Aerogel composite molded body
The aerogel composite molded bodies, formed by precise composition and pressure molding of aerogel and silica ultrafine powders, address the issues of high thermal conductivity and defects in conventional materials, offering enhanced thermal and sound insulation.
Patent Information
- Authority / Receiving Office
- JP · JP
- Patent Type
- Patents
- Current Assignee / Owner
- KROSAKI HARIMA CORP
- Filing Date
- 2020-11-20
- Publication Date
- 2026-07-01
- Estimated Expiration
- Not applicable · inactive patent
AI Technical Summary
Conventional fine porous heat insulating materials using silica ultrafine powder suffer from high thermal conductivity and significant defects such as cracks when aerogel powder is blended in the raw material composition.
Aerogel composite molded bodies are produced by pressure molding a raw material mixture containing aerogel powder with a specific median diameter and silica ultrafine powder, with controlled proportions and optionally incorporating hollow particles and fibers, to achieve low thermal conductivity and reduce defects.
The aerogel composite molded bodies exhibit reduced thermal conductivity and defects, with improved compressive strength and sound absorption properties, making them suitable for thermal and sound insulation.
Smart Images
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Figure 0007883220000002
Abstract
Description
Technical Field
[0001] The present invention relates to an aerogel composite body.
Background Art
[0002] Conventionally, as a heat insulating material, a fine porous heat insulating material obtained by pressure molding a raw material composition containing silica ultrafine powder (fumed silica) as a main raw material is known (for example, Patent Document 1). Although such a fine porous heat insulating material has high heat insulation due to its low thermal conductivity, in order to achieve higher heat insulation, a material capable of achieving a lower thermal conductivity is required.
Prior Art Documents
Patent Documents
[0003]
Patent Document 1
Summary of the Invention
Problems to be Solved by the Invention
[0004] The inventors of the present invention focused on aerogel, which is known as a material having a very low thermal conductivity, and obtained the idea of obtaining a molded body such as a heat insulating material in which aerogel powder is blended in a raw material composition. However, it was found that simply blending aerogel powder in the raw material composition would cause significant generation of defects (cracks) in the molded body.
[0005] An object of the present invention is to provide an aerogel composite body having a low thermal conductivity and reducing the generation of defects in the molded body.
Means for Solving the Problems
[0006] As a heat insulating material and the like, the inventors of the present invention repeated tests and studies on the composition of the raw material composition and the like in order to have a low thermal conductivity and reduce the generation of defects in the molded body, and as a result, arrived at the present invention.
[0007] In other words, according to one aspect of the present invention, the following aerogel composite molded article is provided. An aerogel composite molded body obtained by pressure molding a raw material mixture containing aerogel powder and silica ultrafine powder excluding the aerogel powder, The aerogel powder has a median diameter of 1 μm or more and 45 μm or less. The raw material formulation is an aerogel composite molded article containing 1% by mass or more and 55% by mass or less of the aerogel powder. [Effects of the Invention]
[0008] According to the present invention, an aerogel composite molded article can have low thermal conductivity and reduce the occurrence of defects in the molded article. [Modes for carrying out the invention]
[0009] The aerogel composite molded article of the present invention is obtained by pressure molding a raw material mixture containing aerogel powder and silica ultrafine powder excluding the aerogel powder (hereinafter simply referred to as "silica ultrafine powder"). By including aerogel powder and silica ultrafine powder in the raw material mixture in this way, low thermal conductivity can be achieved and the occurrence of defects in the molded article can be reduced.
[0010] The aerogel powder used in the present invention has a median diameter (d50) of 1 μm or more and 45 μm or less. Such aerogel powder can be obtained by appropriately grinding an aerogel obtained by a known method such as supercritical drying or atmospheric pressure drying of an aerogel raw material (e.g., silica gel). That is, it can be obtained by grinding an aerogel obtained by a known drying method so that the median diameter is 1 μm or more and 45 μm or less. Known aerogels include silica aerogel, alumina aerogel, zirconia aerogel, polymer aerogel, and carbon aerogel. In the present invention, one or more of these aerogels, selected from silica aerogel powder, alumina aerogel powder, zirconia aerogel powder, polymer aerogel powder, carbon aerogel powder, etc., can be used as the aerogel powder. However, to achieve a lower thermal conductivity, it is preferable to use silica aerogel powder.
[0011] If the median diameter of the aerogel powder is less than 1 μm, the fine porosity structure of the aerogel is impaired, and a sufficient reduction in thermal conductivity cannot be obtained. On the other hand, if the median diameter of the aerogel powder exceeds 45 μm, the amount of springback after molding increases, resulting in numerous defects in the molded product. The median diameter of the aerogel powder is preferably 15 μm or more and 25 μm or less. Furthermore, the maximum particle size of the aerogel powder is preferably 600 μm or less.
[0012] In this invention, aerogel powder is included in the raw material formulation in an amount of 1% by mass or more and 55% by mass or less. If the aerogel powder content is less than 1% by mass, low thermal conductivity cannot be achieved. On the other hand, if the aerogel powder content exceeds 55% by mass, the amount of springback after molding increases, and a large number of defects occur in the molded product. The aerogel powder content in the raw material formulation is preferably 2% by mass or more and 30% by mass or less, and more preferably 4% by mass or more and 15% by mass or less.
[0013] In the present invention, it is preferable that the aerogel powder contains hollow particles. The hollow particles block the fine interconnected pores (vacancies) remaining in the aerogel, suppressing heat conduction via air molecules, thereby further reducing the thermal conductivity. Furthermore, by sealing a gas with a lower thermal conductivity than air (for example, carbon dioxide) inside the hollow particles, the thermal conductivity can be further reduced.
[0014] The hollow particles are not particularly limited, but can be nano-hollow particles, micro-hollow particles, or both. Nano-hollow particles are preferably prepared to have an outer diameter of 30 nm to 360 nm and a spherical shell thickness of 7.5 nm to 65 nm. The outer diameter corresponds to approximately 1 / 2 to 5 times the mean free path of air at room temperature and pressure. Thus, because the size of the hollows in nano-hollow particles is on the same order as the mean free path of air, when added to aerogel, they contribute significantly to reducing thermal conductivity. Micro-hollow particles are preferably prepared to have an outer diameter of 1 μm to 23 μm and a spherical shell thickness of 0.35 μm to 3 μm. The outer diameter is larger than 15 times the mean free path of air at room temperature and pressure, and in addition to contributing to reducing thermal conductivity, they also have the effect of increasing the structural strength of the aerogel network. Although aerogels retain the fine interconnected pores described above, the added hollow particles block these pores, suppressing heat conduction through gases such as convection that would otherwise occur through these pores, thereby enhancing the heat insulation effect. Nano-hollow particles can be manufactured, for example, by the soft template method. Specifically, a particle consisting of a core and a spherical shell is produced by modifying the surface of a polymer electrolyte with ammonia in ethanol and coating it with silica (SiO2). By washing or calcining this particle, the medium that was encapsulated in the core is removed, and a hollow particle is produced. For the production of micro-hollow particles, the double emulsion method is preferred, for example. From a dispersed multiphase system consisting of an oil phase containing a surfactant and an aqueous phase consisting of a precursor and a surfactant, an emulsion is produced by emulsification, with the oil phase as the continuous phase and droplets mainly composed of the aqueous phase. By adding the aqueous phase to this emulsion, it changes to an emulsion with droplets mainly composed of gel in the continuous aqueous phase. Micro-hollow particles are produced by washing / filtration or calcination of this emulsion.
[0015] Aerogel powder containing such hollow particles can be obtained, for example, by the following method. To explain using silica aerogel as an example, silica aerogel containing hollow particles is mainly produced in the following two steps: forming a wet gel using the sol-gel method, and drying the wet gel. The wet gel consists of a network of nanostructured solid silica and a liquid solvent, and is produced by hydrolyzing and condensing silica precursor molecules. This silica precursor is produced by mixing TEOS (Tetraethyl orthosilicate) and methanol. Further, hollow particles are added to this mixture, along with a total of 6.3 g of oxalic acid (0.01 M), and finally 1.5 g of ammonium hydroxide (NH4OH 0.5 M) is added to form an alcoholol. This alcoholol gels when left at room temperature. When this wet gel is dried, it becomes a silica aerogel containing hollow particles, and when this silica aerogel is pulverized, it becomes a silica aerogel powder containing hollow particles.
[0016] The content of hollow particles in the aerogel powder is preferably 0.01% by mass or more and 30% by mass or less, more preferably 0.1% by mass or more and 15% by mass or less, and most preferably 1% by mass or more and 10% by mass or less.
[0017] In the present invention, the content of ultrafine silica powder in the raw material formulation is preferably 40% by mass or more and 95% by mass or less. This further reduces the occurrence of defects in the molded article. As the silica ultrafine powder, in addition to fumed silica, silica ultrafine powder obtained by the sedimentation method, silica ultrafine powder obtained by the gel method, etc. can be used. Here, the "ultrafine powder" means, for powders in which relatively spherical primary particles such as the sedimentation method are obtained, those with a primary particle diameter of 5 nm or more and 200 nm or less, and for powders with a complex shape and a difficult-to-specify particle diameter such as fumed silica, the specific surface area is 50 m 2 / g or more and 500 m 2 / g or less. When fumed silica is included as the silica ultrafine powder, the specific surface area of the fumed silica is preferably 100 m 2 / g or more and 400 m 2 / g or less. Thereby, the occurrence of defects in the molded body can be further reduced. That is, as described above, fumed silica has a complex shape, and a small specific surface area means that the fumed silica is short, resulting in a weak entanglement of the raw material particles and a low strength of the molded body. On the other hand, a large specific surface area means that the fumed silica is long, resulting in a strong entanglement of the raw material particles and a high strength of the molded body. Considering these, the specific surface area of fumed silica is preferably 100 m 2 / g or more and 400 m 2 / g or less.
[0018] In the present invention, the raw material composition preferably contains 0.5% by mass or more and 10% by mass or less of fibers. Thereby, the compressive strength of the molded body can be improved, and the occurrence of defects in the molded body can also be reduced. The fiber may be either an inorganic fiber or an organic fiber. Examples of the inorganic fiber include silica fiber, glass fiber, alumina fiber, etc. Examples of the organic fiber include natural fibers such as cotton, hemp, and silk, and synthetic fibers such as aramid, polyamide, polyester, polyethylene, acrylic, rayon, and cellulose nanofiber.
[0019] In the present invention, the raw material composition may appropriately include powders such as fumed alumina, silicon carbide, titanium dioxide, iron oxide, zirconium oxide, zirconium silicate, zinc oxide, mica, and metallic aluminum, in addition to the aerogel powder, silica ultrafine powder, and fibers mentioned above. Then, after mixing the raw material mixture as needed, the aerogel composite molded body of the present invention is obtained by pressure molding. Methods such as uniaxial pressure molding, biaxial pressure molding, and CIP molding can be used for pressure molding. The pressure molding conditions can be appropriately determined according to the desired properties of the aerogel composite molded product. Furthermore, a binder may or may not be added to the raw material mixture before pressure molding.
[0020] The aerogel composite molded body of the present invention can be suitably used as a thermal insulation material, but it can also be used as a sound-absorbing material. That is, the aerogel composite molded body of the present invention is porous, and when sound waves strike it, resistance acts as the air inside the molded body vibrates, and the sound energy is converted into thermal energy by friction, resulting in a sound absorption effect, so it can also be used as a sound-absorbing material. [Examples]
[0021] Table 1 shows the raw material formulation and evaluation results of an aerogel composite molded article, which is an example of the present invention, and Table 2 shows the raw material formulation and evaluation results of a comparative example.
[0022] [Table 1]
[0023] [Table 2]
[0024] In the raw material formulations shown in Tables 1 and 2, "Silica Aerogel Powder A" refers to silica aerogel powder obtained by appropriately grinding silica aerogel obtained by a known drying method of drying aerogel raw material (silica gel) at atmospheric pressure, and "Silica Aerogel Powder B" refers to silica aerogel powder containing hollow particles obtained by supercritical drying. The "remainder" refers to fumed alumina and silicon carbide powder.
[0025] After mixing the raw material formulations for each example, without adding a binder, the molding pressure was 10 kg / cm². 2 By uniaxial compression molding, a molded body measuring 50 mm in width, 50 mm in length, and 20 mm in thickness was obtained. For each example of the molded body, the thermal conductivity, the number of defects (cracks), and the compressive strength were evaluated, and an overall evaluation was performed based on these evaluation results. The evaluation methods and criteria for each evaluation item are as follows. <Thermal conductivity> The thermal resistance and thermal conductivity of thermal insulating materials were measured at room temperature according to JIS A1412-1 "Method for measuring thermal resistance and thermal conductivity of thermal insulating materials - Part 1: Protective hot plate method (GHP method)". The relative value was calculated by setting the thermal conductivity (W / mK) of Comparative Example 1, a general silica insulating material, to 100. A smaller relative value indicates lower thermal conductivity (higher insulating performance). In the evaluation of thermal conductivity, a relative value of less than 80 was marked as ○ (good), a value between 80 and 95 was marked as △ (acceptable), and a value of 95 or higher was marked as × (poor). <Number of defects> The number of visible linear defects was counted on all four sides of the molded body measuring 50mm wide x 50mm long x 20mm thick. A total of 0-10 linear defects was rated as ○ (good), 11-30 as △ (acceptable), and 31 or more as × (poor). Note that ○ and △ indicate a level of defect suitable for use as insulation material, etc. <Compressive strength> A test piece measuring 40mm wide x 40mm long x 20mm thick was cut from the aforementioned molded body measuring 50mm wide x 50mm long x 20mm thick. The compressive stress was measured under conditions of 0.05 to 0.2 MPa / s according to JIS R2206-2 "Test method for compressive strength of refractory bricks - Part 2: Method using packing," and the relative value was calculated by setting the compressive strength (MPa) of Comparative Example 1, a general silica insulation material, to 100. A larger relative value indicates higher compressive strength of the molded body and fewer defects, indicating a better quality. In the evaluation of compressive strength, a relative value of 80 or higher was marked as ○ (good), a value between 50 and 80 was marked as △ (acceptable), and a value below 50 was marked as × (poor). <Overall Rating> In each of the above evaluations, a score of ○ (Good) was given when all scores were ○, a score of △ (Acceptable) was given when there were no × scores but at least one was △, and a score of × (Poor) was given when at least one score was ×.
[0026] Examples 1 to 15 shown in Table 1 are aerogel composite molded articles that fall within the scope of the present invention. Their overall evaluations were ○ (good) or △ (acceptable), and good evaluations were obtained for thermal conductivity, number of defects, and compressive strength. In particular, Examples 5 to 12 are aerogel composite molded articles in which the aerogel powder content and median diameter, silica ultrafine powder (fumed silica) content and specific surface area, and fiber content are all within the above-mentioned preferred range. Their overall evaluation was ○ (good), and a better evaluation was obtained compared to the other examples. In addition, Example 7 used "Silica Aerogel Powder B," which is silica aerogel powder containing hollow particles, and the thermal conductivity decreased significantly.
[0027] Comparative Example 1, shown in Table 2, is a general silica insulation material that does not contain aerogel powder. The number of defects in the molded product was small and the compressive strength was sufficient, but the thermal conductivity was evaluated as × (poor). Comparative Example 2 was an aerogel composite molded article with an excessively high aerogel powder content, resulting in a negative (×) rating for the number of defects and compressive strength of the molded article. Comparative Example 3 was an aerogel composite molded article in which the median diameter of the aerogel powder was too small, resulting in a thermal conductivity evaluation of × (poor). Comparative Example 4 was an aerogel composite molded article in which the median diameter of the aerogel powder was too large, and the number of defects and compressive strength of the molded article were evaluated as × (poor).
Claims
1. An aerogel composite molded body obtained by pressure molding a raw material mixture containing aerogel powder and silica ultrafine powder excluding the aerogel powder, The aerogel powder has a median diameter of 1 μm or more and 45 μm or less. The aforementioned raw material formulation is an aerogel composite molded article containing 1% by mass or more and 55% by mass or less of the aerogel powder.
2. The aerogel composite molded article according to claim 1, wherein the raw material formulation contains 40% by mass or more and 95% by mass or less of the silica ultrafine powder.
3. The aerogel composite molded article according to claim 1 or 2, wherein the raw material composition contains 0.5% by mass or more and 10% by mass or less of fibers.
4. The aerogel composite molded article according to any one of claims 1 to 3, wherein the aerogel powder includes hollow particles.
5. The aerogel composite molded article according to any one of claims 1 to 4, wherein the median diameter of the aerogel powder is 15 μm or more and 25 μm or less.
6. The aerogel composite molded article according to any one of claims 1 to 5, wherein the aerogel powder content in the raw material blend is 2% by mass or more and 30% by mass or less.
7. The aerogel composite molded article according to any one of claims 1 to 5, wherein the content of the aerogel powder in the raw material blend is 4% by mass or more and 15% by mass or less.
8. The aforementioned silica ultrafine powder contains fumed silica, and the fumed silica has a specific surface area of 100 m². ２ / g or more 400m ２ An aerogel composite molded article according to any one of claims 1 to 7, wherein the amount is less than or equal to / g.