length such that the average fiber length is 3 mm or less and / or the number percentage of fibers with a fiber length of 3 mm or more is 20% or less, is dispersed in an aqueous medium, and the beaten treatment is performed by applying the following treatment to the obtained dispersion. Examples of aqueous mediums include water itself, or a mixed medium of water and an organic solvent, which is one or more of the following: monohydric alcohols such as ethanol, n-propanol, isopropanol, and butanol; polyhydric alcohols such as ethylene glycol, diethylene glycol, and glycerin; ketones such as acetone; nitrile solvents such as acetonitrile; pyrrolidone solvents, etc. The blending ratio of the organic solvent in the above-mentioned mixture of organic solvent and water is preferably less than 50% by mass, more preferably 30% by mass or less, and particularly preferably 20% by mass or less. The higher the water ratio, the better the defibrillation, and the higher the organic solvent ratio, the more the aggregation of fine fibers is suppressed during the drying process after defibrillation. Therefore, it is preferable to set the ratio of organic solvent in consideration of the balance between defibrillation and aggregation suppression. Beating is distinguished from grinding as a pretreatment in this embodiment in that it is a wet process, and it is distinguished from grinding as a pretreatment in this embodiment in that the fiber length of the cellulose subjected to the treatment is different.

[0142] In this beating process, the cellulose raw material (e.g., pulp sheets) is dispersed in an aqueous medium using a pulper or homomixer as needed, and then finely refined using beating equipment such as a beater, disc refiner, high-pressure homogenizer, water jet, disc mill, ball mill, bead mill, mascolloider, or homomixer. The beating process may be carried out in one stage or in multiple stages. In the case of multiple stages, the same equipment may be used multiple times, or different equipment may be used in combination.

[0143] Furthermore, it is preferable to homogeneously disperse the cellulose raw material in an aqueous medium using the above-mentioned pulper or homomixer before the beating treatment. In particular, when chemically modifying the cellulose raw material before the beating treatment, the hydrophilicity of the cellulose raw material is reduced, so it is preferable to perform dispersion treatment using a mixer such as a homomixer with a peripheral speed of 10 m / s or more in one embodiment, preferably 20 m / s or more, more preferably 25 m / s or more, and 90 m / s or less in one embodiment, preferably 80 m / s or less, more preferably 50 m / s or less. By reducing clumps and the like in the dispersion treatment, homogeneous cellulose fine fibers can be obtained by homogeneous beating treatment. In this case, highly purified water such as distilled water or ion-exchanged water may be effective as the water in the aqueous medium.

[0144] <Applications of cellulose microfibers> The cellulose microfibers in this embodiment have a moderate fineness that is neither too coarse nor too fine, and also exhibit good homogeneity, making them suitable for use as a reinforcing filler for fiber-reinforced resins. Furthermore, they can be used as a prepreg material by forming them into sheets and impregnating them with resin, or used in building materials such as concrete.

[0145] Fiber-reinforced resin One aspect of the present invention provides a fiber-reinforced resin comprising cellulose microfibers and a resin according to the present disclosure. In one aspect, the resin is impregnated with cellulose microfibers. Methods for obtaining the fiber-reinforced resin are not particularly limited, but include a method of mixing a resin dissolved in a solvent with cellulose microfibers and drying the solvent, a method of mixing cellulose microfibers with a dispersant and the like and then drying them, and adding them to a melt-kneaded resin using a twin-screw extruder, a method of wet-processing cellulose microfibers to form a sheet and then impregnating it with a resin to create a composite, and a method of mixing cellulose microfibers and synthetic fibers, forming a nonwoven fabric for example by wet-processing, and then performing a hot press at a temperature above the melting point of the synthetic fibers. In one embodiment, the method for producing a fiber-reinforced resin may be a method in which cellulose fine fibers are mixed with synthetic fibers (synthetic short fibers in one embodiment), a nonwoven fabric is formed by wet papermaking, and the nonwoven fabric is then molded by hot pressing (hereinafter referred to as the nonwoven fabric method), or a method in which a slurry of cellulose fine fibers is prepared, dried in a known dryer such as a spray dryer or vacuum dryer to obtain a dry powder, and then the dry powder is added when the resin is melt-kneaded in a twin-screw extruder.

[0146] <Resin> The resin used in this embodiment (i.e., the matrix resin) may be a thermosetting resin, a photocurable resin, or a thermoplastic resin. Among these, thermoplastic resins are preferred because the cellulose microfibers of this embodiment have excellent heat resistance. The cellulose microfibers of this embodiment can be suitably compounded with resins having a melting point of 200°C or higher and a melt-mixing temperature of 250°C or higher. Examples of thermoplastic resins include styrene resins, acrylic resins, aliphatic or aromatic polycarbonate resins, aliphatic or aromatic polyester resins (polyethylene terephthalate, polylactic acid, etc.), linear polyolefin resins, cyclic olefin resins, aliphatic or aromatic polyamide resins, polyphenylene ether resins, polyvinyl alcohol resins, polyoxyalkylene resins, polyphenylene sulfide resins, thermoplastic polyimide resins, polyacetal resins, polysulfone resins, amorphous fluorine resins, epoxy resins, and the like. These thermoplastic resins may be used individually or in combination of two or more.

[0147] More preferred examples of thermoplastic resins are one or more selected from the group consisting of polyolefins (polyethylene, polypropylene, etc.), polyesters (polyethylene terephthalate, polylactic acid, etc.), polyamides (PA6, PA66, PA4, PA12, aromatic polyamides, etc.), polyacrylonitrile, polymethyl methacrylate, polystyrene, polyvinyl alcohol, polyphenylene ether, polyoxymethylene, and polyphenylene sulfide.

[0148] The melting point of the thermoplastic resin may, in one embodiment, be 80°C or higher, or 90°C or higher, or 100°C or higher, or 120°C or higher, or 140°C or higher, or 160°C or higher, or 180°C or higher, or 200°C or higher, and in one embodiment, it may be 300°C or lower, or 250°C or lower, or 230°C or lower. In this disclosure, the melting point refers to the peak top temperature of the endothermic peak (the hottest peak if there are two or more peaks) that appears when the temperature is increased at a heating rate of 10°C / min using a differential scanning calorimetry (DSC).

[0149] When using the nonwoven fabrication method, the synthetic fibers must have a melting point because they are melted during the heat pressing process. Examples of resins with a melting point include polyethylene, polystyrene, polypropylene, ABS resin, polycarbonate, polyamide 6, polyamide 12, polyamide 66, polyvinyl chloride, methacrylic resin, polyvinyl alcohol, polyvinylidene chloride, polyvinylidene fluoride, polyetherimide, polyoxymethylene, polysulfone, polyethylene terephthalate, and polyphenylene sulfide, but any resin with a melting point is acceptable. The melting point of these resins is preferably 250°C or lower. This is because cellulose microfibers, which mainly consist of type I crystals, begin to undergo significant weight loss due to thermal decomposition or oxidation between 260°C and 300°C, causing the composite to discolor and losing the inherent strength of cellulose. From the viewpoint of forming fiber-reinforced resin by heating and melting (e.g., hot pressing in the nonwoven fabric method) while suppressing the decomposition of cellulose, a lower melting point of the resin is preferable, preferably 250°C or lower, and more preferably 230°C or lower. Considering the heat resistance during use, the melting point of the resin may be 80°C or higher in one embodiment.

[0150] <Content of cellulose microfibers and resin in fiber-reinforced resin> The content of cellulose microfibers in the fiber-reinforced resin is preferably 1% by mass or more, more preferably 5% by mass or more, even more preferably 10% by mass or more, and even more preferably 20% by mass or more, in terms of having a good reinforcing effect. If the content of cellulose microfibers is too high, the continuous layer of resin in the fiber-reinforced resin tends to be broken up, which tends to reduce the performance of the fiber-reinforced resin, and in one embodiment, the fluidity during molding of the fiber-reinforced resin tends to be low, making molding defects more likely. Therefore, the upper limit is preferably 60% by mass or less, more preferably 50% by mass or less, and even more preferably 40% by mass or less.

[0151] The resin content in the fiber-reinforced resin is preferably 50% by mass or more, or 60% by mass or more, in that the strength of the fiber-reinforced resin tends to increase as the matrix resin forms a continuous layer. From the viewpoint of obtaining a good reinforcing effect by the cellulose microfibers without making the content of the cellulose microfibers too low, it is preferably 99% by mass or less, or 95% by mass or less, or 90% by mass or less.

[0152] <Composite fabrication using nonwoven fabrication method> As a method for obtaining a fiber-reinforced resin containing cellulose microfibers and resin, for example, a nonwoven fabrication method may be used. In one embodiment, the nonwoven fabric contains the cellulose microfibers of the Disclosure, and in another embodiment, it contains the cellulose microfibers of the Disclosure and synthetic fibers. According to the compounding rules for fiber-reinforced resins, the strength of the fiber-reinforced resin largely depends on the orientation and continuity of the fibers in the resin, and controlling the orientation and continuity of the fibers is advantageous in controlling the strength of the fiber-reinforced resin. By using this nonwoven fabrication method, the cellulose microfibers in the resin form continuous layers by hydrogen bonding, and the continuous layers become a structure in which they are highly oriented in a two-dimensional plane, resulting in a material with excellent strength.

[0153] A preferred example of the cellulose microfiber content in the nonwoven fabric may be within the same range as described above for the cellulose microfiber content in the fiber-reinforced resin.

[0154] The synthetic fiber content in the nonwoven fabric is preferably 50% by mass or more, or 60% by mass or more, because the synthetic fibers can be melted during the production of the fiber-reinforced resin to form a continuous layer, which tends to increase the strength of the fiber-reinforced resin, and also because the dewatering load during the papermaking process in nonwoven fabric production is small. From the viewpoint of obtaining a good reinforcing effect by the cellulose fine fibers without making the cellulose fine fiber content too low, it is preferably 99% by mass or less, or 95% by mass or less, or 90% by mass or less. The synthetic fiber content may be set arbitrarily for the purpose of adjusting the strength, elastic modulus, and fracture strain, but it is more preferably 60% by mass or more and 90% by mass or less.

[0155] A method for producing fiber-reinforced resin by the nonwoven fabric method is described below. In one embodiment, the nonwoven fabric method includes a slurry preparation step of stirring and mixing cellulose fine fibers and synthetic fibers in a water-containing medium to obtain a slurry, a papermaking step of obtaining a wet molded body (wet nonwoven fabric) from the slurry by a wet papermaking method, a drying step of drying the wet molded body to obtain a nonwoven fabric, and a hot pressing step of hot pressing the nonwoven fabric at a temperature above the melting point of the synthetic fibers in the nonwoven fabric to obtain a fiber-reinforced resin.

[0156] (Synthetic fiber) The synthetic fibers used in the nonwoven fabric method are, in one embodiment, synthetic staple fibers. Synthetic staple fibers refer to synthetic polymer fibers that have been cut to an arbitrary fiber length, and are sometimes called cut fibers or simply staple fibers. In one embodiment, synthetic staple fibers may have an average fiber length of 20 mm or less, or in another embodiment, 10 mm or less. Synthetic staple fibers may be fibrillated fibers obtained by fibrillating fibers that have been cut after spinning by beating or the like, or fibrillated fibers obtained by spinning and then cutting multi-branched fibers obtained by flash spinning or electrospinning. Preferred examples of the material of the synthetic fibers are as exemplified above for resins.

[0157] The average fiber diameter of the synthetic fibers is preferably 0.1 μm or more, 0.3 μm or more, or 1.0 μm or more, from the viewpoint of the availability of synthetic fibers, and preferably 50 μm or less, 40 μm or less, or 25 μm or less, from the viewpoint of facilitating uniform blending with cellulose fine fibers and the formation of a homogeneous nonwoven fabric. When the synthetic fibers have a relatively small average fiber diameter (e.g., 10 μm or less), the difference in fiber diameter between cellulose fine fibers and synthetic fibers is small, resulting in a low coefficient of variation in air permeability resistance and good uniformity of the structure within the nonwoven fabric. On the other hand, when the synthetic fibers have a relatively large average fiber diameter (e.g., more than 40 μm), the difference in fiber diameter between cellulose fine fibers and synthetic fibers is large, and although there is a tendency for greater variation in the structure within the nonwoven fabric, the nonwoven fabric can be made with a high basis weight (e.g., 200 g / m²). 2 In the above case, a good (i.e., low) coefficient of variation in air permeability resistance can be observed.

[0158] The average fiber length of the synthetic fibers is preferably 0.5 mm or more, or 1.0 mm or more, or 1.5 mm or more, from the viewpoint of obtaining nonwoven fabrics and fiber-reinforced resins with good mechanical properties, and preferably 20 mm or less, or 15 mm or less, or 10 mm or less, from the viewpoint of facilitating the uniform dispersion of cellulose fine fibers among the synthetic fibers.

[0159] The average fiber diameter and average fiber length of synthetic fibers are measured by the following method: Each synthetic fiber sample is dispersed in water to a concentration of 0.01 to 0.1% by mass, and if necessary, subjected to sonication (for several minutes). The dispersed sample is then dropped onto a glass slide, sandwiched between cover slips to prevent air from entering, and the edges of the cover slips are sealed with nail polish (the concentration of the aqueous dispersion is adjusted so that the fibers do not entangle when photographed with a microscope). Subsequently, an image is acquired using a microscope (Keyence VHX-7000 model, magnification adjusted so that the long side of the fiber is included in the image), and the major and minor diameters of 100 fibers are measured for each sample. The average of these is then used to determine the average fiber length and average fiber diameter.

[0160] The melting point of the synthetic fiber is preferably 300°C or lower, and more preferably 250°C or lower, from the viewpoint of preventing thermal degradation of cellulose fine fibers during hot pressing. On the other hand, if the melting point is too low, the practicality as a fiber-reinforced resin is low, so the melting point is preferably 90°C or higher, and more preferably 160°C or higher.

[0161] The polymers that make up synthetic fibers include those mentioned above as resins. Among these, polyamides, polyesters (polyethylene terephthalate, polylactic acid, etc.), polyoxymethylene, and polyacrylonitrile are preferred polymers because they have high affinity with cellulose fine fibers and are easy to blend uniformly. In addition, polyphenylene sulfide, polyphenylene ether, polyester, and aromatic polyamides are suitable for applications requiring heat resistance. The following is an example of the specific procedure for the nonwoven fabrication method. The nonwoven fabrication method includes a slurry preparation step of stirring and mixing cellulose fine fibers and synthetic fibers in a water-containing medium to obtain a slurry, a papermaking step of obtaining a wet molded body from the slurry by a wet papermaking method, a drying step of drying the wet molded body to obtain a nonwoven fabric, and a hot pressing step of hot pressing the nonwoven fabric at a temperature above the melting point of the synthetic fibers in the nonwoven fabric to obtain a fiber-reinforced resin.

[0162] (Slurry preparation process) In this process, cellulose microfibers and synthetic fibers are stirred in a water-containing medium to monodisperse the bundled synthetic fibers and distribute them highly evenly within the cellulose microfibers. Known stirring devices such as homomixers and blender mixers can be used as stirring devices. Here, the total solid content concentration of the cellulose microfibers and synthetic fibers is preferably 3.0% by mass or less, or 1.0% by mass or less, or 0.8% by mass or less, from the viewpoint of increasing the elastic modulus of the fiber-reinforced resin finally obtained by highly dispersing the cellulose microfibers and synthetic fibers, and from the viewpoint of increasing the orientation of the cellulose microfibers in the two-dimensional direction to increase strength and fracture strain. From the viewpoint of shortening the filtration time and improving productivity, it is preferably 0.05% by mass or more, or 0.1% by mass or more, or 0.25% by mass or more. At this time, dispersants such as surfactants and viscous agents may be used to improve the dispersibility of the synthetic fibers or to improve the mixability of the synthetic fibers and cellulose microfibers.

[0163] (Paper making process) In this process, the slurry is dewatered by a wet papermaking method to obtain a wet nonwoven fabric as a wet molded body. In one embodiment, dewatering is performed by suction filtration of the slurry on a porous substrate. In the papermaking method, any filter material can be used that has a pore size that allows cellulose fine fibers and synthetic fibers to remain after dewatering the slurry. Specific filter materials include filter paper, filter cloth, and metal mesh. At this time, a more effective dewatering effect can be obtained by combining suction filtration with a pressing process in which the wet molded body is subjected to contact pressure from above with a roll or the like.

[0164] Using papermaking equipment such as inclined wire paper machines, wire mesh paper machines, or cylinder wire paper machines allows for the desirable production of wet molded articles in a flat sheet shape with few defects. Furthermore, using metal molds for pulp molding allows for the production of wet molded articles in a desired shape.

[0165] While papermaking can be done in a continuous or batch manner depending on the purpose, from an industrial standpoint, when obtaining flat sheets, it is preferable from a cost perspective to produce long sheets using continuous papermaking with a paper machine and then form them into roll-shaped products. In particular, in the case of continuous papermaking using a paper machine, in the case of ordinary papermaking (for example, papermaking using beaten pulp fibers and synthetic fibers), the shear stress generated by the movement of the wire belt and the aqueous dispersion of fibers fed onto the papermaking wire causes the fibers in the aqueous dispersion to be oriented in the direction of the movement of the wire belt. As a result, in the flat sheet obtained, anisotropy in physical properties (strength, modulus, etc.) occurs between the direction of movement (machine direction, MD) and the direction perpendicular to it (transverse direction, TD) due to the orientation of the fibers. In contrast, the continuous papermaking method of this embodiment has the advantage that the difference in physical properties between the MD direction and the TD direction is less pronounced. This characteristic is thought to be due to the fact that when a flat sheet as a nonwoven fabric is produced in a paper machine, the cellulose microfibers form isotropic soft aggregates based on inter-fiber association in the aqueous dispersion containing cellulose microfibers and synthetic fibers fed into the paper machine, and the synthetic fibers are incorporated into these soft aggregates (i.e., integrated) to form a composite soft aggregate. As a result, even if the synthetic fibers have an anisotropic shape, they are incorporated in an unoriented (i.e., disordered and non-anisotropic) state within the composite soft aggregate.

[0166] The composite soft aggregate possesses sufficient strength to prevent collapse due to shear stress caused by belt running over a water dispersion, as in the conventional papermaking process described above. Therefore, the composite soft aggregate can be deposited and dewatered on a belt while the synthetic fibers remain fixed in an unoriented state, and a non-anisotropic sheet can be formed through subsequent drying treatments. Normally, in continuous papermaking, the MD / TD ratio of physical properties such as tensile strength, tensile modulus, flexural strength, flexural modulus, and linear thermal expansion coefficient increases with the running speed during papermaking (usually 5 m / min or more) (see Comparative Example I-8 of this disclosure). However, when a flat sheet of this embodiment is produced by a continuous papermaking method, the MD / TD ratio can be 1.6 or less, preferably 1.4 or less, and more preferably 1.2 or less, in one embodiment (see Example I-27 of this disclosure). Furthermore, the method of this embodiment exhibits the advantageous characteristic that anisotropy is less likely to appear not only in areas with high flatness but also in areas with high curvature, even during three-dimensional molding such as the pulp molding method.

[0167] (drying process) In this process, the wet molded body is at least dried to obtain a nonwoven fabric. The drying method is not particularly limited, but it is preferable to use a constant-length drying oven that can dry the liquid medium while maintaining a constant width of the wet molded body, such as a drum dryer or pin tenter. Using such an oven minimizes changes in the internal structure of the nonwoven fabric during drying and makes it easier to control the orientation of the cellulose microfibers within the nonwoven fabric. The air permeability resistance of the nonwoven fabric can be controlled by the composition ratio of cellulose microfibers and synthetic fibers constituting the slurry, the overall basis weight, the dispersion method of the raw solution, the blending conditions of various additives, and the average fiber diameter of the cellulose microfibers.

[0168] From the viewpoint of drying efficiency (particularly from the viewpoint of obtaining good productivity by increasing the evaporation rate of the liquid medium), the drying temperature is preferably 45°C or higher, 60°C or higher, 80°C or higher, 85°C or higher, or 90°C or higher. From the viewpoint of preventing thermal deformation of the hydrophilic polymer constituting the nonwoven fabric (specifically, cellulose microfibers and other components), preventing a decrease in energy efficiency that affects costs, and furthermore, from the viewpoint of preventing the reaction of the reactive crosslinking agent when one is used, it is preferably 180°C or lower, 150°C or lower, 120°C or lower, 115°C or lower, or 110°C or lower. For example, performing multi-stage drying, in which low-temperature drying is first performed at a temperature of 100°C or lower, and then drying at a temperature above 100°C, is also effective in obtaining a nonwoven fabric with high uniformity. For example, the above conditions are suitable when block polyisocyanate is used as the reactive crosslinking agent.

[0169] (Hot pressing process) In this process, the nonwoven fabric obtained in the drying process is pressed using a heated mold, melting and flowing the synthetic fibers contained in the nonwoven fabric, filling the voids, and obtaining a fiber-reinforced resin, which is a composite of cellulose microfibers and resin. At this time, since the cellulose microfibers do not melt due to the heat, it is possible to maintain a state in which they are highly oriented in the two-dimensional plane within the nonwoven fabric. The heating temperature can be any temperature above the melting point of the synthetic fibers, but near the melting point, the viscosity of the resin is high, and voids may remain inside the composite. Therefore, it is preferable that the heating temperature be at least 10°C higher than the melting point of the synthetic fibers. In addition, multiple layers of nonwoven fabric may be laminated and subjected to the heat pressing process in order to adjust the thickness of the molded product.

[0170] <Melting and mixing method> In one embodiment, a slurry of cellulose fine fibers may be prepared in the same manner as described above in the nonwoven fabrication method, and this slurry may be subjected to a known dryer such as a spray dryer or vacuum dryer to obtain a dry powder. The fiber-reinforced resin may then be produced by adding the dry powder when melt-kneading the resin using a twin-screw extruder.

[0171] <Applications of fiber-reinforced resins> The fiber-reinforced resin obtained by this embodiment, which is a composite of cellulose microfibers and resin, exhibits excellent mechanical properties in terms of elastic modulus, strength, and fracture strain, and is suitable for a wide range of applications such as automotive parts, building materials, and home appliances.

[0172] This disclosure also includes the following items: ≪Item group I≫ [1] Cellulose microfibers having at least a surface that is chemically modified, In the measurement using a fiber shape analyzer, the length-weighted average fiber length of fibers with a fiber length of 100 μm or more is between 110 μm and 500 μm. Among fibers with a fiber length of 100 μm or more, the number frequency of fibers with a length-weighted fiber length of 411 μm or more is 54% or less. Cellulose microfibers. [2] In the measurement of an automated fiber shape analyzer (1) Average fiber diameter is 42.5 μm or less, (2) Fine fiber area ratio is 90% or less, (3) Among fibers with a fiber length of less than 100 μm, the number frequency of fibers with a fiber length of 20 μm or more and 56 μm or less is 30% or more and 97% or less, (4) Fibrillation rate is 5% or less, A cellulose microfiber as described in item 1 above, which satisfies all of the following conditions. [3] Cellulose microfibers as described in item 1 or 2 above, wherein the chemical modification is acetylation and the degree of acetylation is 0.5 to 1.3. [4] Cellulose microfibers as described in any of items 1 to 3 above, having a glucose content of 90% by mass or more in the constituent sugar analysis. [5] Scanning electron microscope (SEM) images of the surface of a sample obtained by casting and drying a 5 ppm ppm DMSO dispersion of cellulose microfibers, showing that the occupied area relative to the total area occupied by cellulose microfibers was 15 μm². 2 Cellulose microfibers as described in any of the above items 1 to 4, wherein the proportion of the total occupied area of ​​ultrafine fibers that are less than 10% is between 10% and 80%. [6] Cellulose microfibers having a cellulose type I crystalline structure, as described in any of items 1 to 5 above. [7] Cellulose microfibers as described in any of items 1 to 6 above, having a crystallinity of 60% or more. [8] A fiber-reinforced resin comprising cellulose fine fibers as described in any of items 1 to 7 above and a resin with a melting point of 200°C or higher. [9] A nonwoven fabric containing cellulose microfibers as described in any of items 1 to 7 above.

[10] A nonwoven fabric as described in item 9 above, containing 50% by mass or more of synthetic fibers with a melting point of 300°C or lower.

[11] A fiber-reinforced resin comprising the nonwoven fabric described in item 9 above and a resin impregnated in the nonwoven fabric.

[12] A method for producing a fiber-reinforced resin comprising cellulose microfibers and resin, The process includes a step of obtaining a fiber-reinforced resin by heat-pressing the nonwoven fabric described in item 10 above, A method for producing fiber-reinforced resin, wherein the hot pressing is performed at a temperature above the melting point of the synthetic fiber.

[0173] ≪Item group II≫ [1] In the measurement of an automated fiber shape analyzer, (i) Average fiber length is 130 μm or more and 350 μm or less. (ii) Average fiber diameter is 35 μm or less, (iii) The ratio of fine fiber area is 75% or less. (iv) Among fibers with a fiber length of less than 100 μm, the number frequency of fibers with a fiber length of 20 μm or more and 56 μm or less is 75% or less. (v) Among fibers with a fiber length of 100 μm or more, the number frequency of fibers with a fiber length of 411 μm or more is 30% or less, (vi) Fibrillation rate is 5.0% or less, Cellulose microfibers that meet all of these requirements. [2] Cellulose fine fibers as described in item 1 above, wherein in a 0.75% by mass aqueous dispersion slurry, the reciprocal of the yield strain (γ) in strain dispersion measurement, 1 / γ, is 200 or more. [3] Cellulose microfibers as described in item 1 or 2 above, wherein the zeta potential is between -50mV and 50mV. [4] A fiber-reinforced resin comprising 1.0% by mass or more of cellulose fine fibers as described in any of items 1 to 3 above, and a resin. [5] A nonwoven fabric containing 1.0% by mass or more of the cellulose fine fibers described in any of the above items 1 to 3. [6] A nonwoven fabric as described in item 5 above, containing 50% by mass or more of synthetic fibers with a melting point of 250°C or lower. [7] A method for producing a fiber-reinforced resin comprising cellulose microfibers and synthetic resin, The process includes a step of obtaining a fiber-reinforced resin by heat-pressing a nonwoven fabric containing cellulose microfibers and synthetic fibers. The nonwoven fabric is the nonwoven fabric described in item 5 or 6 above. A method for producing fiber-reinforced resin, wherein the hot pressing is performed at a temperature above the melting point of the synthetic fiber.

[0174] ≪Item group III≫ [1] Cellulose microfibers of plant origin with a halogen content (more specifically, the content of halogens bound to cellulose) of 250 ppm by mass or less. [2] Cellulose microfibers as described in item 1 above, having a whiteness of 50% or more. [3] A method for producing cellulose microfibers as described in item 1 or 2 above, A method for producing cellulose microfibers, comprising the step of defibrating a cellulose raw material having a halogen content (more specifically, the content of halogens bound to cellulose) of 300 ppm by mass or less. [4] The method for producing cellulose microfibers according to item 3 above, wherein the cellulose raw material is a chemically modified product. [5] The method for producing cellulose microfibers according to item 4, wherein the chemically modified product is an acetylated product. [6] A method for producing cellulose microfibers according to any of items 3 to 5 above, wherein the cellulose raw material is derived from cotton. [7] A method for producing cellulose microfibers according to any one of items 3 to 6 above, wherein the defibration is a beating treatment using a discreeter. [8] A resin composition comprising cellulose fine fibers as described in item 1 or 2 above, and a resin. [9] A step of obtaining cellulose microfibers by any of the methods described in items 3 to 7 above, A step of mixing the cellulose fine fibers and the resin to obtain a resin composition, A method for producing a resin composition containing [the specified element]. [Examples]

[0175] The present invention will be described in detail below based on examples and comparative examples, but the present invention is not limited to these examples.

[0176] Example I: ≪Measurement method≫ [Automatic fiber shape analyzer measurement] Various properties of cellulose microfibers were evaluated using an automated fiber shape analyzer (MorfiNeo, TechPap) following the procedure below. 1. Cellulose microfibers were dispersed in pure water to prepare 1 L of an aqueous dispersion. Here, the final solid content concentration of the cellulose microfibers was 0.003 to 0.005% by mass. For aqueous dispersions with a cellulose microfiber content of less than 2% by mass before dilution (i.e., Production Examples 6, 7, and 11), they were simply mixed with a spatula or the like. For aqueous dispersions, hydrated cakes, or powders with a cellulose microfiber content of 2% by mass or more (i.e., Production Examples 1 to 5, 8 to 10, 12, and Production Comparative Examples 1 to 7), a high-shear homogenizer (manufactured by IKA, product name "Ultra Turrax T18") was used with the treatment conditions: dispersion treatment was performed at a rotational speed of 25,000 rpm for 5 minutes. For all production examples, since they were dispersed in a medium other than water, after performing the dispersion treatment in a sufficient amount of pure water using the above high-shear homogenizer under the treatment conditions: rotational speed of 25,000 rpm for 5 minutes, the medium was removed by means such as suction filtration, and then, again using the above high-shear homogenizer in pure water, the dispersion treatment was performed under the treatment conditions: rotational speed of 25,000 rpm for 5 minutes so that the final solid content concentration was 0.003 to 0.005% by mass, thereby replacing the medium with water. 2. The aqueous dispersion prepared in 1. was supplied to an autosampler for measurement. 3. The measurement results were output in txt format (or csv format). 4. Each shape parameter was extracted or calculated from the measurement results. For each parameter, the following values in the measurement results were used.

[0177] Length-weighted mean fiber length in normal fibers (fibers with a fiber length of 100 μm or more): Mean length-weighted Length [μm] Mean fiber length in normal fibers (fibers with a fiber length of 100 μm or more): Mean arithmetic length [μm] Number frequency of fibers with a fiber length of 411 μm or more in normal fibers: Calculated from the length-weighted fiber length distribution (length-weighted Fiber lemgth, μm) of normal fibers. Mean fiber diameter: Mean fiber width [μm] Fine fiber area ratio: Fine content, % in Area The frequency of fibers with a fiber length of 20 μm to 56 μm in fine fibers (fibers with a fiber length of less than 100 μm) was calculated from the fiber length distribution of fine fibers (Fine length, μm: FL). Fibrillation rate: Macrofibrillation index [%]

[0178] [Specific surface area, and average fiber diameter calculated from specific surface area] Using a specific surface area and pore distribution analyzer (Nova-4200e, Quantachrome Instruments), approximately 0.2 g of cellulose microfiber was dried under vacuum at 120°C for 5 hours. The amount of nitrogen gas adsorbed at the boiling point of liquid nitrogen was then measured at five points (multi-point method) within a relative vapor pressure (P / P0) range of 0.05 to 0.2. The BET specific surface area (m²) was then calculated using the same instrument program. 2 The measurement was performed by calculating ( / g).

[0179] The average fiber diameter was calculated from the specific surface area using the following formula. The density of cellulose is 1.5 g / cm³. 3 Therefore, the volume per gram of cellulose is 6.7 × 10 -7 (m 3 It is / g). If the equivalent average fiber diameter of cellulose microfibers is r (m), then the average outer circumference of the cellulose microfibers = πr and the average cross-sectional area of ​​the cellulose microfibers = 0.25πr 2 Therefore, per gram of cellulose microfiber, the total fiber length = 6.7 × 10 -7 (m 3 ) / average cross-sectional area (=0.25πr 2 ) Total surface area = Specific surface area (m²) 2 ) = 6.7 × 10 -7 (m 3 ) / average cross-sectional area (=0.25πr 2 )×average outer circumference length (=πr)=6.7×10 -7 (m 3 ) / 0.25r Therefore, for example, a specific surface area of ​​40 m² is required. 2 The average fiber diameter r of the CNF is calculated to be 67 nm.

[0180] [Area occupied by ultrafine fibers] The occupied area ratio was measured using a field emission scanning electron microscope (FE-SEM Regulus8220 / 5060FQ, manufactured by Hitachi, Ltd.) following the procedure below.

[0181] 1. A cellulose microfiber aqueous dispersion with a solid content concentration of 0.2-2% by mass was diluted with dimethyl sulfoxide (DMSO) to a solid content of 5 ppm by mass. The mixture was then stirred for 30 seconds at 3000 rpm using a homogenizer (IKA, product name "Ultra-Turrax T18") to obtain a DMSO dispersion. 2. A smooth substrate (silicon wafer) was coated with osmium plasma and heated to 130°C on a hot plate. 3. 7 μL of DMSO dispersion was dropped onto the center of a heated, smooth substrate, and the mixture was allowed to stand and dry under heating to fix the cellulose microfibers onto the substrate. 4. The substrate on which the obtained cellulose microfibers were immobilized was scanned using a scanning electron microscope (SEM) at an acceleration voltage of 1.5 kV, an observation magnification of 400x, and a resolution of 400 pixels or more per 100 μm, to capture four images at any different location on the substrate. 5. The threshold value of 15 μm is obtained from the number of pixels in the scale bar of the SEM image. 2 The number of pixels corresponding to that was calculated. 6. From the acquired SEM images, binarized images were created using the MaxEntropy method with the image processing software ImageJ. 7. The binarized image was analyzed using ImageJ's Analyze Particle function to calculate the area (pixels) of individual cellulose microfibers. 8. The particle analysis results of the four captured images are combined, pixels smaller than 2 pixels are removed as noise, and a threshold of 15 μm area is set. 2 Fibers smaller than 15 μm are considered ultrafine fibers, and 15 μm is the total area of ​​cellulose microfibers. 2 The ratio of the area of ​​extremely fine fibers smaller than a certain size was calculated.

[0182] [Glucose content] The glucose content of cellulose microfibers was determined by analyzing the constituent sugars, following the procedure outlined in the National Renewable Energy Laboratory (NREL), USA, 2008, based on the analytical procedure of the U.S. Department of Energy (Sluiter, A., Hames, B., Ruiz, R., Scarlata, C., Sluiter, J., Templeton, D., Crocker, D.: Determination of structural carbohydrates and lignin in biomass. National Renewable Energy Laboratory (NREL), USA, 2008).

[0183] 200 mg of the sample (anhydrous base) was mixed with 3 ml of 72% sulfuric acid and allowed to swell at 30°C for 1 hour. Then, it was poured into a 125 ml pressure-resistant bottle with 84 ml of pure water and hydrolyzed at 120°C for 1 hour. After that, the mixture was filtered by suction while still hot using a 1G-3 glass filter (weighed constant at 105°C) to separate the solid and liquid. The filtrate was then diluted to 100 ml, and the constituent sugars (glucose, mannose, xylose) were quantified by high-performance liquid chromatography (HPLC) (Agilent Technology, 1260 Infinity II).

[0184] [DS] The degree of acetyl substitution (DS) of cellulose microfibers was evaluated using an infrared spectrometer (JASCO Corporation, FT / IR-6200) and a nuclear magnetic resonance spectrometer (NMR) (Bruker Corporation, AVANCE III 500MHz) according to the following procedure. The degree of acetyl substitution (DS) was calculated from the reflected infrared absorption spectrum of cellulose microfibers based on the peak intensity ratio between the peak derived from the acetyl group and the peak derived from the cellulose backbone. The peak of the C=O absorption band based on the acetyl group was at 1730 cm⁻¹. -1 The peak of the CO absorption band based on the cellulose backbone chain appears at 1030 cm⁻¹. -1It appears in [location]. The DS of cellulose microfibers is obtained by creating a correlation graph between the DS obtained from solid-state NMR measurements of cellulose microfibers (described later) and the modification rate (IR index 1030), which is defined as the ratio of the peak intensity of the absorption band of C=O based on acetyl groups to the peak intensity of the absorption band of CO in the cellulose backbone chain. The calibration curve substitution degree DS = 4.13 × IR index (1030) is calculated from the correlation graph. This was obtained by using [a specific method / tool].

[0185] The method for calculating the DS of cellulose microfibers using solid-state NMR is as follows: For freeze-pulverized cellulose microfibers... 13 Solid-state NMR measurements were performed, and the area intensity (Inf) of the signal attributed to a single carbon atom from the modifying group was calculated using the following formula, based on the total area intensity (Inp) of the signals attributed to carbon atoms C1-C6 from the pyranose ring of cellulose that appear in the range of 50 ppm to 110 ppm. DS = (Inf) × 6 / (Inp) Since the modifying group is an acetyl group, a 23 ppm signal assigned to -CH3 was used.

[0186] 13 The conditions for the 13C solid-state NMR measurement were as follows: Equipment:Bruker Biospin Avance500WB Frequency: 125.77MHz Measurement method: DD / MAS method Waiting time: 75 seconds NMR sample tube: 4mmφ Total number of times: 640 (approximately 14 hours) MAS: 14,500Hz Chemical shift reference: Glycine (External reference: 176.03 ppm)

[0187] [Crystallization] The crystallinity of cellulose microfibers was evaluated using an X-ray diffractometer (MiniFlex II, Rigaku Corporation) by the following method. The crystallinity was determined by the Segal method from the diffraction pattern (2θ / deg. of 10 to 30) when the sample was measured by wide-angle X-ray diffraction using the following equation. Crystallinity (%) = [I (200) - I (amorphous) / I (200) × 100 I (200) : Diffraction peak intensity due to the 200 plane (2θ = 22.5°) in cellulose I crystals I (amorphous) : Halo peak intensity due to the amorphous in cellulose I crystals, which is the peak intensity on the low-angle side (2θ = 18.0°) 4.5° lower than the diffraction angle of the 200 plane

[0188] [Measurement of whiteness] Using a spectrocolorimeter and color difference meter (PF700 type manufactured by Nippon Denshoku Industries Co., Ltd.), the measurement was carried out in accordance with "Method for Measuring Diffuse Blue Light Reflectance of ISO Whiteness of Paper, Paperboard and Pulp (JIS P8148·ISO 2470)". The slurry of the cellulose raw material or cellulose microfibrils was sheeted using a suction filtration device equipped with a polytetrafluoroethylene (PTFE) membrane filter so that the basis weight was 50 g / m 2 or more, dried at 80 °C until it reached the equilibrium moisture content, a cellulose sheet was prepared, and used for the above measurement.

[0189] [Measurement of halogen content in cellulose raw material or cellulose microfibrils] (Immersion and filtration treatment) The cellulose raw material or cellulose microfibrils were immersed in pure water at 25 °C for 48 hours. Specifically, the cellulose raw material or cellulose microfibrils were immersed in pure water with a solid content of 2% by mass in a glass beaker with a total volume of 200 mL, stirred for 1 hour with a 3-1 motor (BL-600 type manufactured by HEIDON, SUS-made propeller blade, 100 rpm), and then allowed to stand. Next, using a Teflon (registered trademark) membrane filter (pore size 1 μm), vacuum filtration was carried out to prepare a sheet with a basis weight of 10 g / m 2 and filtration drying was performed in a ventilated oven at 70 °C until the moisture content was 10% by mass or less to obtain the treated cellulose raw material or treated cellulose microfibrils.

[0190] (Halogen content measurement) 50 mg of the processed cellulose raw material or processed cellulose fine fibers described above was weighed into a quartz sample boat. The sample boat was placed in an electric furnace (manufactured by Mitsubishi Chemical Analytic Corporation) and burned at 1000°C. The gas generated by combustion cooled to room temperature via a cooling section and was bubbling through a fluororesin tube into an absorption solution (the absorption solution consisted of 10 mg / L tartrate ions, 600 mg / L hydrogen peroxide, 2.7 mmol / L sodium carbonate, and 0.3 mmol / L sodium bicarbonate dissolved in deionized water). The halogen content of this absorption solution was quantified using an ion chromatograph (THERMOFISHER INTEGRION CT model) through a fluororesin tube. The quantification was performed based on calibration curves created using samples with various halogen content levels. In this process, the moisture content in the treated cellulose raw material or treated cellulose microfibers was subtracted using the loss on drying method (2.00 g of cellulose sample was placed in a glass weighing bottle, dried at 60°C for 15 hours, then at 105°C for 2 hours, and weighed in a desiccator to a constant weight. The weight was then measured and calculated using the following formula: Moisture content (mass%) = (weight of sample before drying - weight of sample after drying) / (weight of sample before drying) x 100). Finally, the value (mass ppm) converted to the dry mass (i.e., water-free state) of the treated cellulose raw material or treated cellulose microfibers was used as the halogen content remaining in the cellulose fibers.

[0191] [Heat resistance evaluation: Appearance of fiber-reinforced resin] Regarding the appearance of fiber-reinforced resin samples obtained by kneading cellulose microfibers and resin, samples that were clearly burnt were classified as poor, samples that were slightly burnt were classified as acceptable, and samples that showed no discoloration were classified as good.

[0192] [Tensile test] Multipurpose test specimens (as fiber-reinforced resin) conforming to ISO-37 were molded from the compound using an injection molding machine with a maximum clamping pressure of 75 tons. Tensile tests were conducted under conditions conforming to JIS K6920-2, and the tensile strength, tensile modulus, and fracture strain were measured. Since polyamide resin undergoes changes due to moisture absorption, the specimens were stored in aluminum moisture-proof bags immediately after molding to suppress moisture absorption.

[0193] [Bending test] For the bending test, strips measuring 10 mm wide, 80 mm long, and 4 mm thick were prepared for fiber-reinforced resin produced by injection molding, and strips measuring 2.5 mm wide and 50 mm long were cut from sheet-like fiber-reinforced resin produced by nonwoven fabrication. The bending strength, bending modulus, and bending strain were measured under conditions compliant with JIS K7171:2008. Since polyamide resin undergoes changes due to moisture absorption, it was stored in an aluminum moisture-proof bag immediately after molding to suppress moisture absorption.

[0194] [Thermal stability of resins] Multipurpose test specimens, similar to those used for tensile testing, were placed in resealable polyethylene bags, stored at 100°C for one month, then returned to room temperature and left for one day before being visually inspected. Specimens that showed no visible discoloration were classified as good, while those that showed visible discoloration were classified as poor.

[0195] [Recyclability of resins] Strips similar to those used for the bending test were cut to a diameter of 5 mm or less with a cutter and processed in two passes using an ultracentrifugal grinder (Retsch ZM200 model, screen opening φ2 mm, rotation speed 10,000 rpm). In each example and comparative example, melt mixing and injection molding were performed according to the method described in each example, and after repeating this five times, the bending strength was measured. Compared to before storage, a bending strength retention rate of 90% or more was considered good, and less than 90% was considered poor.

[0196] ≪Materials used≫ [pulp] (Linter Pulp A) Linter pulp A (hereinafter referred to as pulp A), a natural cellulose obtained from Nippon Paper Pulp Trading Co., Ltd., had a length-weighted average fiber length of 1660 μm as measured by the aforementioned automatic fiber shape analyzer.

[0197] (Linter Pulp B) Linter pulp B (hereinafter referred to as pulp B), a natural cellulose obtained from Nippon Paper Pulp Trading Co., Ltd., had a length-weighted average fiber length of 1006 μm as measured by the aforementioned automatic fiber shape analyzer.

[0198] (Wood pulp C) Wood pulp (NBLP) C (hereinafter referred to as Pulp C), a natural cellulose obtained from Nippon Paper Pulp Trading Co., Ltd., had a length-weighted average fiber length of 1315 μm as measured by the aforementioned automatic fiber shape analyzer.

[0199] (Acetylated Linter Pulp D) The above pulp A was immersed in dimethyl sulfoxide to a pulp concentration of 5% by mass, and 0.1% by mass of potassium carbonate was added as a catalyst. The pulp was then thoroughly dispersed and swollen with a stirring blade. The mixture was heated to 60°C, vinyl acetate was added, and acetylation was carried out to obtain acetylated linter pulp D (hereinafter referred to as acetylated pulp D).

[0200] (Acetylated Linter Pulp E) The above pulp B was immersed in dimethyl sulfoxide to a pulp concentration of 5% by mass, and 0.1% by mass of potassium carbonate was added as a catalyst. The pulp was then thoroughly dispersed and swollen with a stirring blade. The mixture was heated to 60°C, vinyl acetate was added, and acetylation was carried out to obtain acetylated linter pulp E (hereinafter referred to as acetylated pulp E).

[0201] [Cellulose microfibers] (Manufacturing Example 1) Pulp A was immersed in water to a solid content of 1.5% by mass, and the slurry obtained by dispersing it using a lab pulper (manufactured by Aikawa Iron Works Co., Ltd.) was introduced into a defibration apparatus equipped with a single disc refiner (manufactured by Aikawa Iron Works Co., Ltd., SDR14 type lab refiner, pressurized disc type) and tanks A and B connected by wiring via the disc refiner, to defibrate the pulp. First, the slurry was sent from tank A, into tank B via the disc refiner, and stored. Once the processing of the slurry in tank A was completed, the slurry was continuously sent from tank B to tank A via the disc refiner and stored, thereby controlling the number of times the slurry passed through the disc refiner (number of passes) to perform defibration. A ball screw type jack and a reduction gear were provided as a blade spacing adjustment mechanism for the disc refiner. The fluctuation in the blade spacing during the beating process after reaching the desired blade spacing was 0.005 mm or less as measured by a displacement sensor. For the disc refiner, a blade with a blade width of 4.0 mm and a groove ratio of 0.89 (disc blade A) was used, with a blade spacing of 0.25 mm, and 30 passes were made. Then, a blade with a blade width of 0.8 mm and a groove ratio of 0.53 (disc blade B) was used, with a blade spacing of 0.25 mm, and 30 passes were made.

[0202] The obtained slurry was subjected to three passes at 80 MPa using a high-pressure homogenizer (NS3015H, manufactured by Nilo Soavi). Similar to the disc refiner treatment described above, two tanks were used in the high-pressure homogenizer treatment, and the number of passes treated with the high-pressure homogenizer was controlled to defibrillate the material.

[0203] The obtained unmodified cellulose microfiber slurry was filtered under reduced pressure to obtain a wet cake with a solid content of 18% by mass. This wet cake was placed in a reaction vessel, and dimethyl sulfoxide (DMSO) was added to bring the solid content to 2% by mass. Potassium carbonate equivalent to 0.1% by mass was added, and the mixture was heated to 60°C while stirring homogeneously. Vinyl acetate was added, and acetylation was carried out until the desired degree of substitution was achieved. After the reaction, 10% by mass of quench water was added, and the mixture was thoroughly washed away from the solvent and other contaminants by repeatedly stirring and filtering with 50 times the amount of pure water relative to the cellulose solid content using a pressure filter to obtain a wet cake of acetylated cellulose microfibers.

[0204] (Manufacturing example 2) Similar to Manufacturing Example 1, pulp A was immersed in water to a solid content of 1.5% by mass, dispersed in a lab pulper, and then processed using a disc refiner with a blade width of 2.5 mm and a groove ratio of 0.36, passing 50 times with a blade spacing of 0.20 mm. Subsequently, a disc refiner with a blade width of 0.6 mm and a groove ratio of 0.60 was used, passing 100 times with a blade spacing of 0.10 mm. High-pressure homogenization was not performed.

[0205] The obtained unmodified cellulose microfiber slurry was filtered under reduced pressure to obtain a wet cake with a solid content of 18% by mass. This wet cake was placed in a reaction vessel, and dimethyl sulfoxide (DMSO) was added to bring the solid content to 2% by mass. Potassium carbonate equivalent to 0.1% by mass was added, and the mixture was heated to 60°C while stirring homogeneously. Vinyl acetate was added, and acetylation was carried out until the desired degree of substitution was achieved. After the reaction, 10% by mass of quench water was added, and the mixture was thoroughly washed away from the solvent and other contaminants by repeatedly stirring and filtering with 50 times the amount of pure water relative to the cellulose solid content using a pressure filter to obtain a wet cake of acetylated cellulose microfibers.

[0206] (Manufacturing Example 3) Similar to manufacturing example 1, pulp B was immersed in water to a solid content of 1.5% by mass, dispersed in a lab pulper, and then processed 50 times using a disc refiner with a blade width of 2.5 mm and a groove ratio of 0.36, with a blade spacing of 0.20 mm. After that, 50 times were processed using a blade width of 0.8 mm and a groove ratio of 0.53, with a blade spacing of 0.20 mm.

[0207] The resulting slurry was processed in five passes using a high-pressure homogenizer.

[0208] The obtained unmodified cellulose microfiber slurry was filtered under reduced pressure to obtain a wet cake with a solid content of 18% by mass. This wet cake was placed in a reaction vessel, and dimethyl sulfoxide (DMSO) was added to bring the solid content to 2% by mass. Potassium carbonate equivalent to 0.1% by mass was added, and the mixture was heated to 60°C while stirring homogeneously. Vinyl acetate was added, and acetylation was carried out until the desired degree of substitution was achieved. After the reaction, 10% by mass of quench water was added, and the mixture was thoroughly washed away from the solvent and other contaminants by repeatedly stirring and filtering with 50 times the amount of pure water relative to the cellulose solid content using a pressure filter to obtain a wet cake of acetylated cellulose microfibers.

[0209] (Manufacturing example 4) Similar to Manufacturing Example 1, pulp A was immersed in water to a solid content of 3.0% by mass, dispersed in a lab pulper, and then processed 30 times using a disc refiner with a blade width of 2.5 mm and a groove ratio of 0.36, with a blade spacing of 0.20 mm. After that, a blade with a blade width of 0.6 mm and a groove ratio of 0.60 was used, and processed 30 times with a blade spacing of 0.20 mm.

[0210] The resulting slurry was processed in five passes using a high-pressure homogenizer.

[0211] The obtained unmodified cellulose microfiber slurry was filtered under reduced pressure to obtain a wet cake with a solid content of 18% by mass. This wet cake was placed in a reaction vessel, and dimethyl sulfoxide (DMSO) was added to bring the solid content to 2% by mass. Potassium carbonate equivalent to 0.1% by mass was added, and the mixture was heated to 60°C while stirring homogeneously. Vinyl acetate was added, and acetylation was carried out until the desired degree of substitution was achieved. After the reaction, 10% by mass of quench water was added, and the mixture was thoroughly washed away from the solvent and other contaminants by repeatedly stirring and filtering with 50 times the amount of pure water relative to the cellulose solid content using a pressure filter to obtain a wet cake of acetylated cellulose microfibers.

[0212] (Manufacturing example 5) Similar to Manufacturing Example 1, pulp A was immersed in water to a solid content of 1.5% by mass, dispersed in a lab pulper, and then processed 100 times using a disc refiner with a blade width of 2.5 mm and a groove ratio of 0.36, with a blade spacing of 0.15 mm. After that, a blade with a blade width of 0.8 mm and a groove ratio of 0.53 was used, and processed 50 times with a blade spacing of 0.15 mm.

[0213] The resulting slurry was subjected to 10 passes in a high-pressure homogenizer.

[0214] The obtained unmodified cellulose microfiber slurry was filtered under reduced pressure to obtain a wet cake with a solid content of 18% by mass. This wet cake was placed in a reaction vessel, and dimethyl sulfoxide (DMSO) was added to bring the solid content to 2% by mass. Potassium carbonate equivalent to 0.1% by mass was added, and the mixture was heated to 60°C while stirring homogeneously. Vinyl acetate was added, and acetylation was carried out until the desired degree of substitution was achieved. After the reaction, 10% by mass of quench water was added, and the mixture was thoroughly washed away from the solvent and other contaminants by repeatedly stirring and filtering with 50 times the amount of pure water relative to the cellulose solid content using a pressure filter to obtain a wet cake of acetylated cellulose microfibers.

[0215] (Manufacturing example 6) Similar to Manufacturing Example 1, acetylated pulp D was immersed in water to a solid content of 1.5% by mass, dispersed in a lab pulper, and then processed for 75 passes using a disc refiner with a blade width of 2.5 mm and a groove ratio of 0.36, with a blade spacing of 0.05 mm. After that, a blade with a blade width of 0.8 mm and a groove ratio of 0.53 was used, and processed for 40 passes with a blade spacing of 0.05 mm.

[0216] The resulting slurry was subjected to 10 passes in a high-pressure homogenizer.

[0217] (Manufacturing example 7) Similar to Production Example 1, acetylated pulp E was immersed in water to a solid content of 1.5% by mass, dispersed in a lab pulper, and then processed 50 times using a disc refiner with a blade width of 0.8 mm and a blade groove ratio of 0.53, with a blade spacing of 0.15 mm. Only one disc refiner treatment was performed, and the resulting slurry was subjected to 10 passes in a high-pressure homogenizer.

[0218] (Manufacturing example 8) Similar to Manufacturing Example 1, pulp A was immersed in water to a solid content of 1.5% by mass, dispersed in a lab pulper, and then processed 100 times using a disc refiner with a blade width of 2.5 mm and a groove ratio of 0.36, with a blade spacing of 0.15 mm. After that, a blade with a blade width of 0.8 mm and a groove ratio of 0.53 was used, and processed 50 times with a blade spacing of 0.15 mm.

[0219] The resulting slurry was processed in three passes using a high-pressure homogenizer.

[0220] The obtained unmodified cellulose microfiber slurry was filtered under reduced pressure to obtain a wet cake with a solid content of 18% by mass. This wet cake was placed in a reaction vessel, and dimethyl sulfoxide (DMSO) was added to bring the solid content to 2% by mass. Potassium carbonate equivalent to 0.1% by mass was added, and the mixture was heated to 60°C while stirring homogeneously. Vinyl acetate was added, and acetylation was carried out until the desired degree of substitution was achieved. After the reaction, 10% by mass of quench water was added, and the mixture was thoroughly washed away from the solvent and other contaminants by repeatedly stirring and filtering with 50 times the amount of pure water relative to the cellulose solid content using a pressure filter to obtain a wet cake of acetylated cellulose microfibers.

[0221] (Manufacturing example 9) Similar to Manufacturing Example 1, pulp A was immersed in water to a solid content of 1.5% by mass, dispersed in a lab pulper, and then processed 100 times using a disc refiner with a blade width of 2.5 mm and a groove ratio of 0.36, with a blade spacing of 0.15 mm. After that, a blade with a blade width of 0.8 mm and a groove ratio of 0.53 was used, and processed 50 times with a blade spacing of 0.15 mm.

[0222] The resulting slurry was processed in five passes using a high-pressure homogenizer.

[0223] The obtained unmodified cellulose microfiber slurry was filtered under reduced pressure to obtain a wet cake with a solid content of 18% by mass. This wet cake was placed in a reaction vessel, and dimethyl sulfoxide (DMSO) was added to bring the solid content to 2% by mass. Potassium carbonate equivalent to 0.1% by mass was added, and the mixture was heated to 60°C while stirring homogeneously. Vinyl acetate was added, and acetylation was carried out until the desired degree of substitution was achieved. After the reaction, 10% by mass of quench water was added, and the mixture was thoroughly washed away from the solvent and other contaminants by repeatedly stirring and filtering with 50 times the amount of pure water relative to the cellulose solid content using a pressure filter to obtain a wet cake of acetylated cellulose microfibers.

[0224] (Manufacturing example 10) Similar to manufacturing example 1, pulp A was immersed in water to a solid content of 1.5% by mass, dispersed in a lab pulper, and then processed for 10 passes using a disc refiner with a blade width of 2.5 mm and a groove ratio of 0.36, with a blade spacing of 0.05 mm. After that, a blade with a blade width of 0.8 mm and a groove ratio of 0.53 was used for 10 passes with a blade spacing of 0.05 mm.

[0225] The resulting slurry was subjected to 10 passes in a high-pressure homogenizer.

[0226] The obtained unmodified cellulose microfiber slurry was filtered under reduced pressure to obtain a wet cake with a solid content of 18% by mass. This wet cake was placed in a reaction vessel, and dimethyl sulfoxide (DMSO) was added to bring the solid content to 2% by mass. Potassium carbonate equivalent to 0.1% by mass was added, and the mixture was heated to 60°C while stirring homogeneously. Vinyl acetate was added, and acetylation was carried out until the desired degree of substitution was achieved. After the reaction, 10% by mass of quench water was added, and the mixture was thoroughly washed away from the solvent and other contaminants by repeatedly stirring and filtering with 50 times the amount of pure water relative to the cellulose solid content using a pressure filter to obtain a wet cake of acetylated cellulose microfibers.

[0227] (Manufacturing Example 11) Similar to Production Example 1, acetylated pulp E was immersed in water to a solid content of 1.5% by mass, dispersed in a lab pulper, and then processed for 40 passes using a disc refiner with a blade width of 0.8 mm and a blade groove ratio of 0.53, with a blade spacing of 0.10 mm. Only one disc refiner treatment was performed, and the resulting slurry was subjected to 10 passes in a high-pressure homogenizer.

[0228] (Manufacturing Example 12) Similar to Manufacturing Example 1, pulp B was immersed in water to a solid content of 1.5% by mass, dispersed in a lab pulper, and then processed for 70 passes using a disc refiner with a blade width of 2.5 mm and a groove ratio of 0.36, with a blade spacing of 0.15 mm. After that, a blade with a blade width of 0.6 mm and a groove ratio of 0.60 was used for 40 passes with a blade spacing of 0.15 mm.

[0229] The resulting slurry was subjected to 10 passes in a high-pressure homogenizer.

[0230] The obtained unmodified cellulose microfiber slurry was filtered under reduced pressure to obtain a wet cake with a solid content of 18% by mass. DMSO was added to the wet cake, stirred, and then filtered by suction twice to remove water. DMSO-substituted cellulose microfibers were added to a DMSO solution containing maleic anhydride, and the reaction was carried out while heating until the desired degree of substitution was achieved. After the reaction, the mixture was washed repeatedly with pure water, acetone, and pure water to remove the solvent, unreacted reagents, and by-products, yielding a wet cake of maleic acid-modified cellulose microfibers.

[0231] (Comparative example 1) Using the disc refiner and high-pressure homogenizer described in Manufacturing Example 1, pulp A was immersed in water to a solid content of 1.5% by mass, dispersed with a lab pulper, and then processed 20 times using a disc refiner with a blade width of 2.5 mm and a groove ratio of 0.36, with a blade spacing of 0.30 mm. After that, 50 times were processed using a blade with a blade width of 0.8 mm and a groove ratio of 0.53, with a blade spacing of 0.35 mm.

[0232] The resulting slurry was processed in a single pass using a high-pressure homogenizer.

[0233] The obtained unmodified cellulose microfiber slurry was filtered under reduced pressure to obtain a wet cake with a solid content of 18% by mass. This wet cake was placed in a reaction vessel, and dimethyl sulfoxide (DMSO) was added to bring the solid content to 2% by mass. Potassium carbonate equivalent to 0.1% by mass was added, and the mixture was heated to 60°C while stirring homogeneously. Vinyl acetate was added, and acetylation was carried out until the desired degree of substitution was achieved. After the reaction, 10% by mass of quench water was added, and the mixture was thoroughly washed away from the solvent and other contaminants by repeatedly stirring and filtering with 50 times the amount of pure water relative to the cellulose solid content using a pressure filter to obtain a wet cake of acetylated cellulose microfibers.

[0234] (Manufacturing Comparison Example 2) Similar to Manufacturing Example 1, pulp B was immersed in water to a solid content of 1.5% by mass, dispersed in a lab pulper, and then processed for 120 passes using a disc refiner with a blade width of 2.5 mm and a groove ratio of 0.36, with a blade spacing of 0.50 mm. Subsequently, a disc refiner with a blade width of 0.6 mm and a groove ratio of 0.60 was used, with a blade spacing of 0.03 mm, for 100 passes. High-pressure homogenization was not performed.

[0235] The obtained unmodified cellulose microfiber slurry was filtered under reduced pressure to obtain a wet cake with a solid content of 18% by mass. This wet cake was placed in a reaction vessel, and dimethyl sulfoxide (DMSO) was added to bring the solid content to 2% by mass. Potassium carbonate equivalent to 0.1% by mass was added, and the mixture was heated to 60°C while stirring homogeneously. Vinyl acetate was added, and acetylation was carried out until the desired degree of substitution was achieved. After the reaction, 10% by mass of quench water was added, and the mixture was thoroughly washed away from the solvent and other contaminants by repeatedly stirring and filtering with 50 times the amount of pure water relative to the cellulose solid content using a pressure filter to obtain a wet cake of acetylated cellulose microfibers.

[0236] (Manufacturing Comparison Example 3) Similar to Production Example 1, pulp C was immersed in water to a solid content of 1.5% by mass, dispersed in a lab pulper, and then processed for 40 passes using a disc refiner with a blade width of 2.5 mm and a blade groove ratio of 0.36, with a blade spacing of 0.35 mm. Only one disc refiner treatment was performed, and the resulting slurry was processed in two passes using a high-pressure homogenizer.

[0237] The obtained unmodified cellulose microfiber slurry was filtered under reduced pressure to obtain a wet cake with a solid content of 18% by mass. This wet cake was placed in a reaction vessel, and dimethyl sulfoxide (DMSO) was added to bring the solid content to 2% by mass. Potassium carbonate equivalent to 0.1% by mass was added, and the mixture was heated to 60°C while stirring homogeneously. Vinyl acetate was added, and acetylation was carried out until the desired degree of substitution was achieved. After the reaction, 10% by mass of quench water was added, and the mixture was thoroughly washed away from the solvent and other contaminants by repeatedly stirring and filtering with 50 times the amount of pure water relative to the cellulose solid content using a pressure filter to obtain a wet cake of acetylated cellulose microfibers.

[0238] (Manufacturing Comparison Example 4) Similar to Manufacturing Example 1, pulp A was immersed in water to a solid content of 1.5% by mass, dispersed in a lab pulper, and then passed through five passes using a disc refiner with a blade width of 4.0 mm and a blade groove ratio of 0.89, with a blade spacing of 0.40 mm. Only one stage of disc refiner processing was performed, and high-pressure homogenization processing was not performed.

[0239] The obtained unmodified cellulose microfiber slurry was filtered under reduced pressure to obtain a wet cake with a solid content of 18% by mass. This wet cake was placed in a reaction vessel, and dimethyl sulfoxide (DMSO) was added to bring the solid content to 2% by mass. Potassium carbonate equivalent to 0.1% by mass was added, and the mixture was heated to 60°C while stirring homogeneously. Vinyl acetate was added, and acetylation was carried out until the desired degree of substitution was achieved. After the reaction, 10% by mass of quench water was added, and the mixture was thoroughly washed away from the solvent and other contaminants by repeatedly stirring and filtering with 50 times the amount of pure water relative to the cellulose solid content using a pressure filter to obtain a wet cake of acetylated cellulose microfibers.

[0240] (Comparative Example 5) Similar to Manufacturing Example 1, pulp C was immersed in water to a solid content of 1.5% by mass, dispersed in a lab pulper, and then processed 50 times using a disc refiner with a blade width of 2.5 mm and a groove ratio of 0.36, with a blade spacing of 0.05 mm. Subsequently, 50 passes were made using a blade width of 0.8 mm and a groove ratio of 0.53, with a blade spacing of 0.03 mm.

[0241] The resulting slurry was processed in a high-pressure homogenizer for 20 passes.

[0242] The obtained unmodified cellulose microfiber slurry was filtered under reduced pressure to obtain a wet cake with a solid content of 18% by mass. This wet cake was placed in a reaction vessel, and dimethyl sulfoxide (DMSO) was added to bring the solid content to 2% by mass. Potassium carbonate equivalent to 0.1% by mass was added, and the mixture was heated to 60°C while stirring homogeneously. Vinyl acetate was added, and acetylation was carried out until the desired degree of substitution was achieved. After the reaction, 10% by mass of quench water was added, and the mixture was thoroughly washed away from the solvent and other contaminants by repeatedly stirring and filtering with 50 times the amount of pure water relative to the cellulose solid content using a pressure filter to obtain a wet cake of acetylated cellulose microfibers.

[0243] (Comparative example 6) Similar to Manufacturing Example 1, pulp A was immersed in water to a solid content of 1.5% by mass, dispersed in a lab pulper, and then processed for 120 passes using a disc refiner with a blade width of 2.5 mm and a groove ratio of 0.36, with a blade spacing of 0.03 mm. After that, a blade with a blade width of 0.8 mm and a groove ratio of 0.53 was used, and processed for 60 passes with a blade spacing of 0.03 mm.

[0244] The resulting slurry was processed in a high-pressure homogenizer for 15 passes.

[0245] The obtained unmodified cellulose microfiber slurry was filtered under reduced pressure to obtain a wet cake with a solid content of 18% by mass. This wet cake was placed in a reaction vessel, and dimethyl sulfoxide (DMSO) was added to bring the solid content to 2% by mass. Potassium carbonate equivalent to 0.1% by mass was added, and the mixture was heated to 60°C while stirring homogeneously. Vinyl acetate was added, and acetylation was carried out until the desired degree of substitution was achieved. After the reaction, 10% by mass of quench water was added, and the mixture was thoroughly washed away from the solvent and other contaminants by repeatedly stirring and filtering with 50 times the amount of pure water relative to the cellulose solid content using a pressure filter to obtain a wet cake of acetylated cellulose microfibers.

[0246] (Comparative example 7) In manufacturing comparison example 7, a single disc refiner was used in which the amount of movement when the runner portion was pulled in the truss direction was 0.3 mm.

[0247] Pulp A was immersed in water to a solid content of 1.5% by mass, dispersed in a lab pulper, and then processed for 80 passes using a disc refiner with a blade width of 2.5 mm and a groove ratio of 0.36, with a blade spacing of 0.20 mm. After that, a blade with a blade width of 0.8 mm and a groove ratio of 0.53 was used, and processed for 100 passes with a blade spacing of 0.10 mm.

[0248] The resulting slurry was processed in five passes using a high-pressure homogenizer.

[0249] The obtained unmodified cellulose microfiber slurry was filtered under reduced pressure to obtain a wet cake with a solid content of 18% by mass. This wet cake was placed in a reaction vessel, and dimethyl sulfoxide (DMSO) was added to bring the solid content to 2% by mass. Potassium carbonate equivalent to 0.1% by mass was added, and the mixture was heated to 60°C while stirring homogeneously. Vinyl acetate was added, and acetylation was carried out until the desired degree of substitution was achieved. After the reaction, 10% by mass of quench water was added, and the mixture was thoroughly washed away from the solvent and other contaminants by repeatedly stirring and filtering with 50 times the amount of pure water relative to the cellulose solid content using a pressure filter to obtain a wet cake of acetylated cellulose microfibers.

[0250] The evaluation results of the obtained chemically modified cellulose microfibers are shown in Tables 1 and 2.

[0251] Manufacturing of fiber-reinforced resins (Composite formation by injection molding: Examples I-1 to I-12, Comparative Examples I-1 to I-7) Using the obtained chemically modified cellulose microfibers, fiber-reinforced resin composites were fabricated by injection molding according to the following procedure. 1. The wet cakes of chemically modified cellulose microfibers prepared in Production Examples 1-12 and Production Comparative Examples 1-7 were each dispersed in hexafluoroisopropanol (hereinafter referred to as HFIP) at a rotation speed of 12,000 rpm for 3 minutes using a homogenizer (IKA Ultra-Turrax T18) to a solid content concentration of 1 vol%. 2. A solution was prepared by dissolving polyamide 6 (manufactured by Ube Industries, Ltd., 1013B) in HFIP at a solid content of 1% by mass. 3. Place ingredients 1 and 2 into a container so that the solid content mass ratio of chemically modified cellulose microfibers to polyamide 6 is 1:9, and mix them at 2,000 rpm for 5 minutes using a rotating / intersecting mixer (Sinky Co., Ltd., Awatori Rentaro ARE-310). 4. The resulting mixture from step 3 was cast onto a release film (manufactured by Mitsui Chemicals Tohcello Co., Ltd., X88B) and dried in an oven at 80°C for 1 hour. 5. The 4 was ground using a benchtop grinder (Labonext Mini Speed ​​Mill MS-05). 6.5 The powder was dried in a vacuum dryer for more than 24 hours. 7.6 was kneaded in a small kneader (DSM Xplore MC 15HT) at a temperature of 250°C and a rotation speed of 200 rpm for 2 minutes. 8. After mixing was complete, the resin was poured into an injection molding machine (Xplore IM12) to produce strip-shaped test specimens with a width of 10 mm, a length of 80 mm, and a thickness of 4 mm for bending tests, and multi-purpose test specimens (as fiber-reinforced resin) conforming to ISO-37 for tensile tests. Table 3 shows the evaluation results of the bending and tensile tests performed on the obtained test specimens.

[0252] (Resin composite formation by nonwoven fabric method - 1: Examples I-13 to I-24, Comparative Examples I-8 to I-14) Short polypropylene fibers (cut length: 2.0 mm, fineness: 0.2T) and the chemically modified cellulose fine fibers prepared above were added to pure water in a solid content mass ratio of 80:20 to obtain a slurry with a solid content concentration of 0.5% by mass. This slurry was stirred for 4 minutes in a household mixer to prepare a papermaking slurry. The prepared papermaking slurry was placed in a batch-type paper machine (Kumagai Riki Kogyo Co., Ltd. automatic square sheet machine, 25 cm x 25 cm, 80 mesh) equipped with a filter cloth (Shikishima Canvas Co., Ltd. TT35) at a basis weight of 300 g / m². 2 The material was added in such a manner, and then the papermaking (dewatering) process was carried out with a reduced pressure of 50 kPa relative to atmospheric pressure.

[0253] The wet paper, consisting of the concentrated composition in a wet state, which was placed on the resulting filter cloth, was peeled off the wire and measured at 1 kg / cm². 2It was pressed with pressure for 1 minute. Then, it was dried for approximately 120 seconds in a drum dryer set to a surface temperature of 130°C to obtain a nonwoven fabric. Four 10cm square pieces of the obtained nonwoven fabric were cut out and laminated, and then sandwiched between 0.1μm thick PET films. This was then pressed using a hot press at a temperature of 200°C and a molding pressure of 10kg / cm². 2 The PET film was heated and molded for 5 minutes. Here, the thickness of the molded product was controlled by placing 1.5 mm stainless steel spacers between the PET films. Afterward, the heating of the hot press was terminated, and the entire press was slowly cooled with a blower for approximately 30 minutes while maintaining the pressure. When the press temperature fell below 90°C, the pressure was released, and a sheet-shaped resin-reinforced resin was obtained. Table 4 shows the results of the bending test performed on the obtained resin-reinforced resin.

[0254] (Resin composite formation by nonwoven fabric method - 2: Examples I-25 to I-36, Comparative Examples I-15 to I-21) Short fibers made of polyamide 66 (cut length: 2.0 mm, fineness: 0.6 T) and the chemically modified cellulose fine fibers prepared above were added to pure water in a solid content mass ratio of 80:20 to obtain a slurry with a solid content concentration of 0.5% by mass. This slurry was stirred for 4 minutes in a household mixer to prepare a papermaking slurry. The prepared papermaking slurry was placed in a batch-type papermaking machine (Kumagai Riki Kogyo Co., Ltd. automatic square sheet machine, 25 cm x 25 cm, 80 mesh) equipped with a filter cloth (Shikishima Canvas Co., Ltd. TT35) at a basis weight of 300 g / m². 2 The material was added in such a manner, and then the papermaking (dewatering) process was carried out with a reduced pressure of 50 kPa relative to atmospheric pressure.

[0255] The wet paper, consisting of the concentrated composition in a wet state, which was placed on the resulting filter cloth, was peeled off the wire and measured at 1 kg / cm². 2 It was pressed for 1 minute under pressure. Then, it was dried for approximately 120 seconds in a drum dryer set to a surface temperature of 130°C to obtain a nonwoven fabric. Four 10cm square pieces of the obtained nonwoven fabric were cut out and laminated, and then sandwiched between 0.1μm thick Teflon® sheets. This was then pressed using a hot press at a temperature of 300°C and a molding pressure of 10kg / cm². 2The PET film was heated and molded for 5 minutes. Here, the thickness of the molded product was controlled by placing 1.5 mm stainless steel spacers between the PET films. Afterward, the heating of the hot press was terminated, and the entire press was slowly cooled with a blower for approximately 30 minutes while maintaining the pressure. When the press temperature fell below 90°C, the pressure was released, and a sheet-shaped fiber-reinforced resin was obtained. Table 5 shows the results of the bending test performed on the obtained fiber-reinforced resin.

[0256] [Table 1]

[0257] [Table 2]

[0258] [Table 3]

[0259] [Table 4]

[0260] [Table 5]

[0261] Example II: ≪Measurement method≫ [Automatic fiber shape analyzer measurement] Various properties of cellulose microfibers were measured using an automated fiber shape analyzer (Morfi neo, Technidyne) according to the following procedure. 1. Cellulose microfibers were dispersed in pure water to prepare a 1 L aqueous dispersion. The final solid content concentration was adjusted to approximately 0.004% by mass. Since all cellulose microfibers were aqueous dispersions with a solid content concentration of 2% by mass or less, the dispersion treatment was performed by shaking in a sealed container with a filling rate of 75% by volume or less. 2. The aqueous dispersion prepared in step 1 was subjected to an autosampler and measured. 3. The measurement results were output in txt format (or csv format). 4. Shape parameters similar to those in Example I were extracted or calculated from the measurement results.

[0262] [Specific surface area, and average fiber diameter calculated from specific surface area] The same measurements were taken as in Example I.

[0263] [Measurement of rheological properties of cellulose microfibers] The rheological properties of a cellulose microfiber aqueous dispersion were measured using the following procedure, and the reciprocal of the yield strain (1 / γ) was calculated. The measurement equipment and conditions used were set as follows. (Measurement conditions) Measuring instrument: Rheometer HAAKE MERS (manufactured by Thermo Fisher Scientific) Measuring jig: Coaxial double cylinder (Cup: CCB25 DIN, Rotor: CC25 DIN Ti) Measurement mode: Oscillation Control method: Stress control Control range: 0.01 ~ 100 Pa Temperature: 25℃ 1. Cellulose microfibers were dispersed in pure water. The final solid content concentration of the cellulose microfibers was set to 0.75% by mass. Since all of the cellulose microfibers were aqueous dispersions with a solid content concentration of 2% by mass or less, the dispersion treatment was performed by shaking them in a sealed container with a filling density of 75% by volume or less. 2. The aqueous dispersion prepared in step 1 was left to stand at 25°C for at least 24 hours. 3. A jig was attached to the rheometer, and 17.0 ± 1.0 g of cellulose microfiber aqueous dispersion was added using a dropper. 4. Measurements were taken, and the yield strain (γ) was calculated using LVE analysis, and its reciprocal (1 / γ) was calculated.

[0264] [Whiteness measurement] The same measurements were taken as in Example I.

[0265] [Measurement of halogen content in cellulose raw materials or cellulose microfibers] The same measurements were taken as in Example I.

[0266] [Tensile test] Using the method described below, multipurpose test specimens conforming to ISO-37 were prepared, and tensile tests were conducted under conditions conforming to JIS K6920-2 to measure tensile strength, tensile modulus, and fracture strain.

[0267] [Dynamic viscoelasticity measurement] Using the method described below, multipurpose test specimens conforming to ISO-37 were prepared, and DMA measurements were performed under the following conditions to determine the storage modulus at 150°C. Equipment: Gabo Eplexer 500N Measurement mode: Tensile Measurement temperature range: -130 to 200°C Heating rate: 3°C / min Static load strain: 0.5% Dynamic load strain: 0.3% Vibration frequency: 10Hz Contact load: 1N

[0268] [Bending test] From the plate-like composite obtained by the nonwoven fabrication method, strips measuring 25 mm in width and 50 mm in length were cut out, and their bending strength, bending modulus of elasticity, and bending fracture strain were measured under conditions compliant with JIS K7171.

[0269] [Thermal stability of resins] The same measurements were taken as in Example I.

[0270] Preparation of Cellulose Microfibers (Cellulose microfiber A) Using linter pulp, a natural cellulose obtained from Nippon Paper Pulp Trading Co., Ltd., the linter pulp was immersed in water to a concentration of 1.5% by mass, and after simple dispersion using a lab pulper (manufactured by Aikawa Iron Works), the liquid was sent to a tank. The slurry was then refined while circulating by a single disc refiner (pre-stage) connected to the tank, which had a blade width of 2.5 mm, a groove width of 7.0 mm, and a blade-to-groove ratio of 0.36. At this time, operation was started with a blade-to-blade distance of 1.0 mm, and the blade-to-blade distance was gradually reduced until the final blade-to-blade distance was 0.05 mm. After the blade-to-blade distance reached 0.05 mm, operation was continued while monitoring the flow rate, and the operation was terminated when the entire slurry had passed through the disc section 10 times. Subsequently, the slurry was refined while circulating by a single disc refiner (post-stage) equipped with a blade width of 0.6 mm, a groove width of 1.0 mm, and a blade-to-groove ratio of 0.6. At this time, operation was started with a blade spacing of 1.0 mm, and the blade spacing was gradually reduced until the final spacing was 0.05 mm. After the blade spacing reached 0.05 mm, operation was continued while monitoring the flow rate, and the operation was terminated when the entire slurry had passed through the disc section 10 times. The obtained cellulose microfibers were designated as cellulose microfiber A (MFC-A). The analysis results of various fiber shape parameters and rheological properties are shown in Table 6.

[0271] (Cellulose microfiber B) Cellulose microfiber B (MFC-B) was obtained using the same method as cellulose microfiber A, except that the number of processing cycles using a single disc refiner (subsequent stage) was set to 30. The results of the analysis of various fiber shape parameters and rheological properties are shown in Table 6.

[0272] (Cellulose microfiber C) Using linter pulp, a natural cellulose obtained from Nippon Paper Pulp Trading Co., Ltd., the linter pulp was immersed in water to a concentration of 1.5% by mass, and after simple dispersion using a lab pulper (manufactured by Aikawa Iron Works), the liquid was sent to a tank. The slurry was then refined while circulating by a single disc refiner (pre-stage) connected to the tank, which had a blade width of 2.5 mm, a groove width of 7.0 mm, and a blade-to-groove ratio of 0.36. At this time, operation was started with a blade-to-blade distance of 1.0 mm, and the blade-to-blade distance was gradually reduced until the final blade-to-blade distance was 0.3 mm. After the blade-to-blade distance reached 0.3 mm, operation was continued while monitoring the flow rate, and the operation was terminated when the entire slurry had passed through the disc section 90 times. Subsequently, the slurry was refined while circulating by a single disc refiner (post-stage) equipped with a blade width of 0.8 mm, a groove width of 1.5 mm, and a blade-to-groove ratio of 0.53. At this time, operation was started with a blade spacing of 1.0 mm, and the blade spacing was gradually reduced until the final spacing was 0.15 mm. After the blade spacing reached 0.15 mm, operation was continued while monitoring the flow rate, and the operation was terminated when the entire slurry had passed through the disc section 40 times. The obtained cellulose microfibers were designated as cellulose microfibers C (MFC-C). The analysis results of various fiber shape parameters and rheological properties are shown in Table 6.

[0273] (Cellulose microfiber D) Cellulose microfibers C were subjected to 10 micronization processes at an operating pressure of 100 MPa using a high-pressure homogenizer (NS015H, manufactured by Nilo Soavi, Italy), and the resulting cellulose microfibers were designated as cellulose microfibers D (MFC-D). The results of the analysis of various fiber shape parameters and rheological properties are shown in Table 6.

[0274] (Cellulose microfiber E) Using linter pulp, a natural cellulose obtained from Nippon Paper Pulp Trading Co., Ltd., the linter pulp was immersed in water to a concentration of 1.5% by mass, and after simple dispersion using a lab pulper (manufactured by Aikawa Iron Works), the liquid was sent to a tank. The slurry was then refined while circulating by a single disc refiner (pre-stage) connected to the tank, which had a disc with a blade width of 2.5 mm, a groove width of 7.0 mm, and a blade-to-groove ratio of 0.36. At this time, operation was started with a blade-to-blade distance of 1.0 mm, and the blade-to-blade distance was gradually reduced until the final blade-to-blade distance was 0.05 mm. After the blade-to-blade distance reached 0.05 mm, operation was continued while monitoring the flow rate, and the operation was terminated when the entire slurry had passed through the disc section 90 times. Subsequently, the slurry was refined while circulating by a single disc refiner (post-stage) equipped with a disc with a blade width of 0.8 mm, a groove width of 1.5 mm, and a blade-to-groove ratio of 0.53. At this time, operation was started with a blade spacing of 1.0 mm, and the blade spacing was gradually reduced until the final blade spacing was 0.05 mm. After the blade spacing reached 0.05 mm, operation was continued while monitoring the flow rate, and the operation was terminated when the entire slurry had passed through the disc section 90 times. The obtained cellulose microfibers were designated as cellulose microfibers E (MFC-E). The analysis results of various fiber shape parameters and rheological properties are shown in Table 6.

[0275] (Cellulose microfiber F) Using linter pulp, a natural cellulose obtained from Nippon Paper Pulp Trading Co., Ltd., the linter pulp was immersed in water to a concentration of 1.5% by mass, and after simple dispersion using a lab pulper (manufactured by Aikawa Iron Works), the liquid was sent to a tank. The slurry was then refined by circulating it through a single disc refiner (only one unit) connected to the tank, which had a blade width of 2.5 mm, a groove width of 7.0 mm, and a blade-to-groove ratio of 0.36. At this time, operation was started with a blade distance of 1.0 mm, and the blade distance was gradually reduced until the final blade distance was 0.05 mm. After the blade distance reached 0.05 mm, operation was continued while monitoring the flow rate, and the operation was terminated when the entire slurry had passed through the disc section 150 times. The obtained cellulose fine fibers were designated as microfibrillated cellulose F (MFC-F). The analysis results of various fiber shape parameters and rheological properties are shown in Table 6.

[0276] (Cellulose microfiber G) Using linter pulp, a natural cellulose obtained from Nippon Paper Pulp Trading Co., Ltd., the linter pulp was immersed in water to a concentration of 1.5% by mass, and after simple dispersion using a lab pulper (manufactured by Aikawa Iron Works), the liquid was sent to a tank. The slurry was then refined while circulating by a single disc refiner (pre-stage) connected to the tank, which had a blade width of 2.5 mm, a groove width of 7.0 mm, and a blade-to-groove ratio of 0.36. At this time, operation was started with a blade-to-blade distance of 1.0 mm, and the blade-to-blade distance was gradually reduced until the final blade-to-blade distance was 0.05 mm. After the blade-to-blade distance reached 0.05 mm, operation was continued while monitoring the flow rate, and the operation was terminated when the entire slurry had passed through the disc section 10 times. Subsequently, the slurry was refined while circulating by a single disc refiner (post-stage) equipped with a blade width of 0.6 mm, a groove width of 1.0 mm, and a blade-to-groove ratio of 0.6. At this time, operation was started with a blade spacing of 1.0 mm, and the blade spacing was gradually reduced until the final blade spacing was 0.05 mm. Operation was terminated immediately after the blade spacing reached 0.05 mm (the number of times the disc section passed over is conveniently expressed as 0), and the obtained cellulose microfibers were designated as cellulose microfibers G (MFC-G). The analysis results of various fiber shape parameters and rheological properties are shown in Table 6.

[0277] (Cellulose microfiber H) Using linter pulp, a natural cellulose obtained from Nippon Paper Pulp Trading Co., Ltd., the linter pulp was immersed in water to a concentration of 1.5% by mass, and after simple dispersion using a lab pulper (manufactured by Aikawa Iron Works), the liquid was sent to a tank. The slurry was then refined by circulating it through a single disc refiner (only one unit) connected to the tank, which had a blade width of 0.8 mm, a groove width of 1.5 mm, and a blade-to-groove ratio of 0.53. At this time, operation was started with a blade distance of 1.0 mm, and the blade distance was gradually reduced until the final blade distance was 0.05 mm. After the blade distance reached 0.05 mm, operation was continued while monitoring the flow rate, and the operation was terminated when the entire slurry had passed through the disc section 90 times. The obtained cellulose fine fibers were designated as cellulose fine fibers H (MFC-H). The results of the analysis of various fiber shape parameters and rheological properties are shown in Table 6.

[0278] (Cellulose microfibers I) Using linter pulp, a natural cellulose obtained from Nippon Paper Pulp Trading Co., Ltd., the linter pulp was immersed in water to a concentration of 1.5% by mass, and after simple dispersion using a lab pulper (manufactured by Aikawa Iron Works), the liquid was sent to a tank. The slurry was then refined while circulating by a single disc refiner (pre-stage) connected to the tank, which had a disc with a blade width of 4.0 mm, a groove width of 4.5 mm, and a blade-to-groove ratio of 0.89. At this time, operation was started with a blade-to-blade distance of 1.0 mm, and the blade-to-blade distance was gradually reduced until the final blade-to-blade distance was 0.05 mm. After the blade-to-blade distance reached 0.05 mm, operation was continued while monitoring the flow rate, and the operation was terminated when the entire slurry had passed through the disc section 30 times. Subsequently, the slurry was refined while circulating by a single disc refiner (post-stage) equipped with a disc with a blade width of 0.8 mm, a groove width of 1.5 mm, and a blade-to-groove ratio of 0.53. At this time, operation was started with a blade spacing of 1.0 mm, and the blade spacing was gradually reduced until the final spacing was 0.05 mm. After the blade spacing reached 0.05 mm, operation was continued while monitoring the flow rate, and the operation was terminated when the entire slurry had passed through the disc section 30 times. The obtained cellulose microfibers were designated as Cellulose Microfiber I (MFC-I). The analysis results of various fiber shape parameters and rheological properties are shown in Table 6.

[0279] (Cellulose microfibers J) Cellulose microfibers J (MFC-J) were obtained using the same method as for cellulose microfibers A (MFC-A), except that the number of processing cycles using a single disc refiner (subsequent stage) was 180. The results of the analysis of various fiber shape parameters and rheological properties are shown in Table 6.

[0280] (Cellulose microfiber K) Using linter pulp, a natural cellulose obtained from Nippon Paper Pulp Trading Co., Ltd., the linter pulp was immersed in water to a concentration of 1.5% by mass, then simply dispersed using a lab pulper (manufactured by Aikawa Iron Works), and finally transferred to a tank. The slurry was then refined by circulating it through a single disc refiner (only one unit) connected to the tank, which had a disc with a blade width of 4 mm, a groove width of 4.5 mm, and a blade-to-groove ratio of 0.89. At this time, operation was started with a blade-to-blade distance of 1.0 mm, and the blade-to-blade distance was gradually reduced until the final blade-to-blade distance was 0.05 mm. After the blade-to-blade distance reached 0.05 mm, operation was continued while monitoring the flow rate, and the operation was terminated when the entire slurry had passed through the disc section 250 times. Next, the cellulose was subjected to 10 micronization processes at an operating pressure of 100 MPa using a high-pressure homogenizer (NS015H, manufactured by Nilo Soavi, Italy), and the resulting cellulose microfibers were designated as cellulose microfibers K (MFC-K). The results of the analysis of various fiber shape parameters and rheological properties are shown in Table 6.

[0281] (Cellulose microfiber L) Using linter pulp, a natural cellulose obtained from Nippon Paper Pulp Trading Co., Ltd., the linter pulp was immersed in water to a concentration of 1.5% by mass, and after simple dispersion using a lab pulper (manufactured by Aikawa Iron Works), the liquid was sent to a tank. The slurry was then refined by circulating it through a single disc refiner (only one unit) connected to the tank, which had a blade width of 2.5 mm, a groove width of 7.0 mm, and a blade-to-groove ratio of 0.36. At this time, operation was started with a blade distance of 1.0 mm, and the blade distance was gradually reduced until the final blade distance was 0.3 mm. After the blade distance reached 0.3 mm, operation was continued while monitoring the flow rate, and the operation was terminated when the entire slurry had passed through the disc section 90 times. The obtained cellulose fine fibers were designated as microfibrillated cellulose L (MFC-L). The analysis results of various fiber shape parameters and rheological properties are shown in Table 6.

[0282] Manufacturing of fiber-reinforced resins (Example II-1-1) Using MFC-A as the cellulose microfiber, a composite was fabricated by injection molding according to the following procedure. 1. Cellulose microfibers were concentrated by suction filtration (filter medium: TT35 manufactured by Shikishima Canvas Co., Ltd.) to obtain a wet cake with a solid content of approximately 20% by mass. 2. The wet cake was dispersed in hexafluoroisopropanol (hereinafter referred to as HFIP) at a rotation speed of 12,000 rpm for 3 minutes using a homogenizer (manufactured by IKA, product name "Ultra-Turrax T18") to a final concentration of 1 volume%. 3. A solution was prepared by dissolving polyamide 6 (manufactured by Ube Industries, 1013B, melting point 225°C) in HFIP at a concentration of 1% by mass. 4. Combined 2 and 3 in the same container so that the solid content mass ratio of MFC-A and polyamide 6 was 1:9, and mixed at 2,000 rpm for 5 minutes using a rotation / revolution mixer (Sinky Co., Ltd., Awatori Rentaro ARE-310). 5. The mixture from step 4 was cast in a film-like manner onto a release film (manufactured by Mitsui Chemicals Tohcello, X88B) and dried in an 80°C oven for 1 hour. 6.5 was ground using a benchtop grinder (Labonext Mini Speed ​​Mill MS-05). 7.6 The powder was dried in a vacuum dryer for more than 24 hours. 8.7 was kneaded in a small kneader (DSM Xplore MC 15HT) at a temperature of 250°C and a rotation speed of 200 rpm for 2 minutes. 9. After mixing was complete, the mixed product was poured into an injection molding machine (Xplore IM12) to produce a multipurpose test specimen as composite 1-A in accordance with ISO-37.

[0283] Table 6 shows the results of evaluating composite 1-A using the aforementioned tensile tests and dynamic viscoelasticity measurements.

[0284] (Example II-1-2) A composite was prepared in the same manner as in Example II-1-1, except that MFC-B was used as the cellulose microfiber, to obtain composite 1-B. The results of evaluating the obtained composite 1-B by the aforementioned tensile test and dynamic viscoelasticity measurement are shown in Table 6.

[0285] (Example II-1-3) A composite was prepared in the same manner as in Example II-1-1, except that MFC-C was used as the cellulose microfiber, to obtain composite 1-C. The results of evaluating the obtained composite 1-C by the aforementioned tensile test and dynamic viscoelasticity measurement are shown in Table 6.

[0286] (Example II-1-4) A composite was prepared in the same manner as in Example II-1-1, except that MFC-D was used as the cellulose microfiber, to obtain composite 1-D. The results of evaluating the obtained composite 1-D by the aforementioned tensile test and dynamic viscoelasticity measurement are shown in Table 6.

[0287] (Example II-1-5) A composite was prepared in the same manner as in Example II-1-1, except that MFC-E was used as the cellulose microfiber, to obtain composite 1-E. The results of evaluating the obtained composite 1-E by the aforementioned tensile test and dynamic viscoelasticity measurement are shown in Table 6.

[0288] (Example II-1-6) A composite was prepared in the same manner as in Example II-1-1, except that MFC-F was used as the cellulose microfiber, to obtain composite 1-F. The results of evaluating the obtained composite 1-F by the aforementioned tensile test and dynamic viscoelasticity measurement are shown in Table 6.

[0289] (Example II-1-7) A composite was prepared in the same manner as in Example II-1-1, except that MFC-G was used as the cellulose microfiber, to obtain composite 1-G. The results of evaluating the obtained composite 1-G by the aforementioned tensile test and dynamic viscoelasticity measurement are shown in Table 6.

[0290] (Example II-1-8) A composite was prepared in the same manner as in Example II-1-1, except that MFC-H was used as the cellulose microfiber, to obtain composite 1-H. The results of evaluating the obtained composite 1-H by the aforementioned tensile test and dynamic viscoelasticity measurement are shown in Table 6.

[0291] (Example II-1-9) A composite was prepared in the same manner as in Example II-1-1, except that MFC-I was used as the cellulose microfiber, to obtain composite 1-I. The results of evaluating the obtained composite 1-I by the aforementioned tensile test and dynamic viscoelasticity measurement are shown in Table 6.

[0292] (Comparative Example II-1-1) A composite was prepared in the same manner as in Example II-1-1, except that MFC-J was used as the cellulose microfiber, to obtain composite 1-J. The results of evaluating the obtained composite 1-J by the aforementioned tensile test and dynamic viscoelasticity measurement are shown in Table 6.

[0293] (Comparative Example II-1-2) A composite was prepared in the same manner as in Example II-1-1, except that MFC-K was used as the cellulose microfiber, to obtain composite 1-K. The results of evaluating the obtained composite 1-K by the aforementioned tensile test and dynamic viscoelasticity measurement are shown in Table 6.

[0294] (Comparative Example II-1-3) A composite was prepared in the same manner as in Example II-1-1, except that MFC-L was used as the cellulose microfiber, to obtain composite 1-L. The results of evaluating the obtained composite 1-L by the aforementioned tensile test and dynamic viscoelasticity measurement are shown in Table 6.

[0295] (Example II-2-1) Short polypropylene fibers (cut length: 2.0 mm, fineness: 0.2 T, melting point: 160°C) and MFC-A were added to pure water in a solid content mass ratio of 80:20, resulting in a final solid content concentration of 0.5% by mass. The slurry was then stirred in a household mixer for 4 minutes to prepare a papermaking slurry. The prepared papermaking slurry was placed in a batch-type paper machine (Kumagai Riki Kogyo Co., Ltd., automatic square sheet machine, 25cm x 25cm, 80 mesh) with a filter cloth (Shikishima Canvas Co., Ltd. TT35) set up, with a basis weight of 300g / m². 2The material was added in this manner, and then the papermaking (dewatering) process was carried out with a reduced pressure of 50 kPa relative to atmospheric pressure.

[0296] The wet paper, consisting of the concentrated composition in a wet state, which was placed on the resulting filter cloth, was peeled off the wire and measured at 1 kg / cm². 2 It was pressed for 1 minute under pressure. Then, it was dried for approximately 120 seconds in a drum dryer set to a surface temperature of 130°C to obtain a wet nonwoven fabric, nonwoven fabric S1. Four 10cm square pieces of nonwoven fabric were cut from the obtained nonwoven fabric S1 and laminated, and then sandwiched between 0.1μm thick PET films. This was then pressed using a hot press at a temperature of 200°C and a molding pressure of 10kg / cm². 2 The material was pressure-molded for 5 minutes. Here, the thickness of the molded product was controlled by placing 1.5 mm stainless steel spacers between the PET films. Afterward, the heating of the hot press was terminated, and the entire press was slowly cooled with a blower for approximately 30 minutes while maintaining the pressure. When the press temperature fell below 90°C, the pressure was released, and composite 2-A, formed into a plate, was obtained. The results of the bending test performed on the obtained composite 2-A are shown in Table 7.

[0297] (Example II-2-2) A composite was prepared in the same manner as in Example II-2-1, except that MFC-B was used as the cellulose microfiber, to obtain composite 2-B. The results of evaluating the obtained composite 2-B by the bending test described above are shown in Table 7.

[0298] (Example II-2-3) Composite 2-C was obtained by preparing a composite in the same manner as in Example II-2-1, except that MFC-C was used as the cellulose microfiber. The results of evaluating the obtained composite 2-C by the bending test described above are shown in Table 7.

[0299] (Example II-2-4) A composite was prepared in the same manner as in Example II-2-1, except that MFC-D was used as the cellulose microfiber, to obtain composite 2-D. The results of evaluating the obtained composite 2-D by the bending test described above are shown in Table 7.

[0300] (Example II-2-5) A composite was prepared in the same manner as in Example II-2-1, except that MFC-E was used as the cellulose microfiber, to obtain composite 2-E. The results of evaluating the obtained composite 2-E by the bending test described above are shown in Table 7.

[0301] (Example II-2-6) A composite was prepared in the same manner as in Example II-2-1, except that MFC-F was used as the cellulose microfiber, to obtain composite 2-F. The results of evaluating the obtained composite 2-F by the bending test described above are shown in Table 7.

[0302] (Example II-2-7) A composite was prepared in the same manner as in Example II-2-1, except that MFC-G was used as the cellulose microfiber, to obtain composite 2-G. The results of evaluating the obtained composite 2-G by the bending test described above are shown in Table 7.

[0303] (Example II-2-8) A composite was prepared in the same manner as in Example II-2-1, except that MFC-H was used as the cellulose microfiber, to obtain composite 2-H. The results of evaluating the obtained composite 2-H by the bending test described above are shown in Table 7.

[0304] (Example II-2-9) A composite was prepared in the same manner as in Example II-2-1, except that MFC-I was used as the cellulose microfiber, to obtain composite 2-I. The results of evaluating the obtained composite 2-I by the bending test described above are shown in Table 7.

[0305] (Example II-2-10) Using MFC-A as the cellulose microfiber, a composite was fabricated by injection molding according to the following procedure. 1. Short polypropylene fibers (cut length: 2.0 mm, fineness: 0.2 T, melting point: 160°C) were placed on a release film (manufactured by Mitsui Chemicals Tohcello, X88B) and heated in a 200°C oven to melt them. 2. The cooled and solidified material from step 1 was then ground using a benchtop grinder (Labonext Mini Speed ​​Mill MS-05). 3. Cellulose microfibers and rosin ethylene oxide adduct (Harima Chemicals Co., Ltd., rosin-polyethylene glycol ester) were added to a sealed planetary mixer (manufactured by Kodaira Seisakusho Co., Ltd., product name "ACM-5LVT", with hook-shaped stirring blades) in a mass ratio of 80 / 20 for cellulose microfibers / rosin ethylene oxide adduct. The mixture was stirred at 70 rpm for 60 minutes at room temperature and pressure, then the pressure was reduced (-0.1 MPa), and the mixture was placed in a 40°C bath and coated and dried under reduced pressure at 307 rpm for 2 hours to obtain powdered cellulose microfiber formulation A. 4. The powders from 2 and 3 were mixed so that the mass ratio of cellulose fine fibers to polypropylene was 20:80, and the mixture was kneaded for 5 minutes at a temperature of 200°C and a rotation speed of 200 rpm using a small kneader (DSM Xplore MC 15HT). 5. After mixing was complete, the mixed product was poured into an injection molding machine (Xplore IM12) to produce rectangular test pieces (10 mm × 75 mm × 4 mm) as composite 2-A2.

[0306] Table 7 shows the results of the evaluation of composite 2-A2 by the bending test described above.

[0307] (Comparative Example II-2-1) A composite was prepared in the same manner as in Example II-2-1, except that MFC-J was used as the cellulose microfiber, to obtain composite 2-J. The results of evaluating the obtained composite 2-J by the bending test described above are shown in Table 7.

[0308] (Comparative Example II-2-2) A composite was prepared in the same manner as in Example II-2-1, except that MFC-K was used as the cellulose microfiber, to obtain composite 2-K. The results of evaluating the obtained composite 2-K by the bending test described above are shown in Table 7.

[0309] (Comparative Example II-2-3) A composite was prepared in the same manner as in Example II-2-1, except that MFC-L was used as the cellulose microfiber, to obtain composite 2-L. ​​The results of evaluating the obtained composite 2-L by the bending test described above are shown in Table 7.

[0310] (Comparative Example II-2-4) The composite was prepared in the same manner as in Example II-2-10, except that MFC-J was used as the cellulose microfiber. The resulting composite was designated Composite 2-J2, and the results of the bending test described above are shown in Table 7.

[0311] [Table 6]

[0312] [Table 7]

[0313] As is clear from Tables 6 and 7, the composites obtained in Examples II-1-1 to II-1-9 and Examples II-2-1 to II-2-10 exhibit excellent properties in strength, modulus of elasticity, and fracture strain, regardless of the composite molding method. On the other hand, the composites obtained in Comparative Examples II-1-1 to II-1-3 and Comparative Examples II-2-1 to II-2-4 do not exhibit excellent properties in at least one of the following areas: strength, modulus of elasticity, and fracture strain. This is thought to be due to the following factors: excessive refinement occurred in cellulose microfibers J due to a large number of passes in the disc refiner (subsequent stage); excessive refinement and excessive fibrillation occurred in cellulose microfibers K due to beating at high viscosity and processing in a high-pressure homogenizer; and insufficient refinement occurred in cellulose microfibers L due to a wide gap between the blades of the disc refiner and a small number of passes. [Industrial applicability]

[0314] The cellulose microfibers of the present invention, when compounded with resin, provide a fiber-reinforced resin with excellent elastic modulus, strength, and fracture strain, making them suitable for use as a reinforcing material for resins used in automobiles, housing, home appliances, construction, and the like. [Explanation of Symbols]

[0315] 11 blades 12 grooves 21 rotary blades 22 Fixed blade W B Blade width W G Groove width W L Distance between blades

Claims

1. A powder of cellulose microfibers, wherein the cellulose microfibers, in the measurement by a fiber shape automatic analyzer, (i) the length-weighted average fiber length of fibers with a fiber length of 100 μm or more is 110 μm or more and 500 μm or less, (ii) the fine fiber area ratio is 90% or less, (iii) among the fibers with a fiber length of less than 100 μm, the number frequency of fibers having a fiber length of 20 μm or more and 56 μm or less is 97% or less, and (iv) the average fiber diameter in terms of specific surface area is 20 to 150 nm, and all of the above are satisfied, a powder.

2. The powder according to Claim 1, wherein the average fiber length of the cellulose microfibers is 110 μm or more and 500 μm or less.

3. The powder according to Claim 1, comprising a dispersant.

4. The powder according to Claim 1, wherein in the measurement by the fiber shape automatic analyzer, the average fiber diameter of the cellulose microfibers is 42.5 μm or less.

5. The powder according to Claim 1, wherein in the measurement by the fiber shape automatic analyzer, the number frequency of fibers having a fiber length of 411 μm or more among the fibers with a fiber length of 100 μm or more of the cellulose microfibers is 54% or less.

6. The cellulose microfibers, in the measurement by a fiber shape automatic analyzer, (i) the average fiber length is 130 μm or more and 350 μm or less, (ii) the average fiber diameter is 35 μm or less, (iii) the fine fiber area ratio is 75% or less, (iv) among the fibers with a fiber length of less than 100 μm, the number frequency of fibers having a fiber length of 20 μm or more and 56 μm or less is 75% or less, (v) among the fibers with a fiber length of 100 μm or more, the number frequency of fibers having a fiber length of 411 μm or more is 30% or less, and (vi) the fibrillation rate is 5% or less, and all of the above are satisfied, the powder according to Claim 1.

7. The powder according to Claim 1, wherein the glucose content in the constituent sugar analysis of the cellulose microfibers is 90% by mass or more.

8. In the scanning electron microscope (SEM) image of the surface of a sample obtained by casting and drying a 5 mass ppm DMSO dispersion of cellulose microfibrils, the ratio of the total occupied area of ultramicrofibrils with an occupied area of less than 15 μm 2 to the total area occupied by cellulose microfibrils is 10% or more and 80% or less. The powder according to claim 1.

9. The powder according to Claim 1, wherein the cellulose microfibers have a crystalline structure of cellulose type I.

10. The powder according to Claim 1, wherein the crystallinity of the cellulose microfibers is 60% or more.

11. The powder according to Claim 1, wherein the halogen content of the cellulose microfibers is 250 ppm by mass or less.

12. The powder according to Claim 1, wherein the whiteness of the cellulose microfibers is 50% or more.

13. The powder according to claim 1, wherein the length-weighted average fiber length of the fibers having a fiber length of 100 μm or more of the cellulose microfibers is 130 μm or more and 350 μm or less.

14. The powder according to claim 1, wherein the number frequency of the fibers having a fiber length of 411 μm or more among the fibers having a fiber length of 100 μm or more of the cellulose microfibers is 30% or less.

15. The powder according to claim 1, wherein the fine fiber area ratio of the cellulose microfibers is 75% or less.

16. The powder according to claim 1, wherein the number frequency of the fibers having a fiber length of 20 μm or more and 56 μm or less among the fibers having a fiber length of less than 100 μm of the cellulose microfibers is 30% or more and 75% or less.

17. The powder according to claim 1, wherein the fibrillation rate of the cellulose microfibers is 5% or less.

18. The cellulose microfibers in the measurement by the fiber shape automatic analyzer (iv) the number frequency of the fibers having a fiber length of 20 μm or more and 56 μm or less among the fibers having a fiber length of less than 100 μm is 30% or more and 97% or less, and (vi) the fibrillation rate is 5% or less, The powder according to claim 1, further satisfying the above conditions.

19. A method for producing the powder according to any one of claims 1 to 18, wherein the halogen content of the cellulose microfibers is 250 mass ppm or less, and the method includes a step of defibrating a cellulose raw material having a halogen content of 300 mass ppm or less.

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