JP7232983B2 - Insulation sheet, manufacturing method thereof, electronic device, battery unit - Google Patents

Description

TECHNICAL FIELD The present invention relates to a heat insulating sheet, a manufacturing method thereof, and an electronic device. In particular, the present invention relates to a high-strength heat insulating sheet, a manufacturing method thereof, an electronic device, and a battery unit.

In the automotive and industrial equipment fields, high-performance insulation sheets with excellent compression characteristics are required to ensure heat flow control from heat-generating parts in narrow spaces, product safety, and fire spread prevention. Such a heat insulating sheet is expected to be applied, for example, to an inter-cell separator of a lithium ion battery module.

The safety standards for lithium-ion batteries require a fire spread resistance test. The fire spread resistance test is a method of testing for the presence or absence of ignition or explosion due to thermal chain reaction to other cells including adjacent cells when one cell in a battery module undergoes thermal runaway. In order to prevent thermal runaway to adjacent cells, there is a concept of safety design in which a material with excellent thermal insulation is sandwiched between cells. Theoretically, it is possible to prevent heat chain and fire spread to some extent by increasing the thickness of a material with high thermal conductivity.

However, since the battery module is installed inside the equipment, the space in which it is installed is limited and there are size restrictions. There is the difficulty of not doing so.

In order to achieve both of these, a thin and highly heat-insulating material is desired for the inter-cell separator. Moreover, assuming that the active material deteriorates and expands in the course of the charge/discharge cycle of the battery, and the cell swells, it is desired that the heat insulating sheet also have a characteristic that is resistant to crushing. That is, when the battery module is initially assembled, the load applied to the heat insulating sheet, which is the inter-cell separator, is relatively small at 1 MPa or less. Therefore, it is important to design the material of the heat insulating sheet considering the compression characteristics.

Silica airgel is known as a substance with low thermal conductivity. Silica silica airgel has a network structure in which silica particles on the order of several tens of nanometers are connected by point contact, and has an average pore diameter of 68 nm or less, which is the mean free path of air. Therefore, the thermal conductivity is lower than that of still air. Therefore, while silica airgel has attracted attention as an excellent heat insulating material, its extremely low strength against various deformation modes such as compression, bending, and shearing has been regarded as a practical problem.

The inventors have devised a thin and uniform sheet-like heat insulating material which is made by combining silica airgel and non-woven fabric fibers to improve handleability (Patent Document 1). This thin insulating sheet is easy to handle and relatively strong against bending.

Japanese Patent No. 6064149

However, when a conventional heat insulating sheet is sandwiched between battery cells and the like, the airgel is compressed and crushed especially under a high load, and the heat insulating effect is greatly reduced compared to when the load is low.

Accordingly, an object of the present application is to provide a heat insulating sheet that can be used even under a high load, a method for manufacturing the same, an electronic device, and a battery unit.

In order to solve the above problems, a composite producing step of impregnating the nonwoven fabric fiber structure with a sol prepared by adding a carbonate ester to a water glass composition to produce a hydrogel-nonwoven fiber composite, and is mixed with a silylating agent to modify the surface, and a drying step of removing the liquid contained in the composite by drying below the critical temperature and pressure. Use

Furthermore, due to the use of carbonate ester as a gelling agent, sodium carbonate is by-produced in the airgel, and carbon dioxide is generated in the process of silylation, which causes a decrease in compressibility performance. It becomes possible to remove effectively by processing in the vertical type in the water washing process.

In addition, a heat insulating sheet containing airgel and non-woven fabric fibers, having a compressibility of 40% or less at 0.30 to 5.0 MPa, and a thermal resistance of 0.01 m ² K/W or more when compressed is used.

Further, an electronic device is used in which the heat insulating sheet is arranged between the electronic component that generates heat and the housing.

Also, a battery unit in which the heat insulating sheet is arranged between batteries is used.

The high-strength insulation sheet of the present embodiment has a compressibility of 40% or less at 5 MPa, which makes it difficult to collapse, and a thermal resistance at 5 MPa of 0.01 m ² K / W or more, so it is effective even in a high-temperature compression environment. heat transfer delay effect.

A diagram of a chemical formula for explaining the gelation mechanism of water glass by carbonate ester according to the embodiment. Flow diagram of a method for manufacturing a high-strength insulation sheet according to an embodiment FIG. 2 is a diagram showing the relationship between the SiO ₂ concentration of water glass and the compressibility of the heat insulating sheet according to the embodiment. FIG. 2 is a diagram showing the relationship between the SiO ₂ concentration of the water glass and the thermal resistance of the heat insulating sheet according to the embodiment; FIG. 2 is a diagram showing the relationship between the SiO ₂ concentration of the water glass and the thermal conductivity of the heat insulating sheet according to the embodiment; Graph showing the relationship between the SiO ₂ concentration of the water glass of the embodiment and the bulk density of the heat insulating sheet FIG. 2 is a diagram showing the relationship between the SiO ₂ concentration of the water glass and the specific surface area of the airgel according to the embodiment. FIG. 2 is a diagram showing the relationship between the SiO ₂ concentration of the water glass and the pore volume of the airgel according to the embodiment. FIG. 2 is a diagram showing the relationship between the SiO ₂ concentration of water glass and the average pore size of airgel according to the embodiment. FIG. 2 is a diagram showing the relationship between the SiO ₂ concentration of the water glass of the embodiment and the compressibility of the heat insulating sheet at each applied pressure. Sectional view showing application example 1 of the heat insulating sheet of the embodiment Sectional drawing which shows the application example 2 of the heat insulation sheet of embodiment The figure which shows the sheet arrangement|positioning in water washing of the heat insulation sheet of embodiment. A diagram showing the arrangement of the heat insulating sheet according to the embodiment when the heat insulating sheet is immersed in an aqueous solution of hydrochloric acid. FIG. 4 is a diagram showing the sheet arrangement in the silylation treatment of the heat insulating sheet according to the embodiment;

Next, this embodiment will be described with reference to preferred embodiments of the invention.
<Design concept of high-strength insulation sheet>
Several airgel composite heat insulating sheets composed of silica airgel and non-woven fibers have been known so far. Many of them are being improved in handling. However, it did not have the strength to withstand compression of 5 MPa and the high thermal resistance value of 0.01 m ² K/W or more during compression.

The high-strength heat insulation sheet of the present embodiment is a heat insulation sheet composed of at least two components, a high-density airgel and a nonwoven fiber structure. Here, the heat insulating sheet of the present embodiment has high strength. This is due to the "high-density aerogel" which is densely combined without gaps in the voids of the continuous non-woven fabric.

Silica airgel generally refers to low-density silica porous bodies, with bulk densities less than approximately 0.3 g/cm ³ . In its synthesis, a low-concentration silica raw material such as alkoxysilane or water glass and a mineral acid or base as a gelling agent are usually used. Here, in the case of water glass, there is a limitation that the silica concentration used for airgel synthesis is 6% by weight or less. This is because when a mineral acid or an organic acid is added as a gelling agent, the hydrolysis and dehydration condensation of sodium silicate proceed rapidly, and at a silica concentration of 7 weight or more, the reaction rate is too fast and heterogeneous nucleation is induced. This is because a uniform gel cannot be obtained.

Therefore, the existing airgel synthesis method could not increase the silica concentration and could not obtain a high-density aerogel. Also, it was not possible to increase the strength of the airgel by increasing the density of the airgel.

<Compression characteristics of high-strength insulation sheet>
The compressibility of the heat insulating sheet of the present embodiment when pressurized at 0.30 MPa to 5 MPa is preferably 40% or less, more preferably 30% or less.

<Thermal resistance of high-strength insulation sheet>
The thermal resistance of the heat insulating sheet of the present embodiment when pressurized at 0.30 MPa to 5 MPa is preferably 0.010 m ² K/W or more, more preferably 0.015 m ² K/W or more. preferable.

<Thermal conductivity of heat insulating sheet>
Although the thermal conductivity of the heat insulating sheet of the present embodiment cannot be generalized due to the degree of compressibility, it is sufficient if it is 100 mW/mK or less.

<Bulk Density of Thermal Insulation Sheet>
The bulk density of the heat insulating sheet of the present embodiment is preferably 0.3 g/cm ³ to 0.5 g/cm ³ .

<Pore characteristics of airgel>
The specific surface area of the high-density airgel of the present embodiment is preferably 300m ² /g to 600m ² /g. The average pore size of the high-density airgel is preferably 10-70 nm.

<Raw material species and silica concentration of airgel>
General-purpose silica raw materials such as alkoxysilanes and water glass are used as raw materials for high-density airgel. Water is added to obtain the desired silica concentration to prepare a dispersion or solution for use.

Water glass containing Na ions is preferably used because it is believed that Na ions affect the densification and densification of the porous structure in high-density aerogels. The silica concentration in the raw material dispersion or solution should be high in order to synthesize a high-density airgel, preferably 14 to 20%.

<Gelling agent for airgel synthesis and its concentration>
In order to synthesize a new aerogel capable of uniformly gelling high-concentration silica raw materials of 8% by weight or more, the inventors have made earnest efforts to search for a gelling agent. As a result, we found that carbonic acid esters are suitable for synthesizing high-density aerogels by uniformly gelling high-concentration water glass raw materials.

Carbonate ester is used as a gelling agent for the high-density aerogel of the present embodiment. Carbonic acid esters are known to hydrolyze into carbonic acid and alcohol under basic conditions, although they are generally resistant to acidity. In the present embodiment, the carbonic acid produced by this hydrolysis is used for gelation.

The gelation mechanism of water glass by carbonate ester will be explained using ethylene carbonate as an example with reference to FIG. 1 showing the chemical structure.

As a first step, when ethylene carbonate 103 is added to and dissolved in an aqueous solution of sodium silicate 101, which is basic with a pH of 10 or higher, hydroxyl ions 102 in the raw material nucleophilically attack the carbonyl carbon of ethylene carbonate 103, resulting in ethylene carbonate. Hydrolysis of 103 proceeds.

As a result, carbonate ions 104 and ethylene glycol 105 are produced in the system.

In the second step, the sodium silicate 101 and carbonate ions 104 react to proceed the dehydration condensation reaction of silicic acid. At this time, sodium carbonate 107 is produced as a by-product. When a network structure consisting of siloxane bonds develops, water glass loses fluidity and gels. A hydrogel 106 is thus obtained. Much of the sodium carbonate 107 remains in the hydrogel 106.

As described above, when a carbonate ester is used as a gelling agent, the reaction proceeds in two stages, so it is possible to control the reaction rate of the hydrolysis of sodium silicate 101 and the dehydration condensation reaction, resulting in uniform gelation. It is characterized by being achievable.

Dimethyl carbonate, diethyl carbonate, dipropyl carbonate, ethylmethyl carbonate, ethylene carbonate, propylene carbonate and the like are used as the carbonate ester. Any carbonic acid ester can uniformly gel the high-concentration silica raw material. Therefore, dimethyl carbonate and ethylene carbonate, which dissolve relatively easily in water, are preferably used from the viewpoint of the solubility in water and the hydrolysis reaction rate of carbonate esters.

As for the addition amount of the carbonate ester, a uniform gel can be produced by adding 0.5 to 10.0 parts by weight of the carbonate ester relative to the total amount of the silica raw material. Although the gelation time varies depending on the concentration of silica and the concentration of the gelling agent, it is preferably 3.0 to 6.0 parts by weight in terms of productivity (speed of impregnating the raw material liquid into the nonwoven fabric, etc.) and the cost of the gelling agent.

Note that the carbonate ester is not a solvent but a gelling agent.

<Thickness of insulation sheet>
The thickness of the insulating sheet of the embodiment is 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 thickness of the heat insulating sheet is less than 0.03 mm, the heat insulating effect in the thickness direction is reduced. Therefore, the heat transfer in the thickness direction from one side to the other side cannot be reduced unless the heat insulating sheet realizes a very low thermal conductivity at a level close to that of a vacuum. When the thickness of the heat insulating sheet is 0.05 mm or more, the heat insulating effect in the thickness direction can be secured. On the other hand, if the heat insulating sheet is thicker than 1.5 mm, it will be difficult to incorporate it into a vehicle or industrial equipment. In particular, in the in-vehicle field, if the thickness is more than 3.0 mm, it becomes more difficult to incorporate it into equipment.

<Content rate of high density silica xerogel in heat insulating sheet>
The ratio of the high-density silica airgel to the weight of the heat insulating sheet cannot be generalized because the optimum range varies depending on the basis weight, bulk density, and thickness of the non-woven fabric fiber. However, the ratio of the high-density silica airgel to the weight of the heat insulating sheet should be at least 50% by weight or more. If the ratio is less than 50%, the heat resistance becomes small and at the same time the strength of the heat insulating sheet cannot be maintained. Also, the ratio should be 80% by weight or less. If the ratio is higher than 80%, the heat resistance is increased, but the flexibility is insufficient, and repeated use may cause the silica airgel to fall off.

<Metsuke of non-woven fabric>
The basis weight of the nonwoven fabric fibers used for manufacturing the heat insulating sheet of the embodiment is preferably 5 to 200 g/m ² in order to maintain the minimum required rigidity as a support for high-density airgel. The basis weight is the weight of the fiber per unit area.

<Bulk density of nonwoven fiber>
The bulk density of the nonwoven fabric fibers is preferably in the range of 100 to 500 kg/m ³ from the viewpoint of increasing the content of silica xerogel in the heat insulating sheet of the embodiment to further reduce the thermal conductivity.

A bulk density of at least 100 kg/m ³ is required to form a continuous nonwoven fabric with mechanical strength. In addition, when the bulk density of the nonwoven fabric is higher than 500 kg/m ³ , the space volume in the nonwoven fabric is reduced, so the amount of silica xerogel that can be filled is relatively reduced, and the heat resistance value is reduced. Numerical values are also explained in the following examples.

<Material of non-woven fiber>
Materials of the non-woven non-fiber used for manufacturing the heat insulating sheet of the embodiment include inorganic fiber-based glass wool, glass paper, rock wool, resin-based polyethylene terephthalate (PET), polyphenylene sulfide (PPS), polypropylene ( PP), polytetrafluoroethylene (PTFE), natural wool, cellulose, and the like can be used.

<Method for producing high-strength heat insulation sheet>
FIG. 2 shows an outline of a method for manufacturing a heat insulating sheet according to an embodiment. The basic synthesis procedure consists of three steps (a) to (c).

(a) Complex formation step:
A nonwoven fiber structure is impregnated with a sol prepared by adding carbonate ester and distilled water to a water glass composition, which is a silica raw material, and mixed to form a gel. Then, while sandwiched between films, the thickness is regulated using a biaxial roll or the like to form a hydrogel-nonwoven fiber composite.
For example, when a water glass raw material is used, when a carbonate ester is added as a gelling agent, the dehydration condensation of silicic acid is accompanied by the formation of sodium carbonate, which is incorporated into the gel to form a very basic hydrogel. can be obtained.

(b) Surface modification step:
The hydrogel-nonwoven fiber composite produced in step (a) is washed with water. The hydrogel-nonwoven fiber composite is then dipped in hydrochloric acid and then mixed with a silylating agent for surface modification. The reason for the treatment with hydrochloric acid is to pre-treat so that the next silylation treatment can proceed efficiently.
Known methods and known materials can be used for the silylation and the silylating agent. The method of treating with is preferable because the silylation treatment can be performed quickly.
The surface modification step is a step of immersing the fiber in water, an aqueous solution of hydrochloric acid, or a silylating agent, and it is preferable to increase the contact area between the surface of the hydrogel-nonwoven fabric fiber and the immersing liquid. For this purpose, it is preferable to treat the hydrogel-nonwoven fabric with the surface direction upright in the tank.
By increasing the silica concentration in the high-density aerogel of this example, the strength of the hydrogel-nonwoven fabric fiber increases, and since it does not bend, it becomes possible to stand on its own.
<(b) Washing step in surface modification step>
In step b, when this hydrogel is immersed in hydrochloric acid, a neutralization reaction between hydrochloric acid and sodium carbonate occurs, and carbon dioxide is rapidly generated. When using a non-woven fiber structure, such as glass paper, in which many fibers are crossed in parallel with the surface direction and the fibers are less entangled, many bubbles are generated in the fiber sheet due to the generation of carbon dioxide gas. Therefore, the sodium carbonate is removed by washing with water before being immersed in hydrochloric acid.

FIG. 13 shows the removal of the sodium carbonate 52 from the heat insulating sheet 51 by washing with water. The surface of the heat insulating sheet 51 is arranged vertically with respect to the bottom surface of the washing tank 55 .
As a result, the specific gravity of sodium carbonate 52 is large, so it goes to the bottom of the tank after elution. Furthermore, a difference in concentration occurs in the vertical direction in the tank, and convection occurs in the tank so as to equalize the concentration.
On the other hand, when the heat insulating sheet 51 is placed in the horizontal direction, it is difficult for the concentration difference to occur in the tank, and convection does not occur so much. Therefore, the elution of sodium carbonate into the water 56 is slower than in the vertical arrangement.
At this time, the angle of the surface of the heat insulating sheet 51 with respect to the bottom surface is 90°±45°, more preferably 90°±20°, because a space is required for causing convection.
<(b) Hydrochloric acid immersion step in surface modification step>
FIG. 14 shows the removal of carbon dioxide 53 from the insulating sheet 51 during immersion in an aqueous solution of hydrochloric acid 58 .
The surface of the heat insulating sheet 51 is arranged vertically with respect to the bottom surface of the hydrochloric acid bath 57 . As a result, the specific gravity of the carbon dioxide 53 is small, so that after the elution, the carbon dioxide 53 goes up to the top of the tank and mainly escapes from the upper part/upper end of the workpiece. On the other hand, when the heat insulating sheet 51 is placed horizontally, the glass fibers have irregularities in density (unevenness in density), and the dense portions act like a film, preventing the escape of gas and swelling.
At this time, the angle of the surface of the heat insulating sheet 51 with respect to the bottom surface is 90°±30°, more preferably 90°±20°, because it is necessary to release the generated gas.
<Silylation step in (b) surface modification step>
FIG. 15 shows the removal of insulating sheet 51 and hydrochloric acid 54 in the silylation process. Silylation tank 59 contains silylation agent 60 . The surface of the heat insulating sheet 51 is arranged vertically with respect to the bottom surface of the silylation bath 59 . As a result, since the specific gravity of the hydrochloric acid 54 is large, the hydrochloric acid 54 goes downward, and mainly escapes from the lower surface/lower end of the workpiece. On the other hand, when the heat insulating sheet 51 is placed horizontally, the glass fibers have irregularities in density (uneven density), and the dense portions act like a film, hindering the discharge of hydrochloric acid and swelling.
At this time, the angle of the surface of the heat insulating sheet 51 with respect to the bottom surface is 90°±45°, more preferably 90°±30°, because it is necessary to discharge the generated hydrochloric acid.

(c) Drying step:
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.

Hereinafter, this embodiment will be described based on examples. However, this embodiment is not limited to the following examples. All reactions were carried out under air.

<Evaluation>
In the examples, ethylene carbonate was used as the gelling agent, and the silica concentration of the water glass raw material was changed to prepare heat insulating sheets, and the thermal conductivity, compressibility, and thermal resistance were evaluated.

A heat flow meter HFM 436 Lambda (manufactured by NETZCH) was used for thermal conductivity measurement.

The compressibility was measured using a desktop precision universal testing machine Autograph AGS-X (manufactured by Shimadzu).

The thermal resistance value was calculated by dividing the thickness of the heat insulating sheet obtained from the compressibility at a pressure of 5 MPa by the thermal conductivity.

Furthermore, the microstructure of the silica airgel was evaluated using a high-precision gas/vapor adsorption measurement device BELSORP-max42N-VP-P (manufactured by Microtrack Bell).

Detailed conditions for each example and comparative example will be described below. In addition, Table 1 shows the results.

実施例１乃至実施例９、比較例１乃至比較例７の結果について記載する。
ＷＧ；水ガラス，ＥＣａｑ．；炭酸エチレン水溶液，ＨＣｌａｑ．；塩酸水溶液，ＮＨ_３ａｑ．；アンモニア水，ＧＰ；ガラスペーパー
＜合格基準＞
（１）かさ密度評価
断熱シートのかさ密度は０．３以上０．５ｇ／ｃｍ^３以下を合格とした。断熱シートのかさ密度が０．３ｇ／ｃｍ^３未満だと、加重をかけたときに潰れやすい。かさ密度が０．５ｇ／ｃｍ^３より大きいと、加重に対して潰れにくくなるが、熱伝導率が高くまた熱抵抗が小さくなる。このため、圧縮時において、断熱シートは熱連鎖が起きやすくなる。

The results of Examples 1 to 9 and Comparative Examples 1 to 7 will be described.
WG; water glass, ECaq. ; ethylene carbonate aqueous solution, HClaq. aqueous hydrochloric acid, NH ₃ aq. ; Ammonia water, GP; Glass paper <Acceptance criteria>
(1) Evaluation of Bulk Density A heat insulating sheet with a bulk density of 0.3 or more and 0.5 g/cm ³ or less was regarded as acceptable. If the bulk density of the heat insulating sheet is less than 0.3 g/cm ³ , it will easily collapse when a load is applied. When the bulk density is more than 0.5 g/cm ³ , the material is less likely to collapse under load, but the thermal conductivity is high and the thermal resistance is low. For this reason, heat chain is likely to occur in the heat insulating sheet during compression.

(2) Evaluation of Thermal Conductivity A thermal conductivity of 100 mW/mK or less of the heat insulating sheet was accepted. If the thermal conductivity of the heat insulating sheet is higher than 100 mW/mK, the thermal resistance will be small, so thermal chain reaction will easily occur even during compression.

(3) Gel Filling Rate An airgel filling rate of 50% by weight or more and 80% by weight or less in the heat insulating sheet was accepted. If the airgel has a filling rate of less than 50% by weight, it is easily crushed and the thermal resistance during compression becomes small. When the airgel has a filling rate of more than 80% by weight, it is difficult to crush, but the solid heat transfer component increases, so the thermal resistance during compression may decrease.

(4) Evaluation of Specific Surface Area A specific surface area of the heat insulating sheet of 300 m ² /g or more and 600 m ² /g or less was judged to be acceptable.

If the thermal conductivity of the heat insulating sheet is less than 300 m ² /g, the particle size of the particles constituting the porous body is large, so the thermal conductivity is high and the thermal resistance is small, so that thermal chaining occurs even during compression. easier.

If the specific surface area of the heat insulating sheet is more than 600 m ² /g, the particles forming the porous body have small particle diameters and are likely to be crushed during compression.

(5) Evaluation of Pore Volume A heat insulating sheet with a pore volume of 0.15 ml/g or less was accepted. If the pore volume of the heat insulating sheet is more than 0.15 ml/g, the heat insulating sheet is likely to be crushed during compression, so that the heat resistance is reduced and thermal chain is likely to occur.

(6) Evaluation of Compressive Characteristics Compressibility of the heat insulating sheet at 5.0 MPa was judged as acceptable if it was 40% or less. In order to effectively suppress the heat chain even under high load, the heat insulating sheet must withstand compression to some extent and suppress the increase of the solid heat transfer component. If the compressibility of the heat insulating sheet at 5.0 MPa is higher than 40%, the advantage over conventional heat insulating sheets is lost.

(7) Thermal resistance value evaluation A thermal resistance value of 0.01 m ² K/W or more of the heat insulating sheet at 5.0 MPa was regarded as acceptable.

It is sufficient to actually apply a load and measure the thermal conductivity. However, especially when the load is high, it collapses due to compression, and it is difficult to measure the thermal conductivity during compression.
A thermal resistance value was calculated from the thickness of the heat insulating sheet obtained from the compressibility and the thermal conductivity measured by the heat flow meter HFM, and was comparatively evaluated.

If the thermal resistance value at 5.0 MPa is less than 0.01 m ² K/W, heat chain is likely to occur during compression.

(8) Comprehensive evaluation Conditions that satisfy all conditions were regarded as pass as comprehensive evaluation.

<Example 1>
6 parts by weight (1.23 g) of ethylene carbonate (white crystals) was added to an aqueous solution of water glass (silica concentration: 14%, 20.5 g) prepared by diluting the water glass raw material with distilled water, and the mixture was thoroughly stirred and dissolved. to prepare a sol solution.

Next, the sol solution was poured into a non-woven fabric fiber (material: glass paper, thickness 0.63 mm, basis weight 100 g/m ² , dimension 12 cm square) to uniformly impregnate the non-woven fabric fiber with the sol solution. 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 gelation, the impregnated nonwoven fabric together with the film was passed through a biaxial roll with a gap of 1.00 mm (including the thickness of the film), and excess gel was squeezed out from the nonwoven fabric to regulate the thickness to 1.00 mm.

Next, after the film was peeled off and the gel sheet was immersed in 6N hydrochloric acid, it was allowed to stand at room temperature of 23° C. for 10 minutes to incorporate hydrochloric acid into the gel sheet. Next, the gel sheet was immersed in a mixture of octamethyltrisiloxane as a silylating agent and 2-propanol (IPA), placed in a constant temperature bath at 55° C., and allowed to react for 2 hours. When the trimethylsiloxane bond started to form, the hydrochloric acid solution was discharged from the gel sheet, and two liquids were separated (siloxane in the upper layer, hydrochloric acid solution in the lower layer, and 2-propanol). A heat insulating sheet was obtained by transferring the gel sheet to a constant temperature bath set at 150° C. and drying it in an air atmosphere for 2 hours.

As a result of evaluating the thermal conductivity and compressive properties of this heat insulating sheet, the compressibility was 35.8%, the thermal resistance was 0.02 m ² K/W, and the overall evaluation was acceptable.

<Example 2>
A sheet was produced under the same process conditions as in Example 1, except that the silica concentration was changed to 16% and the amount of ethylene carbonate added was changed to 3 parts by weight. As a result of evaluating this heat insulating sheet, the compressibility was 30.1%, the thermal resistance was 0.017 m ² K/W, and the overall evaluation was acceptable.

<Example 3>
A sheet was produced under the same process conditions as in Example 2, except that the silica concentration was changed to 18%.
As a result of evaluating this heat insulating sheet, the compressibility was 23.3%, the thermal resistance was 0.015 m ² K/W, and the overall evaluation was acceptable.

<Example 4>
A sheet was produced under the same process conditions as in Example 2, except that the silica concentration was changed to 20%. As a result of evaluating this heat insulating sheet, the compressibility was 21.3%, the thermal resistance was 0.015 m ² K/W, and the overall evaluation was acceptable.
<Example 5>
A sheet was produced under the same process conditions as in Example 4, except that the thickness of the glass paper was changed to 1.03 mm. As a result of evaluating this heat insulating sheet, the compressibility was 21.0%, the thermal resistance was 0.026 m ² K/W, and the overall evaluation was acceptable.
<Example 6>
A sheet was produced under the same process conditions as in Example 5, except that the amount of ethylene carbonate added was changed to 4 parts by weight. As a result of evaluating this heat insulating sheet, the compressibility was 14.1%, the thermal resistance was 0.025 m ² K/W, and the overall evaluation was acceptable.
<Example 7>
A sheet was produced under the same process conditions as in Example 5, except that the amount of ethylene carbonate added was changed to 5 parts by weight. As a result of evaluating this heat insulating sheet, the compressibility was 13.8%, the thermal resistance was 0.022 m ² K/W, and the overall evaluation was acceptable.
<Example 8>
A sheet was produced under the same process conditions as in Example 5, except that the amount of ethylene carbonate added was changed to 5 parts by weight. As a result of evaluating this heat insulating sheet, the compressibility was 10.4%, the thermal resistance was 0.023 m ² K/W, and the overall evaluation was acceptable.

<Comparative Example 1>
A sheet was produced under the same process conditions as in Example 1, except that the silica concentration was changed to 6%.
As a result of evaluating this heat insulating sheet, the compressibility was 72.5%, the thermal resistance was 0.013 m ² K/W, and the overall evaluation was unacceptable.

<Comparative Example 2>
A sheet was produced under the same process conditions as in Example 1, except that the silica concentration was changed to 8%.
As a result of evaluating this heat insulating sheet, the compressibility was 67.3%, the thermal resistance was 0.015 m ² K/W, and the overall evaluation was unacceptable.

<Comparative Example 3>
A sheet was produced under the same process conditions as in Example 1, except that the silica concentration was changed to 10%.
As a result of evaluating this heat insulating sheet, the compressibility was 63.8%, the thermal resistance was 0.015 m ² K/W, and the overall evaluation was unacceptable.

<Comparative Example 4>
A sheet was produced under the same process conditions as in Example 1, except that the silica concentration was changed to 12%.
As a result of evaluating this heat insulating sheet, the compressibility was 52.4%, the thermal resistance was 0.016 m ² K/W, and the overall evaluation was unacceptable.

<Comparative Example 5>
A sheet was produced under the same process conditions as in Example 1, except that the silica concentration was changed to 6% and 12N hydrochloric acid was used as the gelling agent. As a result of evaluating this heat insulating sheet, the compressibility was 71.9%, the thermal resistance was 0.013 m ² K/W, and the overall evaluation was unacceptable.

<Comparative Example 6>
A sheet was formed under the same process conditions as in Example 1 except that a sol prepared by removing Na ions from an aqueous solution of water glass with a silica concentration of 6% using an ion exchange resin and using a 1N aqueous ammonia solution as a gelling agent. made. As a result of evaluating this heat insulating sheet, the compressibility was 74.6%, the thermal resistance was 0.013 m ² K/W, and the overall evaluation was unacceptable.

<Compression characteristics of high-strength insulation sheet>
The compressibility of the heat insulating sheet of the present embodiment when pressurized at 0.30 to 5 MPa is preferably 40% or less, more preferably 30% or less. FIG. 3 is a graph plotting the compressibility of the heat insulating sheet when pressurized at 5 MPa against the silica concentration of the water glass. When the compressibility is more than 40%, it is difficult to suppress thermal chain during compression. If the compressibility is 30% or less, heat chain during compression can be effectively suppressed.

<Thermal resistance of high-strength insulation sheet>
The thermal resistance of the heat insulating sheet of the present embodiment when pressurized at 0.30 to 5 MPa is preferably 0.010 m ² K/W or more, more preferably 0.015 m ² K/W or more. preferable. FIG. 4 is a graph plotting the thermal resistance of the heat insulating sheet when pressurized at 5 MPa with respect to the silica concentration of the water glass. When the thermal resistance is less than 0.010 m ² K/W, it is difficult to suppress heat chain during compression. If the thermal resistance is 0.015 m ² K/W or more, heat chain during compression can be effectively suppressed.

<Thermal conductivity of high-strength insulation sheet>
Although the thermal conductivity of the heat insulating sheet of the present embodiment cannot be generalized due to the degree of compressibility, it is sufficient if it is 100 mW/mK or less. FIG. 5 is a graph plotting the thermal conductivity of the heat insulating sheet against the silica concentration of the water glass. When the thermal conductivity is more than 100 mK/W, it is difficult to suppress thermal chain during compression.

<Bulk density of high-strength insulation sheet>
The bulk density of the heat insulating sheet of this embodiment is preferably 0.3 to 0.5 g/cm ³ . In FIG. 6, the abscissa plots the silica concentration of the raw material water glass when the heat insulating sheet was produced, and the ordinate plots the bulk density of the heat insulating sheet. From FIG. 6, when ethylene carbonate is used, the bulk density of the heat insulating sheet tends to increase as the silica concentration increases. When hydrochloric acid or aqueous ammonia was used, it was 0.2 g/cm ³ at a silica concentration of 6%. If the bulk density is less than 0.3 g/cm ³ , it will easily collapse when a high load is applied. Therefore, the compressibility is large and the thermal resistance is small. Further, when the bulk density is more than 0.5 g/cm ³ , the primary silica particles are remarkably coarsened and the airgel itself shrinks, and the expected thermal resistance value cannot be obtained even under no load.

<Specific surface area of high-density airgel>
The specific surface area of the high-density airgel of the present embodiment is preferably 300-600 m ² /g. In FIG. 7, the abscissa plots the silica concentration of the raw material water glass when the heat insulating sheet was produced, and the ordinate plots the specific surface area of the airgel.

It can be seen from FIG. 7 that when ethylene carbonate is used, the specific surface area of the airgel gradually decreases as the silica concentration increases, and tends to take a minimum value around 14% silica concentration.

When hydrochloric acid and aqueous ammonia were used, they were about 500 and 750 m ² /g, respectively, at a silica concentration of 6%. At this time, if the specific surface area is less than 300 m ² /g, significant coarsening of the primary silica particles and shrinkage of the airgel itself occur, and an expected thermal resistance value cannot be obtained even under no load.

On the other hand, when the specific surface area is more than 600 m ² /g, the primary particles of silica are remarkably fine and the density of the airgel is lowered, so that the expected thermal resistance value cannot be obtained under high load. The specific surface area of general low-density aerogels is greater than 600 m ² /g, which is a result of the fact that the primary particles of silica are very small and the resulting aerogels have a low bulk density.

<Pore volume of high-density airgel>
In FIG. 8, the abscissa plots the silica concentration of the raw material water glass when the heat insulating sheet was produced, and the ordinate plots the pore volume of the airgel. It can be seen from FIG. 8 that when ethylene carbonate is used, the pore volume of the airgel gradually decreases as the silica concentration increases, and tends to take a minimum value around 14% silica concentration. When hydrochloric acid was used, it was 2.0 ml/g at a silica concentration of 6%, and when ammonia water was used, it was 4.4 ml/g at a silica concentration of 6%. At this time, when the pore volume is 1.5 ml/g or more, it is likely to be crushed when a high load is applied, resulting in a large compressibility and a small thermal resistance.

The average pore size of the high-density airgel is preferably 10-70 nm.

<Average pore size of high-density airgel>
In FIG. 9, the abscissa plots the silica concentration of the raw material water glass when the heat insulating sheet was produced, and the ordinate plots the average pore diameter of the airgel. From FIG. 9, it can be seen that when ethylene carbonate is used, the average pore diameter is about 60 nm when the silica concentration is 10% or less, and the average pore diameter is about 30 to 40 nm when the silica concentration is 14% or more. When hydrochloric acid was used, it was about 40 nm at a silica concentration of 6%, and when ammonia water was used, it was about 30 nm at a silica concentration of 6%. At this time, if the average pore diameter is less than 10 nm, significant coarsening of the primary silica particles and shrinkage of the airgel itself occur, and an expected thermal resistance value cannot be obtained even under no load. Moreover, when the average pore diameter is larger than 70 nm, it becomes difficult to suppress the air convection, so the thermal resistance becomes small.

<Silica concentration and compressibility>
FIG. 10 shows the relationship between the silica concentration and compressibility in the example and the comparative example. A pressure of 5 MPa to 0.3 MPa was applied to each sample.

In the case of a pressure of 5 MPa, Examples 1 to 4 have a compressibility of 40% or less, which is preferable.

In the case of a pressure of 2 MPa, Examples 1 to 4 have a compressibility of 30% or less, which is more preferable.

In the case of a pressure of 1 MPa, Examples 1 to 4 have a compressibility of 20% or less, which is more preferable.

The thermal resistance during compression also has a similar tendency. Examples 1 to 4 are 0.010 m ² K/W or more at 0.30 to 5.0 MPa.

<Results>
In Examples 1 to 4, heat insulating sheets were produced using water glass having a silica concentration of 14 to 20% and ethylene carbonate. As a result, the compressibility at 5.0 MPa was as small as 40% or less, and the thermal resistance value was 0.01 m ² K/W or more.

In Comparative Examples 1 to 4, heat insulating sheets were produced using water glass having a silica concentration of 6 to 12% and ethylene carbonate. As a result, the compression rates at 5.0 MPa were all greater than 40%.

In Comparative Examples 5 and 6, heat insulating sheets were produced using water glass with a silica concentration of 6% using an aqueous hydrochloric acid solution and an aqueous ammonia solution, respectively. With a gelling agent other than ethylene carbonate, when the silica concentration was increased to 8% or more, uniform gelation did not occur, making it impossible to prepare a heat insulating sheet.

From the above results, it was found that the heat insulation sheet composed of high-density airgel-nonwoven fiber, which is synthesized using a water glass solution with a silica concentration of 14 to 20% and carbonic acid ester, is excellent as a high-strength heat insulation sheet. It has been found to be effective in inhibiting linkage.

(as a whole)
The heat insulating sheet contains airgel and nonwoven fabric fibers as main components and does not contain other compounds as main components. The sum of airgel and nonwoven fibers is 90% or more of the total weight.

FIG. 11 is a cross-sectional view showing Application Example 1 of the heat insulating sheet of the embodiment.

The heat insulating sheet 10 of the embodiment can be arranged between the electronic component 12 and the housing 11 that generate heat in an electronic device. The heat of the electronic component 12 is not transmitted to the housing 11. - 特許庁Electronic component 12 is mounted on substrate 13 . The heat insulating sheet 10 may be covered with a cover that covers the surface. The insulating sheet 10 may be laminated with a thermally conductive material such as a graphite sheet.

FIG. 12 is a cross-sectional view showing Application Example 2 of the heat insulating sheet of the embodiment.
A battery unit in which the heat insulating sheet 10 of any of the above-described embodiments is arranged between the batteries 15 of an automobile is preferable because not only heat insulation between the batteries 15 but also fire spread prevention can be achieved.
Battery 15 is not limited to automotive applications. The battery 15 may be a battery for various mobile objects or a battery for a home power storage device.
The heat insulating sheet 10 may be combined with another sheet or the like.

<Evaluation of influence by treatment method>
The thickness was measured using a digital indicator ID-H0530 (manufactured by Mitutoyo).

<Example 9>
5 parts by weight (1.025 g) of ethylene carbonate (white crystals) was added to an aqueous solution of water glass (silica concentration: 20%, 20.5 g) prepared by diluting the water glass raw material with distilled water, and the mixture was thoroughly stirred and dissolved. to prepare a sol solution.

Next, the sol solution was poured into a non-woven fabric fiber (material: glass paper, thickness 1.03 mm, basis weight 140 g/m ² , dimension 12 cm square) to uniformly impregnate the non-woven fabric fiber with the sol solution. 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 gelation, the impregnated nonwoven fabric together with the film was passed through a biaxial roll with a gap of 1.00 mm (including the thickness of the film), and excess gel was squeezed out from the nonwoven fabric to regulate the thickness to 1.00 mm.

Next, after peeling off the film and immersing the gel sheet in pure water in the vertical direction (the angle is about 90 degrees with respect to the horizontal direction), the gel sheet is allowed to stand for 5 minutes to remove the sodium carbonate. After that, it was vertically immersed in 6N hydrochloric acid and allowed to stand at room temperature of 23° C. for 10 minutes to incorporate hydrochloric acid into the gel sheet. Next, the gel sheet was vertically immersed in a mixture of octamethyltrisiloxane and 2-propanol (IPA) as a silylating agent, placed in a constant temperature bath at 55° C., and allowed to react for 2 hours. When the trimethylsiloxane bond started to form, the hydrochloric acid solution was discharged from the gel sheet, and two liquids were separated (siloxane in the upper layer, hydrochloric acid solution in the lower layer, and 2-propanol). A heat insulating sheet was obtained by transferring the gel sheet to a constant temperature bath set at 150° C. and drying it in an air atmosphere for 2 hours.

As a result of evaluating the thermal conductivity and compression characteristics of this heat insulating sheet, the thermal conductivity was 49.02 mW/mK, the compressibility was 12.4%, and the thickness variation (standard deviation) was 0.029 mm.
The thickness variation (standard deviation) can be at least 0.040 mm or less. Homogenization can be achieved by tilting.

In Examples 1 to 7, the thickness variation (standard deviation) was greater than about 0.040 mm.

<Results of impact by treatment method>
In Example 9, a heat insulating sheet was produced by immersion treatment in the vertical direction in pure water, 6N hydrochloric acid, and a mixture of octamethyltrisiloxane and 2-propanol (IPA) as a silylating agent. As a result, the compressibility at 5.0 MPa was as small as 12.4%, and the thickness variation was also as small as 0.029 mm.
The cause of thickness variation is the influence of air bubbles.
From the results of Example 9 and Examples 1 to 8, it was found that by performing the processes in the vertical direction, such as washing with water, immersion in an aqueous solution of hydrochloric acid, and silylation, a higher-strength insulation sheet was realized, and thermal chaining was achieved even under high-load conditions. It has been found to be effective in suppressing In other words, by performing processing while tilting in the vertical direction, better characteristics with less variation can be obtained.

The heat insulating sheet of the present embodiment, which has improved compressive strength and is composed of at least two components of high-density airgel and non-woven fiber structure, exhibits a sufficient heat insulating effect even in narrow spaces in electronic equipment, in-vehicle equipment, and industrial equipment. It is widely used because it can It is applied to all products related to heat, such as information equipment, portable equipment, displays, and electrical equipment.

10 Insulation sheet 11 Case 12 Electronic component 13 Substrate 15 Battery 51 Insulation sheet 52 Sodium carbonate 53 Carbon dioxide 54 Hydrochloric acid 55 Washing tank 56 Water 57 Hydrochloric acid tank 58 Hydrochloric acid 59 Silylation tank 60 Silylating agent 101 Sodium silicate 102 Hydroxyl ion 103 Carbonic acid Ethylene 104 Carbonate ion 105 Ethylene glycol 106 Hydrogel 107 Sodium carbonate

Claims (15)

Non-woven fabric fibers are impregnated with a basic sol having a pH of 10 or higher, which is prepared by adding 1 to 10 parts by weight of carbonate ester as a gelling agent instead of a solvent to the water glass composition, to obtain a hydrogel-non-woven fabric composite. a complex generating step for generating
a surface modification step of mixing the complex with a silylating agent to modify the surface;
a drying step of removing the liquid contained within the composite by drying below a critical temperature and pressure ;
A method for producing a heat insulating sheet, wherein the thickness variation of the heat insulating sheet is 0.040 mm or less . Non-woven fabric fibers are impregnated with a basic sol having a pH of 10 or higher, which is prepared by adding 1 to 10 parts by weight of carbonate ester as a gelling agent instead of a solvent to the water glass composition, to obtain a hydrogel-non-woven fabric composite. a complex generating step for generating
a surface modification step of mixing the complex with a silylating agent to modify the surface;
a drying step of removing the liquid contained within the composite by drying below a critical temperature and pressure;
A method for producing a heat insulating sheet, wherein the heat insulating sheet has a thickness of 0.03 to 3.0 mm. Non-woven fabric fibers are impregnated with a basic sol having a pH of 10 or higher, which is prepared by adding 1 to 10 parts by weight of carbonate ester as a gelling agent instead of a solvent to the water glass composition, to obtain a hydrogel-non-woven fabric composite. a complex generating step for generating
a surface modification step of mixing the complex with a silylating agent to modify the surface;
a drying step of removing the liquid contained within the composite by drying below a critical temperature and pressure;
A method for producing a heat insulating sheet, wherein the nonwoven fabric contains at least one selected from glass wool, glass paper, rock wool, polyethylene terephthalate, polyphenylene sulfide, polypropylene, polytetrafluoroethylene, wool and cellulose. Non-woven fabric fibers are impregnated with a basic sol having a pH of 10 or higher, which is prepared by adding 1 to 10 parts by weight of carbonate ester as a gelling agent instead of a solvent to the water glass composition, to obtain a hydrogel-non-woven fabric composite. a complex generating step for generating
a surface modification step of mixing the complex with a silylating agent to modify the surface;
a drying step of removing the liquid contained within the composite by drying below a critical temperature and pressure;
A method for producing a heat insulating sheet, wherein the airgel has an average pore size of 10 to 70 nm. Non-woven fabric fibers are impregnated with a basic sol having a pH of 10 or higher, which is prepared by adding 1 to 10 parts by weight of carbonate ester as a gelling agent instead of a solvent to the water glass composition, to obtain a hydrogel-non-woven fabric composite. a complex generating step for generating
a surface modification step of mixing the complex with a silylating agent to modify the surface;
a drying step of removing the liquid contained in the complex by drying below the critical temperature and pressure, wherein in the surface modification step, the complex is surface-modified with a silylating agent. A method for manufacturing an insulating sheet that is pre-washed with water. 6. The method for producing a heat insulating sheet according to claim 5, wherein in the surface modification step, the composite is erected at an angle of 90±45 degrees with respect to the bottom surface of the treatment tank and the water washing step is performed. Non-woven fabric fibers are impregnated with a basic sol having a pH of 10 or higher, which is prepared by adding 1 to 10 parts by weight of carbonate ester as a gelling agent instead of a solvent to the water glass composition, to obtain a hydrogel-non-woven fabric composite. a complex generating step for generating
a surface modification step of mixing the complex with a silylating agent to modify the surface;
and a drying step of removing the liquid contained in the composite by drying below the critical temperature and pressure, wherein in the surface modification step, the composite is placed against the bottom surface of the treatment vessel. A method for manufacturing a heat insulating sheet in which a hydrochloric acid immersion treatment is performed while standing at an angle of 90 degrees ± 30 degrees. Non-woven fabric fibers are impregnated with a basic sol having a pH of 10 or higher, which is prepared by adding 1 to 10 parts by weight of carbonate ester as a gelling agent instead of a solvent to the water glass composition, to obtain a hydrogel-non-woven fabric composite. a complex generating step for generating
a surface modification step of mixing the complex with a silylating agent to modify the surface;
and a drying step of removing the liquid contained in the composite by drying below the critical temperature and pressure, wherein in the surface modification step, the composite is placed against the bottom surface of the treatment vessel. A method for manufacturing a heat insulating sheet in which the silylation treatment is performed while standing at an accuracy of 90°±45°. A heat insulating sheet containing airgel and nonwoven fabric fibers and having a compressibility of 40% or less at 0.30 to 5.0 MPa,
A heat insulating sheet having a thickness of 0.03 to 3.0 mm . A heat insulating sheet containing airgel and nonwoven fabric fibers and having a compressibility of 40% or less at 0.30 to 5.0 MPa,
A heat insulating sheet, wherein the nonwoven fabric contains at least one selected from glass wool, glass paper, rock wool, polyethylene terephthalate, polyphenylene sulfide, polypropylene, polytetrafluoroethylene, wool and cellulose. A heat insulating sheet containing airgel and nonwoven fabric fibers and having a compressibility of 40% or less at 0.30 to 5.0 MPa,
The heat insulating sheet, wherein the airgel has an average pore size of 10 to 70 nm. Containing airgel and non-woven fibers, the compressibility at 0.30 to 5.0 MPa is 40% or less
A heat insulating sheet of
A heat insulating sheet, wherein the ratio of the airgel to the weight of the heat insulating sheet is 50% by weight or more. A heat insulating sheet containing airgel and nonwoven fabric fibers and having a compressibility of 40% or less at 0.30 to 5.0 MPa,
The heat insulating sheet, wherein the thickness variation of the heat insulating sheet is 0.040 mm or less. An electronic device comprising the heat insulating sheet according to any one of claims 9 to 13 arranged between an electronic component that generates heat and a housing. A battery unit in which the heat insulating sheet according to any one of claims 9 to 13 is arranged between batteries.

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