JP2020060291A - Heat insulating material, method of manufacturing the same, electronic device and automobile using the same - Google Patents

Abstract

To provide a heat insulation material whose heat transfer coefficient is not increased, even when the heat insulation material is smashed, compressed and deformed by expansion of a battery.SOLUTION: A heat insulation material containing a macropore and a mesopore is used. A insulation material manufacturing method is used, including a sol-preparation step of preparing sol, in which a micropore is introduced, by adding a gelatinizer to NaOin sodium silicate, in a manner that a mole ratio is smaller than 0.1 to 0.75, so as to remain non-reacted Na and non-cross linked oxygen in a siloxane skeleton; an impregnation/gelation step of impregnating a non-woven fiber structure with sol and producing a hydrogel/nonwoven fiber complex; a hydrophobic step of mixing the produced hydrogel/nonwoven fiber complex with a silylation agent and surface-modifying it; and a drying step of drying liquid contained in the surface-modified hydrogel/nonwoven fiber complex at less than critical temperature and pressure and removing it.SELECTED DRAWING: Figure 1

Description

  The present invention relates to a heat insulating material, a manufacturing method thereof, an electronic device using the same, and an automobile. In particular, it relates to an airgel composite heat insulating material, a manufacturing method thereof and its use.

  Currently, as an excellent heat insulating material, a heat insulating material in which silica airgel is held in fibers is used (Patent Documents 1 to 3).

Patent No. 6064149 Japanese Patent Application No. 2014-79802 Japanese Patent Application No. 2013-181138

  The conventional heat insulating material using silica airgel has a problem that when it is sandwiched and used in various devices, it is compressed and its density is increased, and its thermal conductivity is increased (= thermal resistance is decreased).

  Therefore, an object of the present application is to provide a heat insulating material that does not increase in thermal conductivity even if it is compressed and deformed, a manufacturing method thereof, an electronic device using the same, and an automobile.

A heat insulating material including an airgel having macropores and mesopores is used. An electronic device using the above heat insulating material is used between an electronic component that generates heat and a housing. An automobile using the above heat insulating material between batteries is used.

Further, by adding a gelling agent to NaO _{2 in} sodium silicate in a molar ratio of 0.1 to 0.75 or less, unreacted Na and non-crosslinked oxygen are left in the siloxane skeleton. A sol preparation step of adjusting the sol having macropores introduced therein, an impregnation / gelation step of impregnating the non-woven fiber structure with the sol to form a hydrogel-nonwoven fiber composite, and the above-mentioned hydrogel-nonwoven fiber A hydrophobizing step of mixing the complex with a silylating agent for surface modification, and a drying step of removing the liquid contained in the surface-modified hydrogel-nonwoven fiber composite by drying at a temperature below the critical temperature and pressure. A method of manufacturing a heat insulating material including, is used.

  The airgel composite heat insulating material having macropores and mesopores of the present invention has a large number of macropores that do not contribute to the reduction of thermal conductivity due to compressive deformation, resulting in a decrease in thermal conductivity, resulting in a gap between rectangular batteries. When used in, even if the battery expands, it ensures the same or better thermal insulation than before expansion.

The figure which shows the pore distribution which the airgel of embodiment can take. The figure which shows unreacted Na and non-bridging oxygen in the siloxane skeleton of the embodiment. The figure which shows the silica airgel which has a macropore and mesopore of embodiment. Figure showing the result of pore distribution measurement by mercury porosimetry The figure of the solid image by the micro X-ray CT measurement of the airgel composite heat insulating material of Example 1 and Comparative Example 1, and the XY, YZ, XZ tomographic image. The figure which shows the distribution of the macropore (porosity) in the film thickness direction of the airgel composite heat insulating material of Example 1 and Comparative Example 1.

Next, the present embodiment will be described with reference to preferred embodiments of the invention.
<Design concept of airgel composite insulation with macropores>
Several airgel composite heat insulating materials composed of silica airgel and non-woven fiber have been known so far. Many of them have improved handling. However, the airgel composite heat insulating material does not have sufficient strength to withstand a load of 5 MPa. Therefore, in the airgel composite heat insulating material, the mesopores are crushed by the compressive deformation. As a result, in the airgel composite heat insulating material, the number of contact points between silica particles rapidly increases, the density increases, and the thermal conductivity increases.

The greatest feature of the airgel composite heat insulating material of the present embodiment is that the airgel has macropores 2 of 1 to 10 μm and mesopores 1 of 2 to 50 nm. Therefore, the thermal conductivity of the airgel composite heat insulating material does not increase (deteriorate) even when a load as high as 5 MPa is applied to the heat insulating material. Rather, the thermal conductivity of the airgel composite heat insulating material decreases (improves). The mechanism will be described later.
A bimodal pore distribution of macropores 2 and mesopores 1 is preferred. Here, the bimodal pore distribution means that there are two peaks in the pore distribution, and is also called "bimodal" or "bimodal". However, it does not have to be bimodal.

  FIG. 1 shows a pattern of pore distribution that the airgel can take. The horizontal axis is the hole diameter. The vertical axis represents the number. Table 1 shows the ratio of each mesopore 1 and macropore 2 in FIG. In addition,% in Table 1 is a volume ratio.

  As shown in FIG. 1, there are eight kinds of pore distribution patterns (a) to (h), but the airgel of the embodiment of the present application has the mesopores 1 and macroscopic particles as shown in (g) and (h). It has both pore distributions of pores 2. Note that (h) is not necessarily bimodal.

  The pore distribution of the mesopores 1 is 2 to 50 nm, the average pore diameter is 20 to 40 nm, and the volume ratio to the total pore volume is 15 to 60%.

  Here, the average pore diameter D can be obtained by the gas adsorption method and is as follows. It can be calculated only from the two physical properties, specific surface area A and total pore volume V. This average pore diameter D is considered by representing all pores by one (large) cylindrical pore. One large cylindrical pore has volume V and surface area A (side area). Since it is cylindrical, the volume V, surface area A, and cylinder height H can be determined by the following equations.

V = πD ² H / 4 (Equation 1)
A = πDH ... (Equation 2)
Eliminating H from these equations 1 and 2 gives the following equation.
D = 4V / A (Equation 3)
The macropores 2 have a pore distribution of 1 to 10 μm, an average pore diameter of 2 to 6 μm, and a volume ratio of 7 to 60% with respect to the total pore volume. Within this range, micropores smaller than 2 nm and macropores larger than 50 nm and smaller than 1 μm may be provided. It is preferable that there are no macropores larger than 10 μm. The ratio of macropores in the composite material can be obtained by micro X-ray CT measurement having a resolution of about 1 μm as a porosity.

At this time, metal oxide nanoparticles such as silica (SiO ₂ ), titania (TiO ₂ ), alumina (Al ₂ O ₃ ), zirconia (ZrO ₂ ) and resorcinol-formaldehyde (RF ), Polyimide, organic compounds such as urethane, and carbon aerogel obtained by firing RF aerogel.

  The mechanism that exhibits a peculiar behavior as described above is crushed by sacrificing the macropores 2 existing inside the heat insulating material at the time of pressing. On the other hand, it is considered that the mesopore distribution survives and is maintained without being crushed. In a porous material having a pore size distribution larger than 68 nm, which is the mean free path of static air (nitrogen molecules), heat transfer is likely to occur due to convection of air, and therefore the thermal conductivity is generally high. Therefore, the reason why the thermal conductivity of the heat insulating material having the bimodal distribution is reduced by pressing is that the convection of air is suppressed by the disappearance of the macropores.

<Heat transfer characteristics after compression of airgel composite heat insulating material having macropores 2>
The thermal conductivity of the composite heat insulating material of the embodiment when pressurized at 0.75 to 5 MPa is preferably 1 to 10% lower than the initial thermal conductivity, and more preferably 5 to 10% lower.

  When the thermal conductivity of the composite heat insulating material is less than 1% as compared with the initial heat conductivity, it is difficult to suppress the thermal chain during compression of the composite heat insulating material.

  When the thermal conductivity of the composite heat insulating material is 5 to 10% as compared with the initial heat conductivity, the thermal chain during compression of the composite heat insulating material can be effectively suppressed.

<Material type and material concentration of airgel composite insulation>
As a raw material for an airgel having a bimodal distribution, a general-purpose raw material such as a known metal alcoside or water glass is used, and water is added to a desired raw material concentration to prepare a dispersion liquid or a solution. .

  Examples of the metal species include Si, Ti, Al and Zr. Since it is considered that Na ions affect the densification and densification of the porous structure in the high-density airgel, water glass containing Na ions is preferably used. The silica concentration in the raw material dispersion liquid or solution is not particularly limited as long as it is a concentration capable of synthesizing an airgel, but is preferably 6 to 22%.

<Gelling agent and concentration of airgel composite heat insulating material>
The type of gelling agent used for synthesizing the airgel having mesopores and macropores of the present embodiment is not particularly limited, and any known one may be used. For example, mineral acids such as hydrochloric acid, sulfuric acid, nitric acid and phosphoric acid, organic acids such as formic acid, acetic acid, citric acid and tartaric acid, and carbonic acid such as carbon dioxide and carbonic acid ester are used. This applies not only to silica but also to titania, alumina and zirconia.

The addition amount of the gelling agent is such that the stoichiometric ratio is 0.50 or less with respect to NaO _{2 in} sodium silicate. For example, in 100 g of a sodium silicate aqueous solution containing 5 wt% NaO ₂ , 8 mmol of NaO ₂ is present.

  However, by adding a gelling agent at a stoichiometric ratio of 0.50, that is, 4 mmol or less, unreacted Na3 and non-bridging oxygen 4 can be left in the siloxane skeleton as shown in FIG. This applies not only to silica but also to titania, alumina and zirconia.

By doing so, defects can be introduced at the molecular level, and macropores 7 are generated in the skeleton of the silica airgel 6 having the mesopores 5, as shown in FIG. Macropores are formed by such a mechanism. The addition amount of the gelling agent is 0.1 to 0.50 in terms of molar ratio with respect to the stoichiometric amount of NaO ₂ in sodium silicate from the viewpoint of productivity (impregnation speed of the raw material liquid into the nonwoven fabric, etc.) and cost. Is preferred.

<Thickness of airgel composite insulation>
The airgel composite heat insulating material has a thickness in the range of 0.03 mm to 3.0 mm, preferably in the range of 0.05 mm to 1.5 mm. If the airgel composite heat insulating material is thinner than 0.03 mm, the heat insulating effect in the thickness direction will decrease, so if you do not realize a very low heat conductivity close to that of vacuum, from one side The heat transfer in the thickness direction to the other surface cannot be satisfactorily reduced. When it is thicker than 0.05 mm, the heat insulating effect in the thickness direction can be secured. On the other hand, if the airgel composite heat insulating material is thicker than 1.5 mm, it becomes difficult to incorporate it into vehicle / industrial equipment. Particularly in the field of automobiles, if the thickness is greater than 3.0 mm, it becomes more difficult to incorporate the device.

<Non-woven fiber fabric weight>
The basis weight of the non-woven fabric fibers used in the production of the airgel composite heat insulating material is preferably 5 to 200 g / m ^{2 in} order to maintain the minimum rigidity necessary for the support of the airgel. The basis weight is the weight of fibers per unit area.

<Bulk density of non-woven fiber>
The bulk density of the non-woven fiber is preferably in the range of 100 to 500 kg / m ³ from the viewpoint of increasing the content of silica xerogel in the airgel composite heat insulating material and further reducing the thermal conductivity.
In order to form a non-woven fabric with mechanical strength as a continuous body, a bulk density of at least 100 kg / m ^{3 is} required. When the bulk density of the non-woven fabric is larger than 500 kg / m ³ , the space volume in the non-woven fabric is small, so that the silica xerogel that can be filled is relatively reduced and the thermal conductivity is increased.

<Material of non-woven fiber>
The materials of the non-woven fiber used for manufacturing the airgel composite heat insulating material include inorganic fiber type glass wool, glass paper, rock wool, resin type polyethylene terephthalate (PET), polyphenylene sulfide (PPS), polypropylene (PP), poly Tetrafluoroethylene (PTFE), natural wool, cellulose, carbon felt or the like can be used.

<Method for manufacturing airgel composite heat insulating material>
In order to prepare bimodal airgel with macropores and mesopores, it is necessary to strategically introduce defects at the molecular level into the siloxane network. The basic synthesis procedure consists of 3 steps, a) to c).
a) A non-woven fiber structure is impregnated with a sol prepared by adding a gelling agent to Na ₂ O in a sodium silicate composition in a molar ratio of less than 0.1 to 0.75, and a hydrogel Producing a composite of non-woven fibers.
b) The hydrogel-nonwoven fiber composite produced in step a) is mixed with a silylating agent for surface modification.
c) The liquid contained in the surface-modified hydrogel-nonwoven fiber composite obtained in step b) is removed by drying below the critical temperature and pressure.

  The present embodiment will be described below based on examples. However, the present embodiment is not limited to the following examples. All reactions were performed under air. The conditions and results are shown in Table 2.

<Evaluation>
In the examples, using sodium silicate as a raw material and carbonic acid ester as a gelling agent, a heat insulating sheet was prepared by changing the silica concentration of the water glass raw material, and the thermal conductivity, compressive strain, and thermal resistance value were evaluated.

  A heat flow meter HFM436 Lamda (manufactured by NETZCH) was used for the thermal conductivity measurement. The mesopores of the airgel composite heat insulating material were evaluated using a high precision gas / vapor adsorption amount measuring device BELSORP-max42N-VP-P (manufactured by Microtrac Bell). The ratio (as void ratio) and distribution of macropores was examined by nondestructive inspection by micro X-ray CT (three-dimensional measurement X-ray CT device: TDM1000-IS / SP (made by Yamato Scientific Co., Ltd.), three-dimensional volume. Rendering software: VG-StudioMAX (manufactured by Volume Graphics)). Detailed conditions of each example and comparative example will be described below.

<Passing criteria for thermal conductivity after compression>
The condition where the thermal conductivity after performing the pressing treatment at 5.0 MPa and 50 ° C. for 30 minutes three times was 5% or more lower than the initial thermal conductivity was regarded as acceptable. If it is less than 5%, it is difficult to effectively suppress the heat chain even under high load.

<Example 1>
A gelling agent (ethylene carbonate) was added to a sodium silicate aqueous solution (SiO ₂ concentration 20 wt%, Na ₂ O concentration 5 wt%) so that the molar ratio to Na ₂ O was 0.375, and the mixture was well stirred and dissolved. To prepare a sol solution.

Next, the sol solution was impregnated into the nonwoven fabric by pouring the sol solution into the nonwoven fabric fiber (material: glass paper, thickness 1 mm, basis weight 155 g / m ² , size 12 cm square). The nonwoven fabric impregnated with the sol solution was sandwiched between PP films (thickness: 50 μm × 2 sheets) and left at room temperature of 23 ° C. for 3 minutes to gel the sol. After confirming the gelation, the impregnated non-woven fabric together with the film was passed through a biaxial roll in which the gap was set to 1.00 mm (including the film thickness), excess gel was squeezed out from the non-woven fabric, and the thickness was controlled to aim at 1.00 mm.

  Next, the film was peeled off, the gel sheet was immersed in 6N hydrochloric acid, and then left at room temperature for 23 minutes at 23 ° C. to incorporate hydrochloric acid into the gel sheet. Then, the gel sheet was immersed in a mixed solution of octamethyltrisiloxane which is a silylating agent and 2-propanol (IPA), and placed in a constant temperature bath at 55 ° C. for reaction for 2 hours. When the trimethylsiloxane bond started to be formed, the hydrochloric acid water was discharged from the gel sheet, and two liquids were separated (siloxane in the upper layer, hydrochloric acid water in the lower layer, and 2-pronol). The gel sheet was transferred to a constant temperature bath set at 150 ° C. and dried in an air atmosphere for 2 hours to obtain a heat insulating sheet.

  As a result of measuring the thermal conductivity of this airgel composite heat insulating material, it was 45 mW / mK. Further, as shown in FIG. 4, which is the result of the pore distribution measurement by the mercury porosimeter, the presence of macropores of 1 μm or more was confirmed by 15% or more.

  FIG. 5 shows a stereoscopic image of the airgel composite heat insulating material and XY, YZ, and XZ tomographic images acquired by micro X-ray CT measurement. Although the resolution of this device is 1 μm, the presence of macropores of 1 μm was visually confirmed.

FIG. 6 shows the distribution of macropores (porosity) in the film thickness direction. It was quantitatively found that in Example 1, the ratio of macropores in the vicinity of the surface was relatively small, and the number of macropores was larger than that in Comparative Example 1.
In Example 1, the ratio of macropores determined from the micro X-ray CT image was 9.25% (Table 2).

  Next, the thermal conductivity after compression was evaluated and found to be 42 mW / mK, which was 7% lower than the initial thermal conductivity (Table 2).

<Comparative Example 1>
A sheet was produced under the same process conditions as in Example 1, except that the addition amount of the gelling agent was changed to 0.75. As a result of measuring the thermal conductivity of this airgel composite heat insulating material, it was 46 mW / mK. Further, as a result of the pore distribution measurement by the mercury intrusion porosimeter, as shown in FIG. 4, the mesopore distribution was confirmed, but the presence of macropores was not confirmed. On the other hand, in the micro X-ray CT measurement, which is a nondestructive inspection, as shown in FIGS. 5 and 6, the presence of macropores was confirmed although the number was smaller than in Example 1. The ratio of macropores was 5.30% (Table 2). Next, the result of thermal conductivity evaluation after compression was 46 mW / mK, and no change was observed with respect to the initial thermal conductivity (Table 1).

It is preferable to use the heat insulating sheet of the embodiment between the batteries of the automobile. Since the battery of the automobile is frequently expanded and contracted by charging and discharging, the heat insulating sheet of the embodiment is suitable for it.
In addition, in an electronic device, the heat insulating sheet may be used between the electronic component that generates heat and the housing.

(as a whole)
Although silica has been described as the aerogel, titania, alumina, zirconia and the like are also applicable. The same applies to the pore size, concentration, and characteristics.

The heat insulating sheet of the embodiment is widely used because it can exhibit a sufficient heat insulating effect even in a narrow space in electronic devices, in-vehicle devices, and industrial devices. Furthermore, it is applied to all products related to heat, such as mobile devices, displays, and electrical components.

1 Mesopore 2 Macropore 3 Na
4 Non-crosslinked oxygen 5 Mesopores 6 Silica airgel 7 Macropores

Claims (11)

An insulating material including an airgel having macropores and mesopores. The heat insulating material according to claim 1, comprising the airgel having macropores of 1 to 10 µm and mesopores of 2 to 50 nm. The average pore diameter of the mesopores is 20 to 40 nm,
The heat insulating material according to claim 1, wherein the airgel has an average pore diameter of 2 to 6 μm. The heat insulating material according to any one of claims 1 to 3, comprising an airgel having the macropores in an amount of 7 to 60 vol% with respect to the total pore volume and the mesopores in an amount of 15 to 60 vol% with respect to the total pore volume. . The heat insulating material according to any one of claims 1 to 4, wherein the non-woven fabric fiber holds the airgel. The heat insulating material according to claim 1, wherein the thermal conductivity after compression is lower than the initial thermal conductivity by 5% or more. The heat insulating material according to claim 6, wherein the thermal conductivity after compression by 5 MPa is lower than the initial thermal conductivity by 5% or more. The heat insulating material according to any one of claims 1 to 7, wherein the airgel is silica aerogel. An electronic device using the heat insulating material according to any one of claims 1 to 8 between an electronic component that generates heat and a housing. An automobile using the heat insulating material according to any one of claims 1 to 8 between batteries. A gelling agent is added to NaO _{2 in} sodium silicate so that the molar ratio becomes smaller than 0.1 to 0.75, and unreacted Na and non-crosslinked oxygen are left in the siloxane skeleton to leave macropores. A sol preparation step for adjusting the introduced sol,
An impregnation / gelling step of impregnating the non-woven fiber structure with sol to generate a hydrogel-nonwoven fiber composite,
A hydrophobizing step of surface-modifying the produced hydrogel-nonwoven fiber composite with a silylating agent;
And a drying step of removing the liquid contained in the surface-modified hydrogel-nonwoven fiber composite by drying at a temperature below the critical temperature and pressure.

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