cellulose particles

Abstract

To provide: cellulose particles which are light in weight and have improved re-dispersibility in water-based liquids; and a dispersion of cellulose particles.SOLUTION: Cellulose particles comprise at least 50 mass% of microfibrous cellulose having an average fiber diameter of 1,000 nm or less and have a tap bulk density of 0.1-200 mg / cm3 and an average particle diameter of 0.1-1,000 μm. There is also provided a dispersion of cellulose particles.SELECTED DRAWING: Figure 2

Description

[Technical Field]

[0001] The present invention relates to cellulose particles to It is related to. [Background technology]

[0002] Fine fibrous cellulose, obtained by micronizing cellulose fibers, has a low environmental impact and has recently been the subject of research into its applications in various fields, with potential applications in fields such as plastic materials, cosmetics, clothing, and construction.

[0003] Fine fibrous cellulose is generally used in an aqueous dispersion with a concentration of 5% by mass or less, and when dried, it has the property of agglomerating and forming particles depending on the storage conditions. Once granulated, fine fibrous cellulose maintains its particulate state even when added to water, and it is difficult for the particles to be easily redispersed by breaking down the agglomerates.

[0004] In this regard, there are several technologies that focus on the dispersibility of fine fibrous cellulose, and one example is disclosed in Patent Document 1. Patent Document 1 discloses a technology in which the problem to be solved by the invention is to provide a powdered nanofiber that can improve dispersibility in a matrix component such as a resin, and the means for solving the problem is a powdered nanofiber blended with a dispersant, where the dispersant is at least one type selected from the group consisting of a P-OH group, a -COOH group, a -SOH group, and / or a metal base thereof, and an imidazoline group.

[0005] Furthermore, Patent Document 2, which discloses related technology, aims to solve the problem of the invention by providing cellulose particles that are small in diameter, maintain flexibility, and reduce skin irritation, and the solution is cellulose particles that have an average particle size D50 of 1 μm or more and 50 μm or less, a bulk density of 0.30 g / mL or less, a specific volume of 3.0 mL / g or more, and a linseed oil absorption of 100 mL / 100 g or more.

[0006] However, the technology disclosed in Patent Document 1 aims to improve the dispersibility of powdered nanofibers in a matrix component that is a solid component such as a resin, and does not disclose any knowledge regarding whether the powdered nanofibers will break down and be well dispersed and mixed when the matrix component is an aqueous liquid.

[0007] Furthermore, although the technology disclosed in Patent Document 2 envisages the use of cellulose particles as an additive in makeup products, it does not disclose what matrix component to use, and therefore does not disclose knowledge regarding dispersibility in aqueous liquids. Furthermore, Patent Document 3 is a technology related to porous cellulose particles with high sphericity, and is not closely related to the problem of the present invention. [Prior art documents] [Patent documents]

[0008] [Patent Document 1] Japanese Patent Application Publication No. 2017-210596 [Patent Document 2] Japanese Patent Application Publication No. 2019-206662 [Patent Document 3] JP 2020-50840 A Summary of the Invention [Problem to be solved by the invention]

[0009] The present invention has been made in view of the above circumstances, and an object of the present invention is to provide cellulose particles and a cellulose particle dispersion that have improved redispersibility in aqueous liquids. [Means for solving the problem]

[0010] The above problem is solved by the following aspects. (First aspect) The average fiber diameter is 1000 nm or less Fine fibrous cellulose They aggregate with each other, improving redispersibility in aqueous liquids. Cellulose particles, The cellulose particles contain 50% by mass or more of the fine fibrous cellulose and have a packed bulk density of 0.1 to 200 mg / cm3 , average particle size 0.1 to 1000 μm, specific surface area 20 to 5000 m 2 / g, Cellulose particles characterized by:

[0011] The cellulose particles of the above embodiment contain 50% by mass or more of fine fibrous cellulose having an average fiber diameter of 1000 nm or less, and are composed of relatively fine cellulose fibers that are aggregated together as the main component. 3 The cellulose particles are relatively large, lightweight, and bulky, and it is presumed that when dispersed in an aqueous dispersion medium, the fibers constituting the cellulose particles partially unravel, resulting in a physically dispersed state. Therefore, the cellulose particles are unlikely to precipitate even when redispersed in an aqueous liquid. [Effects of the Invention]

[0012] According to the present invention, cellulose particles having light weight and improved redispersibility in aqueous liquids are provided. and become. [Brief explanation of the drawings]

[0013] [Figure 1] FIG. 1 is an explanatory diagram of a spray-freeze granulation device. [Figure 2] 1 is an SEM image of cellulose particles. [Figure 3] 1 is an SEM image of cellulose particles. [Figure 4] 1 is an SEM image of cellulose particles. [Figure 5] 1 is an SEM image of cellulose particles. [Figure 6] FIG. 2 is a cross-sectional view of FIG. 1 taken along the line Z-Z. [Figure 7] FIG. 10 is a diagram showing the results of a redispersion test. [Figure 8] 1 is an SEM image of particles of Comparative Example 1. [Figure 9] FIG. 10 is a side view of a dryer according to another embodiment. [Figure 10] FIG. 10 is a view of the dryer of FIG. 9 as seen from the Y direction. DETAILED DESCRIPTION OF THE INVENTION

[0014] DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The following describes an embodiment of the present invention. The present embodiment is merely an example of the present invention. The scope of the present invention is not limited to the scope of the present embodiment.

[0015] The cellulose particles according to the present invention contain 50% by mass or more of fine fibrous cellulose having an average fiber diameter of 1000 nm or less, and have a packed bulk density of 0.1 to 200 mg / cm. 3 and an average particle size of 0.1 to 1000 μm. Before explaining the cellulose particles, the fine fibrous cellulose that is the raw material for the cellulose particles will be explained.

[0016] (fine fibrous cellulose) Fine fibrous cellulose can be obtained by defibrating (refining) raw material pulp, and can be produced by known processing methods such as chemical processing and mechanical processing.

[0017] As the raw material pulp for fine fibrous cellulose, one or more of the following can be selected and used: wood pulp made from hardwoods, softwoods, etc.; non-wood pulp made from straw, bagasse, cotton, hemp, bast fibers, etc.; and deionized paper pulp (DIP) made from waste brown paper, waste envelopes, waste magazines, waste flyers, waste cardboard, white waste paper, imitation waste paper, reclaimed waste paper, recycled waste paper, and broke paper. The above-mentioned raw materials may also be in the form of a pulverized material, such as cellulose powder. In recent years, there has been an increasing demand for products containing organic ingredients that are environmentally friendly. Therefore, wood pulp made from hardwoods or softwoods derived from plants other than waste paper is particularly suitable.

[0018] The wood pulp can be one or more selected from chemical pulps such as hardwood kraft pulp (LKP), softwood kraft pulp (NKP), sulfite pulp (SP), dissolving pulp (DP), etc., and mechanical pulp (TMP). In particular, chemical pulps such as hardwood kraft pulp (LKP) and softwood kraft pulp (NKP), which are wood pulps that increase the cellulose content, are preferred, and bleached pulp (BKP) is also suitable.

[0019] As the mechanical pulp, for example, one or more types can be selected and used from stone ground pulp (SGP), pressurized stone ground pulp (PGW), refiner ground pulp (RGP), chemi-ground pulp (CGP), thermo-ground pulp (TGP), ground pulp (GP), thermo-mechanical pulp (TMP), chemi-thermomechanical pulp (CTMP), refiner mechanical pulp (RMP), bleached thermo-mechanical pulp (BTMP), etc.

[0020] From the viewpoint of producing fine fibrous cellulose having a relatively small average fiber diameter, it is preferable to use kraft pulp, which is easy to defibrate and has high dispersibility. In particular, when applying to white products (e.g., emulsions, gels), it is convenient if the fine fibrous cellulose itself is white, and from the viewpoint of improving the high whiteness, it is more preferable to use LBKP and NBKP.

[0021] The fine fibrous cellulose may be subjected to a pretreatment prior to defibration. For example, the pretreatment may involve mechanically pre-beating the raw pulp or chemically modifying the raw pulp. The pre-beating method is not particularly limited, and known methods can be used.

[0022] Examples of chemical pretreatments of raw pulp include hydrolysis of polysaccharides with an acid (e.g., sulfuric acid, etc.) (acid treatment), hydrolysis of polysaccharides with an enzyme (enzyme treatment), swelling of polysaccharides with an alkali (alkali treatment), oxidation of polysaccharides with an oxidizing agent (e.g., ozone, etc.) (oxidation treatment), reduction of polysaccharides with a reducing agent (reduction treatment), oxidation with a TEMPO catalyst (oxidation treatment), anionization (anion treatment) or cationization (cation treatment) by phosphate esterification, carbamate conversion, etc.

[0023] Examples of the alkali used in the alkali treatment include sodium hydroxide, lithium hydroxide, potassium hydroxide, aqueous ammonia solution, and organic alkalis such as tetramethylammonium hydroxide, tetraethylammonium hydroxide, tetrabutylammonium hydroxide, and benzyltrimethylammonium hydroxide. From the viewpoint of production costs, it is preferable to use sodium hydroxide.

[0024] By subjecting the fine fibrous cellulose to an enzyme treatment, an acid treatment, or an oxidation treatment, it is possible to lower the water retention of the fine fibrous cellulose, increase the crystallinity, and improve the homogeneity. A low water retention of the fine fibrous cellulose is preferable because it is easier to dehydrate and dry.

[0025] When raw pulp is treated with an enzyme, acid, or oxidation, the amorphous regions of hemicellulose and cellulose contained in the pulp are decomposed, which reduces the energy required for the refining process and improves the uniformity and dispersibility of cellulose fibers. The dispersibility of cellulose fibers contributes to improving the homogeneity of the molded product, for example. However, excessive pretreatment is preferably avoided because it reduces the aspect ratio of the fine fibrous cellulose.

[0026] Examples of fine fibrous cellulose that has been modified by anionization to introduce anionic functional groups include fine fibrous cellulose that has been esterified with phosphorus oxoacid, fine fibrous cellulose that has been carbamate-modified, and fine fibrous cellulose in which the hydroxyl groups of the pyranose rings have been directly oxidized to carboxyl groups.

[0027] Fine fibrous cellulose modified by the introduction of anionic functional groups has relatively high dispersibility, which is presumably due to the localized charge imbalance caused by the anionic functional groups, which easily form hydrogen bonds with water and organic solvents in the dispersion.

[0028] Esterification with phosphorus oxoacid, an example of anionization, of cellulose fibers can reduce the fiber material size, resulting in fine fibrous cellulose with a large aspect ratio, excellent strength, high light transmittance, and high viscosity. Esterification with phosphorus oxoacid can be performed using the method described in JP 2019-199671 A. An example of such a method is modified fine fibrous cellulose, in which hydroxy groups of cellulose fibers are modified to introduce phosphite ester groups.

[0029] Cellulose fibers can be defibrated using the following defibration devices and methods. Defibration can be performed using one or more of the following: homogenizers, such as high-pressure homogenizers and high-pressure homogenizers; grinders, grinders, and other mill-type friction machines; refiners, such as conical refiners and disc refiners; and various bacteria. However, defibration of cellulose fibers is preferably performed using devices and methods that use a water flow, particularly a high-pressure water flow, to refine the fibers. This device and method results in extremely uniform dimensions and uniform dispersion of the resulting fine fibrous cellulose. In contrast, using a grinder that grinds the fibers between rotating grindstones, for example, makes it difficult to uniformly refine the cellulose fibers, and in some cases, there is a risk that some undisintegrated fiber clumps may remain.

[0030] Grinders used to defibrate cellulose fibers include, for example, the Masscolloider manufactured by Masuko Sangyo Co., Ltd. Devices that use high-pressure water flow to pulverize the fibers include, for example, Starburst (registered trademark) manufactured by Sugino Machine Co., Ltd. and Nanovater (registered trademark) manufactured by Yoshida Kikai Kogyo Co., Ltd. High-speed rotary homogenizers used to defibrate cellulose fibers include the Clearmix-11S manufactured by M Technique Co., Ltd.

[0031] The present inventors have found that when cellulose fibers are defibrated using both a method of grinding between rotating grindstones and a method of refining with a high-pressure water jet, and the fibers obtained are observed under a microscope, the fibers obtained using the method of refining with a high-pressure water jet have a more uniform fiber width.

[0032] Defibration using a high-pressure water stream is preferably carried out by pressurizing a cellulose fiber dispersion using a pressure intensifier to, for example, 30 MPa or more, preferably 100 MPa or more, more preferably 150 MPa or more, and particularly preferably 220 MPa or more (high-pressure conditions), spraying it from a nozzle with a pore diameter of 50 μm or more, and then reducing the pressure to, for example, 30 MPa or more, preferably 80 MPa or more, and more preferably 90 MPa or more (reduced-pressure conditions). The pulp fibers are defibrated by the cleavage phenomenon caused by this pressure difference. If the pressure under the high-pressure conditions is low or if the pressure difference from the high-pressure conditions to the reduced-pressure conditions is small, the defibration efficiency decreases, and repeated defibration (spraying from the nozzle) becomes necessary to achieve the desired fiber width.

[0033] As a device for defibrating using a high-pressure water stream, a high-pressure homogenizer is preferably used. A high-pressure homogenizer is a homogenizer capable of ejecting a cellulose fiber slurry at a pressure of, for example, 10 MPa or more, preferably 100 MPa or more. When cellulose fibers are treated with a high-pressure homogenizer, collisions between the cellulose fibers, pressure differences, microcavitation, and the like act to effectively defibrate the cellulose fibers. Therefore, the number of defibration treatments can be reduced, and the production efficiency of fine fibrous cellulose can be improved.

[0034] The high-pressure homogenizer used is preferably one that causes cellulose fiber slurry to collide in a straight line against each other. Specifically, for example, a counter-collision type high-pressure homogenizer (MICROFLUIDIZER (registered trademark), wet jet mill) is used. In this device, two upstream flow paths are formed so that the pressurized cellulose fiber slurry collides against each other at the confluence. The cellulose fiber slurry collides at the confluence, and the collided cellulose fiber slurry flows out from the downstream flow path. The downstream flow path is arranged perpendicular to the upstream flow path, and the upstream and downstream flow paths form a T-shaped flow path. When such a counter-collision type high-pressure homogenizer is used, the energy applied from the high-pressure homogenizer is converted to collision energy to the maximum extent possible, allowing for more efficient defibration of cellulose fibers.

[0035] The fine fibrous cellulose obtained by defibration can be dispersed in an aqueous medium to form a dispersion before mixing with inorganic fine particles. The aqueous medium is particularly preferably entirely water (aqueous solution). However, the aqueous medium may also contain other liquids, some of which are compatible with water. Examples of other liquids that can be used include lower alcohols having 3 or less carbon atoms.

[0036] In this specification, fine fibrous cellulose in which the hydroxy groups of the cellulose fibers have been substituted (modified) and phosphorus oxo acid ester groups have been introduced is referred to as modified fine fibrous cellulose (hereinafter also referred to as "modified CNF"), and may be distinguished from unmodified fine fibrous cellulose in which the hydroxy groups of the cellulose fibers have not been substituted (hereinafter also referred to as "unmodified CNF"). Therefore, fine fibrous cellulose is a concept that includes both modified fine fibrous cellulose and unmodified fine fibrous cellulose.

[0037] The fine fibrous cellulose forming the cellulose particles of this embodiment may consist of only unmodified fine fibrous cellulose, may consist of only modified fine fibrous cellulose, or may contain both unmodified and unmodified fine fibrous cellulose.

[0038] When the cellulose particles are formed from modified fine fibrous cellulose, the dispersion obtained by dispersing the cellulose particles in a dispersion medium exhibits a transparent color. On the other hand, when the cellulose particles are formed from unmodified fine fibrous cellulose, the dispersion obtained by dispersing the cellulose particles in a dispersion medium exhibits a white color. By adjusting the ratio of modified fine fibrous cellulose to unmodified fine fibrous cellulose in the fine fibrous cellulose that forms the cellulose particles, a dispersion having a color intermediate between white and transparent can be produced. To produce this dispersion, for example, when producing cellulose particles as the dispersoid of the dispersion, it is preferable to use a mixture of modified fine fibrous cellulose and unmodified fine fibrous cellulose as the fine fibrous cellulose that is the raw material for the cellulose particles.

[0039] The cellulose particles are in the form of a white powder whether the raw material is modified or unmodified fine fibrous cellulose. Since modified fine fibrous cellulose has a smaller average fiber diameter than unmodified fine fibrous cellulose, when compared with cellulose particles of the same mass, cellulose particles formed from modified fine fibrous cellulose tend to have a larger specific surface area than cellulose particles formed from unmodified fine fibrous cellulose.

[0040] The raw material pulp is preferably defibrated so that the physical properties of the resulting fine fibrous cellulose have the desired values ​​or evaluations as shown below.

[0041] <Average fiber diameter> The upper limit of the average fiber diameter (average fiber width; average diameter of a single fiber) of fine fibrous cellulose is 1000 nm or less, preferably 500 nm or less, more preferably 100 nm or less, and particularly preferably 50 nm or less. If the average fiber diameter of fine fibrous cellulose exceeds 1000 nm, the formed cellulose particles will have a relatively small specific surface area, i.e., will have a poor porous shape. On the other hand, there is no particular lower limit for the average fiber diameter of fine fibrous cellulose.

[0042] The average fiber diameter of the fine fibrous cellulose can be adjusted, for example, by selecting the raw material pulp, pre-treating it, defibrating it, etc.

[0043] The average fiber diameter of the fine fibrous cellulose is measured as follows. First, 100 ml of an aqueous dispersion of fine fibrous cellulose with a solid content of 0.01 to 0.1% by mass was filtered through a Teflon® membrane filter and solvent-substituted once with 100 ml of ethanol and three times with 20 ml of t-butanol. The sample was then freeze-dried and osmium-coated to obtain a sample. This sample was then observed using an SEM electron microscope at a magnification of 3,000x to 30,000x, depending on the width of the fibers constituting it. Specifically, two diagonal lines were drawn on the observed image, and three straight lines were arbitrarily drawn passing through the intersections of the diagonal lines. The widths of a total of 100 fibers intersecting with these three straight lines were then visually measured. The median diameter of the measured values ​​was then taken as the average fiber diameter.

[0044] <Average fiber length> The average fiber length of the fine fibrous cellulose (average length of single fibers) is, for example, preferably 0.01 to 1000 μm, more preferably 0.05 to 500 μm. If the average fiber length exceeds 1000 μm, the fibers will become intricately entangled with each other when the fine fibrous cellulose is dried, making it easier for other substances to be supported, and the intricate entanglement will make it difficult for the particles to disintegrate when redispersed.

[0045] The average fiber length can be adjusted as desired by, for example, selecting the raw pulp, pre-treating it, defibrating it, and the like.

[0046] The average fiber length of the fine fibrous cellulose is measured in the same manner as in the case of the average fiber diameter, by visually measuring the length of each fiber. The median length of the measured values ​​is taken as the average fiber length.

[0047] <Axle ratio> The axial ratio of the fine fibrous cellulose (average fiber length / average fiber width) is preferably 10 to 1,000,000, more preferably 50 to 500,000, and particularly preferably 100 to 100,000. If the axial ratio of the fine fibrous cellulose is less than 10, the cellulose component is almost in a particulate form, making it difficult to form cellulose particles. On the other hand, if the axial ratio exceeds 1,000,000, the degree of entanglement between the fibers becomes too great, making it difficult to obtain cellulose particles with the desired average particle size.

[0048] <Crystallinity> The lower limit of the crystallinity of the fine fibrous cellulose is preferably 50 or more, more preferably 60 or more, and particularly preferably 65 or more, and the upper limit is preferably 100 or less, more preferably 95 or less, and particularly preferably 90 or less. If the crystallinity is less than 50, the entanglement of the fibers will be weak due to the influence of temperature changes during drying, and the ability to retain other substances will be weak, making it difficult to form cellulose particles of the desired particle size.

[0049] The crystallinity is a value measured by X-ray diffraction in accordance with JIS-K0131 (1996) "General rules for X-ray diffraction analysis." Note that fine fibrous cellulose has an amorphous portion and a crystalline portion, and the crystallinity refers to the proportion of the crystalline portion in the entire fine fibrous cellulose.

[0050] <Pseudo particle size distribution> The pseudo particle size distribution curve of the fine fibrous cellulose preferably has one peak. When there is one peak, the fine fibrous cellulose has high uniformity in fiber length and fiber diameter, and the fine fibrous cellulose easily becomes entangled with each other during the production of cellulose particles, so that the produced cellulose particles are difficult to unravel even when redispersed. Furthermore, the cellulose particles have small particle size variations. If the cellulose particles are in the form of inorganic fine particles supported thereon, the cellulose particles will be sufficiently dispersed in the cosmetic when incorporated as one component of the cosmetic.

[0051] The peak value of the fine fibrous cellulose is measured in accordance with ISO-13320 (2009). More specifically, a particle size distribution measuring device (Seishin Enterprise Co., Ltd.'s laser diffraction / scattering particle size distribution measuring device) is used to examine the volumetric particle size distribution of an aqueous dispersion of the fine fibrous cellulose. The mode diameter of the fine fibrous cellulose is then measured from this distribution. This mode diameter is taken as the peak value. It is preferable that the fine fibrous cellulose has a single peak in the pseudo-particle size distribution curve measured by laser diffraction in an aqueous dispersion state. Fine fibrous cellulose having a single peak is thus preferred because it has undergone sufficient micronization and can exhibit good physical properties as fine fibrous cellulose. The peak value of the pseudo-particle size distribution of the particle size of the fine fibrous cellulose having the single peak is, for example, preferably 300 μm or less, more preferably 200 μm or less, and particularly preferably 100 μm or less. If the peak value exceeds 300 μm, there will be a large number of relatively large fibers, the particle size of the cellulose particles will vary greatly, and the cellulose particle shape will tend to be non-uniform.

[0052] The peak value of the particle size of the fine fibrous cellulose and the median diameter of the pseudo-particle size distribution can be adjusted, for example, by selecting the raw material pulp, pre-treating it, defibrating it, etc.

[0053] <Water retention> The water retention of the fine fibrous cellulose is not particularly limited, but for example, for unmodified fine fibrous cellulose, it is 500% or less, more preferably 100 to 500%. If the water retention exceeds 500%, the fine fibrous cellulose itself has high water retention and poor dehydration, so even if it is produced through a drying process, the drying time becomes long and productivity decreases. The lower limit of the water retention of the fine fibrous cellulose is not particularly limited, but a value of 100% or more is preferable because it improves the dispersibility of the fine fibrous cellulose.

[0054] The water retention of the fine fibrous cellulose can be adjusted as desired by, for example, selecting the raw material pulp, pre-treating it, defibrating it, etc.

[0055] The water retention of the fine fibrous cellulose is a value measured in accordance with JAPAN TAPPI No. 26 (2000).

[0056] <Pulp viscosity> The pulp viscosity of the defibrated fine fibrous cellulose is 1 to 10 cps, more preferably 2 to 9 cps, and particularly preferably 3 to 8 cps. Pulp viscosity is the viscosity of the solution obtained by dissolving cellulose in a copper ethylenediamine solution. A higher pulp viscosity indicates a higher degree of polymerization of cellulose, which also affects the strength of the fiber itself.

[0057] (additives) Additives can be added to improve the dispersibility of cellulose particles produced through the drying process in a solvent. The additives can be added to the fine fibrous cellulose before freezing and mixed uniformly. One or more additives selected from the group consisting of polyhydric alcohols, polysaccharides, and water-soluble polymers can be used. The additive blend ratio (additive:fine fibrous cellulose) is 1:99 to 50:50, preferably 50:50, based on solids. If the blend ratio of additives to fine fibrous cellulose is too high, the dried product (cellulose particles) will be sticky, losing the lightweight feel of the cellulose particles of the present invention and making them difficult to handle. On the other hand, if the blend ratio is too low, the dispersion effect in the target solvent may be impaired.

[0058] As the additive, polyhydric alcohols such as glycerin, propylene glycol, butylene glycol, pentanediol, dipropylene glycol, hexanediol, and heptanediol can be used, but are not limited to these. Glycerin is particularly preferred from the viewpoint of thickening properties and dispersibility of composite particles.

[0059] Examples of polysaccharides that can be used include, but are not limited to, quince seeds, veegum, xanthan gum, and hyaluronates. Hyaluronates are particularly preferred in terms of thickening properties and dispersibility of cellulose particles.

[0060] Examples of water-soluble polymers include, but are not limited to, polyvinyl alcohol, polyvinylpyrrolidone, carboxyvinyl polymer, and polyethylene glycol. In particular, polyvinylpyrrolidone is preferred from the viewpoint of viscosity-increasing properties and dispersibility of cellulose particles.

[0061] (Inorganic fine particles) The cellulose particles may contain inorganic fine particles. Inorganic fine particles can impart various functions to the cellulose particles. For example, metallic inorganic fine particles have the effect of diffusely reflecting incident light. Therefore, by incorporating inorganic fine particles into the cellulose particles, the cellulose particles can be imparted with the effect of diffusely reflecting light. For example, by using cellulose particles containing inorganic fine particles as one component of a cosmetic, the cosmetic can be made to have the effect of suppressing the transmission of sunlight. By applying a cosmetic having the effect of suppressing the transmission of sunlight to the skin, a sunscreen effect can be achieved.

[0062] The content of inorganic fine particles in cellulose particles may be set at an upper limit of 50% by mass, preferably 45% by mass or less, and at a lower limit of 0% by mass, preferably 5% by mass or more. If the content exceeds 50% by mass, the ratio of inorganic fine particles to fine fibrous cellulose becomes large, the specific gravity of the cellulose particles becomes large, and there is a risk that high redispersibility in the dispersion medium will be impaired. On the other hand, if the content is 5% by mass or more, the effect of suppressing sunlight transmission is sufficiently exhibited.

[0063] The upper limit of the primary particle diameter of the inorganic fine particles may be 10 μm, preferably 5 μm or less, and more preferably 1 μm or less. If the primary particle diameter of the inorganic fine particles exceeds 10 μm, the inorganic fine particles are difficult to support by the fine fibrous cellulose. Furthermore, the surface area of ​​the cellulose particles is not sufficiently large. The lower limit of the inorganic fine particles is not particularly limited, but may be 1 nm, preferably 2 nm or more, and more preferably 3 nm or more. If the primary particle diameter of the inorganic fine particles is 1 nm or more, when the inorganic fine particles are mixed with a slurry of the fine fibrous cellulose, the inorganic fine particles tend to disperse and cling to the fine fibrous cellulose.

[0064] The primary particle diameter of the inorganic fine particles can be measured by observation under an electron microscope, and the average value of the obtained particle diameters is taken as the measured value.

[0065] Although inorganic fine particles can be used as they are, hydrophilic treatment is preferred because it makes them more compatible with aqueous dispersions of fine fibrous cellulose. The surface treatment agent used for hydrophilic treatment has the effect of suppressing the surface activity of the inorganic fine particles, improving the dispersibility of the inorganic fine particles, and improving transparency and squeaking. The surface treatment agent for inorganic fine particles is not particularly limited as long as it is a treatment agent that can be dispersed in aqueous dispersions of fine fibrous cellulose, but those containing silicic anhydride or hydrated silicic acid are preferred.

[0066] The inorganic fine particles are not particularly limited, and known inorganic fine particles can be used, including, for example, barium titanate, lead zirconate titanate, silicon carbide, silicon nitride, aluminum nitride, alumina, zirconia, zircon, titanium oxide, zinc oxide, iron oxide, and cerium oxide. Cellulose particles containing these powders and fine fibrous cellulose are preferred because they have excellent redispersibility in liquids. From the perspective of suppressing sunlight transmission, for example, one or a combination of two or more selected from the group consisting of titanium oxide, zinc oxide, iron oxide, and cerium oxide can be used. In particular, when the inorganic fine particles are titanium oxide, rutile type particles are preferred because they improve the suppression of sunlight transmission in the cosmetic composition.

[0067] The shape of the inorganic fine particles that can be contained in the cellulose particles is not particularly limited, but can be, for example, spherical, rod-like, needle-like, spindle-like, plate-like, polygonal, or the like.

[0068] The inorganic fine particles may be attached to the surface of the fine fibrous cellulose in the cellulose particles, or may be encapsulated in the fine fibrous cellulose. When the inorganic fine particles are encapsulated in the fine fibrous cellulose, the cellulose particles can support the inorganic fine particles not only on the surface but also inside, resulting in excellent transmission suppression against sunlight irradiation from various angles. Here, encapsulation can refer to a state in which a portion of the surface of the inorganic fine particles is covered with the fine fibrous cellulose, or a state in which the inorganic fine particles cannot be observed when the cellulose particles are observed from the outside because they are covered with the fine fibrous cellulose.

[0069] The inorganic particles can be added to the fine fibrous cellulose before freezing and mixed uniformly.

[0070] (cellulose particles) The cellulose particles according to this embodiment preferably contain 50% by mass or more, more preferably 60% by mass or more, and even more preferably 70% by mass or more of fine fibrous cellulose, with the upper limit being 100% by mass. If the mass percentage of fine fibrous cellulose in the cellulose particles is less than 50% by mass, the desired bulk density and specific surface area of ​​the cellulose particles of the present invention may not be obtained.

[0071] The cellulose particles according to this embodiment preferably have a packed bulk density of 0.1 to 200 mg / cm 3 and the average particle size is in the range of 0.1 to 1000 μm, and more preferably the packed bulk density is in the range of 0.1 to 150 mg / cm 3 and the average particle size is in the range of 0.1 to 700 μm, and more preferably the packed bulk density is in the range of 0.1 to 100 mg / cm 3 The packed bulk density and the average particle size are factors that are strongly related to redispersibility, and for example, even if the average particle size is 1000 μm, which is the upper limit of the above range, the packed bulk density may be 200 mg / cm, which is the upper limit of the above range. 3 If the average particle size exceeds 1000 μm, the upper limit of the above range, the packed bulk density will be 0.1 mg / cm3, which is the lower limit of the above range. 3 If the density falls below this level, the cellulose particles will become ultra-lightweight and porous, but they will not be able to maintain their shape in the air for long periods of time and will tend to disintegrate, making them very difficult to handle.

[0072] The average particle size of cellulose particles was measured using a measuring device conforming to ISO-13320 (2009), specifically the laser diffraction / scattering particle size distribution measuring device (particle size distribution) "LA-960V2," using a dry method without removing the moisture adhering to the cellulose particles.

[0073] (specific surface area) The specific surface area of ​​the cellulose particles is preferably 20 m 2 / g or more, more preferably 30m 2 / g or more, more preferably 40m 2 / g or more, and the upper limit of the specific surface area is not particularly limited, but is 5000 m 2 / g. The specific surface area is 20m 2 If the specific surface area is less than 5000 m / g, the contact area between the cellulose particles and the dispersion medium is small when the cellulose particles are placed in the dispersion medium, making them difficult to adapt to each other and resulting in poor redispersibility. 2 A particle density exceeding 1 / g is preferable in terms of reducing particle weight and redispersibility, but is very difficult to produce.

[0074] The specific surface area was measured by the BET method. Specifically, the measurement was performed using a Quantachrome Instruments NOVA4200e measuring instrument, using the nitrogen gas adsorption method. The test method complies with JIS Z8830:2013.

[0075] (viscosity) Cellulose particles have many hydrogen bonding points in the cellulose fibers, and when mixed with a dispersion medium that has affinity for cellulose particles (such as water or an organic solvent), they disperse to form a dispersion liquid. The dispersed cellulose particles lose their degree of freedom as the polar groups in the cellulose particles themselves bond with other cellulose particles through hydrogen bonds or the like, resulting in a viscous liquid.

[0076] In a dispersion, cellulose particles are dispersed and bonded to each other through hydrogen bonds and other factors, giving the dispersion viscosity. When shear force is applied to the dispersion, the hydrogen bonds weaken and the viscosity decreases. This gives the cellulose particles thixotropy. The viscosity varies depending on the concentration of cellulose particles in the dispersion and the raw material of the cellulose particles.

[0077] When a dispersion containing 2% by mass of cellulose particles (note that in this specification, the dispersion medium when measuring B-type viscosity is water) is measured under conditions of 25°C and 6 rpm, the B-type viscosity should be 1000 cps or more, preferably 1000 to 30,000 cps, and more preferably 1500 to 20,000 cps. If the B-type viscosity is less than 1000 cps, re-dispersibility in the dispersion medium may be poor. When a dispersion containing 2% by mass of cellulose particles is measured under conditions of 25°C and 60 rpm, the B-type viscosity should be 100 cps or more, preferably 100 to 10,000 cps, and more preferably 200 to 9,000 cps. If the B-type viscosity is less than 100 cps, the ratio to the B-type viscosity at 6 rpm is small, and re-dispersibility in the dispersion medium may be poor.

[0078] The Ti value at 25°C of a dispersion containing 2% by mass of cellulose particles should be 2 or greater, preferably 3 or greater, and more preferably 4 or greater. The Ti value indicates the property of decreasing viscosity when subjected to shear stress (pseudoplasticity), and the larger the value, the better the spread of a dispersion containing 2% by mass of cellulose particles when applied to the skin, for example. Furthermore, the closer the Ti value of a cellulose particle dispersion is to the Ti value measured when a 2% by mass dispersion of fine fibrous cellulose required to produce the cellulose particles is measured under the same conditions as those used to measure the cellulose particle dispersion (i.e., the Brookfield viscosity of the dispersion at 25°C and 6 rpm and the Brookfield viscosity of the dispersion at 25°C and 60 rpm), the higher the redispersibility can be said to be.

[0079] The Ti value can be calculated using the following formula 1. [Formula 1] (Ti value) = (B-type viscosity of dispersion at 25°C and 6 rpm) / (B-type viscosity of dispersion at 25°C and 60 rpm)

[0080] Here, B-type viscosity was measured in accordance with JIS-Z8803 (2011) "Method for measuring viscosity of liquids." B-type viscosity is the resistance torque when stirring a dispersion, and the higher the viscosity, the more energy is required for stirring.

[0081] The B-type viscosity and Ti value of the dispersion can be adjusted by several factors. For example, the B-type viscosity can be adjusted by changing the properties of the cellulose particles themselves and the concentration of cellulose particles in the dispersion. When the cellulose particles are not modified, a cellulose particle concentration of 1 to 3% by mass in the dispersion exhibits high redispersibility. When the cellulose particles are modified, a cellulose particle concentration of 0.5 to 2.0% by mass in the dispersion exhibits high redispersibility. If the concentration exceeds the above range, the amount of cellulose particles in the dispersion will be too high, resulting in an extremely high B-type viscosity. If the concentration is below the above range, the amount of cellulose particles will be too low, resulting in a viscosity similar to that of water.

[0082] When either fine fibrous cellulose or cellulose particles are dispersed in water to form a dispersion, the dispersion has a certain B-type viscosity. If the B-type viscosity of the fine fibrous cellulose dispersion is V0 and the B-type viscosity of a dispersion of cellulose particles produced using the fine fibrous cellulose as a raw material (i.e., a cellulose particle dispersion) is V1, the viscosity change rate PV can be expressed by the following equation: PV(%)=(V1 / V0)×100 The B-type viscosity of the dispersion varies depending on whether the fine fibrous cellulose is modified or unmodified. Therefore, when the fine fibrous cellulose is unmodified, the fine fibrous cellulose concentration (or cellulose particle concentration) in the dispersion should be set to 2% by mass, and when the fine fibrous cellulose is modified, the fine fibrous cellulose concentration (or cellulose particle concentration) in the dispersion should be set to 0.5% by mass.

[0083] The viscosity change rate PV varies depending on the rotation speed when measuring the B-type viscosity, and for the fine fibrous cellulose and cellulose particles of this embodiment, the viscosity change rate PV at a rotation speed of 6 rpm is preferably 30% or more, more preferably 40% or more. If the viscosity change rate PV is less than 30%, the cellulose particles will have a high solidity and will lack a lightweight feel. Furthermore, for the fine fibrous cellulose and cellulose particles of this embodiment, when the rotation speed is 60 rpm, the viscosity change rate PV is preferably 40% or more, more preferably 45% or more.

[0084] (moisture content) The moisture content of the cellulose granules is preferably 50% or less, more preferably 40%, and even more preferably 30% or less. If the moisture content exceeds 50%, the amount of water adsorbed by the cellulose granules increases, and the lightweight feel is lost.

[0085] (bulk density) The bulk density of the cellulose particles of this embodiment is preferably 0.1 to 200 mg / cm3. 3 , more preferably 0.1 to 150 mg / cm 3 , and more preferably 0.1 to 100 mg / cm 3 The compacted bulk density is 0.1 mg / cm 3 If the packed bulk density is less than 200 mg / cm, the powder will easily disintegrate in the air, resulting in poor handling. 3 If the density exceeds this, the fibers will form strong agglomerates, resulting in poor dispersibility.

[0086] (Compression degree) In addition, the cellulose particles have a packed bulk density of 0.1 to 200 mg / cm as described above. 3The degree of compression is preferably 50% or less, more preferably 45% or less, and even more preferably 40%. Because the cellulose granules of this embodiment are relatively lightweight, the voids are eliminated during the compression process performed to measure the packed bulk density after measuring the loose bulk density (i.e., the voids are eliminated, causing the cellulose granules to be densely packed together inside the container), resulting in little change in the density of the cellulose granules themselves and little collapse of the particle shape. Furthermore, since the cellulose granules are not spherical with excellent sphericity but are uneven granules (although it is difficult to describe), numerous voids of various shapes and sizes are generated when packed into a container. If the degree of compression exceeds 50%, the voids between the particles are filled and the cellulose granules are disintegrated, which may result in a loss of the lightness of the particles. Furthermore, in the case of cellulose granules produced by hot drying, even if the degree of compression is 50%, the bulk density is 200 mg / cm. 3 Above this value, the fibers are tightly agglomerated to form solid particles, so they only fill the gaps between the particles, and the particles themselves do not collapse easily.

[0087] The packed bulk density and loose bulk density are items used to calculate Carr's fluidity index, and were measured in accordance with ASTM D6393-99, a compressibility measurement method, using the "Multitester MT-02 Multifunctional Powder Property Measuring Instrument" (manufactured by Seishin Enterprise Co., Ltd.).

[0088] (Manufacturing) Cellulose particles can be produced by freeze-drying cellulose nanofiber raw materials, vacuum drying, heat drying, spray drying, or the spray-freeze-vacuum drying method of this embodiment, but the spray-freeze-vacuum drying method is particularly preferred because it allows the production of porous cellulose particles. Porous cellulose particles allow other substances to be loaded into the numerous pores formed in the cellulose particles, or the large surface area to be utilized. This allows the cellulose particles to be endowed with properties not found in cellulose.

[0089] The cellulose granules according to the present invention can be produced by freeze-drying, but for example, a spray-type freeze granulation apparatus 1 shown in Fig. 1 is preferred because it can produce particles with a relatively low specific gravity. The spray-type freeze granulation apparatus 1 comprises a freeze granulation tank 8, a spray mechanism 7 that sprays raw material M onto the top of the freeze granulation tank 8, and a drying section 6 that is provided below the freeze granulation tank 8 and dries the frozen cellulose granules. The raw material M sprayed into the freeze granulation tank 8 is instantly frozen in the freeze granulation tank 8 to become a frozen body P. The frozen body P falls naturally into the drying section 6 and is stored therein. The drying section 6 is separably connected to the freeze granulation tank 8, and is separated from the freeze granulation tank 8 when the frozen body P has been stored therein, and is sealed so that the frozen body P can be dried to obtain cellulose granules.

[0090] Examples of raw material M include a slurry or dispersion of fine fibrous cellulose. The fine fibrous cellulose used in raw material M may be fine fibrous cellulose consisting of one group, or a combination of fine fibrous cellulose consisting of two groups. When a combination of fine fibrous cellulose consisting of two groups is used, it may be a mixture of fine fibrous cellulose group C1 having an average particle size R of 11 to 1000 nm and fine fibrous cellulose group C2 having an average particle size R of 1 to 10 nm in a mixing ratio of 1:99 to 99:1.

[0091] The spraying mechanism 7 has a raw material flow path to which the raw material M is supplied, a compressed gas flow path to which the compressed gas A is supplied, and a nozzle 5 (also called a two-fluid nozzle) that sprays a mixed fluid of the supplied raw material M and compressed gas A into the freeze granulation tank 8. Examples of the type of the nozzle 5 include a three-fluid type, a four-fluid type, a pressurized type, an ultrasonic type, and a centrifugal spray type.

[0092] The base end of the raw material flow path is connected to a raw material tank that stores raw material M, and a pump provided in the raw material flow path causes raw material M to flow from the raw material tank to the nozzle 5. The base end of the compressed gas flow path is connected to a compressed gas supply device such as a compressor or a cylinder, and when the compressed gas supply device is started, compressed gas flows into the nozzle 5. Examples of compressed gases include air, nitrogen, and rare gases.

[0093] In addition to the fine fibrous cellulose, raw material M may contain additives, inorganic particles, and the following materials: plasticizers (phthalate esters, citrate esters, etc.), emulsifiers (e.g., nonionic surfactants, anionic surfactants, cationic surfactants, amphoteric surfactants, phospholipids, etc.), and particularly preferred are ester or ester-ether types of nonionic surfactants. Examples of materials that can be added to raw material M include glycerin fatty acid esters, polyglycerin, fatty acid esters, propylene glycol fatty acid esters, sorbitan fatty acid esters, and sorbitol fatty acid esters, as well as alkylene glycol adducts thereof, polyalkylene glycol fatty acid esters, sucrose fatty acid esters, polysorbate 20, polysorbate 60, polysorbate 80, polyoxyalkylene alkyl ethers, and polyoxyethylene alkylphenyl ethers.

[0094] The freeze granulation tank 8 is composed of three tanks, specifically, three cylinders of different diameters arranged concentrically with the same axis in the vertical direction. These three cylinders, from the inside out, are the inner tank wall 2, the middle tank wall 3, and the outer tank wall 4. The inner tank surrounded by the inner tank wall 2 is the freezing tank 12 for freezing the raw material M. The bottomed middle layer surrounded by the inner tank wall 2 and the middle tank wall 3 is the cooling medium-filled tank 13 filled with a cooling medium. The bottomed outer tank surrounded by the outer tank wall 4 and the middle tank wall 3 is the vacuum insulation tank 14 for maintaining a constant temperature inside the tank. The freezing tank 12 is preferably configured so that the lower end of the inner tank wall 2 is detachably connected to a flange 4a formed at the upper end of the drying section 6.

[0095] The freezing tank 12 freezes the raw material M sprayed from a nozzle 5 provided near the top surface to form a frozen body P. The temperature of the freezing tank 12 is preferably kept at -10°C to -200°C by the cooling medium supplied from the cooling medium filling tank 13.

[0096] The cooling medium filled vessel 13 is filled with a cooling medium for cooling the freezing vessel 12. As the cooling medium, for example, liquid nitrogen, liquid argon, liquid helium, dry ice, etc. can be used.

[0097] The vacuum insulation tank 14 is surrounded by an intermediate tank wall 2 and an outer tank wall 4, with the upper ends of the intermediate tank wall 2 and the outer tank wall 4 closed, and the lower ends of the intermediate tank wall 2 and the outer tank wall 4 closed, so that no fluid can flow into the vacuum insulation tank 14 from the outside, a vacuum state is maintained, and heat transfer between the cooling medium filled in the cooling medium filled tank 13 and the outside air is unlikely to occur.

[0098] The cooling medium tank 13 has a cooling medium supply pipe 15 extending from the outside into the cooling medium tank 13, and is configured so that the cooling medium N is supplied into the cooling medium tank 13, and has a cooling medium introduction pipe 16 that introduces the cooling medium gas vaporized from the cooling medium N in the cooling medium tank 13 into the freezing tank 12, and is configured so that the cooling medium gas is introduced into the freezing tank 12.

[0099] The frozen body P formed in the freeze granulation tank 8 is stored in the drying section 6, which is detachably attached to the freeze granulation tank 8. After a predetermined amount of frozen body P has been stored in the drying section 6, the drying section 6 is separated from the freeze granulation tank 8, sealed, and freeze-dried to obtain cellulose particles. The configuration of the dryer 100 according to this embodiment will be described below.

[0100] The dryer 100 has a drying section 6 and a vacuum mechanism. The drying section 6 can have a cylindrical wall with a vertical axis and a bottom continuous with the wall. The cylindrical wall can be provided with an openable and closable exhaust section (not shown), which allows gas inside the drying section 6 to be exhausted as exhaust gas D. The upper edge of the cylindrical wall forms a flange 4a, which is detachably connected to the lower edge of the freeze granulation tank 8. After the frozen body P produced in the freeze granulation tank 8 falls into the drying section 6, the drying section 6 is removed from the freeze granulation tank 8, and the flange 4a is covered with a top lid, which is then sealed, and the frozen body P is freeze-dried.

[0101] The drying process of the frozen body P can be performed as follows. The drying section 6 is configured so that the base end of a gas pipe 21 for evacuation can be connected. The gas sucked into the gas pipe 21 is guided to a cooling trap 22 connected to the tip of the gas pipe 21, where a portion is concentrated and separated as a concentrated liquid or concentrated solid. The remaining gas is sucked by a vacuum pump 24 provided at the other end of a gas pipe 23 connected to the cooling trap 22. When the vacuum pump 24 is started with the drying section 6 sealed, the air pressure inside the drying section 6 decreases, and sublimable or vaporizable substances contained in the frozen body P (e.g., water when the raw material M is a dispersion liquid consisting of water and fine fibrous cellulose) sublimate or vaporize and are sucked into the vacuum pump 24, leaving the remainder as cellulose particles. During the drying process, the drying section 6 may be rocked or vibrated to prevent the frozen bodies P from agglomerating with each other and to dry each frozen body P evenly. The vibration or rocking of the drying section 6 may be performed manually or by providing a vibration or rocking mechanism. When vibrating, for example, the flange portion formed in a substantially circular shape can be gripped at both ends of the diameter (parts indicated by symbols 4a and 4a in FIG. 1) and swung back and forth. When rocking, for example, the diameter can be used as the axis of rotation, and the rotation can be alternately rotated clockwise and counterclockwise. The pivot angle to the clockwise or counterclockwise is not particularly limited, but a value of 30° to 100° is sufficient to rock the frozen body P in the drying section 6. Rocking or vibration is not essential in the drying process; the frozen body P may be vacuum-dried while stationary. Although this cannot be generally stated, rocking or vibration during drying may result in a relatively higher bulk density of the cellulose particles produced.

[0102] A dryer 200 according to another embodiment will be described with reference to Figures 9 and 10. The dryer 200 differs from the dryer 100 shown in Figure 1 described above in that it is provided with a shaft 30 for swinging the drying section 6. By providing a swing mechanism on the shaft 30, the drying section 6 can be configured to rotate, for example, 100° clockwise or counterclockwise as viewed in Figure 10 around the shaft 30.

[0103] Cellulose particles 11 and 12 produced by the above-described production method are shown in Figures 2 to 5. The cellulose particles 11 shown in Figures 2 and 3 were produced using a spray-freeze granulation apparatus 1 and a 2% by mass aqueous dispersion of unmodified fine fibrous cellulose (ELLEX (registered trademark)-S) as the raw material. Numerous pores 11a were observed in the cellulose particles 11. The cellulose particles 11 shown in Figures 4 and 5 were produced using a spray-freeze granulation apparatus 1 and a 2% by mass aqueous dispersion of modified fine fibrous cellulose (ELLEX (registered trademark)-Star) as the raw material. Numerous pores 12a were observed in the cellulose particles 12. The drying process involved vacuum drying in a vacuum dryer ("EYELA FDU-2110" manufactured by Tokyo Rikakikai Co., Ltd.) while the particles were left stationary. An example of the freeze granulation tank 8 is the "Freeze Granulation Chamber CS30" manufactured by Priss, and an example of the dryer 200 is the "TFD-10" barrel freeze drying unit manufactured by Priss. [Example]

[0104] (Adjustment of Test Examples and Comparative Examples) <Test Example 1> Examples are shown below. Test Example 1 was produced as follows. A dispersion of unmodified fine fibrous cellulose (ELLEX (registered trademark)-S, a product of Daio Paper Co., Ltd.) dispersed in water to a concentration of 2% by mass was used as a raw material and supplied to a spray-type freeze granulation device to obtain cellulose particles, which were designated Test Example 1. The average fiber diameter of the fine fibrous cellulose was 50 nm. The raw material was sprayed into the spray-type freeze granulation device and frozen to obtain a frozen body as an intermediate. This frozen body was then vacuum-dried to obtain cellulose particles. The fine fibrous cellulose was frozen using a Priss "Freeze Granulation Chamber CS30," and after obtaining the frozen body, it was dried while shaking using a Priss barrel freeze drying unit "TFD-10" manufactured by Priss until the frozen body was completely dried.

[0105] <Test Example 2> Test Example 2 was produced as follows. Using the same dispersion as used in Test Example 1 as a raw material, fine fibrous cellulose was supplied to a PRIS "Freeze Granulation Chamber CS30" to obtain a frozen body as an intermediate, and this frozen body was vacuum dried to obtain cellulose particles, which were used as Test Example 2. In order to dry the frozen body while it was left standing, the frozen body was placed in a vacuum dryer (Tokyo Rikakikai Co., Ltd. "EYELA FDU-2110") and vacuum dried while it was left standing.

[0106] <Test Example 3> Test Example 3 was produced as follows. A mixture was obtained by mixing the same unmodified fine fibrous cellulose ("ELLEX (registered trademark)-S" manufactured by Daio Paper Co., Ltd.) as the fine fibrous cellulose used in Test Example 1 with a citric acid ester in a mixing ratio of 75%:25%. This mixture was dispersed in water to a concentration of 2% by mass, and the resulting dispersion was used as a raw material and frozen using a Pris Co. "Freeze Granulation Chamber CS30." A frozen body was obtained, and then dried while shaking using a Pris Co. "TFD-10" barrel freeze-drying unit manufactured by Pris Co., Ltd. until the frozen body was completely dried. The cellulose particles obtained after drying were designated Test Example 3.

[0107] <Test Example 4> Test Example 4 was produced as follows. Fine fibrous cellulose in which hydroxy groups had been modified to phosphite groups ("ELLEX (registered trademark)-Star" manufactured by Daio Paper Co., Ltd.) was dispersed in water to a concentration of 0.5% by mass, and the resulting dispersion was used as a raw material. This dispersion was frozen using a Pris Co., Ltd. "Freeze Granulation Chamber CS30" to obtain a frozen body. The frozen body was then dried while being shaken using a Pris Co., Ltd. "TFD-10" barrel freeze drying unit until the frozen body was completely dried. The cellulose particles obtained after drying were designated Test Example 4. The average fiber diameter of the fine fibrous cellulose was 4 nm.

[0108] <Test Example 5> Test Example 5 was produced as follows: The same dispersion liquid as that used in Test Example 4 was supplied as a raw material to a PRIS "Freeze Granulation Chamber CS30" to obtain a frozen body as an intermediate, and this frozen body was vacuum dried to obtain cellulose particles, which were used as Test Example 5. In order to dry the frozen body while it was left standing, the frozen body was placed in a vacuum dryer (Tokyo Rikakikai Co., Ltd. "EYELA FDU-2110") and vacuum dried while it was left standing.

[0109] <Comparative Example 1> In Comparative Example 1, unmodified fine fibrous cellulose ("ELLEX (registered trademark)-S," a product manufactured by Daio Paper Co., Ltd.) and glycerin (glycerin manufactured by Fujifilm Wako Pure Chemical Industries, Ltd.) were mixed in a mixing ratio of 71%:29% to obtain a mixture, which was then supplied to a drum dryer and dried by thermal drying to obtain a dried product, which was then pulverized to obtain cellulose particles with an average particle size of 53.1 μm, which were designated as Comparative Example 1. An SEM image of the particles of Comparative Example 1 is shown in FIG. 8. Compared to the cellulose particles of this embodiment, the particles of Comparative Example 1 had a solid interior, a small specific surface area, and a high density.

[0110] <Comparative Example 2> Comparative Example 2 is a cellulose granule produced by the same production method as Comparative Example 1, except that the cellulose granules had an average particle size of 238.8 μm.

[0111] <Comparative Example 3> Comparative Example 3 was produced as follows: Comparative Example 3 was an aqueous dispersion of unmodified fine fibrous cellulose (ELLEX (registered trademark)-S, manufactured by Daio Paper Co., Ltd.) adjusted to a concentration of 2% by mass.

[0112] <Comparative Example 4> Comparative Example 4 was prepared as follows. An aqueous dispersion of fine fibrous cellulose ("ELLEX (registered trademark)-Star" manufactured by Daio Paper Co., Ltd.) in which hydroxy groups had been modified to phosphite groups was adjusted to a concentration of 0.5% by mass. (Comparative Examples 3 and 4 are aqueous dispersions of fine fibrous cellulose before being processed into cellulose particles.)

[0113] The physical properties of the test examples and comparative examples were measured, including compressibility, loose bulk density, packed bulk density, specific surface area, moisture content, average particle size, median size, cumulative 10% size, and cumulative 90% size.

[0114] Compressibility is one of the items used to calculate Carr's fluidity index, and was measured in accordance with ASTM D6393-99 Compressibility Measurement Method. Measurements were performed using the "Multi-function Powder Property Measuring Instrument Multitester MT-02" (manufactured by Seishin Enterprise Co., Ltd.). The specific surface area was measured according to the BET multipoint method (N2 gas adsorption method). The instruments used for the measurement were "3Flex" (manufactured by Micromeritics) and "Smart VacPrep (pretreatment device)" (manufactured by Micromeritics). The cellulose particles prepared in the test examples and comparative examples were degassed (dried under reduced pressure) at 60°C for 20 hours in the pretreatment device, and then the specific surface area was measured by the N2 gas adsorption method. The equipment used to measure the average particle size, median size, cumulative 10% size, and cumulative 90% size was the "Laser Diffraction / Scattering Particle Size Distribution Measuring Device (Particle Size Distribution) LA-960V2 (Dry Measurement)" (manufactured by HORIBA).

[0115] The blending ratios of the raw materials for the test examples and comparative examples are shown in Table 1, and the physical properties are shown in Table 2.

[0116] [Table 1]

[0117] [Table 2]

[0118] (Viscosity test, etc.) The prepared cellulose particles of each of the test examples and comparative examples were added to water to the concentration (redispersion concentration) shown in Table 3, and dispersed in a homogenizer at 8000 rpm for 1 minute to obtain a redispersion liquid. The homogenizer used was a "T-25" manufactured by IKA.

[0119] The Brookfield viscosity of each redispersion was measured twice under different conditions. The first measurement was for a water temperature of 25°C and 6 rpm, and the second measurement was for a water temperature of 25°C and 60 rpm. The Ti value was calculated as follows: Ti value = (B-type viscosity measured under measurement conditions of 25°C and 6 rpm) / (B-type viscosity measured under measurement conditions of 25°C and 60 rpm)

[0120] The viscosity change rate (6 rpm) was calculated using [Formula 2], and the viscosity change rate (60 rpm) was calculated using [Formula 3]. [Formula 2] 1. Test Examples 1 to 3 and Comparative Examples 1 and 2 (Viscosity change rate (6 rpm)) = (B-type viscosity of X (6 rpm)) / (B-type viscosity of Comparative Example 3 (6 rpm)) × 100 Here, X is any one of Test Example 1, Test Example 2, Test Example 3, Comparative Example 1, and Comparative Example 2. 2. Test Examples 4 and 5 (Viscosity change rate (6 rpm)) = (B-type viscosity of Y (6 rpm)) / (B-type viscosity of Comparative Example 4 (6 rpm)) × 100 Here, Y is Test Example 4 or Test Example 5.

[0121] [Formula 3] 1. Test Examples 1 to 3 and Comparative Examples 1 and 2 (Viscosity change rate (60 rpm)) = (B-type viscosity of X (60 rpm)) / (B-type viscosity of Comparative Example 3 (60 rpm)) × 100 Here, X is any one of Test Example 1, Test Example 2, Test Example 3, Comparative Example 1, and Comparative Example 2. 2. Test Examples 4 and 5 (Viscosity change rate (60 rpm)) = (B-type viscosity of Y (60 rpm)) / (B-type viscosity of Comparative Example 4 (60 rpm)) × 100 Here, Y is Test Example 4 or Test Example 5.

[0122] The viscosity change rate (average) is the value obtained by adding the viscosity change rate (6 rpm) to the viscosity change rate (60 rpm) and dividing the result by 2.

[0123] [Table 3]

[0124] When comparing Comparative Examples 1 and 2 with Test Examples 1 to 5 for Brookfield viscosity (6 rpm), Test Examples 1 to 5 showed higher values. This tendency was also observed for Brookfield viscosity (60 rpm). Furthermore, when comparing Comparative Examples 1 and 2 with Test Examples 1 to 5 for Ti value, Test Examples 1 to 5 showed higher values. It can be seen that Test Examples 1 to 5 have excellent thixotropy.

[0125] The viscosity change rate is a numerical expression of the type B viscosity of cellulose particles produced from fine fibrous cellulose as a starting material, when the type B viscosity of the raw material fine fibrous cellulose is taken as 100%. The closer the viscosity change rate is to 100%, the closer the type B viscosity of the cellulose particles is to the type B viscosity of the raw material fibrous cellulose, and the closer the viscosity change rate is to 0%, the more the type B viscosity of the cellulose particles deviates from the type B viscosity of the raw material fibrous cellulose.

[0126] (Redispersion test) The following redispersion test was carried out: In the relevant drawings, reference numeral 20 denotes the interface.

[0127] The cellulose particles produced (Test Examples 1-5, Comparative Examples 1-2) were dispersed in water to a concentration of 2.0% by mass for Test Examples 1-3 and Comparative Examples 1-2, and to a concentration of 0.5% for Test Examples 4-5. The particles were then redispersed in a homogenizer (IKA T-25) at 8000 rpm for 1 minute to obtain a redispersion. (Note that Comparative Example 3 was an aqueous dispersion of microfibrous cellulose with a concentration of 2.0% by mass, and Comparative Example 4 was an aqueous dispersion of microfibrous cellulose with a concentration of 0.5% by mass, which correspond to the aqueous dispersions before processing into cellulose particles.) After dispersion, the particles were transferred to a stoppered bottle and allowed to stand for 20 minutes. Photographs of the dispersion state are shown in FIG. 7.

[0128] In all of Test Examples 1 to 5, the cellulose particles were dispersed over a wide area in water, and no clear interface between the cellulose particles was observed. The redispersions of Test Examples 4 and 5 were highly transparent because the fine fibrous cellulose used had excellent transparency. On the other hand, in Comparative Examples 1 and 2, an interface 20 was observed.

[0129] In Test Examples 4 and 5, the dispersions in water were transparent. This can be explained as follows: Test Examples 4 and 5 were made from microfibrous cellulose, which is highly hydrophilic and has excellent transparency. When dispersed in water, water penetrates between the fibers that make up the cellulose particles, dissociating the hydrogen bonds between the fibers and allowing the particles to be redispersed with high dispersibility in the dispersion medium, which is thought to be why Test Examples 4 and 5 were transparent. In addition, Comparative Example 3 was less likely to settle when dispersed in water.

[0130] (others) Unless otherwise specified, the JIS, TAPPI and other test and measurement methods shown in the above specification are carried out at room temperature, particularly 25°C, and at atmospheric pressure, particularly 1 atm. [Industrial Applicability]

[0131] The cellulose particles and cellulose particle dispersion of the present invention can be provided as particles having improved redispersibility in aqueous liquids. [Explanation of symbols]

[0132] 11 Cellulose particles 11a Pores in cellulose particles 12 Cellulose particles 12a Pores in cellulose particles 20 Interface

Claims

1. A cellulose particle comprising fine fibrous cellulose having an average fiber diameter of 1000 nm or less, which is formed by mutual aggregation, and which has improved redispersibility in aqueous liquids, The cellulose particles contain 50% by mass or more of the fine fibrous cellulose, and have a packed bulk density of 0.1 to 200 mg / cm 3 , an average particle size of 0.1 to 1000 μm, and a specific surface area of ​​20 to 5000 m 2 / g. Cellulose particles characterized by:

2. The pulp viscosity of the fine fibrous cellulose is 1 to 10 cps. The cellulose particles according to claim 1.

3. The crystallinity of the fine fibrous cellulose is 50 or more and 100 or less. The cellulose particles according to claim 1.

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