Organic-inorganic composite insulation

Abstract

To provide a heat insulator of a low environmental load which presents an excellent heat insulation performance by effectively utilizing not inorganic fillers such as hollow particles, xerogel and aerogel obtained by a complicated high-cost composition approach but natural resources of inorganic fillers and cellulose nanofibers existing in nature.SOLUTION: The present invention relates to a heat insulator which contains fillers and cellulose and in which a cavity is formed. In the heat insulator, the filler is an eggshell of a natural material or a composite carbonate of calcium carbonate that is a main component of dolomite or an eggshell or calcium carbonate that is the main component of dolomite and magnesium carbonate. The cellulose is cellulose nanofibers of which the fiber diameter is less than 30 nm. The fillers are fixed by the contribution of the cellulose nanofibers as a dispersant, a binder and a matrix.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to an organic-inorganic composite material that is made of naturally occurring or similar materials and is suitable as a heat insulating material that has low environmental impact and excellent heat insulating properties. [Background technology]

[0002] In recent years, the term "thermal management" has become increasingly common, and the function of insulation has become increasingly important from the perspective of energy conservation.Insulating materials are used in a wide range of applications, from small and thin films to large plates, sheets, and blocks, for electronic components, large equipment, refrigerators, automobiles, homes, boilers, and factory facilities.

[0003] In particular, electronic equipment applications require thin, high-performance materials, and it is difficult to create thin films using foamed resins such as styrene foam, urethane foam, polyethylene foam, and phenol foam, or inorganic fibers such as glass wool and rock wool, while natural fibers such as cellulose fiber and wool have poor insulating properties.

[0004] Patent Document 1 is an example of a thin film thermal insulation material, but its thermal conductivity is only 0.046 W / m·K. Furthermore, Patent Document 2 describes that eggshell waste powder can be effectively utilized by combining it with cellulose microfibril fiber to produce a biodegradable, versatile material by freeze-drying, and that this material can be used as a heat insulating material, but there is no mention whatsoever of its heat insulating performance. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] Japanese Patent Application Publication No. 2019-95046 [Patent Document 2] Japanese Patent Publication No. 2020-516782 Summary of the Invention [Problem to be solved by the invention]

[0006] An object of the present invention is to provide an insulating material with low environmental impact that exhibits excellent insulating performance while effectively utilizing natural resources, such as cellulose nanofibers and inorganic fillers that exist in nature and have a structure equivalent to that of hollow particles, xerogels, and aerogels, rather than inorganic fillers such as hollow particles, xerogels, and aerogels that are obtained by complicated and costly synthesis methods. [Means for solving the problem]

[0007] As a result of extensive research to achieve the above object, the present invention was completed, which has the following configuration. [1] A thin film or sheet-like insulating material containing a filler and cellulose and having voids formed therein, wherein the filler is natural eggshell or dolomite, or calcium carbonate, which is the main component of eggshell, or a composite carbonate of calcium carbonate and magnesium carbonate, which are the main components of dolomite, the cellulose is cellulose nanofiber with a fiber diameter of less than 30 nm, the cellulose nanofiber serves as a dispersant, binder, and matrix to fix the filler, the thin film or sheet-like insulating material has a thickness of 1 mm or less, and has a thermal conductivity of 0.01 to 0.04 W / m K. [2] A bulk insulation material containing a filler and cellulose and having voids formed therein, wherein the filler is natural eggshell or dolomite, or calcium carbonate, which is the main component of eggshell, or a composite carbonate of calcium carbonate and magnesium carbonate, which are the main components of dolomite, the cellulose is cellulose nanofiber with a fiber diameter of less than 30 nm, the cellulose nanofiber serves as a dispersant, binder, and matrix to fix the filler, the thickness of the bulk insulation material is 2 to 5 mm, and the thermal conductivity is 0.04 to 0.09 W / m K. [3] The heat insulating material according to [1] or [2], wherein the filler is a fine particle that passes through a mesh with an opening of 25 microns. [Effects of the Invention]

[0008] According to the present invention, it is possible to reduce the cost of inorganic fillers and to effectively utilize natural materials or discarded resources. Furthermore, since the inorganic filler is composed of a composition containing CO2, synthetic dolomite and other materials can also lead to CO2 fixation, making it possible to obtain an environmentally friendly, high-performance insulation material. [Brief explanation of the drawings]

[0009] [Figure 1] 1 is a conceptual diagram of an organic-inorganic composite heat insulating material according to an embodiment of the present invention. [Figure 2] FIG. 1 is a conceptual diagram of a measurement device for a heat flux evaluation method used in the present invention. [Figure 3] 1 is an organic-inorganic composite heat insulating sheet produced in Example 1 of the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0010] The heat insulating material of the present invention contains a filler and cellulose, and has voids formed inside. The filler is natural eggshell or dolomite, or calcium carbonate, which is the main component of eggshell, or a composite carbonate of calcium carbonate and magnesium carbonate, which are the main components of dolomite. The cellulose is cellulose nanofibers with a fiber diameter of 10 to 30 nm, and the cellulose nanofibers serve as a dispersant, binder, and matrix to fix the filler in place.

[0011] The thin film or sheet-like insulating material of the present invention has a thickness of 1 mm or less and a thermal conductivity of 0.01 to 0.04 W / m·K, and the bulk-like insulating material of the present invention has a thickness of 2 to 5 mm and a thermal conductivity of 0.04 to 0.09 W / m·K.

[0012] The filler used in the present invention is an inorganic filler, which is a natural material such as eggshell or dolomite, or calcium carbonate, which is the main component of eggshell, or a composite carbonate of calcium carbonate and magnesium carbonate, which are the main components of dolomite.

[0013] The eggshell used in the present invention is not limited as long as it is an animal eggshell whose main component is calcium carbonate, but chicken eggshells, which are available in large quantities, are preferred. Eggshells are porous bodies with pores necessary for the egg's respiration and humidity control. The eggshell used in the present invention is preferably a fine powder of 25 μm or less.

[0014] The calcium carbonate used in the present invention is preferably commercially available nano-sized calcium carbonate. Commercially available nano-sized calcium carbonate, obtained by reprocessing natural calcium carbonate, has a fine powder with a particle size of around 30 nm, which forms aggregates and has pores, giving it a structure similar to that of eggshell powder. Therefore, it can be used as a filler for the heat insulating material of the present invention. Furthermore, natural seashells are also primarily composed of calcium carbonate, and if crushed to nano size, they can be used as a filler for the heat insulating material of the present invention.

[0015] Dolomite is a natural mineral formed when coral deposited on the seabed turns into limestone (CaCO3) over a long period of time, and some of the calcium in the limestone is replaced with magnesium in seawater. Therefore, its main component is a complex carbonate of calcium carbonate and magnesium carbonate, and is expressed by the chemical formula CaMg(CO3)2, and can be used as a filler for the insulation material of this invention. Dolomite includes natural dolomite and synthetic dolomite, but it is preferable to use synthetic dolomite, which has consistent quality and provides stable performance.

[0016] The cellulose nanofibers used in the present invention may be any cellulose nanofibers as long as they have a fiber diameter of less than 30 nm. They may be unmodified, modified, or modified cellulose nanofibers. A typical modified cellulose nanofiber is TEMPO-oxidized cellulose nanofiber, and commercially available products can be used. Modified cellulose nanofibers include sulfate ester cellulose nanofibers, acetylated cellulose nanofibers, and urethane-modified cellulose nanofibers. The average fiber length of these cellulose nanofibers is usually 0.2 to 50 μm. The cellulose nanofibers serve as a dispersant, binder, and matrix in the heat insulating material of the present invention, fixing the filler.

[0017] In the thin film or sheet-like thermal insulation material of the present invention, the ratio of the inorganic filler to the cellulose nanofibers is preferably 10:90 to 90:10 by weight. If the inorganic filler ratio is less than 10, the filler cannot be uniformly dispersed, which is undesirable. If the inorganic filler ratio exceeds 90, the filler will fall off from the insulating material after molding, which is undesirable.

[0018] In the bulk thermal insulation material of the present invention, the ratio of the inorganic filler to the cellulose nanofibers is preferably 50:50 to 99:1 by weight. More preferably, the ratio of inorganic filler to cellulose nanofibers is 80:20 to 99:1 by weight, and most preferably, the ratio of inorganic filler to cellulose nanofibers is 90:10 to 99:1 by weight. If the inorganic filler content is less than 50, the shrinkage rate during molding is large, making molding difficult. On the other hand, if the inorganic filler content exceeds 99, the filler will fall off from the thermal insulation material after molding, causing it to lose its shape, which is undesirable.

[0019] Next, a method for producing the heat insulating material of the present invention will be described. In the production of the heat insulating material of the present invention, first, a cellulose nanofiber inorganic filler dispersion solution is prepared as follows: First, cellulose nanofibers and a solvent are mixed and stirred until the gel-like cellulose nanofibers become a sol. Any solvent capable of dispersing the cellulose nanofibers and inorganic filler can be used, including water (distilled water) and organic solvents such as alcohol, but distilled water is usually sufficient. The amount of solvent added can be determined based on the blending amounts of cellulose nanofibers and inorganic filler, the solvent used, and the form of the insulation material (sheet, thin film, bulk, etc.), but any amount that ensures fluidity is sufficient. Typically, the amount of solvent added is about 1 to 10 times the total weight of the cellulose nanofibers and inorganic filler. The solvent is added to the cellulose nanofibers to form a sol, and the inorganic filler is added and stirred to obtain an aqueous dispersion in which the cellulose nanofibers and inorganic filler are dispersed. The dispersion can be used to produce sheet-type insulating materials and bulk-type insulating materials.

[0020] Next, the manufacturing methods of the thin film and sheet-type thermal insulation materials will be described. First, a method for manufacturing the thin film thermal insulating material will be described. The heat insulating material of the present invention can be coated as a thin film on the surface of a substrate. The thin film heat insulating material can be produced by forming a film directly on a substrate such as metal, ceramic, or resin using a conventional coating method using the cellulose nanofiber inorganic filler dispersion aqueous solution, and then drying the film. Coating methods include spraying, spinning, blade coating, bar coating, and dip coating, but spraying is the most effective. Drying is achieved by heating the substrate to a temperature several degrees higher than the boiling point of the solvent. Since rapid heat treatment can cause deformation of the film, it is desirable to gradually increase the heat treatment temperature to prevent shrinkage and peeling.

[0021] Next, a method for producing the sheet-shaped thermal insulation material will be described. The thermal insulation material of the present invention can be manufactured in the form of a free-standing sheet of thermal insulation material. The sheet-shaped heat insulating material can be produced by forming a film from the cellulose nanofiber inorganic filler dispersion solution by injection molding, extrusion molding, blade method, bar coating method, papermaking method, or spray method. When manufactured by the film-forming method, a film is formed on a substrate, dried, and then peeled off from the substrate to obtain a free-standing sheet-like insulating material. While metal, ceramic, resin, etc. can be used as the substrate, it is more preferable to use diatomaceous earth or gypsum, which have good water absorption properties. It is then preferable to form a mold on the substrate and place the aqueous dispersion on it to form a film. The dispersion film formed on the substrate is then air-dried together with the substrate at room temperature. The desired thickness can be adjusted by repeating film formation and air-drying. After adjusting the thickness, a sheet with the water evaporated can be obtained by leaving it to air-dry for an entire day. For more thorough solvent removal, it is recommended to dry it in a dryer heated to a temperature several degrees higher than the boiling point of the solvent. It is preferable to gradually increase the heat treatment temperature during heating. After drying, the dried sheet can be peeled off from the substrate to obtain a free-standing sheet.

[0022] Next, a method for producing the bulk insulating material will be described. Bulk insulation can be manufactured by pressure molding or casting. To manufacture bulk insulation material by casting, the cellulose nanofiber inorganic filler dispersion is poured into a container and dried. The container may be made of metal or resin. In the case of a resin container, Teflon (registered trademark), polypropylene, polyvinyl chloride, or the like is preferable. The sample is dried at room temperature and left to stand until it naturally comes off the molding container. It is then removed from the container and dried for 3 hours or more in a dryer heated to a temperature several degrees higher than the boiling point of the solvent to obtain the bulk insulation material. To manufacture bulk insulation by pressure molding, inorganic filler and cellulose nanofibers are thoroughly mixed and stirred without adding a solvent until they become homogeneous, and then the mixture is filled into a mold and pressurized at room temperature to obtain the bulk insulation.

[0023] By producing sheets, membranes, or bulk bodies using the manufacturing method described above, it is possible to produce organic-inorganic composite insulation materials that exhibit excellent thermal insulation performance and do not collapse even at low densities, as shown in the conceptual diagram in Figure 1, where the cellulose nanofibers become entangled with the inorganic filer when the solvent evaporates, ensuring voids. [Example]

[0024] The present invention will be described in more detail below based on examples, but the present invention is not limited to these examples.

[0025] The raw materials used in this example are as follows: (filler) Eggshell powder: Commercially available eggshell powder was passed through a mesh with 25 micron openings to collect the powder, which had been adjusted for particle size. Synthetic dolomite: Shiraishi Central Laboratory's Shiratsuka A powder was used, the particle size of which was adjusted by passing it through a mesh with 25 micron openings and collecting it. Nano-sized calcium carbonate: Hakuenka O manufactured by Shiraishi Central Research Institute Co., Ltd. was used. (Cellulose nanofiber) Cellulose nanofiber: Rheocrysta (fiber diameter 3 nm) manufactured by Daiichi Kogyo Seiyaku Co., Ltd. was used.

[0026] The thermal conductivity, density and porosity of the heat insulating material were determined as follows. (Thermal conductivity of insulation material) Using a heat flux sensor manufactured by GreenTTEG, the device shown in Figure 2 was assembled and the heat flux was evaluated using the steady-state method. The thermal conductivity was calculated using the following formula: Thermal conductivity (W / m K) = measured voltage (μV) / sensor sensitivity [μV / (W / m 2 )] × sample thickness (m) / temperature difference (K) (Insulation density) The obtained heat insulating material was cut into a size of 10 x 10 mm, and its weight (g) was measured with a microelectronic balance and its thickness (mm) with a micrometer, and the density was calculated using the following formula. Density (g / cm 3 ) = weight (g) ÷ [10 (mm) × 10 (mm) × thickness (mm) × 10 -3 ] (Porosity of insulation material) The theoretical density was calculated using the rule of mixtures based on the densities of the filler and cellulose nanofibers, and the porosity was calculated using the following formula. Porosity (%) = (1 - density ÷ theoretical density) x 100

[0027] Example 1 The solid weights of the eggshell powder and the cellulose nanofiber were weighed out to be 1g:9g, 2g:8g, 5g:5g, 8g:2g, and 9g:1g, respectively, and thoroughly mixed. After that, distilled water was added in an amount equal to the total weight of the solids, and mixed to form a paste. The paste was formed into a sheet by bar coating onto a diatomaceous earth plate equipped with a guide to ensure a coating area of 50 x 50 mm. After coating, the sheet was dried at room temperature under a slightly reduced pressure airflow. To ensure a sheet thickness of 100 μm or more, film formation and drying were repeated until the sheet was sufficiently dried, after which it was further dried at a temperature of 110 °C or less to remove moisture. The sheet was then peeled off from the diatomaceous earth plate to obtain a free-standing insulating sheet. The weight ratio of the filler to the total weight of the filler and cellulose nanofiber of the obtained sheet-shaped insulation material, as well as the sheet thickness, density, porosity and thermal conductivity are all shown in Table 1. Figure 3 shows photographs of sheet insulation materials with weight ratios of eggshell powder to cellulose nanofiber of 1:9 and 9:1.

[0028] <Example 2> Except for using synthetic dolomite (Shiraishi Central Research Institute Co., Ltd.'s Hakuenka A) as the filler, a sheet-shaped insulation material was produced in the same manner as in Example 1. Table 1 shows the weight ratio of the filler to the total weight of the filler and cellulose nanofiber of the obtained sheet-shaped insulation material, as well as the sheet thickness, density, porosity, and thermal conductivity.

[0029] Example 3 Except for using nano-sized calcium carbonate (Shiraishi Central Research Institute, Hakuenka O) as the filler, a sheet-shaped insulation material was produced in the same manner as in Example 1. The weight ratio of the filler to the total weight of the filler and cellulose nanofiber of the obtained sheet-shaped insulation material, as well as the sheet thickness, density, porosity, and thermal conductivity are all shown in Table 1.

[0030] Example 4 The solid weights of the eggshell powder and the cellulose nanofiber were weighed out to be 9.5g:0.5g, 9g:1g, and 9.9g:0.1g, respectively, and thoroughly mixed. After that, distilled water was added in an amount twice the total weight of the solids, and mixed to form a paste. The paste was poured into a polypropylene mold and thoroughly dried under a slightly reduced pressure airflow, and then further dried at a temperature of 110°C or less to remove moisture. The weight ratio of the filler to the total weight of the filler and cellulose nanofibers of the obtained bulk insulation material, as well as the thickness, density, porosity and thermal conductivity of the sheet are all shown in Table 1.

[0031] <Comparative Example 1> Polyvinyl alcohol (polymerization degree 500) manufactured by Kanto Chemical Co., Inc. was weighed out to a volume of distilled water so that the polyvinyl alcohol concentration was 10%, and polyvinyl alcohol powder was added thereto and thoroughly dissolved. The eggshell powder and the polyvinyl alcohol were weighed out so that the solid weights of the powder and the polyvinyl alcohol were 9.5 g:0.5 g, and the mixture was thoroughly stirred and mixed to prepare a paste. The paste was poured into a polypropylene mold, thoroughly dried under a slightly reduced pressure airflow, and finally cured at 110°C. The weight percentage of the filler in the obtained bulk body, the thickness, density, porosity and thermal conductivity of the sheet are all shown in Table 1.

[0032] <Comparative Example 2> A solution was prepared by mixing an epoxy resin (GAN: glycidylamine type epoxy resin) manufactured by Nippon Kayaku Co., Ltd. and an epoxy curing agent (MH-700G: acid anhydride equivalent 164) manufactured by New Japan Chemical Co., Ltd. in a weight ratio of 10:8. The eggshell powder and the epoxy resin solution were weighed out so that the weights were 9.5 g:0.5 g and 9 g:1 g, and then thoroughly mixed and stirred to prepare a paste. The paste was poured into an aluminum foil mold and cured at 150°C for 1 hour. The obtained bulk body had a two-layer structure due to the settling of eggshell powder, so the density and thermal conductivity were not evaluated. This is due to the increase in the weight of the inorganic filler particles as they penetrated the pores of the epoxy resin.

[0033] [Table 1] [Industrial Applicability]

[0034] According to the present invention, it is possible to reduce the cost of inorganic fillers and effectively utilize natural materials, natural-material-derived materials, or discarded resources. Furthermore, because the inorganic filler is composed of a composition containing CO2, synthetic dolomite and other materials can also contribute to CO2 fixation, making it possible to obtain an environmentally friendly, high-performance insulation material. This allows for a wide range of uses for low-environmental-impact, high-performance insulation materials, such as sheets, thermal insulation paints, and bulk products.

Claims

1. A thin film or sheet-like heat insulating material containing filler and cellulose and having voids formed therein, The filler is a natural eggshell or dolomite, or calcium carbonate, which is a main component of eggshell, or a composite carbonate of calcium carbonate and magnesium carbonate, which are main components of dolomite, The cellulose is a cellulose nanofiber having a fiber diameter of less than 30 nm, The cellulose nanofibers serve as a dispersant, binder, and matrix to fix the filler, and the thin film or sheet-like insulating material has a thickness of 1 mm or less and a thermal conductivity of 0.01 to 0.04 W / m K (however, flame-retardant materials containing aluminum hydroxide are excluded).

2. A bulk insulation material containing a filler and cellulose and having voids formed therein, The filler is a natural eggshell or dolomite, or calcium carbonate, which is a main component of eggshell, or a composite carbonate of calcium carbonate and magnesium carbonate, which are main components of dolomite, The cellulose is a cellulose nanofiber having a fiber diameter of less than 30 nm, The cellulose nanofibers serve as a dispersant, binder, and matrix to fix the filler, and the bulk insulating material has a thickness of 2 to 5 mm and a thermal conductivity of 0.04 to 0.09 W / m K (however, flame-retardant materials containing aluminum hydroxide are excluded).

3. 3. The heat insulating material according to claim 1, wherein the filler is a fine particle that passes through a mesh with an opening of 25 microns.

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