Method for manufacturing fiber-reinforced cement board and its raw material composition

Abstract

This invention provides a method for manufacturing thin fiber-reinforced cement boards with excellent design qualities. [Solution] A method for manufacturing fiber-reinforced cement boards, characterized by preparing a raw material mixture consisting of 25.0-39.5% by mass of cement, 40.0-50.0% by mass of silica, 0-14.0% by mass of calcium carbonate as powder, 2.5-16.5% by mass of seashell granules, and 5.0-10.0% by mass of organic fibers, and then producing a cement slurry layer by adding a predetermined amount of water to the raw material mixture and laminating the resulting slurry layer onto a making roll.

Description

Technical Field

[0001] The present invention relates to a method for manufacturing a fiber-reinforced cement board and its raw material formulation.

Background Art

[0002] Conventionally, in order to increase the added value of fiber-reinforced cement boards such as slate boards, surface painting or attaching a decorative sheet for surface decoration may be performed. In addition, fiber-reinforced cement boards used as building materials tend to be preferred in finishes that utilize the texture of cement, and finishes without surface painting are also being carried out. However, since the color of the cement constituting the fiber-reinforced cement board is gray, conventional fiber-reinforced cement boards can only obtain a gray texture and it is difficult to achieve good design properties.

[0003] As a method for producing a thin fiber-reinforced cement board with excellent design properties, a raw material containing cement, an inorganic material, and reinforcing fibers is mixed to form a fiber-reinforced cement board by a wet process, and an embossed pattern is applied to the surface while the fiber-reinforced cement board is in an uncured state. Then, it is known to grind to a depth below the deepest part of the concave portion of the embossed pattern to finish the surface flat (for example, see Patent Document 1).

Prior Art Documents

Patent Documents

[0004]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0005] In the method described in Patent Document 1, an embossed pattern is applied to the surface of an uncured fiber-reinforced cement board using an embossing die, thereby creating areas with different filling conditions within the fiber-reinforced cement board. Subsequently, the embossed pattern applied to the surface is ground down to below the deepest part of the recesses to finish the surface to a flat surface, thereby obtaining a fiber-reinforced cement board with excellent design, which has a smooth surface with a pattern (a variation in shade) derived from the embossed pattern while retaining the texture of the inorganic material. Furthermore, by manufacturing the fiber-reinforced cement board using a papermaking method, the fiber-reinforced cement board can be made thin.

[0006] Incidentally, thin fiber-reinforced cement boards with designs different from those applied by embossing are also desired.

[0007] Therefore, the present invention aims to provide a method for manufacturing a thin fiber-reinforced cement board with excellent design properties, and a raw material formulation thereof. [Means for solving the problem]

[0008] The present invention provides a raw material formulation comprising 25.0-39.5% by mass of cement, 40.0-50.0% by mass of silica, 0-14.0% by mass of calcium carbonate as powder, 2.5-16.5% by mass of seashell granules, and 5.0-10.0% by mass of organic fibers. The present invention relates to a method for producing fiber-reinforced cement boards, characterized by producing a cement slurry layer by adding a predetermined amount of water to the aforementioned raw material mixture and then laminating the resulting slurry onto a making roll.

[0009] The present invention also relates to a raw material formulation for fiber-reinforced cement board, characterized by containing 25.0 to 39.5% by mass of cement, 40.0 to 50.0% by mass of silica, 0 to 14.0% by mass of calcium carbonate as powder, 2.5 to 16.5% by mass of seashell granules, and 5.0 to 10.0% by mass of organic fibers. [Effects of the Invention]

[0010] The fiber-reinforced cement board obtained by including seashell grains in the raw material formulation has a design characteristic of seashell grains. Furthermore, when the amount of seashell grains is 2.5% by mass or more, the seashell grains become more visible, resulting in a fiber-reinforced cement board with superior design. In addition, when the amount of cement is 39.5% by mass or less, the seashell grains are less likely to be covered by the cement, making them more visible, and the fiber-reinforced cement board with superior design. Moreover, when a thin fiber-reinforced cement board is produced by papermaking using a raw material formulation with a seashell grain content exceeding 16.5% by mass, the seashell grains tend to overlap and pop out in the cement slurry layer and fiber-reinforced cement board. However, when the amount of seashell grains is 16.5% by mass or less, the seashell grains are less likely to overlap and pop out in the cement slurry layer and fiber-reinforced cement board. As a result, the fiber-reinforced cement board becomes smoother and more aesthetically pleasing, and the manufacturing equipment (e.g., belts) is less likely to be damaged by the seashell particles, resulting in better quality fiber-reinforced cement boards. Therefore, according to the present invention, it is possible to manufacture thin fiber-reinforced cement boards with good quality and excellent aesthetic appeal, and the manufacturing equipment is less likely to be damaged. [Brief explanation of the drawing]

[0011] [Figure 1] Figure 1 is a schematic diagram of the manufacturing process of a fiber-reinforced cement board according to one embodiment of the present invention. [Figure 2] Figure 2 is a flowchart illustrating the manufacturing method of the slurry used to produce the fiber-reinforced cement board shown in Figure 1. [Figure 3] Figure 3 is a flowchart illustrating a manufacturing method for producing fiber-reinforced cement board using the slurry obtained by the manufacturing method shown in Figure 2. [Figure 4] Figure 4 shows photographs of the surface of the fiber-reinforced cement board of Example 1 ((A) before grinding, (B) after grinding). [Modes for carrying out the invention]

[0012] One embodiment of the present invention will be described below with reference to the attached drawings.

[0013] <Manufacturing process for fiber-reinforced cement board> Figure 1 is a schematic diagram of the manufacturing process for fiber-reinforced cement board 80. Figure 1 shows only the main parts when fiber-reinforced cement board 80 is manufactured using a general manufacturing method. Based on Figure 1, the general outline of the manufacturing process for fiber-reinforced cement board 80 will be explained.

[0014] The fiber-reinforced cement board 80 is manufactured by the manufacturing equipment 1 from a slurry 14 made by adding water to a raw material mixture containing cement, silica, calcium carbonate as powder, seashell granules, and organic fibers. First, the slurry 14 is made into a green board 70 by the papermaking method in the papermaking device 10 (papermaking process). Then, the green board 70 is pressed in the press device 20 (pressing process), cured in the curing device 40 (first curing device) (first curing process), cut to the desired size in the cutting device 30 (cutting process), and cured in the curing device 40 (second curing device) (second curing process) to become a fiber-reinforced cement board 80. The surface of the fiber-reinforced cement board 80 is ground in the grinding device 50 (grinding process).

[0015] <Specific manufacturing process for fiber-reinforced cement boards> Figure 2 is a flowchart showing the manufacturing method for the slurry used to produce the fiber-reinforced cement board shown in Figure 1. Figure 3 is a flowchart showing the manufacturing method for producing a fiber-reinforced cement board using the slurry obtained by the manufacturing method shown in Figure 2.

[0016] <Raw material mixture> As shown in Figure 2, the raw material mixture is obtained by blending cement, silica, calcium carbonate as powder, seashell granules, and organic fibers in predetermined mass percentages (S1).

[0017] 〔cement〕 Cement is added for the hardening and strength development of fiber-reinforced cement boards. The amount of cement in the raw material formulation is 25.0 to 39.5% by mass, preferably 27.0 to 39.0%, and more preferably 30.1 to 38.0% by mass. If this amount is too small, it is difficult to form the fiber-reinforced cement board and the strength decreases. If this amount is too large, the hardness increases excessively, the deflection amount decreases, and the fiber-reinforced cement board is likely to be damaged. Also, the shell grains are covered with cement and the design quality deteriorates. Examples of cement include ordinary Portland cement, white Portland cement, fly ash cement, blast furnace cement, silica cement, alumina cement, and ordinary eco-cement. These may be used alone or in combination of two or more.

[0018] [Silica] The silica is added to improve the strength of the fiber-reinforced cement board. The amount of silica in the raw material formulation is 40.0 to 50.0% by mass, preferably 38.0 to 48.0%, and more preferably 38.9 to 46.8% by mass. If this amount is too small, the strength of the fiber-reinforced cement board decreases. If this amount is too large, the fiber-reinforced cement board has excessive hardness and is likely to be damaged due to a decrease in the deflection amount.

[0019] [Calcium carbonate as a powder] Calcium carbonate as a powder (hereinafter also referred to as "calcium carbonate powder" or simply "calcium carbonate") is an optional component and is added as a bulking agent when added. The amount of calcium carbonate in the raw material formulation is 0 to 14.0% by mass, preferably 0 to 13.0%, and more preferably 0 to 12.1% by mass. Calcium carbonate may not be added, but if added, if it is too much, the proportion occupied by other raw materials becomes small, causing problems in formability and strength reduction. As the calcium carbonate powder, pulverized limestone or the like can be used.

[0020] The average particle size of the calcium carbonate powder is preferably 50 to 300 μm, and more preferably 100 to 200 μm. Calcium carbonate powder with such an average particle size can be obtained, for example, by crushing limestone and then sieving it. In this application, the average particle size refers to the 90% volume mean diameter (D90), which can be determined, for example, by measurement using laser diffraction. The upper limit of the particle size of the calcium carbonate powder is preferably less than 0.5 mm, and more preferably less than 0.4 mm. The lower limit of the particle size of the calcium carbonate powder is not particularly limited, but is, for example, 0.02 mm or more. The upper limit of the particle size can be determined by the method described later.

[0021] [Seashell grains] The seashell granules are added to the fiber-reinforced cement board for surface decoration and effective utilization of waste materials. The amount of seashell granules in the raw material mixture is 2.5 to 16.5% by mass, preferably 2.8 to 16.2%, and more preferably 3.0 to 15.1% by mass. If the amount is too low, it becomes difficult to recognize the design of the seashell granules, and if the amount is too high, the seashell granules will not overlap easily in the cement slurry layer or fiber-reinforced cement board and will not easily come loose. As a result, the fiber-reinforced cement board will have increased smoothness and superior design, and the seashell granules will not easily damage the manufacturing equipment (e.g., belts) of the fiber-reinforced cement board. However, if the seashell granules overlap easily in the cement slurry layer or fiber-reinforced cement board and come loose, the smoothness of these surfaces will be lost, and there is a risk of damaging the manufacturing equipment. As shell granules, for example, shell granules from oysters, scallops, clams, abalone, turban shells, cockles, surf clams, turban shells, whelks, turban shells, pen shells, surf clams, cockles, ark clams, ark clams, abalone, and pearl oysters can be used. These may be used individually or in combination of two or more types. Crushed shells can also be used as shell granules.

[0022] The shell granules are preferably pulverized with a minimum particle size of 0.5 mm or more and a maximum particle size of less than 4.5 mm, and more preferably with a minimum particle size of 1.0 mm or more and a maximum particle size of less than 3.5 mm. With this configuration, the minimum particle size of the shell granules is 0.5 mm or more, making the shell granules more visible, and the fiber-reinforced cement board has an even better design. Furthermore, the maximum particle size of the pulverized material is less than 4.5 mm, making it less likely for the shell granules to fly off. In addition, the shell granules are less likely to peel off even when a grinding process is performed. Such pulverized material can be obtained, for example, by crushing the shells and then sieving them. The minimum and maximum particle sizes can be determined, for example, using a sieve. For example, pulverized material that passes through a sieve with a mesh size of 4.5 mm can be pulverized material with a maximum particle size of less than 4.5 mm. Also, pulverized material that remains on a sieve with a mesh size of 0.5 mm can be pulverized material with a minimum particle size of 0.5 mm or more.

[0023] The total amount of calcium carbonate and seashell granules in the raw material formulation is 2.5 to 30.5% by mass. The upper limit of this total amount is preferably 16.5% by mass or less, more preferably 16.0% by mass or less, even more preferably 15.5% by mass or less, and particularly preferably 15.1% by mass or less. The lower limit of this total amount is preferably 2.8% by mass or more, and more preferably 3.0% by mass or more. Although calcium carbonate and seashell granules are non-hardening fillers, this total amount can improve moldability, strength, and design aesthetics.

[0024] [Organic Fibers] Organic fibers are added to improve the shape retention, strength, and toughness of fiber-reinforced cement boards. The amount of organic fibers in the raw material mixture is 5.0 to 10.0% by mass, preferably 6.5 to 9.5%, and more preferably 7.17 to 8.83% by mass. If the amount is too low, the fiber-reinforced cement board will be easily broken under pressure, and if the amount is too high, the papermaking properties will decrease. The organic fibers may be natural fibers and / or synthetic fibers. Examples of natural fibers include pulp. Examples of synthetic fibers include polypropylene fibers and vinylon fibers. These may be used individually or in combination of two or more types.

[0025] 〔slurry〕 Next, the raw material mixture is mixed with a predetermined amount of water to form a slurry 14 (S2). The concentration of the raw material composition in the slurry 14 in the slurry tank 12 is preferably 1 to 9% by mass, and more preferably 2 to 7% by mass. If this concentration is too low, the thickness of the fiber-reinforced cement board will be too thin, and if this concentration is too high, the thickness of the fiber-reinforced cement board will be too thick. Furthermore, by keeping this concentration within the above range, when multiple slurry tanks 12 are used, the concentration of the raw material composition in the slurry 14 can be easily stabilized between the slurry tanks 12, and the surface smoothness of the resulting fiber-reinforced cement board is further improved. The slurry 14 is sent to the slurry tank 12.

[0026] [Papermaking process] In the papermaking process, the slurry 14 is transformed into a green sheet 70 by the papermaking method (S11). In the papermaking process, a papermaking apparatus 10 is used. Specifically, the slurry 14 is supplied to a slurry tank 12, and is formed onto a papermaking felt 11 via a cylinder 13 to form a cement slurry layer. The cement slurry layer is wound onto a making roll 15 and stacked, then cut and unfolded by a cutting device on the making roll 15 to form a flat green sheet 70. In this embodiment, three slurry tanks 12 are used, and three cement slurry layers are stacked on the papermaking felt 11. Alternatively, the three cement slurry layers can be wound onto the making roll 15 multiple times to stack even more cement slurry layers and obtain a green sheet 70 of a desired thickness. Although there are three slurry tanks 12 in the embodiment shown in Figure 1, the number of slurry tanks can be one, two, or four or more. In addition, conventionally known making rolls can be used as the making roll 15, for example, the making roll described in Japanese Patent Publication No. 5070159 can be used.

[0027] [Pressing process] In the pressing process, the green plate 70 is pressed (S12). Specifically, the green plate 70 containing two or more cement slurry layers is pressed by the pressing device 20. By pressing the green plate containing two or more cement slurry layers before curing, the layers are tightly bonded, making it difficult for the fiber-reinforced cement board obtained during curing to separate. The pressing process is optional, but it is more desirable to perform it with a pressing pressure of 0.9 to 20 MPa. If the pressing pressure is too high, too much moisture is removed, resulting in insufficient water for the cement hydration reaction and a decrease in handling strength.

[0028] [Primary curing process] In the primary curing process, the raw board 70 is cured and given handling strength to become a fiber-reinforced cement board (S13). The fiber-reinforced cement board, having been given handling strength, becomes easier to cut in the next process, the cutting process. The raw board 70 is cured in the curing device 40. In the primary curing process, atmospheric pressure steam curing is performed.

[0029] [Cutting process] In the cutting process, the fiber-reinforced cement board 80, which has been given handling strength in the primary curing process, is cut to the desired size (S14). The fiber-reinforced cement board 80 is cut by the cutting device 30. If the fiber-reinforced cement board 80 is already the desired size without cutting, the cutting process does not need to be performed.

[0030] [Secondary curing process] In the secondary curing process, the fiber-reinforced cement boards 80, which have been cut to the desired size in the cutting process, are cured (S15). The fiber-reinforced cement boards 80 are cured using a curing device 40. Curing methods in the secondary curing process include natural curing and autoclave curing. The method of the secondary curing process is preferably adjusted as appropriate depending on the materials and proportions of the raw material mixture. For example, if the raw material contains fibers with low heat resistance (e.g., vinylon fibers), natural curing is preferable. Also, from the viewpoint of allowing the cement and silica contained in the raw material mixture to react more thoroughly, autoclave curing is preferable. In the case of autoclave curing, although it varies depending on the raw materials used, it is desirable to set the temperature between 110°C and 181°C. A temperature of 110°C or higher can improve the physical properties of the fiber-reinforced cement boards 80, such as strength. Also, a temperature of 181°C or lower can prevent over-curing and allow for energy-efficient curing.

[0031] In this embodiment, primary curing and secondary curing processes are performed as curing steps. However, if a cutting process is not performed, the primary curing process may be omitted, and only the secondary curing process may be performed as the curing process.

[0032] [Grinding process] In the grinding process, the surface of the fiber-reinforced cement board 80, which has been cured in the secondary curing process, is ground (S16). This makes the surface of the fiber-reinforced cement board 80 flat and exposes the seashell grains that were present inside the fiber-reinforced cement board 80, further improving its aesthetic appeal. The surface of the fiber-reinforced cement board 80 is ground by the grinding device 50. Sandpaper can be used in the grinding process. The grit size of the sandpaper is preferably #30 to #120. If the grit of the sandpaper is too coarse, the smoothness of the surface will decrease, and if the grit of the sandpaper is too fine, grinding will take a long time and productivity will decrease. As sandpaper, for example, a belt sander can be used.

[0033] [Fiber-reinforced cement board] By manufacturing the fiber-reinforced cement board 80 from the above-mentioned raw material mixture, it becomes a thin board with good quality and excellent design, and the manufacturing equipment is less likely to be damaged during the manufacturing process of the fiber-reinforced cement board 80. The thickness of the fiber-reinforced cement board 80 is, for example, 0.6 to 16.5 mm, more specifically 2 to 10 mm, and more specifically 3 to 8 mm.

[0034] Furthermore, the present invention is not limited to the embodiments described above. Nor is it limited by the effects and advantages described above. Moreover, the present invention can be modified in various ways without departing from the spirit of the invention.

[0035] [Disclosure items] Each of the following items is a disclosure of a preferred embodiment.

[0036] [Item 1] The raw material mixture consists of 25.0-39.5% by mass of cement, 40.0-50.0% by mass of silica, 0-14.0% by mass of calcium carbonate as powder, 2.5-16.5% by mass of seashell granules, and 5.0-10.0% by mass of organic fibers. A method for producing fiber-reinforced cement boards, characterized by producing a cement slurry layer by forming a slurry by adding a predetermined amount of water to the aforementioned raw material mixture and then laminating the resulting slurry layer onto a making roll.

[0037] The fiber-reinforced cement board obtained by including seashell grains in the raw material formulation has a design characteristic of seashell grains. Furthermore, when the amount of seashell grains is 2.5% by mass or more, the seashell grains become more visible, resulting in a fiber-reinforced cement board with superior design. In addition, when the amount of cement is 39.5% by mass or less, the seashell grains are less likely to be covered by the cement, making them more visible, and the fiber-reinforced cement board with superior design. Moreover, when a thin fiber-reinforced cement board is produced by papermaking using a raw material formulation with a seashell grain content exceeding 16.5% by mass, the seashell grains tend to overlap and pop out in the cement slurry layer and fiber-reinforced cement board. However, when the amount of seashell grains is 16.5% by mass or less, the seashell grains are less likely to overlap and pop out in the cement slurry layer and fiber-reinforced cement board. As a result, the fiber-reinforced cement board becomes smoother and more aesthetically pleasing, and the manufacturing equipment (e.g., belts) is less likely to be damaged by the shell particles, resulting in better quality fiber-reinforced cement board. Therefore, this configuration makes it possible to manufacture thin fiber-reinforced cement boards with good quality and aesthetic appeal, and also reduces damage to the manufacturing equipment.

[0038] [Item 2] A method for manufacturing a fiber-reinforced cement board according to item 1, characterized by pressing a green board, which has been unfolded from the making roll, with two or more layers of cement slurry, and curing it.

[0039] With this configuration, pressing the green board containing two or more layers of cement slurry before curing the green board ensures tight adhesion between the layers, making it difficult for the fiber-reinforced cement board obtained during curing to separate.

[0040] [Item 3] The method for manufacturing a fiber-reinforced cement board according to item 2, characterized by grinding the surface of the fiber-reinforced cement board obtained by curing the green board.

[0041] With this configuration, the surface of the fiber-reinforced cement board can be finished to a flat surface by grinding, and the shell grains that were present inside the fiber-reinforced cement board can be exposed, further improving its aesthetic appeal.

[0042] [Item 4] A method for producing a fiber-reinforced cement board according to any one of items 1 to 3, characterized in that the total amount of calcium carbonate and seashell granules in the raw material mixture is 2.5 to 16.5% by mass.

[0043] With this configuration, the bending strength of the fiber-reinforced cement board is increased because the total amount of the mixture is 16.5% by mass or less.

[0044] [Item 5] The method for manufacturing fiber-reinforced cement boards according to any one of items 1 to 4, characterized in that the aforementioned seashell grains are pulverized material with a lower limit of particle size of 1.0 mm or more and an upper limit of particle size of less than 3.5 mm.

[0045] With this configuration, the lower limit of the particle size of the crushed seashell particles is 1.0 mm or larger, making the seashell particles more visible and giving the fiber-reinforced cement board an even better aesthetic appearance. Furthermore, the upper limit of the particle size of the crushed material is less than 3.5 mm, making it less likely for the seashell particles to fly off. In addition, the seashell particles are less likely to peel off even after the grinding process.

[0046] [Item 6] A raw material formulation for fiber-reinforced cement board, characterized by containing 25.0-39.5% by mass of cement, 40.0-50.0% by mass of silica, 0-14.0% by mass of calcium carbonate as powder, 2.5-16.5% by mass of seashell granules, and 5.0-10.0% by mass of organic fibers.

[0047] [Item 7] The raw material mixture for fiber-reinforced cement board described in item 6, characterized in that the aforementioned seashell particles are crushed material with a lower limit of particle size of 1.0 mm or more and an upper limit of particle size of less than 3.5 mm. [Examples]

[0048] The present invention will be described in detail below with reference to examples, but these examples are not intended to limit the present invention.

[0049] (Example 1) Fiber-reinforced cement boards were manufactured using raw material formulations with the mixing ratios of each material shown in Table 1 below. For the calcium carbonate powder, limestone was crushed and then classified (sieved using a mesh sieve) to adjust the average particle size to 150 μm. For the shell particles, oyster shells were crushed and then classified (sieved using a mesh sieve) to adjust the mixture so that only shell particles with a particle size range of 1.0 to 3.5 mm remained (lower limit of particle size 1.0 mm or more, upper limit of particle size less than 3.5 mm). The average particle size, lower limit of particle size, and upper limit of particle size were measured using the methods described above.

[0050] Specifically, first, cement, silica, calcium carbonate powder, oyster shell granules, pulp, and polypropylene fibers were mixed with water in a mixer to create a slurry, which was then sent to a slurry tank. Here, the concentration of the raw materials in the slurry tank was adjusted to 2-7% by mass. Next, the slurry was formed onto felt using a cylinder, creating three layers of cement slurry (0.2 mm thick) (total thickness 0.6 mm (= 0.2 mm x 3 layers)). The three cement slurry layers were then wound 10 times on a making roll to a predetermined thickness of 6 mm, and then cut to unfold into a flat sheet (size: thickness 6 mm, length 2445 mm, width 935 mm). The papermaking properties were visually inspected. The results are shown in Table 1. Finally, the flat sheet was subjected to 17.7 MPa (180 kg / cm²). 2The material was pressed with a press pressure of ) to adjust the thickness (5 mm), then subjected to primary curing (temperature 60°C, humidity 50%), cut to the specified size (length 2420 mm, width 910 mm), and then autoclave curing (155°C) to obtain a fiber-reinforced cement board. The surface of this fiber-reinforced cement board was ground with a #30 belt sander to obtain a fiber-reinforced cement board with a thickness of 5 mm. Note that grinding with a belt sander removes only a few microns, and this grinding hardly changes the thickness of the fiber-reinforced cement board.

[0051] The bulk density and flexural strength (longitudinal and transverse directions) of the resulting fiber-reinforced cement boards were measured to confirm their aesthetic appeal. The longitudinal flexural strength is measured in the direction of the papermaking process, and the transverse flexural strength is measured perpendicular to the papermaking process. The bulk density of the fiber-reinforced cement boards was measured according to JIS A5430:2001 "Fiber-reinforced cement boards" 6.3 Apparent density. The flexural strength of the fiber-reinforced cement boards was measured according to JIS A1408:2017 "Bending and impact tests for building boards." The aesthetic appeal of the fiber-reinforced cement boards was evaluated visually by inspecting the surface. The results are shown in Table 1 below.

[0052] (Examples 2-8, Comparative Examples 1-6) Fiber-reinforced cement boards were manufactured in the same manner as in Example 1, except that the mixing ratios of each material were changed to those shown in Table 1 below. The formability and design properties were evaluated, and the bulk density and flexural strength were measured. The results are shown in Table 1 below.

[0053] Figure 4 shows photographs of the surface of the fiber-reinforced cement board of Example 1 ((A) before grinding, (B) after grinding). The white areas indicate the presence of seashell grains.

[0054] [Table 1]

[0055] As shown in Table 1, in Examples 1 to 8, which are within the scope of the present invention, no seashell particles protruded from the substrates such as green boards and fiber-reinforced cement boards. Furthermore, in the fiber-reinforced cement boards, the seashell particles were sufficiently exposed on the surface without being covered by the cement. On the other hand, in Comparative Examples 1 and 2, where the amount of seashell particles was low at 2.0% by mass, the aesthetic properties of the seashell particles could not be recognized. Also, in Comparative Examples 3 and 4, where the amount of cement was high at 43.0% by mass and 40.0% by mass, the seashell particles were covered by the cement and their aesthetic properties could not be recognized. Moreover, in Comparative Examples 5 and 6, where the amount of seashell particles was high at 17.0% by mass, the seashell particles protruded from the substrate.Therefore, it can be seen that the present invention makes it possible to manufacture thin fiber-reinforced cement boards with good quality and excellent aesthetic properties, and also makes the manufacturing equipment less susceptible to damage.

[0056] Furthermore, in Examples 1 to 8, where the total amount of calcium carbonate powder and seashell granules was 16.5% by mass or less, the flexural strength was higher compared to Comparative Examples 5 and 6, where the total amount was 17.0% by mass. Therefore, it can be seen that a total amount of calcium carbonate powder and seashell granules of 16.5% by mass or less results in higher flexural strength. [Explanation of symbols]

[0057] 1 Manufacturing equipment 10 Paper making equipment 11 Felt for papermaking 12 Slurry Tank 13 Cylinders 14 Slurry 15 Making-of 20 Pressing device 30 Cutting device 40 Curing device 50 Grinding device 70 raw board 80 Fiber-reinforced cement board

Claims

1. The raw material mixture consists of 25.0-39.5% by mass of cement, 40.0-50.0% by mass of silica, 0-14.0% by mass of calcium carbonate as powder, 2.5-16.5% by mass of seashell granules, and 5.0-10.0% by mass of organic fibers. A method for producing fiber-reinforced cement boards, characterized by producing a cement slurry layer by forming a slurry by adding a predetermined amount of water to the aforementioned raw material mixture and then laminating the resulting slurry layer onto a making roll.

2. A method for manufacturing a fiber-reinforced cement board according to claim 1, characterized by pressing a raw board unfolded from the making roll with two or more layers of cement slurry and curing it.

3. The method for manufacturing a fiber-reinforced cement board according to claim 2, characterized by grinding the surface of the fiber-reinforced cement board obtained by curing the green board.

4. A method for producing a fiber-reinforced cement board according to any one of claims 1 to 3, characterized in that the total amount of calcium carbonate and seashell granules in the raw material mixture is 2.5 to 16.5% by mass.

5. The method for manufacturing a fiber-reinforced cement board according to any one of claims 1 to 3, characterized in that the aforementioned seashell grains are pulverized material with a lower limit of particle size of 1.0 mm or more and an upper limit of particle size of less than 3.5 mm.

6. A raw material formulation for fiber-reinforced cement board, characterized by containing 25.0 to 39.5% by mass of cement, 40.0 to 50.0% by mass of silica, 0 to 14.0% by mass of calcium carbonate as powder, 2.5 to 16.5% by mass of seashell granules, and 5.0 to 10.0% by mass of organic fibers.

7. The raw material mixture for fiber-reinforced cement board according to claim 6, characterized in that the seashell particles are pulverized with a lower limit of particle size of 1.0 mm or more and an upper limit of particle size of less than 3.5 mm.

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