PROCESS OF PRODUCING A CALCIUM SILICATE PLATE

Abstract: The present invention provides a method of manufacturing a calcium silicate board having a bulk specific gravity of approximately 0.5 to 0.8, which method achieves a decrease in the bulk specific gravity and an increase in the matrix strength of the board without impairing productivity, and the calcium silicate board obtained by this method. A method of manufacturing a calcium silicate board according to the present invention is characterized in that a material slurry comprising 5 to 30wt% of calcium silicate hydrate slurry as a solid component, 17 to 50wt% of calcareous material, 13 to 45wt% of silica containing material, 2 to 8 wt% of fiber material, and 5 to 40wt% of inorganic fillers is formed through conventional processes and the obtained molded body is subjected to a hydrothermal reaction in a pressure container.

Description: INDUSTRIAL FIELD OF THE INVENTION The present invention relates to a method of manufacturing a calcium silicate board. RELATED ART AND PROBLEMS Conventionally, calcium silicate boards have been widely used for building materials, in particular, for interior materials because of such characteristics as being light, excellent in workability and dimensional stability, and non-combustible. Calcium silicate boards used for building material are formed using a forming process such as the Hatschek sheet machine process a press mold process or a mono-layer mold process and are manufactured as follows: a molded body is formed from a calcareous material, a silica containing material, reinforcing fibers and fillers, such as light-weight aggregate, then, in general, subjected to curing reaction by saturated water vapor in a pressure container. Generally, the bulk specific gravity of the calcium silicate boards is in a range of from 0.7 to 1.2. Since calcium silicate boards are used as an interior material, such as ceiling materials and wall materials, lightening the boards is desirable, however, according to the above methods it is necessary to mix a considerable amount of light-weight aggregate so as to achieve a bulk specific gravity of 0.5 to 0.8, resulting in a decrease in the specific strength of the boards. In particular, when a light-weight calcium silicate board having a bulk specific gravity of 1.0 or less is manufactured according to the Hatschek sheet machine process, the following problems sometimes occur: because of the low strength and large water content of the molded body before hydrothermal reaction, the redundant water thermally expands during hydrothermal reaction or the vapor pressure increases, resulting in interlayer peeling or bursting. To avoid the above problems, in some methods, a molded body is pressed after forming then subjected to hydrothermal reaction or a molded body is tightened by a turn-buckle during the hydrothermal reaction. However, in accordance with these methods, such problems occur that the bulk specific gravity increases and more labor is required for manufacturing. In addition, Japanese Patent Laid-Open No. 6-287083 discloses a method of removing the redundant water, though this method cannot be commonly used because a specific pressure container or a vapor heater is necessary. Further, conventionally, a material slurry containing a calcareous material and an amorphous silica containing material is heated at a normal pressure for gelation so as to achieve a light-weight board. However, according to this method, the board strength is inevitably reduced, and further, the material is so soft that it is readily shaved during polishing. Therefore, cellulose fibers become extremely fuzzy such that the surface smoothness is impaired when the board is used after coating. Moreover, another method is disclosed in Japanese Patent Laid-Open Nos. 52-105926 and 52-135330, wherein calcium silicate boards exhibiting excellent strength are obtained by adding a xontlite slurry, which is a kind of calcium silicate hydrate, or a crystalline calcium slurry. Since productivity decreases according to these methods, improvement is required from a viewpoint of manufacturing costs. Additionally, in Japanese Patent Laid-Open Nos. 5-213657 and 7-41354, the inventors of the present invention have already disclosed a method of adding both a gelatinized slurry, comprising a calcareous material and an amorphous silica containing material, and a crystalline calcium silicate hydrate slurry. However, in the case of a board laminated by the Hatschek sheet machine process, some problems, such as interlayer peeling or bursting, occur even in this method of adding gels. Furthermore, Japanese Patent Publication No. 58-30259 discloses a method of manufacturing a calcium silicate molded body characterized by the following: a silica containing material and a calcareous material are dispersed in water of which the amount by weight is 15 times or more than that of the materials as a solid component; the resultant mixture is heat-reacted at 130°C or more under a pressurized condition so as to form an aqueous slurry, which has a sedimentation volume of 15 cm 3 /g or more, contains calcium silicate composed of C-S-H or tobermorite; to the aqueous slurry asbestos is added and subjected to dewatering and forming; and the calcium silicate hydrate is transformed by water vapor curing under a pressurized condition. However, the calcium silicate molded body obtained by this method is used as a heat storing material or a heat insulating material, and according to an embodiment of this Publication, the bulk specific gravity thereof is as small as 0.1 to 0.2 g/cm 3 . Thus the calcium silicate molded body cannot be employed for a calcium silicate board used as a building material. An object of the present invention is to provide a method of manufacturing a calcium silicate board having a bulk specific gravity of 1.0 or less, in which the foregoing problems are solved such that peeling or bursting during the hydrothermal reaction is eliminated because the strength of a molded body (green sheet) is improved. The invention does this by using a material having an excellent reactivity with a calcareous material and by primary curing before the hydrothermal reaction. The present invention relates to a method of manufacturing a light-weight calcium silicate board (hereinafter referred to as a calcium silicate board) comprising a step of forming a material slurry into a prescribed shape, the material slurry comprising, as a solid component, 17 to 50wt% of calcareous material, 15 to 45wt% of silica containing material, 2 to 8 wt% of fiber material and 5 to 40wt% of inorganic fillers, and a step of hydrothermally reacting the obtained molded body in a pressure container, wherein 2 to 20wt% of at least one kind of amorphous silica containing material and/or silicate material, each having a specific surface area of 1 m 2 /g or more, is used as a portion of the silica containing material; and, before the hydrothermal reaction, the molded body is subjected to primary curing under conditions where (curing temperature - 15) x curing time ≥ 120°C·hr. A method of manufacturing a calcium silicate board according to the present invention will now be described, by way of example. Calcium hydroxide and quicklime are examples of a calcareous material. Silica sand and sintered diatomaceous earth are examples of a crystalline silica containing material. When the Ca/(Si + Al) molar ratio of the foregoing slurry is less than 0.3, effects on decreasing the specific gravity and increasing the matrix strength are undesirably reduced because of a small production amount of calcium silicate hydrate. Whereas if the ratio exceeds 0.8, undesirably, the moisture content is raised because of an increase in sedimentation volume, thus impairing productivity. In addition, silica sand, flay ash, diatomaceous earth, silicon dust, white carbon, zeolite, and montmorillonite are examples of a silica containing material. Moreover, cellulose fibers, polypropylene, vinylon, glass fibers and carbon fibers are examples of a fiber material. Further, perlite, wallastonite, mica, talc, calcium carbonate and gypsum are examples of inorganic fillers. In addition, as a forming method, any conventional forming process, including the Hatschek sheet machine process, mold press process, and mono-layer mold process, can be used. The fundamental position of a material slurry used for a method of manufacturing a calcium silicate board according to the present invention is a conventional composition, as follows: as a solid component, 17 to 50 wt% of calcareous material, 15 to 45 wt% of silica containing material; 2 to 8 wt% of fiber material; and 5 to 40% of inorganic fillers. The same materials as above can be used as a calcareous material. A calcareous material content of less than 17 wt% or more than 50 wt% is not preferable because it causes a decrease in the flexural strength and an increase in the dimensional change rate due to water absorption. In addition, silica sand, flay ash, etc., can be used as a silica containing material. A silica containing material content of less than 15wt% or more than 45wt% is not preferable because it causes a decrease in the flexural strength and an increase in the dimensional change rate due to water absorption. Moreover, the same materials as above can be used as a fiber material. A fiber material content of less than 2wt% is not preferable because it decreases the flexural strengthand a fiber material content of more than 8wt% undesirably causes a loss of the non-combustibility. Additionally, when polypropylene, vinylon, glass fibers or carbon fibers are used, it is necessary to set the content thereof to 5wt% or less. Further, the same materials as mentioned above can be used as inorganic fillers. An inorganic filler content of less than 5wt% is not preferable because it causes an increase in the dimensional change rate due to water absorption. An inorganic filler content of more than 40wt% is not preferable since it decreases the flexural strength. The first novel characteristic of the present invention is that an amorphous silica containing material or a silicate material of which the specific surface area is 1 m 2 /g or more is used as a portion of a silica containing material of a material slurry having the foregoing composition. "The specific surface area" in this description is estimated by the gaseous N 2 absorption method. It is not preferable that the specific surface area of the amorphous silica containing material or the silicate material be less than 1 m 2 /g, since a green sheet cannot obtain sufficient strength before the hydrothermal reaction due to poor reactivity. Further, the content of the amorphous silica containing material or the silicate material having a specific surface area of 1 m 2 /g or more is in a range of from 2 to 20wt%. A content of less than 2wt% is not preferable because of poor strength reproducibility, and a content of more than 20wt% is not preferable because it reduces the freeness, resulting in a decrease in productivity. When a material having a specific surface area of 1 to 10 m 2 /g is used, the preferable content thereof is 10wt% or more, in the case of a material having a specific surface area of 10 to 100 m 2 /g, the preferable content thereof is 5wt% or more, and in the case of a material having a specific surface area of 100 m 2 /g or more, the preferable content thereof is 2wt% or more. Examples of an amorphous silica containing material having a specific surface area of 1 m 2 /g or more are diatomaceous earth, silicon dust, fly ash, and white carbon. Additionally, examples of a silicate material having a specific surface area of 1 m 2 /g or more are zeolite, pyrophyllite, allophane, montmorillonite mineral, chlorite mineral, and attapulgite. Two or more kinds of these materials can be used together. The second novel characteristic of the present invention is that a green sheet (molded body) is not subjected to the hydrothermal reaction as it is but undergoes primary curing, which green sheet is obtained such that a material slurry composed of the foregoing material compositions is formed into a prescribed shape by, for instance, the Hatschek sheet machine process. Primary curing proceeds under the following conditions: (curing temperature - 15) x curing time ≥ 120°C·hr. The primary curing conditions of less than 120°C hr are not preferable because a green sheet cannot obtain sufficient strength due to a shortage of curing. Primary curing requires a curing temperature of more than 15°C and, preferably, it proceeds under conditions of 240°C·hr or more in a curing temperature range of 30 to 80°C. After the afore-mentioned primary curing, the green sheet may be subjected to a conventional hydrothermal reaction and formed into a calcium silicate board through conventional processes. The hydrothermal reaction can proceed in a pressure container under saturated water vapor at a temperature of 150 to 200°C and, preferably at 170 to 190°C for 5 to 20 hours and, more preferably, for 8 to 12 hours. According to a manufacturing method incorporated in the present invention, a calcium silicate board having a bulk specific gravity of 1.0 or less can be'obtained. EXAMPLES A method of manufacturing a calcium silicate board according to the present invention will be better understood in detail from the following description taken in conjunction with the examples and comparative examples. Example 1 and Comparative Example 1 Manufacturing examples of calcium silicate hydrate slurries essentially consisting of an amorphous material: Slurries essentially consisting of an amorphous material were obtained as follows: calcium hydroxide and silica sand were blended according to formulations. shown in Table 1; each of the mixtures was mixed with 13 times the amount of water and stirred; then each of the resultant mixtures was subjected to a hydrothermal reaction according to the corresponding conditions shown in Table 1. An autoclave for experimental use was employed for the hydrothermal reaction. Experimental No. 1 2 3 4 5 6 Materials Silica Sand Calcium Hydroxide Ca/(Si+Al) Molar Ratio 0.4 0.6 0.8 0.2 1.0 0.6 Temp. (°C) 180 180 150 180 150 180 Time (hr.) 6 4 4 6 4 10 Water Ratio 13 13 13 13 13 13 Stirring Rate (m/min) 100 100 100 100 100 100 Reaction Rate of Crystalline Silica Containing Material 48 57 78 31 95 73 Sedimentation Volume (ml/g) 6.4 7.1 9.0 5.8 14.5 15.8 Materials were prepared according to formulations shown in Table 2. Each of the materials was formed into a slurry having a solid content of 10%, press-molded into 30 by 30 by 0.8 cm pieces at a press pressure of 10 kg/cm 2 , then subjected to a hydrothermal reaction for 10 hours at 180°C under a saturated vapor pressure. Table 2 shows the bulk specific gravity, the flexural strength (under absolute dry conditions) and abrasion index. In Table 2, the filtration rate (ml/sec) is defined as the value of filtered water (ml)/filtration time (second) when one liter of slurry, of which the concentration is 4.2% as a solid component, is put in a Büchner funnel having a diameter of 16 cm and filtered at 50 cmHg. The filtration rate of 30 or more is indicated by o, that of 20 or more and less than 30 is indicated by Δ, and that of less than 20 is indicated by ×. Example 2 and Comparative Example 2 Calcium hydroxide, silica sand, wallastonite, perlite, pulp, an amorphous silica containing material and a silicate material were blended according to formulations shown in Table 3, then each of the mixtures was mixed with 12 times the amount of water and stirred. By further adding water thereto, material slurries of which the solid content was approximately 3wt% were obtained and formed into 6 mm thick sheets by the Hatschek sheet machine process. Then, each of the resultant green sheets was subjected to primary curing according to the conditions, i. e., the temperature and time, shown in Table 3, followed by the hydrothermal reaction for 10 hours at 180°C under a saturated vapor pressure. Table 3 shows peeling and bursting of the green sheets after the hydrothermal reaction, and also, the bulk specific gravity and the flexural strength of the obtained calcium silicate boards under absolute dry conditions. In Table 3, the specific surface area estimated by the gaseous N 2 absorption method is 2.0 m 2 /g for diatomaceous earth, 20 m 2 /g for silicon dust, 220 m 2 /g for white carbon, and 6.5 m 2 /g for zeolite. In addition, O indicates excellent productivity and × indicates inferior productivity. Example 3 and Comparative Example 3 Each of the materials prepared according to formulations shown in Table 4 was mixed with 12 times the amount of water and stirred. The gel used here was obtained by gelation of calcium hydroxide and diatomaceous earth at a weight ratio of 1:1, which gelation proceeded at a water ratio of 5 for 2 hours at 90°C. In the Table, the gel content is shown as a solid component. By further adding water thereto, material slurries of which the solid content was approximately 3wt% were obtained and formed into 6 mm thick sheets by the Hatschek sheet machine process. Then, each of the resultant green sheets was subjected to primary curing according to the conditions, i. e., the temperature and time, shown in Table 4, followed by a hydrothermal reaction in a pressure container for 10 hours at 180°C under a saturated vapor pressure. Table 4 shows the flexural strength of molded bodies immediately after primary curing, the bulk specific gravity, the flexural strength, and interlayer peel strength after the hydrothermal reaction, wherein the latter two are evaluated under absolute dry conditions. In Table 4, the specific surface area estimated by the gaseous N 2 absorption method is 20 m 2 /g for silicon dust, 6.5 m 2 /g for zeolite, and 2.0 m 2 /g for diatomaceous earth. ADVANTAGE By a method of manufacturing a calcium silicate board according to the present invention, it is possible to improve the strength of the green sheet obtained by forming a material slurry into a prescribed shape, thereby preventing the green sheet from peeling, bursting or the like during the hydrothermal reaction.

Claims: A method of manufacturing a light-weight calcium silicate board comprising; a step of forming a material slurry into a prescribed shape, said material slurry comprising, as a solid component, 17 to 50 wt% of calcareous material, 15 to 45 wt% of silica containing material, 2 to 8 wt% of fiber material and 5 to 40 wt% of inorganic fillers; and a step of hydrothermally reacting the obtained molded body in a pressure container, wherein 2 to 20 wt% of at least one kind of amorphous silica containing material and/or silicate material, each having a specific surface area of 1m 2 /g or more, is used as a portion of said silica containing material; and, before said hydrothermal reaction, said molded body is subjected to primary curing under conditions where (curing temperature -15) x curing time ≥120°C.hr. A method according to claim 1, in which the fiber material comprises polypropylene, vinylon, glass fibers or carbon fibers, and its content in the slurry is 5 wt% or less. A method according to claim 1 or 2, in which the silica containing material has a specific surface area of 1 to 10m 2 /g and its content in the slurry is 10 wt% or more. A method according to claim 1 or 2, in which the silica containing material has a specific surface area of 10 to 104m 2 /g and its content in the slurry is 5 wt% or more. A method according to claim 1 or 2, in which the silica containing material has a specific surface area of 100m 2 /g or more and its content in the slurry is 2 wt% or more. A method according to any preceding claim, in which the primary curing is at a curing temperature of 30° to 80°C and (curing temperature -15) x curing time ≥ 240°C.hr. A method according to any preceding claim, in which the hydrothermal reaction in the pressure container proceeds under saturated water vapour at a temperature of 150° to 200°C for 5 to 20 hours. A method according to claim 7, in which the hydrothermal reaction proceeds at 170° to 190°C.

Inventors: ASAMI TAKUYA, IWANAGA TOMOKI, ODA MASAAKI, OSHIO YASUHIDE, SAKIYAMA MASATO, SHIROMOTO SHIGEMITSU, SUGIYAMA TORU, UZUKI SEISHIRO, 3UZUKI, SEISHIRO, ASAMI, TAKUYA, IWANAGA, TOMOKI, ODA, MASAAKI, OSHIO, YASUHIDE, SAKIYAMA, MASATO, SHIROMOTO, SHIGEMITSU, SUGIYAMA, TORU, 3UZUKI, Seishiro, ASK Corporation, ASAMI, Takuya, ASK Corp. Central Res. Lab., IWANAGA, Tomoki, ASK Corp. Central Res. Lab., ODA, Masaaki, ASK Corp. Central Res. Lab., OSHIO, Yasuhide, ASK Corp. Central Res. Lab., SAKIYAMA, Masato, ASK Corp. Central Res. Lab., SHIROMOTO, Shigemitsu, ASK Corp. Central Res. Lab., SUGIYAMA, Toru, ASK Corp. Central Res. Lab.
Applicants: A & A MATERIAL CORP, A & A MATERIAL CORPORATION
Application year: 1996
Main classification: C04B28
IPC codes: C04B28, C04B14, C04B16, C04B38, C04B40