Porous composite particles and method for producing the same

Abstract

To provide porous composite particles capable of improving compression strength of particles by suppressing a content of a binder by overcoming decreasing tendency in, for example, supportability, light weight, and adiabaticity, which are characteristics derived from a porous structure, because pores are buried by increasing a content of a binder by necessity of increasing a content of the binder to improve compression strength of porous particles.SOLUTION: Provided are composite particles containing an inorganic raw material having a median diameter of 0.010 μm to 5.00 μm, an aqueous organic binder and nanofibers, in which the porosity of the composite particles is 20 vol.% to 90 vol.%, and a manufacturing method thereof.SELECTED DRAWING: Figure 3

Description

[Technical field]

[0001] The present invention relates to porous composite particles and a method for producing the same. [Background technology]

[0002] Porous composite particles are used in a wide range of products, including as carriers for catalysts and pharmaceuticals, adsorbents, heat insulation materials, and radio wave absorbers.

[0003] Porous composite particles made from inorganic raw materials alone have low shape retention and low compressive strength, and the particle shape easily collapses, so an organic substance is used as a binder for the inorganic raw materials.

[0004] Non-Patent Document 1 discloses porous particles produced by mixing alumina powder with polyvinyl alcohol as a binder and polyacrylic acid as a dispersant to prepare a slurry, spraying the slurry into frozen n-hexane to obtain frozen particles, and then using a freeze dryer.

[0005] Non-Patent Document 2 discloses ceramic composite particles produced by spray drying a slurry in which cellulose nanofibers are added as a binder to calcium phosphate.

[0006] Patent Document 1 discloses ceramic composite particles produced by spray drying a ceramic slurry to which polyvinyl alcohol is added as a binder.

[0007] However, in order to increase the compressive strength of porous particles, it is necessary to increase the binder content. However, increasing the binder content fills the pores, which creates the problem of reducing the properties derived from the porous structure, such as support ability, light weight, and insulation. [Prior art documents] [Non-patent literature]

[0008] [Non-Patent Document 1] Ibaraki Prefectural Industrial Technology Center Research Report No. 14 p18-20(1985) [Non-Patent Document 2] Gifu Prefectural Industrial Technology Center Research Report, No. 11, p1-4 (2017) [Patent documents]

[0009] [Patent Document 1] JP 2006-282436 A Summary of the Invention [Problem to be solved by the invention]

[0010] In consideration of the problems associated with the above-mentioned conventional technology, one aspect of the present invention aims to provide porous composite particles that can reduce the binder content and improve the compressive strength of the particles, and a method for producing the same. [Means for solving the problem]

[0011] Under these circumstances, the present inventors conducted extensive research to solve the above problems and discovered that porous composite particles containing an inorganic raw material with a median diameter of 0.01 μm to 5 μm, a water-soluble organic binder, and nanofibers can increase compressive strength while achieving a porosity of 20 vol% to 90 vol%, thereby completing the present invention.

[0012] Further, in the present invention, it has been found that the porous composite particles can be produced by the following steps. (1) Inorganic raw materials, a water-soluble organic binder, and nanofibers are mixed in a mixer to obtain a dispersion. (2) The dispersion obtained in step (1) is subjected to a spray-drying granulation method or a freeze-drying granulation method to obtain porous composite particles containing nanofibers and a water-soluble organic binder. Effect of the Invention

[0013] According to one aspect of the present invention, it is possible to provide porous composite particles that can improve the compressive strength of the particles by reducing the binder content. [Brief description of the drawings]

[0014] [Figure 1] FIG. 2 is an integrated pore volume diagram of a porous composite particle according to an embodiment of the present invention. [Diagram 2] FIG. 2 is a differential pore volume diagram of a porous composite particle according to an embodiment of the present invention. [Diagram 3] 1 is a scanning electron microscope image of the porous composite particles of Example 1-1. [Figure 4] FIG. 2 is an integrated pore volume diagram of the porous composite particle of Example 1-1. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0015] The porous composite particles and the method for producing the same according to the present invention will be described below based on preferred embodiments. According to the present invention, it is possible to provide porous composite particles that can improve the compressive strength of the particles by reducing the binder content.

[0016] <Porous composite particles> The porous composite particles of the present invention are porous particles that contain an inorganic raw material, a water-soluble organic binder, and nanofibers. The median diameter of the porous composite particles of the present invention is preferably 1 μm to 500 μm, more preferably 2 μm to 300 μm, and most preferably 3 μm to 200 μm. If the median diameter of the porous composite particles exceeds 500 μm, air tends to be easily taken in during spraying, and coarse air bubbles tend to form in the porous composite particles, resulting in a decrease in particle strength. If the median diameter of the porous composite particles is less than 1 μm, the particle strength decreases and the particle shape tends to collapse during handling. In the present invention, the median diameter of the porous composite particles can be measured by any of a laser diffraction method, a light scattering method, and an image analysis method.

[0017] The porosity of the porous composite particles of the present invention is 20% by volume to 90% by volume, preferably 22% by volume to 85% by volume, and more preferably 24% by volume to 80% by volume. If the porosity of the porous composite particles exceeds 90% by volume, the strength of the particles is significantly reduced, so that the particles easily collapse during handling. If the porosity of the porous composite particles is less than 20% by volume, the adsorption performance and support performance derived from the porous structure are significantly reduced.

[0018] The porosity of the porous composite particles can be measured by either mercury intrusion porosimetry or image analysis.

[0019] 1 shows a graph of the cumulative pore volume of a porous composite particle according to an embodiment of the present invention, measured by mercury intrusion porosimetry. A two-stage change in cumulative pore volume is observed, with the first stage, seen on the side of larger pore diameter, representing the void volume between the porous composite particles when the porous composite particles are filled into a measurement cell, and the second stage representing the pore volume within the porous composite particle. The volume of the porous composite particle is found by subtracting the void volume between the porous composite particles in the first stage from the volume of the cell used in mercury intrusion porosimetry.

[0020] The porosity of the porous composite particle is calculated by dividing the pore volume in the porous composite particle by the volume of the porous composite particle, i.e., the porosity of the porous composite particle (volume %)={(pore volume in the porous composite particle) / (volume of the porous composite particle)}×100.

[0021] The appropriate pore size of the porous composite particles of the present invention is 0.005 μm to 5 μm, more preferably 0.05 μm to 3 μm, and most preferably 0.5 μm to 1 μm. If the pore size of the porous composite particles exceeds 5 μm, the compressive strength tends to decrease. If the pore size of the porous composite particles is less than 0.005 μm, the water or organic solvent sublimated during the preparation of the porous composite particles is not easily removed, and defects such as cracks are likely to occur.

[0022] The pore size of the porous composite particles can be measured by either mercury intrusion porosimetry or image analysis.

[0023] 2 shows a graph of the pore size distribution of the porous composite particle according to the embodiment of the present invention, measured by mercury intrusion porosimetry. The measured pore size distribution has two peaks. The peak on the larger pore size side corresponds to the void size between the porous composite particles, and the peak on the smaller pore size side corresponds to the pore size of the porous composite particle.

[0024] The inorganic raw material used in the present invention is preferably at least one selected from metal oxides and metal non-oxides, and the content of the inorganic raw material is 60.0% by weight to 99.8% by weight, preferably 75.0% by weight to 99.5% by weight.

[0025] The metal oxide is not particularly limited, but examples thereof include aluminum oxide (=alumina), magnesium oxide, silicon dioxide (=silica), calcium oxide, titanium oxide, vanadium oxide, chromium oxide, manganese oxide, iron oxide, cobalt oxide, copper oxide, zinc oxide, yttrium oxide, zirconium oxide, niobium oxide, molybdenum oxide, tantalum oxide, tungsten oxide, apatite, cordierite, mullite, mica, and talc.

[0026] Furthermore, the metal non-oxide is not particularly limited, but examples thereof include aluminum nitride, silicon nitride, boron nitride, titanium nitride, vanadium nitride, chromium nitride, zirconium nitride, niobium nitride, tantalum nitride, silicon carbide, titanium carbide, vanadium carbide, zirconium carbide, niobium carbide, molybdenum carbide, tantalum carbide, tungsten carbide, and sialon.

[0027] The median diameter of the inorganic raw material used in the present invention is 0.010 μm to 5.00 μm, preferably 0.015 μm to 4.00 μm, and more preferably 0.020 μm to 3.00 μm. If the median diameter is larger than 5.00 μm, sedimentation occurs significantly in the dispersion, making it difficult to obtain porous composite particles with a uniform composition. If the median diameter is smaller than 0.010 μm, particle aggregation occurs significantly, causing nozzle clogging during spraying, resulting in a significant decrease in productivity.

[0028] The median diameter of the inorganic raw material can be measured by using any of a laser diffraction method, a light scattering method, and an image analysis method.

[0029] The water-soluble organic binder used in the present invention is a binding agent for inorganic raw materials, and specifically, it is preferably at least one type selected from water-soluble polymers and water-soluble polysaccharides.

[0030] The water-soluble polymer is not particularly limited, but examples thereof include polyvinyl alcohol, polyacrylic acid, polycarboxylic acid, and polylactic acid.

[0031] The water-soluble polysaccharides are not particularly limited, but examples thereof include starch, carboxymethylcellulose, dextrin, and the like.

[0032] The content of the water-soluble organic binder used in the present invention is preferably 0.10% by weight to 20.0% by weight, more preferably 0.15% by weight to 10.0% by weight, and most preferably 0.20% by weight to 5.0% by weight. If the content of the water-soluble organic binder exceeds 20.0% by weight, the pores of the porous composite particles tend to be filled with the water-soluble organic binder, and the properties derived from the porous structure tend to deteriorate. If the content of the water-soluble organic binder is less than 0.10% by weight, it becomes difficult for the porous composite particles to adequately retain their shape, and the shape tends to collapse.

[0033] The nanofibers used in the present invention are fibers having a diameter of 1 to 1000 nanometers and a length of 1000 μm or less with an aspect ratio of 100 or more. Specifically, the nanofibers are preferably at least one type selected from cellulose nanofibers, chitin nanofibers, chitosan nanofibers, and silk nanofibers.

[0034] The content of the nanofibers used in the present invention is preferably 0.10% by weight to 20.0% by weight, more preferably 0.2% by weight to 10.0% by weight, and most preferably 0.4% by weight to 5.0% by weight. If the content of the nanofibers exceeds 20.0% by weight, the pores of the porous composite particles tend to be filled with the nanofibers, and the properties derived from the porous structure tend to be significantly reduced. Also, if the content of the nanofibers is less than 0.10% by weight, the effect of adding the nanofibers tends to be insufficient.

[0035] The weight mixing ratio of the nanofibers to the water-soluble organic binder used in the present invention (nanofibers / water-soluble organic binder) is preferably 0.1 to 10, more preferably 0.3 to 9, and most preferably 0.4 to 8. If the weight mixing ratio exceeds 10, the strength improving effect due to the addition of the water-soluble organic binder tends to decrease. If the weight mixing ratio is less than 0.1, the strength improving effect due to the addition of the nanofibers tends to decrease.

[0036] <Method of manufacturing porous composite particles> The porous particles according to an embodiment of the present invention are produced by the production method shown in the following steps (1) and (2). (1) Inorganic raw materials, a water-soluble organic binder, and nanofibers are mixed in a mixer to obtain a dispersion. (2) The dispersion obtained in step (1) is subjected to a spray-drying granulation method or a freeze-drying granulation method to obtain porous composite particles containing nanofibers and a water-soluble organic binder.

[0037] In step (1), the mixer for mixing the inorganic raw materials, the water-soluble organic binder, and the nanofibers is not particularly limited, and examples thereof include a planetary centrifugal mixer, a rotary ball mill mixer, a bead mill, a homogenizer, and a disperser mixer.

[0038] In step (2), the spray-drying granulation method is not particularly limited, but a preferred method is to spray the dispersion using a two-fluid or more nozzle type, a mechanical dispenser, or a rotating disk type sprayer, and dry the resulting fine droplets with heated dry air to obtain porous composite particles containing inorganic raw materials, nanofibers, and a water-soluble organic binder.

[0039] In step (2), the freeze-drying granulation method is not particularly limited, but for example, the dispersion is sprayed using a two-fluid or more nozzle type, a mechanical dispenser, or a rotating disk type sprayer, and the resulting fine droplets are dropped into frozen air or liquid nitrogen to produce frozen fine droplets.Then, the resulting frozen fine droplets are subjected to a freeze dryer to sublimate the water or organic solvent, thereby obtaining porous composite particles containing inorganic raw materials, nanofibers, and a water-soluble organic binder. EXAMPLES

[0040] The present invention will be described in more detail below with reference to examples, but the present invention is not limited thereto in any way.

[0041] Example 1-1 Step (1): Colloidal silica (ST-N-40, solids concentration 40% by weight, Nissan Chemical), cellulose nanofiber (I-2SX, solids concentration 2% by weight, Daiichi Kogyo Seiyaku), and polyvinyl alcohol (10% by weight, Fujifilm Wako Pure Chemical Industries) were mixed in the weight ratio shown in Table 1-Example 1-1 and the solids concentration of the dispersion was 30% by weight, and the mixture was fed into a planetary centrifugal mixer (ARE-310, Thinky) to prepare a dispersion. Step (2): The dispersion obtained in step (1) was fed to a mechanical dispenser (Aero-Jet, Musashi Engineering), and fine droplets were dropped into liquid nitrogen for rapid freezing, to obtain frozen microparticles. Discharge pressure: 0.1MPa Nozzle diameter: 200μm The resulting frozen microparticles were then subjected to a freeze dryer (FDU-1200, Tokyo Rikakikai) to obtain porous composite particles.

[0042] An electron microscope image of the porous composite particles obtained in Example 1-1 is shown in Figure 3. Spherical particles with a porous structure were obtained.

[0043] Figure 4 shows the cumulative pore volume of the porous composite particles obtained in Example 1-1, measured by mercury intrusion porosimetry. Two stages of change in the cumulative pore volume were observed. From the measurement results, the porosity was 76 volume %. The composition and physical properties of the porous composite particles prepared in Example 1-1 are as shown in Table 1, and the compositions and physical properties of the examples and comparative examples shown below are also shown in Table 1.

[0044] [Table 1]

[0045] Comparative Example 1-1 Porous composite particles were obtained in the same manner as in Example 1-1, except that a dispersion was prepared using only polyvinyl alcohol, which is a water-soluble organic binder, to obtain the porous composite particle composition shown in Comparative Example 1-1 in Table 1.

[0046] Comparative Example 1-2 Porous composite particles were obtained in the same manner as in Example 1-1, except that a dispersion was prepared using only cellulose nanofibers, which are nanofibers, to have the composition of the porous composite particles shown in Comparative Example 1-2 in Table 1.

[0047] Example 1-2 Porous composite particles were obtained in the same manner as in Example 1-1, except that a dispersion was prepared so as to have the composition of the porous composite particles shown in Example 1-2 in Table 1.

[0048] Examples 1-3 Porous composite particles were obtained in the same manner as in Example 1-1, except that an alumina slurry (solid content concentration 60% by weight) made using alumina (TM-DAR, Taimei Chemical Industry Co., Ltd.) as the inorganic raw material and polyacrylic acid (A-6114, Toagosei Co., Ltd.) as the water-soluble organic binder was used and mixed to obtain the composition of the porous composite particles shown in Example 1-3 in Table 1, and a dispersion was prepared so that the solid content concentration was 50% by weight.

[0049] Comparative Example 1-3 Porous composite particles were obtained in the same manner as in Example 1-3, except that a dispersion was prepared using only polyacrylic acid, which is a water-soluble organic binder, to have the composition of the porous composite particles shown in Comparative Example 1-3 in Table 1.

[0050] Examples 1-4 Porous composite particles were obtained in the same manner as in Example 1-1, except that silicon carbide powder (GC#6000, Fujimi) was used as the inorganic raw material, chitosan fiber (EFo-08002, solid content concentration 2 wt%, Sugino Machine) was used as the nanofiber, and starch (Wako Pure Chemical Industries) was used as the water-soluble organic binder, and were mixed to obtain the composition of the porous composite particles shown in Example 1-4 in Table 1, to prepare a dispersion.

[0051] Examples 1-5 Porous composite particles were obtained in the same manner as in Example 1-1, except that mica (A-11, Yamaguchi Mica) and silica (ST-N-40, solid content concentration 40% by weight, Nissan Chemical) were used as the inorganic raw materials, chitin fiber (SFo-20002, solid content concentration 2% by weight, Sugino Machine) was used as the nanofiber, a nozzle with a nozzle diameter of 320 μm was used, and the materials were mixed to obtain the porous composite particle composition shown in Example 1-5 in Table 1, and a dispersion was prepared so that the solid content concentration was 17% by weight.

[0052] Examples 1-6 Porous composite particles were obtained in the same manner as in Example 1-1, except that silk nanofibers (KCo-30005, solid content concentration 5 wt%, Sugino Machine) were used as the nanofibers and a dispersion was prepared so as to have the composition of the porous composite particles shown in Example 1-6 in Table 1.

[0053] Comparative Example 1-4 Porous composite particles were obtained in the same manner as in Example 1-1, except that a paraffin emulsion (N-4040, Orion Chemicals), which is a water-insoluble organic binder, was used instead of the water-soluble organic binder.

[0054] Comparative Examples 1-5 Porous composite particles were obtained in the same manner as in Example 1-1, except that an acrylic emulsion (AS-2000, Toa Gosei), which is a water-insoluble organic binder, was used instead of the water-soluble organic binder.

[0055] Comparative Examples 1-6 Porous composite particles were obtained in the same manner as in Example 1-1, except that a polyethylene emulsion (C-101, Orion Chemicals), which is a water-insoluble organic binder, was used instead of the water-soluble organic binder.

[0056] Example 2-1 Step (1): Alumina (AES-11, Sumitomo Chemical), cellulose nanofiber (FMa-100002, solids concentration 2% by weight, Sugino Machine), and polyvinyl alcohol (solids concentration 10% by weight, Fujifilm Wako Pure Chemical Industries) were mixed to obtain the composition shown in Table 1-Example 2-1, and the solids concentration was adjusted to 50% by weight. The mixture was then fed into a planetary centrifugal mixer (ARE-310, Thinky) to obtain a dispersion. Step (2): The dispersion obtained in step (1) was subjected to a spray dryer (ADL311S, Yamato Scientific), and the fine droplets were rapidly solidified at high temperature to obtain porous composite particles containing inorganic raw materials, nanofibers, and a water-soluble organic binder. Discharge pressure: 0.1MPa Nozzle type: Two-fluid nozzle Nozzle diameter: 250μm Intake air temperature: 150℃ Exhaust temperature: 95℃

[0057] Comparative Example 2-1 Porous composite particles were obtained in the same manner as in Example 2-1, except that a dispersion was prepared using only cellulose nanofibers, which are nanofibers, to have the composition of the porous composite particles shown in Comparative Example 2-1 in Table 1.

[0058] (Compressive strength evaluation method) The compressive strength of the porous composite particles of the above examples and comparative examples was measured using a microcompression tester (MCT-W500, Shimadzu Corporation).

[0059] From Table 1, it can be seen that the porous composite particles of Examples 1-1, 1-3, and 2-1, which contain both nanofibers and a water-soluble organic binder, improve the compressive strength without increasing the binder content, compared with the porous composite particles of Comparative Examples 1-1, 1-2, 1-3, and 2-1, which do not contain nanofibers or a water-soluble organic binder. Furthermore, it can be seen that Example 1-1, which contains both nanofibers and a water-soluble organic binder, improves the compressive strength without increasing the binder content, compared with Comparative Examples 1-4, 1-5, and 1-6, which replace the water-soluble organic binder with a water-insoluble organic binder. [Industrial Applicability]

[0060] The present invention relates to a porous composite particle that can improve the compressive strength of the particle by reducing the binder content, and a method for producing the same. The use of the porous composite powder of the present invention can greatly contribute to industrial fields that require materials with excellent supportability, light weight, and heat insulation.

Claims

1. Porous composite particles comprising 60.0% by weight to 99.8% by weight of an inorganic raw material having a median diameter of 0.010 μm to 5.00 μm, a water-soluble organic binder, and nanofibers, the composite particles having a porosity of 20% by volume to 90% by volume.

2. 2. The porous composite particle according to claim 1, wherein the content of the water-soluble organic binder is 0.10% by weight to 20.0% by weight, and the content of the nanofiber is 0.10% by weight to 20.0% by weight.

3. 3. The porous composite particle according to claim 1, wherein the inorganic raw material is at least one selected from the group consisting of metal oxides and metal non-oxides.

4. 4. The porous composite particle according to claim 1, wherein the water-soluble organic binder is at least one selected from the group consisting of water-soluble polymers and water-soluble polysaccharides.

5. 5. The porous composite particle according to claim 1, wherein the nanofiber is at least one type selected from the group consisting of cellulose nanofiber, chitin nanofiber, chitosan nanofiber, and silk nanofiber.

6. A method for producing the porous composite particles according to any one of claims 1 to 5, which is prepared through the following steps (1) and (2): (1) Inorganic raw materials, a water-soluble organic binder, and nanofibers are mixed in a mixer to obtain a dispersion. (2) The dispersion obtained in step (1) is subjected to a spray-drying granulation method or a freeze-drying granulation method to obtain porous composite particles containing nanofibers and a water-soluble organic binder.

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