Sheet, composite sheet, method for producing sheet, and method for producing composite sheet

Abstract

This sheet comprises a first layer, which is made of natural stone, and a second layer, which is formed on one surface of the first layer. The second layer comprises: a base material including (a) a product of dehydrating condensation of sodium silicate and (b) alumina cement; and inorganic fibers. This composite sheet comprises a substrate, a sheet bonded to the substrate, and a bonding layer with which the substrate and the sheet are bonded to each other. The bonding layer comprises: a base material including (c) a product of dehydrating condensation of sodium silicate and (d) alumina cement; and inorganic fibers.

Description

Sheet, composite sheet, sheet manufacturing method, and composite sheet manufacturing method

[0001] FIELD The present disclosure relates to a sheet, a composite sheet, a method for manufacturing a sheet, and a method for manufacturing a composite sheet.

[0002] A building material made of natural stone is used for the interior and exterior walls of a building. A building material made of natural stone is disclosed in Patent Document 1.

[0003] Japanese Unexamined Patent Publication No. 55-144481

[0004] Sheet-type building materials made from natural stone have been developed. It is thought that these sheet-type building materials can be attached to the building frame using adhesives. Adhesives generally contain organic substances, such as polyester resin or epoxy resin, as their main component. In the event of a fire, organic adhesives burn easily, generating smoke and toxic gases.

[0005] Therefore, it has been difficult to use sheet-shaped building materials in buildings that are required to be non-flammable under the Building Standards Act, etc. In one aspect of the present disclosure, it is preferable to provide a highly non-flammable sheet, a composite sheet, or a method for manufacturing the same.

[0006] One aspect of the present disclosure is a sheet comprising a first layer made of natural stone and a second layer provided on one side of the first layer, the second layer including a matrix containing (a) a dehydration-condensation reaction product of sodium silicate and (b) alumina cement, and inorganic fibers. The sheet according to one aspect of the present disclosure is highly non-flammable.

[0007] Another aspect of the present disclosure is a method for manufacturing a sheet, comprising: heating a raw material made of natural stone to a temperature equal to or higher than the melting point of the natural stone; cooling the raw material; forming a precursor layer on a surface of the raw material, the precursor layer including a solution containing (A) sodium silicate and (B) alumina cement, and inorganic fibers; heating the precursor layer to transform it into a second layer including a matrix containing (a) a dehydration-condensation reaction product of sodium silicate and (b) alumina cement, and the inorganic fibers; and applying a force to the second layer in a direction away from the raw material to obtain a sheet including a first layer made of the natural stone peeled off from a cleavage plane of the raw material, and the second layer provided on one side of the first layer.

[0008] According to a sheet manufacturing method that is another aspect of the present disclosure, a highly non-flammable sheet can be manufactured.

[0009] FIG. 1A is an explanatory diagram showing a raw material and heating of the raw material. FIG. 1B is an explanatory diagram showing a raw material and a precursor layer. FIG. 1C is an explanatory diagram showing a raw material and a second layer. FIG. 1D is an explanatory diagram showing a sheet including the second layer and the first layer peeled from the raw material. FIG. 2A is an explanatory diagram showing a substrate and a bonding precursor layer. FIG. 2B is an explanatory diagram showing a substrate, a bonding precursor layer, and a sheet. FIG. 3C is an explanatory diagram showing a composite sheet. An explanatory diagram showing a method for manufacturing a composite sheet in a second embodiment.

[0010] DESCRIPTION OF SYMBOLS 1...sheet, 3...raw material, 3A...surface, 3B...cleavage surface, 5...burner, 7...precursor layer, 9...second layer, 9A...end, 11...first layer, 13...composite sheet, 15...substrate, 17...bonding precursor layer, 19...bonding layer, 21...convex jig, 23...concave jig

[0011] Illustrative embodiments of the present disclosure will be described with reference to the drawings. First Embodiment 1. Manufacturing Method of Sheet 1 A manufacturing method of sheet 1 will be described with reference to FIGS. 1A to 1D. A raw material 3 shown in FIG. 1A is prepared. The raw material 3 is a plate made of natural stone. Examples of natural stone include slate, sandstone, and shale. The thickness of the raw material 3 is, for example, 8 mm or more and 260 mm or less. The shape of the raw material 3 when viewed in the thickness direction is, for example, rectangular. In this case, the length of each side of the rectangle is, for example, 700 mm or more and 2100 mm or less. The rectangle is preferably a rectangle with a short side length of 700 mm and a long side length of 1300 mm.

[0012] Surface 3A of raw material 3 is heated by burner 5. Surface 3A is one of the main surfaces of the plate. By heating with burner 5, the temperature inside raw material 3 is raised to a temperature equal to or higher than the melting point of raw material 3. The melting points of slate, sandstone, and shale are approximately 1000°C. When raw material 3 is made of slate, sandstone, or shale, the temperature inside raw material 3 is raised to 1000°C or higher.

[0013] In natural stone (e.g., slate, sandstone, shale), the layers that make up the natural stone are ionic bonds. When the natural stone is heated to a temperature above its melting point, the ionic bonds are broken and the natural stone enters a cleavage state. Heating the raw material 3 makes it easier for cleavage planes 3B, which will be described later, to form.

[0014] Next, the raw material 3 is cooled to room temperature. Next, as shown in FIG. 1B , a precursor layer 7 is formed on the surface 3A. The precursor layer 7 is formed as follows: A first solution is prepared. The first solution is a solution containing (A) sodium silicate and (B) alumina cement.

[0015] The mass of component (A) contained in the first solution is preferably greater than the mass of component (B) contained in the first solution. When the mass of component (A) is greater than the mass of component (B), the flame retardancy of the produced sheet 1 is higher.

[0016] The first solution preferably contains 5 to 50 parts by mass of the component (B) per 100 parts by mass of the component (A). When the amount of the component (B) in the first solution is within the above range, the strength of the produced sheet 1 is even higher.

[0017] The first solution may further contain other components, such as shirasu balloons and silicate minerals. Examples of silicate minerals include wollastonite.

[0018] The first solution preferably contains 5 to 20 parts by mass of shirasu balloons per 100 parts by mass of component (A). When the amount of shirasu balloons in the first solution is within the above range, the sheet 1 becomes even lighter.

[0019] The first solution preferably contains 5 to 15 parts by mass of silicate mineral per 100 parts by mass of component (A). When the amount of silicate mineral in the first solution is within the above range, the heat resistance of the sheet 1 is further improved.

[0020] Next, the first solution is applied to the surface 3A. For example, a method using a brush can be used to apply the first solution. Next, a nonwoven fabric is attached to the surface to which the first solution has been applied. Next, the first solution is applied from above the nonwoven fabric. For example, a method using a brush can be used to apply the first solution.

[0021] Next, inorganic fibers are attached to the surface coated with the first solution. Examples of inorganic fibers include glass fibers and basalt fibers. The inorganic fibers are preferably in the form of a cloth or chopped strand mat. Examples of inorganic fibers include glass cloth made of glass fibers, and glass cloth or chopped strand mat made of basalt fibers.

[0022] When glass fiber or basalt fiber is used as the inorganic fiber, the sheet 1 has higher non-flammability than when aluminum fiber or alumina fiber is used. When basalt fiber is used as the inorganic fiber, the sheet 1 has higher mechanical strength. The reason for the high mechanical strength is presumed to be that basalt fiber is not easily corroded even when the first solution is alkaline. Examples of inorganic fibers include chopped strand mats made of basalt fiber.

[0023] Next, the first solution is applied onto the inorganic fibers. Examples of methods for applying the first solution include using a brush. Next, a defoaming roller or the like is used to remove air between the inorganic fibers and the surface 3A, and the inorganic fibers are brought into close contact with the surface 3A. Through these steps, a precursor layer 7 is formed. The precursor layer 7 includes inorganic fibers and the first solution. The first solution has permeated into the inorganic fibers.

[0024] Next, the precursor layer 7 is heated and dried in a drying oven at a temperature of 50°C to 60°C for a period of 3 to 5 hours. At this time, as shown in FIG. 1C , the precursor layer 7 changes into a second layer 9. The second layer 9 includes a matrix and inorganic fibers. The matrix includes (a) a dehydration-condensation reaction product of sodium silicate and (b) alumina cement. The matrix is ​​permeated into the inorganic fibers.

[0025] Component (a) is a product of a dehydration condensation reaction of sodium silicate. Component (a) is, for example, a compound having a skeleton with linked siloxane bonds. Component (a) contains, for example, siloxane. 100 parts by mass of sodium silicate becomes 60 parts by mass of component (a) as a result of the dehydration condensation reaction.

[0026] The mass of component (a) contained in the matrix is ​​preferably greater than the mass of component (b) contained in the matrix. When the mass of component (a) is greater than the mass of component (b), the sheet 1 has higher non-combustibility and strength.

[0027] The base material preferably contains 5 to 25 parts by mass of component (b) per 100 parts by mass of component (a). When the blending amount of component (b) in the base material is within the above range, the strength of the sheet 1 is even higher.

[0028] The base material may further contain other components, such as shirasu balloons and silicate minerals, and wollastonite, for example.

[0029] The base material preferably contains 5 to 20 parts by mass of shirasu balloons per 100 parts by mass of component (a). When the amount of shirasu balloons in the base material is within the above range, the sheet 1 becomes even lighter.

[0030] The base material preferably contains 5 to 15 parts by mass of silicate mineral per 100 parts by mass of component (a). When the amount of silicate mineral in the base material is within the above range, the heat resistance of the sheet 1 is further improved. The thickness of the second layer 9 is, for example, 0.7 mm to 0.9 mm.

[0031] Next, the raw material 3 and the second layer 9 are cooled to room temperature. Next, as shown in FIG. 1D , a force F is applied to the end 9A of the second layer 9 in a direction away from the raw material 3. At this time, cleavage occurs at the cleavage plane 3B of the raw material 3. The portion of the raw material 3 closer to the second layer 9 than the cleavage plane 3B is designated as the first layer 11. The thickness of the first layer 11 is, for example, 0.3 mm or more and 0.6 mm or less.

[0032] The above steps produce the sheet 1. The sheet 1 includes a first layer 11 and a second layer 9. The second layer 9 is provided on one side of the first layer 11.

[0033] Next, the sheet 1 is placed in a curing oven and dried and cured, for example, at a temperature of 40°C for 5 hours. The thickness of the sheet 1 is, for example, 1.0 mm or more and 1.5 mm or less. The sheet 1 can be used, for example, as an interior material for a building. The second layer 9 is attached, for example, to the skeleton of the building.

[0034] 2. Manufacturing Method of Composite Sheet 13 The manufacturing method of composite sheet 13 will be described with reference to Figures 2A to 2C. As shown in Figure 2A, a substrate 15 is prepared. The substrate 15 is a rectangular plate-shaped member. When viewed in the thickness direction, the substrate 15 is smaller than the raw material 3. The substrate 15 is, for example, a calcium silicate plate.

[0035] 2A, a bonding precursor layer 17 is formed on one surface of a substrate 15. The bonding precursor layer 17 is formed as follows: A second solution is prepared. The second solution is, for example, the same solution as the first solution.

[0036] The second solution is applied to the surface of the substrate 15. For example, the second solution may be applied using a brush. Next, inorganic fibers are attached to the surface to which the second solution has been applied. For example, the inorganic fibers may be the same as those used in producing the sheet 1.

[0037] Next, the second solution is applied onto the inorganic fibers. Examples of methods for applying the second solution include using a brush. Next, a defoaming roller or the like is used to remove air between the inorganic fibers and the substrate 15, and the inorganic fibers are brought into close contact with the substrate 15. Through these steps, a bonding precursor layer 17 is formed. The bonding precursor layer 17 includes the second solution and inorganic fibers. The second solution has permeated into the inorganic fibers.

[0038] Next, as shown in FIG. 2B , the sheet 1 is placed on the bonding precursor layer 17. At this time, the bonding precursor layer 17 and the second layer 9 are in contact with each other. Next, a pressure bonding device is used to press the sheet 1 toward the substrate 15. The pressure during pressing is, for example, 10 g / cm. ２More than 50g / cm ２ The crimping time is, for example, about 4 hours.

[0039] Next, the substrate is heated in a curing furnace. The heating temperature is, for example, 40° C. The heating time is, for example, 24 hours. By heating, the bonding precursor layer 17 is transformed into a bonding layer 19 as shown in FIG. 2C . The bonding layer 19 includes a base material and inorganic fibers. The base material includes (c) a dehydration condensation reaction product of sodium silicate and (d) alumina cement. The base material permeates the inorganic fibers. The thickness of the bonding layer 19 is, for example, 0.5 mm or more and 0.8 mm or less.

[0040] The composite sheet 13 is obtained by the above steps. The composite sheet 13 includes a substrate 15, a sheet 1, and a bonding layer 19. The bonding layer 19 bonds the substrate 15 and the sheet 1. The composite sheet 13 can be used, for example, as an interior material for a building. The substrate 15 is attached, for example, to the skeleton of the building.

[0041] 3. Effects of the Sheet 1 and the Composite Sheet 13 (1A) The Sheet 1 and the Composite Sheet 13 are highly non-flammable. High non-flammable means that the sheet 1 and the composite sheet 13 are difficult to burn even in a high-temperature environment.

[0042] (1B) The sheet 1 has a first layer 11 made of natural stone. This provides excellent design. The first layer 11 is a thin layer obtained by cleaving the raw material 3. This makes the sheet 1 lightweight.

[0043] (1C) If the substrate 15 and the sheet 1 are bonded using an adhesive or double-sided tape primarily composed of organic matter, the adhesive or double-sided tape may burn in the event of a fire, easily generating a foul odor, harmful gases, smoke, etc. The composite sheet 13 bonds the substrate 15 and the sheet 1 with a bonding layer 19. The bonding layer 19 includes a base material and inorganic fibers. The base material includes (c) a dehydration condensation reaction product of sodium silicate and (d) alumina cement.

[0044] Therefore, the composite sheet 13 can suppress the generation of bad odors, harmful gases, smoke, etc. in the event of a fire.

[0045] (1D) Basalt fiber can be used as the inorganic fiber contained in the second layer 9 or the bonding layer 19. Basalt fiber is primarily made from basalt. When discarded, basalt fiber returns to the soil. Furthermore, basalt fiber can be reused by pulverizing it. Therefore, when basalt fiber is used as the inorganic fiber contained in the second layer 9 or the bonding layer 19, the sheet 1 and the composite sheet 13 can be easily disposed of and reused. <Second Embodiment> 1. Differences from the First Embodiment The second embodiment has the same basic configuration as the first embodiment, and therefore differences will be described below. Note that the same reference numerals as those in the first embodiment indicate the same configuration, and the preceding description will be referred to.

[0046] In the first embodiment described above, the sheet 1 and the composite sheet 13 have the form of flat sheets. In contrast, in the second embodiment, as shown in Fig. 3, the sheet 1 and the composite sheet 13 have the form of curved sheets, which is different from the first embodiment.

[0047] The composite sheet 13 of the second embodiment can be manufactured as follows. A sheet 1 is manufactured in the same manner as in the first embodiment. A convex jig 21 shown in FIG. 3 is also prepared. The upper surface of the convex jig 21 is upwardly convex and has a curved shape. More specifically, the upper surface of the convex jig 21 has an arc shape with a curvature radius of 400 mm or more.

[0048] The substrate 15, which has been moistened, is placed on the convex jig 21. The substrate 15 is, for example, FR Fuji Board (product name) manufactured by A&A Material Co., Ltd. The substrate 15 can be curved when it is moistened. The substrate 15 assumes a curved shape according to the shape of the convex jig 21.

[0049] Next, similarly to the first embodiment, a bonding precursor layer 17 is formed on the substrate 15 , and the sheet 1 is placed on the bonding precursor layer 17 .

[0050] 3, the concave jig 23 is placed on top of the sheet 1 and pressed against the convex jig 21. The lower surface of the concave jig 23 has a shape that matches the upper surface of the convex jig 21. The shapes of the substrate 15, the bonding precursor layer 17, and the sheet 1 are curved according to the shapes of the convex jig 21 and the concave jig 23.

[0051] Next, the substrate 15, the bonding precursor layer 17, and the sheet 1 are sandwiched between the convex jig 21 and the concave jig 23 and heated and cured. The heating temperature is, for example, 40° C. The heating time is, for example, 4 hours. At this time, the bonding precursor layer 17 is transformed into the bonding layer 19.

[0052] Next, the convex jig 21 and the concave jig 23 are removed to obtain the composite sheet 13. The composite sheet 13 has a curved shape according to the shapes of the convex jig 21 and the concave jig 23.

[0053] 2. Effects of the Sheet 1 and the Composite Sheet 13 According to the second embodiment described above in detail, in addition to the effects of the first embodiment described above, the following effects are also achieved.

[0054] (2A) The composite sheet 13 has a curved shape. The composite sheet 13 can be attached to a body having a curved shape. <Example> 1. Manufacturing of Sheet 1 The sheet 1 was manufactured using the method described in the first embodiment. The detailed manufacturing method was as follows. A raw material 3 shown in FIG. 1A was prepared. The material of the raw material 3 was slate. The thickness of the raw material 3 was 100 mm. When viewed from the thickness direction, the shape of the raw material 3 was rectangular. The length of each side of the rectangle was, for example, 400 mm x 400 mm.

[0055] The surface 3A of the raw material 3 was heated by a burner 5 at 1000°C or higher. The heating time was 2 minutes and 40 seconds. The temperature of the surface 3A immediately after heating was 60°C. Note that the larger the raw material 3, the longer the heating time is preferred. Next, the raw material 3 was cooled to room temperature. Next, as shown in FIG. 1B, a precursor layer 7 was formed on the surface 3A. The precursor layer 7 was formed as follows.

[0056] A first solution was prepared. The composition of the first solution was as follows:

[0057] (A) Sodium silicate: 100 parts by mass (B) Alumina cement: 18 parts by mass Next, the first solution was applied to surface 3A using a brush. Next, a nonwoven fabric was attached to the surface to which the first solution had been applied. Next, the first solution was applied to the nonwoven fabric using a brush. Next, inorganic fibers were attached to the surface to which the first solution had been applied. The inorganic fibers were chopped strand mats made of basalt fibers.

[0058] Next, the first solution was applied onto the inorganic fibers using a brush. Next, a defoaming roller was used to remove air between the inorganic fibers and the surface 3A, and the inorganic fibers were brought into close contact with the surface 3A. Through the above steps, a precursor layer 7 was formed. The precursor layer 7 contained inorganic fibers and the first solution. The first solution had permeated into the inorganic fibers.

[0059] Next, the precursor layer 7 was heated and dried in a drying oven at 40°C for 5 hours. At this time, as shown in Figure 1C, the precursor layer 7 was transformed into a second layer 9. The second layer 9 contained a matrix and inorganic fibers. The matrix contained (a) a dehydration-condensation reaction product of sodium silicate and (b) alumina cement. The matrix had permeated the inorganic fibers. The thickness of the second layer 9 was 0.7 mm.

[0060] Next, the raw material 3 and the second layer 9 were cooled to room temperature. Next, as shown in FIG. 1D , a force F was applied to the end 9A of the second layer 9 in a direction away from the raw material 3. At this time, cleavage occurred at the cleavage plane 3B of the raw material 3. The cleavage plane 3B was parallel to the surface 3A. The portion of the raw material 3 closer to the second layer 9 than the cleavage plane 3B was designated as the first layer 11. The thickness of the first layer 11 was 0.5 mm.

[0061] Through the above steps, sheet 1 was obtained. Sheet 1 had a first layer 11 and a second layer 9. The second layer 9 was provided on one side of the first layer 11. Next, sheet 1 was placed in a curing oven and dried and cured at a temperature of 40°C for 5 hours. The thickness of sheet 1 was 1.2 mm.

[0062] 2. Manufacturing of Composite Sheet 13 The composite sheet 13 was manufactured by the method described in the first embodiment. The detailed manufacturing method was as follows. As shown in FIG. 2A , a substrate 15 was prepared. The substrate 15 was a rectangular plate-shaped member. When viewed in the thickness direction, the substrate 15 was larger than the raw material 3. The substrate 15 was a calcium silicate board.

[0063] Next, a bonding precursor layer 17 was formed on the surface of the substrate 15. The bonding precursor layer 17 was formed as follows. A second solution was prepared. The second solution was the same as the first solution. The second solution was applied to the surface of the substrate 15 using a brush.

[0064] Next, inorganic fibers were attached to the surface coated with the second solution. The inorganic fibers were the same as the inorganic fibers used in the production of Sheet 1. Next, the second solution was applied onto the inorganic fibers using a brush.

[0065] Next, a defoaming roller was used to remove air between the inorganic fibers and the substrate 15, and the inorganic fibers were brought into close contact with the substrate 15. Through the above steps, a bonding precursor layer 17 was formed. The bonding precursor layer 17 contained the second solution and inorganic fibers. The second solution had permeated into the inorganic fibers.

[0066] Next, as shown in FIG. 2B , the sheet 1 was placed on the bonding precursor layer 17. At this time, the bonding precursor layer 17 and the second layer 9 were in contact with each other. Next, using a pressure bonding device, the sheet 1 was pressed toward the substrate 15. The pressure during pressing was 50 g / cm. ２ The compression time was 4 hours.

[0067] Next, the substrate was heated in a curing furnace. The heating temperature was 40°C. The heating time was 24 hours. By heating, the bonding precursor layer 17 was transformed into a bonding layer 19, as shown in FIG. 2C . The bonding layer 19 contained a base material and inorganic fibers. The base material contained (c) a dehydration condensation reaction product of sodium silicate and (d) alumina cement. The base material had permeated into the inorganic fibers. The thickness of the bonding layer 19 was 6.3 mm.

[0068] The composite sheet 13 was obtained by the above steps. The composite sheet 13 included the substrate 15, the sheet 1, and a bonding layer 19. The bonding layer 19 bonded the substrate 15 and the sheet 1 together.

[0069] 3. Evaluation of heat generation property of sheet 1 A heat generation test was carried out on sheet 1 in accordance with ISO-5660. In the heat generation test, the test specimen was heated for 20 minutes. The radiation intensity was 50 kW / m ２ The evaluation was carried out on three test specimens 1A to 1C. The results of the heat generation test are shown in Table 1. The "excessive time" in Table 1 refers to the time when the maximum heat generation temperature continued to exceed 200 kW / m ２ means the time exceeded.

[0070] As shown in Table 1, the heat buildup of test specimens 1A to 1C was low.

[0071] 4. Evaluation of Heat Generation Property of Composite Sheet 13 A heat generation test was carried out on the composite sheet 13 in accordance with ISO-5660. In the heat generation test, the test specimen was heated for 20 minutes. The radiation intensity was 50 kW / m ２ The evaluation was carried out on three test specimens 13A to 13C. The results of the heat generation test are shown in Table 2. The "excessive time" in Table 2 refers to the time when the maximum heat generation temperature continued to exceed 200 kW / m ２ means the time exceeded.

[0072] As shown in Table 2, the heat buildup of test specimens 13A to 13C was low.

[0073] 5. Evaluation of Gas Toxicity of Composite Sheet 13 A gas toxicity test was conducted on composite sheet 13 in accordance with Ministry of Construction Notification No. 1231 of August 25, 1976. The test time was 15 minutes. Evaluation was conducted on two test specimens, 13D and 13E. The results of the gas toxicity test are shown in Table 3. In Table 3, "X" means the average time until the behavior of eight mice ceased. If the mice did not cease behavior, X was 15 minutes. In Table 3, "σ" means the standard deviation of the time until the behavior of eight mice ceased. In Table 3, "X - σ" is the value obtained by subtracting σ from X.

[0074] As shown in Table 3, specimens 13D to 13E were less likely to generate harmful gases. <Other Embodiments> Although the embodiments of the present disclosure have been described above, the present disclosure is not limited to the above-described embodiments and can be implemented in various modifications.

[0075] (1) Multiple functions of one component in the above embodiments may be realized by multiple components, or one function of one component may be realized by multiple components. Also, multiple functions of multiple components may be realized by one component, or one function realized by multiple components may be realized by one component. Also, part of the configuration of the above embodiments may be omitted. Also, at least part of the configuration of the above embodiments may be added to or substituted for the configuration of another of the above embodiments.

[0076] (2) In addition to the above-described sheet or composite sheet, the present disclosure can also be realized in various forms, such as a system that includes a sheet or composite sheet as a component.

Claims

1. A sheet comprising: a first layer made of natural stone; and a second layer provided on one side of the first layer, wherein the second layer includes a matrix containing (a) a dehydration condensation reaction product of sodium silicate and (b) alumina cement, and inorganic fibers.

2. The sheet according to claim 1, wherein the inorganic fibers are basalt fibers.

3. A composite sheet comprising: a substrate; the sheet according to claim 1 or 2 bonded to the substrate; and a bonding layer bonding the substrate and the sheet, wherein the bonding layer comprises a base material containing (c) a dehydration condensation reaction product of sodium silicate and (d) alumina cement, and inorganic fibers.

4. A method for manufacturing a sheet, comprising the steps of: heating a raw material made of natural stone to a temperature equal to or higher than the melting point of the natural stone; after cooling the raw material, forming a precursor layer on the surface of the raw material, the precursor layer including a solution containing (A) sodium silicate and (B) alumina cement, and inorganic fibers; heating the precursor layer to change it into a second layer including a base material containing (a) a dehydration condensation reaction product of sodium silicate and (b) alumina cement, and the inorganic fibers; and applying a force to the second layer in a direction away from the raw material to obtain a sheet including a first layer made of the natural stone peeled off from a cleavage plane of the raw material, and the second layer provided on one side of the first layer.

5. A method for producing a composite sheet, comprising the steps of: producing the sheet by the method for producing a sheet according to claim 4; forming a bonding precursor layer containing inorganic fibers and a solution containing (C) sodium silicate and (D) alumina cement on the surface of a substrate; bonding the bonding precursor layer to the second layer; and heating the bonding precursor layer to change the bonding precursor layer into a bonding layer containing inorganic fibers and a base material containing (c) a dehydration condensation reaction product of sodium silicate and (d) alumina cement.

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