JP3282930B2 - Inorganic plate and method for producing the same - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an inorganic plate used as a building material such as a roof material or a wall material such as a tile, an interior material, an exterior material, and an external member, and a method for producing the same.

[0002]

2. Description of the Related Art Conventionally, a slurry has been prepared by blending a fiber component with cement, and the slurry has been formed to form an inorganic plate. Asbestos has been used as a fiber component. Recently, pulp has been used to replace the fiber component due to the harmfulness of asbestos.

[0003]

However, the pulp conventionally used for the inorganic plate contains a lot of extremely long and extremely short fibers as shown in FIG. Extremely short fibers and extremely thin fibers have a small reinforcing effect because they contain a lot of extremely large and extremely small fibers. There was a problem that the impact strength was poor.

[0004] The present invention has been made in view of the above points, and an object of the present invention is to provide an inorganic plate capable of improving bending strength, frost damage resistance, and impact resistance even when pulp is used as a fiber component. It is intended for. In addition, the slurry containing pulp and the slurry containing asbestos, which have been conventionally used for the inorganic plate, have almost the same water drainage property during papermaking, and there is a problem that the productivity cannot be higher than that of asbestos. Was.

[0005] Furthermore, pulp conventionally used for inorganic plates has a problem in that the ability to capture cement is lower than asbestos because the degree of beating is small, and the yield of slurry decreases. In particular, pulp made from conifers such as fir and hemlock (NUKP and NBKP)
), These softwoods had less fiber cells trapping the cement, resulting in a particularly low slurry yield.

Further, when the degree of beating is increased in order to increase the ability to capture cement, there is a problem that water drainage is reduced and productivity is lower than asbestos.
The present invention has been made in view of the above points, and provides a method of manufacturing an inorganic plate that can improve productivity even when pulp is used as a fiber component and can increase the slurry yield. The purpose is to do so.

[0007]

According to the present invention, there is provided an inorganic board containing cement as a main component and containing at least one of hardwood bleached sulfate pulp and hardwood unbleached sulfate pulp. Alternatively, hardwood unbleached sulfate pulp is characterized by using a fiber having a fiber diameter of 5 to 30 μm and a fiber length of 0.2 to 1.0 mm containing 60% or more of the total number of fibers.

The inorganic plate has a fiber diameter of 20 to 60 μm.
m, a long fiber pulp containing 10% or more of the total number of fibers having a fiber length of 2.0 mm or more can be contained. Further, the method for producing an inorganic plate according to the present invention is a method for producing an inorganic plate in which cement is mixed with at least one of hardwood bleached sulfate pulp or hardwood unbleached sulfate pulp to prepare a slurry, and the slurry is formed into a paper. The method is characterized in that, as the hardwood bleached sulfate pulp or the hardwood unbleached sulfate pulp, a fiber having a fiber diameter of 5 to 30 μm and a fiber length of 0.2 to 1.0 mm containing at least 60% of the total number of fibers is used. Is what you do.

In the present invention, the degree of beating of hardwood bleached sulfate pulp or hardwood unbleached sulfate pulp is 65 SR °.
It can be: Also, a slurry can be prepared by blending sepiolite or silica. Hereinafter, the present invention will be described in detail. As the cement of the present invention, plain Portland cement such as ordinary Portland cement, early-strength Portland cement, and moderate Portland cement,
Any cement such as mixed Portland cement or special cement such as alumina cement or magnesia cement can be used, but it is preferable to use ordinary Portland cement.

In the present invention, a hardwood bleached sulfate pulp (hereinafter abbreviated as LBKP) or a hardwood unbleached sulfate pulp (hereinafter abbreviated as LUKP) can be used as a fiber component. The reason why hardwood-based pulp is used here is that hardwood contains more fiber cells that capture cement than softwood, thereby increasing the yield of slurry higher than softwood-based pulp. can do.

[0011] The LBKP and LUKP of the present invention are composed of fibers having a fiber diameter of 5 to 30 µm and a fiber length of 0.2 to 1.0 mm, which account for 60% or more of the total number of fibers. If the fiber diameter is less than 5 μm, the fiber is too stiff and tends to lump when preparing a slurry. If the fiber diameter exceeds 30 μm, the specific surface area decreases and There is a possibility that the ability to capture cement may be reduced. If the fiber length is less than 0.2 μm, the strength of the inorganic plate is reduced. If the fiber length is more than 1.0 mm, the fibers themselves and the fibers are entangled. As a result, there is a possibility that the ability to capture cement during papermaking may be reduced.

And the above cement is 40 to 60% by weight,
3 to 10% by weight of LBKP or LUKP, 20 to 40% by weight of silica sand or 5 to 25% by weight of silica stone as an aggregate are mixed, and water is added to the mixture to prepare a slurry. Thereafter, the slurry is formed by a round net machine (Hash Check Machine) or a flow-on machine, and the laminate is pressed and formed by a press machine to form a green sheet. It is cured in an autoclave and then dried and hardened to form an inorganic plate.

As shown in FIG. 5, the round net type paper making machine used in the present invention is constructed such that a felt 1 is erected on a plurality of rollers 2 in an endless loop so as to run freely, and a paper making machine main body 3 is formed. A plurality of slurry vats 4 are juxtaposed below the felt 1 below the bottom 3 and a mesh cylinder 5 is rotatably arranged in each slurry vat 4. In addition, a plurality of vacuum chambers 6 are provided, and a making roll 7 that is in contact with the surface of the felt 1 is rotatably provided on the side of the papermaking machine main body 3. Then, the slurry 8 stored in the slurry vat 4 is fed into the felt 1 by the cylinder 5.
Is transferred to the surface of the felt 1, and the slurry 8 stacked on the felt 1 by the travel of the felt 1 is then carried to the upper side of the vacuum chamber 6, where the slurry 8 stacked on the felt 1 by suction of the vacuum chamber 6. Is dehydrated by a specified amount, and then the dewatered slurry is transferred and laminated on the making roll 7 to form a laminate. This laminate is conveyed from the making roll 7 to the next pressure forming step on the belt conveyor 9.

As shown in FIG. 6, the flow-on papermaking machine used in the present invention forms a papermaking machine main body 3 by laying a felt 1 around a plurality of rollers 2 in an endless loop.
A slurry flow vat 10 is provided above the felt 1 above the papermaking machine main body 3, and a plurality of vacuum chambers 6 are provided on the lower surface of the felt 1, making the side of the papermaking machine main body 3 in contact with the surface of the felt 1. It is formed by providing the roll 7 rotatably. Then, the slurry 8 stored in the slurry flow vat 10 is supplied to the surface of the felt 1, and then the slurry 8 laminated on the felt 1 is transported to the upper side of the vacuum chamber 6 by the traveling of the felt 1, where the vacuum chamber 6 is moved. The water contained in the slurry 8 laminated on the felt 1 is dehydrated by a specified amount by the suction of 6, and then the dehydrated slurry is transferred and laminated on the making roll 7 to form a laminate. This laminate is conveyed from the making roll 7 to the next pressure forming step on the belt conveyor 9.

Comparing the round-mesh machine and the flow-on machine, the flow-on machine has no cylinder and has a simpler structure than the round-mesh machine, so that maintenance can be performed easily. Further, in the flow-on papermaking machine, the slurry 8 is supplied directly from the slurry flow vat 10 to the felt 1, so that the amount of the slurry 8 used as it is becomes the papermaking amount, and the management of the laminate is easy to carry out.
Moreover, the yield can be higher than that of the round-mesh type paper making machine.

In the present invention, the LBKP or LUKP
May be used, and thus LBK
When P or LUKP is beaten, the ability to capture cement during papermaking can be improved, and the yield of slurry can be increased. This beaten LBKP or LUK
When P is used, it is 1 to 5 with respect to the solid content of the slurry.
% By weight.

The degree of beating of LBKP or LUKP is 65 SR ° (Shopper Wrigler) or less, and the lower limit is not particularly limited. If the degree of beating (degree of beating or drainage) exceeds 65 SR °, the function as a reinforcing fiber may be reduced and the strength of the inorganic plate may be reduced, and the hard secondary wall of fiber cells may be damaged. The fiber itself may be damaged, and therefore the ability to capture cement may be reduced as compared with the one that is not beaten.In addition, the water drainage of the slurry during the papermaking is reduced, and the papermaking speed cannot be increased. , May lead to a decrease in productivity.

The degree of beating of the shopper type is 0.175 to 0.175 on the bottom of the measuring funnel and the conical seat of the funnel.
It is measured with a measuring device consisting of a funnel tube with a 0.147 mm wire mesh and a circular female valve. Then, the amount of drainage from the stock having a concentration of 0.2% of 1,000 milliliters is measured, and the freeness is determined by the following equation (a). Shopper freeness (SR °) = (1000−X) / 10 (a) X = amount of water (milliliter) discharged from the side view Further, the inorganic plate of the present invention includes the above-mentioned LBKP and LUKP
Apart from the fiber components of softwood bleached sulfate pulp (abbreviated NB
KP) or long-fiber pulp composed of softwood unbleached sulfate pulp (abbreviated as NUKP). This long fiber pulp has a fiber diameter of 20 to 60 μm and a fiber length of 2.0 mm.
The fiber is formed so as to include 10% or more of the total number of the fibers, and can improve the impact resistance of the inorganic plate. If the fiber diameter is less than 20 μm, the impact resistance cannot be improved, and the fiber diameter is 6 μm.
If the number of fibers exceeding 0 μm is too large, the specific surface area becomes small, the bonding with the cement (matrix) becomes insufficient, and the inorganic plate may become brittle. The fiber length is 2.
If the number of fibers less than 0 mm is too large, the impact resistance cannot be improved. The blending amount of the long fiber pulp is preferably 1 to 5% by weight based on the solid content of the slurry.

The slurry of the present invention may contain 0.3 to 5.0% by weight of sepiolite based on the solid content. Sepiolite can prevent separation of water and solids from the slurry, and can control the water drainage during papermaking to be large or small. If the amount is less than 0.3% by weight, the separation of water and solids from the slurry cannot be sufficiently prevented. If the amount exceeds 5.0% by weight, the water drainage becomes too small, and the productivity is lowered. It is also disadvantageous in terms of cost.

Further, the slurry of the present invention may contain 0.5 to 10% by weight of silica based on the solid content. Fine silica such as microsilica or silica fume can be used as this silica, and by blending silica, it is possible to increase or decrease the water drainage during papermaking. The blending amount is 0.
If the amount is less than 5% by weight, the water bleeding property cannot be controlled. If the amount exceeds 10% by weight, the water bleeding property becomes too small, and the productivity is lowered and the cost is disadvantageous.

[0021]

The present invention will be described below in detail with reference to examples. (Example 1) Ordinary Portland cement: 50% by weight Silica sand (No. 8): 30% by weight Silica powder: 15% by weight LBKP: 5% by weight Water was added to such a composition to prepare an 8% concentration slurry. .

The LBKP used in the present embodiment has a fiber length distribution as shown in FIG. 1 (a solid line indicates a distribution of fibers for each fiber length, and a broken line indicates a cumulative distribution thereof). Unbeaten LBKP (Phenix (Philippines),
A fiber having a fiber length of 0.3 to 1.0 mm and a fiber diameter of 7 to 25 μm contains about 90% of the total number of fibers).

This slurry is laminated on a making roll 7 of a round net paper making machine as shown in FIG. Thereafter, the laminate is subjected to a pressure of 300 kg / cm ² and a holding time of 10 kg / cm ² .
Pressurized in seconds to produce a green sheet. The water squeezed out from the lower surface of the press plate is discharged by suction.

To prevent the green sheet from drying,
It is left for 4 hours after packing, and then autoclaved. The autoclave curing conditions are a temperature of 185 ° C. and a holding time of 6 hours. Thereafter, drying and curing were performed to obtain an inorganic plate. (Example 2) Ordinary Portland cement: 50% by weight Silica sand (No. 8): 30% by weight Silica powder: 15% by weight LUKP: 5% by weight Water was added to such a composition to prepare an 8% concentration slurry. .

The LUKP used in this embodiment has a fiber length distribution as shown in FIG. 2 (a solid line indicates a fiber distribution for each fiber length, and a broken line indicates a cumulative distribution thereof). A fiber having a fiber length of 0.3 to 1.0 mm and a fiber diameter of 7 to 25 μm is classified from unbeaten LUKP (manufactured by Hyogo Pulp Industry Co., Ltd.) and contains 60% or more of the total number of fibers.
The other steps are the same as in the first embodiment.

(Example 3) Ordinary Portland cement: 50% by weight Silica sand (No. 8): 30% by weight Silica powder: 15% by weight LBKP: 5% by weight Water was added to such a composition to obtain a slurry having a concentration of 8%. Was prepared.

The LBKP used in this embodiment is obtained by beating the first embodiment to 40 SR °. The other steps are the same as in the first embodiment. (Example 4) Ordinary Portland cement 50% by weight Silica sand (No. 8) 28% by weight Silica powder 15% by weight LBKP 5% by weight Sepiolite (60D) 2% by weight Water is added to such a composition. An 8% strength slurry was prepared.

The LBKP used in this embodiment is the same as that in the third embodiment. Sepiolite is manufactured by Mizusawa Chemical Industries. The other steps are the same as in the first embodiment. (Example 5) Ordinary Portland cement: 50% by weight Silica sand (No. 8): 25% by weight Silica powder: 15% by weight LBKP: 5% by weight Sepiolite: 2% by weight Silica fume: 3% by weight Water was added to such a composition. Was added to prepare an 8% concentration slurry.

The LBKP used in this embodiment is the same as that in the third embodiment. Sepiolite is manufactured by Mizusawa Chemical Industries. The other steps are the same as in the first embodiment. (Example 6) Ordinary Portland cement: 50% by weight Silica sand (No. 8): 25% by weight Silica powder: 15% by weight LBKP: 5% by weight Long fiber pulp: 2% by weight % Slurry was prepared.

The LBKP used in this embodiment is equivalent to that of the third embodiment. Further, the long fiber pulp used in the present example has a fiber length distribution as shown in FIG. 3 (a solid line shows a distribution of fibers for each fiber length, and a broken line shows a cumulative distribution thereof). NBKP (Weyerh
Aeuser, fiber length 2.0mm or more and fiber diameter 30
５３53 μm fibers are contained in about 23% of the total number of fibers).

The other steps are the same as in the first embodiment. (Comparative Example 1) Ordinary Portland cement 50% by weight Silica sand (No. 8) 30% by weight Silica powder 15% by weight LUKP 5% by weight Water was added to such a composition to prepare a slurry having an 8% concentration. .

The LUKP used in this comparative example has a fiber length distribution as shown in FIG. 2 (a solid line indicates a fiber distribution for each fiber length, and a broken line indicates a cumulative distribution thereof). Unbeaten LUKP (Hyogo Pulp & Paper Co., Ltd., fiber length 0.1
１1.7 mm and a fiber having a fiber diameter of 8 to 25 μm). The other steps are the same as in the first embodiment.

(Comparative Example 2) Ordinary Portland cement: 50% by weight Silica sand (No. 8): 30% by weight Silica powder: 15% by weight NUKP: 5% by weight Water is added to such a composition to obtain a slurry having a concentration of 8%. Was prepared.

The NUKP used in this comparative example has a fiber length distribution as shown in FIG. 4 (a solid line indicates a fiber distribution for each fiber length, and a broken line indicates a cumulative distribution thereof). NUKP (manufactured by Hyogo Pulp Industry Co., Ltd., fiber length 0.1 to 3.5)
mm and a fiber diameter of 25 to 48 μm) was beaten to 80 SR °. Others were the same as Example 1.

(Comparative Example 3) Ordinary Portland cement: 50% by weight Silica sand (No. 8): 30% by weight Silica powder: 15% by weight Asbestos (6 classes): 5% by weight % Slurry was prepared.

The asbestos used in this comparative example was LA
It is made by Company B (Canada). Others were the same as Example 1. For the above Examples 1 to 6 and Comparative Examples 1 to 3, productivity, yield, separation of water and solid content of the slurry, and drainage amount of the slurry during papermaking were evaluated. The productivity is indicated by the papermaking length (m) per unit time (1 minute), and the productivity is higher than 61 m / min.
Was given to those having a normal productivity of 45 to 60 m / min, and x was given to those having a low productivity of 44 m / min or less. Table 1 shows the results.

The yield (%) is calculated by using the following equation (b). に is given to those having a high yield of 86% or more, ○ is given to those having a normal yield of 80% to 85%, and Those with a low value of 79% or less were marked with x. Table 1 shows the results. Yield (%) = [slurry concentration (%)-drainage concentration (%)] / slurry concentration (%) × 100 (b) Further, separation of water and solids (slurry separation) is judged silently, and separation is performed. ◎ for those without, ○ for those with some separation
, And those with separation are marked with △. Table 1 shows the results
Shown in

In addition, the amount of drainage during papermaking was judged silently, and a large amount was assigned to a large amount of drainage, a small amount was assigned to a small amount of wastewater, and a medium was assigned to an intermediate amount of wastewater. Table 1 shows the results. Further, bending strength tests were performed on the inorganic plates of Examples 1 to 6 and Comparative Examples 1 to 3. The span of this test was 150 mm (sample full size 200
mm × 200 mm). And high bending strength 22
○ to 0 kg / cm ² or more, low bending strength 22
A mark of less than 0 kg / cm ² was given. Table 1 shows the results.

Further, the above-mentioned inorganic plate was subjected to a freezing-in-water thawing test (according to ASTM C666) to judge the frost damage resistance. The repetition was 300 cycles. Then, ○ was given to those with no significant damage, Δ was given to those with slight damage, and x was given to those with significant damage. Table 1 shows the results. Further, the above-mentioned inorganic plate was subjected to a Charpy test in accordance with JIS G0202. 2.8kg with high Charpy impact value
· The m / cm ² or more of ◎, ○ in that the Charpy impact value ordinary 1.8~2.7kg · m / cm ^2, the Charpy impact value is low 1.8 kg · m / cm less than ² , And each of them was marked with x. Table 1 shows the results.

Then, for Examples 1 to 6 and Comparative Examples 1 and 2, based on the test results, a comprehensive evaluation was given to those having good performance from a comprehensive viewpoint, and a comprehensive evaluation was given to those having poor performance from a comprehensive viewpoint. As x. Table 1 shows the results.

[0041]

[Table 1]

In Table 1, when Examples 1 and 2 and Comparative Example 3 are compared, Examples 1 and 2 using LBKP and LUKP were compared.
2 can obtain almost the same bending strength and impact resistance as Comparative Example 3 using asbestos, and Examples 1 and 2 show Comparative Example 3
It can be seen that the material has bending strength and impact resistance that are comparable to those of Comparative Example 1. Further, it can be seen that the productivity is higher in Examples 1 and 2 using LBKP and LUKP than in Comparative Example 3 using asbestos. This is LBKP or LU
This is because the slurry containing KP is more improved in drainage (water discharge during papermaking) than the slurry containing asbestos. In addition, it can be seen that Examples 1 and 2 have higher frost damage resistance than Comparative Example 3.

In Table 1, when Example 2 is compared with Comparative Example 1, the yield of Example 2 is higher than that of Comparative Example 1, and the bending strength, frost damage resistance, and impact resistance are also different. You can see that it is higher. This is because, in Example 2, LUKP having a fiber length and a fiber diameter within the range specified in the present invention,
In other words, while pulp having an extremely long fiber or an extremely short fiber, or a pulp having a small proportion of an extremely thick fiber or an extremely thin fiber is used, the fiber of Comparative Example 1 is out of the range specified in the present invention. This is because LUKP having a long or fiber diameter, that is, pulp having an extremely long fiber or an extremely short fiber, or a pulp having a large proportion of an extremely thick fiber or an extremely thin fiber is used.

Further, it can be seen from Comparative Example 2 in Table 1 that if NUKP having a high degree of beating is used, the amount of water discharged during papermaking becomes too small, leading to a decrease in productivity. This is LUK
The same applies when the degree of beating of P or LBKP is increased, and is preferably 65 SR ° or less as in the present invention. In addition, comparing Example 1 and Example 3, Example 3 using the beaten LBKP is the same as Example 1 using the unbeaten LBKP.
It can be seen that the yield is higher than that of the case. This is the beaten L
This is because the use of BKP improves the effect of capturing cement as compared with unbeaten LBKP.

Also, as in Examples 4 and 5, when sepiolite or silica fume is blended, the separation of water and solids of the slurry is reduced, and the yield is increased. Furthermore, when long-fiber pulp is contained as in Example 6, the effect of reinforcing the cement with long-fiber pulp having a long fiber length can be improved, and it can be seen that the impact resistance performance is improved.

[0046]

As described above, the inorganic plate according to the present invention is a hardwood bleached sulphate pulp or a hardwood unbleached sulphate pulp having a fiber diameter of 5 to 30 μm and a fiber length of 0.2 to 1.0 mm. Because of the use of those containing 60% or more, the proportion of extremely long fibers or extremely short fibers, or extremely thick or extremely thin fibers is reduced, and even if pulp is used as a fiber component, the bending strength and It can enhance the performance of frost resistance and impact resistance.

The fiber diameter is 20 to 60 μm and the fiber length is 2.
Since a long fiber pulp containing 10% or more of fibers of 0 mm or more is included, the effect of reinforcing cement with long fiber pulp having a long fiber length can be improved, and the impact resistance performance is further improved. Is what you can do. As described above, the inorganic plate manufacturing method of the present invention is a method of preparing a slurry by blending at least one of hardwood bleached sulphate pulp or hardwood unbleached sulphate pulp with cement and preparing the slurry to form a slurry. In the above, as hardwood bleached sulphate pulp or hardwood unbleached sulphate pulp, fibers containing fibers having a fiber diameter of 5 to 30 μm and a fiber length of 0.2 to 1.0 mm are used in an amount exceeding 60% The ratio of long fiber or extremely short fiber, or extremely thick fiber or extremely thin fiber is reduced, and the productivity can be improved as compared with those using asbestos as a fiber component, and the slurry yield is increased. Is what you can do.

Further, since the degree of beating of the hardwood bleached sulfate pulp or the hardwood unbleached sulfate pulp is set to 65 SR ° or less, it is possible to improve the cement capturing effect of the hardwood bleached sulfate pulp or the hardwood unbleached sulfate pulp. It is possible not only to reduce the water drainage of the slurry, but also to increase the yield of the slurry, at the same time without lowering the productivity, and to reduce the separation of water and solids from the slurry. You can do it.

Furthermore, since the slurry is prepared by blending sepiolite, the amount of wastewater during papermaking can be reduced, and the yield of the slurry can be increased. In addition, since the slurry is prepared by mixing silica, the amount of drainage during papermaking can be further reduced, and the yield of the slurry can be further increased.

[Brief description of the drawings]

FIG. 1 is a graph showing the distribution of LBKP used in the present invention for each fiber length and the accumulation thereof.

FIG. 2 is a graph showing the distribution of LUKP for each fiber length used in the present invention and a comparative example of the present invention, and the accumulation thereof.

FIG. 3 is a graph showing the distribution of the long fiber pulp used in the present invention for each fiber length and the accumulation thereof.

FIG. 4 is a graph showing the distribution of NUKP for each fiber length used in a comparative example of the present invention and the accumulation thereof.

FIG. 5 is a schematic view of a round-mesh papermaking machine used in the present invention.

FIG. 6 is a schematic view of a flow-on papermaking machine used in the present invention.

──────────────────────────────────────────────────の Continued on the front page (51) Int.Cl. ⁷ identification code FI C04B 14:10) C04B 14:10) 111: 12 111: 12 (58) Investigated field (Int.Cl. ⁷ , DB name) C04B 28/00-28/36 C04B 38/00-38/10

Claims (6)

(57) [Claims] 1. An inorganic board containing cement as a main component and containing at least one of bleached hardwood sulfate pulp and hardwood unbleached sulfate pulp, wherein the hardwood bleached sulfate pulp or the hardwood unbleached sulfate pulp has a fiber diameter of 5%. ~ 30μ
m, an inorganic plate comprising fibers containing fibers having a fiber length of 0.2 to 1.0 mm and 60% or more of the total number of fibers. 2. A fiber diameter of 20 to 60 μm and a fiber length of 2.0 m.
The inorganic plate according to claim 1, wherein a long-fiber pulp containing at least 10% of fibers of m or more is contained. 3. A method for producing an inorganic plate, wherein a slurry is prepared by blending at least one of hardwood bleached sulfate pulp and hardwood unbleached sulfate pulp with cement, and the slurry is made into an inorganic plate. A method for producing an inorganic plate, comprising using unbleached sulfate pulp containing fibers having a fiber diameter of 5 to 30 µm and a fiber length of 0.2 to 1.0 mm or more of the total number. 4. The method for producing an inorganic board according to claim 3, wherein a hardwood bleached sulfate pulp having a beating degree of 65 SR ° or less or a hardwood unbleached sulfate pulp is used. 5. The method for producing an inorganic plate according to claim 3, wherein a slurry is prepared by blending sepiolite. 6. The method for producing an inorganic plate according to claim 3, wherein a slurry is prepared by blending silica.