Method for manufacturing aerogel powder for refrigerators

Abstract

To provide a method for industrially advantageously producing aerogel powder that exhibits excellent dispersibility in polyurethane foam and is effective in improving the thermal insulation properties of polyurethane foam. [Solution] A method for producing aerogel powder for refrigerators, comprising grinding an aerogel mass with a particle diameter of 1 mm or more using a ball mill in a dry manner so that the average particle diameter is within the range of 20 μm to 30 μm.

Description

[Technical Field]

[0001] This invention relates to a method for producing aerogel powder for refrigerators. [Background technology]

[0002] Polyurethane foam is widely used as insulation for refrigerators. Adding aerogel powder to polyurethane foam is being considered to improve its thermal insulation properties (Patent Document 1). Aerogel is a porous structure made of materials such as silica, carbon, and polymers, and is known as a material with a large pore volume and high thermal insulation properties. A known method for producing aerogel powder is to crush a lump of aerogel (Patent Document 2). [Prior art documents] [Patent Documents]

[0003] [Patent Document 1] Japanese Patent Publication No. 2023-90369 [Patent Document 2] Japanese Patent Publication No. 2024-150636 [Overview of the project] [Problems that the invention aims to solve]

[0004] Aerogel powder is an effective material for improving the thermal insulation properties of thermal insulation materials such as polyurethane foam. However, the inventors' research has shown that if the aerogel mass is crushed too much, the pores on the surface of the aerogel particles are crushed, reducing the thermal insulation effect. On the other hand, if the aerogel mass is not crushed sufficiently, the aerogel particles become entangled and aggregated due to the pores on the surface of the aerogel particles, reducing their dispersibility in thermal insulation materials such as polyurethane foam.

[0005] The present invention aims to provide a method for industrially advantageously producing aerogel powder that exhibits excellent dispersibility in polyurethane foam and is effective in improving the thermal insulation properties of polyurethane foam. [Means for solving the problem]

[0006] The inventors of the present invention have found that pulverizing aerogel aggregates dry using a ball mill so that the average particle size falls within a predetermined range is effective in addressing the above-mentioned problems, and have completed the present invention. Accordingly, the present invention provides the following.

[0007] (1) A method for producing aerogel powder for refrigerators, comprising grinding an aerogel mass with a particle diameter of 1 mm or more using a ball mill in a dry manner so that the average particle diameter is in the range of 20 μm to 30 μm.

[0008] According to the method for producing aerogel powder for refrigerators in (1), the aerogel mass is crushed using a ball mill under the above conditions, so an aerogel powder can be obtained that has excellent dispersibility with foamed urethane and is effective in improving the heat insulation properties of foamed urethane. Furthermore, according to the method for producing aerogel powder for refrigerators in (1), the crushing of the aerogel mass is carried out dry using a ball mill, which is widely used in industry, so it can be carried out industrially advantageously.

[0009] (2) The method for producing aerogel powder for refrigerators as described in (1), wherein the ball diameter of the ball mill is in the range of 5 mm to 15 mm.

[0010] According to the method for producing aerogel powder for refrigerators in (2), since the powder is crushed using balls whose diameter is within the above range, aerogel powder with excellent dispersibility in foamed urethane and that is effective in improving the heat insulation properties of foamed urethane can be obtained more stably.

[0011] (3) A method for producing aerogel powder for refrigerators as described in (1) or (2), wherein the grinding time is within the range of 15 minutes or more and 30 minutes or less.

[0012] According to the method for producing aerogel powder for refrigerators in (3), since the grinding time is within the above range, it is possible to industrially produce aerogel powder that has excellent dispersibility with foamed urethane and is effective in improving the heat insulation properties of foamed urethane, in a more stable manner.

[0013] (4) The pore volume of the aerogel mass is 700 m 2 / g or more 1000m 2 A method for producing aerogel powder for refrigerators, within the range of (1) to (3) or less.

[0014] According to the method for producing aerogel powder for refrigerators in (4), since aerogel lumps with a pore volume within the above range are used as raw materials, it is possible to obtain aerogel powder that is even more effective in improving the thermal insulation properties of foamed urethane. [Effects of the Invention]

[0015] According to the present invention, it is possible to provide a method for industrially advantageously producing aerogel powder that has excellent dispersibility in foamed urethane and is effective in improving the thermal insulation properties of foamed urethane. [Modes for carrying out the invention]

[0016] Embodiments of the present invention will be described below.

[0017] In this embodiment, an aerogel mass with a particle diameter of 1 mm or more is used as the raw material. There is no particular upper limit to the particle diameter of the aerogel mass; for example, it may be 30 mm or less. The particle diameter of the aerogel mass can be measured using a sieve. The pore volume of the aerogel mass is, for example, 700 m³. 2 / g or more 1000m 2 It may be within the range of / g.

[0018] The material of the aerogel mass is not particularly limited, and silica, carbon, and polymers can be used. Physical properties such as the true density, bulk density, and pore volume of the aerogel mass are not particularly limited. For example, in the case of a silica aerogel mass, the true density is 1.0 g / cm 3 or more and 1.0 g / cm 3 or less. The bulk density (apparent density) may be in the range of 0.05 g / cm 3 or more and 0.10 g / cm 3 or less.

[0019] The aerogel mass can be produced, for example, by the supercritical drying method. The supercritical drying method is a method of drying a gel-like aerogel using a supercritical fluid to produce an aerogel mass. The gel-like aerogel can be obtained, for example, by hydrolysis and polycondensation by the sol-gel method. As the supercritical fluid, for example, carbon dioxide can be used.

[0020] In this embodiment, the aerogel mass is dry-crushed using a ball mill. The ball diameter of the ball mill may be, for example, in the range of 5 mm or more and 15 mm or less. The material of the balls is not particularly limited, and for example, alumina, zirconia, stainless steel, or quartz (agate) may be used. The filling rate of the balls in the mill container is not particularly limited, and for example, it may be in the range of 3% by volume or more and 40% by volume or less. The rotation speed of the mill container is not particularly limited, and for example, it may be in the range of 200 rpm or more and 1600 rpm or less.

[0021] The crushing of the aerogel mass is carried out until the average particle diameter of the obtained aerogel powder is in the range of 20 μm or more and 30 μm or less. The crushing time varies depending on conditions such as the filling rate of the balls in the mill container and the rotation speed of the mill container, but for example, it may be in the range of 15 minutes or more and 30 minutes or less.

[0022] When aerogel lumps are crushed using a ball mill, a portion of the surface of the aerogel particles is compressed by the balls, forming a compression layer. This compression layer partially blocks some of the pores in the aerogel particles. Therefore, the resulting aerogel powder has higher true density and bulk density, and smaller pore volume compared to the raw aerogel lumps. The formation of the compression layer on the surface of the aerogel particles makes them less likely to entangle and aggregate. As a result, the aerogel powder has improved dispersibility in polyurethane foam. Furthermore, areas where the compression layer is not formed remain on the surface of the aerogel particles. Therefore, polyurethane foam to which aerogel powder is added has improved thermal insulation properties.

[0023] According to the method for producing aerogel powder for refrigerators of this embodiment, which has the above configuration, the aerogel mass is crushed using a ball mill under the above conditions, so an aerogel powder can be obtained that has excellent dispersibility with foamed urethane and is effective in improving the heat insulation properties of foamed urethane. Furthermore, according to the method for producing aerogel powder for refrigerators of this embodiment, the crushing of the aerogel mass is carried out dry using a ball mill, which is widely used in industry, so it can be carried out industrially advantageously.

[0024] In the method for producing aerogel powder for refrigerators according to this embodiment, by grinding using balls with a ball diameter within the above range in a ball mill, it is possible to obtain aerogel powder with excellent dispersibility in foamed urethane and that is effective in improving the thermal insulation properties of foamed urethane more stably. Furthermore, by setting the grinding time within the above range, it is possible to industrially produce aerogel powder with excellent dispersibility in foamed urethane and that is effective in improving the thermal insulation properties of foamed urethane even more stably. In addition, by using aerogel lumps with a pore volume within the above range, it is possible to obtain aerogel powder that is even more effective in improving the thermal insulation properties of foamed urethane. [Examples]

[0025] Next, the present invention will be described with reference to examples.

[0026] [Example 1] As a silica aerogel mass, having a particle size of 1 mm to 30 mm, a true density of 1.47 g / cm 3 , a bulk density of 0.089 g / cm 3 , a pore volume of 870.2 m 2 / g was prepared. 20 alumina balls with a diameter of 10 mm and 20 g of the silica aerogel mass were put into a mill container with a capacity of 250 cm 3 . Then the mill container was covered and sealed. Next, the mill container was stirred under the conditions of a rotation speed of 300 rpm and a pulverization time of 15 minutes. After stirring, the silica aerogel powder was recovered from the mill container.

[0027] [Examples 2 - 3, Comparative Examples 1 - 2] Silica aerogel powder was produced in the same manner as in Example 1, except that the pulverization time was 20 minutes (Example 2), 30 minutes (Example 3), 10 minutes (Comparative Example 1), and 60 minutes (Comparative Example 2).

[0028] [Reference Example 1] The silica aerogel mass was used as Reference Example 1.

[0029] [Reference Example 2] A commercially available silica aerogel powder obtained by pulverizing the silica aerogel mass using a jet mill was used as Reference Example 2.

[0030] [Physical Property Evaluation] For the silica aerogel powders of Examples 1 - 3, Comparative Examples 1 - 2, and Reference Example 2, the average particle diameter, true density, bulk density, and pore volume were measured by the following methods. The results are shown in Table 1 below together with the pulverization method and pulverization time of the silica aerogel mass.

[0031] (Average Particle Diameter) Measure using a laser diffraction / scattering particle size distribution measuring device (LA - 960, manufactured by HORIBA).

[0032] (True Density) The pressure is measured using a high-precision pressure sensor (absolute pressure gauge) and a built-in true density measuring device (BELPYCNO L, manufactured by MICROTRAC).

[0033] (Bulk density) Silica aerogel powder, volume: 10cm 3 Gently pour the silica aerogel powder into the container. Weigh the mass of the silica aerogel powder poured into the container and calculate the bulk density (apparent density) using the following formula. Bulk density = Mass of silica aerogel powder / Volume of container

[0034] (pore volume) The measurement is performed using the BJH method with nitrogen gas as the adsorbent gas, employing a multi-sample gas adsorption analyzer (AUTOSORB-IQ, manufactured by Cantachrome).

[0035] [Table 1]

[0036] Table 1 shows that in Examples 1-3, where the grinding time was 15-30 minutes, silica aerogel powder with an average particle size of 20-30 μm was obtained. The silica aerogel powders obtained in Examples 1-3 and Comparative Examples 1-2 all had higher true density and bulk density, and smaller pore volume compared to the raw material aerogel mass (Reference Example 1). This is because in Examples 1-3 and Comparative Examples 1-2, a compression layer was formed when a portion of the surface of the aerogel particles was compressed by the balls. The silica aerogel powder obtained in Comparative Example 1, where the grinding time was short (10 minutes), had an average particle size exceeding 30 μm, and its higher true density compared to the silica aerogel powders of Examples 1-3 indicates that less of a compression layer was generated. The silica aerogel powder obtained in Comparative Example 2, where the grinding time was long (60 minutes), had an average particle size smaller than 20 μm and was finer, with higher true density and bulk density, and smaller pore volume compared to the silica aerogel powders of Examples 1-3. Therefore, it can be seen that the silica aerogel powder obtained in Comparative Example 2 has lower thermal insulation properties compared to the silica aerogel powders of Examples 1 to 3.

[0037] [Evaluation of dispersibility in polyurethane foam and its effect on improving thermal insulation] The dispersibility of the silica aerogel powders in Examples 1-3, Comparative Example 1, and Reference Examples 1-2 into foamed urethane, and the thermal conductivity of the foamed urethane to which the silica aerogel powder was added were measured by the following method. The results are shown in Table 2.

[0038] (dispersibility) Prepare a first liquid containing a polyol-containing liquid (manufactured by Sumika Covestro Urethane Co., Ltd.) and a blowing agent, and a second liquid containing polyisocyanate. Add 0.25% by mass of the aerogel powder to the first liquid relative to the polyurethane. Mix the aerogel powder-added first liquid and the second liquid, pour the resulting mixture into a jig, and react and foam it under the conditions of a jig temperature of 40°C and a curing time of 10 minutes to produce polyurethane foam (size: 50mm x 300mm x 400mm).

[0039] The surface of the obtained polyurethane foam is visually inspected, and the number of aggregates with a particle size of 0.5 mm or larger is counted within a 50 mm x 50 mm area of ​​the polyurethane foam surface. If the number of aggregates is 5 or less, it is considered "good," and if it is 6 or more, it is considered "aggregated."

[0040] (Thermal conductivity) The thermal conductivity of polyurethane foam in the thickness direction is measured using a thermal conductivity measuring device (FOX200, manufactured by Eiko Seiki Co., Ltd.). [Table 2]

[0041] The silica aerogel powders obtained in Examples 1-3 exhibited good dispersibility and low thermal conductivity, indicating excellent dispersibility in polyurethane foam and effectiveness in improving the thermal insulation properties of the polyurethane foam. In contrast, the silica aerogel aggregates and jet-milled products of Comparative Example 1 and Reference Example 1, which had shorter grinding times and less compression layer formation, all showed low dispersibility in polyurethane foam and high thermal conductivity. The decrease in dispersibility is thought to be due to the pores on the surface of the silica aerogel particles causing them to intertwine more easily. Furthermore, the increase in thermal conductivity is thought to be due to the formation of many aggregates of silica aerogel particles, which made the reaction between the polyol and polyisocyanate less likely to occur.

Claims

1. A method for producing aerogel powder for refrigerators, comprising grinding aerogel lumps with a particle diameter of 1 mm or more using a ball mill in a dry manner so that the average particle diameter is within the range of 20 μm to 30 μm.

2. The method for producing aerogel powder for refrigerators according to claim 1, wherein the balls of the ball mill have a diameter within the range of 5 mm to 15 mm.

3. A method for producing aerogel powder for refrigerators according to claim 1 or 2, wherein the grinding time is within the range of 15 minutes or more and 30 minutes or less.

4. The pore volume of the aerogel mass is 700 m ２ / g or more 1000m ２ A method for producing aerogel powder for refrigerators according to claim 1 or 2, wherein the powder is within the range of / g or less.

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