SHEET, SEALING MATERIAL, FUEL BATTERY, ELECTROLYSIS CELL, METHOD FOR PRODUCING SHEET, AND METHOD FOR PRODUCING SEALING MATERIAL

Abstract

A sheet and a sealing material based on clay and excellent in an electrical insulating property in a high-temperature environment. A sheet, containing: a first component as a main component; and a second component optionally, in which the first component is clay, a diameter change rate is 10% or less, as thermal dimensional stability, when a weight of the entire sheet is 100% by weight, a content of iron oxide is 6% by weight or less, the second component is a filling material, when the weight of the entire sheet is 100% by weight, a sum of the first component and the second component is 90% by weight or more, and the first component: the second component=20:80 to 100:0 is set, and a sealing material containing the sheet.

Claims

1. A sheet, comprising a first component as a main component, wherein the first component is clay, a diameter change rate is 10% or less, as thermal dimensional stability, and when a weight of the entire sheet is 100% by weight, a content of iron oxide is 6% by weight or less.

2. The sheet according to claim 1, wherein the sheet contains the first component, and a second component optionally, the first component is swelling clay, the second component is a filling material, when the weight of the entire sheet is 100% by weight, a sum of the first component and the second component is 90% by weight or more, and the first component: the second component=20:80 to 100:0 is set.

3. The sheet according to claim 1, wherein the first component is swelling muscovite.

4. The sheet according to claim 1, wherein when the weight of the entire sheet is 100% by weight, a content of alumina is 16% by weight or more.

5. The sheet according to claim 1, wherein the swelling clay is swelling muscovite, and in the swelling muscovite, at least a part of K.sup.+ ions in an interlayer of the muscovite is exchanged with Li.sup.+ ions.

6. The sheet according to claim 2, wherein the second component is a filling material of clay or an oxide.

7. The sheet according to claim 2, wherein in the second component, a volume-based cumulative 50% particle size (D.sub.50) measured by a laser diffraction/scattering particle size distribution analyzer is 5 to 50 m.

8. The sheet according to claim 1, wherein a content of a binder is 0.1% by weight or less.

9. The sheet according to claim 1, wherein when the weight of the entire sheet is 100% by weight, the content of the iron oxide is 3% by weight or less.

10. A sealing material, comprising the sheet according to claim 1.

11. The sealing material according to claim 10, wherein the sealing material is for a fuel battery or an electrolysis cell.

12. A fuel battery or an electrolysis cell, comprising the sealing material according to claim 11.

13. A method for producing the sheet according to claim 1, comprising a step of mixing the first component and the second component to form a mixture.

14. A method for producing a sealing material, comprising a step of incorporating the sheet produced by the method for producing the sheet according to claim 13 as a part of a gasket or a packing.

Description

BRIEF DESCRIPTION OF DRAWINGS

[0058] FIG. 1 is a diagram illustrating a particle size of muscovite used for modification, and a feature and a sheet appearance after modification.

[0059] FIG. 2 is a table showing g a second component used.

[0060] FIG. 3 is a table showing sheets and sealing materials of Examples 1 to 5.

[0061] FIG. 4 is a table showing sheets and sealing materials of Examples 6 to 10.

[0062] FIG. 5 is a table showing sheets and sealing materials of Examples 11 to 14.

[0063] FIG. 6 is a table showing sheets and sealing materials of Comparative Examples 1 to 4.

[0064] FIG. 7 is a table showing a result of measuring volume resistivity.

DESCRIPTION OF EMBODIMENTS

[0065] Hereinafter, an embodiment of the present invention (hereinafter, this embodiment) will be described with reference to the drawings. This embodiment relates to a sheet, a sealing material, a method for producing a sheet, and a method for producing a sealing material.

<Definition>

[0066] In this specification, to (for example, % by weight to % by weight) indicates or more and A or less (% by weight or more and % by weight or less).

[0067] In addition, in this specification, the term include or including indicates including specified constituents, but does not exclude the presence of other constituents.

<Sheet>

[0068] A sheet of this embodiment, for example, can be used for a sealing material. The sheet of this embodiment contains a first component as a main component, and optionally contains a second component.

(First Component)

[0069] The first component is swelling clay, preferably swelling muscovite. Here, the muscovite is a concept including sericite that is another name in a case where the muscovite is fine particles. In addition, the swelling muscovite includes swelling sericite in a case where the swelling muscovite is fine particles. In the swelling muscovite, at least a part of K.sup.+ ions in the interlayer of the muscovite is exchanged with at least one or more types of ions (ions imparting swellability) selected from the group consisting of Lit ions, Ca.sup.2+ ions, and Mg.sup.2+ ions. In the swelling sericite, at least a part of K.sup.+ ions in the interlayer of the sericite is exchanged with at least one or more types of ions (ions imparting swellability) selected from the group consisting of Li.sup.+ ions, Ca.sup.2+ ions, and Mg.sup.2+ ions.

[0070] The muscovite is one type of silicate mineral (phyllosilicate mineral), is represented by Chemical Formula K.sub.2Al.sub.4 (Si.sub.6.Math.Al.sub.2)O.sub.20 (OH).sub.4, and has a triple structure containing Al and K between layers of a silicic acid tetrahedron. The sericite is fine particles of muscovite that is a layered silicate mineral. It is preferable that the muscovite used in this embodiment is not fluorine mica-type muscovite containing fluorine, from the viewpoint of preventing the generation of fluorine-based gas.

[0071] The swelling muscovite that is preferable as the first component can be obtained by exchanging at least a part of K.sup.+ ions in the interlayer of the muscovite with ions such as Li.sup.+ ions by modification. The modification of the muscovite is not particularly limited, and for example, can be performed by mixing lithium nitrate that is heated and melted with muscovite or sericite to react for a predetermined time. The dispersion of the swelling muscovite to water, for example, can be performed by removing the lithium nitrate with filtering and washing, and then, adding pure water, and stirring.

[0072] In the swelling muscovite, a ratio of Lit ions to K.sup.+ ions contained in the interlayer is Li.sup.+:K.sup.+=20 at %: 80 at % to 70 at %: 30 at %, preferably Li.sup.+:K.sup.+=30 at %: 70 at % to 60 at %: 40 at %, more preferably Li.sup.+:K.sup.+=40 at %: 60 at % to 60 at %: 40 at %, and even more preferably Li.sup.+:K.sup.+=40 at %: 60 at % to 55 at %: 45 at %. The same ratio applies to a case where ions to be exchanged are not K.sup.+ but Ca.sup.2+ or Mg.sup.2+.

[0073] When the weight of the entire sheet is 100% by weight, 90% by weight or more of the first component is contained. In addition, in a case where both of the first component and the second component are contained, at least 25% by weight or more, preferably 30% by weight or more, more preferably 50% by weight or more, even more preferably 60% by weight or more, particularly preferably 75% by weight or more, and more particularly preferably 80% by weight or more of the first component is contained when the total weight of the first component and the second component is 100% by weight. In addition, when the total weight of the first component and the second component is 100% by weight, at most 100% by weight or less, 90% by weight or less, 80% by weight or less, 70% by weight or less, 65% by weight or less, and 50% by weight or less of the first component is contained.

[0074] When the total weight of the first component and the second component is 100% by weight, 25 to 100% by weight, 30 to 100% by weight, 40 to 100% by weight, 50 to 100% by weight, 60 to 100% by weight, 65 to 100% by weight, 70 to 100% by weight, 75 to 100% by weight, 80 to 100% by weight, 25 to 95% by weight, 25 to 90% by weight, 25 to 80% by weight, 25 to 75% by weight, 25 to 70% by weight, 25 to 65% by weight, 25 to 60% by weight, and 25 to 50% by weight of the first component is contained.

[0075] In the first component, a volume-based cumulative 50% particle size (D.sub.50) measured by a laser diffraction/scattering particle size distribution analyzer is 5 to 500 m, preferably 7 to 400 m, more preferably 10 to 300 m, even more preferably 10 to 250 m, and particularly preferably 10 to 230 m.

(Second Component)

[0076] The second component is a filling material, preferably a filling material of clay or an oxide. The second component is optionally contained in the sheet. Here, the filling material of the clay or the oxide is at least one or more types selected from the group consisting of muscovite, sericite, talc, kaolinite, and molten silica. Note that as the filling material, a calcined filling material can also be used.

[0077] When the total weight of the first component and the second component is 100% by weight, at least 10% by weight or more, preferably 20% by weight or more, more preferably 25% by weight or more, even more preferably 30% by weight or more, particularly preferably 40% by weight or more, and more particularly preferably 50% by weight or more of the second component is contained. In addition, when the total weight of the first component and the second component is 100% by weight, at most 75% by weight or less, 70% by weight or less, 65% by weight or less, 60% by weight or less, 55% by weight or less, and 50% by weight or less of the second component is contained. By changing the ratio of the second component, it is possible to adjust restorability to any state, but in a case where the ratio is excessively increased, a mechanical strength decreases.

[0078] When the total weight of the first component and the second component is 100% by weight, 0 to 75% by weight, 0 to 70% by weight, 0 to 60% by weight, 0 to 50% by weight, 0 to 40% by weight, 0 to 35% by weight, 0 to 30% by weight, 0 to 25% by weight, 0 to 20% by weight, 5 to 75% by weight, 10 to 75% by weight, 20 to 75% by weight, 25 to 75% by weight, 30 to 75% by weight, 35 to 75% by weight, 40 to 75% by weight, and 50 to 75% by weight of the second component is contained.

[0079] In the second component, a volume-based cumulative 50% particle size (D.sub.50) measured by a laser diffraction/scattering particle size distribution analyzer is 5 to 500 m, preferably 7 to 400 m, more preferably 10 to 300 m, even more preferably 10 to 250 m, and particularly preferably 10 to 230 m.

[0080] In the second component, a weight loss rate when heated to 1000 C. is 15% by weight or less, preferably 13% by weight or less, more preferably 10% by weight or less, even more preferably 8% by weight or less, still even more preferably 7% by weight or less, and particularly preferably 6% by weight or less when the weight before heating is 100% by weight.

[0081] In the second component, the content of iron is small. Specifically, the content of iron in terms of iron oxide (Fe.sub.2O.sub.3) contained in the second component is 3% by weight or less, preferably 2% by weight or less, more preferably 1.5% by weight or less, even more preferably 1.0% by weight or less, still even more preferably 0.8% by weight or less, and particularly preferably 0.5% by weight or less. Here, the content of each component can be measured by fluorescent X-ray analysis (XRF) when notated in terms of oxide. Note that even in a case where the content of each component is notated in terms of oxide, it is not necessary that each component is contained as an oxide.

(Total Ratio of First Component and Second Component in Sheet)

[0082] When the weight of the entire sheet is 100% by weight, the sum of the first component and the second component is 90% by weight or more, preferably 92% by weight or more, more preferably 93% by weight or more, even more preferably 95% by weight or more, still even more preferably 96% by weight or more, and particularly preferably 97% by weight or more.

(Content Ratio of First Component to Second Component)

[0083] A ratio (a weight ratio) of the content of the first component: the content of the second component is 10:90 to 100:0, 15:85 to 100:0, 20:80 to 100:0, 25:75 to 100:0, 30:70 to 100:0, 40:60 to 100:0, 50:50 to 100:0, 60:40 to 100:0, 65:35 to 100:0, 70:30 to 100:0, 75:25 to 100:0, 80:20 to 100:0, 25:75 to 95:5, 25:75 to 90:10, 25:75 to 80:20, 25:75 to 75:25, 25:75 to 70:30, 25:75 to 65:35, 25:75 to 60:40, and 25:75 to 50:50.

<Method for Producing Sheet>

[0084] A method for producing a sheet of this embodiment includes a step of mixing the first component and the second component to form a mixture. A solvent such as water is added to the mixture, and the mixture is adjusted to slurry with an appropriate viscosity, in accordance with a molding method. Then, the mixture is molded by using extrusion molding, a calendering roll, a film applicator, a doctor blade, a bar coater, screen printing, and the like, and dried, and thus, the sheet can be obtained.

<Sealing Material>

[0085] The sheet of this embodiment can be used for a sealing material in various industries, a fuel battery such as a high-temperature fuel battery (SOFC), an electrolysis cell such as a solid oxide electrolysis cell (SOEC), and various pipes such as an exhaust conduit of an automobile, for example, a gasket, a packing, and the like. The sheet of this embodiment can also be used as the sealing material itself, or can also be used by being incorporated as a part of the sealing material such as a gasket or a packing. As the shape of the sealing material as a product, a sheet gasket, a spiral-wound gasket, a serrated gasket, and the like are exemplified, but the shape is not limited thereto.

(Binder-Free)

[0086] The sheet of this embodiment and the sealing material including the sheet described above do not substantially contain a binder. Here, the binder is not particularly limited, and examples thereof include rubber and a pressure-sensitive adhesive. More specifically, examples of the binder include acrylonitrile butadiene rubber, styrene butadiene rubber, polybutadiene rubber, silicone rubber, acrylic rubber, natural rubber, butyl rubber, chloroprene rubber, ethylene propylene rubber, fluorine rubber, urethane rubber, an acrylic pressure-sensitive adhesive, and a silicone-based pressure-sensitive adhesive.

[0087] Not substantially containing the binder indicates that when the total weight of the sheet is 100% by weight, the content of the binder contained is less than 0.1% by weight (0.1% by weight or less), preferably less than 0.05% by weight (0.05% by weight or less), more preferably less than 0.01% by weight (0.01% by weight or less), even more preferably less than 0.001% by weight (0.001% by weight or less), and particularly preferably less than 0.0001% by weight (0.0001% by weight or less). The sheet of this embodiment is not compounded with the binder, and thus, when the sheet is used as the sealing material, sealability is high, and outgasing is not caused.

(Content of Iron)

[0088] In the sheet of this embodiment and the sealing material including the sheet described above, the content of iron is small. Specifically, when the weight of the entire sheet is 100% by weight, the content of iron in terms of iron oxide (Fe.sub.2O.sub.3) contained in the sheet of this embodiment and the sealing material including the sheet described above is 6% by weight or less, preferably 3% by weight or less, more preferably 2% by weight or less, even more preferably 1.5% by weight or less, still even more preferably 1.0% by weight or less, and particularly preferably 0.8% by weight or less.

(Content of Alumina)

[0089] When the weight of the entire sheet is 100% by weight, the content of alumina contained in the sheet of this embodiment and the sealing material including the sheet described above is 16% by weight or more.

[0090] The sheet of this embodiment and the sealing material including the sheet described above have a low iron content, compared to vermiculite-based and phlogopite-based sheets, and thus, have a high insulating property. Therefore, the sheet of this embodiment and the sealing material including the sheet described above can be used for a fuel battery such as a solid oxide fuel battery (SOFC) and an electrolysis cell such as a solid oxide electrolysis cell (SOEC), which are required to have a high insulating property.

(Basis Weight)

[0091] The basis weight of the sheet of this embodiment and the sealing material including the sheet described above is preferably 700 to 1300 g/m.sup.2, more preferably 700 to 1200 g/m.sup.2, even more preferably 750 to 1100 g/m.sup.2, and particularly preferably 800 to 1050 g/m.sup.2.

(Density)

[0092] The density of the sealing material of this embodiment at 2 MPa is preferably 0.5 to 2.5 g/cm.sup.3, more preferably 1.0 to 2.2 g/cm.sup.3, and even more preferably 1.2 to 2.0 g/cm.sup.3. In this application, the density of the sealing material can be greater than 1.4 g/cm.sup.3. As the density at 2 MPa decreases, it is easier for the sealing material to follow the irregularities of the opposite member when compressed, and leakage from the contact surfaces decreases.

[0093] The density of the sealing material of this embodiment at 20 MPa is preferably 0.5 to 2.8 g/cm.sup.3, more preferably 1.0 to 2.8 g/cm.sup.3, and even more preferably 1.2 to 2.8 g/cm.sup.3. In this application, the density of the sealing material can be greater than 1.4 g/cm.sup.3. As the density at 20 MPa increases, the sealing material L is densed when tightened, and substantial leakage decreases.

(Compression Restorability)

[0094] In the sealing material of this embodiment, the value of a compression rate calculated by a method described in Examples is 15% or more, preferably 20% or more, more preferably 25% or more, even more preferably 30% or more, and particularly preferably 40% or more. As the compression rate increases, it is easier for the sealing material to follow the irregularities of the opposite member when compressed, and the leakage from the contact surfaces decreases.

[0095] In the sealing material of this embodiment, the value of a restoration rate calculated by a method described in Examples is 5% or more, preferably 6% or more, more preferably 7% or more, even more preferably 8% or more, and particularly preferably 10% or more. As the restoration rate increases, a reactive force when tightened increases, and the leakage from contact surfaces decreases.

(Thermal Dimensional Stability)

[0096] The sealing material of this embodiment has high heat resistance, in which specifically, a diameter change rate calculated by a method described in Examples is 10% or less, preferably 8% or less, more preferably 5% or less, even more preferably 3% or less, and particularly preferably 1% or less.

(Volume Resistivity)

[0097] The sheet of this embodiment and the sealing material including the sheet described above is excellent in an electrical insulating property in a high-temperature environment. Specifically, in the sheet of this embodiment and the sealing material including the sheet described above, as insulating performance in a high-temperature environment, the value of volume resistivity calculated by a method described in Examples is greater than 2.010.sup.6.Math.cm in a measurement condition of 600 C. and an applied voltage of 100 V, and is 3.810.sup.6.Math.cm or more in a measurement condition of 600 C. and an applied voltage of 300 V.

(Fuel Battery and Electrolysis Cell)

[0098] The sealing material of this embodiment has the features as described above, and thus, can be used for a fuel battery. That is, it is possible to provide a fuel battery including the sealing material of this embodiment. As the fuel battery, a planar SOFC is exemplified, but the fuel battery is not limited thereto. In addition, as an electrolysis cell, a solid oxide electrolysis cell (SOEC) is exemplified, but the electrolysis cell is not limited thereto.

<Method for Producing Sealing Material>

[0099] A method for producing a sealing material of this embodiment includes a step of incorporating the sheet produced by the method for producing a sheet as a part of a gasket and a packing.

Examples

[0100] Hereinafter, the present invention will be described in detail, on the basis of specific examples, but the present invention is not limited thereto.

<1. Production of Swelling Muscovite and Production of Sheet>

[1.1 Production of Swelling Muscovite (Modification of Muscovite)]

[0101] As illustrated in FIG. 1, five types of muscovite with different particle sizes were used. Lithium nitrate of which the weight is 8 times the weight of the muscovite was heated at 370 C. and melted, and was mixed with the muscovite. By causing a reaction at 370 C. for 40 hours, ion exchange was performed. After that, water was added, and suction filtration was performed. Washing with pure water was performed to cause dechlorination. Pure water was added and stirred to obtain slurry.

[1.2 Production of Sheet]

[0102] The slurry obtained in [1.1] described above was condensed, and then, was molded with a doctor blade machine, and dried at 100 C. for 24 hours to produce a sheet. As the appearance of the sheet is illustrated in FIG. 1, swelling muscovite (modified muscovite) was prepared from the muscovite with different particle sizes, and thus, all the muscovite was capable of being formed into sheets. Interlayer ions were examined by a fluorescent X-ray analysis (XRF). As a result thereof, approximately 20 at % to 60 at % of K.sup.+ ions in the interlayer were exchanged with Lit ions (FIG. 1).

[0103] As a first component, LM7, LM11, LM20, and LM42 illustrated in FIG. 1 were used.

[0104] As a second component, muscovite before modification (M7 or 42), talc, kaolin, calcined muscovite (calcined M7), calcined kaolin, molten silica, shown in FIG. 2, were used.

[0105] The second component was added to the slurry of the first component obtained in [1.1] described above at a predetermined ratio, and mixed to form a mixture. The obtained mixture was condensed, and then, molded with a doctor blade machine, and dried at 100 C. for 24 hours to produce sheets of Examples and Comparative Examples. In the sheets of Comparative Examples 2 and 3, swelling vermiculite was used as the first component, instead of the swelling muscovite.

[0106] In Comparative Example 4, a commercially available silicone-laminated phlogopite sheet was used. [0107] <2. Evaluation of Sheet>

[0108] The following evaluation was performed on the sheets of Examples and Comparative Examples. Results are shown in FIG. 3 to FIG. 5.

(Compression Restorability)

[0109] The sheet was punched to be a test piece with an outer diameter of 20 mm. The test piece was subjected to a drying treatment at 100 C. for 24 hours.

[0110] A compression jig provided with three linear gauge sensors at an interval of 120 was set in a universal tester, and the test piece was placed in the center, and a surface pressure of 0.16 MPa was applied. A test force was applied such that a compression velocity was 0.1 MPa per 1 second, and compression was performed until the maximum surface pressure of 20 MPa. After that, the test force was released at the same rate, and restoration was performed until 0.16 MPa.

[0111] From a thickness at a surface pressure of 2 MPa (=a thickness at 2 MPa), a thickness at the maximum surface pressure of 20 MPa (=a thickness at 20 MPa), and a thickness at the end of the test at 0.16 MPa (=a thickness at the restoration to 0.16 MPa), a compression rate and a restoration rate were calculated by the following expression.

[00001]$\mathrm{Compression}\mathrm{Rate}\left[\%\right]=\frac{Thic\mathrm{kness}\left[\mathrm{mm}\right]\mathrm{at}2\mathrm{MPa}-Th\mathrm{ickness}\left[\mathrm{mm}\right]\mathrm{at}20\mathrm{MPa}}{Thic\mathrm{kness}\left[\mathrm{mm}\right]\mathrm{at}2\mathrm{MPa}}$

[00002]$\mathrm{Restoration}\mathrm{Rate}\left[\%\right]=\frac{Thic\mathrm{kness}\left[\mathrm{mm}\right]\mathrm{at}\mathrm{Restoration}\mathrm{to}0.16\mathrm{MPa}-Thic\mathrm{kness}\left[\mathrm{mm}\right]\mathrm{at}2\mathrm{MPa}}{Thic\mathrm{kness}\left[\mathrm{mm}\right]\mathrm{at}\mathrm{Restoration}\mathrm{to}0.16\mathrm{MPa}}$

(Compression Restorability (High Surface Pressure))

[0112] The maximum surface pressure was changed to 125 MPa from the case of evaluating a low surface pressure. The other condition was not changed, and the same test was performed. A case where a crack was observed in the sample after the test was set to Present, and a case where a crack was not observed was set to Absent.

(Thermal Dimensional Stability)

[0113] The sheet was punched to be a test piece with an outer diameter of 20 mm. The test piece was dried at 100 C. for 24 hours, and then, left to cool in a desiccator, and the diameter was measured by using a projector (=a diameter after drying). After that, the test piece was heated at 900 C. for 24 hours in an electrical muffle furnace temperature increase of 200 C./h, a natural temperature decrease), and left to cool. The diameter was measured by using a projector (=a diameter after heating). A diameter change rate was measured by the following expression.

[00003]$\mathrm{Diameter}\mathrm{Change}\mathrm{Rate}\left[\%\right]=\frac{Dia\mathrm{meter}\left[\mathrm{mm}\right]\mathrm{When}\mathrm{Drying}-Dia\mathrm{meter}\left[\mathrm{mm}\right]\mathrm{after}\mathrm{Drying}}{Dia\mathrm{meter}\left[\mathrm{mm}\right]\mathrm{When}\mathrm{Drying}}$

(Sealability)

[0114] The sheet was punched to be a ring-shaped test piece with an outer diameter of 92 mm and an inner diameter of 49 mm. The ring-shaped test piece was subjected to a standard state treatment at 24 C. and 50% RH for 24 hours.

[0115] A leakage amount was measured in the following test condition, with reference to standard EN13555. [0116] Tester: AMTEC temes fl. ail [0117] Gas Type: He [0118] Internal Pressure: 0.5 MPa [0119] Surface Pressure: 20 MPa [0120] Detector: a leak detector

(TG)

[0121] The second component was pulverized with a mortar. A weight loss on heating at each temperature was measured in the following condition by using a TG-DTA device, manufactured by Rigaku Corporation. [0122] Atmosphere: air [0123] Sample Weight: 10 mg [0124] Temperature Increase Rate: 5 C./min [0125] Highest Temperature: 1000 C. [0126] Pan Material: Pt

(Measurement of Volume Resistivity)

[0127] Volume resistivity was measured in the following test condition, with reference to Japanese Industrial Standards JIS C2141, JEC-6148, and JIS C2139. [0128] Temperature: 600 C. [0129] Atmosphere: Atmospheric Air [0130] Measurement Method

[0131] A main electrode, a guard electrode, and counter electrodes were printed on the upper and lower surfaces of a specimen by using a screen printer and a silver paste, and then, subjected to a drying treatment (in the air, 150 C., 12 hours), and then, subjected to a baking treatment (in the air, 700 C., 1 hour, a temperature increase rate of 200 C./h) in an electrical furnace to form each electrode.

[0132] Retention was performed at 600 C. for 15 minutes, and then, a DC voltage (V) was applied to the specimen, and a current (I) after charging for 1 minute was measured to obtain the volume resistance (Rv) of the specimen, and the volume resistivity (v) was calculated from the thickness (t) of the specimen and the electrode area(S) by the following expression.

[0133] In a case where the thickness of the specimen is t (cm), the volume resistivity v is given by the following expression.

[00004]$\begin{array}{c}{}_v=\frac{S}{t}{R}_v=\frac{S}{t}\frac{V}{I}\\ S=\frac{{\left(D_1+g\right)}^2}{4}=1.83{\mathrm{cm}}^2\\ g=\frac{D_2-D_1}{2}=\frac{1.60-1.45}{2}=0.075\mathrm{cm}\end{array}$ [0134] .sub.v: Volume Resistivity (.Math.cm) [0135] t: Thickness of Specimen (cm) [0136] S: Electrode effective Area (cm.sup.2) [0137] Rv: Volume Resistance () [0138] g: Electrode Gap Interval (cm) [0139] D.sub.1: Diameter of Main Electrode (cm) [0140] D.sub.2: Diameter of Guard Electrode (cm)

(Result)

[0141] From results shown in FIG. 3 to FIG. 7, the following results were checked.

[0142] The sheets of Examples contain the first component (swelling muscovite) and the second component (a filling material) as a main component, and do not contain fluorine and a resin such as a binder, and thus, are less likely to cause outgasing.

[0143] The sheets of Examples have a low iron content of 2.1% by weight or less, and thus, have a high insulating property. Specifically, in the sheets of Examples, the value of the volume resistivity was 3.810.sup.6.Math.cm or more in a measurement condition of 600 C. and an applied voltage of 300 V, and insulating performance in a high-temperature environment was excellent. Therefore, the sheets of Examples can be used for a fuel battery and an electrolysis cell required to have a high insulating property.

[0144] For the thermal dimensional stability, it was found that the sheets of Examples did not significantly contract even when heated at 900 C., and thus, have sufficient heat resistance as a sheet for high-temperature application.

[0145] It was found that the sheets of Examples have high heat resistance from the fact that a clay phase remains even when heated at 900 C.

[0146] In a case where a calcined filling material is used as the second component, it is expected that a weight loss amount when heated decreases, and thus, heat resistance is improved.

[0147] In the sheet of Comparative Example 1, the sheet was not capable of being obtained (handling was not available), and thus, it was found that the sheet can be obtained by modifying the muscovite.

[0148] It was checked that as an effect of adding the second component (the filling material), the initial thickness (density) can be controlled, and a compression amount is adjusted.

[0149] It was indicated that as a result of evaluating the compression restorability (125 MPa), breakdown behavior is not observed in the sheets of Examples even when applying a high surface pressure, and the sheets have a sufficient strength when used as the sealing material.

[0150] It was found that the sheets of Examples can be used as the sealing material having a high density when compressed (a density at 20 MPa of 2.1 to 2.5 g/cm.sup.3) and low substantial leakage.

[0151] The sheets of Examples had sufficient sealability when used as the sealing material from the result of a sealing test.

[0152] In contrast, the sheets of Comparative Examples had a high iron content (Comparative Examples 2 to 4).

[0153] Note that the present invention is created with reference to the following technologies and problems of the related art, which are not the essential elements of the present invention, but as necessary, can be appropriately incorporated.

[0154] In a sheet using non-swellable clay of the related art or a sealing material using the sheet described above, an organic or inorganic fiber and a binder were added.

[0155] In PATENT LITERATURE 3, a sealing material containing mica as non-swellable clay, in which an organic fiber and a binder are compounded, is described. In PATENT LITERATURES 4 and 5, a sealing material containing talc as non-swellable clay, in which an inorganic fiber and a binder are compounded, is described. In PATENT LITERATURE 6, a sheet containing fluor-tetrasilisic mica as swellable clay is described. In PATENT LITERATURE 7, a sealing material using a sheet containing fluor-tetrasilisic mica as swellable clay is described.

[0156] The sealing material containing the non-swellable clay, the fiber, and the binder described in PATENT LITERATURES 3 to 5 contained the fiber, and thus, the sealability was insufficient. In addition, in a case where an organic binder or an organic fiber is used, an organic content is burned down to generate voids in a high-temperature environment, and thus, the sealability is degraded. In addition, silicone was used as the inorganic binder, siloxane-based outgasing was caused in a high-temperature environment, and thus, the sealing material was not capable of being used in the vicinity of an electronic part or an electrode. The fluorine mica described in PATENT LITERATURES 6 and 7 can be the sheet without using a fiber and a binder, and has sealability in a high-temperature environment. However, there was a possibility that a slight amount of fluorine-based gas is generated in a high-temperature environment, and thus, there was restriction on use in the vicinity of an electronic part and an electrode.

[0157] In PATENT LITERATURE a 8, sheet containing montmorillonite that is one type of smectite as the swellable clay, and a sealing material using the sheet described above are described. In PATENT LITERATURES 9 to 11, it is described that clay can be modified by a reaction between a molten salt, a concentrated aqueous solution, and the like.

[0158] The smectite described in PATENT LITERATURE 8 can be the sheet without using a fiber and a binder. However, there was a problem that warpage or significant contraction occurs in a high-temperature environment, and there was a problem in dimensional stability. In addition, the sheet was gelled at a comparatively low concentration when produced, and thus, warpage was likely to occur when dried, and there was a problem in the moldability of a thick film. In PATENT LITERATURES 9 to 11, it is described that the clay can be modified by the reaction between the molten salt, the concentrated aqueous solution, and the like. However, the application of the technologies of such literatures was limited to the preparation of a clay dispersion liquid, compounding with a polymer, and mixing with a resin.