JP7564667B2 - Method for producing inorganic particle dispersion, method for producing composite particles, and method for producing molded body - Google Patents

Description

The present invention relates to a method for producing an inorganic particle dispersion, a method for producing composite particles, and a method for producing a molded body.

Inorganic particle dispersions containing inorganic particles such as metal particles and inorganic compound particles are used as industrial materials for various applications. Solvents for dispersing inorganic particles include both organic solvents and aqueous solvents, but from the viewpoint of reducing the burden on the environment, it is preferable to use aqueous solvents, particularly water.

Metal particles and inorganic compound particles have a high specific gravity, so they settle immediately when dispersed in water. Therefore, when processing with a high-pressure homogenizer, the settled metals and inorganic matter (in a high concentration state) can enter the high-pressure homogenizer, causing problems or breakdowns in the piping, check valves, nozzles, etc.

From the viewpoint of the above-mentioned processes, inorganic particle dispersions using water as a solvent are required to have good dispersion stability over a long period of time.
In order to improve the dispersion stability, it is conceivable to add a thickener such as a thickening polysaccharide or a dispersant to the solvent to suppress the precipitation of the inorganic particles, but a large amount of dispersant may be added to ensure the effect. However, such a large amount of dispersant tends to have a significant effect on the surface properties of the inorganic particles, and there is a concern that the original functions of the inorganic particles may be impaired.

For example, Patent Document 1 proposes a metal nanoparticle aqueous dispersion having excellent dispersion stability, which contains a complex of metal nanoparticles and a specific organic compound, and polyvinylpyrrolidone.

Patent No. 6269909

However, the method described in Patent Document 1 requires the blending of various organic compounds, and the manufacturing process is not particularly simple. It would be extremely beneficial to find a more practical method for manufacturing inorganic particle dispersions.

In view of the above, the present invention has been made with the aim of providing a method for producing a practical inorganic particle dispersion liquid with excellent dispersion stability.

The present inventors conducted extensive research to solve the above problems and discovered that a practical inorganic particle dispersion with excellent dispersion stability can be obtained by subjecting inorganic particles and biomass nanofibers to high-pressure dispersion processing. This led to the completion of the present invention. That is, the present invention is as follows.

[1] A method for producing an inorganic particle dispersion, comprising a dispersing step of dispersing inorganic particles using a mixed liquid containing inorganic particles and biomass nanofibers as a pressurized fluid.
[2] The method for producing an inorganic particle dispersion liquid according to [1], wherein the pressure when the pressurized fluid is prepared is 100 to 250 MPa.
[3] The method for producing an inorganic particle dispersion according to [1] or [2], wherein the inorganic particles have an average particle size (D50) of 0.01 to 100 μm.
[4] The method for producing an inorganic particle dispersion liquid according to any one of [1] to [3], wherein the biomass nanofibers have an average fiber diameter of 10 to 100 nm.
[5] The method for producing an inorganic particle dispersion according to any one of [1] to [4], wherein the content of the inorganic particles in the mixed liquid is 0.2 to 60 mass %, and the content of the biomass nanofibers in the mixed liquid is 0.2 to 2 mass %.
[6] The method for producing an inorganic particle dispersion according to any one of [1] to [5], wherein the ratio (Wp/Wf) of the content of the inorganic particles (Wp) to the content of the biomass nanofibers (Wf) is 0.5 to 30.
[7] A method for producing inorganic particle-biomass nanofiber composite particles, comprising the steps of: a dispersion step of dispersing the inorganic particles using a mixed liquid containing inorganic particles and biomass nanofibers as a pressurized fluid; and a drying step of drying the inorganic particle dispersion after the dispersion step with hot air.
[8] The method for producing inorganic particle-biomass nanofiber composite particles according to [7], wherein the temperature during the hot air drying treatment is 140 to 220° C.
[9] A method for producing a molded product, comprising: a dispersion step of dispersing inorganic particles using a mixed liquid containing inorganic particles and biomass nanofibers as a pressurized fluid; a drying step of hot-air drying the inorganic particle dispersion after the dispersion step; and a molding step of placing the inorganic particle-biomass nanofiber composite particles obtained by the hot-air drying step in a molding die and molding the inorganic particle-biomass nanofiber composite particles.

The present invention provides a method for producing a practical inorganic particle dispersion liquid with excellent dispersion stability.

FIG. 1 is a photograph showing the appearance of the molded body of Example 6. FIG. 13 is a photograph showing the appearance of the molded body of Comparative Example 6.

The following describes a method for producing an inorganic particle dispersion, a method for producing inorganic particle-biomass nanofiber composite particles, and a method for producing a molded body according to an embodiment (present embodiment) of the present invention.

[Method of producing inorganic particle dispersion]
The method for producing an inorganic particle dispersion according to this embodiment includes a dispersion step in which a mixed liquid containing inorganic particles and biomass nanofibers is used as a pressurized fluid and the inorganic particles are dispersed.

Examples of inorganic particles include metal particles such as titanium particles, nickel particles, silver particles, and gold particles, and inorganic compound particles such as silica particles, titania particles, alumina particles, zirconia particles, silicon carbide particles, and carbon particles.

The average particle size (median size, D50) of the inorganic particles is preferably 0.01 to 400 μm, and more preferably 0.1 to 100 μm. D50 is measured on a volume basis, and can be measured by dynamic light scattering in the nm order, and by laser diffraction light scattering in the μm order.

Biomass nanofibers are nanofibers that are poorly soluble in water and are made of biological polymers, such as cellulose nanofibers, chitin nanofibers, chitosan nanofibers, silk nanofibers, etc. Among these, cellulose nanofibers (CNFs) are preferred from the standpoints of chemical stability, thermal stability, and cost.
The average fiber diameter of the biomass nanofibers is preferably 10 to 100 nm, more preferably 10 to 40 nm, and even more preferably 10 to 25 nm.
The average length of the biomass nanofibers is preferably 0.5 to 100 μm, and more preferably 1 to 30 μm.
The average fiber diameter and average length of biomass nanofibers can be calculated from the fiber diameter and length (n=approximately 20) measured based on electron microscope photographs or atomic force microscope images taken at an appropriate magnification.

Conventionally used thickening polysaccharides and the like require high concentrations to disperse metal particles and inorganic compound particles with large specific gravity well. In addition, thickening polysaccharides can reduce viscosity and dispersing power when processed with a high-pressure homogenizer. On the other hand, biomass nanofibers form a three-dimensional network in water, and inorganic particles become entangled in this three-dimensional network, thereby stabilizing dispersion. Therefore, compared to dispersants such as thickening polysaccharides, they can exhibit excellent dispersion stability at low concentrations. As a result, processing with a high-pressure homogenizer is possible without any trouble. Furthermore, processing with a high-pressure homogenizer does not cause a significant decrease in viscosity or dispersibility.

Biomass nanofibers are produced by various manufacturing methods, but mechanically defibrated biomass nanofibers produced by mechanical defibration are preferred. Mechanically defibrated biomass nanofibers are obtained by cutting the raw biomass to a specified length using a beater or refiner, and then fibrillating or pulverizing (mechanically pulverizing) it using a high-pressure homogenizer, grinder, impact crusher, bead mill, etc.

On the other hand, chemically modified biomass nanofibers are obtained by making the raw biomass easier to pulverize through chemical processing, and then pulverizing it through mechanical defibration. Thus, chemically modified biomass nanofibers are chemically modified. For example, when chemically modified CNF such as TEMPO oxidized CNF is used, metal ions contained in the salt may act as impurities. Metal ions include sodium, aluminum, copper, and silver. However, mechanically defibrated biomass nanofibers are not chemically modified during pulverization, and only an aqueous medium is used as a medium, so there are no compounds that are likely to have some effect on inorganic particles, and they are chemically and thermally stable. Therefore, by combining mechanically defibrated biomass nanofibers with inorganic particles, the functions of the inorganic particles can be more effectively brought out. In addition, even when processed with a high-pressure homogenizer, mechanically defibrated biomass nanofibers are less likely to experience a decrease in the degree of polymerization.

Here, the mechanically defibrated biomass nanofibers have a content of any one of sodium, aluminum, copper, and silver (preferably, any two of each, and more preferably, any three of each) of 0.1 mass% or less, and preferably 0.01 mass% or less.
The content can be determined by elemental analysis such as high-frequency inductively coupled plasma atomic emission spectrometry, EPMA using an electron probe microanalyzer, or X-ray fluorescence analysis.

When the mechanically defibrated biomass nanofibers are cellulose nanofibers (mechanically defibrated cellulose nanofibers), the degree of polymerization is preferably 100 to 1500, and more preferably 200 to 1000. A degree of polymerization of 100 to 1500 allows a three-dimensional network to be formed in water. The degree of polymerization is the number of connections of glucose units, which are the smallest structural units of cellulose, and is determined by a viscosity method using a copper ethylenediamine solution.

Examples of mechanically defibrated biomass nanofibers that can be used include BiNFi-s manufactured by Sugino Machine Ltd., ELLEX (registered trademark) manufactured by Daio Paper Corporation, and Cellfim manufactured by Mori Machinery Co., Ltd.

As a mixture containing inorganic particles and biomass nanofibers, an aqueous medium containing water as the main component (e.g., 50% by mass or more), preferably water, is used as the medium.

The content of the inorganic particles in the mixed solution is preferably 0.2 to 60% by mass, and more preferably 5 to 30% by mass. By setting the content to 0.2 to 60% by mass, it is possible to ensure the production volume while avoiding equipment troubles, and the inorganic particles can be dispersed efficiently.
The content of biomass nanofibers in the mixed liquid is preferably 0.2 to 2 mass%, and more preferably 0.3 to 1.0 mass%. By having the content be 0.2 to 2 mass%, better dispersion stability of the inorganic particles can be ensured.

The ratio (Wp/Wf) of the inorganic particle content (Wp) to the biomass nanofiber content (Wf) is preferably 0.5 to 30, and more preferably 10 to 25. By keeping Wp/Wf at 0.5 to 30, it is possible to ensure the dispersion stability of the inorganic substances while minimizing the amount of biomass nanofibers added, which increases costs and causes impurities.

As a method for dispersing inorganic particles using the above-mentioned mixed liquid as a pressurized fluid, it is preferable to adopt a method using a high-pressure homogenizer. When the inorganic particles are pulverized by a media-type pulverizer (crusher) such as a bead mill or a ball mill, the inorganic particles may be excessively pulverized and activated, which may cause aggregation or precipitation.
On the other hand, processing with a high-pressure homogenizer does not cause excessive pulverization, as occurs with bead mills or ball mills. In addition, it is highly effective at sharpening the particle size distribution (making the particle size uniform), so reagglomeration and precipitation can be suppressed for a long period of time. Furthermore, the presence of biomass nanofibers improves the effect of suppressing reagglomeration and precipitation. Another major advantage is that the particle size of the resulting inorganic particles can be controlled by controlling the processing conditions of the high-pressure homogenizer (injection pressure and number of injections).

A preferred treatment method is, for example, a treatment in which the mixed liquid is made to collide with a hard body for collision or the fluids collide with each other through one or two spray nozzles with a diameter of 0.1 to 0.8 mm by a high-pressure injection treatment at a pressure of 100 to 250 MPa (more preferably 150 to 200 MPa) as a pressurized fluid. A high-pressure injection treatment at a higher pressure (for example, 300 MPa) may be performed. This high-pressure injection treatment at 100 to 250 MPa is possible not only by a shear force that passes the mixed liquid through a narrow passage at high pressure and low speed like a commercially available high-pressure homogenizer and homogenizes it when released, but also by a collision force caused by colliding the hard body for collision or the fluids with each other, and by cavitation, and is possible to perform continuous treatment at high pressure. Such a defibration method using shear force, collision force, and cavitation is defined as a water jet method (WJ method). In addition, one collision treatment is considered to be one pass, and in order to obtain a more uniform dispersion, repeated collision is preferably performed 1 to 30 passes, more preferably 5 to 20 passes.
As a commercially available high-pressure homogenizer, for example, Starburst manufactured by Sugino Machine Ltd. is preferably used.

By the above-mentioned treatment, an inorganic particle dispersion liquid having excellent dispersion stability can be obtained. In addition, since the materials used are mainly inorganic particles, biomass nanofibers, and water, the treatment is not complicated, and the amount of impurities is extremely small, a very practical inorganic particle dispersion liquid can be obtained.
In particular, an inorganic particle dispersion liquid having a viscosity of 2000 mPa·s or less, preferably 100 to 1500 mPa·s at 25° C. can be obtained. By having a viscosity of 2000 mPa·s or less at 25° C., the handling properties in the subsequent process such as drying can be improved. The above viscosity can be measured with a B-type viscometer (rotation speed: 60 rpm).

[Method of producing inorganic particle-biomass nanofiber composite particles]
The method for producing inorganic particle-biomass nanofiber composite particles according to this embodiment sequentially includes a dispersion process in which a mixed liquid containing inorganic particles and biomass nanofibers is used as a pressurized fluid to disperse the inorganic particles, and a drying process in which the inorganic particle dispersion after the dispersion process is dried with hot air.
The dispersion step has already been described, so the drying step will be described below.

After the dispersion process, the inorganic particle dispersion is dried before being used in more practical applications or processes. The preferred drying method is spray drying. Spray drying is a method of producing a dry powder by spraying the inorganic particle dispersion into a gas and rapidly drying it, and is also called spray drying or spray drying.

Heating in an oven, which is known as one of the drying methods, can cause the fine inorganic particles to re-agglomerate or to be obtained in plate form rather than powder form. However, drying by spray drying produces uniform particles after drying. This makes it easier to carry out subsequent processes such as molding.

In a spray dryer that performs spray drying, the inorganic particle dispersion is turned into minute droplets using a sprayer such as a nozzle or disk-type atomizer, and then dried in a short time by contacting it with hot air. From the viewpoint of efficiency, the hot air temperature (the temperature during hot air drying) is preferably 100 to 300°C, and more preferably 140 to 220°C.

When a disk-type atomizer is used as the sprayer, the rotation speed of the atomizer is preferably 10,000 to 30,000 rpm, and more preferably 15,000 to 25,000 rpm. By setting the rotation speed of the atomizer within the above range, it becomes possible to sufficiently turn the inorganic particle dispersion into fine droplets when sprayed, and it tends to be easier to obtain a powder or granular material with excellent fluidity.
As such a spray dryer, a commercially available device can be used.

The inorganic particle-biomass nanofiber composite particles produced in the above manner are composed of inorganic particles and biomass nanofibers integrated together, i.e., composited together, and depending on the ratio of inorganic particles to biomass nanofibers, multiple biomass nanofibers may be attached to an inorganic particle, or inorganic particles may be attached to a biomass nanofiber.

From a more practical perspective, the inorganic particle-biomass nanofiber composite particles preferably have an average particle diameter D50 of 1.0 to 10 μm, and more preferably 2 to 7 μm.

In addition, when mechanically defibrated biomass nanofibers are used, the inorganic particle-biomass nanofiber composite particles have a content of any one of sodium, aluminum, copper, and silver in the biomass nanofibers (preferably, any two of each, and more preferably, any three of each) of 0.1 mass% or less, and preferably 0.01 mass% or less.
The content can be determined by elemental analysis such as high-frequency inductively coupled plasma atomic emission spectrometry, EPMA using an electron probe microanalyzer, or X-ray fluorescence analysis.

[Method of manufacturing molded body]
The method for producing a molded body according to an embodiment of the present invention includes a dispersion step in which inorganic particles are dispersed using a mixed liquid containing inorganic particles and biomass nanofibers as a pressurized fluid, a drying step in which the inorganic particle dispersion liquid after the dispersion step is subjected to a hot air drying step, and a molding step in which the inorganic particle-biomass nanofiber composite particles obtained by the hot air drying step are placed in a molding die and molded. The dispersion step and drying step have already been described, so only the molding step will be described below.

Usually, in the molding process, an organic polymer binder is added to the material to be molded. In that case, a degreasing process (heat treatment at about 500 to 1000°C before the subsequent firing) is required to remove the binder. Most organic polymer binders are derived from petroleum, which causes the problem of _CO2 emissions. In addition, when many organic polymer binders are used, the strength of the molded body tends to be low, which can cause problems in handling and secondary processability.
In contrast, in this embodiment, by using mechanically defibrated biomass nanofibers, the biomass nanofibers composited with inorganic particles can function as a binder, making an organic polymer binder unnecessary. Furthermore, the strength of the molded body is improved by using mechanically defibrated biomass nanofibers rather than organic polymer binders such as polyvinyl alcohol (PVA), and therefore the handleability and secondary processability are improved.

Examples of molding processes that can be used include die molding, cold isostatic pressing (CIP), hot pressing, hot isostatic pressing (HIP), powder extrusion molding, metal powder injection molding (MIM), powder additive manufacturing, and the like. Compacts that have undergone molding processes are suitable for applications such as automobile parts, tool steel, office automation equipment, medical equipment parts, electromagnetic parts, bearings, powder core parts, metal magnets, friction materials, current collectors, electrical contacts, electrodes, filters, die materials, turbine disks, and the like.

Next, the present invention will be specifically explained using examples, but the present invention is not limited to these.

[Experimental Example 1-1: Inorganic particle dispersion (inorganic particles = titanium oxide particles)]
Using water as a solvent, a mixed liquid containing inorganic particles and biomass nanofibers was prepared in the materials and composition (mass %) shown in Table 1 below.

Details of the materials used are as follows:
Titanium oxide particles: manufactured by Ishihara Sangyo Kaisha, Ltd., product name: ST-01 (D50 = 4.8 μm (manufacturer's published primary particle diameter: 7 nm))
CNF A: manufactured by Sugino Machine Ltd., product name: BiNFi-s WFo-10002 (average fiber diameter = 20 nm), content of any one of sodium, aluminum, copper, and silver is 0.01% by weight or less (undetectable)
TEMPO oxidized CNF B: manufactured by Daiichi Kogyo Seiyaku Co., Ltd., product name: LEOCRYSTA (registered trademark) I-2SX (average fiber diameter = 3 nm)

The mixed liquid prepared in each example was subjected to a pressure of 120 MPa or 200 MPa using a Starburst manufactured by Sugino Machine Ltd., and an oblique collision chamber in which fluids collide with each other was used to prepare an inorganic particle dispersion under the condition of five collisions. The workability during preparation, frequency of trouble occurrence, viscosity after processing, and dispersion stability are shown in Table 2 below.

The workability during preparation, the frequency of occurrence of problems, the viscosity after treatment, and the dispersion stability were measured or evaluated as follows.
- Workability and frequency of problems:
◎: Water, titanium dioxide, and additives are easily mixed (pre-dispersed). Titanium dioxide hardly settles even after leaving it to stand for about an hour. No problems occur with minor stirring during processing using the WJ method.
Good: When mixing water, titanium dioxide, and additives (pre-dispersion), a certain degree of stirring and heating is necessary because the additives become lumpy. Even if left to stand for about an hour, the titanium dioxide hardly settles, but lumps are formed. During processing using the WJ method, minor stirring will not cause any problems.
△: Water and titanium oxide are easy to mix (pre-disperse). If left to stand for about an hour, titanium oxide will precipitate. Stirring is essential during treatment with the WJ method. If there is no stirring, problems may occur.

·viscosity:
The viscosity was measured at 25° C. and 3 minutes after the start of measurement using a Brookfield type viscometer (HBDV-I Prime).

Dispersion stability:
⊚: Titanium oxide does not precipitate even when left to stand for 2 days after treatment by the WJ method.
◯: Titanium oxide does not precipitate even after being left to stand for 2 days after treatment by the WJ method, but gels.
Δ: When the sample was left to stand for 2 days after treatment by the WJ method, titanium oxide was slightly precipitated.
×: When the sample was allowed to stand for 2 days after the treatment by the WJ method, titanium oxide precipitated.

[Experimental Example 1-2: Inorganic particle dispersion (inorganic particles = titanium particles)]
Using water as a solvent, a mixed liquid containing inorganic particles and biomass nanofibers was prepared with the materials and composition (mass %) shown in Table 3 below.

Details of the materials used are as follows:
Titanium particles: titanium powder (D50 = 26.4 μm) manufactured by Fujifilm Wako Pure Chemical Industries, Ltd.
CNF A: Sugino Machine Ltd., product name: BiNFi-s WFo-10002 (average fiber diameter = 20 nm)
TEMPO oxidized CNF B: manufactured by Daiichi Kogyo Seiyaku Co., Ltd., product name: LEOCRYSTA (registered trademark) I-2SX (average fiber diameter = 3 nm)

The mixed liquid prepared in each example was subjected to a pressure of 200 MPa using a Starburst manufactured by Sugino Machine Ltd., and an oblique collision chamber of a type that causes fluids to collide with each other was used to prepare an inorganic particle dispersion under the condition of five collisions. The workability during preparation, frequency of trouble occurrence, viscosity after treatment, and dispersion stability are shown in Table 4 below.
The workability during preparation, the frequency of occurrence of problems, the viscosity after treatment, and the dispersion stability were measured or evaluated in the same manner as in Experimental Example 1-1.

[Experimental Example 2: Inorganic particle-biomass nanofiber composite particle]
The inorganic particle dispersion of Example 1 was subjected to a hot air drying treatment to prepare inorganic particle-biomass nanofiber composite particles according to Example 5.
Furthermore, the inorganic particle dispersion liquid of Comparative Example 2 was subjected to a hot air drying treatment to prepare inorganic particle-thickening polysaccharide composite particles according to Comparative Example 5.
The hot air drying treatment was carried out using a Micro Mist Spray Dryer MDL-050M device manufactured by GF Corporation under the conditions of a flow rate of 20 mL/min, an IN temperature of 200°C, and an OUT temperature of 103°C.
The average particle size (D50) of each of the inorganic particle-biomass nanofiber or thickening polysaccharide composite particles was measured and evaluated by observation using a scanning electron microscope. The results are shown in Table 3 below.

[Experimental Example 3: Molded body]
The inorganic particle-biomass nanofiber composite particles of Example 5 were placed in a mold and subjected to molding to produce a molded body having a shape of 3 mm height x 4 mm width x 36 mm length (Example 6).
Similarly, the inorganic particle-polysaccharide thickening composite particles of Comparative Example 5 were used, and placed in a mold and subjected to molding to produce a molded body having a shape of 3 mm height x 4 mm width x 36 mm length (Comparative Example 6). Photographs of the appearance of the molded body are shown in Figure 1 (Example 6) and Figure 2 (Comparative Example 6). The molding was performed by powder compaction under conditions of 20 MPa for 2 minutes.
When the strength of each compact after powder compaction was evaluated, it was found that the compact in Example 6 was moldable, but in Comparative Example 6, molding defects occurred.

According to the present invention as described above, it is possible to provide the following inorganic particle dispersion, inorganic particle-biomass nanofiber composite particles, and molded body.
(1) An inorganic particle dispersion comprising inorganic particles and biomass nanofibers, wherein the inorganic particles have an average particle diameter of 0.01 to 100 μm and the biomass nanofibers have an average fiber diameter of 10 to 100 nm.
(2) The inorganic particle dispersion liquid according to (1) above, wherein the ratio (Wp/Wf) of the content of the inorganic particles (Wp) to the content of the biomass nanofibers (Wf) is 0.5 to 30.
(3) The inorganic particle dispersion according to (1) or (2) above, which has a viscosity at 25° C. of 2000 mPa·s or less, preferably 100 to 1500 mPa·s.
(4) The inorganic particle dispersion liquid according to any one of (1) to (3) above, in which the content of any one of sodium, aluminum, copper, and silver (preferably, any two of them, and more preferably, any three of them) is 0.01 mass % or less.
(5) Composite particles comprising inorganic particles having an average particle diameter of 0.01 to 100 μm and biomass nanofibers having an average fiber diameter of 10 to 100 nm, the composite particles having an average particle diameter of 1.5 to 10 μm.
(6) The inorganic particle-biomass nanofiber composite particle according to (5) above, in which the content of any one of sodium, aluminum, copper, and silver in the biomass nanofibers (preferably, any two of each, more preferably, any three of each) is 0.01 mass% or less.
(7) A molded article comprising the inorganic particle-biomass nanofiber composite particle according to (5) or (6) above.

Claims (9)

Contains inorganic particles other than calcium carbonate particles and biomass nanofibers ,
A method for producing an inorganic particle dispersion, comprising: a dispersion step of dispersing the inorganic particles using a mixed liquid having a ratio (Wp/Wf) of the content of the inorganic particles (Wp) to the content of the biomass nanofibers (Wf) of 0.5 to 30 as a pressurized fluid. The method for producing an inorganic particle dispersion according to claim 1, wherein the pressure when the pressurized fluid is prepared is 100 to 250 MPa. The method for producing an inorganic particle dispersion according to claim 1 or 2, wherein the average particle diameter (D50) of the inorganic particles is 0.01 to 100 μm. The method for producing an inorganic particle dispersion according to any one of claims 1 to 3, wherein the average fiber diameter of the biomass nanofibers is 10 to 100 nm. The method for producing an inorganic particle dispersion liquid according to any one of claims 1 to 4, wherein the content of the inorganic particles in the mixed liquid is 0.2 to 60 mass %, and the content of the biomass nanofibers is 0.2 to 2 mass %. The method includes a dispersing step of dispersing the inorganic particles using a mixed liquid containing inorganic particles other than calcium carbonate particles and biomass nanofibers as a pressurized fluid, and a drying step of drying the inorganic particle dispersion after the dispersion step with hot air ,
A method for producing inorganic particle-biomass nanofiber composite particles , wherein the ratio (Wp/Wf) of the content of the inorganic particles (Wp) to the content of the biomass nanofibers (Wf) is 0.5 to 30 . The method for producing inorganic particle-biomass nanofiber composite particles according to claim 6 , wherein the temperature during the hot air drying treatment is 140 to 220°C. A method for producing a molded body, comprising a dispersion step in which a mixture containing inorganic particles and biomass nanofibers is used as a pressurized fluid to disperse the inorganic particles, a drying step in which the inorganic particle dispersion after the dispersion step is subjected to a hot air drying step, and a molding step in which the inorganic particle-biomass nanofiber composite particles obtained by the hot air drying step are placed in a mold and molded. the ratio (Wp/Wf) of the content of the inorganic particles (Wp) to the content of the biomass nanofibers (Wf) is 0.5 to 30;
The method for producing a molded article according to claim 8 , wherein the inorganic particles are not calcium carbonate particles.