DE3787284T2 - Foam ceramic tablet and manufacturing process. - Google Patents

Description

The present invention relates to a foamed ceramic plate (board) comprising a heat-foamed inorganic base layer and a fine glaze layer.

Hitherto, boards (sheets) made of inorganic raw materials, such as tiles and roof tiles, have been manufactured by molding the raw materials, drying the molded body, glazing a surface of the molded body and firing it to vitrify its surface so as to prevent surface water absorption of the board (sheet) and give it a beautiful appearance.

However, in the case of a foam ceramic board, a base layer containing foamable raw materials and a glaze layer cannot be fired at the same time because the base layer has a much larger expansion coefficient than the glaze layer and therefore cracks are generated in the glaze layer. On the other hand, if the base layer is glazed after firing, several problems arise which require many treatment processes: when reinforcing rods are embedded in the base layer, the reinforcing rods are deteriorated; and cracks are generated in the base layer due to thermal stress generated therein due to the large temperature difference between the surface portion of the base layer and a core. or inner portion thereof when firing the glaze layer. In addition, there is a risk of pinholes (small holes) occurring because the surface of the foam ceramic plate is porous. The surface is microscopically rough like the surface of an orange due to the traces or marks of foamed particles, although the surface can be described as smooth macroscopically. Thus, a smooth surface like a glass surface cannot be achieved.

The surface strength of the foam ceramic plate is also low, since the plate is only coated with a thin film-like coating that is created by the foaming process.

In addition, when a pattern is formed or imparted to a surface of the foamed ceramic plate, the pattern is transferred to the surface of the plate using, for example, a printing paper made by using a copper plate. This printing paper is made by coating an etched copper plate (a kind of mold) with a printing ink containing a paste, laminating a paper thereon, drying the paper, and peeling it off. A pattern is transferred to the plate by wetting the paper colored with coloring materials with water, placing the paper on the plate, and peeling the paper off. Then, the plate is fired to obtain a pattern. However, in this method using printing papers, the treatment process becomes complicated. In addition, productivity is low and the quality of the obtained pattern is not stable. Specifically, when the paper is peeled off, there is a risk that the transferred pattern becomes irregular, so that the quality of the pattern is not stable. The pattern also becomes irregular due to the foaming of the base layer.

There is therefore no other way to decorate a foam ceramic plate than to apply a relief pattern to the plate or to colour the entire plate. This has not been possible using the conventional method until now. possible to produce a desired beautiful multi-color pattern or a clear (sharp) pattern (for example, a pattern that is clear, sharp, or clearly recognizable).

The aim of the present invention is therefore to solve the above-mentioned problems and, in particular, to provide a foamed ceramic plate and a method for producing the same, wherein the ceramic plate (ceramic sheet) has improved surface smoothness, decoration, surface strength and the like while utilizing the excellent features of a foamed ceramic plate, i.e. its light weight, its heat insulating ability, its refractoriness, its workability, its water or moisture proofness and its ability to be produced in a large size.

This object is achieved by a foam ceramic plate according to claim 1 and a method for its production according to claim 9.

The foam ceramic plate (board) according to the invention is light, can be produced in a large size, is decorative, has improved fire resistance, refractoriness and corrosion resistance.

The present invention relates to a foamed ceramic plate (board) having a base layer containing foamed inorganic raw materials and a fine glaze layer comprising melted and solidified ceramic paper containing inorganic refractory (hard-melting) fibers, the fine glaze layer being obtainable on the surface of the foamed ceramic plate by simultaneously firing a layer containing heat-foamable inorganic raw materials and the ceramic paper (ceramic paper) laminated onto at least one surface of this layer so that they fuse together and form a unit.

The invention also relates to a method for producing a foam ceramic plate (board), which comprises laminating the ceramic paper (ceramic paper) on at least one surface of a base layer containing heat-expandable inorganic starting materials, simultaneously firing the base layer and the ceramic paper (ceramic paper) to fuse them together and form a unit thereof, and cooling the foam ceramic plate. Cooling can be achieved by quenching both surfaces of a resulting foamed plate with at least one cooled pressure roller immediately after fusing (flowing) and optionally the temperature of a surface of the foamed plate can be raised to the softening temperature.

The foam ceramic plate of the present invention has superior surface smoothness and improved surface strength. The plate also has improved appearance because desired colored or printed ceramic papers can be used to decorate the plate, whereby a wide variety of patterns that are surprisingly sharp or clear can be applied to a surface of the foam ceramic plate.

The foam ceramic plate according to the invention is obtainable by applying the following steps:

First, a ceramic paper (ceramic paper) produced by papermaking, for example, from a mixed slurry containing alumina fibers, mullite fibers (those fibers whose main crystal consists of 3Al₂O₃·2SiO₂ and which have superior mechanical strength, heat resistance and corrosion resistance) and an inorganic powder is laminated on a base layer containing foamable inorganic raw materials. The base layer and the ceramic paper are heated and melted, thereby combining a foamed layer of foamable inorganic raw materials and a fine surface layer of ceramic paper.

The foamable inorganic starting materials are produced, for example, by adding foaming agents, such as dolomite and silicon carbide, into powders such as natural glass and artificial glass. Preferably, however, pellets having a diameter of 0.2 to 1 mm are used, prepared by adding flux components and foaming agents to volcanic natural starting materials such as acid clay, kokaseki (a kind of pumice from Niijima in Japan) and sirasu (a kind of pumice from Kakoshima Prefecture in Japan; volcanic sand or volcanic ash and their loose agglomerates) instead of glass powder, grinding the resulting mixture to such an extent that 90% by weight of the ground material passes through a sieve having a mesh size of 44 µm, and pelletizing the powder from the standpoint of uniform temperature distribution and effective diffusion of the gas generated by the foaming.

When flux components are added, they lower the melting point of the materials. Examples of such flux components include Na₂CO₃, Na₂SiO₃, NaNO₃, Na₂HPO₄, Pb₃O₄, 2PbCO₃·Pb(OH)₂, BaCO₃, NaB₄O₇·10H₂O, H₃BO₃, ZnO, glass powder and frit.

The ceramic paper is a sheet-like material obtained by making paper from a slurry containing inorganic powdery raw materials such as feldspar, glass powder and frit; inorganic fibers; organic binders; inorganic binders; flocculants and the like. Examples of a preferred mixture are a mixture of inorganic powdery raw materials and at least one member from the group of alumina fibers and mullite fibers; a mixture of inorganic powdery raw materials, inorganic fibers and pulp fibers; a mixture of inorganic powdery raw materials and pulp fibers and the like. Inorganic powdery raw materials and fibrous raw materials are thus essential components for the ceramic paper. In particular, it is preferred to contain at least one member from the group of alumina fibers and mullite fibers. as they can limit the shrinkage of the ceramic papers (ceramic papers) during the firing stage. By using pre-fired raw materials, shrinkage can be further limited.

It is also possible to use glass fibers, pulp fibers and the like as fiber raw materials. They do not cause problems in the production of sheets. However, there is a problem that many ceramic paper-free portions (those portions which are not coated with ceramic paper and therefore do not have a fine surface layer) appear or exist on the outer edge on the expanded ceramic sheet because the above-mentioned glass fibers and pulp fibers shrink under the action of heat while the base layer is expanded and expanded. It is therefore preferable that the raw materials for the ceramic paper (ceramic paper) contain 4 to 8 wt% of inorganic fibers such as alumina fibers and mullite fibers.

The ceramic paper (ceramic paper) is produced by the papermaking process from a slurry containing the above-mentioned mixture to obtain a sheet-like material. In the papermaking step, a continuous papermaking device is usable. A desired pattern such as an embossed pattern can be given to the ceramic paper by, for example, embossing or punching the ceramic paper produced using papermaking devices or printing the dried ceramic paper by means of suitable printing devices. In the case of using a printing method, the ceramic sheet can be given desired colors in addition to sharp or clear patterns, which has not been possible by the conventional method.

In addition, a colored sheet (a colored ceramic paper) can be obtained by adding colorants such as metal oxides of Cr, Mn, Co, Ni, Cu and the like and pigments. The metal oxide melts and combines with the glass phase and foams during the firing step. In this case, the coloring elements fuse with the glass phase and foam in the ionic state. On the other hand, pigments do not fuse with the glass phase like metal oxide and remain suspended in the glass phase. The pigments are prepared by mixing the above-mentioned metal oxide with kaolin, feldspar and the like, previously firing the mixture, washing the fired mixture and grinding the washed mixture. The pigments used in the invention must be resistant to flux components.

The process for producing a foam ceramic plate (board) according to the invention is explained below.

The foamed ceramic board is manufactured by forming a base layer containing pellet-like foamable inorganic raw materials as described above, laminating the ceramic paper (ceramic paper) on the surface of the base layer, and firing it to integrate the base layer and the ceramic paper into one unit. The foamed ceramic board is also manufactured by forming a base layer on a ceramic paper, laminating another ceramic paper on the surface of the base layer, and firing it so that the base layer and the ceramic papers together form one unit. As the furnace, a carrier tunnel furnace equipped with a heat-resistant mesh conveyor belt therein is preferably used. In case of using a mesh conveyor belt, volatile components generated in the foaming step can diffuse evenly from the upper and lower surfaces of the belt and uniform heat transfer can be carried out on the upper and lower surfaces of the plate.

The firing temperature is determined depending on the proportion of SiO₂, Al₂O₃ and flux components in the mixed raw materials. When metal parts are used for the mesh conveyor belt, rollers and the like, it is preferable to mix the raw materials to fire at the lowest possible temperature. In concrete terms, this means that firing is preferably carried out within the temperature range of 750 to 850ºC.

Although the melting temperature of the ceramic paper may vary appropriately depending on the mixture of the base materials, it is preferable to set it so that the ceramic paper melts at a temperature lower than the firing temperature of the base materials, because the firing of the base materials is a more important factor than the melting temperature of the ceramic paper from the standpoint of product performance and should therefore be set with priority.

When the temperature of the base layer and the ceramic papers in the oven is increased, the base layer and the ceramic papers begin to soften. At the same time, the base layer expands, generating gas and increasing in volume. Thus, the foaming of the base layer progresses. In this case, the ceramic paper laminated to at least one surface of the base layer softens, melts and forms a unit with the foamed base layer.

After foaming is carried out, the foamed ceramic plate comprising a base layer and a ceramic paper (ceramic paper) which form a unit with each other is cooled. In this case, the surface of the foamed ceramic plate is preferably quenched by at least one roller and then it is reheated to make it soft again. The preferred number of rollers varies depending on the thickness, the type of the raw materials of the plate and is not limited according to the invention. The reheating can be carried out, for example, at the atmospheric temperature in the furnace.

The brightness of the colour or the gloss (which can be measured according to JIS Z 8722) can be improved by resoftening the foam ceramic plate after quenching. The reason why the plate is reheated after being pressed and quenched by the roller is that even a glossy vitreous surface melted by heat loses its gloss when pressed by the heating roller and becomes a matte surface. The plate is then transferred to a cooling zone after its surface is reheated and melted to have a gloss, and gradually cooled to remove the thermal stress generated in the plate by quenching, so that the fine layer of ceramic paper and the foamed base layer form a unit with each other. In this way, smooth and glossy foamed ceramic plates can be produced.

Regarding the temperature of the quenching and pressing roll, adhesion of the molten ceramic paper to the surface of the roll can be prevented by pressing the surface of the foamed ceramic sheet with rolls whose temperature is 60 to 70°C lower than the surface temperature of the foamed ceramic sheet. However, it is preferable that the temperature of the rolls be lowered to the solidification temperature of the sheet in order to improve productivity. That is, a general and preferred method is that the surface of the foamed ceramic sheet, whose surface temperature is, for example, 880°C, is quenched to a temperature of 600°C and then reheated to about 850°C.

Hereinafter, a foamed ceramic plate and a method for producing it according to the present invention will be explained in more detail with reference to the following examples and comparative examples. However, it should be noted that the present invention is not limited thereto.

example 1

A mixture of 69% feldspar (wt.%, this also applies below), 17% calcined soda, 10% ZrSiO₄ and 4% sodium nitrate was prepared using a pot mill wet milled to obtain slips each passing through a sieve having a mesh size of 250 µm. To the obtained slips were added 5% of alumina fibers (based on the total weight of the above mixed raw materials), 5% of starch, 2% of acrylic emulsion and an anion or cation as a flocculant. The liquid material was prepared therefrom so that the pulp concentration (the concentration of the raw materials to be made into a paper in a papermaking machine) was not more than 1%. The liquid material was introduced into a papermaking machine to prepare a 50 cm x 50 cm x 0.1 cm sheet.

The finish was applied to the surface of the obtained sheet by means of a roller under a pressure of 20 kg/cm². Then, the sheet was dried for 2 hours by far infrared (FIR) radiation. After drying, six kinds of pigments, each of which was mixed with 201 Cerazol (an oil for kneading pigments, available from Mitamura Shoten K.K.) and adjusted to melt at 850ºC, were directly printed on each ceramic paper using a squeegee roller with six screens each corresponding to a kind of pigment. By drying the printed ceramic paper, the patterned paper was obtained. The mixture of the ceramic paper was adjusted to melt at 850ºC.

Thereafter, a mixture consisting of 71% acid clay, 10% calcined soda (soda ash), 4% sodium nitrate, 10% zircon flower (a powdery material prepared by grinding zircon sand to such an extent that the grain size is not more than 74 µm) and 5% dolomite was dry ground in a pot mill to form a ground material having a grain size of 44 µm/90% (not less than 90% of the ground material passes through a sieve with a mesh size of 44 µm). Thereafter, pellets having a grain diameter of 1 to 2 mm were obtained using a pelletizer from Pan type pellets were used as foamable base material and mixed in such a way that their foaming temperature was 870ºC.

The pellet-shaped foamable inorganic raw materials were placed on a continuous mesh conveyor belt to form a 50 cm x 50 cm x 1 cm layer. A metal wire was embedded in the center of the layer. The above-mentioned ceramic paper was placed on this base layer. The base layer with the ceramic paper was transported into a furnace at a speed of 28 cm/min and heated at a maximum firing temperature of 870°C for 20 min to produce a melt and an integral unit. Then, the fired plate was quenched using 4 rollers each with a diameter of 160 mm. After quenching, the plate was reheated at 850°C for 5 min and melted and cooled in stages. Firing was completed within 150 min after the base layer with the ceramic paper was transported into the furnace. The temperature of the surface of the foamed plate after quenching was 600ºC, while that of the inner portion was 850ºC.

The specific gravity, flexural strength (according to JIS A 1408), smoothness, gloss (according to JIS Z 8741) and wear resistance (according to JIS A 5209) of the obtained foam ceramic sheet were determined. The smoothness was measured using a scanning electron microscope. The results are summarized in Table 1. The shrinkage of the ceramic paper measured by a scanning device (caliber) was 4%. Table 1 Firing temperature Specific gravity Flexural strength (kg/cm²) Smoothness Gloss* Abrasion loss* Ex. 1 Comp. Ex. 1 - Regarding the values of flexural strength, gloss and abrasion loss, three samples were measured and the average value was determined.

Example 2

The procedure of Example 1 was repeated, this time using pulp fibers instead of alumina fibers to produce ceramic papers.

The shrinkage of the obtained foam ceramic plate was measured in the same manner as in Example 1 and was found to be 50%.

Example 3

The procedure of Example 1 was repeated, but this time the quenched foam ceramic plate was not reheated.

The gloss of the obtained foam ceramic plate was determined in the same manner as in Example 1 and was found to be 7.1 (sample 1 = 6.2, sample 2 = 7.2 and sample 3 = 7.8).

Comparison example 1

The procedure of Example 1 was repeated, this time a decorative or protective layer of 5 mm thickness having the composition given below was laminated onto the base layer instead of the ceramic paper, and the foam ceramic plate was not reheated.

Composition of the decorative or protective layer*

acid clay 71%

Calcined soda 10%

Sodium nitrate 4%

Zircon flower 10%

Dolomite 5%

Colorant M142 (dye no., available from Nitto Sangyo Kabushiki Kaisha) 6% (this proportion is based on the total weight of the above 5 components)

Silicon dioxide (grain size 200 mesh) 4% (as above)

* The starting materials of the decorative or protective layer were prepared by mixing and grinding the above components in a pot mill and pelletizing the resulting grain.

The same properties as in Example 1 were determined for the foam ceramic plate obtained. The results are summarized in Table 1.

Example 4

A mixture consisting of 70% fly ash 801 frit (available from Nitto Sangyo Kabushiki Kaisha), 10% glass powder, 10% water cullet and 10% feldspar was wet-ground using a pot mill to obtain slips each of which passed through a sieve with a mesh size of 250 µm. To the obtained slips were added 5% alumina fibers (percent based on the total weight of the above mixed raw materials), 5% starch, 2% acrylic emulsion and an anion or a cation as a flocculant. A liquid material was prepared therefrom so that the pulp concentration (the concentration of papermaking raw materials in a papermaking machine) was not more than 1%. The liquid material was introduced into a paper making machine to produce a 50 cm·50 cm·0.1 cm sheet.

The surface treatment of the obtained sheet was carried out by means of a roller at a pressure of 20 kg/cm2. Then, the sheet was dried by FIR for 2 hours. After drying, six kinds of pigments, each of which was mixed with 201 Cerazole and adjusted to melt at 880ºC, were directly printed on the ceramic paper using a squeegee roller having six screens (grids) each corresponding to one kind of pigment. After drying the printed ceramic paper, a patterned ceramic paper was obtained. The mixture for the ceramic paper was adjusted so that the paper melted at 880ºC.

Then, a mixture consisting of 55% obsidian, 2% soda ash, 15% bentonite, 5% sodium nitrate and 5% lime was dry ground in a pot mill to produce a ground material having a grain size of 44 µm/90% (not less than 90% by weight of the ground material passed through a sieve having a mesh size of 44 µm). Thereafter, pellets having a grain diameter of 1 to 2 mm were produced using a pan-type pelletizer. These pellets were used as a foamable base material and mixed so that their foaming temperature was 900ºC.

In the same manner as in Example 1, foamed ceramic plates were prepared therefrom, except that the above-mentioned ceramic paper and the above-mentioned pellets were used instead of those in Example 1, and the maximum firing temperature and the reheating temperature after quenching were 900ºC and 880ºC, respectively.

The same properties as in Example 1 were determined for the foam ceramic plate obtained. The results are summarized in Table 1.

Example 5

The procedure of Example 1 was repeated except that the quenched ceramic foam plate was not reheated. The gloss of the resulting ceramic foam plate was determined in the same manner as in Example 1 and was found to be 7.1 (sample 1 = 6.7, sample 2 = 7.2 and sample 3 = 7.5).

Comparison example 2

The procedure of Example 4 was repeated, except that a 5 mm thick decorative or protective layer having the composition shown below was laminated onto the base layer instead of the ceramic paper and the foam ceramic plate was not reheated. The starting materials for the decorative or protective layer were prepared in the same manner as in Comparative Example 1.

Composition of the decorative or protective layer

Feldspar 69%

Calcined soda 12%

Sodium nitrate 4%

Zircon 5%

Dolomite 5%

The same properties of the resulting foam ceramic plate were measured as in Example 1. The results are summarized in Table 1.

From Example 1 and Comparative Example 1, and from Example 4 and Comparative Example 2, it can be seen that the bending strength, smoothness and wear resistance are improved and the gloss is increased when a ceramic paper is laminated on the surface of a base layer and the two are fused together to form a unit. When a decorative or protective layer (Comparative Examples 1 to 3) is used, the resulting foamed ceramic plate cannot be printed and has a poor appearance. On the other hand, when a ceramic paper is used, the plate can be provided with multi-color printing with a surprising clarity or sharpness and is therefore very decorative.

The results of Examples 1 to 2 further show that the shrinkage of the ceramic papers can be extremely reduced if aluminum oxide fibers are used as starting materials for the ceramic papers.

The results of Examples 1 and 3 as well as Examples 4 and 5 also show that the gloss of the surface of the foam ceramic plates can be significantly improved by reheating the foam ceramic plates after quenching by rolling.

Claims (9)

1. A foamed ceramic plate (board) comprising a heat-foamed inorganic base layer and a fine glass layer containing inorganic refractory fibers made from melted and solidified ceramic paper and applied to at least one surface of the base layer, which is obtainable by firing the ceramic paper containing inorganic refractory fibers together with the base layer containing heat-fusible inorganic raw materials to fuse them together and cooling the foamed ceramic plate immediately after the melting. 2. Plate according to claim 1, wherein the ceramic paper contains inorganic powdery starting materials and at least one member from the group of alumina fibers and mullite fibers. 3. The plate according to claim 1, wherein the ceramic paper contains inorganic powdery raw materials, inorganic fibers and pulp fibers. 4. The plate of claim 1, wherein the ceramic paper further contains coloring materials. 5. A plate according to claim 4, wherein the coloring material is a metal oxide. 6. A plate according to claim 4, wherein the coloring material is a pigment. 7. Plate according to claim 1, wherein the surface of the ceramic paper bears an embossed pattern. 8. A plate according to claim 1, wherein a pattern is printed on the surface of the ceramic paper with inorganic pigments. 9. Process for producing a foam ceramic plate (board) comprising a heat-foamed inorganic base layer and a fine glass layer containing inorganic refractory fibers, which is made from melted and solidified ceramic paper and is applied to at least one surface of the base layer, characterized in that the ceramic paper containing inorganic refractory fibers is fired together with the base layer containing heat-meltable inorganic starting materials to fuse them together, and that the foam ceramic plate is cooled immediately after melting.