GB2260318A

GB2260318A - An inorganic plate

Info

Publication number: GB2260318A
Application number: GB9119831A
Authority: GB
Inventors: Kenichi Yoshimoto; Kazuhiro Sakamoto; Takayuki Kobayashi; Hirofumi Takai; Tomomi Nagano
Original assignee: Daiken Corp
Current assignee: Daiken Corp
Priority date: 1991-09-17
Filing date: 1991-09-17
Publication date: 1993-04-14
Anticipated expiration: 2011-09-17
Also published as: GB9119831D0; GB2260318B

Abstract

An inorganic plate B e.g. a roof tile comprises a mixture consisting of cement, inorganic granular material, a dispersing agent and water. At least one side has a plurality of steps 3 formed to be approximately perpendicular so that they are similar to the sectional configuration of a natural slate. The plate is formed by placing an extruded shape of the mixture between upper die 2 having a step pattern on its lower surface and lower die 5, moving side frame 4 downward and rolling the shape by moving die 2 downward. The surfaces of the plate may also have grooves (6, Fig. 9) and an irregular pattern (10, Fig. 9). In another embodiment, an extruded body of the cement mixture is cut, pressed and extended by means of upper and lower dies 15, 11 and then a suction force is applied through a filter 12 and cloth 13 to aid in removing the formed plate. <IMAGE>

Description

AN INORGANIC PLATE The present invention relates to an inorganic plate to be used as a building material such as a roofing tile, a wall, a floor, and the like which has a dense particulate structure, a low absorption coefficient, a high yield strength, the sectional configuration of a platy joint pattern or a face pattern, and is thin, and a method for manufacturing the inorganic plate.

Slates which have been used as a roofing tile, a wall and the like are classified into a natural slate and a an artificial slate.

The natural slate has a dense particulate structure, so that it has a low absorption coefficient and a superior waterproof performance. Further, the sectional configuration of the platy joint pattern thereof looks unique. Thus, the slate used as the roof or the wall of a building gives it a high class finish. But it is inferior in use as a building material because it is small in its productive amount, expensive, and heavy.

The artificial slate is inexpensive and can be manufactured in a large quantity because cement which is a material thereof is produced in a large amount. But the artificial slate is harmful for the human body because it contains asbestos. In addition, its particulate structure is not dense and its absorption coefficient is high.

Consequently, water which has permeated into the artificial slate repeatedly freezes and melts in cold districts.

Further, before a.mixture being molded into a slate is hardened, it has a high fluidity. Consequently, in order to form a pattern thereon, it is necessary to keep pressing dies having the pattern formed thereon onto the mixture for a certain period of time. Thus, the productivity of the conventional artificial slate is inferior and corners of concavo-convex portions thereof become round. Therefore, the known art is incapable of forming, on the artificial slate, - such a beautiful concavo-convex pattern as the sectional configuration, of a natural slate, formed by a vertical angle or an almost vertical angle.

An asbestos cement slate contains asbestos harmful for the human body and its absorption coefficient is high, so that it is deformed as a result of the absorption of rain or moisture of atmosphere. Therefore, water which has permeated thereinto repeats freezings and meltings. As a result, the asbestos cement slate tends to crack.

An autoclaved light-weight concrete (ALC) plate includes a great number of air bubbles. Therefore, it is low in its strength and cannot be thinly formed. Further, similarly to the asbestos cement slate, its absorption coefficient is high, so that its dimension is likely to change and water which has permeated thereinto repeatedly freezes and melts. Thus, when it is used as an external wall of a building, the surface thereof is required to be waterproofed.

An inorganic plate according to the present invention comprises: a plate of a flat configuration which is formed from extruding a kneading material including a mixture of cement and inorganic granular material having particle diameters of less than 100 pm in addition to a dispersing agent contained in the weight % of 0.5 to 5.0 of the mixture and water contained in the weight % of 5 to 20 of the mixture, and a plurality of steps provided perpendicularly at least one side of the plate with sharp edges so as to form a shape similar to the sectional configuration of a natural slate.

In a preferred embodiment of the present invention, the plate is formed as a roofing tile including an upper half surface for use to pile up with the other plate, and provided with grooves of reversed U shapes for use to shut out water and a lower half surface for use to dispose to the outside provided with longitudinal grooves, in addition to the sharp edges provided at the lower edge and both side edges of the lower half surface in addition to the side wall of the grooves and concave and convex portions having irregular wave shapes similar to a platy joint pattern of the natural slate.

According to the another aspect of the present invention a method for manufacturing an inorganic plate comprises the steps of adapting a mixture of cement and inorganic granular material having particle diameters of less than 100 zm, kneading the mixture upon adding a dispersing agent contained in the weight % of 0.5 to 5 of the mixture and water contained in the weight % of 5 to 20 of the mixture, extruding the kneading material to form a body of predetermined configuration, cutting the extruding body into a predetermined length, and pressing and extending the cut body by means of upper and lower dies.

According to another preferred embodiment of the present invention, a method for manufacturing inorganic plate comprises the steps of: kneading an inorganic mixture consisting of cement contained in the wt% of 20 ~ 60 thereof; an inorganic granular material, other than the cement, the diameter of which is less than lOOym; a dispersing agent contained in the wt% of 1 , 4 thereof; and water contained in the wt% of 5 ~ 20 thereof; cutting the mixture to a predetermined length after extruding the mixture so as to shape the mixture into a predetermined configuration; and rolling the mixture by upper and lower dies to mold compressively the mixture under heating at least the upper die.

The weight ratio of the water of the mixture to that of the cement thereof is as small as 20 , 33%, but the amount of the dispersing agent contained in the mixture is more than that contained in a known cement mortar. Therefore, the water is dispersed throughout the mixture. Thus, the mixture has a uniform particulate distribution and is high in its grain density. Further, the weight ratio of the water to that of the cement thereof is low and the grain density of the inorganic granular material is high. Accordingly, the viscosity of the mixture is very high, so that it is capable of maintaining its configuration without the help of a supporting member.

Thereafter, the mixture is extruded to shape it into a predetermined sectional configuration, then, cut to a predetermined length. Air which has permeated into the mixture when the above-described materials are kneaded is discharged out of the mixture while the mixture is fed through an extruder. The mixture shaped into a predetermined length is rolled by the upper and lower dies. Thus, the mixture is shaped into a plate.

Besides the above-described method, the following method may also be adopted to obtain a plate: The mixture formed into an appropriate size is rolled by the upper and lower dies and the mixture is prevented from flowing out of the space formed by the upper and lower dies and side frame.

The configuration of the mixture shaped into the plate by the above-described methods is not deformed by sucking air in the vicinity of the upper surface of the upper die or the lower surface of the lower die when the upper die is moved away from the lower die.

In the accompanying drawings: Fig. 1 is a sectional view showing a device for molding an inorganic plate; Fig. 2 is a sectional view showing the inorganic plate formed by the molding device; Fig. 3 is a partial plan view showing the inorganic plate; Fig. 4 is a sectional view taken along the line IV - IV of Fig. 3; Fig. 5 is a photograph showing a front view of the inorganic plate formed by the molding device; Fig. 6 through Fig. 8 show the procedure, for molding a plate; and Fig. 9 is a top plan view of a set being assembled by three sheets of inorganic plates formed by the molding device for use as a roof tile.

An inorganic plate is made of cement, an inorganic granular material other than cement, water, and a dispersing agent.

Cement to be used ranges from 0.5 to 100um in its grain diameter. Any one of the following cements or a mixture thereof is used: Portland cement, silica cement, fly ash cement, alumina cement and the like.

As the inorganic granular material, preferably, silica dust is used. The grain diameter of the silica dust is less than 0.5cm. Other than silica dust, the following may be selected as the inorganic granular material: fly ash, walasnite, and silica flour. The grain diameter of each of these granular materials is greater than that of silica dust by one order.

Dispersing agents include condensation product of naphthalene-sulfonic acid and formaldehyde, refined lignosulfonic acid, melamine-fulfonic acid chelate, and a mixture thereof.

In addition, the following fibers may be contained in a mixture to be shaped into the inorganic plate in order to increase the mechanical strength thereof: a-glass fiber, a carbon fiber, an inorganic fiber, a metal fiber such as a steel fiber, an olefinic group fiber such as a polypropylene and the like, other synthetic fibers, pulp, and other fibers.

The above-described materials are mixed with each other in the following proportions.

The amount of cement ranges from 20 to 60 wt% of the inorganic mixture of the cement and the inorganic granular material.

The amount of silica dust consisting of inorganic granules is smaller than the theoretical amount which can be charged into voids among inorganic granules such as cement, the diameter of which are great. That is, favorably, the amount of silica dust is less than 40 vol% of the inorganic mixture of the cement and the inorganic granules, excluding the silica dust, and more favorably, ranges from 20 to 40%.

Favorably, the amount of the dispersing agent ranges from 0.5 to 5 wt% of the inorganic mixture of the cement and the inorganic granular material, and more favorably, ranges from l to 4wt%.

The amount of water ranges from 5 wt% to 20 wt% of the mixture consisting of the cement and the inorganic granular material excluding the water content of the mixture. That is, the amount of water corresponds to the amount which fills voids formed among inorganic granular material including the cement when the silica dust is charged into the voids. The grain diameter the cement ranges from 0.5 to 100cm. This amount is smaller than the theoretical value (30 to 40 wt%) for filling voids among granules of an inorganic mixture not containing fine granules such as silica dust. As described above, the amount 6f the water is 5 wt% to 20 wt%. More favorably, the amount of water ranges from 5 wt% to 15 wt%.

A fiber is added to the inorganic mixture in the range from 0.5 to 2.0 wt% thereof. The addition of the fiber thereto more than this amount prevents the fluidity of the materials of the mixture, i.e., it is difficult for the mixture to be molded into an inorganic plate.

The method for manufacturing the inorganic plate is described below.

First, the cement and the inorganic granular material containing silica dust are uniformly mixed with each other. Next, water and the dispersing agent are added to this mixture. In addition, the fiber may be added to the mixture as necessary. Then, all the materials are kneaded to uniformly disperse them into each other. As a result, a mixture consisting of the above-described materials is obtained.

Different from the ordinary weight ratio of water to cement, the weight ratio of the water of the mixture to that of the cement thereof is as small as 20 ~ 33%. However, since a large quantity of the dispersing agent is added to the mixture, the water is dispersed throughout the mixture. Consequently, the materials are uniformly mixed with each other and the mixture has a highly dense particulate structure. Further, the ratio of the weight of the water to that of the cement is small and the grain density of the mixture is high. Therefore, the mixture is highly viscous, which means that the mixture is capable of maintaining a configuration without the help of a supporting member.

Since the viscosity of the mixture is high, air is likely to permeate thereinto. Therefore, in order to remove the air which has permeated thereinto and facilitate the molding operation to be carried out thereafter, the mixture is shaped into a predetermined configuration by an extruder and cut to a predetermined length. Thus, a block of a predetermined volume is formed.

Thereafter, the mixture is rolled to mold it into a plate.

The mixture is rolled and molded by a molding device 1 as shown in Fig. 1.

The molding device 1 comprises an upper die 2, a side frame 4, a lower die 5, a conveyor 7 having a netshaped belt 8 which travels along the upper surface of the lower die 5.

A pattern 3 is formed on one side of the lower surface of the upper die 2. The pattern 3 is formed to reproduce the sectional configuration of the platy joint pattern of a natural slate, i.e., a plurality of vertical corners are stepwise formed on one side of the lower surface of the upper die 2.

The mixture (A) molded into a predetermined size is transported between the upper die 2 and the lower die 5 by the conveyor 7.

First, the side frame 4 is moved downward, and the upper die 2 is then moved downward to roll the mixture (A).

At this time, with the downward movement of the upper die 2, the mixture (A) spreads all over the lower die 5 toward the side frame 4. As shown in Fig. 2, when the interval between the upper die 2 and the lower die 5 becomes as predetermined, the mixture (A) fills the space therebetween. Thus, an inorganic plate (B) having the predetermined thickness is obtained with the pattern 3 formed on the upper surface of the plate (B).

Thereafter, the side frame 4 and the upper die 2 are moved upward so that the upper die 2 is separated from the plate (B).

As described previously, the plate (B) separated from the upper die 2 and the side frame 4 has a high viscosity to maintain the configuration shaped by the molding device 1. Accordingly, the pattern 3 formed by the upper die 2 is not deformed. That is, as shown in Fig. 4, neither a vertical face 3a of the plate (B), nor the upper corner 3b, nor the lower corner 3c thereof are not rounded, i.e., the corners thereof remain vertical. Thus, the sectional configuration of a platy joint pattern similar to that of a natural slate can be formed on the plate (B).

In addition, it is possible to form a more complicated pattern on the side face of the plate (B) by horizontally moving the side frame 4 having a pattern formed on the inner face thereof.

Further, heating the upper die 2 at 60 , 800C can reliably keep the upper corner 3b and lower corner 3c of the vertical surface 3a perpendicular.

Conventionally, a mixture obtained by kneading the material of a cement product is not heated. This is because if it takes long for the mixture to be cured, the heated portion of the mixture is dried before the hydration reaction proceeds to a sufficient extent in the heated portion.

As a result, some portions thereof are not sufficiently hardened, i.e., it is not uniformly hardened. However, unlike ordinary cement products, the weight ratio of water to that of cement is low and in addition, the grain density of the mixture is high. Therefore, after the mixture is shaped into a configuration, it is reliably capable of maintaining the configuration by itself. Thus, a heating period of time is short and the mixture is not nonuniformly hardened.

Heating the upper die 2 increases the fluidity of the mixture. As a result, detailed portions of the pattern 3 formed thereon are filled with the mixture. Consequently, heating the mixture allows such a fine and complicated pattern as the sectional configuration of the platy joint pattern of a natural slate to be formed on the plate (B).

When the upper die 2 is heated, water content of the mixture (A) evaporates from the surface thereof. As a result, a vapor layer is formed between the mixture (A) and the upper die 2. The vapor layer facilitates the separation of the upper die 2 from the plate (B). Consequently, a fine and complicated pattern formed on the plate (B) is not damaged.

The plate (B) thus formed is transported from the lower die 5 to a curing chamber (not shown) by the conveyer 7, then, similarly to ordinary cement products, hardened for a long period of time.

As apparent from the foregoing description, a pattern similar to the sectional configuration of the platy joint pattern of a natural slate is formed on the inorganic plate owing to the high viscosity of the mixture consisting of the materials mixed in a novel proportion.

Accordingly, the inorganic plate formed produces the peculiar appearance of a natural slate. With providing at the front edge a plurality of steps formed of a shape having recessions or overhanging projections similar to three to seven layers of a natural slate, at the center a pair of holes each for passing through a nail, at the side edges and the center of the upper surface a set of straight grooves for use as partitions, and at the upper center portion a set of grooves each having a U-shape for shutting off water to be disposed on the upper surface. Such the inorganic plate can be used as a roofing tile, a wall or a floor of a building looks high-class and distinctive.

Fig. 5 and Fig. 9 show the inorganic plate formed of a roofing tile, Fig. 5 showing the top plan view of the roofing tile and Fig. 9 showing the top plan view of a set arrangement assembled by three sheets of the inorganic plates. The roofing plate comprises a flat plate B which is formed from extruding a kneading material including a mixture of cement and inorganic granular material having particle diameters of less than 100 zm in addition to a dispersing agent contained in the weight % of 0.5 to 5.0 of the mixture and water contained in the weight % of 5 to 20 of the mixture, and is provided with a plurality of steps 3 perpendicularly at least one side of the plate having sharp edges so as to form a shape similar to the sectional configuration of a natural slate.As shown in Fig. 5 and Fig. 9, the flat plate B is formed as a roofing tile including an upper half surface Ba for use to pile up with the other plate provided with grooves 6 of reversed U shapes for use to shut out water,and a lower half surface Bb for use to dispose to the outside provided with longitudinal grooves 9 in addition to the sharp edges 3 provided at the lower edge and both side edges of the lower half surface in addition to the side wall of the grooves and concave and convex portions 10 having irregular wave shapes similar to a platy joint pattern of the natural slate. The roofing plate usually has a dimension of 366 x 600 x 6 m/m with the upper half surface of 213 x 600 m/m and the lower half surface of 153 x 600 m/m.

In Fig. 9, three sheets of the flat plates B are assembled into one set arrangement so as to form a part of roofing tile to be provided onto a housing in such a manner that the two sheets are arranged in parallel upon jointing one side edge of one sheet with the other side edge of the other sheet so as to connect with each other in horizontal direction, and another sheet is placed onto the two sheets upon piling up its lower half portion onto the upper half portions of the two sheets so as to connect with each other in vertical direction. With this arrangement, the grooves 6 provided on the upper half surfaces of the two sheets has a function for preventing water to be disposed on the upper half surface from moving up beyond the grooves so as to shut out water.

The heating of the upper die during the molding of the mixture into the inorganic plate allows the upper die to be separated from the molded inorganic plate without changing the pattern formed thereon. Accordingly, a pattern similar to the fine and complicated sectional configuration of the platy joint pattern of the natural slate can be faithfully reproduced. Further, since the mixture can be molded into the inorganic plate during a short period of time, a lot of inorganic plates can be manufactured through a small number of processes.

Another embodiment will be described below with reference to Figs. 6, 7, and 8.

An inorganic plate is manufactured through the process consisting of a mixture, an extrusion, a cutting, a molding by pressure application, and a curing.

First, cement and an inorganic granular material containing silica dust are mixed with each other. Next, water and a dispersing agent are added to the mixture of the cement and the inorganic granular material. At this time, fibers may be added to the mixture as necessary. Then, all the materials are kneaded to uniformly disperse them into each other. As a result, a mixture consisting of the above-described materials is obtained.

In the mixture, fine granules such as silica dust are charged into voids among the inorganic granules of the cement. Then, water is charged into voids among the inorganic granular materials of the silica dust and the cement.

According to the conventional method, in such a case, it is difficult to knead the materials of the mixture and mold the mixture into a certain configuration because surface force which prevents granules from sliding smoothly is increased.

Thus, it is difficult to knead the mixture and shape it into a predetermined configuration.

But the mixture contains a great amount of the dispersing agent. Therefore, fine granular materials are sufficiently dispersed into the voids among cement granules and inorganic granules even though the weight ratio of the water to that of the cement is small. Accordingly, the cement granules and inorganic granules are densely mixed with each other. Thus, the grain density of the mixture obtained is very high. Further, since the mixture is highly viscous, it has a high fluidity. Therefore, it is capable of maintaining a configuration without the help of any supporting member. When pressure is applied thereto, it has a fluidity. Preferably, the fluidity of the mixture corresponds to the case in which a load of 0.7 - l.Okgf is required to move a steel ball 3mm whose outer diameter is 20mm.

After the mixture is introduced into an extruder (not shown), it is shaped into a predetermined sectional configuration while it is being transported by a screw.

Air which has permeated into the mixture while the above-described materials are mixed with each other is not discharged therefrom by its buoyancy because the mixture is highly viscous, however, the air is discharged therefrom while the mixture is being transported through the extruder.

The mixture extruded from the extruder is cut, by a cutting machine (not shown), to a block having a predetermined length, namely, a predetermined volume.

A molding device for molding a block-shaped mixture into an inorganic plate is shown in Figs. 6 through 8.

The molding device comprises a lower die 11, a side frame 14, and an upper die 15.

The lower die 11 comprises a porous filter plate 12 formed on the upper surface thereof and a cotton cloth 13 covering filter plate 12.

The inner dimension (the three dimensions) of the side frame 14 is predetermined and the volume thereof is the same as that of the mixture which has been block-shaped in the cutting process. The side frame 14 may be composed of a plurality of blocks.

In order to easily separate the upper die 15 from the block-shaped mixture, a surface lubricant such as silicon may be applied to the inner surfaces of the side frame 14 and the upper die 15 or the side frame 14 and the upper die 15 may be heated.

The block-shaped mixture (C) cut to the predetermined size in the cutting process is placed on the center portion of the lower die 11 on which the side frame 14 has been placed (refer to Fig. 6.) Next, the upper die 15 is moved downward toward the lower die 11 to apply pressure to the mixture (C). With the dbwnward movement of the upper die 15, the mixture (C) spreads all over the lower die 11 toward the side frame 14.

When the upper die 15 is brought into contact with the side frame 14, i.e., when the interval between the upper die 15 and the lower die 11 becomes as predetermined, the space surrounded by the upper die 15, the side frame 14, and the lower die 15 is filled with the mixture (C). Thus, the mixture (C) is shaped into a plate (D) having a predetermined dimensions (the three dimensions). That is, the volume of the mixture (C) is equal to that of the plate (D).

Therefore, the mixture (C) does not flow out of the side frame 14, which eliminates the need for the provision of a cutting process. Further, plates manufactured by this molding device are all uniform. A concavo-convex pattern formed on the lower surface of the upper die 15 is formed on the plate (D).

As described above, in rolling the highly viscous mixture (C) between the upper die 15 and the lower die 11, silicon is applied to the inner surfaces of the side frame 14 and the upper die 15. The side frame 14 and the upper die 15 are heated to facilitate the separation of the plate (D) from the side frame 14 and the upper die 15. Depending on a situation, there is ~a case in which these methods are not enough to facilitate the separation of the plate (D) from the upper die 15 and side frame 14. To this end, the following method is carried out: When the upper die 15 and the side frame 14 are moved upward, suction force is applied to the air existing on the lower surface of the plate (D) by a suction device (not shown) through the filter 12 and the cotton cloth 13. Thus, the plate (D) is not moved upward together with the upper die 15.Therefore, the plate (D) maintains the configuration shaped by the molding device.

When a pattern has been formed on the plate (D), it is difficult for the upper die 15 to be separated from the plate (D). However, owing to the above-described sucking, the upper die 15 can be easily separated from the plate (D) and the plate (D) is capable of maintaining the configuration shaped by the molding device and the pattern formed thereon is not deformed. Air bubbles which exist on the lower surface of the plate (D) and in the vicinity thereof are removed by the above-described air sucking. Thus, the grain densities of the lower surface of the plate (D) and in the vicinity thereof are high.

Thereafter, the plate (D) is transported to a curing chamber (not shown) together with the lower die 11 or separately therefrom to cure it therein under a certain condition.

The quality of the plate (D) manufactured by the above-described method and an asbestos cement slate commercially available are shown in Table 1. The wt% and vol% of the materials of the plate (D) are shown in Table 2.

Table 1 inorganic asbestos plate cement plate 3 bulk density (g/cm ) 2.1 1.8 water absorption (wt%) 2 14 rate of dimension change 0.02 0.10 due to water absorption 2 MOR (kgf/cm2) 260 190 Table 2 material wtE vol% cement 40 27.9 silica dust 20 19.7 fly ash 27 25.2 dispersing agent 2 2.9 synthetic fiber 1 2.4 water 10 21.9 In the above method, the volume of the blockshaped mixture (C) is the same as that of the inner dimension (the three dimensions) of the side frame 14. Besides, the plate (D) may be manufactured by the following methods: According to one method, the mixture (C) is divided into small blocks, the small blocks are appropriately placed on the lower die 11, and integrated with each other by rolling them.According to another method, an appropriate-sized mixture (C) extruded fromthe extruder and consisting of the above-described materials such as cement is placed on the lower die 11 without cutting it, and is molded into an appropriate volume by rolling it by the upper die 15 and the lower die 11.

As apparent from the foregoing description, voids among cement granules are filled with inorganic granules other than cement in a high density, that is, a resulting inorganic plate has a high grain density. Therefore, the inorganic plate has a low water absorption coefficient, is not varied in its dimension, insusceptible to freezings or meltings, high in its hardness and-mechanical strength, and durable. Thus, the inorganic plate can be used as a roofing tile, an outer wall or the like. In addition, the plate is suitably used in cold districts.

Air which has permeated into the mixture to be shaped into a predetermined sectional configuration is discharged therefrom while the mixture is traveling through an extruder. After the mixture is extruded from the extruder, it is cut to a plurality of blocks each having a predetermined dimension (volume). Therefore, a predetermined amount of mixture can be supplied to a molding device. That is, the sizes (volumes) of rolled plates are all uniform.

Air present under the lower surface of the inorganic plate is sucked when the upper die is moved upward.

Accordingly, the configuration of the inorganic plate is not varied or a pattern formed thereon is not deformed.

Since the side frame of the molding device prevents the mixture being rolled between the dies from flowing outside, the thicknesses and areas of resulting plates are uniform. Therefore, the process for cutting the edges of the plates so as to uniformalize them can be eliminated.

Claims

1. An inorganic plate comprising a plate of a flat configuration which is formed from extruding a kneading material including a mixtureof cement and inorganic granular material having particle diameters of less than 100 zm in addition to a dispersing agent contained in the weight % of 0.5 to 5.0 of the mixture and water contained in the weight % of.5 to 20 of the mixture, and a plurality of steps provided perpendicularly at least one side of the plate with sharp edges so as to form a shape similar to the sectional configuration of a natural slate.

2. A plate as defined in claim 1, wherein the plate is formed as a roofing tile including an upper half surface for use to pile up with the other plate, and a lower half surface for use to dispose to the outside provided with longitudinal grooves, and the sharp edges are provided at the lower edge and both side edges of the lower half surface in addition to the side wall of the grooves.

3. A plate as defined in claim 1 or 2, wherein the plate is formed as a roofing tile including an upper half surface for use to pile up with the other plate provided with grooves of reversed U shapes for use to shut out water, and a lower half surface for use to dispose to the outside.

4. A method of manufacturing an inorganic plate substantially as herein described with reference to and as shown in the accompanying drawings.

4. A plate as defined in claim 1, 2 or 3 wherein the plate is formed as a roofing tile including an upper half surface for use to pile up with the other plate, and a lower half surface for use to dispose to the outside provided with concave and convex portions having irregular wave shapes similar to a platy joint pattern of the natural slate.

5. A method for manufacturing an inorganic plate comprising the steps of adapting a mixture of cement and inorganic granular material having particle diameters of less than 100 pm, kneading the mixture upon adding a dispersing agent contained in the weight % of 0.5 to 5 of the mixture and water contained in the weight % of 5 to 20 of the mixture, extruding the kneading material to form a body of predetermined configuration, cutting the extruded body into a predetermined length, and pressing and extending the cut body by means of upper and lower dies.

6. A method as defined in claim 5 or 6, wherein in the kneading step a dispersing agent is added into the mixture in the weight % of 1 to 5 of the mixture.

7. A method as defined in claim 5 or 6, wherein in the pressing and extending step the movement of the cut plate toward four outsides is regulated by means of a side frame.

8. A method as defined in claim 5, wherein in the pressing and extending step the upper die is heated at a given temperature.

9. A method as defined in claim 5, 6, 7 or 8, further comprising the step of depressing and sucking the pressed and extended body from the one side of either the upper die or the lower die to move away from the other die after the pressing and extending step.

10. An inorganic plate substantially as herein described with reference to and as shown in the accompanying drawings.

11. A method of manufacturing a plate substantially as herein described with reference to and as shown in the accompanying drawings.

Amendments to the claims have been field as follows CLAIMS 1. An inorganic plate which comprises a plate of a flat configuration which is formed by extruding a kneading material including a mixture of cement and inorganic granular material having particle diameters of less than 100 tm in addition to a dispersing agent contained in the weight of % of 0.5 to

5.0 of the mixture and water contained in the weight % of 5 to 20 of the mixture, and a plurality of steps provided perpendicularly at least on one side of the plate with sharp edges so as to form a shape similar to the sectional configuration of a natural slate, is characterised in that the plate is formed as a roofing tile including an upper half surface for use in overlapping another plate provided with grooves of reversed U shapes for use to shut out water, and a lower half surface for use in exposing to the outside provided with longitudinal grooves and concave and convex portions having irregular wave shapes similar to the pattern of natural slate, and sharp edges are provided at the lower edge and both side edges of the lower half surface in addition to the side wall of the grooves.

2. A method of manufacturing an inorganic plate comprising the steps of adapting a mixture of cement and inorganic granular material having particle diameters of less than 100 pu, kneading the mixture upon adding a dispersing agent contained in the weight % of 0.5 to 5 of the mixture and water contained in the weight % of 5 to 20 of the mixture with adding a dispersing agent into the mixture in the weight % of 1 to 5 of the mixture, extruding the kneading material to form a body of predetermined configuration, cutting the extruded body into a predetermined length, and pressing and extending the cut body by means of upper and lower dies, controlling the movement of the cut plate toward four outer edges by means of a side frame, depressing and sucking the pressed and extended body from one side of either the upper die or the lower die to move away from the other die after the pressing and extending step, with the upper die being heated at a given temperature.

3. An inorganic plate substantially as herein described with reference to and as shown in the accompanying drawings.