Thermal insulation sheet and method for manufacturing the same, as well as electronic device and battery unit

Abstract

The present invention aims to provide a thermal insulation sheet that can be used even under high loads, a method for producing the same, and an electronic device and battery cell. To achieve this objective, a method for producing the thermal insulation sheet is provided, comprising the following steps: a composite formation step in which an alkaline sol prepared by adding a carbonate to a water glass composition is impregnated into nonwoven fibers to form a hydrogel-nonwoven fiber composite; a surface modification step in which the composite is mixed with a silylating agent for surface modification; and a drying step in which the liquid contained in the composite is dried below the critical temperature and pressure to remove the liquid. A thermal insulation sheet comprising aerogel and nonwoven fibers and having a compressibility of 40% or less at 0.30 to 5.0 MPa is used. An electronic device is used in which the thermal insulation sheet is positioned between a heat-generating electronic component and its housing. A battery cell is used in which the thermal insulation sheet is positioned between batteries.

Description

Technical Field

[0001] The present invention relates to a heat-insulating sheet, a method for producing the same, and electronic equipment and a battery cell using the same, and more particularly to a high-strength heat-insulating sheet, a method for producing the same, and electronic equipment and a battery cell. Background Art

[0002] In the automotive and industrial equipment fields, high-performance thermal insulation sheets with excellent compression properties are required to control heat flow from heat-generating components within confined spaces, ensure product safety, and prevent fire. Such thermal insulation sheets are expected to be suitable, for example, for use as cell separators in lithium-ion battery modules.

[0003] Lithium-ion battery safety standards require a fire retardancy test. This test examines whether thermal runaway of one cell within a battery module could cause heat diffusion to other cells, including adjacent cells, leading to fire or rupture. To prevent thermal runaway from spreading to adjacent cells, a safety design concept has been proposed, using materials with excellent thermal insulation properties sandwiched between cells. In theory, even materials with high thermal conductivity can prevent heat diffusion or fire retardancy to a certain extent if the thickness is increased.

[0004] However, battery modules are installed inside equipment, so the space for installation is limited and there are size restrictions. This presents the following challenges: in addition to increasing the module's capacity, it is also necessary to achieve fire resistance and miniaturization.

[0005] In order to achieve a balance between high module capacity, fire resistance, and miniaturization, it is desirable to use a thin material with high thermal insulation properties as a cell spacer. In addition, considering that the active material deteriorates and expands during the charge and discharge cycle of the battery, resulting in bulging of the cell, it is also desirable that the thermal insulation sheet has the characteristic of being difficult to crush. During the initial assembly of the battery module, the load applied to the thermal insulation sheet as a cell spacer is less than 1 MPa, that is, relatively small. On the other hand, if the battery expands, a load of up to about 5 MPa may be applied to the thermal insulation sheet. Therefore, it is important to design the material of the thermal insulation sheet taking into account the compression characteristics.

[0006] Silica aerogel is a known material with low thermal conductivity. It consists of a network structure of silica particles measuring tens of nanometers in size connected by point contacts, with an average pore diameter less than the mean free path of air, 68 nanometers. This means it has a lower thermal conductivity than still air. Consequently, silica aerogel has attracted attention as an excellent thermal insulator. However, silica aerogel's extremely low strength against various deformations, such as compression, bending, and shearing, has been considered a practical issue.

[0007] The inventors have designed a thin, homogeneous sheet-like thermal insulation material with improved handling properties by combining silica aerogel with nonwoven fabric fibers (Patent Document 1). This thin thermal insulation sheet has excellent handling properties and is highly resistant to bending.

[0008] On the other hand, as a high-strength thermal insulation material utilizing aerogel, a self-supporting hard composite material has been designed by molding and drying a slurry containing hydrophobic aerogel particles, inorganic binders such as cement, gypsum, lime, surfactants, fibers, etc. in a container (Patent Document 2).

[0009] Prior art literature

[0010] Patent Literature

[0011] Patent Document 1: Japanese Patent No. 6064149

[0012] Patent Document 2: Japanese Patent No. 5934400 Summary of the Invention

[0013] Problems to be solved by the invention

[0014] However, when conventional thermal insulation sheets are used by being sandwiched between battery cells, etc., the aerogel may be compressed and crushed, particularly under high loads, and the thermal insulation effect may be significantly reduced compared to under low loads.

[0015] Therefore, an object of the present invention is to provide a heat-insulating sheet that can be used even under high loads, a method for producing the same, and an electronic device and a battery cell using the heat-insulating sheet.

[0016] Solutions to the Problem

[0017] To solve the above-mentioned problems, the present invention uses a method for manufacturing an insulating sheet, which includes the following steps: a composite forming step of impregnating non-woven fibers with an alkaline sol prepared by adding carbonate to a water glass composition to form a hydrogel-non-woven fiber composite; a surface modification step of mixing the composite with a silylating agent to perform surface modification; and a drying step of drying the liquid contained in the composite at a temperature lower than the critical temperature and critical pressure of the liquid to remove the liquid. The compressibility of the insulating sheet at 0.30 to 5.0 MPa is 40% or less.

[0018] Furthermore, the present invention uses a thermal insulation sheet comprising aerogel and nonwoven fabric fibers and having a compressibility of 40% or less at 0.30 to 5.0 MPa.

[0019] Furthermore, the present invention uses an electronic device having the above-mentioned heat-insulating sheet disposed between a heat-generating electronic component and a housing. Furthermore, the present invention uses a battery cell having the above-mentioned heat-insulating sheet disposed between batteries.

[0020] Effects of the Invention

[0021] The thermal insulation sheet of the present invention has a compression rate of 40% or less at 5 MPa, which means it is difficult to be crushed, and a thermal resistance of 0.01 m 2 K / w or more. Therefore, it can effectively delay heat transfer even in high-temperature compression environments. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] Figure 1 This is a diagram of a chemical formula explaining the gelation mechanism of water glass using the carbonate according to the embodiment.

[0023] Figure 2 This is a flowchart of a method for manufacturing a thermal insulation sheet according to an embodiment.

[0024] Figure 3 This is a graph showing the relationship between the SiO2 concentration in the water glass composition according to the embodiment and the compressibility of the thermal insulation sheet.

[0025] Figure 4 This is a graph showing the relationship between the SiO2 concentration in the water glass composition according to the embodiment and the thermal resistance of the thermal insulation sheet.

[0026] Figure 5 This is a graph showing the relationship between the SiO2 concentration in the water glass composition according to the embodiment and the thermal conductivity of the thermal insulation sheet.

[0027] Figure 6 This is a graph showing the relationship between the SiO2 concentration in the water glass composition according to the embodiment and the bulk density of the thermal insulation sheet.

[0028] Figure 7 This is a graph showing the relationship between the SiO2 concentration in the water glass composition according to the embodiment and the specific surface area of the aerogel.

[0029] Figure 8 This is a graph showing the relationship between the SiO2 concentration in the water glass composition according to the embodiment and the pore volume of the aerogel.

[0030] Figure 9 This is a graph showing the relationship between the SiO2 concentration in the water glass composition according to the embodiment and the average pore diameter of the aerogel.

[0031] Figure 10 This is a graph showing the relationship between the SiO2 concentration in the water glass composition according to the embodiment and the compression rate of the thermal insulation sheet at various applied forces.

[0032] Figure 11 This is a cross-sectional view of an electronic device as an application example of the thermal insulation sheet according to the embodiment.

[0033] Figure 12 This is a cross-sectional view of a battery cell as an application example of the thermal insulation sheet according to the embodiment.

[0034] Description of Reference Numerals

[0035] 10 Insulation sheet

[0036] 11 Housing

[0037] 12 Electronic components

[0038] 13 substrate

[0039] 15 Batteries

[0040] 101 Sodium silicate

[0041] 102 Hydroxyl ion

[0042] 103 Ethylene carbonate

[0043] 104 carbonate ion

[0044] 105 ethylene glycol

[0045] 106 hydrogel

[0046] 107 sodium carbonate DETAILED DESCRIPTION

[0047] Next, the present invention will be described with reference to preferred embodiments.

[0048] <Design concept of thermal insulation sheet>

[0049] Several aerogel composite insulation sheets made of silica aerogel and non-woven fabrics are known. Most of them have improved in terms of handling properties. However, they do not have the strength to withstand 5 MPa compression or 0.01 m when compressed. 2 High thermal resistance above K / w.

[0050] In contrast, the insulation sheet of this embodiment is composed of at least two components, high-density aerogel and nonwoven fibers, and thus has high strength. This high strength is achieved by the "high-density aerogel" being densely and seamlessly compounded within the voids of the continuous nonwoven fibers.

[0051] Generally speaking, silica aerogel refers to a low-density porous silica body with a bulk density of approximately less than 0.3 g / cm 3. Its synthesis generally uses low-concentration silica raw materials such as alkoxysilane or water glass, as well as gelling agents such as inorganic acids, bases, and organic acids. In the past, when water glass was used as the silica raw material, there was a limit on the silica concentration during aerogel synthesis to 6% by weight or less. The reason for this is that if an inorganic acid, base, organic acid, or the like is added as a gelling agent, the hydrolysis and dehydration condensation of sodium silicate will be rapidly promoted. In other words, if the silica concentration is above 7% by weight, the reaction rate is too fast, causing uneven nucleation and making it impossible to obtain a uniform gel.

[0052] Therefore, conventional silica aerogel synthesis methods cannot increase the silica concentration, resulting in a high-density aerogel. Furthermore, increasing the aerogel's density to improve its strength is also impossible. In contrast, in this embodiment, the method described below is used to produce a high-density aerogel, enabling the formation of a thermal insulation sheet comprising high-density aerogel and nonwoven fibers. Furthermore, this production method can produce a thermal insulation sheet having the following physical properties.

[0053] <Compression rate of thermal insulation sheet>

[0054] The compressibility of the thermal insulation sheet of this embodiment when pressurized at 0.30 MPa to 5 MPa is 40% or less, more preferably 30% or less. This compressibility is measured using a desktop precision universal testing machine (for example, Autograph AGS-X (manufactured by Shimadzu)).

[0055] <Thermal resistance of insulation sheet>

[0056] The thermal resistance of the thermal insulation sheet of this embodiment when pressurized at 0.30 MPa to 5 MPa is preferably 0.010 m 2 K / w or more, more preferably 0.015m 2 K / w or more. The thermal resistance is a value obtained by dividing the thickness of the thermal insulation sheet when pressurized at 0.30 MPa to 5 MPa by the thermal conductivity described below.

[0057] <Thermal Conductivity of Insulation Sheet>

[0058] The thermal conductivity of the thermal insulation sheet of this embodiment depends on the degree of compression and cannot be determined in general terms, but it only needs to be 100 mW / mK or less. This thermal conductivity is a value measured by a heat flow meter.

[0059] <Volume Density of Thermal Insulation Sheet>

[0060] The bulk density of the thermal insulation sheet of this embodiment is preferably 0.3 g / cm 3 ~0.5g / cm 3 .

[0061] <Pore Characteristics of High-Density Aerogel>

[0062] The specific surface area of the high-density aerogel constituting the thermal insulation sheet of this embodiment is preferably 300 m 2 / g~600m 2 / g. Furthermore, the pore volume is preferably less than 1.5 ml / g. Furthermore, the average pore diameter of the high-density aerogel is preferably 10 to 70 nm. The pore characteristics of the high-density aerogel are values measured using a high-precision gas / vapor adsorption measurement device.

[0063] <Thickness of thermal insulation sheet>

[0064] The thickness of the thermal insulation sheet of the present embodiment is preferably in the range of 0.03 mm to 3.0 mm, and more preferably in the range of 0.05 mm to 1.5 mm. When the thickness of the thermal insulation sheet is thinner than 0.03 mm, the thermal insulation effect in the thickness direction is sometimes reduced. For the thermal insulation sheet, if a very low thermal conductivity close to the vacuum level is not achieved, it is impossible to reduce the heat transfer in the thickness direction from one surface to the other surface. In addition, in particular, if the thickness of the thermal insulation sheet is thicker than 0.05 mm, the thermal insulation effect in the thickness direction can be ensured. On the other hand, when the thermal insulation sheet is thicker than 1.5 mm, it is sometimes difficult to install it in a vehicle-mounted / industrial equipment. In particular, in the field of vehicle-mounted equipment, if the thermal insulation sheet is thicker than 3.0 mm, it is even more difficult to install it in the equipment.

[0065] <High-Density Aerogel Content (Filling Ratio) in Thermal Insulation Sheet>

[0066] The optimal range for the proportion of high-density aerogel in the weight of the insulation sheet of this embodiment varies depending on the weight per unit area, volume density, and thickness of the non-woven fabric fibers, and therefore cannot be generalized. However, the proportion of high-density aerogel in the weight of the insulation sheet only needs to be at least 50% by weight. If the proportion is less than 50% by weight, the thermal resistance becomes smaller and the strength of the insulation sheet can no longer be maintained. Alternatively, the proportion only needs to be 80% by weight or less. If the proportion is higher than 80% by weight, although the thermal resistance is improved, the flexibility is insufficient, and the high-density aerogel may fall off due to repeated use.

[0067] <Raw Materials for Thermal Insulation Sheets>

[0068] Next, the types of raw materials, etc., of the nonwoven fabric fibers and high-density aerogel used to obtain the thermal insulation sheet of the present embodiment will be described.

[0069] (About non-woven fabrics)

[0070] Weight per unit area of non-woven fabric fibers

[0071] The basis weight of the nonwoven fabric fibers used in the manufacture of the thermal insulation sheet of this embodiment is preferably 5 to 200 g / m in order to maintain the minimum rigidity required as a support for high-density aerogel. 2 The basis weight is the weight of the fiber per unit area.

[0072] Bulk density of nonwoven fibers

[0073] From the viewpoint of increasing the content of high-density aerogel in the thermal insulation sheet of the embodiment to further reduce the thermal conductivity, the bulk density of the nonwoven fabric fibers is preferably 100 to 500 kg / m 3 In order to form a nonwoven fabric fiber with mechanical strength as a continuous body, it is preferred that the bulk density is at least 100 kg / m 3 In addition, the volume density of non-woven fabric fibers is greater than 500kg / m 3 In the case of , the space volume in the non-woven fabric fibers becomes smaller, so the high-density aerogel that can be filled is relatively reduced, and the thermal resistance value tends to become smaller.

[0074] Material of non-woven fabric fibers

[0075] The nonwoven fabric used in the manufacture of the thermal insulation sheet of the embodiment may be made of inorganic fibers such as glass wool, glass paper, and rock wool; resins such as polyethylene terephthalate (PET), polyphenylene sulfide (PPS), polypropylene (PP), and polytetrafluoroethylene (PTFE); and natural materials such as wool and cellulose. Among these, inorganic fibers are particularly preferred.

[0076] (Regarding the types of raw materials and gelling agents used in the synthesis of high-density aerogels)

[0077] Types of raw materials for high-density aerogel

[0078] A general-purpose silica raw material such as alkoxysilane or water glass is used as the raw material for high-density aerogel. In this embodiment, water is added to the silica raw material to achieve a desired silica concentration, and a dispersion or solution is used in which the silica raw material is dispersed or dissolved in water.

[0079] It is believed that Na ions affect the densification or high density of the porous structure in high-density aerogels. Therefore, among the above-mentioned silica raw materials, water glass containing Na ions is preferably used. In other words, a water glass composition obtained by dispersing or dissolving water glass in water is preferably used. To synthesize high-density aerogels, the silica concentration in the raw material dispersion or solution (especially the water glass composition) is preferably as high as possible, and is particularly preferably 14 to 20% by weight.

[0080] ·Gelating agent and its reaction mechanism

[0081] In this embodiment, a carbonate is used as a gelling agent for gelling the above-mentioned raw materials. Carbonates are generally known to be difficult to change in acidic environments, but are hydrolyzed into carbonic acid and alcohol under alkaline conditions. In this embodiment, the carbonic acid generated by this hydrolysis is used for gelation.

[0082] The inventors conducted extensive research on gelling agents to synthesize novel aerogels that can uniformly gel high-concentration silica compositions (particularly water glass compositions) with a silica concentration of 8% by weight or more. As a result, they discovered that carbonates can uniformly gel high-concentration water glass raw materials and are therefore suitable for synthesizing high-density aerogels.

[0083] Regarding the gelation mechanism of water glass using carbonate, taking ethylene carbonate as an example, Figure 1 The chemical reaction formula is explained.

[0084] As a first step, ethylene carbonate 103, a type of carbonate ester, is added to an alkaline aqueous solution of sodium silicate 101 (water glass composition) with a pH value of 10 or higher and dissolved. As a result, the hydroxyl ions 102 in the raw material (water glass composition) perform a nucleophilic attack on the carbonyl carbon of ethylene carbonate 103, and the hydrolysis of ethylene carbonate 103 is promoted. As a result, carbonate ions (CO3 2- )104 and ethylene glycol 105.

[0085] In the second step, sodium silicate 101 reacts with carbonate ions 104, advancing the dehydration condensation reaction of silicic acid. This produces sodium carbonate 107 as a byproduct. As the network structure formed by siloxane bonds expands, the fluidity of the water glass composition disappears, resulting in gelation. This process yields hydrogel 106. Most of sodium carbonate 107 remains in hydrogel 106.

[0086] As described above, the present embodiment is characterized in that, when carbonate is used as the gelling agent, the reaction proceeds in two stages, thereby enabling the reaction rates of the hydrolysis and dehydration condensation reactions of the sodium silicate 101 to be controlled, thereby achieving uniform gelation.

[0087] The specific example of carbonate comprises dimethyl carbonate, diethyl carbonate, dipropyl carbonate, methyl ethyl carbonate, ethylene carbonate, propylene carbonate etc.No matter which kind of carbonate all can make high concentration silica raw material (water glass composition) gelation equably, if but the alkyl chain of carbonate is longer, then hydrophobicity is stronger, is insoluble in water.Therefore, from the viewpoint of carbonate with respect to the solubility of water and the hydrolysis reaction speed, preferably use dimethyl carbonate, the ethylene carbonate that dissolves easily with respect to water.

[0088] In addition, if with respect to the total amount 100 weight parts of silicon dioxide raw material (water glass composition), and the addition of carbonate is made into the carbonate of 1.0~10.0 weight parts, then can make uniform gel.In addition, carbonate also can mix with the water glass composition under the state of being dissolved or being dispersed in water.Though the required time of gelation is different according to the silicon dioxide concentration in the water glass composition or gelling agent concentration, from the perspective of productivity (alkaline sol described later is impregnated in the speed of nonwoven fabrics etc.) and the relation of gelling agent cost, for the addition of carbonate, with respect to the total amount 100 weight parts of water glass composition, and more preferably 3.0~6.0 weight parts.In addition, carbonate is not a solvent but a gelling agent.

[0089] <Method for Manufacturing Thermal Insulation Sheet>

[0090] The outline of the method for manufacturing the thermal insulation sheet of this embodiment is as follows: Figure 2 As shown in FIG. , the basic synthesis process includes three steps (a) to (c).

[0091] (a) Complex formation process:

[0092] An alkaline sol, prepared by mixing a carbonate with a water glass composition, is impregnated into nonwoven fibers and gelled. The nonwoven fibers impregnated with the alkaline sol are then sandwiched between films and their thickness is controlled using a biaxial roller, for example, to form a hydrogel-nonwoven fiber composite. The hydrogel-nonwoven fiber composite may or may not be washed, as desired.

[0093] (b) Surface modification process:

[0094] The hydrogel-nonwoven fiber composite produced in step (a) is mixed with a silylating agent to perform surface modification. Silylation methods and silylating agents can be selected from known methods and materials. However, a method in which the hydrogel-nonwoven fiber composite is immersed in an aqueous hydrochloric acid solution and then treated with a mixture of siloxane and alcohol is preferred because of its rapid silylation.

[0095] (c) Drying process:

[0096] The liquid contained in the surface-modified hydrogel-nonwoven fiber composite obtained in step (b) is dried at a temperature lower than the critical temperature and lower than the critical pressure of the liquid to remove the liquid.

[0097] Furthermore, in step (a), if a carbonate is added to the water glass composition as a gelling agent, sodium carbonate may be generated as a result of dehydration and condensation of silicic acid. This sodium carbonate then enters the gel, resulting in a highly alkaline hydrogel. Subsequently, in step (b), if such a hydrogel is immersed in hydrochloric acid, a neutralization reaction between the hydrochloric acid and the sodium carbonate occurs, rapidly generating carbon dioxide gas. When using non-woven fabrics, such as cellophane, where fibers are less entangled with each other, this generation of carbon dioxide gas may sometimes result in a large number of bubbles within the fiber sheet. Therefore, it is also possible to remove the sodium carbonate from the hydrogel by washing it with water before immersing it in hydrochloric acid (step (b)).

[0098] [Example]

[0099] The present embodiment will be described below based on examples. However, the present embodiment is not limited to the following examples. All reactions were carried out under atmospheric pressure.

[0100] <Evaluation>

[0101] In the examples, thermal insulation sheets were prepared using ethylene carbonate as a gelling agent and varying the silica concentration in the water glass composition. The bulk density, thermal conductivity, compressibility, and thermal resistance of the resulting thermal insulation sheets were evaluated using the following methods.

[0102] The bulk density was calculated from the volume and weight of the obtained insulation sheet. The thermal conductivity of the insulation sheet was measured using a heat flow meter HFM 436 Lambda (manufactured by NETZSCH). The compressibility of the insulation sheet was measured using a tabletop precision universal testing machine Autograph AGS-X (manufactured by SHIMADZU).

[0103] The thermal resistance value of the thermal insulation sheet was calculated by dividing the thickness of the thermal insulation sheet obtained from the compression ratio when the applied pressure was 5 MPa by the thermal conductivity.

[0104] The microstructure of the silica aerogel (gel filling ratio, specific surface area, pore volume, and average pore diameter) was also evaluated using a high-precision gas / vapor adsorption measurement device, BELSORP-max42N-VP-P (manufactured by Microtrac BEL).

[0105] The detailed conditions of each embodiment and comparative example are described below. In addition, the measurement results are shown in Table 1.

[0106] [Table 1]

[0107]

[0108] wG: water glass, EC aq.: aqueous ethylene carbonate solution, HCl aq.: aqueous hydrochloric acid solution, NH3aq.: aqueous ammonia, GP: cellophane

[0109] <Qualification Criteria>

[0110] The pass criteria for each evaluation were as follows.

[0111] (1) Bulk density evaluation

[0112] For the bulk density of the thermal insulation sheet, 0.3g / cm 3 Above 0.5g / cm 3 The following are judged as qualified. If the bulk density of the insulation sheet is less than 0.3g / cm 3 If the bulk density is greater than 0.5g / cm 3 , although it is difficult to be crushed by the load, the thermal conductivity is high and the thermal resistance is low. Therefore, heat diffusion in the insulation sheet is easy to occur during compression.

[0113] (2) Thermal conductivity evaluation

[0114] The thermal conductivity of the thermal insulation sheet was determined to be acceptable if it was 100 mW / mK or less. If the thermal conductivity of the thermal insulation sheet was higher than 100 mW / mK, the thermal resistance would be low, and thus heat diffusion would be more likely to occur during compression.

[0115] (3) Gel filling rate

[0116] The aerogel filling ratio in the insulation sheet is considered acceptable if it is between 50% and 80% by weight. Aerogel filling ratios below 50% by weight are prone to crushing, resulting in lower thermal resistance during compression. Aerogel filling ratios exceeding 80% by weight are less prone to crushing, but the increased heat transfer component of the solid may result in lower thermal resistance during compression.

[0117] (4) Specific surface area evaluation

[0118] For the specific surface area of aerogel in the thermal insulation sheet, 300m 2 / g above 600m 2 / g or less is considered qualified. If the specific surface area of the aerogel in the thermal insulation sheet is less than 300m 2 / g, the particle size of the porous body is larger, so the thermal conductivity is higher and the thermal resistance is smaller. Therefore, heat diffusion is more likely to occur during compression. On the other hand, the specific surface area of the aerogel in the thermal insulation sheet is greater than 600m 2 When the porous body has a particle size of 0.1 / g, the particle size of the particles constituting the porous body is small and is easily crushed during compression. Therefore, the thermal resistance is small and thermal diffusion is easy to occur.

[0119] (5) Pore volume evaluation

[0120] The insulation sheet is considered acceptable if its pore volume is less than 1.5 ml / g. A pore volume of 1.5 ml / g or greater is more susceptible to crushing during compression. Consequently, the thermal resistance is low, allowing for easier heat diffusion.

[0121] (6) Compression rate evaluation

[0122] The compressibility of the insulation sheet at 5.0 MPa is considered acceptable if it is 40% or less. To effectively suppress heat diffusion even under high loads, the insulation sheet must withstand a certain degree of compression to prevent the increase in solid heat transfer components. If the compressibility of the insulation sheet at 5.0 MPa exceeds 40%, its superiority over conventional insulation sheets is diminished.

[0123] (7) Thermal resistance evaluation

[0124] The thermal resistance of the insulation sheet when compressed at 5.0 MPa is 0.01 m 2 The case of K / w or above is judged as qualified. When evaluating the thermal resistance value, it is sufficient to actually apply a load and measure the thermal conductivity. However, especially when the load is high, it will be crushed by compression, making it difficult to measure the thermal conductivity during compression. Therefore, the thermal resistance value is calculated based on the thickness of the insulation sheet obtained using the compression rate and the actual value of the thermal conductivity measured by the heat flow meter HFM, so as to make a comparative evaluation. If the thermal resistance value under 5.0MPa is less than 0.01m 2 K / w, heat diffusion is likely to occur during compression.

[0125] (8) Comprehensive evaluation

[0126] As a comprehensive evaluation, the conditions that all the above items (1) to (7) are met are judged as passed.

[0127] <Example 1>

[0128] To 100 parts by weight (20.5 g) of a water glass composition (silicon dioxide concentration of 14 wt%) prepared by diluting water glass raw materials with distilled water, 6 parts by weight of an aqueous solution of ethylene carbonate (white crystals) (amount of ethylene carbonate: 1.23 g) were added and stirred thoroughly to dissolve the mixture to prepare an alkaline sol (hereinafter also referred to as a "sol solution").

[0129] Next, the sol solution was poured onto non-woven fabric (material: glass paper, thickness 0.63 mm, unit area weight 100 g / m 2The sol solution was uniformly impregnated into the nonwoven fabric fibers on a 12 cm square (12 cm square). The sol-impregnated nonwoven fabric was sandwiched between two PP films (50 μm thick) and allowed to stand at room temperature (23°C) for 3 minutes to gel the sol. After confirming gelation, the sol-impregnated nonwoven fabric and the films were passed through biaxial rollers set at a gap of 1.00 mm (including the film thickness). Excess gel was squeezed out of the nonwoven fabric, and the thickness was controlled to a target of 1.00 mm.

[0130] Next, the gel sheet after peeling off the film is immersed in 6 equivalents of hydrochloric acid and placed at room temperature 23°C for 10 minutes to allow the hydrochloric acid to enter the gel sheet. Next, the gel sheet is immersed in a mixture of octamethyltrisiloxane and 2-propanol (IPA) as a silylating agent and placed in a 55°C constant temperature bath to react for 2 hours. After the trimethylsiloxane bond begins to form, hydrochloric acid water is discharged from the gel sheet, and a state of two liquid separation occurs (the upper layer is siloxane, and the lower layer is hydrochloric acid water and 2-propanol). The gel sheet is moved to a constant temperature bath set at 150°C and dried in an atmospheric environment for 2 hours to obtain an insulating sheet.

[0131] The thermal conductivity and compression properties of the insulation sheet were evaluated and the results showed that the compression rate was 35.8% and the thermal resistance was 0.02m 2 K / w was judged as qualified as a comprehensive evaluation.

[0132] <Example 2>

[0133] A thermal insulation sheet was prepared using the same process conditions as in Example 1 except that the silica concentration in the water glass composition was changed to 16 wt % and the amount of ethylene carbonate aqueous solution added was changed to 3 parts by weight. The results of evaluation of the thermal insulation sheet showed that the compression ratio was 30.1% and the thermal resistance was 0.017 m 2 K / w was judged as qualified as a comprehensive evaluation.

[0134] <Example 3>

[0135] A thermal insulation sheet was produced under the same process conditions as in Example 2 except that the silica concentration in the water glass composition was changed to 18 wt %. The thermal insulation sheet was evaluated and found to have a compression ratio of 23.3% and a thermal resistance of 0.015 m 2 K / w was judged as qualified as a comprehensive evaluation.

[0136] <Example 4>

[0137] A thermal insulation sheet was produced under the same process conditions as in Example 2 except that the silica concentration in the water glass composition was changed to 20 wt%. The thermal insulation sheet was evaluated and found to have a compression ratio of 21.3% and a thermal resistance of 0.015 m 2K / w was judged as qualified as a comprehensive evaluation.

[0138] <Example 5>

[0139] A heat insulating sheet was produced using the same process conditions as in Example 4 except that the thickness of the cellophane was changed to 1.03 mm. The heat insulating sheet was evaluated and found to have a compression ratio of 21.0% and a thermal resistance of 0.026 mm. 2 K / w was judged as qualified as a comprehensive evaluation.

[0140] <Example 6>

[0141] A thermal insulation sheet was produced under the same process conditions as in Example 5 except that the amount of ethylene carbonate aqueous solution added was changed to 4 parts by weight. The thermal insulation sheet was evaluated and found to have a compression ratio of 14.1% and a thermal resistance of 0.025 m 2 K / w was judged as qualified as a comprehensive evaluation.

[0142] <Example 7>

[0143] A thermal insulation sheet was produced under the same process conditions as in Example 5 except that the amount of ethylene carbonate aqueous solution added was changed to 5 parts by weight. The thermal insulation sheet was evaluated and found to have a compression ratio of 13.8% and a thermal resistance of 0.022 m 2 K / w was judged as qualified as a comprehensive evaluation.

[0144] <Example 8>

[0145] A thermal insulation sheet was produced under the same process conditions as in Example 5 except that the amount of ethylene carbonate aqueous solution added was changed to 6 parts by weight. The thermal insulation sheet was evaluated and found to have a compression ratio of 10.4% and a thermal resistance of 0.023 m 2 K / w was judged as qualified as a comprehensive evaluation.

[0146] <Comparative Example 1>

[0147] A thermal insulation sheet was produced using the same process conditions as in Example 1 except that the silica concentration in the water glass composition was changed to 6 wt %. The thermal insulation sheet was evaluated and found to have a compression ratio of 72.5% and a thermal resistance of 0.013 m 2 K / w was judged as unqualified as a comprehensive evaluation.

[0148] <Comparative Example 2>

[0149] A thermal insulation sheet was produced under the same process conditions as in Example 1 except that the silica concentration in the water glass composition was changed to 8 wt%. The thermal insulation sheet was evaluated and found to have a compression ratio of 67.3% and a thermal resistance of 0.015 m2 K / w was judged as unqualified as a comprehensive evaluation.

[0150] <Comparative Example 3>

[0151] A thermal insulation sheet was produced under the same process conditions as in Example 1 except that the silica concentration in the water glass composition was changed to 10 wt%. The thermal insulation sheet was evaluated and found to have a compression ratio of 63.8% and a thermal resistance of 0.015 m 2 K / w was judged as unqualified as a comprehensive evaluation.

[0152] <Comparative Example 4>

[0153] A thermal insulation sheet was produced using the same process conditions as in Example 1 except that the silica concentration in the water glass composition was changed to 12 wt %. The thermal insulation sheet was evaluated and found to have a compression ratio of 52.4% and a thermal resistance of 0.016 m 2 K / w was judged as unqualified as a comprehensive evaluation.

[0154] <Comparative Example 5>

[0155] A thermal insulation sheet was prepared using the same process conditions as in Example 1 except that the silica concentration in the water glass composition was changed to 6% by weight and 12N hydrochloric acid was used as the gelling agent. The evaluation results of the thermal insulation sheet showed that the compression ratio was 71.9% and the thermal resistance was 0.013m 2 K / w was judged as unqualified as a comprehensive evaluation.

[0156] <Comparative Example 6>

[0157] A thermal insulation sheet was prepared using the same process conditions as in Example 1 except that a 1N aqueous ammonia solution was used as a gelling agent for a sol prepared by removing Na ions from a water glass composition having a silica concentration of 6% by weight using an ion exchange resin. Evaluation of the thermal insulation sheet revealed a compressibility of 74.6% and a thermal resistance of 0.013 m 2 K / w was judged as unqualified as a comprehensive evaluation.

[0158] <Evaluation of each item>

[0159] Compression properties of thermal insulation sheets

[0160] The compression rate of the thermal insulation sheet of the embodiment when pressurized at 0.30 to 5 MPa is preferably 40% or less, more preferably 30% or less. Figure 3This graph shows the relationship between the compressibility of the thermal insulation sheets produced in each example and comparative example when pressurized at 5 MPa and the silica concentration in the water glass composition. If the compressibility exceeds 40%, it is difficult to suppress heat diffusion during compression. If the compressibility is 30% or less, heat diffusion during compression can be effectively suppressed.

[0161] Thermal resistance of insulation sheet

[0162] The thermal resistance of the thermal insulation sheet of this embodiment when pressurized at 0.30 to 5 MPa is preferably 0.010 m 2 K / w or more, more preferably 0.015m 2 K / w or above. Figure 4 This is a graph showing the relationship between the thermal resistance of the thermal insulation sheets produced in each embodiment and comparative example when pressurized at 5 MPa and the concentration of silica in the water glass composition. 2 K / w, it is difficult to suppress the heat diffusion during compression. If the thermal resistance is 0.015m 2 K / w or more can effectively suppress heat diffusion during compression.

[0163] Thermal conductivity of insulation sheet

[0164] The thermal conductivity of the thermal insulation sheet of this embodiment depends on the magnitude of the compression rate and cannot be determined in general terms, but it only needs to be 100 mW / mK or less. Figure 5 This is a graph showing the relationship between the thermal conductivity of the thermal insulation sheets produced in each example and comparative example and the silica concentration in the water glass composition. When the thermal conductivity exceeds 100 mK / w, it is difficult to suppress heat diffusion during compression.

[0165] Bulk density of insulation sheet

[0166] The bulk density of the thermal insulation sheet of this embodiment is preferably 0.3 to 0.5 g / cm 3 . Figure 6 This is a graph showing the silica concentration in the water glass composition when the thermal insulation sheet was prepared in each example and comparative example, plotted on the horizontal axis, and the bulk density of the obtained thermal insulation sheet on the vertical axis. Figure 6 It can be seen that when ethylene carbonate is used, the bulk density of the insulation sheet tends to increase with increasing silica concentration. On the other hand, when hydrochloric acid or ammonia water is used, the bulk density is 0.2 g / cm2 at a silica concentration of 6 wt%. 3 . The volume density is less than 0.3g / cm 3In the case of a high load, it is easy to crush. Therefore, a large compression ratio will lead to a small thermal resistance. In addition, when the bulk density is greater than 0.5g / cm 3 In the case of , significant coarsening of the silica primary particles or shrinkage of the aerogel itself occurs, and the expected thermal resistance value cannot be obtained even under no load.

[0167] Specific surface area of aerogel

[0168] The specific surface area of the high-density aerogel of this embodiment is preferably 300 to 600 m 2 / g. Figure 7 This is a graph showing the silica concentration in the water glass composition used to make the thermal insulation sheets produced in Examples 1, 4, and Comparative Examples on the horizontal axis and the specific surface area of the aerogel on the vertical axis. Figure 7 It can be seen that when ethylene carbonate is used, the specific surface area of the aerogel tends to gradually decrease as the silica concentration increases, and reaches a minimum value near a silica concentration of 14 wt %.

[0169] When hydrochloric acid or ammonia water is used, the specific surface area is 500m2 at a silica concentration of 6 wt%. 2 / g、750m 2 / g. At this time, the specific surface area is less than 300m 2 / g, the silica primary particles will be significantly coarsened or the aerogel itself will shrink, and the expected thermal resistance value cannot be obtained even under no load. In addition, when the specific surface area is greater than 600m 2 / g, the silica primary particles will be significantly refined or the aerogel will be low-density, and the expected thermal resistance value cannot be obtained under high load. In addition, the specific surface area of general low-density aerogels is greater than 600m 2 / g, but in the present embodiment, this is a result reflecting the fact that the primary silica particles are very small and the bulk density of the generated aerogel is low.

[0170] Pore volume of aerogel

[0171] Figure 8 This is a graph showing the silica concentration in the water glass composition when the thermal insulation sheets were prepared in Examples 1, 4, and Comparative Examples on the horizontal axis and the pore volume of the aerogel on the vertical axis. Figure 8It can be seen that when ethylene carbonate is used, the following trend is observed: the pore volume of the aerogel gradually decreases with increasing silica concentration, reaching a minimum value near a silica concentration of 14 wt%. When hydrochloric acid is used, the pore volume is 2.0 ml / g at a silica concentration of 6 wt%, and when ammonia water is used, the pore volume is 4.4 ml / g at a silica concentration of 6 wt%. When the pore volume is 1.5 ml / g or more, if a high load is applied, it is easily crushed, the compression rate is large, and the thermal resistance is low. Therefore, the average pore diameter of the aerogel is preferably 10 to 70 nm.

[0172] Average pore size of aerogel

[0173] Figure 9 This is a graph showing the silica concentration in the water glass composition when the thermal insulation sheets were prepared in Examples 1, 4, and Comparative Examples on the horizontal axis and the average pore size of the aerogel on the vertical axis. Figure 9 It can be seen that when ethylene carbonate is used, the average pore diameter is about 60nm when the silica concentration is less than 10% by weight, and the average pore diameter is about 30-40nm when the silica concentration is more than 14% by weight. When hydrochloric acid is used, the average pore diameter is about 40nm when the silica concentration is 6% by weight, and when ammonia water is used, the average pore diameter is about 30nm when the silica concentration is 6% by weight. When the average pore diameter is less than 10nm, significant coarsening of the primary silica particles or shrinkage of the aerogel itself will occur, and the expected thermal resistance value cannot be obtained even when there is no load. In addition, when the average pore diameter is greater than 70nm, it is difficult to suppress air convection, so the thermal resistance is relatively small.

[0174] Silica concentration and compressibility

[0175] exist Figure 10 The relationship between the silica concentration in the water glass composition when making the insulation sheet in the examples and comparative examples and the compressibility of the obtained insulation sheet is shown in the figure. A pressure of 5MPa to 0.3MPa is applied to each insulation sheet. When a pressure of 5MPa is applied, the compression ratios of the insulation sheets of Examples 1 to 4 are all 40% or less, which is a preferred value. When a pressure of 2MPa is applied, the compression ratios of the insulation sheets of Examples 1 to 4 are 30% or less, which is a more preferred value. When a pressure of 1MPa is applied, the compression ratios of the insulation sheets of Examples 1 to 4 are 20% or less, which is a further preferred value. In addition, the thermal resistance during compression also shows the same trend. For the insulation sheets of Examples 1 to 4, the thermal resistance is 0.010m when a pressure of 0.30 to 5.0MPa is applied. 2 K / w or above.

[0176] <Summary of Results>

[0177] As described above, in Examples 1 to 4, water glass compositions with a silica concentration of 14 to 20% by weight and ethylene carbonate were used to produce thermal insulation sheets. As a result, the compression ratio at 5.0 MPa was as low as 40% or less, and the thermal resistance was 0.01 m / s. 2 K / w or more. On the other hand, in Comparative Examples 1 to 4, thermal insulation sheets were produced using water glass compositions with silica concentrations of 6 to 12 wt% and ethylene carbonate. As a result, the compression ratios at 5.0 MPa were all greater than 40%.

[0178] In Comparative Examples 5 and 6, thermal insulation sheets were produced using aqueous hydrochloric acid or aqueous ammonia as a gelling agent for a water glass composition having a silica concentration of 6 wt%, and the results were substantially the same as those in Comparative Example 1. When a gelling agent other than ethylene carbonate was used, uniform gelation was not achieved when the silica concentration was increased to 8 wt% or more, and a thermal insulation sheet could not be produced.

[0179] The above results indicate that a thermal insulation sheet comprising high-density aerogel-nonwoven fibers synthesized from a water glass composition having a silica concentration of 14 to 20% by weight and carbonate is an excellent high-strength thermal insulation sheet and can effectively suppress heat diffusion even under high load conditions.

[0180] <Other>

[0181] The thermal insulation sheet contains aerogel and nonwoven fibers as main components and does not contain other compounds as main components. The total amount of aerogel and nonwoven fibers accounts for 90% by weight or more of the total weight of the thermal insulation sheet.

[0182] Figure 11 Detailed Description of the Invention Application Example 1 of the thermal insulation sheet according to the embodiment is shown in FIG. Figure 11 This diagram schematically illustrates the structure of an electronic device having a heat-generating electronic component 12 and a housing 11. The thermal insulation sheet 10 of the embodiment can be placed between the heat-generating electronic component 12 and the housing 11 in the electronic device. The thermal insulation sheet 10 of the embodiment prevents heat from the electronic component 12 from being transferred to the housing 11. Furthermore, the electronic component 12 is mounted on a substrate 13. Alternatively, the thermal insulation sheet 10 may be covered with a cover to cover the surface. Alternatively, the thermal insulation sheet 10 may be laminated with a thermally conductive material, such as a graphite sheet.

[0183] Figure 12 2 shows an application example 2 of the thermal insulation sheet according to the embodiment. Figure 12This diagram illustrates a battery unit with multiple batteries, used in automobiles and other applications. In such a battery unit, placing any of the aforementioned thermal insulation sheets 10 between batteries 15 not only provides thermal insulation between batteries 15 but also prevents fire spread, making this a preferred method. Batteries 15 are not limited to automotive applications. They can also be used as batteries for various mobile devices or household storage devices. Thermal insulation sheet 10 can also be combined with other sheet materials.

[0184] Industrial Applicability

[0185] The thermal insulation sheet of this embodiment, composed of at least two components, high-density aerogel and nonwoven fabric, boasts enhanced compressive strength and is widely used because it can effectively insulate even within the confined spaces of electronic devices, automotive equipment, and industrial equipment. This sheet is used in all heat-sensitive products, including information equipment, portable devices, displays, and electrical components.

Claims

1. A method for manufacturing a thermal insulation sheet, characterized in that: Including the following processes: A composite forming step of impregnating non-woven fibers with an alkaline sol prepared by adding carbonate to a water glass composition to form a hydrogel-non-woven fiber composite; a surface modification step of mixing the composite with a silylating agent to perform surface modification; as well as a drying step of removing the liquid by drying the liquid contained in the composite at a temperature lower than the critical temperature and the critical pressure of the liquid; In the composite forming step, the pH value of the water glass composition is 10 or higher, the SiO2 concentration in the water glass composition is 14% by weight or higher and 22% by weight or lower, and the amount of the carbonate added is 1 to 10 parts by weight relative to 100 parts by weight of the water glass composition. The thermal insulation sheet has a compressibility of 40% or less at 5.0 MPa.

2. The method for manufacturing a thermal insulation sheet according to claim 1, wherein: The pH value of the alkaline sol is above 10.

3. The method for manufacturing a thermal insulation sheet according to claim 1, wherein: The non-woven fabric fibers are inorganic fibers.

4. The method for manufacturing a thermal insulation sheet according to claim 1, wherein: The carbonate ester is soluble in water and is easily hydrolyzed under alkaline conditions with a pH value of 10 or above to generate carbonate ions and glycol.

5. A thermal insulation sheet, characterized in that: It is manufactured by the manufacturing method according to claim 1, The thermal insulation sheet comprises aerogel and non-woven fabric fibers, and has a compression rate of 40% or less at 5.0 MPa. The pore volume of the aerogel is less than 1.5 ml / g.

6. The thermal insulation sheet according to claim 5, wherein: Thermal resistance when compressed at 5.0MPa is 0.01m 2 K / W or above.

7. The thermal insulation sheet according to claim 5, wherein: The specific surface area of the aerogel is 300m 2 / g above 600m 2 / g or less.

8. The thermal insulation sheet according to claim 5, wherein: The bulk density of the thermal insulation sheet is 0.3 g / cm 3 Above 0.5g / cm 3 the following.

9. An electronic device, characterized in that: The heat insulating sheet according to any one of claims 5 to 8 is arranged between the heat-generating electronic component and the housing.

10. A battery cell, characterized in that: The thermal insulation sheet according to any one of claims 5 to 8 is arranged between batteries.

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